Papers by Author: Qiang Xue

Abstract: The ultrafine grinding of white cement and its hydration were studied. The ultrafine grinding parameters, such as crushing pressure and feeding pressure of jet mill in a lab scale were optimized. The influence of the particle size distribution of ultrafine white cement and the usage of water reducer on the standard thickness and early age strength of white cement paste was investigated. The results indicated that the ultrafine white cement with d₅₀=4.62 µm and d₉₀=10.48 µm can be obtained when the crushing pressure was 0.7 MPa and the feeding pressure was 0.4 MPa. The standard thickness of white cement paste decreased from 30.5 % of the raw material to 26.0% of the ultrafine white cement (d₅₀=4.42 µm, d₉₀=10.26 µm). The use of 2% naphthalene-based water reducer can reduce 15.4% water consumption. The 3d compressive strength of pure ultrafine white cement sample reached 174% of that of raw white cement. The 28d compressive strength of ultrafine white cement with 3% naphthalene-based water reducer added was 22.9% of that of pure ultrafine white cement. A large number of needle-shape nanometer ettringite (AFT) was generated in the early stage of hydratration and layered C-H-S was formed with the decreasing of the amount of AFT in the later stage of hydratration. It’s supposed that the formation of the large number of needle-shape nanometer AFT was related to the reducing of the particle size of C₃A during the ultrafine grinding and the no adjustment of the amount of the added gypsum, which resulted in the faster hydration of C₃A.

Abstract: Surface modification is very important to industrial application of the magnesium hydroxide (MDH) powder, which is used as a kind of environment-friendly flame-retardant. In this paper, a kind of MDH powder surface-modified with silicane coupling agent and stearic acid is synthesized, and its potential usage in the flame-retardant treatment of flexible PVC is studied. The influence of the surface treatment to the dispersion of the powder in PVC, the flame-retardant and other physical properties of the MDH flame-retardant treated flexible PVC are discussed in detail. The surface modification mechanism of MDH is studied by the FTIR analysis, and then the surface modification model is established. Results show that molecules between the surface of the particle and these two modifiers form stable chemical bonds, and this kind of surface modification can improve the MDH’s dispersion and the compatibility of the flexible PVC. When the flame-retardant flexible PVC is produced according to the mass composition of PVC/DOP/MDH=100:50:80 and a few other additives, its oxygen index is 31.5, the elongation at break is 240%, the tensile strength is 13.0MPa, the hypothermia tendering is +30/-0, the volume resistivity at 20°C is 3.2×1011Ω•m. These index are just correspondent with requires of the halogen-free fire-retardant flexible PVC.