Effect Of Heat Treatment On The Structure And Properties Of Basalt Fiber

As one of our country’s four priority high-performance fibers,basalt fiber has the advantages of high strength,good high temperature stability,strong chemical stability,low production cost,and environmental protection,so its use range is becoming wider and wider.In this paper,we have successfully prepared the glass-ceramic basalt fiber by heat treatment,and we studied the crystallization mechanism of basalt fiber.We also studied the effect of heat treatment on the mechanical properties and chemical properties on basalt fiber.The details are as follows.Firstly,we studied the preparation of glass-ceramic basalt fibers.The basalt fiber was heattreated by the "two-step" heat treatment process,and the glass-ceramic basalt fiber containing the diopside phase and the augite phase was prepared.The orthogonal experiment method was used to explore the effect of heat treatment system on the tensile strength of glass-ceramic basalt fiber.The results showed that the effect of heat treatment on the tensile strength of basalt fiber was in the following order: crystallization temperature>nucleation temperature>nucleation time>crystallization time.Based on the DSC curve of basalt fiber measured by high temperature synchronous thermal analyzer,the crystallization activation energy and crystal growth index of basalt fiber are calculated according to Kissinger equation and Augis-Bennett equation.The results show that the crystallization activation energy of basalt fiber is 150.36 k J/mol,The crystal growth index of basalt fiber at a heating rate of 10K/min is 3.62,indicating that basalt fiber is relatively easy to devitrify,and the devitrification method is overall devitrification.Secondly,we studied the effect of heat treatment on the mechanical properties on basalt fiber.The results showed that with the increase of the nucleation temperature and the extension of the nucleation time,the tensile strength of the fiber increases first and then decreases;when the crystallization temperature increases from 830 ℃ to 930 ℃,the tensile strength of the glass-ceramic basalt fiber The strength is reduced by 41.63%;the extension of the crystallization time will also reduce the tensile strength of the fiber.The microstructure of the glass-ceramic basalt fiber was characterized by FT-IR,Raman,XRD and SEM.The results showed that crystallization is the main reason for the decrease in mechanical properties of basalt fiber.The crystals in the fiber destroy the glass network structure in the fiber.Laser microscopic Raman spectroscopy shows that during the crystallization process,Fe,Ca,and Mg ions in the fiber increase the number of non-bridging oxygen in the polarized fiber bridging oxygen in the glass network structure,which leads to the stretching vibration of Si-O.The peak is red-shifted.The oxidation of Fe2+ in the fiber to Fe3+ after heat treatment also leads to the depolymerization of the Si-O-Si and Al-O-Al tetrahedral structure,which makes the tensile strength of the fiber lower.Finally,we studied the effect of heat treatment system on the chemical stability of basalt fiber.The glass-ceramic basalt fibers immersed in seawater and HCl solution were characterized by SEM,EDS and ICP.The results show that the seawater resistance of the glass-ceramic basalt fiber is better than that of the initial fiber,and the acid resistance is worse.Under the same experimental environment,the weight rate of the glass-ceramic basalt fiber in seawater is 76.19% lower than that of the initial fiber,and the weight loss rate in the hydrochloric acid solution is 644.23% higher than that of the initial fiber.This is because the crystal layer composed of diopside and augite phase crystals on the surface of glass-ceramic basalt fibers can inhibit the damage of the silicon-oxygen tetrahedral structure in the fibers by seawater,which improves the seawater resistance of the fibers.Diopside and augite phase crystals will be eroded by hydrochloric acid.After being eroded,the fiber surface will have holes,which increase the contact area of hydrochloric acid and fiber,accelerate the exchange of H+ in hydrochloric acid and metal ions in the fiber,so that the fiber’s acid resistance deteriorates.The heat treatment system affects the chemical stability of the fiber by affecting the size and number of crystals in the fiber.In short,we have successfully prepared glass-ceramic basalt fiber by the "two-step" heat treatment process.When the heat treatment was nucleation temperature 760 ℃,nucleation time 2h,crystallization temperature 830 ℃,crystallization time 2h,the tensile strength of glass-ceramic basalt fiber is highest.Compared with the initial basalt fiber,the weight loss rate of the glass-ceramic basalt fiber in seawater is reduced by 76.19%,and the seawater resistance is significantly improved.