氢氧化镁分解动力学的研究

以硼泥为原料与硫酸反应制备出七水硫酸镁,以氢氧化钠为沉淀剂制备出符合标准HG/T 3607-2000的氢氧化镁.利用XRD,SEM和TEM对氢氧化镁进行了表征,DTA-TG对氢氧化镁的热分解动力学进行了研究.XRD结果表明:制备粉体为单一Mg(OH)2.SEM和TEM结果表明:样品为片状或针状纤维,片直径大小不一,在20～50 nm之间,针状纤维形状不规则,大小不一致,长度在20～100 nm之间.利用Kissinger法和Ozawa法计算出的氢氧化镁热分解反应活化能分别为135.14和141.61 kJ·mol-1.利用Coats-Redfern法和Dolye法判断氢氧化镁热分解反应机理函数为A1.5.     

阻燃高分子复合材料中氢氧化镁的制备及其表面改性

以氢氧化镁为代表的无卤阻燃剂,由于其具有良好的阻燃、抑烟性能及环保特点,已日益得到学术界和产业界的重视.在实际应用过程中,人们发现阻燃剂的形貌对其阻燃性能具有较大影响,因此本文重点综述了化学沉淀法制备不同形貌及尺寸的氢氧化镁和各影响因素对其制备的影响,以及当前氢氧化镁表面改性的一些新方法,如:大分子改性等,使得其在复合加工过程中,能与高分子材料具有良好的相容性.     

甜菜碱制备工艺的研究

甜菜碱[(CH3)3N+CH2COO-],是一种季铵型水溶性生物碱,可作为甲基供体,具有促进动物蛋白质和脂肪代谢、缓和应激、调节渗透压、增进食欲、稳定维生素、参与预防球虫病 [1-3],也可作为多功能表面活性剂,广泛用于制备护发护肤用品[4-5].甜菜碱的盐酸盐可用于胃酸缺乏、动脉粥样硬化、肝脏疾病、止痛、治疗风湿病、糖尿病等[6-8].甜菜碱制备方法[9-15]有天然甜菜糖蜜提取法和化学合成法.前者由于原料来源有限而使其应用推广具有一定的局限性.传统合成方法采用氯乙酸钠和三甲胺反应,生成的氯化钠很难除去[16].近年来对此的研究如采用强阳离子交换树脂法,溶剂法或者将氢氧化钠改为氢氧化钙[17-18]等.     

绿色环保型氢氧化镁阻燃剂

介绍了阻燃剂的种类和发展趋势,并重点介绍了氢氧化镁阻燃剂的阻燃机理、特点、应用和发展。指出氢氧化镁阻燃剂是一种新型的、对环境友好的无机阻燃剂。     

微波法高度分散CuCl2-β沸石上CO吸附的IR光谱研究

近年来, 人们发现含铜沸石对NO和CO等有害气体的直接分解具有较高的活性和较好的稳定性[1～3]. 催化剂的活性与其铜含量密切相关, 而由传统离子交换法制得的沸石催化剂中铜含量较低, 且受沸石骨架中铝含量的限制[4]. 直接固态离子交换法是将金属离子引入沸石中的有效途径[5～7]. 本文采用微波法制备了CuCl2高度分散的β沸石, 用XRD和29Si MAS NMR对催化剂进行了表征, 并以CO吸附IR光谱法考察了CuCl2在β沸石中的扩散机理.     

纳米晶MgSO4·5Mg(OH)2·3H2O合成与表征

纳米材料由于具有表面、体积和量子尺寸效应的特殊性而受到广泛重视[1～3]. 微米级硫氧镁晶须作为塑料添加增强和阻燃剂已有报道[4～7]. 纳米晶MgSO4*5Mg(OH)2*3H2O不仅对塑料起补强作用, 而且其粒度小, 使塑料变得更致密, 强度、韧性与防水性能大大提高. 目前纳米材料的合成方法多种多样[8～10], 本文采用水热法制得纳米硫氧镁晶粒, 产物纯度高、分散性好且粒度易控制.     

溶胶-凝胶模板法制备BaTiO3纳米线及其光催化性能

纳米线为准一维纳米材料[1],因其具有优异的光学、电学及力学性能而引起人们的极大关注.它的制备方法有许多种,如分子束外延法、光刻法、CVD法、模板法[2]等.其中模板法由于具有实验装置简单,操作容易,形态可控,适用面广等特点而成为纳米材料合成领域的一大焦点.常用的模板有:有序空洞阵列氧化铝模板、含有孔洞无序分布的高分子模板、纳米洞孔玻璃模板.其中阳极氧化铝(AAO)模板具有孔径均一、排列有序、孔密度高、热稳定性好且孔径大小可控等优点,成为模板合成法中最常用模板之一[3].     

