自蔓延高温合成技术及其制备新材料的研究

介绍了自蔓延高温合成技术的发展和国内外研究的概况,分析了SHS技术研究与发展的几个重要方向,介绍了SHS研究的最新动向。对中国学者在此领域的工作所取得的成果给予了介绍和评价。     

多孔陶瓷制备技术的进展

多孔陶瓷是一种含有较多孔隙的无机功能材料,在化工、冶金、运输等领域有着广泛的应用前景.对多孔陶瓷的制备技术及最新研究进展进行了详细的综述,报道了一种在自蔓延高温合成法和发泡法基础上创新的制备方法--自蔓延高温合成喷射法,并对未来研究方向进行了展望,认为今后对多孔陶瓷制备技术的研究将沿着对现有技术进行改进及结合其他种类材料的制备技术进行创新等两个方向开展.     

SHS结合密实化技术制备材料进展

SHS结合密实化技术可以一步完成材料的合成与致密化过程,这是该领域研究的最新方向.本文介绍了国内外正在研究的几种典型的SHS结合密实化技术,对它们的优劣进行了分析,认为SHS/QP方法是一种有希望的材料制备技术.     

自蔓延高温技术制备ZrC粉体(英文)

采用自蔓延高温合成(self-propagating high-temperature synthesis,SHS)技术,以 Zr+C 为反应体系合成了 ZrC 粉末。研究了实验参数对 SHS过程中点火电流、燃烧温度的影响。采用了 3 种碳源,研究了其对最终产物形貌及化学组成的影响。通过添加不同含量的 NaCl 作为 SHS 稀释剂,控制产物粒径及形貌。结果表明:炭黑是高温自蔓延法制备 ZrC 粉体的最佳碳源。由该体系制备的 ZrC 粉末粒径在 0.5～1 μm之间,氧含量为 0.38%。随稀释剂 NaCl 含量增加,体系燃烧温度降低,产物粒径减小。当 NaCl 含量为 30% (质量分数)时,体系燃烧温度下降至 1 810 K,产物 ZrC 粉末的粒径减小至 50 nm。     

自蔓延高温合成制备单相氮化硅镁粉体

通过自蔓延高温合成技术制备了以MgSiN2为主相的粉体,然后利用酸洗工艺除去杂质得到单相MgSiN2粉体.研究了原料配比、稀释剂MgSiN2的添加量和N2压力对燃烧合成产物相组成的影响,并探讨了酸洗条件对洗除MgO杂质的影响.研究结果表明,以化学计量比配制的原料,难以通过自蔓延高温合成法直接合成单相的MgSiN2粉体;...     

自蔓延高温合成V3TiNi0.56Al0.2贮氢材料及其电化学性能

钒基固溶体贮氢合金因其贮氢量大而成为近年来研究的热点,但传统的纯金属熔炼成本高,限制了其应用。文中从理论上计算了V2O5-TiO2-Ni-Al体系的绝热温度Tad=2879 K和单位质量反应热q=-2.80 kJ/g,表明能够进行自蔓延高温反应,且自蔓延高温合成法制备出了钒基固溶体型贮氢合金V3TiNi0.56Al0.2,通过实验研究了V3TiNi0.56Al0.2贮氢合金的组织结构和电化学性能。结果表明,组织结构与真空感应熔炼制备的基本相同,V3TiNi0.56Al0.2合金最大放电容量为350 mA.h/g,活化性能较好,但循环性能和高倍率放电能力差。     

自蔓延高温合成技术的发展与应用

自蔓延高温合成技术是20世纪后期诞生的一门新兴的前沿科学，在粉体合成及陶瓷涂层内衬的制备等方面充分显示其优越性。本文对自蔓延高温合成技术的概念、国内外基本情况进行了阐述，同时简要介绍了自蔓延高温合成的燃烧理论．对利用自蔓延合成技术进行粉体合成及陶瓷内衬钢管的应用研究等作了较为详尽的说明。     

陶瓷材料的SHS超快速致密化技术

自蔓延高温合成(self-propagating high-temperature synthesis,SHS)是一种在数秒～几十秒内即可完成的合成技术,但是直接产物是多孔状的.在SHS产物还处于高温软化状态时立即快速加压(quick pressing,QP),可以一步实现合成和致密化获得致密材料,这一技术被称为SHS/QP技术.传统的高温烧结的致密化过程主要靠原子扩散实现,SHS/QP过程如此之快,其致密化机理尚不明确.为此,探讨了SHS/OP技术制备金属陶瓷和复相陶瓷的致密化机理.研究了SHS/OP技术制备金属陶瓷、复相陶瓷和叠层复合材料的结构和工艺过程,并制备了密实材料.结果表明:基于塑性变形机理,SHS/QP技术能制备出密实、晶粒基本不长大的纳米陶瓷.     

