Growth and characterisation of potassium cobalt nickel sulfate hexahydrate for UV light filters

A new single crystal for ultraviolet light filter, KCNSH (Potassium Cobalt Nickel Sulfate Hexahydrate) was designed and its crystal structure was studied using X‐ray diffraction in this paper. The empirical of the title compound is K₂Co_0.1Ni_0.9(SO₄)₂.6H₂O with formula weight 437.15. KCNSH crystal belongs to the monoclinic space group P2(1)/c, a=6.1390(3)Å, b=12.1839(6)Å, c=9.0095(4)Å, α=γ=90°, β=105.060(2)°, V=650.74(5)ų, Z=2, Dc=2.231g/cm³. Using the cooling solution method, we have grown a deep green KCNSH crystal with dimension of 12×12×40mm³. The transmission spectrum of KCNSH in the range from UV to near IR wavelengths, its thermal properties, and the relationship between the structure and optical transmission properties are also studied and further discussed in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystalloluminescence and Mechanoluminescence Spectra of Ba(ClO3)2 · H2O and 2 K2SO4 · Na2SO4 Crystals

Crystalloluminescence and mechanoluminescence of Ba(ClO₃)₂ · H₂O and 2 K₂SO₄ · Na₂SO₄ crystals are investigated. The crystalloluminescence spectra are almost similar to the photoluminescence spectra; however, they differ completely from the mechanoluminescence spectra. The crystalloluminescence excitations may take place due to the various processes: (i) the recombination of ions, (ii) from amorphous to crystalline transition, (iii) from the phase change during the crystallization, and (iv) from the dielectric breakdown by the electric field produced due to the creation of microfracture during the crystal growth. It is concluded that the crystalloluminescence excitation in Ba(ClO₃)₂ · H₂O and 2K₂SO₄ · Na₂SO₄ crystals may be chemical in origin.     

Temperature‐concentration oscillations as a result of nanoheterophase structure of concentrated aqueous solutions of salts

Detailed precision investigation of aqueous solutions of NaBr·2H₂O, KBr, RbNO₃, and K₂SO₄ salts showed oscillations of crystal‐solution phase equilibria in the temperature range of 15–45 °C. The maximum deviations from the smooth correlation between the saturation temperature and the salt concentration (up to 4% of concentration and up to 10 °C) were found to correspond to simplest salt‐water ratios. Recently, similar trends were observed for NaNO₃, KNO₃ and K₂CrO₄ solutions. Oscillation amplitudes for saturation temperature in the investigated series decreased in the following orders: Na⁺→K⁺, Rb⁺, NH₄⁺ (nitrate systems), CrO₄^2–→SO₄^2– and Br^–→NO₃^– (potassium systems), and NO₃^–→Br^– (sodium systems). Increase in total content of impurities (2‐4‐fold) in solution results in 1.5‐2‐fold elevation of the oscillation amplitudes. A concept of nanoheterophase solution was suggested to account for the observed temperature‐concentration oscillations. The concept is based on the original experimental data on interrelated variation of different properties of aqueous salt solutions depending on their concentrations. Characteristic features of the phase diagrams are discussed and influence of the oscillations on crystal growth is elucidated. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of glaserite from aqueous solutions

Crystallization of glaserite (double salt of potassium and sodium sulphate) from aqueous solutions was studied by determining solubility, metastable zone width, growth and dissolution kinetics. Solubility measurements confirmed the presence of a large range of mother liquor compositions from which the precipitation of glaserite at about 73 – 76 wt% K₂SO₄ is obtained: inside this region the solubility lines resulted curvilinear. The metastability zone is quite large, ranging from 14 to 23 °C, and mainly increases by increasing the Na₂SO₄ content in the mother liquor. The growth rate of glaserite is second order, slightly size dependent and primarily controlled by diffusion as for K₂SO₄ but both growth and dissolution constants are quite lower than those for K₂SO₄.     

Phase formation in molten system (Na/K)2O‐TiO2‐P2O5. Crystal structures of NASICON and langbeinite‐related phosphates (K/Na)1+xTi2(PO4)3 (x = 0 and 0.357)

Crystallization of high temperature self‐flux of system Na₂O‐K₂O‐TiO₂‐P₂O₅ was investigated at different molar ratios (Na+K)/P = 0.9; 1.0 or 1.2 and Na/K = 1.0 or 2.0 over the temperature range 1000–650°C. The conditions of formation of complex phosphates K_0.10Na_0.90Ti₂(PO₄)₃ (NASICON‐related) and K_0.877Na_0.48Ti^ІІІ_0.357Ti^ІV_1.643(PO₄)₃ (langbeinite‐related) have been established. The new obtained compounds were investigated using FTIR‐spectroscopy, powder and single crystal X‐ray diffraction and optical microscopy methods. The influence of alkaline metal nature on the structure formation of complex phosphates in the high temperature self‐fluxes is discussed.     

