Naval Power and Force Projection

Summer 2017

Military magazines in the United States and Canada, covering Armor and Mobility, focuses on tactical vehicles, C4ISR, Special Operations Forces, latest soldier equipment, shelters, and key DoD programs

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Page 20 of 35

the region or to close some or all of their operations." 9 said Wesley Turnbow, President, Metal Finishing Association of Southern California Sodium Dichromate and Dilute Chromate Seals Are Major Sources of Hex Chromium Emissions SCAQMD survey testing performed in plating shops in Southern California has revealed that while the hex chrome emissions directly over the chromic acid anodize tank and conversion coating tanks are controlled and relatively low, the emissions directly over the sodium dichromate seal are staggering – as high as 682,000 ng/m3 – one hundred times as high as that of the chromic acid anodize tank. 10 Although the vapor pressure of chromium is very low, it is believed that the aerosols generated by the wet steam mist above the seal tank and from micro-boiling on the tank heaters are carrying hexavalent chromium into the ventilation and out into the atmosphere. Consortium Works towards Common Goal A consortium of local metal finishers, the Metal Finishing Association of Southern California (MFASC), and CHEMEON Surface Technology of Minden, Nevada has been talking and working with SCAQMD and Prime Aerospace Contractors to mitigate the problems. The group has started an outreach campaign to the stakeholders within the aerospace manufacturing sector, explaining the problem and potential downsides to the continued use of hexavalent chromium seals. The outreach consists of direct calls and emails to the engineers who control the processing specifications within the aerospace companies. CHEMEON Offers Safer Alternative Of course, industrial controls can be used – this is very costly, and will result in some plating shops closing rather than make the large infrastructure investment required. A better choice is to use a seal without hexavalent chromium. Many anodic seal replacements under consideration in recent years are problematic for a variety of reasons and have not been pursued as viable alternatives to dichromates. For instance, the most commonly used seal, nickel acetate, considered a mid-temp seal generally at 160-190ºF, or higher, is energy consuming, and is a regulated pollutant and possible carcinogen. The room temperature nickel- fluoride seal is effective as a possible alternative but is a bath where time must be tightly controlled because of the aggressive fluoride content and is a possible causative factor in dissolution of the oxide if the bath is not maintained properly. The high purity DI hot water seal at 205ºF works well but is time consuming, expensive to heat, prone to contamination and must be dumped frequently. Another option is the use of the relatively new sealing technologies afforded by the trivalent chromium compounds originally developed and patented by the United States Navy in the early part of the 21st century. 10 CHEMEON Surface Technology was one of the first licensees to bring the product to market - first as CHEMEON TCP-HF and then later derivatives such as TCP-HF SP (Spray) and TCP-NP (No Prep). These trivalent chromium compounds are much safer than their hexavalent counterparts. They have very low toxicity, do not cause chronic exposure problems, and are non-carcinogenic. 11 Because the trivalent chromium seal operates at room temperature, there is no aerosol formation from micro-boiling or steam, and very little chemistry is released into the air. The TCP compounds have been available in commercial form since approximately 2006 and have slowly been working their way into Prime aerospace contractor approvals and specifications. Much of the original focus for the trivalents was in the area of replacement for hexavalent chromate conversion coatings on aluminum. In recent years, the original patents that discuss use of the trivalent chromium zirconates as a sealant for anodized aluminum have been reexamined and developed into robust processes and products. Aerospace Primes such as Sikorsky and Pratt and Whitney have patented variants of the original work, and have included TCP-HF and TCP-NP as a sealant in their specifications and processes. 12 13 In 2010, the United States Navy approved the use of CHEMEON TCP-HF as a post-anodize seal at their Fleet Readiness Center Southeast (FRCSE) in Jacksonville FL for Types I, IC, II, IIB, and III. 14 Corrosion resistance, paint adhesion, and fatigue life meet or exceed specification. 15 The FRCSE services naval aircraft including the F/A-18 Hornet, F/A-18- Super Hornet, E/A-6B Prowler, and SH-60 Seahawk. CHEMEON's Trivalent chromate products exceed specification as an anodize seal Studies at the CHEMEON R&D facility have shown that TCP-HF performs as well, or better, than sodium dichromate and hydrothermal seals. Corrosion resistance exceeds 1800 hours for Type II and 1000 hours for Type III coatings. Paint adhesion, wear resistance, dielectric strength are all comparable to the traditional hexavalent seals. 16 The Navy studied the performance of TCP-HF as a sealer and found the performance to be "as good as or better than chromate in corrosion resistance and equal to chromate in paint adhesion. TCP is far superior to water for sealing." 17 Ambient Air Sampler monitors Cr(VI) Hexavalent Chrome Emissions in Southern California. OmniFT photo used courtesy of Mesa Laboratories, Inc. (Chemeon TCP-HF) Research & Testing at the CHEMEON Laboratory reaffirms CHEMEON TCP-HF (Hex Free) proven performance as an anodic seal. (Chemeon TCP-HF) INDUSTRY PARTNER NP&FP and DoD P&E | Summer 2017 | 19

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