Study On The High Strength And Performance Of Continuous Basalt Fiber

The continuous basalt fiber（CBF）,as a non-metal inorganic material,is manufactured by drawing the melted volcanic rocks in the temperature of about 1500℃and forming continuous fibers with golden brown color.It is known as a pollution-free green industry raw material in the 21 century.Typically,the"basalt"in CBFs is a generic term for igneous rocks that can be used to produce continuous fibers,including basalt,andesite,dolerite,pyroxene,andesitic basalt,etc.Due to its excellent mechanical propertiesand durability,the CBF is one of the four high-tech fibers（carbon fibers,aramid fibers,high molecular weight polyethylene fibers and continuous basalt fibers）in China.Although the development of CBF is late among all the high-tech fibers,it is still prized due to its high cost performance and wide applications.In recent years,the production and application technology has been rapidly developed.However,because of many technical bottlenecks existing in production,there are many problems that restrict the development of CBF,such as big divergence in performance,small production capacity,high production cost,backward production equipment,etc.Moreover,as the development of wind power,automobile,aircraft,boat and civil construction,there are growing demand for high performance fiber-reinforced composite materialsand stable production source of corrosion resistant high-strength CBF.In regard of the existing problems in the quality and performance stability and the demand for high-strength CBF in the application fields,in this thesis,the technical method and related theoretical analysis are achieved to improve the stability and strength of CBF by studying the melting mechanism and mixing method of the basalts.The main research contents and the innovation points are listed below:（1）First,the melting process was investigated for andesite,andesitic basalt,tholeiite,and alkali basalt（generally called basalt）through high temperature microscopic analysis,differential scanning calorimetry（DSC）and X-ray diffraction（XRD）,and was further explained by mineral phase diagram.The effect of the chemical composition and the mineral components on the melting temperature（melting process）is systematically analyzed,the optimized heat reaction and melting process are established,and mechanism of the melting process is proposed.These results are the essential theoretical basis for the CBF production technology of stability and high performance.Meanwhile,based on the mineral components,the melting process and melting mechanism,the factors that affect melt homogeneity are examined,and it is proposed to improve the homogenization of basalt melt by avoiding infusible mineral components and optimizing the melting temperature.Through these studies,the stability problem of the CBF is fundamentally solved.（2）Because the basalt is a natural ore,its components are fixed for a certain region.So it is different with the glass batch,in which the type or content of the chemical composition can be adjusted to reach certain requirement of fiber performance.However,the basalt components vary with different regions,so there must be a single type natural basalt corresponding to different requirements for fiber performance.In the thesis,single natural basalt ores are first studied to determine the factors affecting the tensile strength of CBF.The effect of the chemical composition and mineral component on the tensile strength,melting properties（melting temperature and viscosity）and fiber forming properties（crystallization temperature and fiber-forming temperature range）,and the effect of melting properties（melting temperature and viscosity）and fiber forming properties（crystallization temperature and fiber-forming temperature range）on the tensile strength have been investigated for andesite,andesitic basalt,and tholeiite.The results show that,for the homogeneous basalt melt,the tensile strength of CBF is determined by the chemical composition（mainly by the SiO₂ content）.The mineral components of basalts are decisive in the melting properties and fiber forming properties,while the melting properties and fiber forming properties of the basalts are decisive in the homogeneity of the basalt glass melt and further affect the filament tensile strength.The study also reveals that when the weight content of SiO₂ is between 50%and 57%（mainly for andesitic basalt and tholeiite）,the filament tensile strength of basalt fiber is highest that is 3370.46MPa.In this case,the basalt is easy to melt and homogenize;the hemispheric temperature（melting temperature）is between 1280℃and 1470℃,the viscosity is between 250dPa·s and 650dPa·s at 1300℃,the upper limit crystallization temperature is between 1240℃and 1290℃,and fiber-forming temperature range is-90℃to 20℃.The study in this thesis provides a specific technique solution to select appropriate basalt ore for high-strength CBFs production.（3）Mixing technique is a method to realize the composition stability and performance improvement of natural basalt ores by crushing,preblending and granularity/distribution controlling for different regions or mineral occurrences.In this thesis,two types of individual basalts are mixed to improve the filament tensile strength of CBF.The high SiO₂ content basalt was added into the low SiO₂ content basaltto form basalt mixture;the tensile strength,melting properties（melting temperature and viscosity）,fiber forming properties（crystallization temperature,fiber-forming temperature range）,and their relationship are investigated.Compared to the CBFs of individual basalt,whether the SiO₂ content of basalt mixtures is more,close to or less than that of individual basalts,the filament tensile strength of basalt mixtures is always higher.Moreover,the melting properties and the fiber-forming properties are optimized.This is because that the change of mineral component in basalt mixtures facilitates the optimization of the melting properties and the fiber-forming properties,further the homogeneity of glass melt,and then the improvement of the tensile strength of CBFs.（4）The tensile strength of CBFs is dependent on the chemical composition,mineral component,melting properties（melting temperature and viscosity）and fiber forming properties（crystallization temperature,fiber-forming temperature range）.Among them,chemical composition and mineral component are the internal factors that affect the tensile strength,while the melting properties（melting temperature and viscosity）and fiber forming properties（crystallization temperature,fiber-forming temperature range）are the external factors.In the case of sufficient homogeneity of the basalt glass melt,the tensile strength of CBFs is dependent on both the chemical composition and the mineral component;otherwise,it is dependent on the mineral component,because the mineral component affect the melting properties（melting temperature and viscosity）and fiber forming properties（crystallization temperature,fiber-forming temperature range）which determine the homogeneity of the basalt glass melt.It can be revealed from the study in the thesis that,no matter for the CBFs of individual basalt or for the CBFs of basalt mixtures,the SiO₂ content is 50%-57%for the highest filament tensile strength,because the homogeneity of the basalt glass melt is good and the tensile strength is determined by chemical composition and the mineral component.When the SiO₂ content is more than 57%,the homogeneity of the basalt glass melt is bad,so the tensile strength of CBFs is mainly determined by the melting properties;when the SiO₂ content is less than 50%,the homogeneity of the basalt glass melt is also bad,and the tensile strength of CBFs is mainly determined by the fiber-forming properties.