HYDROTHERMAL CONVERSION OF AMORPHOUS NIFE2-XALX(OH)(8) INTO CRYSTALLINE PHASES

Mixtures of amorphous hydroxides prepared from Fe-III, Al-III and Ni-I I nitrate solutions in proportion to obtain a series of compounds with 0.1 (if necessary 0.05) increments for x in NiFe2-xAlx(OH)(8), have b een subjected to hydrothermal ageing at 150 degrees C in mother-liquor for one or six months. X-Ray, IR, TG and magnetic studies revealed no influence of ageing time on the properties of the crystalline phases obtained. It was proved that for certain values of x, it is possible t o obtain hydrothermally a pure phase of nickel ferrite-aluminate solid solutions, displaying magnetic characteristics similar to those of so lid solutions produced by standard ceramic methods. At x=0.5 the spine l phase deteriorates, the haematite structure appears and the nickel i ons engage (till x=2)in the formation of layered double hydroxides (LD Hs), accompanied from x=0.8 by the boehmite phase. At x=1.8 the spinel phase appears again, having a lattice parameter corresponding to 0.72 Al3+ in the ferrite structure.