Structural elucidation of synthetic calcium silicates

Abstract

A series of synthetic calcium silicates has been produced comprising nano-sized plates. The starting calcium silicate referred to as nano-structured calcium silicate, NCS, appears itself X-ray amorphous but contains impurities of calcite. These impurities decompose during the dry thermal conversion of the material into wollastonite. NCS can be enriched with calcium or silicon, respectively. The silicon enriched NCS can be hydrothermally transformed into a sheet material related to Ca7Si16O38(OH)2. The X-ray pattern of this material was sufficient to allow the calculation of its unit cell with a comparatively high figure of merit. The calcium enriched NCS can form two very distinctly different ceramic materials upon hydrothermal treatment, one a band material (formed below 200 °C) and the other a rose petal shaped material (formed above 210 °C). The X-ray diffraction patterns could not be resolved. The fit between the observed and calculated patterns was less than 50% as expressed in comparatively low figures of merit (unusually <20), which is attributed to calcium carbonate impurities in the samples disrupting the long range order. The patterns of these calcium enriched samples could be best compared to those of tobermorite or truscotite.

Nano-structured calcium silicate hydrate functionalised with iodine

“…The properties of NCaSilH samples were in the range expected for this class of materials regarding their surface area, oil sorption, elemental composition, and particle size [24]. Details are available on request and match those reported in the literature [23][24][25][26].…”

“…13). Only at temperatures above 720°C (973 K), when the NCaSilH structure itself breaks down [25,26], all iodine was released. Fig.…”

“…After this the slope of both release graphs leveled slightly, with the TGA showing a step at approximately 360°C (633 K), attributed to the carbonisation (confirmed optically and through analysis of the gases released) of the spacer compound 2-ethoxyethanol (see Section 1). The next step in the TGA at approximately 720°C (973 K) was attributed to the crystallisation of nano-structured calcium silicate hydrate to wollastonite [25,26]. This crystallisation coincided with a drastic reduction in surface area (>500-25 m 2 g À1 ).…”

“…Nano-structured calcium silicate hydrate comprises nano-sized plates forming a very porous structure [23][24][25][26]. The backbone of the plates is formed by silicate tetrahedra, as established by 29 Si nuclear magnetic resonance, linked together by sharing two oxygen atoms in an ionosilicate-type chain similar to wollastonite in terms of its short range order [25,26] The surface of the silicate plates is covered in silanol groups and calcium ions, which can react with each other on drying, collapsing the structure [24].…”

“…The backbone of the plates is formed by silicate tetrahedra, as established by 29 Si nuclear magnetic resonance, linked together by sharing two oxygen atoms in an ionosilicate-type chain similar to wollastonite in terms of its short range order [25,26] The surface of the silicate plates is covered in silanol groups and calcium ions, which can react with each other on drying, collapsing the structure [24]. To prevent this, the silicate can be modified in a reinforcement process, by acid treatment or reaction with a spacer compound.…”