Journal of Materials Science

Friction measurements on particles adhered to compacted powder surfaces have been undertaken by the centrifuge technique to investigate the influence of the variations in the chemical structure of a series of salts of salmeterol. Two mathematical models have been used to evaluate the experiments, and the coefficient of static friction, the friction force and the theoretical shear force on compacted powder surfaces of lactose monohydrate and salmeterol xinafoate have been derived. The results show differences in the mechanism of friction and also divide the five compounds into comparatively hard (salmeterol base and sulfate) and soft (salmeterol 4-chlorobenzoate, salicylate and xinafoate) materials. The hydrophilic nature of the particulate material was found to be indicative of its friction properties on a hydrophobic surface, and vice versa. The ability of a material to adsorb water is reflected in the relative hydrogen bonding coefficient (Hansen-solubility parameter), and a linear relationship was found between this coefficient and the friction force obtained. Water can act as a lubricant reducing the friction between two surfaces. The friction between like materials in contact was found to be minimal. The results also imply that no general descriptor of the chemical structure of related compounds, which would allow the prediction of friction properties, exists. Instead, the descriptor needs to be chosen according to the properties of the surfaces in contact, or friction experiments have to be performed.

Coordination compounds are very promising as energetic materials and catalysts for improving the comprehensive performance of solid propellants. In this study, to obtain insensitive energetic materials with excellent performance, graphene oxide (GO) as template, nitrogen-rich 3-amino-1,2,4 triazole (AMTZ) and Co(NO3)2·6H2O as ligands, a new energetic coordination compound (GO + Co + AMTZ) was synthesized. The morphology, molecular structure, element, and thermal decomposition property of the product were characterized by scanning electron microscope, X-ray diffractometer, Fourier transform infrared (FTIR), Raman spectra, X-ray photoelectron spectroscopy, differential scanning calorimetry (DSC), and thermogravimetry analysis (TG). The results showed that Co ions are used as bridges to coordinate with the O atoms of the hydroxyl and carboxyl groups on the GO surface and the N atoms of AMTZ, respectively. GO + Co + AMTZ has good thermal stability, high heat release, and insensitivity. And the catalytic effect of GO + Co + AMTZ to AP was studied using DSC. Compared with pure AP, the decomposition peak temperature of GO + Co + AMTZ/AP moved forward to 299.57 °C, and the heat release increased to 4935 J g−1, which indicated that GO + Co + AMTZ has an obvious catalytic effect. In addition, the gas phase decomposition products of GO + Co + AMTZ were tested using TG-IR, and the catalytic mechanism was further analyzed. The NO2 gas produced by the thermal decomposition could oxidize the dissociation product NH3 of AP, thereby accelerating the thermal decomposition of AP. Overall, due to its higher energy, insensitivity, and high-energy catalysis, GO + Co + AMTZ has potential application prospects in solid propellants.

We report experimental observations on the way that flowing polyethylene melts can crystallise within a processing channel geometry. Using a recently developed Multipass Rheometer (MPR), we present rheological, rheo-optic and coupled X-ray data that follow the evolution of crystallisation, as molten polyethylene flows into a slit geometry. Optical observations show that fibrous crystallisation occurs initially at the walls of the slit and not, as expected, in the entrance region to the slit. The coupled X-ray, rheology and rheo-optic data lead us to speculate that a coil-stretch transition of the polymer chains occurs at the wall of the slit and this acts as the primary cause of fibrous X-ray nucleation. At high wall shear rates we identify evidence to suggest that slip occurs between the flowing polymer and the solid wall and this in turn causes the onset of fibrous crystallisation to be surpressed. The experimental observations are generally consistent with certain theoretical predictions made by Brochard and de Gennes.

