WEC 1

Glass

WEC 2

Ceramic materials divide into three categories:

1. Glasses – melting & solidification processing

2. Traditional ceramics – particulate processing

3. New ceramics – particulate processing

Introduction of Ceramics

Classification + Applications of CeramicsClassification + Applications of Ceramics

Glasses Clay products

RefractoriesAbrasivesCement Functionalceramics

- optical

- composite

- reinforce - containers/ - household

- wares - bricks

- bricks for high T (furnaces)

- sandpaper - cutting wheel - polishing

materials

- composites - structural

as construction

- engine - rotor -valve -bearing

- sensors- windshield

Traditional or ClassicalCeramics

Advanced Ceramics

- thermal protection materials

3WEC

WEC 4

Glass Glass is one of three basic types of ceramics. Glass is

distinguished by its amorphous (non crystalline) structure.

Structure : Network formers

Molecules that link up with each other to form long chains and

networks. Hot glass cools, chains unable to organize into a

pattern. Solidification has short-range order only.

Amorphous structure occurs by adding impurities (Na+,Mg2+,Ca2+, Al3+).

Impurities: interfere with formation of crystalline structure

WEC 5

Glass Raw Materials

1. Glass forming oxides: usually the dominant constituent

SiO2, B2O3, P2O5, etc.

2. Fluxes: reduce melting temperatures

Na2O, PbO, K2O, Li2O, etc.

3. Property modifiers: added to tailor chemical durability,

expansion, viscosity, etc.

CaO, Al2O3, etc.

4. Colorants: oxides with 3d, 4f electron structures; minor

additives (<1 wt%)

5. Fining agents: minor additives (<1 wt%) to help promote

bubble removal

As-, Sb-oxides, KNO3, NaNO3, NaCl, fluorides, sulfates

What is Glass?• Fusion of sand (SiO2), soda (Na2CO3) & lime (CaO)

that produces a transparent solid when cooled.• A 3D network of atoms which lacks the repeated,

orderly arrangement typical of crystalline materials.

• Physical Properties: hard, elastic, brittle, non-conductor of electricity, density, refractive index, etc.

• Chemical: resistant to all but fluorine and very strong bases.

The primary uses for glass are in windows, containers, light bulbs and eyewear.

• Borosilicate Glass (pyrex): 5% borax (Na2B4O7) is added to resist breaking when heated or cooled.

• Colored Glass: metal oxides or colloidal iron (Fe) & sulfur (S) are added to change its color.

• Lead Glass: Pb increases refractive index & density

What Types of Glass Are There?

What Types of Glass Are There?• Flat glass: made by a “float glass

process”; molten glass is floated on a pool of tin while cooling. Commonly found in doors and windows.

• Laminated glass: used in windshields, two sheets of glass with plastic between them.

• Tempered safety glass: used in car side windows and designed to break into tiny pieces; potassium (K) replaces sodium (Na) on the surface.

• Each force causes a deformation that may leave a visible mark or fracture the glass. This can be used to determine the direction and amount of force.

• Glass acts initially as an elastic surface and bends away when a force is applied. When the force increases beyond its tensile strength, it cracks.

How Do Glass Windows Break?

WEC 10

Glassmaking

1. The ingredients for glass are mixed, and along with a proportion of

cullet (broken glass), are added to a bath furnace, where they are heated

to about 1500°C and fused together.

2. Molten glass is fed as ‘gobs’ to an automatic bottle or jar making

machine.

3. A hot gob is first made into a parison or blank shape (by either pressing

or blowing), which is then blown to the final bottle or jar shape. Surface

coatings (sc) may be applied while hot.

WEC 11

4. The bottles or jars pass into a lehr (an annealing oven), where they

are first reheated to soften the glass to remove stresses, and then

cooled gradually to prevent stresses developing.

5. The bottles or jars are inspected and tested to meet quality

standards. Bottles not passing the quality checks are broken and

returned to the furnace as cullet. Cullet reduces the amount of energy

required to melt the glass ingredients.

