Strengthening of Hot-Pressed Al2O3 by Quenching

Compressive surface stresses were formed in hot-pressed Al₂O₃ by quenching. Flexural strength was improved substantially, up to a maximum of 223,000 psi. The variation of strength with grain size of the quenched bodies was similar to that of the unquenched material, but the strengths were shifted to higher values. The presence of a glassy intergranular phase is not necessary to obtain compressive surface stresses by quenching.     

Thermal-Stress Fracture of a Thermomechanically Strengthened Aluminosilicate Ceramic

The thermal-stress fracture behavior of an aluminosilicate ceramic thermomechanically strengthened by surface compression was investigated using quenching in silicone oil. Comparison with the behavior of the unstrengthened ceramic showed that the strengthening increased the critical quenching-temperature difference required to initiate fracture and also increased the strength retained. The room-temperature strength was not increased further when the strengthened material was quenched from temperatures above the softening point. On the basis of a simple mechanical model, the observations of the critical quenching-temperature difference and strength retained in the temperature range of brittle behavior were verified theoretically. It is concluded that, to improve thermal-stress resistance of ceramics and to avoid catastrophic failure, strengthening by surface compression is to be preferred to increasing the inherent strength of the material.     

Computation of Residual Stresses in Quenched Al2O3

A method of computing the residual stress profile in quenched A1₂O₃ rods was developed. For these calculations, certain material parameters must be determined. Thus, strain rate was measured as a function of stress for 96% A1₂O₃ at 1300° to 1500°C, and the heat-transfer rates of cylindrical samples quenched in several media were determined. Using calculated temperature distributions and measured strain rates, plastic strains were computed for the entire quenching period, and these strains were converted to a profile of residual room-temperature stresses. The substantial increases in flexural strength observed in Al₂O₃ after it is quenched (thermally conditioned) are considered to originate in the residual compressive surface layers.     

Development of Nanoemulsion of Silicone Oil and Pine Oil Using Binary Surfactant System for Textile Finishing

Nanoemulsions of silicone oil and pine oil using a binary surfactant system were prepared. Silicone oil and pine oil were used to achieve softness and mosquito repellency and antibacterial activity respectively when the nanoemulsion was applied on the fabric. A silicone surfactant (AG-pt) and a hydrocarbon surfactant (TDA-6) were used in different proportions to obtain stable nanoemulsions at the lowest possible droplet size. The various emulsification process variables such as ratio of hydrocarbon to silicone surfactant, surfactant concentration, ratio of silicone oil to pine oil, oil weight fraction and sonication time have been studied. The optimal variables include the ratio of hydrocarbon to silicone surfactant of 80:20, surfactant concentration of 8%, ratio of silicone oil to pine oil of 80:20, oil weight fraction of 20% and 15 min of sonication time at 40% of the applied power. Nanoemulsions were found to be very stable with emulsion droplet size around 41 nm. In order to compare different emulsification techniques, emulsions were also prepared using the conventional method. Emulsions analyzed using SEM showed spherical droplets ranging from 40 to 120 nm. Atomic force microscopy was used to evaluate the bounciness, fluffiness and softness of fabric. From this study, it was found that stable nanoemulsion with a lowest possible droplet size of silicone and pine oil could be prepared by ultrasonic emulsification technique in order to deliver multiple properties when applied to fabric.     

Impact strength of polymers 2: The effect of cold working and residual stress in polycarbonates

