Jones Aled R, Winter Rudolf, Greaves G Neville, Smith Ian H
Materials Physics, University of Wales Aberystwyth, Penglais, Aberystwyth SY233BZ, Wales, United Kingdom.
J Phys Chem B. 2005 Dec 15;109(49):23154-61. doi: 10.1021/jp053953y.
The glass-forming reactions between sodium carbonate (Na2CO3) and silica (SiO2) have been investigated by 23Na, 29Si, and 13C magic-angle spinning (MAS) NMR spectroscopy. The multinuclear MAS NMR approach identifies and quantifies reaction products and intermediates, both glassy and crystalline. A series of powdered batches of initial composition Na2CO3.xSiO2 (x = 1, 2) corresponding to a sodium metasilicate (Na2SiO3) and sodium disilicate (Na2Si2O5) stoichiometry were investigated after periods of isothermal and nonisothermal heat treatments at different temperatures. Analysis of the 23Na quadrupolar coupling parameters has identified the early reaction product in all cases as crystalline Na2SiO3. In the nonisothermal experiment, this reaction is preceded by an early silica-rich melt phase formed around 850 degrees C. The early reactions are controlled by solid-state Na+ diffusion across the reaction zone in the grain interface layer. Crystalline Na2SiO3 precipitates in the interface layer, increasing its thickness between the Na2CO3 and the SiO2 grains and slowing down the rate of Na+ migration. This creates a secondary phase, which is temperature dependent. At low temperatures, where Na+ migration is impaired, the production of Na2SiO3 ceases and silica-richer phases are precipitated. In the case of the sodium disilicate batch, where excess SiO2 is present, a secondary reaction of Na2SiO3 with SiO2 forming a glassy phase is observed. A transient carbon-bearing phase has been identified by 13C NMR as a NaCO3- complex loosely bound to bridging oxygens in the silicate network at the SiO2 grain surface.
通过23Na、29Si和13C魔角旋转（MAS）核磁共振光谱研究了碳酸钠（Na2CO3）与二氧化硅（SiO2）之间的玻璃形成反应。多核磁共振MAS方法可识别和量化玻璃态和晶态的反应产物及中间体。研究了一系列初始组成为Na2CO3.xSiO2（x = 1, 2）的粉末批次，分别对应偏硅酸钠（Na2SiO3）和二硅酸钠（Na2Si2O5）的化学计量比，在不同温度下进行等温及非等温热处理后进行分析。对23Na四极耦合参数的分析确定了所有情况下的早期反应产物均为晶态Na2SiO3。在非等温实验中，该反应之前在850℃左右形成了一个早期富含二氧化硅的熔体相。早期反应由固态Na+在颗粒界面层的反应区扩散控制。晶态Na2SiO3在界面层沉淀，增加了其在Na2CO3和SiO2颗粒之间的厚度，并减缓了Na+迁移速率。这产生了一个与温度相关的第二相。在低温下，Na+迁移受阻，Na2SiO3的生成停止，沉淀出更富含二氧化硅的相。在存在过量SiO2的二硅酸钠批次中，观察到Na2SiO3与SiO2发生二次反应形成玻璃相。通过13C NMR鉴定出一种瞬态含碳相，为松散结合在SiO2颗粒表面硅酸盐网络中桥连氧上的NaCO3-络合物。
