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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Distribution of rare earth elements and other critical elements in beneficiated Pennsylvania anthracites

The Pennsylvania Anthracite Fields are in a complex tectonic and metamorphic terrain, historically hosting one of the largest concentrations of coal mining in the USA. Anthracite mining now largely consists of the surface mining of the pillars remaining from the prime years of underground mining. The geochemical study of the sized coal products and the refuse (largely rock) from three preparation plants (breakers) demonstrates that Principal components analysis (PCA) of select major oxide, minor element, and rare earth elements illustrates some differentiation among the products from the individual plants. The rock samples, with abundant quartz and metamorphic Al-Si minerals and with a lower ash-basis REE concentration than the coals, were distinctly separated from the coal samples on the PCA plots. Plots of Gd N /Gd N * vs. Eu N /Eu N * and Ce N /Ce N * vs. Eu N / Eu N * showed differentiation between the individual suites of coals showed that the refuse samples had distinct REE distributions compared to the associated coals. Further, several minor and trace elements show enrichments in the coal samples. Lithium, with concentrations of up to 314 ppm on an ash basis, is among the most promising of the critical elements, exceeding the enrichment of the REY and Sc.

58 GEOSCIENCES↗
DOE OSTI2023

Study of beyond nearest-neighbor environment and intermediate-range order in a sodium aluminosilicate geopolymer using Reverse Monte Carlo modeling

A large scale three-dimensional structural model of a geopolymer with an approximate composition of NaAlSi 2 O 6 .5.5H 2 O obtained by Reverse Monte Carlo (RMC) modeling based on experimental high-energy x-ray diffraction is presented for the first time in order to obtain information regarding beyond nearest-neighbor environment and intermediate-range order (IRO). RMC model exhibits a three-dimensional network consisting of randomly cross-linked AlO 4 and SiO 4 tetrahedral units with uniformly distributed Na atoms and H 2 O molecules. The bond angle distributions, i.e. T-O-T, O-T-O and Na-O-Na angles, are somewhat distorted with lower values compared to analogous crystal systems. The origin of the first peak in the structure factor indicating IRO is investigated using the partial structure factors; Na-Na, Si-Na, Al-Si, O-H, and H-H atom pairs are found to be the main contributors. Ring size distribution analysis demonstrates that the structure mainly involves 6-, 7- and 8-membered rings. Finally, the coherence length of these IRO characteristics is ~10.3 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Enhanced toughness and tear resistance of thin-walled High-Pressure Die-Cast aluminum alloys through Friction stir processing

In this study, we investigate the toughness and resistance to tear of thin-wall high-pressure die-cast (HPDC) aluminum alloys in two different orientations following the implementation of friction stir processing (FSP). The FSP technique was applied to two different HPDC Al-Si alloys: the recyclable-grade, high iron, A380 alloy and the premium-quality, low iron, Aural-5 alloy. Our findings reveal significant tear resistance and strength enhancements for both alloys after FSP modification. Specifically, FSPed A380 alloy requires 126% higher energy to tear, and it has 49% higher tear strength than the HPDC counterpart. Similarly, the tear energy and tear strength of the Aural-5 alloy witness enhancements of 69% and 21%, respectively. In conclusion, these results highlight the potential of FSP as a viable method for augmenting the mechanical properties of HPDC aluminum alloys, thereby opening up new avenues for their utilization in diverse engineering applications for crack obstruction.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Temperature-dependent formation of gradient structures with anomalous hardening in an Al–Si alloy

The temperature effect on forming gradient structure in an Al-Si alloy during surface severe deformation is studied in this report. The intermediate temperature (473 K) produces the steepest gradient structure by an anomalous hardening on the top layer compared to lower (300 K) and higher temperature (673 K) counterparts. Our analysis shows profuse aluminum oxide particles in the top layer of the gradient structure under 473 K and thus lead to anomalous hardening by oxide-dispersion strengthening. Here, the counterintuitive enhancement of strengthening at the intermediate temperature is explained by the dynamic interplay between thermal-driven, mechanical-aided oxidation and the wear-induced loss of surface materials as a function of temperature, which yields a critical processing temperature to achieve the steepest gradient structure.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effect of tool design and pass strategy on defect elimination and uniform, enhanced tensile properties of friction stir processed high-pressure die-cast A380 alloy

