Current Science Activities

Cements and Concretes are such a fundamental part of the infrastructure that it is tempting to overlook the complex and fascinating chemistry involved in their production and use. MTDATA is well suited to modelling their behaviour as long as thermodynamic databases are available for the various liquid and crystalline phases present. One example relates to Portand cements where the database developed at NPL for a very wide range of oxide systems has been used for the calculation of phase equilibria in order to understand aspects of their processing and production. For further information click here.

The database had been used previously to model the potential interaction between the core of a nuclear reactor and the concrete containment in a simulation of the chemistry associated with core meltdown. For further information click here.

More recent work has been concerned with the development and testing of thermodynamic models for calcium silicate hydrate (C-S-H) gels. The engineered component of a low and intermediate level nuclear waste repository in the United Kingdom will almost certainly consist primarily of ordinary Portland cement (OPC) based materials. OPC provides a chemical barrier by its ability to buffer the pH to be higher than about 12 as it dissolves in a percolating groundwater. A high pH in a repository is desirable because it helps to minimize the solubility of many radionuclides, metal corrosion and microbial activity. Reliable models are required in order to assess the likely performance of the chemical barrier and to make predictions beyond the spatial and temporal limits imposed by experiment and observation.The ability of the model to predict the thermodynamic and phase behaviour of C-S-H gels in different aqueous environments, from room temperature up to 85 °C, has been demonstrated by means of a comparison between calculations and measured solubility data, such as pH and calcium and silicon concentrations in solution. For further information click here.

Solders

NPL has participated actively in the development of a thermodynamic database for lead free solders as part of the COST531 European Action. Version 3.0 of the database has just been released to participants. As a result of the scientific work carried out under COST531 two volumes are being published, the first being an Atlas of Phase Diagrams for Lead-Free Soldering by A T Dinsdale, A Watson, A Kroupa, J Vrestal, A Zemanova and J Vizdal, and the second being a Handbook of properties of Lead-Free Solders and Joints by C Schmetterer, H Ipser and J Pearce. The COST531 thermodynamic database is now available for release commercially as a SOLDERS database with the major software platforms for the calculation of phase diagrams. For the scope of the database, please click here. For further information please contact Alan Dinsdale.

NPL is also participating in the development of the thermodynamic database for a new European COST Action concerned with High Temperature Lead Free Solders (MP0602, HISOLD). The aim of this Action is to increase the basic understanding of alloys that can be used as Pb-free alternatives to high temperatures currently exempt from legislation. Such materials would have application in for example aerospace and automotive industries.

NPL has also been collaborating with Loughborough University in the use of thermodynamic data for solders in modelling the reactions at the interface between solders and substrates. This has resulted in the development of a computational interface between MTDATA and MATLAB/ COMSOL Multiphysics to provide a methodology for sophisticated combined thermodynamic / kinetic modelling. For further information click here.

Ionic Liquids

Ionic liquids form potentially the basis of a new industrial technology that could revolutionalise chemical processing as well as impact on many other industries. NPL is supporting effective adoption of this innovative technology by developing and improving physical property characterisation in the context of measurement and modelling of the thermodynamic properties of phase equilibria of ionic liquids.

Data for oxides

NPL is developing a comprehensive thermodynamic database for oxide systems. Together with MTDATA it can be used to give an in-depth understanding of materials and process optimisation problems faced by industry, involving interactions between different types of material, such as slags, mattes, ceramics, glasses, cements and minerals as well as gases and aqueous solutions. The project is support by a number of industrial partners.

Data for elements

The maintenance of standard reference data for the elements has, for a number of years, been an important part of NPL activities. This is carried out in close collaboration with other members of SGTE. The initial outcome of this work was a publication of data for 78 elements in their condensed phases in CALPHAD (A T Dinsdale, CALPHAD, 1991, 15(4), 317-425). This source has since become widely adopted in the international community as the basis for the critical assessment of thermodynamic data for a wide range of materials.

The so-called unary database has been updated continously and is available in version 4.4. A new publication is being prepared to represent the contents of this database.

Current work is underway to make use of a "two-state" model to represent the properties of the liquid phase below the melting point. This is being tested out on a number of metals and will be the subject of a presentation at the forthcoming conference "Thermodynamics of Alloys" to be held in Krakow in June 2008.

A compliation of data for the molar volumes and expansivities of the elements is also in preparation.

General database development

NPL manages the main Solution Database on behalf of SGTE.

Ab-initio calculations

Over the last thirty years or so the availability of exerimental equipment to measure thermodynamic properties and the number of people to use such equipment have declined dramatically. This period has also seen a dramatic increase in the speed and power of computers, and the development of quantum mechanical software to undertake ab-initio calculations. This means that, in principle, the gaps left from the reduction in experimental capability can start to be filled. NPL is currently involved in attempting to validate these techniques against the best available experimental and critically assessed thermodynamic data for gaseous and condensed phases. NPL is aiming to work with existing users of such software and software developers to identify and understand any glaring discrepancies.

Statistical Mechanics

Software for the calculation of thermodynamic properties of gas phase species from molecular constants, although used widely in developing data for standard publications such as JANAF and TCRAS, are not readily available. NPL is developing such software and has just released a free standalone version for sympathetic use. In the future this capability will be include within MTDATA Studio. Please click here for screenshots of the software and further information.

Thermophysical and thermodynamic properties of Ni base superalloys

NPL is currently involved in various projects which require the development of a thermodynamic database for Ni base superalloys. The main vehicle for this is in support of the development of a capability at NPL to measure accurately temperatures and enthalpies of transitions for high temperature materials using a single pan technique. The database development also supports a Technology Strategy Board project "Improved Modelling of Material Properties for Advanced Power Plant" which has the ultimate aim of developing new improved materials and increase the utilisation of power plant through a better understanding of degradation mechanisms. This will be achieved through integration of various material modelling techniques from nano scale through to macro scale. This work also feeds into the IMPRESS European FP6 project concerned with the development of new intermetallic alloys for industrial applications such as gas turbine blades and hydrogen fuel cells. Ultimately the thermodynamic database will be available commercially in conjunction with MTDATA and the Virtual Measurement System.

Thermophysical and thermodynamic properties of Mg alloys

In support of a related project on measuring thermophysical properties for lightweight alloys, NPL is also developing a thermodynamic database for Mg alloys.

Computational Fluid Dynamics

NPL is currently investigating methods of linking software for the calculation of materials chemistry (such as MTDATA) to third party CFD (Computational Fluid Dynamics) packages in order to study systems where there are significant temperature and concentration gradients.

Molecular Dynamics

Molecular Dynamics, in principle, provides a mechanism for calculating thermodynamic properties from force field data. NPL is looking into methods where this could be applicable in order to provide data where experimental data are lacking or difficult to obtain eg developing equations of state for real gases or measurement of the enthalpies of mixing in ionic melts.

Modelling Heat Transfer with Phase Changes

NPL is currently involved in linking MTDATA to another NPL software package Thermol 3D to provide a powerful system of capable of modelling transient heat transfer.

Updated 1 March 2010