Analysis to Improve the Corrosion Resistance of Microstructured Components for Aggresive Chemical Process Media
- project group: AiF Project 18034 N
The aim of the research was to improve the corrosion resistance of thin-walled, micro-structured apparatuses. For this purpose, the corrosion process in sulfuric acid of varying concentrations and temperatures was to be characterized for a variety of alloys and coatings.
The particularly suitable nickle based alloys Nicrofer 5621 hMoW (2.4602, Hastelloy C-22) and Nicrofer 5923 hMo (2.4605, Alloy 59), as well as the newly developed alloys Nicrofer 3426 hMo (2.4692, Alloy 31 plus) and Nicrofer 5821 hMoN (2.4700, Alloy 2120), were characterized electrochemically in different material conditions.
Tests were run for 1000 hours in 70% sulfuric acid at 85 °C and 100 °C and 95-97% sulfuric acid at 100 °C to be able to form statements about the long-time corrosion resistance.
Different corrosion protection measures based on ultrathin porcelain enamel, the effectiveness of passiv anodic protection through sputtered gold coating, and using different tantalum coatings were examined and compared.
The AiF project showed that different improved or newly developed high-alloyed nickel based alloys are not sufficiently resistant to corrosion by sulfuric acid at 85-100 °C. In addition to the composition the mechanical and thermical history of the alloys impact the type of corrosion respectively the rate of abrasion.
A coating method meeting the demands of micro process engineering regarding
- corrosion resistance
- adhesive strength
- absence of faults
- possibility of applying micro-channels with small width and large aspect ratio
perfectly was found with the CVD coating using tantalum.
However, new questions, that have to be researched in a follow-up proposal prior to the industrial use of CVD tantalum coating or the substitution of nickel based alloys with stainless steel as well as the micro-mechanical structuring by etching, arose:
- Does the jagged surface of the CVD tantalum coating lead to increased fouling because of side reactions or to obstruction of micro-channels, especially compared to milled micro-channels?
- Can flow ratio and pressure losses be significantly improved with nano porcelain enamel?
- Is the adhesive strength of the added layer as expected, i.e. sufficient?
- Does nano porcelain enamel offer the possibility to repair broken CVD tantalum coatings?