A study of the mechanisms of defect formation in K2Ni(SO4)2 · 6H2O/K2Co(SO4)2 · 6H2O bicrystals grown from aqueous solutions

The K₂Co(SO₄)₂ · 6H₂O-K₂Ni(SO₄)₂ · 6H₂O system has been studied, and a series of K₂Ni(SO₄)₂ · 6H₂O/K₂Co(SO₄)₂ · 6H₂O bicrystals have been grown. The processes of defect formation at the substrate/layer interface K₂Co(SO₄)₂ · 6H₂O/K₂Ni(SO₄)₂ · 6H₂O are studied by probe microanalysis, X-ray topography, and optical microscopy. It is found that inclusions and threading dislocations are formed at the interface, due to which elastic stresses relax in the crystal. Nickel is nonuniformly distributed in the layer; its concentration decreases with an increase in the layer thickness, which is indicative of substrate dissolution in the initial stage of interaction. A way for the elastic mismatch stresses to relax in heterostructures of brittle crystals obtained from solutions at low temperatures is proposed which implies the formation of inclusions at the substrate/layer interface. Original Russian Text ? M.S. Grigor’eva, A.é. Voloshin, E.B. Rudneva, V.L. Manomenova, S.N. Khakhanov, V.Ya. Shklover, 2009, published in Kristallografiya, 2009, Vol. 54, No. 4, pp. 679–687.     

Effect of monovalent salts on morphology of calcium carbonate crystallized in Couette‐Taylor reactor

Monovalent ionic additives, Na⁺, K⁺ and NHequation/tex2gif-stack-1.gif impact on the morphology and agglomeration of CaCO₃ crystals. As increasing the additive concentration, the regular shaped crystals such as rhombohedron and spindle are changed to irregular one due to the inclusion of Na⁺ and K⁺ into the crystal structure. The inclusion of Na⁺ and K⁺ is detected using ICP‐AES. The partition of coefficients of Na⁺ and K⁺ are estimated as 9.74 × 10^–4, 9.73×10^–4, respectively and the amount of inclusion in the crystals is about 2×10³ ppm. However, the inclusion of ions does not modify a crystal structure of calcite. Since NH₄⁺ is large in radius, it is not included in crystal but shifts the spindle shape of crystal to the rhombohedral one. It is interesting to find that such modification of crystal morphology begins to appear at high additive concentration (0.05 M). In addition, the crystal agglomeration is promoted because the electric repulsive charge is reduced as increasing the additive concentration. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of potassium sulfate by cooling and salting‐out using 1‐propanol in a calorimetric reactor

A study was made on a isothermal process for the crystallization of potassium sulfate as an alternative to the cooling process. The process employs addition of 1‐propanol to aqueous salt solutions to achieve the “saltingout” of the K₂SO₄. This work was carried out using an automated Mettler Toledo model RC1 reactorcrystallizer with 800 ml capacity, and controlled isothermally at 25 °C to test the crystallization of K₂SO₄ by addition of the alcohol, and from 50 to 10 °C for the cooling crystallization. In both systems, the line of nucleation points was shown to be approximately parallel to the saturation curve, with an average width of 13°C or 3 % mass for crystallization by cooling, compared with 0.2 to 1 % by salting‐out. In experiments on crystallization by cooling, the K₂SO₄ crystals were 0.27 mm in mean size, showed 7 % agglomeration, and contained 8.5 % moisture. Crystals obtained by salting‐out had a mean size of 0.79 mm, 28 % agglomeration, and 9‐10 % moisture content. A crystal shape factor of approximately of 0.7 was obtained in both systems, apart from the agglomeration.     

The Thermal Decomposition of Polyhalite K2SO4 · MgSO4 · 2 CaSO4 · 2 H2O

The thermal decomposition of polyhalite (K₂SO₄ · MgSO₄ · 2 CaSO₄ · 2H₂O) was investigated by DSC/TG and X-ray powder diffraction. The decomposition of the polyhalite starts at 285 °C in releasing the crystal water within one step. Simultaneously the decomposition of the polyhalite into anhydrite and two solid solutions of the compositions K₂SO₄ · 1.76 MgSO₄ · 0.24 CaSO₄ and K₂SO₄ · 0.64 MgSO₄ · 1.36 CaSO₄ is taking place. The mechanism of decomposition runs through K₂SO₄ · MgSO₄ CaSO₄. This phase reacts immediately to the solid solutions, mentioned above.     

