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1.
以硅粉和Si3N4粉体为反应剂,偶氮二甲酰胺(AC发泡剂)为添加剂,利用燃烧合成技术在较低氮气压力下制备了高α相含量的Si3N4粉体.采用X射线衍射和扫描电镜分别对产物的物相组成及显微结构进行了表征,研究了AC发泡剂对α相Si3N4粉体的形成和产物颗粒形貌的影响.结果表明,AC发泡剂能促进硅粉快速氮化,产物中α-Si3N4的含量随着AC发泡剂添加量的增加而增加.当AC发泡剂的添加量为24wt%时,产物中α-Si3N4的含量高达85.2wt%.对AC发泡剂作用下的燃烧合成Si3N4的反应机理做了初步探讨,研究表明:AC发泡剂的分解产物N2、CO、NH3不仅增加了坯体的透气性,而且改变了燃烧反应的传热和传质路线,从而促进了硅粉快速氮化和α-Si3N4粉体的生成. 相似文献
2.
为了提高Si3N4产率和降低成本,采用硅粉、氮气作为原料,碳、二氧化硅作为稀释剂,卤化铵作为化学激励剂,通过机械活化和化学激励法燃烧合成制备Si3N4和SiC复相原料。热力学分析表明:特定的工艺条件下氧化硅和碳替代氮化硅作为稀释剂,当氧化硅和碳含量约30wt%时,能得到氮化硅和碳化硅复合陶瓷粉体。以碳的活度为1计(ac=1),燃烧合成时两者稳定共存的温度为1647K;同时,增大氮气压力和降低氧分压是硅粉完全氮化的条件,而不宜提高合成温度。当满足特定工艺条件时(原料加入量为9%Si3N4及15%淀粉和SiO2的混合物、氮气压力大于3MPa、5小时磨研),燃烧合成产物的主晶相为Si3N4、SiC和Si2N2O,而无游离硅,此产物是烧结Si3N4和SiC复合陶瓷或制备Si3N4结合SiC耐高温材料的理想原料。 相似文献
3.
采用机械活化的3Ti/Si/2C/0.2Al单质粉体为原料,在空气中发生自燃反应,成功地合成了Ti3SiC2基材料. 采用XRD、SEM和EDS等手段,分析了合成产物的相组成和微观结构特征. 结果表明,机械合金化3Ti/Si/2C/0.2Al单质混合粉体,不仅细化了粉体颗粒,而且产生严重的晶格畸变,从而明显提高了粉体的反应活性. 把机械活化的粉体暴露在空气中,会发生剧烈的燃烧反应,并引发自蔓延反应,合成Ti3SiC2,冷却后变成多孔块体产物. 燃烧产物由Ti3SiC2、TiC和微量氧化物组成. 产物中Ti3SiC2含量约为83wt%. 产物表层比较致密和均匀,而内部则粗糙且多孔. 产物的表面是以Al2O3和TiO2为主相的氧化膜,氧化物颗粒大小约为2~4μm. 氧化膜厚度约为5~10μm,比较致密. 内部为Ti3SiC2和TiC材料,板条状Ti3SiC2晶粒长约20~40μm,宽约2~4μm,发育完善. 粒状TiC晶粒大小约为3μm. 相似文献
4.
采用机械活化的3Ti/Si/2C/0.2Al单质粉体为原料,在空气中发生自燃反应,成功地合成了Ti3SiC2基材料. 采用XRD、SEM和EDS等手段,分析了合成产物的相组成和微观结构特征. 结果表明,机械合金化3Ti/Si/2C/0.2Al单质混合粉体,不仅细化了粉体颗粒,而且产生严重的晶格畸变,从而明显提高了粉体的反应活性. 把机械活化的粉体暴露在空气中,会发生剧烈的燃烧反应,并引发自蔓延反应,合成Ti3SiC2,冷却后变成多孔块体产物. 燃烧产物由Ti3SiC2、TiC和微量氧化物组成. 产物中Ti3SiC2含量约为83wt%. 产物表层比较致密和均匀,而内部则粗糙且多孔. 产物的表面是以Al2O3和TiO2为主相的氧化膜,氧化物颗粒大小约为2~4μm. 氧化膜厚度约为5~10μm,比较致密. 内部为Ti3SiC2和TiC材料,板条状Ti3SiC2晶粒长约20~40μm,宽约2~4μm,发育完善. 粒状TiC晶粒大小约为3μm. 相似文献
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以铁尾矿和碳黑为原料,采用碳热还原氮化法合成Si3N4粉.利用X射线衍射法测定产物相组成及相对含量,研究了合成温度和恒温时间对反应过程的影响.结果表明,合成温度对碳热氮化合成Si3N4粉的影响显著,随合成温度的升高,产物中Si3N4相含量增加,1450℃时Si3N4相含量最高,是最佳的合成温度.恒温时间对产物相组成的影响不大,但适当延长恒温时间可使还原氮化反应进行得更充分,恒温8h时产物中Si3N4含量最高,是较理想的恒温时间.合成过程中SiO的挥发导致试样较大的质量损失,且随恒温时间的延长而增大. 相似文献
7.
