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.     

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。     

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.     

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.     

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⁻.     

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。     

The use of CTAB to improve the crystallinity and dispersibility of ultrafine magnesium hydroxide by hydrothermal route

The high-dispersed lamellar ultrafine magnesium hydroxide was obtained at relatively low hydrothermal temperature in the presence of cationic surfactant, cetyl trimethyl ammonium bromide (CTAB). The procedure described in this study is attractive since proper amount of CTAB could promote the dissolution and precipitation of magnesium hydroxide in hydrothermal system, resulting in the well-defined morphology, narrow size distribution and good crystallinity of ultrafine particles. The resultant magnesium hydroxide was characterized by X-ray powder diffraction (XRD), thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), field-emission scanning electron microscopy (FESEM) and laser diffusion analysis. The method led to the production of particles with mean size of 400 nm and a thickness of 60 nm. The optimal conditions of preparation were hydrothermal treatment at 150 °C for 6 h at pH 11 with Mg²⁺/CTAB molar ratio of 80.     

Effects of zinc borate and microcapsulated red phosphorus on mechanical properties and flame retardancy of polypropylene/magnesium hydroxide composites

In this paper, the mechanical properties and flame retardancy of zinc borate (ZB) and microcapsulated red phosphorus (MRP) with modified magnesium hydroxide (MH) in flame-retardant polypropylene (PP) were studied by mechanical properties test, UL-94 test, and thermogravimetric analysis (TGA). The crystallization behaviors of the composites were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The addition of ZB could improve tensile strength and elongation at break of PP/MH composite. The MRP powders had a little effect on the mechanical properties of the PP composites. DSC results showed the addition of ZB and MRP weakened the heterogeneous nucleation effect of MH on PP. The addition of ZB and MRP had a great effect on the flammability of the PP/MH/EG composites. The thermal stability of PP/MH/ZB and PP/MH/ZB/MRP composites was better than that of PP/MH composite.     

Synthesis and growth mechanism of donut-like lead titanate particles by hydrothermal method

Tetragonal perovskite structure PbTiO₃ donut-like particles have been synthesized by a hydrothermal method in strong alkaline environment using lead nitrate (Pb(NO₃)₂) as the lead source and TiCl₄ as the titanium source. The as-prepared particles were characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM), and it was indicated that the phase composition and particles shapes were influenced by the reaction temperature and reaction time. Based on the morphologies and phase evolutions as a function of reaction temperature or reaction time, a mechanism for the growth of the donut-like PbTiO₃ particles was proposed to involve nucleation, agglomeration, phase in situ conversion, dissolution, and recrystallization. The spherical particles were formed by primary nucleation of PbTi_0.8O_2.6 followed by agglomeration into platelets. Then, the platelet PbTi_0.8O_2.6 particles in situ converted into Pb₂Ti₂O₆ particles. Under the effects of temperature, pressure (autogenous pressure), and high solution pH value, the platelet Pb₂Ti₂O₆ particles dissolved from its center of surface and recrystallized to form PbTiO₃ nano-particles which adhered to its edges. Finally, the monocrystal donut-like PbTiO₃ particles were formed as the dissolution of Pb₂Ti₂O₆ particles completed.     

Effect of Surfactants on the Structure and Morphology of Magnesium Borate Hydroxide Nanowhiskers Synthesized by Hydrothermal Route

Magnesium borate hydroxide (MBH) nanowhiskers were synthesized using a one step hydrothermal process with different surfactants. The effect surfactants have on the structure and morphology of the MBH nanowhiskers has been investigated. The X-ray diffraction profile confirms that the as-synthesized material is of single phase, monoclinic MgBO₂(OH). The variations in the size and shape of the different MBH nanowhiskers have been discussed based on the surface morphology analysis. The annealing of MBH nanowhiskers at 500 °C for 4 h has significant effect on the crystal structure and surface morphology. The UV–vis absorption spectra of the MBH nanowhiskers synthesized with and without surfactants show enhanced absorption in the low-wavelength region, and their optical band gaps were estimated from the optical band edge plots. The photoluminescence spectra of the MBH nanowhiskers produced with and without surfactants show broad emission band with the peak maximum at around 400 nm, which confirms the dominant contribution from the surface defect states.     

