Rumin Wang

Adsorption characteristics of graphene oxide nanosheets on cement

Modifying cement with graphene oxide (GO) nanosheets tremendously improves its mechanical properties but decreases its fluidity. The adsorption characteristics between GO and cement play a pivotal role in the influence on fluidity. In this paper, the adsorption characteristics of graphene oxide nanosheets on cement were investigated using scanning electron microscopy (SEM), total organic carbon (TOC), Fourier transform infrared spectra (FTIR) and XPS analyses. The results show that GO nanosheets have a strong adsorption ability on the cement surface. The adsorption data was best fitted with the Freundlich adsorption isotherm model and described by a pseudo-second order kinetics model. The adsorption process includes a chemical reaction where the –COOH groups on the edge of the GO nanosheets react with metal cations. The adsorption layer thickness of the GO nanosheets on the cement was about 10.16 nm.

Optimization and preparation of an allyl phenoxy-modified bismaleimide resin

A thermosetting resin system has been developed by the copolymerization of allyl phenoxy, bismaleimide (BMI), and diallyl bisphenol A and optimized using response surface methodology. An optimized modified resin system with enhanced properties was achieved based on empirical second-order models expressing the relationship between the modifier contents and the mechanical properties. Dicumyl peroxide (DCP) was selected as initiator to further improve the curing behavior and mechanical properties of the optimized resin system. The effect of initiator contents on impact, flexural strength, and heat distortion temperature was also investigated. The curing behavior, morphology, and thermal stability of the optimized resin were carefully characterized using differential scanning calorimeter, scanning electron microscope, and thermogravimetric and dynamic mechanical analyzers, respectively. For evaluating the efficiency of modified BMI resin system, laminated composites using glass fiber cloth were fabricated using a hot press and tested for mechanical properties. The results showed that the DCP reduced the curing temperature significantly, improved the curing process, and proved to be very effective in heat resistance. Meanwhile, the laminated composite with initiator showed 13–27% higher mechanical properties and 5–7% higher retention rate at high temperature when compared with the neat resin composite system. The optimized resin system with higher mechanical properties, good heat resistance, and better manufacturability can be used as matrix resin for making advanced fiber-reinforced composites.

Curing kinetics, thermal and mechanical properties of TDE-85 modified by bicyclo-benzoxazine

To reduce the curing temperature and also to enhance the mechanical properties and the heat resistance of diglycidyl-4,5-epoxy-cyclohexane-1,2-dicarboxylate (TDE-85), it was crosslinked with 4,4-diamino diphenyl sulphone (DDS) using a synthesized bicyclo-benzoxazine (BOZ) crosslinker. The kinetic parameters of the curing reaction were evaluated using Flynn–Wall–Ozawa and Kissingers methods. The gelation time and differential scanning calorimetry (DSC) of non-isothermal testing were performed to determine the curing process of BOZ/DDS/TDE-85 systems. Fourier transform infrared spectroscopy (FTIR) was used to follow the major changes in functional groups during the curing process. The absorbance of the oxazine ring showed a significant reduction and the peak of epoxy group became very weak, indicating that the curing reaction was almost complete. The thermal properties were evaluated by heat distortion temperature (HDT) and thermogravimetric analysis (TGA), exhibiting a higher initial decomposition temperature, decreased rate of decomposition and higher char yield compared to the neat epoxy resin system. BOZ enhanced the stability of the epoxy blend, which restricted the mobility of the chain and hindered the decomposition process. The fractured surface of the cured product was observed by scanning electron microscopy (SEM). The fracture form of BOZ/DDS/TDE-85 systems belongs to typically ductile fracture compared to the neat DDS/TDE-85 system. It was found that the thermal and mechanical properties of BOZ/DDS/TDE-85 systems increased with the addition of a certain amount of BOZ. The impact, flexural, and compressive strengths increased by 43.4%, 13.1%, and 8.5%, respectively. The addition of BOZ lowered the activation energy on account of the reduced viscosity, allowing better contact of the resin with the curing agent. The reaction order and activation energy were found to be 0.92 and 63.15 kJ mol−1, respectively.

By-product processing of Si3N4 saw-tooth nanoribbons during carbon foam processing using pyrolysis–nitridation reactions

Si3N4 saw-tooth nanoribbons (SNSNs) have been synthesized via a novel approach involving a by-product pyrolysis–nitridation process during carbon foam manufacturing at 1450 °C. The SNSNs formed are ribbon shaped, 80–750 nm wide, 70–80 nm thick and several micrometres in length. The process simply involved thermal pyrolysis of a powdered mixture containing carbon foam precursors and silicon powder under flowing high-purity nitrogen. Pyrolysis gases rich in silicon, silicon oxide and active nitrogen vapours promoted the subsequent synthesis of the SNSNs over the outer surface of the carbon foams via a vapour–solid mechanism. The crystal structure, morphology, chemical composition, growth mechanism and photoluminescence (PL) properties have been studied. The infrared adsorption of SNSNs exhibited two absorption bands with all the peaks related to the Si–N bonds of the α-Si3N4 crystalline structure. X-ray photoelectron spectroscopy measurements further confirmed the chemical composition, with minor impurities such as oxygen and carbon. A single nanoribbon has the same width-to-thickness ratio, suggesting a stable morphology resulting from the reduction of the overall surface energy. Intense PL was observed centred at 2.03, 2.48, 2.62, and 3.01 eV, which resulted from the recombination between the intrinsic conduction band edges and silicon dangling bonds with deep-level or trap-level states.