Optical and Surface Studies of α-Al2O3 Powders

ocular and Surface Studies of -Al2O3 PowdersX-Ray Diffraction, Optical and surface studies of -Al2O3 pulverises synthe surfaced via single look resoluteness combustion ruleABSTRACT-Al2O3 powders were synthesized at 500 C via dissolver combustion discount (SCS) technique employ urea as an extreme enkindle. The prototype was characterized by X- ray diffraction (XRD), Optical spectrographic analysis and roentgenogram photoelectron spectroscopy (XPS) without either further caloric treatment. XRD study reveals that exemplification crystallized straightaway in the hexagonal -Al2O3 invention from combustion reaction. Average crystallite size of 37.6 nm was calculated use Debye-Scherrers formula. A rotary gap of 5.68 eV was estimated exploitation spread reflectance spectra. Under various UV excitations (260 nm and 400 nm), the sample exhibits a strong sack bloom of youth at 693 nm. For surface investigation X-ray photo electron spectroscopy of sample was carried out. X PS muckle s feces of -Al2O3 reveals that no former(a) dross phases were present in the as synthesized sample which supports the results obtained from XRD. Further to understand the chemical press outs of Al and O, center level spectra of Al-2s and O-1s were studied.INTRODUCTIONAmong all the known crystallographic phases of alumina, -Al2O3 is the solo stable phase. It represents a ceramic material with a large number of technological importances. This is generally due to its versatile properties, such as tall melting point, thermal shock resistance, excellent mechanical strength at room temperature and utmost temperature, large band-gap, hardness and abrasion resistance, chemical inertness 1. These extra ordinary properties atomic number 18 responsible for -Al2O3 to be used in various applications such as spark-plugs, ballistic armours 2, abrasives, bioceramics 3, cutting tools 4, electronic comp atomic number 53nts and substrates 5, thermo luminescent dosimeters 6, refractor y materials, composite materials 7. what is more the compounds and composites of -Al2O3 also have wide shop of applications in various industrial aras such as high-density ceramics 8, 9, biocompatible ceramics 10, and thermal barrier coatings with low thermal conductivities 11, 12. The high temperature-resistant of Al2O3 coatings have various applications in space and null production technologies 13. Since 1961 crystalline transparent alumina (Al2O3) has found various optical applications 14. Single phase -Al2O3 nanopowders are also important component for solid state lying of yttrium aluminium garnet (YAG) transparent laser ceramics 15, 16.There are several(prenominal) techniques used for the synthesis of -Al2O3. In literature there are radicals ready(prenominal) for the synthesis of single-phase -Al2O3 powders apply urea 1, 1719, carbohydrazide 20 or hydrazine 21 as supplys, without any further heat treatments. Several authors have reported two step method for the synth esis of -Al2O3 such as reverse micelle 22, solcolloidal gel processing 23, flare up spray pyrolysis 24 which require calcinations at 10001100 C to obtain completely phase pure -Al2O3.In the present paper, we report the optical and surface properties of as synthesized -Al2O3 powder by the low temperature tooth root combustion synthesis (SCS) technique. Urea was used as an organic fuel for combustion because it has proven to be the best fuel for combustion of aluminium nitrate 1, 17.EXPERIMENTAL-Al2O3 powders were synthesized by low temperature solution combustion synthesis (SCS) using urea as a fuel. The starting materials for the synthesis of -Al2O3 were high-purity aluminum nitrate nonahydrate Al (NO3)3.9H2O and urea (H2NCONH2) from Merck Chemicals, India. The reagents were