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141. Porosity related to structure in pyrocarbons
Absti‘acts
equivalent and in some cases higher flexoral strengths (1280MN/m* after four impregnation cycles) in comparison with composites without any sulfur addition. Furthermore it is shown that also the gas pressure pyrolysis between subsequent impregnations can be replaced by carbonizations under normal pressure if sulfur additions to the impregnation pitch are applied and that the resulting composites have been improved specific strength. 135. Isomere Polyphentlene ah Matrixprecursors fur Kohlenstoff-KobIeustoff-Verbundkiirper E. Fitzer und F. Grieser (Znstitut fur Chemische Technik, Univ. Karlsruhe, 75 Karlsruhe). This paper is
concerned with synthesis of isomeric polyphenylens and with studies on their suitability as matrix-precursors for C/C-composites. It was tried to correlate the wettingbehavior of the precursors and the mechanical properties of unidirectional reinforced C/C-composites. The wetting behavior of various mixtures of isomeric polyphenylens was studied by “sessile drop” method. Composites with 40 ~01% fibers (Thornel 75) were prepared by the dry winding binderimpregnation process. It was found, that the mechanical properties of the composites are not influenced by the wetting behavior, as long as contact angles fall short of 90” during pyrolysis. 136. New methods for the investigation of processes in the plasma zone during pyrocarbon formation H. Luhleich and P. Pflaum (Kernforschungsanlage Julich, lnstitut fiir Reaktorwerksto#e, D-5170 Jiilich, Postfach 1913). The formation of pyrocarbon is mainly
influenced by the plasma zone (Langmuir zone) adjacent to the hot surface. In order to clarify the mechanisms of pyrolysis, the investigation of the properties of this plasma zone is very important but, because of its very small dimensions, investigation by normal plasma diagnostic techniques is very difficult. Therefore, new methods have to be developed, and the first stage in this development is described here. 137. A model of pyrocarbons and its deposition mechanism R. L. R. Lefevre (OECD High Temperature Reactor Project (Dragon), AEE, Winfrith, England). 138. A quantitative chemical method for the determination of the disordered carbon component in pyrocarbon coatings of fuel particles E. A. Wolfrum and H. Nickel (Znstitutfiirleaktorwerkstoffe der Kemforschungsanlage Jiilich, D-517 Jiilich,
Postfach 1913).The chemical behaviour of the surface of pyrocarbon coatings of nuclear fuel particles was investigated in aqueous suspension by reaction with oxygen at room temperature. The concentration of the basic surface oxides is a function of the concentration of the disordered material component, which has a large internal surface, and can be identified by means of a pH change. Using this fact, a chemical method was developed which may be used for the quantiative determination of the concentration of this carbon component in the pyrocarbon coating.
307
139. Measurement and control of the microstructure of pyrolytic carbon on nuclear fuel particles
J. Guilleray, R. Zeyen, J-P. Audebeau and M. S. T. Price (OECD High Temperature Reactor Project, AEE, Winfrith, England). An initial set of experiments (termed HTRS) gave a good correlation between the observed size of spherical growth features (SGF) of pyrocarbon coatings and the value predicted by the deposition model of Lefevre. This paper gives an assessment of the method of measuring SGF and then applies the validated method to remeasurement of the HTR.5 series. The method is also applied to earlier irradiation results to close the loop manufacture-quality-performance. In addition studies of the deposition zone are reported with results of improvements made to the shape of particles. 140. fiber den Einfiug von Gliihbehandhmgen auf das Mikrogefiige von Pyrokohlenstoff-HfiIIschichten P. Krautwasser, H. Nickel (Znsitut fur Reaktorwerksto#e der Kemforschungsanlage Jiilich GmbH, D-517 Jiilich) and C. S. Yust (Oak Ridge National Laboratory, Oak Ridge, Tenn., U.S.A.). Transmission electron micros-
copy (TEM) and X-ray diffraction in the small and wide angle region were used to study the changes in the microstructure of pyrocarbon coatings as a function of high temperature treatment. The result indicate an ordering of the material with increasing temperature. In spite of specimen densification, i.e. decreasing porosity, an increase in inner surface area up to an annealing temperature of about 1800°Cwas found. This is explained by the measured decrease in pore size up to 1800°C followed by an increase in pore size at higher temperatures. 141. Porosity related to structure in pyrocarbons L. H. Ford, C. F. Bilsby and D. A. Moore (UKAEA, Reactor Group, Reactor Full Element Laboratories, Springfields, U.K.). The structure and porosity distribu-
tion in pyrocarbons deposited in a fluidised bed from either propylene or methane at 1200-2000°Con to nuclear fuel particles has been investigated by transmission and scanning electron microscopy, together with open and closed pore volume measurements. Mechanisms for the formation of the two basic pyrocarbon structures are discussed and a model is proposed to explain the dependence of both open and closed porosity on the deposition conditions and hydrocarbon source gas. 142. La texture des pyrocarbones isotropes de hasse temperature J. Pelissier et L. Lombard (Section d’Etudes de Metallurgic, Centre d’Etudes Nucleaires, B.P. 85 X, 38041 Grenoble, Cedex, France). Isotropic pyrocarbon depositd
on fuel particles from high temperature reactors is studied by transmission electron microscopy. The aim is to determine its texture and to come to a better understanding of its mode of fabrication. The material consist of an agglomerate of spherical growth features similar to those of carbon black. The spherical growth features are formed from cristallites of turbostratic carbon, which the
