The objectives of the proposed project are:
Year 1
1.1 Scale up alternative to chromates so 10x4-in panels can be treated (completed). A scale-up of the process is required to ensure that the same corrosion resistance found on the small scale also works on a larger scale.
1.2 Salt-spray and potentiodynamic corrosion tests of alternate coating on 10x3-in panels (completed). Corrosion testing of 10x4-in panels to determine if the coating is still as effective on the larger scale. Potentiodynamic scans in 0.5 N NaCl were used to test the effectiveness of the process. (This test was found to accurately measure the ability of chromates to provide corrosion protection.)
1.3 Develop wash primer involving phosphate, URI alternate and conductive polymers (underway).
1.4 Measure biofilm formation and biocorrosion on bare and coated samples (underway).
1.5 Initiate development of electrophoretic coatings
Year 2 (this proposal)
2.1 Test URI wash primer with color coat on top for adhesion of paints to metal and also corrosion resistance.
2.2 Continue development of electrophoretic coatings.
2.3 Measure biofilm formation and biocorrosion on coated samples.
Year 3
3.1 Full-scale coating of typical car parts and bridge components
3.2 Test full-scale samples by salt spray and immersion in seawater.
3.3 Measure biofilm formation and biocorrosion on coated samples.
Intermodal
Chromate coatings are very effective in providing corrosion resistance and are widely used in the manufacturing and transportation industries: equipment and car manufacturers as well as auto-body shops use chromate in paints to prevent corrosion; chromate-containing paints are also used in bridges, rail stock and ships. However, chromium (Cr VI) is considered a carcinogen with an extremely low (0.1 mg/m3) personal exposure limit (PEL). At URI, three patents have been filed which lead directly to chromate replacement. Two involve conductive polymers while the third involves a chromium replacement (URI alternate to chromate). At present, these three different techniques are being combined into a paint primer with the intent of providing extensive corrosion resistance for steel and aluminum alloys. Such combined approach holds the promise to revolutionize the corrosion protection treatment area for bridges, cars, ships and rolling stock. Simultaneously, the potential toxic effects of the new formulations on marine life are being examined.
Task 1. Scale up of coating system – Year 1
The present coating system was tested on 1x4-in panels. A scale-up of the process to 10x3-in panels is required to ensure that the same corrosion resistance found on the small scale will also work on a larger scale (Appendix, Figure 1).
Task 2. Corrosion testing – Year 1, 2, and 3
Corrosion testing of 10x3-in panels (Appendix, Figure 2), wash-primer coated samples and typical car parts to determine if the coating is still as effective on the larger scale and primed surfaces. Potentiodynamic scans in 0.5 N NaCl will be used to test the effectiveness of the process. The solutions will be purged with oxygen. (This test was found to accurately measure the ability of chromates to provide corrosion protection.)
Task 3. Biofilm formation and biocorrosion – Year 1, 2 and 3
The effects of chromate and non-chromate coatings on motile marine microorganisms will be measured in terms of cell growth, biofilm formation and biocorrosion. Metal samples of aluminum alloy 2024 T3 will be conversion-coated with chromate and the URI non-chromate alternate. This specific aluminum alloy has the worst corrosion resistance of the current alloys used in marine applications and is regarded as the litmus test for anticorrosion coating measurements.
To measure the effects of the coating on cell growth, metal samples in seawater (plus nutrients) will be inoculated with the motile bacteria Pseudoalteromonas atlantica. The growth rate of the bacteria will be determined. It is expected that some bacteria will adhere to the metal samples and form a biofilm. The extent of biofilm formation will be determined with electron microscopy. The chromate and non-chromate content of the medium, cells in suspension and biofilm will be analyzed by atomic absorption and optical emission spectroscopy. The first set of growth experiments in 200-mL flasks has been completed (Appendix, Figure 3).
The formation of biofilm by P. atlantica and the extent of biocorrosion will be assessed by surface electron microscopy (SEM) and electron impedance spectroscopy (EIS). We have preliminary results on bare 7.6-cm, square aluminum alloy samples (Table 1).
The control for these experiments consists of metal samples in sterile seawater with medium (no bacteria) at the same experimental conditions as samples exposed to bacteria.
Task 4. Development of a wash primer containing the alternate to chromate, phosphate and a conductive polymer – Years 1 and 2
The formulation and process route for a wash primer is very different from a conversion coating. In this task, Dr. Brown’s research group in Chemical Engineering is collaborating with the research group of Dr. Yang in Chemistry to develop a new wash primer. The phosphoric acid in a wash primer is basically an etching agent, which permits good adhesion of coatings. Chromates are usually added to provide good corrosion protection. The chemistry will be modified to allow the URI alternate to be used. A conductive polymer will be added to the formulation to provide additional corrosion resistance.