This work reports implementation of friction stir processing (FSP) to locally modify microstructure and create a defect-free processing zone with the aid of different tool designs and altering the passing strategy for two different process parameter combinations. Here, FSP is applied on high pressure die-cast (HPDC) A380 alloy, a widely used Al-Si alloy fabricated in the die casting sector for automotive and aerospace applications. However, the presence of gas and shrinkage porosity, brittle needle-shaped Fe-containing ß-FeSiAl 5 intermetallic compounds, Al-dendrites, coarse and acicular silicon particles, and large second-phase particulates have a detrimental influence on the uniformity of tensile properties across the thickness direction of an HPDC plate. FSP is able to eliminate porosity, refine microstructure and improve tensile properties. An FSP tool design and a passing strategy are identified for the best microstructure consolidation and uniform enhanced tensile properties. This study noted the importance of tool features such as scroll design and flats on tool pin and multiple pass orientation strategy to find best combination of defect-free refined microstructure and uniform tensile strength and ductility across the processing zone of HPDC Al alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Friction stir processing on a strontium modified, thin-wall, vacuum-assisted high-pressure die-cast Aural-5 alloy to improve tensile and fatigue performance

Here, this study explores the application of friction stir processing (FSP) to enhance the material properties of Sr-modified Aural-5 alloy, with a focus on improved tensile and fatigue properties. Aural-5 is a well-known vacuum-assisted high-pressure die-cast (HPDC) Al-Si7-Mg alloy used in the automotive industry to reduce vehicle weight, enhance fuel efficiency, and lower carbon emissions. This alloy modifies its material chemistry with Sr for fine fibrous networks of eutectic silicon and manganese (Mn) to reduce die soldering. It has significantly less iron (Fe) content resulting in the elimination of detrimental needle-shaped Fe-bearing ß-phase intermetallic and improving ductility. The initial microstructure of as-received HPDC Aural-5 exhibits shrinkage porosity in the middle section, a dendritic microstructure with fibrous Al-Si eutectic colonies, a shear-band structure beneath the die-wall, large dendritic externally solidified crystals (ESCs), needle-shaped Mg 2 Si phase and significant second-phase particulates. Some of those microstructural features, such as porosity, ESCs, needle-shaped Mg 2 Si phase, and large second-phase particles, serve as initiation sites for cracks under mechanical loading, resulting in adverse effects on tensile properties, particularly ductility. FSP effectively transforms the microstructure into a wrought configuration with uniform particle distribution by eliminating porosity and disintegrating dendrites, eutectic colonies, ESCs, second-phase particles, and shear-band structures. FSP-driven microstructure modification enhances yield strength and tensile ductility by ~30% and ~35%, respectively. The fatigue life of the material in a bending mode configuration (stress ratio R = 0.1) after FSP exhibits enhancements ranging from 2.0 to 3.9 times that of the original HPDC Aural-5 alloy, depending on the applied stress level.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Corrosion evaluation of Al-Cu-Mn-Zr cast alloys in 3.5% NaCl solution

Corrosion behavior of cast Al-Cu-Mn-Zr (ACMZ) and RR350 alloys was compared to a cast 319 alloy in 3.5 wt.% NaCl. After 168 h immersion, ACMZ and RR350 alloys suffered from preferential attack adjacent to intermetallic particles decorated at grain boundaries while the attack in 319 occurred in eutectic Al-Si dendritic boundaries. Electrochemical data allowed semiquantitative comparison of alloy resistance to corrosion initiation, and ACMZ type alloys, including RR350 and three alloys with higher Cu, were considered more resistant than 319 due to the absence of deleterious Si particles. In case of 319, such Si particles presumably drove higher micro-galvanic influence to initiate and sustain Al corrosion. With lower susceptibility to corrosion initiation, ACMZ alloys should exhibit higher or at minimum similar resistance compared to cast 319.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Microstructure and properties of additively manufactured Al–Ce–Mg alloys

