Microstructure and strength modification of relaxor ferroelectric ceramics through microwave sintering for multilayer capacitors

Relaxor ferroelectric ceramics with the composition of xPb( Mg_(1/3) Nb_(2/3)O_3-yPb (Zn_(1/3)Nb_(2/3)O_3-zPbTiO_3 was fast sintered in a 2.45 GHz microwave system. Microwave-sintered samples illustrate more rapid densification and much smaller grain size microstructure than eonventional sintered samples. Also the microwave processing significantly increases the dielectric strength and flexural strength of the relaxor so that its strength becomes comparable with modified BaTiO_3, and could obtain comparable dielectric properties in comparison with conventional sintering process. Microwave processing has many advantages for sintering of relaxor ferroelectrie ceramics used as multilayer capacitors.     

Properties, phases and microstructure of microwave sintered W-20Cu composites from spray pyrolysiscontinuous reduction processed powders

The effects of microwave sintering on the properties, phases and microstructure of W-20Cu alloy, using composite powder fabricated by spray pyrolysis-continuous reduction technology, were investigated. Compared with the conventional hot-press sintering, microwave sintering to W-20Cu composites could be achieved with lower sintering temperature and shorter sintering time. Furthermore, microwave sintered W-Cu composites with high densification, homogenous microstructure and excellent properties were obtained. Microwave sintering could also result in finer microstructures.     

溶胶-凝胶法制备 Ni0.5Zn0.5Fe2O4纳米材料特性的研究

利用溶胶．凝聚法制备了Ni0.5Zn0.5Fe2O4粉末材料,烧结温度范围600℃-950℃。对材料的结构、红外、磁学和微波吸收特性进行了研究。材料的XRD图谱和原子力显微镜形貌观察表明,材料在纳米尺度范围之内。在500cm-1--600cm-1波数范围内,材料具有明显的红外吸收特性。材料的晶粒尺寸随着烧结温度的提高而增加,且较高温度烧结的材料具有相对低的矫顽力和饱和磁场。利用反射衰减实验研究材料在6GHz--10GHz波段范围的吸波特性,结果表明,0．33mm厚度的样品在常温下的反射衰减达到1．8dBm。     

Microwave sintering of W-15Cu ultrafine composite powder prepared by spray drying &; calcining-continuous reduction technology

The effects of microwave sintering and conventional H2 sintering on the microstructure and properties of W-15Cu alloy using ultrafine W-15Cu composite powder fabricated by spray drying & calcining-continuous reduction technology were investigated.In comparison to the conventional H2 sintering processing,microwave sintering to W-15Cu can be achieved at lower sintering temperature and shorter sintering time.Furthermore,higher performances in microwave sintered compacts were obtained,but high microwave sintering temperature or long microwave sintering time could result in coarser microstructures.     

常压烧结与微波烧结ZTA陶瓷性能

选择Al2 O3 -ZrO2 系统 ,采用微波烧结及常压烧结两种工艺 ,分别对ZTA陶瓷的力学性能和摩擦性能进行了测试比较 ,简单分析了影响ZTA陶瓷摩擦性能的主要因素 ,微波烧结使陶瓷的烧结温度降低 ,致密度提高 ,摩擦因数增大 ,磨损量减小     

Formation of Ca3SiO5 prepared by electric and microwave burning

A new method of sintering Ca3SiO5 by the combination of conventional and microwave heating methods was studied. The influence of transitional metal oxides such as Fe2O3, Cr2O3, MnO2, and V2O5 used as the additive of microwave absorption on the microwave-promoted burning of Ca3SiO5 was investigated. The experimental results indicate that the new burning technique is capa-ble of promoting the sintering of Ca3SiO5. At 1200-1300°C in an electric furnace, Ca3SiO5 can be obtained only when the sample is heated in a microwave for 110-240 s, and the free lime content is below 40wt%. Based on the experiments, Fe2O3, Cr2O3, MnO2, and V2O5 can enhance microwave sintering. Amongst them, Cr2O3 is the most effective. The characteristic of the X-ray diffraction peaks of Ca3SiO5 is similar to those of standard Ca3SiO5, but the peaks are wider.     

Structure and Mixed Electronic-ionic Conducting Properties of La0.6Sr0.4Co1-yFeyO3（y= 0-1.0） Ceramics Made by a Citrate Method

La0.6Sr0.4Co1-yFeyO3（y= 0-1.0） powders were synthesized by a citrate method, and the structure and mixed electronic-ionic conducting properties of the resulting ceramics were investigated. The synthesized La0.6Sr0.4Co1-yFeyO3 powders have a pure perovskite structure and consist of uniform and fine particles. A perovskite struciure with rhombohedral symmetry was certified for the La0.6Sr0.4Co1-yFeyO3 ceramics. The increase of Co/Fe ratio significantly promoted the grain growth and microstructural densification. The La0.6Sr0.4Co1-yFeyO3 compositions with relatively higher Co/Fe ratio exhibit superior mixed conducting properties. The electronic structure and microstructure of the ceramics are responsible for the variation of the mixed conducting properties with Co/Fe ratio.     

