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All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Polarized Light Microscopy

Polarized light microscopy (PLM) is a technique which employs the use of polarizing filters to obtain substantial optical property information about the material which is being observed. This information can be combined with other microscopy techniques to confirm or elucidate the identity of an unknown material, determine whether a particular contaminant is present (as with asbestos analysis), or to provide important information that can be used to refine a manufacturing or chemical process. PLM was the major microscopy technique in use for identification of materials for nearly a century since its introduction in 1834 by William Fox Talbot, as other techniques such as SEM (Scanning Electron Microscopy), FTIR (Fourier Transform Infrared spectroscopy), XPD (X-ray Powder Diffraction), and TEM (Transmission Electron Microscopy) had not yet been developed. Today, it is still the only technique approved by the Environmental Protection Agency (EPA) for asbestos analysis, and is often the technique first applied for identification of unknown materials. PLM uses different configurations in order to determine different material properties. With each configuration additional clues can be gathered, leading to a conclusion of material identity. With no polarizing filter, the microscope can be used just as a stereo optical microscope, and view qualities such as morphology, size, and number of phases. With a single polarizing filter (single polars), additional properties can be established, such as pleochroism, individual refractive indices, and dispersion staining. With two polarizing filters (crossed polars), even more can be deduced: isotropy vs. anisotropy, extinction angle, birefringence/degree of birefringence, sign of elongation, and anomalous polarization colors, among others. With the use of PLM many of these properties can be determined in a matter of seconds, even for those who are not highly trained. McCrone, a leader in the field of polarized light microscopy, often advised, If you cant determine a specific optical property of a particle after two minutes, move onto another configuration. Since optical properties can be seen so very quickly and easily under polarized light, it is only necessary to spend a maximum of two minutes on a technique to determine a particular property, though often only a few seconds are required.

Engineering↗
DOE OSTI2016

Polarized light microscopy study on the reentrant phase transition in a (Ba 1–x K x )Fe 2 As 2 single crystal with x = 0.24

In this study, a sequence of structural/magnetic transitions on cooling is reported in the literature for hole-doped iron-based superconductor (Ba 1–x K x )Fe 2 As 2 with x = 0.24. By using polarized light microscopy, we directly observe the formation of orthorhombic domains in (Ba 1–x K x )Fe 2 As 2 (x = 0.24) single crystal below a temperature of simultaneous structural/magnetic transition T N ~ 80 K. The structural domains vanish below ~30 K, but reappear below T = 15 K. Our results are consistent with reentrance transformation sequence from high-temperature tetragonal (HTT) to low temperature orthorhombic (LTO1) structure at T N ~ 80 K, LTO1 to low temperature tetragonal (LTT) structure at T c ~ 25 K, and LTT to low temperature orthorhombic (LTO2) structure at T ~ 15 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Crystal c-axis mapping of hcp metals by conventional reflected polarized light microscopy: Application to untextured and textured cp-Titanium

Highlights: • A computer-aided methodology based on reflected PLM was developed for c-axis orientation mapping of hcp structures. • The methodology was applied to two alpha cp-Ti bulk samples with different texture characteristics. • Calibration and validation of the methodology were performed by using EBSD. - Abstract: Nowadays the crystallographic characterization of polycrystalline metals and metallic alloys is usually performed by means of the electron backscatter diffraction (EBSD) technique. However, when dealing with coarse structures presenting intrinsic optical anisotropy, polarized light microscopy (PLM) imaging might be an alternative or a complementary time-efficient technique. Accordingly, a new computer-aided methodology has been developed in the present study and successfully applied on the crystal c-axis characterization of a hexagonal close-packed (hcp) structure, alpha commercial pure-Titanium (cp-Ti). In this sense, the correlation between EBSD-based crystallographic parameters and PLM-based parameters under certain light microscope settings has been first established by direct comparison using a representative amount of random orientations. Finally, PLM-based c-axis mapping and subsequent c-axis texture plotting have been performed and validated with EBSD for untextured and textured cp-Ti.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Laser shock peening effect on the dislocation transitions and grain refinement of Al–Mg–Si alloy

