Preparation And Study Of Infrared Radiation Coating With High Emissivity At High Temperature

The infrared radiation materials with high emissivity at high temperature have been widely used in many industrial applications such as the energy savings for industrial furnace,the efficiency improvement of infrared heater and spacecraft thermal control.In these traditional applications,especially in industry furnace,the infrared radiation materials,added with an amount of inorganic binder,were brushed onto refractory furnace lining,the low bonding force between the coating and the metal substrate and the bad thermal shock resistance restricted their applications in the field of infrared radiation coatings of metal resistor tape,metal enclosures of hood-type annealing furnace and others.Plasma spraying technique have been widely used in preparing wear-resistant coating,thermal carrier coating and abradable seal coating because of its good performance of bonding force and thermal shock resistance.But it is rarely to fred reports about preparing infrared radiation coating by plasma spraying.In this paper,we will adopt plasma spraying to preparae infrared radiation coating.It was reported that the normal total emissivity of coating with NiCr₂O₄ spinel structure is up to 0.89 in 2006.In this paper,the spherical agglomerated particles were fabricated by spray drying with the powders of NiO,Cr₂O₃ and TiO₂.Plasma spray power was acquired by heat treatment from the particles at high temperature. Dark and uniform coating was deposited on the copper sheet substrate by plasma spraying.The shape of particle prepared by spray drying is spherical.The particles meet the requirement of the process of plasma spraying although the decrease in flowability after baking.Powder prepared by spray drying was physical mixture of raw materials and hence no change of phase structure.Powder must be baked for generating high emissivity phase structure.In order to get the optimum temperature for baking,sample B was baked at 750℃,950℃,1050℃and 1200℃.The result shows that the adequately reaction temperature is 1200℃. The XRD analysis reveals that the coating and powder have the same phase structure.While not adding TiO₂,the coating is mainly made up of NiCr₂O₄ and Cr₂O₃,the emissivity is up to 0.89 at 600℃.While the amount of TiO₂ added is 5～15%,the coating is mainly made up of(Cr_0.88Ti_0.12)₂O₃ and NiCr₂O₄,the emissivity is up to 0.91.While the amount of TiO₂ is up to 20～30%,the emissivity decreased as the result of no NiCr₂O₄ in the coating.The plasma spray coating has good performance of bonding force and thermal shock resistance.