含氢氧化镁的阻燃硅烷交联聚乙烯

在硅烷交联聚乙烯体系中 ,添加氢氧化镁阻燃剂制备无卤阻燃的硅烷交联聚乙烯。详细讨论了硅烷和氢氧化镁用量对材料力学性能及阻燃性能的影响。采用了拉伸性能试验、氧指数试验和锥形量热计试验对交联物的性能进行了表征。     

棒状氢氧化镁的合成

以氯化镁和氢氧化钠为原料合成了棒状氢氧化镁粉体。考察了氢氧化钠浓度、陈化温度、陈化时间对氢氧化镁形貌的影响。采用SEM、HRTEM、XRD、TG等对所得氢氧化镁颗粒的形貌、颗粒大小、晶习及热稳定性进行了表征。结果表明,当陈化温度为90℃时,所得棒状氢氧化镁随氢氧化钠浓度的升高及陈化时间的增加,晶形更加完整;当陈化温度在120℃时,所得氢氧化镁颗粒的形貌为片状,不能得到棒状氢氧化镁。     

纳米无机阻燃剂的研究进展

本文概述了纳米三氧化二锑、纳米氢氧化铝、纳米氢氧化镁、纳米层状双氢氧化物无机阻燃剂的制备方法、阻燃性和在纳米阻燃复合材料中的应用,并总结了纳米阻燃剂对复合材料的阻燃机理,提出了在阻燃复合材料方面的研究方向与建议.     

Hydrothermal crystal growth of the potassium niobate and potassium tantalate family of crystals

Single crystals of KNbO₃ (KN), KTaO₃ (KT), and KTa_1−xNb_xO₃ (x=0.44, KTN) have been prepared by hydrothermal synthesis in highly concentrated KOH mineralizer solutions. The traditional problems of inhomogeneity, non-stoichiometry, crystal striations and crystal cracking resulting from phase transitions associated with this family compounds are minimized by the hydrothermal crystal growth technique. Crystals of good optical quality with only minor amounts of metal ion reduction can be grown this way. Reactions were also designed to provide homogeneous distribution of tantalum and niobium metal centers throughout the KTN crystal lattice to maximize its electro-optic properties. Synthesis was performed at relatively low (500-660 °C) temperatures in comparison to the flux and Czochralski techniques. This work represents the largest crystals of this family of compounds grown by hydrothermal methods to date.     

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.     

Facile Synthesis of Leaf-like Cu(OH)2 and Its Conversion into CuO with Nanopores

Leaf-like Cu(OH)₂ single crystals were synthesized via the controlled emulsion interface method using Span80 (sorbitan monooleate) as the stabilizer of the emulsion system. CuO products with nanopores could be simply obtained by the dehydration of Cu(OH)₂, while maintaining the strip-shaped architecture. The phase structures and morphologies were measured by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Experimental results showed that Cu(OH)₂ microleaves were single crystals and the growth direction seemed to be in [111] crystal plane of the orthorhombic Cu(OH)₂. The formation of the nanopores should be attributed to the water loss of the transformation from Cu(OH)₂ to CuO. The formation process of Cu(OH)₂ was investigated by taking TEM images at different stages of the reaction. The formed nanoparticles began to rearrange to form nanorods and microleaves possibly via edge-by-edge and side-by-side oriented-attachments because of the formation of larger crystals greatly reducing the interfacial energy. Besides, CuO microarchitectures exhibit blue shifts in UV-Vis spectra and possess larger band gaps compared with those of bulk crystals.     

Studies on melt flow properties during capillary extrusion of PP/Al(OH)3/Mg(OH)2 flame retardant composites

The apparent melt shear viscosity of polypropylene (PP) composites filled with aluminium hydroxide (Al(OH)₃) and magnesium hydroxide (Mg(OH)₂) was measured by means of a melt flow rate instrument under experimental conditions of temperature ranging from 170 to 195 °C and load varying from 2.16 to 12.5 kg, to identify the effects of particle size and content. The results showed that the melt shear flow of the composites obeyed the power law under the experimental conditions, the dependence of the melt apparent shear viscosity (η_a) on temperature was consistent with the Arrhenius equation, and the sensitivity of the η_a for the composite melts to temperature increased with addition of flame retardant. The η_a of the composites decreased with increasing apparent shear rate. The η_a increased with an increase of the content of flame retardant, but this rate of increase decreased with a rise of temperature or load. When the particle size of flame retardant was smaller than 5 μm, the η_a of the composites increased with increase of particle size of flame retardant, and then reduced with a further increase of particle size of flame retardant.     

Synthesis,characterization, and catalytic properties of the Li-doped ZnO

It has demonstrated that there are major advantages and synergistic effects on flame retardancy in using a combination of borates with magnesium hydroxide. In this paper, a novel 2MgO·B₂O₃·1.5H₂O–Mg(OH)₂ nanocomposite has been controllably prepared by in situ hydrothermal reaction, and the formation mechanism of the nanocomposite was proposed. As a comparison, 2MgO·B₂O₃·1.5H₂O nanobelt and Mg(OH)₂ nanosheet were also prepared. All samples were characterized by XRD, FT-IR, TG, SEM, TEM and HRTEM. Furthermore, their flame-retardant properties were investigated by thermal analysis method and oxygen index method, demonstrating that the flame retardancy of nanocomposite is significantly higher than that of single 2MgO·B₂O₃·1.5H₂O or Mg(OH)₂. The possible flame retarding mechanism has been proposed. It can be predicted that this nanocomposite could serve as a potential flame retardant.     