This paper systematically investigates the effect of laser shock peening without coating parameters on the microstructural evolution, and dislocation configurations induced by ultra-high plastic strains and strain rates. Based on an analysis of optical microscopy, polarized light microscopy, transmission electron microscopy observations and residual stress analysis, the significant influence of laser shock peening parameters due to the effect of plasma generation and shock wave propagation has been confirmed. Although the optical microscopy results revealed no significant microstructural changes after laser shock peening, i.e. no heat effect zone and differences in the distribution of second-phase particles, expressive influence of laser treatment parameters on the laser shock induced craters was confirmed. Moreover, polarized light microscopy results have confirmed the existence of well-defined longish grains up to 455 μm in length in the centre of the plate due to the rolling effect, and randomly oriented smaller grains (20 μm × 50 μm) in the surface due to the static recrystallization effect. Laser shock peening is reflected in an exceptional increase in dislocation density with various configurations, i.e. dislocation lines, dislocation cells, dislocation tangles, and the formation of dense dislocation walls. More importantly, the microstructure is considerably refined due to the effect of strain deformations induced by laser shock peening process. The results have confirmed that dense dislocation structures during ultra-high plastic deformation with the addition of shear bands producing ultra-fine (60–200 nm) and nano-grains (20–50 nm). Furthermore, dislocation density was increased by a factor of 2.5 compared to the untreated material (29 × 10{sup 13} m{sup −2} vs. 12 × 10{sup 13} m{sup −2}). - Highlights: • LSPwC imparts high compressive residual stresses up to − 362 ± 31 MPa. • After LSPwC the microstructure is considerably refined via dislocation transitions. • Results confirmed ultra-fine (60–200 nm) and nano-grains (20–50 nm) after LSPwC. • Reasonable agreements between dislocation density and residual stress are obtained.

36 MATERIALS SCIENCE↗
NASA NTRS2015

NASA Work Experience

I have had the opportunity to support the analytical laboratories in chemical analysis of unknown samples, using Optical Microscopy (OM), Polarizing Light Microscopy (PLM), Fourier-Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEMEDS), and X-ray Powder Diffraction (XPD). I have assisted in characterizing fibers pulled from a spacecraft, a white fibrous residue discovered in a jet refueler truck, brown residue from a plant habitat slated for delivery to the ISS (International Space Station), corrosion on a pipe from a sprinkler, and air filtration material brought back from the ISS. I also conducted my own fiber study in order to practice techniques and further my understanding of background concepts. Furthermore, I had the opportunity to participate in diverse work assignments, where I was assigned to work with other branches of the engineering department for 1-2 days each. The first was in the Materials Science branch where I participated in the construction of the plant habitat intended for use in research aboard the ISS. The second was in the Testing Design branch where I assisted with tensile and hardness testing of over 40 samples. In addition, I have had the privilege to attend multiple tours of the NASA KSC campus, including to the Astronaut Crew Quarters, the VAB (the main area, the Columbia room, and the catwalk), the Visitor Center housing the shuttle Atlantis, the Saturn-V exhibit, the Prototype laboratory, SWAMP WORKS, the Shuttle Landing Facility, the Crawler, and the Booster Fabrication Facility (BFF). Lastly, much of my coursework prepared me for this experience, including numerous laboratory courses with topics diverse as chemistry, physics, and biology.

Florida Tech↗
DOE OSTI2016

Test Results for Caustic Demand Measurements on Tank 241-AX-101 and Tank 241-AX-103 Archive Samples

Caustic demand testing is used to determine the necessary amount of caustic required to neutralize species present in the Hanford tank waste and obtain a target molarity of free hydroxide for tank corrosion control. The presence and quantity of hydroxide-consuming analytes are just as important in determining the caustic demand as is the amount of free hydroxide present. No single data point can accurately predict whether a satisfactory hydroxide level is being met, as it is dependent on multiple factors (e.g., free hydroxide, buffers, amphoteric metal hydroxides, bicarbonate, etc.). This enclosure contains the caustic demand, scanning electron microscopy (SEM), polarized light microscopy (PLM), and X-ray diffraction (XRD) analysis for the tank 241-AX-101 (AX-101) and 241-AX-103 (AX-103) samples. The work was completed to fulfill a customer request outlined in the test plan, WRPS-1505529, “Test Plan and Procedure for Caustic Demand Testing on Tank 241-AX-101 and Tank 241-AX-103 Archive Samples.” The work results will provide a baseline to support planned retrieval of AX-101 and AX-103.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS2016

Crawler Solids Unknown Analysis

Crawler Transporter (CT) #2 has been undergoing refurbishment to carry the Space Launch System (SLS). After returning to normal operation, multiple filters of the gear box lubrication system failed/clogged and went on bypass during a test run to the launch pad. Analysis of the filters was done in large part with polarized light microscopy (PLM) to identify the filter contaminates and the source of origin.

