Metal magnetic materials such as iron, cobalt, nickel, etc. are extremely important absorbing materials. They can make up for shortcomings of large proportion and imperfect high-frequency characteristics of ferrite magnetic materials. Bur such metal powder absorbing materials have the following disadvantages: prone to aggregation and poor single dispersion of the system. They impact seriously on absorbing microwave properties of the powders. Meanwhile, their oxidation resistance and acid alkali resistance is much poor than the ferrite.

Al2O3 is used in surface modification of nano-magnetic metal particles. The thin layer of material has a high absorbing performance in the 1-10GHz band. The liquid was prepared silica coated ultrafine nickel powder to obtain the modified inorganic nickel powder. TEM images of the product appearance, IR and XRD can confirm coating layer exists at the same time to examine the dispersion of the coated product, wettability, oxidation resistance and acid resistance.

Impurities adsorbed on the surface of nickel powder are continuously decomposited and endothermic. The coated nickel powders in this temperature range are relatively stable. Nickel powder in the 350 to 550 ℃ of multiple oxidation exothermic peak, the original nickel powder dispersed well, small aggregates, uneven heating in the heating process, showing the stage oxidation. Silica coated nickel powder in 350 to 550 ℃ showed the continuity of oxidation, may sample well dispersed heat evenly, and with the heat instability of the coating layer of SiO2, nickel powder began to slow oxidation. It can be said that the silica packet nickel products can improve the oxidation resistance of nickel powder.

Water has a wetting effect on coated nickel powder. Nickel powder coated on silica due to the outer layer of SiO2 layer sake, its wettability has been reduced. Water wetting of the coated nickel powder, nickel powder surface dangling bonds arising from the adsorption or surface oxidation, the polarity of-OH groups formed in the surface of the nickel powder, which can be wetted by water. The SiO2 layer of the wetting of water on uncoated nickel powder, but the performance of the water wetting of SiO2. Nickel powder in the oxidation of nitric acid, converted into the green of Ni2 +, its characteristic absorption wavelength λ is380nm. Nickel powder color coated the time required is five times of the non-coated metal powder. It greatly improves the nature of resistance to nitric acid oxidation of nickel powder. SiO2 surface of Ni powder coating layer formation isolation of nickel Ni2 + into the solution and acid exposure, delay discoloration of the time required for the peak of the absorbance curve is low, acid resistance is improved.

The improvement of materials’ absorbing properties by coating technology is a hot issue in the absorbing materials research. And the study has important military value. The researchers use liquid inorganic to modify nickel surface of microwave absorption and have a study in morphology characterization, structure and IR characterization, XRD characterization, oxidation resistance, wettability and acid resistance. The results show that the SiO2 coated on the surface of ultrafine nickel powder in uncertain status. The silica coating improved the dispersion and hydrophobic of nickel powder. It also improves acid resistance and oxidation resistance of nickel powder.Source:http://www.mhcmp.com