两次离心挂浆工艺制备网眼多孔陶瓷

以具有三维网状结构和贯通气孔的聚氨酯泡沫体为载体,采用两次离心挂浆工艺制备了高气孔率、无堵孔且结构均匀可控的氮化硅网眼多孔陶瓷.借助TG-DSC分析了泡沫体的热分解过程,确定了排胶工艺.借助流变测量和光学显微镜观察了挂浆工艺及浆料粘度对泡沫体挂浆量和多孔结构的影响,并对制品材料的微观结构和性能进行了表征.结果表明,与传统辊压工艺相比,采用两次离心挂浆工艺后,改善了多孔结构的均匀性,显著提高了材料强度,为高强度、结构可控、网眼多孔陶瓷的制备提供了一个有效途径.     

真空脱气处理对网眼多孔陶瓷力学性能的改善

采用有机泡沫浸渍工艺制备了碳化硅基网眼多孔陶瓷．研究了真空脱气处理对浆料流变特性和烧结体的力学性能及显微结构的影响．结果表明;脱气处理改善了浆料的流变特性,使浆料在有机泡沫体上的涂覆量增加和结构均匀性得到改善;压汞仪测试数据和ＳＥＭ观察表明脱气处理明显地消除了孔筋内的孔径为１００μｍ左右的大气孔;经脱气处理后,材料的抗弯强度从２．３４ＭＰａ提高到３１８ＭＰａ．脱气处理对网眼陶瓷强度的改善主要来自两方面的贡献：一是相对密度的增加,二是孔筋中大气孔的消除,但后者是最主要的贡献,这个结果与目前建立的开孔陶瓷泡沫的力学模型吻合得很好．     

网眼多孔陶瓷浸渍成型工艺的研究

采用一种具有三维网状结构和连通气孔的氨酯海绵作为骨架来制备网眼多孔陶瓷．采用一种亲水憎水平衡值（ＨＬＢ）＞１２的表面活性剂溶液对海绵体孔筋表面进行改性处理,改善了海绵与水基浆料之间的粘附性,增加了浆料涂覆量．研究了浆料固含量、有机泡沫体网眼大小、对辊间距和挤压次数对浆量涂覆量及结构均匀性的影响．结果表明：浆料固含量和对辊间距是影响涂覆量及结构均匀性的最主要因素．还发现网眼烧结体的相对密度与相对对辊间距具有很好的线性关系,这为预测和优化材料的渗透率及机械强度提供了一定的依据．     

孔结构可控的网眼多孔陶瓷的制备

采用一种具有三维网状结构和贯通气孔的有机泡沫体作为载体,首先利用有机泡沫浸渍工艺制备出高气孔率且几乎没有堵孔的网眼素坯,经过排塑、预烧处理获得具有一定强度的预制体．由于未经烧结,预制体的孔筋呈疏松多孔结构．利用粘度较低、流动性很好的浆料对预制体进行涂覆处理．结果表明：通过这种处理,孔筋上的裂纹被消除,非常细的孔筋被避免,孔筋厚度比较均匀,从而获得了结构非常均匀的网眼陶瓷．相对密度、孔筋厚度、孔径大小可以根据徐覆次数来调节．随着涂覆次数的增加,孔径减小,孔筋厚度增加,相对密度也增加．本工作为网眼陶瓷孔结构的精确设计提供了一种新工艺,对于优化其力学性能、渗透率等性能具有重要意义．     

ZrO2泡沫陶瓷的制备及性能研究

以CeO2/Y2O3复合添加剂共稳定的TZP(四方氧化锆多晶)超细粉末为主要原料,用有机泡沫前驱体浸渍法制备多孔陶瓷。论述了有机泡沫前驱体性质、浸浆工艺、浆料组分以及烧结温度对泡沫陶瓷力学性能与显微结构的影响。得出使用弹性好、孔筋强度高、对浆料有良好吸附性的有机前驱体可以获得力学性能优良的泡沫陶瓷,并且当浆料中Al2O3为5%(w)、浆料涂覆量在0.7 g/cm3、烧结温度在1580℃时可获得最优力学性能的泡沫陶瓷材料。     

