盐卤硼酸盐化学XXX-MgO·2B2O3-18%MgCl2-H2O过饱和溶液结晶动力学

对ＭｇＯ．２Ｂ２Ｏ３－１８％ＭｇＣｌ２－Ｈ２Ｏ过饱和和溶液在不同温度条件下的结晶动力学过程进行测定,给出结晶动力学方程析出固相采用Ｘ－射线粉末衍射、红外光谱和热分析进行物相鉴定,提出使用结晶法合成章氏硼镁石的新方法。     

Chemistry of borate in salt lake brine (XXXIV)

The crystallization processes of hydrated Mg-borates, boric, magnesium hydroxide and Mg-oxychloride from MgO-B₂O₃-18%MgCl₂-H₂O supersaturated solution at 20°C have been studied by kinetic method. The crystallization solid phases were characterized by X-ray powder diffraction, IR spectra, thermal analysis and chemical analysis. The liquid-solid phase diagram of thermodynamic nonequilibrium state has been given. In this phase diagram, there exist eight crystallization fields, boric acid(H₃BO₃), trigomagneborite(MgO · 3B₂O₃ · 7.5H₂O, MgO · 3B₂O₃ · 7H₂O), hungchaoite(MgO · 2B₂O₃ · 9H₂O), inderite(2MgO · 3B₂O₃ · 15H₂O), chloropinnoite(2MgO · 2B₂O₃ · MgCl₂ · 14H₂O), magnesium hydroxide(Mg(OH)₂) and magnesium oxychloride (5Mg(OH)₂ · MgCl₂ · 8H₂O).     

Nucleation and Crystal Formation in Lithium Disilicate‐Apatite Glass‐Ceramic from a Combined Use of X‐Ray Diffraction,Solid‐State NMR,and Microscopy

Glass‐ceramics are multi‐phase materials that are comprised of one amorphous phase and at least one crystalline phase. Their versatile performance and properties can be engineered by alterations of the three fundamental steps – formulation and production of the amorphous base glass, nucleation, and crystallization. Efforts have been made on syntheses of glass‐ceramics with different components, yet little is known about the details of nucleation and crystallization processes that are essential for tailoring glass‐ceramic properties. Herein, we investigate the nucleation and crystallization mechanisms of a multi‐component, that is SiO₂‐Al₂O₃‐CaO‐Li₂O‐K₂O‐P₂O₅‐F, glass‐ceramic system by a combined use of powder X‐ray diffraction (pXRD), solid‐state nuclear magnetic resonance (NMR), and electron microscopic (EM) techniques. The role of P₂O₅ in the nucleation and crystallization processes is particularly studied. We show that the formation of lithium silicate crystals being independent of the P₂O₅‐associated crystals, and the separation of P₂O₅ phases into individual growth domains of lithium orthophosphate and fluorapatite. We also observe the non‐uniform distribution of fluorapatite particles that explains the opalescence effect of this glass‐ceramic.     

Crystallization in the SiO2-Al2O3 System from Amorphous Powders

The crystallization of amorphous chemically homogeneous powders in the SiO₂.Al₂O₃ system has been studied by differential scanning calorimetry and X-ray diffraction. Up to 1300°C only one exotherm has been observed. Only mullite crystallizes for compositions ≤69 mol% Al₂O₃ and spinel for those ≤80%. The crystallizations into mullite and spinel are sharp and exothermic, with an enthalpy of 250–300 J/g. The chemical composition of the crystallized mullite regularly increases from 68 to 76 mol% Al₂O₃ with increasing bulk composition from 60 to 75 mol% Al₂O₃.     

Kinetics of non-isothermal crystallization of some glass-ceramics based on basalt

The crystallization kinetics of some glass-ceramics obtained from Romanian (Şanoviţa) basalt has been studied in non-isothermal conditions using DTA technique. The activation energies of the crystallization processes were calculated using the isoconversional methods Kissinger-Akahira-Sunose and Ozawa-Flynn-Wall. The results obtained show a dependence of the activation energy (E _α) on the crystallized fraction (α) that proves the complex mechanism of the glass-ceramics crystallization process. It has been proved that the Johnson-Mehl-Avrami model cannot be applied for the studied glass-ceramics crystallization process. The effect of 2% TiO₂ as nucleating agent upon the crystallization kinetics and upon the microstructure of the studied glass-ceramics was analyzed.     

