| Research Abstract |
l.Pulse CVI of boron nitride into the Si_3N_4 powder preforms From a gas mixture of B_2H_6,NH_3,Ar and N_2, chemical vapor infiltration (CVI) of BN into Si_3N_4 powder preforms was investigated in use of hot-wall heating system and pressure pulse. At above 1100ﾟC, reaction has completed below 1 sec, thus, the reaction temperature must be kept below 1OOOﾟC. The relationship between the number of pulse and the deposition into deep level showed the favorable hold-time of 1 sec at 1000ﾟC, because surface deposition becomes dominant at longer hold-time such as 5 sec. Flexural strength increased linearly after 3000 pulses and at 1000ﾟC.
2.SiC-infiltration into SiC particulate- and carbon fiber-preforms and po- rous carbon With an rf-heating system, SiC was infiltrated from a gas mixture of CH_3SiCl_3 and H_2 into an SiC particulate preforms. For 4mum powder, surface deposition began above 30000 pulses at 1OOOﾟC, and the flexural strength at this point attained to 200-230 MPa. On the contrary,
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for 50mum powder, packing continued linearly even after 40000 pulse, however, the flexural strength at this point was only 120 MPa. In the case of porous carbon, the packing ratio after 10000 pulse and at 1000ﾟC was about 60% and here the flexural strength was 120 MPa which corresponded to three times that of the original one. Peculiar packing proceeding, from the deepest position to the surface, has been observed here. In the case of carbon fiber preforms, fibers were heated inductively, therefore, SiC fm the respective fibers which resulted in the poor flexural strength.
3.TiN infiltration into SiC or TiC particulate preforms From the gas mixture of TiCl_4-N_2-H_2, TiN was infiltrated into SiC or TiC particulate preforms. The favourable temperature was found to be 830-870ﾟC, but to find a specified condition was severe problem, because the temperature dependence of the reaction rate was markedly steep.
4.Modeling of pulse CVI Pulse CVI process was analyzed using diffusion- related equations which were compared with the experimental results of pulse CVI of TiN into silica-glass capillary the inner diameter of which was 1-100mum. Less
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