热重分析法研究氢氧化镁纳米粉体的非等温分解动力学

以白云石为原料,盐酸酸溶后得到CaCl₂-MgCl₂滤液,采用氨水直接沉淀法制备出符合HG/T 3607-2000Ⅰ型标准的六方片状的纳米氢氧化镁。六方片厚度为25～30 nm,直径为0.3～0.4 mm。利用热重分析法对纳米氢氧化镁在不同升温速率下的热分解动力学进行研究,以期深入了解纳米氢氧化镁热分解制备纳米氧化镁粉体过程的物理化学本质。采用Kissinger法和Ozawa法计算出氢氧化镁热分解反应活化能分别为115.47 kJ·mol^-1和126.04 kJ·mol^-1。对热重分析数据进行处理和拟合,判断纳米氢氧化镁粉体热分解反应机理函数为Avrami-Erofeev（n=1.5）的随机成核和随后生长机理。指前因子为3.077×10¹⁰ s^-1。纳米氢氧化镁经煅烧制备得到的氧化镁纳米球的直径为80～100 nm。     

Influence of CaCl2 on the hydrothermal modification of Mg(OH)2

The influence of CaCl₂ on the hydrothermal modification of Mg(OH)₂ was investigated in this paper. The experimental results indicated that dispersive Mg(OH)₂ hexagonal plates with the regular shape, the enlarged size and the perfect crystallinity were formed by treating the irregular Mg(OH)₂ agglomerates at elevated temperatures in dilute CaCl₂ solutions. Thermodynamic analysis showed that the presence of CaCl₂ at the elevated temperature promoted the formation of MgOH⁺, which was favorable for the formation of Mg(OH)₆⁴⁻ and the growth of Mg(OH)₂ crystals.     

Flame retardant synergism of rubber and Mg(OH)2 in EVA composites

A synergistic effect on flame retardancy was found when acrylonitrile butadiene ultra-fine fully vulcanized powdered rubber (NB-UFPR) was incorporated into ethylene vinyl acetate/nano-magnesium hydroxide (EVA/nano-MH) composite by a new process. The fire performance of EVA and EVA composites was compared in this communication by cone calorimeter test (CCT). The CCT data indicated that the addition of NB-UFPR in EVA/nano-MH system not only reduced the heat release rate, but also prolonged the ignition time of the composite, which is contrary to the effect of NB-UFPR when it was added alone in EVA polymer. Thermogravimetric analysis revealed that nano-MH accelerated the loss of acetic acid, but NB-UFPR assisted to reduce nano-MH's accelerating effect. FTIR spectra showed a new absorption at 3374 cm⁻¹ in the blends of EVA/NB-UFPR and EVA/NB-UFPR/nano-MH.     

氢氧化镁在聚丙烯酰胺体系中的聚沉行为

考察了难沉降的氢氧化镁微粒在高聚合度(分子量1500万)阴离子型聚丙烯酰胺体系中的聚沉行为. 通过分析氢氧化镁悬浮体系在聚沉过程中的沉降体积、团聚粒度分布、表面电位及特征官能团等参数的变化规律,初步探讨了聚丙烯酰胺的聚沉机制. 研究结果表明,聚丙烯酰胺通过吸附架桥和电荷中和两种方式加速氢氧化镁的聚沉速率,且对后继水热产物形貌无明显影响,是一种较为理想的絮凝剂. 在0 125 10 6浓度范围内,聚丙烯酰胺浓度越高,团聚体粒径越大,聚沉效果越显著.     

The encapsulation of Mg(OH)2 sludge in composite cement

A range of magnesium hydroxide waste sludges arising from the re-processing of nuclear fuel exist in the UK and require safe long-term disposal. Similar wastes undergo a cementation process in order to immobilise radioactive material prior to disposal. Simulant magnesium hydroxide sludges have been prepared and their subsequent interactions with composite cement systems based on the partial replacement of ordinary Portland cement with blastfurnace slag and pulverised fuel ash have been studied. This work has concluded that there was little reaction between the sludge and any of the composite cements during hydration. Apart from a small quantity of a hydrotalcite-type phase containing magnesium from the sludge, the main phases detected were C-S-H and unreacted brucite. This indicates that the magnesium in the sludges is encapsulated by the cement, rather than being immobilised or chemically bound within the hardened matrix.     

Preparation and thermal decomposition of 5Mg(OH)2·MgSO4·2H2O nanowhiskers

Magnesium hydroxide sulfate hydrate (MHSH) nanowhiskers were prepared using magnesium chloride, ammonia and magnesium sulfate as raw materials by hydrothermal synthesis without any additional template. X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and thermal analysis (TG-DTA) were employed to characterize the composition and structural features of the MHSH nanowhiskers. It is shown that the thermal decomposition of nanowhiskers followed a three-step scheme. Based on DTA data, the reaction order, activation energy and pre-exponential factor for each step were calculated using a non-isothermal Kissinger method. It is also indicated from Satava method that the first step of the thermal decomposition of nanowhiskers is an A₂ nucleus formation and growth mechanism with integral form of G(a) = [−ln(1 − a)]^1/2. The second step is an A_u branching nuclei mechanism with integral form of G(a) = ln[a/(1 − a)], and the final step is a P_1/2 nucleation mechanism with integral form of G(a) = a^1/2.     

