Results - Details
Search command : Author="Απεραθίτης"
And Author="Ηλίας"
Current Record: 4 of 11
|
|
| Title |
Παραμετρική μελέτη υδροθερμικής σύνθεσης θερμοχρωμικού διοξειδίου του Βαναδίου VO2(M) |
|
Author
|
Δραγάνη, Θεοδώρα
|
|
Thesis advisor
|
Μπίνας, Βασίλειος
Γκαγκαουδάκης, Εμμανουήλ
|
|
Reviewer
|
Μακρής, Κωνσταντίνος
Απεραθίτης, Ηλίας
|
| Abstract |
VO2 vanadium dioxide is widely used in various technological fields with that of
energy efficient "smart" windows attracting intense interest due to the inherent and
reversible structural transition, from single monoclinic to tetragonal rutile structure,
which takes place at a critical transition temperature of T=68o
C. This structural
change is accompanied by changes in the electrical and optical properties of the
material. In specific, at temperature higher than TC the material is converted from a
semiconductor to a metal reflecting the infrared part of the solar radiation while at the
same time a satisfactory percentage of visible light is permeable. In the present
dissertation the development of thermochromic materials took place through the
method of hydrothermal synthesis using V2O5 (vanadium pentoxide) being the source
of vanadium while various acids were used to reduce V2O5 to vanadium dioxide.
During hydrothermal reduction V2O5 was converted to different vanadium oxides as
well as different crystalline polymorphs of VO2. The resulting materials were then
subjected to thermal annealing at high temperatures (>500o
C), in a suitable furnace
under constant nitrogen flow to prevent oxidation, in order to obtain pure VO2 of high
crystallinity. The present work was carried out in three axes. In the first part of
experiments as mentioned above, various reducing agents were used to obtain VO2
and as a result two acids were finally selected as the subject of the study of the rest
parameters of hydrothermal synthesis. The selection criteria were the formation of
pure VO2(M) as well as the high yield of hydrothermal reaction, which results from
the comparison of the quantity of the final product with the initial quantity of V2O5.
For the two selected reducing agents, the effect of the additional urea and thiourea
reagents as well as the annealing temperature on the structural, morphological and
thermochromic characteristics of the samples was studied. The final products were
characterized structural by X-Ray Diffraction (XRD) technique, morphologically
using Scanning Electron Microscope (SEM), while the thermochromic characteristics
were determined by Differential Scanning Calorimetry (DSC). Thus, pure VO2 in the
form of powder, with high crystallinity and improved thermochromic properties achieving a low phase transition temperature of TC≈63.0o
C was synthesized using
hydrothermal reactions with high yields.
|
| Language |
Greek |
| Issue date |
2021-03-24 |
| Collection
|
School/Department--School of Sciences and Engineering--Department of Physics--Graduate theses
|
|
|
Type of Work--Graduate theses
|
| Permanent Link |
https://elocus.lib.uoc.gr//dlib/f/5/9/metadata-dlib-1615454741-466529-29054.tkl
|
| Views |
216 |
Search
