玄武岩制备连续纤维熔融反应热力学研究

Thermodynamics of the melting reaction of basalt for preparing the continuous fiber

玄武岩纤维由天然岩石直接熔融拉丝制备而成,性能优异,其原料调控对纤维制备和性能提升有重要影响,熔融反应的热力学分析是研究原料特征的重要手段。本文以代表性玄武岩样品为原料,分析其矿物组成,进而构建复杂硅酸盐体系热力学模型,研究其在1400℃时的熔融反应热力学。结果表明,单一矿物如长石、辉石熔融反应的吉布斯自由能为负值且相对较小;钛铁矿、磁铁矿、磷灰石等矿物熔融反应的吉布斯自由能为正数。所选玄武岩样品熔融反应的吉布斯自由能为-225~-257 kJ/mol,表明可自发进行;样品熔融过程的理论能耗为2.4~2.5 GJ/t,接近某些玻璃纤维池窑工艺能耗(考虑窑炉热效率)。纤维的制备条件和性能参数与原料的成分关系密切,以直径约9μm的纤维为例,其拉丝温度及缠绕机线速度等条件各不相同,纤维表面光滑,断裂伸长率约3%~4%,弹性模量59~66 GPa,抗拉强度1700~2400 MPa;采用Giordano的模型,计算出不同原料成纤粘度(lgη)约0.70~1.21 Pa·s。本研究的热力学模型及实验结果可为玄武岩纤维制备的原料优选、能耗计算、条件调控及性能预测提供参考。

Basalt fiber is a kind of high-performance fiber produced directly from natural rock by the direct melting and drawing process.The quality control of raw materials has an important effect on the preparation and property improvement of the basalt fiber.Thermodynamic analysis of the melting process is an important way to study the characteristics of raw materials.Using representative basalt samples as the starting materials,their mineral compositions were firstly analyzed,then a thermodynamic model of the complex silicate system was constructed and the thermodynamics of the melting reactions of basalt samples at 1400℃were further studied in this paper.The results show that the Gibbs free energies of melting reactions of the unique minerals,including feldspar and pyroxene,were relatively small negative values,whereas those of ilmenite,magnetite,and apatite were positive values.The Gibbs free energies of melting reactions of the basalt samples vary from-225 kJ/mol to-257 kJ/mol,indicating that the melting reaction could be occurred spontaneously.The theoretical energy consumptions vary from 2.4 GJ/t to 2.5 GJ/t for the basalt melting process.They are close to the energy cost of some glass fibers produced from tank furnace with the considered heat efficiency.The preparation conditions and performance parameters of fibers are closely related to the chemical composition of basalt.The prepared fibers with smooth surface and their diameters of about 9μm were obtained from three basalt samples under different conditions of wiredrawing temperatures and speeds of winding machine.They have elongation rates of fractures varying from 3%to 4%,elasticity modulus varying from 59 GPa to 66 GPa,and tensile strengths varying from 1700 MPa to 2400 MPa.The viscosities of fibration for different basalts calculated by using the Giordano’s model vary from 0.70 Pa·s to 1.21 Pa·s.In conclusion,our presented thermodynamic model and experimental results can provide a reference for the raw-material optimization,energy consumption calculation,condition control,and performance predication for the preparation of continuous basalt fibers.