Observation of Large Photoacoustic Signal Phase Changes during a Diffusion Process

The phase of the photoacoustic signal is known to be a sensitive and accurate means to investigate, both qualitatively and quantitatively, static multilayer heterogeneous systems. According to theory, the maximum phase delay for a very weakly absorbing homogeneous sample should be within 45° of a very strongly absorbing sample, while for heterogeneous samples the phase delay can be greater than 45°. Here we report the observation of photoacoustic phase delays greater than 350° by extending the use of step-scan phase modulation photoacoustic spectroscopy to study a non-repetitive dynamic system in situ, in real time. These large phase delays correspond to sampling several thermal diffusion lengths into the sample. The model system used in this study consisted of a hydrocarbon grease diffusing through a porous Teflon film. The progress of the diffusion was tracked by monitoring both the photoacoustic signal magnitude and the phase of the hydrocarbon grease after isolation from the Teflon film signal contributions at two different phase modulation frequencies.

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Anodic synthesis of TiO2 nanotubes by step-up voltages

Journal of Composite Materials ◽

10.1177/00219983211023791 ◽

2021 ◽

pp. 002199832110237

Author(s):

V Sivaprakash ◽

R Narayanan

Keyword(s):

Corrosion Resistance ◽

Tio2 Nanotubes ◽

Biomedical Applications ◽

Phase Changes ◽

Electrochemical Anodization ◽

Corrosion Resistant ◽

Anodization Process ◽

Anodic Synthesis ◽

Input Potential

Fabrication of TiO2 nanotubes (NTs) has extensive application properties due to their high corrosion resistant and compatibility with biomedical applications, the synthesis of TiO2 nanotubes over titanium has drawn interest in various fields. The synthesis of TiO2 NTs using novel in-situ step-up voltage conditions in the electrochemical anodization process is recorded in this work. For manufacturing the NTs at 1 hour of anodization, the input potential of 30, 40 and 50 V was selected. With increasing step-up voltage during the anodization process, an improvement in the NTs was observed, favoring corrosion resistance properties. The surface of NTs enhances the structure of the ribs, raising the potential for feedback over time. XRD was used to analyze phase changes, and HR-SEM analyzed surface topography. Impedance tests found that longer NTs improved the corrosion resistance.

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In situ observation of phase changes of a silica-supported cobalt catalyst for the Fischer–Tropsch process by the development of a synchrotron-compatible in situ/operando powder X-ray diffraction cell

Journal of Synchrotron Radiation ◽

10.1107/s1600577518013942 ◽

2018 ◽

Vol 25 (6) ◽

pp. 1673-1682 ◽

Cited By ~ 13

Author(s):

Adam S. Hoffman ◽

Joseph A. Singh ◽

Stacey F. Bent ◽

Simon R. Bare

Keyword(s):

High Pressure ◽

Elevated Pressure ◽

Phase Changes ◽

In Situ Observation ◽

X Ray Diffraction ◽

Fischer Tropsch ◽

X Ray ◽

And Performance ◽

Co Nanoparticles

In situ characterization of catalysts gives direct insight into the working state of the material. Here, the design and performance characteristics of a universal in situ synchrotron-compatible X-ray diffraction cell capable of operation at high temperature and high pressure, 1373 K, and 35 bar, respectively, are reported. Its performance is demonstrated by characterizing a cobalt-based catalyst used in a prototypical high-pressure catalytic reaction, the Fischer–Tropsch synthesis, using X-ray diffraction. Cobalt nanoparticles supported on silica were studied in situ during Fischer–Tropsch catalysis using syngas, H2 and CO, at 723 K and 20 bar. Post reaction, the Co nanoparticles were carburized at elevated pressure, demonstrating an increased rate of carburization compared with atmospheric studies.

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Bacteria‐Instructed In Situ Aggregation of AuNPs with Enhanced Photoacoustic Signal for Bacterial Infection Bioimaging

Advanced Healthcare Materials ◽

10.1002/adhm.201901229 ◽

2019 ◽

Vol 9 (1) ◽

pp. 1901229 ◽

Cited By ~ 3

Author(s):

Shi‐Zhao Lu ◽

Xiao‐Yan Guo ◽

Mei‐Shuai Zou ◽

Zi‐Qin Zheng ◽

Yu‐Chuan Li ◽

...

Keyword(s):

Bacterial Infection ◽

Photoacoustic Signal

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Ultra-stable 4H-gold nanowires up to 800 °C in a vacuum

Journal of Materials Chemistry A ◽

10.1039/c9ta01306g ◽

2019 ◽

Vol 7 (41) ◽

pp. 23812-23817 ◽

Cited By ~ 4

Author(s):

Qi Wang ◽

Zhi Liang Zhao ◽

Chao Cai ◽

Hui Li ◽

Meng Gu

Keyword(s):

Phase Changes ◽

Gold Nanowires ◽

Significant Phase ◽

Au Nanowire

The in situ TEM observation disclosed that the 4H-phase Au nanowire can maintain stable ABCB stacking up to 800 °C without significant phase changes or melting.

