A corrosion mechanism of titanium diboride in KF−AlF3−Al2O3 melt

TiB₂ samples were exposed to molten KF?AlF₃?Al₂O₃: 54.8-42.1-3.1 mol% salt, at 680 °C for 50, 100 and 200 h. The corroded samples of TiB₂ were investigated by SEM-EDX, EBSD, XRD, FT-IR and MAS NMR analysis. Corrosion was noted to occur predominantly as pitting attacks on the surface of the investigated materials. An inter-crystal and trans-crystal corrosion were identified on the cross-sections of the samples. A perturbation of TiB bonds was detected (SEM-EDX and NMR analysis), at which a formation of orthorhombic TiO₂ was also identified (EBSD analysis). The subsequent NMR, XRD and FT-IR analysis of the behaviour of TiB₂ powder in molten KF?AlF₃?Al₂O₃ supports the statement about the formation of orthorhombic TiO₂ and mullite type of aluminium borates.     

New catalyst of SO 4 2− /Al2O3–ZrO2 for n-butane isomerization

The catalytic behavior of Al-promoted sulfated zirconia for n-butane isomerization at low temperature in the absence of H₂ and at high temperature in the presence of H₂ was studied. The addition of Al enhances the activity and stability of the catalysts for reaction at 250°C and in the presence of H₂ significantly. After on stream for 120 h, the n-butane conversion of the catalyst containing 3 mol% Al₂O₃ keeps steadily at 88% of its equilibrium conversion and no observable trend of further deactivation has been observed. The difference in behavior of the promoted and unpromoted catalysts at low and high temperature is associated with a change of reaction mechanism from bimolecular to monomolecular. Experimental evidence is presented to show that the promoting effect of Al is different from that of the transition metals. Microcalorimetric measurements of NH₃ adsorption on catalysts reveal that the remarkable activity and stability of the Al-promoted catalysts are caused by an enhancement in the number of acid sites effective for the isomerization reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

On the Role of Calcination Temperature in Pt-SO 4 2− /ZrO2−Al2O3 Preparation and Catalytic Behaviors During the n-Hexane Hydroisomerization

Effects of calcination temperature for Pt-SO ₄ ^2? /ZrO₂?Al₂O₃ (PSZA) catalysts in n-hexane hydroisomerization were investigated by N₂-adsorption, XRD, TG-DTA, FTIR, XPS and H₂-TPR. An optimum calcination temperature is helpful to complete the crystallization process, resulting in better distribution of alumina into zirconia crystal and producing new acid centers responsible for higher catalytic activity.     

Bonding phase formation in eco-friendly periclase−spinel−Al bricks used in RH degassing process

Mere unburnt periclase–spinel–Al bricks have been accepted by steel mills in the chromium-free campaign of the lining materials for Ruhrstahl ?Heraeus (RH) degassers, in terms of comparable/optimistic performance to traditional material, low carbon emission due to unburnt manufacturing process and chromium-free material for eco-friendly steel-making process. Investigations are made on the used periclase–spinel–Al bricks for the thermal evolution of their components and the formation of novel phase and bonding structure. Under the working atmosphere of RH degasser, metallic Al particles got molten above its melting point, leaving Al rim around their circumference, and AlN formed in the gaseous state dispersing into overall matrix of periclase–spinel–Al bricks with rising temperature. AlN formed and Mg reduced in their gaseous state germinated MgAlON whisker initially in the original space of metallic Al particles, and MgAlON whisker grew further all over the matrix. A whisker-interwoven network has been full of the matrix behind the hot face and toward the cold face of the used bricks, which is a completely novel type of bond and distinguished from traditional ceramic one. The whisker-interwoven network is somewhat like the stripe graphite containing microstructure of magnesia–carbon brick, which results in low wettability and high flexibility. The superior performance of periclase–spinel–Al bricks is attributed to such a bonding structure of whisker-interwoven network, which could reduce slag penetration and facilitate thermomechanical stress resistance.     

