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91.
John S. Haggerty A. Lightfoot John E. Ritter Paul A. Gennari S. V. Nair 《Journal of the American Ceramic Society》1989,72(9):1675-1679
Reaction-bonded Si3 N4 (RBSN) made from high-purity Si powder is unusually resistant to degradation caused by exposures to air for up to 50 h at temperatures up to 1400°C. The weight gain during oxidation of this SiH4 -originating RBSN is approximately 10 times less than conventional RBSN. Contrary to normally observed strength degradations, room-temperature strengths of this high-purity, oxidized RBSN (avg = 435 MPa, max. = 668 MPa) remained at their unusually high, as-processed levels after 1000° and 1400°C oxidizing exposures. Fracture toughness values were unaffected by oxidation ( K IC = 2.3 to 2.4 MPa · m1/2 ). This superior oxidation resistance results from the high purity and the small diameter pore channels (0.01 to 0.06 μm) achieved in this SiH4 -originating RBSN. 相似文献
92.
Recently, it has been reported by our group and others1.2 that loss of curing agent is encountered during the curing of small droplets or thin films of amine cured epoxies. In our earlier study3 results were reported on loss of curing agent in small droplets used in conducting the rnicrobond, single fiber test for determination of interfacial shear strength (ISS). It was reported that use of a volatile curing agent (meta-phenylene diamine (m-PDA) with DGEBA resin) resulted in increasing amounts of curing agent being lost (as measured by T8 of the cured droplets) with decreasing droplet size during the processing procedure. Droplets smaller than 150 micrometers were seen to lose up to 40% of the curing agent leading to alteration of the mechanical properties of the droplet and, therefore, causing measured values of ISS to be exceedingly low. Use of a less volatile curing agent (Jeffamine 700, a polyether diamine, Texaco Specialty Chemicals) in combination with DGEBA resin produced results which indicated that loss of curing agent was not occuring. This study was undertaken to show the relationships between film (or droplet) size and the amount of curing agent lost (during the processing) for three different aminecured epoxy systems. 相似文献
93.
The object of the present study was to investigate the effect of superimposed dynamic and static stresses on mechanical and thermal properties of some epoxy adhesives. It was found that combinations of shear creep and torsional oscillations, applied simultaneously to adhesive joints at temperatures within the glassy range of the adhesive, led to strengthening of the joints in shear and to an increase in the glass transition temperature of the adhesive. Similar loading stresses applied at temperatures close to the Tg of the adhesive, led to opposite effects on the above mentioned properties of the joints. The width of the glassy-rubbery transition of the adhesives increased, in the whole range of temperatures used in this study and for all epoxy compositions, as a result of subjecting the joints to superimposed dynamic and static stresses. The broadening of the glass transition was interpreted as a result of the stiffening of polymer network during the combined stressing experiments. A linear relationship was found between the area of endothermal peaks in the first DSC scan of specimens subjected prior to test to superimposed dynamic and static stresses at temperatures below Tg, and the shear strength of the joints. In agreement with this observation and with literature data, a linear relationship was revealed also between the glass transition temperature of the resins (measured in the first DSC scan) and the shear strength of the joints. Based on experimental observations and on some literature information, it was suggested that the strengthening of the joint, as well as the changes in thermal properties of the adhesives, are mainly due to physical processes, such as short-range orientation of network chains and an increase in intermolecular interaction between highly polar sites of the network. The possibility that superimposed stressing led to changes in chemical crosslinking was discussed but it seems that no such reactions occurred. 相似文献
94.
主要介绍了粘接技术在高功率铁氧体移相器上的应用。通过对其工艺途径及关键工序的控制,提出了采用粘接技术完成高功率移相器铁氧体的连接,不仅可以大量地缩短工作时间,而且可以使制造成本大幅度降低。 相似文献
95.
对马钢2号高炉中修后开炉达产操作实践进行了总结。通过制定科学的开炉方案,快速提高煤比、降低焦比,实现了顺利开炉、快速达产达效的目标。 相似文献
97.
The magnetic-field-induced strains (MFIS) of polycrystalline Ni50Mn29Ga21 alloys containing Tb were studied. A large MFIS of-1.10% was obtained under compressive prestress conditions. The addition of Tb can fine the crystal grains, enhance the bending strength obviously, and make MFIS increase further, indicating that a moderate amount of Tb does not hinder twin boundary motion and it conversely makes the material more practical. 相似文献
98.
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100.
轧机机架强度和刚度的研究 总被引:3,自引:0,他引:3
本文对轧机机架的强度和刚度进行了研究。研究结果表明,增加机架横梁的高度是改善轧机机架刚度最有效也是最经济合理的方法。 相似文献