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Materials in Our Daily Life : 95 :

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Materials in Our Daily Life
The basic aim of science is not only to study and understand natural phenomena but also to use this knowledge to make our lives more comfortable. Science and technology have enabled us to develop more economical and convenient methods to recover useful materials from nature and to put them to various uses. Chemistry has enabled us to synthesize new materials which have desired properties, thus, making them even better than natural materials. We need different types of materials to meet our daily needs. Some of them are obtained from nature while others are prepared by man. The materials that we get from nature are called natural materials. Wood, silk, cotton, leather, rubber, coal, etc. are natural materials. However, some materials that we use are manmade. Synthetic textiles like terylene and nylon, cement, glass, plastics, dyes, soap, detergents, fertilizers, insecticides and pesticides are some man-made materials which are commonly used. In this lesson, you will learn about the ways in which various materials are used in making common household items, in construction of houses and other buildings. You will learn about different polymers and their uses in our daily life. In addition, you will learn about the various medicines that help to cure different diseases and keep us healthy. OBJECTIVES After completing this lesson, you will be able to: • differentiate between natural and man-made materials; • name the materials used for making some common household items and for housing purposes; • state the principles involved in preparation and properties of some man-made materials in our daily life; • list various medicines used in some common diseases; • explain harmful effects of man-made materials on the environment. 21.1 COMMON HOUSEHOLD ITEMS We use many things in our house like candles in case of emergency lighting, ink to write, soaps and detergents to wash our clothes, matchbox to light gas stove or candles and many more. Let us now learn about these items of daily use.
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21.1.1 Candles We use candles as emergency light source and for decorative and ceremonial purposes. Usually they are made from a mixture of paraffin wax or some other slow-burning substance like tallow (stearic acid). They are commonly made in cylindrical form but are also made in fanciful designs. They contain a wick at their centre. When lighted with a matchstick heat from its flame liquefies the wax of the candle. This liquefied wax rises up along the wick where it is converted into vapour form, which then catches fire. Now a days, candles are made in a variety of colours, shapes and sizes. Some candles are scented and their aroma spreads in the air when lighted while some

others can float on water. Nainital (in Uttaranchal) is famous for the variety of beautiful and decorative candles manufactured here. 21.1.2 Inks We all use inks in various writing instruments like fountain pens, ball pens, gel pens, roller pens, soft tip pens, etc. Have you ever thought what ink is? Ink is a coloured fluid or a paste that is used for writing or printing. Earlier, black ink, also called India ink, was most widely used. It was made by mixing lamp black or carbon black in water or oil to which some gum was added which stabilized the mixture and also gave it better sticking property. This ink is used even these days but more commonly used inks are solutions of water or alcohol soluble dyes. Inks used in printing are similar in nature but are in the form of thick paste, which has a better sticking property. This is an essential quality as it causes the ink to stick to the typefaces and to paper when it is pressed against it. 21.1.3 Soap and detergents We use soap and detergents to wash our clothes. We wash our hands and take bath with soap. Soap and detergents help in removing dirt, oil and grease. How do soap and detergents remove the dirt and grease? What are the chemicals present in them? What is the difference in soaps and detergents? 21.1.3a Soap Soap has been in use for at least last three thousand years. Soaps are sodium or potassium salts of long chain organic acids (called fatty acids) like stearic acid and palmitic acid. How is soap manufactured? Soap is made by heating oil with sodium hydroxide. The oil and sodium hydroxide solution are fed into an enclosed reaction vessel under high pressure and heated at high temperature. At this temperature, the reaction is completed in a few minutes. The mixture of soap and glycerol is cooled and a concentrated solution of sodium chloride is added. Glycerol dissolves readily in salt solution but soap does not. So, solid soap separates out from the mixture. It is then removed by centrifugation. While still hot it is sprayed into a hot vacuum chamber to dry it. Perfume is added and the particles are compressed into soap cake.
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The basic materials used to manufacture soap are animal fats (lard) or vegetable oils (olive oil, neem oil, etc.) and an alkali, usually sodium hydroxide. Fats and oils are compounds of organic acids (containing 12–14 carbon atoms) and glycerol (commonly called glycerine). When the fat or oil is heated with sodium hydroxide solution, the acids are broken away from glycerol and are neutralized by the alkali to form soap. Soaps produce lather (foam) with soft water. With hard water, which contains calcium and magnesium salts in it, they do not produce lather. Instead they themselves are precipitated as insoluble salts of calcium and magnesium. 21.1.3b Detergents Animal fats and vegetable oils are important foodstuffs and ideally should not be used for making something even as important as soap. In their place, long chain sulphonic acids (usually C8 to C22) are used. Sodium or potassium salts of these sulphonic acids are known as detergents. Detergents can be manufactured in solid form (for washing powders) or in liquid form (for shampoos and liquid soaps).

Unlike soaps detergents can be used with soft as well as hard water. This is because their calcium and magnesium salts are water soluble. ACTIVITY 21.1 Aim : To compare the lather forming ability of soap and detergent in soft and hard water. What is required? Four test tubes, two small pieces of soap and detergent cakes. What to do? Take four test tubes. In two of them take some amount of ordinary tap water which is soft water. In one of them add a small piece of soap while in the other add a small amount of some detergent (a small piece or a small amount of powder). Shake both the test tubes. What do you observe? • Lather is formed in both the test tubes. • Now repeat the above procedure with hard water from a hand pump or a well. • You will find that soap does not form lather but detergent does form lather even with hard water. 21.1.3c Cleansing action of soap and detergent Soaps and detergents form lather or foam with water. Lather removes grease and dirt particles from clothes. Water by itself cannot do it as it does not wet oily or greasy dirt. Addition of soap or detergents improves the wetting property of water and thus helps in removing oily or greasy dirt. 21.1.4 Matchboxes In every house you will find a matchbox. Can you imagine life without it? How would you light up a candle or gas stove without it?
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Do you know how a matchstick catches fire? The head of matchstick consists of a mixture of potassium chlorate and antimony trisulphide bound together by glue. The striking surface on the matchbox is a mixture of red phosphorus and powdered glass held by glue. When a matchstick is struck against the coated surface of the matchbox, some heat is produced that makes the chemicals in the match head react. The heat of this reaction ignites the wood. Be careful Matches must be used carefully. While lighting, it should not be struck so hard on the side of the matchbox that it’s burning head breaks and flies away. This can result in an accident. After using a matchstick, we should not throw it anywhere carelessly. Even when its flame is blown off, the tip of the stick continues to burn slowly as can be seen by the dull red glow at the tip. This is known as after glow. Many accidental fires may occur by this after glow. Therefore, while throwing away a matchstick you should always check that it is completely extinguished and there is no after glow. Sometimes matchsticks are dipped in a solution of borax or sodium carbonate (karborized matches) and dried as a first step in the manufacture of matches. Matchsticks thus treated are completely extinguished when blown away and are safer to use. CHECK YOUR PROGRESS 21.1 1. Give two examples each of natural and man-made materials?

2. Name the substances used for making candles. 3. What are soaps? 4. Can soap be used with hard water to wash clothes? 5. Which type of matches do we use today? 21.2 HOUSING MATERIALS In the last section, we learned about some common household items. In this section, we will learn about two important housing materials – cement and glass. 21.2.1 Cement Do you know what cement is made of and how is it manufactured? a) Raw materials required: Three main raw materials required for manufacture of cement are as follows: • Limestone which is calcium carbonate, CaCO3 • Clay which is mainly a mixture of aluminium silicates containing alumina, Al2O3 and silica, SiO2 • Gypsum which is CaSO4.2H2O b) Manufacture: Limestone and clay are mixed in definite proportion and ground to a fine powdery state. This dry powder is used as such or mixed with water to form a paste and heated in a rotary kiln (a type of furnace). It is slowly made to pass through the kiln wherein limestone and clay combine chemically and form a mixture of calcium silicate, CaSiO3 and calcium aluminate, CaAl2O3. This mixture is in the form of small greenish black or grey-coloured
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hard balls known as clinkers. These clinkers are allowed to cool down and then ground to very fine powder. To this powder, 2-3% gypsum is added and the mixture is again ground to obtain a grayish coloured powder, which is cement. It is then packed in airtight bags to exclude the moisture. Gypsum is added to decrease the setting time of cement. c) Uses: Cement is one of the most important building materials. It is employed in the construction of buildings, roads, bridges, dams, etc. For general uses like plastering or laying of bricks, this powder is mixed with sand and water and the resulting thick paste is used for construction purposes. As a result of chemical reactions between water and cement this mixture sets into a hard mass. Concrete is a mixture of cement, sand, gravel or small pieces of stone and water. It sets to an extremely hard structure. It is used for making floors and roads. Concrete may be further strengthened by filling it around or over a network of steel rods and allowing it to set. It is known as reinforced concrete cement or R.C.C. Such structures are very strong and are used in construction of pillars, roofs of buildings, roads, bridges and dams. 21.2.2 Glass Glass is used for various purposes. You must have seen glasses fitted in windows and doors, looking mirrors, windscreens of vehicles, reading glasses, sunglasses, etc. Have you ever wondered how is glass prepared? What are the raw materials required for manufacturing of different types of glasses? a) Raw materials required: The basic raw materials needed for making glass are: • Washing soda which is sodium carbonate, Na2 CO3.

