Phase relations for the systems ZrO2–WO2–WO3 and HfO2–WO2–WO3 from 1000° to 1700° C were determined by the quenching technique using sealed sample containers. In the system ZrO2–WO3, 1:2 compound, ZrW2O8 forms, having a cubic structure with a= 9.159 A. The ZrW2O8 melts incongruently at 1257°± 3°C to ZrO2 and liquid and has a lower limit of stability at 1105°C, below which ZrO2 and WO3 coexist in equilibrium. One eutectic and one peritectic were established: at 1231°± 3°C and 74 mole % WO3, and at 1257°± 3°C and 71 mole % WO3, respectively. Along the join ZrO2–WO2, no compound formed. Two invariant points were determined: ZrO2, WO2, W, and liquid are in equilibrium at 1430°± 5°C and 76 mole % WO2, whereas WO2, W18O49, W, and liquid coexist at 1530°± 5°C and 89 mole % WO2‐ Equilibrium relations in the system ZrO2–WO2–WO3 were investigated at four temperatures. At 1200°C, a cubic phase with composition near W20O58 was found; it exists in equilibrium with ZrO2, W18O49, W20O58, and WO3. As the temperature increases, the liquid formed along the ZrO2–WO3 join extends into the ternary system, crosses the join ZrO2–W20O58 at 1300°C, and crosses the join ZrO2–W18O49 at 1400°C. The cubic phase can take more zirconium into its solid solution at 1300° than at 1200°C. At 1500°C, the system can no longer be treated as a simple ternary oxide system because of the presence of metallic tungsten, and equilibrium relations are presented on the basis of the system ZrO2–W–WO3. Phase equilibrium relations in the systems HfO2–WO3, HfO2–WO2, and HfO2–WO2–WO3 in the temperature ranges studied are much like those in the corresponding zirconium system.
The Center for Basic Standards develops and maintains the scientific competencies and laboratory facilities necessary to preserve and continue to refine the base physical quantities upon which the Nation's measurement system is constructed. The Center is responsible for the standards of voltage, current, resistance and impedance, temperature, vacuum, leak rate, pressure, mass, length, time and frequency. The Center collaborates closely with the standardizing laboratories of other countries to ensure that measures used in international trade are fully compatible. The Center also performs research at the frontiers of physics in order to improve measurement capability and quantitative understanding of basic physical processes that underlie measurement science. Electricity DivisionMaintains and improves the national standards of electrical measurements; conducts experiments to realize the electrical units in terms of the mechanical units; develops stable electrical standards and improved methods for the dissemination of the units of electrical measurements; determines fundamental physical constants related to electrical units; develops instrumentation for precise electrical measurements directly referenced to the national standards; implements techniques for their use and puts them into practical applications; assists in applying scientific and technological development to measurement problems, especially in other areas of NIST research. Temperature and Pressure DivisionMaintains and improves the national standards of temperature and pressure; conducts research towards the development of new concepts for these standards; calibrates practical standards for the U.S. scientific and technical community in terms of the primary standards; develops methods and devices to assist user groups in the assessment and enhancement of the accuracy of their measurements of temperature and pressure; prepares and promulgates evaluations and descriptions of temperature and pressure measurement processes; coordinates these standards and measurement methods nationally and internationally; and determines the accuracy of the national standards of temperature and pressure with respect to fundamental thermodynamic relations. Lengtti and iVIass DivisionDevelops and uses the competence necessary to implement a more accurate measurement system for length and mass; applies research, utilizing the most advanced technology available, to the improvement of our present standards and devises new standards and new methods for their transfer. Time and Frequency DivisionMaintains, develops, and improves the national standards for time (which are coordinated with the United States Naval Observatory) and frequency, and the time scales based on these standards; carries out research in areas of importance to the further fundamental improvement of frequency standards and their applications focusing on microwave and laser devices, atomic and molecular resonances, and the measurement of fundamental physical phenomena and constants; adapts time and frequency sta...
Reference tables for several thermoelements versus platinum (Pt-67) are given with values of the thermoelectric voltage as a function of temperature in degrees Fahrenheit. Only tables for standard letter-designated thermoelements are included: Types BP, BN, JP, JN, KP (same as EP), KN, TP, and TN (same as EN). These tables supplement those given in NBS Monograph 125 and were calculated from the power series expansions presented in that Monograph. They are based upon the absolute electrical units and the International Practical Temperature Scale of 1968 (IPTS-68).
Phase relations in t h e systems alkaline earth oxide-tungsten trioxide and their stability with metallic tungsten were investigated by the quenching technique using sealed capsules. I n the system BeO-WOs no intermediate compounds were formed. Binary mixtures resulted in a eutectic at 1185'C and 37 mole yo BeO. I n t h e system MgO-W03, t h e 1:l compound was stable and melted congruently at 1358OC. There are two crystalline modifications of this compound. The well-known wolframite-type form is stable below 1165'C. Two eutectics were found : 1 1 2 0 ' C and 28.5 mole % MgO and 1318'C and 55.0 mole yo MgO. In the systems CaO-W03, SrO-W03, and BaO-WO3, two binary compounds are stable. The 1: 1 compounds with t h e scheelite-type structure melt, respectively, at 1580°, 1535", and 147SoC, and form eutectics with WOS at 1135O, 1073", and 935'C, all with a eutectic composition near 75 mole % WO,. The 3: 1 compounds having t h e distorted (NHd3FeF6type structure melt at -2250°, 2225O, and 1795°C. The eutectics between these two compounds are at 149OOC and 56.5 mole % CaO, 1410'C and 57.0 mole yo SrO, and 1320'C and 58.2 mole yc BaO. Phase transformations to an ideal (NH4hFeF6-type structure in Sr3W06 and Ba3W06 were observed at 1100' and 805'C, respectively, by application of both high-temperature X-ray diffraction and DTA. At 1700OC, metallic tungsten exists in equilibrium with liquid, the alkaline earth oxides, W &~B ( t h e 3 : 1 ternary oxides, and with combinations thereof.
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