Additive manufacturing of aluminum alloys is largely dominated by a near-eutectic Al-Si compositions, which are highly weldable, but have mechanical properties that are not competitive with conventional wrought Al alloys. In addition, there is a need for new Al alloys with improved high temperature properties and thermal stability for applications in the automotive and aerospace fields. In this work, we considered laser powder bed fusion additive manufacturing of two alloys in the Al–Ce–Mg system, designed as near-eutectic (Al–11Ce–7Mg) and hyper-eutectic (Al–15Ce–9Mg) compositions with respect to the binary L → Al + Al 11 Ce eutectic reaction. The addition of magnesium is used to promote solid solution strengthening. A custom laser scan pattern was used to reduce the formation of keyhole porosity, which was caused by excessive vaporization due to the high vapor pressure of magnesium. The microstructure and tensile mechanical properties of the alloys were characterized in the as-fabricated condition and following hot isostatic pressing. The two alloys exhibit significant variations in solidification structure morphology. These variations in non-equilibrium solidification structure were rationalized using a combination of thermodynamic and thermal modeling. Both alloys showed higher yield strength than AM Al-10Si-Mg for temperatures up to 350 °C and better strength retention at elevated temperatures than additively manufactured Scalmaloy.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Atomistic study of silicon alloying in the spallation behavior of nanocrystalline aluminum systems

Here, the effect of concentration of the alloying element silicon (Si) on the shock and spall response of aluminum (Al) is studied using classical molecular dynamics (MD) simulations. Silicon is distributed as individual grains and as grain boundaries and the dynamic response under shock is studied for an impact velocity of 1000 m/s. A general trend observed here is that the spallation is almost exclusively intergranular and limited to Al-Si interfaces. The spall strengths are observed to a) decrease with an increase in alloying of Si as grains and b) show little increase for up to 50% grain boundary segregation. An increase in grain size of the whole system showed negligible differences in spall strength, highlighting the significance of concentration of the alloying species rather than its grain size. These results provide an atomistic understanding of light-weight metallic systems under shock compression and pave the way for designing multiphase metal matrix alloys and composites for defense/armor applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Process-dependent anisotropic thermal conductivity of laser powder bed fusion AlSi10Mg: impact of microstructure and aluminum-silicon interfaces

Purpose AlSi10Mg alloy is commonly used in laser powder bed fusion due to its printability, relatively high thermal conductivity, low density and good mechanical properties. However, the thermal conductivity of as-built materials as a function of processing (energy density, laser power, laser scanning speed, support structure) and build orientation, are not well explored in the literature. This study aims to elucidate the relationship between processing, microstructure, and thermal conductivity. Design/methodology/approach The thermal conductivity of laser powder bed fusion (L-PBF) AlSi10Mg samples are investigated by the flash diffusivity and frequency domain thermoreflectance (FDTR) techniques. Thermal conductivities are linked to the microstructure of L-PBF AlSi10Mg, which changes with processing conditions. The through-plane exceeded the in-plane thermal conductivity for all energy densities. A co-located thermal conductivity map by frequency domain thermoreflectance (FDTR) and crystallographic grain orientation map by electron backscattered diffraction (EBSD) was used to investigate the effect of microstructure on thermal conductivity. Findings The highest through-plane thermal conductivity (136 ± 2 W/m-K) was achieved at 59 J/mm 3 and exceeded the values reported previously. The in-plane thermal conductivity peaked at 117 ± 2 W/m-K at 50 J/mm 3 . The trend of thermal conductivity reducing with energy density at similar porosity was primarily due to the reduced grain size producing more Al-Si interfaces that pose thermal resistance. At these interfaces, thermal energy must convert from electrons in the aluminum to phonons in the silicon. The co-located thermal conductivity and crystallographic grain orientation maps confirmed that larger colonies of columnar grains have higher thermal conductivity compared to smaller columnar grains. Practical implications The thermal properties of AlSi10Mg are crucial to heat transfer applications including additively manufactured heatsinks, cold plates, vapor chambers, heat pipes, enclosures and heat exchangers. Additionally, thermal-based nondestructive testing methods require these properties for applications such as defect detection and simulation of L-PBF processes. Industrial standards for L-PBF processes and components can use the data for thermal applications. Originality/value To the best of the authors’ knowledge, this paper is the first to make coupled thermal conductivity maps that were matched to microstructure for L-PBF AlSi10Mg aluminum alloy. This was achieved by a unique in-house thermal conductivity mapping setup and relating the data to local SEM EBSD maps. This provides the first conclusive proof that larger grain sizes can achieve higher thermal conductivity for this processing method and material system. This study also shows that control of the solidification can result in higher thermal conductivity. It was also the first to find that the build substrate (with or without support) has a large effect on thermal conductivity.

