On appearance of “cold” layer in explosive consolidation of powders

Abstract. Numerical modeling of explosive consolidation of powders under two-dimensional conditions has been performed. Various regimes of flow depending on detonation velocity have been considered. The appearance of “cold” layer during explosive consolidation of powders has been studied by calculations. Received 12 July 1999 / Accepted 27 April 2000     

纳米HZSM-5分子筛的热稳定性

Nanosized zeolites have received considerable attention in the field of catalysis for their unique properties.When the crystal size of HZSM-5 is reduced to nanoscale,it exhibits higher catalytic activity,less coke and longer catalytic life in CH3OH conversion to hydrocarbons and C2H4 oligomerization[1].     

多金属氧酸盐纳米粉体室温固相合成、表征及催化性能

多金属氧酸盐纳米粉体室温固相合成、表征及催化性能;多金属氧酸盐;纳米粉体;固相合成;催化性能     

Study of Surface Cell Madelung Constant and Surface Free Energy of Nanosized Crystal Grain

1 INTRODUCTION 2. 1 Madelung constant of crystal Surface energy of crystal grain has crucial influ- The Madelung constant, which is used to calculate ence on the electrical and mechanical performances lattice energy and so on[1], is of central importance in of material, especially for material making up of na- the theory of ionic crystal and property of crystal nosized crystal grains because all outstanding per- structure. There is no special difficulty in calculating formances of the mat…     

纳米ZnO的制备及其气敏性能

螯合物;微乳液;溶胶-凝胶;纳米粒子;纳米ZnO的制备及其气敏性能     

Bi-2223喷雾热分解粉末热处理工艺优化

Bi-2223带材目前在电流引线、超导电机、超导电缆、超导限流器等领域实现了许多示范性应用,载流性能是表征其性能的重要指标,而高质量的前驱体粉末是最终带材性能的关键保障.本文选用具有工艺简单、粉末效率高、批次稳定性好等优点的喷雾热分解法制备的Bi-2223前驱体粉末,利用TG-DSC、XRD、SEM等测试手段对低氧条件下不同保温时间烧结的粉末进行分析,并结合最终带材的载流性能测试结果,获得了最优粉末烧结参数,为后续喷雾热分解粉末的进一步生成Bi-2223相以及高性能粉末的制备提供了依据.     

Convective MHD flow of hybrid-nanofluid within an elliptic porous enclosure

The essential aim of this modeling is to scrutinize the irreversibility and heat transfer of hybrid nanomaterial within a permeable medium. The inner elliptic surface experiences the uniform flux and outer wall maintains cold temperature. To scrutinize the impact of porous region, difference between the temperature of fluid and solid matrix was involved and stream function formulation was applied to simplify the equations. Outputs were obtained by means of CVFEM and its accuracy was check by comparing with previous article. Greater values for Ψ can be obtained with rise of Ra while opposite tendency appears for Ha. When Nhs* = 1, Ha = 1, growth of Ra provides 3.86 times lower values of Nu. Nu declines about 70.1% with growth of Ha when Ra* = 5, Nhs* = 0.01. Unfavorable effect of MHD on Nu declines with augment of Nhs*. Nu reduces about 72.5% with augment of Nhs when Ra* = 5, Ha = 1.     

Development of nanosized oxide composites for catalytic CO oxidation

Abstract

Effect of composition and morphology on the catalytic activity in CO oxidation of Co-, Cu-, Ce-containing oxide materials prepared by citrate method has been studied. It was shown that composites consist of well-dispersed oxides Со₃O₄, CuO and CeO₂ with average crystallite sizes 13–24?nm, 14–26?nm and 3–7?nm, respectively. It was established that Co-, Cu-, Ce-oxide nanocomposites demonstrated higher catalytic activity in CO oxidation in comparison with individual oxides. The ternary oxide system Со₃O₄–CuO–СеO₂ (Со:Cu:Се=10:1:1) was found to possess the highest catalytic activity due to formation finely dispersed particles of CuO and СеO₂ oxides simultaneously with nanosized Со₃O₄ species and formation of large quantity of mobile oxygen at the interfaces between the oxide nanoparticles.     

Crystallization of mould powders used in the continuous casting of steel

Mould powders used in the continuous casting of steel play an important role in the heat transfer and lubrication between the liquid metal strand and mould. A range of industrial fluxes was investigated, each sample being decarburized and milled prior to DTA. On heating, the powders undergo silicate crystallization producing exotherms in the range 600°–1000°C, before melting. The activation energy of crystallization (E _a) was determined from the peak shifts of each flux heated at different rates, and ranged from 100–450 kJ/mol.E _a values increased with flux viscosity and decreased with basicity, suggesting that DTA can be applied to mould powder evaluation for use in continous steel casting.     

Oxidation States of Iron in Doped TiO2-SiO2 Sol-Gel Powders: A 57Fe Mössbauer Study

Ceramic coatings obtained by sol-gel routes are more and more attractive for protective purposes. Improved resistance against wet corrosion of steels can be obtained by doping the covering layer with elements like for instance transition ones. It is of major importance to have a clear-cut knowledge of the oxidation state of the doping element, especially after different heat treatments which usually follow the deposition process. Here we report about the oxidation states of 5 wt.% iron doped TiO₂, SiO₂ and mixed sol powders obtained by the sol-gel method with alkoxide precursors added with FeSO₄, 7 H₂O in organic medium. The evolution of the Fe oxidation state versus various heat treatments is followed by ⁵⁷Fe Mössbauer spectrometry supplemented by XRD data. As-dried samples are amorphous and contain ferric Fe cations, with a local distorted oxygen environment. After heating at 500°C during 3 min, ferrous and ferric oxides are evidenced together solely for silica and mixed silica-titania powders, in marked contrast with titania powders where only ferric species exist. The complete ferric state is restored for all samples after annealing at 900°C for one hour.