Microstructures and mechanical behavior of PM Ti-Mo alloy

1　INTRODUCTIONTitaniumalloyshavebecomewidelyusedbioma terialsforhigh loadimplants ,becauseoftheirgoodbiocompatibility ,excellentcorrosionresistance ,lowdensityandhighspecificstrength .Ti 6Al 4V ,withahighstrengthandagoodmachine ability ,hasbeenthemostsuccessfullyusedTialloyinclinicalapplica tion [1 5] .However ,recentlyscientistshavefoundthatAlandVelementsinthisalloywilldoharmtohumanorganisms ,andshouldbesubstitutedbyothermorehost friendlyelements ,forexample ,Nb ,Zr ,FeandMo[6 10 ] …     

W-Ni-Fe-Cu体系钨合金的液相烧结与低温致密化

采用三元烧结剂Ni-Fe-Cu在低温下（1 573 K）进行了钨合金的液相烧结研究。通过加入2wt%Cu,在1 573 K-30 MPa-90 min的热压条件下成功制备出几乎完全致密并具有较高抗弯强度的93W-3.5Ni-1.5Fe-2.0Cu合金,详细探讨了W-Ni-Fe-Cu体系钨合金的低温致密化机理。     

Microstructural evolution and mechanism of grain growth in magnesia ceramics prepared by high pressure and temperature with ultra-high heating rate

The fast densification method of combustion reaction plus quick pressing was adopted to prepare nanocrystalline ceramics.The densification process of magnesia compact with a particle size of 100 nm was investigated,under the applied pressure of up to 170 MPa,and the temperature range of 1740–2080 K with ultra-high heating rate(above 1700 K/min).High-purity magnesia ceramics with a relative density of 98.8%and an average grain size of 120 nm was obtained at 1740 K,and the grain growth during the densification process was effectively restrained.The characteristic morphology of evaporation-condensation was observed in the compact prepared at 2080 K,which revealed the actual process of mass transfer by gas diffusion.Moreover,the investigation on the microstructure evolution and mechanism of grain growth was carried out,on the basis of as-preserved nanocrystalline ceramics.The result indicated that the grain growth of the nanocrystalline MgO was controlled by the mechanism of evaporation-condensation rather than surface diffusion.Furthermore,the pressure had an influence of restraining the grain growth based on solid diffusion and strengthening the effect of gas diffusion with the increasing temperature.Under the particular conditions,there existed an appropriate temperature for the densification of nanocrystalline magnesia,while the excessive temperature would exaggerate grain growth and impede densification.     

微波与常规方式热处理对Nd2Fe14B/α-Fe纳米交换耦合磁体的作用比较

研究了微波辐射对几种磁性材料的作用 微波的作用决定于材料的种类、形状、大小以及气体压力 与传统的热处理方式相比 ,微波热处理具有显著的特点和优势 ,即其能量利用率很高 ,加热迅速而晶粒生长有限 经微波处理 ,纳米复合永磁体具有明显的剩磁增强作用且表现为单相行为 研究表明 ,金属并非总是微波的反射体     

Crystallization behavior of polymer derived silicon carbide sintered through microwave heating technique

A self-crosslinkable liquid highly branched polycarbosilane(LHBPCS) with 5.07% vinyl group and a C/Si ratio of 1.33 was used as the precursor to prepare Si C ceramic material. Microwave heating technique and conventional heating method were applied for the heating treatment process. It was found that, compared with conventional heating method, microwave heating technique could enhance the crystallinity of Si C ceramic material with small grain size at much lower curing temperature and within shorter time. In addition, the SiO_2 additive could lead to less α-Si C and excess carbon, but worsen the crystallinity of β-Si C in the final samples.     

S355J2W钢自阻加热弯曲成形回弹控制与质量分析

为研究S355J2W高强钢板自阻加热弯曲成形过程中电流密度对回弹的影响及成形件的质量,设计了自阻加热V形弯曲试验和自阻加热几字形弯曲试验,通过改变自阻加热时加载的电流密度大小对成形后零件的回弹现象进行研究.根据试验结果,选择成形精度最高、回弹现象最小的几字形零件进行质量分析,并将其与室温成形的几字形零件进行对比,从而研究自阻加热弯曲成形工艺的优势.将所选取的两个几字形零件分别划分为9个不同的区域,对不同区域的试件进行显微组织观察与力学性能测试,将单向拉伸试验、冲击落锤试验与显微硬度的测试结果作为评价成形件质量的标准,同时将两个零件在力学性能上的差异与显微组织观察的结果联系起来.结果表明:随着电流密度的增大,S355J2W钢自阻加热弯曲成形过程中的回弹得到改善;相比于室温成形的几字形零件,采用自阻加热弯曲成形工艺可以很大程度地改善回弹现象;并且自阻加热成形件的组织更加均匀,其力学性能指标,如抗拉强度,延伸率,冲击韧性和显微硬度也有所提高.     

