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Multicomponent red mud-polyester composites for neutron shielding application
Accepted Manuscript Multicomponent red mud-polyester composites for neutron shielding application Sapana Guru, Sudhir Sitaram Amritphale, Jyotishankar Mishra, Smita Joshi PII:
S0254-0584(18)31077-0
DOI:
https://doi.org/10.1016/j.matchemphys.2018.12.039
Reference:
MAC 21202
To appear in:
Materials Chemistry and Physics
Received Date: 22 May 2018 Revised Date:
11 December 2018
Accepted Date: 14 December 2018
Please cite this article as: Sapana Guru, Sudhir Sitaram Amritphale, Jyotishankar Mishra, Smita Joshi, Multicomponent red mud-polyester composites for neutron shielding application, Materials Chemistry and Physics (2018), doi: 10.1016/j.matchemphys.2018.12.039 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
MULTICOMPONENT RED MUD-POLYESTER COMPOSITES FOR NEUTRON SHIELDING APPLICATION Sapana Guru1*, Sudhir Sitaram Amritphale1, Jyotishankar Mishra2 and Smita Joshi3 1
Council of Scientific and Industrial Research- Advanced Materials and Processes Research Institute,
Hoshangabad Road, Bhopal (M.P.) 462064, India 2
Institute for Plasma Research, Bhat, Gandhinagar, Gujrat.
3
SNGGPG College Bhopal India
*email (corresponding author): [email protected] Phone: 919425375501 Key Words: Red mud, Polyester composites, Neutron shielding, Characterization.
Abstract Novel polyester composites for neutron shielding have been formulated by using processed red mud which is an aluminium industry waste and pure phase material. A method for making neutron shielding materials utilizing processed red mud with boric acid with polyester matrix has been developed. The developed neutron shielding materials have been studied for fast and thermal neutron shielding by using 12 Ci Am-Be radiation source. The total macroscopic cross section of red mud-polyester composites has been calculated and compared in this paper. Developed composites were characterised by X-ray powder diffraction, SEM, FTIR, and thermal analysis etc. Mechanical properties were also measured.
1.INTRODUCTION Nuclear equipment and instrumentations make a considerable use of neutron shielding objects [1]. To protect people and the surroundings from the injurious effects of radiation is very significant work at present. The use of higher accumulated doses of radiation is associated with adverse effects [2, 3] such as killing the tissues of animal bodies. Shielding materials are broadly used for collimating beam lines, shielding detectors and protecting the environment where analysts are working [1].
1
Neutron emission is a kind of ionizing radiation which consists of free neutrons. Since the interaction of neutrons with molecules in the body can cause breaking of molecules and atoms, and can also initiate a reaction which accelerates to other forms of radiations [2-4], these radiations are very hazardous to human body. Higher surface area atom is able to attenuate high speed neutrons and give a better absorption. A hydrogen containing materials is generally used to attenuate neutrons, since it has the capacity to both scatters and slow down the neutrons [5-8].This can be happened by inelastic scattering with heavy elements, such as iron, and by elastic scattering with light nuclei resulting the slow neutrons which are then easily captured in (n,γ ) reactions. Conventionally Cadmium and Boron are used for thermal neutron absorption with the energy 0.025eV. Cadmium has large neutron capture cross section 20.6 kb. It is generally used for neutron shielding but has disadvantage that it produces gamma rays after neutron capture which may require additional gamma ray shielding.The absorption cross section of cadmium also drastically decreases when energy of neutron increases. [1,9-11].Lithium (6Li) is also used as a thermal neutron absorber and it has 0.941 kb thermal neutron capture cross section but naturally abundance of isotope is only 7.5% [12]. An effective neutron shielding material is a combination of low atomic no. elements (i.e. hydrogen) to moderate neutrons and thermal neutron absorbers into single homogeneous composition. These requirements can be satisfied by using composites [13-14]. In this work, we present the development, characterization and shielding properties of a multicomponent composites neutron shielding material in which the red mud from aluminiumindustry waste was used as filler material. Red mud is a waste discarded during the aluminium production from bauxite [15-18].It is mainly multicomponent material and consists of both the major and minor elements. Red mud is basically a mixture of a variety of minerals and has wide range of combinations of Fe2O3 (20-60%), Al2O3 (1030%), SiO2 (2-20%), Na2O (2-10%), CaO (2- 8%), TiO2 (2-10%) [19-24]. 2
Red mud can be used as cheap filler material in polymers for developing light weight, low cost and high strength composites. Red mud has been used in making of gamma shielding materials as resource materials [18, 25-26]. The development of composite for shielding by using red mud containing multi elements has benefited in obtaining highly efficient composite shielding materials having ability of simultaneously and synergistically shielding of neutron. To the best of our knowledge this is the first report where utilization of red mud reinforced with polyester has been investigated in making neutron shielding composites.
