Study On Process And Properties Of BNNTs/B₄C Ceramic Composites By Non Aqueous Tape Casting

In this paper, systematic study was performed on the process parameters of preparing BNNTs/B4C film by non aqueous tape casting. Casting slurry with stable properties, good suspension and moderate viscosity was prepared by exploring and optimizing the casting process. High quality BNNTs/B4C cast film could also be obtained. BNNTs/B4C layered composite ceramic materials were prepared by hot pressing process. The really research contents and conclusions were as follows:Cast film was prepared by non aqueous tape casting with xylene, n-butanol and ethanol as solvent, EC M70 and PVB as binder, DOP as plasticizer, Triton X-100, castor oil, PVP-K30, PEI and TEOA as alternative dispersing agent. The influence of dispersants, binder, plasticizer and milling time on the properties of cast slurry and film was explored. The results showed that the dispersion effect of PVP-K30 was best. Pulp suspension with stable properties and uniform dispersion was obtained by adding 0.8 wt% PVP-K30 and 13 wt% PVB when the ratio (R) of DOP content and PVB content was 2. And BNNTs/B4C cast film with a certain intensity, good flexibility and easy removal was obtained by casting process.It was found that B4C particles could be effective dispersed in mixed solution with the xylene and n-butanol mass ratio of 7:3. The dispersion mechanism was obtained by analyzing the behavior of B4C powder in dispersed system. That was n-butanol had good wettability of B4C powder and preferentially adsorbed on the surface of B4C powder. [CH2OH] of n-butanol was oxidized into [C=O] structure under the action of xylene solution. The [CH2] and [C=O] could form chemical adsorption with B4C, which produced a similar "dissolution" effect in B4C powder. Meanwhile, the action of solvent greatly delayed the agglomeration and sedimentation of B4C powder. Further study found that the chemical adsorption was associated with rich B structure (B13C2) of B4C itself. Since B atom replaced C atom, around substitution B atom generated excess vacancy, which could provide electron pairing. Then the B atom could react and bond with n-butanol. BNNTs/B4C cast film was prepared by using EC M70 and PVB as binder respectively under the condition of optimizing casting process and not using dispersants. Comparing the effect of them, we could found that BNNTs/B4C cast film more compact structure when the binder was PVB. The optimal formula of preparing BNNTs/B4C cast film in this paper was as follows: xylene (17.82 wt%), n-butanol (7.64 wt%) and ethanol (23.09 wt%) as solvent, PVB (4.73 wt%) as binder, DOP (9.45 wt%) as the plasticizer, and the solid content was 37.24 wt%. What’s more, this paper summarized the causes of film defects and the methods of eliminating.BNNTs/B4C ceramic composites were prepared by hot pressing process. The relative density, flexural strength, Vickers hardness and fracture toughness of BNNTs/B4C ceramic reached 99.1%,507.1 MPa,38.1 GPa,5.83 MPa·m1/2 respectively when the sintering temperature was 2080℃.