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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on SrAs by Materials Project

SrAs crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are two inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded in a 6-coordinate geometry to six As2- atoms. There are two shorter (3.21 Å) and four longer (3.26 Å) Sr–As bond lengths. In the second Sr2+ site, Sr2+ is bonded in a 6-coordinate geometry to six As2- atoms. There are four shorter (3.16 Å) and two longer (3.20 Å) Sr–As bond lengths. There are two inequivalent As2- sites. In the first As2- site, As2- is bonded in a 7-coordinate geometry to six Sr2+ and one As2- atom. The As–As bond length is 2.54 Å. In the second As2- site, As2- is bonded in a 7-coordinate geometry to six Sr2+ and one As2- atom. The As–As bond length is 2.60 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(SrAs)4 by Materials Project

Na(SrAs)4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Na1+ is bonded to five As+2.25- atoms to form NaAs5 square pyramids that share corners with six equivalent SrAs7 pentagonal bipyramids, corners with two equivalent NaAs5 square pyramids, and faces with four equivalent SrAs7 pentagonal bipyramids. There are a spread of Na–As bond distances ranging from 2.99–3.41 Å. There are two inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded in a 6-coordinate geometry to six As+2.25- atoms. There are a spread of Sr–As bond distances ranging from 3.07–3.29 Å. In the second Sr2+ site, Sr2+ is bonded to seven As+2.25- atoms to form distorted SrAs7 pentagonal bipyramids that share corners with six equivalent SrAs7 pentagonal bipyramids, corners with three equivalent NaAs5 square pyramids, edges with two equivalent SrAs7 pentagonal bipyramids, faces with three equivalent SrAs7 pentagonal bipyramids, and faces with two equivalent NaAs5 square pyramids. There are a spread of Sr–As bond distances ranging from 3.18–3.47 Å. There are three inequivalent As+2.25- sites. In the first As+2.25- site, As+2.25- is bonded in a 9-coordinate geometry to two equivalent Na1+, six Sr2+, and one As+2.25- atom. The As–As bond length is 2.54 Å. In the second As+2.25- site, As+2.25- is bonded in a 8-coordinate geometry to one Na1+, six Sr2+, and one As+2.25- atom. In the third As+2.25- site, As+2.25- is bonded in a 8-coordinate geometry to one Na1+ and seven Sr2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Impact of an SRA (hexylene glycol) on irreversible drying shrinkage and pore solution properties of cement pastes

Cementitious materials shrink when exposed to decreasing relative humidities, which may result in cracking. Shrinkage reducing admixtures (SRAs) can be used to reduce this drying shrinkage. Although many studies have shown that SRAs reduce the surface tension of the pore solution, the effects of SRAs on other pore solution properties and their relationship to drying shrinkage have been poorly characterized. In this work, we investigate the impact of an SRA (hexylene glycol) on the drying and re-humidification of a cement paste over an extended relative humidity range. The reduction in the first drying shrinkage by the SRA depends on relative humidity. The SRA also significantly reduces the irreversible drying shrinkage. We concluded that the SRA impacts drying shrinkage by acting on the capillary forces, by acting on the specific range of relative humidity over which those forces occur, and potentially by acting on the surface stresses through pore wall adsorption.

36 MATERIALS SCIENCE↗