CVI制备Si3N4p/Si3N4透波材料表征与性能 总被引:1,自引:0,他引:1
以SiCl4-NH3-H2为反应体系,采用化学气相渗透(CVI)法制备Si3N4p/Si3N4透波材料.XRF测试表明试样主要含Si、N、O三种元素.XRD测试表明复合材料主要成分为α-Si3N4和非晶沉积物和非晶SiO2,并有微量的β-Si3N4和晶体Si,高温热处理可使非晶沉积物转变为α-Si3N4和β-Si3N4.SEM照片显示颗粒团间结合不够致密,残留气孔偏大.试样的弯曲强度最高为94MPa,介电常数为4.1-4.8. 相似文献
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燃烧合成法制备CaB6的研究 总被引:1,自引:0,他引:1
以CaO、B2O3、Mg粉为原料燃烧合成制备了CaB6粉末.考察了不同反应体系的差热曲线,采用XRD、SEM以及粒度分析技术对燃烧产物、浸出产物进行了表征.结果表明:Mg-B2O3-CaO反应体系872℃附近放热峰的表观活化能E=15.71kJ·mol-1,反应级数n=1.1,反应的表观活化能很小,说明合成CaB6的反应容易发生.燃烧产物由MgO、CaB6以及少量的Mg3B2O6和Ca3B2O6等组成,在空气中进行燃烧合成反应并不生成氮化物;燃烧产物经硫酸浸出处理后CaB6纯度达92.5%;随着制样压力的增大,CaB6粒度逐渐变小. 相似文献
11.
La0.67Ca0.33MnO3 (LCMO)/La0.67Sr0.33CoO3 (LSCO)/LCMO trilayer films are fabricated on single-crystal substrates NdGaO3 (110) and the interlayer coupling are investigated. Compared with LCMO single layer, sandwiches showed the enhanced metal-insulator transition temperature of LCMO layers. The magnetoresistance is dependent on spacer thickness and the peak value dramatically decreases when LSCO layer is thick enough because of shorting by the LSCO layer. The magnetic coercivity HC shows a nonmonotonic behavior with changing spacer layer thickness and the waist-like hysteresis indicates that there is an indirect exchange coupling between the top and bottom LCMO layers across the spacer layer. 相似文献
12.
Choon-W. Nahm 《Materials Letters》2011,65(9):1299-1301
The varistor properties of the ZnO-Pr6O11-CoO-Cr2O3-Y2O3-In2O3 ceramics were investigated for different concentrations of In2O3. The increase of In2O3 concentration slightly increased the sintered density (5.60-5.63 g/cm3) and slightly decreased the average grain size (3.4-2.9 μm). The breakdown field increased from 6023 to 14822 V/cm with increasing concentration of In2O3. The nonlinear coefficient increased from 17.6 to 44.6 for up to 0.005 mol%, whereas the further doping caused it to decrease to 36.8. In2O3 acted as an acceptor due to the donor concentration, which decreases in the range of 1.02 × 1017 to 0.24 × 1017/cm3 with increasing concentration of In2O3. 相似文献
13.
Transparent glasses in the system (100−x)Li2B4O7–x(SrO---Bi2O3---Nb2O5) (10≤x≤60) (in molar ratio) were fabricated by a conventional melt-quenching technique. Amorphous and glassy characteristics of the as-quenched samples were established via X-ray powder diffraction (XRD) and differential thermal analyses (DTA) respectively. Glass–ceramics embedded with strontium bismuth niobate, SrBi2Nb2O9 (SBN) nanocrystals were produced by heat-treating the as-quenched glasses at temperatures higher than 500 °C. Perovskite SBN phase formation through an intermediate fluorite phase in the glass matrix was confirmed by XRD and transmission electron microscopy (TEM). Infrared and Raman spectroscopic studies corroborate the observation of fluorite phase formation. The dielectric constant (r) and the loss factor (D) for the lithium borate, Li2B4O7 (LBO) glass comprising randomly oriented SBN nanocrystals were determined and compared with those predicted based on the various dielectric mixture rule formalism. The dielectric constant was found to increase with increasing SBN content in LBO glass matrix. 相似文献
14.
