SHS of NbSi<Subscript>2</Subscript>: A Comparison Between Experiments and Simulations

Summary. Computer simulation results for the Self-propagating High-temperature Synthesis (SHS) of the intermetallic compound NbSi₂ are discussed in comparison with experiments for SHS of mechanically activated powders. The variation of wave speed of the propagation front is considered while varying Nb grain size and thermal conductivity of the starting mixture. A co-operating effect of these two parameters (due to the change in morphology of reactants after milling) is outlined.     

Al-Ti-C体系自蔓延高温合成TiC的形态演变

利用真空自蔓延加热-加压装置,采用X射线衍射(X-ray diffraction,XRD)、扫描电镜(scanning electron microscope,SEM)及能谱(energy dispersive spectrum,EDS)等分析测试手段,研究了Al含量、粉末粒度及C/Ti(原子比,下同)对Al-Ti-C体系自蔓延点燃温度、产物相组成及TiC形态的影响。结果表明,Al含量对TiC的尺寸影响最大,随着Al含量由20%(质量分数,下同)增加到50%时,TiC颗粒的尺寸由3～5μm减小到0.7～0.8μm。C粉粒度和C/Ti对TiC的形貌影响最大,当C粉粒度小于75μm或C/Ti≥1时,TiC的形貌为近球形;然而当C粉粒度不小于75μm或C/Ti1时,TiC的形貌为八面体。     

TiC陶瓷滤片的制备及其性能研究

在对TiC陶瓷的性能及其制备工艺进行分析研究的基础上,利用SHS/PHIP技术制备了致密的TiC-TiB2复相陶瓷材料,并对材料进行切割加工成型和清洗,得到和所需滤片形状相同的TiC-TiB2复相陶瓷片,然后再根据TiC和TiB2化学性能的差异,用王水的强腐蚀性溶解其中的TiB2陶瓷相从而得到孔隙大小均匀的、性能优异的TiC陶瓷滤片.用该方法制备的TiC陶瓷滤片,孔隙的直径范围在2～3μm,分布均匀,可以在任何性质的液体中使用,也可用于熔融金属液的过滤.     

自蔓延法制取锰铝中间合金的实验

首次将自蔓延高温合成法（self-propagating high-temperature synthesis,SHS）用于锰铝中间合金的制备。采用Miedema生成热模型、金属间化合物的双参数模型估算了锰铝中间合金的标准生成焓、标准熵及比热容。通过理论计算确定了Mn3O4-Mn2O3-CaO-Al反应体系的绝热温度。以Mn2O3、Mn3O4和CaO、金属Al为原料,进行了锰铝中间合金的自蔓延反应合成试验,采用化学滴定、X射线衍射以及光学显微镜的方法对产物进行分析。理论计算和实验结果表明：反应体系的绝热温度为3 160 K,确定了该体系进行自蔓延反应的可行性。采用自蔓延合成法制备出了锰含量高达78%以上的锰铝中间合金,拓宽了锰铝中间合金的生产工艺。     

Liquid flame: combustion of metal suspensions in liquid sulfur

Thermodynamic calculations show that some metals can react with sulfur without the formation of gaseous products at normal pressure and yet demonstrate sufficiently high flame temperatures to support the propagation of stable flames. For example, a stoichiometric ternary mixture of iron, manganese, and sulfur demonstrates gasless combustion at an equimolar concentration of iron and of manganese with an adiabatic flame temperature of about 2000 °C. Differential thermal analysis of the mixture shows no exothermic reactions below 280 °C. Therefore, sulfur in the mixture can be safely melted (m.p. 119 °C), converting a powder blend into a liquid suspension that is free from gas bubbles. Symmetrical cylindrical flames in shallow pools of suspensions of Fe and Mn powders in liquid sulfur and combustion of the same liquid mixtures in preheated narrow steel tubes have been studied to determine flame propagation speeds as a function of mixture composition. It was found that, contrary to the behavior of the calculated flame temperature, flame speed decreases with the increase of the manganese content in the mixture and is not affected by mixture dilution with the combustion product. Direct measurements of the flame temperatures by thermocouples indicated a weak dependence of the peak flame temperature on mixture composition and revealed a two-stage flame structure. The existence of the two distinct reaction zones in the mixture of two reactive metals with sulfur is in accordance with qualitative theoretical predictions by the theory of flame with parallel reactions existing in the literature. According to theory, the reaction with the higher flame speed in a corresponding binary single-metal–sulfur mixture will form the leading stage of the complex flame front and will govern the flame propagation speed in the ternary composition. The speed of flame propagation in pure Fe–S mixture is almost three times higher than the flame speed in Mn–S mixture. As a result, the iron–sulfur reaction dominates the flame propagation mechanism in Fe–Mn–S suspension.     

