Mechanical, thermal and tribological properties of polyimide/nano-SiO2 composites synthesized using an in-situ polymerization

Polyimide (PI)/nano-SiO2 composites were successfully fabricated via a novel in-situ polymerization. Microstructure, thermal properties, mechanical performance and tribological behaviors of these composites were investigated. The results indicate that nano-SiO2 dispersed homogeneously. Compared with pure PI, thermal stability and heat resistance are higher about 10 °C with the addition of 5 wt% nano-SiO2. Compressive strength and modulus of composite with 5 wt% nano-SiO2 increase by 42.6 and 45.2%, respectively. The coefficient of friction (COF) of composite with 5 wt% nano-SiO2 decrease by 6.8% owing to the thick and uniform transfer films. Excess nano-SiO2 could adversely affect the COF of PI/nano-SiO2 composite. Additionally, wear resistance deteriorates obviously since transfer film exfoliates easily and nano-SiO2 aggregates on the surface of transfer films

Preparation of Sulfur-Free Exfoliated Graphite by a Two-Step Intercalation Process and Its Application for Adsorption of Oils

The sulfur-free exfoliated graphite (EG) was prepared by a two-step chemical oxidation process, using natural flake graphite (NFG) as the precursor. The first chemical intercalation process was carried out at a temperature of 30°C for 50 min, with the optimum addition of NFG, potassium permanganate, and perchloric acid in a weight ratio of 1 : 0.4 : 10.56. Then, in the secondary intercalation step, dipotassium phosphate was employed as the intercalating agent to further increase the exfoliated volume (EV) of EG. NFG, graphite intercalation compound (GIC), and EG were characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FTIR), BET surface area, and porosity analyzer. Also, the uptakes of crude oil, diesel oil, and gasoline by EG were determined. Results show that perchloric acid and hydrogen phosphate are validated to enter into the interlayer of graphite flake. The obtained EG possesses a large exfoliated volume (EV) and has an excellent affinity to oils; thus, the material has rapid adsorption rates and high adsorption capacities for crude oil, diesel oil, and gasoline

Effect of Polymer Addition on the Structure and Hydrogen Evolution Reaction Property of Nanoflower-Like Molybdenum Disulfide

Nano-structured molybdenum disulfide (MoS2) catalysts have been extensively developed for the hydrogen evolution reaction (HER). Herein, a novel hydrothermal intercalation approach is employed to fabricate nanoflower-like 2H–MoS2 with the incorporation of three polymers, polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and polyethylenimine (PEI). The as-prepared MoS2 specimens were characterized by techniques of scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), together with Raman and Fourier transform infrared spectroscopy (FTIR). The HER properties of these lamellar nanoflower-like composites were evaluated using electrochemical tests of linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The existent polymer enlarges the interlayer spacing of the lamellar MoS2, and reduces its stacked thickness. The lamellar MoS2 samples exhibit a promoting activity in HER at low additions of these three polymers (0.04 g/g MoS2 for PVA and PEI, and 0.08 g/g MoS2 for PVP). This can be attributed to the fact that the expanded interlayer of MoS2 can offer abundant exposed active sites for HER. Conversely, high additions of the polymers exert an obvious interference in the HER activity of the lamellar MoS2. Compared with the samples of MoS2/PVP–0.08 and MoS2/PEI–0.04, the MoS2/PVA–0.04 composite exhibits excellent activity in HER, in terms of higher current density and lower onset potential

Hydrogen Evolution Reaction Property in Alkaline Solution of Molybdenum Disulfide Modified by Surface Anchor of Nickel–Phosphorus Coating

Molybdenum disulfide (MoS2) is unfavorable for practical application in the hydrogen evolution reaction (HER) process due to its inert basal surface, inferior conductivity, and limited amount of active edge sites. For the purpose of enhancing the HER performance of this catalyst, the HER activity of its basal surface should be increased. Herein, three types of nickel-phosphorus (Ni–P) coatings—namely, low phosphorus (LP), medium phosphorus (MP) and high phosphorus (HP) —were anchored onto the surfaces of MoS2 nanoparticles via an electroless plating process; thus, three Ni–P/MoS2 composites (Ni–LP/MoS2, Ni–MP/MoS2, and Ni–HP/MoS2) were fabricated. Crystal structures, morphologies, chemical components, and HER performances of each in an alkaline solution were characterized. Both Ni–LP/MoS2 and Ni–MP/MoS2 showed a crystal nature, while the amorphous feature for Ni–HP/MoS2 was validated. The three Ni–P/MoS2 composites exhibited a higher HER activity than the pure MoS2. The HER performance of the Ni–MP/MoS2 composite was more outstanding than those of other two composites, which could be attributed to the presence of metastable nickel phosphides, and the excellent conductivity of Ni–MP coating anchored on the basal surface of MoS2

