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6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

A classical molecular dynamics simulation method for the formation of “dry” gels from boro-aluminosilicate glass structures

In contact with water, glass transforms into amorphous and porous structures called gels. A simulation method based on classical molecular dynamics is proposed here to mimic “dry” gels forming from initial oxide glass structures. Six glass compositions were investigated. Two behaviours were evidenced depending on the initial glass composition, and in particular on the quantity of elements removed. If a large quantity of soluble elements (B, Na) was removed, it induced an increase in the average pore size within the gels, and the time needed to stabilise the gel structure increased because more local atomic rearrangements occurred. The gel network displayed a higher proportion of Si-Q4 at the expense of Si-Q3 and a lower average ring size compared to the glass network, irrespective of the glass composition. Surface effects were also highlighted in the dry gels, such as the presence of 3-coordinated Al and a decrease in the average angle Si-O-Si and Al-O-Al. Our findings will be compared to both wet gels and experimental data in further studies, to help find the best procedure to simulate such structures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effects of Al:Si and (Al+Na):Si Ratios on the Properties of the International Simple Glass, Part II: Structure

High-alumina containing high-level waste (HLW) will be vitrified at the Waste Treatment Plant at the Hanford Site. The resulting glasses, high in alumina, will have distinct composition-structure-property (C-S-P) relationships compared to previously studied HLW glasses. These C-S-P relationships determine the processability and product durability of glasses and therefore must be understood. The main purpose of this study is to understand the detailed structural changes caused by Al:Si and (Al+Na):Si substitutions in a simplified nuclear waste model glass (ISG, International Simple Glass) by combining experimental structural characterizations and molecular dynamics (MD) simulations. The structures of these two series of glasses were characterized by neutron total scattering and 27Al, 23Na, 29Si, and 11B solid-state nuclear magnetic resonance (NMR) spectroscopy. Additionally, MD simulations were used to generate atomistic structural models of the borosilicate glasses and simulation results were validated by the experimental structural data. Short-range (e.g., bond distance, coordination number, etc.) and medium-range (e.g., oxygen speciation, network connectivity, polyhedral linkages) structural features of the borosilicate glasses were systematically investigated as a function of the degree of substitution. The results show that bond distance and coordination number of the cation-oxygen pairs are relatively insensitive to Al:Si and (Al+Na):Si substitutions with the exception of the B-O pair. Additionally, the Al:Si substitution results in an increase of tri-bridging oxygen species, while (Al+Na):Si substitution creates non-bridging oxygen species. Charge compensator preferences were found for Si-[NBO] (Na+), [3]B-[NBO] (Na+), [4]B (mostly Ca2+), [4]Al (nearly equally split Na+ and Ca2+), and [6]Zr (mostly Ca2+). The network former-BO-network former linkages preferences were also tabulated; Si-O-Al and Al-O-Al were preferred at the expense of lower Si-O-[3]B and [3]B-O-[3]B linkages. These results provide insights on the structural origins of property changes such as glass transition temperature caused by the substitutions, providing a basis for future improvements of theoretical and computer simulation models.

Lu, Xiaonan↗
DOE OSTI2020

Materials Data on Al2(SO4)3 by Materials Project

Al2(SO4)3 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. there are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six equivalent SO4 tetrahedra. All Al–O bond lengths are 1.89 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six equivalent SO4 tetrahedra. All Al–O bond lengths are 1.90 Å. S6+ is bonded to four O2- atoms to form SO4 tetrahedra that share corners with four AlO6 octahedra. The corner-sharing octahedra tilt angles range from 26–37°. There is one shorter (1.47 Å) and three longer (1.48 Å) S–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one S6+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one S6+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one S6+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one S6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al4SO18 by Materials Project

