A new solution route to silicates. Part 4.—Subtnicronic zircon powders

Abstract

Submicron-sized zircon powders have been prepared by an aqueous sol-gel process. The starting products were zirconium oxychloride or oxynitrate and a water-soluble silicate. The reaction took place at 120 "C in a PTFE-lined bomb under autogenous pressure or even at 100 "C in refluxing conditions. The resulting powder has been characterized by XRD, IR, EDAX, SEM, TEM and EXAFS. Under pseudo-hydrothermal conditions, zircon was prepared as spherical particles with a very narrow size distribution (mean size 0.6 pm). Crystallinity was improved by thermal curing resulting, at 1100 "C, in disk particles (diameter 0.35 pm; thickness 0.13 pm).

Incipient formation of zircon and hafnon during glass alteration at 90°C

“…06‐0266), and, being the only diffraction peak, it indicates a preferential crystal growth in the ( a , b ) plane of the zircon structure. This is in line with the lens‐shaped morphology of the nanoparticles observed at the surface of the gel, as shown for zircons synthesized by a low temperature hydrothermal route . The slightly larger value of the a parameter, 6.632 Å, than in the reference zircon, 6.604 Å, may arise from the incorporation of OH groups in the structure, observed in hydrothermal zircons synthesized at low temperature .…”

“…Addition of impurities or sol‐gel routes can reduce the synthesis temperature by 500°C or more . Since the pioneering work of Frondel and Colette, zircon has been observed at temperatures down to 120°C under pseudo‐hydrothermal conditions and 100°C under refluxing conditions, often after an amorphous precursor . Overgrowth of porous zircon has been observed around reactive metamict zircon at temperatures evaluated at 100°C in geological formations .…”

Sol gel synthesis of forsterite, M-doped forsterite (M=Ni, Co) solid solutions and their use as ceramic pigments

“…Details of the procedures are given in a previous works. 21 O, Panreac, 99% purity) were used as silicon, magnesium, nickel and cobalt precursors and alkaline salts of NaCl and KCl as the mineralizers. The aqueous mixture was prepared with the stoichiometric molar ratios (Mg:Si = 2:1) for forsterite samples and (Mg:Si = 2 − x:1; M:Si = x:1) (M = Ni, Co and x = 0.2, 0.4, 0.6, 0.8 and 1) for pigment samples, by pouring the various metal salts into the aqueous solutions of H 2 Si 2 O 5 .…”

“…This method presents several advantages (low temperature synthesis, higher purity and control of particle size distribution) compared to the traditional ceramic procedure and compared to the sol-gel alkoxide route, for the preparation of silicates such as zircon, willemite and tin sphene. [21][22][23] In fact it was adopted as the synthesis route in the current investigation. The choice of nickel and cobalt ions as chromophores, was made for two reasons.…”

Effect of sol–gel method on colour properties of the classical cobalt olivine (Co2SiO4) ceramic pigment

“…On the other hand, the bands spanning the range from 3200 to 3600 cm −1 and that around 1600 cm −1 are assigned to the stretching and bending vibrations related to OH, respectively. The presence of hydroxides is frequently observed in powders prepared by this sol-gel route based on silicic acid [11,12].…”