Al,K和Si对钼粉还原及烧结过程的影响

采用液固掺杂技术将不同含量的KOH,H₂SiO₃和Al（NO₃）₃·9H₂O溶液加入到MoO₂粉末中,并通过还原、压制和烧结工艺制备成钼棒。研究了掺杂钼粉的平均费氏粒度、松装密度与掺杂量的关系,采用扫描电子显微镜（SEM）对掺杂钼粉的表面形貌及烧结钼棒的断口形貌进行了分析。研究结果表明,随着K,Al和Si掺杂量的提高,钼粉的粒度及松装密度均呈先减小后增大的变化趋势,且钼棒晶粒中的气孔呈增多趋势。通过SEM分析发现,由于K,Al和Si的掺杂,烧结钼棒的断裂形貌由沿晶断裂逐渐向穿晶断裂转变。综合比较后认为,Mo-0.005Al-0.27K-0.098Si和Mo-0.005Al-0.36K-0.1305Si为最优配方。     

复合添加Al和TiO2对低碳镁碳砖基质物相组成及性能的影响

以电熔镁砂、超细鳞片石墨为主要原料,以热固性酚醛树脂为结合剂,添加Al和TiO2制备低碳镁碳砖,研究复合引入Al粉和TiO2对低碳镁碳砖基质物相组成及性能的影响。结果表明,埋炭热处理后,添加剂与基质反应生成新相MgAl2O4和TiN或Ti(C,N),使低碳镁碳砖的抗氧化性能明显提高,材料的强度显著增加;此外,添加剂的复合引入有利于改善单独引入Al粉时镁碳砖埋炭处理后易水化的问题。     

Effects of Ce-rich RE on microstructure and mechanical properties of as-cast Mg-8Li-3Al-2Zn-0.5Nd alloy with duplex structure

The effects of Ce-rich RE on the microstructure and mechanical properties of as-cast Mg-8Li-3Al-2Zn-0.5Nd-x RE(x = 0, 1, 2, 3 wt%) alloys were investigated. The results indicated that the as-cast Mg-8Li-3Al-2Zn-0.5Nd alloy mainly consisted of α-Mg, β-Li, AlLi, MgLi2 Al and Al2 Nd phases. With the addition of Ce-rich RE in the alloy,Al3 RE and Al2 RE phases generated and gradually grew into net-like or block-like structure. With the addition of RE, Al-RE phases generated by consuming Al element and, thus, less Al element was dissolved in the matrix and less AlLi phase formed. Furthermore, less AlLi phase means that more Li element released to cause the increase ofβ-Li phase and refine the α-Mg phase. Under the influence of these factors, adding more RE led to higher elongation and lower tensile strength and hardness. With the addition of Ce-rich RE, the yield strength and ultimate tensile strength of the as-cast Mg-8Li-3Al-2Zn-0.5Nd alloy gradually decreased from 180 to 152 MPa and from 215 to 193 MPa, respectively, while the elongation was remarkably improved from 21.1% to 40.2%.     

Dielectric properties, electrical modulus and current transport mechanisms of Au/ZnO/n-Si structures

Au/Zn O/n-Si(MIS)structures were fabricated by using the RF sputtering method and their complex dielectric constant(ε~*=ε’-jε’’),electric modulus(M~*=M′+j M’’)and electrical conductivity(σ=σ_(dc)+σ_(ac))values were investigated as a function of frequency(0.7 k Hz-1 MHz)and voltage(-6–(+6 V))by capacitance-voltage(C-V)and conductance-voltage(G/ω-V)measurements to get more information on the conduction mechanisms and formation of barrier height between Au and n-Si.The lnσ-Lnf plots have two different regions corresponding to low-intermediate and high frequencies.Such behavior of lnσ-lnf plots shows that the existence of two different conduction mechanisms(CMs)at low-intermediate and high frequencies.Moreover,the reverse bias saturation current(I_o),ideality factor(n),barrier height(Φ_(Bo))were determined from the forward bias I-V data and they were found as a strong function of temperature.The value of n especially at low temperature is considerably higher than unity.The values ofΦ_(B0)and standard deviation(σ_s)were found from the intercept and slope ofΦ_(Bo)-q/2k T plots as 0.551 e V and 0.075 V for the region I(80–220 K)and 1.126 e V and 0.053 V for the region II(220–400 K),respectively.The values ofΦ_(Bo)and effective Richardson constant(A~*)were found from slope and intercept of activation energy plots as 0.564 e V and 101.084 Acm~(-2)K~(-2)for the region I and 1.136 e V and41.87 Acm~(-2)K~(-2)for the region II,respectively.These results confirm that the current-voltage-temperature(I-V-T)characteristics of the fabricated Au/Zn O/n-Si SBDs can satisfactorily be explained on the basis of TE theory with double GD of the BHs.     