Engineering↗
DOE OSTI2023

Hybrid Al Casting + AM Components for Automotive Applications

Although casting Aluminum (Al) alloys is widely used for automotive application, the conventional casting process is showing limitations for modern vehicle production. A hybrid manufacturing method that is capable of fabricating automotive structures with tailored functionality and tuned attributes at a high production rate is proposed in this project, utilizing the merits of conventional casting methods and additive manufacturing (AM) methods. Ford is interested in supplementing conventional casting processes (e.g., shape casting, high pressure die casting) with local modifications to geometry and microstructure using additive manufacturing techniques. Two additive manufacturing methods, wire-arc and laser hot-wire directed energy deposition AM process, were evaluated by deposition of 4043 filler wire onto high-pressure die cast and permanent mold cast Al-Si alloys. The feasibility of this hybrid manufacturing method was determined through trial deposition and evaluation of defects, microstructure, and mechanical properties. Laser hot-wire deposition was found to be beneficial for this application with low porosity, a refined microstructure, and mechanical properties similar to those reported in the literature for 4043. The mechanical properties of the interface between the A356 casting and deposited 4043 were found to be controlled by the weaker deposit material.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Microstructural refinement in ultrasonically modified A356 aluminum castings

Two A356 aluminum alloys (Al-Si-Mg), one with 0.09 wt.% Fe and one with 0.91 wt.% Fe, were cast in a graphite mold with the simultaneous application of local ultrasonic intensification to refine the as-cast microstructure. Ultrasonication during casting transformed the morphology of primary Al grains from dendritic (~140-290 microns in size) to globular (~33-36 microns in size). The alloy with high Fe exhibited globular grains at distances up to 45 mm away from the ultrasound probe, while the alloy with low Fe exhibited globular grains at distances only up to 6 mm away from the ultrasound probe. Near the location of the ultrasound probe (< 2 mm away), a second non-dendritic microstructural morphology was observed with fine aluminum grains (~9-25 microns in size). This unique fine-grained morphology has not been previously reported, contains a greater concentration of Si relative to the globular microstructure, and may be a large, fully eutectic region. Ultrasonication during casting also transformed the morphology of the ß-Al 5 FeSi phase particles (which are deleterious to the strength and ductility of the alloy) in the high Fe alloy from needle-like to rectangular, which could enable the greater use of secondary Al alloys. Thermodynamic simulations conducted to calculate the solidification paths of the two alloys studied predict that the ß-Al 5 FeSi phase begins to form earlier in the alloy with high Fe. Finally, data suggest that the ß-Al 5 FeSi phase (which is more abundant in alloys with high Fe content) may enhance ultrasonically-induced grain refinement.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Strontium Effects on the Formation of Iron-Intermetallic Phases in Secondary Al–9Si–0.6Fe Alloys

The presence and morphology of Fe-containing intermetallic phases affect the mechanical properties of aluminum alloys, especially in secondary Al–Si-based cast alloys. Although strontium (Sr) addition of 50 to 500 ppm is known to refine the needle-type eutectic silicon structure, the influence of Sr on the formation of Fe-intermetallic phases remains unclear. The present work investigates the combined additions of Sr and Mn to Al–9Si–0.6Fe–0.35Mg (All compositions are in wt pct except otherwise stated.) alloys on the formation of Fe-intermetallic phases at different solidification rates from ~ 1.5 to ~ 60 °C/s. Long and branched-type AlFeSi phase with size ranging from 50 to 120 µm are more common when solidified at the rate of 1.5 °C/s regardless of Sr and Mn additions. However, at the fast solidification rate of 60 °C/s, a 60 ppm Sr addition significantly reduced the average length of needle-shaped AlFeSi phase to less than 3 to 5 µm. Thermodynamic simulations have been performed using CALculation of PHAse Diagrams (CALPHAD) models to predict the formation of various phases and their possible interactions during solidification. The results indicated that the combination of a high solidification rate and about 60 ppm of Sr is beneficial to refining the δ-Al 3 FeSi 2 phase in Al–Si–Mg alloys containing 0.6 pctFe. As a result, this unexpected finding of Fe-intermetallic refinement by low Sr addition (~60 ppm) provides an important guide in designing secondary alloys for sustainable casting applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

