Monday, June 10, 2013

Technical Term in Architectural Glass

About Glass

Modern life just would not be possible without glass. From the jar that holds the morning marmalade, the mirror in which we brush our teeth, the windows and car windscreen we look through, the computer screen many of us use at work every day to the light bulb we switch off last thing at night; glass is around us everywhere. But what is this amazing substance, where does it come from and how is it made?

What is glass?


Glass is a combination of sand and other minerals that are melted together at very high temperatures to form a material that is ideal for a wide range of uses from packaging and construction to fibre optics. A form of glass occurs naturally within the mouth of a volcano when the intense heat of an eruption melts sand to form Obsidian, a hard black glassy type of stone. Man first used this as tips for spears. Today man has mastered the glass-making process and can make many different types of glass in infinitely varied colours formed into a wide range of products. Glass, chemically, is actually more like a liquid, but at room temperature it is so viscous or 'sticky' it looks and feels like a solid. At higher temperatures glass gradually becomes softer and more like a liquid. It is this latter property which allows glass to be poured, blown, pressed and moulded into such a variety of shapes.

How glass is made?


Glass is made by melting together several minerals at very high temperatures. Silica in the form of sand is the main ingredient and this is combined with soda ash and limestone and melted in a furnace at temperatures of 1700°C. Other materials can be added to produce different colours or properties. Glass can also be coated, heat-treated, engraved or decorated. Whilst still molten, glass can be manipulated to form packaging, car windscreens, glazing or numerous other products. Depending on the end use, the composition of the glass and the rate at which it is allowed to cool will vary, as these two factors are crucial in obtaining the properties the glassmaker is seeking to achieve.

