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Fabrication of Thick (>10 μm) GeO 2 Ceramic Films by a Facile Liquid Phase Deposition Process
Author(s) -
Jing Chengbin,
Hou Jinxia,
Zhang Yongheng
Publication year - 2007
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2007.01920.x
Subject(s) - aqueous solution , nucleation , ammonia , materials science , precipitation , sulfuric acid , solubility , substrate (aquarium) , analytical chemistry (journal) , deposition (geology) , stoichiometry , mineralogy , chemical engineering , chemistry , metallurgy , geology , chromatography , organic chemistry , paleontology , physics , oceanography , sediment , meteorology , engineering
GeO 2 thick (>10 μm) ceramic films were fabricated by facile liquid‐phase deposition. The solubility of hexagonal GeO 2 in water was increased ten times on adding aqueous ammonia at 70°C because of the formation of soluble Ge 5 O 11 2– . With the addition of sulfuric acid, the alkaline GeO 2 –aqueous ammonia was neutralized, leading to the transformation of Ge 5 O 11 2− into GeO 2 precipitates. When the H 2 SO 4 /NH 4 OH molar ratio was higher than 11.7, immediate precipitation of GeO 2 particles took place in the solution with no GeO 2 particles deposited on the substrate. When the H 2 SO 4 /NH 4 OH molar ratio was decreased from 5.85 to 0.29, the precipitation process was retarded, leading to the gradual growth of uniform hexagonal GeO 2 thick films on the substrates. The compactness of the film increased with a decrease in the H 2 SO 4 /NH 4 OH molar ratio. The growth of the GeO 2 crystal film followed the Bravais–Freidel–Donnay–Harker and Hartman–Perdok models, and the cubic GeO 2 particles with a size of about 10 μm were finally formed on the film. No GeO 2 precipitate was produced on the substrate when the GeO 2 –aqueous ammonia had an excessively low H 2 SO 4 /NH 4 OH molar ratio (≤0.15) because the GeO 2 solute did not reach the saturation level and the nucleation process could not take place on the substrate. The particles on the film surface deposited from the solution with an H 2 SO 4 /NH 4 OH molar ratio of 0.29 exhibited a nanopore structure. An initial study using this film as a support for KNO 3 catalyst was carried out and the result revealed that the catalyst showed good catalytic activity of diesel soot oxidation.