(Al8O21)2(SO4)4(O2)7 crystallizes in the monoclinic P2_1 space group. The structure is two-dimensional and consists of four oxygen molecules; four sulfuric acid molecules; two trioxidane molecules; and one Al8O21 sheet oriented in the (1, 0, -1) direction. In the Al8O21 sheet, there are eight inequivalent Al sites. In the first Al site, Al is bonded to six O atoms to form a mixture of edge and corner-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles are 33°. There are a spread of Al–O bond distances ranging from 1.89–1.96 Å. In the second Al site, Al is bonded to six O atoms to form distorted edge-sharing AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.85–1.99 Å. In the third Al site, Al is bonded to six O atoms to form a mixture of distorted edge and corner-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles are 36°. There are a spread of Al–O bond distances ranging from 1.84–1.94 Å. In the fourth Al site, Al is bonded to six O atoms to form AlO6 octahedra that share a cornercorner with one AlO5 trigonal bipyramid and edges with three AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.85–1.97 Å. In the fifth Al site, Al is bonded in a 5-coordinate geometry to five O atoms. There are a spread of Al–O bond distances ranging from 1.76–1.92 Å. In the sixth Al site, Al is bonded to six O atoms to form a mixture of distorted edge and corner-sharing AlO6 octahedra. The corner-sharing octahedra tilt angles range from 33–36°. There are a spread of Al–O bond distances ranging from 1.83–1.96 Å. In the seventh Al site, Al is bonded in a distorted rectangular see-saw-like geometry to four O atoms. There are a spread of Al–O bond distances ranging from 1.74–1.82 Å. In the eighth Al site, Al is bonded to five O atoms to form distorted corner-sharing AlO5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 30°. There are a spread of Al–O bond distances ranging from 1.77–1.87 Å. There are twenty-one inequivalent O sites. In the first O site, O is bonded in a bent 150 degrees geometry to two Al atoms. In the second O site, O is bonded in a trigonal non-coplanar geometry to three Al atoms. In the third O site, O is bonded in a distorted trigonal non-coplanar geometry to three Al atoms. In the fourth O site, O is bonded in a trigonal non-coplanar geometry to three Al atoms. In the fifth O site, O is bonded in a water-like geometry to two Al atoms. In the sixth O site, O is bonded in a bent 120 degrees geometry to two Al atoms. In the seventh O site, O is bonded in a water-like geometry to two Al atoms. In the eighth O site, O is bonded in a water-like geometry to two Al atoms. In the ninth O site, O is bonded in a water-like geometry to two Al atoms. In the tenth O site, O is bonded in a water-like geometry to two Al atoms. In the eleventh O site, O is bonded in a bent 150 degrees geometry to two Al atoms. In the twelfth O site, O is bonded in a 2-coordinate geometry to two Al and one O atom. The O–O bond length is 1.53 Å. In the thirteenth O site, O is bonded in a distorted trigonal non-coplanar geometry to three Al atoms. In the fourteenth O site, O is bonded in a 2-coordinate geometry to two Al and one O atom. In the fifteenth O site, O is bonded in an L-shaped geometry to two Al atoms. In the sixteenth O site, O is bonded in a bent 150 degrees geometry to two Al atoms. In the seventeenth O site, O is bonded in a bent 150 degrees geometry to two Al atoms. In the eighteenth O site, O is bonded in a single-bond geometry to one Al atom. In the nineteenth O site, O is bonded in a bent 150 degrees geometry to two Al atoms. In the twentieth O site, O is bonded in a bent 150 degrees geometry to two Al atoms. In the twenty-first O site, O is bonded in a single-bond geometry to one Al atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al(SO6)2 by Materials Project

Al(SO5)2O2 crystallizes in the orthorhombic Pnma space group. The structure is two-dimensional and consists of four oxygen molecules and two Al(SO5)2 sheets oriented in the (0, 0, 1) direction. In each Al(SO5)2 sheet, Al is bonded to six O atoms to form AlO6 octahedra that share corners with four equivalent SO4 tetrahedra. There are a spread of Al–O bond distances ranging from 1.88–1.92 Å. S is bonded to four O atoms to form SO4 tetrahedra that share corners with two equivalent AlO6 octahedra. The corner-sharing octahedra tilt angles range from 42–46°. There are a spread of S–O bond distances ranging from 1.46–1.51 Å. There are five inequivalent O sites. In the first O site, O is bonded in a distorted bent 120 degrees geometry to one Al and one S atom. In the second O site, O is bonded in a single-bond geometry to one S atom. In the third O site, O is bonded in a single-bond geometry to one Al atom. In the fourth O site, O is bonded in a bent 150 degrees geometry to one Al and one S atom. In the fifth O site, O is bonded in a single-bond geometry to one S atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlSO10 by Materials Project

AlSO8O2 is Brookite-like structured and crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four hydrogen peroxide molecules and two AlSO8 clusters. In each AlSO8 cluster, Al is bonded in a 5-coordinate geometry to five O atoms. There are a spread of Al–O bond distances ranging from 1.76–2.17 Å. S is bonded in a tetrahedral geometry to four O atoms. There are a spread of S–O bond distances ranging from 1.44–1.67 Å. There are eight inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one S atom. In the second O site, O is bonded in a bent 120 degrees geometry to one Al and one S atom. In the third O site, O is bonded in a distorted bent 120 degrees geometry to two equivalent Al atoms. In the fourth O site, O is bonded in a single-bond geometry to one S atom. In the fifth O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 1.23 Å. In the sixth O site, O is bonded in a distorted single-bond geometry to one Al atom. In the seventh O site, O is bonded in a distorted bent 120 degrees geometry to one Al and one O atom. In the eighth O site, O is bonded in a distorted single-bond geometry to one S atom.

36 MATERIALS SCIENCE↗