高纯超细氧化镁的制备工艺

以MgCl_2·6H_2O为原料,PVA与CTAB为添加剂,采用氨水直接沉淀制备氢氧化镁前驱体,再经煅烧得到高纯超细氧化镁。研究了温度、镁离子浓度、添加剂用量、原料配比和煅烧温度对氧化镁粒度的影响。确定最佳工艺条件为:反应温度40℃,Mg2+浓度1mol/L,PVA用量0.6%(质量分数),CTAB的用量1.2%(质量分数),n(NH_3·H_2O)∶n(MgCl_2·6H_2O)=3.3∶1,煅烧温度600℃,煅烧时间3h。荧光光谱分析表明,氧化镁纯度达到了99.9%以上;激光粒度和SEM结果显示,粒子分散性较好,平均粒径为190nm,粒度分布呈正态分布。     

用于水性导电油墨的纳米银分散液的制备

运用液相化学还原法,以次磷酸钠(NaH2 PO2 ·H2 O)为还原剂,PVP(聚乙烯吡咯烷酮)为高分子保护剂,六偏磷酸钠为分散剂,还原硝酸银溶液制得了用于水性导电油墨的纳米银分散液。设计4 因素3 水平的正交实验L9(33 ),研究了还原剂用量、保护剂用量、分散剂用量及反应温度对纳米银粉粒度及形貌的影响,获得了制备纳米银分散液的最佳条件:在AgNO3 浓度为1. 0 mol/ L 时,n( NaH2 PO2 ·H2 O) / n( AgNO3 ) 为2. 5 :1,n(PVP) / n(AgNO3 )为1. 5 :1,n(六偏磷酸钠) / n(AgNO3 )为0. 007 :1,反应温度为40 ℃的条件下,制备的纳米银分散液放置30 d 后,经SEM 表征和纳米粒度及电位分析仪测试,可获得主要粒度分布在15 ~60 nm 的纳米银分散液,克服了水性导电油墨填料易絮凝的问题。     

超声振荡法制备纳米TiO_2粉体

以钛酸丁酯为原料,加入适当的模板剂,用超声振荡法制备纳米TiO2粉体,研究分散剂、干燥方式、模板剂等对TiO2粉体粒度分布及结晶性质的影响,借助于X射线衍射(XRD)、透射电镜(TEM)、扫描电镜(SEM)、激光粒度分布等测试手段对制备的TiO2粉体的晶体结构及颗粒粒度分布进行表征。结果表明:在80℃真空干燥、加入OP乳化剂和450℃煅烧条件下制备的纳米TiO2粒度较小,平均粒径为15～25nm,获得的纳米TiO2晶型为锐钛矿型,颗粒近似球形,结晶完好。     

纳米铜微波法的制备及其粒度影响因素的探究

在MCR-3型微波反应器中以CuCl_2·2H_2O为原料,乙二醇为溶剂、还原剂以及分散剂,在碱性条件下,制备了不同粒径的纳米铜粉。考察了CuCl_2的浓度C(CuCl_2)、预置温度T、摩尔比m=n(NaOH)/n(CuCl_2)以及反应时间t对纳米铜粉粒度的影响,并对其影响机理进行了分析。结果表明,采用微波法,通过改变实验条件可以制备出粒度可控的纳米铜,且分散度好,分布均匀,结晶度高,球形性良好;预置温度是影响粒径的主要因素,低于185℃时,粒度依赖性不明显;而当高于185℃时,温度越高,粒径越大。     

硬脂酸溶胶凝胶法制备氧化镁纳米微粒的研究

以硬脂酸为分散剂，采用溶胶凝胶法研究了制备氧化镁纳米微粒的条件，探讨了分散剂用量，反应时间，反应温度，烧结温度和时间对产物粒径与转化率的影响，取得了最佳工艺条件，分别用红外光谱（IR），X射线射末衍射（XRD），透射电镜（TEM）和比表面积（BET）测定，对该纳米微粒的结构与性能进行了表征，结果表明：Mg(NO3)2与CH3（CH2）16COOH的摩尔配比控制在1：1，于90℃反应20min，在470℃热处理3h，得到立方相氧化镁钠米微粒，形貌为椭球体，分散性好，平均粒径约为36nm.     

