Synthesis of monolithic nanoparticulate ZrO2 in a new polymorph of orthorhombic crystal structure at ambient pressure

A new polymorph of self-stabilized o-ZrO2, of orthorhombic crystal structure has been synthesized at ambient pressure. It has the lattice parameters a = 0.3340, b = 0.5535, and c = 0.6364 run in the Pmnb space group. A single phase of o-ZrO2 forms in 2 h of heating of a porous ZrO(OH)(2). xH(2)O Precursor (amorphous) at 500 degreesC in air. The kind of precursor used in this novel o-ZrO2, synthesis is derived by 4 simple hydrolysis of aqueous ZrOCl2. 8H(2)O in reaction with ammonia liquor at a controlled temperature of similar to5 degreesC. At this temperature, ZrO(OH)(2) molecules as soon as they form (ZrOCl2 + 2NH(2)OH --> ZrO(OH)(2) + 2NH(2)Cl) recombine with one another through H-bonded H2O to form a ZrO(OH)(2) - xH(2)O polymer gel. In flowing air at 20-40 degreesC, some of the H2O evaporates leaving behind porous ZrO(OH)(2).xH(2)O with NH4Cl impurities. The o-ZrO2 sample, similar to15 nm average crystallite size, transforms to monoclinic m-ZrO2, with a concomitant growth of similar to23 nm crystallites at temperatures as high as 800 degreesC. A kinetically different process operates in the direct heating of ZrO(OH)(2).xH(2)O gel, forming a tetragonal ZrO2 or m-ZrO2. (C) 2004 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.