Some important heat insulating materials are described as follows: 1. Cork 2. Glass Wool 3. Rock Wool 4. Slag Wool 5. Asbestos 6. Thermocole 7. Reflecting Paper 8. Gypsum 9. Aluminium Foils 10. Expanded Blast Furnace Slag 11. Light Weight Concrete 12. Vermiculite 13. Coconut Fibres 14. Cellulose.
1. Cork:
It is derived from the bark of oak trees. It is ground, sized and baked in moulds. When ground and baked, the natural resin in the cork binds the material into homogeneous mass which can be pressed into flexible sheets or boards etc. It is available in the form of granulated cork, slab cork, and regranulated baked cork.
The structure of cork consists of an aggregation of minute air vessel, provided with thin, strong wall, so that if material is compressed it behaves more like a gas than an elastic solid; unlike the behaviour of spring, which exerts a pressure proportionate to the linear amount of compression. Cork, when compressed, exerts a pressure which increases in a more rapid manner and varies, approximately, inversely as the volume.
Properties:
ADVERTISEMENTS:
Following are the properties of cork:
1. Light in colour.
2. Porous in structure.
3. Specific gravity is about 0.24.
ADVERTISEMENTS:
4. Not affected by moisture.
5. Thermal conductivity is low.
6. Can be easily compressed.
7. Resilient and reasonably elastic when dry.
ADVERTISEMENTS:
Uses:
Following are the uses of cork:
1. Cork sheets and boards are used for insulating walls and ceilings, both against heat and cold and also as a sound insulator.
2. Used as a non-conducting covering for pipes carrying steam or hot water.
ADVERTISEMENTS:
3. Used as non-conducting material for scientific apparatuses.
4. Used in refrigeration and cold storage insulation.
5. Also used for bottle stoppers, vibration pads and floats for rafts and fish nets.
2. Glass Wool:
Glass wool is produced by blowing high pressure jets of steam or air on molten streams of glass at a high temperature. Molten glass is violently scattered in all directions, to give this product.
ADVERTISEMENTS:
Glass wool is a form of fibrous glass with short and fine fibres, scattered in various directions.
It is available in the form of loose fibres, mats, rigid quilts, or semi-rigid slabs or blocks etc.
1. Fibrous in structure.
2. Light in weight.
3. Has good tensile and dielectric strength.
4. Low thermal conductivity.
5. Quite durable.
6. Acts as an excellent insulating material because of the presence of large pockets of air in it.
7. Not affected by low temperatures and has been used successfully at temperatures as low as – 212°C.
Glass fibres have the following characteristics:
(i) Do not catch fire.
(ii) Not easily affected by heat.
(iii) Not spoiled by insects and moisture.
Uses:
1. Mostly used for insulation of pipes, bends, valves etc.
2. Used for panel insulation for all types of industrial equipment.
3. Can be used for thermal and sound insulation of aircraft.
4. Glass wool blocks can be used in the construction of partition walls for thermal insulation purposes.
5. Used in boilers, ovens, cylinder or pipe insulation.
3. Rock Wool:
It is produced from flint rock containing some calcareous matter. In the absence of such a natural rock, flint and lime are mixed in the requisite proportions and melted in a furnace at temperature of about 1700°C. This molten material is then formed into small globules by means of a steam jet.
These globules are then drawn into very fine fibres by hurling them in a large container. These fibres of wool are then formed into boards or blankets (to be used as insulators). It can also be pressed, rolled and secured between fabric of wire-netting of brass or copper.
It is available in the following forms:
Loose fibres, mattresses, mats, boards or felts, rigid or semi-rigid slabs, quilts.
Properties:
1. Soft and flexible.
2. Resilient and woody consistency.
3. Heat and sound proof (due to the presence of millions of minutes dead air cells).
4. Specific gravity is about 0.48.
Uses:
1. Employed for heat and sound insulation purposes.
2. Also used as an electric insulator.
4. Slag Wool:
It is an aggregate of fine filaments of slag produced by blowing air through a stream of blast furnace slag.
It is available in the form of loose fibres.
Uses:
It is used for heat insulation in high temperature furnaces.
5. Asbestos:
Asbestos is a mineral fibre composed of hydrous silicate of magnesia with a small amount of iron oxide and alumina.
Asbestos sheets or boards consist of natural asbestos fibres mixed with a binding agent (usually cement) and then rolled in the form of sheets or boards. These are available in the market under the trade name ‘Salamander’.
Properties:
1. White, grey or brown in colour.
2. Flexible and can resist high temperature.
3. Fire-proof.
4. Unaffected by acids and fumes.
5. Resistant to corrosion and vermin effect.
6. Excellently resists heat and electricity.
Uses:
Employed for heat and sound insulation of buildings. Also used for insulation of furnaces.
6. Thermocole:
Thermocole is one of the trade names of Polystyrene. This product was developed (in USA) during Second World War. It was made by direct extrusion of the foam from raw materials.
1. It has a very attractive, natural, snow white colour.
2. Very light in weight (density: 150 to 300 N/m3). The foam is very light because it contains over 98% (by volume) air, trapped in 3 to 6 million closed cells per litre.