二维层状磁性镁铝水滑石的制备与表征

采用共沉淀法将磁性基质与镁铝水滑石组装制备二维层状磁性镁铝水滑石,考察了在一定的pH值、沉淀生成温度及陈化时间下,不同n(Mg2 )/n(Al3 ),n(Fe2 )/n(Mg2 )比值及焙烧温度对合成磁性镁铝水滑石结构的影响,并借助HRTEM、XRD、VSM、TG-DSC、FT-IR等手段对其晶型结构、磁学性能及结晶度等进行表征,结果表明镁铝水滑石在赋予磁性后,并没有改变其典型的层状结构,证实了将磁性基质与层状材料组装合成的可行性.     

球形氢氧化镁的制备及其晶体生长动力学

制备花状球形氢氧化镁粉体,研究了几种关键因素对镁回收率的影响和氢氧化镁的晶体生长动力学.结果表明,随着反应溶液中Mg~(2 )初始浓度和pH值的提高,镁的回收率提高;提高反应温度使镁的回收率提高,但当温度超过60℃后,反应溶液中氨的大量挥发使其pH值迅速降低,因而镁回收率下降;陈化可以提高镁的回收率,当陈化时间超过60 min后因镁已完全沉淀,回收率不再提高.在最佳工艺条件下用氨法制备的氢氧化镁颗粒为花状球形,形状规则,分散性好,粒度均匀,粒径约2μm,单片厚度约30 nm.晶体生长动力学研究表明,析出Mg(OH)_2晶体的质量和Mg(OH)_2晶粒平均粒径随着时间呈指数增长.     

用改进的液相沉淀法制备ZnS纳米晶

以ZnSO4、（NH4）2S为原料，通过加入分散剂对传统的液相沉淀法进行改进，制备出ZnS的纳米粉末，并探讨了制备过程中沉淀、洗涤、干燥以及晶化等阶段的反应条件对产物的影响。结果表明：以丙三醇为分散剂、原料配比（n(ZnSO4)/n((NH4)2S)杰1：0.9、料液浓度比1：1，c(ZnSO4)、c((NH4)2S)均为0.2mol/L时为沉淀适宜工艺条件；干燥前对沉淀物用无水乙醇进行脱水处理，可有效地控制硬团聚体的产生；沉淀经400-600℃晶化1h，可得立方晶形β-ZnS纳米晶，产物为均匀球形，分散性较好；400℃晶化的产物晶粒尺寸约为40nm；600℃晶化的产物晶粒尺寸约为50nm。     

液相法合成针状镁铝水滑石纳米晶的研究

研究了合成条件(原料种类、加料次序、NaOH浓度和合成温度)对液相法制备镁铝水滑石试样的相组成的影响.以MgCl₂为镁源、NaAlO₂为铝源、NaCO₃和NaOH为沉淀剂,在常压下采用液相法制备了长度约100nm、直径约10nm的Mg₆Al₂(OH)₁₆CO₃-4H₂O针状纳米晶体.并且发现:可溶性原料的选取、最后加入MgC_l2的加料次序、>45℃的合成温度和保证反应溶液的pH>12,是瞬间生成镁铝水滑石纳米晶的充分必要条件.提出镁铝水滑石纳米晶核形成的过程是:均匀分布于溶液中的Al₁₃(OH)₃₂⁷⁺迅速吸附于带羟基OH-的无定型态的Mg(OH)₂表面,并进行Al³⁺扩散,为平衡电价,CO₃^2-也扩散进入Mg(OH)₂,从而在瞬间完成镁铝水滑石晶核的形成.     

