Advancing the Mechanism-Based Framework to Address the Silicate Corrosion Problem in Gas Turbine Tec
Abstract
The proposed project will seek to advance the understanding of the thermochemical interactionsbetween exemplary CMAS compositions an,d a range of coating oxides of interest, based on thefoundation set by the protocol described earlier 16. It is acknowledged that a,full use of the Cal-PhaD databases requires a proper thermodynamic description of the relevant oxides and phases,which is rather lim,ited at the present time. However, an example of what would be feasible usingthe current TCOX10 database is illustrated in Error! No,t a valid bookmark self-reference..These quasi-ternary sections compare the expected reaction paths for YZO (Y4Zr3O12) and GZO(Gd2Zr,2O7) with melt compositions within the class 4 domain in Fig. 2(b), comprising a substantialfraction of the engine deposits. The dia,grams are for one mole of cations total so the positionalong one of the dashed tie-lines would represent the relative amounts of coa,ting oxide and melt.Note that a silicate deposit with a Ca:Si ratio of 0.71would require nearly 15% YZO to reach theonset of apatite, formation after generating first a substantial amount of fluorite. In contrast, onlyabout 3%GZO is needed to trigger apatite format,ion with fluorite following soon thereafter. Theseare thermodynamic scenarios that need complementary kinetic information, but the r,eactivity ofGZO is so high that the experimental observations are in line with these predictions. Reducing theCa:Si ratio of the mel,t to 0.21 at a constant MFA further increases the amount of YZO needed toform apatite, to nearly 30%, but only to ~5% GZO. Moreover,, the reactions with this more acidicmelts lead to the formation of ZrSiO4 (ZS) instead of fluorite or tetragonal zirconia (Z).
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 08, 2022
- Source ID
- N000142212698
Entities
People
- Carlos G. Levi
Organizations
- Office of Naval Research
- United States Navy
- University of California, Santa Barbara