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Feasibility study of recycled CRT glass on elastic and radiation shielding properties used as x-ray and gamma-ray shielding materials
Progress in Nuclear Energy xxx (xxxx) xxx
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Feasibility study of recycled CRT glass on elastic and radiation shielding properties used as x-ray and gamma-ray shielding materials P. Sopapan a, J. Laopaiboon a, O. Jaiboon a, C. Yenchai b, R. Laopaiboon a, * a b
Glass Technology Excellence Center (GTEC), Department of Physics, Faculty of Science, Ubon Ratchathani University, Ubon Ratchathani, 34190, Thailand Department of Nuclear Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, 10330, Thailand
A R T I C L E I N F O
A B S T R A C T
Keywords: CRTs glass Pressure-controlled ultrasonic technique Elastic moduli X-ray attenuation Radiation shielding
Recycled glass derived from discarded cathode ray tubes (CRT) was used as a component for (70-x) CRT–30K2O–xBaO glass systems (where x ¼ 0–20 mol%). Temperature dependence of ultrasonic wave velocities was carried out at 4 MHz frequency using pressure-controlled ultrasonic technique. It was found that the ve locities decreased gradually as BaO content increased. However, sound velocities increased with increasing temperature. Then, both velocities were applied to estimate their elastic properties. Based on the obtained re sults, the elastic moduli and micro hardness of studied glasses increased with the amount of BaO and temper ature, while their Poisson’s ratio remained almost constant. Radiation shielding properties were investigated in terms of μm and HVL at photon energies of 74.23, 97.14, 122, 662, 1173, and 1332 keV by using narrow beam xray attenuation and transmission methods. Their theoretical values were also calculated by WinXCom program and compared with ferrite concrete. The results showed better radiation shielding properties for recycled CRT glass in comparison to ferrite concrete. Furthermore, the values obtained from the experiment in this study are in good agreement with the theoretical data.
1. Introduction The disposal of waste from electric and electronic equipment (WEEE), particularly the cathode ray tubes (CRTs) used in computer and television display monitors, is fast becoming a global environmental issue that must be eliminated urgently (Andreola et al., 2007; Nnorom et al., 2011). Due to the rapid advancement of high-definition television (HDTV) technologies, standard-definition television (SDTV) sets have been largely replaced. Consequently, a large amount of CRT waste has been generated in a short time and has just begun to be managed (Xing et al., 2018; Xu et al., 2012). Typically, these dumped CRTs are moved to be incinerated and discarded in landfills as municipal solid waste (Gong et al., 2016; Yamashita et al., 2010). However, the poisonous effects of the heavy metals contained in the discarded CRT glass on the environ ment and human health, especially lead (Pb), cannot be neglected. Therefore, the eco-efficient management of CRT waste has become a priority of global concern in order to suitably and safely eliminate such waste (Hu and Hui, 2018). One possibility to reducing CRT waste is recycling into a raw mate rial for the production of concrete. There has been extensive research regarding the feasibility of this approach (Walczak et al., 2015; Zhao
et al., 2013). More interestingly, there is the potential for use as a concrete-based shield for application in medical radiation, the industry sector and nuclear power plants (Akkurt et al., 2010; Ling et al., 2012; Meng et al., 2018; Waly et al., 2017). Considerable variability in water contents in concrete, however, remains a major concern for it to be used effectively. Moreover, it is also opaque to visible light. Recycled CRT glass is another source for fabricating new glass material as radiation shielding because of its unique properties including transparency, high strength and excellent corrosion resistance. Also, changes in the composition and preparation processes can alter the glass properties. Hence, it has many possible uses in the nuclear radiation field and has also been examined as a potential engineering material to replace con crete (Laopaiboon et al., 2011). Incidentally, the addition of BaO into recycled glass not only optimizes its radiation shielding property, but also reduces the environmental toxicity of Pb by replacing some Pb atoms with Ba atoms. Barium is less naturally occurring in silicate sys tems than lighter alkaline earths such as Mg, Ca, and Sr. Higher mass for thermal resistance, and radiation resistance with higher electron density of the glass system have been received by the addition of higher atomic number Ba atoms. Consequently, barium silicate components have received a great deal of attention for heat and radiation shielding
* Corresponding author. E-mail address: [email protected] (R. Laopaiboon). https://doi.org/10.1016/j.pnucene.2019.103149 Received 13 March 2019; Received in revised form 15 August 2019; Accepted 11 September 2019 0149-1970/© 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: P. Sopapan, Progress in Nuclear Energy, https://doi.org/10.1016/j.pnucene.2019.103149
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applications (Lara et al., 2004; Rai and Mountjoy, 2014). As mentioned above, the CRT-based glass system has been selected to assess the possibility of using the system as a new radiation shielding material. The radiation shielding properties of the recycled CRT glass were studied. At energies of 74.23 and 97.14 keV, the shielding pa rameters of the glass samples were measured and calculated using the xray attenuation method to stimulate the secondary electrons from tar gets. At energies of 122, 662, 1173 and 1332 keV, the narrow beam transmission technique was applied. The results obtained from these methods were then compared with that from XCOM software and that of ferrite concrete. The ultrasonic contact technique was used to evaluate the elastic properties of the recycled CRT glass and investigation of the effect of temperature on their elastic constants was also carried out.
Table 2 Chemical composition, density (ρ) and molar volume (Vm) of recycled CRT glass samples.
Preparation of the glass specimen was performed using chemically pure and waste materials. BaO and K2O were introduced in the form of BaCO3 and K2CO3, respectively. The CRT waste glass for this research was acquired from the video display components of a computer monitor (Compaq 17 Inch CRT Monitor S710). The fine powder of CRT was obtained by crushing in a mortar. The chemical compositions of CRT glass sample were determined by EDS technique, as shown in Table 1. The fine powder of materials was weighed and mixed together in a ceramic crucible. The homogeneous powder was then melted using the conventional melt quenching method at around 2773 K in an electric furnace. The glass melting was extended to 2 h. The forming process of the glass samples was made on warmed stainless-steel molds, after which each glass sample was put in a muffle furnace for annealing at 723 K. After 2 h, the annealing process of the glass samples was ceased and the glass samples were allowed to cool down slowly to comfortable ambient temperature. Later, cutting and polishing of the prepared glasses were carried out for ultrasonic sound velocity measurements. The chemical compositions of the glass samples are presented in Table 2.