2. EXPERIMENTAL 2.1 (a) Material: The red mud obtained from Hindustan Aluminium Company (HINDALCO) Renukoot India was used. Chemicals Fe2O3 (GR, Rankem India), TiO2 (LR, Ranbaxy India), SiO2 (LR,
CDH
India),
Al2O3
(LR,
Merck
India),
B2O3
(GR,
Merck
India)
Ethylene glycol Pro analysis ( Merck India) and Unsaturated Polyester (Satyen Polymers, India), all chemicals were used as received. In the Present Study three raw materials were developed i) Neutron Shielding 1 (NS1): Red Mud homogenised with boric acid without heating. ii) Neutron Shielding 2 (NS2): Red Mud homogenized with boric acid and heat treatment. iii) Neutron Shielding 3 (NS3): Simulated red mud with pure chemical components that contained in the red mud from industrial waste. 2.1 (b) Neutron shielding polyester composite developed i) Neutron Shielding Polyester Composite 1 (NSPC 1): NS1 composited containing 30 wt% polyester. ii) Neutron Shielding Polyester Composite 2 (NSPC 2): NS2 composited containing 30 wt% polyester. iii) Neutron Shielding Polyester Composite 3 (NSPC 3): NS3 composited containing 30 wt% polyester. 3
2.2 Composite casting: Composites were fabricated by using different filler materials which were reinforced with unsaturated isophthalic polyester resin (density 1.32 g/cm3). Two percent cobalt nephthalate (as accelerator) and MEKP (methyl ethyl ketone peroxide) as hardener was mixed in resin. Composites of three different fillers with 30% resin were made. Gel time of the composites was 20 to 25 mins. Composites were left at room temperature for about 24 hours for curing. After curing characterisation of the composites were done. 2.3 CHARACTERISATION The chemical composition of red mud NS1, NS2 and NS3 was determined by standard wet chemical analysis method [27]. Identification of the phases present in the synthesized material was carried out using X-ray diffraction spectrometer (Bruker – Model D-8) using Cu Kα radiation (λ=1.54 nm), operated at 40 kV and 40 mA at a scan rate of 1˚ 2θ/s in the range 2θ = 10 -70˚ and comparing the interplanar distances and intensity values with those of the corresponding standard peaks using JCPDS. The SEM micrographs of surfaces of samples were taking using a Scanning Electron Microscope (Make JEOL, Japan and M/s OXFORD, UK Model JSM5600/LINK ISIS300) resolution 3.5 nm/138 eV. The SEM has a magnification limit of 0.1 million times. The experimental procedure for the measurement of neutron shielding shown in Fig.1. Fast neutrons are generated using 12 Ci Am-Be neutron source and for thermal neutrons, neutron Howitzer was used along with radiation source 12 Ci Am-Be.
4
Fig. 1: Schematic presentation of fast (left) and thermal (right) neutron shielding measurement.
IR spectra were recorded between 500 and 4000 cm−1 using Bruker alpha Fourier transform infrared spectrometer. The density was measured by water immersion techniques. The density ρ of the sample can be calculated using the following equation ρ = m1ρL/(m1-m2)
(2.4.1)
Where, m1 is sample weight in the air, m2 is sample weight in the water, ρL is density of pure water which is 0.99821g/cm3 at 200C Tensile and Flexural strength was tested with UTM Instron H25KT. Impact test on different specimen carried out on Impact Izod Machine Avery Birmingham. Machine type was 6702 model no. E-62498, Capacity 140 kg/cm and Striking velocity 2.44 m/s. Test were done as per ASTM D 256 using impact tester. Microhardness determination is done using a Leica Germany VMHT 30A microhardness tester. Thermal gravimetric analysis (TGA) was performed by heating the sample at a heating rate of 10 °C/min from 50 to 700 °C on Toledo TGA/DSC-1 of Mettler Company. Thermal conductivity, tested by Lee Disk Method and the readings was taken in every 10 minutes from the temperature range 30°c to 1000C.Then the Thermal-Conductivity is calculated by using the formula given below. Here t is the thickness (cm) and T is instant temperature.
5
(2.4.2)
3. RESULTS AND DISCUSSION 3.1 Analysis of Raw Materials NS1, NS2 and NS3. The Chemical composition of Red mud, NS1, NS2 and NS3 were estimated by standard wet chemical analysis [27]. The chemical analysis showed that different oxide percentage present as follows: Red Mud-Fe2O3 42.0%, Al2O3 24.78 % SiO2 4.61%, B2O3 1.32% TiO2 5.5%. The loss on ignition (LOI) was found to be 13%. NS1- Fe2O3 12.5%, Al2O3 5.45% SiO2 1.25%,B2O3 39.28% TiO2 1.62% The loss on ignition (LOI) was found to be 36% and Boron 13%, NS2- Fe2O3 8.67%, Al2O3 8.41% SiO2 3.23%,B2O3 38.34% TiO2 5.66% LOI 32.85% Boron 12.9%, and for NS3-Fe2O3 13.7%, Al2O3 5.38% SiO2 3.1%,B2O3 35.5% TiO2 12% LOI 18% Boron 11.7%,
3.2 XRD of raw materials and neutron shielding composites: X ray Diffraction pattern of precursor, raw materials and shielding composites are shown in Fig. 2 and Fig. 3. Identification of different phases present in the red mud as such, NS1, NS2, NS3 (Fig. 2) and shielding composites (Fig. 3) were carried out by interplanar spacing (d-values) comparison with reported substance listed in the JCPDS [28]. X ray powder diffraction analysis of materials showed that the presence of different mineralogical phases which act as a precursor materials for obtaining various shielding phases i.e. hematite obtained by iron oxide, aluminium silicate phases due to presence of aluminium and silica respectively. The results of XRD of red mud, NS1, NS2 and NS3 are given in Fig. 2. From the results it is clearly shown that most of the phases present in the red mud and NS1 were similar. Some new phases were identified in the modified neutron shielding material. In NS2 composition iron borate hydrate, 6
calcium aluminate oxide and iron borate phases were found and in NS3 Iron borate, astrophyllite and aluminium silicate phases were identified. It can be seen from the XRD graphs (Fig. 2 and Fig. 3) that as such phases of modified raw materials present in neutron shielding composites.
Fig. 2: XRD spectra of Red Mud, NS1, NS2 and NS3.
7
Fig. 3: XRD spectra of Neat Polyester, NSPC 1, NSPC 2 and NSPC 3.
3.3 SEM study: Modified raw materials and neutron shielding polyester composites were characterised by SEM as shown in Fig. 4 (a-f).The SEM analysis from Fig. 4 (a-c) modified raw materials NS1, NS2 and NS3 the scattered morphology texture can be observed i.e. presence of aluminium silicate with anatase and rutile, spherical hematite etc. It reveals from the micrographs Fig. 4 (d-f) for NSPC 1, NSPC 2 and NSPC 3 respectively that due to presence of different morphology in the filler materials leads to formation of highly compacted, dense and homogeneous shielding composite.
