Determinant of Glass Material’s Parameters for Fiber Optic Application Durability


 The aim of this study was to determine the principle cause of variation in a measured glass durability using a melt-quenching method. Further goal for this study was to find the optimum level of the factor for producing the glass durability. For that purpose, One-Way Analysis of Variance (ANOVA) was performed. From the analysis, it was found that all longitudinal modulus, shear modulus 2 and shear modulus 3 were the significant parameters that produced high quality of glass durability (p<0.05). The mean analysis revealed that the best condition that maximizes the average of Longitudinal Modulus 1, 2 and 3 would be when the erbium concentration was 0.05. It was found that the erbium concentration with 0.03 produced the optimum Longitudinal Modulus 4 and 5. The findings also pointed out that the average of Shear Modulus 2 and 3 was maximized when the erbium concentration was 0.03 and 0.05, respectively.


Introduction
Glass material has been widely used for many types of applications. Glass applications that have been shown globally have gained the attention of many researchers around the world to nd out the effectiveness of glass in various aspects. Nonetheless, the objective of making good glass should always focus on the foundation of elements used which will improve the e ciency of the glass system.
The compatibility of rare earth elements with tellurite oxide has gained a lot of interests nowadays. In the present study, the comparison between silicate and tellurite-based glass shown that rare earth in tellurite glass has lower nonradiative decay rates, larger values of the radiation cross-section, shorter uorescence cross-section and a red shift of radiative transition. Consequently, the tellurite glass has higher possibility of being used as a potential ber host material rather than silicate glass.
The importance of tellurite glass to be used as a laser emission has become a huge phenomenon in the world of photonic. In the development of tellurite glass as a laser glass, Bell et al. (2014) [1] has conducted a research on laser emission of Nd-doped mixed tellurite and zinc oxide glass. Based on the reports, the presence of neodymium oxide in tellurite glass provided a low laser threshold of 8mW and low internal losses. Subsequently, the studied tellurite glass was shown to have long emission lifetime of about 210µs and large stimulated emission cross section of 3.1 x 10 −20 cm 2 . Such features suggested that tellurite laser glass could act well as an e cient photonic devices and ultrashort mode-locked laser pulses. Fares et al. (2014) [2] stated that tellurite oxide, TeO 2 consists of a lone pair of electrons at the equatorial position of TeO 4 units. This effect will result in the limitation of structural rearrangement of these units which gives a disadvantage to the glass formation. Consequently, the formation of pure TeO 2 glass was unstable and crystallized easily. However, the presence of modi e such as alkali, alkaliearth and transition meta oxides in the glass network was necessary to allow the formation of tellurite-based glass.
It has been found that the presence of zinc oxide intends to reduce the intensity of TeO 4 , trigonal bipyramidal. Meanwhile, the intensity of TeO 3 , trigonal pyramidal increases with the addition of ZnO in the glass network. This trend has got good agreement by observing at the conversion of TeO 4 trigonal bipyramidal to TeO 3 trigonal pyramidal. The role of ZnO in the conversion of TeO 4 to TeO 3 structural units has also been studied by Ayuni et al. (2011) [3]. Ayuni et al. (2011) [3] proposed that ZnO was active as a glass former which was formed as ZnO 4 tetrahedra in tellurite glass network. The evidence of ZnO 4 has been found at around 300cm −1 . It has also been stated that the ZnO might form a bridging bond with B 2 O 3 by Zn-O-B since the stretching force constant of Zn-O bonding was substantially lower than that of B-O.
The formation of TeO 3 polyhedra by Zn 2+ modi er ions has been reported by Ma et al. (2014) [4]. In the statement proposed by Ma et al. (2014) [4], tellurite glass contains a variety of structural motives (TeO 4 , TeO 3 and TeO 3+1 ) due to the presence of Zn 2+ modi er ions, which give rise to a broad distribution of structural sites. This is important as it is strongly related to the strength of the glass as shown in some elastic studies. Up to date, only few researchers have done researches on elastic properties against zinc tellurite glasses doped erbium oxide [5]. However, none of the researchers has done a research on prediction and determining the signi cant factors contributing to the glass durability by using One-Way Analysis of Variance (ANOVA). In this study, the glass durability was measured by several parameters which included molar volume, density, thickness, longitudinal velocity, shear velocity, longitudinal modulus and shear modulus. Those parameters were in uenced by erbium concentration (longitudinal velocity square, shear velocity square) and thickness. Furthermore, the ndings from this study proposed the best condition that gives rise to the glass durability.
Density can be identi ed as the amount of matter lled up by a unit volume of such material. It is evaluated in units of g/cm 3 , kg/m 3 or any other mass/Volume unit [6]. In the prospects of science in glasses, density can be identi ed using the principle of Archimedes. The molar volume of a glass material can be de ned as the amount of space obtained by a mol of such material in space. Elasticity can be identi ed as an ability of the material to deform when force is exerted on it and return back to its original shape once force is taken off. Physically, glass can be de ned as a brittle material which displays almost follows the Hookian behaviour. Hooke's law describes the transition energy from elastic potential energy to potential energy stored as a result of deformation of elastic object for instance stretching of spring. Some parameters that are crucial in elastic or glass durability study include longitudinal modulus and shear modulus. For ultrasonic measurement, the samples were required to have a thickness of 5 mm with parallel surfaces. According to Azianty et al., (2012) [7], the evaluation of ultrasonic velocity in both longitudinal and shear modes for elastic properties of glasses can only be determined by nondestructively technique (NDT). NDT is a recommended technique because the properties of the glass samples can be tested using a computer controlled without destroying or changing the physical properties of the sample. The thickness of the sample that had been measured beforehand was entered into the computer whereby the thickness of the sample was required for the calculation of the ultrasonic velocity. The investigation on elastic properties using ultrasonic velocity is crucial especially in explaining and determining the longitudinal and shear velocity which profoundly provide the understanding of the mechanical behavior of the materials. Glasses have only two independent elastic constants which are longitudinal and shear elastic moduli. These two parameters can be attained from the longitudinal and shear velocities as well as the density of the glasses. Therefore, in this study, a glass series involving ve different concentration of erbium oxide were tested using ANOVA. The usage of the software can predict the optimization on the parameters in determining the dependent and independent variables to be applied as the most e cient ber optic application especially in the perspective of durability in this work.

