Mechanochemical synthesis of hydroxyapatite from Ca(OH)2-P2O5 and CaO-Ca(OH)2-P2O5 mixtures

Dry grinding of Ca(OH)₂-P₂O₅ and CaO-Ca(OH)₂-P₂O₅ mixtures was conducted by a planetary ball mill to investigate the mechanochemical solid-phase reaction for the synthesis of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp). HAp was synthesized by grinding of the two sets of mixtures. The formation of HAp from the Ca(OH)₂-P₂O₅ mixture was more advantageous than that from the CaO-Ca(OH)₂-P₂O₅ one. This synthesis reaction from the former mixture was almost completed within 30 min of grinding. The presence and amount of H₂O contained in the starting mixtures played a key role to promote the formation of HAp. Especially, in the former mixture, the prolonged grinding assisted the solid-phase reaction of the intermediate DCPD and Ca(OH)₂ to produce HAp more effectively.     

Solid-state reactions in V x O y (NH4VO3)-P2O5 and V x O y (NH4VO3)-(NH4)2HPO4 closed systems

Solid-state reactions in V _x O _y (NH₄VO₃)-P₂O₅ and V _x O _y (NH₄VO₃)-(NH₄)₂HPO₄ closed systems can be used to synthesize vanadyl hydrogen phosphate at 300°C and a variety of ammonium vanadium phosphates at lower and higher temperatures.     

Thermal polycondensation of ammonium paratungstate, (NH4)10[W12O40(OH)2].4H2O

Connected with the examination of the thermal polycondensation of ammonium paratungstate pentahydrate the chemical and morphological properties of intermediate phases formed during the thermal decomposition of APT have been investigated. We have studied the pH and the turbidity of the aqueous solutions of the intermediate phases, the solubility of the phases, and their rehydratation capability as well as the morphology of the crystallite granules and the grain size distribution. These properties of the original APT have been related to the same properties of the products of decomposition formed between different temperature ranges. The results obtained show unambiguously that each of the above mentioned properties suddenly changes in the temperature range 225 to 250°C. This temperature range coincides with the formation temperature of a new phase called APT II. The most probable formula of APT II is (NH₄)₈ [H₂W₁₃O₄₃(OH)₂]·H₂O.     

Preparation and thermal decomposition of hexa-ammonium tetraphosphate dihydrate(NH4)6P4O13·2H2O

Hexa-ammonium tetraphosphate dihydrate, (NH4)6P4O13·2H2O (HATP), was prepared by the hydrolysis of sodium cyclo-tetraphosphate with sodium hydroxide solution, followed by ion-exchange with ammonium. Thermal decomposition in static air was first carried out dynamically, at a heating rate of 5 K min-1 as used in thermal analysis (thermogravimetric-differential thermal analysis), and also isothermally. To examine the effect of humidity on the thermal decomposition, HATP was heated isothermally in streams of dry and humid air. The products were characterized by X-ray diffraction analysis and high-performance liquid chromatography–flow injection analysis. At 100°C, HATP was decomposed to mono- and triphosphates and to 2 mol diphosphate, and this was accelerated by humidity. Further degradation of the triphosphate to mono- and diphosphates took place slowly. The 2 mol diphosphate also decomposed slowly to 4 mol monophosphate. At temperatures above 150°C, the form I of ammonium polyphosphate (I-APP) was produced. I-APP was further hydrolysed by humidity to shorter-chain phosphates, such as mono-, di- and triphosphates. This revised version was published online in November 2006 with corrections to the Cover Date.     

Phase transformation and sintering behavior of Ca2P2O7

The phase transformation and sintering behaviors of Ca₂P₂O₇ with different phase composition were investigated by using X-ray powder diffraction (XRD), dilatometery and scan electron microscopy techniques in this paper. It is found that although α-Ca₂P₂O₇ (high-temperature form) could be kept during its cooling process, it is metastable and retransformed into β-Ca₂P₂O₇ (low-temperature form) at about 950 °C during its reheating process. This reversible phase transformation was discussed from the point view of polyhedral distortion. The sample from β-Ca₂P₂O₇ calcined at 1000 °C/2 h densifies much faster than that from α-Ca₂P₂O₇ and α+β mixture, and bulk density as high as 98% TD can be obtained as it is sintered at 1150 °C. A dense α-Ca₂P₂O₇ free of micro-crack could not be obtained whatever from the powder of β-Ca₂P₂O₇ or α-Ca₂P₂O₇ or α+β mixture. Such different sintering behavior was explained in related to the reversible phase transformation between α- and β-Ca₂P₂O₇.     