BaO
70 65 60 55 50
0 5 10 15 20
2.8232 2.9372 3.0416 3.1362 3.2266
33.3990 33.1062 32.9398 32.8863 32.8791
M
(2)
ρ
The contact technique was used to evaluate the values of the ultra sonic wave velocities by measuring the elapsed time between the transmitted and received pulses. This elapsed time appeared directly on the monitor of equipment (Sonatest Sitescan 230). The SLG4-10 and SA04-45� models of ceramics transducer probe were used to generate longitudinal and shear acoustic velocities, respectively. Both velocities were measured at 4 MHz using various temperatures of 278, 298 and 318 K (using a thermoelectric generator and hotplate), and their pres sures were controlled by a load cell to obtain constant pressure. Ultra sonic velocities at each temperature can be calculated as given in the following relation: v¼
2x Δt
(3)
where x is the thickness of the specimen in centimeter unit (cm) and t is the time interval (s). The measured sound velocities and the densities of the studied glasses were then used to estimate the elastic constants by the following formulas (Laopaiboon et al., 2016):
At room temperature, density measurement of the proposed glass systems was performed based on Archimedes’ principle in n-hexane. This method is a well-known tool to estimate the value of density in materials by applying the following relation (Shamshad et al., 2017): � � Wa ρ ¼ ρb (1) Wa Wb
Longitudinal modulus: L ¼ ρv2l ;
(4)
Shear modulus: G ¼ ρv2s ;
(5)
Bulk modulus: K ¼ L
where ρb is the density of n-hexane at room temperature. The weight of the glass measured in air and n-hexane are represented by Wa and Wb, respectively. The corresponding molar volume (Vm) of the prepared glass was determined using the expression below:
� � 4 G; 3
Young’s modulus: E ¼ 2ð1 þ σÞG; Poisson’s ratio: σ ¼
L 2G ; 2ðL GÞ
Micro hardness: H ¼
Table 1 Chemical compositions of CRT glass by EDS technique. 37.61 16.55 13.04 8.80 6.47 6.10 5.72 5.71 100.00
CRT
30 30 30 30 30
Vm (cm3/mol) � 0.0075
2.3. Ultrasonic velocity measurement and elastic constant calculation
2.2. Density and molar volume
SiO2 Al2O3 Na2O K2O BaO CaO MgO PbO Total
K2O GS1 GS2 GS3 GS4 GS5
ρ (g/cm3) � 0.0007
where M is the total atomic weight of the glass sample. The density values reported here are the average of at least three independently measured values.
2.1. Sample preparation
mol.%
Composition (mol%)
Vm ¼
2. Materials and methods
Compounds
Sample
ð1 2σÞE ; 6ð1 þ σ Þ
(6) (7) (8) (9)
In amorphous material, the longitudinal and shear moduli are interrelated with the independent elastic constants for an isotropic solid. Young’s modulus, defined as the relationship between stress and strain in a material, is found to be correlated to the bond strength of the glass material. Additionally, the bulk modulus is termed as the pressure rate of change in volume of a material due to a uniform compression in all directions (Matori et al., 2013, 2015). 2.4. Narrow beam transmission and x-ray attenuation methods For the selected radiation energies, the narrow beam x-ray 2
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attenuation and transmission techniques were applied to measure the mass attenuation coefficient of the glasses. The radioisotope source was obtained from the Department of Nuclear Engineering, Chulalongkorn University, Thailand. Photon energies of 1173 and 1332 keV were emitted by radioisotope sources of 60Co. 57Co and 137Cs were used to obtain the photon energies of 122 and 662 keV, respectively. A 2" � 200 NaI(Tl) crystal was used for counting the number of photons transmitted through the glass sample. The geometry of the x-ray attenuation tech nique is shown in Fig. 1. One face aperture of a lead container with 2 mm of collimator width, which was used to store the radioisotope source, was placed behind an adjustable target box. Uranium (U) and lead (Pb) rods were used as the targets. The interaction of photon of 60Co source and target rods created an x-ray beam at photon energies of 74.23 and 97.14 keV. This x-ray beam was controlled to pass through the glass samples. The x-ray was then measured on a 3 � 3 mm XR-100T-CdTe diode detector. The optimum set-up distance between the source to the target and from target to detector were found equal at 30 cm.
ferrite concrete were also calculated and compared to that of the pre pared glass. The chemical compositions of ferrite concrete are shown in Table 3. 3. Results and discussion 3.1. Density and molar volume The experimental values of density and molar volume were calcu lated and tabulated, as shown in Table 2. Variation of both values with mol% of BaO in recycled CRT glass is represented in Fig. 2. It was found that the density of the glass samples increased linearly with an increase of BaO, while their molar volume gradually decreased. The increment of density in the glass by adding BaO is associated with change in the standard atomic weight of its composition. Partial replacement of CRT which has SiO2 (atomic mass is 60.0843 g/mol) is the main component of BaO (atomic mass is 153.3264 g/mol) that leads to an increase of molecular mass and also its density (Matori et al., 2013; Rai and Mountjoy, 2014). This behavior can be observed when heavier modifier oxide has been doped in silicate glasses. In general, the density and molar volume values tend to indicate an adversative direction, as was the case in this study. This means that the partial substitution of CRT by BaO leads to a contraction of the network. A decrease in molar volume indicates a decrease in bond length or the distance between the nuclei of atoms in materials (Shelby, 2005; Singh and Singh, 2013). Therefore, the addition of barium ions changes the glass structure, leading to the formation of non-bridging oxygens (NBOs) (Chanshetti et al., 2011). A similar trend for both values in other glass systems has previously been reported elsewhere (El-bashir et al., 2017; Kaur et al., 2015; Marzouk, 2009).
2.5. Mass attenuation coefficient and half value layer As an alternative technique, WinXCom program is developed for calculating the theoretical shielding performance of a material based on the mixture rule. For many glass systems, the shielding parameters have been calculated using this software, which has been found to obtain accurate values (Gerward et al., 2004). The mass attenuation coefficient (μ/ρ or μm) for mixture of elements can be written as . X μ ρ¼ wi ðμ=ρÞi ; (10) where wi and (μ/ρ)i are the percentage by weight and mass attenuation coefficient of the elemental proportions, respectively. The half value layer (HVL) parameter for glass materials can be determined from the values of linear attenuation coefficient and density using the following expression (Ersundu et al., 2018). HVL¼ 0:693=μ:
3.2. Ultrasonic velocity The variation of acoustic speeds in recycled CRT glass with different BaO contents at temperatures of 278, 298 and 318 K are shown in Figs. 3 and 4. Both the longitudinal and shear velocities decreased gradually as BaO content was increased. It is known that the introduction of alkaline earth metal oxides (MgO, CaO, SrO, and BaO) in silicate glass results in decreased rigidity of the glass network by forming the NBO atoms (Marzouk, 2009). Therefore, the decrease in sound velocities of the studied glasses can be explained by an increase in the number of NBOs due to breaking down the internal glass structure when BaO is added to the glass network. Further, both longitudinal and shear wave velocities in the recycled CRT glasses were found to increase slowly when tem perature was increased in the range of 278–318 K. It has been mentioned that a change is expected in thermodynamic properties such as thermal expansion and compressibility of glass when the temperature of mate rials changes, which may affect the variation of sound wave speed (Chen et al., 2000; Lin, 1985). In the present work, the variation of the ultra sonic wave velocities in recycled CRT glass increases with an increase of temperature, indicating a minor positive temperature coefficient.
(11)
Then, μm and HVL values calculated based on this model were compared to that from the experimental data. Moreover, the values of
3.3. Elastic properties The measured ultrasonic velocities and density values of the recycled CRT glasses were used to calculate the elastic modulus, Poisson’s ratio and micro hardness. In general, most of the factors that influence the ultrasonic velocity and density in the glass samples are also expected to be involved in the obtained elastic constants. For instance, the longitu dinal modulus is dependent on the values of density and longitudinal sound velocity in glasses. Fig. 5 presents the variation of the modulus of elasticity in the recycled CRT glass containing BaO as a function of temperature. It can be seen that the elastic moduli increased linearly with temperature. This behavior reveals that the bonding strength in the glass structure increases as operating temperature increases. In contrast to metal and alloy materials that increase in temperature, resulting in a
Fig. 1. Experimental set-up of narrow beam x-ray attenuation method. 3
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Table 3 Chemical composition of concretes. Concretes
Weight fraction elements H
B
C
O
Na
K
Mg
Al
Si
S
Ca
Fe
Ba
Ordinary Barite Ferrite
0.0100 0.0083 0.0280
– 0.0115 –
0.0010 – –
0.5291 0.3475 0.4554
0.0160 – –
0.0130 – –
0.0020 0.0022 0.0019
0.0338 0.0044 0.0038
0.3370 0.0148 0.0128
– 0.0997 0.0007
0.0440 0.0834 0.0595
0.0140 0.0047 0.4378
– 0.4237 –
Fig. 4. The temperature dependence of shear velocity (vs) for recycled CRT glass adding BaO content.
