Adherence-fracture energy of a glass-bonded thick-film conductor: effect of firing conditions

The effect of firing conditions on the adherence of a glass-bonded Pt-Au printed thick film conductor to a 96 wt % Al₂O₃ substrate was determined by a fracture mechanics measurement of the critical fracture energy for catastrophic thick film-substrate separation. The technique also demonstrated that separation by slow crack growth (delayed failure) occurred in this system. Analysis of the thick film microstructure and fracture surfaces showed that optimum adherence was primarily a result of a mechanically interlocked interface formed between the conductor metal and the glass bonding layer which, in turn, was strongly bonded to the alumina substrate. The two step decrease observed in _IC (from 3.7 to 0.2 J m^–2) with firing temperatures over 860° C resulted from the removal of this interlocking metal-glass interface brought on by metal sintering and glass migration to the substrate. Thus, at 860° C firing temperatures, adherence is controlled by cohesive fracture in the glass bonding phase while above 1000° C it is controlled by adhesive failure of the weak chemical-physical bond at the metal-glass interface.     

考虑导线偏心覆冰对四分裂导线舞动的影响

采用风洞试验获得典型新月形覆冰四分裂导线的升力、阻力和扭矩系数随风攻角的变化规律。基于ABAQUS有限元软件提出一种考虑偏心覆冰作用的导线数值模拟方法,并利用算例验证了该方法的正确性。在此基础上,利用ABAQUS用户自定义子程序UEL编写气动载荷单元,实现考虑偏心覆冰作用的导线舞动数值模拟方法。采用该方法与传统数值模拟方法对典型新月形覆冰四分裂导线的舞动特征进行对比分析。结果表明,该方法能准确反映覆冰导线运动过程的扭转特性。考虑偏心覆冰作用后,覆冰四分裂导线的位移和扭转角幅值明显增大,振动形态更为复杂。因此,在研究覆冰导线舞动时,有必要考虑偏心覆冰作用的影响。     

Thermal impedance of thick-film resistance thermometers below 0.2 K

Contributions to the thermal impedance of thick-film resistors (TFRs) are discussed. Measurements of the heat flow along the resistance layer, through the substrate and through the glass overcoating, are presented for commercial resistors mounted on a copper plate in the 30–170 mK temperature range. Because of the relatively good thermal conductivity of the film material (three orders of magnitude higher than that of alumina), the contribution to the heat flow of the resistance layer is never negligible in spite of the thinness of the latter. Suggestions are given for the best mounting of the TFRs as low-temperature thermometers. Less conventional uses of TFRs as thermometers in bolometers are also considered.     

陶瓷添加物对Ti_3SiC_2基复合材料抗氧化性的影响

为研究陶瓷添加物对Ti3SiC2基复合材料性能的影响,首先,采用反应热压烧结法制备了Ti3SiC2材料及陶瓷添加物含量均为30wt%的SiC/Ti3SiC2、Al2O3/Ti3SiC2和MgAl2O4/Ti3SiC2复合材料。然后,测试了材料的力学性能和导电性,在1 373~1 773K温度范围内对Ti3SiC2基复合材料的抗氧化性进行了研究,并对其烧结试样的物相组成和显微结构等进行了表征。结果表明:Ti3SiC2在高温氧化后的主要产物为TiO2和SiO2;氧化层分为内外2层,内层由TiO2与SiO2这2相混合组成,外层为TiO2;氧化层中存在大量显气孔,结构较为疏松,导致抗氧化性较差。与Al2O3/Ti3SiC2和MgAl2O4/Ti3SiC2复合材料相比,SiC/Ti3SiC2复合材料具有更好的抗氧化性。     

Effect of oxide additives on the morphology of fine-particle silicon carbide

Silicon carbide powders were prepared from pelletized mixtures of fine-particle SiO₂ and petroleum coke with CaO, Fe₂O₃, and Al₂O₃ additions at temperatures from 1770 to 1870 K and atmospheric pressure. The Si loss in the form of SiO and the SiC yield were measured. The materials with CaO additions consisted of needlelike crystallites and a small amount of submicron-sized particles. The materials containing Fe₂O₃ consisted of roughly equal amounts of needlelike crystallites and submicron-sized particles. The introduction of CaO-Fe₂O₃ (10-66% Fe₂O₃) combined additions resulted in materials consisting mainly of submicron-sized particles. In the presence of A1₂O₃, needlelike crystallites did not grow.     