Fabrication of Fe–TiC–Al2O3 composites on the surface of steel using a TiO2–Al–C–Fe combustion reaction induced by gas tungsten arc cladding

The aim of the present study was to fabricate Fe–TiC–Al₂O₃ composites on the surface of medium carbon steel. For this purpose, TiO₂–3C and 3TiO₂–4Al–3C–xFe (0 ≤ x ≤ 4.6 by mole) mixtures were pre-placed on the surface of a medium carbon steel plate. The mixtures and substrate were then melted using a gas tungsten arc cladding process. The results show that the martensite forms in the layer produced by the TiO₂–3C mixture. However, ferrite–Fe₃C–TiC phases are the main phases in the microstructure of the clad layer produced by the 3TiO₂–4Al–3C mixture. The addition of Fe to the TiO₂–4Al–3C reactants with the content from 0 to 20wt% increases the volume fraction of particles, and a composite containing approximately 9vol% TiC and Al₂O₃ particles forms. This composite substantially improves the substrate hardness. The mechanism by which Fe particles enhance the TiC + Al₂O₃ volume fraction in the composite is determined.     

Dissolution of Al<Subscript>2</Subscript>TiO<Subscript>5</Subscript> inclusions in CaO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> slags at 1823 K

Al-Ti-O inclusions always clog submerged nozzles in Ti-bearing Al-killed steel. A typical synthesized Al₂TiO₅ inclusion was immersed in a CaO-SiO₂-Al₂O₃ molten slag for different durations at 1823 K. The Al₂TiO₅ dissolution paths and mechanism were revealed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Decreased amounts of Ti and Al and increased amounts of Si and Ca at the dissolution boundary prove that inclusion dissolution and slag penetration simultaneously occur. SiO₂ diffuses or penetrates the inclusion more quickly than CaO, as indicated by the w(CaO)/w(SiO₂) value in the reaction region. A liquid product (containing 0.7–1.2 w(CaO)/w(SiO₂), 15wt%–20wt% Al₂O₃, and 5wt%–15wt% TiO₂) forms on the inclusion surface when Al₂TiO₅ is dissolved in the slag. Al₂TiO₅ initially dissolves faster than the diffusion rate of the liquid product toward the bulk slag. With increasing reaction time, the boundary reaches its largest distance, the Al₂TiO₅ dissolution rate equals the liquid product diffusion rate, and the dissolution process remains stable until the inclusion is completely dissolved.     

Effect of TiO<Subscript>2</Subscript> on the viscosity and structure of low-fluoride slag used for electroslag remelting of Ti-containing steels

The viscosity of CaF₂-CaO-Al₂O₃-MgO-(TiO₂) slag was measured using a rotating crucible viscometer. Raman spectroscopy analysis was performed to correlate the viscosity to slag structure. The viscosity of the slag was found to decrease with increasing TiO₂ content in the slag from 0 to 9.73wt%. The activation energy decreased from 95.16 kJ/mol to 79.40 kJ/mol with increasing TiO₂ content in the slag. The introduction of TiO₂ into the slag played a destructive role in Al-O-Al structural units and Q4 units by forming simpler structural units of Q2 and Ti₂O₆4- chain. The amount of Al-O-Al significantly decreased with increasing TiO₂ content. The relative fraction of Q4 units in the[AlO₄]5--tetrahedral units shows a decreasing trend, whereas the relative fraction of Q2 units and Ti₂O₆4- chain increases with increasing TiO₂ content accordingly. Consequently, the polymerization degree of the slag decreases with increasing TiO₂ content. The variation in slag structure is consistent with the change in measured viscosity.     

