Hydration of medium reactive magnesium oxide using hydration agents

Water, magnesium acetate, magnesium chloride, acetic acid and hydrochloric acid were used as hydrating agents for an industrially obtained MgO sample. The influence of these different hydrating agents on the pH of the hydrating solution, degree of hydration to Mg(OH)₂, and product surface area was studied as a function of the temperature of hydration. When compared to the hydration in water, all hydrating agents improved the degree of hydration between 5 and 50% at all temperatures. MgCl₂ and a mixture of HCl and Mg(CH₃COO)₂ seemed to be the most effective hydrating agents below 60°C, while at temperatures above 60°C Mg(CH₃COO)₂ formed the largest percentage Mg(OH)₂. Mg(CH₃COO)₂ was the hydrating agent that showed the strongest temperature dependence. The mechanism of the hydration reaction seems to be dependent of the availability of Mg²⁺ ions and the increased formation of Mg(OH)₂ as temperature increases.     

New solid compounds of Tb(III), Ho(III), Er(III) and Yb(III) with chrysin

The time required for maximum hydration of MgO obtained from the calcination of magnesite was determined. The MgO samples were hydrated for different time intervals in both water and magnesium acetate. A thermogravimetric analysis (TG) method was used to determine the degree of hydration to Mg(OH)₂. Increasing the hydration time, the degree of hydration of MgO and surface area of the formed Mg(OH)₂ increased. A leveling effect was observed on the percentage Mg(OH)₂ obtained from hydration in magnesium acetate, and an optimum amount of 85% was obtained after 500 min. For the hydration in water, the leveling effect was only observed after 800 min giving a maximum of 65% Mg(OH)₂.     

Characterization of poly(ethylene-co-vinyl acetate) (EVA) filled with low grade magnesium hydroxide

Low-grade magnesium hydroxide (LG-MH) is a solid by-product that undergoes an endothermic decomposition in the temperature range of 300-750 °C. Due to its thermal behaviour and its lower cost relative to pure Mg(OH)₂, it was studied as a non-halogenated flame retardant filler in a 28% vinyl acetate (VA) content poly(ethylene-co-vinyl acetate) matrix. The solid was characterized by XRF and the crystalline phases determined by XRD, composed predominantly of Mg(OH)₂ and calcium and magnesium carbonates. Particle size reduction was performed by both mechanical as well as air jet milling in order to optimize the particle size distribution.Composites with different filler concentrations were prepared to evaluate the mechanical properties and flame retardancy by means of limiting oxygen index tests. LOI was also determined in specimens filled with commercial flame-retardants to analyse the effectiveness of this solid.     

Mechanism of thermal decomposition of cobalt acetate tetrahydrate

The thermal decomposition of cobalt acetate tetrahydrate (Co(CH₃COO)₂ · 4H₂O) has been studied via thermogravimetric (TG) analysis, in situ X-ray powder diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The results of TG and XRD showed that the parent salt melted and then the dissolved crystalline water was vaporized in two steps. The dehydration process was followed by a major step concerning the decomposition of the acetate group, leading to basic acetate as an intermediate, which then produced CoO and Co in N₂ and H₂ atmosphere, respectively. Three decomposition intermediates Co(CH₃COO)₂ · 0.5H₂O, Co(CH₃COO)₂, and Co(OH)(CH₃COO) were presumed. In situ XRD experiments revealed that the intermediate basic acetate was poorly crystallized or even amorphous. Evolved gases analysis indicated that the volatile products of acetate decomposition were water vapor, acetic acid, ethylenone, acetone, and CO₂. A detailed thermal decomposition mechanism of Co(CH₃COO)₂ · 4H₂O was discussed.     

The effect of calcining conditions on the rehydration of dead burnt magnesium oxide using magnesium acetate as a hydrating agent

Summary Magnesium oxide was produced through calcination of magnesite ore. A rehydration percentage of MgO to Mg(OH)₂ of higher than 60% is obtained using calcination temperatures of 1000°C and below. At these temperatures medium reactive MgO was formed. The extend to which dead burnt MgO (obtained after calcination at 1200°C and higher) may be rehydrated is dependent on the calcination time, but even after 1 h and using magnesium acetate as a hydrating agent only 40% of the initial product has rehydrated to Mg(OH)₂. After 4 and more hours of calcinations at 1200°C, a maximum of approximately 14% of the initial MgO is rehydrated back to Mg(OH)₂. Thermogravimetric analysis was performed on the various compounds to determine the amounts of Mg(OH)₂ that formed.     

