Structure of Ir and Ir-Al<sub>2</sub>O<sub>3</sub> coatings obtained by chemical vapor deposition in the presence of oxygen
By chemical vapor deposition Ir and Ir-Al2O3 coatings are obtained with a thickness of up to 40 μm on steel substrates precoated with a layer of Al2O3. Tris-acetylacetonates of iridium(III) and aluminium(III) are used as precursors. The deposition processes are carried out at atmospheric pressure in the presence of oxygen. The obtained coatings are studied by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The dependences of coating structures and compositions on the preparation conditions are found. An increase in the deposition temperature results in the formation of Ir coatings with loose discontinuous structure, an increase in the size of metal crystallites, and the growth of the oxygen concentration in their composition. An increase in the concentration of precursor vapors in the deposition zone at a constant deposition temperature results in the formation of Ir coatings that consist of differently structured layers (compact, columnar, and granular). Mixed Ir-Al2O3 coatings which composed of metal Ir and amorphous Al2O3 crystallites, which exhibit a pronounced iridium texture in the [111] direction, have the most perfect compact structure. The introduction of the oxide phase in the coating composition halves the Ir crystallite size.