Thermo-physical Characteristics of Nickel-coated Aluminum Powder as a Function of Particle Size and Oxidant

Aluminum particles 15-25 μm in size are widely used in fuel propellants and underwater propulsion systems in national defense research. However, these particles are covered with an aluminum oxide film, which has a high melting point, so ignition is difficult. To improve the ignitability of high-energy aluminum powder and to understand the reaction phenomenon as a function of particle size（15-25 μm, 74-105 μm, and 2.38 mm） and oxidizer（air, CO2, and argon）, the natural oxide films are chemically removed. The particles are then coated with nickel using an electro-less method. The degree of nickel deposition is confirmed qualitatively and quantitatively through surface analysis using scanning electron microscopy/energy dispersive spectroscopy. To characterize the nickel coatings, elemental analysis is also conducted by using X-ray diffraction. Thermogravimetric analysis/differential scanning calorimetry （TGA/DSC） enable comparisons between the uncoated and coated aluminum, and the reaction process are investigated through fine structural analysis of the particle surfaces and cross sections. There are little difference in reactivity as a function of oxidant type. However, a strong exothermic reaction in the smaller nickel-coated aluminum particles near the melting point of aluminum accelerates the reaction of the smaller particles. Explanation of the reactivity of the nickel-coated aluminum depending on the particle sizes is attempted.

The Electrical Conductive Effect of Nickel-coated Graphite/Two-component Silicone-rubber Sealant

Nickel-coated graphite particles and two-component silicone-rubber were compounded to form a conductive composite system. The electrical volume resistivity of the composites were examined and compared under constant tensile strains, cyclic heating-cooling, electric field and repeated cyclic tensile strains in order to study the mechanism of electrical conductivity behaviors of the conductive composites under stress, temperature and current. The results showed that a peak value of the electrical resistivity appeared previously and then gradually increasing with increasing tensile strain. The electrical resistivity displayed positive temperature coefficient effect during the temperature increasing and decreasing. Applying 5A direct current to the conductive composites lesulted in an increase in the electrical resistance immediately, but no changes were detected under lower currents. Under the repeated cyclic strain, the peak value of the electrical resistivity of each cycle increased with the test cycle. All the electrical resistivity changes were attributed to the conductive networks broken-up and rebuilt in the conductive composites.

Microstructure and performance of laser cladding TiB_2 and Nickel-coated graphite composite coating on stainless steel 9Cr18

The antiwear and antifriction coating, which contains TiB2 and Nickel-coated graphite, has been obtained on stainless steel 9Cr18 by laser cladding. The processing method, microstructure, interface, microhardness, tribological properties and the forming mechanisms of the coating are analyzed. Results show that the microstructure of the clad coating are mainly long plume-like primary phase sosoloid Ni-Fe which form the matrix framework, while the in-situ anomalous synthetical TiC grains and uhrafine TiB2 grains uniformly disperse among the framework. The hardness and wear resistance of the coating has been greatly improved, which can be attributed to the reinforcement mechanism of TiC, TiB2, FeC, Fe3C and Cr23 C6. etc. At the same time, the coating has friction-reducing ability.

Preparation and microwave absorption property of Ni/Al powder

As a functional composite material,nickel-coated aluminum powder has been widely used in conductive fillers,electromagnetic shielding materials and other fields due to its advantages of low density,high conductivity and low cost.In this paper,nickel-plated aluminum powder was prepared by a sodium hypophosphite system.The effects of different nickel coating amounts(the percentage of nickel-plating quality to nickel-plated aluminum powder quality)on the morphology,phase,compaction resistivity and electromagnetic parameters of nickel-plated aluminum powder coating were studied.The X-Ray Diffraction(XRD)results proved the successful preparation of nickel-coated aluminum powders with different nickel coating amounts.The Scanning Electron Microscope(SEM)images clearly show the coating effect under different nickel coating amounts.By plating nickel on the surface of aluminum powder,the surface characteristics of aluminum powder are changed,so as to adjust its conductivity,resistance,stability and other properties,thus affecting its electromagnetic performance and wave absorption performance.The results show that the comprehensive absorbing performance is excellent when the nickel coating amount is 40%.The reflection loss of the sample with a thickness of 2.0mm is less than-10 dB in the frequency range of 10.17–12.38 GHz.When the frequency is 10.72 GHz,the minimum reflection loss reaches33:17 dB.