# US 7,745,029 B2 · Ferritic steels for solid oxide fuel cells and other high temperature applications

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- Number: US 7,745,029 B2
- Document ID: US7745029B2
- Status: Granted
- Kind: B2
- Application number: 11/593,927
- Filed: 2006-11-07
- Published: 2008-05-08
- Granted: 2010-06-29
- Earliest claimed: 2006-11-07
- Assignees: General Electric Company
- Inventors: Melvin Jackson; Canan Uslu Hardwicke; Hari Nadathur Seshadri; Amitabh Verma; Sheela Ramasesha; Aravind Dattatrayarao Chinchure; Kaushik Vaidya
- Web page: https://patentgrep.com/patent/US7745029B2

## CPC

- H01M 8/021: Alloys based on iron
- C22C 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides}
- C22C 38/22: with molybdenum or tungsten
- H01M 8/0204: Non-porous and characterised by the material
- H01M 8/0228: in the form of layered or coated products
- H01M 8/12: operating at high temperature, e.g. with stabilised ZrO2 electrolyte
- Y02E 60/50: Fuel cells
- H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

Oxidation-resistant ferritic steel alloys for high temperature applications consist essentially of chromium (Cr) in an amount from about 18 to about 25 atom percent, tungsten (W) in an amount from about 0.5 to about 2 atom percent, manganese (Mn) in an amount less than about 0.8 atom percent, aluminum (Al) in an amount less than about 0.2 atom percent, silicon (Si) in an amount less than about 0.1 atom percent, and rare earth metals that includes neodymium (Nd) in an amount from about 0.002 to about 0.2 atom percent with the balance being iron (Fe). Also disclosed herein are solid oxide fuel cells that include separators formed for the oxidation resistant ferritic alloys.

## Claims

### Claim 1

Oxidation-resistant ferritic steel alloys for high temperature applications consist essentially of chromium (Cr) in an amount from about 18 to about 25 atom percent, tungsten (W) in an amount from about 0.5 to about 2 atom percent, manganese (Mn) in an amount less than about 0.8 atom percent, aluminum (Al) in an amount less than about 0.2 atom percent, silicon (Si) in an amount less than about 0.1 atom percent, and rare earth metals that includes neodymium (Nd) in an amount from about 0.002 to about 0.2 atom percent with the balance being iron (Fe).

### Claim 2 (depends on 1)

The oxidation-resistant ferritic steel alloys as in claim 1, wherein the alloys have an oxide layer of less than about 5 microns after exposure at 850° C. after 1,500 hours.

### Claim 3 (depends on 1)

The oxidation-resistant ferritic steel alloy as in claim 1, wherein the steel alloys have a predicted oxide thickness of less than 30 microns after exposure at 850° C. for 40,000 hours.

### Claim 4 (depends on 1)

The oxidation-resistant ferritic steel alloy as in claim 1, wherein the steel alloys have an area-specific resistivity of less than 18 milliohms-cm2 at 750° C. after exposure at 850° C. for 1,500 hours.

### Claim 5 (depends on 1)

The oxidation-resistant ferritic steel alloy as in claim 1, wherein the steel alloys have a predicted area-specific resistivity of less than 100 milliohms-cm2 after exposure at 850° C. after 40,000 hours.

### Claim 6 (depends on 1)

The oxidation-resistant ferritic steel alloy as in claim 1, wherein rare earth metals further include cerium and/or lanthanum each in an amount from about 0.002 to about 0.2 atom percent.

### Claim 7 (depends on 1)

The oxidation-resistant ferritic steel alloy as in claim 1, wherein the steel alloy has a coefficient of thermal expansion from 10×10−6/° C. to 13×10−6/° C. over a temperature range of room temperature to 750° C.

### Claim 8

Oxidation-resistant ferritic steel alloys for high temperature applications consisting essentially of chromium (Cr) in an amount from about 18 to about 25 atom percent, tungsten (W) in an amount from about 0.5 to about 2 atom percent, manganese (Mn) in an amount less than 0.8 atom percent, aluminum (Al) in an amount less than about 0.2 atom percent, silicon (Si) in an amount less than about 0.1 atom percent, and rare earth metals that includes each one of Ce, La, and Nd in an amount from about 0.002 to about 0.2 atom percent with the balance being iron (Fe).

### Claim 9 (depends on 8)

The oxidation-resistant ferritic steel alloy as in claim 8, wherein the steel alloy has a coefficient of thermal expansion from 10×10−6/° C. to 13×10−6/° C. over a temperature range of room temperature to 750° C.

### Claim 10 (depends on 8)

The oxidation-resistant ferritic steel alloys as in claim 8, wherein the alloys have an oxide layer of less than 5 microns after exposure at 850° C. after 1,500 hours.

### Claim 11 (depends on 8)

The oxidation-resistant ferritic steel alloy as in claim 8, wherein the steel alloys have a predicted oxide thickness of less than 30 microns after exposure at 850° C. for 40,000 hours.

### Claim 12 (depends on 8)

The oxidation-resistant ferritic steel alloy as in claim 8, wherein the steel alloys have an area-specific resistivity of less than 18 milliohms-cm2 at 750° C. after exposure at 850° C. after 1,500 hours.

### Claim 13 (depends on 8)

The oxidation-resistant ferritic steel alloy as in claim 8, wherein the steel alloys have a predicted area-specific resistivity of less than 100 milliohms-cm2 after exposure at 850° C. after 40,000 hours.

### Claim 14

A solid oxide fuel cell, comprising:
at least two fuel cells, each fuel cell comprising an electrolyte plate sandwiched between an anode and a cathode; and
a separator disposed between the at least two fuel cells and configured to provide gas flow channels, the separator formed of a ferritic steel alloy consisting essentially of chromium (Cr) in an amount from about 18 to about 25 atom percent, tungsten (W) in an amount from about 0.5 to about 2 atom percent, manganese (Mn) in an amount less than about 0.8 atom percent, aluminum (Al) in an amount less than about 0.2 atom percent, silicon (Si) in an amount less than about 0.1 atom percent, and a rare earth metal that includes neodymium (Nd) in an amount from about 0.002 to about 0.2 atom percent with the balance being iron (Fe).

### Claim 15 (depends on 14)

The solid oxide fuel cell of claim 14, wherein the electrolyte plate is formed of yttria stabilized zirconia.

### Claim 16 (depends on 14)

The solid oxide fuel cell of claim 14, wherein the steel alloy has an oxide layer of less than 5 microns after exposure at 850° C. after 1,500 hours.

### Claim 17 (depends on 14)

The solid oxide fuel cell of claim 14, wherein the steel alloy has a predicted oxide thickness of less than 30 microns after exposure at 850° C. for 40,000 hours.

### Claim 18 (depends on 14)

The solid oxide fuel cell of claim 14, wherein the steel alloy has an area-specific resistivity of less than 18 milliohms-cm2 at 750° C. after exposure at 850° C. after 1,500 hours.

### Claim 19 (depends on 14)

The solid oxide fuel cell of claim 14, wherein the steel alloy has a predicted area-specific resistivity of less than 100 milliohms-cm2 after exposure at 850° C. after 40,000 hours.

### Claim 20 (depends on 14)

The solid oxide fuel cell of claim 14, wherein the steel alloy has a coefficient of thermal expansion from 10×10−6/° C. to 13×10−6/° C. over a temperature range of room temperature to 750° C.