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101.
Kinetic study of the dehydroxylation of chrysotile asbestos with temperature by in situ XRPD 总被引:6,自引:0,他引:6
The kinetics of the dehydroxylation of chrysotile was followed in situ at high temperature using real-time conventional and
synchrotron powder diffraction (XRPD). This is the first time kinetics parameters have been calculated for the dehydroxylation
of chrysotile. The value of the order of the reaction mechanism calculated using the Avrami model indicates that the rate-limiting
step of the reaction is a one-dimensional diffusion with an instantaneous nucleation or a deceleratory rate of nucleation
of the reaction product. Hence, the rate-limiting step is the one-dimensional diffusion of the water molecules formed in the
interlayer region by direct condensation of two hydrogen atoms and an oxygen atom. The calculated apparent activation energy
of the reaction in the temperature range 620–750 °C is 184 kJ mol−1. The diffusion path is along the axis of the fibrils forming the fibers. The amorphous or short-range ordered dehydroxylate
of chrysotile is extremely unstable because forsterite readily nucleates in the Mg-rich regions. Moreover, it is less stable
than the dehydroxylate of kaolinite, the so-called metakaolinite, which forms mullite at about 950 °C. This difference is
interpreted in terms of the different nature of the two ions Mg2+ and Al3+ and their function as glass modifier and glass-forming ion, respectively.
Received: 10 April 2002 / Accepted: 7 January 2003
Acknowledgements This work is part of a COFIN project (04 Scienze della Terra, NR 17, 2000) supported by MURST. Dr Dapiaggi is kindly acknowledged
for help during the data collection at the Dipartimento di Scienze della Terra, University of Milan. 相似文献
102.
The rate of the reversible homogeneous disproportionation of polysulfides was studied by following the optical absorbance of polysulfide solutions in a continuous plug flow reactor equipped with an on-line photometric detector. In order to avoid heterogeneous slow reactions involving sulfur colloids or precipitate, the reaction was initiated by an abrupt pH change from an undersaturated solution containing predominantly tetrasulfide species to a pH where pentasulfide is the dominant species. The disproportionation was found to follow first order reversible reaction dynamics. At environmentally relevant conditions the characteristic time of the disproportionation reaction is of the order of 10 s. This characteristic time implies that necessary conditions for speciation of the different polysulfide species by chromatography or another separation and subsequent quantification scheme should be of the order of 1 s. 相似文献
103.
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105.
青藏高原上中尺度对流系统(MCSs)的个例分析及其比较 总被引:3,自引:0,他引:3
对1995年7月25—28日高原上连续数日出现MCSs的现象进行了红外云图特征及其演变、大尺度环境背景场和对流有效位能的分析。可以发现,所有这些MCSs有着相似的日变化演变过程;它们的初始对流在中午由于日射加热开始活跃,之后迅速发展,这些MCSs在后下午形成,在傍晚达到最强,之后逐渐减弱。其中26日MCS最为强大,它是在单一的强大的近于圆形的高原反气旋高压背景下受强的低层热力强迫和条件不稳定的驱动而发生的。这些发生条件都与高原本身的热力作用紧密相关,所以它的发生发展主要与高原特有的较为纯粹的热力因子相联系。28日MCS是另一个很强的MCS,它明显地受到中纬度西风槽的斜压区的影响,这二个很强的MCS有着不同的发展机制和显著不同的表现特征。 相似文献
106.
地震动输入能量衰减规律的研究 总被引:6,自引:1,他引:6
对所收集到的266条强震记录,将其按场地条件分类,计算了不同场地条件、不同延性系数下的“绝对”和“相对”输入能量反应谱,然后利用两步回归法,得出了不同场地条件下地震动“绝对”和“相对”两种输入能量的衰减规律,分析了场地条件、延性系数、震级及距离等参数对地震动能量谱的影响,并对两种输入能量衰减规律进行了比较。 相似文献
107.
108.
The climatic impacts of land surface change and carbon management, and the implications for climate-change mitigation policy 总被引:4,自引:0,他引:4
Strategies to mitigate anthropogenic climate change recognize that carbon sequestration in the terrestrial biosphere can reduce the build-up of carbon dioxide in the Earth’s atmosphere. However, climate mitigation policies do not generally incorporate the effects of these changes in the land surface on the surface albedo, the fluxes of sensible and latent heat to the atmosphere, and the distribution of energy within the climate system. Changes in these components of the surface energy budget can affect the local, regional, and global climate. Given the goal of mitigating climate change, it is important to consider all of the effects of changes in terrestrial vegetation and to work toward a better understanding of the full climate system. Acknowledging the importance of land surface change as a component of climate change makes it more challenging to create a system of credits and debits wherein emission or sequestration of carbon in the biosphere is equated with emission of carbon from fossil fuels. Recognition of the complexity of human-caused changes in climate does not, however, weaken the importance of actions that would seek to minimize our disturbance of the Earth’s environmental system and that would reduce societal and ecological vulnerability to environmental change and variability. 相似文献
109.
110.
首次使用HLAFS数值预报产品对黑龙江省暴雨进行分析,结合T63数值预报产品,利用两者提供的物理一08时和20时的实况场和预报场格点资料,对黑龙江省一次暴雨过程进行分析,找出了暴雨发生的物理机制,指出深厚的水汽条件以及水汽的辐合,强烈的上升运动和不稳定能量的存贮和释放是产生暴雨的关键因素。 相似文献