3.1. Structure properties
3.1.1 XRD study
The amorphous nature of the synthesized specimens was established by visual examination and X-ray diffraction explanations (XRD). The XRD result clearly approves the glassy structure of the prepared samples in the (20Na2O-xCdO-(15-x) Al2O3.-25BaO-40P2O5) system as shown in Figure (1). There occurs an extensive humps pattern at around 30° ≤ 2θ ≤ 40° in the diffraction and no sharp peaks which is a typical non-crystalline character of the glass materials [24, 25].
3.1.2 Density and Molar volume
In fact, identifying the internal composition of non-crystalline materials is the main factor in knowing the changes that occur in its physical and chemical properties. In the current study, the density (ρ) and the molar volume (Vm) of the prepared glass samples are determined in an attempt to understand the change in the internal structure of the specimens with the change in the glass composition. The values of ρ and Vm for the studied non-crystalline specimens are presented in Table 1. As is clear from Figure No.2 and Table No.1, the density (ρ) increases while the molar volume (Vm) decreases for the synthesized non-crystalline samples prepared with replacing and aluminum by cadmium in the base glass 20Na2O:25BaO: 15Al2O3:40P2O5. The density values of the non-crystalline sample Cd0; Cd2.5; Cd5; Cd10 and Cd15 are 3.24, 3.27, 3.48, 3.48 and 3.87 g/cm3, respectively. The specimen with the lowest density value is Cd0 (free of CdO), while the highest density value is examined in Cd15 (with 15 mol% CdO/Al2O3 replacement). The increase the density of glass samples by CdO/Al2O3 attributed to the substitution of the Al2O3 compound (molar mass of 101.96 g/mol and density of 3.95 g/cm3) with the CdO compound (molar mass of 128.4112 g/ mol and density of 8.15 g/cm3)[26]. In contrast to the trend of density results for glass specimens, it was found that the molar volume (Vm) decreased by adding CdO at the expense of Al2O3. We found that the molar volume decreases from 37.900 cm3/mol for Cd0 to 32.756 cm3/mol for Cd15 as the CdO/Al2O3 replacement increases up to 15 mol %.
From a theoretical standpoint, and from most previous studies of the density and molar volume of glass, it was found that the two relationships are inversely related to each other [27-29] . Frequently the Vm values are based on the structure compactness of the glasses [27-29]. From the results, it was found that the molar volume of the prepared samples is consistent with the theoretical hypothesis. This means that there is an increase in the structure compactness of the prepared glasses with the increase of cadmium instead of Al2O3.
Thermal stability and prevention of crystallization are important and required properties for the prepared glasses. The results proved that adding CdO can improve the thermal stability and crystallization resistance of prepared non-crystalline solids. The difference between Vm and Vc values can used as a criterion for glass stability[30, 31]. The greater this temperature change, the better is the thermal stability of the system [30, 31]. It has been observed that increasing cadmium at the expense of alumina leads to an increase in the difference in Vc and Vm values (Fig. 3 and Table 1). This proves that the CdO/Al2O3 replacement process led to thermal stability of the glass samples in the prepared system.
