Environmentally Friendly Corrosion Protection

E. Ryabova, J.T. Dawley, O. Niitsoo, C. Mah, and V. Ryabov Advenira Enterprises, Inc.

788 Palomar Ave. Sunnyvale, CA 94985

ABSTRACT

The protection of metals, such as aluminum, steel, and stainless steel from atmospheric, liquid water, and chemical corrosion is vitally important if structures, components, and water distribution systems made from these materials are to have long useful lifetimes without requiring costly maintenance and upkeep. In recent years, the development of environmental friendly, a.k.a. green, anti-corrosion coating technologies has been of particular interest as the negative impact of chromates on the environment and human health has been fully established. The primary challenge for green coatings for industrial applications has been the ability to provide the broad set of anti-corrosion and mechanical properties achieved by chromate conversion coatings. For potable water applications the coating must be able to enhance the useful lifetime of water distribution pipes and mains without adversely affecting the quality of potable water. Two families of barrier coatings, F-series and H-series, have been developed that are low-cost, green, corrosion resistant barrier coatings, which can be deposited on aluminum, stainless steel and similar metals and imparts excellent corrosion resistance without the use or leeching of toxic chromates or other hazardous chemicals. The coatings are colorless, optically transparent, and provide excellent abrasion resistance. This paper will focus on the corrosion resistance and mechanical properties of these coatings. Key words: Barrier coating, EIS, sol-gel, abrasion resistance, corrosion resistance, water leeching

INTRODUCTION Metal corrosion has been a major issue for humankind since it began using metal tools thousands of years ago. Besides being unsightly, corrosion is insidious in that it slowly degrades the structural integrity of a metal object, such as a hammer, boat, building, or bridge, over time to the point where the object is no longer functional or useful. In order to mitigate the effects of corrosion there is a need to inspect, test, and maintain corroded parts, objects and structures at regular intervals to verify that they still meet their original design specifications. This process is very costly.

A 2002 study by CC Technologies Laboratories, Inc.(1), the Federal Highway Administration (FHWA)(2) and NACE International(3), entitled “Corrosion Costs and Preventive Strategies in the United States,” estimated that the total annual direct cost of corrosion in the United States (US) is $276 billion or approximately 3.1% of the nation’s Gross Domestic Product (GDP).1 The study also estimates that the annual indirect cost of corrosion in the US is at least equal to the direct cost of corrosion. Indirect costs encompass what customers pay as a result of the effect of corrosion on public safety, property damage, environmental contamination, waste production, and public inconvenience. By adjusting for inflation, Generation 2 Materials Technology (G2MT)(4) has estimated that the total cost of corrosion (direct plus indirect costs) in the US for 2013 approached $1 trillion or 6.1% of GDP.2 Given this extraordinary cost, it is vitally important to implement optimal corrosion control practices to maximize the survivability and useful lifetime of metal structures. In its basic form, corrosion can be described as the electrochemical oxidation of a metal when exposed to an oxidizing environment. Water is the most common corrosion-mediating electrolyte. Corrosion is often a non-uniform process, and the nature of corrosion changes with changes with water pH and chemical composition.3 Over the years, two distinct methods of protecting metals from corrosion have been developed: 1. specialty alloys and 2. protective/barrier coatings. Both methods can be very effective; however, a cost/performance analysis is often the controlling factor in determining which method is implemented. Specialty alloys are much more expensive than steel or aluminum so they are typically only used in applications where those materials would rapidly fail, such as at high temperatures and unique, highly corrosive environments, or where specific material properties are required. Barrier protection layers are perhaps the oldest and most widely used method of corrosion protection. By applying paint (organic), an anodic metal (Zn), a corrosion inhibitor (chromate) or other protective layer (anodization), the base metal is isolated from the surrounding environment. As long as the barrier layer remains intact, the metal is protected and corrosion will not occur. However, because a barrier must remain intact to provide corrosion resistance, a barrier layer or coating must have excellent adhesion to the base metal, as well as abrasion resistance. For many years, chromates have been widely used as barrier protection coatings for aluminum, zinc and other metals. Steel is typically galvanized prior to chromating. Chromate coatings work because the high oxidation state Cr(VI) causes the base metal to remain in the passive regime and since the product of oxidation of chromate is Cr2O3 which itself forms an inert surface film. Another advantage of chromate coatings is their ability to self-heal small imperfections, rubs or scratches. The chromium atoms can move slowly in the coating layer, and will eventually re-coat small scratches or damage. Large cuts or rubbed areas cannot self-heal and require re-treatment. However, chromate coating comes with high health and environmental costs. Hexavalent chromium [Cr(VI)] is a genotoxic carcinogen in humans and is considered an environmental toxin due to its high solubility in water. Some chromate coating baths also contain cyanide.4 Advenira’s Solution Derived Nanocomposite (SDN®) technology is a platform technology for developing coating formulations for a wide array of applications. SDN coating formulations based on appropriately functionalized nanoparticle constituents dispersed in a matrix of sol-gel type hydrolyzates, (metal)

