Impact of Micro Silica Surface Hydroxyl Groups on the Properties of Calcium Silicate Products

Sonja Haastrup, Bianca Jørgensen, Donghong Yu, Yuanzheng Yue

Research output: Contribution to book/anthology/report/conference proceedingArticle in proceedingResearchpeer-review

Abstract

Porous calcium silicates are widely used in insulating systems for high temperature applications. In the production of porous calcium silicates, quicklime and micro silica have been utilized as key raw materials. In the reaction between SiO2 and CaO, the dissolution of SiO2 has been proven to be the limiting step, and therefore large SiO2 surface area is desired. However, other SiO2 surface structure, such as surface impurities (metal ions) and hydroxyl groups might also influence the reaction. In this work, we investigate the influence of micro silica surface hydroxyl groups in the synthesis of calcium silicate. We increase the hydroxyl groups by dispersing the micro silica in 10wt% H2O2 (CS10%), and we remove the hydroxyl groups by drying the micro silica at 650°C and then disperse it in water (CS650). A reference sample is also prepared from as-received micro silica dispersed in water (CSref.). We find that the micro silica dispersed in 10% H2O2 decrease in average sizes, while the silica heated to 650°C increase the average sizes, compared to the as-received micro silica dispersed in demineralized water. From X-ray diffraction, we find that the crystal phase xonotlite does not change for sample CS10% and the crystal phase tobermorite increase compared to CSref. Sample CS650 is mainly composed of Ca(OH)2 after reaction, and hardly any xonotlite and tobermorite crystal phase found. The compressive strength is found to increase for CS10%. The linear shrinkage also increases, which is caused by the increase in tobermorite crystal structure. H2O2 increase the micro silica surface area, and the number of hydroxyl groups on the micro silica surface. By removing hydroxyl groups from the silica surface, we tremendously decrease the surface area and the reactivity of micro silica. The results show that the hydroxyl groups play an important role in the reaction between micro silica and quicklime.
Original languageEnglish
Title of host publicationSupplier Industries enabling refractories
Number of pages3
Place of PublicationAachen
PublisherECREF European Centre for Refractories gemeinnützige GmbH
Publication date18 Oct 2017
Pages222-224
Chapter9
ISBN (Electronic)978-3-9815813-3-1
Publication statusPublished - 18 Oct 2017
EventInternational Colloquium on Refractories - Eurogress Aachen, Aachen, Germany
Duration: 18 Oct 201719 Oct 2017
http://www.ecref.eu/index.php?id=tagungen&L=1

Conference

ConferenceInternational Colloquium on Refractories
LocationEurogress Aachen
CountryGermany
CityAachen
Period18/10/201719/10/2017
Internet address

Cite this

Haastrup, S., Jørgensen, B., Yu, D., & Yue, Y. (2017). Impact of Micro Silica Surface Hydroxyl Groups on the Properties of Calcium Silicate Products. In Supplier Industries enabling refractories (pp. 222-224). ECREF European Centre for Refractories gemeinnützige GmbH.