High-pressure polymorph of TiO2-II from the Xiuyan crater of China

Abundant TiO2-II, a high-pressure polymorph of titanium dioxide, was found in the gneiss fragments of impact-produced breccias from the Xiuyan crater. Rutile in the gneiss was severely fragmented and fine-grained clasts less than 2 ~tm in size had been transformed to TiO2-II. Irregular thin layered TiO2-II is also observed in coarse-grained ruffle fragments, where the TiO2-II layers distributes along fractures and cracks in rutile, About 30 percent of rutile in the gneiss had been transformed to TiO2-II. Fine grains of TiO2-II display light bluish grey to light yellow brown in plane-polarized reflected light. Crystallographic investigation shows that TiO2-II has an orthorhombic structure with space group Pbcn. The cell parameters are a=4.543（1）/~, b=5.491（9）/~ and c=4.895（2） ,~. Its empirical formula calculated on the basis of two oxygen atoms can be written as （Tio.985Feo.oosNbo.oor- Si0.003Zr0.0Ol）l.0O302, or simply formula TiO2. According to the shock effects of quartz and feldspars, the peak shock pressure and post-shock temperature in the TiO2-II-bearing gneiss are estimated to be between 35 and 43 GPa and 300-900~C, respectively. The finding of TiO2-II in the shock-metamorphosed gneiss provides another mineral physics evidence for shock origin of the Xiuyan crater.     

Morphological structure and physicochemical properties of nanotube TiO2

Morphological structure and physicochemical properties of nanotube TiO₂ were investigated. It was found that the TiO₂ nanotube consisted of 2–5 monolayers of TiO₂ molecules, and its inner diameter was between 4.2 and 5.9 nm. The nanotube TiO₂ powder had high specific surface area and pore volume (379 m²/g and 1.431 cm³/g respectively) and its decolorization activity for Reactive Brilliant Red X-3B was 2 times higher than that of raw TiO₂ (p-25). This new type of TiO₂ was hopeful for application in photocatalysis and composite nanomaterial.     

Oxidation behavior of in-situ Al2O3/TiAl composites at 900°C in static air

In-situ Al₂O₃/TiAl composites were successfully synthesized from the starting powders of Ti, Al, TiO₂ and Nb₂O₅. The oxidation behavior of the composites at 900°C in static air was investigated. The results indicate that the composite samples present a much lower oxidation mass gain. Under long-time intensive oxidation exposure, the formed oxide scale is multi-layer. The formation of the outer TiO₂ layer is fine and dense, the internal Al₂O₃ scale has good adhesiveness with the outer TiO₂ scale, and the TiO₂+Al₂O₃ mixed layer forming the protective oxide scale is favorable for the improvement of oxidation resistance. It is believed that the incorporation of Al₂O₃ particulates into the metal matrix decreases the coefficient of thermal expansion of the substrate, and forms a local three-dimensional network structure that can hold the oxide scale. The formation of the oxide scale with finer particle size, stronger adherence, less micro-defects and slower growth rate can contribute to the improvement of oxidation resistance. Nb element plays an important role in reducing the internal oxidation action of the materials, restraining the growth of TiO₂ crystals and promoting the stable formation of the Al₂O₃-riched layer, which is beneficial to improve the oxidation properties.     

Mechanical properties of directionally solidified lead-antimony alloys

The Pb-17wt% Sb alloy was directionally solidified under two solidification conditions: with different temperature gradients (G=0.93–3.67 K/mm) at a constant growth rate (V=17.50 μm/s) and with different growth rates (V=8.3–497 μm/s) at a constant temperature gradient (G=3.67 K/mm) in a Bridgman furnace. Microstructure parameters, such as primary dendrite arm spacing (λ₁), secondary dendrite arm spacing (λ₂), and dendrite tip radius (R), were measured. The microhardness (Hv) and ultimate tensile strength (σ) of the directional solidification samples were also measured. The influences of solidification and microstructure parameters on Hv and σ were investigated. The results obtained in this work were compared with similar experimental researches in literatures. It is shown that the Hv and σ values increase with the increase of G and V, but decrease with the increase of λ₁, λ₂, and R.     