Table 1: The synthesized glass composition and some structural parameters; ρg (density), Vm (molar volume), and Vc (crystalline volume)
Vc
Cm3/mol
|
Vm
Cm3/mol
|
ρg
g/Cm3
|
Glass composition (mole %)
|
Sample
ID
|
P2O5
|
CdO
|
Al2O3
|
BaO
|
Na2O
|
39.790
|
37.900
|
3.24
|
40
|
0
|
15
|
25
|
20
|
Cd0
|
39.538
|
37.755
|
3.27
|
40
|
2.5
|
12.5
|
25
|
20
|
Cd2.5
|
39.287
|
35.667
|
3.48
|
40
|
5.0
|
10
|
25
|
20
|
Cd5
|
38.784
|
33.995
|
3.69
|
40
|
10
|
5
|
25
|
20
|
Cd10
|
38.281
|
32.756
|
3.87
|
40
|
15
|
0
|
25
|
20
|
Cd15
|
3.1.3. FTIR study
FTIR spectroscopy studies were used to get fundamental and essential information about the arrangement of structural units of the glass samples. Figure (4) reveals the FTIR spectra of base and CdO content samples. The IR spectrum of the base glass shows extended absorption from 400 to about 1650 cm-1 revealing far infrared peaks at about 463, 538, 579 cm-1 and also, two small bands at about 692 and 766 cm-1. This is followed by distinct absorption bands at about 910, 1022, 1120 1200, 1387, 1635 cm-1. The rest of the IR spectrum reveals small peak at about 1722 cm-1. All these bands can be confirmed at deconvoluted spectrum at Figure (5). The FTIR spectra of 2.5, 5, 10 and 15 CdO% show gradually changes of some absorption bands at their intensities or wavenumber positions reaching to the final spectrum of sample containing 15 CdO % which can be deconvoluted at Figure (6) which shows a remarkable change than the base sample and can be summarized as follows, two broad far IR bands at about 494, 598 cm-1 were overlapped, band at 914 cm-1 was splatted than the other bands at 1043, 1090 and 1144 cm-1. Small band at about 1284 cm-1 was observed and finally, the intensity of absorption band at 1643 cm-1 was increased. The attribution of all these bands are tabulated and assignment at Table (2). From all these data, it is evident that cadmium oxide (CdO) is considered as conditional oxide possessing the ability to be both situated as modifier and to form glass forming CdO4 units [31]. By increasing the CdO content, the intensity of the broad band which is cited at about 590 cm-1 increases due to the formation of more Cd-O bonds. The small band at about 463 cm-1 which is belongs to Al-O band slightly vanished and overlapped to the Cd-O vibration band due to the disappear of Al from the composition as shown in Table (1).
3.2 Optical properties
The UV-Visible optical absorption spectra for all glass samples were studied and recorded in 190-100 nm spectral range and shown in Figure (7). From this figure, it was noted that there are no sharp absorption edges which mean that the present glass samples are in the glassy state [32].
There was a shift of absorption edge towards longer wavelength with increasing CdO content. This result clearly showed a decrease in the UV-Visible transmission by increasing CdO content. Figure (8) showed the process of determining Eopt. by plotting (αɦυ)0.5 as a function of photon energy (ɦυ) and extending the linear part of the curve to cut off the hn axis. The obtained values of Eopt. are given in Figure (8). It is clearly evident that, the values of Eopt. slightly decrease from 3.87 to 3.46 with increasing CdO content. This can be interpreted by Chung et al. [33] who reported that the increase of CdO content forces the non-bridging oxygens to progressively increase. Urbach energy can be determined by plotting lnα as a function of ɦυ the estimated values of ∆E are present in Figure (9). As shown, ∆E for the investigated glass samples was found to be increases and its values varied between 0.18 to 0.27 eV according to CdO content. as CdO content increases the ∆E increases. This can be discussed as the increasing of the disorder degree in the system. Beside the increase of CdO content localizes some states within the band gap, which seems to be the reason of the observed decrease in the Eopt. values [32].
Table (2): Assignment of FITR bands of the studied samples.
Band position(cm-1)
|
Assignment
|
references
|
1722
|
P-OH groups
|
[34]
|
1635
|
1387
|
P-O asymm. stret. Q3 ;PO2
|
[35]
|
1200
|
PO22-asymm. stret./P=O or P-O symm. stret. Q2
|
[36]
|
1120
|
PO43-symm. stret. or P-O asym.stret. Q1 PO2
|
[35]
|
910
|
P-O-P asymm. stret.
