Pressure dependence of viscosity and self-diffusion in CaAl2Si2O8 melt: A molecular dynamics study

	Pressure dependence of viscosity and self-diffusion in CaAl2Si2O8 melt: A molecular dynamics study
	Zhao, YJ ; Zhang, YG ; Guo, GJ ; Refson, K
刊名	ACTA PETROLOGICA SINICA
	2004-05-01
卷号	20 期号:3 页码:737-746
关键词	CaAl2Si2O8 melt viscosity self-diffusion jump distance pressure
ISSN号	1000-0569
文献子类	Article
英文摘要	Molecular dynamics simulations were used to study the pressure dependence of structure, self-diffusion and viscosity in CaAl2Si2O8 melt from 23 MPa to 15183 MPa at 1999 K. The change with pressure of the relationship between self-diffusion and shear viscosity is also studied and related to microscopic structure of the melt. There exists strong correlation between self-diffusion and melt structure. With the increase of pressure, the formation of fivefold coordination of Si4+ and Al3+ promotes diffusion while the density increase hinders diffusion. The two contradicting effects result in the self-diffusions of Si4+, O2- and Al3+ vary slowly with pressure at first. Then as pressure exceeds 5 GPa, the effect of density increase surpasses that of the formation of fivefold coordination, so there is a rapid decrease in self-diffusion. The self-diffusion of Ca2+, a network-modifying ion, decouples with other ions and decreases monotonously with the increase of pressure. The self-diffusions of these ions are in the order D-Ca > D-Al > D-O > D-Si at pressures below 5 GPa. Viscosity is closely related to the BO (Bridging Oxygen) concentration in the melt. The variation of the concentration of BO below a threshold value almost can not influence viscosity, while as it exceeds the threshold value, little increase of the concentration of BO could result in dramatic increase of viscosity. The value of jump distance in Eyring equation is the key to apply the equation to silicate melt. We found that the jump distances of Si4+ and O2- can be calculated from the quantity of NBO (Non-Bridging Oxygen) in the melt. This makes it possible to calculate self-diffusion of oxygen and silicon from shear viscosity or vise versa, by measuring the NBO% of the melt. The method transforms derivation of dynamic properties to the measurement of melt static property.
WOS关键词	TRANSITION-STATE THEORY ; SILICATE MELTS ; COMPUTER-SIMULATION ; LIQUID SILICATES ; SHEAR VISCOSITY ; OXYGEN ; BULK ; INTERDIFFUSION ; 1500-DEGREES-C ; DIFFUSIVITIES
WOS研究方向	Geology
语种	英语
出版者	SCIENCE CHINA PRESS
WOS记录号	WOS:000222897200038
内容类型	期刊论文
源URL	[http://ir.iggcas.ac.cn/handle/132A11/79629]
专题	中国科学院地质与地球物理研究所
通讯作者	Zhao, YJ
作者单位	1.Chinese Acad Sci, Inst Geol & Geophys, Beijing 100029, Peoples R China 2.Rutherford Appleton Lab, Didcot OX11 0QX, Oxon, England
推荐引用方式 GB/T 7714	Zhao, YJ,Zhang, YG,Guo, GJ,et al. Pressure dependence of viscosity and self-diffusion in CaAl2Si2O8 melt: A molecular dynamics study[J]. ACTA PETROLOGICA SINICA,2004,20(3):737-746.
APA	Zhao, YJ,Zhang, YG,Guo, GJ,&Refson, K.(2004).Pressure dependence of viscosity and self-diffusion in CaAl2Si2O8 melt: A molecular dynamics study.ACTA PETROLOGICA SINICA,20(3),737-746.
MLA	Zhao, YJ,et al."Pressure dependence of viscosity and self-diffusion in CaAl2Si2O8 melt: A molecular dynamics study".ACTA PETROLOGICA SINICA 20.3(2004):737-746.