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Annals of Nuclear Energy 44 (2012) 50–57
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Effect of temperature, irradiation dose, and dose rate on the retention of some radioisotopes in poly(methyl methacrylate)/phosphate/composites O. Alhassanieh a,⇑, Z. Ajji b a b
Nuclear and Radiochemistry Division, Chemistry Department, Atomic Energy Commission of Syria, Damascus, P.O. Box 6091, Syria Polymer Technology Division, Radiation Technology Department, Atomic Energy Commission of Syria, Damascus, P.O. Box 6091, Syria
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Article history: Received 24 October 2011 Received in revised form 12 January 2012 Accepted 15 January 2012 Available online 28 February 2012 Keywords: Poly(methyl methacrylate)/phosphate/ composites Irradiation Retention Radionuclides Temperature Dose
a b s t r a c t Polymer/composites have been prepared successfully consisting of natural phosphate powder and the monomer, N-methyl methacrylate, using gamma irradiation. The polymerization reaction was followed up using a thermogravimetric analyzer (TGA), and the region of the glass transition temperatures (Tg) of the samples was located using a thermomechanical analyzer (TMA) by applying the mode with alternative variable force; the mode with constant force was used to determine the Tg of the pure polymer and the polymer/composite prepared at the same irradiation dose. The effects of temperature, contact time, pH, dose, dose rate, monomer to phosphate ratio, and the concentration of concurrent element (Ca) on the migration of 137Cs, 152Eu and 85Sr from a solid phase consisting of phosphate–poly(methyl methacrylate) composite to groundwater have been investigated. The ability of the produced composites to keep the studied radioisotopes in the solid phase is much higher than mineral phosphate at ambient temperatures. Element ratios of 100% in the solid phase can be achieved for Eu and Sr. Cesium ratio in the solid phase is higher than 95% (dose 15 kGy, dose rate 10.5 kGy/h). High irradiation doses (about 60 kGy) and dose rates (15 kGy/h) lead to quantitative retention of all studied elements in the solid phase, even in the presence of a concurrent element. This behavior can be explained by higher possibilities of crosslinking of the polymer chains due to higher doses and dose rates. High temperatures lead to lowering of retention ratios of the prepared composites. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction In the polymer industry, inorganic fillers such as mica, talc, and calcium carbonate are combined with polymeric materials to improve some of their mechanical and physical properties (Caykara and Guven, 1998). This is a quick method of increasing mechanical resistance of the samples against compression, abrasion, and so forth (Edwards, 1990; Guth, 1945; Kiji et al., 1983; Mathur and Greenzweig, 1978; Papirer et al., 1984; Rehner, 1943; Sharma et al., 1982). The properties of the composite materials are generally affected by the chemical properties of the components and the nature of the interaction between the phases. Studies of reinforcement indicate that stress is effectively transferred between the polymer matrixes and embedded particulate phases over an interfacial region of finite dimension (Donnet and Vidal, 1986). Carbon black has been used for a long time in the rubber industry to modify the polymer properties (Yang et al., 1993; Shaltout et al., 2002). In other publication, silica was used to modify polymeric materials (Çaykara and Gueven, 1998b, 1999; Çaykara et al., 1999). Gypsum and ⇑ Corresponding author. Tel.: +963 11 2132580; fax: +963 11 6112289. E-mail address: cscientifi[email protected] (O. Alhassanieh). 0306-4549/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.anucene.2012.01.007
alumina were also used as filler for preparing polymer composites (Çaykara and Gueven, 1998a; Ajji and Alkassiri, 2003). Polymers and glasses have been considered in the storage of nuclear waste for a number of years. The use of polymer composites in this area is relatively new (Alhassanieh et al., 2011; Ajji and Alhassanieh, 2011). It could be an interesting topic, if the filler in the composite (in this case the phosphate) has the ability to adsorb a number of radioisotopes, which possibly are included in nuclear waste (e.g. lanthanides and actinides (Ghafar et al., 2002)). In recent works mineral phosphate/poly(butyl acrylate) (Alhassanieh et al., 2011) and phosphate/poly(methyl acrylate) (Ajji and Alhassanieh, 2011) composites were prepared, and the effect of several factors such as monomer to phosphate ratio, pH, and contact time on the migration of radioisotopes have been investigated. The presence of polymer chains surrounding phosphate particulates leads to a shielding of the phosphate particles, and consequently to a higher element ratio incorporated in the solid phase in comparison with mineral phosphate (Ghafar et al., 2002). These results show indications that such polymer/composite systems could be considered for using as storage medium for radioactive waste of the studied radionuclides. Possible degradation of polymers by high doses and dos rates led to this work, in
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The phosphate samples were collected from the Khnefies area in Syria. The mineral and elemental composition of the Syrian phosphate has been analyzed in many works (Abbas, 1987; Abbas and Hyder, 1982; Asfahani and Abdul-Hadi, 2001; Takriti and Abdul-Hadi, 1998). The water samples were taken from the Loiuze borehole from the phosphate area. Cation and anion concentrations were determined using HPLC technique. Elemental composition was determined using instrumental neutron activation analysis. Different properties of the water samples were measured such as conductivity, TDS, TOC, density and temperature (Alhassanieh et al., 2011; Ajji and Alhassanieh, 2011). The pH value of the water sample is near neutral, the redox conditions are normal, and the concentration of complexing anions (e.g. phosphate) is very low. The used monomer, methyl methacrylate was of analytical grade. Different ratios (1:1–1:5) of phosphate to monomer were taken, and gamma doses from 15 to 60 kGy were applied. A 60Co gamma facility (Russian type: ROBO) was used, and various dose rates from 3.5 to 15 kGy/h were applied. Dynamic weight loss tests and thermomechanical analysis were used to characterize the prepared composites. The details of experimental setups are described in Ajji and Alhassanieh (2011) and Alhassanieh et al. (2011). The X-ray photoelectron spectra were recorded using a XPS spectrometer (SPECS UHV-System). The FTIR spectra of the monomer, mineral phosphate and the composite were recorded using JOOE Spectrometer (JASCO). DSC (Mettler, DSC20) was used to determine the glass transition temperatures of the prepared samples; all tests were conducted in aluminum pans at a heating rate of 10 °C/min over a temperature range from room temperature to 400 °C. The precision of the used instrument is ±0.2 °C, and the experimental errors in the measurements were estimated to be about ±0.5 °C. A certain volume (about 10 lL) of the radionuclides 137Cs, 152Eu and 85Sr was injected into the phosphate (0.5 g). Methyl methacrylate was added and mixed with the phosphate powder before the irradiation induced polymerization process in the gamma facility. The composite samples were soaked in 4 mL of the groundwater. After phase separation, the element ratios were determined using c-spectrometry (HPGe-Detector, 60% Eff., FWHM = 0.998 at 122 keV and 1.88 at 1332 keV, Canberra 35 plus). The uncertainty of all c-measurements is around 5%. 137Cs was taken from an IAEA-standard. 152Eu and 85Sr were produced by irradiation of their nitrates with a reactor flux of 1011 n/cm2 s. The element ratios in the aqueous phase were calculated according to:
Dw ¼ ðAw =ðAw þ As ÞÞ 100 ¼ C w =C o 100 where Dw is the element ratio in the aqueous phase, Aw is the activity of the liquid phase after phase separation, As is the activity of the solid phase after phase separation, Cw is the element concentration in the liquid phase after phase separation, and Co is the initial element concentration. The pH was changed using LiOH and HClO4 solutions only in pH-dependent experiments. Calcium concentration was changed using their nitrates only in the experiments of concurrent elements.
