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DOE OSTI2020

Materials Data on SiB4 by Materials Project

SiB4 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent B sites. In the first B site, B is bonded in a 1-coordinate geometry to five B and two Si atoms. There are a spread of B–B bond distances ranging from 1.75–1.86 Å. There are one shorter (2.01 Å) and one longer (2.63 Å) B–Si bond lengths. In the second B site, B is bonded in a 6-coordinate geometry to six B atoms. There is one shorter (1.85 Å) and two longer (1.92 Å) B–B bond length. There are two inequivalent Si sites. In the first Si site, Si is bonded in a 4-coordinate geometry to three equivalent B and one Si atom. The Si–Si bond length is 2.17 Å. In the second Si site, Si is bonded in a 2-coordinate geometry to six equivalent B and two equivalent Si atoms.

36 MATERIALS SCIENCE↗

NASA NTRS1996

A Two Phase HfB2-SiB4 Material

A two phase HfB2-SiB4 material which is useful as a high temperature oxidation resistant coating. This invention relates to ceramic coatings and more particularly to ceramic coatings containing metal borides. Boride materials are known to have good oxidation resistance, with HfB2 considered to be the best pure boride for oxidation applications. It has been shown that the addition of 10 to 20 percent SiC to HfB2 increases the oxidation resistance. The HfB2-SiC materials are prepared by hot pressing powder mixtures. Hot pressing powder mixtures has limited ability to produce fine grained multiphase materials due to particle coarsening during the sintering process. Additionally, the purity of the final monolithic structure is limited to the purity of the starting powders. Chemical vapor deposition (CVD) offers a method of producing highly pure multiphase ceramics, with better control of microstructure. Researchers have tried to produce HfB2-SiC coatings by CVD but without success.

SILICON COMPOUNDS↗

DOE OSTI2020

Materials Data on Y5(SiB4)2 by Materials Project

Y5Si2B8 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. there are two inequivalent Y sites. In the first Y site, Y is bonded in a 12-coordinate geometry to nine B and three equivalent Si atoms. There are a spread of Y–B bond distances ranging from 2.64–2.97 Å. There are one shorter (3.07 Å) and two longer (3.13 Å) Y–Si bond lengths. In the second Y site, Y is bonded to two equivalent B and four equivalent Si atoms to form corner-sharing YSi4B2 octahedra. The corner-sharing octahedral tilt angles are 57°. Both Y–B bond lengths are 2.74 Å. All Y–Si bond lengths are 2.91 Å. There are three inequivalent B sites. In the first B site, B is bonded in a 9-coordinate geometry to four equivalent Y and five B atoms. There are a spread of B–B bond distances ranging from 1.76–1.83 Å. In the second B site, B is bonded in a 3-coordinate geometry to six equivalent Y and three B atoms. The B–B bond length is 1.85 Å. In the third B site, B is bonded in a 9-coordinate geometry to five Y and four equivalent B atoms. Si is bonded in a 9-coordinate geometry to eight Y and one Si atom. The Si–Si bond length is 2.35 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Dy5(SiB4)2 by Materials Project

Dy5Si2B8 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. there are two inequivalent Dy sites. In the first Dy site, Dy is bonded in a 12-coordinate geometry to nine B and three equivalent Si atoms. There are a spread of Dy–B bond distances ranging from 2.63–2.97 Å. There are one shorter (3.06 Å) and two longer (3.12 Å) Dy–Si bond lengths. In the second Dy site, Dy is bonded to two equivalent B and four equivalent Si atoms to form corner-sharing DySi4B2 octahedra. The corner-sharing octahedral tilt angles are 57°. Both Dy–B bond lengths are 2.73 Å. All Dy–Si bond lengths are 2.91 Å. There are three inequivalent B sites. In the first B site, B is bonded in a 9-coordinate geometry to four equivalent Dy and five B atoms. There are a spread of B–B bond distances ranging from 1.76–1.83 Å. In the second B site, B is bonded in a 3-coordinate geometry to six equivalent Dy and three B atoms. The B–B bond length is 1.84 Å. In the third B site, B is bonded in a 9-coordinate geometry to five Dy and four equivalent B atoms. Si is bonded in a 9-coordinate geometry to eight Dy and one Si atom. The Si–Si bond length is 2.35 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Sm5(SiB4)2 by Materials Project