|
[36]
|
766
|
asymm. stret. of P-O-P rings or AlO4 units
|
[36]
|
580 - 538
|
bending vib. of P=O-P or vibration of Cd-O bond
|
[37]
|
475 – 466
|
bending vib. of AlO6 units
|
[38]
|
463
|
asymm. bending vib. of P-O-P
|
[36]
|
3. 3 Gamma shielding study
The effectiveness of materials used for radiation protection to block harmful rays is one of the concerns that have attracted researchers recently, and this is verified through the use of mathematical and theoretical estimates. For this study, we used the Phy-X online software [23] to measure the radiation shielding parameters of the glass samples under examination. These parameters include the mass (MAC) and linear (LAC) attenuation coefficients, half (HVL), value layers, mean free paths (MFP), and effective atomic number (Zeff) spanning the energy range of 10-3 to 15 MeV are studied to understand how CdO/Al2O3 replacements supports Radiation shielding in the glasses. MAC and LAC generally describes the interaction probability between gamma photons and the mass per unit are for certain medium [23]. The MAC and LAC for all Cd0, Cd2.5, Cd5, Cd 10 and Cd15 glass specimen were calculated and plotted against gamma ray energy in Figures (10,11) respectively, for changing content of CdO. From the figures, it is obvious that the MAC and LAC are highest at lower gamma-ray energies. However, when the energy is increased, the MAC and LAC decrease rapidly and then decreases gradually for all the prepared glass specimens. It was also observed from effect of CdO/Al2O3 replacements (Figures 10 and 11) on each of the MAC and LAC parameters. The results have proven that adding cadmium in different quantities leads to an increase in both MAC and LAC values. This can be attributed to the addition of cadmium affected the structural properties of the prepared glass by significantly increasing the density. One of the most important scientific constants is that increasing the density of the glass is one of the most important physical factors that enhance the medium’s ability to attenuate radiation photons. Moreover, both parameters (MAC and LAC) depend no only on the density but also on the photon energy [1, 10]. On the other hand, HVL it is considered one of the most important factors that determine the effectiveness of prepared materials to protect against gamma rays. The HVL refers to the thickness that decreases the intensity of a gamma ray, which is diminished by 50% [39]. Figure 12 shows the graphical representation of the HVL based on the change in gamma ray energy. The HVL first shows its minimum value in the range of 0.01 to 0.1 MeV and then a significant increase of values until it reaches a maximum at 15 MeV for all prepared glasses. This phenomenon can be explained by the fact that at low energy levels a glass of small thickness is required, which is reflected in the low HVL values attributed to the photoelectric processes [40]. However, in the medium and high energy ranges, this requires materials with a higher thickness in order to reduce the penetration of gamma rays into the prepared materials and thus reduce health damage [41]. It is noted also from Figure 12 that replacing aluminum with cadmium reduces HVL values. This can be attributed to an increase in the density of the specimens with an increase in the CdO content in the non-crystalline samples as it is known that there is an inverse relationship between the density and the values [42, 43]. On the other hand, mean free paths (MFP) is a very important factor in determining the efficiency of prepared materials to protect against harmful rays in the fields of ionizing radiation shielding. Figure 13 shows the behavior of the MFP with the intensity of energy of gamma rays from 10-3 to 15 MeV for all synthesized non-crystalline specimens. The results indicate that the behavior of MFP is the same as that of HVL as the values increase slowly from 0.01 to 0.1 MeV, and they increase very quickly, reaching the maximum value at 15 MeV. The data obtained indicate that the supreme values of the MFP correspond to the energy of the 15 MeV gamma ray [39, 40]. The effective atomic number (Zeff) is important parameter for radiation shielding materials demonstrates the efficiency of materials used for ionizing radiation shielding. The effective atomic number is a crucial parameter to consider when selecting glasses for radiation shielding [44]. The results show that There is an increase in Zeff below 0.1 MeV and decreases after that which is due to domination of pair production in the energy region. Zeff is maximum at 0.04 MeV for all the prepared glasses as shown in Figure 14. The shielding capability of improved materials is positively connected with larger values of Zeff. This suggests that a greater number of gamma rays experience attenuation while passing through materials characterized by higher Zeff values [41]. The results, taken from Figure 14, also showed that adding cadmium at the expense of aluminum led to an increase in Zeff values in different energy values from 0.001 to 15 MeV. The Zeff values results show like actions to both MAC and LAC values. The Zeff results reflect that the higher the cadmium contents in the samples, the greater the protective properties against harmful radiation [15]. According to the Zeff values, Cd15 non-crystalline sample has the greatest shielding characteristics against nuclear radiations.