• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 2355
  • 811
  • 307
  • 239
  • 71
  • 66
  • 40
  • 33
  • 29
  • 29
  • 25
  • 18
  • 14
  • 11
  • 11
  • Tagged with
  • 4858
  • 698
  • 654
  • 520
  • 492
  • 438
  • 424
  • 358
  • 348
  • 317
  • 311
  • 303
  • 285
  • 259
  • 257
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Development of titanium alloys for hydrogen storage

Abdul, Jimoh Mohammed 11 October 2016 (has links)
A thesis submitted to the Faculty of Engineering and Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy in Engineering Johannesburg, 2016 / The thesis investigated the effect of partial substitution of Cr or Ti with 2-6 at.% Fe, or 0.05-0.10 at.% Rh/Pd on the structure, hardness, corrosion behaviour and hydrogen storage characteristics of an arc-melted Ti35V40Cr25 at.% alloy. The effects of an annealing and a quenching heat treatment on the properties were also investigated. Melting of the eight alloys was done in a water-cooled, copper-hearth arc melting furnace under an argon atmosphere. Each of the eight ingots was cut into three: one as the as-cast sample and the other two separately quartz-sealed and loaded in two batches in a heat treatment oven and heated to 1000 °C for 1 hour. The first set of quartz tubes were immediately removed and broken in cold water to quench the alloy, hence locking the microstructure. The second batch was loaded into the furnace, heated to 1000 °C for 1 hour and then slowly furnace-cooled. The alloys (as-cast and heat treated) were characterised for phase identification using optical microscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) with Electron Diffraction X-ray Spectroscopy (EDS) using an Oxford system. Thermo-Calc software was used to model the phases using the Solid Solution 4 and Titanium 3 Databases. The hardness values (under a 2 kg load) of all samples were recorded. Potentiodynamic corrosion tests were performed in 6M KOH at 25 °C, and Tafel curves were recorded from -1.4V to -0.2V with a scanning rate of 1mV/sec. A Sievert’s apparatus was used for pressure composition temperature (PCT) measurements at 30, 60 and 90 °C. All the alloys contained a primary bcc (V) phase. The secondary phases were a combination of αTi, Ti(Cr,V)2 Laves phases (C14, C15 or C36) and a minor ωTi phase. The cell volume of the primary (V) phase decreased with addition of Fe and 0.05 Rh but increased with 0.1 Rh and Pd. The hardness of the base alloy increased with additions of Fe and 0.10 at.% Pd, but decreased with additions of Rh and 0.05 at.% Pd. Additions of Rh, Pd and 2 at.% Fe decreased the corrosion rate, while additions of 5 and 6 at.% Fe increased the corrosion rate. The reversible hydrogen storage capacity (RHSC) of the base alloy, otherwise known as useful capacity, was enhanced with addition of Pd and Rh, but decreased with Fe addition. Both annealing and quenching increased the hardness of the 0.05 at.% Rh and all the Fe containing alloys. Heat treatment decreased the hardness of the base alloy, both Pd alloys and v the 0.10 at.% Rh samples. Quenching decreased the hardness of the 0.10 at.% Rh and both Pd-containing alloys. The corrosion rate of the 0, 5 and 6 at.% Fe, 0.05 at.% Rh and the Pd-containing alloys decreased after annealing.at.% FeThe rate increased after annealing the 2 at.% Fe and 0.10 at,% Rh samples. The as-cast sample containing 2 at.% Fe had the lowest corrosion rate (0.0004 mm/y) and the quenched 6 at.% Fe was the least corrosion resistant sample with a corrosion rate of 0.037 mm/y. The quenched 5% Fe alloy had the highest hardness (460 MPa), while the annealed 0.10 at.% Rh sample had the lowest (388 MPa). The quenched 0.05 at.% Pd sample had the highest RHSC (2.28 wt%) while the lowest RHSC of 0.44 wt% was observed in the as-cast 2 at.% Fe sample. Annealing improved the RHSC of all samples except the base Ti35V40Cr25 and 6 at.% Fe alloys, while quenching was detrimental to RHSC of all the samples but the 2 at.% Fe, 0.05 at.% Pd and 0.10 at.% Rh alloys. Increasing the addition of palladium from 0.05 to 0.10 at.% Pd showed no significant improvement on RHSC of the base alloy, thus addition of 0.05 at.% Pd would be sufficient. The RHSC of the annealed 0.05 Rh alloy (2.25 wt% H) was close to the value of the 0.10 at.% Pd, so rhodium could be considered as an alternative to the quenched 0.05 at.% Pd. The RHSC was 1.56, 0.44, 0.75 and 0.68 wt% for 0, 2, 5 and 6 at.% Fe as-cast alloys respectively. Although the 2 at.% Fe alloy had the lowest RHSC, it could find its application as electrode in 6M KOH solution electrolyte because of its low corrosion rate. / MT2016
82

