焙烧-活化过程中湿氟石膏的化学相变体特征及改性机理

Chemical variants and modification mechanism for water-saturated fluorgypsum in calcination and activation process

通过SEM/EDX,XRD和DTA-TGA等表征湿氟石膏化学组成、物相特征、热力学性能;研究外加硅酸盐、含钙铝化合物等改性剂的湿氟石膏在焙烧活化过程中的化学相变体特征及改性机理。研究结果表明：湿氟石膏主要以二水硫酸钙存在;在120~150℃湿氟石膏脱除结晶水生成半水石膏;外加4.2%的改性剂、经200℃下焙烧2 h后得到的改性氟石膏粉完全满足《建筑石膏》（GB 9776—2008）要求,其中,半水硫酸钙质量分数为70.9%;初凝时间为5 min,终凝时间为9 min;遇水2 h后抗折强度为1.9 MPa,抗压强度为4.2 MPa;在焙烧活化过程中,氟石膏粉中游离CaO与硅酸盐通过水化作用形成C-S-H凝胶;含钙、铝化合物与硫酸钙进一步反应生成钙矾石针状骨架结构的硫酸铝钙,增强了半水石膏的水化特性和机械强度。

The chemical composition, mineralogical properties and thermal dynamic characteristics of water-saturated fluorgypsum were investigated using scanning electron microscopy with energy dispersing spectrum （SEM/EDX）, X-ray diffraction （XRD）, differential thermal analysis and thermogravimetric analysis （DTA-TGA）. Chemical variants characteristics and modification mechanism of water-saturated fluorgypsum in calcinations and activation process with external modifiers, such as silicate, calcium and aluminum-containing salts, were also studied. The results show that gypsum in water-saturated fluorgypsum mainly exists in form of calcium sulphate dihydrate, and crystal water of water-saturated fluorgypsum is mainly dehydrated and hemihydrated gypsum is formed at 120-150 ℃. The fluorgypsum powder with 4.2% external modifiers after being calcinated at 200 ℃ for 2 h can meet the Standard of Calcined Gypsum （GB 9776-2008）. The content of hemihydrated gypsum in modified fluorgypsum powder is 70.9%, and the initial and final setting time is 5 min and 9 min, breaking and compressive strengths after water-saturation for 2 h are 1.9 MPa and 4.2 MPa, respectively. In calcinations and activation process, free CaO and silicate reacted forming C-S-H gel while ettringite-similar compound containing Ca（A102）2 and CaSO4 is proposed from hemihydrated gypsum and calcium and aluminum-containing salts, which enhances hydraulic characteristics and mechanical strengths of hemihydrated gypsum.