The Preparation And Properties Of Some Electromagnetic Shielding Materials

With the development of electronic industry and hi-tech products in military, the electromagnetic and electronic devices are extensively applied. Researches in the electromagnetic wave radiation, electromagnetic wave leakage are payed high attention worldwide. Particularly, in recent years, the researchs on electromagnetic shielding and absorbing materials is becoming a focusing field in physics, chemistry, materials science. Following our previous researches, we prepared two types of electromagnetic materials composed of ultra-fine nickel powders and mixed-valence molybdenum oxide powders. Beginning with their preparation, using corresponding measurements and characteristics, we evaluated the shielding effects of products from different preparation processes, and discussed their applications in the area of electromagnetic shielding.A nickel precursor were prepared from a hexahydrate of nickel chloride and a dihydrate of oxalic acid. Under nitrogen atmosphere and at given temperatures, the ultra-fine nickel powders were prepared by thermal decomposition of precursors in the tubular furance. By changing the temperatures or the duration of the pyrolysis, a serious of different nickel powders were obtained.Some mixed-valence molybdenum oxide powders were prepared under nitrogen atmosphere and at given temperatures, by the pyrolysis of the precursor precipitated from the ammonium molybdate solution with a dihydrate of oxalic acid and hydrazine as additives. The conductivities of the samples varied with the contents of both molybdenum and ammonium were obtained under different reaction conditions.The contents of nickel, molybdenum, ammonium of samples were determined by chemical analysis. Thermal effect, specific surface area and element composing of samples were measured by TG-DSC, BET and element analysis, respectively. Particle sizes, morphologies, and constitutes of crystal phases were shown in SEM and XRD patterns. Their resistivities, granularities, and shielding effects also have been characterized. Results show that the nickel powders and the molybdenum oxide powders have good conductivities and electromagnetic shielding effects. As the conducting coatings, they may have potential application in electromagnetic radiation shielding and environmental protection.Finally, based on a summarization, a brief outlook in the electromagnetic shielding research was made.