Method of optimizing composite preparation for electrical properties: maximum capacitance electrodes

• US 5,096,663 A
• Filed: 05/29/1990
• Issued: 03/17/1992
• Est. Priority Date: 05/29/1990
• Status: Expired due to Term

• Current Assignee: Auburn University
• Original Assignee: Auburn University
• Inventors: Tatarchuk, Bruce J.
• Primary Examiner(s): Lechert, Jr., Stephen J.
• Application Number:
  US07/529,870
• Time in Patent Office: 658 Days
• Field of Search: 419/11, 419/24, 419/34, 419/37, 419/38, 419/58
• US Class Current: 419/11
• CPC Class Codes: B22F 3/002 Manufacture of articles essentially made from metallic fibres
• CPC Class Codes: C04B 35/634 Polymers C04B35/636 takes precedence
• CPC Class Codes: C04B 35/63416 Polyvinylalcohols [PVA]; Polyvinylacetates
• CPC Class Codes: C04B 35/63432 Polystyrenes
• CPC Class Codes: C04B 35/63452 Polyepoxides
• CPC Class Codes: C04B 35/63456 Polyurethanes; Polyisocyanates
• CPC Class Codes: C04B 35/63468 Polyamides
• CPC Class Codes: C04B 35/63484 Urea-formaldehyde condensation polymers
• CPC Class Codes: C04B 35/6365 Cellulose or derivatives thereof
• CPC Class Codes: H01G 11/38 Carbon pastes or blends; Binders or additives therein
• CPC Class Codes: H01G 11/40 Fibres
• CPC Class Codes: H01G 11/70 characterised by their structure
• CPC Class Codes: H01G 11/86 specially adapted for electrodes carbonisation or activation of carbon for the manufacture of electrodes H01G11/34
• CPC Class Codes: H01M 2300/0008 Phosphoric acid-based
• CPC Class Codes: H01M 4/8621 containing only metallic or ceramic material, e.g. made by sintering or sputtering
• CPC Class Codes: H01M 4/8647 consisting of more than one material, e.g. consisting of composites
• CPC Class Codes: Y02E 60/13 Energy storage using capacitors
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

Composites of a matrix of metal fibers and carbon fibers interlocked in and interwoven among a network of fused metal fibers are inherently capable of displaying a broad range of values of a particular physical property. Where the composite is made by sintering a preform of the fiber network dispersed in a matrix of an organic binder, the value of the physical property of the resulting composite is a function of several independent variabiles which can be controlled during composite fabrication. With particular regard to the capacitance of a stainless steel-carbon fiber electrode, there is described a method of optimizing capacitance during electrode fabrication.

Claims

1. A method of optimizing the capacitance of a stainless steel fiber-carbon fiber composite electrode made by sintering in a hydrogen atmosphere a preform of a network of stainless steel and carbon fibers dispersed in a matrix of an organic binder, where the capacitance is optimized with respect to the independent variables of sintering temperature between a minimum temperature of T_min and a maximum temperature of T_max, sintering time, and the weight ratio of stainless steel fibers to carbon fibers at a constant carbon content between a minimum ratio of ratio_min and a maximum ratio of ratio_max, said method of optimizing comprising determining within the envelope bounded by T_min, T_max, ratio_min and ratio_max :

the rate equation, including apparent activation energy, for the increase in capacitance of the composite electrode;

the rate equation, including apparent activation energy, for the decrease in capacitance of the composite electrode;

from the two prior rate equations, the optimal sintering time at which the capacitance is maximized at a given sintering temperature and a given stainless steel to carbon ratio within said envelope;

the capacitance at the optimal sintering time as a function of the sintering temperature and stainless steel to carbon ratio;

choosing the temperature, T_opt, at which the capacitance is maximized with respect to a stainless steel to carbon ratio within said envelope, and choosing that stainless steel to carbon ratio at T_opt where the capacitance is a maximum.

2. The method of claim 1 where the weight ratio of stainless steel fibers to carbon fibers is between about 99 and about 0.02.

