Research On Surface Metallization Modification And Properties Of Continuous Al₂O₃ Fibers

Continuous alumina fiber is recognized as a new high performance inorganic fiber at present world due to its excellent properties,such as the high strength,the high modulus,anti-corrosion performance,oxidation resistance and insulation at high temperatures.Composite materials,the matel matrix ones,the ceramic matrixons and the resin matrix ones can be prepared with continuous alumina fibers.The poor wettability between alumina fibers and metal has been a key problem restricting the development of metal matrix composites,which can be solved by surface metallization.In this paper,we adopt a simple but effective way,the chemical plating,to deposit a metal coating on the fiber,and copper,nickel and silver coating were deposited respectively.The effect of plating solution composition,the concentration and process conditions on adhesion between coating and fiber,oxidation resistance,anti-corrosion performance and strength retention rate was investigated systematacially with different kinds of tests respectively,the preparation mechanism of coating is analyzed and discussed,and the main conclusions are as follows:（1）The best chemical coppoer plating parameters are as follows:copper sulfate is the main salt,whose concentration is 10g/L;potassium sodium tartrate acts as complexing agent,and the concentration is 40g/L;formaldehyde acts as reducing agent,with a concentration of15ml/L;the potassium hydroxide concentration is 9g/L;the plating temperature is 60℃;plating time is 10min.With the parameters revealling above,a uniform,fine and complete copper coating can be prepared on the surface of continuous alumina fiber,with which the fiber weight gain can reach 31 wt%,and the resistance value is as low as 0.3Ω/cm.Basides,the results show that the adhesion between coating and fiber is good;the oxidation resistance of plated fiber is strong,and the fiber can still maintain a certain strength after plating.At the same time,this plating parameter is suitable for various forms of alumina fiber and different Si O₂content.By observing the growth evolution of the copper particles corresponding to different plating times,we reveal the growth mechanism of the chemical plating of copper,and the copper particles show the growth pattern in three stages of"growth-maturation-decline".（2）The best chemical nickle plating parameters are as follows:the concentration of nickel sulfate 35g/L,the concentration of sodium citrate is 30g/L,the concentration of sodium hypophosphite is 25g/L,the concentration of ammonium chloride is 20g/L,and the plating temperature is 75℃,with which a smooth coating was deposited.And the weight gain rate of nickel plated fiber can reach 30 wt%,the resistance value is as low as 0.8Ω/cm.The results suggest that,the adhesion between coating and fiber is good,the nickel plating fiber has good oxidation resistance.The growth mechanism of nickel particles depositing on the fiber was revealed by observing the corresponding coating morphology of different concentrations,presenting a four stage of"nucleation-island-network-film forming"（3）By studying the influence of four reducing agents on the chemical silver plating process of continuous alumina fiber,we find that the best reducing agent is sodium potassium tartrate.Besides,we draw a conclusion with a comparative analysis of the experimental studies that the best chemical palting parameters are as follows:the concentration of silver nitrate is 10g/L,the concentration of sodium potassium tartrate is10g/L,ammonia is 2.67mol/L),KOH is 0.02mol/L,ethanol is 30ml/L,and the plating temperature is 40℃.Then a continuous,smooth,dense silver coating can be prepared,with a weight gain rate up to 9.61 wt%as well as the resistance values 0.4Ω/cm.What’s more,the test results under the optimal process diapaly that silver-plated fiber has better oxidation resistance and corrosion resistance,the average grain size order of each reducing agent was calculated by xile formula:D_glucose>D_formaldehyde>D_sucrose>D_{potassium sodium tartrate}.At the same time,by observing the evolution of different morphology of the coating,the growth mechanism of chemical silver plating is revealed.The nanoparticles are changed from small to big,from less to more and the coating forms in three steps of"reducing crystallization into nucleation core growth to form primary particles and merge to form secondary particles".（4）After surface pretreatment of continuous alumina fiber,different kind of metel coating can be deposited on the fiber,the copper,the nickle and the silver.A leather core structure was confirmed by the cross-section morphology.And the core part is continuous aluminum oxide fiber,and the leather is metal coating.Moreover by establishing the relevant evaluation mechanism of plated fiber,and obtaining the relevant index curve of plated fiber,which can be used to guide industrial production.