Structural Role of Cerium Oxide in Lead Silicate Glasses and Glass Ceramics

Gomaa El-Damrawi,Amal Behairy

doi:10.4236/jmmce.2018.63031

Abstract

Silicate glasses and glass ceramics in the system CeO2-PbO-SiO2 have been studied as a function of the structure factors R and K. The latter two factors are defined as: R = (CeO2 + PbO)/SiO2 and K = (SiO2/CeO2) molar ratios. In this glass, PbO is fixed at 50 mol% and CeO2 increases at the expense of SiO2. NMR investigations have revealed that increasing R which is accompanied with decreasing K leads to reasonable decrease in the shielding of silicon atoms. The chemical shift (δ) showed an increasing behavior due to increasing non-bridging oxygen atoms (NBO) in silicate network. It is evidenced that NBO in cerium free glass is much lower than that of glasses containing CeO2. Increasing R is clearly leading to higher chemical shift and higher NBO. This reflects that CeO2 has an effective structural role, since it would be consumed in all cases as an intermediate oxide. The main portions from CeO2 and PbO inter as glass modifiers which are consumed to form NBO atoms. A limited portion of CeO2 acts as glass former which consumed to form tetrahedral cerium containing NBO due to modification by PbO as a modifier oxide. Increasing R = [(CeO2 + PbO)/SiO2] from 1 to 2.34 leads to a frequent increase of NBO in the average glass network. FTIR spectroscopy of the glasses showed a clear shift of the main absorbance peak toward the low wavenumber with increasing R which confirms the increasing silicate units containing NBO atoms. XRD of the investigated materials revealed the presence of some nanostructures from cerium silicate crystalline phases. Formation of separated phases containing micro clusters is found to depend on NBO concentration, since NBO can facilitate process of phase separation. Majority of modifier are consumed to form NBO in the glass network and the rest are aggregated or separated to form silicate phase riches with cerium cations. In such case, some of silicon atoms are electrically compensated with both Pb and Ce cations.

Highlights

Glass ceramics containing PbO are useful to be studied because of their importance in several fields of applications [1] [2] [3] [4] [5]
In this study is to offer more information on the short range structure of cerium lead silicate glass ceramics in a wide range of composition
The values of Q0 = 29%, Q1 = 44%, Q2 = 23%, Q3 = 4% and Q4 = 0% are obtained values characterize ternary cerium lead silicate glass of R = 1.86. This leads one to confirm that the major portion from CeO2 and PbO can be introduced as glass modifier, since silicate units contain a mixture from Q1 and Q0 types are formed with higher concentration than that of Q2 and Q3 in glass free from CeO2

Summary

Introduction

Glass ceramics containing PbO are useful to be studied because of their importance in several fields of applications [1] [2] [3] [4] [5]. PbO can modify silicate network similar to alkali oxide at low concentration [12] [13] In such situation, the modifiers are consumed to form silicate units containing NBO atoms [12] [13] [14]. Several investigations have been done to characterize micro-structure of lead silicate glasses, the role of PbO and CeO2 in studied silicate glass ceramics has not been fully explored. The role of cerium ions as an agent for phase separation and crystallization has to be studied In this regard, glasses are investigated with SEM, FTIR, XRD spectroscopies and the obtained data is compared with that of base glass, free from CeO2

Experimental

X-Ray Diffraction Method

Results and Discussion

Conclusion