炭黑含量对短纤维增强反应烧结碳化硅结构与性能的影响

以短碳纤维为增强体改性反应烧结碳化硅陶瓷,研究了炭黑含量对短纤维增强反应烧结碳化硅陶瓷结构与性能的影响。随着炭黑含量的增加反应烧结碳化硅的体积密度增加、游离硅含量降低。炭黑含量为12%(质量分数)、短纤维含量为30vol%时材料的断裂韧性达到5.5 MPa·m1/2;但炭黑含量过高时炭黑在浆料中的均匀性降低,烧结体中的缺陷增加。热分析表明反应烧结碳化硅复合材料的热膨胀系数随炭黑含量的增加略有提高,因此应限制炭黑的加入量。

奎宁环促进的缺电性含氮芳杂环碳氢硅基化反应研究

以过硫酸铵为氧化剂,以氢硅烷为硅基源,开发了一项奎宁环促进的缺电性含氮芳杂环碳氢硅基化反应新技术.新反应以氢原子转移和硅自由基生成为特征,绿色温和,操作简便,易于放大,底物适用范围广,官能团兼容性强,可有效实现多类型缺电性含氮芳杂环上硅基的高效引入.此外,与基于碳硅键断裂的偶联反应相结合,新反应在缺电性含氮芳杂环快速修饰中也展现出了广阔的应用前景.

玄武岩纤维增强酚醛树脂复合材料高温热分析研究

通过对B7/S157玄武岩纤维增强酚醛树脂复合材料和G/S157玻璃纤维增强酚醛树脂复合材料体系进行高温热分析研究、热力学计算及高温反应产物成分分析,结果表明:玄武岩纤维中的氧化铁及氧化亚铁成分可在化学反应中充当催化剂,改变材料体系中碳硅反应历程,使得碳硅反应可在相对较低温度下进行,促进材料的吸热效应,有别于玻璃纤维增强防热复合材料。

Single-atom catalysis: Bridging the homo-and heterogeneous catalysis

Single-atom catalysis,the catalysis by single-atom catalysts(SACs),has attracted considerable attention in recent years as a new frontier in the heterogeneous catalysis field.SACs have the advantages of both homogeneous catalysts(isolated active sites)and heterogeneous catalysts(stable and easy to separate),and are thus predicted to be able to bridge the homo-and heterogeneous catalysis.This prediction was first experimentally demonstrated in 2016.In this mini-review,we summarize the few homogeneous catalysis progresses reported recently where SACs have exhibited promising application:a)Rh/ZnO and Rh/CoO SAC have been used successfully in hydroformylation of olefin of which the activity are comparable to the homogeneous Wilkinson’s catalyst;b)a Pt/Al2O3 SAC has shown excellent performance in hydrosilylation reaction;and c)M-N-C SACs(M=Fe,Co etc.)have been applied in the activation of C–H bonds.All of these examples suggest that fabrication of suitable SACs could provide a new avenue for the heterogenization of homogeneous catalysts.These pioneering works shed new light on the recognition of single-atom catalysis in bridging the homo-and heterogeneous catalysis.

Synthesis of acetals and ketals catalyzed by tungstosilicic acid supported on active carbon

Catalytic activity of activated carbon supported tungstosilicic acidin synthesizing 2-methyl-2-ethoxycarbonylmethyl- 1,3-dioxolane, 2,4-dimethyl-2-ethoxycarbonylmethyl-1,3-dioxolane, cyclohexanone ethylene ketal, cyclohexanone 1,2-propa- nediol ketal, butanone ethylene ketal, butanone 1,2-propanediol ketal, 2-phenyl-1,3-dioxolane, 4-methyl-2-phenyl-1,3-dioxolane, 2-propyl-1,3-dioxolane, 4-methyl-2-propyl-1,3-dioxolane was reported. It has been demonstrated that activated carbon supported tungstosilicic acid is an excellent catalyst. Various factors involved in these reactions were investigated. The optimum conditions found were: molar ratio of aldehyde/ketone to glycol is 1/1.5, mass ratio of the catalyst used to the reactants is 1.0%, and reaction time is 1.0 h. Under these conditions, the yield of 2-methyl-2-ethoxycarbonylmethyl-1,3-dioxolane is 61.5%, of 2,4-dimethyl- 2-ethoxycarbonylmethyl-1,3-dioxolane is 69.1%, of cyclohexanone ethylene ketal is 74.6%, of cyclohexanone 1,2-propanediol ketal is 80.1%, of butanone ethylene ketal is 69.5%, of butanone 1,2-propanediol ketal is 78.5%, of 2-phenyl-1,3-dioxolane is 56.7%, of 4-methyl-2-phenyl-1,3-dioxolane is 86.2%, of 2-propyl-1,3-dioxolane is 87.5%, of 4-methyl-2-propyl-1,3-dioxolane is 87.9%.