3. The method of claim 1 where the carbon fibers have a diameter from about 20 nm to about 1 mm.

4. The method of claim 1 where the carbon fibers have a surface area between 1 and about 1500 square meters per gram.

5. The method of claim 4 where the carbon fibers have a surface area between about 50 and 1350 square meters per gram.

6. The method of claim 5 where the carbon fibers have a surface area between about 250 and about 1000 square meters per gram.

7. The method of claim 1 further characterized in that the composite electrode has a surface area from about 0.001 to about 1350 square meters per gram.

8. The method of claim 1 where the stainless steel fibers have a diameter from about 0.1 to about 10 microns.

9. The method of claim 1 where the weight ratio of stainless steel to carbon is from about 10 to about 0.02.

10. The method of claim 1 where the binder is cellulose.

11. The method of claim 1 where the binder is an organic resin.

12. The method of claim 11 where the resin is selected from the group consisting of polyurethanes, polyvinyl alcohols, epoxy resins, styrene-butadiene latex, urea-formaldehde resins, melamine-formaldehyde resins, and polyamide-polyamine epichlorohydrin resins.

13. The method of claim 1 where the binder is present in an amount from about 2 to about 80 weight percent of the total preform.

14. The method of claim 13 where the binder is cellulose present in an amount between about 10 and about 60 weight percent.

15. A method of optimizing a physical property of a metal fiber-carbon fiber composite which is a network of said fibers having a plurality of bonded junctions at the metal fiber crossing points and made by sintering in a hydrogen atmosphere a preform of a network of metal and carbon fibers dispersed in a matrix of an organic binder, where the physical property is optimized with respect to the independent variables of sintering temperature between a minimum temperature of T_min and a maximum temperature of T_max, sintering time, and the weight ratio of metal fibers to carbon fibers at a constant carbon content between a minimum ratio of ratio_min and a maximum ratio of ratio_max, said method of optimizing comprising determining within the envelope bounded by T_min, T_max, ratio_min and ratio_max :

the rate equation, including apparent activation energy, for the increase in the value of said physical property of the composite;

the rate equation, including apparent activation energy, for the decrease in the value of said physical property of the composite;

from the two prior rate equations, the optional sintering time at which the value of said physical property is maximized at a given sintering temperature and a given metal to carbon ratio within said envelope;

the value of said physical property at the optimal sintering time as a function of the sintering temperature and metal to carbon ratio;

choosing the temperature, T_opt, at which the value of said physical property is maximized with respect to a metal to carbon ratio within said envelope, and choosing that metal to carbon ratio at T_opt where the value of said physical property is a maximum.

16. The method of claim 15 where the metal is selected from the group consisting of aluminum, titanium, vanadium, chromium, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, hafnium, tantalum, tungsten, rhenium, osmium, platinum, gold, antimony, berrylium, iridium, silicon, magnesium, manganese, gallium and their alloys.

17. The method of claim 15 where the weight ratio of metal fibers to carbon fibers is between about 99 and about 0.02.

18. The method of claim 15 where the carbon fibers have a diameter from about 20 nm to about 1 mm.

19. The method of claim 15 where the carbon fibers have a surface area between 1 and about 1500 square meters per gram.

20. The method of claim 19 where the carbon fibers have a surface area between about 50 and 1350 square meters per gram.

21. The method of claim 20 where the carbon fibers have a surface area between about 250 and about 1000 square meters per gram.

22. The method of claim 15 where the metal fibers have a diameter from about 0.1 to about 10 microns.

23. The method of claim 15 where the weight ratio of metal to carbon is from about 10 to about 0.02.

24. The method of claim 15 where the binder is cellulose.

25. The method of claim 15 where the binder is an organic resin.

26. The method of claim 15 where the resin is selected from the group consisting of polyurethanes, polyvinyl alcohols, epoxy resins, styrene-butadiene latex, urea-formaldehde resins, melamine-formaldehyde resins, and polyamide-polyamine epichlorohydrin resins.

27. The method of claim 15 where the binder is present in an amount from about 2 to about 80 weight percent of the total preform.

28. The method of claim 27 where the binder is cellulose present in an amount between about 10 and about 60 weight percent.