非水解溶胶-凝胶法合成镁铝尖晶石纳米粉体及其烧结性能

以无水氯化铝、无水氯化镁为前驱体和无水乙醇为氧供体，采用非水解溶胶-凝胶法合成镁铝尖晶石纳米粉体，利用XRD、SEM和激光粒度等表征了粉体晶相、颗粒粒径与形貌及烧结性能。结果表明，在900℃可合成单一镁铝尖晶石纳米粉体，一次粒子平均粒径为50nm左右，存在可通过球磨消除的软团聚，在1600℃烧结3h可以得到气孔少、颗粒结合紧密、相对致密的镁铝尖晶石烧结体。     

非水解溶胶-凝胶法合成镁铝尖晶石纳米粉体及其烧结性能

以无水氯化铝、无水氯化镁为前驱体和无水乙醇为氧供体,采用非水解溶胶-凝胶法合成镁铝尖晶石纳米粉体,利用XRD、SEM和激光粒度等表征了粉体晶相、颗粒粒径与形貌及烧结性能。结果表明,在900℃可合成单一镁铝尖晶石纳米粉体,一次粒子平均粒径为50nm左右,存在可通过球磨消除的软团聚,在1600℃烧结3h可以得到气孔少、颗粒结合紧密、相对致密的镁铝尖晶石烧结体。     

溶胶-凝胶法制备Al2O3纳米粉

以Al(NO3) 3和NH3·H2 O为原料制备AlOOH勃姆石溶胶 ,加入PVA作为分散剂 ,干燥后制成干凝胶。干凝胶经不同温度下煅烧得到不同晶型的Al2 O3纳米粉。X—射线衍射分析结果表明 ,勃姆石干凝胶在煅烧过程中的物相变化为AlOOH→ε-Al2 O3→ -Al2 O3→δ -Al2 O3→θ -Al2 O3→α-Al2 O3,采用电子显微镜和BET比表面积法测量出Al2 O3纳米粉的颗粒大小     

溶胶-凝胶法制备纳米氧化镁

以六水硝酸镁为前驱体,采用柠檬酸溶胶一凝胶法合成了不同粒径（10～100nm）和结晶度的纳米MgO粉末。研究了柠檬酸的作用机理、不同的工艺条件（水、无水乙醇、柠檬酸的加入量）对溶胶一凝胶稳定性的影响以及焙烧温度对粉末晶体粒径、结晶度的影响。结果表明：未引入柠檬酸时,凝胶的稳定性较差．氧化镁产物粒径较大且团聚较严重。引入柠檬酸后,并当水：六水硝酸镁：柠檬酸：乙醇=100：9：9：2．1（摩尔比）时可形成稳定的凝胶体系。焙烧温度对制得的MgO粉末的化学成分和晶体形貌基本无影响,但对粉末结晶度和粒径有显著的影响。500℃焙烧制得的纳米氧化镁粉末粒径为10nm左右,结晶度低,粒子间有一定的团聚;600℃的粉末粒径为30～60nm,结晶度有所提高,粒子的分散性较好;900℃的粉末粒径为50～100nm,结晶度更高,晶相更完整。     

溶胶-凝胶法制备PZT纳米粉

本文主要讨论以溶胶-凝胶法制备PZT纳米陶瓷粉的部分反应条件、烧结温度及时间的选择。     

溶胶-凝胶法制备纳米氧化锌

以醋酸锌为原料,柠檬酸三铵为改性剂,通过溶胶-凝胶法制备了纳米氧化锌.分别研究了主盐浓度、溶剂用量、改性剂用量、胶溶剂种类、干燥温度和时间、煅烧温度和时间等条件的影响.使用傅立叶变换红外光谱仪测定氧化锌前驱体及产物的化学组成,用X射线衍射仪考察氧化锌微粒晶体的晶型结构并计算其大小.最终所得产物粒径在40 nm左右,且分散性较好,颗粒均匀.     

多孔片状镁铝尖晶石的制备

在催化剂载体和吸附等领域,具有介孔结构的片状镁铝尖晶石因比表面积大、活性位点丰富、不易团聚等特性,受到越来越多的关注。以铝丝为铝源、镁粉为镁源、无水乙醇为溶剂,Na2Mo O4为熔盐,采用熔盐辅助非水解溶胶–凝胶法制备多孔片状镁铝尖晶石。借助X射线衍射仪、场发射扫描电子显微镜等测试手段研究了热处理温度及保温时间对镁铝尖晶石合成与形貌的影响,运用透射电子显微镜(TEM)观察片状晶体的微观结构,采用氮气吸附脱附测试对样品的比表面积和孔径进行了表征。结果表明：热处理温度和保温时间均对镁铝尖晶石形貌有较大影响。优选热处理温度为900℃,保温时间为8 h,可制备出具有介孔结构的片状镁铝尖晶石,片的长度为140～160 nm。所制得样品的比表面积为76 m2/g。TEM和氮气吸附脱附曲线测试结果表明,样品存在明显的介孔结构。为制备多孔片状镁铝尖晶石提供了一种新思路。     

超细镁铝尖晶石粉体制备及表征

在实验室条件下分别进行了溶胶-凝胶法、凝胶-沉淀法和固相合成法实验,制备了不同粒度的镁铝尖晶石超细粉体,并对其进行了XRD分析,发现其相组成单一,纯度较高.经过激光粒度分析仪测得凝胶-沉淀法和固相合成法制得的粉体平均粒径分别为505和1780 nm,且分布比较均匀.通过SEM发现溶胶-凝胶法一次粒子为纳米级,团聚比较严重,在1000℃的最佳焙烧温度下可以获得比较完全的尖晶石相和团聚现象不很明显的镁铝尖晶石粉体.     