3.1. Polymerization reaction and characterization of the composites 3.1.1. Polymerization reaction Natural phosphate powder was used without drying because it has been previously showed that there is no significant influence of drying on the radiation induced polymerization conversion by preparing polymer/gypsum/composites (Ajji and Alkassiri, 2003). Fig. 1 shows typical TGA thermograms of mixtures, which are irradiated at different doses. The first step in the thermogram corresponds to the evaporation of the rest monomer in the samples; the second step corresponds to the decomposition of the polymer. The yields of polymerization are shown in Fig. 2 with respect to the irradiation doses. It is obvious that the polymerization conversion increases with increasing the irradiation dose, and achieves a conversion around 97% using an irradiation dose of 12 kGy. This can be explained that the radical concentration, which acts as initiator, increases with increasing the irradiation dose and thus the reaction conversion. 3.1.2. Glass transition temperature TMA spectrum has been recorded using an alternated force of 0.3 N in order to ensure the existence of a real glass transition, and to show the Tg region (Fig. 3). It can be observed that the elongation increases considerably at the Tg region. In order to determine the Tg, TMA spectra were recorded with constant force; the Tg of poly(methyl methacrylate) and poly(methyl methacrylate)/ phosphate/composite were 109.1 °C and 110.5 °C, respectively. 100 6 kGy 4 kGy 2 kGy
95 90
Weight (%)
2. Experimental
3. Results and discussion
85 80 75 70 65
100
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o
Temperature [ C] Fig. 1. Typical TGA thermograms of N-methyl methacrylate/phosphate/mixtures irradiated at different gamma doses.
100
Polymerization yield (%)
which mineral phosphate/poly(methyl methacrylate) composites have been prepared, and characterized, with the aim of studying the effect of temperature, irradiation dose and dose rate on the migration of some radioisotopes to an aqueous phase consisting of natural ground water.
80 60 40 20 0 0
2
4
6
8
10
12
14
Irradiation dose [kGy] Fig. 2. Polymerization conversion of N-methyl methacrylate/phosphate/mixtures versus the irradiation dose.
O. Alhassanieh, Z. Ajji / Annals of Nuclear Energy 44 (2012) 50–57
DSC spectra were also recorded for pure poly(methyl methacrylate) and poly(methyl methacrylate)/phosphate/composite in order to compare and ensure their Tgs as represented in Fig. 4. It can also be seen (Fig. 5) that the Tg of the poly(methyl methacrylate)/phosphate/composite is higher than the Tg of poly(methyl methacrylate); Tg of pure poly(methyl methacrylate) amounts to
80 70 60
Phos.
50
T [%]
52
40 30 20 10 0
Deformation (%)
-10 80 70 60
Comp. 15 kGy
T [%]
50 Polymer/ phosphate/ composite Pure poly(methyl methacrylate)
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80
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140
40 30 20
160
10
o
Temperature [ C]
0
Fig. 3. TMA thermogram with alternated force for pure poly(methyl methacrylate) and poly(methyl methacrylate)/phosphate/composites, which are irradiated at 12 kGy.
-10
70 60
Deformation (%)
T [%]
50 40
comp. 60 kGy
30 20 10 0 -10
0
500
1000
1500
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2500 -1
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wave no. [cm ]
Polymer/ phosphate/ composite Pure poly(methyl methacrylate)
Fig. 6. FTIR spectra of mineral phosphate and the composites.
80
100
120
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160
o
Temperature [ C] Fig. 4. TMA thermograms applying a constant force for pure poly(methyl methacrylate) and poly(methyl methacrylate)/phosphate/composites irradiated at 12 kGy.
Heat Flow
Polymer/ phosphate/ composite Poly(methyl methacrylate)
60
75
90
105
120
135
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165
o
Temperature [ C] Fig. 5. DSC thermograms of pure poly(methyl methacrylate) and poly(methyl methacrylate)/phosphate/composites irradiated at 12 kGy.
Fig. 7. A typical XPS spectrum for a composite irradiated with 60 kGy.
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100
Dose 20 kGy, Phos./Mon. 1/1 Dose rate 7 kGy, pH 8, t 24 h Eu Sr Cs
75
D w [%]
75
Dw [%]
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Dose 20 kGy, Phos./Mon. 1/1 Dose rate 15 kGy, pH 8, t 24 h Eu Sr Cs
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Dw [%]
75
D w [%]
50
T [ C]
80
0
T [ C]
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0
T [ C]
Fig. 8. Effect of temperature on the fraction of Eu, Cs, and Sr in the liquid phase for various dose rates.
