钙辅助溶胶-凝胶碳热还原法合成超细氮化铝粉体

以硝酸铝、葡萄糖和硝酸钙为原料,通过溶胶-凝胶工艺获得了组分均匀的Al2O3、C和CaO前驱体,进而利用碳热还原反应合成超细氮化铝粉体,探讨了钙助剂对氮化铝合成温度及粉体颗粒生长的影响规律。结果表明：钙助剂的添加,通过与前驱体中氧化铝在较低温度下发生反应,先后生成CaAl4O7、Ca3Al10O18、CaAl2O4和Ca12Al14O33等铝酸钙相;上述铝酸钙相能在较低温度下形成液相,可有效促进氮化铝的合成和粉体颗粒的生长,从而在1400 ℃合成纯相氮化铝。当原料中钙铝摩尔比为0.0262时,在1350 ℃氮化得到了粒径60-80 nm的氮化铝粉体,仅有少量铝酸钙相存在;当氮化温度上升至1400 ℃时,铝酸钙相因挥发而消失,得到粒径100-180 nm的单相氮化铝粉体。     

Effect of Ca-compound on low temperature synthesis of AIN ultrafine powders by carbothermal reduction nitride route from sol-gel precursor

以硝酸铝、葡萄糖和硝酸钙为原料,通过溶胶-凝胶工艺获得了组分均匀的Al2 O3、C和CaO前驱体,进而利用碳热还原反应合成超细氮化铝粉体,探讨了钙助剂对氮化铝合成温度及粉体颗粒生长的影响规律.结果表明:钙助剂的添加,通过与前驱体中氧化铝在较低温度下发生反应,先后生成CaAl4 O7、Ca3 Al10O18、CaAl2 O4和Ca12Al14O33等铝酸钙相;上述铝酸钙相能在较低温度下形成液相,可有效促进氮化铝的合成和粉体颗粒的生长,从而在1400℃合成纯相氮化铝.当原料中钙铝摩尔比为0.0262时,在1350℃氮化得到了粒径60～80 nm的氮化铝粉体,仅有少量铝酸钙相存在;当氮化温度上升至1400℃时,铝酸钙相因挥发而消失,得到粒径100～180 nm的单相氮化铝粉体.     

制备高纯度α-Al_2O_3粉体的工艺研究

以硝酸铝和碳酸铵为原料,采用化学沉淀法,在不同硝酸铝浓度下制备Al2O3的前驱体Al(OH)3,再经不同温度煅烧得到Al2O3粉体。利用TG-DTG、XRD、BET及SEM等分析手段对粉体的性能进行了表征。结果表明,煅烧温度对Al2O3的晶型有着重要的影响,硝酸铝浓度为0.1 mol/L时制备出的粉体分散性较好,经1 200℃煅烧能制备出纯度较高的形貌类似球形的α-Al2O3粉体。     

薄水铝石粒度对煅烧形成α-Al2O3粉体的影响

研究了薄水铝石粒度对其煅烧形成α-Al2O3粉体的影响.先用水热法制备出均匀分散的纳米、亚微米及几个微米的薄水铝石前驱体,用x射线衍射仪和电子显微镜分析了薄水铝石在不同温度煅烧所得产物的相结构及形貌.结果表明,粒度30～100 nm的薄水铝石在1200℃煅烧1 h转变为α-Al2O3,为蠕虫状的烧结颗粒;粒度0.4～0.6 μm的薄水铝石在1 250℃煅烧1 h可转变为α-Al2O3,颗粒尺寸变化不大,仍在0.4～0.6 μm范围内;粒度1 μm左右的薄水铝石在1350℃下煅烧2 h尚不能完全转变为α相,并已出现明显烧结.因此,以水热法制备的亚微米级薄水铝石晶体作为前驱体,经直接煅烧可以制备出分散性较好的亚微米级α-Al2O3粉体.     