(1) CC Technologies Laboratories, Inc., 6141 Avery Rd., Dublin, OH 43016 (2) Federal Highway Administration (FHWA), 1200 New Jersey Ave., SE, Washington, DC 20590. (3) NACE International, 15835 Park Ten Place Houston, Texas 77084. (4) Generation 2 Materials Technology LLC, 2501 Central Pkwy, C13 Houston, TX 77092.

organic monomers and oligomers or a mixture of the above. SDN coating formulations allow a high degree of tuning of coating properties via careful selection of major components, their ratios, and additives. We have developed two corrosion resistant formulations, F-series and H-series, with each having unique advantages. The properties of these protective coatings on metal substrates, and their potential for use and anticorrosion coatings for industrial and water distribution and storage systems will be discussed in this paper.

MATERIALS AND METHODS

The F-series and H-series coating formulations are proprietary liquid coating formulations. They were synthesized from standard grade precursors and solvents that were used as received. The base synthesis procedure for each formulation family is different, but both involve standard chemical synthesis, purification, and filtration methods. F-series formulations contain nanoparticles in an inorganic-organic matrix and an alcoholic solvent. H-series formulations are solvent-free, with a different composition of nanoparticles in an organic-inorganic matrix. Both formulations allow the deposition of densely cross-linked coatings, which is crucial to their performance as a physical barrier in an aqueous environment. Materials Coated and Preparation A variety of substrate materials were used for this study, including 6061, 6016, 5052, and 2024 aluminum alloys, 1000 series cold-rolled or mild steel (CRS), electro-galvanized CRS (EGS) and 304 and 316 stainless steel. The four grades of aluminum were selected to cover a wide range of potential applications, such as automotive, architecture, general use, and aerospace. Cold-rolled steel is commonly used for structural applications and piping, but is readily susceptible to corrosion without a protective coating. 304 and 316 stainless steels are the most widely used austenitic stainless steels. Even though they have good overall corrosion resistance, 304 and 316 are known to be susceptible to pit corrosion when exposed to high chloride environments, especially if the pH is low. All substrates were cleaned with a commercial alkaline cleaner/degreaser followed by rinsing with deionized water and isopropanol, and drying in clean dry air (CDA) prior to coating. The cleaner also contained additives to help prevent flash rust formation on cleaned CRS surface. In general, the metal coupons were coated immediately after cleaning. Characterization of Coating Properties Corrosion Testing In terms of characterization, multiple techniques were employed to study the anti-corrosion properties of F-series and H-series coatings. Electrochemical impedance spectroscopy (EIS) measurements were taken with a Solartron 1287 Electrochemical Interface† and Solartron 1260 Impedance/Gain-Phase Analyzer†. The test cell details are as follows: 3.5 wt% NaCl electrolyte, 15 cm2 cell, Ag/AgCl reference electrode, graphite counter electrode, and 50 mV signal amplitude. EIS data acquisition and analysis were performed using ZPlot and ZView software for Windows†. In-house acid bubble testing was used as another method of characterizing the anti-corrosion properties of the coatings, using 1M or 11.65M HCl for coatings on Al, and 1M H2SO4 for coatings on CRS. The pH value for both 1M HCl and 1M H2SO4 is approximately 0, so all of the test solutions are highly acidic. The bubble test is quite common in the semiconductor industry and is often used as a measure of the corrosion resistance of anodized coatings.5 For the bubble test, the coating surface is exposed to an acid solution by attaching a 25 mm diameter tube to the coating surface and filling the