非化学计量比镁铝尖晶石粉体的制备及性能

将异丙醇镁铝双金属醇盐滴加到含有5%(质量分数)EDTA分散剂的水解液中,制得镁铝氢氧化物无色透明溶胶,后经干燥、高温焙烧得到非化学计量比的铝镁尖晶石粉体。研究了Mg/Al摩尔比、焙烧温度、干燥工艺流程以及助溶剂的添加对粉体材料性能影响。结果表明:Mg/Al摩尔比在1.0:(2.5～4.0)范围内,1 200℃焙烧后对应粉体为纯相镁铝尖晶石结构,随铝含量增加,衍射峰向大角度方向偏移,且粉体颗粒粒径逐渐增大,Mg O·1.25Al_2O_3粉体红外透过率较高,可潜在应用于红外隐身等材料。     

溶胶-凝胶法制备纳米氧化镁

以六水硝酸镁为前驱体，采用柠檬酸溶胶-凝胶法合成不同粒径（10～100nm）和结晶度的纳米氧化镁粉末。研究了柠檬酸的作用机理，不同的工艺条件（水、无水乙醇、柠檬酸的加入量）对溶胶-凝胶稳定性的影响以及焙烧温度对粉末晶体粒径、结晶度的影响。结果表明：未引入柠檬酸时，凝胶的稳定性较差，氧化镁产物粒径较大且团聚严重。     

纳米级镁铝尖晶石粉末的合成新方法

总结了关于热处理气氛对于应用溶胶-凝胶拧檬酸法合成纳米级镁铝尖晶石粉末的影响。以BET特定表面积测蹙方法、晶粒尺寸、同步热分析以及微观观察为基础,在对先驱物进行热处理时使用氩气气氛会明显的减小合成陶瓷粉末的晶粒尺寸。与空气气氛中进行的热处理相比,在柠檬酸中残留的含碳材料在阻碍颗粒烧结方面发挥了很重要的作用。在氩气气氛下进行缓慢的加热为获得尺寸为5-7nm的纳米级镁锅尖晶石粉末提供了机会。本文所述的新方法经氩气处理利用溶胶-凝胶泞檬酸法合成尺寸在20～100nm的纳米级镁锅尖晶石粉末会遇到突然加热的问题。     

Fabrication of MgAl2O4 Spinel Scaffolds and Sonochemical Synthesis and Deposition of Hydroxyapatite Nanorods

Hydroxyapatite (HAp) is one of the most emerging biocompatible ceramic widely used as scaffolds in various biomedical applications such as orthopedics and dentistry. In spite of the superior properties for biomedical applications, they exhibit poor mechanical properties. This has lead to the concept of fabricating composite out of bioactive and bioinert material to derive bioactivity in combination with desirable mechanical properties. In this study, bioinert magnesium aluminate (MgAl₂O₄) spinel scaffolds are prepared through polymeric foam replication process followed by sintering. Sintered foams have exhibited good structural integrity and the stress–strain curves recorded during the uniaxial compression have shown a plateau indicating high‐energy absorption capability. Sonochemical process has been employed for the simultaneous synthesis and deposition of HAp formulation from the stoichiometric solution of precursors on the spinel scaffolds. Sonochemical process has resulted in the formation of phase pure HAp with unique morphology of nanorods coated throughout the three‐dimensional foam structures. Cytotoxicity evaluation of this new scaffold material has not shown any alteration in the viability, growth, and morphology of the cells. The new scaffold material thus developed is expected to have high potential for biomedical applications.     

溶胶凝胶法制备尖晶石LiMn2O4合成条件的研究

采用溶胶凝胶合成法制备尖晶石LiMn2O4锂离子电池正极材料,详细研究了合成条件对产物结构和电化学性能的影响。结果表明,在以LiBr为Li源,乙酸锰为锰源,溶胶凝胶法制备尖晶石锂锰氧的最佳工艺条件是:Li/Mn=1.05/2;合成时溶液pH=7.5;采用分段式升温,以8℃/min从室温升温到450℃,保温5小时;再5℃/min的升温速率升温到650℃,再恒温12小时,然后自然冷却到室温,可得到结晶度较高,晶体结构完整,电化学性能较好的尖晶石型LiMn2O4。     

