Sodium-sulfur cell component protected by a high chromium alloy and method for forming
AssigneeElectric Power Research Institute, Inc.
InventorsDong-Sil Park, Debajyoti Chatterji, Manfred W. Breiter
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Abstract
A corrosion resistant contiguous duplex chromium-carbon-iron alloy layer bonded to a steel and other similar ferrocarbon substrate for use as a cell casing for a sodium-sulfur cell. The outer layer includes in excess of 60 weight % chromium. The duplex layer is formed by pack chromizing in a pack of chromium and ammonium halide at elevated temperatures in hydrogen or inert gas atmosphere.
Claims15
An electrically conductive, corrosion resistant component for a sodium-sulfur cell comprising a ferrocarbon substrate and a non-porous chromium-iron-carbon duplex alloy surface layer chemically diffusion-bonded to the substrate, said duplex alloy surface layer comprising contiguous outer and inner layers, said outer layer containing in excess of about 60 weight % chromium, and said inner layer containing less than about 50 weight % chromium in direct contact with the substrate.
A method for forming a corrosion resistant layer on a ferrocarbon substrate comprising pack chromizing said substrate by totally submerging it in a solid pack of a chromium source and a halide activator at an elevated temperature to generate chromium halide at sufficient vapor pressure to diffuse the chromium into said substrate to form a duplex chromium-carbon-iron alloy layer chemically diffusion bonded to said substrate, said duplex alloy layer comprising contiguous outer and inner layers, said outer layer containing in excess of about 60 weight % chromium, and said inner layer containing less than about 50 weight % chromium in direct contact with the substrate, the vapor pressure of chromium halide in said solid pack being maintained at a predetermined level to form said duplex layer by providing a solid barrier over said pack and ferrocarbon substrate to inhibit loss of chromium halide vapor from said pack.
Dependencies are inferred from the claim text.