Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 2(9), 14-17, Sept. (2012) Res.J.Chem. Sci. International Science Congress Association 14 Ultrasonic Investigation on Sodium and Calcium Tungsten Phosphate Glass SystemSumathi T.* and Kannappan A.N. Department of Physics, DDE, Annamalai University, Annamalainagar – 608 002, INDIA Available online at: www.isca.in Received 14th May 2012, revised 22nd May 2012, accepted 2nd June 2012Abstract Ultrasonic velocity and density measurements in WO – NaO – P and WO-CaO-P composition glasses have been made at the room temperature by making use of pulse echo overlap method. These values are used to evaluate elastic moduli such as longitudinal, Young’s, bulk and shear moduli, Poisson’s ratio, acoustic impedance, micro hardness, Debye temperature and thermal expansion coefficient. The structural and physical properties of the glass samples have been discussed in the light of the above parameters. Keywords: Elastic moduli, Micro hardness, X-ray diffraction, Debye temperature. Introduction Investigation of the elastic and acoustic properties of glasses is significant from the point of view of their application in certain devices such as delay lines, light modulators and solid state sensors. The propagation of acoustic waves in bulk glasses has been of considerable interest in understanding the mechanical properties. During the last two decades, ultrasonic study of liquid mixtures has gained much importance in assessing the nature of molecular interactions present in the mixturesStudy of ultrasonic velocities in glasses and their variation with composition and temperature, helps in understanding various changes taking place in structural configuration. Elastic properties are very informative about the structures of solids and they are directly related to inter-atomic potentials4. Glasses being isotropic and have only two independent elastic constant: longitudinal and shear elastic moduli. These two parameters are obtained from the longitudinal and shear sound velocities and density of the glass. The elastic moduli of glasses are influenced by many physical parameters, which involve the measurement of ultrasonic velocities. The study of elastic properties of glasses has inspired many researchers6,7. Phosphate glasses have several advantages over conventional silicate and borate glasses due to their superior physical properties such as high thermal expansion coefficient, low melting and softening temperatures. Phosphate based glasses find wide applications in various fields due to its varied physico-chemical properties. WO exhibits electrochromic properties which make it suitable for variable reflection mirrors, dazzle free mirrors in automobiles, variable sun protection system usually called ‘smart window’ (variable transmittance) and surfaces with tunable emittance of thermal control of satellites. It has been recognized as a significant chromic material that can be colored through electro-, photo-, gas-, laser- and thermochromism processes. The present work aims to measure the ultrasonic velocity (both longitudinal and shear) and density for two series of glasses namely WO – NaO – (WNP) and WO – CaO – P (WCP) glasses. These values have been used to evaluate longitudinal Young’s, bulk and shear moduli, Poisson’s ratio, acoustic impedance, micro hardness, Debye temperature and thermal expansion coefficient, which will give further insight into the rigidity and structure of glasses. Material and Methods The samples of WO – NaO – P (WNP) and WO – CaO – (WCP) glass system having different compositions were prepared by melting appropriate mixture of WO, NaNO, CaCO and P using Analar grade (minimum assay 99.9%) chemicals. The compositions in mol% of different glass specimen are listed in table 1. Table-1 the required amount (approximately 20g) in mol% of different chemicals in powder form were weighed using single pan balance (Model SHIMAD2U AX 200) having an accuracy of + 0.0001g. The homogenization of the appropriate mixtures of the component of chemicals was