改性干燥法制备纳米氧化镁粉体的研究

以六水氯化镁和尿素为原料,采用均匀沉淀法制备出氢氧化镁沉淀,利用不同改性干燥法除去沉淀中的湿分,再将干燥的氢氧化镁粉体经马弗炉煅烧得到纳米氧化镁粉体,通过透射电子显微镜和X射线衍射仪的表征与分析,研究了改性干燥方式对纳米氧化镁粉体形貌、颗粒尺寸和团聚情况的影响,讨论了改性干燥的基本原理和改性剂的作用。研究结果表明,改性干燥方式对纳米氧化镁颗粒形貌和大小的影响不大,对其颗粒间团聚状态影响很大。     

单分散纳米二氧化硅的制备

以正硅酸乙酯为原料,氨水为催化剂,采用化学沉淀法,通过合理地控制反应条件,制备了单分散球形纳米二氧化硅颗粒。通过激光粒度分析、X射线衍射及透射电镜等测试手段对制备的二氧化硅颗粒进行表征。结果表明:当最佳试验条件为正硅胶乙酯与乙醇、氨水的物质的量为1∶6∶4,表面活性剂的添加量为3%时,制备的纳米氧化硅粒度分布均匀,且呈规则的球形,粒径为50~90 nm,为无定形态二氧化硅。     

动态高温X射线衍射法研究水镁石的热分解过程

用水镁石矿粉矿作原料,用差热-热重分析和动态高温X射线衍射法研究水镁石的热分解过程,以及在不同温度和保温时间下的相变机理。结果表明:400℃是Mg(OH)2向MgO转变的相变点,水镁石在450～800℃的升温区间,产物均为纳米级MgO粉体,其晶粒度由23 nm增加到176 nm。水镁石在900℃下煅烧3 h,Mg(OH)2已经完全分解为MgO,杂质主要存在形式是CaMgSiO4和Mg2SiO4,约占总质量的2%左右。     

晶型控制剂对纳米氧化镁形貌的影响

对晶型控制剂的种类及用量进行对比,通过形貌和物相的表征和分析,研究晶型控制剂对纳米氧化镁形貌及分散作用的影响。结果表明:采用羧基类和羟类两种晶型控制剂,一羧基类和一羟基类晶型控制剂生成纳米氧化镁为球形,团聚严重;而多羧基类和多羟类晶型控制剂均有利于纳米氧化镁颗粒沿片状分布;加入不同用量的晶型控制剂,乙二胺四乙酸用量为6 mg/L时,有利于纳米氧化镁颗粒沿片状分布,且氧化镁晶粒度仅为26.13 nm,聚乙二醇用量为1.2 mg/L时较利于纳米氧化镁生成片状。     

Preparation of nanocrystalline MgO by surfactant assisted precipitation method

Nanocrystalline magnesium oxide with high surface area was prepared by a simple precipitation method using pluronic P123 triblock copolymer (Poly (ethylene glycol)-block, Poly (propylene glycol)-block, Poly (ethylene glycol)) as surfactant and under refluxing conditions. The prepared samples were characterized by X-ray diffraction (XRD), N₂ adsorption (BET) and scanning and transmission electron microscopies (SEM and TEM). The obtained results revealed that the refluxing time and temperature and the molar ratio of surfactant to metal affect the structural properties of MgO, because of the changes in the rate and extent of P123 adsorption on the prepared samples. The results showed that the addition of surfactant is effective to prepare magnesium oxide with high surface area and affects the morphology of the prepared samples. With increasing the P123/MgO molar ratio to 0.05 the pore size distribution was shifted to larger size. The sample prepared with addition of surfactant showed a plate-like shape which was completely different with the morphology of the sample prepared without surfactant. The formation of nanoplate-like MgO was related to higher surface density of Mg ions on the (0 0 1) plane than that on the other planes of the Mg(OH)₂ crystal. The (0 0 1) plane would be blocked preferentially by the adsorbed P123 molecules during the growing process of Mg(OH)₂ nanoentities and the growth on the (0 0 1) plane would be markedly restricted, and the consequence is the generation of nanoplate-like MgO. In addition, increase in refluxing temperature and time increased the specific surface area of the prepared MgO samples.     