• Limestone which is calcium carbonate, CaCO3. • Sand which is silica, SiO2. b) Manufacture: The raw materials are mixed in a definite proportion. These are then ground and the mixture is heated in a furnace. Sometimes scrap glass is also mixed with other raw materials. By doing so glass can be recycled and it also helps in melting of the mixture. The fused mixture is then allowed to cool. The glass so produced is transparent, non-crystalline and brittle. c) Types of glass and their uses: There are various types of glasses depending upon their composition and the purpose of their use. • Soda-lime glass: The glass produced as given above is called sodalime glass or soft glass. It is used for manufacture of bottles ordinary crockery, ordinary laboratory glass apparatus like soda glass test tubes etc. • Hard glass: If instead of sodium carbonate, potassium carbonate is used for making glass another variety of glass known as hard glass is produced. It can withstand very high temperatures. It is used for making hard glass laboratory apparatus like hard glass test tubes, beakers, conical flasks etc.
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• Borosilicate glass: It is sodium aluminium borosilicate. It can withstand rapid heating and cooling without breaking. It is used for making kitchenware and laboratory apparatus. It is sold under the trade names Borosil and Pyrex. • Flint or optical glass: It is used for making lenses, prisms, spectacles, etc. because of its excellent optical properties. It is composed of alkalis, lead oxide and silica. It is also known as flint glass. A superior variety of optical glasses is made by adding cerium oxide. It cuts harmful ultra violet rays that are harmful to eyes. It is known as Crooke’s glass. • Coloured glass: It is made by adding small quantities of oxides of different metals to basic ingredients. Blue glass contains traces of cobalt or copper oxide, green glass contains chromium ferrous oxide, red glass contains selenium oxide. • Fibre glass: It is produced by passing molten glass through rotating spinners when it gets converted into fine threads. It is used as an insulating material for heat, electricity and sound in different equipment like electric ovens, geysers, refrigerators, etc. It is also used for reinforcing plastics and rubber to make bodies of cars and scooters and safety helmets. CHECK YOUR PROGRESS 21.2 1. What is mixed with cement before using it for construction purposes? 2. Which type of glass can withstand rapid heating and cooling without breaking? 3. What is the role of small pieces of stone that are added to cement when it is used to make floor or roads? 4. How is coloured glass made? 21.3 SOME IMPORTANT CHEMICALS A large number of chemicals are used in industry and in our homes for various purposes. In this section we would learn about some such useful chemicals.

21.3.1 Washing soda Washing soda is used for washing of clothes. It is because of this chemical used that the clothes washed by a washerman appear so white. Chemically, washing soda is sodium carbonate decahydrate (Na2CO3.10H2O). It is an important chemical required as basic raw material in hundreds of industries. Now let us learn about the raw materials used in its manufacture and how is it manufactured. a) Raw materials required: The raw materials required to manufacture washing soda are • Lime stone is calcium carbonate (CaCO3) • Sodium chloride (NaCl) in the form of brine • Ammonia (NH3) b) Manufacture: Washing soda is manufactured by Solvay process. In this process, firstly, carbon dioxide is obtained by heating limestone strongly. CaCO3 CaO + CO2
lime stone quick lime carbon dioxide Materials in Our Daily Life : 101 :

It is then passed through cold brine (a solution of concentrated NaCl in water), which has previously been saturated with ammonia. NaCl(aq) + CO2(g) + NH3(g) + H2O(l) NaHCO3(s)+ NH4Cl(aq)
Sodium chloride ammonia sodium hydrogen carbonate ammonium chloride

NaHCO3 being sparingly soluble in water, crystallizes out. It is calcinated (heated strongly in a furnace) to get sodium carbonate. 2NaHCO3 Na2CO3 + CO2 + H2O Ammonia used in this process is regenerated by first converting the quicklime obtained earlier with water and then reacting it with ammonium chloride obtained from carbonating tower. CaO + H2O Ca(OH)2
quick lime slaked lime

Ca(OH)2 + 2NH4Cl CaCl2 + 2NH3 + 2H2O ammonium chloride calcium chloride c) Uses: Washing soda is used in the manufacture of glass, water glass, caustic soda, borax and soap powders. It is also used for the softening of water, as laboratory reagent and as a starting material for the preparation of a number of other sodium compounds. Of course, its most common use in laundry is for washing of fabrics and clothes from which it gets its name. 21.3.2 Baking soda You must have seen your mother using baking soda while cooking some dals. If you ask her why she uses it, she would tell that it helps in cooking some items faster which otherwise would take much longer time. Chemically, baking soda is sodium hydrogen carbonate or sodium bicarbonate and its formula is NaHCO3. a) Manufacture: You have already learned in the previous section that it is the primary product of the Solvay process used to manufacture washing soda. It gives small white crystals sparingly soluble in water. Its solution in water is alkaline in nature. b) Uses: Baking soda is mainly used in the baking industry. When sodium hydrogen carbonate or its solution is heated, it gives off carbon dioxide. It is this carbon dioxide which raises the dough during baking. The sodium

carbonate produced during the heating of sodium hydrogen carbonate gives bitter taste. Therefore, usually baking powder is used, which is a mixture of baking soda, NaHCO3 and an acid like tartaric acid. The latter is added to neutralize the sodium carbonate formed in the reaction given above, to avoid its bitter taste. You must have eaten cakes. They are made so soft and fluffy by using baking powder. Baking soda is also used in medicines to neutralize the excessive acidity in the stomach. Mixed with a solid acid such as citric or tartaric acid, it finds use in effervescent drinks used to cure indigestion. Another important use of baking soda is in certain types of fire extinguishers about which you have already learned in lesson 14.
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21.3.3 Bleaching powder Have you ever wondered at the whiteness of a new white cloth? How is it made so white? It is done by bleaching the cloth at the time of its manufacture. Bleaching is a process of removing colour from a cloth to make it whiter. Bleaching powder has been used for this purpose since long. Chemically, it is calcium oxychloride and its formula is CaOCl2. Now we shall learn about the raw materials required for its manufacture and how it is manufactured from them. a) Raw materials required: The raw materials required for manufacture of bleaching powder are • Slaked lime, Ca(OH)2 • Chlorine gas, Cl2 b) Manufacture: It is prepared in a vertical tower made of cast iron with inlets for chlorine and hot air near the base. The dry slaked lime, calcium hydroxide, is fed into the chlorinating tower from the top. It moves downward slowly and meets the upcoming current of chlorine. As a result of the reaction between them it is converted into bleaching powder which collects at the bottom. Ca(OH)2 + Cl2 CaOCl2 + H2O c) Uses: It is used mainly for bleaching cotton, linen and wood pulp in textile and paper factories. Apart from this, it is used as a disinfectant and germicide for the sterilization of water, in rendering wool unshrinkable and for the manufacture of chloroform. It also finds use as an oxidizing agent in many chemical industries. 21.3.4 Plaster of Paris You must have seen beautiful designs made on the ceiling and walls of rooms in many houses. They are made with Plaster of Paris, also called POP. a) Manufacture: It is manufactured from gypsum which is hydrated calcium sulphate (CaSO4.2H2O) found in nature. When gypsum is heated at about 325 K, it loses part of its water of crystallization to form CaSO4. ½H2O or 2CaSO4.H2O which is plaster of Paris. When made into a paste with a little water, Plaster of Paris sets to a hard mass, which expand with hardening. b) Uses: Plaster of Paris finds use in making casts and patterns. It is used for making plaster casts to hold fractured bones in position while they set. It is also used for making chalks for writing on blackboard. Now a days it is increasingly being used for plastering the walls, pillars and ceilings and to make ornamental patterns on them.

