Low Field Microwave Absorption in Nanostructured Ferrite Ceramics Consolidated by Spark Plasma Sintering

The low field microwave absorption (LFMA at 9.5?GHz) properties of clusters of Zn_0.5Ni_0.5Fe₂O₄ ferrite nanoparticles (NPs) consolidated by spark plasma sintering (PSP at temperatures in the 350?C500?°C range) are analyzed. LFMA measurements were carried out at 77 and 300?K. The clusters, formed by ??6 nm NPs, were first obtained by the forced hydrolysis in a polyol method from the corresponding metal acetates. It is found that the sign of LFMA, associated with the spin arrangement in the ferrite depends on the degree of consolidation. For monodispersed NPs, no change of sign is observed at low temperatures. For the as-produced clusters and the consolidated samples, a progressive change in the sign of the signal is observed as the sintering temperature is increased. This change of sign is associated with the occurrence of the triangular or canted Yafet?CKittel spin arrangement.     

放电等离子烧结(SPS)技术

放电等离子烧结（SPS）技术是一种新型的材料制备技术。介绍了SPS技术的发展概况、原理、特点及在材料制备领域的应用。最后，对SPS主发展前景进行了展望。     

放电等离子烧结技术

本文介绍了近几年来在日本迅速发展的放电等离子烧结技术,除概要地介绍了这种烧结新技术的原理和特点外,着重介绍了放电等离子烧结技术在制备梯度功能材料和快速烧结细晶粒陶瓷方面的重要应用,其中后者包括了作者最近在日本大阪府立产业技术研究所取得的部分研究结果．     

放电等离子烧结TiB_2过程中Pa第二峰研究

放电等离子烧结ＴｉＢ２过程中真空室气压Ｐａ有二个峰值，本文对Ｐａ第二峰进行了研究．研究结果表明：Ｐａ第二峰是烧结过程中化学反应导致的气相沉积所致．原始粉末和烧结工艺对Ｐａ第二峰有影响，而Ｐａ第二峰也影响烧结材料的微观结构．     

放电等离子烧结技术的应用

本文主要介绍了一种粉末烧结技术——放电等离子烧结。首先从结构设计上进行了介绍,放电等离子烧结的主要原理是在粉末进行压力烧结的同时施加电流,最终实现材料的致密化。放电等离子烧结的主要优点是烧结温度低、时间短、升温快、材料致密等。最后列举了放电等离子烧结技术在热电材料、硬质材料、功能梯度材料等的应用实例,论述表明放电等离子烧结技术是一种可以制备高性能材料的烧结技术。     

Annealing-induced Grain Refinement in a Nanostructured Ferritic Steel

A nanostructured surface layer with a mean ferrite grain size of ～8 nm was produced on a Fe-9Cr steel by means of surface mechanical attrition treatment. Upon annealing, ferrite grains coarsen with increasing temperature and their sizes increase to ～40 nm at 973 K. Further increasing annealing temperature leads to an obvious reduction of ferrite grain sizes, to ～14 nm at 1173 K. The annealing-induced grain refinement is analyzed in terms of phase transformations in the nanostructured steel.     

放电等离子烧结TiB2过程中Pa第二峰研究

放电等离子烧结TiB2过程中真空室气压Pa有二个峰值,本文对Pa第二峰进行了研究,研究结果表明：Pa第二峰是烧结过程中化学反应导致的气相沉积所致,原始粉末和烧结工艺对Pa第二峰有影响,而Pa第二峰也景响烧结材料的微观结构。     

One-Step Synthesis and Sintering of MgB2 by Spark Plasma Sintering

We have studied the one-step procedure for simultaneous synthesis and sintering of SiC-doped MgB₂ by the spark plasma sintering technique. Two types of composition, one in which Mg is strongly deficient, with the atomic ratio $\mathrm{B/Mg} = 3.75$ , and one in which Mg content is slightly higher than the stoichiometric value, specifically $\mathrm{B/Mg} = 1.87$ , were investigated. The amount of SiC was 12 wt.% and 9 wt.%, respectively. For comparison we also studied the way the deficit of Mg can be compensated in a second process of sintering. The sample with Mg deficit shows that SiC is left almost unreacted but the results are spectacular: the highest critical temperature, 36.5 K, the highest upper critical field and the highest self-field critical current density 6.7×10⁵ A/cm² at 10 K. In the sample with overstoichiometric Mg, SiC is decomposed, carbon diffuses within MgB₂ but the critical temperature is only of 35.8 K and the zero-field critical current density is one order of magnitude lower. The compensation of the deficit of Mg in the two-step procedure is not efficient. The critical temperature is even lower, 35.8 K, the upper critical field is also lower despite SiC decomposition and C diffusion within MgB₂ and the critical current density is slightly above 10⁵ A/cm². However, at low temperatures and fields of order 7 T the sample with overstoichiometric Mg and the sample prepared by the two-step procedure have higher critical current density.     

