Progress in Organic Coatings 64 (2009) 327338

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Progress in Organic Coatings

journa l homepage: www.e lsev ier .com

Review

Solge io

Duhua WDepartment o

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Article historReceived 31Received in rAccepted 12

Keywords:SolgelCorrosion reProtective co

Contents

1. Intro2. Gen

2.1.2.2.

3. Corr3.1.

3.2.

3.3.4. Chal

4.1.4.2.4.3.

5. ConcAcknRefe

1. Introdu

Metalstheir alloy

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0300-9440/$doi:10.1016/jf Coatings and Polymeric Materials, North Dakota State University, Fargo, ND 58105, USA

l e i n f o

y:October 2007evised form 12 August 2008August 2008

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a b s t r a c t

Solgel protective coatingshave shownexcellent chemical stability, oxidation control andenhancedcorro-sion resistance for metal substrates. Further, the solgel method is an environmentally friendly techniqueof surface protection and had showed the potential for the replacement of toxic pretreatments and coat-ings which have traditionally been used for increasing corrosion resistance of metals. This review coversthe recent developments and applications of solgel protective coatings on different metal substrates,such as steel, aluminum, copper, magnesium and their alloys. The challenges for industrial productionsand future research on solgel corrosion protective coatings are also briey discussed.

2008 Published by Elsevier B.V.

duction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327eral background of solgel coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328

Brief history of solgel chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328Preparation of solgel coatings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

osion protective solgel coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329Steel substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3293.1.1. Metal oxide coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3293.1.2. Organicinorganic hybrid solgel coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3313.1.3. Inhibitor doped solgel coatings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3323.1.4. Inorganic zinc-rich coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332Aluminum substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3333.2.1. Metal oxide coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3333.2.2. Organicinorganic hybrid solgel coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3343.2.3. Hybrid solgel magnesium-rich coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335Copper and magnesium substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336

lenges and future studies of solgel corrosion protective coatings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337Basic theory studies of solgel coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337Optimization and new synthesis routes of solgel coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337New raw materials and multiple component systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337

lusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337owledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337rences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337

ction

, such as iron, aluminum, copper and magnesium ands are used in amyriad of structural,marine, aircraft appli-

onding author.dress: Gordon.Bierwagen@ndsu.edu (Gordon.P. Bierwagen).

cations and cultural heritage, etc. While these metals are usefulbecause of their physical characteristics, such as stiffness and highstrength toweight ratios, they are highly susceptible to corrosion inaggressive environments. Corrosion is always the major reason ofenergy andmaterial loss. It was reported that 1/5 of energy globallyand average 4.2% of gross national product (GNP) is lost each yeardue to corrosion [1] and the economic impact of corrosion is esti-mated to be greater than $100,000,000,000 per year in the United

see front matter 2008 Published by Elsevier B.V..porgcoat.2008.08.010l coatings on metals for corrosion protect

ang, Gordon. P. Bierwagen / locate /porgcoat

n

328 D. Wang, Gordon.P. Bierwagen / Progress in Organic Coatings 64 (2009) 327338

States alone [2]. This cost includes the application of protectivecoatings (paint, surface treatment, etc.), inspection and repair ofcorroded surfaces and structures, and disposal of hazardous wastematerials. A generic way to protect metals from corrosion is toapply protective lms or coatings, which also permit the desiredproperties of the substrate to be coated through the chemicalmod-ication of the coatings [3,4], such as mechanical strength, opticalappearance, bioactivity, etc.

There are several techniques for the deposition of coatingson metals, including physical vapor deposition (PVD), chemicalvapor deposition (CVD), electrochemical deposition, plasma spray-ing and solgel process. There are many advantages using solgelcoatings, several most important features are listed as follows[5,6]:

(A) Solgel processing temperature generally is low, frequentlyclose to room temperature. Thus thermal volatilization anddegradation of entrapped species, such as organic inhibitors,is minimized.

(B) Since liquid precursors are used it is possible to cast coatings incomplex shapes and to produce thin lms without the need formachining or melting.

(C) The solgel lms are formed by green coating technologies:It uses compounds that do not introduce impurities into theend product as initial substances, thismethod iswaste-free andexcludes the stage of washing.

Ten year ago, Guglielmi [7] has already discussed the potentialof solgel coatings as a corrosion inhibiting system for metal sub-strates. Since then, a great deal of work has been done to makevarious solgel based protective coatings. This review will intro-duce the basic chemistry involved in solgel processes, then theprogress and development of solgel protective coatings on metalsubstrate, such as steel, aluminum, etc. Finally some problems andfuture work on solgel coatings will be summarized br