Journal of Central South University of Technology
The ablation properties of C/C composites with four different needled preforms prepared by isothermal chemical vapor infiltration (ICVI), which are super-thin mat lay-up, 0 degrees/90 degrees weftless fabric lay-up, 0 degrees/45 degrees weftless fabric lay-up and 0 degrees/45 degrees twill fabric lay-up, were quantitatively evaluated by performing the ablation tests with an engine torch. And their ablation discrepancies were analyzed according to the surface characteristic, porosity and thermal diffusivity. The results show that the 0 degrees/45 degrees weftless composite has a flat eroded surface with no obvious macroscopic pits. Its thickness and mass erosion rates are decreased by about 46.8% and 34.8%, 25.0% and 27.5%, and 17.5% and 19.4% compared with those of the mat, the 0 degrees/90 degrees weftless and the 0 degrees/45 degrees twill composites, respectively. The ablation properties are mainly controlled by the thermo-chemical effect (oxidation), and a little by the thermo-mechanical effect (mechanical denudation). The needling fiber bundles play an important role in accelerating the ablation process and resulting in the heterogeneous ablation.
关键词:
C/C composites;ablation;fiber architecture;isothermal chemical vapor;infiltration;thermal diffusivity;carbon-carbon;cfrc composites
朱健
,
张晶
,
方方
,
郑时有
,
陈国荣
,
孙大林
稀有金属材料与工程
以AB3型贮氢合金中的LaNi3合金为参考相,选取CeNi3、LaY2Ni9和CeY2Ni93种合金为研究对象,运用X射线衍射技术结合Rietveld结构精修的方法,研究了A侧元素对AB3型贮氢合金晶体结构的影响.研究表明,LaNi3、LaY2Ni9和CeY2Ni9的晶体结构均与PuNi3型结构相吻合,具有R-3 m的空间点群,而CeNi3的空间点群则为P63/mmc.与LaNi3相比,LaY2Ni9合金的点阵常数a和c分别减小了0.7%和2.0%,晶胞体积减小了3.3%;与CeY2Ni9相比,LaY2Ni9合金的点阵常数a减小了0.9%,c增加了0.7%,晶胞体积减小了1.2%.A侧原子的点阵位置具有选择性,即原子半径大的原子倾向于占据点阵中3a位置,半径小的原子倾向于占据6c位置.
关键词:
AB3型贮氢合金
,
稀土元素
,
X射线衍射
,
Rietveld结构精修
Chuansong WU
,
Jinqiang GAO
材料科学技术（英文）
Achieving an effective utilization and exploitation of TIG welding arcs require a thorough understanding of the plasma properties and its physical processes. Through simultaneous solutions of the set of conservation equations for mass, momentum, energy and current, a mathematical model has been developed to predict the velocity, temperature, and current density distributions in argon welding arcs. The predicted temperature fields in arc regions, and the distribution of current density and heat flux at the anode agree well with measurements reported in literatures. This work could lay the foundation for developing a comprehensive model of the TIG welding process where a dynamic, two-way coupling between the welding arc and the weld pool surface is properly represented.
关键词:
Welding
,
null
,
null
,
null
杜晓辉
,
张海涛
,
李雪礼
,
谭争国
,
刘宏海
,
高雄厚
催化学报
doi:10.1016/S1872-2067(11)60622-6
以NaY分子筛为原料,采用二次交换二次焙烧工艺,制得了LaNH4Y-1,LaY-1,LaNH4Y-2和LaY-2四种分子筛样品.采用粉末X射线衍射结合Rietveld结构精修确定了La离子在分子筛中的分布.结果表明,在离子交换过程中,La离子首先定位于分子筛超笼里；经焙烧脱水后,La离子迁移到分子筛方钠石笼并定位在SI'位置.T-O-T键角的变化表明,LaNH4Y-1表现出最大的骨架扭曲性和结构不稳定性.La离子定位在SI'位置与O3配位,增加了T-O3的键长,表明稀土离子不仅通过控制骨架脱铝抑制晶胞收缩,还可能通过影响T-O3键长使晶胞增大.在REY分子筛中,稀土的主要作用是稳定分子筛结构,从而调节其酸性和催化活性.采用红外光谱和NH3程序升温脱附考察了La离子和NH4+对分子筛酸性的影响,并总结了稀土离子稳定Y型分子筛的机理.
