Preparation of lamellar magnesium hydroxide nanoparticles via precipitation method

Lamellar magnesium hydroxide (MH) nanoparticles were synthesized via surfactant-free precipitation method using MgCl₂ ·6H₂O and NaOH as raw materials, urea and ethanol as assistant additives. The products were characterized by XRD, TEM, EDS, FTIR and Raman spectroscopy. It is found that the prepared nanoparticles are almost hexagonal lamellas when ethanol is added into the reaction system, which indicates that ethanol is helpful to regulate the morphology of MH nanoparticles. In addition, high-purity MH nanoparticles can be obtained when urea is employed. Both XRD patterns and EDS analysis suggest that the generation of impurities was prevented by adding urea, particularly, under the condition of high concentration raw materials. The possible purification mechanism is due to the coordination interaction of urea with Mg²⁺, which can prevent the impurity from generating.     

Preparation and characterization of polystyrene grafted magnesium hydroxide nanoparticles via surface-initiated atom transfer radical polymerization

Polystyrene grafted magnesium hydroxide nanoparticles [PS–Mg(OH)₂] were prepared by the followed two steps: first magnesium hydroxide nanoneedles modified by α-bromoisobutyric acid [BA–Mg(OH)₂] were synthesized through injecting alkaline into magnesium chloride solution; then polystyrene grafted magnesium hydroxide particles [PS–Mg(OH)₂] were successfully prepared by the surface-initiated atom transfer radical polymerization (SI-ATRP) of styrene from the macroinitiators, BA–Mg(OH)₂, in toluene system with the catalysts of 2,2′-bipyridine and Cu(I)Br. The obtained PS–Fe₃O₄ nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), transmission electron microscope (TEM), sedimentation test, and viscosity test. The FT-IR analyses showed that the polystyrene had been covalently grafted onto the surfaces of the nanoneedles [BA–Mg(OH)₂]. The graft polymerizations exhibited the characteristics of the controlled/“living” polymerization. TEM showed that grafted polymer chains on nanoparticles could prevent the aggregation of PS–Mg(OH)₂ nanoparticles markedly in toluene and improve their compatibility with organic phase. The graft parameters could be calculated from the elemental analysis (EA) results, and linear plots of percentage of grafting (PG %) and conversion of monomer (C %) versus polymerizing time were achieved, respectively. Narrow molecular weight distribution (M _w/M _n) for the graft polymer samples were characterized by the gel permeation chromatography (GPC).     

Hydrophobic magnesium hydroxide nanoparticles via oleic acid and poly(methyl methacrylate)-grafting surface modification

Hydrophobic magnesium hydroxide nanoparticles were obtained by means of grafting poly(methyl methacrylate) (PMMA) onto the surface of nanoparticles after oleic acid (OA) modification. The introduction of functional double bonds was firstly conducted on the surface of nanoparticles by OA modification, followed by dispersion polymerization on the particles surface in ethanol solution using methyl methacrylate (MMA) as monomer, azoisobutyronitrile (AIBN) as initiator and polyvinylpyrrolidone (PVP) as stabilizer to graft PMMA on the surface of OA-modified magnesium hydroxide. The obtained composite particles were characterized by XRD, FTIR, TGA, FESEM-EDS, and the compatibility with organic solution was determined by sedimentation test. The results show that the organic macromolecule PMMA could be successfully grafted on the surface of OA-modified magnesium hydroxide nanoparticles, with the dispersibility and the compatibility of nanoparticles greatly improved in organic phase.     

卤水-烧碱直接沉淀法制备纳米氢氧化镁的研究

以苦卤水、烧碱为原料,采用直接沉淀法在表面活性剂的辅助下制备出纳米氢氧化镁粉体。实验研究了反应温度、反应物物质的量比、表面活性剂、不同干燥方式和滴加方式等对所得粉体粒度的影响,通过X射线衍射仪（XRD）和扫描电子显微镜（SEM）对粉体进行表征,用差热-热重分析仪（TG-DTA）分析了产物的热稳定性,并用激光粒度测试仪测试了产物的粒度大小及其分布情况。实验表明：在合适的反应温度及物质的量比下,用PEG200作为表面活性剂、正丁醇共沸蒸馏干燥制得的粉体为流动性较好且厚度约为10 nm的片状纳米氢氧化镁粉体。     

