IBDP Design Technology

Final Production / 4.2c /
Glass

The rapid pace of technological discoveries is very evident in the manufacture and use of glass in electronic devices. Different properties have been presented in glass for aesthetic or safety considerations for many years but the future of glass seems to be interactivity alongside electronic systems. The structure of glass is not well understood but as more has learned its use is becoming increasingly prominent in building materials and structural applications.

4.2c.1 | Characteristics and applications of glass

Glass is a non-crystalline, often transparent solid, that has widespread practical, technological, and decorative use. Glass products are most often shaped by rapid cooling (quenching) of its molten form. Some glasses such as volcanic glass are naturally occurring. Glass tends to be hard and brittle. Glass will survive for very long periods if not disturbed, and many examples of glass fragments exist from early glass-making cultures.

Glass is non-porous and can be made incredibly smooth, making it easy to sterilise and sanitise. It is also a hard material making it resistant to scratches and blemishes. Most glass is largely unreactive which makes it ideal for use as containers for food, drinks, and certain chemicals. Glass is resistant to most chemicals, so will not react with the substance it comes in contact with. Glass, unlike most plastic polymers, is UV light resistant. Glass remains inert even at very high temperatures, allowing it to be sanitised with heat. If tempered, glass can resist thermal shock.

The agents used to colour glass are generally metal oxides. The same oxides may produce different colours with different glass mixtures. Venetian glass is a very bright and colourful glass made in Venice, Italy. Primarily made on the island Murano, it is world-renowned for being colourful, elaborate and skillfully made, and a great example of how different oxides are used in glass making.

The most familiar, and historically the oldest, types of manufactured glass are silicate glasses based on the chemical compound silica (silicon dioxide, or quartz), the primary constituent of sand. The most well-known silicate glasses are soda-lime glass and borosilicate glass.

Soda–lime glass, contains around 70% silica, and accounts for around 90% of manufactured glass. Soda–lime glass is transparent and easily formed. However, it has a high thermal expansion and poor resistance to excessive heat. Soda–lime glass is typically used for windows, bottles, light bulbs, and jars.

Borosilicate glass typically contains 5–13% boron trioxide (B2O3). Borosilicate glasses have fairly low coefficients of thermal expansion. They are, therefore, less subject to stress caused by thermal expansion and thus less vulnerable to cracking from thermal shock. Borosilicate glass is commonly used for e.g. labware, household cookware, and sealed beam car headlamps. Pyrex is a brand of borosilicate glass consisting of between 60 to 80% silicon dioxide, mixed with 10 to 25% boron oxide, 2 to 10% sodium oxide and 1 to 4% aluminium oxide. Due to its specific properties, Pyrex is generally used in temperature-sensitive applications, including measuring jugs, thermometers, lab equipment, microwave and oven doors. Like scientific equipment glass, Borosilicate glass is non-porous and can assist in reducing cross-contamination issues in food production.

Toughened or Tempered glass has been heat treated - with the outside of the glass being held in compression while in the inside is in tension. This is achieved by heating the glass to almost melting point then chilling the outside of the glass with jets of air, while the centre remains hot and plastic. The outside of the glass therefore cools and hardens before the inside. On cooling, glass will contract but due to the different rates of cooling, the degree of contraction will be different between the inside and outside parts. This leaves the outside in compression and the protected inside in tension. Toughened glass shatters into small granular piece. This are not sharp, large shards like plate glass, making it much safer to use in many applications - car windscreens.

What properties are required of each of the applications of glass below?

Laminated glass consists of two thin sheets of glass with a plastic film glued between them. When the glass is put under pressure and fractures, the plastic bonded sheet retains the fragments. This is why laminated glass is often called ‘safety glass’. The plastic layer also stops the propagation of cracks. Bulletproof glass is a form of laminated glass. The bullet does not pass through the glass as the plastic laminate absorbs the energy of the moving bullet. This can require multiple layers of glass and plastic film, depending on the type of bullet you want to stop.

Gorilla glass is a brand of specialised tempered glass, developed and manufactured by Dow Corning for the use with mobile devices. Gorilla glass is designed to be light, thin and damage resistant. It mainly gets its strength from an ion exchange that creates a more densely packed glass.

Glass is now used extensively as a construction material. Plate glass and glass bricks are often chosen as both wall or floor materials. Glass used in construction has high compressive strength and low thermal conductivity. It lets in light and can trap heat. The use of glass in the form of plates or bricks for walls and flooring materials has become very popular due to their specific properties:

Mechanical & Physical - Resistance to tensile and compressive forces. Strong in compression. Thermally conductive and transparent.
Aesthetic and Psychological properties - Allows natural light into buildings and can visually link spaces. Vegetation and trees can be grown under glass - making it a nicer place to work and providing clean air. Switchable glass can be used to increase privacy at the flip of a button.

Other common glass-containing materials are composites like fibreglass, glass wool and ceramic glass. These materials have properties regular glass does not have. Fibreglass for instance is lightweight and corrosion resistant and is a good electric insulator. Glass wool is an excellent thermal and sound insulation material and ceramic glass is almost impervious to thermal shock: it can be used in cooktops.

4.2c.2 | Recovery and disposal

It is estimated that it takes 1 million years for glass to naturally degrade. And glass does not contaminate the soil in the same way other materials do.

Most glass can however be recycled endlessly (there is almost no degradation). And glass has been recycled for many years. In the EU 71% of glass bottles and jars are recycled, greatly reducing the need for virgin materials. In many countries, it would be socially unacceptable or even financially prohibitive (fines, extra taxes) not to recycle glass responsibly.

Adding crushed glass, called cullet, to the molten mixture promotes the melting of the sand in the mix and lowers the melting point, and therefore reduces the amount of energy required. Using 25% cullet in the mix will reduce the energy required by the furnace by 5%.

Mixed glass can be crushed and formed into glass aggregate that can be used in the constructions industry. For instance as a foundation layer for roads. This is an example of down-cycling though as the value of the material becomes less.

Page updated

Report abuse