Investigation of the Transition Reaction of Tobermorite to Xonotlite under Influence of Additives

Abstract

The objective of the present work was to investigate the transition reaction of the calcium silicate hydrate tobermorite into xonotlite under influence of additives. Tobermorite is the main binding agent in steam hardened building materials and the appearance of xonotlite indicates the progress of hardening and an overcuring of the material. Hydrothermal experiments under addition of sucrose, calcium formate and calcium chloride dihydrate to the main components quartz and lime were done using temperatures of 220˚C and a reaction time of 40.5 h. All experiments were performed with powders as well as with pressed educts. The products of all syntheses were analyzed with XRD, SEM/EDX and FTIR. The references as well as the syntheses with calcium chloride dihydrate led to the formation of 11 Å tobermorite and xonotlite. The former showed the best results and even synthesis with pressed educts and calcium chloride dihydrate revealed an accelerating effect of the additive. In contrast syntheses with sucrose had the worst reactivity and led to the formation of calcite beside the CSH-phase scawtite. The additive calcium formate was only slightly oppressing the crystallization of tobermorite and favouring the formation of xonotlite. Syntheses with pressed pellets and sucrose or calcium formate showed generally worse results.

Room-temperature adsorption behavior of cesium onto calcium silicate insulation

“…Among these groups of the bands, we observed the shift of vibrational mode occurred by the interaction with Cs + on the silicate tetrahedral second intense absorption with wavenumber of 550-400 cm -1 . This is the O-Si-O deformation or bending mode (Yu et al, 1999;Mostafa et al, 2009;Hartmann et al, 2015). Initially, in sample without Cs loading, this mode has a sharp peak at 462 cm -1 and a shoulder at 456 cm -1 (black line), which the absorbance intensity difference between them is about 60%.…”

Synthesis and Structural Characterization of CSH-Phases in the Range of C/S = 0.41 - 1.66 at Temperatures of the Tobermorite Xonotlite Crossover

“…Both clearly show the impurities of calcite in the sample. OH-vibrations (3618 cm −1 ) in the spectrum of the synthetic sample 1.3ab belong to xonotlite (small amounts) [1] [7].…”

“…Ca-rich phases crystallize at first during the hydrothermal process, e.g. α-C 2 SH, followed by the amorphous gel-like CSH-II [5]- [7]. Thereon the crystalline CSH-I occurs.…”

“…Thereon the crystalline CSH-I occurs. The next step is the formation of band-like crystals of 11 Å tobermorite and long needles of xonotlite [2] [7]. The final phase is gyrolite with hexagonal plates [2].…”

“…Below 100˚C xonotlite transforms into tobermorite. Usually temperatures tight above 200˚C yield to xonotlite crystals of proper quality [5]- [7]. An early structural investigation was performed by Mamedov and Belov (1955) [13] and later by Kudoh and Takeuchi (1979) [14].…”