Fabrication of Intermetallic Compounds by Spark Plasma Sintering

The characteristics of spark plasma sintering, a new method of powder processing, were investigated. Four systems of intermetallic compounds—Ti-Al, Ti-Al-Cr, Mo-Si, and Mo-Si-Nb—were fabricated, and the formation process of compounds, the formed phases, and the microstructure of samples were observed. During the sintering of all the compositions of mixed powders, most of the compounds were formed by combustion reaction which occurred at almost the same temperature as the conventional combustion reaction temperature. The fabricated samples were well densified, however, the relative densities of the Mo-Si samples were lower than the Ti-Al samples. Ultrasonic images show that no internal defects were found in any sample and the grain size became finer with the increase in the Cr content in the Ti-Al system and Nb content in the Mo-Si system. The formed phases of Ti:Al=1:1 composition samples were TiAl and Ti₃Al phases, and Ti-Al added Cr samples consisted of TiAl, Ti₃Al, Cr₂Al, and Cr₉Al₁₇ phases. The sample synthesized with Mo:Si=1:2 mixed powders had only MoSi₂ phases, and Mo-Si samples with added Nb consisted of four phases: MoSi₂ with a small amount of Mo₅Si₃ phases in the matrix and Nb₅Si₃ with unreacted Nb for dispersed phases.     

Fabrication of Iron-base Alloy by Spark Plasma Sintering

Fe-2Cu-2Ni-lMo-0.8C (wt pct) elemental mixed powders were rapidly sintered within 6 min by spark plasma sintering, and the effects of sintering parameters on the densification degree and performance of the assintered materials were investigated. Results showed that when a proper combination of pulse electric current and constant electric current was employed for sintering, the density and bend strength of the as-sintered material reached the maxima, being 7.61×103 kg/m3 and 1540 MPa, respectively. Its corresponding fracture morphology was characterized as the mix of ductile, intergranular and cleavage fractures.     

Spark Plasma Sintering as a Useful Technique to the Nanostructuration of Piezo‐Ferroelectric Materials

This review gathers detail on the processing of piezo‐ferroelectric ceramic materials by spark plasma sintering for the first time. The results reported here clearly indicate that it is a powerful technique and opens the possibility of processing ceramics with controlled sub‐micron or even nanoscale grain sizes.     

SPS制备亚微米晶氧化铝陶瓷

以商业α-Al₂O₃粉体为原料, MgO为烧结助剂, 采用放电等离子烧结技术(SPS)制备亚微米晶氧化铝陶瓷. 系统研究了烧结温度、烧结助剂含量对亚微米晶氧化铝陶瓷的致密化过程及显微结构的影响. 分析结果表明, 1250℃以及0.05wt%分别是最佳的烧结温度和烧结助剂含量; 在此条件下获得的亚微米晶氧化铝陶瓷, 其相对密度达到99.8%TD(theoretical density),平均晶粒尺寸约0.68μm,显微硬度(HV5)达到20.75GPa,在3～5μm中红外范围内直线透过率超过83%. 当MgO掺杂量超过0.1wt%时, 第二相MgAl₂O₄形成, 引起光散射, 降低红外透过率.     

放电等离子烧结技术制备透明氧化铝陶瓷

采用放电等离子烧结技术(SPS)制备了透明氧化铝陶瓷,研究了样品在模具内部的位置对其光学性能的影响,结果表明,在模具中心处样品的直线透过率最高(波长为640nm时为51%,波长为2000nm时为84%),这主要是由于模具内部温度分布不均引起样品晶粒尺寸不同所致.     

Al Alloy Nanocomposite Reinforced with Physically Functionalized Carbon Nanotubes Synthesized via Spark Plasma Sintering

Nanocrystalline Al–11.5Si (in wt%) powders were prepared by high-energy ball milling of microcrystalline Al–Si powders, which were subsequently mixed with pristine and physically functionalized multiwalled carbon nanotubes (MWCNTs) separately and were consolidated by spark plasma sintering. Improvement in MWCNT dispersion was observed as a result of functionalization, which resulted in improved densification of the nanocomposites (NCs). Scanning electron microscopy was performed to understand the agglomeration and dispersion of CNTs. Distribution of MWCNTs, the dislocation activity, and the effect of primary Si particles in NC matrix were studied by carrying out transmission electron microscopy. Nanoindentation was performed to measure the elastic modulus and microhardness of the NCs which showed appreciable improvement for functionalized MWCNT reinforced NC.     

Silicon Carbide Diffusion Bonding by Spark Plasma Sintering

This work reports results of silicon carbide plates, disks, pipes, and pipe–disk couples bonded by a spark plasma sintering apparatus. The joining was conducted at 1900 °C for 30 min with a 35 MPa uniaxial pressure. The samples were analyzed by Scanning acoustic microscopy, which in turn revealed a low amount of small defects at the samples’ periphery. Scanning acoustic microscopy results were verified through scanning electron microscopy and nanoindentation. It was concluded that Spark Plasma Sintering technique may serve as a valid and effective tool for diffusion bonding of high-temperature-resistant silicon carbide with different geometries.