Bulk MgB2 superconductor with high critical current density synthesized by self-propagating high-temperature synthesis method

Pure MgBMgB2 超导体 临界密度 自我传播 预热温度 超导电性SHS method, bulk MgB₂ superconductor, superconductivityProject supported by the Natural Science Foundation of Gansu province of China (Grant No ZS032-B25-019).2005-03-187/2/2005 12:00:00 AMPure MgB2 bulk samples are successfully synthesized by self-propagatlng hlgh-temperature synthesis （SHS） method. The experiments show that the best preheating temperature is 250℃, the highest Jc values of the prepared MgB2 reach 1.5×10^6A/cm^2 （10K, 0.5T） and 1.7×10^6A/cm^2 （20K, 0T）, and the MgB2 particle sizes range from 2 to 5μm. The advantages of this method are that it is simple, economical and suitable for the manufacture of bulk MgB2 materials on industrial scale.     

Layering fabrication,structure, and electromagnetic properties of perovskite phases by hybrid process: self-propagated high-temperature synthesis and selective laser sintering

The paper discusses the fundamentals and the requirements for layer-by-layer manufacturing of three-dimensional porous parts from complex metal oxide systems (piezoceramics PbTi_1?xZr_xO₃; hexaferrites – BaFe_12?xCr_xO₁₉ and SrFe₁₂O₁₉; spinels – Li_0.5Fe_2.5?xCr_xO₄ and high-temperature superconducting ceramics (HTSC) – YBa₂Cu₃O_7?y) and examines the main aspects of the overlapped processes associated with the self-propagated high-temperature synthesis (SHS) and selective laser sintering (SLS). These two techniques presently offered are joined as the original solutions in this external magnetic field. The perovskite phase compositions, morphology, and element distribution of the fabricated samples were analyzed by the X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped the EDX analysis. Optimal regimes for the three-dimensional (3D) parts laser synthesis and some of their electro physical properties were estimated for conducting the concurrent SHS-SLS reactions, both for the case with the applied dc magnetic field and without it.     

空间外差光谱仪中窄带滤光片的光谱特性研究

高光谱空间外差干涉光谱仪的光谱响应由窄带滤光片的光谱特性决定,由于窄带滤光片的制备水平与理论值存在差距,使得发生光谱展宽或波长漂移等现象,在空间外差光谱仪中形成高频和低频光谱混叠从而导致复原光谱失真。在分析滤光片对仪器光谱响应性能影响的基础上,通过在空间外差光谱仪核心干涉组件光栅的胶合过程中,根据窄带滤光片实测波长透过率曲线,利用可调谐激光器动态监测调整光谱仪基频波长的方法改善对其造成的光谱混叠。结果表明,通过实测滤光片特性调整光栅偏转角度来改变基频波长,可最大程度地有效利用仪器所能覆盖的光谱范围,根据干涉图的复原光谱信号可知试验装置的有效光谱范围从758~770.9 nm增加至756~770.9 nm。     

（Al2O3＋TiB2）／Al复合陶瓷与Al连接的研究

（Ａｌ２Ｏ３＋ＴｉＢ２）／Ａｌ复合陶瓷与Ａｌ连接的研究赵金龙董国峰高钦（大连理工大学铸造工程研究中心１１６０２４）关键词：铝；界面／自蔓延高温合成；（Ａｌ２Ｏ３＋ＴｉＢ２）分类号：ＴＢ３３２利用自蔓延高温合成（Ｓｅｌｆ－ＰｒｏｐａｇａｔｉｎｇＨｉｇ...     

自蔓延法制备陶瓷复合材料

自蔓延法制备陶瓷复合材料赵金龙，周文龙，季首华，徐延伟（大连理工大学铸造工程研究中心１１６０２４）关键词：陶瓷复合材料／自蔓延高温合成；三氧化二铝；碳化钛；硼二钛分类号：ＴＢ３３２自蔓延高温合成（ＳＨＳ）方法是由前苏联科学家Ｍｅｒｚｈａｎｏｖ在１９６...