Fig. 2. Variation of density and molar volume as a function of BaO concentration.
Although the elastic moduli increase with incremental BaO content, Poisson’s ratio almost maintains a constant value when the BaO content is increased from 0 to 20 mol% in recycled CRT glass, as shown in Fig. 6. As well known, the variation in Poisson’s ratio value is the result of the change in cross-link density. This observation supports the minor effect of BaO addition on the changes in cross-link density in our glass. The value of elastic moduli was found to be sensitive to the changes in glass structure, including changes in both the dimension of the glass network and its cross-link density. Therefore, the addition of BaO only results in change in the dimensionality of the structure. In addition, there are indications on the Poisson’s ratio and glass structure relations from a significant amount of research. For the first suggestion, Poisson’s ratio is equal to 0.25 if glass is deformed only through stretching or compression in its structural unit. Secondly, the values of Poisson’s ratio will be less than 0.25 when a part of the energy leads to the contortion of bond bending of the SiO4 tetrahedral. Finally, if the deformation of ions in the glass under stresses excluding network distortion occurs, Poisson’s ratio will be more than 0.25 (Chen et al., 2000). The value of Poisson’s ratio of our glass remains unchanged as BaO content in the glass is varied. This indicates that the BaO content has no significant effect on Poisson’s ratio. However, the changes of Poisson’s ratio values in range of 0.23–0.27 are influenced by the temperature in the glass. The micro-hardness (H) of a glass material is defined as the wear resistance and strength to penetration, suggesting the disposed stress in its free volume. The openness of the amorphous materials over that of the corresponding solids is determined by the free volume in the glass (Gaafar et al., 2009). Fig. 7 demonstrates the increase of micro hardness of our glass when the BaO content is increased. As stronger ionic bonds have been introduced in the glass structure, this may indicate a strengthening of the glass network or/and an increase in its rigidity (El-Adawy and Moustafa, 1999). Moreover, it can be seen in Fig. 7 that the micro hardness of the recycled CRT glasses with the addition of BaO concentration increases as the temperature is increased.
Fig. 3. The temperature dependence of longitudinal velocity (vl) for the recy cled CRT glass adding BaO content.
decrease in the elastic modulus due to an increase in the vibration of atoms in the crystal structure, glass materials become even stiffer with enhanced modulus of elasticity. As expected, the elastic moduli of our studied glass increased as temperature increased. In addition, it also can be observed that there is an increasing of all elastic moduli with increasing BaO concentration. The increase in shear and bulk modulus can be ascribed to the change in the coordination number of the studied glass when BaO is increased. When Ba atoms are doped in the glasses, oxygen bonds in the glass network are attacked, leading to the formation of loose-packed structures (Marzouk, 2010). Moreover, the density of the studied glasses is an important variable that increases elastic moduli in the proposed glass systems. 4
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Fig. 5. Elastic moduli (L, G, K and E) of recycled CRT glass adding BaO content as a function of temperature.
Fig. 6. The temperature dependence of Poisson’s ratio in recycled CRT glass adding BaO content.
Fig. 7. The temperature dependence of micro hardness in recycled CRT glass adding BaO content.
3.4. Radiation shielding properties
μm and lower HVL values are required (Kaur and Singh, 2014). The experimental values of μm were measured and calculated using the
The mass attenuation coefficient (μm) and half value layer (HVL) values of recycled CRT glass added with BaO as a function of energy are summarized in Tables 4 and 5, respectively. They are important pa rameters to estimate the shielding properties of the glasses (Kaur et al., 2015). For better x-ray and gamma-ray shielding performance, higher
narrow beam transmission and x-ray attenuation methods, while the theoretical values were obtained from WinXCom program. Energies of 74.23, 97.14, 122, 662, 1173 and 1332 keV were used as authentic data to evaluate the radiation shielding parameters. Fig. 8 shows the μm of
5
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Table 4 Mass attenuation coefficients (μm) of recycled CRT glass systems. Energy (keV)
Mass attenuation coefficient (cm2/g) GS1
74.23 97.14 122 662 1173 1332
GS2
GS3
GS4
GS5
Ex.
Th.
Ex.
Th.
Ex.
Th.
Ex.
Th.
Ex.
Th.
0.6403 0.5350 0.3613 0.0787 0.0560 0.0514
0.6834 0.5707 0.4128 0.0786 0.0592 0.0544
0.8719 0.6085 0.4144 0.0789 0.0561 0.0518
0.8794 0.6434 0.459 0.0786 0.0594 0.0542
1.0683 0.6984 0.4678 0.0798 0.0578 0.0527
1.0754 0.7161 0.5047 0.0785 0.0596 0.054
1.2578 0.7771 0.5277 0.0809 0.0584 0.0534
1.2714 0.7888 0.5509 0.0785 0.0598 0.0537
1.4497 0.8602 0.6098 0.0810 0.0591 0.0539
1.4674 0.8615 0.5961 0.0785 0.0600 0.0535
Table 5 Half value layer (HVL) parameter of recycled CRT glass systems. Energy (keV)
Half value layer (cm) GS1
74.23 97.14 122 662 1173 1332
GS2
GS3
GS4
GS5
Ex.
Th.
Ex.
Th.
Ex.
Th.
Ex.
Th.
Ex.
Th.
0.3916 0.4687 0.6940 3.1197 4.3857 4.7717
0.3669 0.4393 0.6075 3.1896 4.2336 4.6067
0.2753 0.3944 0.5792 2.9913 4.2079 4.5589
0.2729 0.3731 0.523 3.0548 4.0400 4.4317
0.2165 0.3311 0.4943 2.8555 3.9430 4.3254
0.215 0.3229 0.4582 2.9445 3.8800 4.2856
0.1780 0.2880 0.4242 2.7304 3.7804 4.1346
0.1761 0.2838 0.4063 2.8516 3.7440 4.1689
0.1499 0.2527 0.3564 2.6527 3.6327 3.9850
0.1481 0.2523 0.3646 2.7703 3.6243 4.0658
glass systems and ferrite concrete as a function of energy. It is clear that a decrease in the exponential curve of μm values is observed when the energy of incident photon is higher. This means the μm value does not depend only on the constituent elements of substance, but also on the photon energy. As shown in Fig. 9, the variation of the μm (sum in teractions) values with incident photon energy may be ascribed to the relative domination of the attenuation mechanisms, such as photoelec tric effect, pair production, coherent scattering, and incoherent scat tering. For low photon energy (1 keV < E < 100 keV), the μm shows that the photoelectric absorption is a dominant mechanism over other in teractions (Issa et al., 2019). Further, a rapid downward trend is observed as the energy is increased. It has been found that the μm values
increase with the increment of BaO content in glass matrix, possibly due to an increase of density in the proposed glasses. Therefore, the addition of BaO in the glass matrix improves its shielding properties. Moreover, it was likewise found that the values of μm parameter obtained from the experiment and WinXCom of the glass samples are much higher than ferrite concrete at the same photon energies. This result indicates that the recycled CRT glass has better shielding properties in terms of mass substance than standard nuclear radiation shielding concrete. For radiation shielding applications, HVL has been found to be a very useful parameter when designing shields from the required material. Fig. 10 shows the calculated values of HVL obtained from the experi mental and theoretical results. HVL is observed to increase when
Fig. 8. Mass attenuation coefficient (μm) of prepared glass and ferrite concrete as a function of energy. 6
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Fig. 9. Variation of partial mass attenuation coefficients versus incident photon energy for shielding material.