103.7 °C, and Tg of poly(methyl methacrylate)/phosphate/composites is 110.2 °C. This increase in the Tg of polymer/composites compared with pure polymer could be attributed to the interaction between the polymer chains and the filler particulates, which decrease the segmental mobility of the chains near the filler particles. This behavior has been observed in other composite systems, and has been explained based on reduced mobility of molecular segments in the vicinity of the filler particulates (Çaykara, 1998).
and in connection with monomer to phosphate ratio (1:1–5:1, Fig. 9). Temperatures between 25 and 80 °C were taken. Higher temperatures could cause vibrations in the solid and the aqueous phase. The decreased consistence due to the vibrations in the solid phase creates gaps, which allows the migration of the radioisotopes out of this phase. This effect can be compressed by the use of higher monomer to phosphate ratios (more than 4:1) and higher dose rates (higher than 10.5 kGy/h). 3.3. Effect of irradiation dose
3.1.3. FTIR Spectroscopy and X-ray photoelectron spectroscopy (XPS) FTIR and XPS spectra of mineral phosphate and composites were recorded. The composites were exposed to different doses. Fig. 6 shows the FTIR spectra of the phosphate (upper panel), composite prepared with an irradiation dose of 15 kGy (middle panel), and composite prepared with an irradiation dose of 60 kGy (lower panel). The adsorption bands in the upper spectrum are at 3424.9, 1653.6, 1049.1, 800.3, and 591.1 cm1 corresponding to O–H, H–OH, P–O, Ca–O, and PO3 4 respectively. In the spectra of the composites there are no bands corresponding to P–O–C, which should appear at a wavelength around 1456 cm1. There are also no differences in the middle and lower spectrum resulting from different irradiation doses. The recorded XPS spectra (single spectra and scans) do not show any indications of bounding between mineral phosphate and the polymer. The spectra show also no changes depending on the applied doses. Fig. 7 (XPS spectrum) gives the binding energy of the of 2p binding of phosphorus. Its obviously that the there is no change in the binding energy between mineral phosphate and the phosphate–polymer-composite, which means that the phosphate play only the role of a filler. 3.2. Effect of temperature The effect of temperature has been studied in two experiment series, in connection with dose rate (3.8, 7, 10.5, 15 kGy/h, Fig. 8)
Increasing the irradiation dose leads during the polymerization process to an increase in the polymerization conversion. After a total conversion, the following could take place: Crosslinking, which leads to smaller pore size and decreasing the leaching/mobility of elements. Degradation of polymer chains, which allow higher leaching/ migration of species to the solution. 3.3.1. Impact of irradiation dose on time dependence Fig. 10 shows the element ratios of the investigated elements in the aqueous phase as a function of contact time of the phases. Strontium and europium do not show any tendency to migrate into the liquid phase, even after more than three months. Moreover, there is no effect of the applied dose on the migration of these elements. The strontium ratio in the solid phase rose up from about 15% to 100% in comparison with mineral phosphate. The equilibrium of cesium is reached in about 2 h. It’s ratio in the liquid phase after equilibrium is 5%. 3.3.2. Impact of irradiation dose on pH dependence Fig. 11 shows the element ratios in the aqueous phase as a function of irradiation doses for various pH values. The retention of strontium and europium is 100%, and that of cesium is
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100
100 Dose 20 kGy, Phos./Mon. 1/1 Dose rate 10.5 kGy, pH 8, t 24 h Eu Sr Cs
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Dose 20 kGy, Phos./Mon. 1/2 Dose rate 10.5 kGy, pH 8, t 24 h Eu Sr Cs
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Dw [%]
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T [ C] Fig. 9. Effect of temperature on the fraction of Eu, Cs, and Sr in the liquid phase for various monomer to phosphate ratios.
100
100 75 Dose 15 kGy, pH 8 Dose rae 10.5 kGy/h Eu Sr Cs
50 25
Dw [%]
Dw [%]
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0 0
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75 Dose 45 kGy, pH 8 Dose rae 10.5 kGy/h Eu Sr Cs
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Dose 30 kGy, pH 8 Dose rae 10.5 kGy/h Eu Sr Cs
200
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t [h]
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50 25 0
0 0
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t [h]
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t [h]
Fig. 10. Fraction of Cs, Eu, and Sr in the liquid phase as a function of time for various doses.
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100 0
t =24, pH 4, T 25 C Dose rae 10.5 kGy/h Eu Sr Cs
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D w [%]
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Dose [h]
Fig. 11. Fraction of Cs, Eu, and Sr in the liquid phase as a function of the applied dose for various pH values.
about 94%. The pH value does not show any effect on the retention of the investigated elements. Changing of pH does not lead to changes of cesium speciation (Alhassanieh, 2009), which
Dw [%]
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explain its behavior. Higher doses cause crosslinking, which leads to smaller pore size and decreasing the leaching/mobility of cesium.
50 25
50 25
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0 1E-3
0.01
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1
1E-3
CCa [mol/l]
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t =24, Dose 45 kGy, T 25 C Dose rae 10.5 kGy/h, pH 8 Eu Sr Cs
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t =24, Dose 60 kGy, T 25 C Dose rae 10.5 kGy/h, pH 8 Eu Sr Cs
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25
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0 1E-3
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Fig. 12. Fraction of Eu, Cs, and Sr in the liquid phase as a function of calcium concentration for various doses.
1
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3.3.3. Impact of irradiation dose on the effect of concurrent element Changing the concentration of possible concurrent elements (e.g. calcium) in the aqueous phase leads usually to shifting of equilibriums in the liquid phase and consequently to exchange phenomena between the phases, which causes higher isotope ratios in the liquid phase and as a result less retention (Fig. 12). Taking the effect of irradiation dose in consideration, we found that possible crosslinking between polymer chains at higher doses decrease the effect of the concurrent element.
3.4. Effect of dose rate Generally, high dose rates cause lower molecular weights and network structure could be built, which leads to small pore sizes in polymer and consequently the retention possibilities in the composite should increase. Four different dose rates (3.8, 6, 10.5, and 15 kGy/h) were applied. The total dose in all cases was 15 kGy. Strontium and europium reside in all cases in the solid phase, even in the case of a dose rate about 3.8 kGy/h, in which the polymerization was not completed after a total dose of 20 kGy. The cesium ratio in the liquid phase become to a minimum by a dose rate of 10.5 kGy/h and it does not change by increasing the dose rate (Fig. 13).
