Technology of Material, Glass

1. TECHNOLOGY OF MATERIAL:
GLASS
BY ANONG S.
FOR STUDY PURPOSE AT CIDI ONLY.

2. 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.
GLASS
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.

3. Types of Glass:
Glasses may be devised to meet almost any imaginable
requirement. There are many different types of glass with
different chemical and physical properties and each can be
made by a suitable adjustment to chemical compositions.
For many specialized 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.
The main types of glass include:
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. Sodium borosilicate glass is widely used
across the chemical industry, pharmaceutical sector for laboratory apparatus, for ampoules and other
pharmaceutical containers, various high intensity lighting applications and as glass fibres for textile and
plastic reinforcement - as well, of course, for common household oven and cookwares.
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.

4. GLASS FOR CONSTRUCTION
LAMINATED GLASS
Laminated safety glass which made from at least 2 sheets of tempered
or heat strengthened glass which bonded together across the entire
surface by the special film widely used interlayer is a PVB
(Poly Vinyl Butyral) which is strong, elastic, firmly bonded and
protect the Ultra Violet Ray over 99%. Special film keeps the broken
glass in its shape and not fallen apart.
Advantage: High safety when the glass was broken. Protection
against defenestration (Comprising 2 panes of glass with a least
2 PVB interlayer). Prevent outside disturbance.
Prevent sunlight or ultraviolet which causes pale color furniture and
inner decorations.
Application: The place that would like to utilize sunlight and reduce the
heat transfers into the premise. Window glass that requiring safety.
Large or sloping windows, windows above a certain height.
Show case, show window, aquarium glass, glass balustrade.
High rise building. Residential, commercial building.

5. TEMPERED GLASS
Like tempered steel, the strength of glass can be increased by rapid cooling in
the manufacturing process. By quickly cooling glass from 1200 degrees to 400-
600 degrees, it will become 4 times stronger than normal glass. Often referred
to as safety glass, it is highly resistant to breakage. When it is broken, this glass
will break into small, almost square shapes, not dangerous shards. Because of
the way it breaks, tempered glass will remain in the window instead of flying
about and is much easier to clean up.
Application: Tempered glass is used anywhere potential impacts with objects is
a concern. As a result of its safety and strength, toughened glass is used in a
variety of demanding applications, including passenger vehicle windows, shower
doors, architectural glass doors and tables, refrigerator trays, as a component
of bulletproof glass, for diving masks, and various types of plates and cookware.
Broken tempered glass
HEAT STRENGTHENED
Not as strong as tempered glass, heat strengthened glass is manufactured
using a lower temperature and whose strength is 2 times greater than
standard glass. It’s break pattern is also similar to tempered glass in that
when broken, will break in a square type pattern and remain in the window
frame. Not considered as safety glass.

6. REFLECTIVE GLASS
Reflective glass is glass that has been treated with a metallic coating
to allow it to reflect heat. It is not reflective in the sense that it acts as
a mirror, although some products do indeed have a highly reflective
surface, but rather in the sense that it reflects radiation rather than
absorbing it. This type of glass is used in environmentally friendly
construction with the goal of reducing heat gain and loss, making
structures much cheaper to heat and cool over the course of the year.
Advantages: For both external and internal use, give high light reflectance and unique appearance. Low
light transmittance improves visual comfort against direct sunlight, provides internal privacy, one-way
observation effect in certain lighting condition even in buildings with large glazed areas.
Application: Offices, commercial buildings, schools, industrial buildings
TINTED GLASS
Various colors can be added to the glass formula during manufacturing.
The tinting materials help filter sunlight as it passes through. This
reduces the amount of solar, or heat gain. Tinted glass is typically used
in large southern exposures where tremendous amounts of heat gain
can be anticipated.

7. OBSCURE GLASS
At least one side of the glass is finished in one of a various number of
textures that impede clarity. Often used in bathroom windows, shower
doors, or anywhere you want to allow light to enter but not prying eyes,
this glass can be tinted and tempered (required for shower doors).
WIRE GLASS
Actually 2 sheets of glass sandwiching a woven metal grid. Typically
limited to commercial applications, primarily in the shipping and
receiving or warehousing areas of a business, this glass is very
difficult to break. It is also unattractive to look through.
LOW-E GLASS
A highly energy efficient glass that reflects heat producing long-wave and
ultraviolet light. It has been treated with an invisible metal or metallic oxide
coating, creating a surface that reflects heat, while allowing light to pass through.
This energy-saving technology first became available in 1979 and continues to grow
in popularity. Windows treated with Low-E coatings are proven to reduce energy
consumption, decrease fading of fabrics, such as window treatments, and increase
overall comfort in your home.

8. SELF-CLEANING GLASS
A recent innovation is so-called self-cleaning glass, aimed at building,
automotive and other technical applications. A nanometre-scale coating
of titanium dioxide on the outer surface of glass introduces two
mechanisms which lead to the self-cleaning property. The first is a
photo-catalytic effect, in which ultra-violet rays catalyse the breakdown
of organic compounds on the window surface; the second is a hydrophilic effect in which water is attracted
to the surface of the glass, forming a thin sheet which washes away the broken-down organic compounds.
Usage: Titanium dioxide has become the material of choice for self-cleaning windows, and hydrophilic self-
cleaning surfaces in general, because of its favorable physical and chemical properties. Not only is titania
highly efficient at photocatalysing dirt in sunlight and reaching the superhydrophilic state, it is also non-
toxic, chemically inert in the absence of light, inexpensive, relatively easy to handle and deposit into thin
films and is an established household chemical that is used as a pigment in cosmetics and paint and as a
food additive.
Mechanism: The anatase phase is the most photocatalytic among its polymorphic structures. Moreover,
ultraviolet irradiation creates surface oxygen vacancies at bridging sites, resulting in the conversion of
relevant Ti4+ sites to Ti3+ sites which are favourable for dissociative water adsorption. These defects
presumably influence the affinity to chemisorbed water of their surrounding sites, forming hydrophilic
domains, whereas the rest of the surface remains oleophilic. Hydrophilic domains are areas where
dissociative water is adsorbed, associated with oxygen vacancies that are preferentially photogenerated
along the direction of the plane; the same direction in which oxygen bridging sites align.