有机泡沫法制备多孔羟基磷灰石生物支架

采用有机泡沫法制备了多孔羟基磷灰石(HA)支架,考察了水解预处理工艺、粘结剂聚乙烯醇(PVA)和固相HA的含量对孔隙率的影响,利用扫描电子显微镜(SEM)观察了支架的孔结构.研究结果表明,采用有机泡沫法可获得孔径均匀的多孔HA支架;有机泡沫(海绵)模板经过水解处理后,其挂浆量增加;支架的孔隙率随PVA含量的增加而增大;浆料中固相HA含量在70%左右为宜,此时材料的孔隙率最大.     

用于多孔陶瓷制备的有机模板处理工艺

以硅溶胶为表面改性剂,从提高与水基浆料的相容性、增加表面粗糙度入手,对有机模板进行了表面处理.对处理前后有机模板的表面形貌、力学性能及对涂覆量的影响进行了研究.结果表明,表面处理以后,有机模板更容易被水基浆料均匀涂覆,且回弹力得到显著增强,涂覆量也得到显著提高.这将有利于多孔陶瓷内部缺陷的减少和强度的提高.     

改性酚醛基活性炭泡沫的制备与表征

采用前驱体共混改性法,以FeCl2/NH4NO3为改性剂,得到改性酚醛泡沫,经高温炭化/水蒸汽活化制备出改性酚醛基活性炭泡沫.通过氮气吸附、TG、XRD、SEM、FT-IR等技术对产品的物理化学性质进行了表征,结果表明,改性后的炭泡沫比表面积为311.19m2/g,总孔容为9.687mL/g,孔径分布范围广,引入了有益于酸性气体脱除的含氮基团和Fe离子,特别是二者同时存在时可产生交互衍化作用.     

聚碳硅烷低温烧结碳化硅网眼多孔陶瓷的研制

通过有机模板复制法,以聚碳硅烷(Polycarbosilane,PCS)为粘结剂和烧结助剂,通过离心工艺二次挂浆制备出低温烧结高强度碳化硅网眼多孔陶瓷.系统地研究了烧结温度、保温时间等工艺参数对制得的碳化硅网眼多孔体微观结构与性能的影响.研究结果表明:最佳烧结温度为1100℃,合适的保温时间为1h,且所制备的网眼多孔体的孔筋厚度均匀.用10PPI(pores per inch)和25PPI有机模板制得的网眼多孔体抗压强度分别为(1.08±0.21)MPa和(2.19±0.32)MPa,耐火温度高达1690℃,而且抗热震性能优良.当淬冷温度大约为1400℃,用25PPI有机模板,经PCS浆料二次挂浆制备的网眼多孔体的热震损伤参数(Dts)仅为0.36.     

熔渗反应烧结泡沫SiC的组织及性能

采用有机泡沫浸渍结合熔渗反应烧结技术制备了一种高性能泡沫SiC,该种泡沫陶瓷由SiC陶瓷孔筋形成类似于泡沫的三维网络连通结构,平均孔径尺寸约2 mm,相对密度15%~42%(体积分数),具有高的可控性,其强度随密度增加而提高,压缩强度11~48 MPa,弯曲强度7~25 MPa。研究了材料受力时的变形行为,结果表明,该种泡沫SiC具有不同于常见报道中的泡沫陶瓷的形变机制,其应力应变曲线只有弹性变形阶段,原因在于材料整体均匀性高,陶瓷孔筋组织致密且晶粒细小,受力时表现出良好的整体协调性。材料具有优良的热导性能。同时该种材料还可以加工成复杂形状,可适应各种应用需求。     