Solid solutions between ettringite, Ca6Al2(SO4)3(OH)12·26H2O, and thaumasite, Ca3SiSO4CO3(OH)6·12H2O

A series of solid solution phases between ettringite, Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O, and thaumasite, Ca₃SiSO₄CO₃(OH)₆·12H₂O, have been prepared and analysed by X-ray powder diffraction and full pattern fitting. Solid solutions were shown to exist with both the ettringite structure (space group P31c) and the thaumasite structure (space group P6₃, c-axis halved). A possible discontinuity was identified, characterised by a gap in the a-dimension of the solid solution phases produced. This discontinuity is believed to correspond to a switch between the ettringite space group and the thaumasite space group. It is suggested that any discontinuity in the solid solution is caused by differences in the hydrogen bonding of the two structures.     

A zinc phosphate, [NH3(CH2)3NH3][Zn4(PO4)2(HPO4)2], possessing alternate inorganic and organic layers

A new zinc phosphate of the formula, [NH₃(CH₂)₃NH₃][Zn₄(PO₄)₂(HPO₄)₂], has been synthesized hydrothermally starting from a zinc amine complex. It crystallizes in the monoclinic space group C2/c; a=17.279(1), b=5.193(1), c=20.115(1) Å, β=92.6(1)°; V=1803.1(2) ų; Z=4; D_calc=2.05 g cm⁻³; μ (MoKα)=5.62 mm⁻¹. The final R, and wR₂=0.037, 0.093 obtained for 136 observed data [I>2σ(I)]. The structure consists of macroanionic sheets of interconnected ZnO₄ and PO₄ tetrahedra in the ab plane. The sheets are held together by hydrogen bond interactions with the organic structure-directing amine, forming alternate inorganic–organic layers in this material. Hydrogen bond interactions between the inorganic layers, via the terminal –OH group, leads to the formation of pseudo one-dimensional channels.     

Nucleation studies in supersaturated aqueous solutions of (NH4)H2PO4 doped with (NH4)2C2O4·H2O

Induction periods were measured for various supersaturated aqueous solutions of ammonium dihydrogen orthophosphate doped with ammounium oxalate monohydrate by the direct vision method. Various critical nucleation parameters were calculated based on classical theory for homogeneous crystal nucleation and the results reported and discussed. The critical nucleation parameters increased with increase in doping concentration.     

Crystal Structure of Double Co(NH3)6 3 + Np(V) Malonates Co(NH3)6(NpO2C3H2O4)2A·H2O (A = OH and NO3)

X-ray diffraction analysis of Co(NH₃)₆(NpO₂C₃H₂O₄)₂NO₃·H₂O (I) and Co(NH₃)₆(NpO₂· C₃H₂O₄)₂OH·H₂O (II) showed that they consist of [NpO₂C₃H₂O₄] _n ^{n -} infinite anionic chains, [Co(NH₃)₆]^{3 +} cations, NO₃ ^- (I) and OH^- (II) anions, and molecules of crystallization water. The anionic chain structure is similar to that in the known compound Co(NH₃)₆(NpO₂C₃H₂O₄)₂C₃H₃O₄. Neptunium(V) atoms occur in hexagonal-bipyramidal environment. The coordination capacity of malonate anions is 6, and they simultaneously coordinate three neptunyl(V) cations NpO₂ ⁺ in the chain.     

Structure and properties of phosphorodiamidic acid: HPO2(NH2)2 at room temperature

At room temperature, phosphorodiamidic acid (HPO₂(NH₂)₂) has a mobile hydrogen, which leads to P-NH ₃ ⁺ and P-O⁻ groups in limiting form. According to the spectroscopic analysis, a limiting (zwitterion) or a medium form (compound with mobile hydrogen) is prominent. This mobile hydrogen leads phosphorodiamidic acid to react with itself giving P-N(H)-P bridges and ammonium. We obtained a major compound ammonium salt of diamido 1, 2 imidodiphosphate which is present as ³¹P MAS NMR, a crystallographic nonequivalency.     

