Pyroceramic material

Phase separation is not always a surface phenomenon. The glass that is eventually changed into a pyroceramic material has a nucleating agent mixed throughout... 

The phase separation producing opalescence and photosensitivity are production-created. That is, during the production of the glass, the phase separation occurs. The phase separation that occurs with pyroceramic material and Vycor requires baking the glass at high temperatures for an extended time. This elevated temperature provides the time for the molecules to align and/or separate themselves in a crystalline pattern. 

A pyroceramic material is a special type of glass that has been devitrified by controlled nucleation of crystals. It has certain properties that are like glass and other properties that are like ceramics. Standard round tubing, not square, flat, or distorted walls. 

The ramp of pressure to about 3 GPa observed in shock-loaded fused quartz has been used very effectively in acceleration-pulse loading studies of viscoelastic responses of polymers by Schuler and co-workers. The loading rates obtained at various thicknesses of fused quartz have been accurately characterized and data are summarized in Fig. 3.6. At higher peak pressures there are no precise standard materials to produce ramp loadings, but materials such as the ceramic pyroceram have been effectively employed. (See the description of the piezoelectric polymer in Chap. 5.)... 

Pyrocerams, 21 381 Pyro-Chek 68PB, 11 470-174 Pyrochemical processes, in plutonium metal preparation, 19 676 Pyrochlore, 17 133-134, 140, 141 colorants for ceramics, 7 347t Pyroelectricity, 11 95, 100, 106, 107 Pyroelectric materials, smart, 22 708t, 709 Pyroform process, 25 171 Pyrogallol... 

A third technique to produce tempered ware uses two glasses (or ceramics) formed together (laminated), each with different thermal coefficient of expansion. This is used to make Correll dishes by Coming. For this tableware, a pyrocer-amic material with one type of thermal coefficient of expansion is covered with another pyroceramic with a greater thermal coefficient of expansion and is then baked until the outer layer melts uniformly. Materials with greater thermal coefficients of expansion will expand more when heated and will contract more when cooled. The greater contraction (once cooled) of the outside material causes compression. 

Pyroceramic is a translucent material made by Coming that has both glass and ceramic properties. 

The interfacial resistance between the coating and the lower thermocouple plate is different from the interfacial resistance between the substrate-measurement plate due to light oxidation of the steel substrate, which is not observed for the coating. We have observed that the interfacial resistance of ceramics depends primarily on the surface finish of the ceramic material, since ceramics are chemically stable. Therefore, we use an interfacial resistance that was previously measured between Pyroceram 9606, of the same surface finish as the FGM coating, and the upper thermocouple plate as our interfacial resistance function for the coating-measurement plate interface [6]. Thermal conductivity of the FGM coating can then be extracted from the total conductance data by using these interfacial resistances and the thermal conductivity data for 410 stainless steel. The estimated uncertainty of the measurement system is 5%. 

One of the main drawbaeks in the generation of thermal eonduetivity data on plasties remains the paucity of reference materials. Reference materials are important because they provide an important baseline for the calibration of instruments. Most thermal conductivity instruments require calibration to materials of known thermal conductivity. The National Institute of Standards (NIST) and other standards-setting institutions have characterized a number of metals, ceramics, glasses, and even insulation. These are not suitable as reference materials because they tend to possess a thermal conductivity that is higher or lower than those of plastics. For example, the NIST reference glass materials Pyrex 7740 and Pyroceram 9606 possess a thermal conductivity of 1 W/m-K which is five times greater than that of most plastics. The other reference materials are still more inapplicable. Many fluids, on the other hand, possess thermal conductivities similar to plastics. The transient line-source technique, however, is the only technique that can use such reference materials. 

Heat flux transducers are typically thermopiles, which produce an output proportional to the heat flux. They present an experimental means to measure heat flux rather than calculate it from the voltage applied to the primary heater. However, the heat flux transducer must be calibrated using materials of known thermal conductivity. Calibration establishes a relationship between the voltage signal of the transducer and the heat flow through it. Typical materials used include Pyroceram 9606 and Pyrex 7740 glasses, both of which are NIST standards. 

Because of its greater stiffness and toughness, and lower thermal expansion, pyroceram is more useful than glass as a structural material. 

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