Community Research and Development Information Service - CORDIS

Characterization of dispersions for process control in the production of particulate magnetic media

Research was carried out in order to help improve the efficiency of producing magnetic media and to expedite the development of new products. Success was achieved in designing and building a new type of rapid rise-time variable pulse-width magnetometer with which to measure the properties of dispersions on time scale below 1 ms and down to approximately 5 µs. At the faster time scales there is not time for the particles to move before their magnetization changes and the measurement therefore gives a kind of 'flash picture' of the momentary state of the dispersion. The longer time scales approach those found in certain orienting systems and thus provide design information for those systems. The ability to distinguish stages in the factory dispersion process was demonstrated. By devising an improved theory, the analysis of filter blocking has with success been brought into use in formulation development. An improved form of dispersion magnetometry was found to provide more information. In particular, the monitoring of the kneading stage of new metal particle formulations has been advanced and quantified, and, in parallel the process of orienting such dispersions better understood and improved. The experimental results were used to develop and test the mathematical model. After a Monte-Carlo simulation was unable, because of the difficulty in handling dynamic systems, to simulate laboratory magnetic measurements on dispersions, a molecular dynamics model was produced which gave very good agreement. Putting in the experimental time responses, the model can calculate dynamic processes such as orientation.

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