Kinetic studies of the crystallization process of glass-ceramics based on basalt

The crystallization kinetic of the basalt glass ceramic of the oxide composition, (%): SiO₂ − 50.82; Al₂O₃ − 12.05; Fe₂O₃ − 9.28; CaO − 15.48; MgO − 11.08; Na₂O+K₂O − 1.14; TiO₂ − 0.15, with addition of 10% TiO₂ as nucleating agent has been studied using thermal analysis under non-isothermal conditions. In this order, the non-isothermal DTA curves were obtained at different heating rates between 4 and 20°C min⁻¹ in the temperature range of 25–1000°C using a Derivatograph-C (MOM, Hungary). The kinetic parameters of the crystallization process were calculated on the basis of Ozawa-Flynn-Wall, Friedman, Budrugeac-Segal and non-parametric kinetic methods.     

DTA/DSC study of nanocrystallization in oxyfluoride glasses

Crystallization of glasses of the Na₂O-Al₂O₃-SiO₂-LaF₃ system was studied by DTA/DSC, XRD and TEM methods. It has been found that the nanocrystallization of LaF₃ in the NAS-based glass strongly depends on ratio of Na₂O/(SiO₂+Al₂O₃) and amount of doped LaF₃. Analysis of the local atomic interactions in the structure of oxyfluoride glasses has been used to explain the course of the crystallization. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of the Composition of Raw Materials and Nucleating Agents. Crystallization behavior of nepheline-pyroxenic glass

Different combination of raw materials and nucleating agents were incorporated in the batch of nepheline-pyroxene glass to demonstrate their effect on the crystallization process. The effect of TiO₂, Cr₂O₃ and LiF with respect to crystallization of base glass was studied by differential thermal analysis (DTA).These materials improved the crystallization of glass between 50 to 150°C of heat treatment. When LiF+TiO₂ and TiO₂+Cr₂O₃ were put together in the glass batches, the rate of crystallization of glass was increased in the same manner. The presence of TiO₂+LiF+Cr₂O₃ improved the crystallization of the glass by decreasing the heat temperature by about 60°C. CaO/MgO and CaO/Na₂O ratios played an important role in the rate of crystal growth. The increase in the CaO/MgO ratio lowers the crystallization temperature by values ranging between 37 and 46°C. This revised version was published online in August 2006 with corrections to the Cover Date.     

Casting synthesis of Bi12SiO20

Polycrystalline bismuth silicate Bi₁₂SiO₂₀ has been obtained by fusing a stoichiometric mixture of Bi₂O₃ and SiO₂ followed by crystallization of the melt by casting with no seeding.     

Non-isothermal crystallization kinetics of V2O5-MoO3-Bi2O3 glasses

Characteristic temperatures, such as T _g (glass transition), T _x (crystallization temperature) and T _l (liquidus temperature) of glasses from the V₂O₅-MoO₃-Bi₂O₃ system were determined by means of differential thermal analysis (DTA). The higher content of MoO₃ improved the thermal stability of the glasses as well as the glass forming ability. The non-isothermal crystallization was investigated and following energies of the crystal growth were obtained: glass #1 (80V₂O₅·20Bi₂O₃) E _G=280 kJ mol^-1, glass #2 (40V₂O₅·30MoO₃·30Bi₂O₃) E _G=422 kJ mol^-1 and glass #3 (80MoO₃·10V₂O₅·10Bi₂O₃) E _G=305 kJ mol^-1. The crystallization mechanism of glass #1 (n=3) is bulk, of glass #3 (n=1) is surface. Bulk and surface crystallization was supposed in glass #2. The presence of high content of a vanadium oxide acts as a nucleation agent and facilitates bulk crystallization. This revised version was published online in August 2006 with corrections to the Cover Date.     

Solid-state crystallization process and mechanism of B-Al-ZSM-5 zeolite

Ｉｎｃｏｍｐａｒｉｓｏｎｗｉｔｈｔｈｅａｌｕｍｉｎｕｍａｎａｌｏｇｕｅｓ,ｂｏｒｏｎｃｏｎｔａｉｎｉｎｇＭＦＩｔｙｐｅｚｅｏｌｉｔｅｈａｓｂｅｅｎｅｘｐｅｃｔｅｄｔｏｈａｖｅｍｉｌｄｅｒａｃｉｄｉｃｐｒｏｐｅｒｔｉｅｓａｎｄｓｐｅｃｉｆｉｃｃａｔａｌｙｔｉｃｐｅｒｆｏｒｍａｎｃｅ.Ｕｐｔｏｎｏｗ,ｍｕｃｈｗｏｒｋｈａｓｂｅｅｎｄｏｎｅｉｎｔｈｉｓａｓｐｅｃｔ[1—5],ｉｎｃｌｕｄｉｎｇｓｙｎｔｈｅｓｉｓ,ｓｔｒｕｃｔｕｒａｌｃｈａｒａｃｔｅｒｉｚａｔｉｏｎａｎｄｃａｔａｌｙｓｉｓ,ｅｔｃ.Ｔｈｅｒｅａｒ…     