increasing the energy of the incident photon. In addition, it is noticeable that the HVL values decrease when the amount of BaO is higher at all photon energy. It has been stated that more interactions of the photon in glass material lead to a decrease in the HVL values, resulting in better shielding efficiency in terms of thickness requirements of the glass as a consequence (Kaur et al., 2015; Singh et al., 2015). Therefore, the decrease of the HVL values implies that the addition of BaO in glass systems can enhance their shielding properties. HVL values have also been compared with those of ferrite concrete at the same photon energy.
It was found that the HVL values of the studied glasses is lower than ferrite concrete at energies of 74.23, 97.14 and 122 keV, while it is higher for energies of 662, 1173 and 1332 keV. Therefore, the HVL parameter as well as the shielding properties depend on the energies of radioisotope source and BaO concentrations. The HVL of the recycled CRT glass without the addition of BaO at the energy of 74.23 keV is higher than ferrite concrete. This demonstrates that the undoped glass system possessed lower shielding properties than ferrite concrete.
Fig. 10. Half value layer (HVL) of prepared glass and ferrite concrete as a function of energy. 7
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4. Conclusion
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Conversion of covalent to ionic behavior of Fe2O3–CeO2–PbO–B2O3 glasses for ionic and photonic application. J. Alloys Compd. 546, 224–228. https://doi.org/10.1016/j.jallcom.2012.08.105. Singh, K., Singh, S., Dhaliwal, A.S., Singh, G., 2015. Gamma radiation shielding analysis of lead-flyash concretes. Appl. Radiat. Isot. 95, 174–179. https://doi.org/10.1016/j. apradiso.2014.10.022. Walczak, P., Małolepszy, J., Reben, M., Rzepa, K., 2015. Mechanical properties of concrete mortar based on mixture of CRT glass cullet and fluidized fly ash. Procedia Eng. 108, 453–458. https://doi.org/10.1016/j.proeng.2015.06.170. Waly, E.S.A., Fusco, M.A., Bourham, M.A., 2017. Impact of specialty glass and concrete on gamma shielding in multi-layered PWR dry casks. Prog. Nucl. Energy 94, 64–70. https://doi.org/10.1016/j.pnucene.2016.09.017. Xing, M., Wang, J., Fu, Z., Zhang, D., Wang, Y., Zhang, Z., 2018. Extraction of heavy metal (Ba, Sr) and high silica glass powder synthesis from waste CRT panel glasses by phase separation. J. Hazard. Mater. 347, 8–14. https://doi.org/10.1016/j.jhazmat. 2017.12.046. Xu, Q., Li, G., He, W., Huang, J., Shi, X., 2012. Cathode ray tube (CRT) recycling: current capabilities in China and research progress. Waste Manag. 32, 1566–1574. https ://doi.org/10.1016/j.wasman.2012.03.009. Yamashita, M., Wannagon, A., Matsumoto, S., Akai, T., Sugita, H., Imoto, Y., Komai, T., Sakanakura, H., 2010. Leaching behavior of CRT funnel glass. J. Hazard. Mater. 184, 58–64. https://doi.org/10.1016/j.jhazmat.2010.08.002. Zhao, H., Poon, C.S., Ling, T.C., 2013. Utilizing recycled cathode ray tube funnel glass sand as river sand replacement in the high-density concrete. J. Clean. Prod. 51, 184–190. https://doi.org/10.1016/j.jclepro.2013.01.025.
In this study, recycled cathode ray tube glass was successfully fabricated into new radiation shielding glass. The ultrasonic velocities of the studied glass were found to decrease when BaO was increased, indicating the formation of more NBOs. In addition, the ultrasonic ve locities and elastic moduli in the recycled CRT glass depended on the temperature. The mass attenuation coefficient (μm) values of the studied glass were found to depend on the content of BaO. It was also observed that the μm of the studied glass was higher than that of ferrite concrete at same photon energies. The half value layer at energies of 74.23, 97.14 and 122 keV of our glass systems is lower than that of ferrite concrete, implying better shielding material in terms of thickness requirements. Furthermore, the experimental values of radiation shielding parameters are in good agreement with the calculated values from WinXCom pro gram. The elastic and shielding properties observed in this study indi cate that the recycled CRT glass containing BaO is a potential candidate for radiation shielding applications. Acknowledgments The authors wished to thank Glass Technology Excellence Center (GTEC), Department of Physics, Ubon Ratchathani University, Thailand for the use of their ultrasonic flaw detector and Department of Nuclear Engineering, Chulalongkorn University, Thailand for measuring the narrow beam x-ray attenuation and transmission methods. Thanks also go to the Science Achievement Scholarship of Thailand (SAST) for financial support during this study. One of the authors (R. Laopaiboon) would like to thank Dr. Ussadawut Patakum from MTEC for analysis of CRT glass by EDS technique. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.pnucene.2019.103149. References Andreola, F., Barbieri, L., Corradi, A., Lancellotti, I., 2007. CRT glass state of the art a case study: recycling in ceramic glazes. J. Eur. Ceram. Soc. 27, 1623–1629. https://doi.org/10.1016/j.jeurceramsoc.2006.05.009. Akkurt, I., Akyıldırım, H., Mavi, B., Kilincarslan, S., Basyigit, C., 2010. Radiation shielding of concrete containing zeolite. Radiat. Meas. 45, 827–830. https://doi.org/ 10.1016/j.radmeas.2010.04.012. Chanshetti, U.B., Shelke, V.A., Jadhav, S.M., Shankarwar, S.G., Chondhekar, T.K., Shankarwar, A.G., Sudarsan, V., Jogad, M.S., 2011. Density and molar volume studies of phosphate glasses, FU. Phys. Chem. Tech. 9, 29–36. https://doi.org/ 10.2298/FUPCT1101029C. Chen, C.C., Wu, Y.J., Hwa, L.G., 2000. Temperature dependence of elastic properties of ZBLAN glasses. Mater. Chem. Phys. 65, 306–309. https://doi. org/10.1016/S0254-0584(00)00256-X. El-Adawy, A., Moustafa, Y., 1999. Elastic properties of bismuth borate glasses. J. Phys. D Appl. Phys. 32, 2791–2796. https://doi.org/10.1088/0022-3727/32/21/312. El-bashir, B.O., Sayyed, M.I., Zaid, M.H.M., Matori, K.A., 2017. Comprehensive study on physical, elastic and shielding properties of ternary BaO-Bi2O3-P2O5 glasses as a potent radiation shielding material. J. Non-Cryst. Solids 468, 92–99. https://doi. org/10.1016/j.jnoncrysol.2017.04.031. Ersundu, A.E., Büyükyıldız, M., Ersundu, M.C., Sakar, E., Kurudirek, M., 2018. The heavy metal oxide glasses within the WO3-MoO3-TeO2 system to investigate the shielding properties of radiation applications. Prog. Nucl. Energy 104, 280–287. https://doi. org/10.1016/j.pnucene.2017.10.008. Gaafar, M.S., Afifi, H.A., Mekawy, M., 2009. Structural studies of some phosphoborate glasses using ultrasonic pulse-echo technique, DSC and IR spectroscopy. Physica B 404, 1668–1673. https://doi.org/10.1016/j.physb.2009.01.045. Gerward, L., Guilbert, N., Jensen, K.B., Levring, H., 2004. WinXCom—a program for calculating X-ray attenuation coefficients. Radiat. Phys. Chem. 71, 653–654. http s://doi.org/10.1016/j.radphyschem.2004.04.040. Gong, Y., Tian, X.M., Wu, Y.F., Tan, Z., Lv, L., 2016. Recent development of recycling lead from scrap CRTs: a technological review. Waste Manag. 57, 176–186. https ://doi.org/10.1016/j.wasman.2015.09.004. Hu, B., Hui, W., 2018. Lead recovery from waste CRT funnel glass by high-temperature melting process. J. Hazard. Mater. 343, 220–226. https://doi.org/10.1016/j.jh azmat.2017.09.034.