纳米氢氧化镁的超重力沉淀法制备及沉降性能

针对传统沉淀法存在的问题,提出采用一种新的液-液反应机制——撞击流-旋转填料床（IS-RPB）反应器制备纳米氢氧化镁,通过单因素实验和正交试验研究了镁离子初始浓度、镁离子和氢氧根离子摩尔浓度比、转速、液体流量及反应温度等因素对氢氧化镁浆料沉降性能的影响规律,确定了最佳工艺条件。研究表明：在镁离子初始浓度为0.70mol/L、镁离子和氢氧根离子摩尔浓度比为1/2、转速为900r/min、液体流量为40L/h、反应温度为70℃的最佳工艺条件下,得到了粒径为60~80nm的六方片状氢氧化镁,其沉降性能良好。     

高温沉淀-水热法制备纳米氢氧化镁的性能

以氯化镁和氢氧化钠为原料,采用高温沉淀－水热法制备了高分散纳米片状氢氧化镁,采用扫描电子显微镜和X射线衍射仪对其形貌和晶体结构进行了表征,并在EVA中进行了初步应用研究。结果显示,该氢氧化镁分散性高,过滤性能好,与EVA的相容性好,且随水热时间的增加而进一步改善。经3 h水热改性的氢氧化镁,其填充量为50％的EVA混合物的转矩流变性能和力学性能优良,平衡扭矩为15 N·m,拉伸强度为11 MPa,断裂伸长率达到430％。     

均相沉淀法制备超细氢氧化镁

以氯化镁、氢氧化钠为原料,采用均相沉淀法制备超细氢氧化镁。研究了分散剂种类对氢氧化镁产率和粒径的影响,以及分散剂种类、氯化镁浓度、反应温度等因素对氢氧化镁沉降速率的影响,同时分别选择水、乙醇两种不同的反应介质,对氢氧化镁的粒径及产率进行对比。结果表明,以葡萄糖作为分散剂,氯化镁浓度为0.75 mol/L,反应温度为60 ℃,所得氢氧化镁产率较高,且粒径较小（约为6.4 μm）、粒度分布较均匀。     

In situ synthesis of hydrophobic magnesium hydroxide nanoparticles in a novel impinging stream-rotating packed bed reactor

Hydrophobic Mg(OH)_2nanoparticles were successfully synthesized via an in situ surface modification method in a novel impinging stream-rotating packed bed(IS-RPB) reactor using oleic acid(C_(17)H_(33)COOH, OA) as a surface modifier, magnesium chloride hexahydrate in the presence of ethanol as a precursor, and sodium hydroxide as a precipitant. The products were characterized by Fourier transform infrared spectroscopy(FTIR), Field emission scanning electron microscopy(FESEM), X-ray diffraction(XRD), and thermogravimetry-differential scanning calorimetry(TG-DSC). Compatibility with organic solutions was determined by sedimentation tests. The prepared nanoparticles exhibited regular hexagonal lamella with an average diameter of 30 nm when OA is added to the reaction system; this result indicates that OA regulates the morphology of the Mg(OH)_2nanoparticles.XRD revealed that the high-purity Mg(OH)_2product presents a brucite structure, and the I_(001)/I_(101) of hydrophobic Mg(OH)_2(0.86) was higher than that of the blank Mg(OH)_2(0.63). FTIR analysis showed that OA bonded to the surface of the Mg(OH)_2. Compared with the blank Mg(OH)_2product, the product obtained through the proposed method possesses excellent hydrophobic properties, including a high water contact angle of 101.4° and good compatibility with liquid paraffin. TG-DSC analysis indicated that the total percentage of mass loss of hydrophobic Mg(OH)_2(40.88%) was higher than that of the blank Mg(OH)_2product(33.18%). The in situ surface modification method proposed in this work presents potential use in the large-scale production of Mg(OH)_2nanoparticles.     

纳米Mg(OH)_2·Al(OH)_3苯甲酸乙酯包复体的制备研究

采用液相共沉淀法首先合成出纳米氢氧化镁和氢氧化铝的复合物Mg(OH)2.Al(OH)3,再制备出纳米Mg(OH)2.Al(OH)3与苯甲酸乙酯的包复体,运用TEM、XRD、TG-DTA研究复了合物及包复体的性能。结果显示复合物的平均粒径为55nm,包复体的平均粒径为75nm。包复体有较高的热稳定性,且均匀分散在有机溶剂中。     

One-step synthesis of hydrophobic magnesium hydroxide nanoparticles and their application in flame-retardant polypropylene composites

Hydrophobic magnesium hydroxide (MH) nanoparticles were prepared by a one-step synthesis method in a high-gravity environment generated by a novel impinging stream-rotating packed bed (IS-RPB) reactor. The reactant solutions were simultaneously and continuously pumped into the IS-RPB reactor, and then Tween 80 was added as a surface modifier. The morphology, structure, and properties of blank and hydrophobic MH were characterized. The effects of MH nanoparticles on the flame retardancy, thermal stability, and mechanical properties of PP/MH composites were also studied. We found that the obtained MH nanoparticles exhibited hexagonal lamella with a mean size of 30 nm, excellent hydrophobic properties (e.g., high water contact angle of 112°), and improved thermal stability of MH. The limiting oxygen index (LOI) further showed that increased MH loading can significantly improve flame-retardant performance, which reached 29.3% for PP/MH composites with 30 wt% hydrophobic samples. The thermal stability and mechanical properties of the PP/MH composites with hydrophobic samples were also much higher than those of PP/MH composites with blank MH. Results showed that the one-step synthesis had high potential application in the large-scale production of hydrophobic MH nanoparticles.     

