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AFRL02 is a ubiquitous test dust in the field of particle deposition in gas turbine engines. The traditional recipe for AFRL02 is 34 mass percent quartz, 30 mass percent gypsum, 17 mass percent aplite, 14 mass percent dolomite, and five mass percent halite. In the present study, albite was substituted for aplite, and hematite was added for certain tests. This thesis seeks to unpack the synergies that exist between minerals during deposition of the heterogeneous AFRL02 mixture in gas turbine engines and demonstrate that incoming mineral phases and eutectic chemistry are major factors in the deposition phenomenon through their relation to eutectic melt formation and subsequent deposit properties, such as melting temperature, viscosity, and surface tension. Capture efficiency measurements, deposit morphology analyses, and X-ray diffraction results are reported and discussed for deposition experiments performed with the Impingement Deposition Rig at The Ohio State University. In each experiment, one gram of a mineral dust (0-10µm particle diameter distribution) was injected into an 894K, 57m/s coolant flow impinging normally on a Hastelloy X plate with a surface temperature of 1033K, 1144K, or 1255K. Besides AFRL02, single mineral dusts, dual mineral dusts, and AFRL02-like dust blends lacking in one mineral were tested. The results of the experiments elucidate that the deposition behavior of single minerals cannot explain the composite deposition of heterogeneous mixtures of minerals. For example, gypsum had the highest capture efficiency of any single mineral in ARFL02, and yet removing gypsum from AFRL02 counterintuitively raised the capture efficiency of that blend when compared to AFRL02. Quartz was found to erode albite deposits but stick to and build upon dolomite and halite deposits, even though quartz did not deposit significantly as a single mineral. Quartz also chemically reacted with gypsum and dolomite to form wollastonite and diopside, respectively. Finally, it was found that the capture efficiency of each blend increased with plate temperature, but not according to the same trend. Results are interpreted through the lens of CaO-MgO-Al2O3-SiO2 eutectic chemistry – influenced by advances in the field of agglomeration in Fluidized Bed Combustion – and credible explanations of deposition behavior based on mineral phase and eutectic chemistry are put forward. This thesis concludes by revisiting a handful of well-known, key trends in the field of deposition in gas turbine engines and explaining how mineral chemistry might manifest itself in each of these trends. |