Preparation of high homogeneity BaO-TiO2-SiO2 gel

In BaO-TiO₂-SiO₂ system, crystallization from various gel by heating depended on the sol-gel processes and gel homogeneity. Through the condensation reaction of Si(OAc)₄ and TiAcAc(O ⁱ Pr)₃ in tetrahydrofuran solvent, homogeneous TiO₂-SiO₂ sol with oligomers of relatively large molecular weight was obtained. The gel prepared by mixing the binary sol, Ba(OAc)₂, and Si(OMe)₄ was the most homogeneous in term of suppression of crystallization. By heating the above gel, only Ba₂TiSi₂O₈ crystal appeared, which was observed in a melt quenched glass. In the case of the gels made by other sol-gel processes, TiO₂ or BaTiO₃ crystal was first observed from the heated gels prior to the precipitation of Ba₂TiSi₂O₈.     

Influence of Preparation Conditions on Crystallization Behavior of the Complex Alkoxide Derived PbTiO3 Powder

PbTiO₃ powders were prepared by hydrolysis of the complex alkoxide derived from Pb(OCOCH₃)₂ and Ti(OCH₂CH₃)₄, and their crystallization behaviors were investigated by DTA. Influence of conditions of synthesis and hydrolysis of the Pb-Ti complex alkoxide and heating atmosphere on crystallization behavior of powder was examined.Powders consisting of spherical particles with submicron diameter could be obtained by using the reaction time over 16 hr for synthesis, and the use of acetone-ethanol solvent with ammonia catalyst for the hydrolysis of the complex alkoxide. The resultant powders crystallized to tetragonal PbTiO₃ perovskite above 250°C under O₂ flow, and then transformed to cubic perovskite at 490°C. The powder heated at 250°C for 1 hr in O₂ consisted of well-crystallized tetragonal perovskite crystals of cubic shape of 0.2 to 1 µm in size.     

Non-Isothermal Crystallization of Cordierite Glasses

A study is reported of the crystallization behaviour of some glass compositions which belong in the system MgO-Al₂O₃-SiO₂ and which lead to vitreous ceramics with α-cordierite as a main phase. DTA, X-ray diffraction and dilatometric analysis were used to investigate the influence of the type and concentration of the nucleation agents. The activation energies of crystallization were calculated and the crystalline phases were identified. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nonisothermal crystallization kinetics and microstructure evolution of calcium lanthanum metaborate glass

This paper reports results on the crystallization kinetics of 35.5CaO–7.25La₂O₃–57.25B₂O₃ glass under nonisothermal conditions based on the studies carried out from the differential thermal analysis upon using various well-established models. The crystalline phases formed during the optimized ceramization process have been confirmed from the X-ray diffraction. The activation energies of the first (formation of CaLaB₇O₁₃) and second (formation of LaBO₃) crystallization events have been estimated using the conventional methods of Kissinger, Augis–Bennett, Ozawa, and Matusita, and the results are found to be in good agreement with each other. The Avrami exponents that are determined by these models for the crystallization of CaLaB₇O₁₃ and LaBO₃ are found to be in the range of (1.81–2.35) and (4.03–4.65), respectively. This indicates that the formation of CaLaB₇O₁₃ is dominated by a surface crystallization, whereas LaBO₃ is formed by three-dimensional bulk crystallization with an increased rate of nucleation. This observation is further validated by microstructural investigation, which shows the formation of CaLaB₇O₁₃ phase as a surface layer and a bulk crystallization of LaBO₃ in optimally ceramized samples.     