Crystal structure of octapotassium octasulfatodiceriate pentahydrate

Single crystals without Co and Ni have been crystallized by the substitution method in the K₂Ni(SO₄)₂-Ce(SO₄)₂-H₂SO₄-H₂O system using K₂Co(SO₄)₂ · 6H₂O, K₂ (Co,Ni)(SO₄)₂ · 6H₂O, or K₂Ni(SO₄)₂ · 6H₂O as protocrystals. The structure of the single crystals obtained has been established by X-ray diffraction analysis. The crystal structure contains dimer complex anions [Ce₂(μ-SO₄)₂(SO₄)₆]⁸⁻, K⁺ cations, and crystallization water molecules.     

Thermal “order‐disorder” behaviour in (Na1‐xKx)4B8O14 solid solutions investigated by X‐ray powder diffraction

In the potassium‐rich part of the binary system Na₄B₈O₁₄‐K₄B₈O₁₄ solid solutions have been found that can be described with the formula (Na_1‐xK_x)₄B₈O₁₄ with 0.45 ≤ x < 1.0. The crystal structures of (Na_0.25K_0.75)₄B₈O₁₄ and (Na_0.45K_0.55)₄B₈O₁₄ were refined at room temperature by the Rietveld method. The solid solutions crystallize like K₄B₈O₁₄ in the triclinic crystal system, space group P ‐1, with K partially substituted for Na. An ordered distribution of the alkali atoms over the four cation sites at room temperature has been discovered. The structure of (Na_0.25K_0.75)₄B₈O₁₄ was also refined for data collected at 300 and 500 °C. The refinements show that sodium and potassium atoms are less ordered at higher temperatures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of potassium sulphate from glaserite

The crystallization of K₂SO₄ from aqueous solutions of glaserite (a double salt of sodium and potassium sulphate) was investigated in an MSMPR cooling apparatus at 35 °C. The precipitation of K₂SO₄ at an average purity of 93 wt.% was obtained and the crystallization kinetics were derived from the experimental data. The nucleation and growth rates here obtained were, respectively, remarkably higher and slightly lower than those relevant to pure K₂SO₄: this behaviour may be explained by a faster nucleation and a slower growth of crystals containing also Na₂SO₄. The effect of small (0.05%) calcium additions to the feed was also tested, which caused an increase of supersaturation and a depression of the growth kinetics, whereas the nucleation one was not appreciably modified.     

Temperature‐concentration oscillations of crystal‐solution phase equilibria in the presence of trace impurities of surface‐active agents

Using the examples of aqueous salt solutions NaNO₃, KNO₃, RbNO₃, K₂SO₄, NaBr·2H₂O, KBr, and NH₄NO₃, it was experimentally proven that the new phenomena, i.e. temperature‐concentration oscillations of crystal‐solution phase equilibria detected previously in the range of 15–45 °C remain in the presence of trace impurities (10^‐4–10^‐3 wt. %) of ion‐active organic matters. The signs of breaks transformation into pair oscillations of “maximum‐minimum” type are established for the K₂SO₄, NaBr, KBr solutions. The efficiency of influence of trace impurities on phase equilibria sharply rises in the areas of the temperature‐concentration oscillations (the saturation temperature ranges up to 10 K). The impurity efficiency is promoted by the presence of the amides in its content (as compared with the sulphates) and an increase in length of the hydrocarbon radical. The phenomenon is absent in case of an addition of ion‐inactive compounds. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Elastic and Thermoelastic Properties of Triclinic K2Cr2O7

Large single crystals of optical quality of triclinic K₂Cr₂O₇ have been grown from aqueous solutions. Their morphological and growth properties are not compatible with point symmetry 1 . Complete sets of the elastic constants and their temperature derivatives were determined from ultrasonic resonances of plane-parallel plates. The elastic behaviour and also the thermal expansion are highly anisotropic. Owing to very strong photoelastic effects these crystals are suited for certain acousto-optic deflection devices.     

Vickers microhardness of K<Subscript>2</Subscript>Co(SO<Subscript>4</Subscript>)<Subscript>2</Subscript> · 6H<Subscript>2</Subscript>O single crystals and fracture geometry around impressions of vickers,knoop, and spherical indenters

The microhardness on the (010) and (001) planes in K₂Co(SO₄)₂ · 6H₂O crystal has been measured by the Vickers indentation method. Its values are, respectively, 11500 and 1300 MPa. No microhardness anisotropy of the first kind is revealed on either plane. The fracture geometry under indentation by a spherical indenter and Vickers and Knoop indenters is studied. The crystal has lower brittleness than the isomorphic Cs₂Ni(SO₄)₂ · 6H₂O crystal.     