8
NS1 (a)
NSPC 1 (d)
NS2 (b)
NSPC 2 (e)
NS3 (c)
NSPC 3 (f)
Fig. 4 : SEM images of NS1, NS2, NS3, NSPC 1, NSPC 2 and NSPC 3 with the same magnification. The locations where the arrows pointed indicated: 1-anatase, 2-spherical hematite, 3-hexagonal cancrinite and 4-rutile respectively.
3.4 FTIR Analysis : The nature of chemical bonds of shielding composites was investigated by FTIR spectroscopy. The FTIR spectra for neat polyester and polyester composites, NSPC 1 NSPC 2 and NSPC 3 are shown in Fig. 5. The characteristic peaks of developed composites were characterized by FTIR spectroscopy. The vibration band of polyester for hydroxyl stretching vibration was observed at 3565 cm-1 while for the boric acid modified polyester composites NSPC 1, NSPC 2 hydroxyl stretching occurred at same frequency 3198 cm-1 and for NSPC 3 it was found at 3128 cm-1. A red shift has been observed in hydroxyl stretching vibration which may be due to hydroxyl groups’ disappearance and hydrogen bonding formation between polymer and OH bond. The alkyl stretching band of HCH for neat polyester, NSPC 1, NSPC 2 and NSPC 3 were found at 1516 cm-1, 1510 cm-1,1508 cm-1 and 1457cm1
respectively and red shift observed due to the interaction of filler with the polymer matrix.1714 cm-
9
1
,1740cm-1,1739cm-1 and 1701 cm-1 peaks were attributed to C-O stretching vibrations for neat
polyester, NSPC 1, NSPC 2 and NSPC 3 respectively. The peak at 993 cm-1 in case of raw red mud could be attributed to Si-O stretching vibration and the same peak observed for NSPC 1 , NSPC 2 and NSPC 3 1061, 1062 and 998 cm-1 respectively. In the characteristic peak of Si-O due to polymer-filler interaction a blue shift observed. The peak at 705 cm-1 in case of NSPC-2 observed which could be attributed to FeBO3 formation in the sample. Stretching B-O bond were found at 1188 cm-1, 1189 and 989 cm-1 for NSPC 1, NSPC 2 and NSPC 3. Peak 472 cm-1 and 542 cm-1 attributed to Fe-O in NSPC 1, NSPC 2 respectively and no peak was observed in NSPC 3[29].
Fig. 5: IR Spectra of Polyester, NSPC 1, NSPC 2 and NSPC 3.
10
3.5 Measurement of neutron shielding : During developing a neutron shielding material, absorption of ionizing radiation in the developed material is a practical concern. In shielding materials, intensity of fast neutrons gets reduced, they became thermalized and absorbed by neutron absorbing elements and generally characterise by the parameters the effective removal cross-sections and the macroscopic thermal neutron cross section. Neutron interacts with the nuclei of atoms of absorbing material either by scattering or absorption. It is described by total microscopic cross section (t) which is sum of microscopic cross section scattering (s) and the microscopic cross section absorption (a). The no. of nuclei within this environment also added to the shielding characteristics, the total macroscopic cross section (t) expressed as: t = (NA/A) *t
(3.5.1)
Where is the density (g cm-3), NA is Avogadro's number and A is the atomic mass, has the dimensions of the inverse of the length and its unit is cm-1. When neutron beam passes through a matter, it is shielded due to absorption and scattering. The expression of neutrons in matter as follows: I = I0exp[-t x]
(3.5.2)
Where I0 and I are respectively the intensities of neutrons before and after absorption respectively, x (cm) is the thickness of the material medium.
Fast neutrons has energy level in the range of MeV, in this energy range absorption cross section is low as comparison with the scattering cross-section. These fast neutrons cannot be absorbed as such, but they slowed down during the passage and get absorbed by heavy elements when their energy in range of the thermal energy (0.025 eV). The neutron adsorption characteristics of the three different materials developed (NSPC 1, NSPC 2 and NSPC 3) are studied using fast neutrons and thermal neutrons. The required thickness of 11
shielding material where one half of the incident neutrons have been attenuated is termed as half value layer (HVL). Similarly the thickness of the shielding material where one tenth of its incident neutrons have been attenuated is termed as tenth value layer (TVL). From equation 3.5.2, these are defined as HVL = 0.693 / t
(3.5.3)
TVL = 2.3026/t
(3.5.4)
The experimental procedure (Fig. 1) followed for t measurement is described as follows. Fast neutrons are generated using 12 Ci Am-Be neutron source. For fast neutron detection a precision long counter (PLC) was used. Thermal neutron fluence rate of 1000n/cm2/sec at thermal neutron detector location was produced by using neutron Howitzer and 12Ci Am-Be neutron source. BF3 thermal neutron detector with sensitivity of 10 counts per centimetre square per second (n/cm2/sec) was used for the measurement. Howitzer and BF3 detector was arranged in narrow geometry. The attenuation factor was measured as the ratio of count rates obtained without and with sample in between the source and detector. The t was measured using equation 3.5.2 and the results obtained from the experiment for fast neutron and thermal neutron are tabulated in table 1. Thermal neutron absorption is determined mainly by the type of material and its atomic number density. The results obtained from the thermal neutron irradiation experiment for developed neutron shielding polyester composites is shown in Fig. 6. From the Fig. 6 it can be seen red modified polyester composites i.e NSPC 1, NSPC 2 have better neutron absorption capabilities and shows better total macroscopic cross section (Σt) and mass removal cross section (Σt/ρ) than NSPC 3.
12
t [cm-1],t/[ cm2/gm]
5.00 4.00 3.00 2.00 1.00 0.00
Fig. 6: Σt of developed neutron shielding polyester composites for thermal neutrons.
