Crystal growth,structure, crystalline perfection and characterization of zinc magnesium ammonium sulfate hexahydrate mixed crystals ZnxMg(1−x)(NH4)2(SO4)2·6H2O

Mixed crystals Zn_xMg_(1?x)(NH₄)₂(SO₄)₂·6H₂O of the two well-known Tutton's salts Zn(NH₄)₂(SO₄)₂·6H₂O and Mg(NH₄)₂(SO₄)₂·6H₂O were grown with varying molar proportions (x=0.10–0.90) by slow evaporation solution growth technique. The mixed crystal Zn_0.54Mg_0.46(NH₄)₂(SO₄)₂·6H₂O is crystallizing in monoclinic system with space group P2₁/c and cell parameters a=6.2217(4) Å, b=12.5343(7) Å, c=9.2557(6) Å, β=106.912(3)°. The coexistence of zinc and magnesium ions in the mixed crystal was confirmed by inductively coupled plasma (ICP), atomic absorption spectroscopy (AAS) and energy dispersive X-ray spectroscopy (EDS). Compositional dependence of lattice parameters follows Vegard's relations. Slight variations are observed in FT-IR and XRD of pure and mixed crystals. Comparison of crystalline perfection as evaluated by high-resolution X-ray diffraction (HRXRD) for mixed crystals of various proportions reveals a reasonably good crystalline perfection for the mixed crystal with nearly equimolar ratio of Zn and Mg. The surface morphology of the mixed crystals changing with composition was studied by scanning electron microscopy (SEM). UV–vis studies reveal that the transparency of the mixed crystals was not much affected.     

Effects of cadmium on crystallization of calcium phosphates

The precipitation of calcium phosphates in the presence of increasing cadmium amount was studied at 25 °C in dilute ammoniacal solutions ([Ca] = [P] = 0.005 M). An amorphous precipitate, an apatite‐like calcium phosphate and the compound Cd₅H₂(PO₄)₄·4H₂O are found according to pH and Cd concentration. The nucleation of hydroxyapatite is greatly delayed by cadmium, which influences also its crystallinity, but the effect tends to vanish with time. The role of cadmium is discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Composition and morphology control of Fex(PO4)y(OH)z·nH2O microcrystals

A series of Fe_x(PO₄)_y(OH)_z·nH₂O microcrystals were prepared by the hydrothermal reaction at 150 °C. The ratio of Fe²⁺/Fe³⁺ in Fe_x(PO₄)_y(OH)_z·nH₂O microcrystals can be adjusted by using Na₂S₂O₃·5H₂O as a reducing agent. The morphology control of Fe_x(PO₄)_y(OH)_z·nH₂O microcrystals was realized through regulating the molar ratio of LiAc·2H₂O/FeCl₃. Further, the morphology, structure and composition of Fe_x(PO₄)_y(OH)_z·nH₂O microcrystals were also investigated by x‐ray diffraction (XRD), x‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) techniques. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of ramiform precipitates formed on SiO2–TiO2 gel coatings by electric field hot water treatment

The shape of the precipitates on sol–gel derived SiO₂–TiO₂ coatings at the negative electrode changed from granular to ramiform by applying an electric field to the substrates during a hot water treatment, whereas such changes in the shape of titania nanocrystals with the electric field were not observed at the positive electrode. The granular and ramiform precipitates were identified as anatase (TiO₂) and hydrated titania (n(TiO₂) · mH₂O), respectively. The ramiform shape of the titania precipitates became significant with increasing the applied voltage, while the coatings gradually became dark-colored due to the reduction of Ti⁴⁺ to Ti³⁺. The coatings with ramiform precipitates showed an excellent wettability for water.     