Improved oxidation resistance of chemical vapor reaction SiC coating modified with silica for carbon/carbon composites

To protect carbon/carbon (C/C) composites from oxidation, a SiC coating modified with SiO2 was prepared by a complex technology. The inner SiC coating with thickness varying from 150 to 300 μm was initially coated by chemical vapor reaction (CVR): a simple and cheap technique to prepare the SiC coating via siliconizing the substrate that was exposed to the mixed vapor (Si and SiO2) at high temperatures (1 923?2 273 K). Then the as-prepared coating was processed by a dipping and drying procedure with tetraethoxysilane as source materials to form SiO2 to fill the cracks and holes. Oxidation tests show that, after oxidation in air at 1 623 K for 10 h and thermal cycling between 1 623 K and room temperature 5 times, the mass loss of the CVR coated sample is up to 18.21%, while the sample coated with modified coating is only 5.96%, exhibiting an obvious improvement of oxidation and thermal shock resistance of the coating. The mass loss of the modified sample is mainly contributed to the reaction of C/C substrate with oxygen diffusing through the penetrating cracks formed in thermal shock tests.

Enhanced oxygen reduction reaction performance over Pd catalysts by oxygen-surface-modified SiC

Obtaining a detailed understanding of the surface modification of supports is crucial;however,it is a challenging task for the development and large-scale fabrication of supported electrocatalysts that can be used as alternatives to Pt-based catalysts for the oxygen reduction reaction(ORR).In this study,commercial silicon carbide(SiC)was modified through surface oxidization(O-SiC)to support the use of Pd nanoparticles(Pd NPs)as electrocatalysts for ORR.The obtained Pd/O-SiC catalysts exhibited better ORR activity,stronger durability,and higher resistance to methanol poisoning than that exhibited by commercial Pt/C.The role of the support in enhancing the ORR performance,especially the oxidization of SiC surfaces,was discussed in detail based on the experimental characterizations and density functional theory calculations.The underlying mechanism of the superior ORR performance of Pd/O-SiC catalysts was attributed to the charge transfer from SiC_(x)O_(y)to Pd NPs on the surfaces of SiC and the strong metal–support interactions(SMSIs)between Pd and SiC_(x)O_(y).The charge transfer enhanced the ORR activity by inducing electron-rich Pd,increased the adsorption of the key intermediate OOH,and decreased the Gibbs free energy of the critical ORR step.Furthermore,SMSIs enhanced the ORR stability of the Pd/O-SiC catalyst.This study provided a facile route for designing and developing highly active Pd-based ORR electrocatalysts.

Investigation of Propene Oligomerization Catalyzed by Phosphotungstic Acid Catalysts

In this paper, the propene oligomerization reaction catalyzed by phosphotungstic acid supported on two kinds of silica gel was studied, it had been found out that the conversion of propene catalyzed by the type A silica gel-phosphotung- stic acid catalyst was 3.38 m%, while the conversion of propene catalyzed by the type B silica gel-phosphotungstic acid catalyst was 90.1 m% with a nonene selectivity of 42.33 m%, and a dodecene selectivity of 31.79 m%. The influence of reaction temperature, pressure and liquid hourly space velocity （LHSV） on the reaction catalyzed by the type B silica gel- phosphotungstic acid catalyst was investigated. It had been verified that when the reaction temperature increased from 170 ~C to 190 ~C, the conversion of propene increased while the selectivity of nonene and dodecene decreased; when the re- action pressure increased from 3.5 MPa to 4.5 MPa, the conversion of propene increased also, and the selectivity of nonene and dodecene changed very little. The conversion of propene at a space velocity of between 0.5 h-1 and 1.0 h-~ was higher than that achieved at 2.0 h-~, but the selectivity of nonene and dodecene did not show regular fluctuations. An optimum conversion of propene （91.05 m%） and an optimum selectivity of nonene and dodecene （89.51 m%） could be achieved at a reaction temperature of 170 ~C, a reaction pressure of 4.5MPa, and a LHSV of 1.0 fit. The experiments on catalyst life showed that the activity of the type B silica gel-phosphotungstic acid catalyst could be only maintained in 25 hours, and the reason was explained also.

