Study On The Influence Of Basalt Glass Composition On High Temperature Thermophysical Properties

Heat storage material is a new type of application material that can flexibly regulate the storage and release of thermal energy,has broad application prospects in solar thermal storage and utilization,industrial waste heat recovery and building heating.Basalt glass is prepared by melting basalt ore in a high temperature furnace at 1400～1500℃and then quenching.The high temperature resistance of basalt glass has obvious advantages in the field of high temperature heat storage,and the study of its comprehensive thermophysical properties is essential to explore its new application methods.Basalt fiber,aramid fiber,carbon fiber and ultra-high molecular weight polyethylene fiber are called four high-tech fibers in China.The thermophysical properties of basalt glass,such as viscosity and crystallization property,are of great significance to the fiber production process and performance control.However,due to the variety of components in basalt glass,the structure is too complex,the existing research mainly focuses on the structure or melt performance of basalt glass,and the process performance of basalt fiber.These studies have not systematically investigated the influence mechanism of chemical composition on the structure and thermophysical properties of basalt glass.In this paper,intermediate,basic and ultrabasic basalt are selected as raw materials,and basalt glass is prepared by melting and quenching.Infrared absorption spectroscopy and Raman spectroscopy are used to characterize its microstructure in detail;the thermophysical properties such as specific heat capacity,glass transition temperature,thermal expansion and thermal conductivity were comprehensively evaluated;on this basis,the influence law and mechanism of small molecular oxides（B₂O₃,Li₂O and Na₂O）on the structure and thermophysical properties of basalt glass were deeply explored.The main contents and relevant conclusions of the study are as follows:（1）The basalt glass prepared from intermediate,basic and ultra-basic basalt ore has significantly reduced adsorbed water content and easily decomposed silanol hydroxyl Si-OH content,and improved structural stability.The content of Si O₂and Al₂O₃in the three basalt glasses decreases in turn,the framework of glass network connected by[Si O₄]and[Al O₄]tetrahedrons becomes loose,glass transition temperature and thermal stability gradually decreases.Among the three types of glass,intermediate basalt glass has the highest volume heat storage density and thermal conductivity.The volume heat storage density between100°C and 1000°C is 2847.6 MJ/m³,which is much higher than the currently preferred molten nitrate heat storage material（900 MJ/m³）,and has obvious advantages in sensible heat storage field.（2）After B₂O₃,Li₂O and Na₂O were adding into intermediate basalt glass,Raman spectroscopy and infrared absorption spectroscopy show that the content of non-bridging oxygen in the glass system increased,which reduced the connectivity of[Si O₄]and[Al O₄]tetrahedral networks,caused the glass structure to depolymerize,and the high temperature viscosity,glass transition temperature and glass softening temperature all decreased.（3）B₂O₃has two forms of[BO₃]and[BO₄]in glass.[BO₃]and[BO₄]groups combine to form a boron-rich phase containing pentaborate and six-membered cyclic borate.The phase separation in the glass system promotes glass crystallization,and borate groups hinder the movement of alkali metal and alkaline earth metal ions,which reduces the specific heat capacity and thermal conductivity.Alkali metal ions are located in the interval of the glass network,Li⁺and Na⁺have difference influences on the properties of basalt glass.The radius of Li⁺is smaller than that of Na⁺,it is easier to move in the network gap,and the electric field strength is larger.It also has antipolarization effect on Si-O bond in the network.Therefore,Li₂O has a stronger depolymerization effect on basalt glass,and has a more significant effect on reducing viscosity and increasing thermal expansion coefficient.The specific heat capacity of glass is obviously increased due to the intensification of atomic vibration.When 6%Li₂O is added into basalt glass,the volumetric heat capacity and thermal conductivity reach the maximum.Compared with BG-1,the average heat capacity and thermal conductivity increase by about 8%and 2.6%respectively.In this paper,the thermal storage performance of basalt glass is comprehensively evaluated,and the interaction mechanism between composition,structure and performance of basalt glass is analyzed in detail,which provides experimental data and theoretical support for predicting and optimizing the performance of basalt glass and its derivatives.