共查询到20条相似文献,搜索用时 15 毫秒
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B. Hilczer P. Piskunowicz H. G. Darwish L. Szczepańska 《International Journal of Thermophysics》1992,13(4):719-728
Differential thermal analysis (DTA) studies of NaNH4SO4·2H2O, NaND4SO4·2H2O, and NaNH4SeO4·2H2O single crystals were performed in the temperature range of the ferroelectric-paraelectric phase transition and of the dehydration process. The first-order phase transition at the Curie point was confirmed for NaNH4SO4·2H2O, whereas the transition in the isomorphous NaNH4SeO4·2H2O at the Curie temperature was found to be similar to a contineous (second order) with considerable higher transition enthalpy. Dehydration process of the crystals studied was found to proceed in two stages, with maximum dehydration rates at 355 and 400K. A linear decrease in thermal energy related to the long-range ordering in NaNH4SO4·2H2O crystals was observed with the dose of -cobalt-60 irradiation and discussed with respect to the radiation induced decrease in spontaneous polarization. 相似文献
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LiZnPO4-LnPO4体系离子导电性的研究 总被引:2,自引:0,他引:2
采用柠檬酸盐溶胶-凝胶法制备了低温相α-LiZnPO4和以LiZnPO4为基质稀土磷酸盐(LnPO4)掺杂的(LiZnPO4)1-x-(LnPO4)x(Ln3+=Nd3+、Sm3+、Er3+、X=0.1;Ln3+=La3+,X=0.1、0.2、0.4、0.6)的超细粉体并对它们进行DTA、TG和XRD的表征.讨论了室温下不同比例、不同稀土磷酸盐的掺杂对基质LiZnPO4离子导电率的影响.测试结果表明,LiZnPO4-LnPO4体系是由α-LiZnPO4和LnPO4两相组成;由于α-LiZnPO4烧结体的相对密度(d=58)极小,室温下样品几乎不显示导电性,而适量的非导电相LnPO4的掺入有助于提高烧结体的相对密度,增大体系的晶界电导率. 相似文献
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以8Cr4Mo4Ni4V轴承钢为研究对象,通过奥氏体等温保温实验,研究加热温度和保温时间对奥氏体晶粒尺寸的影响,采用平均截点法对不同热处理条件下的晶粒尺寸进行统计分析。结果表明:随着加热温度和保温时间的增加,奥氏体晶粒尺寸逐渐增大,当加热温度超过1100℃或保温时间超过120min时,实验钢晶粒开始发生显著粗化。当加热温度超过1150℃时晶粒已完全粗化。通过线性回归的方法,获得了8Cr4Mo4Ni4V轴承钢的奥氏体晶粒尺寸随加热温度和保温时间演化的数学模型,为指导航空轴承钢锻造与热处理过程提供理论依据。 相似文献
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采用分离式Hopkinson压杆装置对TC4钛合金和DT4电磁纯铁的帽形试样进行动态冲击实验,以研究两种材料高应变率下的绝热剪切行为,并分析材料热物理性能和力学性能对其绝热剪切敏感性的影响。实验所得流变应力-时间的关系曲线以及微观的金相分析都表明:尽管两种材料都发生了绝热剪切失效,但是TC4材料中的绝热剪切过程比较短暂,在失稳后的几个微秒之内材料就丧失了承载能力,并且带旁基体无明显塑性流变;而DT4材料中绝热剪切带的形成和扩展过程却要经历约60μs的时间,而带旁边的基体材料沿剪切方向发生了明显的塑性流变。通过对比两种材料绝热剪切带的扩展能,揭示了材料的比热、热导率和动态强度等参数对绝热剪切过程的影响。 相似文献
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通过可逆加成-裂解链转移自由基聚合(RAFT)和活性阴离子开环聚合(ROP)方法合成了星型嵌段共聚物PEO4-b-PNIPAAm4。首先通过活性阴离子聚合合成了分子量为8000、分子量分布为1.1的四臂星型聚环氧乙烷(PEO4),PEO4的末端羟基和DDAT进行酯化反应,得到大分子RAFT引发剂。然后引发N-异丙基丙烯... 相似文献
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Ti,Zr,Nb,Ta等金属具有优越的生物相容性,被广泛应用到生物材料中.日本学者Yoshimitsu Okazaki等人研究了铸造Ti-15Zr-4Nb-4Ta合金、Co-Cr-Mo和Ti-6Al-7Nb合金的室温力学性能和疲劳强度,并对Ti-15Zr-4Nb-4Ta合金制作的假牙牙托进行了超过1年的临床观察. 相似文献
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The interaction of an obliquely incident plane wave with an arbitrary birefringent plane structure can be described exactly by a so-called 4 × 4 layer matrix. However, its formation is rather complex, and therefore a simplified method to set up this matrix is proposed. It is deduced from the boundary conditions for the tangential components of the E and the H fields at the interfaces of the birefringent layer and the phase shifts of the four waves within the layer between both interfaces. The refractive indices and the directions of polarization of the four waves are calculated from the well-known dispersion relation in the principal coordinate system and a coordinate transformation. Transmission curves of Lyot filters made of uniaxial and biaxial materials are calculated in the cases of plane waves of finite or infinite lateral extension that are incident under Brewster's angle upon the filter positioned outside or within a laser resonator. The special examples given for a quartz filter and a YAlO(3) filter are characterized by a high selectivity within a broad bandwidth if Fabry-Perot effects can be neglected. Transmission curves of a quartz filter were verified by measurements. 相似文献
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利用力学性能测试和微观结构观察,研究了V-4Cr-4Ti合金的时效与冷加工强化,以及冷加工与氧含量对时效进程的影响.结果表明:钒合金在时效处理过程中产生了Ti-(C,O,N)沉淀相,其中650℃×3 h时效处理的V-4Cr-4Ti合金可以取得比较好的综合力学性能;时效与冷加工能对该合金起到综合的强化效果,但冷加工对时效进程有抑制作用.另外,氧含量增加对该合金的时效强化进程有促进作用. 相似文献