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1.
Tin at a pressure of 39 kb and at 314 degrees C has tetragonal symmetry with an atom at each point of a body-centered tetragonal lattice. The unit cell dimensions are a equal to 3.81 A, c equal to 3.48 A, and c/ a = 0.91. The melting curve of tin was observed up to 45 kb and the boundary line between the tin I and tin II phases was observed to 70 kb by x-ray diflraction techniques. 相似文献
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T Irifune K Kuroda N Funamori T Uchida T Yagi T Inoue N Miyajima 《Science (New York, N.Y.)》1996,272(5267):1468-1470
Pressure-induced amorphization of serpentine was observed at temperatures of 200° to 300°C and pressures of 14 to 27 gigapascals with a combination of a multianvil apparatus and synchrotron radiation. High-pressure phases then crystallized rapidly when the temperature was increased to 400°C. These results suggest that amorphization of serpentine is an unlikely mechanism for generating deep-focus earthquakes, as the temperatures of subducting slabs are significantly higher than those of the rapid crystallization regime. 相似文献
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Skelton EF Ayers JD Qadri SB Moulton NE Cooper KP Finger LW Mao HK Hu Z 《Science (New York, N.Y.)》1991,253(5024):1123-1125
Metallic filaments with submicrometer diametere have been fabricated. Standard diffraction techniques with conventional x-ray sources were unsuccessful in identifying the structure of these materials. However, with the use of synchrotron radiation produced on a wiggler beam line, diffraction data were obtained in measurement periods as short as 10 milliseconds. Two cylindrical single crystals of bismuth were studied, each with a diameter of 0.22 +/- 0.02 micrometer. The volume of sample illuminated for these measurements was 0.38 cubic micrometer, less than 0.5 femtoliter. The crystals are grown in glass capillaries, and, because bismuth expands on solidification, they are under a residual hoop stress. The crystallographic data indicate the presence of a linear compressive strain of about 2 percent, which is assumed to be the result of a residual stress of about 2 gigapascals. 相似文献
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In situ x-ray diffraction measurements revealed that FeS, a possible core material for the terrestrial planets, transforms to a hexagonal NiAs superstructure with axial ratio (c/a) close to the ideal close-packing value of 1.63 at high pressure and high temperature. The high-pressure-temperature phase has shorter Fe-Fe distances than the low-pressure phase. Significant shortening of the Fe-Fe distance would lead to metallization of FeS, resulting in fundamental changes in physical properties of FeS at high pressure and temperature. Calculations using the density of the high-pressure-temperature FeS phase indicate that the martian core-mantle boundary occurs within the silicate perovskite stability field. 相似文献
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Simultaneous x-ray diffraction and electrical resistance measurements on barium establish, with certainty, that Bridgman's 78-kb resistance transition is identical with his 59-kb volumetransition. During this transition, the bodycentered cubic structure changes to hexagonalclose packed. Lattice parameters for the latter structure at 62 kb (volume scale) are: a = 3.90 A, c = 6.15 A, and c/a = 1.58. Compression (AV/Vo) at 62 kb is 0.359 + 0.005 compared to 0.345 previously reported by Bridgman. Below the transition, at 49 kb, compression is 0.300 +/- 0.005 compared to Bridgman's 0.288. Bridgman's 17-kb volume transition was not detected by x-ray diffraction. 相似文献
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In situ synchrotron x-ray diffraction measurements of FeO at high pressures and high temperatures revealed that the high-pressure phase of FeO has the NiAs structure (B8). The lattice parameters of this NiAs phase at 96 gigapascals and 800 kelvin are a = 2.574(2) angstroms and c = 5.172(4) angstroms (the number in parentheses is the error in the last digit). Metallic behavior of the high-pressure phase is consistent with a covalently and metallically bonded NiAs structure of FeO. Transition to the NiAs structure of FeO would enhance oxygen solubility in molten iron. This transition thus provides a physiochemical basis for the incorporation of oxygen into the Earth's core. 相似文献
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Wolf SG Landau EM Lahav M Leiserowitz L Deutsch M Kjaer K Als-Nielsen J 《Science (New York, N.Y.)》1988,242(4883):1286-1290
