Triple points of various materials

TABLE 5.30 Triple Points of Various Materials Continued)... 

RTDs are constructed of a resistive material with leads attached and placed into a protective sheath. Platinum resistance thermometers are the international standard for temperature measurements between the triple point of H2 at 13.81 K (24.86°R) and the freezing point of antimony at 630.75°C (1,167.35°F). The RTD elements include platinum, nickel of various purities, 70% nickel/30% iron (Balco), and copper, listed in order of decreasing temperature range. Their features and relative performance characteristics in comparison with other sensors are tabulated in Table 3.169. 

A systematic study of the sorption and pore condensation behavior of nitrogen, argon and krypton in various silica materials (MCM-48, MCM-41 and Controlled Pore Glass (CPG)) at 87 and 77 K is presented. A detailed characterization with respect to surface area, pore volume and pore size distribution together with a comparison of sorption hysteresis in MCM-48 and MCM-41 silica materials of nearly equal pore size has been performed. In addition we focus on the sorption and phase behavior of argon and krypton below the bulk triple-point temperature. 

Besides solid-fluid equilibria, some pure materials can exist in more than one stable solid structure, giving rise to solid-solid equilibria. Examples include equilibria between the fee and bcc forms of iron, equilibria between rhombic and monoclinic sulfur, and equilibria among the many different phases of ice. Such solid-solid phase transitions are accompanied by a volume change and a latent heat, and these two quantities are related through the Clapeyron equation (8.2.27). When a pure material can undergo solid-solid phase transitions, then the substance usually exhibits multiple triple points. Besides the usual solid-vapor-liquid point, the pure substance might also exist in solid-solid-liquid or solid-solid-solid equilibria. Several such triple points occur in water, caused by equilibria involving various forms of ice [13]. 

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