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Low temperature sintering of nickel ferrite powders

Inactive Publication Date: 2005-04-28
ARCONIC INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0009] This need is met by the method of the present invention of producing a sintered nickel ferrite component in which particles of iron oxide and nickel oxide are blended with an alkaline metal borate mineralizer. The mixture is shaped into a green compact. The green compact is sintered at temperatures less than about 1400° C. It has been found that use of an alkaline metal borate mineralizer allows for sufficient densification at temperatures less than 1400° C. with larger grain sizes and greater uniformity through the thickness of the sintered component as compared to components produced according to the prior art. The

Problems solved by technology

The most significant challenge to the commercialization of inert anode technology is the anode material.
In addition, the thermal energy which is stored in the anode following high temperature sintering creates thermal stresses within the anode that can result in failure of the anode.
H

Method used

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  • Low temperature sintering of nickel ferrite powders
  • Low temperature sintering of nickel ferrite powders
  • Low temperature sintering of nickel ferrite powders

Examples

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Example

Example 1 Comparative

[0022] A mixture containing 68.2 wt. % Fe2O3, 29.8 wt. % NiO and 2 wt. % mixture of polyethylene glycol (PEG) and polyvinyl alcohol (PVA) binders was pressed into a compact and sintered in air at 1500° C. for two hours. FIGS. 1A and 1B are photomicrographs of the resultant component after polishing near its edge and in the bulk of the component, respectively. FIGS. 1C and 1D are photomicrographs of the component after thermal etching near the edge and in the bulk, respectively. It can be seen that away from the edge area, the grain sizes are significantly reduced with increased quantity of grain boundaries.

Example

Example 2

[0023] A mixture of 68.2 wt. % Fe2O3, 29.8 wt. % NiO, 2 wt. % mixture of PEG and PVA binders and 0.045 wt. % boron from lithium borate were pressed into a die to produce a green compact. The compact was sintered in air at 1200° C. for two hours. FIGS. 2A and 2B are photomicrographs of the resultant component as polished in the edge area and in the bulk of the component, respectively. FIGS. 2C and 2D are photomicrographs of the component after thermal etching near the edge and in the bulk, respectively. It can be seen that the quantity of grain boundaries does not increase within the bulk of the component from the edge area and that the grain sizes are larger and more uniform than those produced in Example 1.

[0024] Example 2 was repeated except that sodium borate was used in place of lithium borate. FIGS. 3A and 3B are photomicrographs of the resultant component as polished in the edge area and in the bulk of the component, respectively. FIGS. 3C and 3D are photomicrograph...

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Abstract

Method of producing sintered nickel ferrite powder having steps of mixing the particles of iron oxide and nickel oxide with an alkali metal borate mineralizer, compacting the mixture to produce green compact and heating the compact at temperatures less than about 1400° C. Resulting product which may be in the form of a non-consumable electrode for electrolysis of alumina, exhibits satisfactory mechanical properties and electrical properties with enhanced chemical stability while being produced at significantly lower sintering temperatures than previously employed.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an improved process for sintering nickel ferrite powder, more particularly to including a mineralizer in the nickel ferrite powder which allows for reduced sintering temperatures to achieve high densification of the powder into a shaped component. [0003] 2. Prior Art [0004] Conventional production of aluminum by the Hall-Heroult process involves electrolysis of alumina dissolved in molten salts of aluminum fluoride and sodium fluoride using carbon anodes. The anodes are suspended in a bath of the electrolytic fluid. Electric current supplied to the anodes results in production of electrons for reducing the alumina to aluminum which accumulates as a molten aluminum pad. The molten aluminum pad acts as a liquid metal cathode. During this process, the carbon anodes continually react with oxygen released during the reduction of alumina to produce CO2 thereby decomposing and consuming the...

Claims

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Application Information

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IPC IPC(8): C25C3/12C25D3/44
CPCC25C3/12
Inventor EASLEY, MICHAEL A.KOLEK, PAULA L.RAMOS, JORGE A.STEWART, PATRICIA A.DIMILIA, ROBERT A.DYNYS, JOSEPH M.WIESERMAN, LARRY F.WEIRAUCH, DOUGLAS A. JR.
Owner ARCONIC INC
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