Recycling Glass


The British Glass Recycling Glass website, is a site for children, students and grown-ups (parents, teachers and other members of the public) to find out about Recycling Glass and how it benefits the environment when you recycle it.
Types of Glass
When people speak of glass, they ordinarily mean a transparent, shiny substance that breaks rather easily. They may think of the glass in windows and the glass used in eyeglasses as being the same material. Actually, they are not. There are many kinds of glass. Several important kinds of glass are discussed in this article.
Flat glass is used chiefly in windows. It is also used in mirrors, room dividers, and some kinds of furniture. All flat glass is made in the form of flat sheets. But some of it, such as that used in automobile windshields, is reheated and sagged (curved) over molds.
Glass containers are used for packaging food, beverages, medicines, chemicals, and cosmetics. Glass jars and bottles are made in a wide variety of shapes, sizes, and colors. Many are for common uses, such as soft-drink bottles or jars for home canning. Others are made from special glass formulas to make sure there will be no contamination or deterioration of blood plasma, serums, and chemicals stored in them see.
Optical glass is used in eyeglasses, microscopes, telescopes, camera lenses, and many instruments for factories and laboratories. The raw materials must be pure so that the glass can be made almost flawless. The care required for producing optical glass makes it expensive compared with other kinds of glass.
Fiberglass consists of fine but solid rods of glass, each of which may be less than one-twentieth the width of a human hair. These tiny glass fibers can be loosely packed together in a woollike mass that can serve as heat insulation. They also can be used like wool or cotton fibers to make glass yarn, tape, cloth, and mats. Fiberglass has many other uses. It is used for electrical insulation, chemical filtration, and firefighters' suits. Combined with plastics, fiberglass can be used for airplane wings and bodies, automobile bodies, and boat hulls. Fiberglass is a popular curtain material because it is fire-resistant and washable.
Laminated safety glass is a “sandwich” made by combining alternate layers of flat glass and plastics. The outside layer of glass may break when struck by an object, but the plastic layer is elastic and so it stretches. The plastic holds the broken pieces of glass together and keeps them from flying in all directions. Laminated glass is used where broken glass might cause serious injuries, as in automobile windshields.
Bullet-resisting glass is thick, multilayer laminated glass. This glass can stop even heavy-caliber bullets at close range. Bullet-resisting glass is heavy enough to absorb the energy of the bullet, and the several plastic layers hold the shattered fragments together. Such glass is used in bank teller windows and in windshields for military tanks, aircraft, and special automobiles.
Tempered safety glass, unlike laminated glass, is a single piece that has been given a special heat treatment. It looks, feels, and weighs the same as ordinary glass. But it can be several times stronger. Tempered glass is used widely for all-glass doors in stores, side and rear windows of automobiles, and basketball backboards, and for other special purposes. It is hard to break even when hit with a hammer. When it does break, the whole piece of glass collapses into small, dull-edged fragments.
Colored structural glass is a heavy plate glass, available in many colors. It is used in buildings as an exterior facing, and for interior walls, partitions, and tabletops.
Opal glass has small particles in the body of the glass that disperse the light passing through it, making the glass appear milky. The ingredients necessary to produce opal glass include fluorides (chemical compounds containing fluorine). This glass is widely used in lighting fixtures and for tableware.
Foam glass, when it is cut, looks like a black honeycomb. It is filled with many tiny cells of gas. Each cell is surrounded and sealed off from the others by thin walls of glass. Foam glass is so light that it floats on water. It is widely used as a heat insulator in buildings, on steam pipes, and on chemical equipment. Foam glass can be cut into various shapes with a saw.
Glass building blocks are made from two hollow half-sections sealed together at a high temperature. Glass building blocks are good insulators against heat or cold because of the dead-air space inside. The blocks are laid like bricks to make walls and other structures.
Heat-resistant glass is high in silica and usually contains boric oxide. It expands little when heated, so it can withstand great temperature changes without cracking. This quality is necessary in cookware and other household equipment, and in many types of industrial gear.
Laboratory glassware includes beakers, flasks, test tubes, and special chemical apparatus. It is made from heat-resistant glass to withstand severe heat shock (rapid change in temperature). This glass is also much more resistant to chemical attack than ordinary glass.
Glass for electrical uses. Glass has properties that make it useful in electrical applications: ability to resist heat, resistance to the flow of electric current, and ability to seal tightly to metals without cracking. Because of these properties, glass is used in electric light bulbs and for picture tubes in television sets.
Glass optical fibers are glass fibers used to transmit information as pulses of light. Thin, extremely pure optical fibers are used to carry telephone and television signals and digital (numeric) data over long distances. Glass optical fibers are also used in control board displays and in medical instruments.
Glass tubing is used to make fluorescent lights, neon signs, glass piping, and chemical apparatus. Glass tubing is made from many kinds of glass and in many sizes.
Glass-ceramics are strong materials made by heating glass to rearrange some of its atoms into regular patterns. These partially crystalline materials can withstand high temperatures, sudden changes in temperature, and chemical attacks better than ordinary glass can. They are used in a variety of products, including heat-resistant cookware, turbine engines, electronic equipment, and nose cones of guided missiles. Glass-ceramics have such trade names as Pyroceram, Cervit, and Hercuvit.
Radiation-absorbing and radiation-transmitting glass can transmit, modify, or block heat, light, X rays, and other types of radiant energy. For example, ultraviolet glass absorbs the ultraviolet rays of the sun but transmits visible light. Other glass transmits heat rays freely but passes little visible light. Polarized glass cuts out the glare of brilliant light. One-way glass is specially coated so that a person can look through a window without being seen from the other side.
Laser glass is an optical glass containing small amounts of substances that enable the glass to generate laser beams efficiently. Such glass is used as the active medium in solid-state lasers, a type of laser that sends light out through crystals or glass (One substance commonly used in laser glass is the element neodymium. Researchers are using glass lasers in an attempt to harness nuclear fusion (the joining of atomic nuclei) as a source of commercially useful amounts of energy. In their experiments, powerful glass lasers heat hydrogen atoms until hydrogen nuclei fuse, releasing large amounts of energy.
"Invisible glass" is used principally for coated camera lenses and eyeglasses. The coating is a chemical film that decreases the normal loss of light by reflection. This allows more light to pass through the glass.
Photo chromic glass darkens when exposed to ultraviolet rays and clears up when the rays are removed. Photo chromic glass is used for windows, sunglasses, and instrument controls.
Photosensitive glass can be exposed to ultraviolet light and to heat so that any pattern or photograph can be reproduced within the body of the glass itself. Because the photographic print then becomes an actual part of the glass, it will last as long as the glass itself.
Photochemical glass is a special composition of photosensitive glass that can be cut by acid. Any design can be reproduced on the glass from a photographic film. Then when the glass is dipped in acid, the exposed areas are eaten away, leaving the design in the glass in three dimensions. By this means, lacelike glass patterns can be made.
Heavy metal fluoride glass is an extremely transparent glass being developed for use in optical fibers that transmit infrared rays. Infrared rays are much like light waves but are invisible to the human eye. In optical fibers, infrared light transmits better over distance than visible light does.
Chalcogenide glass is made up of elements from the chalcogen group, including selenium, sulfur, and tellurium. The glass is transparent to infrared light and is useful as a semiconductor in some electronic devices. Chalcogenide glass fibers are a component of devices used to perform laser surgery.
Sol-Gel glass can be used as a protective coating on certain solar collectors or as an insulating material. It is also used to make short, thick tubes that are drawn into optical fibers. To make Sol-Gel glass, workers dissolve the ingredients in a liquid. They then heat the liquid. The liquid evaporates, leaving behind small particles of glass. Heating these particles fuses (joins) them to form a solid piece of glass. The temperatures involved in Sol-Gel processes are often lower than those needed to make ordinary glass.