The element ratios were investigated as a function of monomer to phosphate ratio. Fig. 14 shows the element ratios in the liquid phase as a function of monomer to phosphate ratio. High monomer to phosphate ratios lead to encapsulation of the phosphate including the radioisotopes, and consequently to better retention.
100
Dw [%]
t 24 h, Dose 20 kGy mon: phos 1:1, pH 8.2 Eu Sr Cs
50 25 0 2
4
6
8
10
12
Dose rate [kGy/h]
14
16
Fig. 13. Fraction of Eu, Cs, and Sr in the liquid phase as a function of dose rate.
100
Dw [%]
80
t 24 h, Dose 10.5 kGy Dose rate 15 kGy, pH 8.2 Eu Sr Cs
60 40 20 0 1
2
3
Composites have been prepared from natural phosphate and methyl methacrylate using gamma irradiation. The conversion of polymerization was about 97% by exposure of the samples to a dose of 12 kGy. Also the glass transition temperatures have been determined for the pure polymer and composites prepared at the same irradiation dose. The retention of cesium, strontium and europium in the composites is quantitative under certain conditions (polymer to phosphate ratios more than 3:1, dose rates more than 10.5 kGy/h, and doses about 60 kGy). Contact time and pH have not any effect on the retention probability. Higher doses, dose rates, and monomer to phosphate ratios lead to better retention, while higher temperatures cause higher migration ratios. This temperature effect can be compensated by applying higher irradiation doses and dose rates. Acknowledgments The authors would like to thank Prof. Dr. I. Othman (Director General of AECS) and Prof. Dr. T. Yassin (Head of chemistry department in AECS) for their encouragement. Our thanks are extended to Dr. O. Mrad, Ms. L. Stas, M. Soakia, A. Aqiel, H. Koussa, A. Mougrabeya, and S. Shashit for their efforts during the experiments. References
3.5. Effect of monomer to phosphate ratio
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4. Conclusion
4
mon. : phos. ratio
5
Fig. 14. Fraction of Eu, Cs, and Sr in the liquid phase as a function of monomer to phosphate ratio.
Abbas, M., 1987. Geochemie de l’uranium des phosphorites des Palmyrides Centrals Syrie, These Sci., Louis Pasteur U., Strasbourg, France, 166 pp. Abbas, M., Hyder, M., 1982. Syrian Phosphate and its Radioactive Materials. AECS G/ RSS 21. Ajji, Z., Alkassiri, H., 2003. Preparation of gypsum/polymer/composites using Gamma radiation. In: Proceedings of the Symposium on Radiation Technology in Emerging Industrial Applications, Beijing, China, 6–10 November 2000, pp. 41–45. Ajji, Z., Alhassanieh, O., 2011. Preparation of poly(methyl acrylate)/phosphate/ composites and its possible use as storage medium for radioactive isotopes. J. Radioanal. Nucl. Chem. 287, 69–75. Alhassanieh, O., 2009. Element Speciation and Element Correlations in Groundwater of the Southern and Eastern Area of Syria. Report on a Scientific Study, AECSCnRSS 842. Alhassanieh, O., Ajji, Z., Alkourdi, H., Haloum, D., 2011. Migration of strontium, cesium, and europium from poly(butyl acrylate)/phosphate/composites prepared using gamma radiation. Appl. Rad. Isotopes 69, 448–454. Asfahani, J., Abdul-Hadi, A., 2001. Geophysical natural c-ray well logging and spectrometric signatures of south AL-Abter phosphatic deposits in Syria. Appl. Rad. Isotopes 54, 543–549. Çaykara, T., Gueven, O., 1998a. Effect of preparation methods on the thermal properties of ploy(acrylic acid)/alumina composites. Polym. Compos. 19, 193– 197. Çaykara, T., Gueven, O., 1998b. The effect of preparation methods on the thermal properties of ploy(acrylic acid)/silica composites. J. Appl. Polym. Sci. 70, 891–895. Çaykara, T., Gueven, O., 1999. Kinetic analysis of the radiation induced polymerization of an acrylic acid-silica system. Eur. Polym. J. 35, 113–119. Çaykara, T., Eroglu, M.S., Gueven, O., 1999. Thermal and oxidative degradation of vinyl triethoxy silane-methyl methacrylate copolymers. Polym. Degrad. Stab. 63, 65–70. Donnet, J.B., Vidal, A., 1986. Carbon black: surface properties and interactions within elastomers. In: Abe, A., Albertsson, A.C., Duncan, R., Dusek, K., de Jeu, W.H., Kausch, H.H., Kobayashi, S., Lee, K.S., Leibler, L., Long, T.E., Manners, I., Möller, M., Nuyken, O., Terentjev, E.M., Voit, B., Wegner, G., Wiesner, U. (Eds.), Advances in Polymer Science. Springer-Verlag, Berlin, pp. 103–110. Edwards, D.C., 1990. Polymer-filler interaction in rubber reinforcement. J. Mater. Sci. 25, 4175–4185. Ghafar, M., Abdul-Hadi, A., Alhassanieh, O., 2002. Distribution of some elements in a solid-aqueous system: mineral phosphate in contact with groundwater. J. Radioanal. Nucl. Chem. 254, 159–163. Guth, E., 1945. Theory of filler reinforcement. J. Appl. Phys. 16, 20–25. Kiji, J., Konishi, H., Taninaka, T., Okano, T., Yamashita, S., Kohojiya, S., 1983. Calcium carbonate modified with 1,2-polybutadiene. A potential reinforcing filler for synthetic rubber. Angew. Makromol. Chem. 111, 53–62. Mathur, K.K., Greenzweig, J.E., 1978. Effect of surface area and surface treatment of calcium carbonate fillers on the performance of calendered vinyls. Plastic Eng. 34, 53–62. Papirer, E., Schultz, E., Turchi, C., 1984. Surface properties of a calcium carbonate filler treated with stearic acid. Eur. Polym. J. 20, 1155–1162. Rehner, J., 1943. Theory of filler reinforcement in natural and synthetic. The stress in and about particles. J. Appl. Phys. 14, 638–645.
