Synthesis and sintering of Mg<Subscript>2</Subscript>Si thermoelectric generator by spark plasma sintering

Raw Mg,Si powder were used to fabricate Mg2Si bulk thermoelectric generator by spark plasma sintering （SPS）.The optimum parameters to synthesize pure Mg2Si powder were found to be 823 K,0 MPa,10 min with excessive content of 10wt% Mg from the stoichiometric Mg2Si.Mg2Si bulk was synthesized and densified simultaneously at low temperature （823 K） and high pressure （higher than 100 MPa） from the raw powder,but Mg,Si could not react completely,and the sample was not very dense with some microcracks on the surface.Then,Mg,Si powder reacted at 823 K,0 MPa,10 min in SPS chamber to form Mg2Si green compact,again sintered by SPS at 1023 K,20 MPa,5 min.The fabricated sample only contained Mg2Si phase with fully relative density.     

等离子烧结法制备FeAl/Al2O3复合材料

利用机械活化-放电等离子烧结的方法,将Fe-Al-Al2O3粉末经机械活化后快速烧结,得到致密且晶粒细小的FeAl/Al2O3块体复合材料.研究表明,在w（球）∶w（粉）=13∶1、转速170 r/min、球磨时间25 h的球磨参数下,粉体中的纳米级Al2O3颗粒,在细化和活化Fe、Al金属粉末的同时,还能有效地阻止金属粉末在烧结前合金化生成金属间化合物.在烧结压力40 MPa、烧结温度1050℃、加热时间15 min、保温时间10min的烧结参数下,制备的FeAl/Al2O3复合材料的致密度可达96.4%.     

Nanostructuring and thermoelectric properties of bulk N-type Mg<Subscript>2</Subscript>Si

Preparation and thermoelectric properties of nanostructured n-type Mg₂Si bulk materials were reported. Nanosized Mg₂Si powder was obtained by mechanical milling of the microsized Mg₂Si powder prepared by solid-state reaction. The bulk materials with 30 nm and 5 µm were prepared by spark plasma sintering of the nanosized and microsized Mg₂Si powder, respectively. Both the samples show n-type conduction and the Seebeck coefficient of the sintered samples increase determinately with the grain size decrease from 5 µm to 30 nm. On the other hand, the electrical and thermal conductivity decrease with the decrease of grain size. Accordingly, decreasing their grain size increases their thermoelectric-figure-of-merit. A maximum thermoelectric figure of merit of 0.36 has been obtained for the nanostuctured Mg₂Si sample at 823 K, which is 38% higher than that of microsized Mg₂Si bulk materials and higher than results of other literatures. It could be expected that the properties of the nanocomposites could be further improved by doping optimization.     

Effect of Annealing Process on Microstructure and Mechanical Properties of Ultrafine Copper Prepared by Spark Plasma Sintering

The spark plasma sintering (SPS) method is used to prepare the ultrafine copper with the average grain size less than 10 μm and the tensile strength greater than 280 MPa.The ultrafine copper is annealed at different temperatures for 60 min,and the annealing microstructure is observed and the hardness and the deformation behavior of the bulk copper are tested.The results indicate that the grains grow very slowly when the annealing temperature is less than 450 ℃.However,the grain growth becomes remarkable whe...     

Solid State Reaction Synthesis and Thermoelectric Properties of Mg2Si doped with Sb and Te

Doped with Sb and Te, Mg₂ Si based compounds were prepared respectively by solid state reaction at 823K for 8h. Effects of dopants of Sb and Te on the structure and thermoelectric properties of the compounds were investigated. By calculating the values of the electrical conductivity for Sb-doped sample, the mechanism of electric conduction at 625 K is different. The figure of merit for sample doped with 0.4wt% Te at 500K is 2.4×10⁻³W/mK², and it reaches 3.3×10⁻³ W/mK² at 650K for the sample doped with 0.5wt% Sb. The values are more than 1.4 times and 2.3 times of the pure Mg₂Si sample. JIANG Hong-yi : Born in 1961     

