HDPE/OMMT纳米复合材料挤出胀大比的影响因素研究

利用流变分析仪研究了高密度聚乙烯(HDPE)/有机蒙脱土(OMMT)纳米复合材料在挤出过程中的挤出胀大行为及其影响因素,深入讨论了剪切应力、剪切速率、口模温度、口模长径比及OMMT用量对HDPE/OMMT纳米复合材料挤出胀大比B的影响.结果表明,B值随着剪切应力或剪切速率的增加而增大,并且与剪切应力近似呈线性关系;随着口模温度的升高或长径比的增加而减小,当口模长径比较小时,B值受剪切应力或剪切速率的影响尤为显著;同时B值随OMMT用量的增加而逐渐减小.     

脱硫石膏制备硫酸钙晶须的影响因素研究

以脱硫石膏为原料,采用水热法工艺制备硫酸钙晶须,并借助XRD、高分辨显微镜等分析方法,深入探讨了不同搅拌速率和不同硫酸镁加入量对硫酸钙晶须生长行为的影响。结果表明：随着搅拌速率的不断增加,硫酸钙晶须的长径比呈先升高后降低的趋势,当搅拌速率为90r／min时,长径比达到最大,其值为75．78;随着硫酸镁加入量的增加,硫酸钙晶须的长径比呈先升高后降低的趋势,当硫酸镁的含量为3％时,长径比达到最大值73.88。     

碳化硅改性三元乙丙橡胶复合材料的非线性电阻特性

采用纳米碳化硅(SiC)或SiC晶须改性的三元乙丙橡胶制备复合材料,研究了SiC用量对复合材料体积电阻率的影响,分析了非线性电阻产生的机理。结果表明,在低场强区(电场强度小于10 kV/mm),复合材料的电阻率随着SiC用量的增加缓慢下降;在高场强区(大于20 kV/mm),复合材料的电阻率随着SiC用量的增加快速下降;SiC用量增大时,SiC粒子间的距离减小,非线性效果增强;采用大长径比的SiC晶须作为改性材料可以降低非线性电阻的临界电场强度。     

圆锥式混炼器对EP/ZnO晶须复合材料性能的影响

采用自制的圆锥式混炼器对环氧树脂(EP)/ZnO晶须复合材料进行共混。研究了ZnO晶须含量、混炼器混合和机械混合两种方式以及混炼器混炼间隙对EP/ZnO晶须复合材料力学性能和导热系数的影响。研究发现,无论采用何种混合方式,随着ZnO晶须含量的增加,EP/ZnO晶须复合材料的力学性能都呈现出先增大后减小的趋势;混炼器混合的效果好于机械混合。EP/ZnO晶须复合材料的拉伸强度和冲击强度在混炼器混炼间隙为1 mm、ZnO晶须质量分数分别为5%和2%时取得最大值,分别为31.55 MPa和12 kJ/m2,相比同体系下的机械混合方式,EP/ZnO晶须复合材料的拉伸强度和冲击强度分别提高了14.3%和74.4%。继续增大混炼器混炼间隙会导致EP/ZnO晶须复合材料的力学性能变差。EP/ZnO晶须复合材料的导热系数随ZnO晶须含量的增加而增大,但混合方式对其影响不大;当ZnO晶须含量相同时,随着混炼器混炼间隙的增大,EP/ZnO晶须复合材料的导热系数有小幅增加。     

盐酸法副产物氯化钙废液制备碳酸钙晶须的研究

以盐酸法湿法磷酸工艺中产生的副产物氯化钙废液为原料,采用碳酸钠为沉淀剂,在常温下直接进行了碳酸钙晶须的制备研究。研究了反应时间、氯化钙浓度对碳酸钙晶须长径比的影响以及碳酸钠加入量对碳酸钙晶须产率和纯度的影响,并采用电子扫描电镜(SEM)照片和X射线光电子能谱分析(XPS)对试验结果进行了分析,结果表明:碳酸钙晶须的长径比随反应时间的延长先增后减,当反应时间为110min时,长径比达最大值;而随着氯化钙浓度的增加,碳酸钙晶须的长径比减小;碳酸钠的加入量对碳酸钙晶须的纯度影响不大,当碳酸钠以碳酸钠与钙离子的摩尔比为1.06∶1加入时,碳酸钙晶须的产率达99%。制得的碳酸钙晶须晶型完整,没有颗粒状的碳酸钙存在。     