Elastic,Piezoelectric and Dielectric Constants of Pentaerythritol

The elastic, piezoelectric and dielectric constants of pentaerythritol, C(CH₂OH)₄, have been computed employing the method of long waves and the unscreened rigid ion potential model developed by RAMAMOORTHY and KRISHNAMURTHY. Piezoelectric contribution is taken into account in the computation of elastic constants. This is the first report on the piezoelectric and dielectric constants of pentaerythritol. In the notations followed by LANDOLT-BORNSTEIN the computed piezoelectric constants are: _g14 = 4.82, _g15 = 4.37, _g31 = 16.21 and _g36 = 5.89 (in unit of 10⁻¹Vm/N) and the static dielectric constants are: K₁ = 2.38 and K₃ = 2.47. The hydrogen bonding in pentaerythritol has no effect on its dielectric behaviour. Calculation of acoustic velocities in piezoelectric crystals and as a special case to the crystals of class 4 is explained in detail. Sound velocities calculated from the elastic, piezoelectric and dielectric constants computed in the present investigation agree with the experimental values determined by the ultrasonic method.     

Elastic properties of the dithionates Na2S2O6 · 2 H2O,K2S2O6, Rb2S2O6, CaS2O6 · 4H2O and SrS2O6 · 4 H2O

Single crystals of the title compounds having optical quality and dimensions of several cm were grown from aqueous solutions. The elastic and thermoelastic constants were determined from ultrasonic resonance frequencies of thick plates. The true point symmetry of K₂S₂O₆ and Rb₂S₂O₆, which is screened by a hexagonal hypermorphy, could be clearly revealed to be trigonal (32) by the existence of the elastic constant c₁₄. In the case of CaS₂O₆ · 4H₂O and SrS₂O₆ · 4H₂O the constant c₁₄ of the specimens appeared too small to confirm the trigonal symmetry group required from electrooptic and non-linear optic effects unambiguously. The isotypy of K₂S₂O₂ and Rb₂S₂O₆ as well as that of CaS₂O₆ · 4H₂O and SrS₂O₆ · 4H₂O is confirmed by their elastic behaviour. The mean elastic stiffness of dithionates is closely related to that of the corresponding sulphates. In the vicinity of the second-order phase transition of K₂S₂O₆ near 235 K weak anomalies of the temperature derivatives of the longitudinal elastic stiffnesses are observed.     

Crystal structures of low-symmetry cancrinite and cancrisilite varieties

The high-sodium variety of cancrinite [Si_6.3Al_5.7O₂₄][Na₂(H₂O)₂][Na_5.7(CO₃)_0.9(SO₄)_0.1(H₂O)_0.6] (Kovdor Massif, Kola Peninsula, Russia) and the calcium-containing variety of cancrisilite [Si_6.6Al_5.4O₂₄][(Na_1.2Ca_0.4)(H₂O)_1.6][Na₆(CO₃)_1.3(H₂O)_1.2] (Khibiny Massif, Kola Peninsula, Russia) are studied. The trigonal unit cell parameters of the crystal structures under investigation are as follows: a = 12.727(4) Å, c = 5.186(2) Å, and space group P3 for the former mineral and a = 12.607(4) Å, c = 5.111(1) Å, and space group P3 for the latter mineral. The reduced symmetry of the new varieties as compared to the symmetry of typical cancrinite and typical cancrisilite is associated with the specific features in the arrangement of the carbonate groups and water molecules in channels. This inference is confirmed by the IR spectroscopic data.     

Minerals successions crystallisation related to tunisian natural brines

Natural brines sampled from Sebkhats in southern part of Tunisia are considered to be seawater‐type solutions. The equilibrium solubility of this kind of solutions might be described by the fivefold seawatertype system Na⁺, K⁺, Mg²⁺, Cl^‐, SO₄^2‐ // H₂O. The crystallisation sequences of salts, observed under solar evaporation, of two different Tunisians brines is discussed. Very important differences between the foreseeable results, based on the Equilibrium Solubility Diagram at 25 °C, and the experimental ones are settled. An attempt to explain the differences, based on the so‐called “solar sequences” as well as the “solar diagram” of evaporation, is made. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of calcium phosphate based bioactive quaternary P2O5-CaO-Na2O-K2O glasses

Calcium phosphate based bioactive quaternary glass systems P₂O₅-CaO-Na₂O-K₂O were prepared by melt growth technique. Glasses were prepared in five different compositions by fixing P₂O₅ at 47 mol% and CaO at 30.5 mol% and by varying the K₂O and Na₂O concentrations. The structural properties of the glasses are analyzed using X-ray diffraction (XRD) studies and scanning electron microscopy (SEM) studies; and the composition of the glasses are studied using energy dispersive X-ray spectrum (EDS). The microhardness of the glass systems are studied by Vickers hardness measurements and the bioactivity of the glasses are studied using in vitro study. The thermal properties have been examined by means of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The ultrasonic velocity measurements show that the addition of K₂O contents produces non-bridging oxygen ion and hence weaken of the glass structure. The weakening of the glass structure reduces the ultrasonic velocity and hence an increase in attenuation.