Microstructure and properties of W-15Cu alloys prepared by mechanical alloying and spark plasma sintering process

W-15Cu composite powders prepared by mechanical alloying （MA） of raw powders were consolidated by spark plasma sintering （SPS） process at temperature ranged 1 230-1 300 ℃ for 10 min and under a pressure of 30 MPa. By using high energy milling, particles containing very fine tungsten grains embedded in copper, called composite particles, could be produced. The W grains were homogeneously dispersed in copper phase, which was very important to obtain W-Cu alloy with high mechanical properties, fine and homogeneous microstructure. The microstructure and properties of W-15Cu alloys prepared by SPS processes at different temperature were researched. The results show that W-15Cu alloys consolidated by SPS can reach 99.6 % relative density, and transverse rupture strength （TRS） is 1 400.9 MPa, Rockwell C hardness （HRC） is 45.2, the thermal conductivity is 196 W/m-K at room temperature, the average grain size is less than 2 μm, and W-15Cu alloy with excellent properties, homogeneous and fine microstructure is obtained.     

纳米晶Li7Si3合金的制备与性能表征

为研究纳米结构锂电池阳极材料的特性,试制了纳米晶Li-Si合金.采用优化的纳米晶合金块体材料制备工艺,即熔炼制备粗晶Li7Si3合金铸锭、高能球磨得到Li7Si3非晶粉末,结合放电等离子烧结(spark plasma sintering,SPS)制备得到了纳米晶Li7Si3合金,并对其进行了Rietveld结构精修和杨氏模量测定.结果表明:纳米晶Li7Si3单胞结构参数为a=b=0.4452 nm(比粗晶增加0.38%),c=1.8239 nm(比粗晶增加0.58%),单胞体积Vo=0.313 070nm3(比粗晶增加1.35%).利用纳米压痕法测定纳米晶Li7Si3合金的杨氏模量为(30.6±2.4)GPa.     

Comparative study of β-Si3N4 powders prepared by SHS sintered by spark plasma sintering and hot pressing

β-Si3N4 powders prepared by self-propagating high-temperature synthesis (SHS) with additions of Y2O3 and Al2O3 were sintered by spark plasma sintering (SPS). The densification, microstructure, and mechanical properties of Si3N4 ceramics prepared using this method were compared with those obtained by hot pressing process. Well densified Si3N4 ceramics with finer and homogeneous microstructure and better mechanical properties were obtained in the case of the SPS technique at 200℃ lower than that of hot pressing. The microhardness is 15.72 GPa, the bending strength is 716.46 MPa, and the fracture toughness is 7.03 MPa.m1/2.     

Crystallization of Pd40Cu30Ni10P20 bulk metallic glass with and without pressure

The glass-transition behavior of Pd40Cu30Ni10P20 bulk metallic glass was investigated by differential scanning calorimetry （DSC） and X-ray powder diffraction （XRD）. The effect of pressure on the crystallization behavior of Pd40Cu30Ni10P20 bulk glass was studied by in situ high-pressure and high-temperature X-ray powder diffraction using synchrotron radiation. Phase analyses show at least six crystalline phases in the crystallized sample, namely, monoclinic, tetragonal CuaPd-like, rhombohedral, fcc-Ni2Pd2P, fcc-（Ni, Pd） solid solution, and body-centered tetragonal （bct） NiaP-like phases. The onset crystallization temperature increases with pressure having a slope of 1 1 K/GPa in the range of 0 to 4 GPa. The results are attributed to the competing process between the thermodynamic potential barrier and the diffusion activation energy under pressure.     

Fabrication and Microstructure Evolution of Niobium-Niobium Silicide Composites by Spark Plasma Sintering

By using Nb and Si elemental powders as raw materials,dense Nb/Nb 5 Si 3 composites were successfully fabricated by a spark plasma sintering(SPS)technology.The microstructure of the fabricated composites was analyzed by OM,SEM,XRD and EPMA;the microstructure evolution of the composites was also investigated by a quenching test.The experimental results show that the prepared composites consist of Nb and Nb 5 Si 3 phases;Nb particle uniformly distributes in the in-situ synthesized Nb5 Si3 matrix.During the SPS process,an interfacial reaction occurs between Nb and Si particles to synthesize Nb 5 Si 3 until reactant silicon has been completely depleted.     

