GB1495561A - Blocking of micropores in a structure - Google Patents

Abstract

1495561 Filling micropores of a structural member CENTRAL ELECTRICITY GENERATING BOARD 20 March 1975 [1 April 1974] 14420/74 Heading D1P A method of blocking micropores in a structural member such as a sodium/water heat-exchanger comprises exposing one of the faces of the exchanger to a vapour phase carbonyl, oxide or hydroxide of nickel and exposing the other face with a suitable reactant thereby causing the deposition of nickel or an oxide thereof in the micropores nickel oxide if deposited, being subsequently reduced to nickel by passing a reducing gas over the face of the exchanger to be in contact with sodium in use. Preferably the face to be in contact with sodium is exposed to vapour phase nickel carbonyl carried by oxygen-free carbon monoxide and the opposite face is exposed to either an oxygen-containing gas, e.g. air, or an inert gas, e.g. oxygen-free Argon or Nitrogen thereby depositing either the oxide of the nickel or the nickel itself in the micropores, the inert gas being a gas which does not react chemically with the other materials in the context. If oxide of nickel is deposited in the micropores continued circulation of the carbonyl and carbon monoxide or purging the carbonyl containing carbon monoxide with carbonyl free carbon monoxide and then passing carbon monoxide or another effective reducing agent, e.g. hydrogen, will cause the exposed surface of the nickel oxide plugs in the micropores to be reduced to metallic nickel. The carbonyl is passed over the face of the exchanger to be in contact with sodium and particularly so when using nickel oxide to block pores. Preferably one face of the exchanger is exposed to nickel carbonyl in an inert gas and the other face to a gas containing 0.1 to 1% by volume of hydrogen sulphide or carbon disulphide in air or in an inert carrier gas, which may be the same as that used for the carbonyl and which contains traces of water vapour up to 0.2% by volume and/or oxygen upto 2% by volume, the gases on the two faces being at substantially the same pressure. The nickel carbonyl is preferably transported in an inert carbon monoxide-free carrier gas such as nitrogen, argon or carbon dioxide and may constitute 10-20% by volume of the total gas phase on the carbonyl side of the member. The process may be carried out at temperatures of 290-400 K. and preferably at room temperatures, e.g. 290 K to 300 K. In a modified form one face of the exchanger is exposed to a mixture of nickel carbonyl and hydrogen sulphide with an inert carrier gas and the opposite face is exposed to air or to nitrogen containing oxygen or water vapour, the gases being at substantially equal pressures and at 290 K to 330 K. The method may be carried out at ambient temperature and at ambient pressure.