Table 1: Measurements of neutron shielding properties
Sample
X [cm] [gm/cc]
I0/I
Fast neutron shielding NSPC-1 1.35 1.63 1.13 NSPC-2 1.3 1.73 1.13 NSPC-3 1.65 1.79 1.16 Thermal neutron shielding NSPC-1 1.35 1.63 409.18 NSPC-2 1.3 1.73 306.89 NSPC-3 1.65 1.79 603.00
t [cm-1]
t/ [cm2/gm]
0.091 ±0.002 0.094±0.005 0.090±0.005
0.0555 0.0543 0.0503
4.455±0.002 4.405±0.004 3.879±0.005
2.7331 2.5462 2.1676
3.6 Density measurement: Water immersion technique was used to determine the density of the composite materials. The densities of the composites NSPC 1, NSPC 2 and NSPC 3 is found to be increased as compare to neat polyester (1.35 g/cm3). The densities of composites were found to be 1.63 g/cm3 1.73 g/cm3 and 1.79 g/cm3 respectively.
13
3.7 Mechanical measurement: Dog-bone (Fig. 7) types of samples were used for tensile test. At both the ends of specimen uniaxial load is applied. The ASTM D-638M91 standard test method was used and the length of the test section should be 180 mm [30]. According to the results it can be observed tensile strength of the composite samples decreases with incorporation of filler content. The tensile strength of neat polyester is 174 MPa and values for neutron shielding composites NSPC 1, NSPC 2 and for NSPC 3 were found to be 13 MPa, 16 MPa and 14 MPa respectively. The reduced tensile properties may be due to weak interface chemical reaction between filler and matrix and non uniform distribution of tensile stress. Flexural Properties of the samples were tested according to ASTM standard D-790-03 [31]. During bending flexural strength is the maximum tensile stress before the breaking point. The three-point bend test is conducted an all the composite samples in the universal testing machine Instron. Span length 180 mm (Fig. 7) and cross head speed of 10 mm/min were maintained. The flexural strength values for the samples NSPC 1, NSPC 2 and for NSPC 3 were found to be 31 MPa, 15.5 MPa and 24 MPa respectively. In addition, the flexural strength of the wall tiles should be higher than 15 MPa (for thickness < 7.5 mm) and 12 MPa (for thickness > 7.5 mm), according to Brazilian standard NBR 138182.
NSPC 1
NSPC 2
NSPC 3
Fig. 7: Specimen for Mechanical Testing (Tensile and Flexural)
14
Impact properties (Fig. 8) of the composites were carried out with low velocity instrument impact test. The test was done as per ASTM D 256 using impact tester [32]. The strength of NSPC 1, NSPC 2 and for NSPC 3 materials is found to be 19.79 J/cm2, 59.58 J/cm2 and 46.72 J/cm2 respectively.
Fig. 8: Tested Specimen of Impact strength
The microhardness test was done to determine penetration resistance of the composites. Composites were tested at Vickers scale and values for NSPC 1, NSPC 2 and NSPC 3 are found to be 47, 42 and 46 respectively. The test was done as per ASTM-E-384.
3.8 Thermal Analysis: Thermal stability of shielding composites was measured by thermogravimetric method. The TGA curve (Fig. 9) shows a total weight loss of shielding composites were found to be 50 %, 42% and 44% for NSPC 1, NSPC 2 and NSPC 3 respectively. At the first stage, the weight loss at 200oC in comparison to ambient temperature is found to be 18%, 20% and 6% for NSPC 1, NSPC 2 and NSPC 3 respectively. It can be ascribed to the presence of adsorbed water and de-hydroxylation reaction (2OH- 2O2- + H2O) of structural OH in the iron oxide. At second stage between 200 – 400 0C weight losses is due to polyester degradation and the values were found to be 45% ,41% and 38% for NSPC 1, NSPC 2 and NSPC 3, respectively. Finally at 7000C, NSPC 1, NSPC 2 and NSPC 3 have residue 49%, 42% and 44% respectively.
15
Fig. 9: TGA thermogram of NSPC 1, NSPC 2 and NSPC 3.
Differential scanning calorimetry of the samples was done and all the composite materials were found to have higher peak than glass transition temperature of polyester. It can be explained due to bonds of polymer chain with filler which inhibits the particle motions of polymer chain. The endothermic peaks exhibited by composites are NSPC 1 1140C, NSPC 2 1200C and 1530C and for NSPC 3 at 4270C respectively. The effective thermal conductivity was experimentally obtained using Lee Disk method with circular disc samples of 110 mm in diameter and 3 ~5 mm in thickness. It is noticed that experimental results are close to each other. It has been found that thermal conductivity of experimental study of all three composites is increased (neat polyester 0.22 at 1000C) with adding filler content. NSPC 1 0.47 W/m k, NSPC 2 0.45 W/m k and NSPC 3 0.48 W/m k. The materials should have low thermal conductivity but sufficient to remove heat from the transported elements such as irradiated fuel elements [6].
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4. CONCLUSION Analytical and experimental investigation on neutron shielding composites showed the compatibility of modified red mud with polyester resin is fairly good. The industrial waste can be used as potential filler materials to produce cost effective neutron shielding composites. The studies optimise the multicomponent lightweight and high temperature sustaining polyester composites for neutron shielding. It is evident from the studies that processed red mud containing polyester composites (NSPC 1 and NSPC 2) has better attenuation coefficient values than composite which contains simulated red mud with pure chemical components (NSPC 3). The X-ray powder diffraction studies of neutron shielding material confirmed the presence of new shielding phases (NSPC 2 borate hydrate, calcium aluminate oxide, iron borate and NSPC 3 astrophyllite, aluminium silicate, iron borate). The morphological studies performed using SEM revealed that all the polyester composites were compacted and dense. Mechanical properties of the material confirm that composites having strength equal to that of wall tile. Shielding test of samples verified the correct manufacturing process. In future this research can be applied to the practices in nuclear science and technology.
ACKNOWLEDGEMENT The authors gratefully acknowledge the financial support of Board of Research in Nuclear Sciences sanction No: 2007/36/54-BRNS/2548.Authors are grateful to Director CSIR-AMPRI Bhopal for providing necessary institutional facilities and encouragement. We acknowledge thanks to Permali Wallace (M.P.) India for analysis of samples.
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ACCEPTED MANUSCRIPT
Highlights:
Modified Red Mud polyester composites for neutron shielding are made and characterized.
