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对流效应和溶质浓度对KNbO3晶体界面形貌稳定性的影响 总被引:1,自引:0,他引:1
研究了在不同对流形态对KNbO3晶体生长形貌的影响。在温度梯度较小的扩散-平流区域,晶体以枝蔓晶的形态生长;而在温度梯度的较大的扩散-对流区域,生长出的晶体呈现光滑晶面。通过测定不同区域KNbO3晶体界面附近的溶质浓度分布,从对流效应降低晶体界面附近的溶质浓度分布的不均匀性的角度研究了对流效应对晶体界面形貌稳定性的影响,证明对流效应提高了晶体界面形貌稳定性,与晶体界面弥散度的理论计算相一致。同时解释了扩散-对流区域的晶体尺寸大于扩散-平流区域的晶体尺寸的原因。观察并定性地解释了不同溶质浓度KNbO3形成不同的界面非稳定形貌,当KNbO3重量百分比为20wt%时形成骸晶,30wt%时形成枝蔓晶。 相似文献
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研究了在不同对流形态对KNbO3晶体生长形貌的影响.在温度梯度较小的扩散-平 流区域,晶体以枝蔓晶的形态生长;而在温度梯度较大的扩散-对流区域,生长出的晶体呈现 光滑晶面.通过测定不同区域KNbO3晶体界面附近的溶质浓度分布,从对流效应降低晶体界 面附近的溶质浓度分布的不均匀性的角度研究了对流效应对晶体界面形貌稳定性的影响,证明 对流效应提高了晶体界面形貌稳定性,与晶体界面弥散度的理论计算结果相一致.同时解释了 扩散-对流区域的晶体尺寸大于扩散-平流区域的晶体尺寸的原因.观察并定性地解释了不同 溶质浓度KNbO3形成不同的界面非稳定形貌,当 KNbO3重量百分比为20wt%时形成骸晶, 30wt%时形成枝蔓晶. 相似文献
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为了研究循环加载过程中织构对多晶材料Baushinger效应的影响,利用经典晶体塑性模型及含随动硬化的晶体塑性模型模拟AA6104铝合金循环加载力学行为.研究了多晶体中晶粒取向差异对材料宏观塑性行为的影响.详细分析了经典晶体塑性模型可描述多晶体循环加载Bauschinger效应机理,定量分析了多晶有限元模型中晶体取向差异对模拟结果的影响.结果表明多晶体中由于晶粒取向差异而造成的晶粒间相互作用力使得多晶体模型宏观卸载时晶粒内的残余应力是产生Bauschinger效应的主要原因,采用含随动硬化的晶体塑性模型能够较好地模拟具有织构的AA6014铝合金的循环加载过程. 相似文献
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为了研究一维平板声子晶体中弹性波的全反射隧穿效应,利用传输矩阵法计算了弹性波在大于全反射角入射一维平板方形声子晶体的透射率。在透射波中发现了全反射隧穿效应,并且全反射隧穿峰具有优良的多通道滤波特性。得出了一维平板声子晶体的全反射隧穿的滤波特性随模式量子数、平板厚度以及周期数的变化规律,为设计性能优良的多通道声子晶体滤波器提供了理论依据。 相似文献
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为了研究一维声子晶体中弹性波的全反射贯穿效应,利用转移矩阵法计算了弹性波在大于全反射角入射一维声子晶体的透射率。在透射波中发现了两条透射峰带,即出现了全反射贯穿效应。得出了贯穿效应随入射角的变化规律、贯穿效应随介质厚度的变化规律以及贯穿效应随周期数的变化规律。并利用波的量子理论和渐逝波的理论对一维声子晶体的贯穿效应作出了定性的理论解释 相似文献
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采用柠檬酸钠-鞣酸还原法制备出胶体金,并用紫外可见分光光谱对胶体金粒径及形态进行了评价,结合Zeta电位分析了胶体金的稳定性,利用多重金属沉积法对玻璃表面新鲜的汗潜、油潜手印进行了显现.结果表明,合成的胶体金粒径为10~35m,且胶体金颗粒形态均一,稳定性强.多重金属沉积法具有选择性吸附强、背景污染小等特点,其显现效果与粉末法相当,甚至优于粉末法. 相似文献
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《工程爆破》2022,(4)
为了研究钨粉形貌对钨铜合金药型罩破甲性能的影响,采用了4种不同颗粒形貌的钨粉,利用机械合金化法和冷等静压旋压工艺制备钨铜合金药型罩,并对钨铜合金药型罩射孔弹进行了地面静破甲穿钢靶试验,通过试验分析钨粉形貌对钨铜合金药型罩破甲性能的影响。结果表明:钨粉颗粒完整、形貌为多面体的钨粉,其松装密度达到9.564 g/cm3,制备的钨铜合金药型罩的破甲深度达到338.3 mm,破甲稳定性达到99.21%;而钨粉颗粒有缺陷、形貌为类球状的钨粉,其松装密度仅为7.142 g/cm3,制备的钨铜合金药型罩的破甲深度达到338.3 mm,破甲稳定性达到99.21%;而钨粉颗粒有缺陷、形貌为类球状的钨粉,其松装密度仅为7.142 g/cm3,制备的钨铜合金药型罩的破甲深度为288.1 mm,破甲稳定性为92.7%,分别下降了17.4%和7.6%。 相似文献
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《Science and Technology of Advanced Materials》2001,2(1):209-212
The morphological evolution near the absolute stability limit during directional solidification has been studied systematically on dilute Al–Mn alloys. It is found that the interfacial morphology of Al–0.52wt%Mn and Al–1.2wt%Mn alloys changes from coarse cellular structure to fine cells, and then again to be coarsened with the increase of velocity to near the absolute stability limit. This indicates that there exists a minimum cell spacing corresponding to the maximum effective constitutional supercooling. As the growth rate approximates to or exceeds the critical velocity of absolute stability by calculation according to M–S theory, the interfacial morphology of Al–0.52wt%Mn alloy may still retain a cellular structure. For Al–1.2wt%Mn alloy, when the growth velocity is near the absolute stability limit, the fine cells may change to a band or grain-like structure which in some cases takes an oscillating manner, which possibly implies the existence of a non-linear effect during high growth rate. 相似文献
