水热法制备超细球形氧化铝粉体

以较为经济的水合硫酸铝为铝源,尿素为沉淀剂,利用水热法在内胆为聚四氟乙烯的水热釜中制备氧化铝前驱体,然后将烘干后的前驱体进行高温煅烧,制得超细球形氧化铝粉体。重点探究了水热反应温度、反应时间对产物微观形貌及粒度的影响,并对氧化铝粉体煅烧前后的微观形貌进行了对比。实验结果表明:前驱体的形貌具有遗传性;在水热反应温度120℃,反应时间2 h时,煅烧温度1200℃,煅烧时间为2 h,得到了成球率99.9%、球平均粒径1.61μm、分散性好的球形氧化铝粉体。     

YAG超细粉体的制备与表征

以Y2O3、Nd2O3、Al(NO3)3·9H2O、(NH4)2SO4为原料,分别采用碳酸氢铵和碳酸铵两种沉淀剂,通过共沉淀法制备了YAG超细粉体.采用热重-差热分析(TG-DTA)与红外光谱(IR)对前驱体进行分析研究.对不同温度下煅烧的粉体进行X射线衍射(XRD)与透射电镜(TEM)分析.研究结果表明:采用碳酸氢铵作为沉淀剂得到的前驱体经1000 ℃煅烧可获得纯YAG相,颗粒尺寸为60～150 nm;而采用碳酸铵作为沉淀剂得到的前驱体经900 ℃煅烧即可获得纯YAG相,颗粒尺寸较小,约为40～50 nm,具有良好的分散性.     

化学共沉淀法制备Yb:YAG纳米粉体的研究

以碳酸氢铵或氨水为沉淀剂,采用化学共沉淀法制备Yb:YAG透明陶瓷纳米粉体,利用扫描电镜、X射线衍射对粉体的形貌和物相结构进行表征。研究表明:以碳酸氢铵为沉淀剂制备的前驱体在1 200℃煅烧后可制得无杂质的YAG(Y3Al5O12)粉体,以氨水为沉淀剂制备的前驱体在1 200℃煅烧后制得的YAG粉体中有杂质相YAM(Y4Al2O9);以碳酸氢铵为沉淀剂制备的YAG粉体的分散性好,碳酸氢铵溶液与母盐溶液中铝离子浓度最佳配比为10∶1,粉体粒度在100~250 nm。     

沉淀法制备纳米α-Al2O3的工艺

利用硝酸铝溶液和碳酸铵溶液的沉淀反应制备一种氧化铝的前驱体-氢氧化铝。研究了pH值、溶液浓度、分散剂用量对纳米氧化铝粒径的影响。用差热、透射电子显微镜、比表面、激光粒度分析仪等测试手段对产物进行分析。结果表明，当反应温度45℃、pH=5．0、分散剂用量为1．0％（质量百分数）、铝盐浓度为0．1mol／L时，制得的产物经800℃煅烧1．0h，颗粒大小为5—10nm；在1210℃煅烧1．0h可转化为α-Al2O3，一次粒子粒径为40nm左右。     

液相共沉淀法合成浸渍阴极用Ba5CaAl4O12

Ba5CaAl4O12是浸渍阴极电子发射最主要的活性物质。采用液相共沉淀法，通过调节共沉淀反应的金属盐溶液浓度、溶液的pH、沉淀剂的加入方式及洗涤方式，制备出分散良好的超细碳酸钡、碳酸钙、氢氧化铝的混合前驱体粉末，经1200℃煅烧2h，得到超细粉末。采用XRD，SEM分析产物粉末的物相组成、颗粒形貌，结果表明产物为具有Ba5CaAl4O12结构的结晶颗粒，粒径在0．2～0.5μm。     

以硫酸镁为原料制备氧化镁晶须的工艺研究

以硫酸镁为原料、碳酸铵为沉淀剂,首先通过沉淀结晶反应制得三水碳酸镁等前驱体,再经过滤、干燥和煅烧工序制得氧化镁晶须。研究反应温度、反应物物质的量比、碳酸铵的滴加速率以及硫酸镁初始浓度对前驱体晶须生长及晶形的影响,采用XRD和SEM对前驱体和最终所得晶体进行表征。结果表明：反应温度、反应物物质的量比、碳酸铵的滴加速率以及硫酸镁初始浓度对三水碳酸镁的生长、形态及颗粒大小都有显著的影响,通过实验优化了最佳工艺条件。由此推测晶须的产生和生长机制是各个晶面按螺旋位错规律生长的液-液-固（L-L-S）机理。     