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Progress in Nuclear Energy journal homepage: http://www.elsevier.com/locate/pnucene
Feasibility study of recycled CRT glass on elastic and radiation shielding properties used as x-ray and gamma-ray shielding materials P. Sopapan a, J. Laopaiboon a, O. Jaiboon a, C. Yenchai b, R. Laopaiboon a, * a b
Glass Technology Excellence Center (GTEC), Department of Physics, Faculty of Science, Ubon Ratchathani University, Ubon Ratchathani, 34190, Thailand Department of Nuclear Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, 10330, Thailand
A R T I C L E I N F O
A B S T R A C T
Keywords: CRTs glass Pressure-controlled ultrasonic technique Elastic moduli X-ray attenuation Radiation shielding
Recycled glass derived from discarded cathode ray tubes (CRT) was used as a component for (70-x) CRT–30K2O–xBaO glass systems (where x ¼ 0–20 mol%). Temperature dependence of ultrasonic wave velocities was carried out at 4 MHz frequency using pressure-controlled ultrasonic technique. It was found that the ve locities decreased gradually as BaO content increased. However, sound velocities increased with increasing temperature. Then, both velocities were applied to estimate their elastic properties. Based on the obtained re sults, the elastic moduli and micro hardness of studied glasses increased with the amount of BaO and temper ature, while their Poisson’s ratio remained almost constant. Radiation shielding properties were investigated in terms of μm and HVL at photon energies of 74.23, 97.14, 122, 662, 1173, and 1332 keV by using narrow beam xray attenuation and transmission methods. Their theoretical values were also calculated by WinXCom program and compared with ferrite concrete. The results showed better radiation shielding properties for recycled CRT glass in comparison to ferrite concrete. Furthermore, the values obtained from the experiment in this study are in good agreement with the theoretical data.
1. Introduction The disposal of waste from electric and electronic equipment (WEEE), particularly the cathode ray tubes (CRTs) used in computer and television display monitors, is fast becoming a global environmental issue that must be eliminated urgently (Andreola et al., 2007; Nnorom et al., 2011). Due to the rapid advancement of high-definition television (HDTV) technologies, standard-definition television (SDTV) sets have been largely replaced. Consequently, a large amount of CRT waste has been generated in a short time and has just begun to be managed (Xing et al., 2018; Xu et al., 2012). Typically, these dumped CRTs are moved to be incinerated and discarded in landfills as municipal solid waste (Gong et al., 2016; Yamashita et al., 2010). However, the poisonous effects of the heavy metals contained in the discarded CRT glass on the environ ment and human health, especially lead (Pb), cannot be neglected. Therefore, the eco-efficient management of CRT waste has become a priority of global concern in order to suitably and safely eliminate such waste (Hu and Hui, 2018). One possibility to reducing CRT waste is recycling into a raw mate rial for the production of concrete. There has been extensive research regarding the feasibility of this approach (Walczak et al., 2015; Zhao
et al., 2013). More interestingly, there is the potential for use as a concrete-based shield for application in medical radiation, the industry sector and nuclear power plants (Akkurt et al., 2010; Ling et al., 2012; Meng et al., 2018; Waly et al., 2017). Considerable variability in water contents in concrete, however, remains a major concern for it to be used effectively. Moreover, it is also opaque to visible light. Recycled CRT glass is another source for fabricating new glass material as radiation shielding because of its unique properties including transparency, high strength and excellent corrosion resistance. Also, changes in the composition and preparation processes can alter the glass properties. Hence, it has many possible uses in the nuclear radiation field and has also been examined as a potential engineering material to replace con crete (Laopaiboon et al., 2011). Incidentally, the addition of BaO into recycled glass not only optimizes its radiation shielding property, but also reduces the environmental toxicity of Pb by replacing some Pb atoms with Ba atoms. Barium is less naturally occurring in silicate sys tems than lighter alkaline earths such as Mg, Ca, and Sr. Higher mass for thermal resistance, and radiation resistance with higher electron density of the glass system have been received by the addition of higher atomic number Ba atoms. Consequently, barium silicate components have received a great deal of attention for heat and radiation shielding
* Corresponding author. E-mail address: [email protected] (R. Laopaiboon). https://doi.org/10.1016/j.pnucene.2019.103149 Received 13 March 2019; Received in revised form 15 August 2019; Accepted 11 September 2019 0149-1970/© 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: P. Sopapan, Progress in Nuclear Energy, https://doi.org/10.1016/j.pnucene.2019.103149
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applications (Lara et al., 2004; Rai and Mountjoy, 2014). As mentioned above, the CRT-based glass system has been selected to assess the possibility of using the system as a new radiation shielding material. The radiation shielding properties of the recycled CRT glass were studied. At energies of 74.23 and 97.14 keV, the shielding pa rameters of the glass samples were measured and calculated using the xray attenuation method to stimulate the secondary electrons from tar gets. At energies of 122, 662, 1173 and 1332 keV, the narrow beam transmission technique was applied. The results obtained from these methods were then compared with that from XCOM software and that of ferrite concrete. The ultrasonic contact technique was used to evaluate the elastic properties of the recycled CRT glass and investigation of the effect of temperature on their elastic constants was also carried out.
Table 2 Chemical composition, density (ρ) and molar volume (Vm) of recycled CRT glass samples.
Preparation of the glass specimen was performed using chemically pure and waste materials. BaO and K2O were introduced in the form of BaCO3 and K2CO3, respectively. The CRT waste glass for this research was acquired from the video display components of a computer monitor (Compaq 17 Inch CRT Monitor S710). The fine powder of CRT was obtained by crushing in a mortar. The chemical compositions of CRT glass sample were determined by EDS technique, as shown in Table 1. The fine powder of materials was weighed and mixed together in a ceramic crucible. The homogeneous powder was then melted using the conventional melt quenching method at around 2773 K in an electric furnace. The glass melting was extended to 2 h. The forming process of the glass samples was made on warmed stainless-steel molds, after which each glass sample was put in a muffle furnace for annealing at 723 K. After 2 h, the annealing process of the glass samples was ceased and the glass samples were allowed to cool down slowly to comfortable ambient temperature. Later, cutting and polishing of the prepared glasses were carried out for ultrasonic sound velocity measurements. The chemical compositions of the glass samples are presented in Table 2.
