- Email: [email protected]
106. Observations concerning the determination of porosity in graphites
ABSTRACTS
222
106. Observations concerning the dete rmination of porosity in graphites.* J. M. Dickinson (Los Alamos ScientiJic Laboratory, University of California, Los Alamos, New Mexico). From an examination of a number of graphites using helium pycnometry, vapor pressure measurements, metallography, and the repeated intrusion and distillation of mercury, it was concluded that the results of mercury porosimetry measurement above some critical pressure range often reflect the effect of the measurement as well as the existing porosity. A method employing small-particle statistical techniques developed by Lewis and Goldman”) was applied to porosity measurements and numerical descriptions of the pore size distributions were obtained. Both lognormal and non-functional models were employed and examples are given for a number of graphites. * Work performed under the auspices of the United 1. LEWIS H. D. and GOLD,\~ANA., LA Report-3656.
States
Atomic
Energy
Commission.
107. Modification of pore size distribution in artificial graphites natural gas. Study by means of a new mercury porosimeter
densified by thermal cracking using y rays absorption.
of
L. Bochirol, M. Ortega and R. Teoule (C.E.A. Centre d’gtudes Nueliaires, Grenoble, France). A brief description of the porosimeter is given. It is specially designed for measurements of pore size distribution heterogeneities. Evolution of pore size distribution after deposition of pyrocarbon inside the porosity of conventional nuclear graphites is described. Comments are made on main parameters of deposition process, which uses natural gas thermal cracking at about 1000°C. The products show an improved resistance to radiolytic corrosion in CO,. 108. Low permeability graphite: A study of selected organic impregnants. D. R. Perels (National Institute of Metallurgy, Johannesburg, South Africa). Not presented at the Conference. IV. REACTIVITY AND SURFACES 109. Unsteady state transfer effects in the oxidation of graphite. J. T. Klaschka, J. B. Lewis, J. R. Stevens and R. Murdoch (Atomic Energy Research Establishment, Harwell, The effect of in-pore mass transport in limiting the steady state oxidation of nuclear graphite in air is now well understood. Hitherto, however, the unsteady state conditions, which arise when graphite is heated in an inert gas and suddenly exposed to air, have not been examined. We have developed a mathematical model which enables the temperature and gas concentration profiles inside a large block of graphite treated in this way to be calculated. The model has been tested experimentally and the observed local temperature changes and external gas concentration found to be in reasonable agreement with the calculated values.
England).
110. Air oxidation
studies
in a long graphite
channel.
P. Hawtin, J. A. Gibson and R. A. Huber (Atomic Energy Research Establishment, Harwell, England). The effect of in-pore mass transport in limiting the rate of oxidation of a 14 ft-high vertical channel of nuclear graphite, exposed to air along the bore only, has been examined. Oxidations were carried out in the first transition zone, with a finite concentration of oxygen at the exterior of the channel and with oxygen concentration gradients in both the axial and radial directions. The local gas compositions at points in the bore and at the exterior were measured and were found to agree well with those calculated from an extension of an existing mathematical model. 111. Combustion behavior of ultra-pure, dense carbon spheres at atmospheric pressure. I. A new experimental technique for deter mining the depth of reaction during internal burning. R. H. Essenhigh (Pennsylvania State University, University Park, Pennsylvania) and R. W. Froberg (Stackpole Carbon Company, St. Marys, Pennsylvania). A technique has been developed for continuously measuring the extent of internal burning during the oxidation of carbon spheres in air at temperatures from 500 to 1200°C. Carbon spheres (0.5~in. dia.) were hung from a recording balance into an electrically heated vertical tube furnace. Inert and/or oxidizing gases were fed through the tube at 0.1 and 1 .O cm/set STP. The burning sphere was weighed continuously by the balance and measured simultaneously with a calibrated telescope-projector. It was found that below 700°C the spheres burned at constant volume. Above 1 lOO”C, the reaction was confined to the geometrical surface of the sphere. Between 700°C and 1 lOO”C, the depth of penetration of the reaction into the sphere decreased from R (sphere radius) to zero. The employment of this technique and the results of
222
106. Observations concerning the dete rmination of porosity in graphites.* J. M. Dickinson (Los Alamos ScientiJic Laboratory, University of California, Los Alamos, New Mexico). From an examination of a number of graphites using helium pycnometry, vapor pressure measurements, metallography, and the repeated intrusion and distillation of mercury, it was concluded that the results of mercury porosimetry measurement above some critical pressure range often reflect the effect of the measurement as well as the existing porosity. A method employing small-particle statistical techniques developed by Lewis and Goldman”) was applied to porosity measurements and numerical descriptions of the pore size distributions were obtained. Both lognormal and non-functional models were employed and examples are given for a number of graphites. * Work performed under the auspices of the United 1. LEWIS H. D. and GOLD,\~ANA., LA Report-3656.
