MINISTRY OF
EDUCATION AND TRAINING
VIETNAM ACADEMY OF
SCIENCE AND TECHNOLOGY
GRADATE UNIVERSIY OF SCIENCE AND TECHNOLOGY
-----------------------------
NGUYEN VAN CHI
RESEARCH ON FABRICATION AND CHARACTERISTIC
PROPERTIES OF ZIRCONIUM OXIDE FILM
COMBINATION WITH SILANE ON STEEL SUBSTRATE AS
PRETREATMENT FOR ORGANIC COATING
Major: Metal
Code: 9.44.01.29
SUMMARY OF DOCTORAL THESIS IN MATERIALS SCIENCE
Ha Noi – 2020
This thesis was done at: Graduate University of Science and
Technology - Vietnam Academy of Science and Technology
Supervisors 1: Dr. PHAM Trung San
Supervisors 2: Assoc.Prof. Dr. TO Thi Xuan Hang
Reviewer 1: .....................................................
Reviewer 2: .....................................................
Reviewer 3: .....................................................
The dissertation will be defended at Graduate University of
Science and Technology, 18 Hoang Quoc Viet street, Hanoi.
Time: .............,.............., 2020
This thesis could be found at National Library of Vietnam,
Library of Graduate University of Science and Technology,
Library of Institute of Materials and Science, Library of Vietnam
Academy of Science and Technology
1
INTRODUCTION
The urgency of the thesis
Surface pretreatment of the steel substrate before painting had
significant effect on coating adhesion and corrosion protection
performance. Pretreatment not only increases the adhesion between the
paint and the substrate, but also improves the long-term corrosion
protection. Phosphate or chromate pretreatment has been widely used
for this purpose. However, these methods are often increasingly
restricted by international conventions because of several drawbacks
from environmental, energy and process points of view. The trend of
finding alternative methods has been interested in research and
application recently. These conversion coatings are usually transition
metal oxides such as zirconium, titanium, vanadium, molybdenum.
Among them, A promising emerging pretreatment technique is one of
potential replacements for phosphating and one of them is the
application of zirconium oxide or organo-silane. The outstanding
advantage of zirconia is that the film is made of nano properties,
environmentally friendly, cost-saving, simple technology, applicable on
mutli-metal. However, the disadvantage is that it is necessary to use
deionized or ultrafiltration water because the formed film is quite
sensitive to the ions in the washing water and easily forms rust during
stages. Besides, organo-silane is also considered as a promising surface
pretreatment method because of its increased ability to bond between
organic coating and metal substrate and effective corrosion protection.
However, the basic disadvantage of the silane is that it depends how the
surface was treated, the cleanliness of the surface and the density of
hydroxyl group. Therefore, it is necessary to clean the surface well
before pretreatment to promote the effectiveness.
2
A combination of Zr based and silane based pretreatment on
metal substrates in different ways has been performed recently such
as: The hot-dip galvanized steel surface was treated, firstly, with
zirconium nitrate salt then silane; the doped silane pretreatment on
galvanised steel subtrate; Ce-silane-ZrO2 composite coating on 1060
aluminum. The results confirmed that the combined film had higher
corrosion resistance, less porosity, less microscopic cracking and
better pre-treatment than that of each component.
Several methods can be applied to combine between zirconia and
silane. Sol-gel is an atomic scale method which to form zirconia
films with the advantage of high uniformity, the stages of the
reaction can be controlled. However, compared to the chemical
dipping method, sol-gel method requires more stages, higher
temperature, more by-products, it is limited in industrialization. The
zirconia/silane film could also be formed by two steps in two
solutions, however, the one-solution method would allow a simpler
process, at the same time, propose a mechanism for zirconia and
silane to be together formed film on the substrate.
Factors directly related to films forming by the method of
immersion in hexaflorozirconic acid solution could be mentioned as:
temperature, pH, concentration and dipping time. Several studies
have shown that when the temperature of the solution was increased,
the corrosion performance and properties of the zirconia film were
reduced. Solution pH and concentration are two directly correlated
parameters. However, a low concentration hexaflorozirconic acid
solution (with pH of about 3 to 4) usually leaded to a zirconia film
with better pretreatment effect, and when the pH was changed, it
would affect the forming film decisively.
3
Based on the above discusses, with the desire to manufacture a
steel surface pretreatment film which is effective as phosphate and
chromate, the topic of the thesis was chosen: "Research on
fabrication and characteristic properties of zirconium oxide film
combination with silane on steel substrate as pretreatment for
organic coating”.
Goals of the thesis
- Preparing of zirconia/silane combined films on steel subtrate for
organic coatings to replace phosphate and chromate pretreatment;
- Proposing the mechanism of film formation process and
assessing characteristics of morphology, composition, electro-
chemical properties and bonding of the zirconia/silane film.
Main contents of the thesis
- Research on preparation of zirconium oxide film on steel and
selecting initial conditions on solution pH and dipping time as basis
parameters for manufacturing zirconia/silane film;
- Research on manufacturing zirconia/silane films on steel
substrates; explain the process of formation and their characterization
of morphology, composition, electrochemistry and bonding;
- Study the role of zirconia/silane pretreatment film for powder
coating.
Scientific and application of the thesis
On the scientific side, the thesis has contributed new points in the
research of steel surface treatment films for coatings to replace
phosphates and chromate.
In practice, the results of the thesis are the basis for the
development of technology for manufacturing steel surface treatment
films for environmentally friendly coatings in Vietnam.