equivalent and in some cases higher flexoral strengths (1280MN/m* after four impregnation cycles) in comparison with composites without any sulfur addition. Furthermore it is shown that also the gas pressure pyrolysis between subsequent impregnations can be replaced by carbonizations under normal pressure if sulfur additions to the impregnation pitch are applied and that the resulting composites have been improved specific strength. 135. Isomere Polyphentlene ah Matrixprecursors fur Kohlenstoff-KobIeustoff-Verbundkiirper E. Fitzer und F. Grieser (Znstitut fur Chemische Technik, Univ. Karlsruhe, 75 Karlsruhe). This paper is
concerned with synthesis of isomeric polyphenylens and with studies on their suitability as matrix-precursors for C/C-composites. It was tried to correlate the wettingbehavior of the precursors and the mechanical properties of unidirectional reinforced C/C-composites. The wetting behavior of various mixtures of isomeric polyphenylens was studied by “sessile drop” method. Composites with 40 ~01% fibers (Thornel 75) were prepared by the dry winding binderimpregnation process. It was found, that the mechanical properties of the composites are not influenced by the wetting behavior, as long as contact angles fall short of 90” during pyrolysis. 136. New methods for the investigation of processes in the plasma zone during pyrocarbon formation H. Luhleich and P. Pflaum (Kernforschungsanlage Julich, lnstitut fiir Reaktorwerksto#e, D-5170 Jiilich, Postfach 1913). The formation of pyrocarbon is mainly
influenced by the plasma zone (Langmuir zone) adjacent to the hot surface. In order to clarify the mechanisms of pyrolysis, the investigation of the properties of this plasma zone is very important but, because of its very small dimensions, investigation by normal plasma diagnostic techniques is very difficult. Therefore, new methods have to be developed, and the first stage in this development is described here. 137. A model of pyrocarbons and its deposition mechanism R. L. R. Lefevre (OECD High Temperature Reactor Project (Dragon), AEE, Winfrith, England). 138. A quantitative chemical method for the determination of the disordered carbon component in pyrocarbon coatings of fuel particles E. A. Wolfrum and H. Nickel (Znstitutfiirleaktorwerkstoffe der Kemforschungsanlage Jiilich, D-517 Jiilich,
Postfach 1913).The chemical behaviour of the surface of pyrocarbon coatings of nuclear fuel particles was investigated in aqueous suspension by reaction with oxygen at room temperature. The concentration of the basic surface oxides is a function of the concentration of the disordered material component, which has a large internal surface, and can be identified by means of a pH change. Using this fact, a chemical method was developed which may be used for the quantiative determination of the concentration of this carbon component in the pyrocarbon coating.
307
139. Measurement and control of the microstructure of pyrolytic carbon on nuclear fuel particles
J. Guilleray, R. Zeyen, J-P. Audebeau and M. S. T. Price (OECD High Temperature Reactor Project, AEE, Winfrith, England). An initial set of experiments (termed HTRS) gave a good correlation between the observed size of spherical growth features (SGF) of pyrocarbon coatings and the value predicted by the deposition model of Lefevre. This paper gives an assessment of the method of measuring SGF and then applies the validated method to remeasurement of the HTR.5 series. The method is also applied to earlier irradiation results to close the loop manufacture-quality-performance. In addition studies of the deposition zone are reported with results of improvements made to the shape of particles. 140. fiber den Einfiug von Gliihbehandhmgen auf das Mikrogefiige von Pyrokohlenstoff-HfiIIschichten P. Krautwasser, H. Nickel (Znsitut fur Reaktorwerksto#e der Kemforschungsanlage Jiilich GmbH, D-517 Jiilich) and C. S. Yust (Oak Ridge National Laboratory, Oak Ridge, Tenn., U.S.A.). Transmission electron micros-
copy (TEM) and X-ray diffraction in the small and wide angle region were used to study the changes in the microstructure of pyrocarbon coatings as a function of high temperature treatment. The result indicate an ordering of the material with increasing temperature. In spite of specimen densification, i.e. decreasing porosity, an increase in inner surface area up to an annealing temperature of about 1800°Cwas found. This is explained by the measured decrease in pore size up to 1800°C followed by an increase in pore size at higher temperatures. 141. Porosity related to structure in pyrocarbons L. H. Ford, C. F. Bilsby and D. A. Moore (UKAEA, Reactor Group, Reactor Full Element Laboratories, Springfields, U.K.). The structure and porosity distribu-
tion in pyrocarbons deposited in a fluidised bed from either propylene or methane at 1200-2000°Con to nuclear fuel particles has been investigated by transmission and scanning electron microscopy, together with open and closed pore volume measurements. Mechanisms for the formation of the two basic pyrocarbon structures are discussed and a model is proposed to explain the dependence of both open and closed porosity on the deposition conditions and hydrocarbon source gas. 142. La texture des pyrocarbones isotropes de hasse temperature J. Pelissier et L. Lombard (Section d’Etudes de Metallurgic, Centre d’Etudes Nucleaires, B.P. 85 X, 38041 Grenoble, Cedex, France). Isotropic pyrocarbon depositd
on fuel particles from high temperature reactors is studied by transmission electron microscopy. The aim is to determine its texture and to come to a better understanding of its mode of fabrication. The material consist of an agglomerate of spherical growth features similar to those of carbon black. The spherical growth features are formed from cristallites of turbostratic carbon, which the