† Trade name

tube with the acid solution. When the coating starts to break down, the acid will attack the metal surface and liberate H2 bubbles. The amount of time it takes for a continuous stream of bubbles to appear from the surface of a coating can be used to compare the corrosion resistance of one barrier coating versus another. Coatings with varying thickness can be compared by dividing the time by the total coating thickness (typically expressed in Vµm-1). It should be noted that defects in the coating will cause premature failure, so multiple tests (3+) are run on each sample simultaneously to verify the results. Cyclic accelerated corrosion testing data was acquired using the GMW14872 specification up to 72 cycles and the SAE J2334 specification up to 80 cycles.6-7 For this study, the GMW14872 test was performed on F-series coated aluminum (6016 and 5052), CRS and EGS panels, as well as and H-series coated Al (5052) and EGS panels. A single 24 h cycle consisted of the following stages: 1.) 8 h ambient stage at 25±3°C, 45±10% RH with a salt fog stress (NaCl: 0.9%, CaCl2: 0.1%, NaHCO3: 0.075%), 2.) 8 h humid at 49±2°C, 100% RH, and a 3.) 8 h dry stage at 60±2°C, ≤30% RH. Test panels were scribed prior to the test and the scribe creep was evaluated after 26, 48 and 72 cycles. The SAE J2334 test was performed on H-series coated CRS, zinc phosphate coated CRS, and E-coat coated CRS reference panels. A single 24 h cycle consisted of the following stages: 1.) 6 h 50°C, 100% RH, 2.) 15 min ambient stage with a salt fog stress (NaCl: 0.5%, CaCl2: 0.1%, NaHCO3: 0.075%), and a 3.) 17.75 h dry stage at 60°C, 50% RH. Mechanical and Thermal Properties Multiple techniques were also used to provide detailed information on the general properties of the coatings. Thermal cycling was performed in an environmental chamber. The test panels were subjected to 100 test cycles of -50ºC to 125ºC, with 3ºC per minute ramp rate, and 15-minute hold at the lowest and highest temperature. Abrasion resistance was measured using a Taber Industries 5135 rotary abraser† with CS-10 wheels and a 1 kg load. The abrasion testing was done in accordance to ASTM 4060.8 A Defelsko Positest AT-A† system was used to measure pull-off adhesion strength on various substrate materials. A 0.7 MPas-1 ramp rate and 14 mm diameter dollies were used during the pull-off tests. Microhardness measurements were taken with a Fischerscope HM 2000S† using a 5 mN max load and 10 sec loading settings. Pencil hardness measurements were performed as per ASTM D3363.9 Water Extraction Testing Water extraction testing was performed according to NSF/ANSI 6110 standard by a State of California certified water quality testing laboratory. A 24 hr. extraction (±2 hr.) of sample mass to deionized water at a 1:20 ratio was conducted at room temperature, followed by analytical testing for heavy metals (analysis methods SW6010B and SW7470A) and organic contaminants (methods SW8260B, SW8270C, 8260TPH and SW8015B(M)). Fully coated 10x10x0.3 cm polycarbonate panels were used for the water extraction test.

RESULTS AND DISCUSSION Corrosion resistant coatings must be durable so that they can withstand real world handling and exposure conditions without being easily damaged. However, for many anti-corrosion coatings, there is often a trade-off between mechanical and corrosion properties. It is important to understand the limitations of any coating so that the proper coating can be selected for a given application. For this study, the properties of F-series and H-series coatings were tested using coatings that were 10-20 µm thick. Microhardness and pencil hardness data for the F-series and H-series coatings is shown in † Trade name

Table 1. The Martens hardness (HM) of the F coating is double that of the H coatings. F coating also has the highest Vickers hardness (HV), and the lowest plastic deformation component at indentation (nplast), as well as indentation creep (CIT1) that is closely related to plastic deformation. The H-series has a significantly higher plastic deformation component, which indicates a more flexible coating. It should be noted that the measured hardness values are independent of the substrate as long as the coatings are properly cured. The pencil hardness tests confirm that the F-series coating is much harder than the H-series coating (8H vs 4H).