Alanine- and taurine-salicylal Schiff base complexes of magnesium

The complexes of α-alanine-salicylal Schiff base of magnesium (α-ASSM), β-alanine-salicylal Schiff base of magnesium (β-ASSM) and taurine-salicylal Schiff base of magnesium (TSSM) were synthesized. The formulae of the complexes are Mg[OC₆H₄CHNCH(CH₃)COO]·2H₂O, Mg[OC₆H₄CHNCH₂CH₂COO]·2H₂O and Mg[OC₆H₄CHNCH₂CH₂SO₃]·2H₂O. The crystal structure belongs to orthorhombic system with the lattice parameters: a=1.6954 nm, b=2.0873 nm and c=2.3037 nm for the β-ASSM, to orthorhombic system with the lattice parameters: a=1.5586 nm, b=1.8510 nm and c=2.6240 nm for the β-ASSM, to monoclinic system with the lattice parameters: a=1.3232 nm, b=1.4960 nm, c=2.1543 nm and β=98.04° for the TSSM, respectively. The results of the thermal decomposition processes and infrared spectra of the complexes show that the complexes may possess different coordination structures.     

Struktur und thermische Zersetzung von Bis(triethanolamin)kupfer(II)-acetat [Cu{N(CH2CH2OH)3}2](CH3COO)2

Structure and Thermal Decomposition of Bis(triethanolamine)copper(II) Acetate [Cu{N(CH₂CH₂OH)₃}₂](CH₃COO)₂ Bis(triethanolamine)copper(II) acetate [Cu{N · (CH₂CH₂OH)₃}₂](CH₃COO)₂ was prepared using the basic components; the structure was determined by single crystal X-ray diffraction. The complex crystallizes in the monoclinic space group P2₁/c with a = 9.101 Å, b = 13.136 Å, c = 9.819 Å, β = 111.63°. Details of the synthesis, X-ray data, and the thermal decomposition are reported.     

Study on the equilibrium in the M(CH3COO)2 ? CH3OH ? H2O system (M  Mg2+, Ca2+, Ba2+) at 25°C

The complex formation and dehydration processes in the system M(CH₃COO)₂? CH₃OH? H₂O have been studied by the methods of the physico-chemical analysis at 25°C; (M = Mg²⁺, Ca²⁺ and Ba²⁺). In the Mg(CH₃COO)₂? CH₃OH? H₂O system. methanol was found to behave as a solvent in which complex formation reactions take place, including also methanolation of Mg²⁺. The fields of equilibrium existence of two new compounds have been found: Mg(CH₃COO)₂ · 3H₂O · CH₃OH and Mg(CH₃COO)₂ · 1,5 CH₃OH. In the systems M(CH₃COO)₂? CH₃OH? H₂O (M = Ca²⁺, Ba²⁺), methanol was found to react as a dehydrating reagent.     

纳米阻燃氢氧化镁/聚氧化乙烯复合聚合物电解质

合成了纳米氢氧化镁作为聚氧化乙烯(PEO)基聚合物电解质的增塑剂和阻燃剂,并对其进行X射线衍射(XRD)、透射电子显微镜(TEM)和热重(TG)分析研究.制得的氢氧化镁为片状六方晶体,尺寸在50-80nm之间,纳米氢氧化镁在340℃时开始热分解.对纳米氢氧化镁/PEO复合聚合物电解质的电化学研究结果显示:纳米氢氧化镁/PEO复合聚合物电解质的离子电导率随着添加纳米氢氧化镁的质量分数的增加先增大后减小,其在5%-10%之间时,复合聚合物电解质的离子电导率达到最大值.纳米氢氧化镁的添加使复合聚合物电解质的阳极氧化电位有一定程度的提高,纳米氢氧化镁具有改善PEO阳极抗氧化能力的作用.     

