Browsing by Author "Volk, Michael"
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Item Data for "Simulation of natural alteration of iron oxides in soil: conversion of synthetic ferrihydrite to hematite without artificial dopants, observed with magnetic methods" collected at the University of Minnesota between 2016 and 2020(2020-03-12) Bilardello, Dario; Banerjee, Subir K; Volk, Michael; Soltis, Jennifer A; Penn, R. Lee; dario@umn.edu; Bilardello, Dario; University of Minnesota Institute for Rock MagnetismWe present the results of a new study on the conversion of pure, undoped synthetic ferrihydrite, wet-annealed at pH 6.56 and 90 ℃ without stabilizing ligands, to nanophase goethite, hematite and an intermediate magnetic phase, likely to be nanophase maghemite. Our analysis included magnetic field and temperature dependent properties and characterization by powder x-ray diffraction, Mössbauer spectra and high-resolution transmission electron microscopy. Unlike most other studies of ferrihydrite alteration we sampled alteration products after 0.5 hours, and then in a geometric progression to 32 hours, yielding an extremely detailed examination of the earliest alteration phases. There are many similarities to the latest studies of pure ferrihydrite alteration but with a significant difference: we observe very early appearance of oriented nanophase goethite along with a soft magnetic contribution, while rhombohedral hematite crystals are formed later, as reported in the previous studies. Our observations attest to the non-uniqueness of the magnetic enhancement process and to its strong dependence on environmental conditions, with important implications for the proposed hematite/goethite ratio as a reliable proxy for paleoprecipitation intensity.Item IRM Quarterly, Volume 27, Number 4 (Winter 2017). Cover article: Magnetic tests and characterization protocols: mineralogy and grain size / domain state Part I: isothermal strong field tests(University of Minnesota. Institute for Rock Magnetism, 2018-02) Volk, Michael; Jackson, Mike; Bilardello, DarioItem IRM Quarterly, Volume 28, Number 2 (Summer 2018). Cover article: Magnetic tests and characterization protocols: mineralogy and grain size / domain state Part II: isothermal weak field tests(University of Minnesota. Institute for Rock Magnetism, 2018-08) Volk, Michael; Bilardello, Dario; Jackson, Mike