The rheology of collapsing zeolites amorphized by temperature and pressure

Abstract

Low-density zeolites collapse to the rigid amorphous state at temperatures that are well below the melting points of crystals of the same composition but of conventional density. Here we show, by using a range of experimental techniques, how the phenomenon of amorphization is time dependent, and how the dynamics of order-disorder transitions in zeolites under temperature and pressure are equivalent. As a result, thermobaric regions of instability can be charted, which are indicative of polyamorphism. Moreover, the boundaries of these zones depend on the rate at which temperature or pressure is ramped. By directly comparing the rheology of collapse with structural relaxation in equivalent melts, we conclude that zeolites amorphize like very strong liquids and, if compression occurs slowly, this is likely to lead to the synthesis of perfect glasses.

Amorphization Induced by Pressure: Results for Zeolites and General Implications

“…First of all, our results strongly support the existence of the LDA phases reported by Greaves et al [6]. Two of the considered zeolites (all-SiO 2 and Na-A) present an LDA phase, which supports the claim that such phases are common.…”

“…Such defects are predicted to occur at about 5 GPa in Na-ZK4 and Na-A, which is consistent with experimental data [6,7], and only above 11 GPa in all-SiO 2 . The Na cations, on the other hand, impede the collapse of the rings at whose centers they are located; i.e., there is no formation of new Si-O bonds between atoms on opposite sides of Nahosting rings.…”

“…Recent work [6] on the nanoporous aluminosilicates known as zeolites has renewed the interest in PIA. It was shown that a zeolite may present two distinct PIA phases: a low-pressure ( 2 GPa) low-density amorphous phase (LDA), which might constitute a ''perfect'' glass with negligible configuration entropy, and a high-pressure ( 6 GPa) high-density amorphous phase (HDA).…”

The Influence of the Framework and Extraframework Content on the High Pressure Behavior of the GIS Type Zeolites: The Case of Amicite

“…Details of the structural refinements are reported in Table 1. 4.71 GPa. The projection of the structure at P amb (rev) is not reported, this being virtually identical to that at P amb .…”

“…For instance, among the physical properties of microporous materials investigated under compression, worthy of mention are: the so called P-induced amorphization processes (PIA) (e.g., [1][2][3][4][5][6]), the effect of pressure on the ionic conductivity (e.g., [7,8]), the P-induced over-hydration (PIH) (e.g., [9][10][11][12][13][14]) and the penetration of gas, like Ar, Xe, and CO 2 [15][16][17]. High pressure experiments on porous materials have recently led to the synthesis of linear carbon based polymers in pure silica zeolites.…”