Synthesis of magnesium borates using sodium borate and magnesium sulfate

Synthesis conditions of magnesium borate compounds in aqueous medium using Na₂B₄O₇ · 10H₂O and MgSO₄ · 7H₂O were determined. The effects of B/Mg mole ratio, pH, reaction time and precipitation temperature on the reaction performed at 90 °C were examined. 0.04Na₂O · MgO · 1.23B₂O₃ · 3.42H₂O and 0.06Na₂O · MgO · 1.65B₂O₃ · 3.34H₂O were synthesized at optimum B/Mg mole ratios of 3.60 and 4.80 by precipitation at 5 °C and the amorphous compounds formed were identified by B, Mg, Na and XRD analyses and some physical tests.     

Effect of the surfactant nature on the thermo-stability of surface modified SnO2 nanoparticles

The modification of particle surface properties by the addition of small surfactant molecules in the initial sol is one strategy to minimize the strong tendency to aggregation and coarsening of nanoparticles prepared from the sol–gel process. In this work, the effect of the nature of the surfactant, Tiron^® ((OH)₂C₆H₂(SO₃Na)₂ · H₂O, anionic) or Catechol^® (C₆H₄-1,2-(OH)₂, non-ionic) or Maptac^® ([N(CH₃)₃(CH₂)₃NHCOC(CH₂CH₃)]⁺Cl^?, cationic), grafted on the SnO₂ nanoparticles on the mesoporosity of powders fired at 600 °C is presented. SnO₂ powders were prepared from an one-pot sol–gel route in which the hydrolysis of SnCl₄ · 5H₂O in aqueous solution was carried out in presence of the surfactant. The Fourier transform infrared (FTIR) spectroscopy and gravimetric and differential thermo-analysis (TG/DTA) results show that the thermo-stability of surface grafted SnO₂ nanoparticles obeys the following series: Tiron^® > Catechol^® > Maptac^®. The N₂ adsorption isotherms results evidence that the mesopores texture (specific surface area, pore volume and average pore size) can be tuned in a controlled way by increasing the amounts of Tiron^® or Catechol^® molecules grafted on the surface of SnO₂ nanoparticles.     

Sodium tracer diffusion in sodium boroaluminosilicate glasses

Sodium tracer diffusion coefficients, D*_Na, have been measured using the radioactive isotope Na-22 in sodium boroaluminosilicate (NBAS) glasses containing either a small amount of As₂O₃ or Fe₂O₃. The chemical compositions of the first type of glasses are given by the formula [(Na₂O)_0.71(Fe₂O₃)_0.05(B₂O₃)_0.24]_0.2[(SiO₂)_x(Al₂O₃)_1 ? x]_0.8 and those of the second type of glasses correspond to the formula [(Na₂O)_0.73(B₂O₃)_0.24(As₂O₃)_0.03]_0.18[(SiO₂)_x(Al₂O₃)_1 ? x]_0.82. Tracer diffusion measurements were performed at different temperatures between 198 and 350 °C. Pre-annealing of the glass samples at their glass transition temperatures in common air was found to lead to changes in the values of sodium tracer diffusion coefficients. For the NBAS glasses containing Fe₂O₃, after pre-annealing for 5 h, the activation enthalpy derived for the sodium tracer diffusion increases almost linearly from 57.5 to 71.3 kJ/mol with a decrease in the alumina content while the pre-exponential factor of the sodium tracer diffusion coefficient increases from 2.1 · 10^? 4 to 5.3 · 10^? 4 cm²/s. For the iron-free NBAS glasses pre-annealed for 5 h, the activation enthalpy varies between 63.9 and 71.4 kJ/mol while the pre-exponential factor varies between 1.5 · 10^? 4 and 1.2 · 10^? 3 cm²/s. In addition, it was observed that the considered glasses take up water when annealed at 300 °C in wet air with P_H2O = 474 mbar.     