Synthesis of dental resins using diatomite and nano-sized SiO2 and TiO2

The mechanical properties of dental composites were improved by porous diatomite and nano-sized silica (OX-50) used as co-fillers.The resin composites,filled with silanized OX-50 and silanized diatomit...     

Improvement of tensile behaviours of a γ'-Co3(Al,W) strengthened polycrystalline Co-9Al-4.5W-4.5Mo-2Ta-0.02B alloy at room-and high-temperatures by doping Ce

The microstructures and tensile behaviours of cerium (Ce) doped polycrystalline Co-9Al-4.5W-4.5Mo-2Ta-0.02B alloys (doped 0.05 and 0.2 at.% Ce) at room temperature (RT) and 600–800 °C were investigated. In-suit tensile test under SEM was conducted to understand the deformation and damage mechanisms at RT. Aged at 800 °C for 50 h, the 0.05Ce alloy consisted of a Co solid-solution matrix (γ-Co_SS) and nano-scale cuboidal γ′-Co₃(Al, W) precipitates, while for the 0.2Ce alloy, κ-Co₃(W, Mo) precipitates and γ′-depleted zone were present at the grain boundaries in addition to the γ/γ′ microstructure. The 0.05Ce alloy exhibited flow stress anomalies at 700 °C. With higher Σ1∼3 boundary fraction and cleaned-up grain boundary, the 0.05Ce alloy always showed greater strength and elongation than the 0.2 Ce alloy with the grain boundary precipitates at temperatures up to 800 °C. Doped 0.05 at.% Ce made the Co-9Al-4.5W-4.5Mo-2Ta-0.02B alloy have an excellent elongation of 6.1% at 700 °C, owing to a mixed transgranular dimple plus intergranular cleavage fracture. The slip bands transferring through the low-angle grain boundary and slipping of the γ′-Co₃(Al, W) in the 0.5Ce alloy resulted in excellent ductility of 20.4% at RT.     

Al掺杂TiO_2的制备及酸化处理对其光催化活性的影响

锐钛矿相TiO2的光催化活性高于金红石相。采用化学溶液分解法制备了Al掺杂锐钛矿TiO2,并用硝酸对其进行酸化处理。利用TG-DTA、XRD、FTIR、BET和UV-vis等手段对样品进行了表征,通过对甲基橙的降解分析了酸化处理对Al掺杂TiO2光催化活性的影响。结果表明:掺杂Al能有效抑制TiO2由锐钛矿向金红石转变。酸化处理因能增大Al掺杂TiO2的比表面积而使其光催化活性提高。Al/Ti掺杂比为1∶4的样品在酸化处理后具有的光催化活性最高,60min后对甲基橙的降解达到100%。     

Effect of sintering temperature on the physical properties and electrical contact properties of doped AgSnO<Subscript>2</Subscript> contact materials

AgSnO₂ electrical contact materials doped with Bi₂O₃, La₂O₃, and TiO₂ were successfully fabricated by the powder metallurgy method under different initial sintering temperatures. The electrical conductivity, density, hardness, and contact resistance of the AgSnO₂/Bi₂O₃, AgSnO₂/La₂O₃, and AgSnO₂/TiO₂ contact materials were measured and analyzed. The arc-eroded surface morphologies of the doped AgSnO₂ contact materials were investigated by scanning electron microscopy (SEM). The effects of the initial sintering temperature on the physical properties and electrical contact properties of the doped AgSnO₂ contact materials were discussed. The results indicate that the physical properties can be improved and the contact resistance of the AgSnO₂ contact materials can be substantially reduced when the materials are sintered under their optimal initial sintering temperatures.     