Polarized Light Microscopy↗
NASA NTRS1993

Thin film processing of photorefractive BaTiO3

During the period covered by this report, October 11, 1991 through October 10, 1992, the research has progressed in a number of different areas. The sol-gel technique was initially studied and experimentally evaluated for depositing films of BaTiO3. The difficulties with the precursors and the poor quality of the films deposited lead to the investigation of pulsed laser deposition as an alternative approach. The development of the pulsed laser deposition technique has resulted in continuous improvements to the quality of deposited films of BaTiO3. The initial depositions of BaTiO3 resulted in amorphous films, however, as the pulsed laser deposition technique continued to evolve, films were deposited in the polycrystalline state, then the textured polycrystalline state, and most recently heteroepitaxial films have also been successfully deposited on cubic (100) oriented SrTiO3 substrates. A technique for poling samples at room temperature and in air is also undergoing development with some very preliminary but positive results. The analytical techniques, which include x-ray diffraction, ferroelectric analysis, UV-Vis spectrophotometry, scanning electron microscopy with x-ray compositional analysis, optical and polarized light microscopy, and surface profilometry have been enhanced to allow for more detailed evaluation of the samples. In the area of optical characterization, a pulsed Nd:YAG laser has been incorporated into the experimental configuration. Now data can also be acquired within various temporal domains resulting in more detailed information on the optical response of the samples and on their photorefractive sensitivity. The recent establishment of collaborative efforts with two departments at Johns Hopkins University and the Army Research Lab at Fort Belvoir has also produced preliminary results using the metallo-organic decomposition technique as an alternative method for thin film processing of BaTiO3. RF and DC sputtering is another film deposition approach that should be initiated in the near future. Other techniques for optical characterization, which may even allow for intragrannular (within single grains) investigations, are also being considered.

Schuster, Paul R.↗
DOE OSTI2018

Mechanisms of Rotational Dynamics of Chiral Liquid Crystal Droplets in an Electric Field

The dynamics of the orientational structure of chiral nematic (CN) droplets in an isotropic medium in dc and ac electric fields is investigated by the polarized light microscopy technique. It is shown theoretically that the dynamics of rotational processes in these kinds of systems is determined by electroconvective processes developing due to the flexoelectric polarization associated with the initial configuration of the director field in droplets. It is established experimentally that the linear and quadratic regions of dependence of the rotational velocity of droplets on the electric field strength are explained by the above-mentioned mechanisms. Numerical simulation on the basis of the approach developed gives good agreement with experimental data.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Liquid Crystal Enabled Early Stage Detection of Beta Amyloid Formation on Lipid Monolayers

Liquid crystals (LCs) can serve as sensitive reporters of interfacial events, and this property has been used for sensing of synthetic or biological toxins. Here it is demonstrated that LCs can distinguish distinct molecular motifs and exhibit a specific response to beta-sheet structures. That property is used to detect the formation of highly toxic protofibrils involved in neurodegenerative diseases, where it is crucial to develop methods that probe the early-stage aggregation of amyloidogenic peptides in the vicinity of biological membranes. In the proposed method, the amyloid fibrils formed at the lipid-decorated LC interface can change the orientation of LCs and form elongated and branched structures that are amplified by the mesogenic medium; however, nonamyloidogenic peptides form ellipsoidal domains of tilted LCs. Moreover, a theoretical and computational analysis is used to reveal the underlying structure of the LC, thereby providing a detailed molecular-level view of the interactions and mechanisms responsible for such motifs. The corresponding signatures can be detected at nanomolar concentrations of peptide by polarized light microscopy and much earlier than the ones that can be identified by fluorescence-based techniques. As such, it offers the potential for early diagnoses of neurodegenerative diseases and for facile testing of inhibitors of amyloid formation.

Sadati, Monirosadat↗