以PVB为造孔剂采用硅树脂制备泡沫陶瓷

采用硅树脂为先驱体,利用先驱体转化法与添加造孔剂法相结合制备SiOC泡沫陶瓷.通过对造孔剂聚乙烯醇缩丁醛(PVB)和硅树脂的热分析制定温度曲线,研究了裂解温度、造孔剂含量对泡沫陶瓷抗压强度及孔隙率的影响,采用XRD、SEM及EDS对SiOC泡沫陶瓷进行了物相、微观结构和成分分析.结果表明,在1000～1400 ℃温度范围内,随着温度的升高,泡沫陶瓷的抗压强度先升高后降低,而孔隙率逐渐降低;造孔剂含量对泡沫陶瓷的性能也有明显的影响,随着造孔剂含量的增加,试样的抗压强度逐渐减小,而孔隙率逐渐增大.当裂解温度为1250 ℃,PVB的含量为50%(质量分数,下同)时,所制得的泡沫陶瓷的抗压强度为52.3 MPa,孔隙率为72%.XRD研究表明,随着温度的逐步升高,硅树脂的裂解产物发生了由非晶态向晶态的转变.微观结构分析显示,SiOC泡沫陶瓷呈三维网状结构,微孔分布较均匀.     

不同造孔剂对陶瓷结合剂性能的影响

本文研究了加入石墨和CaCO3两种造孔材料对陶瓷结合剂性能的影响，通过改变加入量和烧结工艺，制备不同的试样，通过测定其抗折强度，气孔率和SEM照片观察，结果发现：石墨加入量和烧结温度影响陶瓷结合剂强度；当石墨加入量较少，烧结温度较低时，其强度较好；CaCO3的加入量对磨具的抗折强度影响不明显，但影响成孔的尺寸，在允许的范围内加入量越多，得到的气孔尺寸越大，气孔分布均匀，孔壁光滑；CaCO3的造孔效果比石墨好。     

基于空心氧化铝微球造孔的陶瓷结合剂金刚石砂轮

研究空心氧化铝微球质量分数和粒径（0.2, 0.4, 0.6 mm）对砂轮的总气孔率、抗弯强度、硬度和微观结构的影响,制备以空心氧化铝微球为造孔剂的陶瓷结合剂金刚石砂轮,并研究砂轮对石英玻璃的磨削性能。结果表明:随着空心氧化铝微球质量分数增加,砂轮总气孔率升高,抗弯强度和硬度降低;空心氧化铝微球质量分数相同时,其粒径越小,砂轮的总气孔率越高,抗弯强度和硬度越低;制备的空心氧化铝微球陶瓷结合剂金刚石砂轮可用于磨削石英玻璃,加工后石英玻璃的表面粗糙度从0.5113 μm降至0.0206 μm。      

凝胶注模成型制备微多孔氮化硅陶瓷

采用凝胶注模法,在无其它添加剂的条件下,通过提高单体含量,成功制备出高性能微多孔氮化硅陶瓷,陶瓷抗弯强度高达137 MPa以上,气孔率高达50%以上,孔中径小于1 μm.结果表明:随着有机单体含量的增加,氮化硅微多孔陶瓷气孔率单调增加;随着固含量的增大,氮化硅微多孔陶瓷气孔率单调下降,抗弯强度先上升然后又下降,固含量有一优化值,此时陶瓷体抗弯强度最大;随着烧结温度的增加,氮化硅陶瓷强度单调增加,而气孔率单调下降.     

