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71.
72.
硼改性酚醛树脂在摩擦材料上的应用 总被引:18,自引:0,他引:18
用硼化合物对酚醛树脂进行改性,使硼元素以结合键形式存在于酚醛树脂中,提高酚醛树脂的耐热性,应用于摩擦材料,使其摩擦系数稳定,磨损率低。 相似文献
73.
Orhan ?çelli Salih Erzeneo?lu 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2008,266(14):3226-3230
The transmission of gamma-rays of some boron compounds (H3BO3, Na2B4O7) and the trommel sieve waste (TSW) have been measured by using an extremely narrow-collimated-beam transmission method in the energy range 15.74-40.93 keV. Molecular, atomic and electronic cross-sections and effective atomic numbers have been determinated on the basis of mixture rule and compared with the results obtained from theory. 相似文献
74.
采用焙烧的方式处理含硼尾矿,以常压碱解率来评价其焙烧前后的反应活性。在TG-DTA热分析的基础上,研究了焙烧温度对含硼尾矿活性的影响,并采用X射线衍射对含硼尾矿焙烧矿样的物相组成进行了表征分析。结果表明:焙烧能显著提高含硼尾矿的活性。焙烧温度达到700℃之前,活性随着焙烧温度升高而增大;焙烧温度700℃时,活性达到70.10%,相比未经焙烧的含硼尾矿活性提高了26.69%。活性提高的主要原因在于,通过焙烧,不易碱解的含硼矿物硼镁石(Mg_2(OH)[B_2O_4(OH)])脱水分解成易于碱解的遂安石(Mg_2B_2O_5)。 相似文献
75.
以Si粉为烧结助剂,SiC颗粒为增强剂,采用真空热压烧结工艺制备了SiCp/B4C陶瓷基复合材料。研究了SiCp对复合材料力学性能的影响。借助X射线衍射、扫描电镜等分析了复合材料的物相组成和微观结构。研究表明:添加的SiCp中粒径小的颗粒被包裹在主晶相中,粒径较大的颗粒分布在晶界上,形成"晶内-晶间"混合型复合陶瓷。当SiCp含量为4wt.%时,复合材料的弯曲强度和断裂韧性分别达到431MPa和5.41MPa.m1/2。复合材料力学性能的提高主要是由于残余应力引起的晶界强化以及断裂方式的转变。 相似文献
76.
S. Carlos B. Oliveira 《Electrochimica acta》2010,55(15):4599-4605
The effect of boron doped diamond (BDD) surface termination, immediately after cathodic and anodic electrochemical pre-treatments, on the electrochemical response of a BDD electrode in aqueous media and the influence of the different supporting electrolytes utilized in these pre-treatments on the final surface termination was investigated with [Fe(CN)6]4−/3−, as redox probe, by cyclic and differential pulse voltammetry and electrochemical impedance spectroscopy. The cyclic voltammetry results indicate that the electrochemical behavior for the redox couple [Fe(CN)6]4−/3− is very dependent on the state of the BDD surface, and a reversible response was observed after the cathodic electrochemical pre-treatment, whereas a quasi-reversible response occurred after anodic electrochemical pre-treatment. Differential pulse voltammetry in acetate buffer also showed that the potential window is very much influenced by the electrochemical pre-treatment of the BDD surface. Electroactivity of non-diamond carbon surface species (sp2 inclusions) incorporated into the diamond structure was observed after cathodic and anodic pre-treatments. Electrochemical impedance spectroscopy confirmed the cyclic voltammetry results and indicates that the BDD surface resistance and capacitance vary significantly with the electrolyte and with the electrochemical pre-treatment, caused by different surface terminations of the BDD electrode surface. 相似文献
77.
《Journal of the European Ceramic Society》2023,43(9):3941-3949
The effects of B4C content on the specific stiffness and mechanical and thermal properties of pressureless-sintered SiC ceramics were investigated. SiC ceramics containing 2.5 wt% C and 0.7–20 wt% B4C as sintering aids could be sintered to ≥ 99.4% of the theoretical density at 2150 °C for 1 h in Ar. The specific stiffness of SiC ceramics increased from 136.1 × 106 to 144.4 × 106 m2‧s−2 when the B4C content was increased from 0.7 to 20 wt%. The flexural strength and fracture toughness of the SiC ceramics were maximal with the incorporation of 10 wt% B4C (558 MPa and 3.69 MPa‧m1/2, respectively), while the thermal conductivity decreased from ∼154 to ∼83 W‧m−1‧K−1 when the B4C content was increased from 0.7 to 30 wt%. The flexural strength and thermal conductivity of the developed SiC ceramic containing 20 wt% B4C were ∼346 MPa and ∼105 W‧m−1‧K−1, respectively. 相似文献
78.
L. A. J. Garvie H. Hubert P. Rez P. F. McMillan P. R. Buseck 《Journal of Alloys and Compounds》1999,290(1-2)
Hexagonal boron nitride (hex BN) containing significant amounts of C and O substituting for N (hex BCNO) was synthesized at 75 kbar and 1700°C from mixtures of C, B2O3, and amorphous B contained in a hex BN crucible. Hex BCNO is a minor constituent of the product and occurs as small, <30 nm diameter, rounded pseudohexagonal particles adhering to materials with the α-rhombohedral B structure. Electron energy-loss spectroscopy with a transmission electron microscope was used to quantify their elemental ratios. Up to 50% of the N in hex BN is replaced by C and O, e.g., BN0.49O0.38C0.11. The electron energy-loss near-edge fine structure of the core-loss edges was used to elucidate the possible structures of hex BCNO. The core-loss edges of B, C, N, and O exhibit orientation-dependent intensity changes, which indicates that they occupy similar anisotropic bonding sites in graphite-like BCNO layers. For a composition of BN0.5O0.4C0.1, regions with B–N3, B–N2O, and B–NO2 units predominate. In addition, some grains have significant quantities of B–O3 and B–C3 units. Boron–boron bonding is either absent or infrequent. 相似文献
79.
Timothy Tomko Ramakrishnan Rajagopalan Parvana Aksoy Henry C. Foley 《Electrochimica acta》2011,(15):10137
Boron/nitrogen substituted carbons were synthesized by co-pyrolysis of polyborazylene/coal tar pitch blends to yield a carbon with a boron and nitrogen content of 14 at% and 10 at%, respectively. The presence of heteroatoms in these carbons shifted the hydrogen evolution overpotential to −1.4 V vs Ag/AgCl in aqueous electrolytes, providing a large electrochemical potential window (∼2.4 V) as well as a specific capacitance of 0.6 F/m2. An asymmetric capacitor was fabricated using the as-prepared low surface area carbon as the negative electrode along with a redox active manganese dioxide as the positive electrode. The energy density of the capacitor exceeded 10 Wh/kg at a power density of 1 kW/kg and had a cycle life greater than 1000 cycles. 相似文献
80.