碳化硅网眼多孔陶瓷的制备

本工作采用有机泡沫浸渍工艺制备了具有相互贯通气孔的碳化硅网眼多孔陶瓷．通过选择合适的流变剂获得了对海绵具有良好涂覆性能的浆料．探讨了粘结剂对网眼多孔陶瓷性能的影响,结果表明：硅溶胶是一种比较理想的粘结剂．ＸＲＤ、ＳＥＭ研究了烧结制品的晶相组成及显微结构,同时还对烧结制品的孔筋密度、气孔率、力学性能等进行了表征．本工作在１４５０℃下保温１ｈ获得了气孔率为７５％～８５％、抗弯强度达２．５ＭＰａ以上的碳化硅网眼多孔陶瓷,其主要晶相由α－ＳｉＣ、α－Ａｌ_２Ｏ_３、方石英和莫来石组成．     

An Innovative Approach fro Improving the Reliability of Reticulated Porous Cermaics

An innovative approach has been developed to fabricate reticulated porous ceramics(RPCs) with uniform macrostruc-ture by using the polymeric sponge as the templates.In this approach,the coating process comprises of two stages.In the first stage,the thicker slurry was used to coat uniformly the sponge substrate.The green body was preheated to produce a reticulated perform with enough handling strength after the sponge was burned out.In the second stage,the thinner slurry was used to coat uniformly the perform .The population of the microscopic and macroscopic flaws in the structure is reduced significantly by recoating process.A few filled cells and cell faces occur in the fabrication and the struts were thickened.A statistical evaluation by means of Weibull statistics was carried out on the bend strength data of RPCs, which were prepared by the traditional approach and innovative approach, respectively.The result shows that the mechanical reliability of RPCs is improved by the innovative approach.This innovative approach is very simple and controlled easily,and will open up new technological applications for RPCs.     

An Innovative Approach for Improving the Reliability of Reticulated Porous Ceramics

An innovative approach has been developed to fabricate reticulated porous ceramics (RPCs) with uniform macrostruc-ture by using the polymeric sponge as the templates. In this approach, the coating process comprises of two stages. In the first stage, the thicker slurry was used to coat: uniformly the sponge substrate. The green body was preheated to produce a reticulated preform with enough handling strength after the sponge was burned out. In the second stage, the thinner slurry was used to coat uniformly the preform. The population of the microscopic and macroscopic flaws in the structure is reduced significantly by recoating process. A few filled cells and cell faces occur in the fabrication and the struts were thickened. A statistical evaluation by means of Weibull statistics was carried out on the bend strength data of RPCs, which were prepared by the traditional approach and innovative approach, respectively. The result shows that the mechanical reliability of RPCs is improved by the innovative approach     

纳米碳管/羟基磷灰石复合材料的凝胶注模

采用凝胶浇注成型工艺制备了纳米碳管/ 羟基磷灰石复合材料坯体。研究了p H 值、分散剂、固相含量(纳米碳管和羟基磷灰石在料浆中的质量分数) 、分散工艺等因素对料浆和复合材料坯体性能的影响, 对坯体的力学性能进行了测试, 借助扫描电镜分析了坯体的微观组织。实验发现, 料浆的p H 值应控制在10～12 的范围内;聚甲基丙烯酸铵的浓度为0. 6 %时, 羟基磷灰石悬浮体流动性最好; 十二烷基磺酸钠的浓度在SDS/ CNTs = 1 %～2 %时, 纳米碳管/ 羟基磷灰石复相料浆的粘度最低; 采用球磨法制备的复相料浆固相含量达到55 % , 复合材料坯体的抗弯强度达到57. 403 MPa 。      

Mechanical property improvements in Nicalon SiC fibre reinforced silicon nitride ceramics by oxide coating of Si3N4 starting powders

