Boron nitride （BN） powders were synthesized by pyrolysis at various temperatures to investigate the hydrolysis mechanism of borazine-derived BN pyrolysized below 1200 ℃. The BN was hydrolysized near room tem-peratu...Boron nitride （BN） powders were synthesized by pyrolysis at various temperatures to investigate the hydrolysis mechanism of borazine-derived BN pyrolysized below 1200 ℃. The BN was hydrolysized near room tem-perature at 65% or 90% relative humidity （RH） over 45 days. The long-term hydrolysis mechanism and structure evolution were investigated by a measurement of mass growth and by X-ray diffraction （XRD）, Fourier-transform infrared （FT-IR） spectroscopy, and scanning electron microscopy （SEM） analyses. The sam-ples pyrolysized below 1200 ℃ were very sensitive to moisture, and their mass growth was closely related to the pyrolysis temperature. At 25 ℃ and 65% RH, the sample pyrolysized at 400 ℃ exhibited almost 100 wt% mass growth within 8 days, while the sample pyrolysized at 1200 ℃ exhibited about 20 wt% mass growth. The XRD analysis suggested a hydrolysis mechanism that corresponded to the interlayer spacing in the BN, which was consistent with the results reported. should be directly due to the residual N-H bonds On the other hand, the instability of borazine-derived BN in the compound, as suggested by FT-IR analysis.展开更多
The Si3N4-BN composites have been prepared via die pressing and precursor infiltration and pyrolysis route using borazine as precursor, and the effect of sintering additives on properties of the composites has been in...The Si3N4-BN composites have been prepared via die pressing and precursor infiltration and pyrolysis route using borazine as precursor, and the effect of sintering additives on properties of the composites has been investigated. After sintering additives are adopted, the a to β phase transition of Si3N4 and the mechanical properties of the composites at both room temperature and high temperature are all increased with small extent. When using Y2O3＋Al2O3 as additives, the phase transition of Si3N4 and the mechanical properties of the composites have better results. The β-Si3N4 content is 17.47%. The flexural strength, elastic modulus and fracture toughness of the composites are 188.74 MPa, 84.34 GPa and 2.96 MPa.m1/2, respectively. After exposed at 1 000 ℃ in the air for 15 min, the flexural strength of the composites is 154.62 MPa with a residual ratio of 81.92%. The elongated β-Si3N4 grains appear in all composites with different sintering additives. Relatively more rod like β-Si3N4 grains can be observed in composites with Y2O3＋Al2O3 as additives, making it to possess better mechanical properties.展开更多
基金supported by the National Natural Science Foundation of China (No. 90916019)
文摘Boron nitride （BN） powders were synthesized by pyrolysis at various temperatures to investigate the hydrolysis mechanism of borazine-derived BN pyrolysized below 1200 ℃. The BN was hydrolysized near room tem-perature at 65% or 90% relative humidity （RH） over 45 days. The long-term hydrolysis mechanism and structure evolution were investigated by a measurement of mass growth and by X-ray diffraction （XRD）, Fourier-transform infrared （FT-IR） spectroscopy, and scanning electron microscopy （SEM） analyses. The sam-ples pyrolysized below 1200 ℃ were very sensitive to moisture, and their mass growth was closely related to the pyrolysis temperature. At 25 ℃ and 65% RH, the sample pyrolysized at 400 ℃ exhibited almost 100 wt% mass growth within 8 days, while the sample pyrolysized at 1200 ℃ exhibited about 20 wt% mass growth. The XRD analysis suggested a hydrolysis mechanism that corresponded to the interlayer spacing in the BN, which was consistent with the results reported. should be directly due to the residual N-H bonds On the other hand, the instability of borazine-derived BN in the compound, as suggested by FT-IR analysis.
基金Founded by the National Natural Science Foundation of China(Nos.90916019 and 50902150)Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province and Aid Program for Innovative Group of National University of Defense Technology
文摘The Si3N4-BN composites have been prepared via die pressing and precursor infiltration and pyrolysis route using borazine as precursor, and the effect of sintering additives on properties of the composites has been investigated. After sintering additives are adopted, the a to β phase transition of Si3N4 and the mechanical properties of the composites at both room temperature and high temperature are all increased with small extent. When using Y2O3＋Al2O3 as additives, the phase transition of Si3N4 and the mechanical properties of the composites have better results. The β-Si3N4 content is 17.47%. The flexural strength, elastic modulus and fracture toughness of the composites are 188.74 MPa, 84.34 GPa and 2.96 MPa.m1/2, respectively. After exposed at 1 000 ℃ in the air for 15 min, the flexural strength of the composites is 154.62 MPa with a residual ratio of 81.92%. The elongated β-Si3N4 grains appear in all composites with different sintering additives. Relatively more rod like β-Si3N4 grains can be observed in composites with Y2O3＋Al2O3 as additives, making it to possess better mechanical properties.
