Si_3N_4-hBN复相陶瓷在氢氟酸和冰晶石熔盐中的腐蚀行为研究

Corrosion Behavior of Si_3N_4-hBN Composite Ceramics in HF Solutions and Cryolite Molten Salt

利用热压烧结工艺制备了不同h BN含量的Si_3N_4-h BN复相陶瓷,研究了Si_3N_4陶瓷和h BN质量分数为10%的Si_3N_4-h BN复相陶瓷,在40℃不同摩尔浓度的HF溶液和850℃冰晶石熔盐中的腐蚀行为。结果表明:Si_3N_4基陶瓷在酸和熔盐中腐蚀时,都表现为失重现象。其中,在HF溶液中的腐蚀格外严重,随着腐蚀液浓度的升高,腐蚀速率逐渐增大,失重愈发明显,Si_3N_4-10%h BN复相陶瓷较Si_3N_4陶瓷腐蚀严重;在冰晶石熔盐中的腐蚀,前20 h时Si_3N_4-10%h BN复相陶瓷的腐蚀速率远高于Si_3N_4陶瓷,当20 h后Si_3N_4陶瓷腐蚀速率逐渐超过Si_3N_4-10%h BN复相陶瓷,最终的腐蚀速率表现为Si_3N_4-10%h BN复相陶瓷高于Si_3N_4陶瓷。腐蚀失重原因归为两点:腐蚀试样本身的致密度和原始形貌以及腐蚀试样本身Si_3N_4的含量。

Si3N4-hBN composite ceramics with different hBN content were prepared by hot pressed sinter- ing process. Then the corrosion behavior of Si3N4 ceramic and Si3N,-10% （mass fraction） hBN composite ceramics was studied in HF solution with various molarities at 40 ℃ and cryolite molten salt at 850℃ re- spectively. The results show that that the Si3N4 ceramics were suffered from significant corrosion in the above acid solution and molten. The corrosion of the two type ceramics in HF solutions was particularly serious, and their corrosion rate increased gradually with the increasing HF concentration, while the corro- sion of Si3N4-10%hBN ceramics was much serious than that of Si3N4 ceramics. In cryolite molten salt, the corrosion rate of Si3N4-10%hBN was much higher than that of Si3N, ceramic for the initial 20 h, hereafter the corrosion rate of Si3N4 ceramics gradually exceeded that of Si3N4-10%hBN ceramics, and in the final corrosion stage the corrosion rates of the two type ceramics reversed again. It is thought that the corro- sion performance of the ceramics may be subjected to the microstructure and the Si3N4 content of the as prepared ceramics.