Preparation of magnesium hydroxide nanoplates using a bubbling setup

Magnesium hydroxide [MH] with hexagonal nanoplates were synthesized from lightly calcined magnesia (MgO), nitrogen fertilizer ((NH₄)₂SO₄) and alkaline air (NH₃), using a large bubbling setup designed by the authors. The effects of various reaction conditions, including the addition of surfactant, magnesium source, concentration of ions, and initial pH of reaction solution on the morphology, particle sizes, and dispersion properties of the synthesis products were investigated. XRD, SEM, laser particle size analyzer and TG-DTA have been employed to characterize these products. The experimental results showed that the regular-shaped MH products were about 2 μm in mean particle size (D50) and nanometers in thickness, and were loose enough for filtering. The diffraction intensity of the (001) direction was higher than that of the (101) direction. The Mg²⁺ conversion in the continuous setup reached 71% and the decomposition temperature of products was 404 °C.     

Effect of process parameters on the synthesis of nanocrystalline magnesium oxide with high surface area and plate-like shape by surfactant assisted precipitation method

A surfactant assisted precipitation method was employed for the preparation of nanocrystalline magnesium oxide with high specific surface area and plate-like shape. Ammonium hydroxide and polyvinyl alcohol (PVA) were used as precipitant and polymeric surfactant, respectively. The effects of several process parameters such as refluxing time, refluxing temperature and magnesium oxide to PVA monomer unit mole ratio (MgO/PVA) were investigated on the structural properties of the powders. The obtained results showed that the increase in refluxing time and temperature increased the specific surface area and decreased the crystallite size. The results revealed that the polymeric surfactant (PVA) has a significant effect on the synthesis of MgO nanocrystals and led to obtain a powder with higher surface area and plate-like shape.     

花瓣状纳米氢氧化镁及氧化镁的微波辅助合成

在微波辅助下,以硫酸镁、NH₃•H₂O-NH₄Cl缓冲溶液为原料,通过均相沉淀反应制备了纳米氢氧化镁,经煅烧又得到了纳米氧化镁。采用X射线衍射（XRD）、透射电镜（TEM）、扫描电镜（SEM）、热重分析（TG）等分别对纳米氢氧化镁和氧化镁的结构、形貌及热稳定性进行了分析测试。结果表明,纳米氢氧化镁的结晶性能较好,其形貌为由厚度约40 nm的纳米片团聚而成的花瓣状;纳米氧化镁亦保持了氢氧化镁花瓣状形貌。并对微波辅助下纳米氢氧化镁形成的可能机理进行了初步探讨。     

Rod-like morphological magnesium hydroxide and magnesium oxide via a wet coprecipitation process

Rod-like Mg(OH)₂ nanoparticles have been synthesized via a wet coprecipitation with some kinds of very small quantity of foreign ions(0.4 mol% of Cu²⁺, Ni²⁺, Fe³⁺ and Zn²⁺). The microstructure, morphology and thermal stability were characterized by transmission electron microscope (TEM), selected area electron diffraction (SAED), X-ray diffraction and thermogravimetric analysis (TGA). The results showed that the obtained Mg(OH)₂ crystals with foreign ions possessed rod-like morphology and higher thermal stabilities while Mg(OH)₂ samples obtained without foreign ions performed lamellar morphology; moreover, the subsequent MgO calcined from the corresponding Mg(OH)₂ preserved the original morphological features, but exhibited some mesoporous structures of about 5 nm according to the results of TEM and N₂ adsorption–desportion.     