CHECK YOUR PROGRESS 21.3 1. What is the common name of NaHCO3? 2. Name the process used for manufacture of washing soda? 3. Which chemical can be used for removing stains of ink from clothes? 4. What is the chemical formula of Plaster of Paris?
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21.4 FIBRES: NATURAL AND SYNTHETIC Fibre is a fine thread like material, like cotton, which is woven or knitted into a cloth. We need different types of clothes, such as cotton, silk, nylon, polyester, etc. to suit different weather conditions. Fibres are made of polymers. Cotton consists of cellulose. Some of these like cotton, wool and silk are obtained from nature. They are called natural fibres. Many of them are man-made like nylon, polyester, terylene, liakra, etc. They are called synthetic fibres. 21.4.1 Polymers Many things that we see around us and use are polymers. We use plastic buckets, containers, electrical switches, etc. The clothes that we wear are made of polymers like cotton, wool, terylene, etc. Polymers are big molecules which are formed when a large number of small molecules join one another. The word polymer means many parts. The small molecules which make a polymer are called monomers. For example, ethene (C2H4) molecules join together and form the polymer known as polythene. a) Nylon: Nylon is a polymer of small monomeric units called amide (-CO-NH-) i.e. it is a polyamide. It is prepared by reaction of adipic acid and hexamethylenediamine. Terylene is crease resistant, durable and is not damaged by insects like moths and by mildew (fungi that form a white growth on plants and materials like cloth and paper). b) Polysters: Polyesters are another category of polymers. One important member of this family is dacron which is also known as terylene. It is prepared by reaction between terephthalic acid and ethylene glycol. It is crease resistant, durable and is not damaged by insects like moths and mildew. Therefore, it is suitable for making garments because they can be set into permanent creases and pleats. It has also been used to repair or replace segments of blood vessels. In the form of thin sheets it is used for manufacture of adhesive tapes and recording tapes. 21.4.2 Rubber a) Natural rubber: Natural rubber is chemically poly-cis-isoprene which is formed from the monomer isoprene. It comes from the sap of the Para rubber tree, Hevea brasiliensis. Trees are tapped by making a spiral cut through the bark. The sap is called latex. It is a white milky liquid. It is a suspension of tiny particles of rubber in water. These particles can be separated when acid is added to it and solid rubber is obtained. Raw rubber is soft and pliable i.e. it can be easily bent. It does not possess the main property that we associate with rubber, elasticity i.e. the ability to return to its original shape after stretching. Rubber is made elastic by heating it with a small amount (1 to 3%) of sulphur. This process is known as vulcanization. Apart from sulphur other substances are also added to natural rubber to modify its properties. Carbon black is added to make it stronger, flexible and more

resistant to wear and tear. For making car tyres, 2 parts of rubber are mixed
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with 1 part carbon black. If flexibility is not important fillers, such as clay or chalk, are added to make rubber hard and stiff. Rubber for floor tiles and mats contains fillers of this type. b) Synthetic rubber: Synthetic rubber supplements the natural rubber and helps save precious trees. Its properties are similar and sometimes better than those of natural rubber. The most common variety of synthetic rubber is made from the monomer butadiene CH2CH.CH.CH2. It can be vulcanized just like natural rubber. It has particularly good resistance to wear and tear, which makes it especially useful for making tyres. Other types of synthetic rubbers are made by mixing other monomers like styrene and chloroprene (commonly known as neoprene) with butadiene. 21.4.3 Plastics You must be using comb, toothbrush, jars and buckets in your house. All these items of daily use are made of plastic. Plastics are synthetic or man-made polymers. Let us learn about some of these. a) Polythene is a polymer made from ethene (CH2=CH2). It is one of the most commonly used materials. It is a soft plastic, which softens on heating. It is used for making bottles, buckets, and pipes, as covering for electrical wires and cables and as film for making bags. b) Polyvinyl chloride (PVC) is made from the monomer vinyl chloride (CH2=CHCl). It is used for making rain coats, handbags, toys including dolls, electrical goods and as a covering of electrical wires. c) Bakelite (Phenol-formaldehyde resin) is made by reacting phenol and formaldehyde. It is hard and quite a strong material. It is used for making combs, electrical switches, and plugs and for making handles of many kitchen utensils and electrical appliances like pans, pressure cookers, electric irons, kettles, and toasters. CHECK YOUR PROGRESS 21.4 1. What is a monomer? 2. What is the name of monomeric unit of natural rubber? 3. Why is sulphur added to rubber? 4. What is the full form of PVC? 21.5 MEDICINES Whenever we feel sick, we go to the doctor for medicines (also called drugs). Medicine is a substance used for treating diseases or illness. Let us study about some common types of medicines. 21.5.1 Anaesthetics Anaesthetics are drugs which produce a loss of sensation and consciousness. General anaesthetics result in loss of sensation and consciousness in the entire
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body. Examples are divinyl ethers, cyclopropane, etc. They are used during major surgical operations. Some anaesthetics like Novocain and Xylocaine which show their effect in a limited area are called local anaesthetics. They are used during small surgical operations and tooth extraction. 21.5.2 Antibiotics

Antibiotics are medicines which are used to kill bacteria, fungi and moulds. The first antibiotic discovered was penicillin which is very effective for pneumonia, bronchitis, sore throat, etc. Ampicillin is a slight modification of penicillin. It has wider applications. Other commonly used antibiotics are streptomycin, tetracycline and chloramphenicol. 21.5.3 Analgesics Analgesics are used for relieving pain. Aspirin, paracetamol, morphine are some examples of analgesics. They must be used only under medical supervision. 21.5.4 Antacids Antacids are used to treat acidity in stomach. Digene, ranitidine and omeprazole are some examples of antacids. 21.5.5 Antipyretics Antipyretics are the medicines which are used to bring down body temperature in high fever. Their administration leads to perspiration which brings down the temperature. Common examples are aspirin, paracetamol, analgin and phenacetin. In this section you learned about some important types of medicines. However, it must be remembered that medicines should always be taken on the advice of a doctor. CHECK YOUR PROGRESS 21.5 1. What is the use of the drug paracetamol? 2. What is the use of ranitidine? 3. Name an antibiotic. 4. Which types of medicines are used for relieving pain? 21.6 HARMFUL EFFECTS OF MAN-MADE MATERIALS In this lesson you have learnt about various materials that are useful to us. Many of them are obtained from natural resources while a large number of them are man-made. These days the latter are being used extensively. However, after use their disposal becomes a problem. Many of them are toxic in nature and pollute air and water. Some of them are so stable that they are not degraded easily and they get accumulated in the environment. Such materials should be recycled in order to avoid such problems. In the next lesson you will learn about the harmful effects of man-made materials and the related environmental problems in detail.
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LET US REVISE • Of all the materials that we see around us some are obtained from nature while others are prepared by man. • Candles are made from a mixture of paraffin wax and stearic acid. • Inks are coloured fluids or pastes that are used for writing or printing. • Soaps are sodium or potassium salts of long chain fatty acids while detergents are sodium or potassium salts of long chain sulphonic acids. Detergents can give lather even with hard water whereas soaps cannot. • Safety matches have a mixture of potassium chlorate and antimony trisulphide and glue at the head of match sticks and a mixture of red phosphorus and powdered glass on the striking surface. The heat generated when the match stick is struck starts the ignition. • Cement is one of the most important building material manufactured from limestone, clay and gypsum.

• Concrete is a mixture of cement, sand gravel and water. It sets to an extremely hard structure. • Glass is prepared by heating a mixture of washing soda, limestone and sand in a furnace. • Soda glass is used for manufacture of bottles, ordinary crockery, laboratory apparatus, etc. • Hard glass is made by using potassium carbonate in place of sodium carbonate. It can withstand very high temperatures and is used for making laboratory apparatus. • Borosilicate glass is sodium aluminium borosilicate and can withstand rapid heating and cooling. It is used for making kitchen and laboratory ware. • Flint glass is used for making lenses, prisms, spectacles, etc. • Coloured glass is made by adding small quantities of oxides of different metals. • Fibre glass is a mass of fine threads of glass used as an insulating material for heat, electricity and sound and reinforcing plastics and rubber. • Washing soda (Na2CO3.10H2O) is prepared by Solvay process. It is used in the manufacture of glass, caustic soda, borax and soap powders. It is used for softening of water, as a laboratory reagent and as a starting material for many sodium compounds. • Baking soda (NaHCO3) is the primary product of Solvay process. It is mainly used in baking industry and in fire extinguishers. • Baking powder is a mixture of baking soda and tartaric acid. • Bleaching powder (CaOCl2) is prepared by mixing chlorine and slaked lime. It is used for bleaching cotton, linen and wood pulp and for sterilization of water. • Plaster of Paris (CaSO4. ½H2O) is prepared by heating gypsum (CaSO4.2H2O). It is used for making casts and patterns and for plastering the walls, pillars and ceilings and to make ornamental patterns on them.
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• Polymers are big molecules formed when a large number of small molecules join together. Cotton, wool, terylene, etc. are some polymers. Nylon, polyesters, rubber and plastics are some important polymers. • Medicine is a substance used for treating diseases or illness. Anaesthetics, antibiotics, analgesics, antacids and antipyretics are some important types of drugs that are used. TERMINAL EXERCISES A. Multiple choice type questions. Choose the correct answer of the following: 1. The glass that can withstand rapid heating and cooling without breaking is (a) hard (b) soda-lime glass (c) borosilicate (d) flint 2. Novocain is an (a) antipyretic (b) analgesic (c) anaesthetic (d) antibiotic 3. Chloramphenicol is an (a) antibiotic (b) antipyretic (c) antacid (d) analgesic 4. Which of the following is not a raw material required for manufacture of washing soda? (a) Lime stone (b) Ammonia (c) Slaked lime (d) Sodium chloride