3. Compressive strength = 0.07 to 0.1 MN/m2; cross breaking strength = 0.14 to 0. 18 MN/m2.
4. Very low value of thermal conductivity.
5. Highly resistant to moisture.
6. Odourless, chemically stable and resistant to fungus attack.
7. Fully resistant to water, salt, soaps, bleaching agents and HCl (35%), HNO3 (upto 50%), H2SO4 (upto 95%), caustic soda, caustic potash, strong ammonia, alcohols and silicon oil.
8. Not resistant to organic solvents like benzene, paint thinners and saturated aliphatic hydrocarbons like petroleum and gasoline.
9. Very good shock-protecting properties.
10. Ability of being moulded into well-fitting, contoured cases.
Uses:
1. Thermocole (with operational range of – 200°C to 80°C) is an excellent material for cold insulation in refrigerators, cold storages, air-conditioning, chilled pipelines and chemical processes.
2. It is used for industrial insulation and insulation for buildings, against extremes of climate.
3. In the form of specially made flexible sheets, thermocole can be used on intermediate concrete floors in multistorey buildings, to reduce impact sound transmission.
4. It is used for packing electronic goods like transistors, radios, tape recorders and calculating machines, clocks, medicine bottles, cameras etc.
5. It is also used for air-dropped packaging, decorative and gifts packaging and edge protecting packaging.
7. Reflecting Paper:
Reflecting paper (also known as building paper) is a strong tough paper which is lined with aluminium or copper foil on the exposed side, which reflects back heat waves coming from a source and this keeps the walls and the enclosed rooms cool.
Sometimes, reflecting coatings of Varnishes, paraffins, gums or synthetic resins are applied to various grades of paper of fibrous materials.
1. Strong and tough in nature.
2. Heat-resistant.
3. Possesses adequate dielectric strength.
Uses:
Used for heat insulation purposes.
8. Gypsum:
It is a hydrated sulphate of calcium (CaSO4.H2O) occurring in monoclinic crystals.
It seldom occurs in nature in pure state; contains impurities such as alumina, calcium carbonate, magnesium carbonate and silica upto 6 percent.
When it is burnt in kilns, ‘Plaster of Paris’ is obtained.
After mixing with asphalt and casting into slabs, it is burnt in a kiln to form very strong sheets which possess very good insulating properties.
1. Crystalline and fibrous in structure.
2. Controls the setting time of cement.
3. Gypsum boards are good insulators of heat.
Uses:
Employed for heat insulation purposes, Ceiling panels made of gypsum are used for suspended ceilings.
9. Aluminium Foils:
These are very thin foils or sheets of aluminium and are also known as ‘Alfoils’.
These are available in the form of paper-backed foils, separated layers of foils and some rigid materials faced with foils.
1. Light in weight.
2. Low thermal conductivity.
3. Possess smooth and shining surface.
4. Low emissivity (which decreases the radiation losses).
5. Resistant to ordinary atmospheric gases.
Uses:
Used as heat insulator in refrigerators.
10. Expanded Blast Furnace Slag:
It is obtained during the production of iron and steel. It is collected in the form of liquid slag which collects on top of the molten iron.
It is highly resistant to corrosion and attack by insects and microscopic organisms.
It is also a good fire-resistant. But it has high water absorption properties and can be used only in situation where there is no risk of moisture penetration.
Uses:
It can be used in the roofs and in floors above the level of damp proof course.
11. Light Weight Concrete:
Light weight concrete, also known as cellular concrete, consists of crushed slag or grits and cement mixed with aluminium powder. Bubbles of hydrogen gas are then liberated through the concrete mix which form cells and render the plaster porous or form a foam like cellular concrete, known as light weight concrete.
It is made in the form of cellular concrete.
Uses:
Employed for lining walls and roofs for heat and sound insulation of buildings.
12. Vermiculite:
It is the geological name given to a group of hydrated, laminar minerals which are aluminium-iron-magnesium silicates and resemble mica in appearance.
It possesses excellent fire resisting properties.
Vermiculite concrete can be made by mixing vermiculite, Portland cement and concrete. By varying the density, different strength and thermal properties can be obtained.
Uses:
1. Low density vermiculite is used for insulating roofs and wall cavities as loose filler material.
2. Vermiculite can be used for protection of steel girders and stanchions. It can be bonded with bitumen and used as a composite thermal insulation and water-proofing material.
3. Vermiculite concrete can be used for in situ roofing and also for making blocks, tiles and slabs.
13. Coconut Fibres:
The fibres obtained from the outer layers of coconut are hard and elastic. The felted fibres are sandwiched between paper and covered on both sides with a layer of bitumen. Such a material is completely water repellent.
1. Employed for underfloor insulation and floating floors.
2. Also used for internal insulation of walls.
14. Cellulose:
It is made by converting paper waste or other wood to fibre form by addition of some chemicals like borax, boric acid, aluminium sulphate etc.
Mostly cellulose insulating material is obtained by shredding and pulverizing waste paper and mixing it with dry chemicals.
Uses:
It is used as loose fill in the insulation of ceilings and walls of residential and commercial buildings, both for new construction and retrofit purposes.