The solid state phase transformation of potassium sulfate

Abstract

Potassium sulfate single crystals that are grown from aqueous solutions lose upon the first heating up to 1% of mass that is assumed to be water. This mass loss occurs in the vicinity of the PT from orthorhombic to hexagonal K2SO4. Only in the first heating run of K2SO4 that has not yet released water, pretransitional thermal effects can be observed in the DTA curve. If K2SO4 crystals are grown from solutions containing 4 wt.% Cd, Cu, or Fe, only Cu or Fe can be incorporated significantly with concentrations of several 0.1%. The phase transformation temperature measured for such solid solutions depends on the heating rate. For pure K2SO4, the phase transformation temperature is independent on heating rate 581.3 deg. C and the enthalpy of transformation is (5.8+/-0.2) kJ/mol.Comment: 11 pages, 6 figures, 1 tabl

Growth and Analysis of NSH and KMNSH Crystals by Slow Evaporation Technique

“…Several other crystals such as cesium nickel sulphate hexahydrate (CNSH) [3], iron nickel sulphate twelvehydrate (FNSH) [4], rubidium nickel sulphate hexahydrate (RNSH) [5], and ammonium cobalt nickel sulphate hexahydrate (ACNSH) [6] are also reported as UV filter materials. Similar research work carried out on potassium sulphate [7,8], potassium cobalt nickel sulphate hexahydrate (KCNSH) [9,10], bis thiourea magnesium sulphate (BTMS) [11], and magnesium sulphate heptahydrate [12] crystals is also reported. In the search of newer crystalline materials with better filter transmission property and higher thermal stability, the growth of potassium magnesium nickel sulphate crystal has been carried out in this research work.…”

Effect of on the growth and thermal properties of K2SO4 crystal

“…The hysteresis phenomena, cracking, and electrical ''pretransition phenomena'' were attributed to rotational disorder of SO 2À 4 ions [8] and inclusions of OH þ 3 [6]. The present authors reported recently, that the addition of Cd 2þ to the nutrient solution during K 2 SO 4 crystal growth leads to an improvement of the crystalline quality [9]. In this paper, the influence of Cd 2þ on the growth and on thermal and optical properties of K 2 SO 4 crystal is studied in more detail.…”

“…The transition temperature T t can be determined from the intersection of the extended basis line with the tangent at the inflection point (extrapolated onset). It is remarkable that for pure K 2 SO 4 , T t as obtained from the first heating or cooling runs, respectively, differ considerably by a hysteresis of about 8 K. For K 2 SO 4 :Cd 2þ this hysteresis is only 4.5 K. It was reported recently that the hysteresis is reduced considerably for both K 2 SO 4 and K 2 SO 4 :Cd 2þ in subsequent (starting from the second) heating/cooling runs [9]. Hence it can be suggested that the effect of Cd 2þ on hysteresis is similar to the effect of annealing for K 2 SO 4 crystal, if the first heating/cooling run is considered as annealing for the undoped crystal.…”

“…The crystals were characterized by inductively coupled plasma-optical emission spectroscopy (ICP-OES), by X-ray powder diffractometry, and by simultaneous differential thermal analysis/thermogravimetry (DTA/TG), as described recently [9]. A NETZSCH STA409CD DTA/TG/ QMS (QMS ¼ quadrupole mass spectrometer) system with skimmer coupling of the QMS was used for the simultaneous analysis of gaseous species that are evaporating from the sample during heating [10].…”

“…In contrast, the higher dopant concentration in K 2 SO 4 :Fe 2þ leads to remarkable hysteresis of 0.4 K and shifts the melting point to T f ¼ ð1070:4 AE 0:1Þ C. In analogy to Fig. 6 of [9] which represents a model for the b/a phase transformation, an extended two phase region a/liquid can explain the shift of T f and the hysteresis.…”