The Beneficial Effect of Iron in Aluminum-Cerium-Based Cast Alloys

Iron (Fe) has been considered a major impurity since it is detrimental to the mechanical properties of many cast aluminum alloys due to the formation of Fe-containing brittle intermetallic phases. Fe is found naturally as an impurity in bauxite ore, resulting in Fe contamination of aluminum alloys with increasing contamination from current recycling practices. The Al–Ce–Fe system was investigated using CALPHAD (CALculation of PHAse Diagrams) modeling and experimental casting techniques. It was found that additions of Fe to the Al–Ce system are beneficial to the strength (slightly) and ductility (significantly) of the ternary alloys, which is attributed to the formation of fine metastable Al 8 CeFe 2 phase with aggregate morphology and equilibrium Al 10 CeFe 2 phase, suppressing coarse proeutectic Al 11 Ce 3 phase in near-eutectic Al–Ce alloys. Heat treatment study showed that the metastable Al 8 CeFe 2 phase transforms to predicted equilibrium Al 10 CeFe 2 phase at 500 °C, with essentially no intermetallic or grain coarsening; thus, the alloy displayed excellent property retention. The Al–Ce–Fe alloy system offers opportunities for sustainable, recyclable alloy development using low-cost Fe and low-cost cerium (a byproduct of rare-earth extraction).

42 ENGINEERING↗
DOE OSTI2020

Materials Data on AlSi by Materials Project

AlSi is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Al is bonded in a body-centered cubic geometry to eight equivalent Si atoms. All Al–Si bond lengths are 2.73 Å. Si is bonded in a body-centered cubic geometry to eight equivalent Al atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al4Si by Materials Project

Al4Si crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are six inequivalent Al sites. In the first Al site, Al is bonded to nine Al and three equivalent Si atoms to form distorted AlAl9Si3 cuboctahedra that share corners with six equivalent SiAl6 cuboctahedra, corners with twelve AlAl9Si3 cuboctahedra, edges with six equivalent SiAl6 cuboctahedra, edges with eighteen AlAl9Si3 cuboctahedra, and faces with twelve AlAl9Si3 cuboctahedra. There are three shorter (2.84 Å) and six longer (2.85 Å) Al–Al bond lengths. All Al–Si bond lengths are 2.73 Å. In the second Al site, Al is bonded to twelve Al atoms to form AlAl12 cuboctahedra that share corners with three equivalent SiAl6 cuboctahedra, corners with nine AlAl9Si3 cuboctahedra, edges with three equivalent SiAl6 cuboctahedra, edges with twenty-one AlAl9Si3 cuboctahedra, and faces with eighteen AlAl9Si3 cuboctahedra. There are six shorter (2.85 Å) and three longer (2.88 Å) Al–Al bond lengths. In the third Al site, Al is bonded to twelve Al atoms to form AlAl12 cuboctahedra that share corners with three equivalent SiAl6 cuboctahedra, corners with nine AlAl9Si3 cuboctahedra, edges with three equivalent SiAl6 cuboctahedra, edges with twenty-one AlAl9Si3 cuboctahedra, and faces with eighteen AlAl9Si3 cuboctahedra. There are three shorter (2.84 Å) and six longer (2.85 Å) Al–Al bond lengths. In the fourth Al site, Al is bonded to twelve Al atoms to form AlAl12 cuboctahedra that share corners with three equivalent SiAl6 cuboctahedra, corners with nine AlAl9Si3 cuboctahedra, edges with three equivalent SiAl6 cuboctahedra, edges with twenty-one AlAl9Si3 cuboctahedra, and faces with eighteen AlAl9Si3 cuboctahedra. There are a spread of Al–Al bond distances ranging from 2.84–2.88 Å. In the fifth Al site, Al is bonded to twelve Al atoms to form AlAl12 cuboctahedra that share corners with three equivalent SiAl6 cuboctahedra, corners with nine AlAl9Si3 cuboctahedra, edges with three equivalent SiAl6 cuboctahedra, edges with twenty-one AlAl9Si3 cuboctahedra, and faces with eighteen AlAl9Si3 cuboctahedra. There are three shorter (2.84 Å) and six longer (2.85 Å) Al–Al bond lengths. In the sixth Al site, Al is bonded to twelve Al atoms to form AlAl12 cuboctahedra that share corners with three equivalent SiAl6 cuboctahedra, corners with nine AlAl9Si3 cuboctahedra, edges with three equivalent SiAl6 cuboctahedra, edges with twenty-one AlAl9Si3 cuboctahedra, and faces with eighteen AlAl9Si3 cuboctahedra. There are a spread of Al–Al bond distances ranging from 2.84–2.88 Å. Si is bonded to six equivalent Al atoms to form distorted SiAl6 cuboctahedra that share corners with eighteen AlAl9Si3 cuboctahedra, edges with six equivalent SiAl6 cuboctahedra, and edges with eighteen AlAl9Si3 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al4Si19 by Materials Project

