熔盐对ZrO2纤维模板辅助燃烧合成ZrB2纤维的影响

以ZrO₂纤维、B₂O₃粉、Mg粉为原料,分别以NaCl、MgCl₂及NaCl、MgCl₂复合盐为稀释剂,采用模板辅助燃烧合成法,经酸洗制备了ZrB₂短纤维,采用试算法计算了反应体系绝热温度,并对产物进行XRD和SEM表征。结果表明:反应体系的绝热温度随着熔盐掺量的增加而降低,掺NaCl体系绝热温度下降较为明显,尤其是在熔盐掺量较高的情况下。加入NaCl后产物物相主要为ZrB₂以及少量残余的ZrO₂,加入MgCl₂后产物中还有少量Mg₃B₂O₆。加入熔盐不仅能避免ZrO₂纤维的熔融,使产物更容易保持原料中纤维的形状,还能减小产物的晶粒尺寸,加入MgCl₂能促进产物晶粒的发育,随着MgCl₂掺量的增加,纤维上的颗粒逐渐发育成棱角分明的六方状晶体。从残余的ZrO₂含量和晶粒尺寸分析,单盐的效果要优于复合盐,MgCl₂的效果优于NaCl。

Effects of Molten Salt on ZrO2 Fibers Template Assisted Combustion Synthesis of ZrB2 Fibers

The short ZrB₂ fibers were synthesized by template assisted combustion synthesis, taking ZrO₂ fibers, Mg and B₂O₃ as raw materials, NaCl, MgCl₂ and their compound salts as diluents. The adiabatic temperature of the systems was calculated by trial method. The effects of molten salt content on the phase composition and micromorphology of the products were investigated by XRD and SEM, respectively. The results showed that the adiabatic temperature decreased with the increment of molten salt content. The adiabatic temperature drop of the system with NaCl was more obvious, especially in high molten salt content condition. The NaCl added samples comprised of ZrB₂ and small amounts of residual ZrO₂. Small amount of Mg₃B₂O₆ was found in the sample added with MgCl₂. The addition of molten salt could prevent the ZrO₂ fibers from melting and make it easier for product to maintain the shape of original fiber. The crystallite size of the product could be reduced by NaCl and MgCl₂ in the systems. MgCl₂ could promote the crystallization of ZrB₂ and they grew into the hexagon crystals of clear boundaries with the increasing content of MgCl₂. From the analysis of residual ZrO₂ and grain size, the effect of single salt was superior to compound salt, and MgCl₂ was more effective than NaCl.