Materials And Methods
Weighing of chemicals A glass series of zinc tellurite doped with erbium oxide was utilized in this work. A conventional meltquenching method [8] was used to formulate a series of ve different erbium oxide concentration. The raw materials for zinc tellurite glasses doped with erbium oxide were TeO 2 (Sigma-Aldrich, 99.995%), zinc oxide, ZnO (Alfa Aesar, 99.99%) and erbium oxide, Er 2 O 3 (Alfa Aesar, 99.9%).
The raw materials were weighed by using an electrical balance with an accuracy of ±0.0001g and mixed thoroughly to obtain 13 g of mixed powder. The mixture was then transferred into the alumina crucible and was pre-heated at 400 0 C for one hour by using the rst electrical furnace. The purpose of pre-heating process is to remove the excess hydrogen molecules from the mixture. The mixture in the alumina crucible was then heated for a melting process at 900 0 C by using the second electrical furnace for two hours whereas the stainless-steel mould was preheated at 400 0 C in the rst electrical furnace concurrently. This concurrent process would prevent the thermal shock to happen. The molten of the mixture was formed during this process and was poured into cylindrical stainless-steel mould that is the process of melt-quenching method. The cylindrical stainless-steel mould containing the glass sample was heated for annealing process at 400 0 C for another one hour [9].
The aim of the annealing process was to enhance the mechanical strength and remove strain. The glass sample was then allowed to cool down at room temperature for the whole night. The obtained glass sample was polished at a thickness of ~5 mm by using different grade of sand papers (1000 grid, 1500grid, and 2000 grid) in order to obtain a smooth and parallel surface on both sides of the glass sample. Figure 1 displays the sequence of making the glass samples [10].
The experiment of this study applied the concept of randomization. Randomization is one of the principles of experiment which involves random allocation of treatments onto experimental units. In this experiment, the principle of randomization was applied to eliminate bias as well as to reduce the effect of extraneous factors which were not under the direct control of the experimenter. Finally, all the desired measurements of parameters were recorded.

Data analysis
One-Way Analysis of Variance (ANOVA) is extensively used in determining the principal cause of variation in a measured response. Hence, in achieving the aims of the study, ANOVA was hired. On top of that, the Post Hoc test was performed to further investigate the factor levels that are signi cantly different. Mean analysis was then employed in nding the condition (best combination of factor levels) that maximizes the average response. The variables involved in this study were illustrated in the following table [11].      All the outputs in this section suggesting the optimum (maximum/minimum) level of the factors for the response variables.

