A STUDY OF THE KF-ZrF$sub 4$ SYSTEM

The solid state reactions in the KF - ZrF/sub 4/ system were followed by differential thermal analysis and by x-ray annlysis. Melts contain~g less than 33.3% ZrF/sub 4/ were prepared from potassium fluoride and K/sub 2/ZrF/sub 6/. Melts with more than 33.3% ZrF/sub 4/ were made by fusing the calculated amounts of K/sub 2/ZrF/sub 6/ and (NH/sub 4/)/sub 3/ ZrF/sub 7/ in a current of CC/sub 2/ The phase diagram for the KF - ZrF/sub 4/ system, constructed on the basis of the thermal and x-ray analyses, has 28 different regions. The compounds K/sub 3/ZrF/ sub 7/, K/sub 5/Zr/sub 2/F/sub 13/, K/sub 2/Zr F/sub 6/, K/sub 3/Zn/sub 2/F/sub 11/, K/sub 7/Zn/sub 6/F/sub 31/ and KZrF/sub 4/ were found in t his system. The fluorozirconates K/sub 3/ZrF/sub 7/ and KZrF/sub 5/ melt congruently at 923 and 455 deg C respectively. The fluorozirconates K/sub 5/Zr/sub 2/F/sub 13/ and K/ sub 2/ZrF/sub 6/ are formed by peritectic reactions with K/sub 3/ZrF/sub 7/ and K/ sub 3/ZrF/sub 7/ respectively at 848 and 585 deg C respectively. The fluorozirconates K/sub 3/Zr/sub 2/F/sub 11/ and K/sub 7/Zr/sub 6/F/sub / 3>i/sub 1/ exist only as,solid below 327 and 380 deg C respectively. The eutectic between KF andmore » K/sub 3/ZrF/sub 7/ occurs at 760 deg C and 13% ZrF/sub 4/; the eutectic between K/sub 3/ZrF/sub 2/ and KZrF/sub 5/ occurs at 430 deg C and 47% ZrF/sub 4/, while the eutectic between KZrF/sub 5/ and ZrF/sub 4/ occurs at 440 deg C and 60% ZrF/sub 4/. A number of modifications of K/sub 2/ZrF/sub 6/ were detected. The fluorozirconate KZrF/sub 5/ undergoes polymorphic transformatfons at 400 and 424 deg C. A fluorozirconate with a composition of K/sub 3/Zr/sub 2/F/ sub 11/ undergoes a polymorphic transition at 313 deg C. The colapound K/sub 3/ ZrF/sub 7/ has a single modification and forms a solid solution with K/sub 2/ZrF/ sub 6/ (in the region of 73 to 75% KF). (TTT)« less