SHS反应熔粘法制备金属基陶瓷涂层管

用自蔓延高温合成(SHS)在钢管内壁生成Al_2O_3陶瓷涂层,制备了金属/陶瓷复合管。选择合适的添加剂及添加量,可以显著改善陶瓷层的涂覆质量。测试了复合管的抗热冲击性能。     

自蔓延高温合成Ti3AlC2 和Ti2AlC及其反应机理研究

以Ti,Al和C的粉体混合物为原料,在纯氩气气氛,25MPa压力,1600℃保温4h条件下,自蔓延高温合成了Ti3AlC2和Ti2AlCT,利用X射线衍射分析（XRD）和扫描电镜（SEM）等手段对反应产物进行了研究,提出了自蔓延高温合成Ti3AlC2和Ti2AlC应具备的条件,并探讨了Ti,Al和C自蔓延高温合成Ti3AlC2和Ti2AlC的反应机理,结果表明,Ti3AlC2和Ti2AlC能够由Ti,Al和C元素经高温自蔓延合成反应来制备,其制备的必要条件是需要极快的加热速率以防止铝熔化并且改变钛的转移路线,Ti3AlC和Ti2AlC综合了金属材料和陶瓷材料的优点,成功的应用自蔓延高温方法合成Ti2AlC2和TiAlC必将成为该类材料纯块体的合成和制备提供好的原料,从而这类材料的实际应用将起到极大的推动作用。     

Fabrication and thermoelectric properties of Yb-doped ZrNiSn half-Heusler alloys

Half-Heusler (HH) alloys constitute an important class of materials that exhibit promising potential in high-temperature thermoelectric (TE) power generation. In this work, we synthesized Zr_1?x Yb _x NiSn (x?=?0, 0.01, 0.02, 0.04, 0.06 and 0.10) HH alloys using a time-efficient levitation melting and spark plasma sintering procedure. X-ray diffraction showed that the samples were predominantly single phased, and that the lattice constant increased systematically with increasing Yb doping ratio. The doping effects of Yb on the thermoelectric properties were studied. It was found that Yb doping consistently decreased the electrical and thermal conductivities. On the other hand, the effects of Yb doping on the Seebeck coefficient were found to be non-monotonic. The magnitude of the Seebeck coefficient (n-type) was increased upon Yb doping up to x?=?0.02, above which Yb doping introduced notable p-type conduction. As a result, the room-temperature Seebeck coefficient of the x?=?0.10 sample became positive although the magnitude was not high. The thermoelectric figure of merit, ZT, reached a maximum of ～0.38 at 900 K for the x?=?0.01 sample. Selective doping on the Ni and Sn sites are necessary to further optimize the TE performance of Zr_1?x Yb _x NiSn alloys.     

Microstructure and Mechanical Properties of Silicon Nitride Materials Fabricated from SHS Powders

Two different silicon nitride powders, one produced by self-propagating high-temperature synthesis (SHS) and one commercial, have been equally processed to obtain dense materials. Y₂O₃ powders as a sintering aid and hot-pressing techniques were used to process the materials. The fracture toughness and strength of the materials prepared have been evaluated and the results comparatively discussed as a function of the microstructure, with special emphasis on the characteristics of the initial powders.     

Synthesis, Sintering, Microstructure, and Mechanical Properties of Ceramics Made by Exothermic Reactions

Al₂O₃-TiC, Al₂O₃-TiC_0.5N_0.5, Al₂O₃-WC, Al₂O₃-SiC, and Al₂O₃-HfB₂ powders were synthesized by the aluminothermic reduction of oxides in the presence of carbon or boron. The reacted powders were milled to reduce the size of agglomerates and subsequently densified without applied pressure to near-theoretical density. Microstructures and mechanical properties of composites made from exothermically reacted powders were compared with similar ceramics made from commercially available powders. In situ sintering was possible in the Al₂O₃-TiC system using a closed graphite crucible to contain reaction gases. The synthesis of β -SiC at temperatures above 1400°C via the direct reaction of the elements (SHS) was compared with SiC made by the magnesiothermic reduction of SiO₂ in the presence of C after removing the MgO by leaching.     