Gas absorption into aqueous reactive slurries of calcium and magnesium hydroxide in a multiphase reactor

Investigation of absorption of SO₂ into aqueous slurries of fine and reactive hydroxide particle of calcium and magnesium was carried out in a stirred vessel at 298 K at realistically high mass transfer coefficients. Enhancement in the rate of gas absorption was measured at different solid loadings and speed of agitation. The absorption process is theoretically analyzed using two different models. For the SO₂–Ca(OH)₂ system, a single reaction plane model was used and for the SO₂–Mg(OH)₂ system, a two reaction plane model incorporating the solids dissolution promoted by the reactions with the absorbed SO₂ in the liquid film was employed. A correct procedure was adopted to estimate the contribution of the suspended particles in the enhancement of gas absorption. Theoretical enhancement factors thus obtained compared well with the experimental data. The extra enhancement observed for the SO₂–Mg(OH)₂ system could be explained from the reaction between SO₂ and the dissolved [SO₃]²⁻.     

六方片状氢氧化镁的合成及其第一性原理分析

分别以硝酸镁和氯化镁为原料,氨气为沉淀剂,采用一步水热法制备六方片状氢氧化镁,并利用扫描电镜（SEM）和X射线衍射（XRD）对产品进行表征。采用第一原理赝势平面波方法,对氢氧化镁的各个经常显露面族的能量、电子结构和布居数进行理论计算。结果表明,p轨道对氢氧化镁晶体各表面的结构稳定性起着主导作用,氢氧化镁晶体（001）面的总能量较低,O-Mg和H-Mg键的结合力较强,存在热力学稳定性,会成为顽强显露晶面,较好地解释了氢氧化镁六方片状形貌的成因。     

氨状态对氨法制备氢氧化镁颗粒性质的影响

氨法是制备氢氧化镁的主要方法之一,根据氨进入反应体系状态不同分为氨水法和氨气法两种工艺。为了确定氨水与氨气对氢氧化镁颗粒性质的影响,以氯化镁为原料,分别以氨水和氨气为沉淀剂制备氢氧化镁,并利用扫描电镜(SEM)、X射线衍射(XRD)、激光粒度分布仪对产品进行了表征。结果表明：两种沉淀剂制备的氢氧化镁颗粒晶型均随沉淀反应温度的升高趋向完整,颗粒的分散性也随温度的升高得到改善;当反应温度达到75℃以上时,氨气法制备的氢氧化镁呈四方块状(六面体结构),颗粒的规则程度和分散性优于氨水法产品;氨水浓度对氨水法制备的氢氧化镁颗粒粒度及形貌也有较大影响,随氨水浓度的升高,产品粒度及分散性趋向于氨气法产品。本文研究可为氢氧化镁制备中氨法的选择及应用提供参考。     

直接沉淀法制备微细均匀氢氧化镁粉体的研究

本文以苦卤和工业氨水为原料,采用直接沉淀法制得了粒径较小且分布均匀、分散性良好的片状Mg(OH)_2粉体,研究了温度、氨镁比、加料速度和存放时间对产品粒径和产量的影响,得出其最佳工艺条件为:温度25℃,氨镁比2∶1,加料速度36mL·min~(-1),存放时间3h。并采用了超声波粒度分析仪、X射线衍射仪、热重分析仪和扫描电子显微镜表征产品的粒径大小及分布、晶型结构、热行为和形貌。     

高分散纳米氢氧化镁的快速制备及性能研究

以氯化镁为原料,以氨水为沉淀剂,采用高温沉淀-水热法快速制备了高分散纳米片状氢氧化镁。采用扫描电子显微镜和X射线衍射仪对高分散纳米氢氧化镁的形貌和晶体结构进行了表征;同时将其填充到乙烯-乙酸乙烯酯共聚物（EVA）树脂中,采用转矩流变仪、拉力试验机和氧指数仪对EVA/氢氧化镁混合物的流变性能、力学性能和阻燃性能进行了研究。结果显示,所制备的氢氧化镁产品为六方薄片,分散性高,过滤性好,与EVA的相容性好,且随水热时间的增加而进一步改善。氢氧化镁填充量为50%（质量分数）的EVA混合物的转矩流变性能和力学性能优良,平衡扭矩为17 N.m,拉伸强度为10.9 MPa,断裂伸长率达到470%。     

二丙基次膦酸铝和氢氧化镁对PA6的复合阻燃作用

通过极限氧指数测定、垂直燃烧实验和锥形量热分析研究了二丙基次膦酸铝(ADPP)和氢氧化镁(MH)对尼龙6(PA6)的复合阻燃作用。结果表明:ADPP与MH对PA6无协同阻燃作用,ADPP复配少量的MH(质量分数10%)阻燃PA6的LOI和垂直燃烧级别变化不大,总热释放量(THR)和最高热释放速率(PHRR)略有增加,但热稳定性有明显改善。残余物分析结果表明,复合少量的MH略增加了材料的成炭性,但炭层结构变得比较松散,因而对ADPP阻燃PA6的影响不大。而随着MH用量增加,成炭性明显下降,因而降低了ADPP对PA6的阻燃作用。