Ceramic matrix composites are attractive as candidate materials for high-temperature applications offering some advantages compared to monolithic ceramics and high-temperature metal alloys. SiC fibre reinforced silicon nitride is one such composite system. However, the processing route is critical to the production of a reliable composite. In this study, silicon nitride matrix densification was improved and sintering temperature was lowered by coating of Si₃N₄ particles with oxides deposited from hydrolysed metal alkoxides. The solution containing oxide coated Si₃N₄ powders was used as a slurry to infiltrate Nicalon SiC fibre tows. Following previous studies, the fibres were heat-treated in carbon monoxide to improve mechanical and surface properties. Infiltrated green bodies were hot-pressed at elevated temperatures to produce dense composites. The results showed that particle coating accelerated densification kinetics, eliminated pores and reduced the required hot-pressing temperature. There was also less fibre degradation as a result of the lower temperature of densification. Bending strength and fracture toughness of the composites were measured and fractography was conducted using scanning electron microscope. Composites manufactured using coated Si₃N₄ powders showed improved properties, specifically matrix stiffening and delayed crack initiation under load.     

Flexible ceramic-reinforced polyurethane composite coatings on synthetic fibres: Process of continuous liquid film coating and its influence on the coating thickness

A concept for the realisation of composite layers on the surface of synthetic fibres by continuous liquid film coating of spread roving or monofilaments with a slurry containing ceramic particles and a polymeric binder is successfully demonstrated. Polyamide 6 monofilaments were coated with alumina particles and a polyurethane elastomer based binder system to achieve higher abrasion resistance. Under frictional load, the coating is abraded in small units consisting of some particles and the surrounding polyurethane matrix, which predetermines it to be used as sacrificial layer. The slurries showed shear thinning behaviour. Increasing the content of the rheological agent (carboxymethylcellulose [CMC]) led to an exponential increase of the viscosity, which therefore can be tailored by varying the CMC content. An increase of fibre radius, slurry viscosity or withdrawal speed led to an increase of the coating thickness, which is in accordance to published results of Newtonian or non-Newtonian coating fluids.     

表面疏水修饰增强改性硅藻土调湿性能及其对聚氨酯膜透湿性的影响

水性聚氨酯(PU)是一种环保绿色的涂层材料,广泛应用于皮革、纺织、建筑涂层等领域。作为皮革、纺织涂层时,聚氨酯的透湿性决定服装的穿着舒适性,而常规水性聚氨酯的透湿性较差,需要对其进行改性获得透湿性优异的涂层。本文采用CaCl₂和十七氟癸基三甲氧基硅烷(FAS-17)对硅藻土进行改性,研究了改性条件对硅藻土结构和性能的影响,将调湿性能较好的改性硅藻土(FAS-17-CaCl₂-D)与PU复合,研究复合膜的透湿性。结果表明：采用质量浓度为30wt%CaCl₂和0.8wt%FAS-17改性的硅藻土综合性能最好,改性后硅藻土的比表面积、孔隙结构增大,调湿性能提高,FAS-17表面疏水修饰进一步强化了其调湿作用。将性能最好的FAS-17-CaCl₂-D与PU复合后,FAS-17-CaCl₂-D/PU透湿性随着FAS-17-CaCl₂-D用量的增加先增大后减小,复合膜的疏水性提高。1%FAS-17-CaCl₂-D与PU复合制备的复合膜透湿率最大,...     

纳米Fe2O3对聚氨酯/聚偏氟乙烯复合涂层摩擦学性能的影响

利用M-2000型摩擦磨损试验机考察了干滑动下纳米Fe2O3改性的聚氨酯/聚偏氟乙烯(PU/PVDF)复合涂层的摩擦磨损性能。采用扫描电子显微镜分析了纳米Fe2O3在复合涂层中的分布以及涂层的磨损表面。结果显示纳米Fe2O3在涂层中分布比较均匀,少量的纳米Fe2O3的加入不仅降低了聚氨酯/聚偏氟乙烯复合涂层的摩擦系数,而且还提高了聚氨酯/聚偏氟乙烯复合涂层的抗磨性。负载对复合涂层的摩擦磨损性能有较大的影响,随着负载的增加,涂层的磨损率升高。