Gas pressure and temperature measuring system (GTM) for in-situ data acquisition during planetary ball milling

Up to now physical and chemical processes taking place during milling of powders are mostly unknown. Information about mixing, degree of activation, amorphization and phase transformation or changes in particle size occurring during milling are obtained only gradually by analyses of the milled powders. These investigations have to be carried out with specimens outside the mill. In this case the state of powder is normally not exactly the same as in the running milling process. Therefore the FRITSCH GmbH, (Idar-Oberstein/ Germany) in co-operation with the Fraunhofer-institute for Applied Materials research, Department for Powder Metallurgy and Composite Materials (Dresden/ Germany) developed the GTM-measuring system allowing to receive data about progress of milling. The basic idea of the novel measuring system is the quick and continuous determination of temperature and pressure during the whole milling process. Measuring the temperature of the milling container describes only the `integral' temperature as a result of all processes occurring during milling (grinding-, impact- and phase transformations processes). The huge heat capacity of both the container and the balls compared with the mass of the powder smear the calorical effects. A continuous and sensitive measurement of gas pressure inside the milling vial is carried out in order to measure very quickly and detect small temperature changes. The measured gas pressure includes not only information about the temperature increase arising from friction, impacts and phase transformations but also the interaction of gases with the surfaces formed during milling (adsorption and desorption of gases) under consideration of the total volume of the powder (solution and release of gases during milling). The influence of temperature on the gas pressure can be regarded through the measurement of the basic heating of the system.