Todays objectives-glass and clay products and processingWhat are standard glass additives, and how do they effect structure and properties?How do specific volume and viscosity vary with temperature?How are glass sheets and containers prepared?Why are annealing and tempering important for glass?What are the steps in processing clays?What is slip, and what is hydroplasticity?Describe castingDescribe extrudingDescribe dryingDescribe firingPrimary glass resource: Corning Museum of Glass (www.cmog.org)

History of GlassThe history of the origin of glass can be categorized by periods according to the methods of the manufacturing process as follows: The First Period: 1700 BC through 100 ADPrimitive method of making glass using molds. The Second Period: 100 AD through 400-500 ADGlassblowing technique discovered, and glass manufacture becomes a more practical process.The Third Period: 4-500 AD ~ 1200 ADMiddle Ages, characterized by Byzantine glass. The Fourth Period: 1200 AD ~ 1900 ADVenetian glass, foundation for modern glass making is set. The Fifth Period: 1900 AD ~ presentGlass objects used as everyday goods; large scale manufacturing.

Mesopotamian glassAs early as 3,300 years ago, secret "instructions" for furnace building and glassmaking in Mesopotamia were written on clay tablets in a cuneiform script. Typical instructions include: When you set up the foundation of a good furnace to make glass, first search in a favorable month for a day of good omenYou regularly perform libation offerings (drink of honey and liquid butter honoring a deity). On the day when you plan to make (glass), you make a sheep sacrifice.Place juniper incense on the incense burnerPour out a libation; only then can you make the fire in the hearth of the furnace and place the glass in the furnace. The wood that you burn in the hearth of the furnace should be thick, peeled poplar wood, which has no knots, bound together with leather straps, cut in the month of the Abu (Jul. or Aug.). If you want to produce zagindur-colored (blue) glass, you finely grind separately:10 minas (about one pound) of immanakku-stone (quartz)15 minas of naga-plant ashes1 2/3 minas of 'white plant.' Mix these together. Place the mixture into a cold furnace that has four openings, As soon as the mixture glows yellow, you pour it on a kiln fired brick and this is called zuk-glass....

Glasses and glass ceramicsNow commonly applied for:ContainersWindowsDecorationLensesFiberglass (insulation)FiberopticsRoad signsCompositesChemically, glass is comprised of noncrystalline silica plus additives:CaONa2OK2OAl2O3

Basic Unit: Glass is amorphous Amorphous structure occurs by adding impurities (Na+,Mg2+,Ca2+, Al3+) Impurities: interfere with formation of crystalline structure.GLASS STRUCTURE

GlassGlass composition determines propertiesnoncrystallineThermal expansion coefficient of pyrex is 1/3 that of standard silica glass.

glassSiO2Na2OCaOAl2O3B2O3otherFused silica>99.5%Pyrex (borosilicate)813.52.513Container (soda-lime)7416514 MgOfiberglass551615104 MgO

Specific volume (1/r) vs Temperature (T): Glasses: --do not crystallize --spec. vol. varies smoothly with T --Glass transition temp, Tg Crystalline materials: --crystallize at melting temp, Tm --have abrupt change in spec. vol. at TmAdapted from Fig. 13.5, Callister, 6e.GLASS PROPERTIES

Amorphous materials (glasses)For non-crystalline ceramics, deformation occurs by viscous flow.The deformation rate is proportional to the applied stress.Common units are N*s/m2 = Pa*s (or Poisies=0.1Pa*s)Viscosity unit, giving the inverse of how well the material flows. Water at 25 C is 0.001 Pa*s.Motor oil (SAE10W) is 0.132 at 25 C.Glass is 1014 Pa*s = 1015 Poisies (a crystal is infinite).

Viscosity decreases with T - (sample flows easier) Impurities lower TdeformGLASS VISCOSITY VS T AND IMPURITIES

Glass platesOriginally, glass plates made one at a time using the Pittsburgh process (vertically draw a continuous sheet of glass of a consistent width from the tank).Pilkington discovered how to make glass continuously.

Float Glass, Pilkington, 1950.Originally able to make only 6mm thick glass, now made as thin as 0.4mm and as thick as 25mm. There are around 260 float plants worldwide with a combined output of about 800,000 tonnes of glass a week. A float plant, which operates non-stop for between 11-15 years, makes around 6000 kilometres of glass a year.http://www.pilkington.com/pilkington/corporate/english/education/float+process/default.htm

The Floating partMolten glass, at approximately 1000C, is poured continuously from a furnace onto a shallow bath of molten tin. It floats on the tin, spreads out and forms a level surface.Thickness is controlled by the speed at which solidifying glass ribbon is drawn off from the bath. After annealing (controlled cooling) the glass emerges as a 'fire' polished product with virtually parallel surfaces.

Annealing: --removes internal stress caused by uneven cooling.HEAT TREATING GLASSChemical tempering is also possible.

Pressing: GLASSFORMING Blowing: Adapted from Fig. 13.7, Callister, 6e. (Fig. 13.7 is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.)Fabricating Glass in other shapes

CrizzlingProlongued exposure to chemical attack can lead to local microcracks, Crizzling.Eventually leads to failure.

Ceramic HistoryIn 221 BC during the Qing Dynasty, Qin Shi Huang was the Emperor in reign. The Terra Cotta Army was built as a way of creating an illusion of strength and manpower.Discovered in 1974.Most soldiers standing in formation, many with their horses ready for battle. en.wikipedia.org/wiki/Terracotta_Army

7000 soldiers thus far discovered

*Terra-Cotta (cooked earth) is nothing more than weathered clay, mixed with sand or pulverized fired clay, molded and fired to a high enough temperature that it is harder and more compact than brick. Ranges from red to white depending on the local clay color.Pots, blocks (like brick, but mostly hollow with an internal frame of some kind to make the overall structure stronger but lighter).