•
Neutron shielding properties of the developed composites has been investigated and calculated.
•
Prospects of modified red mud polyester composites are discussed.
AC C
EP
TE D
M AN U
SC
RI PT
•
S0254-0584(18)31077-0
DOI:
https://doi.org/10.1016/j.matchemphys.2018.12.039
Reference:
MAC 21202
To appear in:
Materials Chemistry and Physics
Received Date: 22 May 2018 Revised Date:
11 December 2018
Accepted Date: 14 December 2018
Please cite this article as: Sapana Guru, Sudhir Sitaram Amritphale, Jyotishankar Mishra, Smita Joshi, Multicomponent red mud-polyester composites for neutron shielding application, Materials Chemistry and Physics (2018), doi: 10.1016/j.matchemphys.2018.12.039 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
MULTICOMPONENT RED MUD-POLYESTER COMPOSITES FOR NEUTRON SHIELDING APPLICATION Sapana Guru1*, Sudhir Sitaram Amritphale1, Jyotishankar Mishra2 and Smita Joshi3 1
Council of Scientific and Industrial Research- Advanced Materials and Processes Research Institute,
Hoshangabad Road, Bhopal (M.P.) 462064, India 2
Institute for Plasma Research, Bhat, Gandhinagar, Gujrat.
3
SNGGPG College Bhopal India
*email (corresponding author): [email protected] Phone: 919425375501 Key Words: Red mud, Polyester composites, Neutron shielding, Characterization.
Abstract Novel polyester composites for neutron shielding have been formulated by using processed red mud which is an aluminium industry waste and pure phase material. A method for making neutron shielding materials utilizing processed red mud with boric acid with polyester matrix has been developed. The developed neutron shielding materials have been studied for fast and thermal neutron shielding by using 12 Ci Am-Be radiation source. The total macroscopic cross section of red mud-polyester composites has been calculated and compared in this paper. Developed composites were characterised by X-ray powder diffraction, SEM, FTIR, and thermal analysis etc. Mechanical properties were also measured.
1.INTRODUCTION Nuclear equipment and instrumentations make a considerable use of neutron shielding objects [1]. To protect people and the surroundings from the injurious effects of radiation is very significant work at present. The use of higher accumulated doses of radiation is associated with adverse effects [2, 3] such as killing the tissues of animal bodies. Shielding materials are broadly used for collimating beam lines, shielding detectors and protecting the environment where analysts are working [1].
1
Neutron emission is a kind of ionizing radiation which consists of free neutrons. Since the interaction of neutrons with molecules in the body can cause breaking of molecules and atoms, and can also initiate a reaction which accelerates to other forms of radiations [2-4], these radiations are very hazardous to human body. Higher surface area atom is able to attenuate high speed neutrons and give a better absorption. A hydrogen containing materials is generally used to attenuate neutrons, since it has the capacity to both scatters and slow down the neutrons [5-8].This can be happened by inelastic scattering with heavy elements, such as iron, and by elastic scattering with light nuclei resulting the slow neutrons which are then easily captured in (n,γ ) reactions. Conventionally Cadmium and Boron are used for thermal neutron absorption with the energy 0.025eV. Cadmium has large neutron capture cross section 20.6 kb. It is generally used for neutron shielding but has disadvantage that it produces gamma rays after neutron capture which may require additional gamma ray shielding.The absorption cross section of cadmium also drastically decreases when energy of neutron increases. [1,9-11].Lithium (6Li) is also used as a thermal neutron absorber and it has 0.941 kb thermal neutron capture cross section but naturally abundance of isotope is only 7.5% [12]. An effective neutron shielding material is a combination of low atomic no. elements (i.e. hydrogen) to moderate neutrons and thermal neutron absorbers into single homogeneous composition. These requirements can be satisfied by using composites [13-14]. In this work, we present the development, characterization and shielding properties of a multicomponent composites neutron shielding material in which the red mud from aluminiumindustry waste was used as filler material. Red mud is a waste discarded during the aluminium production from bauxite [15-18].It is mainly multicomponent material and consists of both the major and minor elements. Red mud is basically a mixture of a variety of minerals and has wide range of combinations of Fe2O3 (20-60%), Al2O3 (1030%), SiO2 (2-20%), Na2O (2-10%), CaO (2- 8%), TiO2 (2-10%) [19-24]. 2
Red mud can be used as cheap filler material in polymers for developing light weight, low cost and high strength composites. Red mud has been used in making of gamma shielding materials as resource materials [18, 25-26]. The development of composite for shielding by using red mud containing multi elements has benefited in obtaining highly efficient composite shielding materials having ability of simultaneously and synergistically shielding of neutron. To the best of our knowledge this is the first report where utilization of red mud reinforced with polyester has been investigated in making neutron shielding composites.
