I. Arpshofen

Determination of the enthalpy of mixing of liquid alloys using a high-temperature mixing calorimeter

A high-temperature mixing calorimeter that allows the measurement of the enthalpy of mixing of liquid alloys at temperatures ranging up to 1800 K is described. The suitability of the apparatus is shown by the measurement of the enthalpy of mixing of liquid Al-Cu, Al-Ni, and Cu-Ni alloys. The results are compared with data from literature and are discussed using an association model.

CALORIMETRIC DETERMINATION OF THE ENTHALPIES OF FORMATION OF LIQUID NI-ZR ALLOYS

The enthalpies of formation of liquid Ni-Zr alloys have been measured through the composition range 0 < Xzr < 0.4, where Xzr is the mole fraction of Zr. Four independent runs were made at temperatures ranging from 1740 to 1743 K and one at 1838 K. The compositional dependence of the enthalpies of formation could be fitted quite well with polynomial representations according to the subregular as well as to the sub-subregular solution approximations. The influence of chemical short-range order was found to differ from the earlier Ni-Ti results.

Calorimetric determination of the enthalpies of formation of liquid Ni-Ti alloys

The enthalpies of formation of liquid Ni-Ti alloys have been measured independently with two different calorimeters, one set at 1741 and the other at 1838 K. Measurements were made within the composition range 0 < XTi < 0.5 where XTi is the mole fraction of Ti. A minimum in the compositional dependence of ΔMH between XTi = 0.3 and XTi = 0.4 shows definitively that the solution is not regular. Rather there is indication that atomic packing considerations lead to the persistence of short-range order in the liquid phase above and in the vicinity of the efficiently packed intermetallic phase at Ni3Ti.

Calorimetric methods in metallurgy

Abstract After a brief introduction on the thermodynamics of alloy formation, the principles of calorimeter construction are discussed, considering mainly the isothermal and the adiabatic mode of operation as well as the methods of quantitative differential thermoanalysis (DTA) and the twin or differential calorimeter. Several examples for the practical realization of these principles are given. Some important sources of errors are discussed. Finally, an outlook on the future prospect of calorimetry is given.

Thermodynamics of liquid and undercooled liquid Al-Ni-Si alloys

Abstract The partial and the integral enthalpies of mixing of liquid Al–Ni–Si alloys have been determined by high-temperature isoperibolic calorimetry for three sections with constant concentration ratios of Ni and Si at 1575±3 K. With a view to a direct use of the thermodynamic properties, the values of the integral enthalpy of mixing of the ternary alloys together with the literature values of the constituent binaries Al–Ni, Ni–Si and Al–Si are analytically described by the thermodynamically adapted power series according to the right-hand Colinet geometry using a least-squares regression analysis. A regular association model adequately describes the thermodynamic properties of liquid and undercooled liquid Al–Ni–Si alloys. The Δ H ( x Al , x Ni , x Si ), Δ S ( x Al , x Ni , x Si ) and Δ G ( x Al , x Ni , x Si ) functions show the existence of essential contributions of ternary interactions among the alloy components. The strongest tendency toward chemical short-range ordering in the liquid state occurs near to compositions corresponding to the intermetallic compound Ni 2 AlSi.

Enthalpy of mixing of liquid Al-Cu-Si alloys

Abstract The partial and the integral enthalpies of mixing of liquid Al–Cu–Si alloys have been measured by high temperature calorimetry at 1575±3 K. Results for three sections with constant concentration ratios of Al and Si are given in tabular form. A least-square regression analysis of the integral enthalpy of mixing data results in the following relationships (in kJ mol−1; T=1575±3 K): Δ H =x Al x Cu α Al–Cu +x Al x Si α Al–Si +x Cu x Si α Cu–Si +x Al x Cu x Si α Al–Cu–Si α Al–Cu =(−75.6±6.5)+(−63.8±8.8)x Al +(232±33)x 2 Al +(−131±28)x 3 Al α Al–Si =−12.6+2.5x Si α Cu–Si =(−16.2±2.2)+(97.7±37.1)x Cu +(−1138±208)x 2 Cu +(3514±489)x 3 Cu + (−4748±515)x 4 Cu +(2216±199)x 5 Cu α Al–Cu–Si =(−241.7±8.8)+(1165±32)x Al +(891±34)x Si +(−935±30)x 2 Al +(−640±35)x 2 Si + +(−1563±52)x Al x Si . The minimum of ΔH changes with composition from −14.5 kJ mol−1 (Cu–25at.%Si) to −17.3 kJ mol−1 (Al–60at.%Cu). The presence of additional ternary interactions or ternary associates in the liquid state could not be observed.

Die anwendung des setaram-kalorimeters zur messung von mischungsenthalpien flüssiger legierungen. II

Abstract Based on an earlier work, a report is given on the following improvements in the operation of the Setaram high temperature calorimeter: (1) Reduction of measurement errors by the use of a voltage stabiliser. (2) Thereby, a more exact determination of the sensitivity of the apparatus as a function of the sample mass is possible. (3) A method is described for the correction of measurement data afflicted by systematic errors. (4) A simple interpretation of the measured values as partial mixing enthalpies of the alloy element is given. (5) Finally, influences of the calibration substance, geometry factors and the possibility of obtaining additional information from the temperature-time curve are discussed.

Enthalpy of mixing of liquid and undercooled liquid ternary and quaternary Cu-Ni-Si-Zr alloys

Abstract The partial and the integral enthalpies of mixing of liquid Si–Zr, Cu–Si–Zr, Ni–Si–Zr and Cu–Ni–Si–Zr alloys with mole fractions of zirconium in the range from 0 up to 30 at.% have been determined by high-temperature isoperibolic calorimetry at 1575–1720 K. The data of the constituent ternaries were described using a regular association model. The enthalpy of mixing of liquid and undercooled liquid Cu–Ni–Si–Zr alloys were estimated for all compositions on the basis of the model description of the constituent binary and ternary systems.

Zur Frage nach einem Nachschmelzeffekt bei den Metallen Indium und Zinn

Analog wie beim Gallium und bei der intermetallischen Verbindung Hg5Tl2 wurden auch an Indium und Zinn Untersuchungen zum Nachweis eines Nachschmelzeffektes durchgefuhrt. Sowohl bei Indium als auch bei Zinn ist nach den Ergebnissen der Differential-Thermoanalyse ein Nachschmelzeffekt zu erwarten, allerdings in wesentlich geringerem Mase als beim Gallium.

Konstruktion eines Torsions-Oszillations-Viskosimeters für Temperaturen bis etwa 360 K

Um Aufklarung daruber zu gewinnen, ob beim Gallium und bei der intermetallischen Verbindung Hg5Tl2 kurz nach dem Aufschmelzen und vor dem Erstarren Abweichungen von der “normalen” Temperaturabhangigkeit der Viskositat zu beobachten sind und um ferner festzustellen, ob zwischen den Werten der Viskositat wahrend des Aufheiz- und des Abkuhlungsvorgangs eine Hysterese auftritt, wird ein Viskosimeter benotigt, das folgenden Anforderungen genugt: a) Der zur Aufnahme eines Mespunkts benotigte Zeitraum mus klein sein. Es kommt daher praktisch nur ein Torsions-Oszillations-Viskosimeter in Frage. Die Schwingung dieses Gerates mus zudem in einem kurzen Zeitraum (etwa 10 s) von der Ausgangsamplitude so weit herabgedampft sein, das eine Erfassung des logarithmischen Dekrements der Dampfung hinreichend genau moglich ist. Daraus ergibt sich die weitere Forderung: b) Die Schwingung mus verhaltnismasig schnell sein.