GLASS FACT

Types of Glass
There are many different types of glass with different chemical and physical properties. Each can be made by a suitable adjustment to chemical compositions, but the main types of glass are:
·         Borosilicate Glass
·         Commercial Glass
·         Glass Fibre
·         Lead Glass

Glasses may be devised to meet almost any imaginable requirement. For many specialised applications in chemistry, pharmacy, the electrical and electronics industries, optics, the construction and lighting industries, glass, or the comparatively new family of materials known as glass ceramics, may be the only practical material for the engineer to use.
Types of special glass include:
·         Alkali-barium Silicate Glass
·         Aluminosilicate Glass
·         Glass Ceramics
·         Optical Glass
·         Sealing Glass
·         Technical Glass
·         Vitreous Silica
Alkali-barium Silicate Glass
Without this type of glass, watching TV would be very dangerous. A television produces X-rays that must be absorbed, otherwise they could in the long run cause health problems. The X-rays are absorbed by glass with minimum amounts of heavy oxides (lead, barium or strontium). Lead glass is commonly used for the funnel and neck of the TV tube, while glass containing barium is used for the screen.
Aluminosilicate Glass
A small, but important type of glass, aluminosilicate, contains 20% aluminium oxide (alumina-Al2O3) often including calcium oxide, magnesium oxide and boric oxide in relatively small amounts, but with only very small amounts of soda or potash. It is able to withstand high temperatures and thermal shock and is typically used in combustion tubes, gauge glasses for high-pressure steam boilers, and in halogen-tungsten lamps capable of operating at temperature as high as 750°C.

Borosilicate Glass

Most of us are more familiar with this type of glass in the form of ovenware and other heat-resisting ware, better known under the trade name Pyrex.Borosilicate glass, the third major group, is made mainly of silica (70-80%) and boric oxide (7-13%) with smaller amounts of the alkalis (sodium and potassium oxides) and aluminium oxide. This type of glass has a relatively low alkali content and consequently has good chemical durability and thermal shock resistance (it doesn't break when changing temperature quickly.)As a result it is widely used in the chemical industry, for laboratory apparatus, for ampoules and other pharmaceutical containers, for various high intensity lighting applications and as glass fibres for textile and plastic reinforcement.

Commercial Glass

Most of the glass we see around us in our everyday lives in the form of bottles and jars, flat glass for windows or for drinking glasses is known as commercial glass or soda-lime glass, as soda ash is used in its manufacture.
The main constituent of practically all commercial glass is sand. Sand by itself can be fused to produce glass but the temperature at which this can be achieved is about 1700°C. Adding other minerals and chemicals to sand can considerably reduce the melting temperature.
The addition of sodium carbonate (Na2CO3), known as soda ash, to produce a mixture of 75% silica (SiO2) and 25% of sodium oxide (Na2O), will reduce the temperature of fusion to about 800°C. However, a glass of this composition is water-soluble and is known as water glass. In order to give the glass stability, other chemicals like calcium oxide (CaO) and magnesium oxide (MgO) are needed. These are obtained by adding limestone which results in a pure inert glass.
Commercial glass is normally colourless, allowing it to freely transmit light, which is what makes glass ideal for windows and many other uses. Additional chemicals have to be added to produce different colors of glass such as green, blue or brown glass.
Most commercial glasses have roughly similar chemical compositions of:
70% - 74% SiO2 (silica) 12% - 16% Na2O (sodium oxide) 5% - 11% CaO (calcium oxide) 1% - 3% MgO (magnesium oxide) 1% - 3% Al2O3 (aluminum oxide)
Flat glass is similar in composition to container glass except that it contains a higher proportion of magnesium oxide.
Within these limits the composition is varied to suit a particular product and production method. The raw materials are carefully weighed and thoroughly mixed, as consistency of composition is of utmost importance in making glass.
Nowadays recycled glass from bottle banks or kerbside collections, known as cullet, is used to make new glass. Using cullet has many environmental benefits, it preserves the countryside by reducing quarrying, and because cullet melts more easily, it saves energy and reduces emissions.
Almost any proportion of cullet can be added to the mix (known as batch), provided it is in the right condition, and green glass made from batch containing 85% to 90% of cullet is now common.
Although the recycled glass may come from manufacturers around the world, it can be used by any glassmaker, as container glass compositions are very similar. It is, however, important that glass colours are not mixed and that the cullet is free from impurities, especially metals and ceramics.
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Glass Ceramics