球磨镁和石墨混合粉末的相结构及其氢化行为

研究了机械球磨对镁和石墨混合粉末相结构和吸氢性能的影响。结果发现：随着球磨时间的增加,石墨由晶态转变为非晶,而镁的颗粒尺寸则逐渐减小。在温度为573 K,H2压力为1MPa的条件下,样品的吸氢量随着球磨时间的增加而减少。这主要是由于在吸氢的过程中,部分非晶碳与镁形成了MgaC3,消耗了可与氢反应的镁,阻碍了镁与氢的反应,导致样品吸氢量下降。     

Fabrication of Fe-6 .Swt%Si Bulk by Spark Plasma Sintering

Fe-6.5 wt % Si composite compact was fobricated by spark plasma sintering (SPS) . Mechanical alloying( MA )was used to prepare Fe-Si composite powders. The composite powders were sintered by SPS at elevsated temperature from 500℃ to 700℃ . The experimental results indicate that the non-equilibrium state of composite Fe-Si is preserved in the compact. The density of the bulk rises with the increasing temperature and there is no diffusion of silicon and iron in the interface.     

Atomic force microscope study of WC-10Co cemented carbide sintered from nanocrystalline composite powders

In order to compare the spark plasma sintedng （SPS） process plus hot isostatic press （HIP） with vacuum sintedng plus HIP, an investigation was carried out on the topography, microstructure and gain size distribution of nanocrystalline WC-10Co composite powder and the sintered specimens prepared by SPS plus HIP and by vacuum sintering plus HIP by means of atomic force microscopy （AFM）. The mechanical properties of the sintered specimens were also investigated. It is very easy to find cobalt lakes in the specimen prepared by vacuum sintering plus HIP process. But the microstructure of the specimen prepared by SPS plus HIP is more homogeneous, and the grain size is smaller than that prepared by vacuum sintering plus HIP. The WC-10Co ultrafine cemented carbide consolidated by SPS plus HIP can reach a relative density of 99.4%, and the transverse rupture strength （TRS） is higher than 3540 MPa, the Rockwell A hardness （HRA） is higher than 92.8, the average grain size is smaller than 300 nm, and the WC-10Co ultrafine cemented carbide with excellent properties is achieved. The specimen prepared by SPS with HIP has better properties and microstructure than that prepared by vacuum sintering with HIP.     

Fabrication of Ti_2AlC by Spark Plasma Sintering from Elemental Powders and Thermodynamics Analysis of Ti-Al-C System

A ternary-layered carbide Ti 2 AlC material could be synthesized by spark plasma sintering(SPS)technology using elemental powder mixture of Ti,Al and active carbon.By means of XRD and SEM,phases were identified and microscopically evaluated.The experimental results show that the main phase in the product was fully crystallized Ti 2 AlC with small particle size when sintered at 1200 C.The syn-thesis temperature of SPS was 200-400 C lower than that of hot pressing(HP)or hot isostatic pressing(HIP). Through thermodynamics calculations,the mechanism of Ti 2 AlC was studied by calculating changes of Gibbs free energy of reactions.     

Fabrication of High-purity Ternary Carbide Ti3AlC2 by Spark Plasma Sintering （SPS） Technique

The effect of silicon on synthesis of Ti3AlC2 by spark plasma sintering （SPS） from TiC/Ti/Al powders was investigated. X-ray diffraction （XRD） and scanning electron microscope （SEM） were used for phase identification and microstructure evaluation. The results show that addition of silicon can considerably accelerate the synthesis reaction of Ti3AlC2 and fully dense, essentially single-phase （purity 〉98%） polycrystalline Ti3AlC2 could be successfully obtained by sintering 2TiC/lTi/lAl/0.2Si powders at 1 200- 1 250 ℃ under a pressure of 30 MPa. SEM photographs show that the obtained Ti3AlC2 samples from mixtures powders are in plane-shape with a size of about 2-5 μm and 10-25 μm in the thickness dimension and elongated dimension, respectively.     