5. Which of the following is a man-made material? (a) Glass (b) Wood (c) Leather (d) Silk B. Descriptive type questions. 1. What are candles made of ? 2. What are the basic materials used for the manufacture of soaps? 3. What is concrete? 4. Mention two uses of bleaching powder. 5. Name the two substances used for making nylon. 6. For printing purpose why is ink used in the form of thick paste? 7. How striking the matchstick on the side of the matchbox helps in lighting it? 8. Why is gypsum added to the powdered clinkers during manufacture of cement? 9. Mention four uses of washing soda. 10. Give two examples each of antibiotics and analgesics. 11. What is an antipyretic? Give two examples. 12. What is vulcanization process? Why is natural rubber vulcanized? 13. List the raw materials required for manufacture of bleaching powder and describe its process of manufacture. 14. How is Plaster of Paris manufactured? Give its two uses. 15. Name three plastics and give one use of each one of them. 16. What is a candle made of? Explain the process of lighting it.
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17. Differentiate between soaps and detergents. Why soaps do not form lather with hard water while detergents can? 18. List the raw materials required for the manufacture of cement. Describe the process of manufacture of cement briefly. 19. How is soda-lime glass manufactured? Describe briefly. What changes are made in the raw materials in the manufacture of optical glass and Borosil glass? How is colour imparted to glass? 20. Describe the process of manufacture of washing soda giving appropriate chemical equations. Mention two of its uses. 21. What are the monomeric units of polythene and polyvinyl chloride? Give three uses of each of these. ANSWERS TO CHECK YOUR PROGRESS 21.1 1. Natural materials: Any two of the following – wood, silk, cotton, leather and rubber Man-made materials: Any two of the following – synthetic textiles like terylene and nylon, cement, glass, plastics, dyes, soap, detergents, fertilizers, insecticides and pesticides. 2. Candles are made from mixtures of paraffin wax and stearic acid. 3. Soaps are sodium or potassium salts of fatty acids. 4. No, because soap is precipitated out as salts of calcium and potassium in hard water. 5. Safety matches 21.2 1. Sand and water 2. Borosilicate glass

3. To increase the strength of cement 4. By adding small quantities of different metals 21.3 1. Baking soda 2. Solvay process 3. Bleaching powder 4. CaSO4. H2O or CaSO4.1/2H2O 21.4 1. Monomer is a substance whose small molecules combine with one another and make a polymer. 2. Isoprene 3. To make rubber elastic 4. Polyvinyl chloride
Materials in Our Daily Life : 109 :

21.5 1. As an antipyretic or to get relief from fever 2. It is an antacid used to reduce acidity 3. Ampicillin or penicillin 4. Analgin or analgesic GLOSSARY Analgesics: Medicines which are used for relieving pain. Antacids: Medicines which are used to treat acidity in stomach. Antibiotics: Medicines which are used to kill bacteria, fungi and moulds. Antipyretics: Medicines which are used to bring down body temperature in high fever. Bakelite: Phenol-formaldehyde resin made by reacting phenol and formaldehyde. Baking powder: Mixture of baking soda and tartaric acid. Baking soda: Common name of NaHCO3. Bleaching powder: Common name of CaOCl2. Borosilicate glass (Borosil glass): Sodium aluminium borosilicate and can withstand rapid heating and cooling. Concrete: Mixture of cement, sand, gravel and water. Dacron: Polyester prepared by reaction between terephthalic acid and ethylene glycol. Detergents: Sodium or potassium salts of long chain sulphonic acids. Fibre glass: Mass of fine threads of glass used as an insulating material for heat, electricity and sound and reinforcing plastics and rubber. Flint or optical glass: Lead-potash lime glass which is used for making lenses, prisms, spectacles, etc. General anaesthetics: Those drugs which result in loss of sensation and consciousness in the entire body. Hard glass: Variety of glass that can withstand very high temperatures. Ink: Coloured fluid or a paste, which is used for writing or printing. Local anaesthetics: Drugs which show their effect in a limited area. Man-made materials: Materials which are prepared by man. Medicine: Substance used for treating diseases or illness.

Monomers: Small molecules which make a polymer by joining one another. Natural materials: Materials which we get from nature. Nylon: Polymer of small monomeric units called amide (-CO-NH-) i.e. it is a polyamide Plaster of Paris: Common name of CaSO4 ½H2O.
: 110 : Materials in Our Daily Life

Polymers: Big molecules formed when a large number of small molecules join together. Polythene: Polymer made from ethene (CH2=CH2). Polyvinyl chloride (PVC): Polymer is made from the monomer vinyl chloride (CH2=CHCl). Reinforced Concrete Cement (RCC): Concrete that is strengthened by filling it around or over a network of steel rods and allowing it to set. Rubber: Chemically poly-cis-isoprene which is formed from the monomer isoprene. Soaps: Sodium or potassium salts of long chain fatty acids. Synthetic rubber: Made from the monomer butadiene (CH2CH.CH.CH2). Vulcanization: The rocess of heating of rubber with a small amount (1-3%) of sulphur to make it elastic. Washing soda: Common name of Na2CO310H2O http://www.nios.ac.in/secscicour/CHAPTER21.pdf

Warm Glass
Guide to Fusing, Slumping, and Related Kiln-forming Techniques
• • • • • • • •

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Delphi Glass

Dichro Depot Dichroic and More Ed Hoy's International

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SUMMARY OF COEFFICIENT OF EXPANSION FOR COMMON GLASSES AND METALS (with melting points for common metals) All figures times 10 (-7)
Glass information

Metals information

Type of Glass Bullseye tested compatible (Also Uroboros 90) Effetre (Moretti) sheets and rods (some variation; should test) Spectrum System 96 (also Uroboros 96) Borosilicate (Pyrex)

Coefficient of expansion 90

104

96 32.5 83 to 87 (depends on manufacturer) May be even higher or lower

Window (float) glass (Also includes most bottles)

Source: Manufacturer's data

Type of metal Aluminum Brass, navy Copper Gold Iron, cast Lead Silver

Coefficient of Expansion 248 212 176 140 108 295 191

Melting point (°F) 1218 1650 1981 1945 2300 621 1764

Melting point (°C) 659 900 1081 1061 1260 328 962

Steel, high carbon Steel, stainless Tin

121 171 398

2500 2600-2750 788

1374 1430-1507 415

Note: These are for pure metals. Alloys can vary widely. I have seen other sources with slightly different COEs, but most are close to these figures. (And besides, they're close enough for government work.) Source: U.S. Military Training Circular No. 9-237, "Welding Theory and Application." For a technical discussion of the thermal expansion calculation for glass, go here: http://glassproperties.com/expansion/ExpansionMeasurement.htm

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Thermal expansion
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Thermodynamics

Branches[show] Laws[show] Systems[show] System properties[show]
Material properties[hide]

Specific heat capacity c =

T N 1 Compressibility β = − V 1 Thermal expansion α = V
Property database

Equations[show] Potentials[show]

Internal energy Enthalpy

U(S,V) H(S,p) = U + pV

Helmholtz free energy A(T,V) = U − TS Gibbs free energy G(T,p) = H − TS
History and culture[show] Scientists[show]
• • •

v d e

Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.[1] When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is limited in size, and only occurs within limited temperature ranges (see examples below). The degree of expansion divided by the change in temperature is called the material's coefficient of thermal expansion and generally varies with temperature.

Contents
[hide]


• •

• • • • • • • •

1 Overview o 1.1 Predicting expansion o 1.2 Contraction effects o 1.3 Factors affecting thermal expansion 2 Coefficient of thermal expansion o 2.1 General volumetric thermal expansion coefficient 3 Expansion in solids o 3.1 Linear expansion  3.1.1 Effects on strain o 3.2 Area expansion o 3.3 Volumetric expansion  3.3.1 Isotropic materials o 3.4 Anisotropic materials 4 Expansion in gases 5 Expansion in liquids 6 Apparent and Absolute Expansion 7 Examples and Applications 8 Thermal expansion coefficients for various materials 9 See also 10 References 11 External links

[edit] Overview
[edit] Predicting expansion
If an equation of state is available, it can be used to predict the values of the thermal expansion at all the required temperatures and pressures, along with many other state functions.

