and cooled to room temperature the cooled mixture was filtered and washed with di water the wet precursor cake was transferred to a beaker containing washing agent and the mixture was stirred or sonicated until a major portion of water was replaced with washing agent the mixture is divided into three parts part one was filtered and dried in an oven part two was transferred to a beaker and heated to slowly evaporate the agent on a hotplate until it dried the loosely packed powder cake obtained from parts 1 and 2 were ground with pestle and mortar and stored in a separate sample bottles part three was dried with a spray drier agglomerate free spinel nanopowders were obtained after calcination of the hydroxide powder at a temperature between 400 u00b0 c and 1300 u00b0 c in case where soft agglomerates are formed a mild milling is employed to break them into nano powders typically bet surface area of the final spinel powder is in the range of 50 u02dc 200 m 2 g a mixed solution of magnesium sulphate hydrate and aluminum sulphate heptahydrate mg 2 al 3 1 2 was prepared in di water and heated in a beaker the sulphate solution was dropped to a warm ammonia water solution at a constant dropping rate using a peristaltic.