Pressure-transmitting properties of pyrophyllites from different localities
Objectives:Pyrophyllite,as a sealed pressure medium,has been widely used in high-pressure research for laboratories and industrial synthesis.A highly efficient pressure transfer medium can generate higher cell pressure at the same loading force.The use of a highly efficient pressure transfer medium reduces the risk of anvil rupture and produc-tion costs.Therefore,it is important to develop a suitable and efficient pressure-transmitting pyrophyllite.Methods:The pressure calibration of four pyrophyllites from different localities at room temperature was conducted in a 6×8 MN multi-anvil large-volume press.The relationship between loading force and cell pressure at room temperature was estab-lished.The influence of mineral composition changes in pyrophyllite on pressure-transmitting efficiency was studied us-ing X-ray diffraction.Results:By investigating the influence of mineral composition changes in pyrophyllite on pres-sure-transmitting efficiency,the results are as follows:(1)When achieving the same cell pressure,the required loading force for Pyrophyllite 4 is 10% lower than those for the other three pyrophyllites,indicating that Pyrophyllite 4 has the best pressure-transmitting efficiency.(2)As cell pressure increases,the relationship between cell pressure and loading force begins to deviate from linearity,and the pressure-transmitting efficiency of pyrophyllite gradually decreases.When the cell pressure exceeds 5.00 GPa,applying higher loading force does not significantly increase the cell pressure.(3)Higher hardness minerals(such as Diaspore,Boehmite)in pyrophyllite can effectively improve pressure-transmit-ting efficiency in the low-pressure stage(cell pressure 2.55-3.68 GPa).When the minerals in pyrophyllite undergo phase transformation to form new minerals with higher hardness(such as Muscovite and Kaolinite)in the high-pressure stage(cell pressure of 5.50 GPa),pressure-transmitting efficiency can be effectively improved.Conclusions:Pyrophyllite 4 has better pressure-transmitting efficiency than Pyrophyllite 2 does in the high-pressure stage,but it is prone to failure in sealing due to the changes in mineral composition.However,Pyrophyllite 2 shows good elastic recovery effect and seal-ing performance and can stably complete compression and decompression work.Considering both pressure-transmit-ting efficiency and sealing effect,Pyrophyllite 2 has better application value and economic benefits.
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