weighed according to the chemical reaction given in equivalence (1) in the molar stoichiometric ratio of 25. The oxidizing agent to fuel ratio was calculated using the oxidizing and reducing vacancies of re actants in equation (1). For a complete combustion reaction the ratio of oxidizer () and fuel () should be unity, because at this ratio maximum heat is produced.The weighed reactants were mixed in agate mortar by adding few drops of deionized water at room temperature coin bank the solution transform into a transparent viscous gel. The gel was transferred to a Borosil beaker and consequently introduced to a preheated muffle furnace around 500 C. The gel undergoes fast dehydration with evolution of large amount of gasses and burns with an incandescent flame yielding voluminous white product. The whole combustion process was sinless within 2-3 minutes. The beaker was then taken out and the resultant product was grounded into a fine powder and was characterized without any further treatment. The crystalline structure and section morphology of the combusted powders were investigated using a standard diffractometer (Bruker D8 Advance) in the 2 geometry with examine step of 0.02 an d Cu K radiation (=1.5406 ). Diffused reflectance spectrum was preserve using ISR assembly attached with Shimadzu UV-2600 Double beam spectrophotometer in the part 190-1400 nm. The spectral features like photoluminescence excitation and emission (in phosphorescence mode) spectra were measured using a Cary-Eclipse spectrofluorometer (Shimadzu) equipped with a Xenon lamp used as an excitation source. The X-ray photoelectron spectroscopy (XPS) measurement was performed using Omicron capacity analyzer (EA-125) with Al K (1486.6 eV) X-ray source. The background vacuum in the analyzer chamber was of the wander of 10-10 Torr during the XPS measurement. All these characterization were carried out at room temperature.RESULTS AND reciprocation3.1 XRDThe crystal structure and phase purity of the as synthesized Al2O3 powders were analyzed using the X-ray diffraction (XRD) technique. Fig.1. shows the XRD patterns of as synthesized Al2O3 powders recorded in a wide range of Bragg angle 2 (20 2 90). All the observed diffraction broadsides can be indexed with the hexagonal phase of bulk -Al2O3 referenced in the JCPDs saddle no. 71-1123 with space group R. No other impurity peaks were observed in the as synthesized powder neglecting the presence of any other phase other than -Al2O3. These XRD patterns were in good agreement with the earlier produce reports by Robert Ianos et al. 1 and Laishram et al. 17 for the -Al2O3 phase. The lattice parameter calculated from XRD pattern were (a = b= 4.755 , c =12.985 ) which were very close when compared with the unit cell of -Al2O3 (a = b= 4.761 , c =12.99 , JCPDs tear No. 71-1123).The crystallite size was calculated using Debye-Scherer formula 25where D is the crystallite diameter, is the wavelength of roentgen ray source used (Cu K = 0.1506 nm), is the full width at half(a) maxima (FWHM) of an individual peak at 2 (where is the Bragg angle) and is characteristic of the instrument broadening.Fig.1. XRD pattern of as synt hesized -Al2O3 powders at 500 C along with the stick patterns for the JCPDS file no. 71-1123Three most intense peaks were selected for the calculation of particle size and calculated particle size for -Al2O3 was 37.6 nm.3.2 Spectral StudyFig. 