Preparation of ultrafine α-Al_2O_3 powders by catalytic sintering of ammonium aluminum carbonate hydroxide at low temperature

1 INTRODUCTIONUltrafine alumina with extensively excellentproperties such as high heat resistance ,high corro-sion resistance ,good electrical insulation and cata-lytic abilities , etc ,is a very i mportant branch ofultrafine powder materials and widely applied infields of ceramics , metallurgy , electron and cata-lysts[1 ,2]. The thermal decomposition of ammoni-umaluminum carbonate hydroxide ( AACH) is anew method developed in recent years for produ-cing ultrafine alumina powders , and …     

利用纳米铝和沉淀法制备纳米α-Al2O3粉体

以Al(NO3)3·9H2O、氨水和纳米铝粉为原料,采用液相沉淀法制备出Al(OH)3溶胶,经过真空抽滤和高温煅烧获得了纳米α-Al2O3粉体.研究了反应体系pH值、纳米铝粉添加和煅烧温度对Al(OH)3溶胶质量以及Al2O3晶型转化温度的影响.结果表明,反应体系pH值为9时可以获得团聚少、分散性好的Al(OH)3溶胶,添加摩尔分数为3%的纳米铝粉作为籽晶可以使α-Al2O3的转变温度降至1000℃左右.实验获得的纳米α-Al2O3粉体粒度分布均匀,无明显团聚,近似球形,平均粒径约为20 nm.     

α-Al2O3颗粒形貌对其坯体烧结性能的影响

通过对α-Al2O3颗粒形貌及其烧结体断面显微结构的分析，以及坯体的线收缩率、密度和吸水率的测定，研究了α-Al2O3颗粒形貌对坯体烧结性能的影响。结果表明：坯体在高温下产生的膨胀，对坯体的烧结致密和均匀显微结构的形成，产生了持续的不利影响。α-Al2O3颗粒形貌对坯体烧结性能产生不同程度的影响。     

Study on sulphide capacity of CaO-SiO2-Al2O3-MgO-FetO slags

The sulphide capacity of CaO-SiO2-Al2O3-MgO-FetO slags was studied at 1773 K using gas-slag equilibrium techniques. Utilizing a Pt crucible, the slag was equilibrated with a mixture of gases, namely, CO, CO2, SO2 and N2 to provide the partial pressure of oxygen and sulphur. It was shown that at fixed FetO and Al2O3 contents and a fixed { （?O）＋（%MgO）}/（%SIO2） ratio, the sulphide capacity decreases with increasing MgO content. At a constant （?O）/（%SiO2） ratio and constant MgO and Al2O3 contents, increasing the FetO content of the slags also results in an increase of the sulphide capacity. The rising basicity of （?O）/（%SiO2） from 1.0 to 1.4 at fixed MgO, FetO and Al2O3 contents significantly increases the sulphide capacity.     

反应条件对CuO／Y2O3-ZrO2-Al2O3催化甲烷燃烧性能的影响

采用溶胶凝胶法制备CuO／Y2O3-ZrO2-Al2O3催化剂。研究了反应气甲烷与空气体积比和反应气体流速对CuO／Y2O3-ZrO2-Al2O3,催化剂性能的影响,结果显示：VCH4：VAir=1：25且气体流速为1800Loh-1时,该催化剂具有较好的催化活性和高温热稳定性。     

α-Al2O3纳米镀镍层中纳米粉含量测定方法的研究

Al2O3经高温1200℃转化为α-Al2O3，其粒径在1—100nm的α-Al2O3在金属镀层显示良好的抗蚀性和耐磨性，比常规镀层各方面性能均有大幅改善，因而测定镀层中的纳米材料多少是十分重要。本法对镀层通过物理方法剥离，用1 1盐酸溶解基体Fe及表层Cr,110℃烘干称重，硝酸溶样，用容量法测定镀层中Ni、Co，其差值为纳米α-Al2O3的含量。     

碳酸铝铵热分解法制备α-Al2O3纳米粉体

为了获得更好的α-Al2O3纳米粉体，以硫酸铝铵和碳酸氢铵合成的碳酸铝铵为原料，经过不同的加热升温方式，研究了碳酸铝铵热分解过程中不同的Al2O3相转变历程。研究结果表明，通过提高低温段的升温速度来加快碳酸铝铵的热分解速率，会使各Al2O3相的转化速度明显增大，相转化温度明显降低，对α-Al2O3的生成产生有利的影响。最终在较碳酸铝铵常规热分解更低的温度、更短的保温时间，获得晶粒尺寸更小、分散性更好的单相α-Al2O3粉体。     

第一原理计算α-Al2O3电子态密度性质分析

利用第一性原理中的DFT理论计算了α-A l2O3晶体结构的能带结构和电子态密度,计算过程用软赝势表示原子芯区电子,结构优化后的晶格常数与实验值误差在很小的范围内.分析了A l和O的s和p轨道对分态密度的影响,依据晶体场理论分析了态密度成键轨道和反键轨道的归属.结果表明,禁带能隙约为8 eV,导带位于6.7~17.5 eV,对(110)晶面切片电子密度分析,发现氧原子周围强烈的电子定域分布.α-A l2O3电子的布居分析发现,在铝和氧之间存在明显电子转移.     

