Study On The Properties Of Ultra Fine Metal Powder Coated By Atomic Layer Deposition

Atomic layer deposition(ALD)technology,widely used in semiconductor,microelectronics and other fields,is an advanced coating technology and had achieved remarkable results.However,there are few research reports on ultrafine metal powders coated by ALD.Due to high surface activity of superfine metal powders,the iron and copper powder is susceptible to oxidation at high temperature and humid environment,which will affect their performance greatly,so we need to address the oxidation problem especially in the harsh environment.The purpose of this paper is to prepare coated metal powders with excellent properties by atomic layer deposition,to improve the oxidation resistance of iron powder and copper powder,and to adjust microwave absorbing properties of carbonyl iron powder.The application prospective of atomic layer deposition for powder modification were also discussed,the main topics in this research are as following:(1)Carbonyl iron powders were modified via atomic layer deposition for the first time.TMA and water were used as precursors,amorphous alumina layer was grown on the surface of carbonyl iron powders.By adjusting the ALD reaction process parameters,the effects of different processing conditions were investigated.25,50 and 75 ALD cycles of alumina coated carbonyl iron powders were further prepared and analyzed by SEM and TEM.The alumina thin layer was found in good contact with the particle surface,compact and uniform.The morphology of the coated material was clear,which showed excellent surface coating conformity by atomic layer deposition.The characterization of coated carbonyl iron powder was also analyzed by thermal weight loss characterization,the results showed that the coated material has excellent oxidation resistance,which increases with the number of ALD cycles.Hydrochloric acid corrosion test also showed that the coated material has good corrosion resistance.Electromagnetic performance before and after modification of carbonyl iron powder were studied by vector network analyzer and other technical means.It was also found the complex permittivity of coated carbonyl iron powder decreased greatly while the complex permeability was almost the same.Therefore,the electromagnetic parameters and microwave absorption properties of the modified material was also improved.We also studied ALD alumina coated copper fine powers.Effects of different pretreatment process such as direct coating,isopropanol cleaning,and hydrochloric acid cleaning were investigated.From the experimental results,we found that the relatively good thermal stability can be obtained by hydrochloric acid cleaning,which can increase the initial oxidation temperature for 110 degrees.The volume resistivity measurement showed electrical conductivity of the conductive coating material was reduced.The results of atomic layer deposition coated copper powders with different particle sizes are further discussed.The results show that the material with small particle size needs a large amount of precursor pressure.Because of the advantages of good film quality,good repeatability and controllable thickness,atomic layer deposition can be widely used in the field of powder modification.