微波辅助溶液燃烧法制备MgAl_2O_4粉体

将硝酸镁、硝酸铝、尿素按物质的量比为1 2 6.66制得透明混合前驱液,用低温燃烧技术与微波加热技术相结合的方法制备了高纯度、低团聚的镁铝尖晶石(MgAl2O4)粉体。研究了燃烧反应过程中,微波输出功率(200、400、600、700 W)对Mg Al2O4粉体晶体结构、形貌及比表面积的影响。结果表明:微波高效加热方式导致燃烧反应瞬间产生大量气体,促进了Mg Al2O4超细颗粒的形成。同时,随着微波输出功率的增加,尿素氧化加速,利于MgAl2O4晶粒的生长发育。在微波功率700W,微波时间2 min的条件下,可制备结晶完整,粒度分布均匀(平均晶粒尺寸为56.03 nm)的Mg Al2O4粉体。     

Role of Fuel on Cation Disorder in Magnesium Aluminate (MgAl2O4) Spinel Prepared by Combustion Synthesis

Magnesium aluminate spinel (MgAl₂O₄) forms an interesting system having tetrahedral and octahedral voids filled with near similar sized divalent Mg²⁺ and trivalent Al³⁺ cations. Structural disorder (e.g., Mg–Al antisite defects) can be tuned by synthetic conditions. This study reports the evolution of Mg/Al disorder in MgAl₂O₄ prepared by combustion synthesis using different types of fuels. The effect of nature of fuel and the final calcination temperature (600°C–900°C for 9 h) on degree of cation ordering has been investigated combining powder X‐ray (XRD) and neutron (NPD) diffraction. The results indicate very high degree of inversion in the samples crystallized at low annealing temperature, which on further annealing reduces toward the thermodynamically stable values. Raman spectroscopy, probing MgO₄, and AlO₄ tetrahedral bonds, confirmed the results at a local level.     

Synthesis of MgAl2O4 Whiskers by an Oxidation-Reduction Reaction

Magnesium aluminate whiskers were synthesized by an oxidation—reduction reaction between MgO, C, and Al in a CO and CO₂ atmosphere. The oxygen partial pressure suitable for MgAl₂O₄ whisker growth ranged from 10^−12.1 to 10^−11.5 MPa. The average whisker diameter and length formed at 1500°C for 8 h were ∼3.1 μm and ∼4 mm, respectively. The whiskers grew in the [111] direction.     

Electrochemical Impedance Spectroscopy of Transparent Polycrystalline Magnesium Aluminate (MgAl2O4) Spinel

Transparent polycrystalline magnesium aluminate spinel is one of few materials capable of fulfilling certain demanding optical applications. However, LiF additive typically required to enhance sintering and impart transparency also degrades mechanical properties and causes scatter, precluding wider application. To shed light on the cause of altered properties, electrochemical impedance spectroscopy was performed between 500°C and 900°C, in oxidizing and reducing atmosphere, on fully dense, polycrystalline spinel compacts hot‐pressed with and without LiF. In combination with electron microscopy, chemical analysis, and secondary‐ion mass spectroscopy, bulk and grain‐boundary dielectric behavior were related to microstructure and chemistry. Decades higher conductivity than for comparable single crystals correlated with Al₂O₃‐rich stoichiometry, impurities, and small grain size, and suggested increased conduction and current‐line detouring along Mg‐depleted, impurity‐rich, field‐parallel grain boundaries. LiF addition reduced conductivity by one decade and increased the activation energy for conductivity, attributed to impurity removal, larger grain size, and point defects caused by lithium incorporation.     

透明MgAl2O4晶须的制备与表征

本文采用MgO粉和金属Al粉为原料,在氮气气氛下制备MgAl2O4晶须,研究了TiO2、SiO2或Cr2O3等供氧添加剂和制备条件对晶须合成率的影响并分析了晶须的物相组成和结构.结果表明:最佳MgO/Al=2/3;添加SiO2或Cr2O3不利于晶须合成;添加TiO2对合成晶须有促进作用,最佳TiO2加入量为40%;采用氧化铝坩埚比采用釉面陶瓷坩埚好,最佳保温时间为6 h.合成的晶须为MgAl2O4,空间群Fd3M,晶格常数a=b=c=0.8083 nm,MgO 28.3%,Al2O3 71.7%;晶须呈透明柱状,最大长度为20～30 mm,长径比20～400.     

Synthesis and characterization of nano MgAl2O4 spinel by the co-precipitated method

Magnesium aluminate (MgAl₂O₄) spinel powders were prepared by co-precipitation of stoichiometric amounts of magnesium and aluminum chlorides at 80 °C. Some sintering aids such as ZnO and MnO₂ were added in the form of chlorides during the precipitation to study their effect on densification. The co-precipitated materials were a mixture of Mg–Al double hydroxide with the presence of few amounts of gibbsite and brucite. After heat-treatment of the precipitated powders up to 1000 °C, a crystalline spinel powder was obtained. The presence of 0.5, 1, 2 and 3 wt.% of ZnO or MnO₂ as sintering aids increased sinterability after firing up to 1550 °C. The highest density was obtained for the samples containing 2 wt.% ZnO or 3 wt.% MnO₂ which reached about >94 and 96% theoretical density (TD), respectively. The mechanical properties increased by adding ZnO or MnO₂, an exception being the sample containing 0.5 wt.% of ZnO for which relatively smaller value were obtained.