- Indian Journal of Engineering& MaterialsSciences Vol. 5, December 1998, pp. 343-346.l Particle size determination: Viscosity study Kinnari Parekh, R V Upadhyay & R V Mehta Department of Physics, Bhavnagar University, Bhavnagar 364 002, India Received 6 February 1998; accepted 16September 1998.Magnetic and rheologicalpropertiesof the laboratory synthesized three different magneticfluids are reported. Using log-normal size distribution the magnetisation data were fitted and the pat:ticle size, domain rnagnetisation and the size distribution are obtained. The particle size were also determined from the viscosity measurement and it was found thatthe sizecorresponds to the mediandiameter of the numberdistribution. The effect of polydispersity on the viscosityis also discussed. The particle size and its distribution play an im- is same as a peak size of tJIe log-normal volume portant Tole to determine the various physical and distribution function. magnetic properties of the magnetic fluid. There In the present paper, the results obtained from are various techniques to determine the size of viscosity measurement for three different fluids particles, like, X-ray, magnetisation. viscosity, etc., prepared in kerosene having particles of (i) Mn-Zn but each experiment measures different aspect of (50%) ferrites, (ii) Mn-Fe (50%) ferrites and (iii) the particle size: a solid content, a magnetic con- Fe-Zn (50%) ferrites have been reported. tent and an equivalent hydrodynamic size which includes the effect of surfactant coatings. If a sys- Experimental Procedure ; tern is a mono-dispersed, the particle size obtained Preparation of magnetic fluids-The standard from viscosity will be greater than that obtained co-precipitation technique has been used to prepare from magnetisation measurement. But a magnetic the fine magnetic particles. The starting materials fluid is a polydispersed system, therefore, to de- of GPR grades, FeC13 6H2O, MnC12 4H2O, ZnSO4 termine the particle size distribution, one has to 7H2O and FeSO4 7H2O were used to obtain ions of consider various size distribution functions and Fe3+, Mn2+, Zn2+and Fe2+in an aqueous solution. choose the one which gives the best fit to the ob- The detailed procedure and conditions for prepara- served characteristics. For a magnetic fluid the tion of fine particles are given elsewhere2.3. The most widely used function is a log-normal distri- particles obtained are then coated with oleic acid bution function which is given as and dispersed in kerosene. The resulting fluids are 1 (In( D/ Dm»2 stable and are liquid at room temperature and solid P(D) dD= exp[ -2] dD below 200K. J(2;)li2o-D 20- ctural characterization-X-ray patterns :. ~l) were recorded on a Philips PW 1130/90 X-ray dif- where, D ~s particle SIze, a IS standard devIatIon fractometer using CuKa. radiation (A = 1.54l4A). and In D'll IS mean of In D. The X-ray diffraction pattern for Mn-Zn, Mn-Fe For a.poly?isperse.d system it wa~ obs~rv~d that and Fe-Zn systems were analysed by X-ray Riet- the particle size obtaIned from the VISCOSIty IS sen- vield refinement programme and it confirms the sitive to the peak size diameter of the log-normal formation of single phase spinel (i.e. fcc with a volume distribution function'. To u~ders~and this space group of Fd3m) structure. The parameters result three kerosene based magnetIc fluIds were derived from the fit are given in Table 1. s~nthe.sjze~. The s~udy reported .here s~ows that Magnetisation measurement-The magnetisa- vIscosity gtves the.slze of the partIcle whIch co~e- tion measurements were carried out using search- sponds to the median diameter of the number dIS- coil method. Fig. 1 shows the reduced magnetisa- tribution of log-normal distribution function which