effected by repeated grinding using a mortar. The homogenous mixture was put in a platinum crucible and placed in a muffle furnace. Melting was carried out under controlled conditions at temperatures from 1073 – 1173K and 1123–1273K for systems I and II respectively. The molten sample was cast into a copper mould having the dimension of 10mm diameter and 6mm height. Then the glass samples were annealed at 473K for two hours to avoid the mechanical strain developed during the quenching process. The density of the glass samples were measured using Archimede’s principle. Ultrasonic longitudinal and shear velocities of the specimen were determined by using Pulse-Echo method by using X-cut and Y-cut quartz transducers having the fundamental frequency of 10 MHz. Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 2(9), 14-17, Sept. (2012) Res. J. Chem. Sci. International Science Congress Association 15 Table-1 Composition of glasses Sample No Nomenclature Composition in mol%Remarks Plate I WO-NaO- 2 O 5 WO-NaO- 2 O 5 1. 2. 3. 4. 5. WNP 1 WNP 2 WNP 3 WNP 4 WNP 5 20 – 35 – 45 17 – 38 – 45 14 – 41 – 45 11 – 44 – 45 8 – 47 – 45 mol% of Pis constant Plate II WO-CaO - 2 O 5 WO-CaO - 2 O 5 Remarks 1. 2. 3. 4. 5. WCP 1 WCP 2 WCP 3 WCP 4 WCP 5 15 – 40 – 45 13 – 42 – 45 11 – 44 – 45 9 – 46 – 45 7 – 48 – 45 mol% of Pis constant The ultrasonic longitudinal and shear velocities of the specimen were determined by using the pulse-Echo method. From XRD it was found that the nature of the sample was amorphous. Theory and Calculations: The elastic constants of the glass specimen were calculated at room temperature from the measured density (), longitudinal velocity (U) and shear velocity (Us) by using the following standard expressions, Longitudinal Modulus L = U (3) Shear Modulus G = U (4) Bulk Modulus K = L - G (5) Young’s Modulus E = (1 + s ) 2G (6) Poisson’s ratio = (2 (7) Acoustic impedance Z = U  r (8) Micro hardness H = (1-2) 1(6 (9) Debye temperature = (10) Mean sound velocity = (11) Thermal expansion co-efficient a = 23.2 (U – 0.57457) (12) Results and Discussion The experimental values of density (), longitudinal velocity (U) and shear ultrasonic velocity (U) and the calculated longitudinal modulus (L), shear modulus (G), bulk modulus (K) and Young’s modulus (E) of the different glass specimen with respect to change in mol% of NaO and CaO are listed in table 2. Table 2 the Poisson’s ratio (), acoustic impedance (Z), microhardness (H), Debye temperature () and thermal expansion coefficient () are presented in table 3. In WNP and WCP glasses, the density () show a continuous decrease with increase in mol% of NaO and CaO respectively, which is due to structural change takes place in glass network. The structure of glass depends on the nature of ions entering in the network and hence the density. With increase in concentration of NaO and CaO the density of the glasses decreases, probably due to the size effect with the replacement of tungsten atoms by the lighter sodium and calcium atoms. Similar results were observed by some authors7,9. It is observedfrom the table 2, both longitudinal(U) and shear velocity (U) increase linearly with increase in mol% of NaO and CaO in both WNP and WCP glass systems, but the rate of increase of U is greater than that of U. The increase in ultrasonic velocity (both longitudinal and shear) is attributed to an increase in packing density because of the transformation of coordination of tungsten ion. Due to this increase in packing density, the rigidity of the glass system increases and hence ultrasonic velocities and elastic constants also increase. From the table 2, it is observed that the longitudinal, shear, bulk and Young’s moduli increase over the entire range of composition of NaO in WNP and CaO in WCP glass systems. The increase in the values of the elastic constants has been attributed to an increase in the packing density and rigidity and hence the formation of stronger structural building units in the glass network11. The variation of Poisson’s ratio in WNP and WCP