多种光谱法解析陶瓷板表面凹坑缺陷的复杂成因

Understanding the Complicated Causes of Concavity Defect at Porcelain Tile Surface via Multispectroscopy Approach

采用尿素还原剂SNCR(选择性非催化还原)工艺脱硝制备的陶瓷板坯料经成型和烧成,陶瓷板表面常常出现凹坑状表面缺陷,其成因难以通过坯料的常规化学成分分析判定。通过XRD,FTIR和TGA-FTIR等多光谱结合的方法分析揭示其形成机理。研究结果表明:尿素脱硝坯料和氨水脱硝坯料受热过程中所释放的主要气体是CO 2和H 2O,但前者不仅释放气体量明显大于后者,而且还释放HNCO和NH 3气体,残余尿素会促使气体释放量进一步增大;尿素脱硝坯料中存在HOCN,HNCO及其盐类等反应产物,它们会在500℃以上逐渐分解产生额外的CO 2气体;陶瓷板在高温烧成阶段,坯体中形成大量液相使表面气孔封闭,坯料中氰酸盐和异氰酸盐持续分解所产生的大量气体难以排出,在液相中聚集成气泡,在烧成后的降温过程中气泡破裂或塌陷,最终造成了陶瓷板表面的凹坑状缺陷。采用多种光谱结合的方法,以坯料在XRD谱中17.80°的氰酸钠衍射峰、FTIR谱中2226 cm-1的氰酸根吸收峰以及TGA-FTIR谱中2241 cm^-1的氰酸气体吸收峰等特征参数为判据,可以预判坯料质量进而提高陶瓷板成品率。

The concavity defects frequently appear at the surface of porcelain tile produced with the blank via SNCR(Selective Non-Catalytic Reduction)denitrification using urea reductant.The general chemical analysis of the blank cannot judge the causes of the defects.A multispectroscopy approach combining XRD,FTIR,TGA-FTIR adopted in this study reveals the forming mechanisms of the concavity.The results demonstrate that the blank denitrification by urea and that by ammonia mainly release CO 2 and H 2O during heating.However,the former release not only much gases than the latter but it can releases HNCO and NH 3.The residual urea in the blank could augment the gas flow further.The blank denitrification by urea contains cyanic acid,isocyanic acid and their salts,which could decompose beyond 500℃and release additional CO 2.In the high temperature stage of sintering,the massive liquid is formed and seals the surface pore of the body.The cyanate and isocyanate in the blank decompose continuously and produce excessive gases,which cannot escape from the body and congregates to be bubbles in the liquid.During the cooling stage after sintering,the bubbles break or collapse,resulting in a concavity at the surface of porcelain tile.Using the multispectroscopy approach and adopting characteristic parameters such as the peak of sodium cyanate at 17.80°in XRD pattern,absorbance peak of cyanate radical at 2226 cm^-1 in FTIR spectrum and absorbance peak of gaseous cyanic acid at 2241 cm^-1 in TGA-FTIR spectrum as the criterion,the quality of the blank could be valued previously and thus the porcelain tile yield could be promoted.