高压差热分析方法（HP-DTA）研究钙蒙脱石-氯化钙-水体系中的脱水作用

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	高压差热分析方法（HP-DTA）研究钙蒙脱石-氯化钙-水体系中的脱水作用
	王世杰
	1992
学位授予单位	中国科学院地球化学研究所
学位授予地点	中国科学院地球化学研究所
学位名称	博士
摘要	在开放（P_水
其他摘要	Under both open (P_(water < P_(total)) and close (P_(water) = P_(total)) experimental conditions three hundred runs were made to determine the dehydration of the system of Ca-montmorillonite -CaCl_2-H_2O at pressures to 800bar using high-pressure differential thermal analysis (HP-DTA). Ca-exchanged montmorillonite (SWy-1). From the work of the thesis, it is important to recognize that the interlayer dehydration of Ca-montmorillonite is controlled by water fugacity of the system. New knowledge about the controlling factor of the interlayer dehydration of Ca-montmorillonite strongly enhances understanding of the geochemical processes happened at the subsurface of the earth because smectite is an important component of many geological systems. In both system of CaSWy-H_2O and CaSWy the interlayer dehydration reactions of Ca-montmorillonite process in two stages, the temperature of dehydration increases with pressures, especially in the pressure range of 0-100bar, the increase rate of dehydration temperature changes much faster than the other pressure ranges. At the same pressure, the temperature of the dehydration occurs at about 50 ℃ and 110 ℃ above the liquid-vapor curve of water. However, at pressures above the critical point of water, the dehydration temperature increases only slightly. Meanwhile, the patterns of HP-DTA curve change with the variation of pressure. These characteristics are interpreted to represent that the density of the interlayer water of Ca-montmorillonite is denser than that of free water; and that the interlayer water has two distinctly different H_2O molecular configurations; and that the pattern of two water configurations changes with pressure, but the energy between these two water configurations is constant. The experimental data were used to obtain the enthalpy of the interlayer adsorption force of Ca-montmorillonite at 1 atm. These are, for the CaSWy-H_2O system, first interlayer dehydration reaction ΔH_(iw)~I = 7.74KJ/mol and second interlayer dehydration ΔH_(iw)~II = 20.74KJ/mol; and, for the CaSWy system, first interlayer dehydration reaction ΔH_(iw)~I = 8.13 KJ/mol and second interlayer dehydration ΔH_(iw)~(II) = 21.28 KJ/mol. Those values show that there is no difference to use whether CaSWy-H_2O system or CaSWy system to study the dehydration of Ca-montmorillonite. On the basis of the experiments, Author also pointed out that the sample factor which affected the peak position of DTA and the pattern of the DTA curve in fact was contributed to cause the change of water fugacity around the sample particles. The concentrations of resulting fluids of CaCl_2-H_2 in the process of experiment are 0.5M、1M、2.82M、5.63M、11.26M、and 16.9M by mixing the known weight percent of CaCl_2 solid: 0.9、1.8、5、10、20 and 30 wt.% with CaSWy uniformly. Compared with CaSWy system, the water fugacity of the CaSWy-CaCl_2 system is reduced and the dehydraation temperature of Ca-montmorillonite is decreased substantially. The rate of temperature reduction is proportional to the concentrations of CaCl_2-H_2O fluids in the ranges of 0-11.26M. But when the concentrations of CaCl_2-H_2O fluids are equal or greater than 11.26M the rate of temperature reduction changes slightly. Further, the dehydration temperature reduction of Ca-montmorillonite is more pronounced at higher pressures. When the concentrations of CaCl_2-H_2O fluids are equal to 5.63、11.26M and 16.9M respectively the dehydration temperature can be below the boiling temperature of water, so the dehydration of Ca-montmorillonite would act as buffers of water fugacity and would result in overpressure in the shales. The experimental data were used to obtain the equation of dehydration vant't Hoff line in the presence of 0、0.5M、1M、2.82M、5.63M、11.26M and 16.9M concentrations of CaCl_2-H_2O fluids respectively. Thee equations are: 0%: 1np= 15.008 - 7.237 * (1000/T) (0.5M) 0.9%: 1np=14.634-6.781* (1000/T) (1M) 1.8%: 1np = 15.347-7.130 * (1000/T) (2.82M) 5%: 1np = 14.717 - 6.381 * (1000/T) (5.63M) 10%: 1np = 14.270-5.806 * (1000/T) (11.26M) 20%: 1np = 14.580 - 5.831 * (1000/T) (16.9M) 30%: 1np = 14.412 - 5.519 * (1000/T) On the basis of these equations the water fugacity coefficients (￡) of 0.5M、1M、2.82M、5.63M、11.26M and 16.9M concentrations of CaCl_2-H_2O fluids are calculated respectively at different pressures and temperatures. Then the thermodynamic model of interlayer dehydration temperature relation between the CaSWy system and the CaSWy-CaCl_2 system is established by using calculated water fugacity coefficient (￡): TD' = [T_1T_D(ΔH_(tw) + ΔH_(sv)~(salt)）/[T_1(ΔG + ΔH_(dn)~(water))-T_D~ (ΔH_(av)~(water)-ΔH_(sv)~(salt)) If the concentrations of CaCl_2-H_2O fluids are in the ranges of 0-1M, the difference of values between ΔH_(dh)~(water) and ΔH_(dn)~(salt) is to be neglected, and then, the above equation is changed to TD' = (TD*ΔH_(dh))/(ΔG + ΔH_(dh)） From this model the dehydration temperature of Ca-montmorillonite can be calculated in the presence of CaCl_2-H_2O fluid concentrations up to 16.9M. In the sedimentary basins Ca-montmorillonite is stable under normal burial pressures and temperatures. In the absence of K~+ and lower salinity Ca-montmorillonite would exist stably at significant depth in the crust, so smectites play an important role in the ocenic chemistry and in the water origin of subducted zones. It is Ca-montmorillonite not Na-vermiculite should be consided firstly in the selection of backfill to dispose radioactive waste if the other conditions are the same. In the engineering of hydrocarbon exploration and production the explusion of interlayer water of smectite may be one of causes which make the wellbore hole enlargement or the wellbore subsurface erosion or sloghing because of sudden reduction of pressure.
页数	45
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3872
专题	研究生_研究生_学位论文环境地球化学国家重点实验室
推荐引用方式 GB/T 7714	王世杰. 高压差热分析方法（HP-DTA）研究钙蒙脱石-氯化钙-水体系中的脱水作用[D]. 中国科学院地球化学研究所. 中国科学院地球化学研究所,1992.

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