Developments in platinum electroplating for aero-engine applications

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Developments in platinum
electroplating for
aero-engine applications
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DEVELOPMENTS IN PLATINUM ELECTROPLATING
FOR AERO-ENGINE APPLICATIONS
BY
SEYED. ESMAIL. HADIAN,
P.G.Dipl.(Brunel), MSc, MPhil(CNAA)
Sheffield City Polytechnic
A thesis submitted in fulfilment of
the regulations for the degree of
Doctor of Philosophy
of
Loughborough University of Technology
October 1993
Supervisor: Dr.D.R.Gabe
IPTME
Loughborough University Of Technology
Industrial Supervisor: Mr.M.Dean
C.U.K Ltd, Hatfield, Herts
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S.E.HADIAN,1993
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ABSTRACT
The electro-deposition of platinum on
mild-steel and nimonic alloys substrates using more than
twenty baths have been investigated. It has been shown
that the cell efficiency can be improved markedly with
lower current density, pH value and plating temperature.
Distinct differences between direct and pulsed processes
revealed themselves in the cathode current efficiency
data. Implications of using pulse plating to control the
quality of electrodeposits have been considered.
The experimental work reported in this thesis is to a
large extent based on cell efficiency and potentiodynamic
polarisation which is considered to be a powerful tool for
evaluating potential coating solutions. The cathodic
polarisation characteristics of platinum solutions has
been studied quantitatively.
An excellent technique (electroless) has been developed
in an attempt to successfully apply platinum deposit on
commonly used mild steel or_nimonic alloys using 'Q'salt
manufactured by Johnson Matthey.
A series of different designed experiments were used to
evaluate the high value ranges of throwing power{localised
plating) capabilities and opportunities for extending that
capability to replace the Brush plating. Throwing power is
currently used for those blades which require the plati
num/rhodium plating for RB211 Blades at concave aerofoil
sections manufactured by Rolls Royce situated at Derby in
U.K. The investigation employed different size and shape
of anodes/cathodes to explore the effects of various
factors in the Ni-plating and then as this technique has
been established using nickel rather than noble metals, it
was used to implement this feature in platinum and rhodium
plating.
PREFACE
The work presented in this thesis was carried out
at the C.U.K Ltd's laboratory in Hatfield, Herts and
Loughborough University of Technology during the period
from July 1989 to October 1993. During this period the
candidate has not been registered for any other university
degree.
The research reported here is, as far as can be ascer
tained, original except where due reference has been to
previous work.
I would like to thank Dr D.R.Gabe, my supervisor, for his
considerable help and guidance during this project.
I would also like to express my grateful thanks to Mr
M.Dean, my industrial supervisor at C.U.K Ltd, to whom I
am greatly indebted for his patient supervision and en
couragement. Similarly I would like to thank Mr
D.Maxwell-Lyte, laboratory supervisor,Mr D.Clark, Labora
tory Chemist, and all technical staff in the C.U.K Engi-
neering company for their invaluable help, advice and
constant support.
TABLE OF CONTENTS
Page No
Abstract
Preface
Table of Contents
CHAPTER 1: INTRODUCTION 1
1.0 Developments in Platinum Electroplating for
Aero-Engine Applications
1.1 Summary
1.2 History of Platinum 2
1.2.1 Occurrence
1.2.2 Extraction
1.3 Physical and Chemical Properties 4
1. 3.1 Uses 4
1.4 Characteristics of the Platinum Metals 7
1.5 General Considerations 10
(a) Molten Cyanide Electrolytes 13
(b) Electroless Plating 14
1.6 Anodes and Plating Salts 15
1.7 Protective Coatings for gas turbines 15
1.7.1 Summary
1.7.2 Introduction 16
1.7.3 Environmental Degradation of High
Temperature Alloys 17
1.7.4 Surface Coatings 18
1.7.5 Property Requirements of Turbine
Aerofoil Coating System 18
1.7.6 Classification of Current Coating 19
1.7.7 Concluding Remarks 20
1.8 Coatings for Corrosion control 21
CHAPTER 2:
2.0 Principles of Electrodeposition 24
2.1 Basic Electroplating Theory
2.2 Mechanism of general Electrodeposition 25
2.3 Electrode Potentials 29
2.4 Electrolytic Crystallization 32
2.5 Electrolytes for the Deposition of Platinum 33
2.5.1 Platinum Plating 34
2.5.2 Powell and Scott Bath 36
2.5.3 Platinum Plating from Alkaline solutions
38
2.5.4 Sulphato-Dinitrio-Platinate Solution 39
2.5.1.1 Plating Conditions 41
2.5.5 Platinum 209 43
2.5.5.1 Bath Maintenance 43
2.5.5.1.1 Platinum Metal
2.5.6 Platinum Solution 3745 44
2.5.6.1 Bath Maintenance 45