Cu-Cr2O3/Al2O3催化剂上乳酸乙酯加氢制丙二醇研究

在间歇反应器上考察了通过共沉淀法制备得到的一系列不同负载的Cu-Cr2O3/Al2O3催化剂的催化加氢效果.研究结果表明:当n(Cu)∶n(Cr)=2∶1时有最佳的催化剂活性,n(Cu)∶n(Cr)=1∶1时有最佳的1,2-丙二醇选择性.在反应温度为200℃、氢气压力为3MPa、搅拌速率为500r/min和n(Cu)∶n(Cr)=2∶1的Cu-Cr2O3/Al2O3催化剂作用下,反应6h,实现了乳酸乙酯的完全转化,其中1,2-丙二醇的收率达到了95.3%.     

微波加热法合成蜂窝状堇青石载体Al2O3涂层

采用微波加热法在堇青石蜂窝陶瓷基体表面涂覆多孔Al2O3涂层,研究了制备条件对堇青石蜂窝陶瓷表面Al2O3涂层中Al2O3的质量分数的影响。通过BET、SEM对涂层结构及形貌进行了表征,结果表明,采用微波加热法制备的Al2O3涂层均匀、稳定,具有较大的比表面积、孔容和较高的Al2O3质量分数。     

CuCl2/Al2O3催化氮杂环的N-芳基化反应

研究了以CuCl2/Al2O3作为金属铜催化剂高效催化氮杂环与卤代芳烃的N-芳基化反应制备N-芳基杂环化合物.实验结果表明:在无有机配体存在下CuCl2/Al2O3催化剂具有良好的催化活性和重复使用性.以咪唑与碘苯的反应作为模板反应优化反应条件,考察了反应物配比、催化剂种类、碱的种类、溶剂的选择、反应温度以及反应时间等因素对反应收率的影响,确定了最佳反应条件,在此条件下制备N-苯基咪唑的收率达99%.而且,所选择的催化反应体系可应用于合成一系列N-芳基杂环化合物.     

导热界面材料及导热填料Al2O3的技术研究

介绍了导热界面材料的分类、主要技术指标、导热机理,并论述了作为导热填料Al₂O₃的技术指标对导热界面材料性能的影响,讨论了Al₂O₃的形貌对填充性能的影响。结果表明,颗粒形貌越规整,体系黏度越低,填充率越高,以及颗粒结晶程度越高,热导率越高。并阐述了填料Al₂O₃的杂质对导热界面材料的性能影响,最后提出导热填料Al₂O₃技术发展趋势。     

圆柱形微波多模烧结腔烧结Al2O3陶瓷的性能

应用微波加热技术进行高纯Al2O3陶瓷烧结是一种理想的选择.本文使用一种新型的圆柱形微波多模烧结腔体进行了Al2O3陶瓷的烧结研究,该设备可在短时间内达到较高的烧结温度,并能实现坯体的整体烧结.分别对纯Al2O3粉体和Al2O3/MgO混合粉体进行了烧结实验,结果表明,添加MgO作为助烧剂烧结得到的陶瓷试样的相对密度高于纯Al2O3粉体烧结得到的陶瓷试样,在1 700℃下保温40 min,其相对密度可以达到理论密度的97.8%,维氏硬度达22.3 HV/GPa.从SEM图中可观察到试样微观结构良好,晶粒大小均匀,致密化程度高.     

Na2SiO3含量对等离子体电解氧化Al2O3-ZrO2复合陶瓷层形成机制的影响

铸造Al-Si合金表面ZrO2陶瓷层可有效提高基体的隔热及抗高温氧化性能,采用等离子体电解氧化方法在Al-Si合金表面制备了氧化锆涂层.涂层的组成、结构通过SEM、XRD进行研究.结果表明:K2ZrF6体系成膜速度较快,30min膜厚可达92μm,膜层表面和截面没有明显的等离子体放电形成的微孔,大量聚集的Zr(OH)4在等离子体放电产生的热化学作用下分解为ZrO2,表面出现大量2μm～5μm的陶瓷颗粒.K2ZrF6复合Na2SiO3体系成膜速度较慢,30min膜厚仅为27μm,表面和截面存在较多喷射状孔洞,随着溶液浓度的增大,成膜速度均呈先增后减的趋势.K2ZrF6复合Na2SiO3体系中,陶瓷层主要由α-Al2O3、γ-Al2O3、Al2(OH)3F3和m-ZrO2组成,α-Al2O3为陶瓷层的主晶相.K2ZrF6体系中陶瓷层的主要成分为t-ZrO2、m-ZrO2、α-Al2O3和γ-Al2O3,t-ZrO2为涂层的主晶相.涂层中m-ZrO2较少,而t-ZrO2含量高,表明生成的α-Al2O3起到稳定高温相t-ZrO2的作用.     