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Xingguo Geng 《Science and Technology of Advanced Materials》2013,14(1):209-212
The morphological evolution near the absolute stability limit during directional solidification has been studied systematically on dilute Al–Mn alloys. It is found that the interfacial morphology of Al–0.52wt%Mn and Al–1.2wt%Mn alloys changes from coarse cellular structure to fine cells, and then again to be coarsened with the increase of velocity to near the absolute stability limit. This indicates that there exists a minimum cell spacing corresponding to the maximum effective constitutional supercooling. As the growth rate approximates to or exceeds the critical velocity of absolute stability by calculation according to M–S theory, the interfacial morphology of Al–0.52wt%Mn alloy may still retain a cellular structure. For Al–1.2wt%Mn alloy, when the growth velocity is near the absolute stability limit, the fine cells may change to a band or grain-like structure which in some cases takes an oscillating manner, which possibly implies the existence of a non-linear effect during high growth rate. 相似文献
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采用射频磁控溅射技术在Ti6Al4V基体上成功制备了含氟羟基磷灰石梯度复合涂层(HAF/YSZ)。利用X射线光电子能谱(XPS)、电子探针(EDX)、扫描电镜(SEM)等对涂层的成分分布、形貌、界面结合进行表征。通过模拟体液(SBF)实验,分析和评价了HAF/YSZ涂层在模拟人体条件下的生物性能。结果表明,所制备涂层表面粗糙,呈多孔岛状结构,有利于新生骨组织的生长;涂层与基体结合紧密,各层间相互扩散,整体一致性较好;经模拟体液浸泡后,涂层表面有新生物质沉积,表现出较好的生物活性及稳定性;梯度复合涂层较氟含量单一的氟羟基磷灰石涂层具有更好的抗体液溶解能力及稳定性。 相似文献
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根据已经报导的实验结果对在典型的AlMn二元合金中二十面体准晶的凝固形貌及合金成分、冷速的关系进行了研究,对二十面体准晶与相应的晶体的凝固形貌进行了比较。实验结果与理论分析表明,在晶体凝固中适用的形貌稳定性理论也可以应用了二十面体准晶的凝固形貌予测及控制。 相似文献
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The poly(urea–formaldehyde) (PUF) microcapsules filled with epoxy resins have potential for self-healing or toughening polymeric composites. A series of PUF microcapsules containing epoxy resins were synthesized by selecting different process parameters including surfactant type, surfactant concentration, adjusting time for pH value and heating rate. The effects of process parameters on the size and surface morphology of microcapsules were discussed. The storage stability, solvent resistance and the mechanical strength of microcapsules were investigated. The morphology of microcapsules was observed using scanning electron microscopy (SEM) and optical microscopy (OM). The results indicate that the formation of microcapsules is affected by the surfactant type. The size of microcapsules can be controlled by the surfactant concentration. The surface morphology of microcapsules can be adjusted by the surfactant concentration, the adjusting time for pH and the heating rate. The microcapsules prepared by using surfactant sodium dodecylbenzene sulfonate (SDBS) show good storage stability, excellent solvent resistance and appropriate mechanical strength. 相似文献