Comparison of Mg–Al layered double hydroxides intercalated with OH− and CO32− for the removal of HCl,SO2, and NO2

Journal of Porous Materials - Two different Mg–Al layered double hydroxides (LDHs), OH?Mg–Al LDH and CO3?Mg–Al LDH, are prepared and utilized for the efficient removal...     

Al2O歧化法制备微细Al2O3/Al复合粉体

真空条件下,以Al2O3和Al为原料,通过Al2O歧化法制备微细Al2O3/Al复合粉体.XRD和SEM分析表明:在反应温度为1200～1400℃时,随着温度的升高,粉体中氧化铝含量升高;冷凝温度约为550～750℃时,复合粉体中的氧化铝包括稳定晶型和不稳定晶型;冷凝温度约为1100～1300℃时,复合粉体中的氧化铝全部为稳定晶型;冷凝温度约为550～650℃时,复合粉体的平均粒径小于0.5μm;冷凝温度约为750℃时,铝熔化、微粒团聚;冷凝温度约为1100～1200℃时,铝形成铝珠,氧化铝为不规则状、平均粒径小于2μm;冷凝温度约为1300℃时,氧化铝为片状.因此,通过选取合适的反应温度、冷凝温度,可以控制Al2O3/Al复合粉体中氧化铝的含量、晶型和粒径.     

Processing of reactive Ni−Al powders via the LabRAM**

Reactive Ni−Al materials have been developed using a variety of methods, with high energy ball milling (HEBM) being one of the most common means for tailoring reaction behavior. Powder production limitations associated with HEBM, including the addition of process control agents, have inspired the exploration of an alternate manufacturing technique: acoustic dry milling with the Resodyn Laboratory Resonant Acoustic Mixer (LabRAM). The influence of acoustic milling time, intensity, and media size with respect to microstructure and reactive behavior of Ni−Al powders were evaluated in this work. After just 20 min of milling, a reactive composite Ni−Al microstructure was produced. Milling intensity and media size were directly proportional to the formation of more homogeneous composite powders. The reaction onset temperature was decreased to 446 °C, or ≈200 °C lower than that of unprocessed material. The method shows promise for the production of reactive powder for a host of applications.     

High‐activity catalyst of SO 4 2− /ZrO2 supported on γ‐Al2O3 for n‐butane isomerization

A series of Al₂O₃supported SO ₄ ^2– /ZrO₂ superacid catalysts (named SZ/Al₂O₃) were prepared by a precipitation method and their catalytic behavior for nbutane isomerization at low temperature in the absence of H₂ and at high temperature in the presence of H₂ was studied in this paper. The catalytic activities of some of these catalysts were enhanced significantly at both low and high temperatures. At 250°C after 6 h on stream, the steady activity of the most active sample, 60%SZ/Al₂O₃, is about two times higher than that of conventional SZ. The texture properties of catalysts were studied by the methods of XRD and the adsorption of N₂. Experimental evidence of IR of adsorbed pyridine indicates that the significant activity enhancements of SZ/Al₂O₃ catalysts are caused by the increasing of the amount of strong acid sites.     

Preparation and characterisation of LaNixCo1−xO3 thin films on polycrystalline Al2O3-substrates

The perovskite LaNi_xCo_1−xO₃ exhibits metallic conductivity with a change from p- to n-type conduction around x=0·5, thus being a candidate for electrodes or buffer layers in thin film technology. Thin films of LaNi_xCo_1−xO₃ have been grown onto polycrystalline Al₂O₃ substrates by Chemical Solution Deposition (CSD) of nitrate solutions in ethanol/butylacetate. The solutions were applied by dip-coating. After pyrolysis the compounds are formed in air at temperatures between 600°C and 750°C. Formation of the perovskite phase was confirmed by grazing angle X-ray diffraction. Electron micrographs revealed that the obtained films were smooth and crack-free and consisted of nanocrystalline LaNi_xCo_1−xO₃ particles. The thickness of the films was between 200 nm and 400 nm, depending on the conditions of the dipcoating procedure. Specific conductivities of the film were measured using the van der Pauw-method and were found to be around 400 S/cm for LaNiO₃ and around 1 S/cm for LaCoO₃ at room temperature.     