CaO-SiO2-Fe2O3-Al2O3渣系对高磷铁水脱磷行为的影响

以w(P)=0.48%的高磷铁水为研究对象,采用高温热态实验研究1 400℃时CaO-SiO_2-Al_2O_3-Fe_2O_3渣系的脱磷行为,分析碱度、渣中Fe_2O_3与Al_2O_3含量对CaO-SiO_2-Al_2O_3-Fe_2O_3渣系脱磷的影响。结果表明:随着碱度逐渐增大,渣系脱磷率呈先逐渐增大后略有降低的变化趋势,主要是由于自由O~(2-)和Ca~(2+)的引入促进了磷氧络离子PO_4~(3-)及Ca~(2+)-PO_4~(3-)弱离子对的进一步生成;随着Fe_2O_3含量的增加,渣系脱磷率逐渐升高,渣中的Fe_2O_3加速了氧化钙的熔化速度,同时使渣系的氧化性提高,进而使渣系脱磷能力提高;w(Al_2O_3)=1%～3%时,渣系脱磷率维持在77%左右,进一步增大渣中Al_2O_3含量,渣系脱磷率逐渐下降,主要原因在于Al_2O_3改变了渣中液相比例,进而影响了脱磷反应物与产物在渣-金间的传质过程。     

纳米α-Al2O3前驱体溶剂化与洗涤分离的研究

以工业Al(OH)3为原料,用沉淀法制备了纳米α-Al2O3粉体.探讨了制备工艺过程中前驱体溶剂化与洗涤分离的条件;研究了前驱体溶剂化在分离过程中对过滤速度的影响,并取得了最佳工艺条件.用X射线衍射仪(XRD)、透射电镜(TEM)、红外吸收光谱(IR)和激光粒度分析仪,对实验所得粉末的结构进行了表征.结果表明:采用无水乙醇洗涤后,降低了溶剂化程度,加快了洗涤速度,所得的α-Al2O3粉体粒径为59.3 nm,形貌为纤维状,并且分散好、粒径均匀.     

Structure and mechanical properties of ZrO2-mullite nano-ceramics in SiO2-Al2O3-ZrO2 system

ZrO2-mullite nano-ceramics were fabricated by in-situ controlled crystallizing from SiO2-Al2O3-ZrO2 amorphous bulk. The thermal transformation sequences of the SiO2-Al2O3-ZrO2 amorphous bulk were investigated by X-ray diffraction, infrared spectrum, scanning electron microscope and differential scanning calorimetric. And the mechanical properties of the nano-ceramics were studied. The results show that the bulks are still in amorphous state at 900 ℃ and the t-ZrO2 forms at about 950 ℃ with a faint spinel-like phase which changes into mullite on further heating. ZrO2 and mullite become major phases at 1 100 ℃ and an amount of m-ZrO2 occur at the same time. The sample heated at 950 ℃ for 2 h and then at 1 100 ℃ for 1 h shows very dense and homogenous microstructure with ball-like grains in size of 20-50 nm. With the increase of crystallization temperature up to 1 350 ℃, the grains grow quickly and some grow into lath-shaped grains with major diameter of 5 μm. After two-step treatment the highest micro-hardness, flexural strength and fracture toughness of the samples are 13.72 GPa, 520 MPa and 5.13 MPa·m1/2, respectively.     

Preparation and Gas Permeation of Supported γ-Al2O3 Membranes Used as Substrate Layer for Microporous Membranes

γ-Al₂O₃ membranes were successfully deposited on the top of porous α-Al₂O₃ support by sol-gel process and characterized by means of XRD, SEM, N₂ adsorption and gas permeation. The γ-Al₂O₃ membranes, free of pin-holes and cracks, adhere tightly to the supports and have a thickness of about 7 μm. When sintered at 400°C, γ-Al₂O₃ membranes have a narrow pore size distribution, with a pore diameter of 3.6nm, and the transport of both H₂ and CO₂ in supported γ-Al₂O₃ membrane is governed by Knudsen mechanism, with H₂ permeance of 3.3×10⁻⁶ molm⁻² Pa⁻¹ s⁻¹ and H₂/CO₂ permselectivity close to the ideal Knudsen value at 50°C. The γ-Al₂O₃ membranes are suitable for being used as the substrates of microporous membranes. Founded by the Doctor Science Foundation of Chinese Education Ministry (Grant No. 98053301).     

