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Open Access Publications from the University of California

Scholarly Works (6 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2014)

The high fracture toughness of stabilized zirconia makes it one of the most widely applicable high temperature structural materials. However, it is not typicality considered for optical applications since the microstructure achieved by traditional processing makes it opaque. The aim of this dissertation is to develop processing methods for the introducing new functionalities of light transparency and light emission (photoluminescence) and to understand the nanostructure-property relationships that make these functionalities possible. A processing study of rare-earth (RE) doped Zirconium Oxide (ZrO2, zirconia) via Current Activated Pressure Assisted Densification (CAPAD) is presented. The role of processing temperature and dopant concentration on the crystal structure, microstructure and properties of the RE: ZrO2 is studied. Microstructural shows sub-100 nm grain size and homogeneous dopant distribution. X-ray diffraction and Raman analysis show that with increased dopant concentration the material changes from monoclinic to tetragonal. Structural analysis shows the material shows high hardness and toughness values 30% greater than similarly processed yttria-stabilized zirconia. Despite birefringence in the tetragonal phase, optical characterization is presented showing the samples are both highly transparent and photo-luminescent. Special attention is paid to analyzing structural and photoluminescence development during densification, as well as the role of oxygen vacancies on the optical properties of the densified material. This material is shown to be a promising candidate for a number of applications including luminescence thermometry and high temperature light emission.

    Cover page: Processing of Transparent Rare Earth Doped Zirconia for High Temperature Light Emission Applications
    • Thesis
    • Peer Reviewed
    UC Riverside Electronic Theses and Dissertations (2011)

    Experimental studies are presented that aim to utilize phase change materials (PCM's) to enhance thermal energy storage systems for concentrated solar thermal power (CSP) systems. Both laboratory scale and prototype flow loop scale experiments were conducted. Background and motivation of the system is presented followed by experimental results and experimental system design.

    Laboratory experiments were performed to determine the effectiveness of various surface treatments on changing the nucleation kinetics and enhancing heat transfer in the system. Experimental data is presented to show the effectiveness of both surface finish and surface material treatments.

    A large scale flow loop was designed and built to determine real heat transfer during solidification. Extensive design calculations were performed along with CAD design before the apparatus was constructed. Once the system was built, systematic testing and development led to a fully functional system ready for actual heat transfer testing.

      Cover page: Phase Change Materials for Thermal Energy Storage in Concentrated Solar Thermal Power Plants
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2017)
      This corrects the article DOI: 10.1038/ncomms6446.
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2014)
        A thermal diode is a two-terminal nonlinear device that rectifies energy carriers (for example, photons, phonons and electrons) in the thermal domain, the heat transfer analogue to the familiar electrical diode. Effective thermal rectifiers could have an impact on diverse applications ranging from heat engines to refrigeration, thermal regulation of buildings and thermal logic. However, experimental demonstrations have lagged far behind theoretical proposals. Here we present the first experimental results for a photon thermal diode. The device is based on asymmetric scattering of ballistic energy carriers by pyramidal reflectors. Recent theoretical work has predicted that this ballistic mechanism also requires a nonlinearity in order to yield asymmetric thermal transport, a requirement of all thermal diodes arising from the second Law of Thermodynamics, and realized here using an 'inelastic thermal collimator' element. Experiments confirm both effects: with pyramids and collimator the thermal rectification is 10.9 ± 0.8%, while without the collimator no rectification is detectable (<0.3%).
          Cover page: A photon thermal diode
          • Article
          • Peer Reviewed
          LBL Publications (2020)
          This article describes the development and testing of a novel, water-cooled, active optic mirror system (called "REAL: Resistive Element Adjustable Length") that combines cooling with applied auxiliary heating, tailored to the spatial distribution of the thermal load generated by the incident beam. This technique is theoretically capable of sub-nanometer surface figure error control even at high power density. Tests conducted in an optical metrology laboratory and at synchrotron X-ray beamlines showed the ability to maintain the mirror profile to the level needed for the next generation storage rings and FEL mirrors.
            Cover page: Adaptive shape control of wavefront-preserving X-ray mirrors with active cooling and heating.
            • Article
            • Peer Reviewed
            LBL Publications (2019)
            An ongoing collaboration among four US Department of Energy (DOE) National Laboratories has demonstrated key technology prototypes and software modeling tools required for new high-coherent flux beamline optical systems. New free electron laser (FEL) and diffraction-limited storage ring (DLSR) light sources demand wavefront preservation from source to sample to achieve and maintain optimal performance. Fine wavefront control was achieved using a novel, roomtemperature cooled mirror system called REAL (resistive element adjustable length) that combines cooling with applied, spatially variable auxiliary heating. Single-grating shearing interferometry (also called Talbot interferometry) and Hartmann wavefront sensors were developed and used for optical characterization and alignment on several beamlines, across a range of photon energies. Demonstrations of non-invasive hard x-ray wavefront sensing were performed using a thin diamond single-crystal as a beamsplitter.
              Cover page: Collaborative development of diffraction-limited beamline optical systems at US DOE light sources
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