Glass Flashcards
(24 cards)
which of the four types of material is glass
A ceramic
How was glass made in the past and what was its major imperfection
A casting process that involved melting silica based material such as sand then pouring it into a metal tray which would cool and set into glass structure. It wasn’t very optically clear.
key properties of glass
transparent, brittle, high stiffness, reasonable compressive strength, relatively low strength in tension (varies), hard but easily damaged, resistant to corrosion
What are the basic characteristics of glass (not properties)
amorphous/non-crystalline material with no long range repeating order. (random macrostructure)
Typically produced from cooled liquids
softens over temperature, doesn’t have a clear melting point.
What is the atomic structure of most glasses
Silicon dioxide tetrahedron. Glass is not like diamond or sand in that the structure binding the tetrahedrons is random instead of ordered. Glass has no dislocations
What is the glass transition temperature
This is the temperature at which the change of specific volume as a result of the change of temperature reduces. On a graph it would be seen as an abrupt change of gradient.
How would one reduce the viscosity of glass
Adding alkali oxides. These break up the structure by forming bonds between the silicon and oxygen from the alkali oxides. Also increasing temperature.
sodium and calcium are network modifiers. Define network modifier
Chemicals that break up the structure of glass.
Which oxides, in abundance order, does the most common glass, soda lime glass contain
silica, soda (sodium oxide), lime (calcium oxide), magnesium oxide and alumina
Why are oxides of transition metals added to glass
They add colour
Why are metal oxides added to glass
They can control chemical durability, viscosity and melting temp
What is arsenic oxide added for
A very small amount is added for bubble removal
Why is glass transparent
No interfaces to scatter light
What are the three zones of fracture
Mirror, mist and hackle. (smooth, slightly rough to very coarse)
What is static fatigue
The phenomena that glass reduces in strength over time under constant load. This because stretching the silicon and oxygen bond makes silica more prone to reacting with water. This causes silica at the cracks exposed to the air become silica hydroxide, which makes the crack bigger.
Why does glass have increased strength under rapid loading
fast stress drives cracks faster than water can diffuse to the crack tips.
What happens to the viscosity of glass as temperature is raised
It decreases
What is the temperature required to melt silica in glass manufacture
1500 degrees celsius
What is manufacturing process of glass
raw materials, batch formation, melting, cooling , forming, annealing, quality control, packaging
What is the most process of making flat glass and give a brief description
float process, involves continuously pouring molten glass onto a shallow bath of molten tin. The process is performed in an inert hydrogen/ nitrogen atmosphere so the tin doesn’t oxidise. The glass floats on the tin and spreads out to form a level surface. Thickness controlled at the rate at which the glass is drawn off the tin bath.
What is annealing and where does it take place
slow cooling to reduce stress build up. Takes place in a lehr
How can the strength of glass be improved
If cooled down really rapidly, the surface of the glass cools before the inside. Faster cooling means lower density or higher volume. This causes the surface to become compressed so that any stresses applied must overcome this compression to apply any tensile stresses to the glass
What is laminated glass
Two or more layers of glass bonded together using a specialised plasticised interlayer
What is structural glass
An amorphous glass bonded with polymer interlayer formed from cooling molten raw materials
