Research Journal of Chemical Sciences ___ ______________________________ ______ ____ ___ ISSN 22 31 - 606X Vol. 3 ( 2 ), 59 - 64 , February (201 3 ) Res. J. Chem. Sci. International Science Congress Association 59 Combustion Synthesis of Boron Nitride by Glycine Route P. Karthick Kannan 1 , R. Saraswathi 1 , L. John Berchmans 2* 1 Department of Materials Science, School of Chemistry, Madurai Kamaraj University, Madurai 625021, Tamil Nadu, INDIA 2 Electropyrometallurgy Div ision, CSIR – Central Electrochemical Research Institute, Karaikudi 630006, Tamil Nadu, INDIA Available online at: www.isca.in Received 20 th December 201 2 , revised 3 rd January 201 3 , accepted 17 th January 201 3 Abstract Crystalline boron nitride (BN) powders were prepared by combustion method using glycine as a fuel. Experiments were carried out by heating dehydrated borax (Na 2 B 4 O 7 ) with NaNO 2 , KNO 3, NH 4 NO 3 in N 2 atmosphere at 350 0 C and glycine was used as a fuel as well as a source for nitrogen. Borax was used as a boron source and nitrogen compounds (NaNO 2 , KNO 3, NH 4 NO 3 ) were used as the nitrogen source. The reactions were carried out in a tantalum autoclave having the provisions for the purging of N 2 and vent gases. Th e as prepared samples were systematically characterized by X - ray diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectroscopy (FTIR), UV - Visible spectroscopy (UV) and Photoluminescence spectroscopy (PL). The reaction has r esulted in the form of hexagonal boron nitride with high purity and good yield. Keywords : Boron nitride, c ombustion synthesis, b orax, g lycine . Introduction Boron nitride (BN) forms both hard diamond like cubic phase and softer graphite like sp 2 - bonded phases analogous to carbon. Recently, it is found in many applications like cutting tools, grinding and abrasive machines, super hard protective coatings, high frequency and high temperature devices 1 - 4 . It possesses excellent properties such as extreme har dness, high thermal conductivity, chemical inertness, transparency and electrically insulating property 5,6 . Several investigations were made on the preparation of BN tubes and powders 7,8 . C - BN crystals were prepared by Hao et al. 9 by a low pressure benzene thermal synthesis using BCl 3 and Li 3 N. BN nanotubes and nanowires have been synthesized by heating H 3 BO 3 with MWCNT in NH 3 atmosphere 10 . Tang et al. 11 reported the synthesis of tubular form of BN by heating a mixture of B and Fe 2 O 3 in flowing ammonia gas. Hao et al. 12 prepared BN nanocrystals using benzene thermal reactions at low temperature. Hollow sphere BN was synthesized by Chen et al. using BBr 3 and NaNH 2 as raw materials 13 . Crystalline BN nanoparticles were prepared by heating H 3 BO 3 with urea in N 2 atmosphere 14 . Fu et al. 15 prepared BN nanotubes and nanocrystals by extended vapor - liquid - solid method. Nanocage like 16 nanocapsule like 17 boron nitride powders were synthesized using single source precursor method and arc melting process. From the lite rature survey, it has been revealed that boron nitride has been prepared by vapor - liquid - solid method, crystal growth method, thin film techniques and conventional chemical method. In these studies, it has been often emphasized that the reaction time and t emperature are the crucial factors controlling the properties of boron nitride. Further, from a commercial point of view, these methods are not economical since expensive reactants have been employed. Presently, there has been a concerted effort by many re searchers on the preparation of boron nitride by low temperature synthesis routes. In this view, combustion method has been adapted for the synthesis of boron nitride. There have been many reports on the preparation of oxide nanomaterials 18,19 , ferrites, o rthoferrites, garnets 20 and advanced ceramics 