Al2O3 loss prediction model of selective laser melting Al2O3–Al composite

The element/phase loss is undesirable but existing during selective laser melting (SLM) of materials with volatile element/phase, which not only changes the material composition but also affects the molten pool flow. In the previous researches, the effect of remelting on the element/phase loss was neglected during the SLM process, instead, laser energy density was thought to be uppermost. In fact, the SLM process fabricates the parts in a manner of line by line and layer by layer, i.e., additive character, and the remelting in the overlap zone occurs during the SLM process. In this paper, three different Al₂O₃ loss prediction models of SLM Al₂O₃–Al composite by considering the additive character of SLM and the distribution of the Al₂O₃ associated with the different molten pool driving forces were developed. By comparing with the experimental results and predicted results, it is found that the Al₂O₃ is distributed on both sides of the molten pool under the combined action of the Marangoni flow and the evaporation recoil pressure. This kind of Al₂O₃ distribution enhances the effect of the remelting on the Al₂O₃ loss, i.e., the remelting brings a logarithmic increase in the Al₂O₃ loss rate. This determines the final Al₂O₃ loss rate of the SLMed 3D samples. During this study, although the Al₂O₃ loss rate of the single-track is only 33%, the loss rate of SLMed 3D samples increases significantly to 97% when the hatching space of 60 μm and scanning speed of 200 mm/s are utilized, i.e., almost no Al₂O₃ in the 3D sample. Thus, it is more important to reduce the remelting, i.e., overlap rate for reducing the element/phase loss. This study is a benefit for understanding and reducing the element/phase loss in SLM.     

Al2O3-3Al2O3·2SiO-ZrO2耐火材料的相组成

Al<,2>O<,3>-SiO<,2>-ZrO<,2>系耐火材料应用范围广,特别被用作陶瓷辊,具有力学强度高、抗热震性能优良、耐碱类化合物侵蚀和高温蠕变率低的特性.Al<,2>O<,3>-SiO<,2>-ZrO<,2>系耐火材料性能很大程度上取决于其结晶相和玻璃相的总量和化学成分,采用定量XRPD和XRF研究了原料中Al<,2>O<,3>/SiO<,2>比和氧化铝颗粒尺寸分布对结晶相和玻璃相的总量及其化学成分的影响.耐火材料由莫来石、刚玉、ZrO<,2>的多晶体和总量各异的玻璃相组成.莫来石含量及其晶胞参数和成分随烧成温度改变,但主要受原料中Al<,2>O<,3>/SiO<,2>比的影响.     

Al2O3-SiO2质材料抗Al2O3附着的研究

通过实验和热力学分析确认了Al2O3-SiO2质浸入式水口内衬材料的组成对Al2O3附着量的影响.在Al2O3-SiO2质材料中,以Al2 O3-3Al2O3@2SiO2的抗Al2O3附着效果最好,故认为使用不合C的Al2O3-3Al2O3@2SiO2材料制作防止Al2O3堵塞的浸入式水口内衬是可行的.     