We report a facile and effective aerosol-spray strategy toward high-performance anodes for lithium-ion batteries by incorporating mesoporous SnO2 spheres of high-capacity materials with surface-modified carbon nanotubes (MCNTs). SnO2 nanocrystals are self-assembled into mesoporous spheres, and MCNTs with abundant carboxylic groups serve as a conductive scaffold. Driven by the strong interaction between the surface of metal oxide and the carboxylic groups on CNTs, a robust nanocomposite architecture is in situ formed. Such nanocomposite architecture possesses several advantages as an anode for lithium-ion batteries. First, mesoporous SnO2 spheres inherit the advantageous features of conventional nanoparticles, such as the capability to accommodate volume expansion and reduce Li+ diffusion distance. Second, the robust interface between nanocrystals in the SnO2 spheres provides the high structural stability that would prolong the life span of the electrode. Third, MCNTs that strongly bind to SnO2 spheres serve as a three-dimensional network, offering both improved electronic transport and mechanical strength of the electrode. Therefore, as-prepared nanocomposite delivers high capacity of 963 mAh g−1 at 0.1 C and 701 mAh g−1 at 5 C, respectively. Significantly improved cycling performance is achieved over the bare SnO2 spheres counterpart.

Arc discharge plasma nitriding (ADPN) of stainless steel was achieved using the thermionic electrons generated from column arc discharge to ionize the working gas to form a high-energy plasma. The column arc current is a key influential factor in the ADPN technique. AISI 420 martensite stainless steel (420 SS) was nitrided at a low temperature of ~ 440 °C to improve its mechanical properties and corrosion resistance using a highly efficient low-pressure ADPN technique. The arc plasma was generated by applying arc currents ranging from 100 to 130 A. The results of arc currents on the microstructure, mechanical characteristics, tribological properties, and corrosion performance of treated layers were investigated. The results revealed that the nitrided layers are primarily composed of expanded martensite (αN), Fe4N and Fe2-3 N, and a high arc current leads to the formation of a compound layer composed of Fe2-3 N and Fe4N. The surface microhardness and wear resistance of 420 SS were greatly improved following ADPN compared with conventional plasma nitriding. The samples treated at the higher arc current have a thicker nitrided layer and a tough surface with a higher fraction of Fe2-3 N, which shows the best wear and corrosion performance.

This article develops a constitutive model for the yield stress of SiC reinforced aluminum alloy composites based on the modified shear lag model, Eshelby’s equivalent inclusion approach, and Weibull statistics. The SiC particle debonding and cracking during deformation have been incorporated into the model. It has been shown that the yield stress of the composites increases as the volume fraction and aspect ratio of the SiC particles increase, while it decreases as the size of the SiC particles increases. Four types of aluminum alloys, including pure aluminum, Al–Mg–Si alloy, Al–Cu–Mg alloy, and Al–Zn–Mg alloy, have been chosen as the matrix materials to verify the model accuracy. The comparisons between the model predictions and the experimental counterparts indicate that the present model predictions agree much better with the experimental data than the traditional modified shear lag model predictions. The present model indicates that particle failure has important effect on the yield stress of the SiC reinforced aluminum alloy composites.

Optical microscope (OM), energy dispersive X-ray (EDX) analysis, differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscope (TEM) were applied to investigate the solidification microstructures and phases of Al–9.6 wt.% Mg alloy which solidified under 4 GPa high pressure with the melting temperature 1,153 K. Fine dendritic microstructures were obtained, and the second dendritic arm spacing reduced. Area fraction of the primary α-Al phase increased and that of the second phase decreased. In addition, the solid solubility of Mg in α-Al phase increased. The lattice constant of α-Al phase increased. Specially, the new double phase regions (α-Al′ + Al x Mg y ) formed besides a small amount of Al3Mg2 phases under high pressure. The Al x Mg y phase presented a mean size of about 20 nm, and had the hexagonal structure with the lattice constant of a = 0.288 nm, c = 0.8165 nm probably. Wherein the lattice constant of α-Al′ phase differed from that of α-Al phase greatly. Moreover, evolution mechanism of microstructures and phases under 4 GPa high pressure was discussed.

Interfacial diffusion has been evidenced in a eutectic-like Ni, Cr-TaC composite, using high resolution autoradiographic techniques. The structure of the fibre-matrix interface has been determined by using high voltage electron microscopy. The fibre-matrix interface has been shown to be a diffusion short circuit in the temperature range 700° C to 900° C.