Buffered Chemical Polishing (BCP) was the most conventional polishing method for superconducting radiofrequency (SRF) Niobium (Nb) cavity surface preparation before the discovery of Electropolishing (EP), which is superior to BCP in high gradient performance. The High Field Q-slope (HFQS) is entirely eliminated by taking the low-temperature bake (LTB) post EP, which guarantees high gradient performance in EP'ed cavities. The mechanism of the HFQS is well understood for EP'ed cavities. On the other hand, there is no common consensus on the HFQS with BCP, since even BCP with LTB does not always resolve the HFQS. BCP is much easier to apply and still a vital preparation technology for very complicated SRF structures like low beta cavities. Therefore, overcoming the issue of HFQS with BCP is highly beneficial to the SRF community. This thesis mines a large number of available data sets on BCP'ed cavity performance with fine grain, large grain, and even single-crystal niobium materials under different experimental settings. We found that all existing explanations for HFQS with BCP are inconsistent with some experimental results, and propounded nitrogen contamination as a new model to explain the result. Our conclusion is made based on previously unresolved phenomena which include (1) applying multiple BCP post EP; the maximum gradient does not always agree with roughness; (2) cavity treated with EP acid adding a drop of nitric acid started to have non-resolvable HFQS; (3) maximum field of BCP single-crystal cavities are lower than EP large grain cavities; (4) temperature map shows no high roughness area heating for a large-grain BCP cavity. We then checked that nitrogen contamination agrees with all existing data and nicely explains unresolved phenomena.According to this result, we have started developing a new nitrogen-free chemical polishing acid. Hydrogen peroxide with HF mixture was reported able to react with Nb, and there is no extra element contamination in it, so we replace the conventional BCP with this mixture to start our study.We discovered that this new acid could not provide sufficient smooth finishing surface, even after we adjusted all the parameters. However, adding a copper catalyst allows this acid to provide a smooth surface similar to or even better than conventional BCP. The copper remnant can be neglected according to an EDS study on the Nb surface. We studied the reaction mechanism and deduced that several other metals that can be promising as catalysts. One of those is iron, which was later shown to have the catalyst effect; this proved the mechanism we found is right. Further study can focus on other potential catalysts (such as Pb and Sn) and testing cavities treated by these acids. Pb is superconducting under operation temperature, may reduce potential harm to cavity performance, and Sn may react with Nb and generate Niobium Tin on its surface, which is another promising material for SRF cavities. These studies will offer more possibilities for SRF material.
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