Sm5Si2B8 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. there are two inequivalent Sm+2.80+ sites. In the first Sm+2.80+ site, Sm+2.80+ is bonded in a 12-coordinate geometry to nine B+0.75- and three equivalent Si4- atoms. There are a spread of Sm–B bond distances ranging from 2.70–3.03 Å. There are one shorter (3.16 Å) and two longer (3.20 Å) Sm–Si bond lengths. In the second Sm+2.80+ site, Sm+2.80+ is bonded to two equivalent B+0.75- and four equivalent Si4- atoms to form corner-sharing SmSi4B2 octahedra. The corner-sharing octahedral tilt angles are 57°. Both Sm–B bond lengths are 2.88 Å. All Sm–Si bond lengths are 2.97 Å. There are three inequivalent B+0.75- sites. In the first B+0.75- site, B+0.75- is bonded in a 9-coordinate geometry to four equivalent Sm+2.80+ and five B+0.75- atoms. There are a spread of B–B bond distances ranging from 1.79–1.84 Å. In the second B+0.75- site, B+0.75- is bonded in a 3-coordinate geometry to six equivalent Sm+2.80+ and three B+0.75- atoms. The B–B bond length is 1.89 Å. In the third B+0.75- site, B+0.75- is bonded in a 9-coordinate geometry to five Sm+2.80+ and four equivalent B+0.75- atoms. Si4- is bonded in a 9-coordinate geometry to eight Sm+2.80+ and one Si4- atom. The Si–Si bond length is 2.35 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Tb5(SiB4)2 by Materials Project

Tb5Si2B8 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional and consists of four silicon molecules and one Tb5B8 framework. In the Tb5B8 framework, there are two inequivalent Tb+3.20+ sites. In the first Tb+3.20+ site, Tb+3.20+ is bonded in a 9-coordinate geometry to nine B3- atoms. There are a spread of Tb–B bond distances ranging from 2.65–2.98 Å. In the second Tb+3.20+ site, Tb+3.20+ is bonded in a linear geometry to two equivalent B3- atoms. Both Tb–B bond lengths are 2.76 Å. There are three inequivalent B3- sites. In the first B3- site, B3- is bonded in a 9-coordinate geometry to four equivalent Tb+3.20+ and five B3- atoms. There are a spread of B–B bond distances ranging from 1.76–1.84 Å. In the second B3- site, B3- is bonded in a 3-coordinate geometry to six equivalent Tb+3.20+ and three B3- atoms. The B–B bond length is 1.85 Å. In the third B3- site, B3- is bonded in a 9-coordinate geometry to five Tb+3.20+ and four equivalent B3- atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ho5(SiB4)2 by Materials Project

Ho5Si2B8 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. there are two inequivalent Ho sites. In the first Ho site, Ho is bonded in a 12-coordinate geometry to nine B and three equivalent Si atoms. There are a spread of Ho–B bond distances ranging from 2.62–2.95 Å. There are one shorter (3.04 Å) and two longer (3.11 Å) Ho–Si bond lengths. In the second Ho site, Ho is bonded to two equivalent B and four equivalent Si atoms to form corner-sharing HoSi4B2 octahedra. The corner-sharing octahedral tilt angles are 57°. Both Ho–B bond lengths are 2.71 Å. All Ho–Si bond lengths are 2.89 Å. There are three inequivalent B sites. In the first B site, B is bonded in a 9-coordinate geometry to four equivalent Ho and five B atoms. There are a spread of B–B bond distances ranging from 1.75–1.83 Å. In the second B site, B is bonded in a 3-coordinate geometry to six equivalent Ho and three B atoms. The B–B bond length is 1.83 Å. In the third B site, B is bonded in a 9-coordinate geometry to five Ho and four equivalent B atoms. Si is bonded in a 9-coordinate geometry to eight Ho and one Si atom. The Si–Si bond length is 2.35 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2021

A Modified Vegetation Photosynthesis and Respiration Model (VPRM) for the Eastern USA and Canada, Evaluated With Comparison to Atmospheric Observations and Other Biospheric Models

Atmospheric CO 2 measurements from a dense surface network can help to evaluate terrestrial biosphere model (TBM) simulations of Net Ecosystem Exchange (NEE) with two key benefits. First, gridded CO 2 flux estimates can be evaluated over regional scales, not possible using flux tower observations at discrete locations for model evaluation. Second, TBM ability to explain atmospheric CO 2 fluctuations due to the biosphere can be directly tested, an important objective for anthropogenic emissions monitoring using atmospheric observations. Here, we customize the Vegetation Photosynthesis and Respiration Model (VPRM) for an eastern North American domain with strong biological activity upwind of urban areas. Parameters are optimized using flux tower observations from a historical database with sites in (and near) the domain. In addition, the respiration model (originally a linear function of temperature) is modified to account for impacts of changing foliage, non-linear temperature, and water stress. Flux estimates from VPRM, the Carnegie-Ames-Stanford Approach (CASA) model and the Simple Biosphere Model v4 (SiB4), are convolved with footprints from atmospheric transport models for evaluation with CO 2 observations at 21 towers in the domain, with roughly half of the towers used here for the first time. Results show that the new respiration model in VPRM helps to correct a growing season sink bias in the atmosphere associated with underestimated summertime respiration using the original model with annual parameters. The new VPRM also better explains fine-scale atmospheric CO 2 variability compared to other TBMs, due to higher resolution diagnostic phenology, the new respiration model, domain-specific parameters, and high-quality input data sets.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2020

