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Modelling of the static and dynamic properties of tho-type silicates

Cauchi R., Grima J. N.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

2014

Vol. 18, No 1

5--65

Auxetic materials are materials exhibiting a negative Poisson’s ratio in one of their planes. This phenomenon has been studied in various materials. Zeolites are crystalline substances whose structure is characterised by the framework of linked tetrahedra, each consisting of four oxygen atoms surrounding a cation. The resulting interstitial spaces make them efficient for use as adsorbents and molecular sieves, and many studies have been focused on this aspect. Some of these zeolites may exhibit auxeticity at least in one of their planes. THO (and similar systems, such as NAT and EDI) together with the all-silica equivalent of these have been studied extensively via static simulations for their negative Poisson’s ratio in the (001) plane. In this paper a study of the all-silica equivalent of THO has been carried out via both static and dynamic simulations using the same force-field, where the system was subjected to stress along the x direction. The hypothesised semi-rigid mechanism of deformation, proposed by Grima et al. was then projected over this framework. The results obtained confirmed auxeticity along this plane by means of the COMPASS force-field, in both static and dynamic studies and compared well with the proposed mechanism of semi-rigid rotating polygons. It also showed that as the Young’s modulus of this mechanism increases other mechanisms of deformation increase in importance.

Zeolites in Tertiary basaltoids from Rębiszów (Lower Silesia, SW Poland)

Adamczyk Z.

Archiwum Mineralogiczne

2001

T. 54

23-32

Several minerals from zeolite group have been found in Rębiszów basaltoid deposits: gobbinsite, natrolite, gismondine, garronite, thomsonite and phillipsite. For the first time gobbinsite has been recognized in basaltoids from Lower Silesia. Moreover, a new phase has been distinguished on the basis of some determined parameters (such as calculation of chemical formulae and X-ray diffraction patterns), belonging to zeolite group and occurring together with other zeolites. Origin of the whole assemblage of zeolite minerals can be related to hydrothermal activity of post-magmatic solutions within thermal contraction cracks of congealing basaltoid lava.