Scanning and transmission electron microscopy examinations of composite hybrid chromate and chromate phosphate conversion coatings exposed in hot 100% relative humidity environments
Conversion coatings are sine qua non in the finishing of aluminium alloys. They may be put into service without coating of paints. However, for aesthetics in architectural applications, paint overcoat is common. Chromate phosphate coatings are relatively less toxic than chromate which gained the pri...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Elsevier
2023-08-01
|
| Series: | Hybrid Advances |
| Subjects: | |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S2773207X23000507 |
| _version_ | 1797740444462874624 |
|---|---|
| author | Peter P. Ikubanni Makanjuola Oki Adesoji A. Adediran Sarah A. Akintola Adekunle A. Adeleke |
| author_facet | Peter P. Ikubanni Makanjuola Oki Adesoji A. Adediran Sarah A. Akintola Adekunle A. Adeleke |
| author_sort | Peter P. Ikubanni |
| collection | DOAJ |
| description | Conversion coatings are sine qua non in the finishing of aluminium alloys. They may be put into service without coating of paints. However, for aesthetics in architectural applications, paint overcoat is common. Chromate phosphate coatings are relatively less toxic than chromate which gained the pride of place until recently. Thus, aluminium specimens coated with hybrid chromate/phosphate conversion coatings have been subjected to 100% relative humidity for 480 h at 313K in comparison to chromate coatings and bare aluminium. Scanning electron microscopy examination revealed that initial dried river bed morphologies on coated specimens were obliterated. The friable outer coatings collapsed into the cracks/environment leaving a relatively smooth surface after exposure. Additionally, transmission electron microscopy of sections before and after exposure revealed similar texture and morphological striations nearly parallel to each other throughout the length of the coatings to the metal/coating interface. These were not disrupted as well as the metal/coating interface which remained relatively smooth with no visible corrosion products after exposure. Thus, the coatings formed effective barrier between the substrate and the relatively harsh environment. From EDS, elemental compositions were the same albeit, spectral intensities remained relatively constant after humidity exposure regimes. The coatings are made up of either Cr, O and Al for chromate and Cr, P, O and Al for chromate/phosphate. At deliberately breached regions, the coatings prevented spread of corrosion and paint delamination over the substrates. On the other hand, bare aluminium was decorated with mounds of hydrated aluminium oxide/hydroxide after exposure as revealed in the SEM/TEM. |
| first_indexed | 2024-03-12T14:12:32Z |
| format | Article |
| id | doaj.art-58841f5c53eb4d0290971b739240da57 |
| institution | Directory Open Access Journal |
| issn | 2773-207X |
| language | English |
| last_indexed | 2024-03-12T14:12:32Z |
| publishDate | 2023-08-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Hybrid Advances |
| spelling | doaj.art-58841f5c53eb4d0290971b739240da572023-08-21T04:20:54ZengElsevierHybrid Advances2773-207X2023-08-013100067Scanning and transmission electron microscopy examinations of composite hybrid chromate and chromate phosphate conversion coatings exposed in hot 100% relative humidity environmentsPeter P. Ikubanni0Makanjuola Oki1Adesoji A. Adediran2Sarah A. Akintola3Adekunle A. Adeleke4Department of Mechanical Engineering, Landmark University, PMB 1001, Omu-Aran, Kwara State, Nigeria; Corresponding author.Greenfield Creations (Corrosion Consultants) Ltd, Benue Close, Agbara Industrial Estate, Agbara, 112102, Ogun State, NigeriaDepartment of Mechanical Engineering, Landmark University, PMB 1001, Omu-Aran, Kwara State, NigeriaDepartment of Petroleum Engineering, University of Ibadan, Ibadan, Oyo State, NigeriaDepartment of Mechanical Engineering, Nile University of Nigeria, FCT, Abuja, NigeriaConversion coatings are sine qua non in the finishing of aluminium alloys. They may be put into service without coating of paints. However, for aesthetics in architectural applications, paint overcoat is common. Chromate phosphate coatings are relatively less toxic than chromate which gained the pride of place until