前驱体预处理及卤化铵添加剂对α-氧化铝微粉颗粒形貌的影响

以工业氢氧化铝为前驱体,通过X射线衍射(XRD)和扫描电镜(SEM)分析方法,研究了前驱体经轻烧再经球磨预处理的物相转变及形貌演变,并进一步研究了在预处理后的前驱体中添加氟化铵、氯化铵以及氟化铵和氯化铵的复合物后,经过高温煅烧所得α-氧化铝的颗粒形貌演变规律。实验结果表明:前驱体经650℃轻烧再经3 h球磨,所得样品主要物相为γ-氧化铝,样品由颗粒尺寸小于10μm的不规则片状颗粒组成,其中包含大量尺寸小于1μm的不规则颗粒;预处理后的前驱体经1 400℃煅烧2 h,所得样品为α-氧化铝,蠕虫状空间网络结构得到部分抑制;在预处理后的前驱体中加入1%氟化铵(质量分数)时,在相同条件下煅烧所得样品为粒度分布在1μm左右的片状α-氧化铝,但片状结构尚不规则,粒度分布也不均匀;在预处理后的前驱体中加入1%氯化铵(质量分数)时,对α-氧化铝的颗粒形貌影响不大,所得样品形貌与无添加剂时类似,但初始晶粒尺寸略显细化;与单一加入1%氟化铵(质量分数)相比,在预处理后的前驱体中加入0.5%氟化铵(质量分数)和0.5%氯化铵(质量分数)复合添加剂时,促使片状α-氧化铝转变为圆饼状α-氧化铝,且粒度分布更为均匀,绝大部分圆饼状颗粒尺寸分布在1μm左右。     

钇稳定纳米氧化锆的制备工艺研究

用溶胶-凝胶法制备了钇稳定纳米氧化锆(YSZ),系统研究了沉淀剂滴加方式、锆离子浓度、溶剂、干燥方式和煅烧温度对产物性能的影响,并采用FT-IR、TG-DSC、XRD、SEM等对前驱体干凝胶粉末和产物进行了表征。结果表明：以水作溶剂,采用正加方式,选择锆离子浓度为0.5 mol/L,真空干燥,550 ℃煅烧2 h,可得到粒径为39 nm左右、组分为单一四方相的YSZ粉体。     

沉淀法制备Nd：Y2O3纳米陶瓷粉体及性能表征

以硝酸钇和硝酸钕为起始原料，分别以碳酸氢铵、尿素和草酸铵为沉淀剂，采用反滴的方式，通过控制滴定速度和PH值等条件，沉淀法制得前驱体粉料。前驱体经去离子水洗一无水已醇洗涤一去离子水洗可提高Y2O3粉体活洗。研究结果表明：选用不同沉淀剂，煅烧所得Y2O3粉末都跟标准的Y2O3粉末的XRD图谱吻合，只是由于结晶度的不同而表现出峰值强度的不同。不同沉淀剂对煅烧后所得Y2O3粉末的形貌影响显著。碳酸氢铵、草酸铵作为沉淀剂所得粉体的团聚现象较严重，颗粒之间产生部分烧结颈。所得粉体为片层状。尿素溶液作为沉淀剂时，粉体分散较好，但粒度分布很宽，有大颗粒存在，所得粉体接近球形。     

纳米Fe_2O_3/壳聚糖复合微球的制备

以硫酸铁铵为原料,尿素为均匀沉淀剂,采用均匀沉淀法合成具有实用价值的纳米氧化铁。在Fe~(3+)浓度为0.2mol·L~(-1),尿素为0.3mol·L~(-1),95℃下反应4h,300℃下煅烧3h,得砖红色Fe_2O_3磁性粉末,颗粒均匀分散,方法简单,易于工业化生产。     

10-mol%-Gd2O3-Doped CeO2 Solid Solutions via Carbonate Coprecipitation: A Comparative Study

10mol% Gd₂O₃-doped CeO₂ solid solutions (20GDC) have been synthesized via carbonate coprecipitation using ammonium bicarbonate (AHC) and urea as the precipitants. The precursors and the resultant oxide powders were characterized via chemical analysis, X-ray diffractometry (XRD), Brunauer–Emmett–Teller (BET) analysis, and high-resolution scanning electron microscopy (HRSEM). Sinterabilities of the 20GDC oxides in air were studied by constant-rate-of-heating (CRH) sintering and the conventional ramp-and-holding sintering methods. The precursor processed by both methods is hydroxyl carbonate but shows quite different particle morphologies in the two cases. Highly sinterable 20GDC oxides that can be densified to >99% of the theoretical at 1050°C within 4 h have been obtained via the AHC method.     

