Characterization of boron carbide particles and its shielding behavior against neutron radiation A. Seyhun Kipcak, Pelin Gurses, Emek M. Derun ⇑ , Nurcan Tugrul, Sabriye Piskin Yildiz Technical University, Department of Chemical Engineering, Esenler, Istanbul, Turkey article info Article history: Available online 5 April 2013 Keywords: Boron carbide XRD FT-IR Raman Neutron permeability abstract Boron minerals, considered future essential materials, can be used as raw materials in the production of boron carbide. In this study, boron carbide, the hardest material after diamond and cubic boron nitride, is characterized and the neutron shielding behavior is investigated. The characterization and structural evaluation of the boron carbide sample was performed using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FT-IR) and Raman Spectroscopy. In addition, a neutron Howitzer was used to measure the neutron permeability of boron carbide samples of various thicknesses. The sample composed of 12.5 g of boron carbide powder and 3 g of Wax Ò had the lowest neutron permeability rate (62.1%). Pellet 3 had the smallest total macroscopic cross section of boron carbide particles, 0.722 ± 0.0071 cm 1 . Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction As crucial raw materials for boron carbide production, the development, production and marketing of boron minerals will create economic value for Turkey in the near future. Because of the superior properties of boron carbide, such as high hardness and high neutron absorption, its applications range from nuclear reactors to armor materials used by the defense industry [1,2]. Boron carbide is produced using a boron source, such as boric acid (H 3 BO 3 ) or boron oxide (B 2 O 3 ), and a carbon source, such as activated carbon or petroleum coke. The reaction occurs between 1400–1600 °C in a graphite resistance furnace or an arc furnace as follows [3]: 4H 3 BO 3 þ 7C ! B 4 C þ 6CO þ 6H 2 O or 2B 2 O 3 þ 7C ! B 4 C þ 6CO ð1Þ The preparation of boron carbide nanoparticles using a carbother- mal reduction method was studied by Baohe et al. using the follow- ing mixture ratios: B 2 O 3 /C (2.0–4.0), B/B 2 O 3 /C and B/C (3.5–4.5). Depending on the reaction conditions, the size of the formed product ranged from 50 to 250 nm, and a clear relationship be- tween the shapes and sizes of the reactants and products was ob- served [4]. Alizadeh et al. established that optimal boron carbide yields were obtained using a ratio of 1.6 for boron oxide to carbon active and 1.8 for boron oxide to petroleum coke [5]. Using B 2 O 3 and carbon (<5 lm, 99.5%), Jung et al. found that 2B 2 O 3 + XC reactions with up to 57.1% carbon content yielded a boron carbide powder that was free of carbon [6]. Due to its high neutron permeability, this high-tech material is widely applied and studied in the field of nuclear energy. Gwaily et al. prepared boron carbide samples using different amounts of rubber and different thicknesses (2, 3, 6 and 9 mm). Their experi- mental results showed that the logarithmic permeability decreased linearly as the thickness of the sample was increased [7]. Celli et al. studied the neutron permeability of boron carbide in three different materials: a crispy mix (10% epoxy resin and 90% B 4 C), an elastobore (50% B 4 C and 50% elastomer) and a ceramic material. The crispy mix had the highest neutron permeability, whereas the elastobore had the lowest permeability [8]. In the study by Ersez et al., a 120 mm-thick pellet consisting of Pb (96%) and Sb (4%) ab- sorbed sufficient neutron radiation to satisfy radiation limit data [9]. In the study by Chichester and Blackburn, bismuth or lead alone showed inadequate neutron shielding behavior, whereas better shielding behavior was obtained by adding bismuth to a polyethylene matrix [10]. In the context of neutron shielding, Adib and Kilany the use of Bi as a cold neutron filter in terms of the temperature and optimal Bi-single crystal thickness [11]. In the experiments of Sakuraia et al., the metathesis-polymer matrix ‘metathene’ performed sufficiently as a biological and medical shielding material [12]. Singh et al. produced several samples of PbO–B 2 O 3 and Bi 2 O 3 –PbO–B 2 O 3 by varying the component concentrations. By comparing the experimental and theoretical results, the authors found that the substitution of lead for bismuth lead to an increased resistance to gamma radiation [13].A 0196-8904/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.enconman.2012.08.026 ⇑ Corresponding author. Tel.: +90 212 383 4776; fax: +90 212 383 4725. E-mail address: [email protected](E.M. Derun). Energy Conversion and Management 72 (2013) 39–44 Contents lists available at SciVerse ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
Transcript
Energy Conversion and Management 72 (2013) 39–44
Contents lists available at SciVerse ScienceDirect
A. Seyhun Kipcak, Pelin Gurses, Emek M. Derun ⇑, Nurcan Tugrul, Sabriye PiskinYildiz Technical University, Department of Chemical Engineering, Esenler, Istanbul, Turkey
Boron minerals, considered future essential materials, can be used as raw materials in the production ofboron carbide. In this study, boron carbide, the hardest material after diamond and cubic boron nitride, ischaracterized and the neutron shielding behavior is investigated.
