thermochimica acta ELSEVIER Thermochimica Acta 285 (1996) 325-336 Thermal decomposition of hexahydrated nickel iron citrate N.S. Gajbhiye*, Seema Prasad Department of Chemistry, Indian Institute of Technology, Kanpur 208016 U.P., India Received 30 August 1995; accepted 10 February 1996 Abstract The citrate precursor method has been used to synthesise ultrafine NiFe20 4. The citrate precursor, Ni3Fe60¢(C6H6OT)8-6H20 , was isolated by thermal heat treatment at around 100°C. Thermal decomposition of the hydrated precursor was investigated by TG, DTA and DTG techniques, and gas and chemical analyases. The citrate precursor, on decomposition in air, yields pure and stoichiometric NiFe20 4. The decomposition consists of three major steps. The dehydration step of the citrate precursor is overlapped by the formation of an acetonedi- carboxylate complex. The citrate groups are completely destroyed in the temperature range 200-320°C resulting in the formation of NiFeEO 4 with the evolution of acetone and CO 2 gas. The free CO z gas is trapped in the lattice and is released above 320°C. The ultrafine NiFe204 particles have been observed as clusters having a crystallite size of 5.93 nm and a surface area of 120.0 m 2 g- 1. The citrate precursor and decomposed products were characterized by IR. NMR, XRD, SEM and surface area measurements. Keywords: Citrate; Ferrite; Precursor; Thermal Decomposition; Ultrafine I. Introduction Magnetism of fine particles is of considerable interest from the points of view of basic scientific understanding and technological applications. The preparation of spinel ferrites has been technologically important to the microwave industries for a long time. In the past ten years or so the production of ferrites with small particle characteristics has been important for high speed digital tape or disk recording [1] and has a future application as a repulsive suspension for use in levitated railway systems [2]. This has * Corresponding author. Tel: 0325 296/0325 329; Fax: 512 250260/250007. 0040-6031/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved PII S0040-6031 (96)02906- 1