Phase Equilibria Data for Oxide Systems
The materials and process optimisation problems faced by industry tend to be complex in nature, involving interactions between many different types of material, such as slags, mattes, ceramics, glasses, cements and minerals as well as gases and aqueous solutions. This complexity has often stood in the way of the kind of in-depth understanding necessary for successful and efficient process control. Now, through the NPL oxide database, the tools are available for oxide based systems which make such an understanding possible.
The basic principle which underlies these projects is that phase equilibria for multi-component systems can be calculated reliably from critically assessed thermodynamic data for smaller sub-systems using MTDATA, thermodynamics and phase equilibria software from NPL. Models have already been developed and thermodynamic parameters derived for liquid oxides, crystalline solutions and stoichiometric substances within the K2O-Na2O-CaO-MgO-Cu-Fe-O-Al2O3-SiO2-S system with additions of B2O3, CaF2, CoO, Cr-O, Li2O, Nb2O5, NiO, MnO, P2O5, PbO, V2O5, ZnO, ZrO2, PbO, Co-Cu-Fe-Ni-S-O mattes and metallic phases, and dilute solutions of OH-, SO42-, CO32- in selected liquid oxides. Predictions of volume and density changes in the CaO-MgO-Fe-O-Al2O3-SiO2 system are possible and models have been developed to allow viscosities of oxide liquids and critical cooling rates for glass formation to be calculated.
Current work, determined by the wishes of the NPL/MIRO RC192 project's industrial partners, includes increased coverage of CaF2, CoO, Cr-O, Cu-O, NiO containing systems and carbonate capacity modelling, addition of the new oxide TiO2 and extension of the Co-Cu-Fe-Ni-S-O metal / matte system to include Cr and Pb. Complementary work on modelling the electrical conductivity of liquid oxides and the development of a database covering trace elements such as As and Sb in the main oxide system is also planned.
Exploratory work on modelling hydrated phases such as the calcium aluminate silicate hydrate gels important in cement chemistry and their interactions with aqueous solutions of different salinities over a range of temperature has begun. Further work to generate a practical database for use in predictive calculations relating to cements is also anticipated.
Combined with existing data for alloys and gases, the NPL oxide database has already been used successfully to solve problems associated with iron formation in zinc blast furnaces, to assist in the extraction of copper and precious metals, to provide information on liquidus temperatures and primary phases of relevance to glass making, to assess the consequences of a nuclear reactor core meltdown and to model the behaviour of fly ash in coal combustion. The power of this database as a predictive tool will increase still further as its coverage continues to grow.
The project's partners are able to use the existing database to make predictive calculations which are directly relevant to their own particular processes and which cover composition and temperature ranges beyond the scope of paper based phase diagram compilations. The feasibility of more economic and environmentally sound routes can be explored, better choices of materials can be made and experimental and pilot plant studies can be directed more efficiently. In addition, partners will continue to steer the project in terms of the choice of systems to be covered and the priority assigned to each as well as gaining access to the MTDATA calculation software under preferred terms.
For more details of the coverage of these subsets or for more information about the project, please contact John Gisby