The characterization and structural evaluation of the boron carbide sample was performed using X-RayDiffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), FourierTransform Infrared Spectroscopy (FT-IR) and Raman Spectroscopy. In addition, a neutron Howitzer wasused to measure the neutron permeability of boron carbide samples of various thicknesses. The samplecomposed of 12.5 g of boron carbide powder and 3 g of Wax� had the lowest neutron permeability rate(62.1%). Pellet 3 had the smallest total macroscopic cross section of boron carbide particles,0.722 ± 0.0071 cm�1.
� 2013 Elsevier Ltd. All rights reserved.
1. Introduction
As crucial raw materials for boron carbide production, thedevelopment, production and marketing of boron minerals willcreate economic value for Turkey in the near future. Because ofthe superior properties of boron carbide, such as high hardnessand high neutron absorption, its applications range from nuclearreactors to armor materials used by the defense industry [1,2].
Boron carbide is produced using a boron source, such as boricacid (H3BO3) or boron oxide (B2O3), and a carbon source, such asactivated carbon or petroleum coke. The reaction occurs between1400–1600 �C in a graphite resistance furnace or an arc furnaceas follows [3]:
4H3BO3 þ 7C! B4Cþ 6COþ 6H2O or 2B2O3 þ 7C
! B4Cþ 6CO ð1Þ
The preparation of boron carbide nanoparticles using a carbother-mal reduction method was studied by Baohe et al. using the follow-ing mixture ratios: B2O3/C (2.0–4.0), B/B2O3/C and B/C (3.5–4.5).Depending on the reaction conditions, the size of the formedproduct ranged from 50 to 250 nm, and a clear relationship be-tween the shapes and sizes of the reactants and products was ob-served [4]. Alizadeh et al. established that optimal boron carbideyields were obtained using a ratio of 1.6 for boron oxide to carbonactive and 1.8 for boron oxide to petroleum coke [5]. Using B2O3 and
carbon (<5 lm, 99.5%), Jung et al. found that 2B2O3 + XC reactionswith up to 57.1% carbon content yielded a boron carbide powderthat was free of carbon [6].
