METHOD FOR IMPREGNATION OF GRAPHITE

• US 3,844,972 A
• Filed: 10/24/1958
• Issued: 10/29/1974
• Est. Priority Date: 10/24/1958
• Status: Expired due to Term

• Current Assignee: Geoffrey R. Tully Jr, Leslie D. Christensen
• Original Assignee: Geoffrey R. Tully Jr, Leslie D. Christensen
• Inventors: Tully, Geoffrey R. Jr., Christensen, Leslie D.
• Primary Examiner(s): Quarforth, Carl D.
• Assistant Examiner(s): Nelson, P. A.
• Application Number:
  US04/769,521
• Time in Patent Office: 5,849 Days
• Field of Search: 23/14.5A 204/193.38,154.38 117/220,228,119,113,65 106/56 252/31.1R 176/82 264/.5 423/261
• US Class Current: 252/639
• CPC Class Codes: C04B 35/52 based on carbon, e.g. graphite
• CPC Class Codes: C04B 41/009 characterised by the material treated
• CPC Class Codes: C04B 41/4505 characterised by the method of application
• CPC Class Codes: C04B 41/50 with inorganic materials
• CPC Class Codes: C04B 41/81 Coating or impregnation
• CPC Class Codes: G21C 3/64 Ceramic dispersion fuel, e.g. cermet
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors
• CPC Class Codes: Y10T 428/30 Self-sustaining carbon mass or layer with impregnant or other layer

Abstract

Impregnation of graphite with uranyl nitrate dihydrate in tertiary butyl alcohol solution.

Claims

1. A PROCESS FOR IMPREGNATING POROUS GRAPHITE WITH URANYL NITRATE DIHYDRATE DISSOLVED IN TERTIARYL BUTYL ALCOHOL AND THEREAFTER REMOVING SAID SOLVENT, COMPRISING THE STEPS OF SUBJECTING SAID RAPHITE TO A VACUUM TO EGAS SAME, ENVELOPING SAID GRAPHTE PIECE WITH SAID SOLUTION AND PRESSURIZING AN AIR-SPACE THEREOVER LIMITED IN A VOLUME PREFERABLY TO A SPACE ABOUT ONEFIFTH THE TOTAL VOLUME OF THE GRAPHITE PIECE TO FORCE SAID SOLUTION INTO SAID GRAPHITE AND THEREAFTER EVACUATONG SAID AIR-SPACE TO A PRESSURE APPROACHING BUT NOT LOWER THAN. 19 IN. HG, SAID EVACUATED SPACE BEING THEREAFTER CLOSED TO THE EVACUATION MEANS FOR A PERIOD OF TIME OF THE ORDER OF AT LEAST 30 MINUTES FOR MAXIMUM PENETRATION IN THE OVERPRESSURE STEP, REPEATING SAID EVACUATION AND PRESSURIZATION STEPS UNTIL SAID GRAPHITE PIECE IS IMPREGNATED TO A DESIRED DEPTH, REMOVING SAID PEICE FROM SAID SOLUTION, FREEZING SAID IMPREGENATED SOLUTION, SUBJECTING SAID GRAPHITE PIECE CONTAINING SAID FROZEN SOLUTION TO A VACCUM, CONTACTING SAID GRAPHITE PIECE WITH AN OVERPRESSURE OF NON-REACTIVE GAS HEATED TO A TEMPERATURE IN THE RANGE OF FROM 40* TO 55*C FOR A PERIOD OF TIME NOT LONGER THAN 2 MINUTES, EVACUATING SAID GAS AND SUBLIMED SOLVENT FROM AID GRAPHITE, AND ALTERNATELY REPEATING SAID LATTER PRESSURE AND VACUUM STEPS UNTIL ALL OF SAID SOLVENT HAS BEEN REMOVED.