Kinetic characteristics of liquid phase sintering of mechanically activated W-15wt% Cu powder

The kinetic characteristics of W grain growth operated by diffusion controlled Oswald ripening （DOR） during liquid phase sintering were studied. A liquid phase sintering of W-15wt%Cu was carried out by pushing compacts into a furnace at the moment when the temperature increased to 1340℃ for different sintering times. The results show that liquid phase sintering produces the compacts with considerably low relative density and inversely, rather high homogeneity. On the basis of the data extracted from the SEM images, the kinetic equation of W grain growth, G^n = G0^n ＋ kt, is determined in which the grain growth exponent n is 3 and the grain growth rate constant k is 0.15 μm^3/s. The cumulative normalized grain size distributions produced by different sintering times show self-similar. The cumulative distribution function is extracted from the curves by non-linear fitting. In addition, the sintering kinetic characteristics of W-15wt%Cu compacts were also investigated.     

Effects of activated sintering process on properties and microstructure of W-15Cu alloy

The effects of activated sintering technology of H2 atmosphere sintering on the microstructure and properties of W-15Cu alloy using ultrafine W-15Cu composite powder fabricated by spray drying calcining-continuous reduction technology were investigated.The experimental results showed that W-15Cu alloy,consolidated by activated sintering technology of H2 atmosphere sintering for 1 h at 1300 ℃,with 98.5 % relative density,transverse rupture strength 1218 MPa,Vickers hardness HV0.5 378,average grain size about 1.2 μm and thermal conductivity 192 W/m·K,was obtained.In comparison to the normal sintering process,activated sintering process to W-15Cu alloy could be achieved at lower sintering temperature.Furthermore,better properties in activated sintered compacts were obtained,and activated sintering process resulted in finer microstructure and excellent properties.     

Dielectric Properties of （AgxNa1-x）（NbyTa1-y）O3 System Prepared by Liquid Method

The dielectric properties of （AgxNa1-x）（NbyTa1-y）O3 were investigated, and its dielectric loss and capacitance were measured. The dielectric properties of nanometer （AgxNa1-x）（NbyTa1-y）O3 ceramic prepared by liquid method were better than that by conventional solid method. The average grain size of the nanometer powder（34 nm） obtained by citrate-gel method was small near 500 nm and homogeneous and the microstructure was dense and uniform. In addition, the sintering temperature had a great effect on properties. The dielectric properties of resultant samples were as follows： ε〉500, tgδ〈6 10^-4, αc〈 10 ppm/℃, ρv〉1 012Ω·cm.     

Microstructure and mechanical properties of 8YSZ ceramics by liquid-phase sintering with CuO-TiO2 addition

The 8% (mass fraction) yttrium-partially-stabilized zirconia (8YSZ) ceramic was fabricated via liquid phase sintering at 1 200–1 400 °C by adding different mass ratios of CuO-16.7%TiO₂ (molar fraction) as sintering aid. Relative density, microstructure, Vickers hardness and bending strength as a function of sintering temperature and additive content were investigated. The experiment results show that liquid phase sintering at low temperature can be realized through adding CuO-16.7% TiO₂ to 8YSZ. The Vickers hardness and bending strength of samples with sintering aid are generally much higher than those of samples without sintering aid for all sintering temperatures, and increase with the increase of sintering temperature. When the addition content of CuO-16.7% TiO₂ is beyond 0.5%, the relative density, Vickers hardness and bending strength decrease with the increase of the mass ratio of sintering aid. Low additions of sintering aid are beneficial to aiding densification; high additions of sintering aid are detrimental to the sintered properties mainly due to greater amounts of pores generated by the volatilization of oxygen with the eutectic reaction between copper oxide and titanium dioxide. It is found that the fine grain size and high relative density are two main reasons of the high bending strength and Vickers hardness of the materials.     

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     

Refinement role of electromagnetic stirring and calcium in AZ91 magnesium alloy

Effects of calcium addition and electromagnetic stirring on the microstructure of AZ91 magnesium alloy and refinement mechanism were investigated. The results show that calcium addition ranging from 0.1wt% to 0.3 wt% does not lead to formation of any new phases but cause the refinement of ascast microstructure.However, combined calcium alloying and electromagnetic stirring significantly decrease the grain size, change the morphologies of the β-Mg17Al12 phases,and reduce their volume percentage. The minimum grain size of AZ91 alloy is obtained in the case of the addition of 0.2 wt%Ca with exciting voltage of 100 V. The microstructural refinement is attributed to the increase of the degree of undercooling and nucleation temperature of primary α-Mg phases on the basis of DTA analysis results.     

相场法模拟烧结后期陶瓷晶粒生长及气孔组织演化研究

采用相场模型模拟了烧结后期陶瓷微观组织演化过程。在二维模拟系统中分别设置不同大小、含量以及数量的气孔,分析了气孔的脱钩现象,研究了烧结后期气孔对陶瓷晶粒生长动力学的影响规律。模拟结果表明,陶瓷晶粒尺寸与气孔率和气孔数量成反比,与气孔尺寸成正比。