606GLANCE
vides low maintenance, environmental compatiblil- deep-sea floats, potting compounds, and other com-
ity, and worker safety in metal operations. posites.
Use: Desirable when aggressive metal removal and
extreme requirements are desired. For grinding,
glass, borosilicate. See glass, heat-resistant.
milling, and turning in automotive, aviation, tool-
ing, and bearings.
glass ceramic. A devitrified or crystallized form
of glass whose properties can be made to vary over a
glance. A mineralogical term meaning brilliant or wide range.
lustrous; used to describe hard, brittle materials that Properties: Rupture modulus up to 50,000 psi, d 2.5,
exhibit a bright reflecting surface when fractured. thermal shock resistance 900C, highest continuous-
Examples of such materials are hard asphalts use temperature 700C. Glass ceramics lie between
(glance pitch) and ores of certain metals such as lead borosilicate glasses and fused silica in high-temper-
glance (galena). ature capability.
Derivation: A standard glass formula to which a
nucleating agent, such as titania, has been added, is
Glaser coupling. Coupling of terminal acety-
melted, rolled into sheet, and cooled. It is then heat-
lenes by shaking an aqueous solution of cuprous
ed to a temperature at which nucleation occurs, caus-
chloride−ammonium chloride and the alkyne in an
ing formation of crystals.
atmosphere of air or oxygen.
Use: Range and stove tops, laboratory bench tops,
architectural panels, restaurant heating and warming
glass. A ceramic material consisting of a uniform-
equipment, telescope mirrors.
ly dispersed mixture of silica (sand) (75%), soda ash
See nucleation; “Pyroceram”; “Cer-vit.”
(20%), and lime (5%), often combined with such
metallic oxides as those of calcium, lead, lithium,
“Glassclad 6C” [United Chemical]. TM
cerium, etc., depending on the specific properties
for a chlorine terminated polydi methylsiloxane tel-
desired. The blend (or “melt”) is heated to fusion
omer.
temperature (approximately 700–800C) and then
Use: To form a siliconized surface.
gradually cooled (annealed) to a rigid, friable state,
often referred to as vitreous. Technically, glass is an
glass electrode. See electrode, glass.
amorphous, undercooled liquid of extremely high
viscosity that has all the appearances of a solid. It has
glass enamel. A finely ground flux, basically
almost 100% elastic recovery.
lead borosilicate, intimately blended with colored
See glass, optical.
ceramic pigments. Different grades give character-
Properties: (Soda-lime glass.) Lowest electrical
istics of acid resistance, alkali resistance, sulfide
conductivity of any common material (below 10
−6
resistance, or low lead release to meet requirements
mho/cm). Low thermal conductivity. High tensile
for various uses. Firing range 540–760C.
and structural strength. Relatively impermeable to
Use: For fired-on labels and decorations on glass-
gases. Inert to all chemicals except hydrofluoric,
ware, tumblers, milk bottles, beverage bottles, glass
fluosilicic, and phosphoric acids and hot, strong
containers, illuminating ware, architectural glass,
alkaline solutions. Continuous highest-use tempera-
and signs.
ture about 121C but may be higher, depending on
See porcelain enamel.
composition. Good thermal insulator in fibrous
form. Molten glass is extrudable into extremely fine
filaments. Glass is almost opaque to UV radiation;
glass fiber. (fibrous glass; fiberglass). Gener-
in the absence of added colorant it transmits 95–98% ic name for a manufactured fiber in which the fiber-
of light to which it is exposed. Noncombustible. forming substance is glass (Federal Trade Commis-
Occurrence: Natural glass is rare but exists in the sion). Noncombustible.
form of obsidian in areas of volcanic activity and Properties: Tensile strength 15 g/denier, elongation
meteor strikes. Excellent sand for glassmaking oc- 3–4%, d 2.54, no moisture regain, loses strength at
curs in Virginia (James River), Pennsylvania, Mas- >315C, softens at approximately 815C.
sachusetts, New Jersey, West Virginia, Illinois, and See glass.
Maryland; also in southern Germany and the Czech Derivation: Molten glass is extruded at high speed
Republic. through extremely small orifices.
Available forms: Plate, sheet, fiber, filament, fabric, Hazard: A suspected carcinogen. TLV: 10 mg/m
3
rods, tubing, pipe, powder, beads, flakes, hollow (dust).
spheres. Use: Thermal, acoustic, and electrical insulation
See sodium silicate. (coarse fibers in bats or sheets); decorative and utili-
Use: Windows, structural building blocks, chemical ty fabrics such as drapes, curtains, table linen, carpet
reaction equipment, pumps and piping, vacuum backing, tenting, etc.; tire cord as belt between tread
tubes, lightbulbs, glass fibers, yarns and fabrics, and carcass; filter medium; reinforced plastics; light
containers, optical equipment. Minute glass spheres transmission for communication signals; reinforce-
with partial vacuum interior and treated exterior are ment of cement products for construction use.
available for compounding with resins for use in See fiber, optical.