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151. Creep of carbon mixes
ABSTRACTS
369
149. Mechanical and thermal properties of heat-treatedcoal H. Honda, Y. Sanada and T. Furuta (Resources Research Institute, Kuwquchi, Saitama, Jq~n). Studies of the hardness (Shore and Brinell), the mechanical strength (compression and transverse), the dynamic Young’s Modulus, the thermal conductivity and the thermal expansion coefficient for coalcarbon compact as a function of heat treatment temperature (HTT) were carried out. Coal-carbon compact was made from Akabira weakly caking coal (d.a.f. C=83.4%) powder under pressure of 2000 kg/cm’ at room temperature without binder. The values of Brine11 hardness, the mechanical strength, and the dynamic Young’s modulus increase with increase of HTT, have a maximum at HTT 1200°C and then decrease with HTT, although the Shore hardness value shows two maxima over the temperature range 500 to 3150°C. The values of the mechanical strength of coal-carbon compact are very large in comparison with the ordinary pitch-bonded carbons. This depends upon the rigid binding among coal particles which occurred through the carbonization process. The thermal conductivity of coal-carbon increases with the increase of HTT. Good correlation between the thermal and the electric conductivity has been found. In Akabira coal-carbon, the thermal expansion coefficient decreases with increase of HTT, shows a minimum at about HTT 15OO”C, and increases with HTT.
150. Properties of a low-permeation graphite for molten-salt nuclear reactors” W. H. Cook and A. Taboada (Oak Ridge National Laboratory, Oak Ridge, Tennessee). The properties of a new high-density nuclear grade graphite designed specifically for use without cladding with molten salts is described. These properties are indicated relative to the Oak Ridge National Laboratory MoltenSalt Reactor Experiment, a 10 MW thermal reactor that uses molten fluoride fuel at approximately 1200°F in contact with unclad graphite inside a special nickel-base alloy vessel. The graphite has an average bulk density of 1.86 g/cm3 and is basically an impregnated, extruded petroleum coke bonded with coal tar pitch heated to 5070°F or higher. It has a low permeation that prevents salt from penetrating the matrix of the graphite under pressures as high as 150 psig, or three times the maximum design pressure for the Molten-Salt Reactor Experiment. The average tensile strength of the graphite is 5440 psi parallel to the grain in the absence of flaws. The modulus of elasticity is 3.2 x lo6 and 1.0 x lo6 psi parallel and perpendicular to the grain, respectively. Thermal conductivity of the graphite at 90°F is 110 and 60 Btu/ft hr”F parallel and perpendicular to the grain, respectively. Initial data indicate that its contraction under irradiation exceeds that of low-density (1.70 g/cm3) needle-coke grade AGOT graphite; however, contraction is relatively low for a fine-grained, impregnated graphite. *Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation.