关键词:
LaY型分子筛
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Rietveld结构精修
,
镧离子迁移
,
骨架结构
,
热稳定性
ZHU Xiaolong LIN Leyun Surface Technology Center
,
General Research Institute for Nonferrous Metals
,
Beijing
,
110083
,
ChinaTo whom correspondence should be addressed
材料科学技术（英文）
The corrosion product films of two kinds of B30 tubes(similar to CDA 715)exposed to seawat- er for various periods of time were investigated by SEM,AES and XPS.The results show that the pro- tective corrosion product film is thin,uniform and adherent.FeOOH is found to be present in the film surface,which confirms the hypothesis that iron hydroxide segregates at the surface of the film.The FeOOH promotes Ni enrichment in the corrosion layer by preventing Ni from running off.The corro- sion product film with no protectiveness is of lay- ered structure,loose and bad adherence.The for- mer film is formed through direct oxidation and the latter by precipitation and redeposition from dis- solved species.
关键词:
Cu-Ni alloy
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null
,
null
YU Xuejie WANG Jianlin Shanghai Iron and Steel Research Institute
,
Shanghai
,
ChinaZHOU Tianjian Anhui Institute of Technology
,
Hefei
,
China YU Xuejie
,
Senior Engineer
,
Shanghai Iron Steel Research Institute
,
1001 Taihe Road
,
Wusong
,
Shanghai
,
China.
金属学报(英文版)
In order to clarify that the IFP and the “Type 2”α phase are also arising from TiC,a metastable β-Ti alloy was selected for investigation in this work.The results showed that af- ter heating the alloy just below the α+β→β transus temperature and quenching,the TiC lay- er existed at the α/β interface.The morphology of TiC is similar to that of the IFP arising from TiH_2 in the α-β two-phase alloys.The IFP TiC also provided an easy crack path or the crack initiation sites.The fracture is also identical to that caused by IFP TiH_2.The arced diffractions(characteristic of “Type 2”α)were found in the selected area diffraction pat- terns of some specimens which had been isothermally aged after solid solution treatment.The particles which bring on the arced diffractions may be TiC on the basis of structure and lat- tice parameter analysis,not the so called “Type 2”α phase.
关键词:
interface phase(IFP)
,
null
,
null
,
null
Chenming XU
,
Hongming GAO
,
Guangjun ZHANG
,
Lin WU
材料科学技术（英文）
An arc light radiation phenomenon in TIG welding process was studied through experiments and theoretical analysis. The arc spectra were acquired under a variety of welding parameters from 200 nm to 1000 nm wavelength range in TIG. The influence of welding parameters on the arc radiation was discussed. The radiation energy from lines emission mechanisms was calculated and the comparison was made with the one from the continuum emission mechanisms. The result shows that the radiation energy from the line emission mechanisms is equal to the one from the background. Based on the experiments and analysis, a physical model of arc light radiation has been developed. In this model, the arc plasma was presumed to be in local thermal equilibrium (LTE) with light thinness property. The Bolzmann distribution and Saha equation were applied to establish the arc light radiation model. This helps lay the foundation for further mathematical modeling of the arc light radiation.
关键词:
Spectral diagnosis
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null
,
null
,
null
Xinlian WANG
,
Jiarong LEI
,
Dezhi WANG
,
Ningkang HUANG
材料科学技术（英文）
Sapphire crystals with different orientations may cone from implantation of Nb+ ions under different conditions and succedent annealing at reducing atmosphere. Optical analysis results show that the main optical absorption bands lay in the higher energy side of the spectra in the samples. The absorption curves were evaluated by Gaussian fitting based on the F-type centers, which were confirmed by luminescence measurements. The results of Gaussian fitting show that there were F center, F+ center, F2 center, F2+ center and F2+2 center in the Nb+ ions implanted sapphire. After annealing at different temperature, all types of color centers decreased, and the higher the annealing temperature, the more the defects decreased. Sub-micrometer particles were observed by the scanning electron microscopy.
关键词:
Ion implantation
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null
,
null