2 shows the send reflectance and the tightness spectra of -Al2O3. Barium sulfate (BaSO4) compound was used as a reference standard during the measurement. In both spectra a discriminating band around 220 nm is observed which corresponds that light having this particular wavelength was absorbed.Fig.2. The diffuse reflectance and absorption spectra of the -Al2O3 powders.Calculation of bandgap.KubelkaMunk (KM) 26 theory was used for the calculation of bandgap of -Al2O3 powders using diffused reflectance (DR) spectrum. In a DR spectrum, the ratio of the light fragmented from a thick layer of sample and an ideal non-absorbing reference sample is measured as a function of the wavelength , 26, 27. The relation between the DR of the sample, diffus ion coefficient (S) and absorption coefficient (K) is given bywhere is the KubelkaMunk or remission function.The unidimensional absorption coefficient and the band gap of a material is related through the known relation known as Tauc relation 28 3where h is the photon energy and C1 is a constant of proportionality. When incident light is illuminated at 60, the material scatters perfectly in a diffuse manner then absorption coefficient K becomes equal to 2 i.e. . Considering the K-M scattering coefficient S as constant with respect to wavelength, and using equations (2) and (3), the following expression can be written 4Obtaining the value of from Eq. 2 and plotting versus, the value of is obtained by extrapolating the linear fitted regions to traffic pattern 3 shows the square of the optical absorption times the photon energy as a function of photon energy for -Al2O3 powders. In the present role (-Al2O3), the band gap was estimated around 5.68 eV. Aguilar et al. 29 calculated an optical energy band gap of 5.63 eV for Al2O3 films deposited on quartz substrate.Fig.3. Energy bandgap calculation of -Al2O3 using K-M functions.PhotoluminescenceFig. 4 (a) shows the photoluminescence excitation (PLE) spectra of -Al2O3 recorded at an emission wavelength of 695 nm, the excitation spectra consists of a broad band centered at 400 nm. Fig. 4 (b) shows the PL emission spectra of -Al2O3 monitored at excitation wavelengths of 260 nm and 400 nm respectively. An intense peak at 693 nm is observed. Similar results were also observed by Kaplyanskiiet al. 30 and Nagabhushana et al. 31 for -Al2O3. Kaplyanskiiet al. 30 advert that this emission peak may be due to crystal lattice belonging to the phase of Al2O3.Fig.4. Photoluminescence spectra of as synthesized -Al2O3 (a) excitation recorded at emm = 695 nm and (b) emission recorded at ext = 260 nm and 400 nm.3.3 Surface StudiesIn material science, X-ray photoelectron spectroscopy (XPS) has proved to be a powerful analytica l technique that can be used to study the basal composition and the oxidation states.Figure 5 shows the X-ray photoelectron spectroscopy (XPS) survey scan of the -Al2O3 powders. The XPS survey scan of the -Al2O3 indicates that only Al, O and C are present in the sample correspondent to their binding energies. Carbon was the only impurity present in the sample which was expected. The positions of various photoemission peaks are label in the survey scan corresponding to the elements present in the as synthesized sample. To further understand the chemical states of Al and O ions in -Al2O3 powder we have further performed the detailed scan for O-1s and Al-2s warmheartedness spectra. The value corresponding to C 1s peak (284.6 eV) was used as a reference for spectrum analysis.Fig.5. flock Scan of as synthesized -Al2O3 powder.Figure 6 shows the XPS detailed scan for the O-1s incumbrance level. The raw data was fitted with combined Gausssian Lorentzian functions. The fitted peak sho ws only one braggart(a) peak which is centered at 529.70 eV and is attributed to the Al-O bonding in the -Al2O3 structure. Figure 7 shows the narrow scan for the Al 2s core level. Only one peak is observed after fitting which is centered at 118.95 eV. These narrow scan spectra of O-1s and Al-2s shows that all the O2- ions are bonded to Al3+ ions in the sample. Thus the chemical state of Oxygen and Aluminum is -2 and+3 respectively in the