Polycrystalline cubic boron nitride (PcBN) composites were prepared through high-temperature and high-pressure (HTHP) sintering process. Cubic boron nitride (cBN) powders with particle sizes of 0.2, 1, 3, and 8 μm were selected as raw materials, and Al-Co-TiN was employed as a binder. The effect of particle size of initial cBN powders on the microstructure, relative density, flexural strength, microhardness, fracture toughness and abrasive ratio of sintered PcBN composite were systematically studied. The results showed that synthesized products were mostly made of cBN, TiN, AlN, TiB 2 and CoN phases. The mechanical properties of sintered PcBN composites first increased and then decreased with a reduction in the particle size of cBN powders. When the particle size of initial cBN powder was 1 µm, the binder was observed to be evenly distributed around the cBN grains in the sintered product. Moreover, there was a close bonding between cBN grains and the binder in the sintered product when the particle size of initial cBN powders was 1 µm, consequently, the optimal mechanical properties were achieved. The maximum values for relative density, flexural strength, microhardness, fracture toughness and abrasive ratio were 99.1%, 607 MPa, 47.06 GPa, 6.52 MPa·M 1/2 and 7125, respectively.
Li Zhen,Li Zhigang,Yang Lingling,Xie Yuanzhe,Shi Jie,Wang Ruiyong,Chang Junbiao
In this paper, the interactions of pepsin with CYD (cytidine) or nucleoside analogs, including FNC (2′-deoxy-2′-β-fluoro-4′-azidocytidine) and CMP (cytidine monophosphate), were investigated by fluorescence, UV–visible absorption and synchronous fluorescence spectroscopy under mimic physiological conditions. The results indicated that FNC (CYD/CMP) caused the fluorescence quenching by the formation of complex. The binding constants and thermo-dynamic parameters at three different temperatures were obtained. The hydrophobic and electrostatic interactions were the predominant intermolecular forces to stabilize the complex. The F atom in FNC might weaken the binding of nucleoside analog to pepsin. Results showed that CYD was the strongest quencher and bound to pepsin with higher affinity.
危险品化学品经营许可证（带存储）