水滴模板法制备聚乳酸微纳米纤维薄膜

目的采用水滴模板法制备聚左旋乳酸(PLLA)微纳米纤维薄膜,研究聚合物溶液浓度和环境湿度(相对湿度)对微纳米纤维形貌和直径的影响。方法在不同质量浓度(10、25、50mg/mL)的PLLA/四氢呋喃(THF)溶液和不同环境湿度(40%、50%、60%、70%)条件下,通过水滴模板法制备PLLA微纳米纤维薄膜。采用扫描电子显微镜(SEM)对薄膜的表面形貌进行观察,用Image J软件对电镜照片中的微纳米纤维进行直径测量,计算平均直径,并统计直径分布。由纤维的平均直径计算薄膜表面积与体积之比。用密度法计算薄膜的孔隙率。结果水滴模板法制备的PLLA微纳米纤维薄膜具有光滑连续的三维网络状结构,其直径范围可控制在200～1000 nm之间,孔隙率90%,表面积与体积比在6～8μm~(-1)左右。直径随着聚合物溶液浓度的增加而变大,随环境湿度的增高先减小后增大,孔隙率和表面积与体积比的变化规律与直径相反。结论 PLLA三维微纳米纤维结构形成的主要机理是,水滴模板过程中溶剂的快速挥发引起孔壁温度急剧降低,导致热致相分离。在环境温度为25℃,THF为溶剂,溶液用量为50μL及气体流量为300m L/min的动态气氛条件下,采用水滴模板法制备PLLA微纳米纤维膜的适宜条件为:溶液浓度25mg/mL,环境湿度50%。该条件下获得的微纳米纤维直径分布范围为200～900 nm,平均直径为476 nm,薄膜孔隙率以及表面积与体积之比分别为96.7%和8.4μm~(-1)。     

以尿素为造孔剂制备开孔NiAl金属间化合物

以尿素为造孔剂,利用燃烧合成技术成功制备孔洞结构和力学性能可控可调的开孔NiAl金属间化合物,并对材料的宏观和微观形貌、准静态压缩性能进行分析。通过调整尿素的体积分数和颗粒大小,多孔NiAl金属间化合物的孔隙率可控制在57.57%-84.58%,孔径大小可控制在0.4-2.0mm。准静态压缩实验表明,多孔NiAl金属间化合物的力学性能可用Gibson-Ashby模型来解释。     

不同无机铵盐对陶瓷结合剂CBN砂轮造孔的应用研究

分别研究了无机铵盐NH4F、NH4Cl、（NH4）2SO4和NH4HCO3的不同添加量对低温陶瓷结合剂CBN砂轮造孔的影响,采用气孔率、抗折强度以及试样SEM断口形貌对造孔效果进行了评价。结果表明：NH4Cl使砂轮开裂,不能作为低温陶瓷结合剂CBN造孔剂。NH4F造孔效果不明显,不适合造孔。（NH4）2SO4造孔剂的质量分数应控制在5％以内,质量分数达到5％时,砂轮孔隙率为36．14％,抗折强度为29．03MPa,气孔皆为小孔,气孔可调性差。NH。HCO,造孔剂质量分数应控制在15％以内,质量分数为5％时,砂轮孔隙率为34．19％,抗折强度为40．32MPa;质量分数增加到15％时,孔隙率达到42．5％,抗折强度为29．16MPa,且大孔径气孔比例随质量分数的提高而提高,气孔可调性好。     

Sol-gel法制备石英纤维增强石英陶瓷基复合材料及其性能研究（英文）

以硅溶胶和无机硅树脂为原料,通过液相渗积-原位固化成型技术和溶胶-凝胶法(So1-gel)制备了2.5D石英纤维增强石英陶瓷基复合材料。研究了无机硅树脂凝胶的差热分析,并对复合材料的致密化、机械强度及不同热处理温度对微州结构的影响做了分析,结果显示So1-gel法是制备SiO_(2f)/SiO_2复合材料的有效措施,浸渍无机硅树脂原料的复合材料密度由1.63 g/cm~3增加到1.72 g/cm~3,抗拉伸强度和压缩强度分别达到50和130 MPa,均有大幅度的提高,基体与纤维界面的脱黏和纤维的拔出说叫复合合材料为非脆性断裂。     

金属结合剂金刚石多孔砂轮的试验研究(Ⅰ)——造孔剂添加量的优化设计

本文以两种廉价无毒物质为主要造孔材料,通过正交试验设计,研究得到不同孔隙率的金属结合剂金刚石节块所需造孔剂的添加量,并分析孔隙率对力学性能的影响。试验结果表明：通过在青铜基结合剂中加入适量的造孔剂材料,金属结合剂金刚石节块中的孔隙率可高达46％,孔隙率与造孔剂添加量之间以及孔隙率与抗弯强度之间存在一定的对应关系,可为实际生产多孔金属结合剂金刚石砂轮的配方选择提供一定的基础数据和试验经验。     