Preparation and spectral properties of Nd3 +-doped transparent glass ceramic containing Ca5(PO4)3F nanocrystals

A Nd^3 +-doped transparent oxyfluoride glass ceramic containing Ca₅(PO₄)₃F nanocrystals was prepared by thermal treatment at the crystallization temperature for the precursor glass. The transmittances of the precursor glass and the glass ceramic with a thickness of about 2 mm are up to 84.7% and 77.4% in the visible range. The volume fraction of Ca₅(PO₄)₃F nanocrystals in the glass ceramic is about 19% and the ingress fraction of Nd^3 + ions into the Ca₅(PO₄)₃F nanocrystals is about 32%. The peak absorption cross-section increases to 224% at 807 nm and the full width at half maximum for the 807 nm band decreases from 17.5 to 3.5 nm after the crystallization process. The peak stimulated emission cross-section increases from 1.89 × 10^? 20 to 2.42 × 10^? 20 cm² at 1062 nm and the effective width of the emission line for the 1062 nm band decreases from 34 to 29 nm after the crystallization process. The improvement of spectroscopic properties indicates that the glass ceramic is potentially applicable as the 1.06 μm laser material.     

Synthesis and characterization of M2O–MgO–WO3–P2O5 (M = K, Rb, Cs) glass system

Transparent glasses of the composition M₂O–MgO–WO₃–P₂O₅ (M = K, Rb, Cs), corresponding to the crystalline phases of M₂MgWO₂(PO₄)₂, have been prepared and studied by Raman and IR spectroscopy as well as DTA. Moreover, the thermally stimulated depolarization and dc conductivity have been measured. The glass transition temperature is 797, 795 and 773 K for the K-, Rb- and Cs-containing glass, respectively. Raman and IR studies have shown that these glasses have very similar structure. The main building blocks are pyrophosphate groups, WO₆ octahedra and magnesium–oxygen polyhedra. The dc conduction in these glasses is controlled by hopping of small polarons. The potassium containing glass was shown to be very stable whereas the rubidium and cesium glasses have significantly higher tendency for crystallization and phase separation. It seems, therefore, that the potassium containing glass is a suitable material for the preparation of samples containing non-linear and ferroelectric nanocrystals of the K₂MgWO₂(PO₄)₂ phosphate.     

Characterization of iron phosphate glasses prepared by microwave heating

Phosphate glasses have been prepared by melting batch materials in electric furnaces, induction furnaces, and in microwave ovens. In the present work mixtures of (NH₄)₂HPO₄ and Fe₃O₄ or Fe₂O₃ were exposed to microwave energy, heated to 1200 °C, and cast to produce iron phosphate glasses. Glasses were also produced in electric furnaces for comparison. The material was analyzed by X-ray diffraction, Mössbauer spectroscopy, and differential thermal analysis. For magnetite-based glasses produced in an electric furnace, the Fe²⁺/(Fe²⁺ + Fe³⁺) ratio is compatible with the value in the batch material. The Fe²⁺/(Fe²⁺ + Fe³⁺) ratio is higher for glasses produced in a microwave oven. Glasses with nominal composition 55Fe₃O₄–45P₂O₅ (mol%) produced in an electric furnace present an arranged magnetic phase with hyperfine field that could be associated to hematite (estimated to be 21%). All the glasses submitted to heat treatments for crystallization present the following crystalline phases: FePO₄, Fe₃(PO₄)₂, Fe(PO₃)₃, Fe(PO₃)₂ and Fe₇(PO₄)₆. The amount of these phases depends on the glass composition, and glass preparation procedure. Microwave heating allows to reach melting temperatures at high heating rates, making the procedure easy and economical, but care should be taken concerning the final Fe²⁺/(Fe²⁺ + Fe³⁺) ratio.     

