Humidity related magnetite alteration in an experimental setup

2020 ◽  
Vol 224 (1) ◽  
pp. 69-85
Author(s):  
Qi Zhang ◽  
Erwin Appel ◽  
Helge Stanjek ◽  
James M Byrne ◽  
Christoph Berthold ◽  
...  
Keyword(s):  
Room Temperature ◽  
Atmospheric Conditions ◽  
Low Temperature Oxidation ◽  
Surface Layers ◽  
Entire Volume ◽  
Temperature Oxidation ◽  
Lattice Constants ◽  
Dry Conditions ◽  
Low Humidity ◽  
Mössbauer Analysis

SUMMARY Low-temperature oxidation (LTO) of magnetite is an alteration process which occurs under normal atmospheric conditions, causing maghemitization. The use of magnetic properties as palaeoclimate proxies requires improved understanding of how humidity and temperature affect such processes. We exposed natural magnetite, with grain size ranging from <1 to ∼30 μm, to different humidity conditions at room temperature and 70 °C for 1 yr. Changes in room temperature setups were very minor, but in all 70 °C setups alteration was detected by magnetic and mineralogical properties. Lowering of the Verwey transition temperature (Tv) turned out to be the most sensitive indicator of LTO, and also lattice constants correlate well with the shift of Tv. Thermomagnetic curves and XRD-results indicate that LTO affects the entire volume of the particles rather than only surface layers. The sample exposed to high relative humidity (rH) >90  per cent at 70 °C showed the strongest degree of LTO with an increase of the oxidation degree by ∼3 per cent according to Tv, and it was the only setup where partial alteration to hematite was indicated by Mössbauer analysis. The sample with extremely dry conditions (rH of ∼5 per cent) at 70 °C, and the sample that was exposed to cycles of high and low humidity in 2-weeks alternation at 70 °C, both revealed a smaller degree of LTO. The smallest change of the high temperature setups was observed for the sample with intermediate rH of ∼13 per cent. The results suggest a non-linear sensitivity of magnetite alteration to humidity conditions, high humidity strongly favours alteration, but alteration is strongly reduced when extreme humidity alternates with dry conditions, suggesting an importance of seasonality in natural weathering.

Room temperature ultraviolet emission from ZnO nanocrystallites fabricated by the low temperature oxidation of metallic Zn precursors

2003 ◽  
Vol 127 (1) ◽  
pp. 21-24 ◽  
Author(s):  
Tae-Won Kim ◽  
Tadashi Kawazoe ◽  
Shunsuke Yamazaki ◽  
Jungsik Lim ◽  
Takashi Yatsui ◽  
...  
Keyword(s):  
Low Temperature ◽  
Room Temperature ◽  
Low Temperature Oxidation ◽  
Ultraviolet Emission ◽  
Temperature Oxidation

Low Temperature Oxidation of Silicon After Copper Ion Implantation

1995 ◽  
Vol 398 ◽  
Author(s):  
E.J. Jaquez ◽  
T.L. Alford ◽  
N.D. Theodore ◽  
D. Adams ◽  
Jian Li ◽  
...  
Keyword(s):  
Ion Implantation ◽  
Room Temperature ◽  
Silicon Oxide ◽  
Rutherford Backscattering Spectrometry ◽  
Copper Ion ◽  
Low Temperature Oxidation ◽  
Temperature Oxidation ◽  
Silicon Oxide Layer ◽  
Moving Interface ◽  
Transmission Electron

ABSTRACTSilicon oxide films ( > 1μm ) were grown at room-temperature after low-energy copper-ion implantation of Si(100) substrates. The structural properties of the silicon oxide layer and the implanted silicon were characterized by Rutherford backscattering spectrometry and transmission-electron microscopy. During room temperature oxidation a portion of the implanted copper resided on the surface and a portion moved with the advancing Si/SiOx interface. This study revealed that the oxide growth rate was dependent on the amount of Cu present at the moving interface. The resulting oxide formed was approximately stoichiometric silicon dioxide.

scholarly journals Influence of Co-Precipitation Agent on the Structure, Texture and Catalytic Activity of Au-CeO2 Catalysts in Low-Temperature Oxidation of Benzyl Alcohol