The Effect of Flower-Like Magnesium Hydroxide Nanostructure on the Thermal Stability of Cellulose Acetate and Acrylonitrile–Butadiene–Styrene

Flower-like magnesium hydroxide (Mg(OH)₂) nanostructures were synthesized via a simple hydrothermal reaction at relatively low temperature. The Mg(OH)₂ nanostructures were then added to acrylonitrile–butadiene–styrene (ABS) and cellulose acetate (CA) polymers. The effect of Mg(OH)₂ nanostructures on the thermal stability of the polymeric matrixes has been investigated. The thermal decomposition of the nanocomposites shifts towards higher temperature in the presence of the Mg(OH)₂. The enhancement of thermal stability of nanocomposites is due to endothermically decomposition of magnesium hydroxide that releases of water and dilutes combustible gases. Nanostructures and nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), UL-94 test and limiting oxygen index (LOI) analysis.     

Thermal stability of new zinc acetate-based complex compounds

New zinc acetate based complex compounds (of general formula Zn(CH₃COO)₂·1?2L·nH₂O) containing one or two molecules of urea, thiourea, coffeine and phenazone were prepared namely: Zn(CH₃COO)₂·2.5H₂O, Zn(CH₃COO)₂·2u·0.5H₂O, Zn(CH₃COO)₂·tu·0.5H₂O, Zn(CH₃COO)₂·2tu, Zn(CH₃COO)₂·cof·2.5H₂O, Zn(CH₃COO)₂·2cof·3.5H₂O, Zn(CH₃COO)₂·2phen·1.5H₂O. The compounds were characterized by IR spectroscopy, chemical analysis and thermal analysis. Thermal analysis showed that no changes in crystallographic modifications of the compounds take place during (heating in nitrogen before) the thermal decompositions. The temperature interval of the stability of the prepared compounds were determined. It was found that the thermal decomposition of hydrated compounds starts by the release of water molecules. During the thermal decomposition of anhydrous compounds in nitrogen the release of organic ligands take place followed by the decomposition of the acetate anion. Zinc oxide and metallic zinc were found as final products of the thermal decomposition of the zinc acetate based complex compounds studied. Carbon dioxide and acetone were detected in the gaseous products of the decomposition of the compounds if ZnO is formed. Carbon monoxide and acetaldehyde were detected in the gaseous products of the decomposition, if metallic Zn is formed. It is supposed that ZnO and Zn resulting from Zn acetate complex compounds here studied, possess different degree of structural disorder. Annealing takes place by further heating above 600°C.     

Hydration of medium reactive industrial magnesium oxide with magnesium acetate

Medium reactive magnesium oxide reacts incompletely with available water to form magnesium hydroxide. To enhance the hydration of medium reactive magnesium oxide, the effect of magnesium acetate as hydrating agent was studied. The extent to which different parameters (concentration of magnesium acetate, solution temperature and solid to liquid ratio of MgO to magnesium acetate) influence the hydration rate of a medium reactive industrial sample of magnesium oxide were evaluated. The degree of rehydration measured as percentage Mg(OH)₂being formed, increases from approximately 56% using 0.5 M magnesium acetate solutions at 25°C to 64% at 50°C, to more than 70% at 70°C. The major part of rehydration of the medium reactive MgO sample occurs within the first few minutes of the reaction for all three temperatures studied. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ternäre Acetate der Lanthanide mit Caesium: Dimere und Trimere in CsLu(CH3COO)4 bzw. Cs2[Lu3(CH3COO)10(OH)(H2O)]. Synthese,Kristallstrukturen und Thermolyse

