Na₂WO₄-ZnO-WO₃体系表面张力及熔盐镀钨的研究

【作者】 高玉红；

【导师】 李运刚；

【作者基本信息】 河北理工学院 ， 钢铁冶金， 2002， 硕士

【摘要】 金属钨具有很多优异性能,如耐磨、耐蚀和耐高温烧蚀等特殊性能,但其价格昂贵、脆性高、难于进行常规机械加工的特性使得钨表面层的制备技术显得格外重要。本文就Na2WO4-ZnO-WO3熔盐体系的表面张力以及用该体系在耐热钢表面电镀钨机理及工艺条件进行研究,为镀层应用于液锌环境中腐蚀及腐蚀磨损条件下,奠定了坚实的应用基础。。采用拉筒法首次测定了Na2WO4-ZnO-WO3熔盐体系的表面张力与组成、温度的关系。认为在800～900℃范围内,熔盐体系的表面张力与温度成线性关系,随着温度的升高而降低;熔盐的离子结构与熔盐的组成有关:随着WO3摩尔含量的增加,离子结构趋于复杂化,同一温度下,随着WO3的增加其表面张力降低。熔体的表面张力随ZnO摩尔含量的增加而增大,ZnO的加入使熔体的离子结构简单化。采用循环伏安法和计时电位法对NZW熔盐体系的电化学反应机理进行了详细研究。认为:钨的电化学反应为一步6电子放电的准可逆反应;反应机理为:WO42-+6e→W0+4O2-;得到了钨离子的扩散系数为D=4.77×10-7 cm2/s (920℃)。借助金相显微镜、扫描电镜对Na2WO4-ZnO-WO3熔盐镀钨体系的阴极产物与工艺条件的关系进行了研究,确定了析出金属钨的温度范围;于耐热钢基体上,在900~950℃的温度范围内可以得到性能良好的金属钨镀层;对比了直流电镀和脉冲电镀对镀层的影响;在电流密度I=40mA/cm2的直流电镀条件下得到的钨镀层抗热震性良好,能经受900℃~室温的热冲击;钨镀层与基体结合良好。更多还原

【Abstract】 Because of its many excellent wear/corrosion/high temperature resistant properties along with its costliness and brittleness, tungsten has found varieties of application in surface technology. In the present work, the electroplating of tungsten, one of the most promising methods to produce tungsten coating on refractory steel, from Na2WO4-ZnO-WO3 molten salts and salts’surface tension have been studied in order to make the coatings applied in liquid zinc.The surface tensions of melts were measured as function of composition and temperature. It was found that the surface tensions decreases with the temperature rising at 800~900℃, the relationship of them flows beeline approximately. Ion structures of melts relate to their compositions, and ion structures complex gradually and the surface tension decrease with the addition of WO3 at the same temperature. The surface tensions of melts rise with the concentration of ZnO increasing. The proper concentration of ZnO can simplified ion structure of melts.Cyclic voltammetry and chronopotentiometry have been applied to investigate the electrochemical mechanism of tungsten deposition in NZW melts. It was found that the electrodeprocess is a 6-electron transferred qui-reversible process. The diffusion coefficient of tungsten ion in NZW was measured as 4.77×10-7 cm2/s (920℃).By means of metallography and SEM, the optimum temperature was determined as follows: the temperature is about 900~950℃. Direct current and pulsing current were applied. The coating gained at 40mA/cm2 has well heat-shakeproof capability and can stand heat-impact from 900℃to room temperature. The coating and substrate link well.更多还原