络合溶胶-凝胶法制备Al_2O_3纳米晶及其表征(英文)

以异丙醇铝为原料,用聚乙二醇(PEG1000)络合溶胶-凝胶法合成了Al2O3纳米晶,并采用差热-热重分析、X射线衍射、透射电子显微镜等对络合前驱体及粉体进行表征;探讨了PEG1000及煅烧温度对纳米Al2O3相结构、粒子尺寸、形貌及分散性的影响规律.结果表明:PEG1000增强了纳米Al2O3粒子的分散性.干凝胶在600～900℃煅烧后得到γ-Al2O3相;在600℃煅烧条件下,得到γ-Al2O3粒子形貌为针状结构,长度约为50～60nm.随着煅烧温度的升高,γ-Al2O3针状粒子长度逐渐减小,在750℃煅烧后,得到γ-Al2O3粒子长度为20～30nm;在900℃煅烧条件下,γ-Al2O3粒子形貌为颗粒状,平均粒径尺寸为10nm;当干凝胶在1 000℃煅烧后得到θ-Al2O3和α-Al2O3的混合相,所得粒子平均粒径尺寸为20 nm;当干凝胶在1 200℃煅烧后,得到的Al2O3全部转化α-Al2O3相,制得的纳米Al2O3粒子尺寸均一且分散性良好.     

醇-水法制备Al2O3-ZrO2复合粉体及其表征

以Al(OH)3和ZrOCl2·8H2O为起始原料,以NH4HCO3为沉淀剂,在醇-水混合溶液中获得前驱体,将前驱体在空气中煅烧,制备了Al2O3-ZrO2复合粉体.探讨了不同煅烧温度对Al2O3-ZrO2复合粉体的物相组成和显微形貌的影响.采用综合热分析仪、X-射线衍射仪、扫描电镜等手段对粉体进行表征.结果表明:前驱体中含锆化合物主要以无定形的形式存在,当煅烧温度为600℃时,粉体中出现较强的t-ZrO2衍射峰,Al(OH)3的衍射峰肖失.当煅烧温度增加到1200℃时,粉体中主要存在α-Al2O3和t-ZrO2主晶相衍射峰.前驱体经600℃热处理后所制备的Al2O3-ZrO2复合粉体粒度分布均匀且大多数颗粒在50 ～ 100 nm之间;随着煅烧温度的升高,Al2O3-ZrO2复合粉体颗粒出现长大,且其显微形貌由球状颗粒为主逐渐向球状、片状以及短棒状等多样化结构过渡.     

溶胶-凝胶燃烧法合成Cr~(3+):Al_2O_3纳米粉体

采用溶胶-凝胶燃烧法合成出Cr3+:Al2O3纳米粉体.将所制成的干凝胶加热至约500℃使之发生燃烧反应,再将燃烧产物在不同的温度下进行锻烧.利用热重-差热分析、X射线衍射(X-ray diffraction,XRD)、透射电子显微镜(transmission electron mictoscope,TEM)等对干凝胶及煅烧粉体进行表征,测试了纳米粉体的发光性能.研究了合成条件对粉体分散性、发光性能的影响.XRD和TEM分析表明:在1000℃煅烧1h后,粉体为α-Al2O3结构的单相氧化物粉体,颗粒大小为20～35nm.在制备溶胶时添加聚乙二酵可提高粉体的分散性.光谱分析表明:Cr3+:Al2O3纳米粉体的激发峰位于404nm和540nm,发射峰值位于692nm和668nm.     

铝、铝硅溶胶及其粉末的合成

以硝酸铝为铝源、硅溶胶为硅源、柠檬酸为稳定剂,采用溶胶凝胶法制备出了稳定的铝溶胶及铝硅溶胶,分析了硝酸铝与柠檬酸的摩尔比(N/C比)、反应温度、保温时间对铝溶胶形成的影响,确定N/C比3:1、100℃及保温1h是铝溶胶较优的工艺参数。XRD分析表明,经1200℃煅烧2h后,铝凝胶粉转变成了α-Al2O3晶相,铝硅凝胶粉末经1200℃煅烧2h后,样品主要为正交莫来石结构,SEM显示所得粉末为无规则形态。     