添加剂对中间相沥青炭微球形成的影响

以中温煤沥青为原料,分别添加3%(质量分数)的炭黑、硫、氯化铝和对甲苯磺酸于420℃保温2h制备MCMB,研究比较了这4种添加剂对MCMB制备的影响.实验结果表明,炭黑、氯化铝和对甲苯磺酸作添加剂均能制备小粒径的MCMB,其中炭黑作用下制备的MCMB形度好、粒径均一,但表面粘附有炭黑颗粒且收率低;氯化铝作用下制备的MCMB球形度好,表面光洁,单分散性好,粒径分布相对集中,收率较高;对甲苯磺酸作用下制备的MCMB粒径较小时粘结融并现象严重,粒径较大时有较好的球形度与单分散性;硫作添加剂制备的MCMB粒径较大,球形度差,粘结现象严重.氯化铝是其中较好的添加剂.     

Effect of various oxide additives on sintering of BaO-SiO2 system glass-ceramics

Glass-ceramics can be produced by sintering and crystallization of a pressed glass powder pellet. Crystallization prior to complete densification results in a porous glass-ceramic. A small quantity of various oxides was added to and melted with 35.7 BaO-64.3 SiO₂ (mol %) glass and the sintering characteristic of the glass powder was evaluated in terms of the density relative to the bulk glass density after heating at a constant rate. Some oxide additives, such as Al₂O₃ and ZrO₂, increased the per cent relative density while others, such as Na₂O, decreased it. The achieved per cent relative density was compared with crystallization characteristics determined by differential thermal analysis (DTA) and viscosity determined by the beam-bending method. The per cent relative density showed a good correlation with the viscosity at the crystallization temperature, the higher per cent relative density being achieved for systems with the lower viscosity at the crystallization temperature.     

汽车钢板抗凹性试验研究

汽车零件,尤其是外覆盖件的制造过程中选择钢材等级和规格的重要依据之一是抗凹性.以实验评估为基础介绍抗凹性评估相关参量的物理意义及测量原理,并对数种钢板在不同加工硬化和应变硬化状态下的静态抗凹性行为进行分析.研究表明,本抗凹性评估方法合理,可应用于薄板材料的抗凹性研究.     

可移动凹模对板材液压成形影响的研究

为了研究可移动凹模对板材液压成形的影响,进行了有无可移动凹模与不同可移动凹模加载方式(方式1与方式2)的板材液压成形试验.研究结果表明:比较有无可移动凹模对板材液压成形厚度分布的影响,在有可移动凹模时,成形零件厚度分布比较均匀,这种技术有利于提高板材的成形极限;没有可移动凹模,板材难于成形,尤其对于复杂零件;可移动凹模加载方式2比加载方式1更有利于板材厚度的均匀分布.     

In-situ magnetic deposition field effect on sheet resistance of Permalloy films

We have measured the real-time in-situ sheet resistance (R_□) of a Permalloy (Py) film during the film-growth period in a vacuum under various magnetic deposition-field (H) conditions: a longitudinal direct-current (dc) field (H = H_x), a transverse dc field (H = H_y), and a rotating field (H = H_r) with the frequency (f) at 0.6, 1.4, 2.5, 10, and 100 Hz, respectively. The results show that R_□(H_y) > R_□(H_x) ? R_□(H = 0) ? R_□(H = H_r), when Py film is just before or near the coalescence stage of the film-growth process. The reason for these phenomena is that a dc field (H = 0, H_x, or H_y) tends to make the structure of the film more anisotropic, while a rotating field (H = H_r) tends to make the film more isotropic. Moreover, based on the quantum tunneling mechanism, the fact that there will be many more tunneling events through which an electron can be transported down a piece-by-piece connected film with an anisotropic than with an isotropic structure should naturally lead to the observed results above. Finally, we also explain why in the R_□ versus f plot (under the condition of film thickness t_f = 1 nm), there exists a minimum R_□ at f = f_min = 2.5 Hz.     

外加剂对合成六铝酸钙性能的影响

以纳米碳酸钙和工业氧化铝为主要原料,研究了SiO2和Fe2O3两种外加剂对合成六铝酸钙性能的影响,结果表明:六铝酸钙的生成反应在1500℃基本完成.1400℃时,加入SiO2微粉不利于六铝酸钙生成,Fe2O3则能够促进六铝酸钙生成.在整个实验温度范围内,加入SiO2微粉使得材料中生成了适当数量的液相,可以显著促进材料的致密化,Fe2O3的促烧结作用较差.     