glass systems are shown in table 3 The increase in Poisson’s ratio shows that the atoms experience higher transverse contraction strain action on them and hence become more tightly packed. A decrease in cross-link density leads to increase in Poisson’s ratio of atoms or ions. It is seen from the table 3 that the acoustic impedance increases with increase in mole% of NaO and CaO content in both systems confirming the increases in rigidity of the structure of the glass. Similar trend is obtained by by some authors. Further, the increase in microhardness (H), strengthens the softening points, as the network modifier (NWM) content is increased. The continuous increase in microhardness as well as Poisson’s ratio reveals the absence of non bridging oxygen ion (NBO) and this cause the formation of glassy network. The amorphous nature of glass samples was confirmed b X-ray diffraction technique using an X-ray diffractometer. XRD shows no evidence of unmelted or crystalline particles in a quenched glass. The XRD pattern of WNP3 and WCP4 glasses are shown in figure 1 and 2 respectively. Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 2(9), 14-17, Sept. (2012) Res. J. Chem. Sci. International Science Congress Association 16 Table-2 Values of density (rr), Longitudinal velocity (U), Shear velocity (Us ), Longitudinal modulus (L), Shear modulus (G), Bulk modulus (K) and Young’s modulus (E) of WNP and WCP Glass system Name of the sample Density rrx 10-3 kg -3Ultrasonic velocity U ms-1Longitudinal modulus L x 10-9Nm-2Shear modulus G x 10-9 Nm-2Bulk modulus K x 10-9 Nm-2Young’s modulus E x 10-9 Nm-2 Longitudinal (U) Shear (U s ) WNP 1 WNP 2 WNP 3 WNP 4 WNP 53.1921 3.1060 3.0057 2.8727 2.80043502.43 3616.51 3761.72 4002.19 4127.0339.16 40.62 42.53 46.01 47.70 10.23 10.61 10.97 11.72 11.82 25.52 26.47 27.90 30.38 31.94 27.07 28.08 29.10 31.15 31.57 1790.21 1848.25 1910.65 2020.09 2054.83 WCP 1 WCP 2 WCP 3 WCP 4 WCP 5 3.2603 3.1956 3.1414 3.0970 3.0299 4552.40 4675.55 4789.28 4876.92 4988.67 67.57 69.86 72.05 73.66 75.40 17.19 17.76 18.08 18.35 18.68 44.65 46.18 47.94 49.19 50.49 45.70 47.23 48.18 48.96 49.89 2296.12 2357.43 2398.97 2434.26 2482.69 Table-3 Values of Poisson’s ratio (ss) Acoustic impedance (Z), Micro hardness (H), Debye temperature (qq) and Thermal expansion coefficient (aa) of WNP and WCP Glass systems Name of the sample Poisson’s ratio ssAcoustic impedance Z x 10-7 kg m-2 s-1Micro hardness H x 10-9 Nm-2Debye temperature qq K Thermal expansion coefficient aa p K-1 WNP 1 WNP 2 WNP 3 WNP 4 WNP 50.3232 0.3232 0.3262 0.3291 0.3353 1.1180 1.1233 1.1307 1.1497 1.1557 1.2057 1.2506 1.2712 1.3351 1.2980 210.48 218.18 226.25 239.10 244.97 81243.05 83889.70 87258.57 92837.48 95733.77 WCP 1 WCP 2 WCP 3 WCP 4 WCP 5 0.3294 0.3296 0.3325 0.3341 0.3353 1.4842 1.4941 1.5045 1.5104 1.5115 1.9549 2.0176 2.0188 2.0294 2.0512 277.33 285.56 291.90 300.98 308.09 105602.35 108459.43 111097.97 113131.21 115723.81 Figure-1 X-ray diffractogram for WNP3 glass Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 2(9), 14-17, Sept. (2012) Res. J. Chem. Sci. International Science Congress Association 17 Figure-2 X-ray diffractogram for WCP4 glass The observed results are further confirmed by considering another parameter, Debye temperature, obtained directly from the measured velocity. It increases with increase in mol% of NaO and CaO content in both WNP and WCP systems. The increase the Debye temperature is possibly due to the charged center coming closer than the distance required statistically achieving a more effective Coloumbian interaction. Such interaction can give rise to high energy vibrational modes, thereby increasing the Debye temperature10. The thermal expansion coefficient increases with increase in mol% NaO and CaO and hence the rigidity of the structure of the glass. Conclusion The gradual decrease in density with mol% of NaO and CaO of the glass specimen indicates the dependence of density on weight of the metal atom in the network modifier (NWM). 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