Catalysts ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 641
Author(s):  
Lukasz Wolski ◽  
Grzegorz Nowaczyk ◽  
Stefan Jurga ◽  
Maria Ziolek
Keyword(s):  
Gold Nanoparticles ◽  
Catalytic Activity ◽  
Low Temperature ◽  
Benzyl Alcohol ◽  
Low Temperature Oxidation ◽  
Temperature Oxidation ◽  
Oxidation Of Benzyl Alcohol ◽  
Key Factor ◽  
Au Particle Size ◽  
Co Precipitation

The aim of the study was to establish the influence of a co-precipitation agent (i.e., NaOH–immediate precipitation; hexamethylenetetramine/urea–gradual precipitation and growth of nanostructures) on the properties and catalytic activity of as-synthesized Au-CeO2 nanocomposites. All catalysts were fully characterized with the use of XRD, nitrogen physisorption, ICP-OES, SEM, HR-TEM, UV-vis, XPS, and tested in low-temperature oxidation of benzyl alcohol as a model oxidation reaction. The results obtained in this study indicated that the type of co-precipitation agent has a significant impact on the growth of gold species. Immediate co-precipitation of Au-CeO2 nanostructures with the use of NaOH allowed obtainment of considerably smaller and more homogeneous in size gold nanoparticles than those formed by gradual co-precipitation and growth of Au-CeO2 nanostructures in the presence of hexamethylenetetramine or urea. In the catalytic tests, it was established that the key factor promoting high activity in low-temperature oxidation of benzyl alcohol was size of gold nanoparticles. The highest conversion of the alcohol was observed for the catalyst containing the smallest Au particle size (i.e., Au-CeO2 nanocomposite prepared with the use of NaOH as a co-precipitation agent).

scholarly journals Graphene oxide prepared by a room temperature oxidation using a green mechanochemical method.

2021 ◽  
Vol 27 (S1) ◽  
pp. 726-728
Author(s):  
G. Tarango-Rivero ◽  
G. Herrera-Perez ◽  
C. Carreño-Gallardo ◽  
C.G. Garay-Reyes ◽  
I. Estrada-Guel ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Room Temperature ◽  
Mechanochemical Method ◽  
Temperature Oxidation

scholarly journals The influence of high-temperature oxidation on the phase distribution of metal substrate in duplex stainless steel

2021 ◽  
Author(s):  
Minami Matsumoto ◽  
Ken Kimura ◽  
Natsuko Sugiura
Keyword(s):  
Stainless Steels ◽  
Room Temperature ◽  
Phase Distribution ◽  
High Strength ◽  
Metal Substrate ◽  
Temperature Oxidation ◽  
Good Corrosion Resistance ◽  
Mn Oxide ◽  
Typical Type ◽  
Compositional Changes

AbstractDuplex stainless steels (DSSs), which consist of ferrite and austenite phases, are widely used owing to their high strength and good corrosion resistance. However, the oxidation behavior of DSSs is extremely complicated because they have dual phases. In this study, changes in the scale and the metal substrate during oxidation were investigated. UNS S32101 (Fe-21.5%Cr–5%Mn–1.5%Ni–0.3%Mo–0.22%N), which is a typical type of DSS, was annealed at 1473 K for up to 36 ks in air. The microstructure of UNS S32101 consisted of austenite/ferrite phases, the ratio of which was 50:50 at room temperature. After oxidation, Cr, Mn-oxide formed predominantly. The metal substrate beneath the scale changed mostly to ferrite. In the same region, depletion of Mn and N concentrations resulted. The decrease in Mn was due to the formation of Cr, Mn-oxide. In addition, it was revealed that N content of the metal substrate decreased due to the formation of N2 gas along with the depletion of Mn. It was assumed that the decrease in Mn and N, which are austenite-stabilized elements, led to an increase in ferrite in the depletion area of Mn and N. From this result, it was expected that the compositional changes in the Mn/N depletion area were caused by the oxidation of steel.

Sign in / Sign up

Export Citation Format

Share Document