Enthalpies of formation of liquid (copper + manganese) alloys
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I.
INTRODUCTION
IN a series of binary copper-3d-transition metal systems, the enthalpies of formation of liquid copper-manganese alloys in the entire concentration range remained unknown until recently. Filling in this gap is the topic of the present article. The phase diagram of Shunk[1] is redrawn by Massalski et al.[2] The system is characterized by a complete range of solid solutions between copper and g -manganese at ele→L vated temperatures and a nonvariant equilibrium d -Mn ← 1 g -Mn at 1372 K. There is a minimum on the liquidus curve at 1144 K and xMn 5 0.37. At lower temperatures, fcc-solid solutions in the copper corner undergo ordering with the formation of intermetallic compounds Cu5Mn and Cu3Mn. At higher manganese contents (Cu, g Mn), solid solutions decompose, releasing (a Mn) phase. Sato and Kleppa[3,4] measured the enthalpies of formation of liquid alloys by calorimetry at 1368 K in the range from 0 to approximately 70 at. pct Mn. Gashon et al.[5] reported the value of DfH0 for Cu0.9Mn0.1 solid alloy found by solution calorimetry in liquid tin at 738 K. Activities of manganese were measured for solid alloys at 993 to 1093 K by Eremenko et al.[6] using the electromotive force (emf) method and for liquid alloys at 1517 K by Spencer and Pratt[7] using the torsion-effusion technique. The latter results were included with minor corrections by Hultgren et al. in their compilation.[8] The current research is a part of the systematic revision of the thermochemical properties of liquid binary copper alloys with transition metals. II.
EXPERIMENTAL PROCEDURE
Enthalpies of formation of liquid alloys from pure liquid copper and manganese were measured at 1573 K in the entire range of compositions by high-temperature isoperi-
M.A. TURCHANIN, Associate Professor, is with the Department of Technology and Apparatus of Cast Manufacture, Donbass State Mechanical Engineering Academy, 343 913 Kramatorsk, Ukraine. I.V. NIKOLAENKO, Associate Professor, is with the Department of Chemistry, National University of Lesotho, Lesotho, Southern Africa. Manuscript submitted April 12, 1995. METALLURGICAL AND MATERIALS TRANSACTIONS B
bolic heat-flux calorimetry. The instrument used was a selfmade calorimeter similar to the one described elsewhere.[9] Major modifications introduced refer to the replacement of some components of electronic equipment that improved temperature stabilization of the calorimeter core and made the data acquisition system more flexible and versatile. Every calorimeter can be subdivided basically into three parts: a core, an enclosure, and some kind of thermal resistance between the two. In the isoperibolic instrument, the temperature of enclosure is maintained constant at all times. When the thermal resistance between the core and enclosure is small, any thermal event in the core will cause heat exchange between it and the surroundings. If the heat flux between these two parts is measured somehow, one has what is called a ‘‘heat-flux instrument.’’ The theory of heat-flux calorimetry is based on the w
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