O. Alhassanieh, Z. Ajji / Annals of Nuclear Energy 44 (2012) 50–57 Shaltout, N.A., Abou-Zeid, M.M., Moustafa, M.H., El-Miligy, A.A., 2002. Effect of gamma irradiation and degree of loading of carbon black on the properties of styrene–butadiene rubber. Arab. J. Nucl. Sci. Appl. 35, 25–35. Sharma, Y.N., Patel, R.D., Dhimmar, I.H., Bhardwaj, I.S., 1982. Studies of the effect of titanate coupling agent on the performance of polypropylene–calcium carbonate composite. J. Appl. Polym. Sci. 27, 4669–4686.
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Takriti, S., Abdul-Hadi, A., 1998. Determination of 234U/238U activity ratios in syrian phosphates. J. Radioanal. Nucl. Chem. 230, 299–301. Yang, H., Tang, H., Piao, J., Chen-Xinfang, C., 1993. The stabilization effect of radiation crosslinking on positive temperature coefficient performances of carbon black–polymer composites. Rad. Phys. Chem. 42, 135–137.
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Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene
Effect of temperature, irradiation dose, and dose rate on the retention of some radioisotopes in poly(methyl methacrylate)/phosphate/composites O. Alhassanieh a,⇑, Z. Ajji b a b
Nuclear and Radiochemistry Division, Chemistry Department, Atomic Energy Commission of Syria, Damascus, P.O. Box 6091, Syria Polymer Technology Division, Radiation Technology Department, Atomic Energy Commission of Syria, Damascus, P.O. Box 6091, Syria
a r t i c l e
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Article history: Received 24 October 2011 Received in revised form 12 January 2012 Accepted 15 January 2012 Available online 28 February 2012 Keywords: Poly(methyl methacrylate)/phosphate/ composites Irradiation Retention Radionuclides Temperature Dose
a b s t r a c t Polymer/composites have been prepared successfully consisting of natural phosphate powder and the monomer, N-methyl methacrylate, using gamma irradiation. The polymerization reaction was followed up using a thermogravimetric analyzer (TGA), and the region of the glass transition temperatures (Tg) of the samples was located using a thermomechanical analyzer (TMA) by applying the mode with alternative variable force; the mode with constant force was used to determine the Tg of the pure polymer and the polymer/composite prepared at the same irradiation dose. The effects of temperature, contact time, pH, dose, dose rate, monomer to phosphate ratio, and the concentration of concurrent element (Ca) on the migration of 137Cs, 152Eu and 85Sr from a solid phase consisting of phosphate–poly(methyl methacrylate) composite to groundwater have been investigated. The ability of the produced composites to keep the studied radioisotopes in the solid phase is much higher than mineral phosphate at ambient temperatures. Element ratios of 100% in the solid phase can be achieved for Eu and Sr. Cesium ratio in the solid phase is higher than 95% (dose 15 kGy, dose rate 10.5 kGy/h). High irradiation doses (about 60 kGy) and dose rates (15 kGy/h) lead to quantitative retention of all studied elements in the solid phase, even in the presence of a concurrent element. This behavior can be explained by higher possibilities of crosslinking of the polymer chains due to higher doses and dose rates. High temperatures lead to lowering of retention ratios of the prepared composites. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction In the polymer industry, inorganic fillers such as mica, talc, and calcium carbonate are combined with polymeric materials to improve some of their mechanical and physical properties (Caykara and Guven, 1998). This is a quick method of increasing mechanical resistance of the samples against compression, abrasion, and so forth (Edwards, 1990; Guth, 1945; Kiji et al., 1983; Mathur and Greenzweig, 1978; Papirer et al., 1984; Rehner, 1943; Sharma et al., 1982). The properties of the composite materials are generally affected by the chemical properties of the components and the nature of the interaction between the phases. Studies of reinforcement indicate that stress is effectively transferred between the polymer matrixes and embedded particulate phases over an interfacial region of finite dimension (Donnet and Vidal, 1986). Carbon black has been used for a long time in the rubber industry to modify the polymer properties (Yang et al., 1993; Shaltout et al., 2002). In other publication, silica was used to modify polymeric materials (Çaykara and Gueven, 1998b, 1999; Çaykara et al., 1999). Gypsum and ⇑ Corresponding author. Tel.: +963 11 2132580; fax: +963 11 6112289. E-mail address: cscientifi[email protected] (O. Alhassanieh). 0306-4549/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.anucene.2012.01.007
alumina were also used as filler for preparing polymer composites (Çaykara and Gueven, 1998a; Ajji and Alkassiri, 2003). Polymers and glasses have been considered in the storage of nuclear waste for a number of years. The use of polymer composites in this area is relatively new (Alhassanieh et al., 2011; Ajji and Alhassanieh, 2011). It could be an interesting topic, if the filler in the composite (in this case the phosphate) has the ability to adsorb a number of radioisotopes, which possibly are included in nuclear waste (e.g. lanthanides and actinides (Ghafar et al., 2002)). In recent works mineral phosphate/poly(butyl acrylate) (Alhassanieh et al., 2011) and phosphate/poly(methyl acrylate) (Ajji and Alhassanieh, 2011) composites were prepared, and the effect of several factors such as monomer to phosphate ratio, pH, and contact time on the migration of radioisotopes have been investigated. The presence of polymer chains surrounding phosphate particulates leads to a shielding of the phosphate particles, and consequently to a higher element ratio incorporated in the solid phase in comparison with mineral phosphate (Ghafar et al., 2002). These results show indications that such polymer/composite systems could be considered for using as storage medium for radioactive waste of the studied radionuclides. Possible degradation of polymers by high doses and dos rates led to this work, in