Al4Si19 is beta beryllia-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are eight inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four Si+0.63- atoms to form AlSi4 tetrahedra that share a cornercorner with one AlSi4 tetrahedra and corners with eleven SiSi4 tetrahedra. There are a spread of Al–Si bond distances ranging from 2.48–2.51 Å. In the second Al3+ site, Al3+ is bonded to four Si+0.63- atoms to form AlSi4 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiSi4 tetrahedra. There are a spread of Al–Si bond distances ranging from 2.46–2.54 Å. In the third Al3+ site, Al3+ is bonded to four Si+0.63- atoms to form AlSi4 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiSi4 tetrahedra. There are a spread of Al–Si bond distances ranging from 2.49–2.51 Å. In the fourth Al3+ site, Al3+ is bonded to four Si+0.63- atoms to form AlSi4 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiAlSi3 tetrahedra. There are a spread of Al–Si bond distances ranging from 2.46–2.52 Å. In the fifth Al3+ site, Al3+ is bonded to four Si+0.63- atoms to form AlSi4 tetrahedra that share corners with four AlSi4 tetrahedra and corners with eight SiSi4 tetrahedra. There are a spread of Al–Si bond distances ranging from 2.49–2.56 Å. In the sixth Al3+ site, Al3+ is bonded to four Si+0.63- atoms to form AlSi4 tetrahedra that share corners with three AlSi4 tetrahedra and corners with nine SiAl2Si2 tetrahedra. There are a spread of Al–Si bond distances ranging from 2.47–2.57 Å. In the seventh Al3+ site, Al3+ is bonded to four Si+0.63- atoms to form AlSi4 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiSi4 tetrahedra. There are a spread of Al–Si bond distances ranging from 2.44–2.53 Å. In the eighth Al3+ site, Al3+ is bonded to four Si+0.63- atoms to form AlSi4 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiSi4 tetrahedra. There are three shorter (2.49 Å) and one longer (2.52 Å) Al–Si bond lengths. There are thirty-eight inequivalent Si+0.63- sites. In the first Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form corner-sharing SiAlSi3 tetrahedra. There are one shorter (2.37 Å) and two longer (2.38 Å) Si–Si bond lengths. In the second Si+0.63- site, Si+0.63- is bonded to two Al3+ and two Si+0.63- atoms to form corner-sharing SiAl2Si2 tetrahedra. Both Si–Si bond lengths are 2.37 Å. In the third Si+0.63- site, Si+0.63- is bonded to two Al3+ and two Si+0.63- atoms to form corner-sharing SiAl2Si2 tetrahedra. There are one shorter (2.39 Å) and one longer (2.40 Å) Si–Si bond lengths. In the fourth Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form SiAlSi3 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiSi4 tetrahedra. There are one shorter (2.35 Å) and two longer (2.37 Å) Si–Si bond lengths. In the fifth Si+0.63- site, Si+0.63- is bonded to two Al3+ and two Si+0.63- atoms to form SiAl2Si2 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiAl2Si2 tetrahedra. There are one shorter (2.35 Å) and one longer (2.37 Å) Si–Si bond lengths. In the sixth Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with three AlSi4 tetrahedra and corners with nine SiAlSi3 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.35–2.38 Å. In the seventh Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with four AlSi4 tetrahedra and corners with eight SiAl2Si2 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.36–2.40 Å. In the eighth Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with three AlSi4 tetrahedra and corners with nine SiAlSi3 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.36–2.39 Å. In the ninth Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form SiAlSi3 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiAlSi3 tetrahedra. Both Si–Si bond lengths are 2.37 Å. In the tenth Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form SiAlSi3 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiAl2Si2 tetrahedra. There are one shorter (2.35 Å) and one longer (2.37 Å) Si–Si bond lengths. In the eleventh Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with four AlSi4 tetrahedra and corners with eight SiAl2Si2 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.36–2.40 Å. In the twelfth Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form SiAlSi3 tetrahedra that share corners with four AlSi4 tetrahedra and corners with eight SiAl2Si2 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.33–2.39 Å. In the thirteenth Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiSi4 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.36–2.40 Å. In the fourteenth Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with four AlSi4 tetrahedra