牙科复合树脂中无机填料双峰混合体的堆积性能

通过测定用作牙科复合树脂中无机填料的粉体的振实密度 ,使用Mathematica和SAS/STAT软件 ,用统计学的方法得到了双组分粉体混合物的粒度分布与堆积体比容之间关系的经验公式。说明可以使用引入了粒度分布宽度作为变量的改良线性堆积模型预测双峰粉体的堆积密度。结论为双组分粉体大小粒径比相差越大 ,混合物堆积密度越高。该结论为优化牙科复合树脂的组成提供了理论依据     

Fe73．5Cu1Nb3Si13．5B9纳米晶磁粉芯磁性能研究

用Fe73.5Cu1Nb3Si13.5B9纳米晶粉体,加入一定量的塑化剂,通过模压成型方法制备磁粉芯.实验结果表明,在一定粒度范围内,磁导率μ随粉体粒度增大而增大,品质因数Q,随着粒度的增大而减小,且在一定频率范围内,μ呈现良好的频率稳定性;塑化剂质量百分含量α越大,μ越小.当α=6.5%时,μ达到最大值31.8.0～300kHz范围内,α与Q成反比;300～1000kHz范围内,α与Q成正比例关系;磁导率μ随着成型压力的增加而提高,相反,压力越大,Q值越小;磁导率随着磁粉芯测试温度的提高逐渐减小,0≤f≤700kHz范围内,温度升高,Q降低,700kHz≤f≤1000kHz范围内时,温度升高,Q值升高;随退火温度的增加,μ和Q均呈现先增大后减小的趋势.     

气力输送中PVC粉体静电带电影响因素

为了研究工业中常用的聚氯乙烯(PVC)粉体在气力输送过程中的静电影响因素，以PVC粉体为输送对象，以荷质比为指标，研究PVC粉体的下料质量流量、气流速度、气单位体积的气体中所含粉体的质量和球阀开度对粉体带电的影响。结果表明：当下料质量流量一定时，PVC粉体的荷质比会随气流速度增大而增大，随球阀开度减小而减小；当气流速度一定时，PVC粉体的荷质比会随下料质量流量增大而减小，输送颗粒的荷质比存在临界值为0.2μC/kg;当单位体积的气体中所含粉体的质量一定时，下料质量流量对PVC粉体荷质比影响要大于气流速度对其的影响；当下料质量流量一定时，PVC粉体的荷质比会随球阀开度的减小而减小。     

吸附介质结构参数对变压吸附性能的影响

通过对我们自行研制的产氧量为Q＝1－5L／min的双吸附柱的小型PSA分离空气制氧系统进行的吸附过程计算，分析了空气流经PSA多孔吸附介质填充床层时，多孔介质结构参数及操作参数对吸附性能的影响。结果表明：1.渗透率随介质颗粒直径的增大而增大，并且随颗粒直径的增加，其对渗透率的影响增加。而压降随多孔吸附介质颗粒直径的增大而减小。2.渗透率与空隙率基本成正抛物线关系，压降随空隙率的增大而减小。3.压降随着渗透率的增大而减小。4.在不同的毛细管截面形状条件下，空隙率和渗透率的影响较小，而颗粒直径对渗透率的影响较大，颗粒直径较大时，这种影响才比较明显，当吸附介质颗粒直径或空隙率一定时，细长条截面的填充方式具有最高的渗透率。5.对于较低流速范围（约＜0.1m/s），流速对压降的影响较小，否则，影响较大。     

制备工艺因素对碳化硅水基浆料粘度的影响研究

研究了浆料搅拌时间、分散剂含量、粉体含量和p H值等对碳化硅水基浆料粘度的影响。结果表明,水基浆料的粘度随搅拌时间的增加而减小,超过24 h后趋于平稳;水基浆料粘度随分散剂含量的增加而减小,但超过一定含量时反而增大;随着Si C水基浆料中粉体含量的逐渐增加,浆料的粘度总体呈逐渐增大的趋势,粉体含量超过30%时,浆料的搅拌分散时间会延长1.5倍;p H值高于5.5后,水基浆料的粘度随p H值的增加急剧提高,超过8.15时略有下降。通过优化工艺参数,可制备出粘度低于1.0 Pa·s、粉体含量为30%的Si C水基浆料。     

水热介质pH值对纳米(Ce)ZrO_2晶粒制备的影响

用水热法制得纳米 (Ce)ZrO2 粉体 ,其晶粒粒度为 3～ 7nm ,而且为单一分散。用XRD、TEM分析了水热媒介pH值对粒度、m相含量、晶粒形貌的影响关系。结果表明 :水热煤介 pH值增大 ,ZrO2 晶粒也增大 ;pH值减小至酸性时 ,ZrO2 晶粒中出现部分m相 ,且晶粒易团聚     

