Mineralogy of clay raw material from Burkina Faso and Niger used for ceramic wares

Some clay deposits in West Africa provide raw materials for the local and traditional manufacture of ceramic products. We selected three clays in Burkina Faso, with the references ROG, GRI and POT and a fourth one, AKN1 in Niger. These clays have been mined for many years. There is growing demand for such materials and the reserves are sufficient to meet this demand. The ROG and GRI clays are used as construction materials in both fired and unfired bricks. The POT and AKN1 clays are used for producing the porous ware of fired pottery. A study was carried out to look at some of the physico–chemical characteristics of these raw materials in order to enhance their use. This is a preliminary study which will be followed by further investigations into the production of different ceramic wares. An analysis of the chemical and mineralogical composition of the materials and some investigations of their fired properties during a firing cycle up to 1000°C has demonstrated that, taken as a whole, they possess satisfactory characteristics for the described applications.     

Sintering of a clay from Burkina Faso by dilatometry Influence of the applied load and the pre-sintering heating rate

The sintering of a pottery clay from Burkina Faso was studied as a function of the heating rate, at 3 or 10°C/min. The experimental method used was loading dilatometry in isothermal conditions at 1120°C. In these conditions, we found that the densification rate of the material is low, but tend to a limiting value after 2 h at 1120°C, depending on the pre-sintering heating rate and the load used. The relationship between the pre-sintering heating rate and the densification rate indicated the existence of a weakly organised material at higher heating rates. Nevertheless, higher values of shrinkage were observed when the temperature increased continuously. It is, therefore, proposed that the material is subject to a preferential solid state diffusion mechanism at face to face of the remaining kaolinite layers at high temperatures. This mechanism is favoured by higher heating rates, mainly in the temperature range corresponding to the structural reorganisation of the metakaolin phase.     

A conservative finite difference scheme for Poisson–Nernst–Planck equations

A macroscopic model to describe the dynamics of ion transport in ion channels is the Poisson–Nernst–Planck (PNP) equations. In this paper, we develop a finite-difference method for solving PNP equations, second-order accurate in both space and time. We use the physical parameters specifically suited toward the modeling of ion channels. We present a simple iterative scheme to solve the system of nonlinear equations resulting from discretizing the equations implicitly in time, which is demonstrated to converge in a few iterations. We place emphasis on ensuring numerical methods to have the same physical properties that the PNP equations themselves also possess, namely conservation of total ions, correct rates of energy dissipation, and positivity of the ion concentrations. We describe in detail an approach to derive a finite-difference method that preserves the total concentration of ions exactly in time. In addition, we find a set of sufficient conditions on the step sizes of the numerical method that assure positivity of the ion concentrations. Further, we illustrate that, using realistic values of the physical parameters, the conservation property is critical in obtaining correct numerical solutions over long time scales.     

A new thermal performance index for dwelling roofs in the warm humid tropics

This research aims to find a scientific rating scheme for roof system for the warm humid tropics. The overall air-to-air thermal transmittance (U-value) or thermal resistance (R-value) of roof are most widely used properties, but these are based on steady-state heat conduction and do not respond to changing conditions of climate, design and comfort needs. The paper presents a new thermal performance index, which is based on thermal comfort and actual thermal performance of a roof design option. It provides a basis for identifying the optimum roof design for unconditioned and acclimatised regimes. A review of the acceptable limits of ceiling surface temperature is presented. The mathematical modelling for predicting performance of roof based on admittance procedure and derivation of thermal performance index is described. In the proposed scheme the galvanized iron roof is given 0% rating and the roof satisfying the comfort needs for the given climate is rated as 100%. Illustrative examples of built roofs or design options are taken from India and Australia. It clearly shows that the roofs with the highest thermal resistance are not necessarily optimum solutions.