The fluoride ion is crystal chemically very similar to the hydroxyl ion, substituting for hydroxyl in many minerals in which hydrogen bonding is not important. Fluoride substitutions are particularly common in 2:1 layer silicates, such as micas, illites and smectites. The brick and tile industries, which use naturally occurring clays as their primary raw materials, have devoted considerable effort to understanding fluorine evolution during firing of the raw materials due to increasingly stringent fluorine emission regulations. In order to understand fluorine evolution from ceramic raw materials, we have studied a number of phyllosilicate materials used in making bricks. X-ray powder diffraction and fluorine analyses were combined with heating experiments and thermogravimetric analysis to evaluate the chemical and structural changes taking place on heating. Fluorine remained in 2:1 layer silicates to higher temperatures than did hydroxyl, but it behaved identically to hydroxyl in the kaolinite studied. In all cases, fluorine evolution coincided with structural breakdown of the clay host. These results show that fluorine evolution will consistently occur during firing of clay raw materials, and the problems of fluorine emission cannot be readily solved by simple variations of firing temperatures or times.

This paper studies the combinatorics of lattice congruences of the weak order on a finite Weyl group $W$, using representation theory of the corresponding preprojective algebra $\unicode[STIX]{x1D6F1}$. Natural bijections are constructed between important objects including join-irreducible congruences, join-irreducible (respectively, meet-irreducible) elements of $W$, indecomposable $\unicode[STIX]{x1D70F}$-rigid (respectively, $\unicode[STIX]{x1D70F}^{-}$-rigid) modules and layers of $\unicode[STIX]{x1D6F1}$. The lattice-theoretically natural labelling of the Hasse quiver by join-irreducible elements of $W$ is shown to coincide with the algebraically natural labelling by layers of $\unicode[STIX]{x1D6F1}$. We show that layers of $\unicode[STIX]{x1D6F1}$ are nothing but bricks (or equivalently stones, or 2-spherical modules). The forcing order on join-irreducible elements of $W$ (arising from the study of lattice congruences) is described algebraically in terms of the doubleton extension order. We give a combinatorial description of indecomposable $\unicode[STIX]{x1D70F}^{-}$-rigid modules for type $A$ and $D$.

The gamma-ray exposure build-up factors of raw materialsof bricks (soils and fly-ashes) in the state of Punjab were investigatedfor the photon energy range 0.015 to 15 MeV up to 40 mfp penetrationdepth by the geometrical progression (GP) method. Appreciable variationsin the exposure build-up factor (EBF) are noted for the raw materials.The EBFs of the raw materials of bricks change depending on thephoton energy, penetration depth and chemical composition. The build-up factorsare low at low and high photon energies, whereas they are very highin the medium-energy region. The peak energy of the EBF for soilsis 0.3 MeV and 0.2 MeV for fly ashes. The EBFs of the raw materialsof bricks are also compared with those of bricks of red mud andcommon brick materials. Common bricks were found to have the lowestgamma-ray EBF. This study should be useful for emergency preparednessplanning and emergency dose estimation for future planned nuclearpower plants in the state of Punjab.