Some of these "Glass ceramics", formed typically from lithium aluminosilicate glass, are extremely resistant to thermal shock and have found several applications where this property is important, including cooker hobs, cooking ware, windows for gas or coal fires, mirror substrates for astronomical telescopes and missile nose cones. An essential feature of glass is that it does not contain crystals. However, by deliberately stimulating crystal growth in glass it is possible to produce a type of glass with a controlled amount of crystallization that can combine many of the best features of ceramics and glass.

Glass Fiber

Glass fiber has many uses from roof insulation to medical equipment and its composition varies depending on its application. For building insulation and glass wool the type of glass used is normally soda lime. For textiles, an alumino-borosilicate glass with very low sodium oxide content is preferred because of its good chemical durability and high softening point. This is also the type of glass fiber used in the reinforced plastics to make protective helmets, boats, piping, car chassis, ropes, car exhausts and many other items. In recent years, great progress has been made in making optical fibers which can guide light and thus transmit images round corners. These fibers are used in endoscopes for examination of internal human organs, changeable traffic message signs now on motorways for speed restriction warnings and communications technology without which telephones and the internet would not be possible.

Lead Glass

Commonly known as lead crystal, lead glass is used to make a wide variety of decorative glass objects. It is made by using lead oxide instead of calcium oxide, and potassium oxide instead of all or most of the sodium oxide. The traditional English full lead crystal contains at least 30% lead oxide (PbO) but any glass containing at least 24% PbO can be described as lead crystal. Glass containing less than 24% PbO, is known simply as crystal glass. The lead is locked into the chemical structure of the glass so there is no risk to human health. Lead glass has a high refractive index making it sparkle brightly and a relatively soft surface so that it is easy to decorate by grinding, cutting and engraving which highlights the crystal's brilliance making it popular for glasses, decanters and other decorative objects. Glass with even higher lead oxide contents (typically 65%) may be used as radiation shielding because of the well-known ability of lead to absorb gamma rays and other forms of harmful radiation.

Optical Glass
Optical glasses will be found in scientific instruments, microscopes, fighter aircraft and most commonly in spectacles.
The most important properties are the refractive index and the dispersion. The index is a measure of how much the glass bends light. The dispersion is a measure of the way the glass splits white light into the colours of the rainbow. Glass makers use the variations in these characteristics to develop optical glasses.

Sealing Glass

A wide variety of glass compositions are used to seal metals for electrical and electronic components. Here the available glasses may be grouped according to their thermal expansion which must be matched with the thermal expansions of the respective metals so that sealing is possible without excessive strain being induced by differing levels of expansion. For sealing to tungsten, in making incandescent and discharge lamps, borosilicate alkaline earths-aluminous silicate glasses are suitable. Sodium borosilicate glasses may be used for sealing to molybdenum and the iron-nickel-cobalt (Fernico) alloys are frequently employed as a substitute, the amount of sodium oxide permissible depending on the degree of electrical resistance required. With glasses designed to seal to Kovar alloy, relatively high contents of boric oxide (approximately 20%) are needed to keep the transformation temperature low and usually the preferred alkali is potassium oxide so as to ensure high electrical insulation.Where the requirement for electrical insulation is paramount, as in many types of vacuum tube and for the encapsulation of diodes, a variety of lead glasses (typical containing between 30% and 60% lead oxide) can be used.

Technical Glass

Technical is the term given to a range of glasses used in the electronics industry.
Without borate glass the computer revolution would not have been possible as it's vitally important in producing electrical components. This type of glass, contains little or no silica and is used for soldering glass, metals or ceramics as it melts at the relatively low temperature of 450-550°C, well below that of normal glass, ceramics and many metals.
Glass of a slightly different composition is used for protecting silicon semi-conductor components against chemical attack and mechanical damage. Known as passivation glass it is vital in microelectronics technology and the production of the silicon chips inside computers.
Another type of glass - Phosphate Glass - which is a semi conductor, is used in the construction of secondary electron multipliers.
Chalcogenide glass - Similar semi conductor effects are also characteristic of a type of glass that can be made without the presence of oxygen. Some of them have potential use as infrared transmitting materials and as switching devices in computer memories because their conductivity changes abruptly when particular threshold voltage values are exceeded.