Synthesis and structural study of new potassium uranyl selenates K2(H5O2)(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)4 and K3(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)5

Single crystals of new uranyl selenates K₂(H₅O₂)(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₄ (1) and K₃(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₅ (2) were prepared by isothermal evaporation at room temperature. The crystal structure of 1 was solved by the direct method [C2/c, a = 17.879(5), b = 8.152(5), c = 17.872(5) Å, β = 96.943(5)°, V = 2585.7(19) ų, Z = 4] and refined to R ₁ = 0.0449 (wR ₂ = 0.0952) for 2600 reflections with |F _o| ≥ 4σ _F . The structure of 2 was solved by the direct method [P2₁/c, a = 17.8377(5), b = 8.1478(5), c = 23.696(1) Å, β = 131.622(2)°, V = 2574.5(2) ų, Z = 4] and refined to R ₁ = 0.0516 (wR ₂ = 0.1233) for 4075 reflections with |F _o| ≥ 4σ _F . The structures of 1 and 2 are based on [(UO₂)₂(SeO₄)₄(H₂O)₂]^4? layers. The charge of the inorganic layer is compensated by potassium and oxonium ions arranged in the interlayer space. Each K ion is surrounded by seven O atoms belonging to uranyl selenate layers and water molecules, so that it binds with each other the adjacent uranyl selenate structural elements.     

Dielectric characteristics of biocompatible Ca10(PO4)6(OH)2 ceramics

The temperature dependence of the dielectric permittivity and losses of biocompatible Ca₁₀(PO₄)₆(OH)₂ ceramics were studied in a temperature range from 20 to 500°C. An approach to the interpretation of anomalies (bending points) observed in the dielectric characteristics of the ceramic samples is proposed, which takes into account features of the crystal structure of calcium hydroxyapatite and the defects formed in the course of thermal treatments.     

介孔Zr（HPO4）2的合成及表征

以十六烷基三甲基溴化铵(CTAB)为模板剂,采用溶胶-凝胶法配合水热晶化合成了具有短程有序介孔结构的层状化合物Zr(HPO4)2。通过XRD、N2吸附、HRTEM等技术对样品的物相、孔结构和形貌进行了表征,结果表明,按n(CTAB)∶n(Zr)=0.8引入CTAB作为模板剂所合成的前驱体在120℃水热晶化48h,可以得到比表面积为66.9m2/g、孔容为0.11cm3/g、平均孔径为8.1nm的单相Zr(HPO4)2结晶化合物。     

Mechanochemical synthesis of stoichiometric MgFe2O4 spinel

The influence of long-term milling of a mixture of (1) MgO and α-Fe₂O₃, (2) MgCO₃, and α-Fe₂O₃, and (3) Mg(OH)₂ and α-Fe₂O₃ powders in a planetary ball mill on the reaction synthesis of nanosized MgFe₂O₄ ferrites was studied. Mechanochemical reaction leading to formation of the MgFe₂O₄ spinel phase was followed by electron microscopy, (SEM and TEM), X-ray diffraction and magnetization measurements. The spinel phase was observed first in cases (1) and (2) after 5 h of milling, and its formation was observed in all cases after 10 h. The synthesized MgFe₂O₄ ferrite has a nanocrystalline structure with a crystallite size of about 11, 10, and 12 nm, respectively for cases (1)–(3). Magnetic measurements after 10 h of milling show magnetization values of 19.8 J/(Tkg), 23.5 J/(Tkg) and 13.8 J/(Tkg), respectively for the cases (1)–(3).     

Sorption of Radionuclides onto Cerium(IV) Hydrogen Phosphate Ce(PO4)(HPO4)0.5(H2O)0.5

Radiochemistry - The ability of cerium(IV) hydrogen phosphate Ce(PO4)(HPO4)0.5(H2O)0.5 to adsorb radionuclides was studied. The degree of sorption from aqueous solutions exceeds 95% at pH >...     

Chemical etching of (100) GaAs in the (NH4)2Cr2O7-H2SO4-N H4Cl-H2O system

The etching solution containing ammonium dichromate, sulphuric acid and ammonium chloride in water solution allows for the investigation of the influence of individual active components and their concentration on the etching reaction with GaAs. The influence of these agents on etching as well as the temperature and stirring were examined. The etching rate increases with increasing Cl^– ion concentration, increases and subsequently decreases with the increasing of H⁺ ion concentration and remains constant in the wide range of oxidant anion concentration. The effect of stirring on etching rate allows us to estimate regions dominated by diffusion kinetics. The activation energy in the wide range of parameters is constant and equal to 60 kJ mol^–1. Microscopic observations reveal surfaces of various morphologies: smooth; covered with round hills; or with a network of veins. Various profiles of grooves arranged in various directions are revealed due to the preferential characteristic of etching; these profiles are also influenced by the mask material.