Study of the effect of the base,the silica and the niobium sources on the [Nb]-MCM-41 synthesized at room temperature

[Nb]-MCM-41 was synthesized at room temperature by varying the base (tetramethylammonium hydroxide or ammonium hydroxide), the silica source (tetraethyl orthosilicate or tetramethyl orthosilicate), the niobium source (ammonium niobium oxalate, NH₄[NbO(C₂O₄)₂(H₂O)₂] · 3H₂O, or potassium niobate, K₈Nb₆O₁₉) and the order of addition of the niobium source (before or after the silica source). These variations were determinant in the amount of niobium incorporated into the framework and in the structural order of the [Nb]-MCM-41 obtained. Only one method led to the formation of [Nb]-MCM-41 with the desired characteristics and active in the epoxidation of cis-cyclooctene with tert-butyl hydroperoxide leading to 19% conversion and 95% selectivity for cyclooctene oxide after 10 h.     

Preparation and properties of europium-doped phosphosilicate glasses obtained by the sol–gel method

In this work, we report the synthesis of europium-doped phosphosilicate glasses from tetraethylorthosilicate (TEOS), phenyltrietoxysilane (PTES) and ammonium phosphate (NH₄H₂PO₄) prepared by the sol–gel process. The matrix was synthesized by modified Stöber methodology. The alkoxide precursors PTES and TEOS were mixed with NH₄H₂PO₄, in the presence of europium III chloride, using ethanol as solvent in basic catalysis. These materials were studied by photoluminescence spectroscopy (PL), thermal analysis (TGA/DTA), transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). The results obtained for the materials show the formation of conchoidal-fractures, which are characteristics of glass materials. The thermal analysis showed the thermal stability of materials up to 300 °C. Eu III has been used as structural probe due to its photophysical properties. The PL spectra displays the lines characteristics of the Eu (III) ion ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3 and 4). Wide bands were observed, indicating non-homogeneous sites that are characteristic of amorphous systems.     

Investigations on sol–gel process and structural characterization of SiO2-P2O5 powders

The purpose of the study is to investigate the influence of the precursors, pH of the solution and temperature on the gelation and structure evolution of the samples from the SiO₂-P₂O₅ system. Tetraethoxysilane (TEOS) was used as precursor for SiO₂ and triethylphosphate (TEP) or phosphoric acid for P₂O₅, together with water as reagent for hydrolysis reaction and ethylic alcohol as solvent. The pH of the sols was modified by adding hydrochloric acid, in the case of TEP and by adding ammonia, in the case of H₃PO₄. The samples have been prepared starting from P₂O₅/SiO₂ = 1/10 and 1/5 molar ratio, H₂O/TEOS = 1; 2; 3 mass ratios and C₂H₅OH/TEOS = 1 mass ratio. We prepared silico-phosphate samples in the 1.5–5 pH domain and we observed that in all the cases, the lowest gelation time was found in the 3.5–4.5 pH range. We found that for the same pH value samples prepared with H₃PO₄ had a lower gelation time (few days) by comparison with the samples prepared with TEP (weeks), explainable by the low rate of the hydrolysis and condensation reactions of TEP. When the amount of water was increased, the gelation time increased in the case of samples prepared with H₃PO₄ and it was not significantly changed in the case of the samples prepared with TEP. The increasing of the solution temperature up to 40–41 °C yielded a decreasing of the gelation time (hours), especially for the samples prepared with H₃PO₄ by comparison with those prepared using TEP. In all the cases, the increased amount of water resulted in an increasing of the gelation time, even the temperature was raised. FTIR and Raman spectroscopy characterization aimed at getting information about the structural changes in the case of the samples dried in air and also for those heated at 100 °C, 300 °C, 600 °C and 900 °C. Vibration modes specific for SiOEt, SiOH, hydrogen bonds, H₂O and combined vibrations have been observed, which are in agreement with those revealed in literature data. ³¹P and ²⁹Si MAS NMR spectra gave interesting information about first surrounding of P and Si ions meaning the type and proportion of Q species and their evolution starting from the room temperature up to 900 °C.     