151. Creep of carbon mixes S. S. Chari and C. L. Verma (National Physical Laboratory, New Delhi, India). The creep of extruded green carbon rods using petroleum coke as filler and pitch tar as binder was measured at room temperature in torsion creep apparatus designed in this Laboratory. The shear strain creep was found to fit closely the Andrade cubic creep function with steady creep parameter k equal to zero. The creep function could be represented by (s - EO)/eO=j?tn,where E is the shear strain at time t, co is the instantaneous shear strain, p and n are the usual Andrade constants. The factor n increases with stress. The range of values for n is between 0.29 to 0.35. The factor D increases with the stress as p=AP where 6 is the stress and A and m are constants. The value of nl comes out to be 0.4. It was shown that the carbon mix can be regarded as a matrix of aggregates with the binder providing the viscous medium. The creep is due to the movement of individual units within the aggregate and the steady flow results when the aggregates themselves move with respect to each other. 152. Viscoelastic
properties
of carbon
mixes
S. S. Chari (National Physical Laboratory, New Delhi, India). The critical stress in the extrusion of polymers above which the extrudate becomes irregular was found to be a function of the rubberlike
369
149. Mechanical and thermal properties of heat-treatedcoal H. Honda, Y. Sanada and T. Furuta (Resources Research Institute, Kuwquchi, Saitama, Jq~n). Studies of the hardness (Shore and Brinell), the mechanical strength (compression and transverse), the dynamic Young’s Modulus, the thermal conductivity and the thermal expansion coefficient for coalcarbon compact as a function of heat treatment temperature (HTT) were carried out. Coal-carbon compact was made from Akabira weakly caking coal (d.a.f. C=83.4%) powder under pressure of 2000 kg/cm’ at room temperature without binder. The values of Brine11 hardness, the mechanical strength, and the dynamic Young’s modulus increase with increase of HTT, have a maximum at HTT 1200°C and then decrease with HTT, although the Shore hardness value shows two maxima over the temperature range 500 to 3150°C. The values of the mechanical strength of coal-carbon compact are very large in comparison with the ordinary pitch-bonded carbons. This depends upon the rigid binding among coal particles which occurred through the carbonization process. The thermal conductivity of coal-carbon increases with the increase of HTT. Good correlation between the thermal and the electric conductivity has been found. In Akabira coal-carbon, the thermal expansion coefficient decreases with increase of HTT, shows a minimum at about HTT 15OO”C, and increases with HTT.
150. Properties of a low-permeation graphite for molten-salt nuclear reactors” W. H. Cook and A. Taboada (Oak Ridge National Laboratory, Oak Ridge, Tennessee). The properties of a new high-density nuclear grade graphite designed specifically for use without cladding with molten salts is described. These properties are indicated relative to the Oak Ridge National Laboratory MoltenSalt Reactor Experiment, a 10 MW thermal reactor that uses molten fluoride fuel at approximately 1200°F in contact with unclad graphite inside a special nickel-base alloy vessel. The graphite has an average bulk density of 1.86 g/cm3 and is basically an impregnated, extruded petroleum coke bonded with coal tar pitch heated to 5070°F or higher. It has a low permeation that prevents salt from penetrating the matrix of the graphite under pressures as high as 150 psig, or three times the maximum design pressure for the Molten-Salt Reactor Experiment. The average tensile strength of the graphite is 5440 psi parallel to the grain in the absence of flaws. The modulus of elasticity is 3.2 x lo6 and 1.0 x lo6 psi parallel and perpendicular to the grain, respectively. Thermal conductivity of the graphite at 90°F is 110 and 60 Btu/ft hr”F parallel and perpendicular to the grain, respectively. Initial data indicate that its contraction under irradiation exceeds that of low-density (1.70 g/cm3) needle-coke grade AGOT graphite; however, contraction is relatively low for a fine-grained, impregnated graphite. *Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation.
151. Creep of carbon mixes S. S. Chari and C. L. Verma (National Physical Laboratory, New Delhi, India). The creep of extruded green carbon rods using petroleum coke as filler and pitch tar as binder was measured at room temperature in torsion creep apparatus designed in this Laboratory. The shear strain creep was found to fit closely the Andrade cubic creep function with steady creep parameter k equal to zero. The creep function could be represented by (s - EO)/eO=j?tn,where E is the shear strain at time t, co is the instantaneous shear strain, p and n are the usual Andrade constants. The factor n increases with stress. The range of values for n is between 0.29 to 0.35. The factor D increases with the stress as p=AP where 6 is the stress and A and m are constants. The value of nl comes out to be 0.4. It was shown that the carbon mix can be regarded as a matrix of aggregates with the binder providing the viscous medium. The creep is due to the movement of individual units within the aggregate and the steady flow results when the aggregates themselves move with respect to each other. 152. Viscoelastic
properties
of carbon
mixes
S. S. Chari (National Physical Laboratory, New Delhi, India). The critical stress in the extrusion of polymers above which the extrudate becomes irregular was found to be a function of the rubberlike