PP/Al(OH)_3/Mg(OH)_2复合材料的导热性能

制备了PP（聚丙烯）/Al(OH)₃/Mg(OH)₂导热复合材料,并用稳态平板导热系数测试仪在不同测试温度下测定该复合材料的导热系数。结果表明,加入Al(OH)₃和Mg(OH)₂使PP导热系数提高。复合材料的导热系数随着填料含量的增加而非线性提高,随着测试温度的升高而非线性提高,随着填料粒径的增大而非线性增大。     

Determination of potash crystallization kinetics in a laboratory-scale continuous cooling crystallizer

Crystallization kinetics of KCl in a 21.8L continuous mixed-suspension-mixed-product-removal (CMSMPR) potash cooling crystallizer are determined using the method of s-plane analysis (Tavare, 1986). Feed saturated in refined potash, nearly saturated in NaCl and containing 0.75 g of MgSO₄ per 100 g of water is cooled from 54°C to 38°C by two concentric cooling coils. The crystallizer is brought to steady-state and then perturbed by a change in the crysallizer temperature from 38°C to 32°C. Samples are withdrawn every 15 minutes by means of a specially devised sample trap which permits representative sample removal. Samples are sized using sieve-analysis. The crystallization kinetics are correlated as B° = 49,618 G^0,982.     

自牺牲模板法制备氢氧化镁纳米棒

以碱式硫酸镁纳米棒为模板,在较为温和的条件下合成了氢氧化镁纳米棒.用X射线衍射、透射电子显微镜、场发射扫描电子显微镜等对所制备的样品进行表征.结果表明,所制备的样品为纯相的Mg(OH)2纳米棒,直径约为10~100 nm,长度达到几微米.     

PP/AI(OH)_3/Mg(OH)_2复合材料阻燃性能研究

制备了PP(聚丙烯)/Al(OH)_3/Mg(OH)_2/硼酸锌和PP/Al(OH)_3/Mg(OH)_2阻燃复合材料,并测定了复合材料的氧指数(OI)、水平燃烧速度和烟密度。结果表明,OI随着阻燃剂质量分数的增加而升高,随着粒径的增大而降低;燃烧速度随着阻燃剂用量的增加而下降,随着粒径的增大先升后降;烟密度随着阻燃剂用量的增加而降低,随着粒径的增大而增大;添加硼酸锌后具有显著的抑烟效果。     

Effects of the coating characteristics of Y(OH)3 on the electrochemical performance of spherical Ni(OH)2 at elevated temperature

The effects of the coating characteristics of Y(OH)₃ on the high-temperature performance of spherical Ni(OH)₂ were studied. The coating was performed by chemical surface precipitation under different conditions, and the characterization of Y(OH)₃-coating layer was evaluated accordingly. The electrochemical properties of three as-prepared samples with different coating surface were characterized and compared at different temperature. The results reveal that the sample with dense and porous surface retains the excellent performance at elevated temperatures, and the necessary coating amount is only 0.55 at.%. The mechanism analysis suggests that the chemical nature and morphology of the coating layer plays an important role in oxygen evolution reaction (OER). The coating surface with dense and porous morphology, larger relative surface content and higher utilization ratio of yttrium is more effective on controlling OER and improving the high-temperature performance of Ni(OH)₂ electrode for nickel-metal hydride (Ni/MH) batteries.     

Al（OH）3@Zn（OH）2双层包覆氧化铁黄合成及其耐热性能研究

采用共沉淀法对铁黄颜料进行Al（OH）₃/Zn（OH）₂双层异相包覆,提升其耐热性能,并通过XRD、TG-DTA、FT-IR、SEM&EDS等手段对包覆前后铁黄颜料的微观结构进行表征。研究结果表明,包覆质量分数为40%的Al（OH）₃时铁黄颜料的耐热性能较好;第二层包覆Zn（OH）₂,最优包覆质量分数为30%,样品在240 ℃时色差值为1.84。XRD测试结果表明,Al（OH）₃和Zn（OH）₂包覆并没有改变氧化铁黄的特征峰,两者可能以无定形态包覆在铁黄粒子表面。SEM、EDS、FT-IR测试表明,Al（OH）₃/Zn（OH）₂已成功对铁黄颜料进行了包覆;此外,还出现了片状结构对应Al（OH）₃自身成核现象,包锌后出现了团聚现象。TG-DTA表征显示,包覆后样品升温脱水分两步,低温吸热峰对应包覆层物质的脱水,高温吸热峰偏向更高温度,对应包覆颜料耐热性能的提升。     

Effects of precipitation temperature on the powder properties of Mg(OH)2 and calcined MgO

Mg(OH)₂ has been precipitated from MgCl₂ solution with CaO at temperatures in the range 0–55°C and with a final pH of 11.7. The hydroxides, and the oxides derived from them by calcination under standard conditions, have been characterised by settling rate, chemical analysis, tap density, X-ray crystallite size, B.E.T. surface area, electron microscopy and green and fired density of isostatically pressed pellets. Increasing the precipitation temperature affects these parameters in different ways and attempts have been made to correlate these changes.     