Due to its high neutron permeability, this high-tech material iswidely applied and studied in the field of nuclear energy. Gwailyet al. prepared boron carbide samples using different amounts ofrubber and different thicknesses (2, 3, 6 and 9 mm). Their experi-mental results showed that the logarithmic permeability decreasedlinearly as the thickness of the sample was increased [7]. Celli et al.studied the neutron permeability of boron carbide in threedifferent materials: a crispy mix (10% epoxy resin and 90% B4C),an elastobore (50% B4C and 50% elastomer) and a ceramic material.The crispy mix had the highest neutron permeability, whereas theelastobore had the lowest permeability [8]. In the study by Ersezet al., a 120 mm-thick pellet consisting of Pb (96%) and Sb (4%) ab-sorbed sufficient neutron radiation to satisfy radiation limit data[9]. In the study by Chichester and Blackburn, bismuth or leadalone showed inadequate neutron shielding behavior, whereasbetter shielding behavior was obtained by adding bismuth to apolyethylene matrix [10]. In the context of neutron shielding, Adiband Kilany the use of Bi as a cold neutron filter in terms of thetemperature and optimal Bi-single crystal thickness [11]. In theexperiments of Sakuraia et al., the metathesis-polymer matrix‘metathene’ performed sufficiently as a biological and medicalshielding material [12]. Singh et al. produced several samples ofPbO–B2O3 and Bi2O3–PbO–B2O3 by varying the componentconcentrations. By comparing the experimental and theoreticalresults, the authors found that the substitution of lead forbismuth lead to an increased resistance to gamma radiation [13]. A
40 A.S. Kipcak et al. / Energy Conversion and Management 72 (2013) 39–44
phenol-based resin containing 6 wt.% boron was developed as aneutron shielding material by Morioka et al. [14]. Derun and Kip-cak investigated the 12 year neutron shielding performance of sev-eral boron minerals. In their study, the kurnakovite mineralshowed the greatest resistance to neutron radiation [15]. Kipcaket al. analyzed kurnakovite and inderite and found the neutronabsorption for different pellet thicknesses to be 38.8–43.4% and36.8–45.0%, respectively [16, 17].
Because the neutron capture capability of boron carbide is acrucial property, the present study focuses on the shielding behav-ior of boron carbide. For the neutron radiation experiments, theboron carbide particles were prepared as pellets of varying thick-nesses. Prior to performing the neutron permeability experiments,some parameters of the boron carbide were determined using thefollowing identification analyses: X-Ray Diffraction (XRD), Scan-ning Electron Microscopy (SEM), Energy Dispersive Spectroscopy(EDS), Fourier Transform Infrared Spectroscopy (FT-IR) and RamanSpectroscopy.
Fig. 2. XRD pattern of the boron carbide sample.
2. Methodology
2.1. Preparation and identification analyses of the reactives
To characterize boron carbide particles, a boron carbide powderwas obtained from a local producer in Turkey. The characterizationanalysis was performed using the Philips PANanalytical X-Ray Dif-fractometer. X-rays were produced using a Cu Ka tube at 45 kV and40 mA [15–17].
The morphological characteristics, such as shape, size and sur-face structure, were determined using the CamScan Apollo 300SEM equipped with a Back Scattered Electron (BEI), SecondaryElectron (SEI) detectors and an Energy Disperse (EDS) analyzer.
Subsequently, a spectral analysis was performed based on theFourier Transform Infrared Spectroscopy (FT-IR) technique usinga Perkin-Elmer FT-IR spectrometer with a Diamond/ZnSe Crystal.The range of the measurement was 4000–650 cm�1, the resolutionwas 4 cm�1, and the scan number was set to 4. To strengthen theFT-IR analysis, a Perkin–Elmer Raman 400F Spectrometer was usedfor wave numbers ranging from 3280 to 250 cm�1. The exposuretime was set to 4 s, and the number of exposures was set to 4[16, 17].
Fig. 1. Howitzer equipment a
2.2. Thermal neutron permeability experiments
To compare the neutron permeability properties of boron car-bide, samples of three different thicknesses (0.30, 0.55 and0.65 cm) were prepared by homogeneously mixing boron carbidepowders (5.2, 10.4 and 12.5 g) and Wax� (1, 2 and 3 g). After mix-ing the powders and Wax�, the mixture was pelletized using a40 MPa hydraulic press. The neutron permeability experimentswere performed using thermal neutrons generated by a Ra–Besource that was moderated in a Howitzer. A Leybold HeraeusRadioactive Material device (3 mg Ra-Be neutron source with1.11 � 10�8 Bq activity) and a silvered Geiger-Muller (G-M) coun-ter were used in our experiments. The three pellets, each a differ-ent thickness, were exposed to neutrons in the Howitzer device for15 min. Every 300 s, the neutrons passing through each pellet werecounted (I) using the monitoring equipment. Every step was
nd neutron flux scheme.