Coking and Deactivation of Catalyst Inhibited by Silanization Modification in Oxidation of Benzene to Phenol with Nitrous Oxide

The main cause to the deactivation of ZSM-5 catalyst, used for oxidation of benzene to phenol (BTOP) by nitrous oxide, is that the carbon deposition on the catalyst surface blocks the mouth of pores of the catalyst.In the experiments, ZSM-5 catalyst was modified by chemical surface deposition of silicon, and then the effect of modification condition on the catalyst activation was studied. The catalyst samples were characterized by XRF,EPS, XRD, TEM, N2 adsorption at low temperature, pyridine adsorption-infrared technique and etc. All the above results show that the uniform SiO2 membrane can be formed on ZSM-5 crystal surface. The SiO2 membrane covers the acid centers on ZSM-5 surface to inhibit surface coking, to avoid or decrease the possibility of ZSM-5 pore blockage so that the catalyst activity and stability can be improved efficiently. The optimum siliconiting conditions determined by the experiments are as follows: 4% load of silanizing agent, volume (ml)/mass (g) ratio of hexane/ZSM-5=15/1, and 16 h of modification time. Compared with the samples without siliconiting treatment,the samples treated under the above optimum condition can increase the productivity of phenol by 14% for 3 h reaction time and by 41% for 6 h reaction time respectively.

以SiC为连接层主相的SiC陶瓷及其复合材料连接研究进展

由于高脆性、高硬度、高耐磨等特点,SiC陶瓷较难直接加工成大型结构复杂的零部件,发展连接技术是推动其工程化应用的主要方法之一。在众多连接方法中,以SiC为连接层主相的连接方法制备的接头具有连接强度高、接头应力小、抗辐照、抗化学腐蚀和耐高温等优势,成为SiC陶瓷连接重点关注的技术,包括纳米浸渍瞬态共晶相连接(NITE相连接)、硅—碳反应连接(Si—C反应连接)和前驱体连接。本工作从连接机理、连接工艺、接头成分、微观结构和连接强度等方面综述了上述3种以SiC为连接层主相的SiC陶瓷及其复合材料的连接技术,并对3种连接技术的优缺点进行了对比分析,最后对发展趋势进行了展望。

SiC nanowires with thickness-controlled SiO2 shells： Fabrication, mechanism, reaction kinetics and photoluminescence properties

SiC nanowires with thickness-controlled SiO2 shells have been obtained by a simple and efficient method, namely treatment of SiC/SiO2 core-shell nanowires in NaOH solution. The products were characterized by transmission electron microscopy （TEM）, high-resolution transmission electron microscopy （HRTEM）, X-ray diffraction （XRD）, Raman spectroscopy, infrared （IR） spectroscopy, and photoluminescence spectroscopy. The thickness of the SiO2 shell can be effectively controlled by selecting the appropriate processing time, and pure SiC nanowires were also obtained by alkaline cleaning in 1 mol-L-1 NaOH solution for 40 min at 70 ~C. A mechanism for the removal of the SiO2 shells has been proposed, and a two-phase reaction kinetic equation was derived to explain the rate of the removal of the SiO2 shells. The validity of this equation was verified by experiment. This work not only describes an effective experimental method for achieving SiC nanowires with thickness-controlled SiO2 coatings but also provides a fundamental theoretical equation with a certain level of generality. In addition, photoluminescence （PL） measurement results showed that the SiC nanowires sheathed with an optimum SiO2 thickness （3.03 nm） have better photoluminescence properties than either the bare SiC nanowires or SiC nanowires with thicker coatings of SiO2.