LATEST LABORATORY AND FIELD RESULTS FOR NANOSTRUCTURED TITANIA COATINGS

As mentioned in a previous post (Sept. 21, 2009), thermal spray nanostructured ceramic coatings showed enhancements in wear-resistance; bond strength; and toughness, compared to their conventional coating counterparts.  The nanostructured titania coating developed, tested, and patented by FW Gartner, Mogas, and Perpetual Technologies has been applied onto thousands of ball valve components used in hydrometallurgical extraction of nickel and cobalt [1-4].  In addition to the superior abrasion and erosion resistance (Figure 1), the latest evaluation of the remnant scars following exposure to three-body abrasion and both low- and high-angle erosion reveal very unique characteristics that are notably different from those found on conventional coatings of the same composition.  As illustrated in Figure 2, the scars on the nanostructured titania coating show ductile features, i.e., microploughing, plastic deformation, microcutting, with no signs of cracks.  On the other hand, the conventional titania coating shows brittle features, i.e., rough fracture surface, microcracks, fracture along splat boundaries.  These results validate the hypothesis: a unique combination of increased toughness without any compromise in strength/hardness is responsible for the superior wear resistance found in thermal sprayed nanostructured ceramic coatings.

An independent study conducted in 2001 of High Pressure Acid Leach (HPAL) plants indicated that autoclave valve costs were six times greater than expected and represented 30% to 40% of the operating budget.  This was one of the major thrusts towards developing a novel coating for severe-service ball valves.  

 

John Williams, VP of Engineering at Mogas Industries, has stated the following: “While many properties may be individually measured using standardized laboratory tests, there is no substitute for the information gained from actual field installations.  Field performance identifies the interactions of material, design and operations.” [5].  BHP’s Ravensthorpe Nickel Mine took the initiative to accurately track progress of their ball valve assets.  The performance results for the ball valves with nanostructured titania coatings in three of its most severe process environments include: > 300 average cycles and > 300 average days in service for Slurry Inlet Valves; ~ 150 average cycles and ~ 280 average days in service for Slurry Discharge Valves; and, > 1,000 average cycles and 490 average days in service for Vent Valves.  

There is no direct comparison with ball valves with conventional coatings since Ravensthorpe has only specified nanostructured titania coated valves; however, we do have general information from other similar mines that have used ball valves with conventional ceramic coatings, including conventional titania.  In 1999, the goal expressed by Cawse Nickel Operations for a “good run” with an autoclave discharge valve was to achieve either 60 days or 60 cycles of service.  These field results point to notably favorable performance of the nanostructured coating in the harsh HPAL environment.

1. G.E. Kim, “Thermal Sprayed Nanostructured Coatings: Applications and Developments”, Chapter 3 of Nanostructured materials: processing, properties, and applications, edited by C.C. Koch, 2007.
2. G.E. Kim, “Nanostructured Coatings Application in High Pressure Acid Leaching Process”, Invited Speaker at the Surface Technology (SURFTEC) Group Meeting at the National Research Council of Canada, Montreal, Quebec, Canada, 2002. 
3. J. Williams, G.E. Kim, and J. Walker, “Ball Valves with Nanostructured Titanium Oxide Coatings for High-Pressure Acid-Leach Service: Development to Application”, Proceedings of Pressure Hydrometallury 2004, Banff, Alberta, Canada, October 23-27, 2004.
4. G.E. Kim, J. Williams, and J. Walker, “Nanostructured Titania Coated Titanium”, United States Patent No. 6,835,449, December 28, 2004.
5. J. Williams, “Field Performance Review PAL Valves in Service”, ALTA 2009, May 25-30, Perth, Australia.

George E. Kim, Ph.D.

F.W. Gartner

Perpetual Technologies, Inc.

email: gkim@perpetualtech.ca