21 by combustion synthesis. In the present work, we have reported the preparation of boron nitride by combustion method at relatively low temperature, short duration and low cost. Combustion synthesis is an effi cient and economical method for the production of advanced materials in a short time with less operating cost 22 . Material and Methods Analytical grade reagents were used in all the experiments for the synthesis of boron nitride. Borax was used as the boro n source and the nitrogen compounds such as NaNO 2 , KNO 3 , and NH 4 NO 3 were used as the nitrogen source. Glycine was used as a fuel as well as the nitrogen source. Borax which is one of the reactants contains water molecules, which should be removed to achiev e an effective reaction in the system. If water is present in the reactant, it may lead to the formation of unwanted hydroxides and may need high temperature to form the desired compound. Hence, it was melted in a high purity graphite crucible under argon atmosphere and used in the form of fine powders. Prior to the experiment, the reactants were preheated in a vacuum oven to remove the moisture present in the reactants. For the synthesis of boron nitride, stoichiometric quantities of reactants were taken in a high alumina crucible as shown in table - 1. Then the reactants were thoroughly mixed and placed in Research Journal of Chemical Sciences ___ _ _ _______________________________ ______________ _ ________ ISSN 22 31 - 606X Vol. 3 ( 2 ), 59 - 64 , February (201 3 ) Res. J. Chem. Sci. International Science Congress Association 60 a tantalum autoclave. The autoclave was then placed in an electrically heated furnace. It had the provisions for purging of N 2 gas and ventilator for exh aust gases. Nitrogen gas was purged and the whole reaction was carried out in the controlled N 2 atmosphere. The reaction temperature was 350C and the mixture was kept for 5 hours at this temperature. After the completion of the reaction, the resultant foa my product was removed from the alumina crucible and washed with double distilled water. A white crystalline solid was obtained, which was again thoroughly washed with acetone to remove surface impurities and then dried at 60C in a vacuum oven. Table - 1 R eactants system for the synthesis of boron nitride No. Experiments Reactants 1 Route 1 Borax + Sodium nitrite + Glycine 2 Route 2 Borax + Glycine 3 Route 3 Borax + Potassium nitrate +Glycine 4 Route 4 Borax + Ammonium nitrate +Glycine Differential th ermal analysis (DTA) and thermogravimetric analysis (TGA) of the precursor powders were carried out using a STA 1500 PL thermal sciences, version V4.30 analyzer. The DTA/TGA curves were recorded from room tempe rature to 1000 ˚C in air at a heating rate of 10 ˚C/ min. The dried product was examined for its crystallinity and phase purity by powder X - ray diffraction techniue using Cu Kα (2.2 KW) radiation with 2θ vaue ranging from 10° to 70° in PANALYTICAL model X’ PERPRO. The morphoogy of the crystaine BN powder was examined using a Scanning Electron Microscope (SEM) Hitachi model S - 3000 instrument. FTIR spectra of the samples were recorded as the KBr disc in the range 600 - 4000 cm - 1 by using thermo Nicolet m odel from NEXUS 670 spectrophotometer. UV - Vis spectra were recorded using VARIAN CARY 500 scan spectrophotometer. Photoluminescence measurements were carried out at room temperature using VARIAN CARY eclipse fluorescence spectrophotometer at the excitation wavelength of (  max =298 nm). Results and Discussion Thermogravimetric Analysis: Figure 1 shows the TGA/DTA curve for the precursor borax powder. It is noticed that a large amount of water has been removed from the compound from room temperature to 180 O C. The maximum loss in weight occurred at 180 o C is mainly due to removal of chemically bound water followed by the chemical