Preperation And Properties Of Epoxy Matrix Mold Materials Used In The Pressure Casting

Gypsum is the traditional mold material used in the slip casting of ceramics. With the advent of the pressure casting, gypsum has been unable to use in the industrial production of ceramics, because of its low compressive strength and short service life. There is practical significance for developing a new impact-toughened mold material to replace gypsum. To solve the above problem, we prepared a new type of mold material by using epoxy resin as matrix, and studied its properties.Three typical silane coupling agents (WD-10, WD-50 and WD-60) were selected to modify the surface of the silica powder, the capillary curves between silica and the probe liquids (Deionized water, ethylene glycol, methylene iodide and n-octane) were measured by capillary permeability method, and the contact angles were calculated by Washburn equation. The results showed that after using the silane coupling agents, the contact angles between water and the silica powders were increased more than 50%, the hydrophobicity of powders were enhanced. It can be seen from comparing the effect of three types of the silane coupling agents that the modification effect of WD-50 was best. On the basis of the obtained contact angle data, the surface free energies of the silica powders were calculated by Van Oss-Chaudhury-Good method. The results show that the additions of silane coupling agents made the surface free energies reduced by more than 10%, and changed the composition of the surface free energy. The non-polar portion of the surface free energy was increased while the polar portion had a greatly reducing. In contrast, silane coupling agent WD-50 reduced the surface free energy in the greatest extent.The curing kinetics of epoxy resin were studied using dynamic differential scanning calorimetry and isothermal differential scanning calorimetry, and the effect of WD-50 on the curing reaction was explored. The results showed that the curing mechanism of epoxy resin was not changed by the addition of WD-50, but there was a certain degree of influence on the kinetic parameters of the reaction. The theoretical gelling temperature, the curing temperature and post-curing temperature of the epoxy resin were 40?,60? and 90?, respectively. In the dynamic DSC method, the kinetic parameters (including activation energy Ea and the frequency factor A) of the curing reaction were calculated by Arrhenius equation, Ozawa equation and Kissinger equation. In the isothermal DSC method, the kinetic parameters of the curing reaction were calculated by general autocatalytic model and Kamal autocatalytic model. The results showed that there was little difference between the kinetic parameters calculated from the various method, the values of Ea were between 60 kJ/mol and 80 kJ/mol, and the values of 1nA were between 28 min-1 and 34 min-1. The kinetic parameters calculated from Ozawa model and Kissinger model were relatively low among all methods.The homogeneous epoxy mold materials were fabricated by just stirring at low temperatures, it is a simple and facile process. The silica particles were well dispersed in the epoxy matrix by using a silane coupling agent. The compressive modulus and compressive strength of the mold material were systematically enhanced up to 1.8 and 3.4 times respectively, at a relatively low silica loading (20 wt%) in comparison to the silica-free polymer. The compressive modulus and compressive strength of the mold materials generally increased with increasing silica loadings. The overall Young's modulus vs volume fraction curve displayed a concave upward shape, and the dependence of Young's modulus as a function of silica loadings could be successfully predicted by using Kerner's theory. Moreover, the resulting mold materials with a three-dimensional network structure exhibited a high decomposition temperature, and the material's decomposition temperatures of each stage were improved in a small magnitude after the addition of silica powder. The results of water absorption testing showed that the water absorption of the material had been greatly increased by adding silica.The effects of particle sizes and particle gradation of silica powders to the properties of themold materials were investigated, especially the effects to pore size distribution. In this study, four different size silica powders were selected to test, the experimental results showed that the particle sizes of silica powders had no influence to the glass transition temperature and compressive properties of the mold materials. Water absorption of the mold materials promoted slightly with the increasing of the particle sizes. Two silica powders with reasonable particle sizes were selected and used for particle gradation based on the Dinger-Funk model. Then, the mass fraction (92% and 8%, respectively) of the two silica powders in the most closely accumulated state were calculated by using Matlab. The effects of particle gradation to compressive properties, water absorption and pore size distribution were studied and found that particle gradation has no effect on compressive properties of the mold materials. The water absorption has a trend of decrease with the increasing of mass fraction of SS-1 silica powder. The materials had widely pore size distributions, which were basically concentrated in 2?12 nm and had no obvious correlation. The average pore size of BJH desorption and multipoint BET were the smallest when the mass fraction of SS-1 was 92% and the system was in the most closely accumulated state, which was consistent with the water absorption changed with the mass fraction of SS-1, and the reasonable and applicable of particle gradation were verified simultaneously.