2. A process for impregnating graphite having 10 to 20 volume percent voids and uniform pore distribution in the general range of 0.5 to 15 microns in diameter, comprising the steps of preparing a solution off uranyl nitrate dihydrate dissolved in tertiary butyl alcohol solvent of containing an additive selected from the group consisting of lactic acid, acetic acid, monochloroacetic acid and acetic anhydride, said solution being maintained at a temperature above solidification and below about 70* C and having a viscosity in the range of from 10 to 40 centipoises, enveloping said graphite piece with a quantity of said solution sufficient to cover said piece during impregnation of the entire voids space desired to be impregnated, evacuating an air-space smaller than said graphite piece over said solution to a pressure approaching, but not lower than about -19 in. Hg, shutting off said evacuating means upon reaching said pressure for a period of time of at least 30 minutes for maximum penetration during the over-pressure step, whereby bubbles of gas from said graphite seek the level of said evacuated air-space, pressurizing said air-space over said solution with a non-reactive gas for at least 30 minutes at a pressure of 30 psig to force said solution into said graphite, alternately repeating said evacuating and pressurizing steps until impregnation to the desired depth is completed, separating said piece from said solution, freezing said impregnated solution, subjecting said impregnated, frozen graphite to a vacuum, contacting said impregnated, frozen graphite with an overpressure of non-reactive gas heated to a temperature in the range of from 40* to 55* C for a period of time not longer than 2 minutes, whereby a small amount of solvent is sublimed without exudation and alternately repeating said latter pressure and evacuation steps until all of said solvent has been removed.

3. The process of claim 2 in which said impregnant solution is maintained at a temperature in the range of from 50* to 70* C.

4. The process of claim 2 in which the overpressure in said sublimation step cycle is within the range of from 10 to 30 psig.

5. The process of claim 2 in which the vacuum pressure in said sublimation step cycle is 100 to 500 microns Hg, said vacuum being maintained for a period of from 10 l to 30 minutes.

6. A process for impregnating graphite having 10 to 20 volume percent voids and uniform pore distribution in the general range of 0.5 to 15 microns in diameter comprising the steps of preparing a solution of uranyl nitrate dihydrate dissolved in tertiary butyl alcohol and containing an additive selected from the group consisting of lactic acid, acetic acid, monochloroacetic acid and acetic anhydride, said solution being maintained at a temperature above solidification and below about 70* C and having a viscosity in the range of from 10 to 40 centipoises, enveloping said graphite piece with a quantity of solution sufficient to cover said piece during impregnation of the entire voids space desired to be impregnated, evacuating an air-space less than one-fifth the size of said graphite piece over said solution to a pressure approaching, but not lower than about -19 in. Hg, shutting off said evacuating means whereby bubbles of gas from said graphite seek the level of said evacuated air-space for a period of time of the order of at least 30 minutes, pressurizing said air-space over said solution with a non-reactive gas to force said solution into said graphite for a period of at least 30 minutes at a pressure of 30 psig for maximum penetration, and alternately repeating sAid evacuation and pressurization steps until impregnation to the desired depth is completed.

7. A process for impregnating solid graphite having 10 to 20 volume percent voids and uniform pore distribution in the general range of 0.5 to 15 microns diameter with at least 2.00 grams uranium per 100 grams graphite to a depth of at least 650 mils, the steps comprising preparing a solution of uranyl nitrate dihydrate dissolved in tertiary butyl alcohol solvent, said solution containing more than about 20 grams uranium per 100 grams of solution together with an additive selected from the group consisting of lactic acid, acetic acid, monochloroacetic acid and acetic anhydride, said solution being maintained at a temperature above solidification and below about 70* C and having a viscosity in the range of from 10 to 40 centipoises, outgassing a graphite piece to be impregnated to a depth approaching at least 650 mils enveloping said graphite piece with a quantity of said solution sufficient to cover said piece during impregnation of the entire void space desired to be impregnated, said solution being maintained at a temperature of about 50*C during the impregnation cycle, evacuating an air-space about one-fifth the volume of said piece over said solution to a pressure of about -19 in. Hg, shutting off said evacuating means from said air space, whereby bubbles of gas from said graphite seek the level of said evacuated air-space, pressuring said air-space over said solution with a non-reactive gas at an over pressure of 10 to 30 psig for a period of time from 20 to 30 minutes to force said solution into said graphite, alternately repeating said evacuating and pressurizing steps for at least about 12 hours, whereby impregnation to a depth of at least about 650 mils is obtained, separating said piece from said solution, freezing said impregnated solution, subjecting said impregnated graphite containing said frozen impregnant to a vacuum of at least 500 microns Hg for a period of at least 10 to 30 minutes, contacting said impregnated, frozen graphite with 10 to 30 psig overpressure of a non-reactive gas heated to a temperature in the range of 40* to 55*C for a period of time not longer than about 2 minutes, whereby small amounts of solvent are sublimated, and alternatively repeating said latter pressure and evacuation steps until all of said solvent has been removed.