Ternary Acetates of the Lanthanides with Cesium: Dimers in CsLu(CH₃COO)₄ and Trimers in Cs₂[Lu₃(CH₃COO)₁₀(OH)(H₂O)]. Synthesis, Crystal Structures, Thermolysis Single crystals of CsLu(CH₃COO)₄ and Cs₂[Lu₃(CH₃COO)₁₀(OH)(H₂O)] were obtained from an aqueous solution of lutetium and cesium acetate in a 1:1 molar ratio. The crystal structures (CsLu(CH₃COO)₄: monoclinic, P2₁/n (no. 14), Z = 8, a = 1 293.1(2), b = 1 323.8(2), c = 1 622.5(3) pm, β = 92.01(2)°, V_m = 208.97(6) cm³/mol, R = 0.056, R_w = 0.034; Cs₂[Lu₃(CH₃COO)₁₀(OH)(H₂O)]: monoclinic, C2/c (no.15), Z = 4, a = 2 138.5(6), b = 1 378.0(3), C = 1 482.9(4) pm, β = 106.15(2)°, V_m = 632.0(3) cm³/mol, R = 0.049, R_w = 0.036) were determined from four-circle-diffractometer data. The structures consist of dimers and trimers, respectively, that are built by bridging acetate groups. These units are fragments of the infinite chains of the Ho(CH₃COO)₃ type of structure. The isotypic compounds CsM(CH₃COO)₄ with M=Eu? Lu were synthesized and characterized by the X-ray Guinier technique. The thermal decomposition of CsLu(CH₃COO)₄ was examined with thermoanalytical methods (TG/DSC with coupled gas analysis) and the Guinier-Simon technique: it decomposes at 260°C in an endothermic reaction to Lu₂O₃ and Cs₂CO₃.     

Desolvation and Dehydrogenation of Solvated Magnesium Salts of Dodecahydrododecaborate: Relationship between Structure and Thermal Decomposition

Attempts to synthesize solvent‐free MgB₁₂H₁₂ by heating various solvated forms (H₂O, NH₃, and CH₃OH) of the salt failed because of the competition between desolvation and dehydrogenation. This competition has been studied by thermogravimetric analysis (TGA) and temperature‐programmed desorption (TPD). Products were characterized by IR, solution‐ and solid‐state NMR spectroscopy, elemental analysis, and single‐crystal or powder X‐ray diffraction analysis. For hydrated salts, thermal decomposition proceeded in three stages, loss of water to form first hexahydrated then trihydrated, and finally loss of water and hydrogen to form polyhydroxylated complexes. For partially ammoniated salts, two stages of thermal decomposition were observed as ammonia and hydrogen were released with weight loss first of 14 % and then 5.5 %. Thermal decomposition of methanolated salts proceeded through a single step with a total weight loss of 32 % with the release of methanol, methane, and hydrogen. All the gaseous products of thermal decomposition were characterized by using mass spectrometry. Residual solid materials were characterized by solid‐state ¹¹B magic ‐ angle spinning (MAS) NMR spectroscopy and X‐ray powder diffraction analysis by which the molecular structures of hexahydrated and trihydrated complexes were solved. Both hydrogen and dihydrogen bonds were observed in structures of [Mg(H₂O)₆B₁₂H₁₂] ? 6 H₂O and [Mg(CH₃OH)₆B₁₂H₁₂] ? 6 CH₃OH, which were determined by single‐crystal X‐ray diffraction analysis. The structural factors influencing thermal decomposition behavior are identified and discussed. The dependence of dehydrogenation on the formation of dihydrogen bonds may be an important consideration in the design of solid‐state hydrogen storage materials.     

New Sol-Gel Route for Processing of PMN Thin Films

Pyrochlore free Pb(Mg_1/3Nb_2/3)O₃ (PMN) thin films were prepared from mixed-metal precursors solutions using the sol-gel process. Lead acetate [Pb(CH₃COO)₂], magnesium acetate [Mg(CH₃COO)₂] and niobium ethoxide [Nb(C₂H₅O)₅] were used as starting materials, while 2-isopropoxy-ethanol was chosen as solvent. The reactivity of the precursors was investigated in order to understand and control the process and thus to prevent the contamination of the PMN with the pyrochlore phase. The solution was spin-coated on TiO₂/Pt/TiO₂/SiO₂/Si substrate. The thin films were characterized by SEM and XRD while dielectric measurements were performed on the bulk ceramic.     

Synthesis of High Dispersion and Uniform Nano-sized Flame Retardant-Used Hexagonal Mg(OH)<Subscript>2</Subscript>

Nanosized dispersive flake-like magnesium hydroxide (Mg(OH)₂) had been prepared by a hydrothermal method. In the process, when the surfactant polyvinyl pyrrolidone was added, high dispersion, small particle size and large specific surface area of hexagonal crystal magnesium hydroxide was obtained by ultrasonic dispersion and temperature program. The flame retardant of Mg(OH)₂ was systematically explored by scanning electron microscope (SEM), transmission electron microscopy, X-ray diffraction, BET analysis and thermo-gravimetric analysis tests. SEM showed the formation of uniform and small size magnesium hydroxide particle with hexagonal nanoscale. Under the optimized conditions, high nano-sized hexagonal Mg(OH)₂ was acquired with a mean particle size of 134 nm and a specific surface area of 26.66 m²/g. According to TGA results, the sample’s decomposition temperature was 626.9 K, which was consistent with the reported literature. It is vitally prospected that the prepared hexagonal Mg(OH)₂ is to be applied to the industry as a flame retardant.     