Floating Zone Crystal Growth and Structure Analysis of a Novel ScB19 Family Compound, ScB19+xSiy

Single crystals of a novel ScB₁₉ family compound ScB_19+xSi_y were grown by the floating zone method using a four-lamp mirror-type image furnace. A small amount of silicon addition to ScB₁₉ which decomposes at elevated temperatures without melting allowed it to coexist with the liquid phase and as a resultant made the floating zone crystal growth possible. Powder X-ray diffraction analysis confirmed the grown crystals of ScB_19+xSi_y to be isostructural to ScB₁₉. It was found that the crystal structure of ScB_19+xSi_y solved based on single-crystal X-ray data is tetragonal with lattice constants of a, b=1.03081(2) nm, c=1.42589(3) nm, space group P4₁2₁2 or P4₃2₁2 and is basically isotypic with α-AlB₁₂ structure type. In the crystal structure boron atoms form a three-dimensional framework based on interconnected B₁₂ icosahedra and B₂₂ polyhedra. The Sc atoms reside in three of five Al sites in the α-AlB₁₂ structure and Si resides in a bridge site bonding two B₂₂ units.     

Synthesis of Mono-Dispersed Mg(OH)2 Nanoflakelets

Mono-dispersed Mg(OH)₂ nanoflakelets have been prepared with the assistant of 4-(p-nitrophenylazo)resorcinol. The samples were characterized using XRD, TEM, and ED. Electron diffraction analysis showed that single crystalline nanoflakelets were obtained in hydrothermal process, and porous Mg(OH)₂ nanosheets were prepared at lower temperature. Nitrogen adsorption isotherms show that the surface area of Mg(OH)₂ nanosheets is 129 m²/g. Possible growth mechanism of the nanoflakelets is discussed.     

Die Kristallstruktur von Ca9(Ca x Mg1−x )(AsO4)6(AsO3OH) mitx ∼ 0,5

The crystal structure of Ca₉(Ca _x Mg_1–x )(AsO₄)₆(AsO₃OH) withx 0.5 (a=10.73,c=37.74 Å; space group R3c-C _3v ⁶ ;Z=6) was solved from 985 independent X-ray intensities collected on a 4-circle diffractometer, and refined toR=5.7% for all data. This compound is isotypic to Ca₉Mg(PO₄)₆(PO₃OH), a structure of the whitlockite-type.

     

Effects of elastomer on morphology,flammability and rheological properties of HIPS/PS‐encapsulated Mg(OH)2 composites

The effects of elastomer type on morphology, flammability and rheological properties of high‐impact polystyrene/Mg(OH)₂ based on encapsulated by polystyrene have been investigated. The ternary composites characterized by cone calorimetry, horizontal burning rate, limiting oxygen index (LOI), rheology and SEM. Morphology was controlled using poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] triblock copolymer (SEBS) or the corresponding maleinated SEBS (SEBS‐g‐MA). As revealed by SEM observations, composites of HIPS/SEBS/Mg(OH)₂ exhibit separation of the filler and elastomer and good adhesion between SEBS and the filler, whereas composites of HIPS/SEBS‐g‐MA/Mg(OH)₂ exhibit encapsulation of the filler by SEBS‐g‐MA. The flame retardant and rheological properties of ternary composites were strongly dependent on microstructure. The rheological test showed that the composites with encapsulation structure exhibit a stronger solid‐like response at low frequency than those of the composites with separate dispersion structure. The combustion tests showed that the composites with encapsulation structure showed higher flame retardant properties than those of separate dispersion structure at optimum use level of SEBS‐g‐MA. However, with the increase of the content of SEBS‐g‐MA, the flame retardancy of the composite declined somewhat which can be explained that the SEBS‐g‐MA coating acts as a heat and mass transfer barrier due to the formation of encapsulation structure. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2023–2030, 2007     

Effects of polystyrene-encapsulated magnesium hydroxide on rheological and flame-retarding properties of HIPS composites

In this study, polystyrene (PS)-encapsulated magnesium hydroxide (Mg(OH)₂) was successfully prepared by in situ polymerization of styrene on the surface of Mg(OH)₂ in a high-speed mixer. A large amount of PS chemically bonded on Mg(OH)₂ surface was confirmed by means of FT-IR, TGA and SEM. A series of composites of high impact polystyrene (HIPS) were prepared by melt blending in a co-rotating twin-screw extruder. The effects of PS-encapsulated filler on the properties of HIPS composites were studied by SEM, rheology and combustion tests (horizontal burning tests and cone calorimetry). The dispersion and adhesion patterns of PS-encapsulated Mg(OH)₂ in HIPS matrix were investigated through FT-IR and SEM. The experimental results demonstrated that comparing to the composites containing untreated filler, the rheological and flame retardant properties of those containing PS-encapsulated filler were found to be significantly improved. This improvement is mostly attributed to a better dispersion of the encapsulated filler and a strong adhesion between the filler and matrix.