No description available.

No description available.

Ma Lai Ching = 利用熱壓法制備塊体非晶態Pd₄₀Ni₄₀P₂₀合金 / 馬勵貞. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 51). / Text in English; abstracts in English and Chinese. / Ma Lai Ching = Li yong re ya fa zhi bei kuai ti fei jing tai Pd₄₀Ni₄₀P₂₀ he jin / Ma Lizhen. / Acknowledgements --- p.i / Abstract --- p.ii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Introduction to Metallic Glass --- p.1 / Chapter 1.2 --- Applications of Metallic Glass --- p.2 / Chapter 1.3 --- Solidification Process --- p.3 / Chapter 1.4 --- Some Production Methods of Bulk Glassy Alloys --- p.10 / Chapter 1.5 --- Another Production Methods: Powder Consolidation --- p.11 / Chapter 1.6 --- Flaws of the as-Compacted Materials --- p.16 / Chapter 1.7 --- A Solution --- p.17 / References --- p.20 / Figures --- p.22 / Chapter Chapter 2 --- Experimental --- p.31 / Chapter 2.1 --- Production of Pre-Compacted Bulk Metallic Glass --- p.31 / Chapter 2.2 --- Handling of Bulk Glass Before Compaction --- p.34 / Chapter 2.3 --- Compaction Process --- p.35 / Chapter 2.1 --- Sample Analysis --- p.37 / Figures --- p.40 / Chapter Chapter 3 --- Mechanism of fusion of bulk metallic glasses --- p.45 / Abstract --- p.45 / References --- p.51 / Table --- p.52 / Figures --- p.53

Thesis (Ph. D.)--Lehigh University, 2003. / Includes vita. Includes bibliographical references (leaves 100-104).

Στην παρούσα εργασία μελετήθηκαν μια σειρά ύαλοι στο ψευδοδυαδικό υαλοποιήσιμο σύστημα MgSiO3 – Mg2SiO4 συνδυάζοντας την φασματοσκοπία Raman με τις τεχνικές αιώρησης χωρίς επαφή και χρήση CO2 laser για την θέρμανση και την τήξη των υλικών. Μετρήθηκαν τα πολωμένα και αποπολωμένα φάσματα Raman σε συνθήκες περιβάλλοντος για όλες τις συστάσεις. Τα αποτελέσματα έδειξαν ομαλές και συστηματικές αλλαγές στις εντάσεις των κορυφών. Η ανάλυση των κορυφών Raman που παρατηρούνται στα φάσματα έγινε με όρους δονήσεων που οφέιλονται στα διάφορα γεφυρωτικά άτομα οξυγόνου των τετραέδρων SiO4 (ανάλυση ειδών Qn) και διαπιστώνεται η ύπαρξη τους στα άμορφα υλικά ακόμα και στο όριο της σύστασης της ένωσης Mg2SiO4. Στα φάσματα Raman χαμηλών συχνοτήτων παρουσιάζεται η συχνότητα της κορυφής Boson να είναι σταθερή, όπως συμβαίνει και στους τρόπους δόνησης των ειδών Qn, υποδηλώνοντας με αυτό τον τρόπο ότι δεν συμβαίνει καμία απότομη δομική αλλαγή μεταβάλλοντας την σύσταση. Προτείνεται ότι στη σύσταση της ένωσης Mg2SiO4 δημιουργείται ένα ιοντικό γυαλί, το οποίο προέρχεται από ένα πολύ «εύθραυστο» υγρό. / Container-less levitation techniques and CO2 laser heating were used to melt SiO2-MgO mixtures and prepare a series of glasses with compositions from enstatite MgSiO3 to forsterite Mg2SiO4 in intervals of ~0.02 mol% SiO2. Polarized and depolarized Raman spectra measured at ambient conditions for all these glasses show systematic and smooth band intensity changes with composition. Analysis of the Raman band contours in terms of vibrations due to different oxygen bridged SiO4 tetrahedral (Qi, species analysis), undoubtedly shows that bridging oxygens are present in all glass studied even in the limit of the forsterite composition (Mg2SiO4). The Boson peak frequency is invariant and the vibrational modes of the Qi species do not reflect any abrupt structural changes with composition. It is suggested that the forsterite (Mg2SiO4) forms an ionic-like glass arising from a very fragile liquid.

Various aspects of the tunneling states problem in metallic glasses are examined. As a first step, a computer model based on the analogy between local environments in crystalline and amorphous states is developed and used to generate and relax structures for two specific materials, namely Ni(,80)P(,20) and Cu(,33)Zr(,67). The model is found to give a physically realistic picture of the systems examined, in particular by properly accounting for short-range order effects. The structures are then analyzed in terms of single-atom tunneling taking place between two metastable minimum-energy positions. The probability of occurence of such "two-level systems" (TLS's) is shown to be strongly correlated with the degree of relaxation and thus with the density of the system. Further, they are seen to be associated with voids in the structure which disappear upon relaxation, suggesting an analogy with the physical process of annealing metallic glasses below their glass transition temperatures. It is therefore concluded that a reduction of the various low-temperature anomalies in these materials should result from the annealing process. As a verification, the change in superconducting transition temperature T(,c) due to the presence of TLS's is evaluated. In leading to a non-negligible enhancement effect, our model is indeed found to provide a reasonable estimate of the observed drop in T(,c), thus corroborating our hypothesis of a reduction of the TLS density of states upon thermal relaxation.

No description available.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

No description available.

No description available.