[edit] Contraction effects
A number of materials contract on heating within certain temperature ranges; this is usually called negative thermal expansion, rather than "thermal contraction". For example, the coefficient of thermal expansion of water drops to zero as it is cooled to roughly 4 °C and then becomes negative below this temperature; this means that water has a maximum density at this temperature, and this leads to bodies of water maintaining this temperature at their lower depths during extended periods of sub-zero weather. Also, fairly pure silicon has a negative coefficient of thermal expansion for temperatures between about 18 kelvin and 120 kelvin.[2]

[edit] Factors affecting thermal expansion
Unlike gases or liquids, solid materials tend to keep their shape when undergoing thermal expansion. Thermal expansion generally decreases with increasing bond energy, which also has an effect on the hardness of solids, so, harder materials are more likely to have lower thermal expansion. In general, liquids expand slightly more than solids. The thermal expansion of glasses is higher compared to that of crystals.[3] At the glass transition temperature, rearrangements that occur in an amorphous material lead to characteristic discontinuities of coefficient of thermal expansion or specific heat. These discontinuities allow detection of the glass transition temperature where a supercooled liquid transforms to a glass.[4] Absorption or desorption of water (or other solvents) can change the size of many common materials; many organic materials change size much more due to this effect than they do to thermal expansion. Common plastics exposed to water can, in the long term, expand many percent.

[edit] Coefficient of thermal expansion
The coefficient of thermal expansion describes how the size of an object changes with a change in temperature. Specifically, it measures the fractional change in size per degree change in temperature at a constant pressure. Several types of coefficients have been developed: volumetric, area, and linear. Which is used depends on the particular application and which dimensions are considered important. For solids, one might only be concerned with the change along a length, or over some area. The volumetric thermal expansion coefficient is the most basic thermal expansion coefficient. In general, substances expand or contract when their temperature changes, with expansion or contraction occurring in all directions. Substances that expand at the same rate in every direction are called isotropic. For isotropic materials, the area and linear coefficients may be calculated from the volumetric coefficient. Mathematical definitions of these coefficients are defined below for solids, liquids, and gasses.

[edit] General volumetric thermal expansion coefficient
In the general case of a gas, liquid, or solid, the volumetric coefficient of thermal expansion is given by

The subscript p indicates that the pressure is held constant during the expansion, and the subscript "V" stresses that it is the volumetric (not linear) expansion that enters this general definition. In the case of a gas, the fact that the pressure is held constant is important, because the volume of a gas will vary appreciably with pressure as well as temperature. For a gas of low density this can be seen from the ideal gas law.

[edit] Expansion in solids
Materials generally change their size when subjected to a temperature change while the pressure is held constant. In the special case of solid materials, the pressure does not appreciably affect the size of an object, and so, for solids, it's usually not necessary to specify that the pressure be held constant. Common engineering solids usually have coefficients of thermal expansion that do not vary significantly over the range of temperatures where they are designed to be used, so where extremely high accuracy is not required, practical calculations can be based on a constant, average, value of the coefficient of expansion.

[edit] Linear expansion
The linear thermal expansion coefficient relates the change in a material's linear dimensions to a change in temperature. It is the fractional change in length per degree of temperature change. Ignoring pressure, we may write:

where L is the linear dimension (e.g. length) and dL / dT is the rate of change of that linear dimension per unit change in temperature. The change in the linear dimension can be estimated to be:

This equation works well as long as the linear expansion coefficient does not change much over the change in temperature ΔT. If it does, the equation must be integrated. [edit] Effects on strain For solid materials with a significant length, like rods or cables, an estimate of the amount of thermal expansion can be described by the material strain, given by and defined as:

where is the length before the change of temperature and the length after the change of temperature. For most solids, thermal expansion is proportional to the change in temperature:

is

Thus, the change in either the strain or temperature can be estimated by:

where

is the difference of the temperature between the two recorded strains, measured in degrees Celsius or kelvins, and is the linear coefficient of thermal expansion in inverse kelvins.

[edit] Area expansion
The area thermal expansion coefficient relates the change in a material's area dimensions to a change in temperature. It is the fractional change in area per degree of temperature change. Ignoring pressure, we may write:

where A is some area of interest on the object, and dA / dT is the rate of change of that area per unit change in temperature. The change in the linear dimension can be estimated as:

This equation works well as long as the linear expansion coefficient does not change much over the

change in temperature δT. If it does, the equation must be integrated.

[edit] Volumetric expansion
For a solid, we can ignore the effects of pressure on the material, and the volumetric thermal expansion coefficient can be written [5]:

where V is the volume of the material, and dV / dT is the rate of change of that volume with temperature. This means that the volume of a material changes by some fixed fractional amount. For example, a steel block with a volume of 1 cubic meter might expand to 1.002 cubic meters when the temperature is raised by 50 °C. This is an expansion of 0.2%. If we had a block of steel with a volume of 2 cubic meters, then under the same conditions, it would expand to 2.004 cubic meters, again an expansion of 0.2%. The volumetric expansion coefficient would be 0.2% for 50 °C, or 0.004% per degree C. If we already know the expansion coefficient, then we can calculate the change in volume

where ΔV / V is the fractional change in volume (e.g., 0.002) and ΔT is the change in temperature (50 C). The above example assumes that the expansion coefficient did not change as the temperature changed. This is not always true, but for small changes in temperature, it is a good approximation. If the volumetric expansion coefficient does change appreciably

with temperature, then the above equation will have to be integrated:

where T0 is the starting temperature and αV(T) is the volumetric expansion coefficient as a function of temperature T. [edit] Isotropic materials For exactly isotropic materials, and for small expansions, the linear thermal expansion coefficient is one third the volumetric coefficient.

This ratio arises because volume is composed of three mutually orthogonal directions. Thus, in an isotropic material, for small differential changes, one-third of the volumetric expansion is in a single axis. As an example, take a cube of steel that has sides of length L. The original volume will be V = L3 and the new volume, after a temperature increase, will be

We can make the substitutions ΔV = αVL3ΔT and, for isotropic materials, ΔL = αLLΔT. We now have:

Since the volumetric and linear coefficients are defined only for extremely small temperature and dimensional

changes (that is, when ΔT and ΔL are small), the last two terms can be ignored and we get the above relationship between the two coefficients. If we are trying to go back and forth between volumetric and linear coefficients using larger values of ΔT then we will need to take into account the third term, and sometimes even the fourth term. Similarly, the area thermal expansion coefficient is 2/3 of the volumetric coefficient.

This ratio can be found in a way similar to that in the linear example above, noting that the area of a face on the cube is just L2. Also, the same considerations must be made when dealing with large values of ΔT.

[edit] Anisotropic materials
Materials with anisotropic structures, such as crystals (with less than cubic symmetry) and many composites, will generally have different linear expansion coefficients in different directions. As a result, the total volumetric expansion is distributed unequally among the three axes. If the crystal symmetry is

monoclinic or triclinic, even the angles between these axes are subject to thermal changes. In such cases it is necessary to treat the coefficient of thermal expansion as a tensor with up to six independent elements. A good way to determine the elements of the tensor is to study the expansion by powder diffraction.

[edit] Expansion in gases
For an ideal gas, the volumetric thermal expansivity (i.e. relative change in volume due to temperature change) depends on the type of process in which temperature is changed. Two known cases are isobaric change, where pressure is held constant, and adiabatic change, where no work is done and no change in entropy occurs. In an isobaric process, the volumetric thermal expansivity, which we denote βp, is:

The index p denotes an

isobaric process.

[edit] Expansio n in liquids
This section requires expansio n. Theoretically, the coefficient of linear expansion can be found from the coefficient of volumetric expansion (β≈3α). However, for liquids, α is calculated through the experimental determination of β.

[edit] Apparent and Absolute Expansio n
When measuring the expansion of a liquid, the measurement

must account for the expansion of the container as well. For example, a flask, that has been constructed with a long narrow stem filled with enough liquid that the stem itself is partially filled, when placed in a heat bath will initially show the column of liquid in the stem to drop followed by the immediate increase of that column until the flask/liquid/h eat bath system has thermalized. The initial observation of the column of liquid dropping is not due to an initial contraction of the liquid but rather the expansion of the flask as it contacts the heat bath

first. Soon after, the liquid in the flask is heated by the flask itself and begins to expand. Since liquids typically have a greater expansion over solids the liquid in the flask eventually exceeds that of the flask causing the column of liquid in the flask to rise. A direct measurement of the height of the liquid column is a measurement of the Apparent Expansion of the liquid. The Absolute expansion of the liquid is the apparent expansion corrected for the expansion of the containing vessel.[6]