Table 1 Typical microhardness data of the F-series and H-series coatings

Coating HM (N/mm2) CIT1 (%) nplast (%) HV (kg/mm2) Pencil Hardness F-Series 450-500 < 2 16 102-114 8H H-Series 200-240 10-15 60 20-27.5 4H

Table 2 shows a comparison of pull-off adhesion and abrasion weight loss of F and H series coatings on cold-rolled steel (CRS) and Al. Both the F and H-series coatings show excellent pull-off adhesion strength on Al and CRS. In terms of abrasion resistance there is a significant difference between the two coatings. The F-series is highly resistant to wear. In fact is performs better than sealed Type III anodized aluminum in terns of thickness loss per 1000 cycles. The H-series coating has a tenfold increase in abrasion weight loss, compared to the F-series. Although there isn’t a direct correlation between hardness and wear resistance, these results are not unexpected given the much higher hardness of the F-series coating. However, it should be mentioned that the H-series coating is actually still has very good wear resistance. A comparison of typical Taber abrasion values for commercially available corrosion protection coatings based on epoxy and polyurethanes, such as 3M Scotchkote Epoxy 162PWX† and Urethane 165PW†, indicates that the H-series would have 1.5-3x better abrasion resistance (lower mass loss) if tested under the same abrasion conditions.11-12

Table 2 Comparison of pull-off adhesion and abrasion weight loss of F-Series and H-series coatings

Coating

Pull-off adhesion on CRS (MPa)

Pull-off adhesion

on Al (MPa)

Abrasion - Δmass per 1000 cycles

(mg)

Abrasion - Δthickness per

1000 cycles (µm)

F-Series 17.9-20.7 20.7-24.1 1.4 0.15 H-Series 15.5-16.6 16.5-22.3 13.8 4.20 Galvanized Steel - - 39.1 2.30 Type III Anodized Al - - 1.9 0.25 Electroless Ni (6-9% P) - - 16.3 1.14

The ability to withstand various climatic conditions is crucial for the success of protective coating. F-series were deposited Al 5052 and CRS panel and H-series coatings were deposited on Al 5052, CRS and EGS panels were cycled between -50ºC and 125ºC for 100 cycles. During the thermal cycling test, RH values oscillated between 0 and just under 40%. After the 100 cycles, the coatings were inspected for cracking, visual appearance, and changes in adhesion. The H-series panels passed the thermal cycling without changes on all substrates, and so did F-series coated aluminum and CRS. The thermal stress tolerance of the H-series coating in particular is noteworthy since, the highest temperature this coating experienced prior to testing was lower than 65ºC.

† Trade name

The corrosion protection properties of the two types of coatings were investigated using three types of tests - electrochemical impedance spectroscopy (EIS), acid bubble testing, and cyclic accelerated corrosion testing. EIS measurements were performed on samples immersed continuously in a solution of 3.5% NaCl in deionized water at 20°C. 3.5% NaCl is the average salinity of seawater throughout the world. Two types of samples were tested. The first type was polished 304 stainless steel (304SS) coupons. The 304SS grade was selected because it is well known to be susceptible to chloride pit corrosion. The other samples were similar 304SS coupons coated with a 20 µm thick layer of the coating. EIS is a very sensitive technique to subtle changes in a coating, and when data is acquired over time it can be used to estimate water uptake (which alters the coating capacitance) and identify active corrosion. In fact, active corrosion mechanisms are often seen in the EIS Bode plots well before there are visible signs of corrosion. Figure 2 shows typical Bode plots for bare 304SS after 24 hr. and F-series coated 304SS after 24, 336, and 504 hr. of exposure. For the bare 304SS, corrosion commenced immediately upon exposure and is evident in measurements taken at 1 hr., which are not shown here, but are essentially identical to the curves at 24 hr. For the coated samples, if corrosion processes were active, there would be dips in the Bode plot at high frequencies (as is the case for the uncoated samples). The absence of a high-frequency dip permits modeling the response with a single time constant, and suggests that the coating is continuing to provide protection even after 504 hr. (3 weeks) of continuous exposure. Figure 3 shows typical Bode plots for bare 304SS after 24 hr. and H-series coated 304SS after 24, 336, and 2208 hr. of exposure. As with the F-series samples there is an absence of any high-frequency dips in the spectra, which indicates that the coating is still effective as a barrier layer even after 3 months of continuous exposure to 3.5% NaCl solution.

