Artificial Synthesis Of Borate Minerals Based On High-pressure Solid-phase Method

Borate materials are widely used in many fields due to their diverse and excellent physical and chemical properties.At present,the commonly used methods for artificial synthesis of borate materials are mainly hydrothermal/solvothermal methods and solid-phase methods.The hydrothermal method requires a period of several days of experiments under high temperature and high pressure conditions,which makes the synthesis efficiency of this method slower and more dangerous.As a traditional method for crystal synthesis,the solid-phase method has simple experimental procedures,high repeatability,and a short growth period.The high-pressure solid-phase method used in this experiment is a kind of solid-phase method.Through the high-pressure environment up to GPa level,the substance can reach an equilibrium state completely different from that under normal pressure,which is conducive to the synthesis of materials with novel physical and chemical properties.Both tourmaline and johachidolite are natural borate minerals.The former is the earliest pyroelectric and piezoelectric material studied,but the mechanism of some of its properties has not been thoroughly studied;the latter is due to its rare yield.It was not discovered until the middle and late last century,and its high price has brought huge obstacles for scholars to carry out related research.Therefore,this article attempts to synthesize pure lithium-rich tourmaline and compare it with natural tourmaline to explain its pyroelectricity related mechanism;try to synthesize johachidolite to eliminate the problem of lack of resources from the source.Follow-up scholars conduct related research to provide material basis.The synthesis of lithium-rich tourmaline is explored by high-pressure solid-phase method.Through the analysis of the composition of the synthesized product by the stepwise method,it is found that the pre-sintering process consumes a huge amount of B₂O₃,and the loss of flux makes the experimental products under all conditions mainly high melting point reactants Al₂O₃ and Si O₂.Then select the one-step method for synthesis.A one-step synthesis method is adopted for formula 2 and compared with the products at the same pressure and different temperatures,it is found that the reaction is insufficient due to the temperature of 500℃being too low;the products at 700℃are spodumene,kyanite and Al2O3,because the products at this temperature are the associated ore of tourmaline,so it is guessed that the synthesis temperature of elbaite is near this.After analyzing the structural problems of the lithium tourmaline,the target composition was determined to be a liddicoatite with a fixed position of Li and Al at the Y position.Using formula 3,keeping the temperature at 700°C unchanged,after reducing the pressure,johachidolite was found in the product for the first time.Maintaining the above experimental conditions,replacing B₂O₃ in the formula with H₃BO₃,the result was no johachidolite found in the product.The absence of johachidolite is largely related to the replacement of B₂O₃.On the basis of the exploration of liddicoatite,pure johachidolite was artificially synthesized.Based on the CAB system,johachidolite was synthesized for the first time under the conditions of 4GPa and 700℃.The electron probe test of the synthesized sample shows that the molar ratio of the gray-white area n（Ca）:n（Al）:n（B）to the number of atoms in the johachidolite is completely consistent,which is consistent with the test results of the XRD pattern.The Raman spectroscopy test of the sample shows that the peak position corresponds well to the natural johachidolite.The sample was tested by infrared spectroscopy,and after analysis,it was found that the chemical bond corresponding to the position of each peak was consistent with the chemical bond contained in the johachidolite.