Thermally insulating structural components resistant to high temperature corrosive media

Abstract

The invention relates to a thermally insulating structural component ( 10 ) such as a cover of a container ( 5 ), in particular a molten salt electrolytic cell which component ( 10 ) is inert and resistant to corrosive media ( 1 ) at high temperature in the form of liquids, vapours and/or gases, in particular NaAlF4, AlF3, HF or O2, and which during use is exposed to such corrosive media ( 1 ). The component ( 10 ) comprises thermal insulating material ( 30 ) shielded from the corrosive media ( 1 ) by an openly porous or reticulated alumina structure ( 20 ) which is made impermeable by a compact filler material ( 15 ) resistant and inert to the corrosive media and comprising compacted particles of refractory material, in particular alumina cement. The structural component ( 10 ) can have a top metallic shell ( 40 ) which extends over the thermal insulating material ( 30 ) and downwards along lateral sides of the component ( 10 ). The insulating material ( 30 ) can be secured to the alumina structure ( 20 ) through nuts ( 50 ) and bolts ( 60 ).

1 . A thermally insulating cover of a cell for the electrowinning of aluminium from alumina dissolved in a fluoride-based molten electrolyte, which cover is inert and resistant to high temperature corrosive media in the form of liquids, vapours and/or gases that are contained in the cell and that comprise vapours from the electrolyte, and which cover during use is exposed to such corrosive media, said cover comprising thermal insulating material shielded from the corrosive media by an openly porous or reticulated alumina structure which is made impermeable by a compact filler made of material resistant and inert to said corrosive media, the filler material comprising compacted particles of refractory material.  
   
   
       2 . The thermally insulating cover of  claim 1 , wherein said filler completely fills an outermost part of the structure, in particular a outermost bottom part.  
   
   
       3 . The thermally insulating cover of  claim 2 , wherein the filler extends throughout the alumina structure.  
   
   
       4 . The thermally insulating cover of  claim 1  or  2 , wherein the alumina structure is partly filled by the filler, leaving a filler-free part of the alumina structure, in particular a filler-free top part.  
   
   
       5 . The thermally insulating cover of  claim 4 , wherein the filled part forms a layer in the alumina structure.  
   
   
       6 . The thermally insulating cover of any preceding claim, wherein the alumina structure is a plate having a thickness in the range of 20 to 150 mm.  
   
   
       7 . The thermally insulating cover of  claim 6  when depending on  claim 5 , wherein the filler forms a layer in the plate, the layer having a thickness in the range of 10 to 100 mm.  
   
   
       8 . The thermally insulating cover of any preceding claim, wherein the alumina structure is covered with a layer made of the filler material.  
   
   
       9 . The thermally insulating cover of  claim 8 , wherein the layer covering the alumina structure has a thickness in the range of 2 to 10 mm.  
   
   
       10 . The thermally insulating cover of any preceding claim, wherein the refractory material of the filler comprises at least one compound selected from metal oxides, carbides and nitrides.  
   
   
       11 . The thermally insulating cover of  claim 10 , wherein the filler comprises a mixture of metal oxide particles with particles of at least one compound selected from carbides and nitrides.  
   
   
       12 . The thermally insulating cover of any preceding claim, wherein the filler is a slurry-applied filler comprising dried colloidal and/or non-colloidal particles of at least one compound selected from metal oxides, carbides and nitrides and precursors thereof.  
   
   
       13 . The thermally insulating cover of  claim 12 , wherein the filler comprises a cement that consists predominantly of at least one of alumina, silica and titania particles.  
   
   
       14 . The thermally insulating cover of claims  13 , wherein the cement comprises a mixture of silica an alumina, preferably containing at least 80 weight % alumina.  
   
   
       15 . The thermally insulated cover of  claim 12 , wherein the filler comprises a mixture of alumina and titania.  
   
   
       16 . The thermally insulating cover of  claim 12 , wherein the filler comprises particles of at least one compound selected from carbides and nitrides in a dried colloidal metal oxide carrier.  
   
   
       17 . The thermally insulating cover of any preceding claim, which comprises one or more insulating layers and a protective layer that shields the insulating layer(s) from said corrosive media, the protective layer being made of said openly porous or reticulated filled alumina structure.  
   
   
       18 . The thermally insulating cover of  claim 17 , wherein the insulating layer(s) and the protective layer are mechanically secured together.  
   
   
       19 . The thermally insulating cover of  claim 18 , wherein the insulating layer(s) and the protective layer are mechanically secured together by means of one or more metallic attachment members extending through vertical holes of the protective layer and the insulating layer.  
   
   
       20 . The thermally insulating cover of  claim 19 , wherein the or each vertical hole in the insulating layer(s) extends into a recess located in a bottom face of the alumina structure, said recess being arranged to embed a head of one or more of the attachment members, said recess being filled with said filler to protect the attachment member from said corrosive media.  
   
   
       21 . The thermally insulating cover of  claim 17 ,  18 ,  19  or  20 , which comprises a top metallic shell which extends over the insulating layer(s) and downwards along lateral sides of the cover.  
   
   
       22 . A cell for the electrowinning of aluminium from alumina dissolved in a fluoride-based molten electrolyte, comprising a thermally insulating cover as defined in any preceding claim.