BaO
70 65 60 55 50
0 5 10 15 20
2.8232 2.9372 3.0416 3.1362 3.2266
33.3990 33.1062 32.9398 32.8863 32.8791
M
(2)
ρ
The contact technique was used to evaluate the values of the ultra sonic wave velocities by measuring the elapsed time between the transmitted and received pulses. This elapsed time appeared directly on the monitor of equipment (Sonatest Sitescan 230). The SLG4-10 and SA04-45� models of ceramics transducer probe were used to generate longitudinal and shear acoustic velocities, respectively. Both velocities were measured at 4 MHz using various temperatures of 278, 298 and 318 K (using a thermoelectric generator and hotplate), and their pres sures were controlled by a load cell to obtain constant pressure. Ultra sonic velocities at each temperature can be calculated as given in the following relation: v¼
2x Δt
(3)
where x is the thickness of the specimen in centimeter unit (cm) and t is the time interval (s). The measured sound velocities and the densities of the studied glasses were then used to estimate the elastic constants by the following formulas (Laopaiboon et al., 2016):
At room temperature, density measurement of the proposed glass systems was performed based on Archimedes’ principle in n-hexane. This method is a well-known tool to estimate the value of density in materials by applying the following relation (Shamshad et al., 2017): � � Wa ρ ¼ ρb (1) Wa Wb
Longitudinal modulus: L ¼ ρv2l ;
(4)
Shear modulus: G ¼ ρv2s ;
(5)
Bulk modulus: K ¼ L
where ρb is the density of n-hexane at room temperature. The weight of the glass measured in air and n-hexane are represented by Wa and Wb, respectively. The corresponding molar volume (Vm) of the prepared glass was determined using the expression below:
� � 4 G; 3
Young’s modulus: E ¼ 2ð1 þ σÞG; Poisson’s ratio: σ ¼
L 2G ; 2ðL GÞ
Micro hardness: H ¼
Table 1 Chemical compositions of CRT glass by EDS technique. 37.61 16.55 13.04 8.80 6.47 6.10 5.72 5.71 100.00
CRT
30 30 30 30 30
Vm (cm3/mol) � 0.0075
2.3. Ultrasonic velocity measurement and elastic constant calculation
2.2. Density and molar volume
SiO2 Al2O3 Na2O K2O BaO CaO MgO PbO Total
K2O GS1 GS2 GS3 GS4 GS5
ρ (g/cm3) � 0.0007
where M is the total atomic weight of the glass sample. The density values reported here are the average of at least three independently measured values.
2.1. Sample preparation
mol.%
Composition (mol%)
Vm ¼
2. Materials and methods
Compounds
Sample
ð1 2σÞE ; 6ð1 þ σ Þ
(6) (7) (8) (9)
In amorphous material, the longitudinal and shear moduli are interrelated with the independent elastic constants for an isotropic solid. Young’s modulus, defined as the relationship between stress and strain in a material, is found to be correlated to the bond strength of the glass material. Additionally, the bulk modulus is termed as the pressure rate of change in volume of a material due to a uniform compression in all directions (Matori et al., 2013, 2015). 2.4. Narrow beam transmission and x-ray attenuation methods For the selected radiation energies, the narrow beam x-ray 2
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attenuation and transmission techniques were applied to measure the mass attenuation coefficient of the glasses. The radioisotope source was obtained from the Department of Nuclear Engineering, Chulalongkorn University, Thailand. Photon energies of 1173 and 1332 keV were emitted by radioisotope sources of 60Co. 57Co and 137Cs were used to obtain the photon energies of 122 and 662 keV, respectively. A 2" � 200 NaI(Tl) crystal was used for counting the number of photons transmitted through the glass sample. The geometry of the x-ray attenuation tech nique is shown in Fig. 1. One face aperture of a lead container with 2 mm of collimator width, which was used to store the radioisotope source, was placed behind an adjustable target box. Uranium (U) and lead (Pb) rods were used as the targets. The interaction of photon of 60Co source and target rods created an x-ray beam at photon energies of 74.23 and 97.14 keV. This x-ray beam was controlled to pass through the glass samples. The x-ray was then measured on a 3 � 3 mm XR-100T-CdTe diode detector. The optimum set-up distance between the source to the target and from target to detector were found equal at 30 cm.
ferrite concrete were also calculated and compared to that of the pre pared glass. The chemical compositions of ferrite concrete are shown in Table 3. 3. Results and discussion 3.1. Density and molar volume The experimental values of density and molar volume were calcu lated and tabulated, as shown in Table 2. Variation of both values with mol% of BaO in recycled CRT glass is represented in Fig. 2. It was found that the density of the glass samples increased linearly with an increase of BaO, while their molar volume gradually decreased. The increment of density in the glass by adding BaO is associated with change in the standard atomic weight of its composition. Partial replacement of CRT which has SiO2 (atomic mass is 60.0843 g/mol) is the main component of BaO (atomic mass is 153.3264 g/mol) that leads to an increase of molecular mass and also its density (Matori et al., 2013; Rai and Mountjoy, 2014). This behavior can be observed when heavier modifier oxide has been doped in silicate glasses. In general, the density and molar volume values tend to indicate an adversative direction, as was the case in this study. This means that the partial substitution of CRT by BaO leads to a contraction of the network. A decrease in molar volume indicates a decrease in bond length or the distance between the nuclei of atoms in materials (Shelby, 2005; Singh and Singh, 2013). Therefore, the addition of barium ions changes the glass structure, leading to the formation of non-bridging oxygens (NBOs) (Chanshetti et al., 2011). A similar trend for both values in other glass systems has previously been reported elsewhere (El-bashir et al., 2017; Kaur et al., 2015; Marzouk, 2009).
2.5. Mass attenuation coefficient and half value layer As an alternative technique, WinXCom program is developed for calculating the theoretical shielding performance of a material based on the mixture rule. For many glass systems, the shielding parameters have been calculated using this software, which has been found to obtain accurate values (Gerward et al., 2004). The mass attenuation coefficient (μ/ρ or μm) for mixture of elements can be written as . X μ ρ¼ wi ðμ=ρÞi ; (10) where wi and (μ/ρ)i are the percentage by weight and mass attenuation coefficient of the elemental proportions, respectively. The half value layer (HVL) parameter for glass materials can be determined from the values of linear attenuation coefficient and density using the following expression (Ersundu et al., 2018). HVL¼ 0:693=μ:
3.2. Ultrasonic velocity The variation of acoustic speeds in recycled CRT glass with different BaO contents at temperatures of 278, 298 and 318 K are shown in Figs. 3 and 4. Both the longitudinal and shear velocities decreased gradually as BaO content was increased. It is known that the introduction of alkaline earth metal oxides (MgO, CaO, SrO, and BaO) in silicate glass results in decreased rigidity of the glass network by forming the NBO atoms (Marzouk, 2009). Therefore, the decrease in sound velocities of the studied glasses can be explained by an increase in the number of NBOs due to breaking down the internal glass structure when BaO is added to the glass network. Further, both longitudinal and shear wave velocities in the recycled CRT glasses were found to increase slowly when tem perature was increased in the range of 278–318 K. It has been mentioned that a change is expected in thermodynamic properties such as thermal expansion and compressibility of glass when the temperature of mate rials changes, which may affect the variation of sound wave speed (Chen et al., 2000; Lin, 1985). In the present work, the variation of the ultra sonic wave velocities in recycled CRT glass increases with an increase of temperature, indicating a minor positive temperature coefficient.
