This project focused on the overall performance and assessment of the Ecosils SILSBOND coating pretreatment as a replacement for the hexavalent chromium (Cr(VI)) containing DOD-P-15328 wash primer that was formerly in use. The term “wash primer” has been replaced with the term “pretreatment coating.” 

The Ecosil pretreatment coating that has been spray applied onto test substrates is referred to as “SILSBOND." This product is water-based, contains no volatile organic compounds, hazardous air pollutants and is (Cr(VI))-free as well as phosphate-free. The previous Department of War (DoW) wash primer that was used on ground support equipment and vehicles was based on the DOD-P-15328 specification. The former document “DOD-P-15328” allowed for high amounts of isopropanol, zinc chromates (containing Cr(VI)) and phosphoric acid for etching and adhesion purposes. There were nine non-Cr(VI) pretreatments approved in the Qualified Products Database (QPD) and used by the DoW upon initiation of this study. The Army Research Laboratory (ARL) has now qualified 18 alternatives to the DOD-P-15328 coating specification and are referenced to TT-C-490 types III and IV (June 2018).

SILSBOND is a patented, organic-inorganic hybrid pretreatment that synergistically combines advanced silicon compound oligomers and water-soluble inorganic compounds such as zirconium fluoric acid. SILSBOND forms a nano-structured film on a metal surface through immersion or spray application. The film provides a unique “self-sealing” effect that mitigates flash rusting typical of zirconium-based pretreatments on carbon steels. When applied by immersion or spraying, a SILSBOND hybrid film is formed which consists of two distinct regions: (1) an interfacial layer formed on the metal surface during immersion and (2) a surface layer formed on top of the interfacial layer primarily during drying-in-place.

Testing of the Ecosil pretreatment coating(s) was performed on various SILSBOND formulations on Al 2024-T3 and 1020 steel substrates. After evaluation from laboratory results for adhesion, accelerated corrosion, and marine outdoor exposure testing, the best performing formulation was identified as SILSBOND 01 (at 2% concentration ) pretreatment coating which was selected for field testing by both the Naval Surface Warfare Center Carderock Division (NSWCCD) and ARL on non-critical military components for a one- and two-year field test as determined by each service.

The one-year field testing was conducted by the NSWCCD at the Marine Corps Base Hawaii. Field testing was completed during a one-year program July 2021-July 2022 using SILSBOND 01 (2%) pretreatment coating on U.S. Marine Corps (USMC) vehicles with 4”x 6” panels on the Medium Tactical Vehicle Replacement (MTVR). The field test demonstration had coupons (aluminum and steel, 4” x 6” with a 4” diagonal line scribe) mounted onto racks, which were situated to the rear of the USMC MTVR. The coupons comprising a full coating stack-up passed the one-year field testing showing no extensive corrosion, delamination or blistering of the coating from the scribe.

Concurrently with the NSWCCD one-year field testing, the two-year field testing conducted by ARL examined the performance of Ecosil’s SILSBOND 01 (2%) pretreatment coating which evaluated the SILSBOND pretreatment with full military coating systems on non-critical components for a military vehicle such as the Mineresistant Ambush Protected (MRAP). The field test was located at the ARL Cape Canaveral Space Force Station, Florida marine outdoor exposure facility and started December 2020 and completed December 2022. Performance criteria that was evaluated by the field-testing included coating adhesion, intercoat compatibility, and corrosion protection. The limited scale demonstration was performed using vehicle components with participation from the MRAP Program Managers’ Office. Components of this vehicle (MRAP door) were obtained and abrasive blasted to bare metals and treated with Ecosil’s SILSBOND 01 (2%) formulation with representatives from the manufacturer present during the coating process. Identical components were compared using the pretreatment Henkel Bonderite M-NT 7400 and the SILSBOND 01 (2%) pretreatment, resulting in both meeting the requirements called out in TT-C-490.

Both the NSWCCD and ARL field testing of the Ecosil SILSBOND 01 pretreatment coating passed each field test and SILSBOND 01 was approved to the TT-C-490 QPD on June 28, 2023. Thus, the expected benefit to the DoW is a robust, benign Cr(VI)-free pretreatment coating that now populates the QPD which gives end-users an additional option. Having multiple products qualified under the QPD for TT-C-490 encourages open competition between manufacturers and products, and discourages any one company from monopolizing pretreatments within the DoW. This will result in lower cost, and higher quality products through innovation for the DoW end users. (Project Completion - 2025)