Engineering topics

Graule, Thomas

Publications and source records attributed to Graule, Thomas.

5 records

DOE OSTI2022

Aerosol-Assisted Deposition for TiO 2 Immobilization on Photocatalytic Fibrous Filters for VOC Degradation

Atomization and spraying are well-established methods for the production of submicrometer- and micrometer- sized powders. In addition, they could be of interest to the immobilization of photocatalytic nanoparticles onto supports because they enable the formation of microporous films with photocatalytic activity. Here, we provide a comparison of aerosol-assisted immobilization methods, such as spray-drying (SD), spray atomization (SA), and spray gun (SG), which were used for the deposition of TiO 2 dispersions onto fibrous filter media. The morphology, microstructure, and electronic properties of the structures with deposited TiO 2 were characterized by SEM and TEM, BET and USAXS, and UV-Vis spectrometry, respectively. The photocatalytic performances of the functionalized filters were evaluated and compared to the benchmark dip-coating method. Our results showed that the SG and SA immobilization methods led to the best photocatalytic and operational performance for the degradation of toluene, whereas the SD method showed the lowest degradation efficiency and poor stability of coating. We demonstrated that TiO2 sprays using the SG and SA methods with direct deposition onto filter media involving dispersed colloidal droplets revealed to be promising alternatives to the dip-coating method owing to the ability to uniformly cover the filter fibers. In addition, the SA method allowed for fast and simple control of the coating thickness as the dispersed particles were continuously directed onto the filter media without the need for repetitive coatings, which is common for the SG and dip-coating methods. Our study highlighted the importance of the proper immobilization method for the efficient photocatalytic degradation of VOCs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Time and frequency dependent mechanical properties of LaCoO 3 -based perovskites: Neutron diffraction and domain mobility

The study of domain wall movement and texture formation in ferroelastic LaCoO 3 perovskite under constant applied compressive stress has been performed using in situ neutron diffraction. Additionally, it was established that under constant applied compressive stress the domain walls show mobility that may lead both to the shrinkage (creep strain) and to the expansion (negative creep strain) of LaCoO 3 perovskite. The domain wall movement and texture formation can be explained by the availability, mobility, and interaction of twins, stacking faults, antiphase boundaries, dislocations, and point defects, such as oxygen vacancies and their complexes as well as impurity atoms. Lastly, the equation of motion was used to describe the possible mechanisms of domain wall movement under applied stress, and it was determined that the available solutions of this equation allow both for the shrinkage (creep strain) and for the expansion (negative creep strain) of LaCoO 3 perovskite to occur.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Strong photoluminescence emission at low dopant amount in YAG:Ce and YAG:Eu phosphors

Highlights: • YAG:Ce and YAG:Eu materials were prepared by solid state reaction. • Pure YAG phase can be obtained at 1300 °C. • High density materials were synthesized at 1600 °C for 10 h. • The highest PL emission was observed for the YAG:Ce{sub 0.01} and YAG:Eu{sub 0.1} samples. - Abstract: YAG:Ce and YAG:Eu phosphors have been prepared by solid state reaction. The use of submicrometric powders allows preparing pellets with high density, enhancing the photoluminescence (PL) properties. Pellets were prepared by uniaxial pressing and the influence of the thermal treatment on the microstructural and optical properties were also studied. Pure YAG phase was obtained at 1400 °C during 1 h and high density pellets (97%) after sintering at 1600 °C for 10 h. The highest PL emission was achieved for the sintered YAG:Ce and YAG:Eu pellets doped with low dopant concentrations (0.01 mol% for Ce and 0.1 mol% for Eu). Finally, increasing the Ce and Eu concentration the PL intensity decreases and the dopants occupy different positions than the Y one in the YAG lattice.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Non-congruence of high-temperature mechanical and structural behaviors of LaCoO 3 based perovskites

Our paper presents the mechanical behavior of LaCoO 3 and La 0.8 Ca 0.2 CoO3 ceramics under four-point bending in which the two cobaltites are subjected to a low stress of ~8 MPa at temperatures ranging from room temperature to 1000 °C. Unexpected stiffening is observed in pure LaCoO 3 in the 700–900 °C temperature range, leading to a significant increase in the measured Young’s modulus, whereas La 0.8 Ca 0.2 CoO 3 exhibits softening from 100 °C to 1000 °C, as expected for most materials upon heating. we use neutron diffraction, X-ray diffraction and micro-Raman spectroscopy to study the crystal structure of the two materials in the RT–1000 °C temperature range. Despite a detailed study, there is no conclusive evidence to explain the stiffening behavior observed in pure LaCoO 3 as opposed to the softening behavior in La 0.8 Ca 0.2 CoO 3 at high temperatures (above 500 °C).

36 MATERIALS SCIENCE↗

DOE OSTI2015

Hexagonal OsB 2 : Sintering, microstructure and mechanical properties

In this study, the metastable high pressure ReB 2 -type hexagonal OsB 2 bulk ceramics was produced by spark plasma sintering. The phase composition, microstructure, and mechanical behavior of the sintered OsB 2 were studied by X-ray diffraction, optical microscopy, TEM, SEM, EDS, and nanoindentation. The produced ceramics was rather porous and contained a mixture of hexagonal (~80 wt.%) and orthorhombic (~20 wt.%) phases as identified by X-ray diffraction and EBSD analysis. Two boron-rich phases, which do not contain Os, were also identified by TEM and SEM/EDS analysis. Nanoindentation measurements yielded a hardness of 31 ± 9 GPa and Young’s modulus of 574 ± 112 GPa, indicating that the material is rather hard and very stiff; but, it is very prone to crack formation and propagation, which is indicative of a very brittle nature of this material. Improvements in the sintering regime are required in order to produce dense, homogeneous and single phase hexagonal OsB 2 bulk ceramics.

36 MATERIALS SCIENCE↗