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The phosphate samples were collected from the Khnefies area in Syria. The mineral and elemental composition of the Syrian phosphate has been analyzed in many works (Abbas, 1987; Abbas and Hyder, 1982; Asfahani and Abdul-Hadi, 2001; Takriti and Abdul-Hadi, 1998). The water samples were taken from the Loiuze borehole from the phosphate area. Cation and anion concentrations were determined using HPLC technique. Elemental composition was determined using instrumental neutron activation analysis. Different properties of the water samples were measured such as conductivity, TDS, TOC, density and temperature (Alhassanieh et al., 2011; Ajji and Alhassanieh, 2011). The pH value of the water sample is near neutral, the redox conditions are normal, and the concentration of complexing anions (e.g. phosphate) is very low. The used monomer, methyl methacrylate was of analytical grade. Different ratios (1:1–1:5) of phosphate to monomer were taken, and gamma doses from 15 to 60 kGy were applied. A 60Co gamma facility (Russian type: ROBO) was used, and various dose rates from 3.5 to 15 kGy/h were applied. Dynamic weight loss tests and thermomechanical analysis were used to characterize the prepared composites. The details of experimental setups are described in Ajji and Alhassanieh (2011) and Alhassanieh et al. (2011). The X-ray photoelectron spectra were recorded using a XPS spectrometer (SPECS UHV-System). The FTIR spectra of the monomer, mineral phosphate and the composite were recorded using JOOE Spectrometer (JASCO). DSC (Mettler, DSC20) was used to determine the glass transition temperatures of the prepared samples; all tests were conducted in aluminum pans at a heating rate of 10 °C/min over a temperature range from room temperature to 400 °C. The precision of the used instrument is ±0.2 °C, and the experimental errors in the measurements were estimated to be about ±0.5 °C. A certain volume (about 10 lL) of the radionuclides 137Cs, 152Eu and 85Sr was injected into the phosphate (0.5 g). Methyl methacrylate was added and mixed with the phosphate powder before the irradiation induced polymerization process in the gamma facility. The composite samples were soaked in 4 mL of the groundwater. After phase separation, the element ratios were determined using c-spectrometry (HPGe-Detector, 60% Eff., FWHM = 0.998 at 122 keV and 1.88 at 1332 keV, Canberra 35 plus). The uncertainty of all c-measurements is around 5%. 137Cs was taken from an IAEA-standard. 152Eu and 85Sr were produced by irradiation of their nitrates with a reactor flux of 1011 n/cm2 s. The element ratios in the aqueous phase were calculated according to:
Dw ¼ ðAw =ðAw þ As ÞÞ 100 ¼ C w =C o 100 where Dw is the element ratio in the aqueous phase, Aw is the activity of the liquid phase after phase separation, As is the activity of the solid phase after phase separation, Cw is the element concentration in the liquid phase after phase separation, and Co is the initial element concentration. The pH was changed using LiOH and HClO4 solutions only in pH-dependent experiments. Calcium concentration was changed using their nitrates only in the experiments of concurrent elements.
3.1. Polymerization reaction and characterization of the composites 3.1.1. Polymerization reaction Natural phosphate powder was used without drying because it has been previously showed that there is no significant influence of drying on the radiation induced polymerization conversion by preparing polymer/gypsum/composites (Ajji and Alkassiri, 2003). Fig. 1 shows typical TGA thermograms of mixtures, which are irradiated at different doses. The first step in the thermogram corresponds to the evaporation of the rest monomer in the samples; the second step corresponds to the decomposition of the polymer. The yields of polymerization are shown in Fig. 2 with respect to the irradiation doses. It is obvious that the polymerization conversion increases with increasing the irradiation dose, and achieves a conversion around 97% using an irradiation dose of 12 kGy. This can be explained that the radical concentration, which acts as initiator, increases with increasing the irradiation dose and thus the reaction conversion. 3.1.2. Glass transition temperature TMA spectrum has been recorded using an alternated force of 0.3 N in order to ensure the existence of a real glass transition, and to show the Tg region (Fig. 3). It can be observed that the elongation increases considerably at the Tg region. In order to determine the Tg, TMA spectra were recorded with constant force; the Tg of poly(methyl methacrylate) and poly(methyl methacrylate)/ phosphate/composite were 109.1 °C and 110.5 °C, respectively. 100 6 kGy 4 kGy 2 kGy
95 90
Weight (%)
2. Experimental
3. Results and discussion
85 80 75 70 65
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o
Temperature [ C] Fig. 1. Typical TGA thermograms of N-methyl methacrylate/phosphate/mixtures irradiated at different gamma doses.
100
Polymerization yield (%)
which mineral phosphate/poly(methyl methacrylate) composites have been prepared, and characterized, with the aim of studying the effect of temperature, irradiation dose and dose rate on the migration of some radioisotopes to an aqueous phase consisting of natural ground water.
80 60 40 20 0 0
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14
Irradiation dose [kGy] Fig. 2. Polymerization conversion of N-methyl methacrylate/phosphate/mixtures versus the irradiation dose.
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DSC spectra were also recorded for pure poly(methyl methacrylate) and poly(methyl methacrylate)/phosphate/composite in order to compare and ensure their Tgs as represented in Fig. 4. It can also be seen (Fig. 5) that the Tg of the poly(methyl methacrylate)/phosphate/composite is higher than the Tg of poly(methyl methacrylate); Tg of pure poly(methyl methacrylate) amounts to
80 70 60
Phos.
50
T [%]
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o
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Fig. 3. TMA thermogram with alternated force for pure poly(methyl methacrylate) and poly(methyl methacrylate)/phosphate/composites, which are irradiated at 12 kGy.
-10
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Deformation (%)
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comp. 60 kGy
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Fig. 6. FTIR spectra of mineral phosphate and the composites.
80
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o
Temperature [ C] Fig. 4. TMA thermograms applying a constant force for pure poly(methyl methacrylate) and poly(methyl methacrylate)/phosphate/composites irradiated at 12 kGy.
Heat Flow
Polymer/ phosphate/ composite Poly(methyl methacrylate)
60
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o
Temperature [ C] Fig. 5. DSC thermograms of pure poly(methyl methacrylate) and poly(methyl methacrylate)/phosphate/composites irradiated at 12 kGy.
Fig. 7. A typical XPS spectrum for a composite irradiated with 60 kGy.
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100
Dose 20 kGy, Phos./Mon. 1/1 Dose rate 7 kGy, pH 8, t 24 h Eu Sr Cs
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D w [%]
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Dw [%]
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Fig. 8. Effect of temperature on the fraction of Eu, Cs, and Sr in the liquid phase for various dose rates.