[edit] Examples and Applicati ons
For applications using the thermal expansion property, see bi-metal and mercury-inglass thermometer. The expansion and contraction of materials must be considered when designing large structures, when using tape or chain to measure distances for land surveys, when designing molds for casting hot material, and in other engineering applications when large changes in dimension due to

temperature are expected. Thermal expansion is also used in mechanical applications to fit parts over one another, e.g. a bushing can be fitted over a shaft by making its inner diameter slightly smaller than the diameter of the shaft, then heating it until it fits over the shaft, and allowing it to cool after it has been pushed over the shaft, thus achieving a 'shrink fit'. Induction shrink fitting is a common industrial method to pre-heat metal components between 150 °C and 300 °C thereby causing them to expand and allow for the insertion or

removal of another component. There exist some alloys with a very small linear expansion coefficient, used in applications that demand very small changes in physical dimension over a range of temperatures. One of these is Invar 36, with α approximatel y equal to 0.6×10−6/°C. These alloys are useful in aerospace applications where wide temperature swings may occur. Pullinger's apparatus is used to determine the linear expansion of a metallic rod in the laboratory. The apparatus consists of a

metal cylinder closed at both ends (called a steam jacket). It is provided with an inlet and outlet for the steam. The steam for heating the rod is supplied by a boiler which is connected by a rubber tube to the inlet. The center of the cylinder contains a hole to insert a thermometer. The rod under investigation is enclosed in a steam jacket. One of its ends is free, but the other end is pressed against a fixed screw. The position of the rod is determined by a micrometer screw gauge or spherometer. The control of thermal

expansion in ceramics is a key concern for a wide range of reasons. For example, ceramics are brittle and cannot tolerate sudden changes in temperature (without cracking) if their expansion is too high. Ceramics need to be joined or work in consort with a wide range of materials and therefore their expansion must be matched to the application. Because glazes need to be firmly attached to the underlying porcelain (or other body type) their thermal expansion must be tuned to 'fit' the body so that

crazing or shivering do not occur. Good example of products whose thermal expansion is the key to their success are CorningWare and the spark plug. The thermal expansion of ceramic bodies can be controlled by firing to create crystalline species that will influence the overall expansion of the material in the desired direction. In addition or instead the formulation of the body can employ materials delivering particles of the desired expansion to the matrix. The thermal expansion of glazes is controlled by their chemical

composition and the firing schedule to which they were subjected. In most cases there are complex issues involved in controlling body and glaze expansion, adjusting for thermal expansion must be done with an eye to other properties that will be affected, generally trade-offs are required. Heat-induced expansion has to be taken into account in most areas of engineering. A few examples are: Metal framed windows need rubber spacers • Rubber tires


Metal hot water heating pipes should not be used in long straight lengths • Large structures such as railways and bridges need expansion joints in the structures to avoid sun kink • One of the reasons for the poor performa nce of cold car engines is that parts have inefficien tly large spacings until the normal operating temperatu re is achieved. • A gridiron pendulum


uses an arrangem ent of different metals to maintain a more temperatu re stable pendulum length. • A power line on a hot day is droopy, but on a cold day it is tight. This is because the metals expand under heat. Thermometer s are another application of thermal expansion — most contain a liquid (usually mercury or alcohol) which is constrained to flow in only one direction (along the tube) due to changes in volume brought about

by changes in temperature. A bi-metal mechanical thermometer uses a bimetallic strip and bends due to the differing thermal expansion of the two metals.

[edit] Thermal expansio n coefficien ts for various materials
Main article: Thermal expansion coefficients of the elements (data page) This section summarizes the coefficients for some common materials. In the table below, the range for α is from 10−7/°C for hard solids to

10−3/°C for organic liquids. α varies with the temperature and some materials have a very high variation. For isotropic materials the coefficients linear thermal expansion α and volumetric thermal expansion β are related by β = 3α. For liquids usually the coefficient of volumetric expansion is listed and linear expansion is calculated here for comparison. (The formula β≈3α is usually used for solids.)[7]

V ol Li u ne m ar et co ric eff co ici eff en Mat ici t, No eria en α, tes l t, at β, 20 at °C 20 (1 °C 0−6 (1 /° −6 0 C) /° C) Alu min 23 69 ium Ben zoc 12 yclo 42 6 bute ne Bra 19 57 ss Car bon 10 32 stee .8 .4 l Con cret 12 36 e Cop 17 51 per Dia mon 1 3 d Eth 25 75 anol 0 0[8] Gall 5. 17 ium 8 .4

V ol Li u ne m ar et co ric eff co ici eff en Mat ici t, No eria en α, tes l t, at β, 20 at °C 20 (1 °C 0−6 (1 /° −6 0 C) /° C) (III) arse nide Gas 31 95 olin 7 0[7] e Gla 8. 25 ss 5 .5 Gla ss, 3. 9. bor 3 9 osili cate Gol 14 42 d Indi um 4. 13 pho 6 .8 sphi de Inva 1. 3. r 2 6 11 33 Iron .8 .3 Kap 20 60 Du ton [9] Po

V ol Li u ne m ar et co ric eff co ici eff en Mat ici t, No eria en α, tes l t, at β, 20 at °C 20 (1 °C 0−6 (1 /° −6 0 C) /° C) nt ™ Ka pto n® 20 0E N Lea 29 87 d MA 9. CO 3[1 R 0] Ma gne 26 78 siu m 18 Mer 61 2[1 cury 1] Mol ybd 4. 14 enu 8 .4 m Nic 13 39 kel

V ol Li u ne m ar et co ric eff co ici eff en Mat ici t, No eria en α, tes l t, at β, 20 at °C 20 (1 °C 0−6 (1 /° −6 0 C) /° C) Per pe ndi cul 54 Oak [12] ar to the gra in Dou 27 rad glas [13] 75 ial -fir tan Dou 45 ge glas [13] 75 nti -fir al par all Dou 3. el glas 5 75 to -fir [13] gra in Plat inu 9 27 m PV 15 52 C 6

V ol Li u ne m ar et co ric eff co ici eff en Mat ici t, No eria en α, tes l t, at β, 20 at °C 20 (1 °C 0−6 (1 /° −6 0 C) /° C) Qua rtz 0. 1. (fus 59 77 ed) Rub 23 77 ber 1 Par all el to Sap 5. C phir 3[1 axi e 4] s, or [00 1] Sili 2. con 8. 77 Car [15] 31 bide Sili 3 9 con Silv 18 54 er [16] 0. Sita 0. 15 ll [17] 45

V ol Li u ne m ar et co ric eff co ici eff en Mat ici t, No eria en α, tes l t, at β, 20 at °C 20 (1 °C 0−6 (1 /° −6 0 C) /° C) Stai nles 17 51 s .3 .9 stee l De pe 11 33 nds .0 .0 on Stee ~ ~ co l 13 39 mp .0 .0 osi tio n Tita 8. niu 6 m Tun 4. 13 gste 5 .5 n 20 Wat 69 7[1 er 1] ≐ Yb ≐ [1 Ga 0 0 8] Ge

[edit] See also


Autove

nt Grünei sen parameter


[edit] Referenc es
1.
^ Paul A., Tipler; Gene Mosca (2008) . Physic s for Scienti sts and Engin eers, Volum e1 (6th ed.). New York, NY: Worth Publis hers. pp. 66 6–670. ISBN 1429201320. http:// books. google

.com/? id=B MVR3 78Jh0C &pg= PA668 &dq= %22P hysics +for+ Scienti sts+an d+Eng ineers %22+t ipler+ %22th ermal +expa nsion %22& cd=1#.

2.
^ W. Murra y Bullis (1990) . "Chapt er 6". In O'Mar a, Willia m C.; Herrin g, Robert B.; Hunt, Lee P.. Handb ook of semico nducto r silicon techno logy.

Park Ridge, New Jersey: Noyes Public ations. p. 431. ISBN 0815512376. http:// books. google .com/? id=CO cVgAt qeKkC &pg= PA431 &dq=s ilicon +negat ive+ %22co efficie nt+of+ therma l+expa nsion %22#v =onep age&q =silico n %20ne gative %20% 22coef ficient %20of %20th ermal %20ex pansio n %22& f=false .

Retrie ved 2010 -0711.

3.
^ Varsh neya, A. K. (2006) . Funda mental s of inorga nic glasse s. Sheffi eld: Societ y of Glass Techn ology. ISBN 01271 49708.

4.
^ Ojova n, M. I. (2008) . "Confi gurons : thermo dynam ic param eters and symm etry change s at glass transiti

on". Entrop y 10: 334– 364. Bibco de 2008E ntrp..1 0..334 O. doi:10. 3390/e 10030 334.

5.
^ Turcot te, Donal d L.; Schub ert, Gerald (2002) . Geody namic s (2nd ed.). Cambr idge. ISBN 0-521666244.

6.
^ Ganot, A., Atkins on, E. (1883) . Eleme ntary treatis e on physic s experi

mental and applie d for the use of colleg es and school s, Willia m and Wood & Co, New York, page 272-3.

7.
^ab "Ther mal Expan sion". http:// www. ac.ww u.edu/ ~vawt er/Phy sicsNe t/Topi cs/The rmal/T hermE xpan.h tml.

8.
^ Young ; Geller. Young and Geller Colleg e Physic s (8th ed.). ISBN

08053 92181.