Microwave dielectric characteristics of 0.75(Al1/2Ta1/2)O2–0.25(Ti1−xSnx)O2 ceramics

The microwave dielectric characteristics of 0.75(Al_1/2Ta_1/2)O₂–0.25(Ti_1−xSn_x)O₂ ceramics were investigated. The microwave dielectric properties of 0.75(Al_1/2Ta_1/2)O₂–0.25TiO₂ sintered at 1450 °C exhibited a dielectric constant (ϵ_r) of 31.2, a Q·f₀ of 54,590 GHz, and the temperature coefficient of resonant frequency (τ_f) of +12.8 ppm/°C. To control of the τ_f and enhance the Q·f₀ for 0.75(Al_1/2Ta_1/2)O₂–0.25TiO₂, Sn⁴⁺ was substituted for Ti⁴⁺. With an increase of Sn content from 5 to 50 mol%, the ε_r slightly decreased, the Q·f₀ increased and the τ_f shifted from positive to negative value. The τ_f within ±10 ppm/°C of zero was realized for the Sn content below 30 mol% and the microwave dielectric properties had the ε_r value of 31.2–26.3, the Q·f₀ of 54,600–70,700 GHz, and τ_f of +12.8–−9.3 ppm/°C for this compositions. The relationship between microstructure and microwave dielectric characteristics was investigated.     

Al2O3/Al2O3扩散连接机理的研究

采用热压方式进行氧化铝陶瓷材料的扩散连接，并深入探讨了其连接机理，结果表明：采用适当的连接工艺，可使此种材料产生塑性形变，接触面积增加，空洞收缩和闭合，扩散进行充分，1420℃，15MPa热压60min条件下，获得的最高强度为357MPa，超过母材强度平均连接强度为250MPa，是母材平均强度的85％。     

ZnO·Al2O3修饰Al2O3微滤膜的研究

以硝酸锌、硝酸铝、尿素为主要原料,采用均相沉淀法对Al2O3微滤膜进行了ZnO*Al2O3涂覆改性研究.实验结果表明,在适宜的涂覆液浓度、涂覆次数条件下,ZnO*Al2O3改性后可使微滤膜的水通量提高15～20%,且具有较高耐酸碱性能.     

Al2O3-Mi3Al复合材料的机械性能研究

金属间化合物已被用来作为第二相物质增韧增强陶瓷材料。本文研究了Ni3 Al增强Al2 O3 复合材料的热压烧结与性能。含有 1 0Vol% (体积百分数 )Ni3 Al的复合材料在 1 3 50℃、2 5MPa热压 60min其相对密度达到 98%。在不同温度下测试了材料的弹性模量、抗弯强度及断裂韧性 ,并利用扫描电镜对相应试样的显微结构与增强机理进行了分析。     

液相法制备棒状Al2O3及Al2O3-ZrO2陶瓷复合粉体

采用二乙三胺五乙酸（DTPA）为配合剂,以简易的液相法合成出微纳米纤维状Al和Al-Zr前体,煅烧处理制备了棒状α-Al₂O₃和Al₂O₃-ZrO₂复合陶瓷粉体。同时研究了DPTA∶Al³⁺质量比、反应温度与时间对陶瓷粉体形态的影响。利用X射线衍射（XRD）、热分析（TG/DSC）以及扫描电子显微镜（SEM）对粉体进行了表征。结果表明：较高的DTPA∶Al³⁺质量比以及较长的反应时间有利于制备高长径比的纤维棒状Al和Al-Zr配合物前体。合成纳米纤维状α-Al₂O₃和Al₂O₃-ZrO₂前体的最优条件是反应温度60℃,反应时间5.5h,DTPA∶Al³⁺比例为1.2∶1。相应地,该前体煅烧后可以制备出棒状α-Al₂O₃和Al₂O₃-ZrO₂复合陶瓷粉体。     

Hydrothermal synthesis and characterization of nanorods “LixV2−δO4−δ·H2O”

Nanorods “Li_xV_2−δO_4−δ·H₂O” were hydrothermally synthesized with starting agents LiOH·H₂O and V₂O₅, and reducing agent hydrazine monohydrate (NH₂NH₂·H₂O) under alkaline condition at 160 °C. The samples were characterizated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The nanorods obtained have diameters from 80 to 100 nm with length up to several micrometers. Molecular coordination and assembly mechanism can be assumed to explain the formation of one-dimensional nanorods.