recently. Thus, aluminium specimens coated with hybrid chromate/phosphate conversion coatings have been subjected to 100% relative humidity for 480 h at 313K in comparison to chromate coatings and bare aluminium. Scanning electron microscopy examination revealed that initial dried river bed morphologies on coated specimens were obliterated. The friable outer coatings collapsed into the cracks/environment leaving a relatively smooth surface after exposure. Additionally, transmission electron microscopy of sections before and after exposure revealed similar texture and morphological striations nearly parallel to each other throughout the length of the coatings to the metal/coating interface. These were not disrupted as well as the metal/coating interface which remained relatively smooth with no visible corrosion products after exposure. Thus, the coatings formed effective barrier between the substrate and the relatively harsh environment. From EDS, elemental compositions were the same albeit, spectral intensities remained relatively constant after humidity exposure regimes. The coatings are made up of either Cr, O and Al for chromate and Cr, P, O and Al for chromate/phosphate. At deliberately breached regions, the coatings prevented spread of corrosion and paint delamination over the substrates. On the other hand, bare aluminium was decorated with mounds of hydrated aluminium oxide/hydroxide after exposure as revealed in the SEM/TEM.http://www.sciencedirect.com/science/article/pii/S2773207X23000507AluminiumScanning electron microscopy (SEM)Transmission electron microscopy (TEM)Composite/hybrid coatingsCorrosion |
| spellingShingle | Peter P. Ikubanni Makanjuola Oki Adesoji A. Adediran Sarah A. Akintola Adekunle A. Adeleke Scanning and transmission electron microscopy examinations of composite hybrid chromate and chromate phosphate conversion coatings exposed in hot 100% relative humidity environments Hybrid Advances Aluminium Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) Composite/hybrid coatings Corrosion |
| title | Scanning and transmission electron microscopy examinations of composite hybrid chromate and chromate phosphate conversion coatings exposed in hot 100% relative humidity environments |
| title_full | Scanning and transmission electron microscopy examinations of composite hybrid chromate and chromate phosphate conversion coatings exposed in hot 100% relative humidity environments |
| title_fullStr | Scanning and transmission electron microscopy examinations of composite hybrid chromate and chromate phosphate conversion coatings exposed in hot 100% relative humidity environments |
| title_full_unstemmed | Scanning and transmission electron microscopy examinations of composite hybrid chromate and chromate phosphate conversion coatings exposed in hot 100% relative humidity environments |
| title_short | Scanning and transmission electron microscopy examinations of composite hybrid chromate and chromate phosphate conversion coatings exposed in hot 100% relative humidity environments |
| title_sort | scanning and transmission electron microscopy examinations of composite hybrid chromate and chromate phosphate conversion coatings exposed in hot 100 relative humidity environments |
| topic | Aluminium Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) Composite/hybrid coatings Corrosion |
| url | http://www.sciencedirect.com/science/article/pii/S2773207X23000507 |
| work_keys_str_mv | AT peterpikubanni scanningandtransmissionelectronmicroscopyexaminationsofcompositehybridchromateandchromatephosphateconversioncoatingsexposedinhot100relativehumidityenvironments AT makanjuolaoki scanningandtransmissionelectronmicroscopyexaminationsofcompositehybridchromateandchromatephosphateconversioncoatingsexposedinhot100relativehumidityenvironments AT adesojiaadediran scanningandtransmissionelectronmicroscopyexaminationsofcompositehybridchromateandchromatephosphateconversioncoatingsexposedinhot100relativehumidityenvironments AT sarahaakintola scanningandtransmissionelectronmicroscopyexaminationsofcompositehybridchromateandchromatephosphateconversioncoatingsexposedinhot100relativehumidityenvironments AT adekunleaadeleke scanningandtransmissionelectronmicroscopyexaminationsofcompositehybridchromateandchromatephosphateconversioncoatingsexposedinhot100relativehumidityenvironments |