不同碳酸盐沉淀剂热分解法制备纳米氧化锌

以硝酸锌为锌源,分别以碳酸钠和碳酸氢铵为沉淀剂,采用热分解碱式碳酸锌工艺制备纳米氧化锌。通过热重分析、晶型测试、平均粒径测试、微观形貌观察等系列对比,分析了以两种碳酸盐为沉淀剂制备氧化锌的过程,建立了生长动力学方程,对比了微观形貌和分散状态。实验结果表明,以碳酸氢铵为沉淀剂制备的前驱体在煅烧温度为200 ℃后直接生成纳米氧化锌,而以碳酸钠为沉淀剂制备的前驱体在煅烧温度为200~250 ℃时先生成碳酸锌然后在300 ℃时完全转变为氧化锌;两种沉淀剂制备纳米氧化锌的生长过程符合不同指数方程生长关系,以碳酸钠为沉淀剂制备纳米氧化锌的生长满足方程y=2.775 04e^{0.004 76x},而以碳酸氢铵为沉淀剂制备纳米氧化锌的生长满足方程y=5.152 96e^{0.002 85x},对比来看以碳酸氢铵为沉淀剂制备纳米氧化锌在相同温度下得到的晶粒尺寸要小;从粒度分布和透射电镜观察分析,在相同温度下也是以碳酸氢铵为沉淀剂制备的纳米氧化锌的粒径较小。     

Single step hydrothermal synthesis of 3D urchin like structures of AACH and aluminum oxide with thin nano-spikes

3D urchins like ammonium aluminum carbonate hydroxide (AACH) nanostructures with nano-spikes of dia. 20–30 nm were synthesized by a simple, single step hydrothermal technique by using aluminum nitrate and urea as precursor materials. It was found that morphology of the produced structure strongly depends upon the urea concentration. With increasing the amount of urea, the AACH particles having embedded rods like surface features transformed into 3D urchins. The added urea decomposed during hydrothermal treatment and increased the pH of the solution, which affected the morphology of the produced nanostructures. SEM, XRD, FTIR and TGA were employed to characterize the produced structures. On heating, the volatile ingredients of AACH were removed, leaving behind the alumina urchins.     

氧化铝前驱体的制备工艺研究

以硝酸铝为原料,用碳酸氢铵和氨水作混合沉淀剂,采用反向滴定共沉淀工艺,在一定的条件下可以得到物相单一、性能优良的氧化铝前驱体-碳酸铝铵。     

A comparative study of the co-precipitate synthesis of barium-calcium-aluminates impregnants for dispenser cathodes by using different precipitants

In order to optimize the synthesis process of barium-calcium-aluminate (BCA) for the application of impregnated dispenser cathodes, the influence of two precipitants, ammonium carbonate (AC) and ammonium hydrogen carbonate (AHC), on the chemical composition, phase transformation, thermal behaviors and morphology of the precursors was systematically investigated by means of XRD, TG-DSC, FESEM, and EDS mapping analysis. The results revealed that AC precipitant facilities to form NH₄Al (OH)₂CO₃ (AACH) phase and barium calcium carbonate in the precursor, while the product precipitated by AHC comprises amorphous γ-AlOOH phase and the carbonate. Both precursors precipitated by the AC and AHC undergo various stages of phase transformations and finally converted to an emission-active material Ba₃CaAl₂O₇ phase after sintering at 1200?°C. DC emission current values have been measured and the maximum space charge limited current densities are 8.0?±?0.3 and 6.5?±?0.4 A/cm² at 1130 °C_b for the testing cathodes impregnated with the AC and AHC precursor aluminates, respectively. The difference in the emission capacity originates from the barium content in the aluminates prepared with different precipitants.     