挤出条件对PP/硅藻土口模膨胀行为影响

应用熔体流动速率仪测定了3种粒径硅藻土(体积分数为10%)填充聚丙烯(PP)复合材料的口模膨胀比(B),考察口模直径和挤出工艺条件对复合体系口模膨胀行为的影响.结果表明.复合体系的B随着剪切应力和剪切速率的增加而非线性增大,且随着温度的上升而线性下降;当载荷及温度一定时,B随着口模直径增加呈非线性提高,随着口模长径比增加呈非线性减小.     

杂质对硝基磷石膏制备硫酸钙晶须形貌的影响

以硝基磷石膏为原料,通过加压水热法制备硫酸钙晶须,探讨磷、氟、氮等杂质对硫酸钙晶须生长过程的影响,分析杂质对晶须微观形貌及长径比的影响,并通过X射线衍射分析杂质对晶须生长过程的影响。结果表明:可溶性氟化钠、不溶性氟化钙对硫酸钙晶须的生长均具有明显的抑制作用,随着药剂用量的增加,长径比明显变小,且团聚严重;磷酸三钠对硫酸钙晶须的生长具有明显细化作用,当磷酸三钠用量为2%时,磷酸钙晶须平均直径为1.8μm;硝酸钠对硫酸钙晶须的生长影响不大。     

脱硫石膏制备硫酸钙晶须的试验研究

以脱硫石膏为原料通过水热合成法制备硫酸钙晶须,借助X射线衍射仪、扫描电子显微镜、能谱仪、热重分析仪等测试手段进行分析,研究了酸化预处理、料浆浓度以及反应温度对制备硫酸钙晶须的影响。结果表明:酸化预处理可以有效去除原料中的CaCO₃杂质;随着料浆浓度和反应温度的增加,晶须长径比均呈现先增大后减小的趋势;当料浆浓度为3%(质量分数),pH值为6.5,反应温度为120 ℃,反应时间为2 h时,取得的硫酸钙晶须最佳平均长度为161.2 μm,最佳平均长径比为46.06。     

不同固液比和原料粒度对脱硫石膏制备硫酸钙晶须的影响

以脱硫石膏为原料。采用水热法工艺制备硫酸钙晶须。并借助XRD、高分辨显微镜等分析方法,深入探讨了不同固液比和原料粒度对硫酸钙晶须生长行为的影响。结果表明：随着固液比的不断减小,硫酸钙晶须的长径比呈先升高后降低的趋势;当固液比为1：10时,长径比达到最大,其值为68．65;随着原料粒度的减小．硫酸钙晶须的直径不断减小,硫酸钙晶须的长径比不断增加,当原料粒度为1．60μm时,长径比达到68.65。     

硬脂酸系表面改性剂对碳酸钙晶须/天然橡胶复合材料性能的影响

试验研究3种硬脂酸系表面改性剂对碳酸钙晶须/天然橡胶(NR)复合材料物理性能和热稳定性的影响。结果表明:经表面改性剂处理的碳酸钙晶须表面性能提高,与NR界面作用增强;改性碳酸钙晶须/NR复合材料的定伸应力、拉伸强度和撕裂强度均比未改性时有所增大;硬脂酸改性的复合材料综合物理性能较优,硬脂酸或硬脂酸钠改性的复合材料热稳定性提高。     

Al2O3／SiCw陶瓷材料晶须拔出的有限元分析

采用有限元的方法分析了Ａｌ２Ｏ３／ＳｉＣｗ陶瓷材料晶须拔出时中的应力状态及应力分布，研究了晶须拔出时材料界面的断裂模式。结果表明：当裂纹扩展到晶须时，在裂纹尖端附近晶须与基体界面处存在较大的剪应力，从而使界面首先发生剪切破坏，当晶须在裂纹面之间桥联时，由于晶须与基体界面存在较大的径向拉应力而使界面首先发生径向拉伸破坏。     

Two-Dimensional Whisker Percolation in Ceramic Matrix–Ceramic Whisker Composites

A computer model that treats ceramic-powder matrix–ceramic whisker composites as a percolative network of whiskers has been developed. The model calculates the critical fraction of whiskers at the percolation threshold for a two-dimensional random network of whiskers. The computed critical fraction was found to display an inverse dependence on whisker aspect ratio. In addition, the computed critical fraction (27 vol% for a whisker aspect ratio of 7) agreed well with the zero-shrinkage whisker fraction of 30 vol% in the densification of a colloid-pressed alumina–silicon carbide composite that exhibited a two-dimensional orientation of such whiskers.     

