Relationship Between Structure and Glass Transition Temperature in Low-silica Calcium Aluminosilicate Glasses: the Origin of the Anomaly at Low Silica Content

Chitosan-silica (CSSi) hybrid films have been fabricated by sol-gel process using tetraethoxysilane (TEOS) as precursor. The structure of the resulting hybrid has been characterized by Fourier transform infrared spectroscopy (FTIR). Fracture surface has been revealed through a field emission-scanning electron microscopy/energy dispersive spectrometer (FE-SEM/EDS) to probe the dispersion degree and the size ofSiO2particle. Study of morphology using a SEM micrograph and the High Resolution Transmission Electron Microscopy (HRTEM) images of the nanocomposite films suggests that theSiO2nanoparticles are within the range of 2–7 nm in diameter and are uniformly dispersed in the polymer matrix. Thermal properties of these composite materials have been studied as a function of silica, indicating that thermal stability of the chitosan film is enhanced. Dynamical mechanical thermal analysis (DMTA) has been carried out to measure the shift in the glass transition temperature (Tg) of the composites from the maxima of theαtransition curves. The glass transition temperature and the storage modulus show an increase with increasing silica content. The maximum increase in theTgvalue, that is,159.37∘C,is seen with 30 wt% silica. A gradual increase of 3.0 GPa in the modulus relative to the pure polymer is observed.

Download Full-text

New casting glass technique through the use of geopolymers

MATEC Web of Conferences ◽

10.1051/matecconf/201927403004 ◽

2019 ◽

Vol 274 ◽

pp. 03004

Author(s):

Jorge Duran-Suarez ◽

Maria-Angeles Villegas ◽

Rafael Peralbo-Cano ◽

Joâo Castro Gomes

Keyword(s):

Glass Transition ◽

Transition Temperature ◽

Glass Transition Temperature ◽

Water Glass ◽

Silica Content ◽

Mechanical Resistance ◽

Glass Waste ◽

Recycled Glass ◽

Heat Treated ◽

High Temperature Processing

By using silicate inorganic binders and glass waste (colourless or coloured) it is possible to mould technical and artistic elements, which later can be hardened by means of high temperature processing. This procedure is controlled by both the glass transition temperature of binder and of glass waste used as aggregate. "water glass", catalysed with sodium hydroxide was used as a binder of glass shards from common industrial bottles, classified to a grain size distribution below 2 mm. Chemical analysis shows similarity of silica content between binder and aggregates of recycled glass, establishing as main differences in the percentages of chromophore oxides. In addition dilatometry curves of the two materials show close glass transition temperature values (575 and 598 °C, respectively), fact that facilitates sintering between binder and aggregates. The non-heat-treated samples present good compactness and mechanical resistance values, improved with heat-treatment at 700 °C. The high compactness of heated samples, showing rounded aggregate grains and softening of binder could let a good way for obtaining well-consolidated technical elements, made of recycled glass. From this test, it would be possible to use thermal ranges between 550 and 600 °C, as well as shorter exposure times for a proper hardening.

Download Full-text