Liquidus Surfaces of KF-Na₂B₄O₇-K₂WO₄, KF-K₂B₄O₇-K₂WO₄ and KF-B₂O₃-WO₃ Systems

Abstract

In order to search for a molten salt for the molten salt electrolysis of tungsten，the liqu玉dus surfaces of the KF-Na2B407-K2Wg4，KF-K2B407-K2WO4and KF-B20ゴWO3systems were deteτmined by the hot-thermocouple method．In the KF-Na2B407-K2WO4system，a compositional region w玉th low melting Points of about950K spread around a compQsition of KF(50)一Na2B407( 30)一K2WO4 (20mo1％)．In the KF-K2B40ブK2WO4system，a compositional region with low melting Points of about1000K spread around a compositiQn of KF(70)一K2B407(15)一K2WO4(15mo1％)．ln the KF-B20ゴWO3system，a compositionahegion with melting Points between975K and1000K spread around a composition of KF(75)一B203(10)一WO3(15mol％)． 1・INTRODUCTION The pτesent work is a part of a program to develop a new method for coating inexpensive metal substrates with tungsten metal by fused salt electrolysis．The autho1sト51have reported that smooth deposits of molybdenum can be electrolytically obtained at998-1173K in the fused salts of KF-Na2B407-K2MoO4，KF-B20ゴK2MoO4，KF-B203-Na2MoO4，and KF-B20ゴMoO3systems．In analogy with these fused salts，it is expected that a KF-borate(or B203)一tungstate(or WO3)fused salt also gives a smooth deposit of tungsten．For the electrolysis，it is very desirable to know the melting point of tke electrolytic bath．Thus，in the present work the melting points(primaτy crystal． lization temperatures) of the KF-Na2B407-K2WO ，KF-K2B407-K2WO4and KF-B203-WO3 systems were measured．There is no literature on the melting points of these systems． tkermocouple under a stereoscopic microscoPe． In this method，the thermocouple serves not only 2 1 1 2 1 2 2 998K observed 1110K l120K l l20K UO6K