103.7 °C, and Tg of poly(methyl methacrylate)/phosphate/composites is 110.2 °C. This increase in the Tg of polymer/composites compared with pure polymer could be attributed to the interaction between the polymer chains and the filler particulates, which decrease the segmental mobility of the chains near the filler particles. This behavior has been observed in other composite systems, and has been explained based on reduced mobility of molecular segments in the vicinity of the filler particulates (Çaykara, 1998).
and in connection with monomer to phosphate ratio (1:1–5:1, Fig. 9). Temperatures between 25 and 80 °C were taken. Higher temperatures could cause vibrations in the solid and the aqueous phase. The decreased consistence due to the vibrations in the solid phase creates gaps, which allows the migration of the radioisotopes out of this phase. This effect can be compressed by the use of higher monomer to phosphate ratios (more than 4:1) and higher dose rates (higher than 10.5 kGy/h). 3.3. Effect of irradiation dose
3.1.3. FTIR Spectroscopy and X-ray photoelectron spectroscopy (XPS) FTIR and XPS spectra of mineral phosphate and composites were recorded. The composites were exposed to different doses. Fig. 6 shows the FTIR spectra of the phosphate (upper panel), composite prepared with an irradiation dose of 15 kGy (middle panel), and composite prepared with an irradiation dose of 60 kGy (lower panel). The adsorption bands in the upper spectrum are at 3424.9, 1653.6, 1049.1, 800.3, and 591.1 cm1 corresponding to O–H, H–OH, P–O, Ca–O, and PO3 4 respectively. In the spectra of the composites there are no bands corresponding to P–O–C, which should appear at a wavelength around 1456 cm1. There are also no differences in the middle and lower spectrum resulting from different irradiation doses. The recorded XPS spectra (single spectra and scans) do not show any indications of bounding between mineral phosphate and the polymer. The spectra show also no changes depending on the applied doses. Fig. 7 (XPS spectrum) gives the binding energy of the of 2p binding of phosphorus. Its obviously that the there is no change in the binding energy between mineral phosphate and the phosphate–polymer-composite, which means that the phosphate play only the role of a filler. 3.2. Effect of temperature The effect of temperature has been studied in two experiment series, in connection with dose rate (3.8, 7, 10.5, 15 kGy/h, Fig. 8)
Increasing the irradiation dose leads during the polymerization process to an increase in the polymerization conversion. After a total conversion, the following could take place: Crosslinking, which leads to smaller pore size and decreasing the leaching/mobility of elements. Degradation of polymer chains, which allow higher leaching/ migration of species to the solution. 3.3.1. Impact of irradiation dose on time dependence Fig. 10 shows the element ratios of the investigated elements in the aqueous phase as a function of contact time of the phases. Strontium and europium do not show any tendency to migrate into the liquid phase, even after more than three months. Moreover, there is no effect of the applied dose on the migration of these elements. The strontium ratio in the solid phase rose up from about 15% to 100% in comparison with mineral phosphate. The equilibrium of cesium is reached in about 2 h. It’s ratio in the liquid phase after equilibrium is 5%. 3.3.2. Impact of irradiation dose on pH dependence Fig. 11 shows the element ratios in the aqueous phase as a function of irradiation doses for various pH values. The retention of strontium and europium is 100%, and that of cesium is
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100 Dose 20 kGy, Phos./Mon. 1/1 Dose rate 10.5 kGy, pH 8, t 24 h Eu Sr Cs
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Dose 20 kGy, Phos./Mon. 1/2 Dose rate 10.5 kGy, pH 8, t 24 h Eu Sr Cs
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Dw [%]
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T [ C] Fig. 9. Effect of temperature on the fraction of Eu, Cs, and Sr in the liquid phase for various monomer to phosphate ratios.
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Fig. 10. Fraction of Cs, Eu, and Sr in the liquid phase as a function of time for various doses.
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t =24, pH 4, T 25 C Dose rae 10.5 kGy/h Eu Sr Cs
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Fig. 11. Fraction of Cs, Eu, and Sr in the liquid phase as a function of the applied dose for various pH values.
about 94%. The pH value does not show any effect on the retention of the investigated elements. Changing of pH does not lead to changes of cesium speciation (Alhassanieh, 2009), which
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explain its behavior. Higher doses cause crosslinking, which leads to smaller pore size and decreasing the leaching/mobility of cesium.
50 25
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Fig. 12. Fraction of Eu, Cs, and Sr in the liquid phase as a function of calcium concentration for various doses.
1
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3.3.3. Impact of irradiation dose on the effect of concurrent element Changing the concentration of possible concurrent elements (e.g. calcium) in the aqueous phase leads usually to shifting of equilibriums in the liquid phase and consequently to exchange phenomena between the phases, which causes higher isotope ratios in the liquid phase and as a result less retention (Fig. 12). Taking the effect of irradiation dose in consideration, we found that possible crosslinking between polymer chains at higher doses decrease the effect of the concurrent element.
3.4. Effect of dose rate Generally, high dose rates cause lower molecular weights and network structure could be built, which leads to small pore sizes in polymer and consequently the retention possibilities in the composite should increase. Four different dose rates (3.8, 6, 10.5, and 15 kGy/h) were applied. The total dose in all cases was 15 kGy. Strontium and europium reside in all cases in the solid phase, even in the case of a dose rate about 3.8 kGy/h, in which the polymerization was not completed after a total dose of 20 kGy. The cesium ratio in the liquid phase become to a minimum by a dose rate of 10.5 kGy/h and it does not change by increasing the dose rate (Fig. 13).
The element ratios were investigated as a function of monomer to phosphate ratio. Fig. 14 shows the element ratios in the liquid phase as a function of monomer to phosphate ratio. High monomer to phosphate ratios lead to encapsulation of the phosphate including the radioisotopes, and consequently to better retention.
100
Dw [%]
t 24 h, Dose 20 kGy mon: phos 1:1, pH 8.2 Eu Sr Cs
50 25 0 2
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6
8
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12
Dose rate [kGy/h]
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16
Fig. 13. Fraction of Eu, Cs, and Sr in the liquid phase as a function of dose rate.