2. EXPERIMENTAL 2.1 (a) Material: The red mud obtained from Hindustan Aluminium Company (HINDALCO) Renukoot India was used. Chemicals Fe2O3 (GR, Rankem India), TiO2 (LR, Ranbaxy India), SiO2 (LR,
CDH
India),
Al2O3
(LR,
Merck
India),
B2O3
(GR,
Merck
India)
Ethylene glycol Pro analysis ( Merck India) and Unsaturated Polyester (Satyen Polymers, India), all chemicals were used as received. In the Present Study three raw materials were developed i) Neutron Shielding 1 (NS1): Red Mud homogenised with boric acid without heating. ii) Neutron Shielding 2 (NS2): Red Mud homogenized with boric acid and heat treatment. iii) Neutron Shielding 3 (NS3): Simulated red mud with pure chemical components that contained in the red mud from industrial waste. 2.1 (b) Neutron shielding polyester composite developed i) Neutron Shielding Polyester Composite 1 (NSPC 1): NS1 composited containing 30 wt% polyester. ii) Neutron Shielding Polyester Composite 2 (NSPC 2): NS2 composited containing 30 wt% polyester. iii) Neutron Shielding Polyester Composite 3 (NSPC 3): NS3 composited containing 30 wt% polyester. 3
2.2 Composite casting: Composites were fabricated by using different filler materials which were reinforced with unsaturated isophthalic polyester resin (density 1.32 g/cm3). Two percent cobalt nephthalate (as accelerator) and MEKP (methyl ethyl ketone peroxide) as hardener was mixed in resin. Composites of three different fillers with 30% resin were made. Gel time of the composites was 20 to 25 mins. Composites were left at room temperature for about 24 hours for curing. After curing characterisation of the composites were done. 2.3 CHARACTERISATION The chemical composition of red mud NS1, NS2 and NS3 was determined by standard wet chemical analysis method [27]. Identification of the phases present in the synthesized material was carried out using X-ray diffraction spectrometer (Bruker – Model D-8) using Cu Kα radiation (λ=1.54 nm), operated at 40 kV and 40 mA at a scan rate of 1˚ 2θ/s in the range 2θ = 10 -70˚ and comparing the interplanar distances and intensity values with those of the corresponding standard peaks using JCPDS. The SEM micrographs of surfaces of samples were taking using a Scanning Electron Microscope (Make JEOL, Japan and M/s OXFORD, UK Model JSM5600/LINK ISIS300) resolution 3.5 nm/138 eV. The SEM has a magnification limit of 0.1 million times. The experimental procedure for the measurement of neutron shielding shown in Fig.1. Fast neutrons are generated using 12 Ci Am-Be neutron source and for thermal neutrons, neutron Howitzer was used along with radiation source 12 Ci Am-Be.
4
Fig. 1: Schematic presentation of fast (left) and thermal (right) neutron shielding measurement.
IR spectra were recorded between 500 and 4000 cm−1 using Bruker alpha Fourier transform infrared spectrometer. The density was measured by water immersion techniques. The density ρ of the sample can be calculated using the following equation ρ = m1ρL/(m1-m2)
(2.4.1)
Where, m1 is sample weight in the air, m2 is sample weight in the water, ρL is density of pure water which is 0.99821g/cm3 at 200C Tensile and Flexural strength was tested with UTM Instron H25KT. Impact test on different specimen carried out on Impact Izod Machine Avery Birmingham. Machine type was 6702 model no. E-62498, Capacity 140 kg/cm and Striking velocity 2.44 m/s. Test were done as per ASTM D 256 using impact tester. Microhardness determination is done using a Leica Germany VMHT 30A microhardness tester. Thermal gravimetric analysis (TGA) was performed by heating the sample at a heating rate of 10 °C/min from 50 to 700 °C on Toledo TGA/DSC-1 of Mettler Company. Thermal conductivity, tested by Lee Disk Method and the readings was taken in every 10 minutes from the temperature range 30°c to 1000C.Then the Thermal-Conductivity is calculated by using the formula given below. Here t is the thickness (cm) and T is instant temperature.
5
(2.4.2)
3. RESULTS AND DISCUSSION 3.1 Analysis of Raw Materials NS1, NS2 and NS3. The Chemical composition of Red mud, NS1, NS2 and NS3 were estimated by standard wet chemical analysis [27]. The chemical analysis showed that different oxide percentage present as follows: Red Mud-Fe2O3 42.0%, Al2O3 24.78 % SiO2 4.61%, B2O3 1.32% TiO2 5.5%. The loss on ignition (LOI) was found to be 13%. NS1- Fe2O3 12.5%, Al2O3 5.45% SiO2 1.25%,B2O3 39.28% TiO2 1.62% The loss on ignition (LOI) was found to be 36% and Boron 13%, NS2- Fe2O3 8.67%, Al2O3 8.41% SiO2 3.23%,B2O3 38.34% TiO2 5.66% LOI 32.85% Boron 12.9%, and for NS3-Fe2O3 13.7%, Al2O3 5.38% SiO2 3.1%,B2O3 35.5% TiO2 12% LOI 18% Boron 11.7%,
3.2 XRD of raw materials and neutron shielding composites: X ray Diffraction pattern of precursor, raw materials and shielding composites are shown in Fig. 2 and Fig. 3. Identification of different phases present in the red mud as such, NS1, NS2, NS3 (Fig. 2) and shielding composites (Fig. 3) were carried out by interplanar spacing (d-values) comparison with reported substance listed in the JCPDS [28]. X ray powder diffraction analysis of materials showed that the presence of different mineralogical phases which act as a precursor materials for obtaining various shielding phases i.e. hematite obtained by iron oxide, aluminium silicate phases due to presence of aluminium and silica respectively. The results of XRD of red mud, NS1, NS2 and NS3 are given in Fig. 2. From the results it is clearly shown that most of the phases present in the red mud and NS1 were similar. Some new phases were identified in the modified neutron shielding material. In NS2 composition iron borate hydrate, 6
calcium aluminate oxide and iron borate phases were found and in NS3 Iron borate, astrophyllite and aluminium silicate phases were identified. It can be seen from the XRD graphs (Fig. 2 and Fig. 3) that as such phases of modified raw materials present in neutron shielding composites.
Fig. 2: XRD spectra of Red Mud, NS1, NS2 and NS3.
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Fig. 3: XRD spectra of Neat Polyester, NSPC 1, NSPC 2 and NSPC 3.
3.3 SEM study: Modified raw materials and neutron shielding polyester composites were characterised by SEM as shown in Fig. 4 (a-f).The SEM analysis from Fig. 4 (a-c) modified raw materials NS1, NS2 and NS3 the scattered morphology texture can be observed i.e. presence of aluminium silicate with anatase and rutile, spherical hematite etc. It reveals from the micrographs Fig. 4 (d-f) for NSPC 1, NSPC 2 and NSPC 3 respectively that due to presence of different morphology in the filler materials leads to formation of highly compacted, dense and homogeneous shielding composite.
8
NS1 (a)
NSPC 1 (d)
NS2 (b)
NSPC 2 (e)
NS3 (c)
NSPC 3 (f)
Fig. 4 : SEM images of NS1, NS2, NS3, NSPC 1, NSPC 2 and NSPC 3 with the same magnification. The locations where the arrows pointed indicated: 1-anatase, 2-spherical hematite, 3-hexagonal cancrinite and 4-rutile respectively.