添加剂对水热法制备超细氧化铁的影响

以硫铁矿烧渣酸浸液为原料，采用水热法制备超细氧化铁。添加剂对水热产物的物相影响较小，但对水热产物形貌影响较大。当水热反应温度为190℃、反应时间为30min、总铁浓度为3mol／L、n（Fe^2＋）/n（Fe^3＋）取0．145时，加入添加剂CTAB、NaH2PO4、CO（NH2）2水热反应所得产物为椭球形粒子；加入PVP、OP所得水热产物为球形氧化铁粒子，但其粒径差异较大。酸浸液中n（Fe^2＋）／n（Fe^3＋）物质量之比对水热产物物相和形貌有重要影响。当n（Fe^2＋）/n（Fe^3＋）为0时，水热产物为大小均匀的球形超细Fe2O3粒子，其粒径约为0.11μm；当n（Fe^2＋）／n（Fe^3＋）为0．145时，其水热产物颗粒增大、粒径各异，物相为Fe2O3、Fe3O4；当n（Fe^2＋）/n（Fe^3＋）为0.842时，从放大3万倍SEM照片，难以观测其形貌与粒径大小，其物相为Fe3O4。     

Oxidation resistance of silicon nitride ceramics with various additives

Five silicon nitride ceramics with various additives were evaluated for their oxidation resistance at 1300 ° C in flowing dry and wet air. In a dry atmosphere, the oxidation of all types of Si₃N₄ except one proceeded in two stages with different reaction rates nearly following the parabolic law. In a wet atmosphere, all types showed a linear relationship between weight gain by oxidation and water varpour content. The water vapour in the atmosphere slightly accelerated the oxidation. The influence of oxidation on room-temperature strength was complex, but there was no observed distinguishable difference of the effect on the flexural strength between dry and wet oxidation.     

Fracture phenomenology of a sintered silicon nitride containing oxide additives

Crack propagation mechanisms in a sintered silicon nitride containing various oxide additives (ceria, magnesia, zirconia and strontium oxide) were studied as a function of initial flaw size, temperature, applied stress and time. Surface cracks of controlled size were introduced using the microhardness indentation-induced-flaw technique. At 20° C, the fracture stress was found to depend on initial crack size according to the Griffith relationship and extrapolation of the data indicated that processing flaws of 20 to 35 were strength-controlling. The flexural strength was found to be independent of temperature from 20 to 800° C and the mode of crack propagation was primarily transgranular. At temperatures above 800° C the flexural strength decreased significantly, due to viscous flow of the glassy phase present in the material and resulting in sub-critical crack growth (SCG). The mode of crack propagation during SCG was essentially intergranular. Flexural stress-rupture evaluation in the temperature range 800 to 1000° C has identified the stress levels for time-dependent and time-independent failures.     

Influence of hydrogen on the fracture resistance of 65G sheet steel

We present the results of investigations of the influence of hydrogen on the fracture of 65G sheet spring steel. The distribution of strains is determined by the method of digital speckle correlation, the topography of the specimen surface in front of the crack tip is analyzed, and it is shown that the influence of hydrogen makes the fracture strain 1.5 times lower. It is also demonstrated that the crack resistance of 65G steel decreases in hydrogen (as compared with air) by 14%. The fractographic analysis of the fracture surfaces of specimens is performed and the morphology of crack propagation is investigated by the metallographic method. It is shown that the decrease in the operating characteristics of 65G steel under the action of hydrogen manifests itself in the localization of plastic strains and extensive delamination along the joints of the layers of rolling.     

造纸法低定量烟草薄片增强助剂的性能评价

以造纸法制备了低定量烟草薄片,测定了壳聚糖、羧甲基纤维素、羟乙基纤维素和聚乙烯醇的增强性能,及其对烟草浆料和填料留着,以及烟草基片物理性能的影响。研究结果表明,加入壳聚糖的系统助留效果最好,填料留着率提高7.3%;加入羧甲基纤维素和聚乙烯醇的烟草基片具有较好的松厚度和吸液性;加入羟乙基纤维素和壳聚糖的烟草基片分别具有较好的抗干、湿强度。