导电纤维的制备及在防静电陶瓷中的应用

以氧化硅玻璃纤维为载体,采用非均匀成核法在其表面包覆一层锑掺杂二氧化锡（ATO）制备了导电纤维。导电纤维的电阻率随热处理温度升高的变化趋势与ATO基本一致,包覆物加入率为100%、75%、50%、25%和12.5%的ATO包覆氧化硅纤维在500~1200 ℃处理后的电阻率全部低于200 Ω·cm。由于较大的长径比所导致的桥联效应,少量的导电纤维在陶瓷中就能形成完善的导电网络,同时也能极大减少防静电陶瓷中ATO的用量,包覆物加入率为12.5%的ATO包覆纤维作为导电填料时,能节省约77.8%的ATO。     

Quantitative estimation of material properties of porous ceramics by means of composite micromechanics and ultrasonic velocity

This paper describes a nondestructive method for the quantitative estimation of property variations due to porosity in advanced ceramics. The method employs a composite micromechanics which accounts for the effective density and elastic stiffness of a porous composite medium with a measurement of ultrasonic velocity. When the measured velocity is coupled with the theoretically predicted velocity, the unknown pore volume fraction is solved, from which other material properties are determined. The micromechanics model based on the Mori-Tanaka theory can handle ellipsoidal pores with a certain orientation distribution. Given the zero-porosity matrix moduli and the pore aspect ratio, the oblate spheroidal theory is first applied to hot pressed silicon carbide (SiC) samples in the range of about 85–100% of theoretical density and then extended to sintered samples in the density range of 93.6–97.6%. It is shown that the bulk density and elastic modulus of porous ceramics can be estimated accurately by the proposed method.     

均相沉淀法制备YAG球形粉体及透明陶瓷

以Y(NO3)3.6H2O和Al(NO3)3·9H2O为原料,尿素为沉淀剂,采用均相沉淀法合成了成分为5[Al(OH)CO3]·3[Y(OH)CO3]的钇铝石榴石(YAG)先驱体粉末。在沉淀过程中通过控制硫酸根离子的含量可以避免晶核生长时的方向性,有效防止了纳米颗粒硬团聚的形成,先驱体颗粒逐渐球化。经1 100℃煅烧分解,获得平均尺寸为200~400 nm、低团聚的高纯YAG球形粉体。该粉体经模压成型、1 700℃真空烧结,得到晶粒分布均匀、完全透明的YAG陶瓷。     

Fabrication of silicon oxycarbide foams from extruded blends of polysiloxane,low-density polyethylene (LDPE), and polymer microbead

Silicon oxycarbide (SiOC) foams with porosities ranging from 77% to 90% and a cell density higher than 10⁸ cells/cm³ were made from polysiloxane, low-density polyethylene (LDPE), and polymer microbead blends. The polysiloxane, LDPE, and polymer microbeads were compounded directly using a counter-rotated twinscrew extruder. The obtained blends were foamed with gaseous carbon dioxide, cross-linked, and subsequently pyrolyzed. The process resulted in the production of highly porous, open-cell SiOC foams with a bimodal distribution of pore morphology, small spherical pores derived from polymer microbeads and relatively large elongated or equiaxed pores derived from foaming using carbon dioxide and decomposition of LDPE.     

A numerical analysis of ceramics strength affected by material microstructure

To clarify microstructural influences on the ceramic strength, a numerical analysis of the elastic stress distribution around the crack tip for several crack lengths was conducted by using a finite element method (FEM), in which each element was regarded as one grain in a ceramic polycrystal. In the analysis, the anisotropy expected in actual grains was dealt with by randomly assigning different values to the rigidity and the size of each element (i.e., each grain). The FEM results showed that the crack tip stress was dependent on the grain rigidity but was hardly affected by the grain size. A microstructural modification factor f _M for the stress intensity factor was newly introduced to reflect microstructural influences on ceramic strength. The factor f _M was defined as the ratio of the crack tip stress obtained by the FEM analysis to the K-based stress. Statistical aspects of f _M were investigated by generating virtual materials with different combinations of grain rigidity and size. When the f _M distribution was fitted to the two-parameter Weibull distribution function, it was clarified that the distribution shifted toward a lower side with increasing the crack length. The R-curve expressed by an exponential form was applied so that the grain bridging effect in ceramics could be included in the analysis of the strength depending on crack length. It was revealed that the estimated scatter band in the relation of the strength versus the crack length represented the central trend of dispersed experimental results.     

