الفهرس 
Chapter One: IntroductionOnly 14 pages are availabe for public view
 |  | from | 117 |  |  |
| | | from | 117 | | |
Abstract
Using a highly pure chemicals, a series of sodium zinc tellurite
glasses with chemical formula [70(TeO2) - (30-x)(ZnO)−x Na2O where
x=0, 3,7,10 and 15 mol%[ were successfully fabricated by applying meltquenching technique in alumina crucible. All prepared samples were
homogeneous, transparent, clear, no defects, pale yellow in color and are
amorphous in nature since there is no sharp peak observed from the XRD
analysis. Density ρ have been measured. using toluene as the immersion
liquid. The density of all glasses decreases with increasing Na2O.
At heating rate 20℃/min Differential scanning calorimeter (DSC)
was used to investigate The glass transition temperature, Tg, onset
crystallization temperature, Tc, melting temperature, Tm, glass stability
range, ∆𝑇𝑠, and glass factor (Hurby parameter), H, of the present glasses.
which show a good thermal stability of the prepared glass samples. the
addition of Na2O results in an decrease in the thermal parameters Tg, Tc
and ∆T. the thermal expansion coefficient was calculated based on the
theoretical debye temperature and results show an increase in Thermal
expansion coefficient with increasing Na2O mol%. Also the thermal
conductivity and the heat capacity were calculated depending upon the
debye temperature.
Ultrasonic velocity measurements were carried out at 5 MHz in
both shear and longitudinal modes by employing the pulse–echo
technique at room temperature using RITEC RAM-5000 Snap system
was used to determine the elastic properties of the glass samples by
evaluating the shear and longitudinal velocity. All the values of the
related moduli such as longitudinal velocity, shear velocity, longitudinal
modulus, shear modulus, bulk modulus, Young’s modulus, and hardness
decrease with respect to the content of sodium oxide.Also, we have shown that the composition dependence of glass
microhardness and elastic modulu which were in a good agrement with
the results optained fron ultrasonic studies. results showed the reductions
of TS and θD Reduction in TS.. The experimental results were confirmed
theoretically using bond compression model and Makishima and
Mackenzie model which is a function of the chemical composition, the
packing density (Vt), and the dissociation energy (Gt) of the constituting
oxides. And also, Vicher micro hardness were studied we found that HV
decrease with increasing Na2O content. The present study has clarified
that sodium zinc tellurite glasses have the Vicher hardness at room
temperature is around 3Gpa. the elastic modulus (E) and Elastic stiffness
coefficient (C11) Yield strength (σy) also, decreases.
For optical analysis, the UV–vis absorption spectra, refractive
index, molar refraction, electronic polarizability and Metallization
criterion (M) were analyzed in the wavelength range 200-800 nm. From
the UV–vis absorption spectra, several information such as the optical
absorption coefficient, direct and indirect energy band gap were obtained
using taucs model and ASF (Absorption Spectrum Fitting) procedure, a
new method for the determination of optical band gap and the nature of
optical transitions is proposed, The optical absorption edges do not show
any sharp peaks which indicate that the glass samples are amorphous in
nature. In addition, the values of direct energy band gap decrease from
3.25 eV to 2.3 eV whereas the values of indirect energy band gap
decrease from 2.75eV to 2.00 eV as the molar fraction of Na2O increases.
Molar refraction (Rm), electronic polarizability (αm), reflection loss
(RL) and dielectric constant (ε) were increasing based on the increasing of
index of refraction. also Metallization criterion (M) was increased.
FTIR spectra were used to analyze the functional groups present in
the glass. Which indicate that, the tellurite glasses follow the pattern of crystalline α-TeO2,which are formed by[TeO4] groups as trigonal
bipyramids (tbp).The introduction of modifier ions (Na2O) to zinc
tellurite glasses destroy the three dimensional network.
These results indicate the improvement of the optical and thermal
properties of the sodium zinc tellurite glass to use in many different
applications. Especially as a host material for laser systems because it has
a relatively good thermal stability and good mechanical properties. also
as a good optical fiber in the field of optoelectronics duo to the relative
low optical losses.