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Title: Enhanced corrosion resistance and surface bioactivity of AZ31B Mg alloy by high pressure cold sprayed monolayer Ti and bilayer Ta/Ti coatings in simulated body fluid
Award ID(s):
1846887
NSF-PAR ID:
10219885
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Materials Chemistry and Physics
Volume:
256
Issue:
C
ISSN:
0254-0584
Page Range / eLocation ID:
123627
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Abstract

    To assess the variability of redox states among mare basalt source regions, investigation of the valence of Ti, Cr, and V and the coordination environment of Ti in pyroxene and olivine in lunar rocks viaXANES(X‐ray absorption near‐edge structure) spectroscopy has been extended to Apollo 17 basalts: two high‐Ti (70017 and 74275) hand samples, and three very low‐Ti (70006,371, 70007,289B, and 70007,296) basalt fragments from the Apollo 17 deep drill core. Valences of Ti in pyroxene of both suites range from 3.6 to 4, or from 40% to 0% Ti3+, averaging 15–20% Ti3+. Assuming Ti3+is more compatible in pyroxene than Ti4+, then even lower Ti3+proportions are indicated for the parental melts. TheVLTpyroxene exhibits a slightly wider range of V valences (2.57–2.96) than the high‐Ti pyroxene (2.65–2.86) and a much wider range of Cr valences (2.32–2.80 versus 2.68–2.86); Cr is generally reduced inVLTpyroxene compared to high‐Ti pyroxene. Valences of Ti and Cr inVLTpyroxene become less reduced with increasing FeO contents, possibly indicating change in oxygen fugacity during crystallization. Olivine in all samples has very low (<20%) proportions of Ti3+, with no Ti3+and higher proportions of Ti in tetrahedral coordination in theVLTs than in the high‐Ti basalts. Olivine in 74275, including that in a dunite clast, has much higher proportions of Cr2+than the pyroxene in that sample, consistent with previous studies indicating that the olivine grains in this sample are xenocrysts and possibly indicating oxidation just prior to pyroxene crystallization. Results for this sample, theVLTs, and previously studied Apollo 14 and 15 basalts all indicate that mare magmas were in reducing environments at depth, as recorded in early crystallization products, and that later, presumably shallower environments, were relatively oxidizing; single, characteristicfO2s of formation cannot be assigned to these samples. A process likely to account for this feature seen in multiple samples is loss by degassing of a reducing, H‐rich vapor (probably H2) during ascent and/or eruption, causing oxidation of the residual melt, recorded in relatively late‐crystallized pyroxene.

     
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  2. null (Ed.)