The influence of cold working on the toughness improvement in glassy amorphous polycarbonates was studied. Cold working processes, namely rolling and. Steckel rolling were used to produce thickness reductions up to 40 percent in flat-strip specimens. The notched Izod impact strength and tensile properties were measured as a function of strip thickness reduction. It was shown that the toughness enhancement in polycarbonates cold worked to low thickness reductions was due to the residual stress state present as opposed to molecular orientation which becomes significant at higher degrees of cold work. Residual stress measurements were made by using the layer removal technique. Residual tensile stresses as high as 2100 psi were present in 1/4-in. cold-rolled polycarbonate at the surface. The maximum stress in the center of the specimen was 1100 psi in compression. The residual stresses at the surface decreased with increasing thickness reduction. The residual stress state for Steckel rolled. 1/2-in. polycarbonate was also measured and found to be more complex than for the thinner samples, The results demonstrated that surface tensile stresses and interior compressive stresses can produce large values of impact strength if the notch is to be machined after cold working. Thus, the values of impact strength measured from the notch Izod specimen are sensitive to the residual stress state in the polymer. This behavior is in contrast to earlier studies on thermally quenched material in which the material was quenched after notching. The thermal quenching produced surface compressive stresses which were also present at the notch tip. The presence of compressive residual stresses at the center of the notch suppressed the formation of a craze leading to toughness enhancement in cold worked polycarbonate strips. It is shown that by control of residual stresses in polycarbonate, strips at least 1/2 in. in thickness can be made to exhibit ductile failure in the notched Izod impact test.     

Impact strength of polymers: 1. The effect of thermal treatment and residual stress

The effect of thermal annealing and quenching on the notched Izod impact strength of several polymers has been studied. Primary emphasis was placed on polycarbonate, but ABS, PVC, polysulfone, and polymethylmethacrylate were also studied. It was determined that residual stresses created by thermal quenching from above the glass transition temperature can have a great effect on impact strength for the polycarbonate, PVC, and polysulfone polymers studied. In fact, it is shown that the thickness transition observed in impact strength for polycarbonates is governed by the residual stresses and not by thickness. In polycarbonates, quenched sheets up to 3/8 in. in thickness have shown impact strengths of 18 ft-lb/in. whereas sheets 1/8 in. in thickness can be embrittled by annealing, showing an impact strength of 2 ft-lb/in. However, it has been shown that this embrittlement results from the absence of residual stress. Residual stresses having maximum values up to 3000 psi (in Compression) have been determined at the polycarbonate sheet surface using birefringence measurement techniques. The existence of these compressive stresses is postulated to restrict the extent of craze growth at the notch tip, and the impact specimen can yield rather than fail in a brittle manner if the stress state is sufficient.     

影响HTV硅橡胶撕裂强度的因素

考察了白炭黑种类、羟基硅油用量、含氢硅油用量以及不同乙烯基含量生胶并用对热硫化(HTV)硅橡胶撕裂强度的影响。结果显示,气相法白炭黑的补强效果强于沉淀法白炭黑,且比表面积越大,硅橡胶的撕裂强度越高;随着羟基硅油加入量的增加,硅橡胶的撕裂强度先增后趋于稳定;含氢硅油的用量对HTV硅橡胶的撕裂强度基本没有影响;高乙烯基含量生胶和低乙烯基含量生胶并用能显著提高HTV硅橡胶的撕裂强度。较佳配方是:166 g 110-0生胶,4 g 112生胶、80 g QS-102气相法白炭黑、8.5 g羟基硅油、1.0 g含氢硅油、0.5 g乙烯基硅油,此时,HTV硅橡胶的撕裂强度达到21 KN/m。     

Thermal Shock Behavior of Porous Silicon Carbide Ceramics

Using the water-quenching technique, the thermal shock behavior of porous silicon carbide (SiC) ceramics was evaluated as a function of quenching temperature, quenching cycles, and specimen thickness. It is shown that the residual strength of the quenched specimens decreases gradually with increases in the quenching temperature and specimen thickness. Moreover, it was found that the fracture strength of the quenched specimens was not affected by the increase of quenching cycles. This suggests a potential advantage of porous SiC ceramics for cyclic thermal-shock applications.     

Effect of Surface Damage on the Strength of Al2O3 Ceramics with Compressive Surface Stresses

In fully dense fine-grained Al₂O₃ ceramics, fracture originates at surface flaws. The severity of these flaws depends on the methods used to form the surface and any subsequent damage that may have occurred. It is desirable to find ways to minimize the severity of these flaws. Both untreated and quenched Al₂O₃ rods were scratched by rotating them under a diamond point with various loads. The strengths of the quenched rods decreased less than those of the untreated rods. Microscopic examination showed that the compressive surface stresses induced by quenching reduced the penetration of surface damage.     

