ABSTRACT
Continuous silicon carbide fiber-reinforced silicon carbide ceramic matrix composites (SiCf/SiC) are promising as thermal structural materials. In this work, the microstructure and static mechanical properties of 3D-SiCf/SiC with PyC, SiC, and PyC/SiC and without an interface prepared via polymer infiltration and pyrolysis (PIP) were investigated systematically in this paper. The results show that the microstructure and static mechanical properties of SiCf/SiC with an interphase layer were superior to the composites without an interlayer, and the interface debondings are existing in the composite without an interphase, resulting in a weak interface bonding. When the interphase is introduced, the interfacial shear strength is improved, the crack can be deflected, and the fracture energy can be absorbed. Meanwhile, the shear strength of the composites with PyC and PyC/SiC interfaces was 118 MPa and 124 MPa, respectively, and showing little difference in bending properties. This indicates that the sublayer SiC of the PyC/SiC multilayer interface limits the binding state and the plastic deformation of PyC interphase, and it is helpful to improve the mechanical properties of SiCf/SiC.
ABSTRACT
OBJECTIVE: To analyze the current status of maternal HIV infection, mother to child transmission, and the work accomplishments in preventing mother-to-child transmission of HIV (PMTCT). METHODS: During October, 2001 to May, 2009, HIV voluntary consultation and examination were carried out in 339 866 pregnant women in the urban areas, while 594 pregnant women who tested positive were intervened, and interventions were also conducted among 326 babies who were born to HIV positive mothers, including HIV immune body examination on the babies when they were 12 months and 18 months old. RESULTS: A total of 594 pregnant women were found HIV positive, with the positive rate of 0.17% (594/339 866). And the rate was declining year by year. The highest rate was 0.47% (37/7837) in 2002, and the lowest rate was 0.12% (86/73 343) in 2008. Of the 594 positive pregnant women, 228 (38.38%) terminated pregnancy voluntarily, 43 (7.24%) kept on pregnancy and 317 (53.37%) parturients. Of 326 babies born by the 317 parturients, 317 survived.298 received curbing intervention for mother to child transmission (PMTCT), the ratio was 94.01% (298/317). Of 224 babies who were 18 months old, 221 accepted examination, and 7 HIV positive. The maternal infant transmission rate after intervention was 3.17% (7/221). CONCLUSION: Through the prevention of mother-to-child transmission of HIV, the HIV infection status in the pregnant women can be timely observed, which can effectively decrease the level of mother-to-child transmission of HIV.