Preparation And Properties Of High Temperature Resistant Insulating SiO₂ Coating

With the increasing demand for large-scale scientific devices such as spallation neutron sources,particle therapy,and space effect radiation at home and abroad,higher requirements have been put forward for the proton/heavy ion synchrotron high-frequency system:a wider working frequency band,larger dynamic range,higher acceleration gradient,and higher stability.Soft magnetic alloy is the core material of the accelerator.The surface of the soft magnetic alloy needs to be coated with an insulating coating to reduce its eddy current loss at high frequencies during the process of using it.In addition,the defects and dislocations produced in the cold forming process of soft magnetic alloys can cause internal residual stress and hysteresis loss.High-temperature heat treatment(?600°C)is an effective method to reduce residual stress mentioned above.Therefore,the insulation coating for soft magnetic alloy should also meet the requirement of high temperature resistance.SiO₂ coating is one of the most common inorganic coating materials,which has good insulation performance and temperature resistance,and is especially suitable for high temperature insulation coating.In this paper,the sol-gel method was used to prepare high-quality SiO₂ coating on a soft magnetic alloy substrate.The effects of preparation process parameters on the structure and insulation properties of SiO₂ coatings were systematically studied.The main research conclusions are as follows:(1)The silica sol was obtained by small-molecule acid(hydrochloric acid,acetic acid,and sulfuric acid and more)catalyzed tetraethyl orthosilicate(TEOS),and then the SiO₂coating was prepared on the surface of soft magnetic alloys by the dipping coating method.The effect of small-molecular acid on the film-forming properties of SiO₂coating has been studied.The results showed that the quality of the SiO₂ coating was not good and it was prone to dry cracking and pulverization due to the poor bonding force between the SiO₂ coating and substrate.Thus,a complete coating cannot be obtained.(2)The mixture of TEOS and Triethoxymethylsilane(MTES)was catalyzed by phytic acid to obtain the modified silica sol,and the mechanism of phytic acid prepared SiO₂ coating is analyzed.After dipping coating,drying,and heat treatment,a SiO₂coating with a smooth surface was obtained on the surface of the soft magnetic alloy indicating that the film-forming properties have been obviously improved with the catalysis of phytic acid.However,the sheet resistance was still less than that of 10¹⁰?/sq,indicating that the insulation performance needs to be further improved.(3)Based on the phytic acid-catalyzed TEOS+MTES sol,the silane coupling agent3-Glycidoxypropyltrimethoxysilane(KH-560)was added to further improve the film-forming property.The effect of KH-560 on the structure and property of SiO₂ coating was systematically studied.The results showed that the stability and film-forming property can be improved effectively via adding a reasonable amount of KH-560.Especially when the amount of KH-560 is 0.04 mol,the quality of film,the corrosion resistance and the electrical insulation of the SiO₂-coated sample(SiO₂-0.04 KH)was the highest.The SiO₂-0.04 KH sheet resistance was up to 2.95×10¹¹?/sq at 100 V.What's more,the mechanism of KH-560 improving SiO₂ coating performance was further analyzed.In conclusion,the high-quality SiO₂ coating was prepared by the synergistic effect of phytic acid catalysis and KH-560 modification.The obtained SiO₂coating has good high-temperature resistance and excellent insulation performance.This coating has application potential on the soft magnetic alloy of proton/heavy ion synchrotron,which can speed up the progress of equipment localization.