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In-Situ Imaging of Molten High-Entropy Alloys Using Cold Neutrons

Journal of Imaging ◽

10.3390/jimaging5020029 ◽

2019 ◽

Vol 5 (2) ◽

pp. 29 ◽

Cited By ~ 3

Author(s):

Nicholas Derimow ◽

Louis Santodonato ◽

Benjamin MacDonald ◽

Bryan Le ◽

Enrique Lavernia ◽

...

Keyword(s):

Real Time ◽

Liquid State ◽

Single Phase ◽

Neutron Imaging ◽

Phase Changes ◽

Vacuum Furnace ◽

In Situ Observation ◽

Complex Alloy ◽

Phase Liquid

Real-time neutron imaging was utilized to produce a movie-like series of radiographs for in-situ observation of the remixing of liquid state immiscibility that occurs in equiatomic CoCrCu with the addition of Ni. A previous neutron imaging study demonstrated that liquid state immiscibility can be observed in-situ for the equiatomic CoCrCu alloy. In this follow-up study, equiatomic buttons of CoCrCu were placed alongside small Ni buttons inside an alumina crucible in a high-temperature vacuum furnace. The mass of the Ni buttons was specifically selected such that when melted in the same crucible as the CoCrCu buttons, the overall composition would become equiatomic CoCrCuNi. Neutron imaging was simultaneously carried out to capture 10 radiographs in 20 °C steps from 1000 °C to 1500 °C and back down to 1000 °C. This, in turn, produced a movie-like series of radiographs that allow for the observation of the buttons melting, the transition from immiscible to miscible as Ni is alloyed into the CoCrCu system, and solidification. This novel imaging process showed the phase-separated liquids remixing into a single-phase liquid when Ni dissolves into the melt, which makes this technique crucial for understanding the liquid state behavior of these complex alloy systems. As metals are not transparent to X-ray imaging techniques at this scale, neutron imaging of melting and solidification allows for the observation of liquid state phase changes in real time. Thermodynamic calculations of the isopleth for CoCrCuNix were carried out to compare the observed results to the predictions resulting from the current Thermo-Calc TCHEA3 thermodynamic database. The calculations show a very good agreement with the experimental results, as the calculations indicate that the CoCrCuNix alloy solidifies from a single-phase liquid when x ≥ 0.275, which is close to the nominal concentration of the CoCrCuNi alloy (x = 0.25). The neutron imaging shows that the solidification of CoCrCuNi results from a single-phase liquid. This is evident as no changes in the neutron attenuation were observed during the solidification of the CoCrCuNi alloy.

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Impact of initial structural heterogeneity on long-term swelling behavior of MX80 bentonite pellet/powder mixtures

Canadian Geotechnical Journal ◽

10.1139/cgj-2018-0301 ◽

2020 ◽

Vol 57 (9) ◽

pp. 1404-1416

Author(s):

Agustín Molinero Guerra ◽

Nadia Mokni ◽

Yu-Jun Cui ◽

Pierre Delage ◽

Anh Minh Tang ◽

...

Keyword(s):

Mixture Distribution ◽

Structural Heterogeneity ◽

Small Scale ◽

Dry Density ◽

In Situ Tests ◽

Homogeneous Sample ◽

Heterogeneous Distribution ◽

Specific Protocol ◽

Two Samples

To better understand results of SEALEX in situ tests carried out at Tournemire Underground Research Laboratory, the hydromechanical behavior of a pellet/powder MX80 bentonite mixtures prepared at a dry density of 1.49 Mg/m3 were investigated by means of microfocus X-ray computed tomography (μ-CT) observations and laboratory small scale infiltration tests. Radial and axial swelling pressures as well as relative humidity were monitored while wetting. Two configurations were considered: for the first, a pellet/powder mixture was prepared following a specific protocol to minimize initial structural heterogeneity; the second one was specially designed to study a strong heterogeneous mixture distribution. μ-CT observations performed on the two samples during hydration revealed an apparently homogeneous sample for the first mixture after 100 days of hydration. For the second specimen, several voids were still observed after 40 days of hydration. A comparison was made between the in situ and mock-up tests. It was observed that the evolutions of radial and axial swelling pressures depend on the initial heterogeneous distribution of the mixture. This heterogeneity is due to the different dry density values at the vicinity of the different sensors. The final values of axial swelling pressures were different for both configurations for the same global dry density.

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