Effect of urea,NH4OH,and DCCA on texture properties of alumina prepared by ultrasonic spray pyrolysis

Mesoporous alumina particles were prepared by using a spray pyrolysis process of aluminum nitrate precursor using cetyltrimethylammonium bromide (CTAB) as a structure-directing agent. The effects of ammonium hydroxide, urea, and drying-control-chemical agent (DCCA) on the particle morphology and pore properties of alumina particles were studied by means of N₂ physical adsorption, transmission electron microscopy (TEM), and small-angle X-ray diffraction (SAXS) analysis. It was found that using urea rather than NH₄OH in the spray pyrolysis is effective to increase the surface area of alumina with well-organized uniform pores. The addition of NH₄OH led to decrease the surface area as well as the pore regularity. Using both DCCA and urea was a helpful way to improve the surface area, the pore volume, and the pore size distribution of alumina synthesized by spray pyrolysis. The prepared alumina particles had a broad SAXS peak without further reflection peaks indicating hexagonal or cubic symmetry. According to TEM analysis, a long-range ordering of mesopores was not observed. More details on the texture properties and the morphology of alumina particles prepared by with changing the kinds of additives in spray solution were discussed.     

A Decomposition Route for Synthesis of Al2O3 Crystal and its Applications as Thermal Conductivity Filler

Platelike α‐Al₂O₃ powder was obtained at 850°C by thermal decomposition of ammonium aluminum carbonate hydroxide precursor, which was treated by hydrofluoric acid. The results showed the decomposition of the as‐prepared precursors experienced via three steps, adsorption of physical water, dehydration of crystalline water, and decomposition of the precursor, and the activation energies of the above three steps were calculated using the Coats–Redfern method. Meanwhile, the intermediate of (NH₄)₃AlF₆ obtained played an important role in decreasing activation energy of the decomposition and phase transformation. Moreover, the thermal conductivity of the epoxy resin filled with platelike alumina was improved obviously.     

Dispersion and Setting of Powder Suspensions in Concentrated Aqueous Urea Solutions for the Preparation of Porous Alumina Ceramics with Aligned Pores

Highly concentrated alumina powder suspensions have been prepared in aqueous urea solutions of concentrations in the range 200–360 g/100 mL using an ammonium poly(acrylate) dispersant at 80°C. The dispersant concentration for the suspension viscosity minimum in the urea solutions is higher than that in water due to the higher processing temperature. The urea solutions having higher dielectric constant than that of water offer higher interparticle potential that resulted in better dispersion of the powder as evidenced from the lower viscosity and yield stress of the suspensions. The decrease in temperature increased the suspension viscosity and the suspension formed a strong gel when cooled to room temperature due to the crystallization of urea. The minimum urea solution concentration for a 55 vol% alumina suspension to form a dimensionally stable gel is 240 g/100 mL. The compressive strength and Young's modulus of the gels increased with the increase in urea solution concentration. The alumina ceramics prepared by the urea removal followed by sintering at 1500°C had porosity in the range 28–36 vol% with the rectangular rod‐shaped aligned pores.     

沉淀剂对NiW/TiO2-ASA催化剂加氢裂化性能的影响

无定形硅铝的织构性质和酸性质对其加氢裂化性能有很大影响。本文以氨水、碳酸铵、氢氧化钠/尿素、氢氧化钠为沉淀剂,制备了4种含钛无定形硅铝(TiO₂-ASA),并以其为载体负载Ni-W加氢组分,制备了NiW/TiO₂-ASA加氢裂化催化剂,以十氢萘为模型化合物,考察NiW/TiO₂-ASA催化剂的加氢裂化性能,通过X射线衍射(XRD)、氮气吸附-脱附、氨气程序升温脱附(NH₃-TPD)、吸附吡啶原位红外(Py-IR)、扫描电镜(SEM)对TiO₂-ASA和NiW/TiO₂-ASA催化剂进行了表征。结果表明,沉淀剂对TiO₂-ASA的比表面积和孔容影响非常大,以碳酸铵为沉淀剂时,TiO₂-ASA具有高比表面积、窄孔分布的特点,沉淀剂为氢氧化钠时,则可制备出大孔容、宽孔分布的TiO₂-ASA。十氢萘的加氢裂化反应结果表明,以碳酸铵为沉淀剂制备的NiW/TiO₂-ASA催化剂,织...