Figure 2: Electrochemical impedance spectroscopy Bode plots for bare 304SS and F-series (20 µm) coated 304SS coupons versus time.

Figure 3: Electrochemical impedance spectroscopy Bode plots for bare 304SS and H-series (20 µm) coated 304SS coupons versus time.

Table 3 shows the coating properties obtained from EIS circuit analysis for F-series and H-series, coatings. The decrease over time in the impedance modulus (|Z|) of the coated sample at low frequencies, together with the shift in the dip in the low-frequency phase angle in Figure 2 and 3, are consistent with the slow uptake of water into small pores in the coating, but do not indicate corrosive processes. Based on the increase in coating’s capacitance value versus time, it is estimated that the water uptake for F-series is approximately 2.7% after 504 hr. This value is reasonably low and better than values reported for some polyurethane-based paints.13 H-series shows an even lower water uptake with approximately 2.5% after 2208 hr. of continuous exposure. After 20 weeks the water content only increases to 3.5%. The circuit analysis also indicates that the F-series coating has almost 1.75x higher capacitance than the H-series coating. Given that the thickness of the two coatings is the same it suggests that the dielectric constant of the F-series coating is 1.75x higher than the H-series coating. This has been supported by dielectric breakdown tests, not discussed here, that indicate that the F-series coating has a higher dielectric breakdown strength.

Table 3 Coating Parameters Obtained from EIS Circuit Analysis

F-Series Coating Time

(hr) |Z|10mHz (MΩ)

CCoating (pF)

Rpore (MΩ)

Water Uptake (%)

24 20.2 572 8.3 0.0 336 8.4 624 3.0 2.0 504 5.9 645 2.0 2.7

H-Series Coating Time (hr)

|Z|10mHz (GΩ)

CCoating (pF)

Rpore (MΩ)

Water Uptake (%)

24 4.5 327 6.2 0 336 3.8 345 7.5 1.2

2208 15.7 365 79.5 2.5

The corrosion resistance of the coatings has been further evaluated by using the acid bubble test. This test is more rigorous than saltwater because of the very low pH condition coupled with presence of chloride or sulfate ions to accelerate the corrosion process. As shown in Table 4, F-series and H-series

Rs CPEcoating

Rpore Rpr

CPEdl

Element Freedom Value Error Error %Rs Fixed(X) 20 N/A N/ACPEcoating-T Free(+) 1.1316E-09 2.652E-11 2.3436CPEcoating-P Free(+) 0.91673 0.0023174 0.25279Rpore Free(+) 2.671E06 16696 0.62508Rpr Free(+) 2.4035E20 1.776E20 73.892CPEdl-T Free(+) 1.2421E-05 1.8389E-06 14.805CPEdl-P Free(+) 0.79646 0.060068 7.5419

Chi-Squared: 0.0090205Weighted Sum of Squares: 1.2448

Data File: C:\Program Files (x86)\SAI\ZData\Raw Data\123-A12-SS1 (F1A12 - 22um on 304SS)\- 1008.z

Circuit Model File: C:\Program Files (x86)\SAI\ZModels\Coating+pore.mdl

Mode: Run Fitting / Freq. Range (0.01 - 100000)Maximum Iterations: 1000Optimization Iterations: 1000Type of Fitting: ComplexType of Weighting: Calc-Modulus

coated 6061Al and CRS are substantially more resistant to acid exposure than uncoated Al or CRS substrates by at least three orders of magnitude. In both cases, coated Al performs much better than sealed anodized Al, even though the coatings are less than 25% as thick as the anodized layer (75 µm). Electroless Ni coatings also perform much worse than under these test conditions. Coated CRS performs considerably better than galvanized coatings with H2SO4 exposure since the Zn coating is not electrochemically stable at such a low pH.

