Jones Aled R, Winter Rudolf, Florian Pierre, Massiot Dominique
Materials Physics, University of Wales Aberystwyth, Penglais, Aberystwyth SY23 3BZ, Wales, UK.
J Phys Chem B. 2005 Mar 17;109(10):4324-32. doi: 10.1021/jp045705s.
The kinetics of the reaction of batches of powdered quartz and sodium carbonate was studied by in situ (23)Na nuclear magnetic resonance (NMR) spectroscopy using a laser-heated probe. We show for the first time that the technique allows one to study solid-state reactions at high temperatures with good time resolution and without the risk of quenching artifacts. The reaction is controlled by solid-state Na(+) diffusion across the grain interface. Independent of the batch composition, the first reaction product is crystalline sodium metasilicate, Na(2)SiO(3), even if the temperature is high enough for much of the composition space between silica and metasilicate to be above the equilibrium liquidus. Fast Na(+) diffusion allows the reaction front to cross the grain interface and form the solid product before liquid intermediate equilibrium products can be formed. This purely solid-state reaction slows down as the thickness of the interface increases; the reaction is more deceleratory than published models suggest. If excess quartz is present, it reacts in a second step involving a liquid film wetting the excess grains. Once this reaction has started, it pulls the reaction into the thermodynamic regime, which leads to an increase even in the rate of the first step leading to intermediate solid metasilicate.
采用激光加热探头，通过原位（23）Na核磁共振（NMR）光谱研究了多批石英粉与碳酸钠反应的动力学。我们首次表明，该技术能够以良好的时间分辨率研究高温下的固态反应，且不存在淬火伪影的风险。该反应由固态Na(+)跨晶粒界面的扩散控制。与批次组成无关，即使温度足够高，使得二氧化硅和偏硅酸钠之间的大部分组成空间高于平衡液相线，第一个反应产物仍是结晶态的偏硅酸钠（Na₂SiO₃）。快速的Na(+)扩散使反应前沿能够穿过晶粒界面，并在形成液态中间平衡产物之前形成固态产物。随着界面厚度增加，这种纯固态反应会减慢；该反应比已发表的模型所表明的更具减速性。如果存在过量的石英，它会在第二步反应中发生反应，这一步涉及液膜润湿过量的晶粒。一旦该反应开始，它会将反应带入热力学状态，这甚至会导致第一步生成中间固态偏硅酸钠的反应速率增加。