(11)
Then, μm and HVL values calculated based on this model were compared to that from the experimental data. Moreover, the values of
3.3. Elastic properties The measured ultrasonic velocities and density values of the recycled CRT glasses were used to calculate the elastic modulus, Poisson’s ratio and micro hardness. In general, most of the factors that influence the ultrasonic velocity and density in the glass samples are also expected to be involved in the obtained elastic constants. For instance, the longitu dinal modulus is dependent on the values of density and longitudinal sound velocity in glasses. Fig. 5 presents the variation of the modulus of elasticity in the recycled CRT glass containing BaO as a function of temperature. It can be seen that the elastic moduli increased linearly with temperature. This behavior reveals that the bonding strength in the glass structure increases as operating temperature increases. In contrast to metal and alloy materials that increase in temperature, resulting in a
Fig. 1. Experimental set-up of narrow beam x-ray attenuation method. 3
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Table 3 Chemical composition of concretes. Concretes
Weight fraction elements H
B
C
O
Na
K
Mg
Al
Si
S
Ca
Fe
Ba
Ordinary Barite Ferrite
0.0100 0.0083 0.0280
– 0.0115 –
0.0010 – –
0.5291 0.3475 0.4554
0.0160 – –
0.0130 – –
0.0020 0.0022 0.0019
0.0338 0.0044 0.0038
0.3370 0.0148 0.0128
– 0.0997 0.0007
0.0440 0.0834 0.0595
0.0140 0.0047 0.4378
– 0.4237 –
Fig. 4. The temperature dependence of shear velocity (vs) for recycled CRT glass adding BaO content.
Fig. 2. Variation of density and molar volume as a function of BaO concentration.
Although the elastic moduli increase with incremental BaO content, Poisson’s ratio almost maintains a constant value when the BaO content is increased from 0 to 20 mol% in recycled CRT glass, as shown in Fig. 6. As well known, the variation in Poisson’s ratio value is the result of the change in cross-link density. This observation supports the minor effect of BaO addition on the changes in cross-link density in our glass. The value of elastic moduli was found to be sensitive to the changes in glass structure, including changes in both the dimension of the glass network and its cross-link density. Therefore, the addition of BaO only results in change in the dimensionality of the structure. In addition, there are indications on the Poisson’s ratio and glass structure relations from a significant amount of research. For the first suggestion, Poisson’s ratio is equal to 0.25 if glass is deformed only through stretching or compression in its structural unit. Secondly, the values of Poisson’s ratio will be less than 0.25 when a part of the energy leads to the contortion of bond bending of the SiO4 tetrahedral. Finally, if the deformation of ions in the glass under stresses excluding network distortion occurs, Poisson’s ratio will be more than 0.25 (Chen et al., 2000). The value of Poisson’s ratio of our glass remains unchanged as BaO content in the glass is varied. This indicates that the BaO content has no significant effect on Poisson’s ratio. However, the changes of Poisson’s ratio values in range of 0.23–0.27 are influenced by the temperature in the glass. The micro-hardness (H) of a glass material is defined as the wear resistance and strength to penetration, suggesting the disposed stress in its free volume. The openness of the amorphous materials over that of the corresponding solids is determined by the free volume in the glass (Gaafar et al., 2009). Fig. 7 demonstrates the increase of micro hardness of our glass when the BaO content is increased. As stronger ionic bonds have been introduced in the glass structure, this may indicate a strengthening of the glass network or/and an increase in its rigidity (El-Adawy and Moustafa, 1999). Moreover, it can be seen in Fig. 7 that the micro hardness of the recycled CRT glasses with the addition of BaO concentration increases as the temperature is increased.
Fig. 3. The temperature dependence of longitudinal velocity (vl) for the recy cled CRT glass adding BaO content.
decrease in the elastic modulus due to an increase in the vibration of atoms in the crystal structure, glass materials become even stiffer with enhanced modulus of elasticity. As expected, the elastic moduli of our studied glass increased as temperature increased. In addition, it also can be observed that there is an increasing of all elastic moduli with increasing BaO concentration. The increase in shear and bulk modulus can be ascribed to the change in the coordination number of the studied glass when BaO is increased. When Ba atoms are doped in the glasses, oxygen bonds in the glass network are attacked, leading to the formation of loose-packed structures (Marzouk, 2010). Moreover, the density of the studied glasses is an important variable that increases elastic moduli in the proposed glass systems. 4
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Fig. 5. Elastic moduli (L, G, K and E) of recycled CRT glass adding BaO content as a function of temperature.
Fig. 6. The temperature dependence of Poisson’s ratio in recycled CRT glass adding BaO content.
Fig. 7. The temperature dependence of micro hardness in recycled CRT glass adding BaO content.
3.4. Radiation shielding properties
μm and lower HVL values are required (Kaur and Singh, 2014). The experimental values of μm were measured and calculated using the
The mass attenuation coefficient (μm) and half value layer (HVL) values of recycled CRT glass added with BaO as a function of energy are summarized in Tables 4 and 5, respectively. They are important pa rameters to estimate the shielding properties of the glasses (Kaur et al., 2015). For better x-ray and gamma-ray shielding performance, higher
narrow beam transmission and x-ray attenuation methods, while the theoretical values were obtained from WinXCom program. Energies of 74.23, 97.14, 122, 662, 1173 and 1332 keV were used as authentic data to evaluate the radiation shielding parameters. Fig. 8 shows the μm of
5
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Table 4 Mass attenuation coefficients (μm) of recycled CRT glass systems. Energy (keV)
Mass attenuation coefficient (cm2/g) GS1
74.23 97.14 122 662 1173 1332
GS2
GS3
GS4
GS5
Ex.
Th.
Ex.
Th.
Ex.
Th.
Ex.
Th.
Ex.
Th.
0.6403 0.5350 0.3613 0.0787 0.0560 0.0514
0.6834 0.5707 0.4128 0.0786 0.0592 0.0544
0.8719 0.6085 0.4144 0.0789 0.0561 0.0518
0.8794 0.6434 0.459 0.0786 0.0594 0.0542
1.0683 0.6984 0.4678 0.0798 0.0578 0.0527
1.0754 0.7161 0.5047 0.0785 0.0596 0.054
1.2578 0.7771 0.5277 0.0809 0.0584 0.0534
1.2714 0.7888 0.5509 0.0785 0.0598 0.0537
1.4497 0.8602 0.6098 0.0810 0.0591 0.0539
1.4674 0.8615 0.5961 0.0785 0.0600 0.0535
Table 5 Half value layer (HVL) parameter of recycled CRT glass systems. Energy (keV)
Half value layer (cm) GS1
74.23 97.14 122 662 1173 1332
GS2
GS3
GS4
GS5
Ex.
Th.
Ex.
Th.
Ex.
Th.
Ex.
Th.
Ex.
Th.
