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In situ generated homogeneous and functionally graded ceramic materials derived from polysilazane

Reschke, S. ; Haluschka, Christoph ; Riedel, Ralf ; Lences, Z. ; Galusek, D. (2003):
In situ generated homogeneous and functionally graded ceramic materials derived from polysilazane.
In: Journal of the European Ceramic Society, 23 (11), pp. 1963-1970. [Article]

Abstract

The pyrolysis of cross-linked poly(hydridomethyl)silazane pellets via transient isothermal ammonia gas treatment yields amorphous layered ceramic bulk Si/N-Si/N/C-materials with graded carbon content. By this process the C content in the material can be adjusted with high accuracy in the range between 0 and 14 wt.%. The influence of (1) temperature of reactive ammonia treatment (2) time of reactive isothermal ammonia treatment (3) isothermal holding time under inert atmosphere (Ar) before application of ammonia (4) degree of cross-linking of the polycarbosilazane (5) porosity of green compact (6) volume ratio of NH3 in the reactive atmosphere was examined. The temperature of 525 °C and the reactive atmosphere containing 10 vol.% NH3 were found to be optimum for carbon content adjustment. Higher ammonia contents did not allow suitable control of the process, while higher temperature of transient heat treatment caused crack formation in the specimen due to excessive pressure of gaseous reaction products. High degree of cross-linking as well as the annealing of cross-linked green bodies at transient temperature in inert atmosphere decrease the efficiency of the reactive treatment and increase the amount of C in the pre-ceramic continuous random network (CRN). Next to graded materials, samples with bulk homogeneous carbon distribution were generated. However, these require more sophisticated heating schedules and combination of reactive treatment with pre-annealing in inert gas.

Item Type: Article
Erschienen: 2003
Creators: Reschke, S. ; Haluschka, Christoph ; Riedel, Ralf ; Lences, Z. ; Galusek, D.
Title: In situ generated homogeneous and functionally graded ceramic materials derived from polysilazane
Language: English
Abstract:

The pyrolysis of cross-linked poly(hydridomethyl)silazane pellets via transient isothermal ammonia gas treatment yields amorphous layered ceramic bulk Si/N-Si/N/C-materials with graded carbon content. By this process the C content in the material can be adjusted with high accuracy in the range between 0 and 14 wt.%. The influence of (1) temperature of reactive ammonia treatment (2) time of reactive isothermal ammonia treatment (3) isothermal holding time under inert atmosphere (Ar) before application of ammonia (4) degree of cross-linking of the polycarbosilazane (5) porosity of green compact (6) volume ratio of NH3 in the reactive atmosphere was examined. The temperature of 525 °C and the reactive atmosphere containing 10 vol.% NH3 were found to be optimum for carbon content adjustment. Higher ammonia contents did not allow suitable control of the process, while higher temperature of transient heat treatment caused crack formation in the specimen due to excessive pressure of gaseous reaction products. High degree of cross-linking as well as the annealing of cross-linked green bodies at transient temperature in inert atmosphere decrease the efficiency of the reactive treatment and increase the amount of C in the pre-ceramic continuous random network (CRN). Next to graded materials, samples with bulk homogeneous carbon distribution were generated. However, these require more sophisticated heating schedules and combination of reactive treatment with pre-annealing in inert gas.

Journal or Publication Title: Journal of the European Ceramic Society
Journal volume: 23
Number: 11
Uncontrolled Keywords: Carbon content adjustment, Electrical properties, Functionally graded materials, Polysilazane, Precursors-organic, Si–N–C
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Dispersive Solids
Date Deposited: 20 Nov 2008 08:16
License: [undefiniert]
Funders: The financial support of this work by DAAD, Bonn, Germany, NEDO, Tokyo, Japan, BMBF, Bonn, Germany (WTZ project X262.11 and the Slovak Grant Agency (project No. 2/1033) is gratefully acknowledged.
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