Materials Data on SiB by Materials Project

BSi is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. B is bonded to four equivalent Si atoms to form corner-sharing BSi4 tetrahedra. There are one shorter (1.99 Å) and three longer (2.06 Å) B–Si bond lengths. Si is bonded to four equivalent B atoms to form corner-sharing SiB4 tetrahedra.

36 MATERIALS SCIENCE↗

NASA NTRS1987

Silicon carbide sintered body manufactured from silicon carbide powder containing boron, silicon and carbonaceous additive

A silicon carbide powder of a 5-micron grain size is mixed with 0.15 to 0.60 wt% mixture of a boron compound, i.e., boric acid, boron carbide (B4C), silicon boride (SiB4 or SiB6), aluminum boride, etc., and an aluminum compound, i.e., aluminum, aluminum oxide, aluminum hydroxide, aluminum carbide, etc., or aluminum boride (AlB2) alone, in such a proportion that the boron/aluminum atomic ratio in the sintered body becomes 0.05 to 0.25 wt% and 0.05 to 0.40 wt%, respectively, together with a carbonaceous additive to supply enough carbon to convert oxygen accompanying raw materials and additives into carbon monoxide.

Tanaka, Hidehiko↗

NASA NTRS1988

Boron-containing organosilane polymers and ceramic materials thereof

The present invention relates to organic silicon-boron polymers which upon pyrolysis produce high-temperature ceramic materials. More particularly, it relates to the polyorganoborosilanes containing -Si-B- bonds which generate high-temperature ceramic materials (e.g., SiC, SiB4, B4C) upon thermal degradation. The process for preparing these organic silicon-boron polymer precursors are also part of the invention.

Riccitiello, Salvatore R.↗

NASA NTRS1989

Boron-containing organosilane polymers and ceramic materials thereof

The present invention relates to a polyorgano borosilane ceramic precursor polymer comprising a plurality of repeating units of the formula: (R(sup 1) single bond B)(sub p) being linked together at B by second units of the formula: single bond (R sup 2) single bond (Si single bond R sup 3) single bond (sub q), where R(sup 1) is a lower alkyl, cycloalkyl, phenyl, or (R(sup 2)R(sup 3) single bond Si single bond B single bond)(sub n) and R(sup 2) and R(sup 3) are each independently selected from hydrogen, lower alkyl, vinyl, cycloalkyl, or aryl, n is an integer between 1 and 100; p is an integer between 1 and 100; and q is an integer between 1 and 100. These materials are prepared by combining an organo borohalide of the formula R(sup 4) single bond B single bond (X sup 1) (sub 2) where R(sup 4) is selected from halogen, lower alkyl, cycloalkyl, or aryl, and an organo halosilane of the formula: R(sup 2)(R sup 3)Si(X sup 2)(sub 2) where R(sup 2) and R (sup 3) are each independently selected from lower alkyl, cycloalkyl, or aryl, and X(sup 1) and X(sup 2) are each independently selected from halogen, in an anhydrous aprotic solvent having a boiling point at ambient pressure of not greater than 160 C with in excess of four equivalents of an alkali metal, heating the reaction mixture and recovering the polyorgano borosilane. These silicon boron polymers are useful to generate high-temperature ceramic materials, such as SiC, SiB4, and B4C, upon thermal degradation above 600 C.

Riccitiello, Salvatore R.↗

NASA NTRS1993

Ceramic fibers from Si-B-C polymer precursors

Non-oxide ceramics such as silicon carbide (SiC), silicon nitride (Si3N4), and silicon borides (SiB4, SiB6) have thermal stability, oxidation resistance, hardness, and varied electrical properties. All these materials can be prepared in a fiber form from a suitable polymer precursor. The above mentioned fibers, when tested over a temperature range from 25 to 1400 C, experience degradation at elevated temperatures. Past work in ceramic materials has shown that the strength of ceramics containing both carbides and borides is sustained at elevated temperatures, with minimum oxidation. The work presented here describes the formation of ceramic fibers containing both elements, boron and silicon, prepared via the polymer precursor route previously reported by the authors, and discusses the fiber mechanical properties that are retained over the temperature range studied.

Riccitiello, S. R.↗