Self-Propagating High-Temperature Synthesis of α-SiAlON Doped by RE (RE=Eu,Pr,Ce) and Codoped by RE and Yttrium

Self-propagating high-temperature synthesis (SHS) was applied to synthesize α-SiAlON powders doped by RE (RE = Eu,Pr,Ce) and codoped by RE and yttrium. The results showed that the weight ratio of α-SiAlON to (α-SiAlON +β-SiAlON) decreased from 70%, 55%, and 25% for europium-, praseodymium-, and cerium-doped α-SiAlON compositions, respectively, and the weight percentage of α-SiAlON phase increased to 100% for both (Eu,Y) and (Pr,Y) systems and 94% for the (Ce,Y) system, indicating SHS is a promising approach for synthesizing α-SiAlONs stabilized by the cations that could not be incorporated into the α-SiAlON structure by conventional sintering methods.     

Hot Isostatic Pressing of Chromium Nitrides (Cr2N and CrN) Prepared by Self-Propagating High-Temperature Synthesis

Cr₂N, CrN, and their mixtures (with desired fractions) have been prepared via self-propagating high-temperature synthesis (SHS) under a controlled nitrogen pressure, followed by hot isostatic pressing at 1300°C and 196 MPa under an atmosphere of argon gas. The combustion temperature increased as the nitrogen pressure increased. Single-phase Cr₂N was formed at 1040°C under a pressure of 0.18 MPa, and single-phase CrN was formed at 1730°C under a pressure of 2 MPa. The mechanical properties of the dense nitride ceramics (99.2% of the theoretical density) have been examined; the Vickers hardness (11.2 GPa for CrN and 14.5 GPa for Cr₂N) increased linearly as the fraction of Cr₂N increased, whereas the fracture toughness (∼4.7 MPa·m^1/2) and bending strength (∼355 MPa) are constant, regardless of the fraction of Cr₂N/CrN.     

Effect of Fe and Cr Addition on the Sintering Behavior of ZrB2 Produced by Self-Propagating High-Temperature Synthesis

An investigation of the sintering behavior of ZrB₂ powder with Fe and Cr (0 to 20 wt%) addition was conducted. It was observed that Fe addition helps to enhance the density of ZrB₂ only up to 10 wt%. Further addition of Fe degrades the sintering by segregation of Fe-rich phases. Formation of a eutectic phase containing a Fe:Zr ratio of 92.57:7.43 was also found in Fe-added samples. The addition of Cr to a ZrB₂ matrix was found to result in swelling of the samples, leading to several cracks.     

自蔓延高温合成技术研究与应用的新进展

自蔓延高温合成（SHS）技术是一门新兴的学科,因其独特的优越性而吸引着各国学者进行研究。本文从研究和应用两个方面介绍了SHS的具体特点,重点分析了SHS技术在制备粉体、烧结、催化剂、强化致密化、焊接、颜料和涂层等典型的工业化实践应用的新进展,并进行了综合比较和系统归纳总结,通过分析,认为目前SHS应用存在的主要问题是如何获得高致密度的产品和怎样严格控制燃烧过程。     

Effect of Heating Rates on the Synthesis of Al2O3–SiC Composites by the Self-Propagating High-Temperature Synthesis (SHS) Technique

Various aspects of in situ formation of Al₂O₃–SiC composites by the self-propagating high-temperature synthesis (SHS) technique have been investigated using thermal analyses (TG/DTA) of a powder mixture (4Al, 3SiO₂, 3C) and pellets in an argon atmosphere at different heating rates. Both the reaction initiation and peak temperatures are found to increase with the heating rates. At lower heating rates, the powder samples do not reveal any exothermic peak possibly because of poor reactivity and sluggish exothermic reaction. The appearance of exothermic peaks in the DTA plots after melting of aluminum indicates reduction of silica by liquid aluminum. Conversion of aluminum is found to decrease marginally with an increase in heating rates. The apparent activation energy of the process compares well with the interdiffusion activation energy of silicon and oxygen, indicating that oxygen diffusion in Si formed at the reaction front may be the rate-controlling factor for this SHS process. From SEM studies it appears that the formation of SiC whiskers is through liquid-phase mass transfer.     

Fabrication and High-Temperature Phase Stability of Mo(Al,Si)2—MoSi2 Intermetallics

A two-step processing technique was used to make dense, homogeneous intermetallics in the Mo(Al,Si)₂—MoSi₂ system. A variation of self-propagating high-temperature synthesis was used, in which starting pellets were nucleated at room temperature to make intermetallic powders from metallic precursors, followed by uniaxial hot pressing at 1600°—1800°C to achieve densification. The samples were held at the hot-pressing temperatures for several hours; therefore, this study also provided qualitative phase-stability information. The solubility limit of Al for Si in MoSi₂ was <5% at 1800°C. Samples that had 10% Al substituted for Si yielded approximately equal amounts of MoSi₂ and Mo(Al,Si)₂.