1123
Investigation of Surface Interactions between Volatile Chromium Species and Ceramics

Tuesday, 15 May 2018: 10:20
Room 305 (Washington State Convention Center)
G. Tatar, P. Gannon, S. Dansereau, and E. Remington (Montana State University - Bozeman)
Volatile chromium species are formed when chromium containing materials are exposed to high temperature (>500°C) oxidizing environments. These volatile species are often accompanied by detrimental effects, such as cathode poisoning in solid oxide fuel cells and condensation of toxic hexavalent chromium species. The reactive vaporization of chromium species and their detrimental effects are well understood, but less is known about how these species interact with and condense onto various materials. This study investigates how volatile chromium species interact with ceramics over a range of temperatures and exposure times. Preliminary work performed on aluminosilicate fibers suggests that chromium speciation depends on factors such as temperature, chromium loading of a surface, and what material the volatile chromium is interacting with. Additionally, the color of condensed chromium species on these fibers has been linked with the oxidation state of chromium, allowing inferences to be made to known chromium compounds such as chromate, chromium trioxide, and chromia. To extend this work, volatile chromium was generated by flowing humidified air over chromia powder at various temperatures up to 900°C for various time intervals up to 100 hours. Vapor collection materials, including pure and mixed silica and alumina ceramic fibers and coupons, were placed downstream at temperatures ranging from 50-900C. Post exposure characterization of ceramic surfaces was performed using x-ray photoelectron spectroscopy, x-ray diffraction, inductively coupled plasma mass spectroscopy, and colorimetry to obtain information about chromium speciation in the form of oxidation states and phase formation. Results will be presented and discussed in context of advancing fundamental understanding of condensation mechanisms for volatile chromium species.