decomposition of borax at 480 o C. About 35% of the loss in weight is due to the dehydration of water and the chemical decomposition of borax. Beyond 500 o C, there is not much loss in weight, which indicates that compound does not undergo any further change. On observing the DTA curve, three inverse peaks are noticed which are all responsible for the endothermic reactions. The first two pe aks at 85 o C and 151 o C are mainly responsible for the dehydration of water molecules. The third one at 720 o C is responsible for the decomposition and the melting of the salt giving the compound boron tri oxide (B 2 O 3 ). On further heating, the B 2 O 3 decomposes giving boron for the reaction. Figure - 1 TGA/DTA curve for borax Structural Characterization: Figure - 2 shows the XRD spectra of BN sample prepared from the reactant systems described in t able - 2. The XRD spectrum of the BN samples prepa red from route 1 to route 4 are coincided with the standard JCPDS data 23 . For BN sample obtained from route 1, the XRD data exhibits the peaks at 41 o , 55 o which can be indexed as the (1 0 0) and (0 0 4) diffractions of hexagonal phase BN (h - BN). For BN sam ple prepared from route 2, the XRD spectrum shows the peak positions at 41 o , 77 o , 83 o , 88 o corresponding to (1 0 0), (1 1 0), (1 1 2) and (0 0 6) planes of hexagonal phase BN. The XRD pattern for the BN sample prepared from route 3 shows the peaks at 41 o , 44 o , 58 o which can be indexed as (1 0 0), (1 0 1) and (1 0 3) planes of hexagonal phase BN. For BN sample obtained from the route 4, XRD data exhibits the peaks at 41 o , 59 o , 75 o , 81 o corresponding to (1 0 0), (1 0 3), (1 1 0) and (1 1 2) planes of hexagona l phase BN. The calculated lattice constant value for the BN samples prepared from route 1 to route 4 are in good agreement with the standard JCPDS data of h - BN (a=b= 2.605 Ǻ and c  6.653 Ǻ). Table - 2 XRD data of BN samples prepared from route 1 to route 4 Reactant System Crystal structure Estimated lattice constant () Route 1 Hexagonal a, b = 2.520 ; c = 6.597 Route 2 Hexagonal a, b = 2.526 ; c = 6.857 Route 3 Hexagonal a, b = 2.502 ; c = 6.894 Route 4 Hexagonal a, b = 2.514 ; c = 6. 857 Research Journal of Chemical Sciences ___ _ _ _______________________________ ______________ _ ________ ISSN 22 31 - 606X Vol. 3 ( 2 ), 59 - 64 , February (201 3 ) Res. J. Chem. Sci. International Science Congress Association 61 Figure - 2 XRD pattern of boron nitride samples synthesized by combustion method (a) Route 1 (b) Route 2 (c) Route 3 and (d) Route 4 Morphological Characterization: Figure - 3 shows the SEM micrographs of BN samples prepared from Route 1 to Route 4. It depicts the uneven distribution of particles spread over a wide area. It consists of large faceted particles with small incrustations on the surface. The presence of large faceted particles is due to the absorption of moisture on the sur face of the samples. Figure - 3 SEM image of boron nitride samples prepared from (a) Route 1 (b) Route 2 (c) Route 3 and (d) Route 4 Spectral Characterization: Figure - 4 shows the FTIR spectrum of BN samples prepared from route 1 to rout e 4. For BN sample prepared from route 1, the peaks appeared at 708 cm - 1 and 1345 cm - 1 which are assigned to be B - N - B bending and B - N stretching modes of h - BN phase. These values are in good agreement with the literature 24, 25 . Similarly, in other three e xperiments, these values are coinciding with the literature values. Figure - 4 FTIR spectrum of boron nitride samples prepared via (a) Route 1 (b) Route 2 (c) Route 3 and (d) Route 4 Figure - 5 shows the UV reflectance spectra for the BN samples prepared from four different reactant systems. From the reflectance spectra, we have calculated the energy band gap as described by Joshi et al . 