9.
^ "DuPo nt™ Kapto n® 200EN Polyi mide Film". http:// www. matwe b.com/ search/ datash eettext .aspx? matgui d=305 905ff1 ded40f daa34a 18d87 27a4d c.

10.
^ "MAC OR data sheet" (PDF). http:// www. cornin g.com/ docs/s pecialt ymater ials/pis heets/ Macor .pdf.

11.
^ab "Prope rties of

Comm on Liquid Materi als". http:// www. efunda .com/ materi als/co mmon _matl/ Comm on_Ma tl.cfm? MatlP hase= Liquid &Matl Prop= Therm al.

12.
^ "WDS C 340. Class Notes on Therm al Proper ties of Wood ". http:// www.f orestry .caf.w vu.edu /progr ams/w oodind ustries /wdsc3 40_7.h tm.

13.
^abc "the

coeffic ients of therma l expans ion of wood an wood produc ts". http://i r.librar y.oreg onstate .edu/x mlui/b itstrea m/han dle/19 57/159 7/FPL _1487 ocr.pd f.

14.
^ "Sapp hire". http://a merica s.kyoc era.co m/kicc /pdf/K yocera %20Sa pphire. pdf.

15.
^ "Basic Param eters of Silicon Carbid e (SiC)". http://

www.i offe.rs si.ru/S VA/N SM/Se micon d/SiC/ basic.h tml.

16.
^ "Ther mal Expan sion Coeffi cients" . http:// hyperp hysics. phyastr.gs u.edu/ hbase/t ables/t hexp.h tml#c1 .

17.
^ "Star Instru ments" . http:// www.s tarinstru ments. com/ru ssian.h tml.

18.
^ Salvad or, James R.; Guo,

Fu; Hogan , Tim; Kanatz idis, Merco uri G. (2003) . "Zero therma l expans ion in YbGa Ge due to an electro nic valenc e transiti on". Nature 425 (6959) : 702. Bibco de 2003N atur.42 5..702 S. doi:10. 1038/n ature0 2011. PMID 14562 099. http:// www. nature. com/n ature/j ournal/ v425/n 6959/f ull/nat ure020

11.htm l.

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Conta ct us http://en.wikipedia.org/wiki/Thermal_expansion

Thermal Expansion Coefficients at 20 C
Material Glass, ordinary Glass, pyrex Quartz, fused Aluminum Brass Copper Iron Steel Platinum Tungsten Gold Silver Fractional expansion Fractional expansion per degree C x10^-6 per degree F x10^-6 9 4 0.59 24 19 17 12 13 9 4.3 14 18 Thermal expansion discussion HyperPhysics***** Thermodynamics Go Back 5 2.2 0.33 13 11 9.4 6.7 7.2 5 2.4 7.8 10 Index Tables

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Glass For Mirrors
There are very many glasses that can be used for making mirrors and we often get asked about the glass we use and which glass is really the best? This page may not give you a perfect answer, but we hope it helps you understand the question. What may be "best" for one person may not be the right answer for another. The answer will depend to some extent on how much money is available and what environment the mirror is to be used in.

First Principles

The first thing to note is that a glass with good optical transmission properties is not necessary, - light will not be travelling through the glass, - it will be reflecting off the surface.
(Perhaps Cassegrain secondary's excluded? - See the testing page for an explanation.)

So all that is needed is a glass with good physical properties, - but that still leaves plenty of different glasses to choose from. The second thing is cost and manufacture related. Most glasses used for astronomical purposes are a "spin off" from another major market. Plate glass has thousands of uses with windows being the most obvious. Suprax is used for high temperature lamps and laboratory glass-ware and Pyrex is used for millions of household and cooking utensils. Both are trade names for what is really low expansion Borosilicate glass. They are well known by their trade names and the point is that it is large volume production in another market that drives down the cost of these glasses and makes them available for the astronomical community at reasonable prices.

Glass, Temperature & Distortion
The main physical issue with glass for telescope mirrors is the distortion suffered when temperature changes. It is a fact of life that all materials change their size to some extent when they change temperature and glass is no exception. The amount of size change is always small, but can still be significant when compared with the wavelength of light. It is measured by the "Coefficient of Thermal Expansion" and with glass it is generally measured in "Parts Per Million Per Degree Centigrade" or "PPM/Deg C" for short.

As an example: Plate glass can be made of various constituents and has a range of thermal expansion values around the generally published value of 8.6 PPM/Deg C. So assuming 8.6PPM/Deg C: This means that if a sheet of Plate glass 1" thick has its temperature raised by 10 Deg C, it will expand and end up as 1.000086 thick. Since the wavelength of light is about 0.000022", the mirror surface would have moved nearly four wavelengths from its original position. That's not too bad by itself if you can allow the mirror time to stabilise after the temperature change so that every part of the mirror has expanded and reached the new temperature.

Where a glass mirror experiences a sudden change in temperature, - such as moving your telescope from the house to the garden, - the glass close to the surface will adapt fairly quickly, but the glass deep inside the mirror will take longer to adapt. This will mean the mirror distorts and the parabolic curve on the mirror surface "ripples" out of shape until the temperature of the glass stabilises. (And you can forget about obtaining good images from your nominally 1/4 Wave mirror until it does!)
Opposite is an example of what happens to the mirror surface. Glass nearer the surface cools quicker than inside. The corners cool faster than anywhere else. This example is an exaggeration as the real movements are microscopic, - but it will be enough to disturb the images seen through the telescope until the mirror temperature stabilises.

The thicker the mirror, - the longer it takes to adapt. Since larger mirrors have to be thicker for strength, larger mirrors take longer to stabilise. Different glasses have different Coefficients of Thermal expansion, so it is a good idea to use a "low expansion glass" with a very small coefficient if you can - then there is very little expansion to worry about?

If a mirror is made of a glass that does suffer significant expansion, then the time the mirror will take to stabilise after a temperature change is affected by two other factors, the "Thermal Conductivity" and the "Specific Heat"
Thermal Conductivity means how fast heat travels through the glass, - the faster it can travel, the faster the glass stabilises. Metals like copper have very high values. Unfortunately any type of glass is very poor in comparison with metals. Specific heat means how much heat energy is needed to be put into the glass to raise the temperature. This is a bit harder to explain? It is the capacity of the material to absorb heat. A high specific heat means the glass takes longer to stabilise.
An analogy is with batteries. There are many different types and sizes of 9V batteries. Each will keep equipment like a transistor radio working for a different length of time depending on its capacity. The higher the capacity, the longer the radio will keep running. The capacity of the battery is analogous to specific heat in glass. The higher the specific heat, the longer the glass takes to stabilise after a temperature change.

So in a glass for a mirror, we are ideally looking for a glass with a low "Coefficient of Thermal expansion" to limit the expansion suffered with temperature. As subsidiary factors we may take into account high "Thermal Conductivity" and low "Specific Heat" to reduce the time it takes for the glass to stabilise. Finally - cost has to be a consideration - the mirror should be as cheap as possible.

Glass Availability
Unfortunately Oldham Optical does not use thousands of tons of glass a year and is therefore not a priority customer for any of the glass makers. We only use relatively small amounts of glass and have to wait our turn for deliveries. A lot of Pyrex was made in Sunderland until recently. Sunderland is only about 80 miles from our workshop, - so you would expect it was very easy for us to obtain supplies of this glass? Unfortunately the vast majority of Sunderland's output went abroad and there was a very poor distribution

network in this country for the type of disks and sheet we needed. It was often easier to obtain supplies of the similar glass - Suprax - from Germany, - but even then, delivery dates are not guaranteed. One big source of disks for astronomy over the last few years came from the "left over" glass in the kiln after a melt had finished. The kiln would typically contain more glass than was needed to fill the waiting molds. The remaining glass was often cast into simple plain 600mm disks. This emptied the kiln so fresh materials could be used for the next melt. These disks were ideal for astronomical mirrors but it meant the glass makers had to overestimate the amount of glass they required to fulfil their orders before any of these disks would be produced. Delivery dates were unreliable but they were cheap in comparison to placing a special order for the same size disk.
If you needed anything bigger than 600mm, - it always meant a special order.

There are still supplies of these disks to be had, but with better computer control, there is never as much excess glass remaining after a melt to cast into disks. We are able to get sufficient supplies of Pyrex and Suprax for our normal needs, but there is always uncertainty over delivery dates. Sometimes our orders are supplied 3-4 months late. This means we have difficulty offering firm dates for delivery of finished mirrors when an order is placed. An alternate glass produced from 2009 is Supremax. This is produced by Schott in sheets of 1.2m x 1.5m up to 66mm thick. These sheets are then water jet cut into disks as required. This glass now comprises a fair amount of our general output. However delivery dates are still long.
We can usually firm up delivery dates once the glass has arrived. Please don't be afraid to pick up the phone and check the progress of your order.