溶胶-凝胶燃烧法制备SmBO3粉体的工艺条件及其光吸收性能

研究了溶胶-凝胶燃烧法制备SmBO3前驱体过程中的各种影响因素,考察了煅烧温度及煅烧时间对所合成的SmBO3粉体光吸收性能的影响. 结果表明,当加热温度为80℃、H2O/(Sm+B)摩尔比为30、pH值为2、柠檬酸/(Sm+B) 摩尔比为1:1时获得的凝胶在180℃下发生稳定的自燃烧反应,得到白色蓬松的前驱体. 前驱体经750℃煅烧2 h后得到的SmBO3粉体平均颗粒尺寸为100 nm. 在1.05~1.15 mm波长范围,SmBO3粉体对光存在较强的吸收,在1.07 mm波长附近反射率达最低值,约为0.41%,而在1.06 mm波长处反射率约为0.6%.     

纳米Al2O3粉体的热处理工艺参数的优化

以醇铝溶胶-凝胶法制得的水合氧化铝粉为实验原料,通过正交设计,运用(L934)正交表安排热处理实验对水合氧化铝进行热处理,制备具有不同颗粒特性纳米氧化铝粉体,探讨热处理工艺参数对纳米氧化铝颗粒特性的影响规律,优化纳米氧化铝的热处理工艺参数。结果表明:热处理工艺是影响纳米氧化铝颗粒特性的一个重要因素。热处理工艺参数对Al2O3粒子颗粒特性的影响由强到弱的次序为:煅烧温度、煅烧温度点的保温时间、水合氧化铝300℃分解温度点的保温时间;通过控制其热处理工艺参数,可获得一定尺寸范围内的大小均匀、分散性好的球形γ-Al2O3粉体;制备尺寸为8nm的球形γ-Al2O3粉体的最佳的热处理工艺参数为:煅烧温度900℃,煅烧温度点保温4h,300℃温度点不保温。     

Boehmite coating on θ-Al2O3 particles via a sol–gel route

θ-Al₂O₃ powders in slurry form were coated by boehmite nanoparticles prepared from alumina sol that consists of aluminum tri-sec-butoxide (Al(OC₄H₉)₃) as a precursor. The θ-Al₂O₃ powders presented an iso-electrical point (IEP) at pH ∼ 9.2, and formed stable suspensions without notable gravity settling at acidic conditions (pH 3–4). Boehmite nanoparticles with a mean particle size ca. 68 nm were derived from the hydrolysis of Al(OC₄H₉)₃ sol. Well-dispersed boehmite/θ-Al₂O₃ aqueous mixtures consisting of 3 and 9 wt.% of boehmite were then prepared by addition of θ-Al₂O₃ powder into the Al(OC₄H₉)₃ sol followed then by vigorous agitation at 90 °C and in a pH range 3–4. IR and particle-size measurement both revealed possible coating of boehmite on the θ-Al₂O₃ particles. From TEM observation, “thickness” of the boehmite layer did not vary much with the boehmite concentration. Agglomeration of the particles became nonetheless apparent as the boehmite concentration was increased. The boehmite coating on θ-Al₂O₃ surface inhibited grain growth during the θ- to α-phase transformation upon heating. Mean grain size of the boehmite-coated alumina was substantially smaller than that of the un-coated one.     

Methods and Approaches of the Sol–Gel Technology for the Surface Modification of Aluminum Oxide Powders

The results of studies, sol–gel synthesis, and the sedimentation stability of complex multicomponent sol–gel systems of the “silica sol modified with Co(NO₃)₂ · 6H₂O, Al(NO₃)₃ · 9H₂O with α-Al₂O₃ or γ-Al₂O₃ as highly dispersed filler” type are generalized. The physical–chemical processes accompanying the formation of modifying layers on the powder oxide particles are examined. The promising prospects of applying α-Al₂O₃ powders modified with a silicate layer of the composition (wt %) 1.2K₂O · 3Al₂O₃ · 3.2CaO · 12.5Na₂O · 28.1B₂O₃ · 52SiO₂ in the fabrication of ceramic materials with improved strength characteristics are demonstrated.     