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The results of an experimental investigation into the morphology of silica precipitates in internally oxidised silicon-bearing nickel and cobalt alloys are compared with the predictions of theories that concern the growth of spheroidal and extended precipitates and dendritic phases. Some degree of agreement is obtained between theory and experiment and a fairly detailed dependence of morphology on oxidation conditions and diffusion and concentration factors is outlined. Some observations on the stability of internal oxide precipitates are discussed and some conclusions, which are believed, in the main, to be general and applicable to any internally oxidised system, are made as to the dependence of morphology on the conditions of experiment. 相似文献
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Mollmann SH Bukrinsky JT Elofsson U Elversson J Frokjaer S Thalberg K Millqvist-Fureby A 《Drug development and industrial pharmacy》2006,32(6):765-778
Solid insulin formulations obtained by different methods of preparation were compared with respect to chemical stability and morphology. Spray- and freeze-drying, solution enhanced dispersion by supercritical fluids (SEDS) and precipitation into starch microspheres were the methods used for preparation of solid powders. The excipients applied were melezitose, starch, and sodium taurocholate. The stability of the samples was evaluated after storage in open containers at 25°C and 30% RH for 6 months.
All samples were amorphous after processing and storage as detected by XRD, except for the starch microspheres which were semi-crystalline. The spray- and freeze-dried samples containing melezitose and sodium taurocholate experienced a significant water uptake during storage, resulting in changes in morphology and disappearance of Tg. However, the chemical stability of these samples did not seem to be affected by the water uptake. Changes in morphology were not observed for the SEDS powders and the starch microspheres.
The chemical stability of the samples was assessed by HPLC. In general, conventional spray- and freeze drying resulted in samples with higher chemical stability compared to SEDS powders and starch microspheres. Nevertheless, the excipients applied were observed to be of major importance, and further optimization of the formulation as well as processing conditions may lead to slightly different conclusions. 相似文献
All samples were amorphous after processing and storage as detected by XRD, except for the starch microspheres which were semi-crystalline. The spray- and freeze-dried samples containing melezitose and sodium taurocholate experienced a significant water uptake during storage, resulting in changes in morphology and disappearance of Tg. However, the chemical stability of these samples did not seem to be affected by the water uptake. Changes in morphology were not observed for the SEDS powders and the starch microspheres.
The chemical stability of the samples was assessed by HPLC. In general, conventional spray- and freeze drying resulted in samples with higher chemical stability compared to SEDS powders and starch microspheres. Nevertheless, the excipients applied were observed to be of major importance, and further optimization of the formulation as well as processing conditions may lead to slightly different conclusions. 相似文献