Al2O3对PbTe微观结构和热电性能的影响

为研究Al2O3对PbTe微观结构和热电性能的影响,在Tl0.02Pb0.98Te材料中添加纳米Al2O3粉末,用高能球磨加热压方法制备了Tl0.02Pb0.98Te样品,并对样品进行实验分析。结果表明:添加纳米Al2O3粉末有效地强化了样品高温机械性能;同时,纳米Al2O3颗粒弥散分布在晶界,阻止热压过程中晶粒长大,使晶粒尺寸降低了约50倍;晶粒细化后界面增多,能更好地散射长波长声子;由于晶格热导率降低了约20%,Tl0.02Pb0.98Te(Al2O3)0.06样品的ZT在723 K时达到1.3。     

Al2O3-SiC-SiAlON复合材料的制备和性能

以电熔白刚玉、α-Al2O3微粉、Si粉和矾土基β-SiAlON粉为原料,以树脂为结合剂,制备了复合材料试样.研究了1 500℃烧后试样的物相组成、显微结构以及常温物理性能、高温抗折强度和抗热震性.结果表明:(1)在刚玉中引入适量Si粉高温埋碳条件下可合成Al2O3-SiC-SiAlON复合材料,引入适量β-SiAlON可促进Si反应,且复合材料1 500℃烧结良好;(2)复合材料的高温抗折强度和抗热震性随Si粉加入量增加而提高,加入β-SiAlON后材料的高温机械性能进一步提高;(3)材料高温机械性能提高的原因在于Si粉在高温下与C、CO和N2反应生成晶须状或纤维状SiC和絮状O’-SiAlON填充气孔,形成交叉连锁的网络结构,对材料起增强和增韧作用.     

Adsorption of NO and NH3 over CuO/γ-Al2O3 catalyst

The selective catalytic reduction reaction belongs to the gas-solid multiphase reaction, and the adsorption of NH₃ and NO on CuO/γ-Al₂O₃ catalysts plays an important role in the reaction. Performance of the CuO/γ-Al₂O₃ catalysts was explored in a fixed bed adsorption system. The catalysts maintain nearly 100% NO conversion efficiency at 350 °C. Comprehensive tests were carried out to study the adsorption behavior of NH₃ and NO over the catalysts. The desorption experiments prove that NH₃ and NO are adsorbed on CuO/γ-Al₂O₃ catalysts. The adsorption behaviors of NH₃ and NO were also studied with the in-situ diffusion reflectance infrared Fourier transform spectroscopy methods. The results show that NH₃ could be strongly adsorbed on the catalysts, resulting in coordinated NH₃ and NH₄⁺ NO adsorption leads to the formation of bridging bidentate nitrate, chelating bidentate nitrate, and chelating nitro. The interaction of NH₃ and NO molecules with the Cu²⁺ present on the CuAl₂O₄ (100) surface was investigated by using a periodic density functional theory. The results show that the adsorption of all the molecules on the Cu²⁺ site is energetically favorable, whereas NO bound is stronger than that of NH₃ with the adsorption site, and key information about the structural and energetic properties was also addressed.     