Synthesis and thermal behavior of different aluminosilicate gels

In this study a series of different gels (inorganic polymers) was synthesized with a single procedure, although varying the pH of the synthesis medium across a wide range of values. The chemicals used were as follows: a 0.25 M solution of K₂O · SiO₂ · 9H₂O as the source of silica, a 0.25 M solution of Al(NO₃)₃ · 9H₂O as the source of aluminum; and a 0.25 M solution of KOH to regulate the pH. Gel thermal stability was also determined, up to 1200 °C. The results show that at acidic pH both Si-rich and Al-rich gels are formed, which may crystallize into cristoballite and mullite, respectively, under thermal treatment. The gels synthesized at alkaline pH, in turn, remain stable at temperatures over 1200 °C. Depending on their composition, such gels may crystallize into leucite.     

The thermal behavior of 8 mol% yttria-stabilized zirconia nanocrystallites prepared by a sol–gel process

Eight mole percent yttria-stabilized zirconia (8YSZ) nanocrystallites were synthesized at a relatively low temperature using ZrOCl₂ · 8H₂O and Y(NO₃)₃ · 6H₂O as starting materials in an ethanol–water solution by a sol–gel process. The thermal behavior of the 8YSZ nanoparticles was investigated by differential thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy and electron diffraction. The crystallization temperature of the 8YSZ gel powders was estimated to be about 729 K by DTA analysis. When calcined from 773 to 1273 K, the crystallization of the cubic phase was observed by XRD. The crystallite size of the 8YSZ increased from 7.14 to 20.10 nm with calcining temperature increasing from 773 to 1273 K. The activation energy for growth of 8YSZ nanoparticles was found to be 7.26 kJ/mol.     

Growth and shape control of orthorhombic Fe5(PO4)4(OH)3·2H2O single crystalline dendrites

Orthorhombic Fe₅(PO₄)₄(OH)₃·2H₂O single crystalline dendritic nanostructures have been synthesized by a facile and reproducible hydrothermal method without the aid of any surfactants. The influences of synthetic parameters, such as reaction time, temperature, the amount of H₂O₂ solution, pH values, and types of iron precursors, on the crystal structures and morphologies of the resulting products have been investigated. The formation process of Fe₅(PO₄)₄(OH)₃·2H₂O dendritic nanostructures is time dependent: amorphous FePO₄·nH₂O nanoparticles are formed firstly, and then Fe₅(PO₄)₄(OH)₃·2H₂O dendrites are assembled via a crystallization-orientation attachment process, accompanying a color change from yellow to green. The shapes and sizes of Fe₅(PO₄)₄(OH)₃·2H₂O products can be controlled by adjusting the amount of H₂O₂ solution, pH values, and types of iron precursors in the reaction system.     

Spectroscopic properties and ab initio calculations on the structure of erbium–zinc-borate glasses and glass ceramics

Glasses in the (Er₂O₃)_x·(B₂O₃)_(60 ? x)·(ZnO)₄₀ system (0 ≤ x ≤ 15 mol%) have been prepared by the melt quenching technique. X-ray diffraction, FTIR spectroscopy, UV-VIS spectroscopy and ab initio calculations studies have been employed to study the role of Er₂O₃ content on the structure of the investigated glass system.X-ray diffraction and infrared spectra of the glasses reveal that the B–O–B bonds may be broken with the creation of new non-bridging oxygen ions facilitating the formation of Er–O–B linkages. The excess of oxygen can be accommodated in the network by the conversion of sp² planar [BO₃] units to the more stable sp³ [BO₄] tetrahedral structural units. The linkages of the [BO₄] structural units can polymerize in [B₃O₉]^? 9 cyclic trimeric ions which will produce the ErBO₃ crystalline phase. An increase of the efficiency corresponding to the ⁴I_15/2 state to ⁴I_11/2 state (4f–4f) transitions of Er^+ 3 ions was observed for the erbium oxide richest glasses.Ab initio calculations on the structure of the matrix network show the thermodynamic instability of the [BO₄], [ZnO₄] and [Zn₄O] structural units. Formation of three-coordination oxygens was necessary to compensate shortage of oxygens from zinc ions.     