6. Bottles passing inspection and testing are packed for dispatch to

where they will be filled, capped, and labeled.

WEC 12

WEC 13

Shaping Processes in Glassmaking

Shaping processes to fabricate these products can be

grouped into three categories:

1. Discrete processes for piece ware (bottles, jars,

plates, light bulbs)

2. Continuous processes for making flat glass (sheet

and plate glass) and tubing (laboratory ware,

fluorescent lights)

3. Fiber-making processes to produce fibers (for

insulation and fiber optics)

14

Shaping of Piece Ware Ancient methods of hand-working glass included glass blowing. Handicraft methods are still used today for making glassware items of

high value in small quantities. However, most modern glass shaping

processes are highly mechanized technologies for producing discrete

pieces in high quantities.

Piece Ware Shaping Processes

1. Spinning – similar to centrifugal casting of metals

2. Pressing – for mass production of flat products such as dishes, bake

ware, and TV tube faceplates

3. Press-and-blow – for production of wide-mouth containers such as

jars

4. Blow-and-blow - for production of smaller-mouth containers such as

beverage bottles and incandescent light bulbs

5. Casting – for large items such as large astronomical lenses that must

cool very slowly to avoid cracking.WEC

15

Spinning of funnel-shaped glass parts such as back sections of cathode

ray tubes for TVs and computer monitors:

(1) gob of glass dropped into mold; and

(2) rotation of mold to cause spreading of molten glass on mold surface

WEC

WEC 16

Pressing of flat glass pieces:

(1) glass gob is fed into mold from furnace;

(2) pressing into shape by plunger; and

(3) plunger is retracted and finished product is removed (symbols v

and F indicate motion (velocity) and applied force)

17

1. A gob of hot glass drops into the blank (parison) mould.2. The mould is sealed shut by a ‘base’ part and a plunger pushes the glass

into the mould (made from iron). 3. The glass is shaped into a ‘blank’ and also pushed into the neck finish by

the plunger. This part of a jar or bottle is finished to its final shape at this stage.

4. The blank shape (parison) is removed, rotated 180°, and transferred to the blow (finishing) mould.

5. This mould is in two halves, made from fine-grain cast iron, and is highly polished.

6. Air is blown into the hot parison to expand it tightly against the mould walls.

7. The mould opens, the bottle is removed, annealed in the lehr, inspected and tested, and shipped for filling.

WEC

18

1. A gob of hot glass drops into the blank (parison) mould.2. The end is sealed and a puff of air pushes glass into the neck (finish). 3. A puff of air from below pushes glass into the mould and shapes it into

a ‘blank’ or parison, a thick-walled bottle looking vaguely like the final bottle shape.

4. The blank shape (parison) is removed, rotated 180°, and transferred to the blow (finishing) mould.

5. This mould is in two halves, made from fine-grain cast iron, and is highly polished.

6. Air is blown into the hot parison to expand it tightly against the mould walls.

7. The mould opens, the bottle is removed, annealed in the lehr, inspected and tested, and shipped for filling.

WEC

WEC 19

Casting

If molten glass is sufficiently fluid, it can be poured into a

mold. Relatively massive objects, such as astronomical lenses

and mirrors, are made by this method. After cooling and solidifying, the piece must be finished by

lapping and polishing. Casting of glass is not often used except for special jobs. Smaller lenses are usually made by pressing.

WEC 20

Shaping of Flat and Tubular Glass Processes for producing flat glass such as sheet and plate glass:

Rolling of Flat Plate

Starting glass from melting furnace is squeezed through

opposing rolls whose gap determines sheet thickness, followed

by grinding and polishing for parallelism and smoothness

WEC 21

Float Process

Molten glass flows onto the surface of a molten tin bath,

where it spreads evenly across the surface, achieving a

uniform thickness and smoothness - no grinding or

polishing is needed.

WEC 22

Danner Process

Molten glass flows around a rotating hollow mandrel

through which air is blown while the glass is drawn.

WEC 23

Thanks