Glow Phenomenon of Chromium Oxide

Carruthers, J. D.; Sing, K. S. W.; Fenerty, J.

doi:10.1038/213066a0

“…This transformation is associated with the formation of ␣-Cr 2 O 3 , and is sometimes termed the ''glow phenomenon,'' which refers to incandescence associated with the exothermic character of this transformation. 22 This step has been shown to be very sensitive to the chemical nature of the initial chromium compound and the conditions of synthesis. [22][23][24] Of these three reactions, the endothermic dehydration reaction centered at 100°C is the most technologically significant because it is in the range of service temperatures experienced by CCCs.…”

Section: Resultsmentioning

confidence: 99%

“…22 This step has been shown to be very sensitive to the chemical nature of the initial chromium compound and the conditions of synthesis. [22][23][24] Of these three reactions, the endothermic dehydration reaction centered at 100°C is the most technologically significant because it is in the range of service temperatures experienced by CCCs. Thermal analysis was also performed on a CCC made according to the nominal Alodine 1200S chemistry, but without ferricyanide.…”

Section: Resultsmentioning

confidence: 99%

“…The thermal oxidation of Cr͑III͒ to Cr͑VI͒ is a surface phenomenon well known from work on chromium-based catalysts. 22,24,25,29 Although the exact nature of the intermediate compounds formed in this process has not been clearly established, formation of a mixed valency ͑III and VI͒ oxide such as the chromium chromate Cr 2 (CrO 4 ) 3 has been suggested. 29 With the Cr͑VI͒:total Cr ratio at 400°C being approximately 0.30, as much as half of the CCC may be expected to be Cr 2 (CrO 4 ) 3 at the outer surface, with the remainder consisting of the nonstoichiometric Cr͑III͒ oxide.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Dehydration-Induced Loss of Corrosion Protection Properties in Chromate Conversion Coatings on Aluminum Alloy 2024-T3

Laget

¹

,

Jeffcoate

²

,

Isaacs

³

et al. 2003

J. Electrochem. Soc.

View full text Add to dashboard Cite

It is well known that chromate conversion coatings ͑CCCs͒ exhibit a prompt loss in corrosion resistance when exposed to moderately elevated temperatures ͑60-100°C͒. They also suffer a gradual loss in corrosion resistance due to ambient temperature exposure. To better understand the origins of losses in corrosion resistance, CCCs were formed on 99.99% Al, 1100 Al ͓Al-1.0͑Fe, Si, Cu͔͒, and 2024-T3 ͑Al-4.4Cu-1.5Mg-0.6Mn͒, exposed to elevated and ambient temperature exposures for various lengths of time, and characterized using several different methods. The Cr͑VI͒:total Cr ratio in CCCs was estimated by analysis of data derived from X-ray absorption spectroscopy. Corrosion resistance was measured by electrochemical impedance spectroscopy. The evolution of shrinkage cracking was examined by environmental scanning electron microscopy. Cr͑VI͒ leaching experiments were also carried out to characterize the effect of thermal exposure on Cr͑VI͒ release. Thermal analysis and X-ray diffraction were conducted to characterize the temperature-dependent changes in CCCs. Results show that CCCs degrade in several distinct steps over the temperature range of 20 to 500°C. Our findings support the longstanding notion that dehydration is the root cause for losses in corrosion resistance due to aging at ambient and low temperatures (Ͻ150°C). Extended X-ray fine structure measurements indicate a shortening in Cr͑III͒-Cr͑III͒ nearest neighbor distances upon dehydration. This is interpreted as a consolidation in the Cr(OH) 3 backbone of the CCC which leads to shrinkage cracking and immobilization of Cr͑VI͒. This finding is important because it links older observations of the effects of aging and heating on CCCs to newer interpretations of CCC formation based on inorganic polymerization. Overall, these results reveal CCCs to be highly dynamic coatings with corrosion resistance properties that vary considerably in both the short term and long term.

show abstract

“…At 450°C, the third weight loss is observed, associated with an exothermic peak of variable intensity depending on sample. This transformation is referred in the * literature as the onset of a-Cr 2 0 3 , also called "glow phenomenon" (16). It has been shown I to be very sensitive to the chemical environment (16,17).…”

Section: Resultsmentioning

confidence: 99%

Critical Factors for the Transition from Chromate to Chromate-Free Corrosion Protection

