小直径CBN砂轮的磨削特性研究——砂轮修整方法及砂轮要素参数选择

实验研究了小直径 Ｃ Ｂ Ｎ 砂轮平面磨削时砂轮修整方法和砂轮要素（ 接合剂、粒度、硬度、密度） 对磨削过程的影响。磨削过程中 Ｃ Ｂ Ｎ 磨粒的早期脱落影响了小直径 Ｃ Ｂ Ｎ 砂轮 磨削性能的发 挥。 小直径 Ｃ Ｂ Ｎ 砂轮采用杯形（ Ｓｉ Ｃ） 砂轮修整,选择陶瓷接合剂、粒度１７０ ＃ ～２３０ ＃ 、高 硬度和２００ ％ 高密度的要 素参数可取 得良好的磨削效果。     

Anisotropy of the grain size effect on the electrical resistivity of n-type Bi1.9Gd0.1Te3 thermoelectric textured by spark plasma sintering

Spark plasma sintering (SPS) was applied to prepare textured Bi_1.9Gd_0.1Te₃ compounds with various grain structures, tuned by changing in the sintering temperature. The grains forming ordered lamellar structure under texturing are elongated in plane oriented perpendicularly to SPS-pressing direction. As result, average grain size measured parallel to this direction and corresponding to fine-grained samples happened to be much less as compared to relevant size for perpendicular direction characteristic for coarse-grained samples. Anisotropy in electrical resistivity inherent for single crystal was found to be partially recovered in textured samples, i.e. resistivity measured along directions parallel or perpendicular to SPS-pressuring direction is different. Moreover, resistivity for both directions is increasing with decreasing in grain size or with decreasing in intergrain distance. Grain size effect on resistivity due to grain boundary scattering of electrons was found to be anisotropic, since the effect is observed for different ranges of change in average grain sizes.     

Microstructures and mechanical properties of high-entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C ceramics with the addition of SiC secondary phase

The relationships between microstructures and mechanical properties especially strength and toughness of high-entropy carbide based ceramics are reported in this article. Dense (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C (HEC) and its composite containing 20 vol.% SiC (HEC-20SiC) were prepared by spark plasma sintering. The addition of SiC phase enhanced the densification process, resulting in the promotion of the formation of the single-phase high-entropy carbide during sintering. The high-entropy carbide phase demonstrated a fast grain coarsening but SiC particles remarkably inhibited this phenomena. Dense HEC and HEC-20SiC ceramics sintered at 1900 °C exhibits four-point bending strength of 332 ± 24 MPa and 554 ± 73 MPa, and fracture toughness of 4.51 ± 0.61 MPa·m^1/2 and 5.24 ± 0.41 MPa·m^1/2, respectively. The main toughening mechanism is considered to be crack deflection by the SiC particles.     

Creep properties of high dense La9.33Si6O26 electrolyte for SOFCs

High density La_9.33Si₆O₂₆ polycrystals were fabricated by conventional and spark plasma sintering starting from nanopowders synthesized by freeze-drying. The materials exhibit a homogeneous microstructure formed by equiaxed grains with average sizes of 1.1 μm and 0.2 μm-diameter depending on the sintering route. Compressive mechanical tests were performed in air at constant strain rate between 900 and 1300 °C. A gradual brittle-to-ductile transition was found with increasing temperature and/or decreasing strain rate. Grain boundary sliding is the main deformation mechanism in the ductile region, characterized by a stress exponent n = 1 for the conventional sintered (large-grained) material and n = 2 for the spark plasma sintered (fine-grained) material; in both cases, the activation energy for creep was 360 kJ/mol. Effective cation diffusivities have been derived from mechanical data by comparison with appropriate models. The creep properties of lanthanum silicates are reported here for the first time.     

The microstructural origin of rapid densification in 3YSZ during ultra-fast firing with or without an electric field

Recent research has shown that very rapid heating of 3YSZ powder compacts (ultra-fast firing), whether by passing an electric current through the sample (flash sintering) or by using external heat sources, causes a great acceleration of densification rate for a given relative density and temperature. Here, the microstructural evolution of 3YSZ is studied using four sintering methods with widely differing heating rates, produced with or without electric fields. The microstructural development depended greatly on thermal history. Most significantly, slow, conventional heating resulted in pores much larger than the grain size, whereas most pores were smaller than the grain size with the rapid heating methods, whether the heating involved an electric field or not. The smaller pore size clearly provides a major contribution to the acceleration of densification following rapid heating. In contrast, grain growth was not suppressed by rapid heating but was suppressed by an electric field.     