States
Atomic
Energy
Commission.
107. Modification of pore size distribution in artificial graphites natural gas. Study by means of a new mercury porosimeter
densified by thermal cracking using y rays absorption.
of
L. Bochirol, M. Ortega and R. Teoule (C.E.A. Centre d’gtudes Nueliaires, Grenoble, France). A brief description of the porosimeter is given. It is specially designed for measurements of pore size distribution heterogeneities. Evolution of pore size distribution after deposition of pyrocarbon inside the porosity of conventional nuclear graphites is described. Comments are made on main parameters of deposition process, which uses natural gas thermal cracking at about 1000°C. The products show an improved resistance to radiolytic corrosion in CO,. 108. Low permeability graphite: A study of selected organic impregnants. D. R. Perels (National Institute of Metallurgy, Johannesburg, South Africa). Not presented at the Conference. IV. REACTIVITY AND SURFACES 109. Unsteady state transfer effects in the oxidation of graphite. J. T. Klaschka, J. B. Lewis, J. R. Stevens and R. Murdoch (Atomic Energy Research Establishment, Harwell, The effect of in-pore mass transport in limiting the steady state oxidation of nuclear graphite in air is now well understood. Hitherto, however, the unsteady state conditions, which arise when graphite is heated in an inert gas and suddenly exposed to air, have not been examined. We have developed a mathematical model which enables the temperature and gas concentration profiles inside a large block of graphite treated in this way to be calculated. The model has been tested experimentally and the observed local temperature changes and external gas concentration found to be in reasonable agreement with the calculated values.
England).
110. Air oxidation
studies
in a long graphite
channel.
P. Hawtin, J. A. Gibson and R. A. Huber (Atomic Energy Research Establishment, Harwell, England). The effect of in-pore mass transport in limiting the rate of oxidation of a 14 ft-high vertical channel of nuclear graphite, exposed to air along the bore only, has been examined. Oxidations were carried out in the first transition zone, with a finite concentration of oxygen at the exterior of the channel and with oxygen concentration gradients in both the axial and radial directions. The local gas compositions at points in the bore and at the exterior were measured and were found to agree well with those calculated from an extension of an existing mathematical model. 111. Combustion behavior of ultra-pure, dense carbon spheres at atmospheric pressure. I. A new experimental technique for deter mining the depth of reaction during internal burning. R. H. Essenhigh (Pennsylvania State University, University Park, Pennsylvania) and R. W. Froberg (Stackpole Carbon Company, St. Marys, Pennsylvania). A technique has been developed for continuously measuring the extent of internal burning during the oxidation of carbon spheres in air at temperatures from 500 to 1200°C. Carbon spheres (0.5~in. dia.) were hung from a recording balance into an electrically heated vertical tube furnace. Inert and/or oxidizing gases were fed through the tube at 0.1 and 1 .O cm/set STP. The burning sphere was weighed continuously by the balance and measured simultaneously with a calibrated telescope-projector. It was found that below 700°C the spheres burned at constant volume. Above 1 lOO”C, the reaction was confined to the geometrical surface of the sphere. Between 700°C and 1 lOO”C, the depth of penetration of the reaction into the sphere decreased from R (sphere radius) to zero. The employment of this technique and the results of