If Pyrex is requested, we usually import direct from the USA, For Suprax and Supremax, we usually obtain it from Germany through distributors, We have also used some large BVC glass disks from Canada. Plate glass is obtained locally through distributers.

The Best Glass?
So what Glass is best for primary mirrors? - There is no one answer. If the mirror is to be always kept and used in a temperature controlled environment 24 hours a day, - or at least if the mirror can be allowed a fairly long time to settle down and equalise its temperature after being moved, then you can't beat the cheapest glass available, - Plate Glass. There would be no point in paying extra for anything else. If however you are building a space telescope, or are a Professional Astronomer affiliated with a large company or institute, or perhaps a very rich amateur? - Money is no object to you and the mirror will typically be subject to large temperature changes but is needed to be available for use as soon as possible? - You may be considering Schott Zerodur, Corning ULE, Fused Silica or a similar glass with an extremely low thermal expansion. If you are the "average amateur" who keeps his Telescope in the house and then either transports it to site in the back of a car, or perhaps just sets it up in the back garden, - then you may be looking for something between those two extremes, say a low expansion glass that is not that much more expensive than plate glass?
(And don't worry! - You are in very good company, - the 200" Hale Telescope Mirror is Pyrex.)

In practice in the astronomical market, there is very little demand today for plate glass primary mirrors. This is even in the small sizes below 12" diameter where their thermal expansion does not cause any practical problems. While we can produce plate glass mirrors if requested, we just offer low expansion glass primary mirrors as standard. Below is a table listing salient facts and figures of the main types of glass available and used by Oldham Optical for mirrors.
Glass Type Thermal Thermal Relative Coefficie Specific Conductivi Material nt of heat ty Cost Expansio (J/Kg/De (W/M/Deg (Plate n (PPM/ g C) C) Glass=1) Deg C) Comments

Plate Glass

>8.6

0.75

730

1

Produced by Everybody. Suitable for Elliptical flats. Quite suitable for mirrors up to say 12" as these smaller thinner mirrors stabilise quickly? but most customers are now going for a lower expansion Glass even for these smaller sizes Produced by Schott. Our main "Low Expansion Glass" up to mid 2004 after which the kiln was shut down. A supply became available again in 2006. It is popular because its price is close to that of Plate Glass Produced by Corning. Thermal Coefficient marginally better than Suprax, but a bit more expensive than Suprax. Very expensive thicker than 25mm Produced by Everybody. Our main use is Cassegrain secondary's where we need the good transmission characteristics for testing Produced by ASM products of Canada. Definitely a serious option for very large mirrors, but not as popular at the moment for smaller mirrors due to its "looks" (It's Black!) Started getting more use from mid 2004. Readily available up to at least 30"

Suprax 8488

4.3

1.2

?

1.1

Pyrex 7740

3.25

1.13

726

1.3

BK7

7.1

1.11

858

1.1

BVC

2.4-2.8

?

?

1.2

Fused Silica Suprema x 33 Zerodur

0.55

1.38

703

#1 Produced by Schott. Same materials as Borofloat but produced by a rolling process. Potential for mirrors up to 1m diameter up to 65mm thick. Produced by Schott. This has extremely low thermal expansion, - but you have

3.25 >0.02

1.2 1.64

830 821

2.5 >10

to be able to afford it! ULE 7971 Borofloat E6 >0.05 3.25 2.8 1.31 1.11 1.1 776 830 730 #1 #1 #1 Produced by Corning as an alternate to Zerodur. Produced by Schott as an alternative to Pyrex. Produced by Ohara as an alternative to Pyrex.

#1 We simply don't use enough to offer a good price comparison, but assume the price is similar to the other glasses with similar
characteristics. You can also assume that since we use less of these - delivery times are extended.

If money is absolutely no object then Zerodur, ULE or similar glasses are the better choices as they have extremely low thermal expansions,
The Thermal Coefficients for Zerodur and ULE are 0.02 and 0.05PPM respectively, - please do not compare them directly and automatically assume Zerodur is better. The values do change with temperature and at one temperature ULE is zero. Both are so low that for use as a telescope mirror, - any difference is of no consequence.

Even owners of mirrors made of Zerodur or ULE are not able to use their telescopes immediately after moving them out of a warm house into the garden. Although the mirrors would suffer no distortion throughout the cooling period, - there would still be a temperature change to deal with. Convection from the warm surfaces causes air currents that distort the viewing until the mirror has cooled. The same applies to the metal or wood structure of the telescope itself, - that would need to cool down before air convection currents die away. Taking those factors into account - it might be a bit pointless paying extra for a Zerodur or ULE mirror? These glasses would not generally be considered good value for money by most informed amateurs? In practice, for small mirrors up to say 12" Diameter, even a Plate Glass mirror can cool down sufficiently before convection currents from the rest of the telescope structure

die away to allow good viewing, - but we now offer low expansion glass as standard. There is really very little to chose between Pyrex, Suprax or Supremax. All three are very similar Borosilicate glass's from two different manufacturers using two different casting processes. Pyrex and Supremax have nominally lower thermal coefficient of expansion than Suprax, - so on face value look better, - but Suprax cools down marginally faster and is about 20% cheaper. Supremax costs more than Pyrex, but can be available with shorter delivery dates.
As a practical example of a low expansion glass cooling, - a 16" (400mm), Diameter mirror made of 40mm thick Pyrex and manufactured to 1/6λ, was allowed to stabilise at about 10 degrees above the workshop temperature. It was then brought into the workshop and tested over a period of time as it adapted to the new temperature. It rapidly exhibited about 1/2λ of error, and took about 30 minutes to return under 1/6λ. You may expect similar times following transport of a telescope to site in the back of a car.

Note that the main markets for Pyrex and Suprax are in household and laboratory glassware respectively. Blanks are readily available up to about 5-600mm diameter, but sizes bigger than this are rarer and more expensive as their main markets do not require them. Consequently there is a large step change in price at about this diameter. The thickness of a large blank may vary within a few millimetres depending on the supplier. For mirrors at or over 400mm, Black Vitreous Ceramic (BVC) is a serious competitor. It is made by ASM, a small Canadian company. ASM are a much smaller firm than Corning or Schott and it should not come as too much of a surprise that there are slight variations between the batches of glass they produce. They claim a range of 2.4-2.8PPM/Deg C, for their BVC glass.
We have been passed test figures from the Canadian company showing a range of 2.56 -2.64PPM/Deg C, which supports their claims. Note even the worst of the figures quoted, - 2.8PPM/Deg C, is still lower than Pyrex.

The only drawback of BVC is the cosmetic aspect that it is black, instead of the semi-transparent appearance of most other glasses. After adding transport costs from Canada, it is still marginally cheaper than Pyrex at about 500mm diameter and it becomes progressively cheaper as the diameter increases. It can be readily supplied up to 750mm Diameter and it has been supplied up to 1.2M Diameter previously. (However in 2009, supplies of this glass became more difficult to obtain.)

Cassegrain Secondary Mirrors
After reading values in the table, some of you considering a Cassegrain might be worried by the high Thermal Expansion value of BK7 glass that Oldham Optical use for Cassegrain secondary mirrors? Don't forget that even though the thermal expansion of BK7 is twice that of Pyrex/Supremax, - the secondary mirror is less than half as thick as the primary. Even with the higher coefficient it will have stabilised before the primary mirror.

Elliptical Flats
For a similar reason, we consider Plate Glass is perfectly adequate for elliptical flats in Newtonians. The flats are only a fraction of the size and thickness of the main mirror and will always stabilise before the main mirror does. However if a customer wishes the flat to be of low expansion glass - we have no problems supplying, - just make sure we know what you want.

"Normal" Glass Used By Oldham Optical
Unless you have specified a particular glass on your order, you will be supplied with the following:Primary Mirrors for Newtonians and Cassegrains will be low expansion glass from either Pyrex, Suprax or Supremax,

mostly depending on levels in stock or availability at the time the order is placed. If you have a preference for one particular glass, please discuss it with us or make it clear what you want in your order. Cassegrain secondary mirrors are usually BK7. Elliptical flats are usually plate glass.
Note that for primary mirrors above about 450mm diameter, the exact thickness supplied will vary slightly depending on the type of glass and the source it is obtained from. If you do require an exact or specific thickness, then please discuss this with us or make it clear on your order.

And Finally,To finish off this page, - What might convince you about our statement that plate glass is still perfectly suitable in sizes of up to 12" for good observing???? We have already used illustrations of the Hubble and the Hale Mirrors as examples of Fused Silica and Pyrex. Illustrated here is the Oldham 10" reflector. It was photographed early one evening while preparing to do some observing in the back garden of the Oldham residence. Its primary mirror, - as you may well have gathered by now, is genuine 100% Plate Glass.
But if we were replacing it today, we would probably follow fashion and make it of low expansion glass!

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