Preparation And Properties Of ZrO₂ And Al₂O₃ Thin Films

The tungsten-rhenium thermocouple has advantage of good linear relationship of temperature-potential, good thermal stability, low price. It can partially replace the expensive platinum-rhodium thermocouple. But the tungsten-rhenium thermocouples can be easily oxidized in the atmosphere of the high temperature oxidation. It can only be used in the atmosphere of vacuum, inert, reduction temperature measuring conditions. It must be protected if it is used in air or under oxidizing atmosphere. ZrO2 and Al2O3 thin films have the ability of resistance to oxidation at high temperature.They are very suitable for anti oxide thin films on material.We can deposit ZrO2 and Al2O3 on the surface of tungsten-rhenium thermocouple by RF magnetron sputtering to improve the ability of resistance to oxidation at high temperature.Under this condition,In this work, ZrO2 and Al2O3 films were deposited on the he stainless steel by magnetron sputtering technology. The targets we use are pure ZrO2 and Al2O3. the Sputtering power is the RF power. We studied influence of the total gas pressure, substrate temperature and sputtering power conditions on the properties of the films. We analysed surface morphology of the films, phase composition and crystal structure by using SEM, XRD. We study the corrosion resistance of films by testing the tafel curve. We tungsten-rhenium thermocouple which is coated ZrO2 and Al2O3 in high temperature oxidation atmosphere. The results are as follows:For ZrO2 film, When crystal substrate temperature is 300?, the grain of ZrO2 thin film grow obviously.Increasing the substrate temperature at high deposition rate case can improve the corrosion resistance of film. If the pressure of argon gas increase, the grain has the tendency of increasing. If P=400W,substrate temperature is 200?, gas pressure is 0.2Pa, we will get the best morphology, corrosion resistance and binding capacity.The corrosion current is 1.14×10-7A,corrosion potential is -0.133V, binding capacity is 20N, the grain size is 20-50nm.For Al2O3 film,The Al2O3 film will be uneven when the substrate temperature is too low. Low substrate temperature is conducive to change the phase structure of Al2O3 thin films to orthorhombic system.The size of grain and orthorhombic crystallinity of Al2O3 thin film increasing as the pressure increasing. The deposition condition of the good quality is P=400W,substrate temperature is 200?, gas pressure is 1.1 Pa. The binding capacity is 20N,the grain size is 40-80nm.The high temperature oxidation resistant ability of tungsten-rhenium thermocouple wire which is deposited ZrO2 and Al2O3 is improved obviously.The high temperature oxidation resistant ability of thermocouple wire which is deposited ZrO2 doubled. The time of high temperature(1300?)oxidation resistance can be up to 4000 seconds.lt can be used to measure the temperature of rocket or missile engine.