| Microwave absorbing materials have been widely in stealth technology and in electro-magnetic compatibility (EMC) technology, and they are researching hotspot in these technology field. In most of absorbers, the ferrite and metal powder are the main components because of good performance and low cost. But the defect of high density is not benefit for the preparation of light absorber. In response to the need for high performance absorber, in this paper, the composite-coating absorbers with hollow cenosphere as nuclear are prepared by sol-gel and electroless plating technology.The Electroless Ni-P and Ni-Co-P-coating processes is modified by replacing the conventional sensitization and activation steps with only using activation step with AgNO3 activator, and the optimal forming conditions is made certain.The BaFe12O19 and BaRexFe12-xO19 (RE denote Y,Nd and Eu) ultrafine powders with M-type structure are synthesized by sol-gel technique. The effects of the composition of the gel, strength of solution, the amount of complexing agent, the different kinds of anions, the adding of dispersant, and the condition in heat treatment of the gel on crystal phase, morphology and magnetic properties of The BaFe12O19 and BaRexFe12-xO19 were investigated systematically to clarify the optimum forming conditions.Thin films of Barium hexaferrite are prepared on fly ash cenpsphere particles by sol-gel using Fe(NO3)3·9H2O,Ba(NO3)2 and citric acid as raw materials. The prepared films are characterized by differential and thermogravimetric analysis (DTA-TG), X-ray diffraction analysis (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometer(VSM) and Vector Network Analyzer.Some important results are concluded as follows:(1) The Electroless Ni-P and Ni-Co-P-coated cenospheres is preparated by replacing the conventional sensitization and activation steps with only using activation step with AgNO3 activator. The magnetic properties of Ni-P coated cenospheres are δs (27.3emu/g) and Hc (1807.2A/m) , while those of Ni-Co-P coated cenospheres are δs (27.36emu/g) and Hc (2059.5A/m), and those of Ni-P coated cenospheres after heat treatment are δs (2.08 emu/g) and Hc (15620.8A/m). The electroless mechanism is following: the ability of absorbing Ag(NH3)2+ is improved by hydroxy on cenosphere surface after alkali solution liquid rinsing. Then in the coating bath, [Ag(NH3)2]+ are reduced to Ag by H2PO2- . The catalytic action of Ag act as a nucleation sites for subsequent Ni-P or Ni-Co-P deposition.(2) In the process of Ni-P electroless plating, the velocity of reaction is not augmented, while the residual Ni2+ after reaction is increased with the increased concentration of Ni2+. The velocity of reaction is increased, while the residual Ni2+ after reaction is declined with the increased concentration of H2PO2-. The velocity of reaction is fell, while the residual Ni2+ after reaction is declined with the increased mol ratio of Ni2+/[C6H5O7]3-. When the pH is adjusted by NH3.H2O the velocity of reaction is increased with the increase of pH (pH<9.0) and the velocity of reaction is fell with the increase of pH (pH>9.0). But when the pH is adjusted by NaOH the velocity of reaction is increased with the increase of pH. And the velocity of reaction is increased with the increasing temperature and the increasing loading. (3) In the process of Ni-Co-P electroless plating, the velocity of reaction is augmented with the increased concentration of Ni2+. While the mol ratio of /(+) is more then 0.4, the velocity of reaction only change a little with the increased concentration of Ni2+. The velocity of reaction is increased with the increased concentration of H2PO2-. But when the concentration of H2PO2- is more than 0.3mol/l, the velocity of reaction only change a little. There is a little effect of the concentration of H3BO3 on the velocity of reaction, 0.5mol/l is the optimal concentration. The velocity of reaction is increased with the...
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