Table 4 Acid Bubble Test Performance

Exposure to 1M HCl Time to Failure (hr.)

Hr./µm to Failure

Al 6061, 5052, 2024 0.08 - Anodized Al 6061 Type III - Sealed 2 0.03

Electroless Ni plated Al 6061 12 0.5 F-series coated Al 6061, 5052, 2024 2000+ 250+ H-series coated Al 6061, 5052, 2024 2000+ 100+

Exposure to 11.65M HCl H-series coated Al 6061, 5052, 2024 2000+ 100+

Exposure to 1M H2SO4 CRS (1010) 0.2 -

Electrogalvanized Steel 0.4 0.006 304 Stainless Steel 0.7 -

F-series coated CRS 2000+ 250+ H-series coated CRS 2000+ 100+

The goal of accelerated corrosion testing is to predict long-term “real world” performance in a compressed timeframe using a laboratory-based test. Over the years, there have been a wide variety of accelerated corrosion tests developed, such as Prohesion and salt spray, but it is often difficult to correlate the results from these tests with results collected from real world exposure. Field correlated cyclic accelerated corrosion tests, such as SAE J2334 and GMW14872, are much better predictors of real world performance and can be used to evaluate specific corrosion mechanisms. These tests consist of cycles that include multiple stages, such as ambient exposure with stress, high humidity, and drying. The stress application can either be contaminant, thermal, mechanical or other. The test is run for a set number of cycles and the samples are evaluated at various intervals to monitor the degree of corrosion. Correlation studies have determined that 60 cycles of the GMW14872 test are equivalent to 10 years of real world exposure, while 80 cycles of the SAE J2334 test are equivalent to 5 years of real world exposure.14 For the GMW14872 cyclic corrosion tests, Zn-phosphate + e-coat and chromate + e-coat reference panels were included. Prior to exposure, each panel was scribed with a single line through the coating as per GMW14872. The width of the scribe line was measured and then re-measured at intervals throughout the test to see if the scribe line width increased. An increase in width indicates degradation of the coating. The passing criterion in automotive industry is scribe creep ≤ 6 mm after 72 cycles. The F-series coating on Al 6016 and 5052 and the H-series coating on Al 5052 passed 72 cycles and exhibited anti-corrosion performance that is at least equal to that of the reference panels. F-series coatings failed the test on ferrous substrates (EGS and CRS), suggesting interfacial modification (an alternative cleaning protocol or conversion/primer layer) is required for direct-to-metal application to ferrous substrates. The formation of the corrosion byproducts of iron is known to result in large volume expansion that can cause a coating to peel or crack. The exposure of bare CRS by this process allows

for more CRS to be corroded. The high hardness/brittle nature of the F-series coating does not allow the coating to handle the large strains associated with localized corrosion without cracking and delamination. The H-series coating passed the test on EGS, showing comparable performance with the E-coat reference coatings. The results of the SAE J2334 tests on the H-series coatings on bare CRS and zinc phosphate coated CRS panels after 80 cycles indicated that the H-series coating performed as well as the industry standard E-coat reference coatings. As an illustration, Figure 4 shows comparative photographs of the chromate coated Al and F-series coated panels Al after 72 cycles of the GMW14872 accelerated corrosion test. It should be noted that since F-series is colorless (H-series is colorless as well), it does not add the golden hue to Al that chromating does. Figure 5 shows comparative photographs of the E-coat coated CRS and H-series coated CRS panels after 80 cycles of SAE J2334 accelerated corrosion test. Note that the corroded areas on the H-series panels are underneath the edge taping so that they are not considered in the evaluation. The untaped areas show no corrosion. F-series and H-series coatings also preserve their glossy appearance after exposure, as opposed to the matte appearance of chromate and e-coat coatings.

A B

Figure 4: Photographs of A) F-series coated Al panels and B) Chromate + e-coat coated Al reference

panels after 72 cycles using the GMW14872 cyclic accelerated corrosion test.