Sintering and grain growth behaviour of magnesium aluminate spinel: Effect of lithium hydroxide addition

Lithium hydroxide, LiOH, in the amounts ranging from 0.1 to 1.2 wt% has been used as a sintering aid to improve the densification of MgAl₂O₄. The addition of 0.3 wt% LiOH promotes densification and limits grain growth. The activation energy of sintering, calculated using master sintering curve approach, decreases from 790 ± 20 kJ.mol^?1 to 510 ± 20 kJ.mol^?1 with the addition of 0.3 wt% of LiOH. In addition, MgAl₂O₄ was also mixed with 10 wt% of LiOH to amplify the formation of reaction products. High-temperature XRD results showed that secondary phases (MgO and LiAlO₂) are produced above 1040 °C. The secondary phases start to disappear at T > 1200 °C, and MgAl₂O₄ is produced. While adding small amounts of LiOH, up to ca. 0.3 wt%, is beneficial for densification and suppressing grain growth, there exists a critical concentration of Li⁺ that is accounted for by the preferential incorporation of lithium ions into MgAl₂O₄ crystal lattice.     

Synthesis of size-controlled monodisperse Pd nanoparticles via a non-aqueous seed-mediated growth

ABSTRACT: We demonstrated that stepwise seed-mediated growth could be extended in non-aqueous solution (solvothermal synthesis) and improved as an effective method for controlling the uniform size of palladium nanoparticles (Pd NPs) in a wide range. The monodisperse Pd NPs with the size of about 5 nm were synthesized by simply reducing Pd(acac)2 (acac = acetylacetonate) with formaldehyde in different organic amine solvents. By an improved stepwise seed-mediated synthesis, the size of the monodisperse Pd NPs can be precisely controlled from 5 nm to 10 nm. The as-prepared Pd NPs could self assemble to well shaped superlattice crystal without size selection process.     

Synthesis and growth mechanism of aluminum nitride nanowires via a chloride-assisted chemical vapor reaction method

We report a large scaled fabrication of AlN nanowires via a chloride-assisted chemical vapor reaction technique at 1100?°C in flowing N₂ atmosphere using aluminum powders as starting materials. The as-obtained hexagonal AlN nanowires had the length of hundreds of microns and diameter of 20–100?nm, and indicated a single crystalline characteristic. The yield production was significantly increased with ammonium chloride and aluminum chloride addition because of the formation of intermediate gaseous AlCl and HCl. The addition of ammonium chloride and aluminum chloride also promoted the formation of ferric chloride, which served as the catalyst and further facilitated the growth of AlN nanowires. The vapor–liquid–solid and vapor–solid growth mechanism are proposed and discussed in details.     

Morphology and growth mechanism of CVD alumina–silica

The purpose of the present paper is to examine the morphology and growth mechanism of the CVD alumina–silica film deposited at low temperatures and low pressure using the chemical reaction kinetics, the Gibbs–Thomson relation, solidification theory, and supersaturation condensation fusion mechanism. The dense CVD alumina–silica films were deposited on the surface of graphite paper using AlCl₃–SiCl₄–H₂–CO₂ as precursor in the temperature range of 300–550 °C. XRD and SEM were used to examine the phase composition and the microstructure of the CVD alumina–silica, respectively. The CVD alumina–silica films were composed of a large number of spherical particles accumulated by a number of fine-particles. The fusion took place among the solid particles. The spherical morphology and the fusion all resulted from the liquid droplets, which resulted from the supersaturation of the chemical reaction gaseous species in CVD alumina–silica. The liquid droplets were confirmed by comparing the morphology of the CVD alumina–silica with the typical and stable morphology of the solidified mass from liquid.     

Field emission properties and growth mechanism of In2O3 nanostructures

Four kinds of nanostructures, nanoneedles, nanohooks, nanorods, and nanotowers of In₂O₃, have been grown by the vapor transport process with Au catalysts or without any catalysts. The morphology and structure of the prepared nanostructures are determined on the basis of field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), and transmission electron microscopy (TEM). The growth direction of the In₂O₃ nanoneedles is along the [001], and those of the other three nanostructures are along the [100]. The growth mechanism of the nanoneedles is the vapor-liquid–solid (VLS), and those of the other three nanostructures are the vapor-solid (VS) processes. The field emission properties of four kinds of In₂O₃ nanostructures have been investigated. Among them, the nanoneedles have the best field emission properties with the lowest turn-on field of 4.9 V/μm and the threshold field of 12 V/μm due to possessing the smallest emitter tip radius and the weakest screening effect.