Preparation and structure characteristics of nano-Bi2O3 powders with mixed crystal structure

The nano-Bi2O3 powders were prepared by a chemical precipitation method with Bi(NO3)3, HNO3 and NaOH as reactants. The structural characteristics and morphology of nano-Bi2O3 powders were investigated by X-ray diffraction and transmission electron microscopy, respectively. The results show that under the optimum condition that 300g/L Bi(NO3)3 reacts at 90℃ for 2 h, the Bi203 powders with 60 nm on the average and 99.5% in purity are obtained. The prepared nano-Bi2O3 powders contain a mixed crystal structure of monoclinic and triclinic instead of traditional structure of monoclinic α-Bi2O3. And the mixed crystal structure is stable in air. The reason for the appearance of the mixed crystal structure may be that the ionic radius ratio of Bi^3 to O^2- changes easily during the formation of nano-Bi2O3 particles by a chemical precipitation method.     

金属铝在KF-LiF-Na3AlF6-Al2O3体系中的溶解度

用等温饱和法研究了金属铝在KF-LiF-Na3AlF6-Al2O3体系中的溶解过程,实验结果表明：体系温度980℃,分子比（n（NaF）/n（AlF3））=2.3时,溶解度随着钾盐和锂盐含量的增加而增大;钾盐和锂盐质量分数分别为7%时,铝的溶解度（质量分数）分别达到0.148%和0.242%,并且锂盐比钾盐对铝溶解度影响大;钾盐和锂盐共同作用时,铝的溶解度达到0.421%.采用多元回归分析法对铝溶解度与钾盐、锂盐、分子比之间的关系进行研究,得到回归方程为Y=-0.125＋1.962x1＋3.456x2＋0.090x3     

煅烧条件对制备γ-Al2O3的影响

阐述了采用焙烧拟薄水铝石制备高质量的γ-Al2O3的方法，并且分析了制备γ-Al2O3过程中的工艺条件(干燥、成型及煅烧条件)对产品性能的影响，重点讨论了煅烧条件与产品质量的关系，最终得出了制备γ-Al2O3较佳煅烧工艺条件，温度为450℃，时间为10h，升温速度为100℃／h．     

TiO2-Al2O3复合光催化剂的制备及其对甲基橙的降解

以Ti（SO4）2和Al2（SO4）3.18H2O为反应物,用乙醇助溶剂水热法制备了TiO2-Al2O3复合光催化剂,考察了铝/钛摩尔比、水热反应温度、乙醇体积分数及pH值对复合材料光催化效率的影响。X射线衍射测试显示复合材料中的TiO2为锐钛矿和金红石相的混晶结构,紫外-可见漫反射光谱分析表明其吸收光谱发生蓝移,BET测试表明该复合材料具有较大的比表面积。     

Selective catalytic reduction of NO with NH3 over sol-gel-derived CuO-CeO2-MnOx/γ-Al2O3 catalysts

Granular CuO-CeO₂-MnO _x /γ-Al₂O₃ catalysts were synthesized by the sol-gel method. The performance of the CuO-CeO₂-MnO _x /γ-Al₂O₃ catalysts for the selective catalytic reduction (SCR) was studied in a fixed bed system. Preliminary tests were carried out to analyze the behavior of NH₃ and NO over catalyst in the presence of oxygen. The optimum temperature range for SCR over the CuO-CeO₂-MnO _x /γ-Al₂O₃ catalysts is 300–400 °C. The catalysts maintain nearly 100% NO conversion at 350 °C. The °C NH₃ oxidation experiments show that both NO and N₂O are produced gradually with the increase of temperature. The catalysts in this experiment have a stronger oxidation property on NH₃, which improves the denitrification activity at low temperature. The over-oxidation of NH₃ at high temperature is the main cause leading to a decrease in the NO conversion. The NH₃ and NO desorption experiments show that NH₃ and NO can be adsorbed on CuO-CeO₂-MnO _x /γ-Al₂O₃ granular catalysts. The transient response of NH₃ and NO indicates that the SCR reaction proceeds in accordance with the Eley-Rideal mechanism. The adsorbed NO has little influence on the denitrification activity in SCR process. Foundation item: Projects (50776037, 50721005) supported by the National Natural Science Foundation of China