Al-Si合金Al2O3-ZrO2微弧氧化涂层生长机理研究

为了解决Al2O3微弧氧化层不能满足Al-Si合金使用要求的问题,采用微弧氧化法在Al-Si合金表面制备了Al2O3-ZrO2复合膜层,通过SEM、XRD分析测试手段研究膜层的微观表面形貌、组织结构和相组成.结果显示:微弧氧化初期,陶瓷层生长速率较快且反应速率稳定,反应后期陶瓷层生长速率减缓;陶瓷层微观表面形貌比较均匀,有部分放电微孔和裂纹;陶瓷层与金属基体呈犬牙状交错结合;陶瓷层的主要相组成是t-ZrO2、α?Al2O3、m-ZrO2、γ?Al2O3,其中t-ZrO2为膜层主晶相.并根据实验结果研究了微弧氧化涂层的生长机理.     

Effect of Nb on the mechanical properties of Ti/Al2O3 composite

Ti/Al₂O₃ composite with improved mechanical properties was synthesized by the spark plasma sintering. The effect of Nb on the microstructure of the composite was analyzed by TEM, SEM and so on. The experimental results indicate that the bending strength, fracture toughness, micro-hardness and relative density of the composite are 897.29MPa, 17.38MPa·m^1/2, 17.13GPa and 99.24% respectively when adding 1.5vol Nb. The bending strength is improved by reason of forming dislocation ring and transfering fracture mode from integranular to mixture fracture of intergranular and transgranular. The crack propagating is mainly the deflection bridging. It indicates a reduction of crack driving force and an increase in crack growth resistance, which results in toughness enhanced. Funded by the National Natural Science Foundation of China (No. 50232020) and the Natural Science Foundation of Shandong Province (No. 2002F21)     

Chemical reaction of in-situ processing of NiAl/Al2O3 composite by using thermite reaction

NiAl/Al₂O₃ composite were synthesized by thermite reaction of nickel oxide and aluminum powder mixtures. The phase, the microstructure of the composite, as well as the thermite reaction mechanism, were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) combined with differential scanning calorimetry (DSC). The experimental results show that the thermite reaction leads to the interpenetrating network structure of NiAl/Al₂O₃ at 1223K for 60 min and the chemical reaction apparent activation energy is E_ap=166.960±13.496 kJ·mol⁻¹ in the NiO/Al system. Funded by the Younger Teacher Foundation of High School of Anhui Province (No. 2003jq158)     

Preparation of Al2O3-SiO2-TiO2-ZrO2 Composite Ceramic Membranes by Sol-Gel Method

Al2O3-SiO2- TiO2-ZrO2 supported membranes were prepared by Sol-Gel method. These composite ceramic membranes are level, even and no macro crack. There exist several crystalline phases such as Al2O3, TiO2 ( anatase ), Al2 SiO5 , and ZrO2 in these membranes. Changing the molar ratio of Al:Si: Ti : Zr ,the kinds and content of crystal phases of composite membranes could be different, which may lend to a variety of microstructure of membranes. The surface nanoscale topography and microstructure of membranes were investigated by XRD, SEM, AFM, EPMA. The effects of additives and heat treatments on the surface nanoscale topography and microstracture of composite ceramic membranes were also analyzed.     

Fabrication of GaN epitaxial films on Al2O3/Si (001) substrates

Single crystal GaN films of hexagonal modification have been fabricated on Al₂O₃/Si (001) substrates via a low pressure metalorganic chemical deposition (LP-MOCVD) method. the full width at half-maximum of (0002) X-ray diffraction peak for the GaN film 1.1 μm thick was 72 arcmin, and the mosaic structure of the film was the main cause of broadening to the X-ray diffraction peak. At room temperature, the photoluminescence (PL) spectrum of GaN exhibited near band edge emission peaking at 365 nm. Project supported by the “863” Advanced materials Committee of China and the Planning Commission of China.     

Antibiotic properties of Al2O3 doping silver

The preparation technique and properties of Ag-type inorganic antibiotic material carried by Al₂O₃ were studied. The results show that the material has good antibiotic and safety properties, the acute toxicity taken by stomata is LD ₅₀>8 000 mg/kg (little and big white rats), and the normal quantity in subacute toxicity test is 80 mg/(kg · d). The better mass fraction of doping Ag₂O in antibiotic material carried by Al₂O₃ is 4%–8%, and the optimal sintering temperature is from 1 000 °C to 1 100 °C. Foundation item: Project (2002AA327090) supported by National High Technology Research and Development Program of China     

