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Results for “Hf-O-Si”

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All sources NASA NTRS DOE OSTI

DOE OSTI2022

Evaluating Use of Boron- and Hafnium-Modified Polysilazanes for Ceramic Matrix Minicomposites

In this study, the potential of polymer-derived Ceramic Matrix Composites (CMCs) is demonstrated by addition of thin ceramic coatings on Carbon Fiber (CF) bundles. Boron- and hafnium- modified polysilazane liquid precursors were synthesized and used to infiltrate the fiber bundles of CF to fabricate lab-scale Si(B)CN/CF and Si(Hf)CN/CF CMC mini-composites, respectively. The precursor-to-ceramic conversion process was achieved at 800°C with crosslinked precursor to ceramic yield of approx. 90% in Ar environment. The Si(B)CN/CF contained Si-N and B-N bonds, while Si-N and Hf-O-Si bonds were observed for Si(Hf)CN/CF sample with uniform and dense surfaces. Room-temperature tensile tests showed that the Si(Hf)CN/CF sample could reach a tensile strength of ~790 MPa and elastic modulus of 66.88 GPa among the composites. Oxidation study of the Si(Hf)CN/CF mini-composites showed higher stability compared to SiCN/CF and Si(B)CN/CF mini-composites up to 1500°C.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Materials Data on HfSiO4 by Materials Project

HfSiO4 is Zircon structured and crystallizes in the tetragonal I4_1/amd space group. The structure is three-dimensional. Hf4+ is bonded in a 8-coordinate geometry to eight equivalent O2- atoms. There are four shorter (2.13 Å) and four longer (2.27 Å) Hf–O bond lengths. Si4+ is bonded in a tetrahedral geometry to four equivalent O2- atoms. All Si–O bond lengths are 1.64 Å. O2- is bonded in a 3-coordinate geometry to two equivalent Hf4+ and one Si4+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Hf(SiO)2 by Materials Project

Hf(SiO)2 crystallizes in the tetragonal I4_1/amd space group. The structure is zero-dimensional and consists of eight Hf(SiO)2 clusters. Hf4+ is bonded in a linear geometry to two equivalent O2- atoms. Both Hf–O bond lengths are 2.01 Å. Si is bonded in a single-bond geometry to one O2- atom. The Si–O bond length is 1.64 Å. O2- is bonded in a bent 120 degrees geometry to one Hf4+ and one Si atom.

36 MATERIALS SCIENCE↗