浸水时间对不同复合材料吸水率及其力学性能的影响

 以不饱和聚酯树脂（UPR）为基体,玻纤布、苎麻布及碱式硫酸镁晶须为增强材料。采用模压工艺制备复合 材料。研究了不同复合材料在30℃及50℃水中浸泡时间对其吸水率及其力学性能的影响。结果表明,所有复合材料 的吸水率均随着浸泡时间的延长而逐渐增加,且在起初的0~8h时快速吸水,之后趋缓或不变|50℃时的吸水率总是 高于30℃时的吸水率|玻纤布对UPR的增强效果明显优于苎麻布|与晶须混杂后将降低玻纤布或苎麻布增强聚合物复 合材料的拉伸强度和冲击强度,但却将增加弯曲强度和拉伸模量|随着浸泡时间的延长,玻纤布增强或玻纤布与晶 须混杂增强复合材料的拉伸强度在30℃和50℃时均将下降|苎麻布增强复合材料的冲击强度分别在30℃和50℃水温 浸泡16h时达到最大值,分别为49.1kJ/m2 和48.8kJ/m2,比浸水前的冲击强度分别提高98.78% 和97.57%,而苎麻布 与晶须混杂增强复合材料在两个试验温度下的冲击强度均随着浸泡时间的延长而单调增加。     

Rheological Behavior of Injection-Moldable Silicon Powder–Silicon Carbide Whisker Formulations

The rheological behavior of injection-moldable formulations for reaction-bonded Si₃N₄ toughened with silicon carbide whiskers was studied using capillary rheometry. The effects on rheology of the following parameters were examined: solids loading, powder/whisker volume ratio, particle size and type, and binder composition. Two important aspects of the flow behavior were delineated. First, corrections for end effects and slippage along the wall were made in order to interpret the experimental data properly. At high shearing rates (i.e., 10³ s⁻¹) slip may account for more than 50% of the total flow. Such slippage promotes flow into the smallest channels or corners of the mold and may appreciably facilitate molding. Consequently the careful study of slippage is an inherent requirement of the rheological characterization of these concentrated suspensions. Second, the suspension viscosities were delineated. An empirical equation for predicting relative viscosity was developed for formulations containing up to ∼30 vol% of silicon carbide whiskers (with more than 50 vol% total solids). Suspension viscosities generally increased with decreasing particle size and increasing whisker contents. Particle surface roughness appears to affect the shearing behavior. Binders of low molecular weight resulted in higher relative viscosities than higher molecular weight binders, indicating possibly better dispersion of solids when more viscous binders are employed.     

Temperature-dependent fracture strength of whisker-reinforced ceramic composites: Modeling and factor analysis

In this study, a temperature-dependent fracture strength model for whisker-reinforced ceramic composites was developed. This model considers the strength degradation of both whisker and ceramic matrix at elevated temperatures, as well as the evolution of residual thermal stress with temperature. It was verified by comparison with the available flexural strengths of five types of whisker-reinforced ceramic composites at different temperatures, and good agreement between the model predictions and the experimental data is obtained. Moreover, based on the established model, we systematically analyzed the effects of six influencing factors, including the volume fraction and the aspect ratio of whisker, the Young's modulus of matrix and whisker, the thermal expansion coefficient difference and the stress-free temperature, on the temperature-dependent flexural strengths of whisker-reinforced ceramic composites. Some new insights which could help optimize and improve the temperature-dependent fracture strength of whisker-reinforced ceramic composites are obtained.     

