Composition and Structure of Ceramic Fibers Prepared from Polymer Precursors

Polycarbosilane (PCS) thin films were deposited on silicon (and other) substrates and heat treated under vacuum (∼10 −6 torr) at temperatures in the range of 200°-1200°C. At temperatures in the range of 1000°-1200°C, the initially amorphous PCS films transformed to polycrystalline ␤-silicon carbide (␤-SiC). Although PCS films could be deposited at thickness up to 2 µm, the films with thicknesses >1 µm could not be transformed to SiC without extensive cracking. The resulting SiC coatings were characterized using Fourier transform infrared spectroscopy, glancingangle X-ray diffractometry, secondary-ion mass spectroscopy, Raman spectoscopy, transmission electron microscopy, and scanning electron microscopy. The temperature and time dependence of the amorphous-to-crystalline transition could be associated with the evolution of free carbon, oxygen, and hydrogen in the films.

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“…This would then influence the crystallization behavior of the entire thin-film material. 17,23,[29][30][31][32]…”

Section: (3) Microstructural Evolutionmentioning

confidence: 99%

Synthesis of Silicon Carbide Thin Films with Polycarbosilane (PCS)

Colombo

Paulson

Pantano

1997

Journal of the American Ceramic Society

137

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“…The molecular structure of these nanodomains, however, is not directly accessible. Spectroscopic methods such as nuclear magnetic resonance (NMR) 11,12 and Fourier‐transformed infrared spectroscopy (FTIR) provide chemical bond information for the first nearest neighbors, and with great effort the second nearest neighbor, which falls far short of the 1–6 nm scale of the nanodomains. Recently, a model for the nanodomains that is consistent with the creep and crystallization behavior of SiCO and with the information obtained from NMR, FTIR, and Raman has been proposed 13 .…”

Section: Introductionmentioning

confidence: 99%

Preparation of Ultrathin‐Walled Carbon‐Based Nanoporous Structures by Etching Pseudo‐Amorphous Silicon Oxycarbide Ceramics

Peña-Alonso¹,

Sorarù²,

Raj³

2006

Journal of the American Ceramic Society

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Etching polymer‐derived silicon‐oxycarbide ceramics with hydrofluoric acid creates nanoporous structures of specific surface areas as high as 600 m2/g. The change in composition upon etching shows the removal of silica, not carbon. The structure remaining after etching is postulated to consist of a scaffolding of graphene networks with their surfaces decorated with mixed bonds of tetrahedral silicon bonded to both oxygen and carbon (SiOmC4−m, where m=1, 2, or 3). The pores existing within such scaffoldings are presumed to have been filled with SiO2 tetrahedra, which are removed by etching. The measurement of the average pore size and pore volumes permits us to estimate the width of the graphitic domain walls, δW, left behind by the etching process. The smallest value of δW, which corresponds to the specimen with the highest surface area, is approximately 1 nm, which is about equal to the total width of one graphene layer and two SiOmC4–m tetrahedra, one on either side of the graphene sheet. This highest surface area specimen is also believed to have the largest size of the silica domains in the unetched samples. In specimens with smaller domains, the etching is only partially successful in removing the silica, presumably because their small size hinders the access of the etchant to the silica tetrahedra. The above behavior is found for samples with low to moderate carbon content. In one sample with a very high carbon content, the etching process removes some carbon as well as silica.

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“…9 Although it is certainly possible that there is a bias in standardless results from the data at 7 kV, the relative amounts that are plotted in Fig. 4 display great precision.…”

Section: (1) Fibersmentioning

confidence: 96%

“…The highest oxygen concentration, as determined by standardless quantitative analysis, is 9.1 wt% at the surface, and the lowest oxygen concentration in the interior is 7.9 wt%, which is in reasonable agreement with previously reported XPS data on ceramic-grade (CG) Nicalon. 9 Although it is certainly possible that there is a bias in standardless results from the data at 7 kV, the relative amounts that are plotted in Fig. 4 display great precision.…”

Section: (1) Fibersmentioning

confidence: 98%

“…The distribution of the fibers has been reported previously, 6 and the presence of oxygen in Nicalon fibers is known. 8,9 However, we were able to establish the distribution of oxygen by a novel approach that was made possible by PTS. Instead of just exploring the oxygen map or an X-ray line profile across a fiber, we used a combination of image processing and PTS to get a more-quantitative result.…”

Section: (1) Fibersmentioning

confidence: 99%

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Novel Technology for X‐ray Mapping of Ceramic Microstructures

Friel

Greenhut

1997

Journal of the American Ceramic Society

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Field-emission scanning electron microscopy (FESEM) was coupled with a technology called position-tagged spectrometry (PTS) to characterize the microstructure of a ceramicmatrix composite at the submicrometer level. Low-voltage microscopy with an FESEM microscope achieves both high-resolution imaging of uncoated ceramic specimens and submicrometer X-ray resolution with minimal specimen charging. The PTS technology involves scanning the electron beam and collecting X-rays, as in mapping; however, in this case, the X-ray photons are tagged with position information. X-ray maps and full spectra were reconstructed from discrete parts of the composite. The distribution of oxygen within the fibers was measured and found to decrease from the surface to the interior. The composition and phase distribution of the matrix were also revealed at high resolution, and the phase compositions were quantified.

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Composition and Structure of Ceramic Fibers Prepared from Polymer Precursors

Cited by 107 publications

References 19 publications

Synthesis of Silicon Carbide Thin Films with Polycarbosilane (PCS)

Synthesis of Silicon Carbide Thin Films with Polycarbosilane (PCS)

Preparation of Ultrathin‐Walled Carbon‐Based Nanoporous Structures by Etching Pseudo‐Amorphous Silicon Oxycarbide Ceramics

Novel Technology for X‐ray Mapping of Ceramic Microstructures

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