Buchheit¹

1999

View full text Add to dashboard Cite

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503 AGENCY USE ONLY (Leave blank)2. REPORT DATE December 1, 1999 REPORT TYPE AND DATES COVERED Annual Technical Report TITLE AND SUBTITLE Critical Factors for the Transition from Chromate to Chromate-Free Corrosion Protection AUTHOR(S)Rudolph G. Buchheit, et. al. FUNDING NUMBERS N/A PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)The Ohio State University Army Research Laboratory Air Force Research Laboratory PERFORMING ORGANIZATION REPORT NUMBERN/A SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) SERDP901 North Stuart St. Suite 303 Arlington, VA 22203 SPONSORING / MONITORING AGENCY REPORT NUMBERN/A SUPPLEMENTARY NOTESNo copyright is asserted in the United States under Title 17, U.S. code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Government purposes. All other rights are reserved by the copyright owner. 12a. DISTRIBUTION / AVAILABILITY STATEMENTApproved for public release: distribution is unlimited. 12b. DISTRIBUTION CODEA ABSTRACT (Maximum 200 Words)The overall objective of this research program is to acquire a fundamental understanding of the chemical and physical processes and mechanisms of corrosion protection by chromate-based coatings applied to metal surfaces with a specific focus on corrosion protection of aluminum alloys. The key functional attributes of chromate coating formation and breakdown must be identified and understood so that ultimately, they might be duplicated using environmentally friendly corrosion protection methods. Environmentally friendly corrosion protection methods must be found to replace chromate corrosion protection methods because environmental regulations are forcing elimination of products and processes (like chromates) whose formulations use or produce toxic substances. SUBJECT TERMSSERDP Project BackgroundThe Department of Defense (DOD) and Department of Energy (DOE) have committed to replace chromate-based metal finishing in present and next generation systems. At issue is whether this change will occur in a timely manner without performance or cost penalties that could compromise operational readiness. Additionally, undue delay in determining and implementing new corrosion protection practices poses enormous risk for existing assets. Faced with the request from the user community for chromate-free corrosion protection, ...

show abstract

“…The oxidation of Cr(III) to Cr(VI) or even possibly to intermediate valency such as IV or V, is a surface phenomenon well known from work on chromium-based catalysts (16,20,21,23,24). The exact nature of the intermediate compound has not been yet clearly established but it seems to depend on the Cr(HI) starting compound and his chemical environment (25).…”

Section: Imentioning

confidence: 99%

Critical Factors for the Transition from Chromate to Chromate-Free Corrosion Protection

Buchheit¹

2005

View full text Add to dashboard Cite

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503 AGENCY USE ONLY (Leave blank)2. REPORT DATE December 1, 1999 REPORT TYPE AND DATES COVERED Annual Technical Report TITLE AND SUBTITLE Critical Factors for the Transition from Chromate to Chromate-Free Corrosion Protection AUTHOR(S)Rudolph G. Buchheit, et. al. FUNDING NUMBERS N/A PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)The Ohio State University Army Research Laboratory Air Force Research Laboratory PERFORMING ORGANIZATION REPORT NUMBERN/A SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) SERDP901 North Stuart St. Suite 303 Arlington, VA 22203 SPONSORING / MONITORING AGENCY REPORT NUMBERN/A SUPPLEMENTARY NOTESNo copyright is asserted in the United States under Title 17, U.S. code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Government purposes. All other rights are reserved by the copyright owner. 12a. DISTRIBUTION / AVAILABILITY STATEMENTApproved for public release: distribution is unlimited. 12b. DISTRIBUTION CODEA ABSTRACT (Maximum 200 Words)The overall objective of this research program is to acquire a fundamental understanding of the chemical and physical processes and mechanisms of corrosion protection by chromate-based coatings applied to metal surfaces with a specific focus on corrosion protection of aluminum alloys. The key functional attributes of chromate coating formation and breakdown must be identified and understood so that ultimately, they might be duplicated using environmentally friendly corrosion protection methods. Environmentally friendly corrosion protection methods must be found to replace chromate corrosion protection methods because environmental regulations are forcing elimination of products and processes (like chromates) whose formulations use or produce toxic substances. SUBJECT TERMSSERDP Project BackgroundThe Department of Defense (DOD) and Department of Energy (DOE) have committed to replace chromate-based metal finishing in present and next generation systems. At issue is whether this change will occur in a timely manner without performance or cost penalties that could compromise operational readiness. Additionally, undue delay in determining and implementing new corrosion protection practices poses enormous risk for existing assets. Faced with the request from the user community for chromate-free corrosion protection, ...

show abstract

Glow Phenomenon of Chromium Oxide

Cited by 37 publications

References 3 publications

Dehydration-Induced Loss of Corrosion Protection Properties in Chromate Conversion Coatings on Aluminum Alloy 2024-T3

Dehydration-Induced Loss of Corrosion Protection Properties in Chromate Conversion Coatings on Aluminum Alloy 2024-T3

Critical Factors for the Transition from Chromate to Chromate-Free Corrosion Protection

Critical Factors for the Transition from Chromate to Chromate-Free Corrosion Protection

Contact Info

Product

Resources

About