3.4 FTIR Analysis : The nature of chemical bonds of shielding composites was investigated by FTIR spectroscopy. The FTIR spectra for neat polyester and polyester composites, NSPC 1 NSPC 2 and NSPC 3 are shown in Fig. 5. The characteristic peaks of developed composites were characterized by FTIR spectroscopy. The vibration band of polyester for hydroxyl stretching vibration was observed at 3565 cm-1 while for the boric acid modified polyester composites NSPC 1, NSPC 2 hydroxyl stretching occurred at same frequency 3198 cm-1 and for NSPC 3 it was found at 3128 cm-1. A red shift has been observed in hydroxyl stretching vibration which may be due to hydroxyl groups’ disappearance and hydrogen bonding formation between polymer and OH bond. The alkyl stretching band of HCH for neat polyester, NSPC 1, NSPC 2 and NSPC 3 were found at 1516 cm-1, 1510 cm-1,1508 cm-1 and 1457cm1
respectively and red shift observed due to the interaction of filler with the polymer matrix.1714 cm-
9
1
,1740cm-1,1739cm-1 and 1701 cm-1 peaks were attributed to C-O stretching vibrations for neat
polyester, NSPC 1, NSPC 2 and NSPC 3 respectively. The peak at 993 cm-1 in case of raw red mud could be attributed to Si-O stretching vibration and the same peak observed for NSPC 1 , NSPC 2 and NSPC 3 1061, 1062 and 998 cm-1 respectively. In the characteristic peak of Si-O due to polymer-filler interaction a blue shift observed. The peak at 705 cm-1 in case of NSPC-2 observed which could be attributed to FeBO3 formation in the sample. Stretching B-O bond were found at 1188 cm-1, 1189 and 989 cm-1 for NSPC 1, NSPC 2 and NSPC 3. Peak 472 cm-1 and 542 cm-1 attributed to Fe-O in NSPC 1, NSPC 2 respectively and no peak was observed in NSPC 3[29].
Fig. 5: IR Spectra of Polyester, NSPC 1, NSPC 2 and NSPC 3.
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3.5 Measurement of neutron shielding : During developing a neutron shielding material, absorption of ionizing radiation in the developed material is a practical concern. In shielding materials, intensity of fast neutrons gets reduced, they became thermalized and absorbed by neutron absorbing elements and generally characterise by the parameters the effective removal cross-sections and the macroscopic thermal neutron cross section. Neutron interacts with the nuclei of atoms of absorbing material either by scattering or absorption. It is described by total microscopic cross section (t) which is sum of microscopic cross section scattering (s) and the microscopic cross section absorption (a). The no. of nuclei within this environment also added to the shielding characteristics, the total macroscopic cross section (t) expressed as: t = (NA/A) *t
(3.5.1)
Where is the density (g cm-3), NA is Avogadro's number and A is the atomic mass, has the dimensions of the inverse of the length and its unit is cm-1. When neutron beam passes through a matter, it is shielded due to absorption and scattering. The expression of neutrons in matter as follows: I = I0exp[-t x]
(3.5.2)
Where I0 and I are respectively the intensities of neutrons before and after absorption respectively, x (cm) is the thickness of the material medium.
Fast neutrons has energy level in the range of MeV, in this energy range absorption cross section is low as comparison with the scattering cross-section. These fast neutrons cannot be absorbed as such, but they slowed down during the passage and get absorbed by heavy elements when their energy in range of the thermal energy (0.025 eV). The neutron adsorption characteristics of the three different materials developed (NSPC 1, NSPC 2 and NSPC 3) are studied using fast neutrons and thermal neutrons. The required thickness of 11
shielding material where one half of the incident neutrons have been attenuated is termed as half value layer (HVL). Similarly the thickness of the shielding material where one tenth of its incident neutrons have been attenuated is termed as tenth value layer (TVL). From equation 3.5.2, these are defined as HVL = 0.693 / t
(3.5.3)
TVL = 2.3026/t
(3.5.4)
The experimental procedure (Fig. 1) followed for t measurement is described as follows. Fast neutrons are generated using 12 Ci Am-Be neutron source. For fast neutron detection a precision long counter (PLC) was used. Thermal neutron fluence rate of 1000n/cm2/sec at thermal neutron detector location was produced by using neutron Howitzer and 12Ci Am-Be neutron source. BF3 thermal neutron detector with sensitivity of 10 counts per centimetre square per second (n/cm2/sec) was used for the measurement. Howitzer and BF3 detector was arranged in narrow geometry. The attenuation factor was measured as the ratio of count rates obtained without and with sample in between the source and detector. The t was measured using equation 3.5.2 and the results obtained from the experiment for fast neutron and thermal neutron are tabulated in table 1. Thermal neutron absorption is determined mainly by the type of material and its atomic number density. The results obtained from the thermal neutron irradiation experiment for developed neutron shielding polyester composites is shown in Fig. 6. From the Fig. 6 it can be seen red modified polyester composites i.e NSPC 1, NSPC 2 have better neutron absorption capabilities and shows better total macroscopic cross section (Σt) and mass removal cross section (Σt/ρ) than NSPC 3.
12
t [cm-1],t/[ cm2/gm]
5.00 4.00 3.00 2.00 1.00 0.00
Fig. 6: Σt of developed neutron shielding polyester composites for thermal neutrons.
Table 1: Measurements of neutron shielding properties
Sample
X [cm] [gm/cc]
I0/I
Fast neutron shielding NSPC-1 1.35 1.63 1.13 NSPC-2 1.3 1.73 1.13 NSPC-3 1.65 1.79 1.16 Thermal neutron shielding NSPC-1 1.35 1.63 409.18 NSPC-2 1.3 1.73 306.89 NSPC-3 1.65 1.79 603.00
t [cm-1]
t/ [cm2/gm]
0.091 ±0.002 0.094±0.005 0.090±0.005
0.0555 0.0543 0.0503
4.455±0.002 4.405±0.004 3.879±0.005
2.7331 2.5462 2.1676
3.6 Density measurement: Water immersion technique was used to determine the density of the composite materials. The densities of the composites NSPC 1, NSPC 2 and NSPC 3 is found to be increased as compare to neat polyester (1.35 g/cm3). The densities of composites were found to be 1.63 g/cm3 1.73 g/cm3 and 1.79 g/cm3 respectively.