Sol–gel derived alumina–hydroxyapatite–tricalcium phosphate porous composite powders

In this study, alumina–hydroxyapatite–tricalcium phosphate (α-Al₂O₃–HA–TCP) porous composite powders were produced and characterized. At first, boehmite sol (AlOOH) was obtained via sol–gel process by using aluminium isopropoxide (Al(OC₃H₇)₃) as the starting material. Bovine hydroxyapatite (BHA) powders derived from deproteinized bovine bones were added as 10, 20, 30 and 50% weight of the starting material to each boehmite sol. Also Na-alginate was added to the boehmite sol as the dispersive agent. Subsequently, gelation for 3 h at 110 °C was applied to each sol mixture. Finally, gelated samples were heat treated for 2 h at 500, 800, 1000 and 1300 °C. DTA–TGA, XRD, FTIR and SEM-EDS analyses were used to characterize the obtained composite powders composed of α-Al₂O₃–HA–TCP phases. In order to investigate porosity properties, powders were pressed with hydraulic manual press and formed into pellets. Later these pellets were sintered for 2 h at 1300 °C. Apparent porosity and bulk density tests were applied to the pellets. The evaluation of these tests results indicate that a novel α-Al₂O₃–HA–TCP composite material with ～38–44% apparent porosity has been produced.     

Properties of sol–gel derived Al2O3–15 wt.% ZrO2 (3 mol% Y2O3) nanopowders using two different precursors

An alumina–15 wt.% zirconia (3 mol% yttria) nanopowder was synthesized by sol–gel method using salt and alkoxide as precursors. Al(NO₃)₃·9H₂O, ZrOCl₂·8H₂O and Y(NO₃)₃·6H₂O were used as salt precursors and Al(OC₄H₉)₃ and Zr(OC₄H₉)₄ were used as alkoxide precursors. The dried gels of two precursors were heat treated in the range of 450–1350 °C. The powders produced by alkoxide precursors calcined at 750 °C were in the range of 15–75 nm, while those prepared by salt precursors had the size in the range of 30–90 nm. The former powders had a higher surface area and smaller mean pore diameter compared with the later powder, i.e. 152 m²/g and 5.63 nm comparing with 121 m²/g and 9.79 nm, respectively. Therefore phase transformation in the former occurred in lower temperatures.     

Preparation and characterization of cordierite powders

The current paper presents different preparation methods for cordierite ceramic powders: solid state reactions and wet preparation. In the solid state method, γ-Al₂O₃, SiO₂ and Mg(CO₃)₂ were used as raw materials. For wet preparation, the following compounds were used as precursors: silica gel, AlCl₃·6H₂O and Mg(NO₃)₂·6H₂O. The powders obtained by the different methods employed were characterized in what concerns mineralogical composition and granulometric distribution. It was determined that the results are influenced by the nature of raw materials used and the processing conditions.     

Phase Formation and Enhanced Dielectric Response of Y2/3Cu3Ti4O12 Ceramics Derived from the Sol–Gel Process

Y_2/3Cu₃Ti₄O₁₂ (YCTO) ceramics were successfully synthesized by sol–gel method (SG) and solid‐state method (SS), respectively. The optimized processing parameters for the syntheses of precursor powders by sol–gel process were determined as follows: the Ti(OC₄H₉)₄ concentration was 0.50 mol/L, the CH₃COOH volume was 8 mL, and the volume percentage of H₂O was 11.2%. Particularly, on the basis of XRD and TG‐DSC analyses, the phase formation temperature of YCTO‐SG was at least 100°C lower than that of YCTO‐SS. YCTO‐SG ceramics sintered at 1060°C for 25 h showed fine‐grained microstructure, and higher dielectric constant (ε′ ≈ 5.24 × 10⁴) at 1 kHz compared to YCTO‐SS ceramics (ε′ ≈ 0.93 × 10⁴). The higher dielectric constant of the YCTO‐SG ceramics was attributed to the grain size effect. Furthermore, the YCTO‐SG ceramics showed a distinct high‐temperature (>300°C) relaxor‐like behavior. According to the calculated activation energy value, the single ionization of oxygen vacancies was responsible for the conduction and dielectric anomaly behaviors of YCTO‐SG ceramics.     

