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Open Access Publications from the University of California

Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2020)

This work probed the two types of solid degradation in aqueous environment: steel corrosion, and acoustically stimulated mineral dissolution.First, the steel corrosions in gas/oil wells and nuclear power plant environment were studied. The inhibition of corrosion of API-P110 steel by Ca(NO3)2 was first studied using vertical scanning interferometry (VSI) in halide-enriched solutions. The results indicate that, at low concentrations, Ca(NO3)2 successfully inhibited steel corrosion in the presence of both CaCl2 and CaBr2. Statistical analysis of surface topography data reveals that such inhibition results from suppression of corrosion at fast corroding pitting sites. Built on the methodology established from above, the effect of grain orientation on the corrosion rates of austenitic AISI 316L stainless steel was studied. The oxidation rates follow a scaling that is given by: {001} < {101} < {111} for grains undergoing both active and transpassive oxidation. The corrosion tendencies of {001} and {101} grains indicate that the activation energy of dissolution follows a scaling similar to that of the surface energy. However, the high corrosion rates of {111} grains, which featured a surface energy lower than those of the {001} and {101} grains, is attributed to their lower tendency to adsorb passivating species, from solution, that leads to a net reduction in the activation energy of oxidation. Second, this work further investigated the low-temperature pathway of aqueous activation of minerals and industrial alkaline wastes using acoustic stimulation, as an alternative to calcination process in cement production. It is revealed that the acoustic fields enhance mineral dissolution rates (reactivity) by inducing atomic dislocations and/or atomic-bond rupture. The relative contributions of these mechanisms depend on the mineral’s underlying mechanical properties. Based on this new understanding, a unifying model was created that comprehensively describes how cavitation and acoustic stimulation processes affect mineral dissolution rates. On the basis of the mechanisms described above, the effectiveness and efficiency of applying acoustic stimulation in dissolving industrial alkaline wastes were further analyzed. Ultrasonication promoted dissolution of air-cooled blast furnace slag (ACBFS) in a significant and more energy-efficient manner, compared to traditional methods, such as grinding the solute, heating, and/or convectively mixing the solvent. The advantages of acoustic stimulation for dissolution enhancement and for energy savings are also observed for Si release from stainless steel slag (SSS), Class C fly ash, and Class F fly ash. The results demonstrate the wide applicability of acoustic processing, and the outcomes offer new insights into additive-free pathways that enable waste utilization, circularity, and efficient resource extraction from industrial wastes that are produced in abundance globally. The results yielded from this work provide enhanced understanding of corrosion inhibition and suggest processing pathways for improving the oxidation resistance of steels in different industry scenarios. In addition, the results provide insights of additive-free pathway by using acoustic stimulation to enable fast elemental extraction from mineral species into aqueous solution.

    Cover page: Aqueous Degradation of Materials: Studies on Steel Corrosion and Acoustically Stimulated Mineral Dissolution
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2017)
    The solution processing of polycrystalline perovskite films introduces trap states that can adversely affect their optoelectronic properties. Motivated by the use of small-molecule surfactants to improve the optoelectronic performance of perovskites, we demonstrate the use of polymers with coordinating groups to improve the performance of solution-processed semiconductor films. The use of these polymer modifiers results in a marked change in the electronic properties of the films, as measured by both carrier dynamics and overall device performance. The devices grown with the polymer poly(4-vinylpyridine) (PVP) show significantly enhanced power conversion efficiency from 16.9 ± 0.7% to 18.8 ± 0.8% (champion efficiency, 20.2%) from a reverse scan and stabilized champion efficiency from 17.5 to 19.1% [under a bias of 0.94 V and AM (air mass) 1.5-G, 1-sun illumination over 30 min] compared to controls without any passivation. Treating the perovskite film with PVP enables a VOC of up to 1.16 V, which is among the best reported for a CH3NH3PbI3 perovskite solar cell and one of the lowest voltage deficits reported for any perovskite to date. In addition, perovskite solar cells treated with PVP show a long shelf lifetime of up to 90 days (retaining 85% of the initial efficiency) and increased by a factor of more than 20 compared to those without any polymer (degrading to 85% after ~4 days). Our work opens up a new class of chemical additives for improving perovskite performance and should pave the way toward improving perovskite solar cells for high efficiency and stability.
      Cover page: Polymer-modified halide perovskite films for efficient and stable planar heterojunction solar cells
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