处理炼油厂“三泥”水相的陶瓷微滤膜再生方法的研究

采用反冲技术和化学清洗对过滤炼油厂“三泥”水相的陶瓷微滤膜进行再生。通过实验研究，确定了合适的清洗剂为加酶洗衣粉，清洗时间30min，清洗剂浓度8g/L，清洗进加压力为0．2MPa，周期为5min的低压脉冲，同时探讨了反冲对膜通量恢复程度的影响，确定了合适的反冲压力为0．5MPa。     

Spark plasma sintering of undoped SnO<Subscript>2</Subscript> ceramics

Various parameters in spark plasma sintering(SPS),such as sintering temperature,holding time,heating rate,and pressure,were adopted to investigate their effects on the densification of pure SnO2 power.The obtained experimental data show that the SPS process enhances densification.The high-density undoped SnO2 ceramics (96.6% of theoretical) was obtained at much lower temperature (1000℃),within a much shorter time,compared to the conventional sintering process.The high-density undoped SnO2 ceramics (96.6% of theoretical) were obtained by SPS,under the condition of temperature:1000℃,pressure:40MPa,heating-rate:200℃/min,and holding time:3min     

过共品铸造Al-Si—Cu—Mg—Fe合金组织性能研究

通过正交试验和单因素试验,考察了Cu、Mg、Zn、Ni和Fe对Al—18Si过共晶铝硅合金室温及高温（350℃）力学性能的影响规律,利用光学金相显微镜（OM）、扫描电镜（SEM）、能谱分析仪（EDX）对合金中富Cu相、富Fe相的组织组成进行了分析．结果表明：Cu、Mg是提高AI-18Si过共晶铝硅舍金室温及高温强度的主要因素;Zn含量增加明显降低合金350℃时的高温强度,改善合金的室温和高温延伸率;Fe降低合金的室温强度,显著提高合金的高温强度;当Cr：Fe=0．35：1,Mn：Cr=2：1,含铁0．8％～1．2％时,Al-18Si-4．0Cu-0．7Mg-0．2Zn-1.0Ni-（0．8～1．2）Fe合金力学性能σb（25℃））310MPa,延伸率受（25℃）≥0．75%,σb（350℃）〉130MPa,延伸率δs（35℃）〉1．5％;合金中富铜相主要以块状Al。Cu相和白灰色花卉状A15Si。cu2Mg8相存在,富铁相主要以三叶草状、树枝状和棒状Al5Si（Cr,Mn,Fe）相存在．     

添加活性炭烧结氧化镁泡沫陶瓷

氧化镁泡沫陶瓷烧结温度很高,为了降低它的烧结温度,对其制备技术进行了研究.设计了以氧化镁为基体的粉料,采用有机泡沫浸渍工艺制备了氧化镁泡沫陶瓷,研究了不添加活性炭和添加活性炭对烧结温度的影响.当活性炭质量分数为0.1%时,泡沫陶瓷烧结温度由1550℃降到1500℃,体积质量由0.926g/cm³上升到0.977g/cm³.XRD结果表明,添加活性炭并未改变氧化镁的晶格结构;SEM显微分析表明,添加的活性炭在陶瓷中未有残留.粗镁浇注实验结果说明,添加活性炭烧结而成的氧化镁泡沫陶瓷具有良好的过滤能力.     

超导材料MgB2的合成

为了获得高纯度的MgB2块材,以Mg粉和B粉为原料,在流动的氢气中,用传统无压烧结方法成功地制备出MgB2块材.系统研究了传统无压烧结合成MgB2块材的工艺;重点讨论了制备过程中的各项参数对样品纯度的影响,包括烧结温度,保温时间,原料的配比等;并且找出了最佳的工艺参数.实验表明,当Mg和B的原子比为1:2≤n(Mg):n(B)≤1.2:2,烧结温度为750℃,保温3 h得到了成分单一的块材.样品的超导转变温度接近39K.