水热介质pH值对纳米(Ce)ZrO2晶粒制备的影响

用水热法制得纳米 (Ce)ZrO2 粉体 ,其晶粒粒度为 3～ 7nm ,而且为单一分散。用XRD、TEM分析了水热媒介pH值对粒度、m相含量、晶粒形貌的影响关系。结果表明 :水热煤介 pH值增大 ,ZrO2 晶粒也增大 ;pH值减小至酸性时 ,ZrO2 晶粒中出现部分m相 ,且晶粒易团聚     

PVDF粉末颗粒特性表征

利用多晶X射线衍射仪、氮吸附仪、激光粒度仪和偏光显微镜,系统分析不同乳液聚合条件制备的聚偏氟乙烯(PVDF)粉体树脂的结晶度、粒径分布、比表面积和形态等颗粒特征。结果表明,PVDF粉体的颗粒形态为不规则薄片状,粒径分布呈四峰型;随乳液聚合反应时间增加,粉体的结晶度和粒径分布有增大趋势,比表面积有减小趋势。     

液相沉淀法制备超细白炭黑的改性研究

主要研究了以水玻璃和硫酸为原料合成沉淀白炭黑反应过程中，添加表面活性剂聚乙二醇对合成白炭黑的粒度、堆积密度及吸油值的影响，及选择聚乙二醇加入量为6％时分别加入不同量改性剂AF-5及1010对生成白炭黑堆积密度及吸油值的影响。研究发现：随着聚乙二醇添入量的增加，白炭黑的平均粒径及堆积密度减小、吸油值增大；两种改性剂加入量的增加都使白炭黑吸油值不断降低，达到某一值后趋于平缓。结果表明：改性剂的添加可以使白炭黑的性能得到较大改变，从而扩大其应用范围。     

TiO2掺杂Ce0.8Sm0.2O1.9材料的制备与表征

通过凝胶浇注法制备了TiO2掺杂量为0-15％（摩尔分数）的T1O2-Ce0.8Sm0.2O1.9（TixCe0.8xSm0.2O2-y，TSDC）粉体。采用X射线衍射、透射电镜对所得粉体的相组成和颗粒形貌进行了测试分析，考察了粉体的烧结性能。此外，还测定了不同组成TSDC烧结体在空气和氢气气氛中的电导率。研究结果表明：凝胶浇注所得干凝胶在较低温度（500℃）下煅烧后，TiO2和Sm2O3即能完全固溶进CeO2晶格中，形成具有单一立方相结构和纳米粒度的TSDC粉体，且粉体粒径随TiO2掺杂量的增加而增大。上述粉体具有较高的烧结活性，其成形压坯在1400℃烧结后，相对密度可达95％以上。此外，测试气氛对TSDC材料的电导率有明显的影响，在空气中，随着TiO2掺入量的增大，TSDC材料的电导率减小，而在H2气氛中，电导率则明显增大，TiO2的掺入，降低了电导活化能。     

影响二维空气圆柱型光子晶体完全禁带的主要因素研究

研究了晶格结构、填充比、介电常数比三个主要因素对二维空气圆柱型光子晶体完全禁带的影响。利用Bandsolve软件分别优化计算得到不同晶格结构、不同介电常数比的最大完全禁带,以及对应结构参数之间的关系。对于相同介电常数比,六边形晶格可获得较宽的完全禁带;而对于相同晶格结构,介电常数比越大,完全禁带宽度越大。     

Numerical study on compression processes of cohesive bimodal particles and their packing structure

In this study, the compression characteristics of bimodal cohesive particles were investigated using a discrete element method (DEM) simulation. The compression and packing processes were simulated under different conditions of size ratios of 1–4 and fine particle mixing ratios of 0–0.5. The cohesive force was expressed using the surface energy proposed by the Johnson-Kendall-Roberts (JKR) cohesion model having a surface energy of 0–0.2 J/m². The calculated results demonstrated that even in the case of cohesive particles, an increase in the particle size ratio reduced the void fraction of the powder bed during the packing and compression processes. In addition, it was found that the cohesive force decreased the contact number, especially the coarse-coarse contacts, although it had little impact on the void fraction. Our DEM simulations suggested that it is necessary to evaluate the contact numbers even under similar void fractions, which will be essential in the case of different material mixtures, such as all-solid-state batteries.     

滑石粉涂层复合材料的制备及其介电性能和电导率

以玻璃纤维膨体纱织物为基材,以环氧树脂E44为粘着剂,650低分子量聚酰胺为固化剂,以价格低廉、密度较小的滑石粉为吸波材料,制备了滑石粉涂层复合材料。重点探讨了滑石粉含量及涂层厚度对介电常数和电导率的影响。结果表明制备的滑石粉涂层复合材料具备良好的介电性能。在研究的频率范围内,滑石粉的含量、涂层厚度对复合材料的介电常数实部和虚部、损耗角正切值、电导率的实部和虚部影响较大。     

Microscopic investigation of the packing features of soft-rigid particle mixtures using the discrete element method

Soft-rigid mixtures (SRMs) have become popular materials in civil engineering applications for environmental protection because of their outstanding engineering properties. In soft-rigid granular systems, packing features strongly affect shear behavior and directly reflect internal stability. However, the packing features of SRMs have not been previously reported. The aim of this study is to explore the effect of material susceptibility on packing features from a microscopic perspective. First, fifty-three numerical assemblies were established to thoroughly investigate the effects of the size ratio and soft content on several microscopic quantities, e.g., the particle structure, stress network, and local void. Then, the effects of the confining stress and stiffness ratio were analyzed from another eighteen assemblies by six chosen indexes. The results provide microscopic insights into the void structures and stress transmission of SRMs in a packing state.     