陶瓷及陶瓷基复合材料连接的研究进展

综述了近年来陶瓷及陶瓷基复合材料连接的研究进展。包括陶瓷及陶瓷基复合材料润湿机理的研究、润湿性的改善、连接界面组织结构的演变及与接头力学性能的关系、接头连接机理及连接应力的缓解方法。同时,对连接中间层的选择,包括玻璃陶瓷中间层、复合中间层、复合钎料及梯度中间层的研究也进行了归纳总结。分析了目前研究已经取得的突破进展及仍然存在的问题,并对未来陶瓷及陶瓷基复合材料连接的研究方向进行了展望。     

具有密度梯度氧化锆多孔陶瓷的制备研究

采用平均粒径约为10μm的Ca-ZrO2粉和直径为0．2～1mm的Ca-ZrO2空心球，选择适当的比例分数，经叠层模压成型后进行常压烧结，成功制备了具有密度梯度的氧化锆多孔陶瓷，并对构成叠层样品的粉球比为50：50～90：10试样的密度、抗压强度、显微结构、物相等进行了表征。结果表明，对于单配比试样，在相同烧结温度下其密度和抗压强度显著依赖于ZrO2粉和ZrO2空心球的比例分数，ZrO2粉的含量越高，试样的密度和抗压强度越高；其中1700℃烧结的样品，其密度由粉球比为50：50试样的3．18g／cm^3变化到粉球比为90：10试样的3．65g／cm^3，相应地其抗压强度则由49MPa变化到130MPa。     

高强度多孔氮化硅陶瓷的制备及性能研究

以氮化硅为原料,以叔丁醇为溶剂,采用凝胶注模成型工艺和无压烧结工艺,制备出具有高强度和高气孔率的多孔氮化硅陶瓷。在浆料中初始固相含量固定为10vol%的基础上,研究烧结温度和保温时间对多孔氮化硅陶瓷材料的气孔率、孔径尺寸分布、物相组成及显微结构的影响,分析抗弯强度与结构之间的关系。结果表明,通过改变烧结温度和保温时间,可制备气孔率63.3%~68.1%的多孔氮化硅陶瓷;气孔尺寸呈单峰分布,平均孔径为0.97~1.42μm;抗弯强度随烧结温度提高或保温时间延长单调增大,在1750℃保温1.5h下达到最大值(74.2±8.8)MPa。     

钎缝间隙对SiC陶瓷钎焊接头组织及性能的影响

采用Ti-Zr-Ni-Cu钎料,借助SEM,EDS和XRD等分析测试手段,研究了钎缝间隙对SiC陶瓷接头组织性能的影响．结果表明,接头结构由SiC侧至钎缝中心依次为TiC,Zr（S,S）,Ti5Si3＋Zr2Si,Tj（s．s）＋Tj2（Cu,Ni）,（Ti,Zr）（Ni,Cu）．当钎缝间隙为30～50μm时,Si元素与Ti,Zr元素反应,生成少量的细小的针状硅化物,钎缝主要为均一的固溶体组织,此时钎焊接头力学性能较好,抗剪强度可达117MPa;当钎缝间隙小于30μm时,生成贯穿整个钎缝的条状硅化物,同时有连续的、较厚的TiC层沿接头界面生成,严重降低接头性能;而当钎缝间隙大于50μm时,钛的金属间化合物大量增多,同时在钎缝中形成了钛和锆的过共晶化合物,使接头性能下降．     

Fracture detection in concrete by glass fiber cloth reinforced plastics

Two types of carbon (carbon fiber and carbon powder) and a glass cloth were used as conductive phases and a reinforcing fiber, respectively, in polymer rods. The carbon powder was used for fabricating electrically conductive carbon powder-glass fiber reinforced plastic (CP-GFRP) rods. The carbon fiber tows and the CP-GFRP rods were adhered to mortar specimens using epoxy resin and glass fiber cloth. On bending, the electrical resistance of the carbon fiber tow attached to the mortar specimen increased greatly after crack generation, and that of the CP-GFRP rod increased after the early stages of deflection in the mortar. Therefore, the CP-GFRP rod is superior to the carbon fiber tow in detecting fractures. Also, by reinforcing with a glass fiber cloth reinforced plastic, the strength of the mortar specimens became more than twice as strong as that of the unreinforced mortar.