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Synthesis Of Multimetallic Pnictides For Application In Magnetic Refrigeration: Mechanistic Insights Enabling Homogenous Phase Formation
Date of Award
Stephanie L. Brock
ABSTRACTSYNTHESIS OF MULTIMETALLIC PNICTIDES FOR APPLICATION IN MAGNETIC REFRIGERATION: MECHANISTIC INSIGHTS ENABLING HOMOGENOUS PHASE FORMATION by TEPORA PLUMERIA SU’A June 2022 Advisor: Dr. Stephanie L. Brock Major: Chemistry (Inorganic) Degree: Doctor of Philosophy
This dissertation research is focused on two main objectives (1) streamlining the synthesis of complex multimetallic transition metal phosphides (TMP) through the determination of the relative rate of phosphidation of various metal precursors employed in the synthesis of monometallic and bimetallic Fe, Ni, Co- TMP phases and (2) to synthesize magnetically favored transition metal pnictide materials (Fe2-xNixP three dimensional assemblies) and evaluate their magnetic properties for practical magnetic refrigeration applications. Phosphorus incorporation as a function of temperature and time was evaluated to probe how the relative rate of phosphidation of organometallic carbonyl and acetylacetonate salt precursors, towards the formation of monometallic Fe2P, Ni2P, and Co2P, influence the order of precursor addition and the homogenous formation of bimetallic phosphide phases (M2-xM’xP; M, M’ = Fe, Co, Ni). From the relative rate of phosphidation studies we found that where the kinetics for different metals are distinct, multi-step procedures in which pre-alloying steps are employed are necessary to isolate the desired multimetallic phosphide phase. These insights were then translated to establish streamlined synthetic protocols for the formation of new, trimetallic Fe2-x-yNixCoyP phases. The parameters that govern homogenous trimetallic Fe2-x-yNixCoyP formation were evaluated with particular attention paid to the consequences of Fe-incorporation. Due to the sensitive reactivity of Fe(CO)5 (determined by the relative rate of phosphidation studies) and the isolation of adding Fe in a second step it was observed that longer post-injection alloying and reaction times were necessary to achieve elevated iron incorporation. These studies are critical to establishing rational synthetic pathways to the next generation of multimetallic TMP phases. For the first time, bimetallic Fe2-xNixP nanoparticles were assembled into 3D architectures via the oxidative assembly method. Functionalization of the discrete nanoparticles with 1-DDT and 11-MUA and exposure to an oxidant, H2O2, resulted in porous, black monoliths after supercritical drying. The data collected is consistent with amorphous phosphite/phosphate olation linkages in aerogels produced from DDT-capped particles vs a combination of phosphite/phosphate olation linkages and metal-ion cross-linking of pendant carboxylates in aerogels produced from MUA-capped particles. The magnetic properties of three representative samples: discrete nanoparticles, MUA-capped Aerogels (AG), and DDT-capped AG were characterized. Notably, the nanoparticles comprising the aerogel network are magnetically independent, as expected for a disordered 3-D assembly, and the magnetic aerogels can be regarded as a summation of their individual components.
Su'a, Tepora, "Synthesis Of Multimetallic Pnictides For Application In Magnetic Refrigeration: Mechanistic Insights Enabling Homogenous Phase Formation" (2022). Wayne State University Dissertations. 3698.