A discrete element analysis of elastic properties of granular materials

The elastic properties of a regular packing of spheres with different tolerances were evaluated using the discrete element method to elucidate the mechanisms behind the discrepancies between laboratory experiments and theoretical predictions of the classic Hertz-Mindlin contact law. The simulations indicate that the elastic modulus of the packing is highly dependent on the coordination number and the magnitude and distribution of contact normal forces, and this dependence is macroscopically reflected as the influence of confining pressure and void ratio. The increase of coordination number and the uniformity of contact normal forces distribution with increasing confining pressure results in the stress exponent $n$ for elastic modulus being higher than 1/3 as predicted by the Hertz-Mindlin law. Furthermore, the simulations show that Poisson’s ratio of a granular packing is not a constant as commonly assumed, but rather it decreases as confining pressure increases. The variation of Poisson’s ratio appears to be a consequence of the increase of the coordination number rather than the increase of contact normal forces with confining pressure.     

Dielectric and electrical properties of ordinary Portland cement and slag cement in the early hydration period

The dielectric constant and electrical conductivity of ordinary Portland cement (OPC) with water-cement ratios (w/c) of 0.30, 0.35 and 0.40 were measured for the first 30 h hydration, using a microwave technique in the frequency range 8.2–12.4 GHz. It was found that both the dielectric constant and electrical conductivity of the cement paste are sensitive to the water-cement ratio, the higher the w/c value, the greater the dielectric constant and electrical conductivity, and the longer the hydration time. We also found that the higher the frequency the greater the electrical conductivity but the smaller the dielectric constant. The dielectric constant and electrical conductivity of high- and low-slag cement with water-solid ratio (w/s) of 0.40 were measured in the first 30 h after mixing. The changes in dielectric constant and electrical conductivity of low-slag cement with time are similar to that of OPC, but the high-slag cement shows very different dielectric and electrical properties compared with OPC and low-slag cement. The relationship between the dielectric and electrical properties of cement paste and cement hydration was also discussed.     

Dielectric properties of Ni-coated BaTiO/sub 3-/PMMA composite

Dielectric properties of Ni-coated BaTiO(3)-PMMA (polymethyl methacrylate) composite were studied from an embedded capacitor application viewpoint. Volume loading of up to 50% was attempted, and the results were compared with uncoated BaTiO(3)-PMMA composite. Ni-coating on BaTiO(3) powder was found to greatly improve the dielectric properties of the composite, especially the dielectric constant value. K values of about 100 with temperature-stable X7E characteristics were realized.     

粉体堆积密度的理论计算

考察了紧密堆积时多级理想球形颗粒混合粉体的堆积密度的理论值与粒级组分数的关系,紧密堆积时颗粒的粒度分布特征,以及堆积密度的理论值与单一粒径粉体空隙体积分数、颗粒干扰宽度的相关关系。研究表明,原始堆积密度越大,多粒级理想球形颗粒混合粉体达到相同的堆积密度所需的粒级数越少,各粒级的体积含量随着粒级的增加呈指数下降,且原始堆积密度越大,下降速度越快;其粒度分布符合对数正态分布;堆积密度的理论值与单一粉体空隙体积分数、颗粒干扰宽度的符合二元二次非线性关系。     

Some Physical Properties of Pure and Doped Polyvinyl Alcohol under Applied Stress

Thick films of polyvinyl alcohol (PVA) containing very finemetallic powder, copper (Cu), iron (Fe) and aluminum (Al) 2.5% by weight,were prepared by the casting method. The temperature dependence of Young'smodulus at constant stress, the stress dependence of Young's modulus(Y), the stress dependence of dielectric constant (ε) and stressdependence of phonon velocity, were studied. It was found that Young'smodulus (Y) of the pure sample has the lowest value and that of PVA + Alhas the highest value. This can be explained on the basis that Ydepends on the ratio between the energy of molecular interactions andthe energy of thermal motion of the sample units. We also found that thedielectric constant increases with the addition of metallic powder, andwith an increasing applied stress. The phonon velocity increased withincreasing stress. The increase of stress decreases imperfectionsleading to the increased phonon velocity. The electronic absorptionspectra of PVA is not affected by doping Al and Fe, whereas the PVA dopedwith Cu shows a shift of the absorption maxima toward a longer wavelength.The instantaneous elastic behavior may be observed only at lowtemperatures and very short creep times.