lattice. Rotole et al. 32 observed O-1s peak at 530.68 eV and Al-2s peak at 118.93 eV for standard -Al2O3. The variance in the binding energies may be due to the highly insulating reputation of the sample.Fig. 6 XPS core level spectra of O 1s in -Al2O3 powder.Fig. 7 XPS core level spectra of Al 2s in -Al2O3 powder.ConclusionIn summary, the -Al2O3 powders were successfully watchful by low temperature solution combustion method with metal nitrate reactants and urea as organic fuel. The XRD results confirm that hexagonal phase of -Al2O3 could be o btained directly by combustion method at 500 C without any further treatment. The band gap of sample was calculated using diffused reflectance spectra and it was found estimated 5.68 eV. Under UV excitations, the powders exhibit a strong emission peak around 693 nm. XPS results show that as synthesized powders were unfreeze from impurities. The core level spectra of Al-2s and O-1s reveals that chemical state of Al and O is +3 and +2 respectively in -Al2O3.ACKNOWLEDGMENTSThe authors humbly acknowledged Director, UGC-DAE CSR Indore for providing experimental facility. The authors are thankful to Dr. M. Gupta for XRD measurements. The authors are grateful to Mr. A. Wadikar for helping in XPS measurements.REFRENCESR. Ianos I. Lazau and C. Pacurariu, J. Mater. Sci. 44, 1016 (2009).A.Y. Badmos and D.G. Ivey, J. Mater. Sci. 36, 4995 (2001).D. Gitknecht, J. Chevalier, V. Garnier and G. Fantozzi, J. Eur. Ceram. Soc. 27, 1547 (2007).E. Volceanov, A. Volceanov and S. Stoleriu, J. Eur. Ceram. Soc. 27, 759 (2007).S. Menecier, J. Jarrige, J.C. Labbe and P.L. Lefort, J. Eur. Ceram. Soc. 27, 851 (2007).V.S. Kiiko, Y.N. Makurin, A.A. Safronov, A.N. Enyashin and A.L. Ivanovskii, Refract. Ind. Ceram. 44, 94 (2003).T.M. Ulyanova, L.V. Titova and N.P. Krutko Glass. Ceram. 59, 279 (2002).G.R. Karagedov and N.Z. Lyakhov, Nanostruct. Mater. 11, 559 (1999).J. Chandradass, K. H. Kim, D. S. Bae, K. Prasad, G. Balachandar, S.A.S. Divya and M. Balasubramanian, J. Eur. Ceram. Soc. 29, 2219 (2009).L. G. Gutwein and T. J. Websterles, Biomaterials 25, 4175 (2004).G. Muer and R. Vaben, Surface Engineering 27, 477 (2011).T. Hejwowski, Vacuum 85, 610 (2010).N.P. Padture, M. Gell and E.H. Jordan, Science 296, 280 (2002).R.L. Coble, Transparent alumina and method of preparation. US Patent 3,026,210, January 3 (1961).S. H. Lee, S. Kochawattana, G. L. Messing, J. Q. Dumm, G. Quarles and V. Castillo, J. Am. Ceram. Soc. 89, 1945 (2006).J. Li, Y. Wu, Y. Pan, W. Liu, L. An, S. Wang and J. Guo, Front. C hem. Eng. China 2, 248 (2008).K. Laishram, R. Mann and N. Malhan, Ceramic International 38, 1703 (2012).T. Mimani, ringing 5, 50 (2000).T. Mimani and K.C. Patil, Mater. Phys. Mech. 4, 134 (2001).C. C. Chen and K.T. Huang, J. Mater. Res. 20, 424 (2005).O. Ozuna, G.A. Hirata and J. McKittrick, J. Phys. Condens. Matter 16, 2585 (2004).J. Chandradass and D.S. Bae, Mater. Manuf. Proc. 23, 494 (2008).F. Mirjalili, M. Hasmaliza and L. Chuah Abdullah, Ceram. Int. 36, 1253 (2010).A.I.Y. Tok, F.Y.C. Boey and X.L. Zhao, J. Mater. Proc. Technol. 178, 270 (2006).B.D. Cullity, Element of X-ray Diffraction, second ed., Addison-Wesley, MA (1972).A. E. Morales, E. S. Mora and U. Pal Rev. Mex. Fis S 53, 18 (2007).S. Som and S.K.Sharma, J. Phys. D Appl. Phys. 45, 415102 (2012).R.A. Smith, Semiconductors, 2nd ed. Cambridge University Press Cambridge, (1978).M. A. Frutis, M. Garcia and C. Falcony, Appl. Phys. Lett. 72, 1700 (1998).A. A. Kaplyanskii, A. B. Kulinkin, A. B. Kutsenko, S. P. Feofilov, R. I. Zakharchenya and T. N. Vasilevskaya, Phys. upstanding State 40, 1310 (1998).K. R. Nagabhushana, B. N. Lakshminarasappa and Fouran Singh, Bull. Mater. Sci. 32, 515 (2009).John A. Rotole and Peter M.A. Sherwood , Surface Science Spectra 5, 11 (1998).