Task 5. Test wash primer with top-coat over it – Year 1 and 2
Once the wash primer formulations have been determined for corrosion resistance, then a topcoat and a clear coat will be applied to produce a full paint system, typical of bridges and automobiles. This will be tested for corrosion resistance by electron impedance spectroscopy (EIS) and salt spray. Adhesion tests will also be conducted to ensure that the paint will adhere to the metal surface adequately.
Task 6. Develop electrophoretic coatings – Year 1 and 2
Conversion coatings require no topcoat and are applied to parts such as loudspeaker frames, bolts etc. Wash primers can be applied at a plant or in a repair shop or at a job site such as a bridge being repainted. Electrophoretic coatings are the coating of choice for the car industry in their plants. In this task it is the intent to modify electrophoretic coatings to include both conductive polymers and the alternate to chromates. Dr. Brown and Dr. Yang already hold a patent on modification of electrophoretic coatings by including conductive polymers. Bath formulations will be modified to coat samples. Corrosion testing using salt spray and impedance spectroscopy(EIS) will be used to test the corrosion resistance of such a coating. Preliminary results of filiform corrosion tests are shown in Figure 4 (Appendix).
Task 7. Scale up – Year 2 and 3
We expect to coat full-scale parts and test them by salt spray and immersion in seawater. Typical parts would include panels of car bodies, sections of bridges being repainted or test panels attached to bridges being repainted to compare the effectiveness with standard techniques. Lincoln Plating, Nebraska, will cooperate with our research group to use our alternate coating instead of chromate coatings. The US Navy is signing a Broad Agency Agreement (BAA) to further develop these alternates to chromate on aluminum alloys.
Project start date 9/1/02
Continue scale-up of conversion coating process
Continue biological (biofilm, biocorrosion) tests
Optimize wash primer formulation
Continue biofilm and biocorrosion measurements
Project end date 8/31/03
$192,663.00
There have been one undergraduate and six graduate students participating in this project (one of them supported by URITC and one by a URI Foundation prototype grant). Three graduate students have completed their degrees (two masters and one doctorate) and one is currently in an internship at Los Alamos National Laboratory. We expect to have one more graduate and undergraduate students.
The formulation of alternate to chromates has already been underway in the Corrosion Laboratory at URI. As mentioned above, Drs. Brown and Yang have filed a patent and are moving ahead in investigating process variables to ensure the optimum conversion coating for Al 2024 T3. The aim is mainly to investigate surface preparation for adhesive bonding. This work was funded by the U.S. Navy at Newport and did not involve development of a wash primer.
The US Army is funding the development of a wash primer containing a conductive polymer but no alternate to chromates is specified in this project. Therefore, the URITC project described above will widen the scope of both these programs by involving the alternate to chromate with conductive polymers.
Lincoln Plating in Nebraska will work with us in transferring the technology. It is a large commercial coating and plating company with clients awaiting a chromate replacement in aluminum alloys. In fact, we already have samples at URI ready to coat once the correct agreements are in place. This interaction is the technology’s transfer avenue from the research laboratory to industry. The impact of this project will be local, regional, national and international as chromate coatings are used for corrosion protection on many systems such as bolts, nuts and nearly every metal fitting.
Another example is Microfin Corp., a company in Providence, which provides chromate coatings for a wide range of industrial applications. Successful completion of this project will enable them to move from chromate to non-chromate alternatives very easily, a change not possible at present as no viable alternative to chromate exists.
Alcoa and Alcan are familiar with the program and have stated that they will test samples for us as well as help with scale up of the electrophoretic process.
The U.S. Navy is interested in using the alternate to chromate in a fleet application to replace the presently used chromate. A proposal is set to scale up to fleet conditions of ten years of marine service. Contact has already been made with the Navy at Patuxent River, Maryland to conduct some independent testing.
The U.S. Army is funding a study of wash primers based on conductive polymers. In year 3 of this project we expect to be coating prototype parts for testing at Aberdeen Proving Ground in Maryland.
As for the toxicity and environmental effects of the new alternative to chromate, we expect it will be nontoxic, i.e., environmentally friendly, to marine organisms.
The potential benefit is that chromate can be replaced in many applications. This will reduce environmentally harmful products.
Corrosion, structures, paints, biofilm, biocorrosion.