0.3916 0.4687 0.6940 3.1197 4.3857 4.7717
0.3669 0.4393 0.6075 3.1896 4.2336 4.6067
0.2753 0.3944 0.5792 2.9913 4.2079 4.5589
0.2729 0.3731 0.523 3.0548 4.0400 4.4317
0.2165 0.3311 0.4943 2.8555 3.9430 4.3254
0.215 0.3229 0.4582 2.9445 3.8800 4.2856
0.1780 0.2880 0.4242 2.7304 3.7804 4.1346
0.1761 0.2838 0.4063 2.8516 3.7440 4.1689
0.1499 0.2527 0.3564 2.6527 3.6327 3.9850
0.1481 0.2523 0.3646 2.7703 3.6243 4.0658
glass systems and ferrite concrete as a function of energy. It is clear that a decrease in the exponential curve of μm values is observed when the energy of incident photon is higher. This means the μm value does not depend only on the constituent elements of substance, but also on the photon energy. As shown in Fig. 9, the variation of the μm (sum in teractions) values with incident photon energy may be ascribed to the relative domination of the attenuation mechanisms, such as photoelec tric effect, pair production, coherent scattering, and incoherent scat tering. For low photon energy (1 keV < E < 100 keV), the μm shows that the photoelectric absorption is a dominant mechanism over other in teractions (Issa et al., 2019). Further, a rapid downward trend is observed as the energy is increased. It has been found that the μm values
increase with the increment of BaO content in glass matrix, possibly due to an increase of density in the proposed glasses. Therefore, the addition of BaO in the glass matrix improves its shielding properties. Moreover, it was likewise found that the values of μm parameter obtained from the experiment and WinXCom of the glass samples are much higher than ferrite concrete at the same photon energies. This result indicates that the recycled CRT glass has better shielding properties in terms of mass substance than standard nuclear radiation shielding concrete. For radiation shielding applications, HVL has been found to be a very useful parameter when designing shields from the required material. Fig. 10 shows the calculated values of HVL obtained from the experi mental and theoretical results. HVL is observed to increase when
Fig. 8. Mass attenuation coefficient (μm) of prepared glass and ferrite concrete as a function of energy. 6
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Fig. 9. Variation of partial mass attenuation coefficients versus incident photon energy for shielding material.
increasing the energy of the incident photon. In addition, it is noticeable that the HVL values decrease when the amount of BaO is higher at all photon energy. It has been stated that more interactions of the photon in glass material lead to a decrease in the HVL values, resulting in better shielding efficiency in terms of thickness requirements of the glass as a consequence (Kaur et al., 2015; Singh et al., 2015). Therefore, the decrease of the HVL values implies that the addition of BaO in glass systems can enhance their shielding properties. HVL values have also been compared with those of ferrite concrete at the same photon energy.
It was found that the HVL values of the studied glasses is lower than ferrite concrete at energies of 74.23, 97.14 and 122 keV, while it is higher for energies of 662, 1173 and 1332 keV. Therefore, the HVL parameter as well as the shielding properties depend on the energies of radioisotope source and BaO concentrations. The HVL of the recycled CRT glass without the addition of BaO at the energy of 74.23 keV is higher than ferrite concrete. This demonstrates that the undoped glass system possessed lower shielding properties than ferrite concrete.
Fig. 10. Half value layer (HVL) of prepared glass and ferrite concrete as a function of energy. 7
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4. Conclusion
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In this study, recycled cathode ray tube glass was successfully fabricated into new radiation shielding glass. The ultrasonic velocities of the studied glass were found to decrease when BaO was increased, indicating the formation of more NBOs. In addition, the ultrasonic ve locities and elastic moduli in the recycled CRT glass depended on the temperature. The mass attenuation coefficient (μm) values of the studied glass were found to depend on the content of BaO. It was also observed that the μm of the studied glass was higher than that of ferrite concrete at same photon energies. The half value layer at energies of 74.23, 97.14 and 122 keV of our glass systems is lower than that of ferrite concrete, implying better shielding material in terms of thickness requirements. Furthermore, the experimental values of radiation shielding parameters are in good agreement with the calculated values from WinXCom pro gram. The elastic and shielding properties observed in this study indi cate that the recycled CRT glass containing BaO is a potential candidate for radiation shielding applications. Acknowledgments The authors wished to thank Glass Technology Excellence Center (GTEC), Department of Physics, Ubon Ratchathani University, Thailand for the use of their ultrasonic flaw detector and Department of Nuclear Engineering, Chulalongkorn University, Thailand for measuring the narrow beam x-ray attenuation and transmission methods. Thanks also go to the Science Achievement Scholarship of Thailand (SAST) for financial support during this study. One of the authors (R. Laopaiboon) would like to thank Dr. Ussadawut Patakum from MTEC for analysis of CRT glass by EDS technique. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.pnucene.2019.103149. References Andreola, F., Barbieri, L., Corradi, A., Lancellotti, I., 2007. CRT glass state of the art a case study: recycling in ceramic glazes. J. Eur. Ceram. Soc. 27, 1623–1629. https://doi.org/10.1016/j.jeurceramsoc.2006.05.009. Akkurt, I., Akyıldırım, H., Mavi, B., Kilincarslan, S., Basyigit, C., 2010. Radiation shielding of concrete containing zeolite. Radiat. Meas. 45, 827–830. https://doi.org/ 10.1016/j.radmeas.2010.04.012. Chanshetti, U.B., Shelke, V.A., Jadhav, S.M., Shankarwar, S.G., Chondhekar, T.K., Shankarwar, A.G., Sudarsan, V., Jogad, M.S., 2011. Density and molar volume studies of phosphate glasses, FU. Phys. Chem. Tech. 9, 29–36. https://doi.org/ 10.2298/FUPCT1101029C. Chen, C.C., Wu, Y.J., Hwa, L.G., 2000. Temperature dependence of elastic properties of ZBLAN glasses. Mater. Chem. Phys. 65, 306–309. https://doi. org/10.1016/S0254-0584(00)00256-X. El-Adawy, A., Moustafa, Y., 1999. Elastic properties of bismuth borate glasses. J. Phys. D Appl. Phys. 32, 2791–2796. https://doi.org/10.1088/0022-3727/32/21/312. El-bashir, B.O., Sayyed, M.I., Zaid, M.H.M., Matori, K.A., 2017. Comprehensive study on physical, elastic and shielding properties of ternary BaO-Bi2O3-P2O5 glasses as a potent radiation shielding material. J. Non-Cryst. Solids 468, 92–99. https://doi. org/10.1016/j.jnoncrysol.2017.04.031. Ersundu, A.E., Büyükyıldız, M., Ersundu, M.C., Sakar, E., Kurudirek, M., 2018. The heavy metal oxide glasses within the WO3-MoO3-TeO2 system to investigate the shielding properties of radiation applications. Prog. Nucl. Energy 104, 280–287. https://doi. org/10.1016/j.pnucene.2017.10.008. Gaafar, M.S., Afifi, H.A., Mekawy, M., 2009. Structural studies of some phosphoborate glasses using ultrasonic pulse-echo technique, DSC and IR spectroscopy. Physica B 404, 1668–1673. https://doi.org/10.1016/j.physb.2009.01.045. Gerward, L., Guilbert, N., Jensen, K.B., Levring, H., 2004. WinXCom—a program for calculating X-ray attenuation coefficients. Radiat. Phys. Chem. 71, 653–654. http s://doi.org/10.1016/j.radphyschem.2004.04.040. Gong, Y., Tian, X.M., Wu, Y.F., Tan, Z., Lv, L., 2016. Recent development of recycling lead from scrap CRTs: a technological review. Waste Manag. 57, 176–186. https ://doi.org/10.1016/j.wasman.2015.09.004. Hu, B., Hui, W., 2018. Lead recovery from waste CRT funnel glass by high-temperature melting process. J. Hazard. Mater. 343, 220–226. https://doi.org/10.1016/j.jh azmat.2017.09.034.
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