Network structure of multi-component sodium borosilicate glasses by neutron diffraction

Neutron diffraction structure study has been performed on multi-component sodium borosilicate based waste glasses with the composition of (65 − x)SiO_2. · xB₂O₃ · 25Na₂O · 5BaO · 5ZrO₂, x = 5–15 mol%. The maximum momentum transfer of the experimental structure factor was 30 Å⁻¹, which made available to determine the distribution function with high r-space resolution. Reverse Monte Carlo modelling was applied to calculate several partial atomic pair correlation functions, nearest neighbor distances and coordination numbers have been revealed. The characteristic features of Si–O and Si–Si distributions are similar for all glassy samples, suggesting that the Si–O network consisting of tetrahedral SiO₄ units is highly stable even in the multi-component glasses. The B–O correlations proved to be fairly complex, two distinct first neighbor distances are present at 1.40 Å and 1.60 Å, the latter equals the Si–O distance. Coordination number distribution analyzes has revealed 3 and four-coordinated boron atoms. The O–O distribution suggests a network configuration consisting of boron rich and silicon rich regions. Our findings are consistent with a structure model where the boron rich network contains mostly trigonal BO₃ units, and the silicon rich network is formed by a mixed continuous network of ^[4]Si–O–Si^[4] with several different ^[4]B–O–Si^[4] and ^[3]B–O–Si^[4] linkages.     

Thermal conductivity of mixed alkali silicate glasses at low temperature

Thermal conductivity of glass is one of the fundamental properties of it. However, that has not been studied enough. That of only less than 20 compositions has been measured below the room temperature. In this study, we measured the thermal conductivity of xNa₂O · (100 ? x)SiO₂ and (33 ? y)Na₂O · yCs₂O · 67SiO₂ glasses by a transient heating method in the temperature range from about 150 K to room temperature. The conductivity of xNa₂O · (100 ? x)SiO₂ is found to decrease with the increase in alkali content. The dominant factor of this behavior is the decrease in phonon mean free path, which is due to the increase of non-bridge oxygen. Thermal conductivity of (33 ? y)Cs₂O · yNa₂O · 67SiO₂ is decreased with the increase in Cs₂O/(Na₂O + Cs₂O) ratio. The dominant factor of this behavior is the decrease of sound velocity. However, composition dependence of the phonon mean free path also affects the thermal conductivity. Phonon mean free path of 33Cs₂O · 67SiO₂ glass is longer than that of 33Na₂O · 67SiO₂ glass, and should be related to the change in distribution of structural unit in glass. In addition, phonon mean free path of mixed alkali glasses are shorter than that of single alkali glasses.     

Structure and properties of the 70Li2S · (30 − x)P2S5 · xP2O5 oxysulfide glasses and glass–ceramics

The 70Li₂S · (30 ? x)P₂S₅ · xP₂O₅ (mol%) oxysulfide glasses were prepared by the melt quenching method. The glasses were prepared in the composition range 0 ≦ x ≦ 10. The glass–ceramics were prepared by heating the glasses over crystallization temperatures. The PO_nS_3?n (n = 1–3) oxysulfide units were produced in the glasses and glass–ceramics by partial substituting P₂O₅ for P₂S₅. In particular, the P₂OS₆^4? unit would be produced by substituting a small amount of P₂O₅ for P₂S₅. The oxygen atoms were incorporated into the Li₇P₃S₁₁ crystal structure because the diffraction peaks of the oxysulfide glass–ceramic shifted to the higher angle side. The glass–ceramic with 3 mol% of P₂O₅ exhibited the highest conductivity of 3.0 × 10^?3 S cm^?1 and the lowest activation energy for conduction of 16 kJ mol^?1. The P₂OS₆^4? dimer units in the oxygen-incorporated Li₇P₃S₁₁ crystal would improve conductive behavior of the Li₂S–P₂S₅ glass–ceramics.