Fig. 3. BEI images of the boron carbide sample: (a) 40� BEI, (b) 500� SEI (c) 2500� BEI, and (d) 10,000� BEI.
Fig. 4. BEI image and particle size distribution of the boron carbide sample at 40� BEI.
A.S. Kipcak et al. / Energy Conversion and Management 72 (2013) 39–44 41
repeated without a pellet to measure the collimated thermalneutrons (Io). The Howitzer equipment and neutron flux schemeof the experiments were shown in Fig. 1. The neutron permeabili-ties and the neutron permeability rates were calculated accordingto Eqs. (2) and (3), respectively. Note that I and Io can be repre-sented as the transmitted and incident neutron fluxes, respectively[16,17].
Neutron permeability ¼ I=Io ð2Þ
Neutron permeability rate ¼ I=Io � 100 ð3Þ
To characterize the neutron shielding properties of the samples,the total macroscopic cross sections (Rt) were calculated accordingto the Beer–Lambert Law
Table 3EDS results for the boron carbide sample: (a) 3 mm, (b) 400 lm.
(a) (b)
Element wt.% Atomic% Element wt.% Atomic%
B 64.61 66.99 B 62.44 64.88C 35.36 33.00 C 37.55 35.11Ca 0.01 0.00 Ca 0.01 0.00Fe 0.01 0.00 Fe 0.01 0.00Total 100 – Total 100 2013
42 A.S. Kipcak et al. / Energy Conversion and Management 72 (2013) 39–44
I=Io ¼ e�P
tx; ð4Þ
where x is the thickness of the sample. To calculate the total mac-roscopic cross section, Eq. (4) can be rewritten as:
Xt
¼ lnIIo
� �=ð�xÞ ð5Þ
3. Results and discussions
3.1. Boron carbide characterization results
The boron carbide identifications and patterns obtained in theXRD analysis are shown in Table 1 and Fig. 2, respectively. Accord-ing to the XRD analysis, the phases of the boron carbide particles
Fig. 5. SEM images of the boron carbide sample used
Fig. 6. FT-IR spectrum of the
are identified as 01-071-0033 coded boron carbide mixed with00-023-0073 and 01-074-0945 coded elemental boron. The boroncarbide particles were not pure boron carbide.
Fig. 3 shows electron microscope images based on the SEM anal-ysis using 40�magnification. The product has a clustered structureand a smaller size distribution on the surface. In addition, the shapeof the boron carbide is irregular, polyhedral, and sharp-edged; theparticle size varies between 975.99 lm and 1.15 mm (Fig. 4).
Because of the EDS analysis, the boron carbide powder samplewas evaluated at two grain sizes. The elemental compositions ofthe powder obtained using 3 mm and 400 lm particle sizes areshown in Table 3 and Fig. 5, respectively. For the 3 mm particlesize, the weight percentages of B and C are 64.61% and 35.36%,respectively. For the 400 lm particle size, the B and C weight per-centages of boron carbide are 62.44% and 37.55%, respectively.
The infrared absorption spectrum (FT-IR) is shown in Fig. 6. Bor-on carbide is composed of 12 atoms in the homogeneity range ofcarbon-rich B4C–B12C4. Recent studies have shown that boron car-bide has chain configurations that comprise three atoms, such asB–B–B, C–C–C, C–B–C, C–B–B, or B–C–B. These chain configurationslead to different frequency distributions that can be distinguishedfrom one another by examining the vibrational frequency usinginfrared absorption and reflectance spectroscopy [18]. The FT-IRspectrums are shown in Table 2 and Fig. 6.
in the EDS analysis: (a) 3 mm and (b) 400 lm.
boron carbide sample.
Table 2FT-IR results for the boron carbide sample.
