Mechano-Chemical Effects On Slag Cement And Konjac Glucomannan In Vibrating Mills

The cumulation of mechanical energy in solids occurs under the effects of various mechanical stresses, such as compression, impact and shear, leading to the transformations of structure and property of solids. Therefore, the chemical reaction of material is activated by the increase of material reactivity in the mechanical stress field. The mechanochemistry is divided into hard mechanochemistry and soft mechanochemistry based on their mechanical stress difference, which induces the mechano-chemical reaction. The classic mechano-chemical effects, i.e., hard mechanochemistry, aim at the direct sythesis of a product via an intensively grinding process. The problems of using hard mechanochemical method involve unregulated grinding process, contamination and high energy consumption. Recent development is inevitably shifted toward mechano-chemical processes under softer or milder conditions. The soft mechano-chemical effects are correlated to the substances with some surface functional groups, such as OH groups, peroxide, nitrate and metallic carbonate, et al., with a higher reactivity rather than anhydrous oxides. These substances tend to perform chemical reaction under the mechanical activation and allow to decrease the level of mechanical loading under milder mechanochemical conditions, thus leading to reduction of the energy consumption and contamination. This method in the processing of advanced materials has attracted more attentions during recent years.Firstly, this dissertation described the structure and operation mechanism of vibrating mill. The energy utilization of various mills, such as vibrating mill, planetary mill, stirred beads mill, ball mill, disintegrator and jet mill, were evaluated to understand the efficient application of vibrating mill for the mechano-chemcial effect on materials used in this dissertation. The vibrating mill is a kind of efficient grinding equipment for mechano-chemical reaction of materials due to its superior characteristics like intensive mechanical stress (i.e., collision and compression), moderate energy density and a greater adjustment range of stress rate. It is indicated that vibrating mill can be used to induce mechano-chemical effects on inorganic and organic materials, especially on some materials with a greater toughness.Secondly, this dissertation systemically investigated the mechanochemical effects on inorganic and organic materials (i.e., slag cement and konjac glucomannan) in vibrating mills. The mechanisms of mechano-chemical effects on these materials in vibrating mills were analyzed, respectively.This dissertation investigated the mechanical activation of slag cement in an intensive vibrating mill in order to accelerate the hydration and increase the mechanical strength. The results showed that the mechanical activation of slag cement in the vibrating mill could reduce the particle size of slag cement and increase the amount of particles finer than 10?m. The blast furnace slag, silica fume and cement were well mixed in the process of mechanical activation. Meanwhile, the activated slag cement particles possessed a distortion of structure and increased defects. Therefore, the slag cement particles treated by the vibrating mill show a higher rate of hydration due to the decrease of activation energy. The silica particles in slag cement could favor the acceleration of the hydration rate of C₃S by enhancing the nucleation of C-S-H on the surface of silica particles. In the process of hydration of slag cement, the activated samples showed a stronger bonding between H2O and the host structure. The polymerization degree of SiO44- increased with the formation of C-S-H phase. It was also found that the mechanical activation of slag cement in the vibrating mill could enhance the early strength development of slag cement and increase the addition amount of slag into cement, compared to unactivated slag cement.The de-acetylation and esterification of konjac glucomannan by mechano-chemical treatment in a vibrating mill were also investigated, respectively. The results showed that the mechano-chemical treatment under alkaline condition was efficient to remove the acetyls from konjac glucomannan. The alkalinity of modifier could dominate the efficiency of de-acetylation of konjac glucomannan. The swelling property of konjac glucomannan de-acetylated by mechano-chemical treatment in the vibrating mill was improved. The measurement of the konjac glucomannan gel rheology indicated that the mechano-chemical treatment could reduce the thixotropy in the de-acetylated konjac glucomannan. The de-acetylated konjac glucomannan treated by KOH exhibited a higher viscosity than that treated by NaOH. The konjac glucomannan after deacetylation possessed the more hydroxyl groups. The molecules of deacetylated konjac glucomannan could form the more inter-molecular hydrogen bonds, leading to an enhanced connection between konjac glucomannan molecules and water molecules. Therefore, the de-acetylated konjac glucomannan samples possessed a higher swelling property and a greater viscous stability, showing a positive relation with grinding duration. According to the thermogravimetric analysis, the de-acetylated konjac glucomannan samples showed a higher mass loss (around 100 oC) due to the loss of hydroxyl groups of konjac glucomannan, compared to the original konjac glucomannan sample. The mass loss of konjac glucomannan sample treated by KOH was lower than that by NaOH. This illustrated that KOH could be more effective to reduce the mass loss of konjac glucomannan.In addition, the esterification of konjac glucomannan with sodium hexametaphosphate was stimulated by mechano-chemical treatment in a vibrating mill. The aqueous solutions of konjac glucomannan showed a higher transmittance after mechano-chemically esterification. As a flocculant, the treated konjac glucomannan adsorbed more metallic ions rather than the non-treated konjac glucomannan sample. The optimized duration of mechano-chemical treatment of konjac glucomannan for the superior transmittance and adsorption property was 10 min. It was found that the effect of formation of backbone of konjac glucomannan on the adsorption property of konjac glucomannan dominated over the effect of phosphorus content of konjac glucomannan.