Grain size tailoring and enhanced energy storage properties of two-step sintered Nd3+-doped AgNbO3

AgNbO₃ as a lead-free antiferroelectric material, has received widespread attention in recent years due to its promising application in the aspects of energy storage devices. However, the high remnant polarization and low breakdown strength limits its energy storage properties. In this work, Nd³⁺-doped AgNbO₃ (Ag_1−3xNd_xNbO₃, x=0−0.015) ceramics were prepared and a two-step sintering method was employed. The introduction of Nd³⁺ leads to the enhanced stability of the antiferroelectric phase, refined grain size and increased resistivity. Furthermore, by adjusting the pre-heating temperature in the two-step sintering, the homogeneity of microstructure is improved and the resistance of pre-heated samples increases by one order of magnitude compared with normally sintered samples, leading to the enhanced breakdown strength. Ag_0.97Nd_0.01NbO₃ pre-heated at 1100 °C for 2 h exhibits promising energy storage properties, with a recoverable energy storage density of 3.2 J/cm³ and energy efficiency of 52 % under an applied electric field of 210 kV/cm.     

基于特征标志物的粮油食品掺假鉴别技术研究进展

粮油食品掺假鉴别研究一直是国内外食品质量安全领域的研究热点。基于特征标志物的粮油食品掺假鉴别技术具有灵敏度高、特异性好的优点,近年来在该领域发展迅速。本文综述了基于元素分析、色谱-质谱分析、DNA指纹图谱等技术的特征标志物在粮油食品掺假鉴别中的应用和研究进展,展望了发展趋势,为粮油食品中特征标志物的发现及最佳掺假鉴别技术的研究提供了依据。     

部分市售粮食制品微生物污染状况监测分析

为明确我国市售大米、小麦粉和挂面这三大类粮食制品中储藏危害微生物的污染状况,确定是否存在潜在安全风险因子,抽检了市场上59个米类产品、37个小麦粉类产品和25个挂面类产品中的霉菌和菌落总数两个微生物指标。霉菌检测结果显示,米类产品污染数量分布于≤10 CFU/g,典型数值为<10 CFU/g;小麦粉类产品污染数量分布于<10～10³ CFU/g,典型数值为10² CFU/g;挂面类产品污染数量分布于<10～10² CFU/g,典型数值为10² CFU/g;菌落总数检测结果显示,米类产品污染数量分布较广,为10～10⁴ CFU/g,典型数值为10² CFU/g;小麦粉类产品污染数量分布于10～10³ CFU/g,其中在10² CFU/g和10³ CFU/g两个数量级的分布比例相等;挂面类产品污染数量分布于10²～10⁴ CFU/g,...     

Particle breakage of sand subjected to friction and collision in drum tests

This paper presents a laboratory experimental study on particle breakage of sand subjected to friction and collision,by a number of drum tests on granular materials(silica sand No.3 and ceramic balls)to investigate the characteristics of particle breakage and its effect on the characteristics of grain size distribution of sand.Particle breakage increased in up convexity with increasing duration of drum tests,but increased linearly with increasing number of balls.Particle breakage showed an increase,followed by a decrease while increasing the amount of sand.There may be existence of a characteristic amount of sand causing a maximum particle breakage.Friction tests caused much less particle breakage than collision tests did.Friction and collision resulted in different mechanisms of particle breakage,mainly by abrasion for friction and by splitting for collision.The fines content increased with increasing relative breakage.Particle breakage in the friction tests(abrasion)resulted in a sharper increase but with a smaller total amount of fines content in comparison with that in the collision tests(splitting).For the collision tests,the fines content showed a decrease followed by an increase as the amount of sand increased,whereas it increased in up convexity with increasing number of balls.The characteristic grain sizes D₁₀ and D₃₀ decreased in down convexity with increasing relative breakage,which could be described by a natural exponential function.However,the characteristic grain sizes D50 and D60 decreased linearly while increasing the relative breakage.In addition,the coefficients of uniformity and curvature of sand showed an increase followed by a decrease while increasing the relative breakage.     

加拿大某钒钛磁铁矿工艺矿物学研究

针对加拿大某钒钛磁铁矿的矿石特点,利用MLA(矿物参数自动分析系统)、光学显微镜、XRD、XRF等多种分析手段对矿石进行了详细的工艺矿物学研究,查明了矿石的化学成分、矿物组成、含钛矿物的嵌布粒度及解离度特征,有益元素的赋存状态,为该矿的选冶工艺、流程制定及提高回收率提供了理论依据。