Synthesis of Sm-doped strontium barium niobate crystals in glass by samarium atom heat processing

New glasses giving the crystallization of Sm³⁺-doped Sr_xBa_1−xNb₂O₆ (SBN) ferroelectrics have been developed in the Sm₂O₃−SrO−BaO−Nb₂O₅−B₂O₃ system, and the formation of SBN crystal dots and lines by continuous wave Nd:YAG laser (wavelength:1064 nm, power: 1 W) irradiations, i.e., samarium atom heat processing, has been examined. The formation of Sm³⁺-doped SBN non-linear optical crystals is confirmed from X-ray diffraction analyses, micro-Raman scattering spectra, second harmonic generations, and photoluminescence spectra. Sm³⁺-doped SBN crystal dots with the diameters of 20-70 μm and lines with the widths of 20-40 μm are written at the surface of some glasses such as 10Sm₂O₃·10SrO·10BaO·20Nb₂O₅·50B₂O₃ (mol%) by Nd:YAG laser irradiations with the irradiation times of 20-70 s for the dots and with the scanning speeds of 1-5 μm/s for the lines. The present study suggests that the samarium atom heat processing has a potential for the patterning of optical waveguides consisting of ferroelectric SBN crystals in glass substrates.     

Preparation of γ-Alumina Membranes From Sulphuric Electrolyte Anodic Alumina and Its Transition to α-Alumina

Gamma-alumina membrane was prepared from anodic (amorphous) alumina (AA) obtained in a sulphuric acid electrolyte. The transformation scheme, i.e., the crystallization to form metastable alumina polymorphs and the final transition to α-Al₂O₃ with heating was studied by TG-DTA and X-ray diffraction (XRD) using fixed time (FT) method. When heating at a constant rate, the crystallization occurred at 900°C or higher and the final formation of α-Al₂O₃ occurred at 1250°C or higher, which temperatures were higher than the case of using anodic (amorphous) alumina prepared from oxalic acid electrolyte. Relative content of S of the products was obtained by transmission electron microscope (TEM)-energy dispersive spectroscopy (EDS). The proposed thermal change of anodic alumina membrane prepared from sulphuric acid is as follows: 1. At temperatures lower than ca 910°C: Formation of a quasi-crystalline phase or a polycrystalline phase (γ-, δ- and θ-Al₂O₃); 2. 910–960°C: Progressive crystallization by the migration of S toward the surface within the amorphous or the quasi-crystalline phase, forming S-rich region near the surface; 3. 960°C: Change of membrane morphology and the quasi-crystalline phase due to the rapid discharge of gaseous SO₂; 4. 960–1240°C: Crystallization of γ-Al₂O₃ accompanying δ-Al₂O₃; and 5. 1240°C: Transition from γ-Al₂O₃ (+tr. δ-Al₂O₃) into the stable α-Al₂O₃. The amorphization which occurs by the exothermic and the subsequent endothermic reaction suggests the incorporation of SO₃ groups in the quasi-crystalline structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of crystallization processes in some glass ceramic products

The paper presents the kinetic study of the crystallization processes which take place in basalt glasses containing variable amount of nucleation agent (CaF₂, 310%). The activation energies have been calculated using Kissinger's equation and verified with the Ozawa-Flynn-Wall equation. In this order, the DTA curves have been registered with different heating rates, between 4 and 20 degrees/min. A correlation equation between the activation energy and the amount of nucleation agent (% of CaF₂) was established. By X-ray diffraction it was proved that the crystalline phase formed in the crystallization process represents a pyroxenic solid solution, Ca(Mg,Fe)SiO₃. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of nucleating agents on the crystallization of Li<Subscript>2</Subscript>O-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system glass

The processes of nucleation of Li₂O-Al₂O₃-SiO₂ glasses with TiO₂ and TiO₂+ZrO₂ as nucleating agents were discussed. The DTA peak temperature and DTA peak height shown a strong dependence on the nucleation temperature in the glass with TiO₂, while in the glass with TiO₂+ZrO₂ this tendency was small. The optimum nucleation temperatures were 745 and 760°C for two glasses. It suggested that with TiO₂+ZrO₂ as nucleating agents, the crystallization had lower sensitivity for nucleation temperature, and the glass had higher nucleation efficiency than with TiO₂.     

Melt crystallization and segmental dynamics of poly(ethylene oxide) confined in a solid electrolyte composite

The isothermal melt crystallization and the corresponding segmental dynamics, of a high molecular weight poly(ethylene oxide) (PEO) confined by Li₇La₃Zr₂O₁₂ (LLZO) particles in solid electrolyte composites, were monitored by differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS), respectively. Our results show that the overall crystallinity is positively correlated with the surface area of LLZO particles. The primary and secondary crystallization processes are identified by a modified Avrami equation, while two dynamic modes, the α relaxation and α′ relaxation, were in the DRS measurements. The results reveal an unambiguous correlation between the primary crystallization and the α relaxation, while a correlation between the second crystallization and the α′ relaxation concurrently exist in the electrolyte composites. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 466–477