Vitreous Silica
Silica glass or vitreous silica is of considerable technical importance as it has a very low thermal expansion. This difficult to make glass contains tiny holes created using acids and is used for filtration. Porous glasses of this kind are commonly known as Vycor.
All Types Of Glass
Float Glass (5700)
Bent Glass (61)
Mirror (402)
Led Glass (2)
Sheet Glass (166)

History of Glass

A Brief History of glass

From our earliest origins, man has been making use of glass. Historians have discovered that a form of natural glass - obsidian - formed for instance, within the mouth of a volcano as a result of the intense heat of an eruption melting sand - was first used by man as tips for spears.
Archaeologists have found evidence of man-made glass which dates back to 4000BC; this took the form of glazes used for coating stone beads. It was not until 1500 BC that the first hollow glass container was made by covering a sand core with a layer of molten glass.
Glass blowing became the most common way to make glass containers from the First Century BC. However, the glass made during this time was highly colored due to the impurities of the raw material. It was not until the First Century AD when colorless glass was produced and then colored by the addition of coloring materials.
The secret of glass making came to Britain with the Romans. However, the skills and technology required to make glass were closely guarded by the Romans and it was not until the Roman Empire disintegrated that skills for glass making spread throughout Europe and the Middle East.
The Venetians, in particular, gained a reputation for technical skill and artistic ability in the making of glass bottles and a fair number of the city's craftsmen left Italy to set up glassworks throughout Europe.
In Britain, there is evidence of a glass industry around Jarrow and Wearmouth dating back to 680AD, while from the 13th Century, there is evidence of there having been a glass industry in the Weald and the afforested area of Surrey and Sussex around Chiddingford.
A major milestone in the history of glass occurred with the invention of lead crystal glass by George Ravenscroft. He attempted to counter the effect of clouding that sometimes occurred in blown glass by introducing lead to the raw materials used in the process.
The new glass he created was softer and easier to decorate and had a higher refractive index, adding to its brilliance and beauty, and it proved invaluable to the optical industry. It's thanks to Ravenscroft's invention that optical lenses, astronomical telescopes, microscopes and the like became possible.
The modern glass industry only really started to develop in Britain after the repeal of the Excise Act in 1845 relieved the heavy taxation that had been enforced. Before that time, excise duties were placed on the amount of glass melted in a glasshouse and levied continuously from 1745 to 1845.
Joseph Paxton's Crystal Palace at the Great Exhibition of 1851 marked the beginning of the discovery of glass as a building material. The revolutionary new building encouraged the use of glass in public, domestic and horticultural architecture. Glass manufacturing techniques also improved with the advancement of science and better technology.
By 1887 glass making developed from traditional mouth blowing to a semi-automatic process when Ashley introduced a machine capable of producing 200 bottles per hour in Castleford, Yorkshire - more than three times quicker than the previous production methods.
Twenty years later, in 1907, the first fully automated machine was developed in America by Michael Owens from major glass manufacturers Owens of Illinois, and used at its factory in Manchester, Illinois making 2,500 bottles per hour.
Other developments followed rapidly, but it was not until the First World War, when Britain became cut off from essential glass suppliers that glass became part of the scientific sector. Up until then glass was seen as a craft rather than a precise science.
Today, glass making is a modern, hi-tech industry operating in a fiercely competitive global market where quality, design and service levels are critical to maintaining market share.
Modern glass plants are capable of making millions of glass containers a day in many different colours, but green, brown and clear remain the most popular.
Few of us can imagine modern life without glass. It features in almost every aspect of our lives - in our homes, our cars and whenever we sit down to eat or drink. Glass packaging is used for many products, wines, spirits and beers all come in glass as do medicines and cosmetics not to mention numerous foodstuffs.
With increasing consumer concern for the environment, glass has again come into its own proving to be an ideal material for recycling. Glass recycling is good news for the environment. It saves used glass containers being sent to landfill and less energy is needed to melt recycled glass than to melt down raw materials, thus saving energy. Recycling also reduces the need for raw materials to be quarried thus saving precious resources.

The Future of glass

Glass as a material in its own right will always exist. But many new applications and manufacturing processes will involve glass in combination with other materials. Optical fibres, for example, are currently manufactured with one or more different coatings, which are often plastics. With the increasing sophistication of opto-electronic devices, there is an increasing need to combine optical and electronic devices for many applications such as transmission of audio, video and data information. Glasses and ceramics, either alone or composite with other materials, will find increasing application in biological and medical areas. Materials such as photo chromic, electro chromic and thermochrominc glasses, which respond to external stimuli, are being developed with various, sometimes unusual, applications.
By :-  M Z HAQUE
         Asst. Marketing Manager
     



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