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Dw [%]
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t 24 h, Dose 10.5 kGy Dose rate 15 kGy, pH 8.2 Eu Sr Cs
60 40 20 0 1
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3
Composites have been prepared from natural phosphate and methyl methacrylate using gamma irradiation. The conversion of polymerization was about 97% by exposure of the samples to a dose of 12 kGy. Also the glass transition temperatures have been determined for the pure polymer and composites prepared at the same irradiation dose. The retention of cesium, strontium and europium in the composites is quantitative under certain conditions (polymer to phosphate ratios more than 3:1, dose rates more than 10.5 kGy/h, and doses about 60 kGy). Contact time and pH have not any effect on the retention probability. Higher doses, dose rates, and monomer to phosphate ratios lead to better retention, while higher temperatures cause higher migration ratios. This temperature effect can be compensated by applying higher irradiation doses and dose rates. Acknowledgments The authors would like to thank Prof. Dr. I. Othman (Director General of AECS) and Prof. Dr. T. Yassin (Head of chemistry department in AECS) for their encouragement. Our thanks are extended to Dr. O. Mrad, Ms. L. Stas, M. Soakia, A. Aqiel, H. Koussa, A. Mougrabeya, and S. Shashit for their efforts during the experiments. References
3.5. Effect of monomer to phosphate ratio
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4. Conclusion
4
mon. : phos. ratio
5
Fig. 14. Fraction of Eu, Cs, and Sr in the liquid phase as a function of monomer to phosphate ratio.
Abbas, M., 1987. Geochemie de l’uranium des phosphorites des Palmyrides Centrals Syrie, These Sci., Louis Pasteur U., Strasbourg, France, 166 pp. Abbas, M., Hyder, M., 1982. Syrian Phosphate and its Radioactive Materials. AECS G/ RSS 21. Ajji, Z., Alkassiri, H., 2003. Preparation of gypsum/polymer/composites using Gamma radiation. In: Proceedings of the Symposium on Radiation Technology in Emerging Industrial Applications, Beijing, China, 6–10 November 2000, pp. 41–45. Ajji, Z., Alhassanieh, O., 2011. Preparation of poly(methyl acrylate)/phosphate/ composites and its possible use as storage medium for radioactive isotopes. J. Radioanal. Nucl. Chem. 287, 69–75. Alhassanieh, O., 2009. Element Speciation and Element Correlations in Groundwater of the Southern and Eastern Area of Syria. Report on a Scientific Study, AECSCnRSS 842. Alhassanieh, O., Ajji, Z., Alkourdi, H., Haloum, D., 2011. Migration of strontium, cesium, and europium from poly(butyl acrylate)/phosphate/composites prepared using gamma radiation. Appl. Rad. Isotopes 69, 448–454. Asfahani, J., Abdul-Hadi, A., 2001. Geophysical natural c-ray well logging and spectrometric signatures of south AL-Abter phosphatic deposits in Syria. Appl. Rad. Isotopes 54, 543–549. Çaykara, T., Gueven, O., 1998a. Effect of preparation methods on the thermal properties of ploy(acrylic acid)/alumina composites. Polym. Compos. 19, 193– 197. Çaykara, T., Gueven, O., 1998b. The effect of preparation methods on the thermal properties of ploy(acrylic acid)/silica composites. J. Appl. Polym. Sci. 70, 891–895. Çaykara, T., Gueven, O., 1999. Kinetic analysis of the radiation induced polymerization of an acrylic acid-silica system. Eur. Polym. J. 35, 113–119. Çaykara, T., Eroglu, M.S., Gueven, O., 1999. Thermal and oxidative degradation of vinyl triethoxy silane-methyl methacrylate copolymers. Polym. Degrad. Stab. 63, 65–70. Donnet, J.B., Vidal, A., 1986. Carbon black: surface properties and interactions within elastomers. In: Abe, A., Albertsson, A.C., Duncan, R., Dusek, K., de Jeu, W.H., Kausch, H.H., Kobayashi, S., Lee, K.S., Leibler, L., Long, T.E., Manners, I., Möller, M., Nuyken, O., Terentjev, E.M., Voit, B., Wegner, G., Wiesner, U. (Eds.), Advances in Polymer Science. Springer-Verlag, Berlin, pp. 103–110. Edwards, D.C., 1990. Polymer-filler interaction in rubber reinforcement. J. Mater. Sci. 25, 4175–4185. Ghafar, M., Abdul-Hadi, A., Alhassanieh, O., 2002. Distribution of some elements in a solid-aqueous system: mineral phosphate in contact with groundwater. J. Radioanal. Nucl. Chem. 254, 159–163. Guth, E., 1945. Theory of filler reinforcement. J. Appl. Phys. 16, 20–25. Kiji, J., Konishi, H., Taninaka, T., Okano, T., Yamashita, S., Kohojiya, S., 1983. Calcium carbonate modified with 1,2-polybutadiene. A potential reinforcing filler for synthetic rubber. Angew. Makromol. Chem. 111, 53–62. Mathur, K.K., Greenzweig, J.E., 1978. Effect of surface area and surface treatment of calcium carbonate fillers on the performance of calendered vinyls. Plastic Eng. 34, 53–62. Papirer, E., Schultz, E., Turchi, C., 1984. Surface properties of a calcium carbonate filler treated with stearic acid. Eur. Polym. J. 20, 1155–1162. Rehner, J., 1943. Theory of filler reinforcement in natural and synthetic. The stress in and about particles. J. Appl. Phys. 14, 638–645.
O. Alhassanieh, Z. Ajji / Annals of Nuclear Energy 44 (2012) 50–57 Shaltout, N.A., Abou-Zeid, M.M., Moustafa, M.H., El-Miligy, A.A., 2002. Effect of gamma irradiation and degree of loading of carbon black on the properties of styrene–butadiene rubber. Arab. J. Nucl. Sci. Appl. 35, 25–35. Sharma, Y.N., Patel, R.D., Dhimmar, I.H., Bhardwaj, I.S., 1982. Studies of the effect of titanate coupling agent on the performance of polypropylene–calcium carbonate composite. J. Appl. Polym. Sci. 27, 4669–4686.
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Takriti, S., Abdul-Hadi, A., 1998. Determination of 234U/238U activity ratios in syrian phosphates. J. Radioanal. Nucl. Chem. 230, 299–301. Yang, H., Tang, H., Piao, J., Chen-Xinfang, C., 1993. The stabilization effect of radiation crosslinking on positive temperature coefficient performances of carbon black–polymer composites. Rad. Phys. Chem. 42, 135–137.