26 (i.e.) by plotting the graph between E (eV) and {Ln[hν(R max - R min )/(R - R min )]} 2 . Here R max and R min ar e the maximum and minimum reflectance value in the reflectance spectra and R the reflectance at a given photon energy, hν . The extrapoation of straight ine to {Ln[hν(R max - R min )/(R - R min )]} 2 = 0 gives the value of direct band gap for all the BN samples pre pared from route 1 to route 4 are shown in Fig. 6. The band gap value of the BN samples prepared from route 1 to route 4 was estimated to be 5.4 eV, which reveals that homogenous compound formation takes place in all the experiments. Figure - 7 shows the photoluminescence spectra for BN samples prepared from four different reactant systems. From the PL spectrum, we have determined the band gap values for the BN sampes using the Panck’s euation, (1) where λ max is the maximum emission wavelength. By using the equation - 1, the band gap energy value is determined and it is found to be 5.7 eV, which is in good agreement with the literature 27 . The characterization dat a for all the BN samples showed that there is no any significant change in the phase composition of the product for all the reactant system. From the above results, we have concluded that glycine played a vital role in the formation of boron nitride. When borax was heated at high temperature in the presence of glycine, combustion reaction takes place and due to that exothermic reaction, borax decomposed into B 2 O 3 28 . Subsequently it reacts with nitrogen to form BN. Research Journal of Chemical Sciences ___ _ _ _______________________________ ______________ _ ________ ISSN 22 31 - 606X Vol. 3 ( 2 ), 59 - 64 , February (201 3 ) Res. J. Chem. Sci. International Science Congress Association 62 Figure - 5 UV - refle ctance spectra of boron nitride samples synthesized by combustion method Figure - 6 Plot between E (eV) and {Ln[hν(R max - R min )/(R - R min )]} 2 for the determination of band gap value (a) Route 1 (b) Route 2 (c) Route 3 and (d) Route 4 (a) ( b ) ( c ) ( d ) Research Journal of Chemical Sciences ___ _ _ _______________________________ ______________ _ ________ ISSN 22 31 - 606X Vol. 3 ( 2 ), 59 - 64 , February (201 3 ) Res. J. Chem. Sci. International Science Congress Association 63 Figure - 7 Photoluminescence spectrum of boron nitride samples synthesized by combustion method Conclusion Glycine based combustion synthesis is found to be a convenient method to prepare boron nitride. XRD spectra for the sa mples prepared from four reactant systems confirm the presence of hexagonal boron nitride with high degree of crystallinity. UV reflectance spectra for all the BN samples indicate that the estimated band gap value having same magnitude reveals that homoge nous compound formation takes place in all the experiments. The synthesized boron nitride is found to be pure and it is expected to be a suitable material for high temperature applications. Acknowledgement The author sincerely thanks the Director, CECRI f or his kind permission and the staff of electropyrometallurgy Division for their support and encouragement to carry out this work. References 1. Laurence V., Gerard D. and Etoureau J . , Cubic boron nitride: synthesis, physicochemical properties and applicatio ns, Mater. Sci. Eng., B 10 , 149 - 164 (1991) 2. Lipp A., Schwetz K.A. and Hunold K., Hexagonal boron nitride: Fabrication, properties and applications, J. Eu. Ceram. Soc., 5 , 3 - 9 (1989) 3. Gameza L.M., Shipilo V.B. and Sauuchuk V.A., Kinetic Features of Crystalli zation of Cubic Boron Nitride Single Crystals in the BNLiH(N,Se) System, Phys. Status Solidi B 98 , 559 - 563 (1996) 4. Hubacek M. and Sato T., The effect of copper on the crystallization of hexagonal boron nitride, J. Mater. Sci ., 32 , 3293 - 3297 (1997) 5. Paine R.T . and Narula C.K., Synthetic routes to boron nitride , Chem. Rev ., 90 , 73 - 91 (1990) 6. Kroto H.W., Heath