Polyol-mediated synthesis of nanoscale Mg(OH)<Subscript>2</Subscript> and MgO

Nanoscale Mg(OH₂) and MgO is prepared via a polyol-mediated synthesis. With concern to the experimental conditions, spherical particles, 20 and 100 nm in size are realized. Dynamic light scattering proves the presence of non-agglomerated and monodispersed Mg(OH)₂ in as-prepared suspensions of diethylene glycol. Based on the results of infrared spectroscopy, thermal analysis and X-ray powder diffraction, as-prepared Mg(OH)₂ can be dehydrated at a surprisingly low temperature (300 °C) to form MgO with almost similar particle size and shape.

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Graphical abstract Polyol-mediated Synthesis of Nanoscale Mg(OH) ₂ and MgO C. Feldmann*, S. Matschulo, S. Ahlert

     

Characterization of the MgO nano powder synthesized by using a liquid phase precursor method for plasma display panels protecting layer

The characterization of MgO nano powders that were synthesized using a conventional firing liquid phase precursor, rapid firing liquid phase precursor and rapid cooling firing liquid phase precursor were investigated as a function of the heating and cooling rates and the concentration of the impregnated Mg(NO3)2 x 6H2O solution from 1 to 20%. The relative intensity of diffraction peak in the MgO nano powder increased with increasing firing temperature from 800 to 1200 degrees C, indicating a higher crystalline MgO nano powder. In addition, the relative intensities of the MgO nano powder synthesized at the designated temperature showed similar behavior regardless of the impregnated Mg(NO3)2 x 6H2O solution concentration from the XRD analysis. The field emission scanning electron microscope and high resolution transmission electron microscope analysis showed that the size and shape of the MgO nano powder can be controlled by the temperature, the firing and cooling processes, and the impregnated Mg(NO3)2 x 6H2O solution concentration. Moreover, the CL spectra of the synthesized MgO nano powders showed a higher luminance efficiency than commercial MgO nano powder.     

Synthesis of maghemite (γ-Fe2O3) nanoparticles by wet chemical method at room temperature

In this research work an innovative one step method is described for the production of maghemite (γ-Fe₂O₃) nano-particles at room temperature. The nano-particles were characterized using X-ray diffraction (XRD), infrared spectrum (IR), transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS), respectively. The average crystallite and particle size of the maghemite nano-particles were estimated to be 13 and 10 nm, by XRD and TEM, respectively. The TEM image showed that the γ-Fe₂O₃ nano-particles were of approximate spherical shape. Using the method presented here, maghemite nano-particles, 10 nm in size, could be produced without using organic solvent and oxidation.     

Formation of MgO whiskers on the surface of bulk MgB<Subscript>2</Subscript> superconductors during in situ sintering

Magnesium oxide (MgO) whiskers (with diameters of about 60–80 nm) formed on the surface of bulk polycrystalline MgB₂ superconductor at a relative low temperature (720 °C) during in situ sintering process. The reaction between Mg and B powders begins at a temperature below melting point of Mg and maintains till about 750 °C. The residual Mg powders evaporate and react with trace oxygen to form MgO vapor as the temperature exceeds the melting temperature of Mg and a low supersaturation is required for the growth of MgO whiskers. The preformed MgB₂ and MgO crystals act as substrates and the melted Mg powders on the surface of them serve as catalysts during the growth process of MgO whiskers. The growth process of MgO whiskers is dominated by a self-catalytic vapor–liquid–solid (VLS) mechanism.     

Preparation of MgO nanoparticles

MgO nanoparticles have been prepared via hydroxide precipitation from aqueous solutions, followed by the thermal decomposition of the hydroxide. The nanoparticles inherit the platelike shape from the hydroxide and break into isometric particles upon significant superheating. The particle size of the synthesized magnesium oxide powders varies from 30 to 75 nm, depending on the annealing temperature.     

均匀沉淀法制备纳米氧化镁的研究

以ＭｇＣｌ２和ＣＯ（ＮＨ２）２为原料,采用均匀沉淀法制备了纳米ＭｇＯ。考察了反应温度、反应时间、反应物配比及煅烧温度和时间对产物收率与粒径的影响,获得了最佳工艺条件。通过热重分析、Ｘ射线衍射、透射电镜研究了产品的结构性能,所得纳米ＭｇＯ分散性良好,粒度分布均匀,平均粒径３０ｎｍ,粒子形状为球形