A B Figure 5: Photographs of A) H-series coated CRS panels and B) E-coat coated CRS reference panels

after 80 cycles using the SAE J2334 cyclic accelerated corrosion test. National Sanitation Foundation (NSF)(5) and Environmental Protection Agency (EPA)(6) in the USA, and their equivalents throughout the world set the regulations for allowable concentration of inorganic and organic chemicals in drinking water. Both the F-series and H-series coatings were evaluated in a 24 h

(5)NSF International, P.O Box 130140, 789 N. Dixboro Road, Ann Arbor, MI 48105. (6)Environmental Protection Agency, 1200 Pennsylvania Avenue, N.W., Washington, DC 20460.

water extraction test per NSF/ANSI 61 standard for potential leaching of restricted contaminants.15 The results of the extraction tests are reported in Table 5.

Table 5 Selected NSF/ANSI 61 water extraction test results for F-series and H-series coatings

(ND = not detected).

Parameters: H-Series F-Series Unit Heavy Metals (HMS): Zn – US EPA limit is 5 mg/L 0.04 0.023 mg/L HMS: As, Ba, Be, Cd, Cr, Co, Cu, Pb, Mo, Ni, Se, Ag, Tl, V, Hg ND ND mg/L Halogenated compounds (chloroform etc.) ND ND µg/L Phthalates ND ND µg/L Toxic solvents (benzene, pyridine etc.) ND ND µg/L Gasoline, diesel, motor oil ND ND mg/L

No heavy metals and toxic elements (As, Ba, Be, Cd, Cr, Co, Cu, Pb, Mo, Ni, Se, Ag, Tl, V, Hg) were detected in water in contact with either the F-series or the H-series coating. The 0.04 mg/L level of Zn from H-series and 0.023 mg/L Zn from F-series coating are both well below the 5 mg/L EPA national secondary drinking water regulations. The blank contained 0.0129 mg/L Zn. Water in contact with the F-series and H-series coatings was also tested for 139 different organic contaminants, including benzene, styrene, aniline, phthalates and halogenated compounds, as well as gasoline, diesel and motor oil. None of these contaminants were detected from the water in contact with the F-series, suggesting that it has potential for use in contact with potable water. From water in contact with H-series, 2.1 µg/L toluene was detected. The Method Detection Limit (MDL) for toluene was 0.14 µg/L, and Practical Quantitation Limit (PQL) 0.5 µg/L. The US EPA’s total allowable concentration for toluene in drinking water is 1000 µg/L, which is over two orders of magnitude higher than the amount detected. The only other organic contaminant detected in the water in contact with the H-series coating was phenol in 67 µg/L quantity. The PQL for phenol was 14 µg/L. ANSI 61 does not state any official regulatory limit for phenol. However, it does establish a total allowable concentration (TAC) of 2 mg/L, which is well above the level detected. Some water quality organizations recommend a 1 µg/L aesthetic guide value of phenol in drinking water, in order to guarantee the option to chlorinate water without deteriorating its aesthetic quality with respect to taste and odor.16 Further testing may be needed to verify that the H-series coating will not alter the taste or odor of potable water. However, it should be noted that the source of the phenol is likely one of the precursor materials used to synthesize the formulation. If necessary, it should be straight-forward to reduce or eliminate the presence in phenol by identifying which precursor contains the phenol and sourcing a supplier that can provide the precursor without phenol as an impurity.

CONCLUSIONS

Using Advenira’s proprietary SDN™ technology, we have developed two low cost, environmentally friendly, anti-corrosion barrier coatings that can be applied to both ferrous and nonferrous metals. H-series and F-series coatings are multifunctional, nanocomposite coatings that provide anti-corrosion protection over a wide range of pH values and resistance to chloride and sulfate ion attack. When tested using field correlated cyclic accelerated corrosion testing (GMW14872 and SAE J2334), both coatings meet or exceed the corrosion resistance of chromate coatings on Al. H-series also performs very well on CRS, zinc phosphate coated CRS, and EGS. Both coatings also have excellent abrasion resistance. This unique combination of properties makes H-series and F-series useful for a wide variety of applications, ranging from automotive, industrial, and defense.

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