利用碳酸化动力学研究确定Mg（OH）2中残余氯的存在形式

通过碳酸化反应对Ｍｇ（ＯＨ）２中残余氯的溶出动力学进行了研究，得到两种显著不同的表观活化能，可定量、简便地确定杂质氯的存在形式，为氯化镁溶液通氨法生产试剂级Ｍｇ（ＯＨ）２工艺条件的选择提供了理论依据。     

氢氧化镁的水热改性研究及表征

研究了氢氧化镁工业品在一种新型添加剂作用下的水热改性行为，考察了添加剂体系、反应温度、反应时间、添加剂浓度和填充度等因素对水热产物的影响，并用扫描电子显微镜（SEM）、X射线衍射（XRD）和激光粒度仪等对水热产物进行了表征。发现在填充度为67％、添加剂浓度为3mol／L、反应温度为160℃、反应时间为6h时，可获得六方片状、形貌规整、片较厚、分散性良好的水热产物。     

卤水-氨法沉淀制备滤饼状氢氧化镁

以卤水和氨水为原料,制备滤饼状氢氧化镁,主要考察了反应温度和时间、陈化温度和时间、物料配比等条件对制备滤饼状氢氧化镁的影响,得出了最适宜制备工艺条件,在该条件下制备滤饼状氢氧化镁符合HY/T111-2008规定的技术指标,卤水中的镁离子转化率高于95%。     

Detrital Mg(OH)2 and Al(OH)3 in Microwaved Hydrotalcites

Microwave irradiation power (90, 180, 270 or 360 W) determines the composition and the structure of the compounds obtained when pH is increased, decreased or maintained constant during preparation. Although in all cases the X-ray diffraction patterns show that the obtained compounds are hydrotalcite-like, the surface areas (40 up to 240 m²/g) as well as other microcrystalline compounds have to be inferred, such as Al(OH)₃ or Mg(OH)₂.     

Absorption of lean NO in aqueous slurries of Ca(OH)2 with NaClO2 or Mg(OH)2 with NaClO2

The absorption of lean NO in an aqueous slurry of Ca(OH)₂ or Mg(OH)₂ with NaClO₂ was carried out using a stirred tank absorber with a plane gas-liquid interface at 25°C and 1 atm. The rates of absorption of NO and the accompanying desorption of NO₂ for the Ca(OH)₂ slurry were in close agreement with those for the aqueous mixed solution of NaClO₂ and NAOH with higher OH^? concentration, whereas for the Mg(OH)₂ slurry, the absorption rate of NO noticeably exceeded that for the former systems. Furthermore, the ratio of the NO₂ desorption rate to the NO absorption rate considerably exceeded the theoretical prediction for gas absorption with the consecutive reaction (maximum deviation attained 117%). Also, chlorine dioxide was detected in the gas phase. It was deduced from this experimental evidence that there occurs both desorption of the decomposition product ClO ₂ and gas-phase oxidation of No with ClO₂ to produce NO₂.     

Extrusion with Carbon Dioxide (CO2) and Characterization of ABS/Mg (OH)2/Nanoclay Composites

In this paper, carbon dioxide (CO₂) is used to form a high-density microcellular thermoplastic foam structure in order to reduce polymer consumption and facilitate dispersion of Mg (OH)₂ and nanoclay fillers. A twin-screw extruder system was used to predistribute inorganic fillers into the ABS polymer, resulting in composite ABS/filler pellets. This is followed by the use of a single-screw extruder wherein supercritical carbon dioxide is introduced into the formulation. Finally, the resulting foam ABS/filler/CO₂ pellets are injection- molded into test samples. The structure and properties of the composites are characterized using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Furthermore, ABS/Mg(OH)₂/nanoclay polymer composite samples are tested to obtain their yield and tensile strengths, elastic moduli, yield and tensile elongations, izod impact strengths, hardness values, heat deflection temperatures (HDT), Vicat softening points, and melt flow indices (MFI). These tests reveal that for the overall reduction in the amount of polymer in the samples, material properties did not generally deteriorate and even showed improvements in some areas. Moreover, resulting injection-molded samples have been shown to possess dimensional integrity due to the continued expansion of CO₂ during the molding operation.