Spectroscopic studies of paramagnetic impurities in solid parahydrogen matrix. / CUHK electronic theses & dissertations collection

January 2011 (has links)
In this thesis, spectroscopic studies of the catalyzed nuclear spin conversion (NSC) of ortho-H2 molecules in solid H2 matrix and the high-resolution Fourier transform infrared (FTIR) absorption spectra of O2 and NO embedded in matrices of para-H2 crystals are presented. For NSC of ortho -H2, the catalyzed conversion rate was found to be diffusion-determined by setting up systematical kinetic studies of solid H2 samples dopant with O2 and NO. The factors affecting diffusion process were discussed; For the high-resolution FTIR of O2 and NO, sharp lines presumable due to rotational structure were observed. Based on the observation, preliminary analysis of the spectrum was discussed for O2 and NO, respectively. / Yan, Lei. / Adviser: Man-Chor Chan. / Source: Dissertation Abstracts International, Volume: 73-06, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 84-87). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.
83

ABSOLUTE RADIOMETRIC CALIBRATION OF A SPECTROPOLARIMETER.

CASTLE, KENNETH ROBERT. January 1985 (has links)
Two identical instruments have been developed for use in the field to make radiometric measurements. They have been described as spectropolarimeters because of their ability to make polarization measurements in narrow spectral passbands. They have been used as part of a NASA sponsored project to monitor the spectral and temporal response of the thematic mapper satellites. These satellites allow many natural and man-tended resources to be monitored over years of time, thus allowing their use to be planned for in the future. The dissertation discusses the design, fabrication, testing and absolute radiometric calibration of these spectropolarimeter instruments. The outstanding feature of these instruments are that they have been calibrated absolutely, for radiance measurements, to an accuracy of 2% - 3%, in the range of 400 nm to 1040 nm over selected spectral passbands. Previously, field measurements were considered good if they had an absolute accuracy of 10%, implying that the present accuracies are advancing the state-of-the-art for field instrument calibrations. These improved accuracies are the result of using two recently developed calibration standards, both of which use detector based methods. These standards are the Electrically Calibrated Pyroelectric Radiometer (ECPR), and the QED-100 quad detector. The end of the dissertation discusses the attempts made to verify that the accuracies claimed are indeed valid, and it is the author's belief that these accuracies have been verified completely.
84

Re-emission of hydrogen from metal surfaces

Chang, Jin-gor 05 1900 (has links)
No description available.
85

Hydrogen embrittlement of cold worked plain carbon steel

Hsieh, Jang-Hsing 08 1900 (has links)
No description available.
86

First-principles study of hydrogen storage materials

Ma, Zhu. January 2008 (has links)
Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2008. / Committee Chair: Mei-Yin Chou; Committee Member: Erbil, Ahmet; Committee Member: First, Phillip; Committee Member: Landman, Uzi; Committee Member: Wang, Xiao-Qian.
87

Hydrogen mixed conductors properties and applications /

Schreiber, Martha. January 1900 (has links)
Thesis (doctoral)--Technische Universiteit Delft, 1997. / Vita. Includes bibliographical references.
88

Economic analysis of various reforming techniques and fuel sources for hydrogen production

McGlocklin, Kristin Hew, Eden, Mario R. January 2006 (has links) (PDF)
Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references (v.85-89).
89

Hydrogen mixed conductors properties and applications /

Schreiber, Martha. January 1900 (has links)
Thesis (doctoral)--Technische Universiteit Delft, 1997. / Vita. Includes bibliographical references.
90

Gas phase photochemical reactions and reactions of photochemically produced hot hydrogen atoms initiated by 1850 Å radiation

Martin, Richard McKelvy. January 1964 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1964. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 207-212).

Page generated in 0.043 seconds