UHMWPE对有机PTC复合材料的稳定作用

利用传统的熔融－混合方法制备碳黑填充的聚丙烯（PP）／超高分子质量聚乙烯（UHMWPE）复合材料，当P／UHMWPE质量比大于3／7时，碳黑填充PP／UHMWPE复合物的正温度系数（PTC）和负温度系数（NTC）效应类似于碳黑填充的纯PP聚合物，但当质量比等于或小于3／7时，复合物所表现的PTC效应非常相似于碳黑填充充的纯UHMWPE聚合物，在复合物中采用粘度非常高的聚合物作为一种组分可以有效消除NTC效应。     

PP与镁盐晶须复合材料性能的研究

以镁盐晶须增强聚丙烯(PP)复合材料为研究对象，添加马来酸酐接枝聚丙烯(PP-g-MAH)1与PP-g-MAH2界面改性剂来改善两者界面粘合强度及提高复合材料的力学性能；探讨了不同加工工艺流程对复合材料性能的影响。结果显示：采用PP-g-MAH1作界面处理剂的复合物体系其增强效果较好；当PP／PP-g-MAH 1／镁盐晶须的质量比为97／3／30时，复合材料的综合性能最佳。应用扫描电子显微镜(SEM)，分别对不同复合材料进行了界面形态的观察，证明与试验结果一致。     

超高分子量聚乙烯对有机PTC复合材料的超强稳定作用研究

利用传统的熔融 混合方法制备碳黑填充的聚丙烯 (PP) /超高分子量聚乙烯 (UHMWPE)复合物。当PP/UHMWPE混合比大于 3 / 7,碳黑填充PP/UHMWPE复合物的PTC和NTC效应类似于碳黑填充的纯净PP聚合物。然而当重量比等于或小于 3 / 7时 ,复合物所表现的PTC效应非常相似于碳黑填充的纯净的UHMWPE聚合物。在复合物中应用粘度非常高的聚合物作为一种组分可以有效消除NTC效应     

SiC-Whisker-Reinforced Al2O3 Composites by Free Sintering of Coated Powders

SiC whiskers were coated with a thick cladding of finegrained Al₂O₃ powder by controlled heterogeneous precipitation in a concentrated suspension of whiskers. After calcination, the coated whiskers were compacted by cold isostatic pressing and sintered at a constant heating rate of 5°C/min in a helium atmosphere. The parameters which control the coating process and the sintering characteristics of the consolidated powders are reported. Starting with an initial matrix density of 40–45% of the theoretical, composites containing up to ≅20 vol% whiskers (aspect ratio ≅15) were sintered freely to nearly theoretical density below 1800°C. By comparison, a similar composite formed by mechanical mixing of the whiskers and the precipitated Al₂O₃ powder reached a density of only 68% of the theoretical after sintering under identical conditions. For a fixed whisker content, the sinterability of the composites formed from the coated whiskers shows a fairly strong dependence on the whisker aspect ratio.     

An insight into the unloading/reloading loops on the compression curve of natural stiff clays

Oedometer tests were carried out with loading/unloading/reloading on natural stiff clays, Ypresian clays (YPClay), taken from several depths. Common unloading/reloading loops were identified. Further examination of the unloading or reloading curves shows that each path can be satisfactorily considered as bi-linear with a small and a larger slope separated by a threshold vertical stress. This threshold stress can be considered as the swelling pressure corresponding to the void ratio just before the unloading or reloading. Indeed, upon unloading, when the applied stress is higher than the threshold stress or swelling pressure, the mechanical effect is dominant and only small mechanical rebound is observed, corresponding to a small microstructure change; by contrast, when the applied stress is lower than the swelling pressure, physico-chemical effect becomes prevailing and soil swelling occurs with a larger microstructure change. Upon reloading, when the applied stress is lower than the swelling pressure, the microstructure is not significantly affected thanks to the contribution of the physico-chemical repulsive force, leading to a small volume change; on the contrary, beyond the swelling pressure, the mechanical effect becomes dominant giving rise to larger volume changes corresponding to the microstructure collapse. Like unsaturated expansive soils, it is found that there is a good relationship between the swelling pressure (threshold stress) and the void ratio just before the unloading or reloading. This is confirmed by the results from the data reported in the literature about other stiff clays such as Boom and London clays. It can be then deduced that the unloading/reloading loop is rather due to the competition between the mechanical and physico-chemical effects on the microstructure changes than the viscosity effect as commonly admitted.