J.R., Brien S.C.O., Curl R.F. and Smalley R.E., C60: Buckminsterfullerene, Nature 318 , 162 - 163 (1985) 7. Oku T., Synthesis and atomic structures of boron nitr ide nanotubes, Phys., B 323 , 357 - 359 (2002) 8. Guo Q., Xie Y., Yi C., Zhu L. and. Gao P., Synthesis of ultraviolet luminescent turbostratic boron nitride powders via a novel low - temperature, low - cost, and high - yield chemical route, J. Solid State Chem ., 178 , 1925 - 1928 (2005) 9. Hao X., Dong S., Xu X., Cui D., Jiang M., Jiang M.H., Xu X.W. and Li Y.P., The effect of reactants on the benzene thermal synthesis of BN, Mater. Lett ., 58, 2791 - 2794 (2004) 10. Deepak F.L., Vinod C.P., Mukhopadhyay K., Govindraj A. and Rao C. N.R., Boron nitride nanotubes and nanowires, Chem. Phys. Lett. , 353 , 345 - 352 (2002) 11. Tang C.C., Fan S.S., Li P., Liu Y.M. and Dang H. Y., Synthesis of boron nitride in tubular form , Mater. Lett. , 51 , 315 - 319 (2001) 12. Hao X.P., Cui D.L., Shi G.X., Yin Y.Q., X u X.G., Jiang M.H., Xu X.W. and Li Y.P., Low temperature benzene Research Journal of Chemical Sciences ___ _ _ _______________________________ ______________ _ ________ ISSN 22 31 - 606X Vol. 3 ( 2 ), 59 - 64 , February (201 3 ) Res. J. Chem. Sci. International Science Congress Association 64 thermal synthesis and characterization of boron nitride nanocrystals, Mater. Lett ., 51, 509 - 513 (2001) 13. Chen L., Gu Y., Shi L., Yang Z., Ma J. and Quan Y., A room - temperature approach to boron nitride hollow spheres, Solid State Commun., 130 , 537 - 540 (2004) 14. Gomathi A. and Rao C.N.R., Nanostructures of the binary nitrides, BN, TiN, and NbN, prepared by the urea - route, Mater. Res. Bull . , 41 , 941 - 947 (2006) 15. Fu J.J., Lu Y.N., Xu H., Huo K.F., Wang X.Z., Li L., Hu Z. and Chen Y., The synthesis of boron nitride nanotubes by an extended vapour – liquid – solid method, Nanotechnology 5 , 727 - 730 (2004) 16. Zhang Y., He X., Hun J. and Du S., Combustion synthesis of hexagonal boron – nitride - based ceramics, J. Ma ter. Process. Technol., 116, 161 - 164 (2001) 17. Narita I. and Oku T., Combustion synthesis of hexagonal boron – nitride - based ceramics, Diamond Relat. Mater ., 11 , 949 - 952 (2002) 18. Patil K.C., Hegde M.S., Rattan T. and Aruna S.T., Chemistry of Nanocrystalline Oxide Materials: Combustion Synthesis, Properties and Applications , World Scientific, Singapore , ( 2008 ) 19. Pooja D., Sharma S.K., Knobel M., Rani R. and Singh M., Magnetic Properties of Fe doped ZnO Nanosystems Synthesized by Solution Combustion Method, Res. J. C hem. Sci., 1(8) , 48 - 52 (2012) 20. Suresh K., Kumar N.R.S. and Patil K.C., A novel combustion synthesis of spinel ferrites, orthoferrites and garnets, Adv. Mater ., 3 , 148 - 150 (1991) 21. Patil K.C., Advanced ceramics: Combustion synthesis and properti es, Bull. Mater., Sci ., 16 , 533 - 541 (1993) 22. Aruna S.T. and Mukasyan A.S., Combustion synthesis and nanomaterials, Crit. Rev. Solid State Mater. Sci., 12 , 44 - 50 (2008) 23. Joint Committee Powder Diffraction Standard: JCPDS No. 73 - 0925 . 24. Cholet V., V andenbulcke L . , Rouan J.P., Baillif P. and Erre R., Characterization of boron nitride films deposited from BCl 3 - NH 3 - H 2 mixtures in chemical vapour infiltration conditions, J. Mater. Sci ., 29 , 1417 - 1435 (1994) 25. Sahu S. , Kavecky S., Ilesova L., Madejova J., Bertoti I. and Szepvolgyi J., Formation of boron nitride thin films on β - Si3N4 whiskers and α - SiC platelets by dip - coating, J. Eur. Ceram. Soc., 18 , 1037 - 1043 (1998) 26. Joshi G.P., Saxena N.S., Mangal R., Mishra A. and Sharma T.P., Band gap determination of Ni – Zn ferrites, Bull. Mater. Sci ., 26 , 387 - 389 (2003) 27. Zunger A., Katzir A. and Halperin A., Optical properties of hexagonal boron nitride, Phys. Rev., B 13 , 5560 - 5573 (1976) Jiang G., Xu J., Zhuang H. and L.i W., Ceram. Int ., 37 , 1689 - 1691 (2011)