Adsorption of Pb(II) by a polyvinylidene fluoride membrane bearing chelating poly(amino phosphonic acid) and poly(amino carboxylic acid) groups

Pb(II) can cause a hazardous effect on ecosystem and public health due to its high biotoxicity. A polyvinylidene fluoride-type membrane bearing both poly(amino phosphonic acid) and poly(amino carboxylic acid) functional groups was fabricated for the purpose of Pb(II) removal from the aqueous solutions. The adsorption behaviors of the fabricated chelating membrane toward Pb(II) were studied by the series of static and continuous adsorption experiments. When the pH, adsorption equilibrium time, initial Pb(II) concentration, and temperature were 5.1, 300 min, 1.0 mmol g −1 , and 298 K, respectively, Pb(II) uptake of the membrane was 1.1 mmol g −1 . The presence of coexisting metal ions and complexing reagents decreased the Pb(II) uptake. The adsorption kinetic and isotherm adsorption followed pseudo-second-order equation and Langmuir model, respectively; this adsorption process showed a spontaneous and exothermic feature. The bed depth service time and Thomas models were suitable for describing obtained breakthrough curves

Hydrogen Evolution Reaction Property of Molybdenum Disulfide/Nickel Phosphide Hybrids in Alkaline Solution

The hydrogen evolution reaction (HER) property of molybdenum disulfide (MoS2) is undesirable because of the insufficient active edge sites and the poor conductivity. To enhance HER performance of MoS2, nickel phosphide (Ni2P) was combined with this catalyst and three MoS2/Ni2P hybrids (38 wt % Ni2P addition for MoS2/Ni2P-38, 50 wt % Ni2P addition for MoS2/Ni2P-50, and 58 wt % Ni2P addition for MoS2/Ni2P-58) were fabricated via a hydrothermal synthesis process. Morphologies, crystallinities, chemical components, specific surface areas, and HER properties of the fabricated MoS2/Ni2P samples in an alkaline electrolyte were characterized and tested. In addition, the insight into the HER properties of as-prepared catalysts were revealed by the density functional theory (DFT) calculation. Additionally, the stabilities of pure MoS2, Ni2P, and MoS2/Ni2P-50 samples were evaluated. The results show that the addition of Ni2P can enhance the HER property of the MoS2 catalyst. Although HER properties of the above-mentioned three MoS2/Ni2P hybrids are inferior to that of pure Ni2P, they are much higher than that of MoS2. Among as-prepared three hybrids, MoS2/Ni2P-50 exhibits the best HER performance, which may be due to its uniform morphology, large specific surface area, and excellent stability. The MoS2/Ni2P-50 hybrid shows a high cathodic current density (70 mA/cm2 at −0.48 V), small Tafel slope (~58 mV/decade), and a low charge transfer resistance (0.83 kΩ·cm2)

A Study on Adhesive Strength of the Amorphous Electroless Nickel Deposite

四点弯曲法与声发射相结合，用于测定化学镀Ｎｉ－Ｐ镀层与基体的结合强度．实验结果与复合板模型的计算相一致．所测得的声发射曲线与镀层失效的外貌有关，凸起形（即鼓包）镀层失效对应于附着失效，横向裂纹失效对应于镀层的内聚失效．A method which is a combination of the Four Point Bend in mechanics with Acoustic Emission was used to measure the adhensive strength of electroless NiP deposits to substrates.Experimental results obtained by this method was in accordance with calculation by the model of complex plate. It was found that the pattens of the Acoustic Emission curves were related to the appearance of Ni P deposit failure: the convex deposit failure was in correspondance with adhensive failure of a deposit to a substerte and the borizontal crackles with cohensive failure of a deposit.作者联系地址：哈尔滨工程大学化工系,中国核动力研究设计院Author's Address: Dept. of Chem. Erg.,Harbin Engn. Univ., Harbin 15001Huang XinquanNuclear Power Institute of Chian, Cheng Du 61004