Study on α-alumina precursors prepared using different ammonium salt precipitants

Nano-sized α-Al₂O₃ platelets have been produced by the precipitation method employing the starting material of Al(NO₃)₃·9H₂O and ammonium salt precipitants, such as the NH₄OH, (NH₄)₂CO₃ and NH₄HCO₃. The effects of chemical composition of ammonium salt precipitants and aging time of precipitated product on the formation of precursor and final product of α-Al₂O₃ particles were studied. The precursors with different crystal structures were formed depending on the chemical composition of precipitant and the agglomeration of final α-Al₂O₃ particles was found to be greatly affected by the precipitant. The aging time of precipitated precursor also influenced the agglomeration of final α-alumina particles.     

Morphology control of α-Al2O3 platelets by molten salt synthesis

It is of great importance to control the morphology of α-Al₂O₃ plate-like powders since α-Al₂O₃ platelets with different shapes are needed in various applications. This paper was focused on how to control the morphology of α-Al₂O₃ platelets by molten salt synthesis. Results show that the morphology of α-Al₂O₃ platelets is affected by the heating temperature, heating time, the molten salts species, the weight ratio of salt to powders, additives and the addition of nano-sized seeds. Especially, it is very effective to control the morphology of α-Al₂O₃ platelets by adjusting the addition of additives such as Na₃PO₄·12H₂O and TiOSO₄. α-Al₂O₃ flakes with irregular shape are obtained by the addition of Na₃PO₄·12H₂O, while thick α-Al₂O₃ particles with hexagonal shape are obtained by the addition of TiOSO₄. The combination addition of Na₃PO₄·12H₂O and TiOSO₄ makes it possible to obtain thin α-Al₂O₃ platelets with discal shape. A small amount of nano-sized seeds addition also has a strong effect on the size of α-Al₂O₃ platelets. However, if the seeds are added too much, the overlapping and abnormal crystal growth of α-Al₂O₃ platelets occur, and the size distribution becomes nonuniform. The effect mechanism of additives and seeds on the morphology of α-Al₂O₃ platelets was also discussed in this paper.     

硼酸盐热力学基元贡献模型及在MgBO2(OH)纳米晶须水热合成过程分析中应用

以MgCl₂·6H₂O、H₃BO₃、NaOH为原料,控制摩尔比Mg:B:Na=2:3:4,经室温共沉淀及水热转化(220～240℃,6.0～30.0 h)制得了单斜相MgBO₂(OH)纳米晶须。借鉴机械混合模型、基团贡献法思想,根据质量守恒原则将硼酸镁盐按照复盐分子式进行基元拆分,通过引入校正因子k,利用复盐基元的基础热力学数据拟合建立了Δ_fH_m及Δ_fG_m等硼酸盐热力学基础数据估算的基元贡献模型,估算了共沉淀产物Mg₇B₄O₁₃·7H₂O及水热产物MgBO₂(OH)不同温度下的Δ_fH_m、Δ_fG_m热力学数据,得到了25～100℃下共沉淀反应及25～250℃下水热转化的Δ_rH_m、Δ_rG_m。结果显示,共沉淀反应在室温条件下可自发进行,水热转化须借助一定温度条件方能自发实现,且反应趋势随水热温度升高时间延长而增大。该热力学基元贡献模型有望为其他结构复杂复盐化合物纳米结构的湿化学法控制合成分析及预测提供借鉴。     

Ethylene polymerization with heterogeneous Ziegler-Natta catalysts

Summary TiCl₄/SiO₂, Ti(OC₄H₉)₄/SiO₂, MgCl₂/TiCl₄/SiO₂ and MgCl₂/Ti(OC₄H₉)₄/SiO₂ catalysts were prepared by treating silica gel with TiCl₄, Ti(OC₄H₉)₄, MgCl₂/TiCl₄ or MgCl₂/Ti(OC₄H₉)₄ in tetrahydrofuran (THF) solution. Ethylene polymerization was performed with these catalysts activated by common alkylaluminum compounds. The influence of magnesium dichloride on catalyst performance was investigated. MgCl₂ has enhanced the catalyst activity for both titanium compounds. In addition, all catalyst systems were only active when they were washed with AlCl(C₂H₅)₂ (DEAC).