James Griego

Quantification of a Minimum Detectable Soiling Level to Affect Photovoltaic Devices by Natural and Simulated Soils

Soil accumulation on photovoltaic (PV) modules presents a challenge to long-term performance prediction and lifetime estimates due to the inherent difficulty in quantifying small changes over an extended period. Low mass loadings of soil are a common occurrence but remain difficult to quantify. In order to more accurately describe the specific effects of sparse soil films on PV systems, we have expanded upon an earlier technique to measure the optical losses due to an artificially applied obscurant film. A synthetic soil analog was sprayed onto glass coupons at very brief intervals with a high-volume, low-pressure pneumatic sprayer. Light transmission through the grime film was evaluated using a quantum efficiency test stand and UV/vis spectroscopy. A 0.1-g/m2 grime loading was determined to be the limit of mass measurement sensitivity, which is similar to some reports of daily soil accumulation. Predictable, linear decreases in transmission were observed for samples with a mass loading between 0.1 and 0.5 g/m2. A similar change was observed for soiled coupons from an outdoor monitoring station. Collected soil from the field coupons was analyzed to develop a compositional analog for indoor studies. Natural and synthetic soils produced similar decreases in transmission.

Multivariate statistical analysis of micro-X-ray fluorescence spectral images

Multivariate statistical analysis (MSA) is applied to the extraction of chemically relevant signals acquired with a micro-X-ray fluorescence (μ-XRF) mapping (full-spectral imaging) system. The separation of components into individual histograms enables separation of overlapping peaks, which is useful in qualitatively determining the presence of chemical species that have overlapping emission lines, and holds potential for quantitative analysis of constituent phases via these same histograms. The usefulness of MSA for μ-XRF analysis is demonstrated by application to a geological rock core obtained from a subsurface compressed air energy storage (CAES) site. Coupling of the μ-XRF results to those of quantitative powder X-ray diffraction analysis enables improved detection of trace phases present in the geological specimen. The MSA indicates that the spatial distribution of pyrite, a potentially reactive phase by oxidation, has low concentration and thus minimal impact on CAES operations.

TILT-A-WHIRL: A TEXTURE ANALYSIS PACKAGE FOR 3D RENDERING OF POLE FIGURES USING MATLAB

A new MATLAB-based software suite called TILT-A-WHIRL has been applied to XRD data from textured gold films electro-deposited onto nickel substrates. The software routines facilitate phase identification, texture analysis via pole figure visualization, and macrostrain determination. The use of principal component analysis with multivariate curve resolution (PCA/MCR) revealed the extraction of texture components. The unusual hardness properties of one Au film (deposited from a 30% gold depleted BDT-200 bath) were found to be dependent on the (210) out-of-plane preferred orientation of the polycrystalline gold film. The progressive nucleation of Au crystallites during electro-plating has been tied to the improved hardness properties of this film.

Monitoring of CoS2 reactions using high-temperature XRD coupled with gas chromatography (GC)

High-temperature X-ray diffraction with concurrent gas chromatography (GC) was used to study cobalt disulfide cathode pellets disassembled from thermal batteries. When CoS 2 cathode materials were analyzed in an air environment, oxidation of the K(Br, Cl) salt phase in the cathode led to the formation of K 2 SO 4 that subsequently reacted with the pyrite-type CoS 2 phase leading to cathode decomposition between ~260 and 450 °C. Independent thermal analysis experiments, i.e. simultaneous thermogravimetric analysis/differential scanning calorimetry/mass spectrometry (MS), augmented the diffraction results and support the overall picture of CoS 2 decomposition. Both gas analysis measurements (i.e. GC and MS) from the independent experiments confirmed the formation of SO 2 off-gas species during breakdown of the CoS 2 . In contrast, characterization of the same cathode material under inert conditions showed the presence of CoS 2 throughout the entire temperature range of analysis.

X-ray powder diffraction study of La2LiTaO6

The structure of La 2 LiTaO 6 has been derived from the powder X-ray powder diffraction (XRD) data. La 2 LiTaO 6 is monoclinic with unit-cell parameters a = 5.621(1) A, b = 5.776(1) A, c = 7.954(2) A, β = 90.34(2)°, space group P 2 1 / n (14), and Z = 2. The structure of La 2 LiTaO 6 is an ordered perovskite with alternating Li and Ta octahedra. A new set of powder XRD data ( d -spacing and intensity listing) has been generated to replace entry 00-039-0897 within the Powder Diffraction File. The newly elucidated structural data for La 2 LiTaO 6 shall facilitate quantitative analysis of this impurity phase which is often observed during synthesis of the fast-ion conductor phase Li 5 La 3 Ta 2 O 12 .

Phase transition behavior of a processed thermal battery.

In order to fully understand the transition mechanism of a processed thermal battery, Micro Xray Diffraction (i-XRD) and Micro X-ray Fluorescence (i-XRF) were employed to characterize various quench states. The transition of interest in this paper is the formation of Li7Si3 from Li13Si4 (initial anode material). The unit cell conditions during Li13Si4 transition to Li7Si3 show a contraction of 0.04 and 0.02 A (a and b-axis respectively), an expansion in the c-axis of 0.02 A, and an overall reduction in the cell volume from 541.13 A to 539.21 A for the Li13Si4 orthorhombic (Pbam) component. The contraction in the a-b plane results from the loss of lithium atoms, whereas the expansion in the c-axis direction is due to reorganization of the lithium and silicon within the unit cell. Transition processing also requires that an excess of 32⁄3 moles lithium (within anode region) react with sulfur (within cathode region) to form Li2S. Micro-XRF confirms a definite migration of sulfur through the separator region during the transition. These results both explain peak shifts (in anode regions) and the formation of Li2S during transition states.