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Ceramics New

Glass was first produced in ancient Egypt.

4.6.1 Describe the composition of glass.

Glass is composed primarily of silicon dioxide together with some sodium oxide and calcium oxide and small quantities of a few other chemicals.

4.6.2 Explain that glass is produced from sand, limestone and sodium carbonate, and requires large quantities of energy for its manufacture.

Scrap glass is added to new raw materials to make the process more economical.

Glass is produced from all these elements and needs a lot of energy. This is because the in order to produce glass the first thing is to melt all elements, this takes a tremendous amount of energy due to the very high melting points of the materials.

Glass furnace temperatures reach up to 1675°C adding scrap glass leads to savings not only in the raw materials, but also in the energy consumption of the glass furnace.

A video from the NAM of the manufacturing of glass bottles from the mixing of raw materials to labelling.

4.6.3 Describe the characteristics of glass.


Medical Jars
Consider brittleness, transparency, hardness, un-reactivity and aesthetic properties

Characteristics of glass:

  • brittleness, it has a low impact strength and thus will shatter easily (low toughness).
  • transparency, allows light to pass through thus allowing you to see the contents of a jar or through a window.
  • hardness, high hardness and wont scratch readily.
  • un-reactivity - is chemically inert so leaching of acid based contents is not a problem
  • aesthetic properties
  • non-porous, thus will hold liquids or stop moisture seeping from outside.

4.6.4 Explain that the desired characteristics of glass can be accurately determined by altering its composition.

Consider soda glass and Pyrex®.

Pyrex

Soda glass is made of oxides of silicon (SiO2), calcium (CaO) and sodium(Na2O). It is the most common type of glass which is used for windowpanes, glass containers for beverages and food.

Soda glass has a medium resistance to high temperatures and sudden changes of temperature (low thermal shock) and a high resistance to corrosive chemicals. To improve the low thermal shock one can alter the chemical composition which to make Pyrex.

  • Pyrex is made of soda-lime glass and(with 60–80% SiO2, 10–25% B2O3, 2–10% Na2O and 1–4% Al2O3) are added. Pyrex is a brand name and company manufacturing kitchen glassware.

NB: For IB no need to know the chemical compounds just FYI

4.6.5 Outline the differences between toughened and laminated glass.

Consider their responses to being flexed and to impact.

The desired characteristics of glass can also be altered in way to produce toughened and laminated glass which respond differently when being deflected and to impact.

  • How Stuff Works link to safety glass.
Toughened Glass Laminated Glass
* Is heated up to the point of melting
* blasted with cold air
* when it is impacted shatters into little pieces rather than sharp shards
* eg. windscreens of cars
* In toughened glass, the applied tensile load must overcome the
compressive stress at the surface
before the surface can go into tension and fail.
* is layers of glass and plastic sheet
* when impacted the glass fragments are held in place
* This prevents cracks from growing
* it can even be made bullet proof
* eg windscreens or bank teller windows
Laminated Glass Toughened Glass

4.6.6 Explain why glass is increasingly used as a structural material.

Consider the use of plate glass and glass bricks as wall and flooring materials. Consider material properties, for example, resistance to tensile and compressive forces, thermal conductivity and transparency. Consider aesthetic properties and psychological benefits: allows natural light into buildings and can visually link spaces, creating more interesting interiors.
Glass Bricks Plate Glass
Glass tunnel in the Sydney Aquarium Glass flooring (bridge)

Plate glass, glass bricks and flooring are used as a structural material due to the:

  • Aesthetic properties. Glass is can a transparent or translucent material, allowing light to pass through, thus allowing users to see in or out. It will also allow light to it can fill dark areas of building or office. Natural lighting has positive affects on people and well as health reasons. In flooring can add appeal by having lights shine through (dance floors) or over things of interest (aquariums).
  • Thermal Conductivity. Glass can insulate a building thus keeping it cool/warm which in turn be a benefit to the environment (reduced energy consumption) and owner(reduced energy costs).
  • Hardness Compressive strength. Resists scratching and indentation of peoples' shoes or chairs etc. Easily maintained as well since it is non-reactive.

References

Bulleted list and italicised paragraphs are excerpted from Design Technology: guide. Cardiff Wales, UK: International Baccalaureate Organization, 2007.

Images are clickable links to its location.

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Page last modified on January 21, 2013, at 02:54 AM