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21.
本文采用DSC法研究了形变含铝、铌低合金钢组织中珠光体→奥氏体的相变动力学。在此基础上绘制了相变的体积分数与温度之间的关系曲线,并得出的相变激活能随其相变体积分数的变化。 相似文献
22.
Zn-Al系二元相图的研究 总被引:1,自引:1,他引:1
利用高温X射线衍射法(XRD)、示差扫描量热分析法(DSC)、热膨胀法(PRD)等方法重新测定Zn-Al二元体系相图。在XRD曲线图中β(ZnAl)相的存在,表明存在β(ZnAl)固溶单相区;DSC曲线图表明在274~279℃范围内存在共析相变反应;PRD曲线图表明在340℃不存在相变反应。综合XRD、DSC和PRD结果,绘制了部分Zn-Al二元体系相图,为高铝锌基合金的实际相变应用提供参考。 相似文献
23.
复合材料压力容器的树脂体系的固化动力学研究 总被引:2,自引:1,他引:2
本文采用非等温DSC方法对碳纤维增强复合材料压力容器的树脂体系进行固化动力学研究。应用Malek方法处理实验数据,得到此树脂体系机理函数服从一个二参数(m,n)的自催化模型,其中活化能通过Ozawa法得到。通过温度场模拟结果与试验值比较,验证本文建立的动力学模型的可靠性。因此,可为复合材料压力容器固化成型过程中瞬态温度场的模拟提供必要子模型。 相似文献
24.
A series of binary blends of poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), and polytetrahydrofuran (PTHF), characterized by similar average molecular weights, with selected fatty acids (capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid) were prepared by melt mixing. Differential scanning calorimetry was applied to characterize the phase transitions of melting and crystallization, and a synergistic effect was found to occur for PEO/fatty acid blends, as evidenced by the values of the enthalpy of the phase transition. This effect was probably due to hydrogen bonding between PEO and the fatty (carboxylic) acids, which facilitated the formation of crystalline structures; an analysis of IR spectroscopy data showed a shift in the absorption bands of OH groups. The morphology development of the PEO/carboxylic acid blends, as observed with polarizing light microscopy, could be described as spherulitic growth with spontaneous selection of the lamellar thickness. The textures of the individual fibrils, consisting of stacks of several tens of lamellae corresponding to PPO and PTHF, were less regular than the texture of PEO and showed large macroscopic heterogeneity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 861–870, 2003 相似文献
25.
R. Sarathi 《应用聚合物科学杂志》2002,83(13):2843-2849
In the present work tracking phenomena were studied with high‐density polyethylene (HDPE) materials under dc voltage, with NH4Cl and acid rain as contaminants. It was determined that the tracking time of the material depends on the conductivity and flow rate of the contaminant. Furthermore, physicochemical analysis by wide‐angle X‐ray diffraction studies, differential scanning calorimetry, and luminescence spectroscopy was carried out, whereupon it was concluded that the tracking process is a surface‐degradation process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2843–2849, 2002; DOI 10.1002/app.10260 相似文献
26.
Lignin‐based chemicals, starch, and urea were used as modifiers for phenol–formaldehyde resol resins. The effects of the addition stage of the modifiers used in the synthesis of the resins and the type of modification reagent on the structures of the resins and their molar masses and reactivities were investigated. The modifications with corn starch and lignin promoted condensation; this was verified by increased molar masses and high ratios of methylene bridges to the sum of free ortho and para aromatic groups with respect to the corresponding reference resin without a modification reagent. The later the modifier was added to the resin condensation mixture, the more methylene bridges were formed with respect to the amounts of free ortho and para aromatic groups. In addition, when urea or wheat starch was added in the later condensation stage, the final condensation also reached high stages. The modifications with lignosulfonate and starch, as well as the early addition of urea, enhanced p–p′ bridge structures. The lowest condensation stage and, therefore, the highest reactivity were found when wheat starch was added with the starting reagents. The curing heat of the wheat‐starch‐modified resins decreased according to the deferred addition point of starch. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 582–588, 2003 相似文献
27.
Polyurethanes were prepared from toluene diisocyanate (TDI), 1-4-butane diol (BDO) and polycaprolactone-based triols with varying molecular weights. Among each molecular weight triol-based urethane, hard segment content was varied from 20% to 70%. Differential scanning calorimetry, tensile testing, and Iosipescu shear testing were done on all the various urethanes prepared. Thermal characterization data revealed the dependence of phase separation on hard segment content as well as on the triol molecular weight. Tensile data and Iosipescu shear data further confirmed the observations made from the DSC data. The data further indicated that phase separation can greatly improve the modulus of cross-linked segmented urethanes. Adhesion of these urethanes to glass surface was evaluated using soda-lime float glass plate. Urethane samples were cast on the air side of the glass plates and adhesion was measured in shear mode. Adhesion data indicated that in addition to hard segment content, modulus, cross-link density, and molecular weight of the triols, phase separation seems to be a major factor in controlling adhesion. Surfaces of the failed adhesion samples were also analyzed and the failure mode was found to be cohesive, in varying degree, with the different urethane systems. 相似文献
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A series of phosphorus‐containing, wholly aromatic thermotropic copolyesters from acetylated 2‐(6‐oxide‐6H‐dibenz〈c,e〉〈1,2〉oxa phosphorin‐6‐yl)‐1,4‐dihydroxy phenylene, p‐acetoxybenzoic acid, terephthalic acid, and isophthalic acid were prepared by melting polycondensation. The structure and basic properties of the polymers, such as the glass‐transition temperature (Tg), melting temperature (Tm), thermal stability, crystallinity, and liquid crystallinity, were investigated with Fourier transform infrared, elemental analysis, differential scanning calorimetry (DSC), thermogravimetric analysis, wide‐angle X‐ray diffraction, and hot‐stage polarizing optical microscopy. The copolyesters had relatively high Tg values ranging from 183 to 192°C. The Tm values obtained from DSC curves for samples P‐20 and P‐25 were 290 and 287°C, respectively (where the number in the sample name indicates the molar fraction of the phosphorus‐containing monomer in the reactants). The initial flow temperatures of other samples observed with hot‐stage polarizing microscopy were 271–290°C. The 5% degradation temperatures in nitrogen ranged from 431 to 462°C, and the char yields at 640°C were 41–52%. All the copolyesters, except P‐40, were thermotropic and nematic. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1278–1284, 2002 相似文献