Non-aqueous Gelcasting Based Technologies And Their Viability In Preparation Porous Copper

Porous metal materials became one of the hot spot of current research due to theirs properties including low density, good permeability, high temperature resistance and other advantages. Of different methods have been used to fabricate porous ceramics structure, utilization of gelcasting has attracted more attention, due to its advantages that relays on the possibility of producing complex shape with low cost machinability and rapidity in production. Within this context, the main contributions in the present research are as follow:Copper green parts have been gel-cast using three kinds of low-toxicity monomers (HPMA, HEMA and DMAA) with the cross-linker DEGDA in non-aqueous medium. The free radical polymerization of DMAA/DEGDA system in 1,2-Propanediol (PBO) resulted in complex macromolecular network structure to hold copper particles strongly and achieves the homogeneity in theirs distribution in green body.The effect of loaded volume fraction in slurries on properties of copper green and sintered bodies was also investigated. Because of the sedimentation phenomenon that preferably occurred in copper slurries due to high density of particles, a high amount of dispersant range of 0.8?1g is required in preparing low solid loading copper slurries (40-35%), for better particles dispersion and avoids the deformation in the resultant green bodies. Meanwhile slurries loaded with copper volume fraction range of 45?50 vol.% required a dispersant amount range of 0.6-0.8g to achieve good dispersion of particles as well as keeping the viscosity in range suitable for casting without defects. The cross-linked poly-DMAA improves the flexural strength of green bodies for machinability without cracks, even though theirs low solid loading in which the flexural strength decreases from 16 to 8 MPa with solid loading decreases from 50 to 35 vol.%, also variation of 0.05% in density between the up and down sections was achieved. Optimum properties such as porosity, flexural strength and shrinkage were achieved by reasonable selection of temperature and holding time of sintering. Sintering copper green bodies at 970? for 5h resulted in porosity ranged from 32.7 to 51.07% according to copper content, shrinkage of length direction in the range of 5.82 to 14.4% and 5.91 to 14.16% in diameter direction as well as flexural strength varying from 48.5 to 161.5 MPaThe effect of three kinds of pore formers, namely, sodium bicarbonate (NaHCO3), Starch and polymethyl methacrylate) (PMMA), on gelcasting process has been also investigated. The investigation revealed that slurries viscosity and properties of green/sintered bodies has been markedly influenced by the pore formers characteristics such:shape, size and origin (type). Porosity of 35,67% was achieved without adding pore formers while additional porosity in the range 12.27?24.03%,10.65?18.92% and 17.28?28.36% was resulted from NaHCO3, starch and PMMA based-pore formers addition, respectively, with amounts range from 1 to 9 wt.% (based on copper mass).Through the combination of gelcasting with suspension emulsions, porous copper green bodies have been successfully prepared. The addition volume of the oil can control the size and number of pores that formed in the microstructure of resultant green bodies. Gelcasting of copper powder in PBO using polymerization en emulsion resulted in green bodies with good structure and high porosity. Green bodies with density of 1.5 g/cm3 (based on theoretical density) and strength of 4 MPA were prepared with oil/solvent ratio of 1:1.Thus, the significance of these contributions to the producing porous copper structure through non-aqueous gelcasting process will provide a foundation of research for extending the application of metal powder based gelcasting technology and hopefully find good use in the applied technological and industrial sectors.