Facile synthesis of nanosized sodium magnesium hydride, NaMgH3

The ternary magnesium hydride NaMgH 3 has been synthesised via reactive milling techniques.The method employed neither a reactive H2 atmosphere nor high pressure sintering or other post-treatment processes.The formation of the ternary hydride was studied as a function of milling time and ball:powder ratio.High purity NaMgH 3 powder(orthorhombic space group Pnma,a 5.437(2),b 7.705(5),c 5.477(2) ;Z 4) was prepared in 5 h at high ball:powder ratios and characterised by powder X-ray diffraction(PXD),Raman spectroscopy and scanning electron microscopy/energy dispersive X-ray spectroscopy(SEM/EDX).The products formed sub-micron scale(typically 200-400 nm in size) crystallites that were approximately isotropic in shape.The dehydrogenation behaviour of the ternary hydride was investigated by temperature programmed desorption(TPD).The nanostructured hydride releases hydrogen in two steps with an onset temperature for the first step of 513 K.     

基于Li2MnO3的富锂类高比容量锂离子电池正极材料的研究进展

综述了近几年来基于Li2MnO3的高比容量二元和三元富锂类锂离子电池正极材料的研究进展.重点讨论了富锂材料zLi2MnO3.(1-z)LiMO2(0相似文献   

Selective catalytic reduction of NO x by hydrogen over modified Pd/TiO2-Al2O3 catalyst under lean-burn conditions

A series of Ni, Sn and Ca modified Pd/TiO2-Al2O3 catalysts were prepared by the incipient wetness impregnation method and their catalytic performance for the selective catalytic reduction of NOx by H2 was evaluated. The results showed that the NOx conversion and N2 selectivity were improved over Pd-Sn/TiO2-Al2O3 and Pd-Ni/TiO2- Al2O3 catalysts above 200 ℃. More importantly, the N2 selectivity and high-temperature activity of Pd-Sn/TiO2- Al2O3 catalyst was far superior to the single Pd/TiO2-Al2O3 catalyst. The optimal Sn loading was 2 wt.%. X-ray diffrac- tion （XRD） results showed that the interaction between Pd and Sn promotes the dispersion of Pd over TiO2-Al2O3. Temper- ature-programmed reduction （Ha-TPR） results demonstrated that the addition of Sn contributes to the formation of PdO and improving the redox property of Pd/TiOz-Al2O3. The addi- tives of Ni and Sn also facilitated the absorption of NOx and the oxidation of NO to NOa, which play important roles in the selective catalytic reduction of NOx by hydrogen.     

Ti-M分子筛合成及其性能研究

 以高硅丝光沸石(M分子筛),TiO₂粉和HClO₄为原料,水热晶化法合成Ti-M分子筛.运用FT-IR和UV-vis光谱技术表征合成的Ti-M分子筛样品的物化特性,证明了钛原子进入了M分子筛的骨架位,推测出骨架钛在Ti-M分子筛中的确存在.选择环已酮氨氧化为探针反应,考察了Ti-M对此反应的催化活性,结果表明Ti-M分子筛对环已酮氨氧化具有较好的催化性能.     

Isothermal oxidation behavior and mechanism of a nickel-based superalloy at 1000℃

The oxidation behavior of a nickel-based superalloy at 1000℃ in air was investigated through X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy analysis. A series of oxides, including external oxide scales (Cr₂O₃, (TiO₂ + MnCr₂O₄)) and internal oxides (Al₂O₃,TiN), were formed on the surface or sub-surface of the substrate at 1000℃ in experimental still air. The oxidation resistance of the alloy was dependent on the stability of the surface oxide layer. The continuity and density of the protective Cr₂O₃ scale were affected by minor alloying elements such as Ti and Mn. The outermost oxide scale was composed of TiO₂ rutile and MnCr₂O₄ spinel, and the growth of TiO₂ particles was controlled by the outer diffusion of Ti ions through the pre-existing oxide layer. Severe internal oxidation occurred beneath the external oxide scale, consuming Al and Ti of the strength phase γ' (Ni₃(Al,Ti)) and thereby severely deteriorating the surface mechanical properties. The depth of the internal oxidation region was approximately 35 μm after exposure to experimental air at 1000℃ for 80 h.