G. R. Gurbanov 《Inorganic Materials》2012,48(9):888-890
Phase equilibria along the PbSbBiS4-Sb2S3 and PbSbBiS4-Bi2S3 joins of the PbS-Sb2S3-Bi2S3 system have been studied for the first time using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements, and the phase diagrams of the joins have been mapped out. The joins are shown to be pseudobinary with limited series of terminal solid solutions. The solid solutions are p-type semiconductors. 相似文献
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Hollandite-type compounds, Rb2Cr8O16, K2Cr2V6O16 and K2V8O16, were synthesized under high P-T conditions up to 1200°C and 7GPa. The structural refinement using a single crystal of Rb2Cr8O16 confirms that the structure is similar to that of K2Cr8O16. Magnetic measurements indicate that Rb2Cr8O16 is ferromagnetic below 295K, K2Cr2V6O16 paramagnetic down to 77K and K2V8O16 has susceptibility anomaly at 175K. These compounds are all semiconductive and show discontinuities in temperature-resistivity curves at points corresponding to magnetic anomalies. 相似文献
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Epitaxial YBa2Cu3O7/La0.7Ca0.3MnO3 (YBCO/LCMO) bi-layers and La0.7Ca0.3MnO3/YBa2Cu3O7 (LCMO/YBCO) bi-layers were grown on (001)LaAlO3 by pulsed laser deposition, and their microstructures were compared by transmission electron microscopy investigation. In the YBCO(100 nm)/LCMO(150 nm) bi-layers, the LCMO layer consists of columnar grains of ~ 17 nm in diameter and contains mixed orientation domains of [100]c, [010]c and [001]c. The YBCO layer is totally c-axis oriented and the YBCO lattices are tilted − 2.5° to + 2.5° as they grew on the rough surfaces of LCMO columnar grains. For the LCMO(140 nm)/YBCO(140 nm) bi-layers, the LCMO/YBCO interface is sharp and flat. The initial 12-nm thickness of the YBCO layer is composed of c-axis oriented domains, and the upper part of YBCO layer is [100] oriented. The LCMO layer was predominantly [001]c oriented while [100]c-oriented domains were occasionally observed. 相似文献
17.
A systematic study was performed with mixtures consisting of N2, CH4, C2H6 and C3H8, to investigate experimentally phase equilibria and caloric properties and to test the accuracy of thermodynamic correlations. The first part of this Paper reports results of T---p---x---y measurements on ternary systems in the range 20 < p < 120 bar and 140 < T < 220 K. The results are compared with data calculated by generalized equations of state. 相似文献
18.
We investigated the structural and superconducting properties ofc-axis oriented (YBa2Cu3O7)
nY
/(PrBa2Cu3O7)
npr
superlattices with thicknesses of the individual layers down to one unit cell (10nY1; 18>nPr 1). By transmission electron microscopy and X-ray diffraction we find an excellent structural quality of the samples, though the quantitative analysis shows the existence of defects. In superlattices with decoupled YBa2Cu3O7 layers of two unit cell thickness we find a highT
c
value of 75 K. We probed the flux line structure in the superlattices by measurements of the critical current density in magnetic fields. The experiments show that the flux-line dynamics is dominated by the movement of pancake vortices. 相似文献
19.
J.A. Luna-Lpez J. Portelles O. Raymond J.M. Siqueiros 《Materials Chemistry and Physics》2009,118(2-3):341-348
Sr0.3Ba0.7Nb2O6 (SBN) and La0.030Sr0.255Ba0.700Nb2O6 (LSBN) ceramic compounds have been prepared using the traditional ceramic method at two different calcination temperatures (900 and 1000 °C) and later sintered both at 1400 °C. A study of the effects of the calcination temperatures and La substitution on the morphological, compositional, and structural properties of SBN and LSBN is presented using scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis. From Rietveld refinement processes, the XRD patterns were interpreted to evaluate such effects in the structural parameters and the site occupation factors of the heavy metals and oxygen atoms. The effect of the incorporation of La resulted in a 0.25% cell contraction and turned out to be higher than the 0.08% dilation effect produced by the increase of calcination temperature. The La ion with similar effective ionic radius and higher electronegativity is incorporated into the structure occupying the A1 site just like the Sr ions in the SBN compound. Differences in the site occupation factors between the SBN and LSBN samples lead to substantial changes in the physical properties such as temperature of relative dielectric constant maximum, relative dielectric constant, and dielectric loss, correlated with the distortion and the relative orientation of the oxygen octahedra. 相似文献
20.
Xiaohua Sun Ying YangQiaoling Zhang Zhimeng LuoShuang Hou Caihua HuangJun Zou 《Materials Science and Engineering: B》2013,178(18):1244-1248
Bi1.5Zn0.5Nb0.5Ti1.5O7 (BZNT) thin films with different thicknesses as cover layers were deposited on the Ba0.6Sr0.4TiO3 (BST) thin films on the Pt/Ti/SiO2/Si substrates by radio frequency magnetron sputtering method. The microstructure, surface morphology, dielectric and tunable properties of BST/BZNT heterogeneous bilayered films were investigated as a function of the thickness of BZNT films and the effect of BZNT films on the asymmetric electrical properties of BST/BZNT bilayered films was discussed. It was found that BZNT cover layer significantly improved the leakage current and the dielectric loss, and the dielectric constant and tunability of BST/BZNT bilayered thin films simultaneously decreased with the increasing thickness of BZNT films. The BST/BZNT bilayered thin film with a 50 nm BZNT cover layer gave the largest figure of merit (FOM) of 33.48 with the upper tunability of 55.38%. The asymmetric electrical behavior of BST/BZNT bilayered films is probably related to an internal electric field caused by built-in voltages at Pt/BST and BZNT/Au interfaces. 相似文献