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The heat capacity, accurate to about + lye, of Ni,Fe has been measured from 300 t o 1670 K using pulse calorimetry, with heating rates from 20 to 60 K s-l. The specimen was heat treated in the calorimeter to induce various degrees of long-range order, varying in Bragg-Williams parameter from S = 0 to S = 0.96. The heat capacity was measured for various initial values of B. The rapid heating allowed measurements on the ordered structures of Ni,Fe a t temperatures where they were metastable. Below 750 K, the heat capacity-temperature curve was lowered as S increased. The Curie transformation for a high S value was 70 K above that for a disordered condition ( S = 0). Also, the order-disorder transformation was suppressed t o 230 K above the equilibrium transformation temperature using a heating rate of 60 K s-l.Die Warmekapazitat des Ni,Fe wurde auf ungefahr f 1% genau von 300 bis 1670 K mittels eines Impulskalorimeters bei Heizgeschwindigkeiten von 20 bis 60 K 8-l gemessen. Das Probestiick wurde im Kalorimeter mit Warme behandelt, urn verschiedene im Bragg-Williams-Parameter von S = 0 bis S = 0,96 variierende Stufen der Fernordnung herbeizufiihren. Die Warmekapazitat wurde fur verschiedene S -Anfangswerte der Warmekapazitit gemessen. Das schnelle Erhitzen ermoglichte Messungen der geordneten Strukturen des Ni,Fe bei Temperaturen in denen sie metastabil waren. Unter 750 K wurde die Temperaturkurve der Warmekapazitat abgesenkt, wenn S sich erhohte. Die Curie-Transformation eines hohen S-Wertes war 70 K uber der einer ungeordneten Kondition ( S = 0). Auch wurde die Ordnung-Unordnungstransformation bis 230 K iiber der Gleichgewichtsubergangstemperatur mit Hilfe einer Heizgeschwindigkeit von 60 K s-l unterdriickt. l) Research sponsored by the United Statcs Atomic Energy Commission. 2, Permanent address: Oak Ridge National Laboratory, Oak Ridge, Tennessee.

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After annealed, type K (Chromel vs Alumel) thermocouples were heated above 200 °C, their temperature measurements were in error up to 1.3%, as determined by comparison calibrations to working standard 90% Pt–10% Rh/Pt thermocouples or platinum resistance thermometers. Reannealing the type K thermocouples removed the errors. The errors were due to changes in the thermal emf vs temperature relationship of the type K thermocouples, which from previous work of others can be attributed to short-ranged ordering of the Chromel thermoelements. Reannealing the thermocouples removed the errors because the order–disorder transformation is reversible; that is, short-ranged ordering of the Ni and Cr atoms of the Chromel alloy occurs between 200° and 600 °C, and disordering occurs above 600 °C. The traveling gradient method was used to determine the effects of heat treatment on the thermal emf of type K thermocouples, to investigate the kinetics of ordering of Chromel, and to determine the amount of order produced by heat treatments. Though the order–disorder transformation could not be stopped, our results demonstrate that there exists an optimum amount of order in the Chromel thermoelement to yield a repeatable thermal emf vs temperature relationship for a type K thermocouple in a specific application. When the experimental conditions of the application were controlled carefully, isothermal heat treatment to produce the optimum order in the Chromel thermoelements and calibration of the type K thermocouples prior to use essentially eliminated the temperature measurement errors due to order. The optimum amount of order depended on the application and was determined experimentally. Variations from the optimized heating or cooling cycles, changes in the depth of thermocouple immersion during use, or modification of the temperature gradient on the thermocouple caused temperature measurement errors of up to 1% with ordered and calibrated type K thermocouples.