and corners with eight SiAlSi3 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.36–2.40 Å. In the fifteenth Si+0.63- site, Si+0.63- is bonded to two Al3+ and two Si+0.63- atoms to form SiAl2Si2 tetrahedra that share a cornercorner with one AlSi4 tetrahedra and corners with eleven SiAl2Si2 tetrahedra. There are one shorter (2.33 Å) and one longer (2.34 Å) Si–Si bond lengths. In the sixteenth Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with four AlSi4 tetrahedra and corners with eight SiAlSi3 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.36–2.40 Å. In the seventeenth Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form SiAlSi3 tetrahedra that share corners with three AlSi4 tetrahedra and corners with nine SiAl2Si2 tetrahedra. There are one shorter (2.36 Å) and one longer (2.38 Å) Si–Si bond lengths. In the eighteenth Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiAl2Si2 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.36–2.38 Å. In the nineteenth Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form SiAlSi3 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiSi4 tetrahedra. There are one shorter (2.34 Å) and one longer (2.38 Å) Si–Si bond lengths. In the twentieth Si+0.63- site, Si+0.63- is bonded to two Al3+ and two Si+0.63- atoms to form SiAl2Si2 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiAl2Si2 tetrahedra. In the twenty-first Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with two AlSi4 tetrahedra and corners with ten SiAlSi3 tetrahedra. The Si–Si bond length is 2.36 Å. In the twenty-second Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form distorted SiAlSi3 tetrahedra that share a cornercorner with one AlSi4 tetrahedra and corners with eleven SiAl2Si2 tetrahedra. In the twenty-third Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with four AlSi4 tetrahedra and corners with eight SiAlSi3 tetrahedra. The Si–Si bond length is 2.37 Å. In the twenty-fourth Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form distorted corner-sharing SiAlSi3 tetrahedra. In the twenty-fifth Si+0.63- site, Si+0.63- is bonded to two Al3+ and two Si+0.63- atoms to form SiAl2Si2 tetrahedra that share a cornercorner with one AlSi4 tetrahedra and corners with eleven SiSi4 tetrahedra. In the twenty-sixth Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form distorted SiAlSi3 tetrahedra that share a cornercorner with one AlSi4 tetrahedra and corners with eleven SiAl2Si2 tetrahedra. The Si–Si bond length is 2.37 Å. In the twenty-seventh Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with five AlSi4 tetrahedra and corners with seven SiAl2Si2 tetrahedra. In the twenty-eighth Si+0.63- site, Si+0.63- is bonded to two Al3+ and two Si+0.63- atoms to form corner-sharing SiAl2Si2 tetrahedra. In the twenty-ninth Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with four AlSi4 tetrahedra and corners with eight SiSi4 tetrahedra. The Si–Si bond length is 2.38 Å. In the thirtieth Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form distorted SiAlSi3 tetrahedra that share a cornercorner with one AlSi4 tetrahedra and corners with eleven SiAlSi3 tetrahedra. In the thirty-first Si+0.63- site, Si+0.63- is bonded to two Al3+ and two Si+0.63- atoms to form corner-sharing SiAl2Si2 tetrahedra. In the thirty-second Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with three AlSi4 tetrahedra and corners with nine SiAlSi3 tetrahedra. The Si–Si bond length is 2.36 Å. In the thirty-third Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form distorted SiAlSi3 tetrahedra that share a cornercorner with one AlSi4 tetrahedra and corners with eleven SiAl2Si2 tetrahedra. In the thirty-fourth Si+0.63- site, Si+0.63- is bonded to two Al3+ and two Si+0.63- atoms to form SiAl2Si2 tetrahedra that share a cornercorner with one AlSi4 tetrahedra and corners with eleven SiAl2Si2 tetrahedra. In the thirty-fifth Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form distorted SiAlSi3 tetrahedra that share a cornercorner with one AlSi4 tetrahedra and corners with eleven SiSi4 tetrahedra. The Si–Si bond length is 2.37 Å. In the thirty-sixth Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with four AlSi4 tetrahedra and corners with eight SiSi4 tetrahedra. In the thirty-seventh Si+0.63- site, Si+0.63- is bonded to one Al3+ and three Si+0.63- atoms to form corner-sharing SiAlSi3 tetrahedra. The Si–Si bond length is 2.36 Å. In the thirty-eighth Si+0.63- site, Si+0.63- is bonded to four Si+0.63- atoms to form SiSi4 tetrahedra that share corners with three AlSi4 tetrahedra and corners with nine SiAlSi3 tetrahedra.

36 MATERIALS SCIENCE↗