This thesis was performed at the Politecnico di Milano’s Surface and Electrochemical Engineering Laboratories (SEE Lab). The purpose of this series of experiments was to optimize the alternate process of chromium-based conversion coatings that use Cr (III) or Cr (VI), which has been used traditionally as one of the secondary corrosion resistance processes for steels in the industry and has proven to be harmful to human beings and the environment, with the vanadium-based conversion coatings. The experiments were performed on structural steel S-235 samples as the basis of the process, and later the tests were performed on service screws provided by Agrati Group to establish more realistic situational experiments. For both processes, several coating techniques were tried, and later the most optimal process chosen for the final tests was the multiple immersions of the samples, which had undergone metallographic cleaning processes, in a stable solution of NaVO3 and Na2S2O5 while controlling its parameters, i.e., temperature, pH, and molar concentration. Another by-product of this process observed was the generation of dark polyoxovanadate crystals. These crystals were studied, and further experiments were performed in the trial to coat the specimen completely with these polyoxovanadate crystals for them to serve as a secondary sacrificial coating on top of the vanadium conversion coating. The pre- and post-treatment samples were evaluated for corrosion resistance along with their weight difference and microstructural characterization. SEM analysis was conducted on as-treated samples to study the surface morphology due to the submersion process.
Questa tesi è stata svolta presso i Laboratori di Ingegneria Elettrochimica e delle Superfici del Politecnico di Milano (SEE Lab). Lo scopo di questa serie di esperimenti è stato quello di ottimizzare il processo alternativo dei rivestimenti di conversione a base di cromo che utilizzano il Cr (III) o il Cr (VI), tradizionalmente utilizzato come uno dei processi secondari di resistenza alla corrosione per gli acciai nell'industria e che si è dimostrato dannoso per gli esseri umani e l'ambiente, con i rivestimenti di conversione a base di vanadio. Gli esperimenti sono stati eseguiti su campioni di acciaio strutturale S-235 come base del processo, e successivamente i test sono stati eseguiti su viti di servizio fornite dal Gruppo Agrati per stabilire esperimenti in situazioni più realistiche. Per entrambi i processi, sono state sperimentate diverse tecniche di rivestimento e, in seguito, il processo più ottimale scelto per i test finali è stato l'immersione multipla dei campioni, sottoposti a processi di pulizia metallografica, in una soluzione stabile di NaVO3 e Na2S2O5, controllandone i parametri, ossia temperatura, pH e concentrazione molare. Un altro sottoprodotto di questo processo osservato è stata la generazione di cristalli scuri di poliossovanadato. Questi cristalli sono stati studiati e sono stati eseguiti ulteriori esperimenti per rivestire completamente il campione con questi cristalli di poliossovanadato, in modo che servissero come rivestimento sacrificale secondario sopra il rivestimento di conversione del vanadio. I campioni prima e dopo il trattamento sono stati valutati per la resistenza alla corrosione, la differenza di peso e la caratterizzazione microstrutturale. L'analisi al SEM è stata condotta sui campioni trattati per studiare la morfologia superficiale dovuta al processo di immersione.
Optimization of coating process parameters for vanadium based conversion coating and its surface characterization.
SIDDIQUI, MASOOD AHMED
2021/2022
Abstract
This thesis was performed at the Politecnico di Milano’s Surface and Electrochemical Engineering Laboratories (SEE Lab). The purpose of this series of experiments was to optimize the alternate process of chromium-based conversion coatings that use Cr (III) or Cr (VI), which has been used traditionally as one of the secondary corrosion resistance processes for steels in the industry and has proven to be harmful to human beings and the environment, with the vanadium-based conversion coatings. The experiments were performed on structural steel S-235 samples as the basis of the process, and later the tests were performed on service screws provided by Agrati Group to establish more realistic situational experiments. For both processes, several coating techniques were tried, and later the most optimal process chosen for the final tests was the multiple immersions of the samples, which had undergone metallographic cleaning processes, in a stable solution of NaVO3 and Na2S2O5 while controlling its parameters, i.e., temperature, pH, and molar concentration. Another by-product of this process observed was the generation of dark polyoxovanadate crystals. These crystals were studied, and further experiments were performed in the trial to coat the specimen completely with these polyoxovanadate crystals for them to serve as a secondary sacrificial coating on top of the vanadium conversion coating. The pre- and post-treatment samples were evaluated for corrosion resistance along with their weight difference and microstructural characterization. SEM analysis was conducted on as-treated samples to study the surface morphology due to the submersion process.| File | Dimensione | Formato | |
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2022_12_Siddiqui.pdf
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Descrizione: Thesis report
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https://hdl.handle.net/10589/197924