Bond (cm�1) Vibration chain
685.62 Weak B–B bond832.18 B–B–B–C bond1050.04 B–B bond1191.27 B–C bond in icosahedra1379.12 Disordered graphite structure1528.33 Linear C–B–B chain
A.S. Kipcak et al. / Energy Conversion and Management 72 (2013) 39–44 43
The peak at 685.62 cm�1 is the weak vibrational frequency ofthe B-B bond in the absorption band. The peak at 832.18 cm�1,measured over a wide range, represents the B–B–B–C bond thatcomprises amorphous boron, crystalline boron, and boron
Fig. 7. Raman spectrum of th
Fig. 8. Pelleted sample
Table 4Neutron permeabilities of B4C.
Pellet # Mineral Thickness (cm)
1 5.2 g B4C, 1 g Wax� 0.292 10.4 g B4C, 2 g Wax� 0.543 12.5 g B4C, 3 g Wax� 0.66
carbide [16]. The 1050.04 cm�1 vibrational frequency representsthe remaining boron in the form of B–B bonds. The band at1191.27 cm�1 is attributed to B-C bonds in the icosahedra[19]. The peak at 1379.12 cm�1 has a very weak absorptionband and is attributed to the disordered graphite structure.The band at 1528.33 cm�1 has been attributed to either thepresence of free carbon in the boron carbide structure or thevibrations of the linear C–B–B chains that interconnect the ico-sahedra [20].
Because of the fluorescence properties of the boron carbidesample, an accurate Raman characterization analysis could not beperformed. The auto-base line feature was used, and this generatedfluctuations in the spectrum. Based on these bands, the peaks wereobtained, but the accuracy of these peaks could not be ensured(Fig. 7).
44 A.S. Kipcak et al. / Energy Conversion and Management 72 (2013) 39–44
3.2. Thermal neutron permeability results
The thicker an armor material is, the lower the neutron perme-ability. The results of this study are promising. The lowest neutronpermeability rate (62.1 ± 0.29%) was found for pellet 3, which wascomposed of 12.5 g of boron carbide powder and 3 g of Wax�. Theneutron permeability of the pellets composed of 5.2 and 10.4 gboron carbide powder where 63.3 ± 0.22% and 64.9 ± 0.14%,respectively. Using the total macroscopic cross sections of the min-erals, pellet 3 had the lowest total macroscopic cross section,0.722 ± 0.0071 cm�1, and pellet 1 had the highest total macro-scopic cross section, 1.491 ± 0.0074 cm�1. The pellet samples andthe neutron permeability results are shown in Fig. 8 and Table 4,respectively. In the studies by Kipcak et al., kurnakovite and inde-rite minerals had the highest neutron permeabilities. The perme-abilities were 56.6% for the 1.51 cm-thick kurnakovite sampleand 55% for the 1.38 cm-thick inderite sample [16, 17]. The neu-tron permeabilities of boron carbide are lower than these twostudies, but the thicknesses of the boron carbide minerals aremuch less. As a conclusion, it can be said that the thicknesses ofshielding material can be decreased by using boron carbide.
4. Conclusions
The characterization analysis of boron carbide powders werecompared with the literature. As it can be observed from theXRD, SEM, EDS, FT-IR and Raman spectrums, all of the peaks fromour analysis coincide with the characteristic peaks of boroncarbide.
To investigate the usage of boron carbide as a neutron shieldingmaterial, experiments were performed using a Howitzer device.The lowest neutron permeability and the lowest total macroscopiccross section were found for pellet 3, which the sample is com-posed of 12.5 g of boron carbide powder and 3 g of Wax�.
Though there was not a significant difference between theneutron permeabilities of the samples, the neutron permeabilitiesdecreased as the mineral thicknesses was increased. The perme-abilities were not significantly different because the thicknessesof the samples were similar.
By comparing with the studies by Kipcak et al. [16, 17], it can beconcluded that for equivalent thicknesses, boron carbide is a bettershield material than kurnakovite or inderite.
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