A measurement and interpretation on a molecular level of a phase transition in an ordered Langmuir monolayer is reported. The diagram of surface pressure (pi) versus molecular area of a monolayer of chiral (S)-[CF(3)-(CF(2))(9)-(CH(2))(2)-OCO-CH(2)-CH (NH(3)(+))CO(2)(-)] over water shows a change in slope at about pi(s)= 25 millinewtons per meter. Grazing-incidence x-ray diffraction and specular reflectivity measurements indicate a solid-solid phase transition at pi(s). The diffraction pattren at low pressures reveals two diffraction peaks of equal intensities, with lattice spacings d of 5.11 and 5.00 angstroms; these coalesce for pi >/=pi(s). Structural models that fit the diffraction data show that at pi> pi(s) the molecules pack in a two-dimensional crystal with the molecules aligned vertically. At pi < pi(s) there is a molecular tilt of 16 degrees +/- 7 degrees . Independent x-ray reflectivity data yield a tilt of 26 degrees +/- 7 degrees . Concomitant with the tilt, the diffraction data indicate a transition from a hexagonal to a distorted-hexagonal lattice. The hexagonal arrangement is favored because the -(CF(2))(9)CF(3) moiety adopts a helical conformation. Compression to 70 millinewtons per meter yields a unit cell with increased crystallinity and a coherence length exceeding 1000 angstroms. 相似文献
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利用1948~2004年的NCEP/NCAR再分析月平均资料和NOAA卫星中心月平均海温资料,分析探讨了西伯利亚高压异常与海表温度异常的关系,找出海温异常对西伯利亚高压变化影响较大的海区。结果表明,西伯利亚高压面积指数和强度指数与海温有很好的同期相关性。西伯利亚高压中心强度指数和海温的同期相关场的相关型,与面积指数的相关场结构相似,但正相关区域扩大,负相关区的强度明显减弱。西伯利亚高压面积指数和中心强度指数,与同年春季、秋季、夏季大西洋北部海温距平的相关都很显著,与副热带南印度洋、热带南太平洋的显著负相关区及与西南大西洋的显著负相关区都存在明显的季节差异,面积距平的相关系数要大于强度距平的相关系数。对西伯利亚高压异常变率影响较大的主要是副热带南印度洋、中高纬北太平洋、大西洋北部、热带南太平洋和西南大西洋几个海区的海温异常。 相似文献
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以日本柳杉(Cryptomeria japonica D. Don)为试材,采用差热分析仪(附带DSC测试配置)对经温度为80、120、160、180℃,相对湿度分别为0、40%、60%、100%(80℃时最大相对湿度为80%)过热蒸汽处理后的试件进行了测试,探讨不同温度、不同相对湿度条件对木材热稳定性的影响.结果表明:高温高压过热蒸汽处理后的木材与未处理材的热分解机理基本相同;处理木材的温度越高,木材热分解所需温度也随之增高;高温高压过热蒸汽处理材的热稳定性好于未处理材,并随处理温度的升高而提高;相同温度条件下,相对湿度较低时处理的木材,其热稳定性好于相对湿度较高时处理的木材;相同相对湿度条件下,高温处理的木材,其热稳定性好于低温处理的木材. 相似文献
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Mao HK Jephcoat AP Hemley RJ Finger LW Zha CS Hazen RM Cox DE 《Science (New York, N.Y.)》1988,239(4844):1131-1134
The crystal structure and equation of state of solid hydrogen have been determined directly to 26.5 gigapascals at room temperature by new synchrotron x-ray diffraction techniques. Solid hydrogen remains in the hexagonal close-packed structure under these pressure-temperature conditions and exhibits increasing structural anisotropy with pressure. The pressure-volume curve determined from the x-ray data represents the most accurate experimental measurement of the equation of state to date in this pressure range. The results remove the discrepancy between earlier indirect determinations and provide a new experimental constraint on the molecular-to-atomic transition predicted at higher pressures. 相似文献
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应用变温压差膨化干燥法制备了方便米饭,并对方便米饭的品质进行了研究。探讨了预干燥米饭水分含量和冷冻处理次数对方便米饭品质的影响。结果表明,未经冷冻的含水量41-4%的米饭经膨化干燥后在复水时间、复水特性及食味感官方面效果较好。同市售方便米饭相比较,膨化干燥法制成的方便米饭样品B具有良好的复水性能,成品复水后粘度、硬度、弹力性等口感和风味与新鲜米饭较为相似,复水时间只需8min,复水率可达2.57。该研究表明。应用变温压差膨化法可以制备高品质的方便米饭,为方便米饭的工业化生产提供了技术支持。 相似文献
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Hydrogen becomes a solid at 25 degrees C when subjected to a pressure of 57 kilobars. The high-pressure phase appears as a transparent crystalline mass. The refractive index of the high-pressure phase increases sharply with pressure, indicating a density increase of similar magnitude. At 360 kilobars the calculated density of the high-pressure phase is 0.6 to 0.7 grams per cubic centimeter. 相似文献
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木材高温高压热处理是一种相对稳定且非常环保的木材热处理方法。该研究利用BP神经网络建模研究木材高温高压热处理与其力学性能的关系,结果表明BP神经网络在网络构建和预测性能上效果良好。在此基础上对木材热处理的工艺参数进行了分析和优化,这对科学合理地使用木材具有重要意义。 相似文献
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Sanidine: Predicted and Observed Monoclinic-to-Triclinic Reversible Transformations at High Pressure
Hazen RM 《Science (New York, N.Y.)》1976,194(4260):105-107
High sanidine, (K,Na)AlSi(3)O(8), transforms reversibly to a triclinic phase at high pressure. This is analogous to the high-temperature monalbite transformation. Disordered alkali feldspars of various compositions have unit-cell dimensions which are very similar at the transition (a = 8.30 A, b = 12.97 A, c = 7.14 A, and beta = 116.2 degrees ), indicating that the transformation is structurally controlled. Changes in temperature, pressure, and the sodium/potassium ratio cause similar structural variations: angles between adjacent, rigid tetrahedra vary to accommodate changing effective alkali cation sizes. 相似文献
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崔道碧 《湖南农业大学学报(自然科学版)》1990,17(3)
本文对高温、均匀内压作用下球罐的蠕变变形和应力进行了探讨.根据塑性条件及单向拉伸蠕变试验的数据,导出了稳定蠕变阶段受压球罐的应力、应变及直径扩大量的理论公式,且对不计蠕变变形和考虑蠕变变形时球罐的承载能力进行了计算和比较. 相似文献