Effects of temperature and initial molar ratio of Na2O to Al2O3 on agglomeration of fine Al（OH）3 seed in synthetic Bayer solution

Fine Al（OH）3 crystals were aggregated from supersaturated aluminate solution in the batch reaction tanks. By means of laser particle size analyzer and scanning electron microscopy, the influences of temperature and initial molar ratio of Na2O to Al2O3 （aK） on agglomeration of fine seed in Bayer process were investigated. The results show that agglomeration is almost finished in 8 h, and seeds with size less than 2 μm are easily aggregated together, and almost disappear in 8 h under the optimal process conditions. In the aluminate solution with the same moderate initial aK, when the reaction temperature reaches 75 ℃, the secondary nucleation does not occur, and the effect of agglomeration is better. And at the same reaction temperature, when the initial aK is 1.62, the initial supersaturation of aluminate solution is moderate, the binders on the surfaces of the seed are enough to maintain the agglomeration process, and the agglomeration degree is better. From SEM images, agglomeration mainly occurs in the fine particles, the combinations among the fine particles are loose and the new formed coarse crystal shapes are irregular.     

Microstructures and mechanism of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al composites fabricated by the reaction between SiO<Subscript>2</Subscript> and molten aluminum

Al₂ O₃/Al composite was fabricated by the reaction between SiO₂ and molten aluminum. The microstructures of the composite obtained under different reaction conditions were analyzed. The formation mechanism of the composite microstructure was discussed. Results show that the reaction kinetics is influenced remarkably by the reaction temperature, reaction time and the quantity of SiO₂. The morphologies of Al₂O₃ have different features, depending on the reaction temperature. The composite has equaxed Al₂O₃ grains when materials reacted below 1200°C, and the composite is composed of a large number of fine Al₂O₃ grains and aluninum. The composite has a frame-shaped Al₂O₃ microstructure at the reaction temperature of above 1250°C. CHENG Xiao-min: Born in 1964 Funded by the National Natural Science Foundation of China (No. 91522)     

复合活性钎料钎焊Cu与Al2O3的接头组织及性能

为改善紫铜与Al_2O_3陶瓷的连接强度,采用纳米-Al_2O_3增强的AgCuTi复合钎料(Ag Cu Tip)对紫铜与Al_2O_3陶瓷进行了真空钎焊.采用扫描电镜、能谱分析以及剪切试验对钎焊接头微观组织及力学性能进行了分析.钎焊接头典型界面组织为紫铜/扩散层/铜基固溶体+银基固溶体+Ti_2Cu+Ti_3(Cu,Al)3O/Al_2O_3.纳米-Al_2O_3的添加抑制了Al_2O_3侧反应层的生长,并促进钎缝中形成弥散分布的Ti_2Cu相.随着保温时间的延长,铜侧扩散层和Ti_3(Cu,Al)_3O反应层的厚度逐渐增大.保温时间为20 min时,铜母材向钎料过度溶解,降低了接头性能.当钎焊温度为880°C,保温10 min时,接头抗剪强度最高为82 MPa.纳米颗粒的加入细化了钎缝组织并降低了母材与钎缝热膨胀系数的不匹配,因此提高了接头的连接性能.保温时间可影响界面组织及反应层的厚度,进而影响接头的连接强度.     

Study of GaN MOS-HEMT using ultrathin Al2O3 dielectric grown by atomic layer deposition

We report on a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using atomic-layer deposited (ALD) Al₂O₃ as the gate dielectric. Through further decreasing the thickness of the gate oxide to 3.5 nm and optimizing the device fabrication process, a device with maximum transconductance of 150 mS/mm was produced. The drain current of this 0.8 μm gate-length MOS-HEMT could reach 800 mA/mm at +3.0 V gate bias. Compared to a conventional AlGaN/GaN HEMT of similar design, better interface property, lower leakage current, and smaller capacitance-voltage (C-V) hysteresis were obtained, and the superiority of this MOS-HEMT device structure with ALD Al₂O₃ gate dielectric was exhibited. Supported by the National Natural Science Foundation of China (Grant No. 60736033) and the National Basic Research Program of China (“973“) (Grant No. 51327020301)     

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.