Zichun Ding,Lishuai Zong,Weizhao Han,Runze Liu,Siying Wang,Yuhang Wang,Qing Wang,Xigao Jian,Jinyan Wang
A high-temperature resistant resin that forms organic–inorganic hybridization in situ through controllable oxidation process of carborane is reported. The precursor of resin that named CEPN is prepared by esterification reaction between 3-(3,4-dicyanophenoxy) benzoic acid (DPBA) and 1,2-bis (4-hydroxyphenyl)-o-carborane (BHCB). The detailed FT-IR and multi-dimensional XPS analysis prove that the light boron element continuously released by carborane during the curing process is oxidized to form the gradient oxygen barrier layer and the local oxygen consumption area. The resulting oxidized areas significantly decreases the likelihood of the cross-linked network being attacked by hot oxygen and slows down the degradation rate of the system. Based on the above mechanism, the resins showed an impressive heat resistance in nitrogen ( T d5% , 706.7 °C) and air ( T d5% , 666.3 °C) test atmospheres. At the same time, the resin also exhibits excellent thermomechanical stability ( T g , over 550 °C). We believe that the existence of this multi-functional oxidation zone based on the carborane can announces new light on the design concept of high-temperature resistant resin.
Fan Wu,Zhankai Liu,Jian Sheng,Lihan Zhu,Wen-Duo Lu,Bin Qiu,Dongqi Wang,An-Hui Lu
Boron-based catalysts are active and selective in the oxidative dehydrogenation reaction of propane (ODHP) to propylene. Herein, the binary boron-based compounds (boron nitride, boron phosphide, boron carbide, and silicon boride) composed of boron elements and one type of other non-boron elements, and the elemental boron were systematically compared to elucidate how the non-boron elements of binary borides influence their catalytic activity in ODHP. By combined experimental and computational studies, we demonstrated that the non-boron elements can modulate the performance of catalysts by altering the ability of the B-OH site to activate dioxygen and the subsequent activation of propane. In particular, the turnover frequency (TOF) of the catalyst exhibited a high negative linear correlation with the electronegativity of the non-boron element, except for the boron phosphide. This study highlights the importance of the chemical environment around the active boron sites and provides insight into the design of efficient ODHP catalysts.
The brazed joint of sapphire transparent ceramic and Kovar alloy was prepared using AgCuTi and AgCuTiB composite filler, and the main focus was the effect of B element on the wetting behavior, interface composition and joint mechanical performance. The reliable joint of sapphire transparent ceramic and Kovar alloy was obtained by vacuum brazing with AgCu28-6Ti-0.45B (wt%) composite filler. The typical interfacial structure of the joint brazed at 825 °C for 10 min was determined as sapphire/Ti 3 Cu 3 O/Ag(s,s) + Cu(s,s) + disperse TiB/TiFe 2 + TiNi 3 /Kovar. The results showed that the addition of B could contributed to an optimized interfacial structure via (i) in-situ forming fine TiB whisker reinforcement phase and refining the interface structure and (ii) reducing the diffusion degree of alloy side elements to inhibit the generation of brittle phase, and the maximum shear strength of the joint with AgCu28-6Ti-0.45B (wt%) reached 125 MPa more than twice the joint without B additive. On the other hand, the wetting experiment showed that the addition of B as a solid particle decreased the fluidity of the composite filler, and when the addition of B was excessive, no dense TiB whiskers were produced in the interface. This study provides ideas for the optimization and improvement of sapphire composite connection, and points out that the generation of reinforcing phase is accompanied by the reduction of fluidity, so it is necessary to reasonably control the proportion of reinforcing phase.
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