Long-term hydrophobicity and ice adhesion strength of latex paints containing silicone oil microcapsules

Waterborne anti-icing coatings were prepared by embedding silicone oil microcapsules in latex paints. The long-term hydrophobicity and ice adhesion strength of the coatings were examined with a QUV accelerated weathering tester and a pull-off adhesion tester. The effects of silicone oil content and pigment/binder (PB) ratio on the long-term hydrophobicity and the ice adhesion strength of the coatings were investigated. A higher silicone oil content and a PB ratio close to the critical pigment volume concentration favor long-term hydrophobicity of the coatings. An obvious decrease in ice adhesion strength was achieved for coatings with a PB ratio of 5.0 and a silicone oil content of 4.2%. For coatings with the same surface roughness, a higher water contact angle (WCA) led to lower ice adhesion strength. However, for coatings with different surface roughnesses, the ice adhesion strength was found to be dependent on surface roughness rather than on WCA.     

加成型液体乙烯基硅橡胶的研制Ⅰ.乙烯基硅油等对物理机械性能的影响

考察了乙烯基硅油及含氢硅油对加成型液体乙烯基硅橡胶物理机械性能的影响。结果表明，在100份乙烯基硅橡胶中加入10份乙烯基质量分数为10％的硅油，4.6份含氢硅油，用20份经表面处理的白炭黑增强，可得到拉伸强度为3.8MPa，撕裂强度为7.6kN/m，扯断伸长率为162％的乙烯基硅橡胶。     

甲基乙烯基硅橡胶加成硫化研究

探讨了甲基乙烯基硅橡胶中乙烯基含量、多乙烯基硅油、舍氢硅油和氟铂酸对加成硫化硅橡胶物理机械性能的影响。结果表明．在150份乙烯基质量分数为0．13％的硅橡胶中加入1份硅氢基质量分数为1．65％的舍氢硅油、2份乙烯基质量分数为8％的多乙烯基硅油和4份羟基硅油，用40份白炭黑增强，可得到拉伸强度为8．71MPa，撕裂强度为52．14kN／m的乙烯基硅橡胶。     

线性聚醚氨基嵌段有机硅柔软剂的应用特点

以端环氧基硅油、聚醚胺和端环氧基聚醚为主要原料,合成了线性聚醚氨基嵌段有机硅柔软剂;乳化后用于织物的整理。考察了线性聚醚氨基嵌段有机硅柔软剂对织物的白度、摩擦牢度、防水性能和撕破强力等的影响,并用FT-IR表征了产物结构。结果表明,与采用传统有机硅柔软剂氨基硅油和亲水聚醚改性硅油整理的织物相比,经线性聚醚氨基嵌段有机硅柔软剂整理织物的白度、摩擦牢度、防水性能和撕破强力等具有明显的优势,并可很好地平衡手感和亲水性之间的矛盾,具有优良的性能。     

硅油和白炭黑比表面积对硅橡胶性能的影响

气相法白炭黑是硅橡胶补强的最佳填料,羟基硅油是硅橡胶补强中常用的1种结构控制剂。本文研究了羟基硅油的用量以及气相法白炭黑比表面积对硅橡胶力学性能的影响。结果表明:随着羟基硅油用量的增加,硅橡胶的硬度、拉伸强度均逐渐降低,而断裂伸长率却随羟基硅油用量的增加而逐渐增大;随着气相法白炭黑比表面积的增大,硅橡胶的硬度、拉伸强度逐渐增大,而断裂伸长率逐渐减小。     

Crack Growth and Acoustic Emission in Ceramics During Thermal Shock

It is recognized that microcracks may contribute to failure of ceramics undergoing thermal shock, although there is little direct experimental evidence. The combination of acoustic emission (AE) and SEM observations provides such evidence. In this work AE data were analyzed after rapid quenching of samples in silicone oil. A thermal shock resistant material, alumina, and a material resistant to thermal damage, advanced zirconia refractory, have been examined. Cracks were detected by analysis of AE amplitudes and durations and their growth was monitored by systematic SEM observations as thermal shocks of increasing severity were applied. Three-point bending strengths were determined in air after quenching. For the first time SEM images are presented showing early stages of crack initiation for temperature differences less than Δ T_crit , i.e., where the fracture was not believed to occur. Further development of the cracks leads to abrupt strength reduction in alumina and controlled strength loss in zirconia, although AE data did not indicate any particular pattern of catastrophic crack propagation when substantial loss of strength occurred.     