Electrospray ionization mass spectrometry of organogermanium compounds

A detailed study of the solution chemistry and mass spectrometry of six carboxylato-organogermanium compounds in aqueous solution has been carried out using electrospray ionization and MSⁿ techniques. The different types of hydrolysis products and their probable structures, which include the oligomers and their fragment ions plus water adduct ions formed by ion-molecule reactions, are presented, e.g., HO-cyclic-(-Ge(O⁻)CH₂CH₂COO) A, HO-cyclic-(-Ge(O-cyclic-(Ge(O⁻)CH₂CH₂COO)CH₂CH₂COO) B, ⁻OGeO-cyclic-(-Ge(OH)CH₂CH₂COO) C, and ⁻CH=CHGeO-cyclic-(-Ge(OH)CH₂CH₂COO) D, etc. The proposed cyclic structures are confirmed by theoretical calculations. Copyright © 2001 John Wiley & Sons, Ltd.     

采用稀释成盐法从富硼浓缩盐卤中合成的镁硼酸盐化合物及其结构与性质

通过稀释成盐法在富硼浓缩盐卤体系Na-K-Mg-Cl-SO₄中合成了一种新的六硼酸镁Mg[B₆O₇(OH)₆]·5H₂O化合物。根据X射线粉末衍射数据对其晶体结构进行了精修,并采用红外及拉曼光谱法对其结构进行了表征,分析了其光谱及结构特征。结果表明,该化合物由1个Mg原子、1个B₆O₇(OH)₆基团和5个H₂O分子构成,Mg原子以六配位形式与氧结合形成畸变MgO₆八面体构型;热重分析表明,高温分解过程该化合物脱水转化为四硼酸镁MgB₄O₇;通过紫外可见漫反射法求得其禁带宽度为4.44 eV。     

Evidence for the formation of anhydrous zinc acetate and acetic anhydride during the thermal degradation of zinc hydroxy acetate,Zn5(OH)8(CH3CO2)2·4H2O to ZnO

Zinc hydroxy acetate, Zn₅(OH)₈(CH₃CO₂)₂·4H₂O, has been prepared by the precipitation method. It has been demonstrated by FTIR analysis that, contrary to previous reports, the interaction of the acetate anion with the matrix cation is ionic. TG analysis, mass spectral analysis of the evolved gases, and in situ variable temperature PXRD and FTIR analysis have shown that decomposition of the material to ZnO involves the formation of Zn₅(OH)₈(CH₃CO₂), Zn₃(OH)₄(CH₃CO₂)₂ and anhydrous zinc acetate (Zn(CH₃CO₂)₂) as some of the acetate-containing intermediate solid products. The acetate anion is finally lost, at temperatures below 400 °C, as acetic anhydride, (CH₃CO)₂O.     

Thermal decomposition of Cd(CH3COO)2·2H2O studied by a coupled TG-DTA-MS method

The thermal decomposition of cadmium acetate dihydrate in helium and in air atmosphere has been investigated by means of a coupled TG-DTA-MS method combined with X-ray diffraction analysis. Dehydration of Cd(CH₃COO)₂·2H₂O is a two-stage process with Cd(CH₃COO)₂·H₂O as intermediate. The way of Cd(CH₃COO)₂ decomposition strongly depends on the surrounding gas atmosphere and the rate of heating. CdO, acetone and CO₂ are the primary products of decomposition in air. In helium decomposition goes by two parallel and consecutive reactions in which intermediates, Cd and CdCO₃, are formed. Metallic cadmium oxidizes and cadmium carbonate decomposes giving CdO. Some of the metallic cadmium, depending on the heating rate and the concentration of oxygen, evaporates. Acetone is partially oxidized in secondary reactions with oxygen. This revised version was published online in July 2006 with corrections to the Cover Date.