DSpace Repository :: Browsing by Author "Forsén, Olof"

100Cr6 - ainakin satavuotias laakeriteräs

(2009) Haapasalmi, Johanna

Kemian ja materiaalitieteiden tiedekunta | Bachelor's thesis

3D-tulostettujen kappaleiden pintojen parantaminen

(2015-06-12) Kalliokorpi, Tero

Kemiantekniikan korkeakoulu | Bachelor's thesis

6000-sarjan alumiinit

(2015-04-30) Lindqvist, Tom

Kemiantekniikan korkeakoulu | Bachelor's thesis

Lyijyanodien aktivointi metallioksideilla

(2001) Pajunen, Lauri

Helsinki University of Technology | Master's thesis

Passivoituvien metallien aktivointi kovakromauksessa

(2009) Joas, Tony

Helsinki University of Technology | Master's thesis

The aim of this thesis was to find and examine existing activation methods for passive metals in hard chromium plating. Another target was to investigate, which factors have an effect on successful activation process, and to discover a method to measure the activation process with electrochemical measurement methods. In the theoretical part of this work, the principals of hard chromium plating, such as chromium deposition, structure of deposited coating and pre-treatment methods are introduced. The activation process is examined more closely. Activation methods that have been found effective are processed and listed. This research focused on activation methods that are suitable for AISI 316, Monel 400, nickel and Nimonic 75. The preferred activation method for passive metals in literature was cathodic activation in sulphuric acid solution or in sulphuric and hydrofluoric acid solution. In the experimental part of the thesis, suitable activation methods and parameters for passive metals in chromium bath and 10 vol-% sulphuric acid were studied using electrochemical methods. Research methods were potential measurement, polarization, potentiostatic method and impedance measurement. The best surface cleanliness was achieved by using 10 min cathodic activation in sulphuric acid. AISI 316 was held in potential -500 mV, Monel 400 in potential -450 mV, nickel in potential -400 mV and Nimonic 75 in potential -500 mV. Based on the laboratory experiments, metals become passive very quickly after cathodic activation. It was assumed that the time between activation and chromium plating should be as short as possible. The rate of passivation can be easily measured by potential measurement. The influence of passivation and the use of potential measurement in activation control were studied in factory conditions. The plant experiments showed that surface pre-treatments and activation methods seem to have more influence in successful chromium plating than passivation of the surface.