有机硅密封胶中裂解硅油的检测

配制了含裂解硅油的有机硅密封胶和含二甲基硅油的有机硅密封胶,分别测定其力学性能、热性能;并用四氢呋喃浸泡有机硅密封胶,过滤后将滤液进行凝胶渗透色谱（GPC）和硅核磁共振（^29Si NMR）分析。结果显示,与含二甲基硅油的有机硅密封胶相比,含裂解硅油的有机硅密封胶经水紫外、高温老化后的拉伸强度和拉断伸长率下降幅度更大,热分解温度更低;其浸出液的摩尔质量分布更宽,有4个峰存在,且29Si NMR谱图中存在M、D、T链节的特征吸收峰。通过力学性能、热性能测试,再经^29Si NMR和GPC分析,可定性检测有机硅密封胶是否含裂解硅油。     

加成型硅橡胶的制备与耐热稳定性的研究

采用乙烯基硅油为基胶,含氢硅油为交联剂,苯基硅油和氧化铁为耐热添加剂,制备了加成型耐热硅橡胶。研究了苯基硅油中苯基质量分数、苯基硅油用量、氧化铁用量及协同效应对硅橡胶耐热稳定性的影响。结果表明,随着苯基硅油、氧化铁用量和苯基质量分数的增加,硅橡胶的热稳定性明显增强;当苯基质量分数为10．2％,苯基硅油用量为10份,氧化铁用量为6份时,制得了耐热稳定性良好的硅橡胶,经300℃老化48h后,硬度和拉伸强度分别仅下降了3．77％和13．3％,而未改性硅橡胶老化后分别下降55％和79．3％。TGA结果显示,在苯基硅油和氧化铁协同保护作用下,硅橡胶在400。C高温前,热分解速率很低,这种协同保护效应能很好地提高耐热稳定性。     

抗撕型硅橡胶的配方优化

采用正交试验法考察过氧化二异丙苯(DCP)、白发黑、羟基硅油、二苯基硅二醇4个因子对硅橡胶撕裂强度的影响,分析了其差异及产生的原因,并找出了优化的硅橡胶的抗撕裂配方为:100份110-2生胶,0.6份DCP,25份白炭黑,4份羟基硅油,0.6份二苯基硅二醇.此配方得到的硅橡胶混炼胶的撕裂强度大于13 kN/m.     

氨基硅油对阻燃HDPE护套管的改性

通过加入无卤阻燃剂(氢氧化镁)和抑烟剂(水合硼酸锌)使高密度聚乙烯达到阻燃抑烟的效果。测试了试样的拉伸强度、弹性模量、断裂伸长率、氧指数、维卡软化点，并进行了电镜分析。针对无卤阻燃体系韧性下降很大的缺点，采用氨基硅油进行改性。结果表明，氨基硅油可在一定程度上改善材料的韧性，但同时使材料的拉伸强度和模量大幅下降，且不能提高体系的氧指数。     

室温固化含硅甲基丙烯酸酯涂料的性能研究

制备了易溶于溶剂汽油的含硅甲基丙烯酸酯改性的丙烯酸酯共聚物，通过水接触角、吸水率、铅笔硬度以及FT-IR光谱和DSC等测试，研究了丙烯酸酯单体侧链烷基对共聚物溶解性能的影响及含硅丙烯酸酯单体及其共聚工艺对共聚物表面憎水性能和强度的影响。结果表明，采用延时后滴加含硅丙烯酸酯单体和使用催化交联剂及添加羟基硅油共混可使甲基丙烯酸异丁酯和甲基丙烯酸异冰片酯的共聚物膜表面的憎水性能和强度大大提高。