Controlled Formation of ZrO₂ in the Reaction of ZrCl₄ Vapor with Porous Silica and γ-Alumina Surfaces

Abstract

The reaction of ZrCl4 vapor at 300, 450, and 600 °C with silica and γ-alumina preheated at 300 and 600 °C was studied by XRD, FTIR, 1H MAS NMR, and chemical etching with sulfuric acid. NMR and FTIR revealed a consumption of OH groups in the reaction. However, subsequent water vapor treatment brought some of the OH groups of the support back, indicating that part of the surface had been directly chlorinated. The ratio between permanently consumed OH groups and directly chlorinated OH groups depended on the reaction temperature. OH groups were permanently consumed in mono- and bimolecular reactions of ZrCl4, leading to the formation of isolated M−O−ZrCl3 and (M−O)2−ZrCl2 species (M = Al or Si), respectively. Direct chlorination was associated with the formation of crystalline ZrO2 agglomerates, as detected by XRD in the samples prepared at 450 and 600 °C. These agglomerates were insoluble in sulfuric acid. Although at the reaction temperature of 300 °C the samples were amorphous in XRD, the reappearance of some OH groups on the original surface after water treatment, together with etching tests, suggested that agglomerates were also formed at that temperature. In addition to agglomeration and exchange reactions with OH groups, on 600 °C alumina ZrCl4 dissociated to (Al−O) pairs. This led to a higher Zr saturation density and Cl/Zr ratio on alumina than on silica. The reactions of the HCl evolved in the main reactions were considered minor. Increasing the preheat and reaction temperatures decreased the Zr concentration on the surface and thus diminished the surface coverage. The surfaces of the ZrCl4-modified and water-treated silica and alumina surfaces consisted of Zr−OH groups formed in the hydrolysis of isolated ZrCl x species, original OH groups of the supports, and ZrO2 agglomerates formed in the vicinity of siloxanes and (Al−O) pairs.

Formation of Metal Oxide Particles in Atomic Layer Deposition During the Chemisorption of Metal Chlorides: A Review

“…[7,8] The ZrO 2 formation in the ZrCl 4 chemisorption on high surface area substrates has a similar temperature dependency. [9] d #2. The TiO 2 particles formed in the TiCl 4 reaction with high surface area silica are crystalline and have either anatase or rutile structure, [8,33] which phase is formed depending on both reaction temperature and on substrate heat-treatment temperature.…”

“…[15,16] In 1996, Kytökivi et al [9] reported the existence of ZrO 2 particles when they investigated the ZrCl 4 chemisorption on porous high surface area silica and alumina. Compared to the TiO 2 particles observed on high surface area substrates, the ZrO 2 particles were considerably smaller, with dimensions in the order of 10 nm.…”

“…Compared to the TiO 2 particles observed on high surface area substrates, the ZrO 2 particles were considerably smaller, with dimensions in the order of 10 nm. [10] Kytökivi et al [9] suggested that the ZrO 2 particles could originate from the formation and decomposition of hydroxychloride Zr(OH) m Cl 4±m or oxychloride ZrOCl 2 intermediates. Kytö-kivi and Haukka [11] showed, by infrared measurements, that the TiO 2 and ZrO 2 particles are bonded to the silica substrate through Si±O±Ti and Si±O±Zr bonds, respectively.…”

Composition and Microstructure of Zirconia Films Obtained by MOCVD with a New, Liquid, Mixed Acetylacetonato-Alcoholato Precursor

“…However, there are a number of examples showing that under CVD conditions, usually below 1000 C, cubic zirconia may form. [26,30,31,45] This is often attributed to growth kinetic and nucleation influences.…”

“…Examples include oxygen-conductive membranes for use in fuel cells and oxygen sensors, [1±8] high-temperature thermal barrier coatings, [9±12] hard protective layers, [13±15] ferroelectric films, [16±22] optical coatings, [23±25] catalysts, [26,27] and buffer layers for superconductor growth. [28,29] For most applications, the yttriumstabilized tetragonal and cubic (ªYSZº) zirconia modifications are used, due to their superior toughness.…”