13
3.7 Mechanical measurement: Dog-bone (Fig. 7) types of samples were used for tensile test. At both the ends of specimen uniaxial load is applied. The ASTM D-638M91 standard test method was used and the length of the test section should be 180 mm [30]. According to the results it can be observed tensile strength of the composite samples decreases with incorporation of filler content. The tensile strength of neat polyester is 174 MPa and values for neutron shielding composites NSPC 1, NSPC 2 and for NSPC 3 were found to be 13 MPa, 16 MPa and 14 MPa respectively. The reduced tensile properties may be due to weak interface chemical reaction between filler and matrix and non uniform distribution of tensile stress. Flexural Properties of the samples were tested according to ASTM standard D-790-03 [31]. During bending flexural strength is the maximum tensile stress before the breaking point. The three-point bend test is conducted an all the composite samples in the universal testing machine Instron. Span length 180 mm (Fig. 7) and cross head speed of 10 mm/min were maintained. The flexural strength values for the samples NSPC 1, NSPC 2 and for NSPC 3 were found to be 31 MPa, 15.5 MPa and 24 MPa respectively. In addition, the flexural strength of the wall tiles should be higher than 15 MPa (for thickness < 7.5 mm) and 12 MPa (for thickness > 7.5 mm), according to Brazilian standard NBR 138182.
NSPC 1
NSPC 2
NSPC 3
Fig. 7: Specimen for Mechanical Testing (Tensile and Flexural)
14
Impact properties (Fig. 8) of the composites were carried out with low velocity instrument impact test. The test was done as per ASTM D 256 using impact tester [32]. The strength of NSPC 1, NSPC 2 and for NSPC 3 materials is found to be 19.79 J/cm2, 59.58 J/cm2 and 46.72 J/cm2 respectively.
Fig. 8: Tested Specimen of Impact strength
The microhardness test was done to determine penetration resistance of the composites. Composites were tested at Vickers scale and values for NSPC 1, NSPC 2 and NSPC 3 are found to be 47, 42 and 46 respectively. The test was done as per ASTM-E-384.
3.8 Thermal Analysis: Thermal stability of shielding composites was measured by thermogravimetric method. The TGA curve (Fig. 9) shows a total weight loss of shielding composites were found to be 50 %, 42% and 44% for NSPC 1, NSPC 2 and NSPC 3 respectively. At the first stage, the weight loss at 200oC in comparison to ambient temperature is found to be 18%, 20% and 6% for NSPC 1, NSPC 2 and NSPC 3 respectively. It can be ascribed to the presence of adsorbed water and de-hydroxylation reaction (2OH- 2O2- + H2O) of structural OH in the iron oxide. At second stage between 200 – 400 0C weight losses is due to polyester degradation and the values were found to be 45% ,41% and 38% for NSPC 1, NSPC 2 and NSPC 3, respectively. Finally at 7000C, NSPC 1, NSPC 2 and NSPC 3 have residue 49%, 42% and 44% respectively.
15
Fig. 9: TGA thermogram of NSPC 1, NSPC 2 and NSPC 3.
Differential scanning calorimetry of the samples was done and all the composite materials were found to have higher peak than glass transition temperature of polyester. It can be explained due to bonds of polymer chain with filler which inhibits the particle motions of polymer chain. The endothermic peaks exhibited by composites are NSPC 1 1140C, NSPC 2 1200C and 1530C and for NSPC 3 at 4270C respectively. The effective thermal conductivity was experimentally obtained using Lee Disk method with circular disc samples of 110 mm in diameter and 3 ~5 mm in thickness. It is noticed that experimental results are close to each other. It has been found that thermal conductivity of experimental study of all three composites is increased (neat polyester 0.22 at 1000C) with adding filler content. NSPC 1 0.47 W/m k, NSPC 2 0.45 W/m k and NSPC 3 0.48 W/m k. The materials should have low thermal conductivity but sufficient to remove heat from the transported elements such as irradiated fuel elements [6].
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4. CONCLUSION Analytical and experimental investigation on neutron shielding composites showed the compatibility of modified red mud with polyester resin is fairly good. The industrial waste can be used as potential filler materials to produce cost effective neutron shielding composites. The studies optimise the multicomponent lightweight and high temperature sustaining polyester composites for neutron shielding. It is evident from the studies that processed red mud containing polyester composites (NSPC 1 and NSPC 2) has better attenuation coefficient values than composite which contains simulated red mud with pure chemical components (NSPC 3). The X-ray powder diffraction studies of neutron shielding material confirmed the presence of new shielding phases (NSPC 2 borate hydrate, calcium aluminate oxide, iron borate and NSPC 3 astrophyllite, aluminium silicate, iron borate). The morphological studies performed using SEM revealed that all the polyester composites were compacted and dense. Mechanical properties of the material confirm that composites having strength equal to that of wall tile. Shielding test of samples verified the correct manufacturing process. In future this research can be applied to the practices in nuclear science and technology.
ACKNOWLEDGEMENT The authors gratefully acknowledge the financial support of Board of Research in Nuclear Sciences sanction No: 2007/36/54-BRNS/2548.Authors are grateful to Director CSIR-AMPRI Bhopal for providing necessary institutional facilities and encouragement. We acknowledge thanks to Permali Wallace (M.P.) India for analysis of samples.
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ACCEPTED MANUSCRIPT
Highlights:
Modified Red Mud polyester composites for neutron shielding are made and characterized.
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Neutron shielding properties of the developed composites has been investigated and calculated.
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Prospects of modified red mud polyester composites are discussed.
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