Results And Discussion
ANOVA was performed to determine which parameters were signi cantly affecting glass durability.   Tables 3, 4 and 5). Therefore, there were 3 subsets produced (Tables 3, 4 and 5).
The analysis extended to the means plot in determining the optimum or the best condition for produced a quality glass durability. Figure 2 depicted that the average Longitudinal Modulus 1 was maximized when the Longitudinal Velocity Square 1 was 12.202 and the erbium concentration was 0.05. Figure 3, on the other hand showed that the optimum level of average Longitudinal Modulus 2 was reached at Longitudinal Velocity Square 2 of 12.025 and erbium concentration of 0.05. It was also found that the best condition that could maximize the average of Longitudinal Modulus 3 was when the Longitudinal Velocity Square 3 was 12.406 and the erbium concentration was 0.05 ( Figure 4). Meanwhile, in Figure 5, it could be seen that the Longitudinal Velocity Square 4 of 11.586 (erbium concentration -0.03) could maximize the average of Longitudinal Modulus 4. Based on Figure 6, the best condition that could maximize the average of Longitudinal Modulus 5 was Longitudinal Velocity Square 5 of 11.637 with erbium concentration of 0.03. In additional, the nding presented that the best condition that could maximize the average of Shear Modulus 2 was Shear Velocity Square 5 of 3.805 with erbium concentration of 0.03 (Figure 7). Figure 8 revealed that the best condition that could maximize the average of Shear Modulus 3 was when the Shear Velocity Square 5 was 3.715 at erbium concentration of 0.05 [12].
As has been discussed, (p≤0.05) in statistics sight provide the most signi cant data to be applied. This occurrence will eventually create weaker bond, and this is predicted to happen during execution of shear wave throughout the experiment when erbium concentration is 0.01, 0.03, 0.04 and 0.05.
Consequently, the glass network will loosen up and create more free spaces between the atoms which will cause the ultrasonic wave to be transmitted slower and decrease its velocity.
Besides that, the presence of erbium oxide in the glass series proves the ability of the elements to act as a glass modi er that modify the glass structure in the glass system. This condition will cause a decrease in shear velocity. Saddeek (2004) [14] had mentioned that the inclusion of erbium oxide would modify the glass structure by splitting the Te-O-Te bond and promote the conversion of bridging oxygen into nonbridging oxygen by forming a trigonal bipyramid into a trigonal pyramid [15]. Furthermore, the addition of erbium oxide into the glass interstices enables more ions to be opened up which will weaken the glass structure. These explain the reason for the insigni cant values of all shear modulus except for shear modulus 2.
In the meantime, the replacement of lighter molecular weight of tellurium dioxide and zinc oxide by heavier molecular weight of erbium oxide will cause changes in the overall weight of the glass and promotes stronger connection between the bonds in the glass. This indirectly will be a strong indicator to conclude that all values of longitudinal modulus are signi cant as listed in Table 3 [16]. They have also reported that the formation of glass network with large concentration of dopants in the interstices space would increase the molar mass of the glass sample and improve the compactness as well [17].
Furthermore, the increasing compactness of the glass can also cause by the close distance between the molecules where it allows the transmission of the ultrasonic wave to pass through the glass sample easier. Closer distance between the molecules will result in formation of bridging oxygen in the glass system and contributes to the improvement of the connectivity within the glass network. length, inter-atomic spacing within the atoms, the presence of non-bridging oxygen atoms and the rearrangement of the lattice [19][20][21] might affect the vicinity of the glass structure. The bond length of Er atoms which is 2.26 Å is longer than the bond length of Te atoms (1.6 Å) and Zn atoms (1.42 Å). The increase in the bond length of the dopants will enhance the inter-atomic spacing between the atoms which can in uence the escalation of the molar volume in the glass sample [19] that produce numbers of non-bridging oxygen that causes the bond to break. Therefore, the spaces between the glasses are growing exponentially and more excess free volume are formed [22]. Numbers of bridging oxygen can be formed by the formation of more tellurite networks of trigonal pyramid compared to trigonal bipyramid [20]. In addition, the increment of the molar volume can also be predicted by large d-spacing obtained by XRD spectra.
Proper thickness with at parallel surface of the glass sample is another crucial factor to be discussed.
For elastic measurement, the thickness is required to be thicker and both surface of the glass sample must be as parallel as possible. This is to ensure the transmission of ultrasonic wave can propagate smoothly in the glass in order to obtain the smooth wave form. Due to the thinning of the glass sample and less parallel surface of the glass which actually should be equal or more than 5 mm, the ultrasonic wave was most probably can transmit in the glass sample unevenly making the obtained outcome not signi cant to be used.
Therefore, based on the statistical data been compared with physical data, some values of the parameters were highlighted and predicted to be used as indicator for the application. Table 6 list parameter estimates for the signi cant factors that will produce an e cient ber optic durability.

Conclusion
In conclusion, the application of One-Way Analysis of Variance (ANOVA) was quite rare in material science studies. The optimization of glass parameters was done to determine the best outcome that can be utilized for the experimental section. The ANOVA for longitudinal and shear velocities suggested that, at 5% level of signi cance, all longitudinal modulus, shear modulus 2 and shear modulus 3 have been recognized to be the important factors in gaining higher durability of ber optic. In the perspective of physics or materials science, high values of longitudinal modulus and shear modulus were the result of good quality glass sample which can be associated with large values of longitudinal and shear velocities. Therefore, it could be inferred that the glass samples were at good state for ber optic application durability.

Recommendation
There is opportunity to enhance the outcome for study. The future researcher should intensify in examining the cause of insigni cant of a few parameters when using statistical analysis rather than theory. Furthermore, the future study should also consider the number of sample selected in the experiment. Moreover, the future research should contemplate the combination of the treatment involved in this kind of study as well. The implementation of this experiment should scrutinize in term of the calibration of the equipment in ensuring the precision and accuracy of the data that will be collected.