Sodium Aluminoborosilicate Glasses Research Articles

Synthesis of transparent tin-doped indium oxide (ITO)-containing glass-ceramic coating by the sol-gel route for UV/NIR-shielding

Transparent glass-ceramic containing tin-doped indium oxide nano-crystalline phase was synthesized using the sol-gel method. The prepared sol, which was based on sodium aluminoborosilicate glass composition, was applied on soda-lime-silicate glass substrate through the dip-coating technique. Developing such glass-ceramics can offer several advantages, including reducing the total cost of production, enhanced chemical durability and a low-temperature synthesis process. The thermal behavior of the dried gels was investigated using simultaneous thermal analysis (STA), to determine the decomposition temperature of the nitrate salts in the gel, its glass crystallization temperature, and finally to optimize the heat treatment regime and optical properties as well. UV–Vis–NIR spectroscopy of the coated samples after heat treatment at 500 °C for 10 h revealed high visible transparency (T>70%) while indicating significant UV/NIR shielding, i.e. near zero and 10 % transmission, respectively. Phase analysis and crystallization behavior studies were conducted using XRD and FE-SEM to evaluate the morphology and size of the precipitated crystallites. According to the results, the optimum heating program for ITO crystallization was heating temperature and soaking time of 500 °C and 10 h, respectively. The undesirable crystalline phase of InBO3 was precipitated as the main crystalline phase by increasing the heat treating temperature to 550 °C. Furthermore, the glass structure was studied using FTIR spectroscopy demonstrating a highly polymerized glassy network for the coating. The effect of the precursors-to-solvent ratio during the synthesis process on the final optical properties was also investigated.

Effects of magnesium on the structure of aluminoborosilicate glasses: NMR assessment of interatomic potentials models for molecular dynamics

AbstractClassical molecular dynamics simulations have been used to investigate the structural role of Mg and its effect when it is incorporated in sodium aluminoborosilicate glasses. The simulations have been performed using three interatomic potentials; one is based on the rigid ionic model parameterized by Wang et al. (2018) and two slightly different parameterization of the core–shell model provided by Stevensson et al. (2018) and Pedone et al. (2020) The accuracies of these models have been assessed by detailed structural analysis and comparing the simulated nuclear magnetic resonance (NMR) spectra for spin active nuclei (29Si, 27Al, 11B, 17O, 25Mg, and 23Na) with the experimental counterparts collected in a previous work. Our simulations reveal that the core–shell parameterizations provide better structural models. In fact, they better reproduce the NMR spectra of all the investigated nuclei and give better agreement with known experimental data. Magnesium is found to be five coordinated on average with distances with oxygen in between a network modifier (like Na) and an intermediate network formed (like Al). It prefers to lay closer to three‐coordinated B atoms, forming B–NBO bonds, with respect to Si and especially Al. This can explain the formation of AlO5 and AlO6 units in the investigated Na‐free glass, together with a Si clusterization.

Volume nanogratings inscribed by ultrafast IR laser in alumino-borosilicate glasses.

Self-assembled nanogratings, inscribed by femtosecond laser writing in volume, are demonstrated in multicomponent alkali and alkaline earth containing alumino-borosilicate glasses. The laser beam pulse duration, pulse energy, and polarization, were varied to probe the nanogratings existence as a function of laser parameters. Moreover, laser-polarization dependent form birefringence, characteristic of nanogratings, was monitored through retardance measurements using polarized light microscopy. Glass composition was found to drastically impact the formation of nanogratings. For a sodium alumino-borosilicate glass, a maximum retardance of 168 nm (at 800 fs and 1000 nJ) could be measured. The effect of composition is discussed based on SiO2 content, B2O3/Al2O3 ratio, and the Type II processing window is found to decrease as both (Na2O + CaO)/Al2O3 and B2O3/Al2O3 ratios increase. Finally, an interpretation in the ability to form nanogratings from a glass viscosity viewpoint, and its dependency with respect to the temperature, is demonstrated. This work is brought into comparison with previously published data on commercial glasses, which further indicates the strong link between nanogratings formation, glass chemistry, and viscosity.

In-situ crystallization of lanthanide titanate stannate (Ln2TiSnO7) pyrochlore in glass: A glass-ceramic system for potential nuclear waste sequestration

Ln2TiSnO7 (Ln = Nd-Er) pyrochlore glass-ceramics are produced by calcining the pelletized oxide mixture and sodium aluminoborosilicate glass precursor at 1200 °C for 4 h. The ceramic Ln-Ti-Sn oxide mixture is prepared by a soft chemistry route to enhance reactant reactivity and product homogeneity. X-ray diffraction, Raman spectroscopy, and electron microscopy techniques are used to confirm the formation of the pyrochlore structure in glass. The cell parameters of the pyrochlores by Le Bail fitting are consistent with the calculated data. The variation of the lanthanide on pyrochlore A-site has insignificant effect on the Raman F2g mode ∼ 310 cm−1, but has an apparent influence on A1g mode ∼ 504–512 cm−1, which gradually shifts to low frequencies with increasing Ln3+ionic radii. The average sizes of the pyrochlore crystals are ∼ 0.31–0.62 μm, which are uniformly distributed in glass phase. These Ln2TiSnO7 pyrochlore glass-ceramics with mixed elements on B-site, possessing high radiation tolerance feature due to the presence of Sn, could be used as nuclear waste forms.

Synthesis of yttrium titanate stannate (Y2Ti2−xSnxO7, x = 0–2) pyrochlore glass–ceramics as potential nuclear waste form

AbstractY2Ti2−xSnxO7 (x = 0–2) pyrochlore sodium aluminoborosilicate glass–ceramics (GCs) are produced by calcining the pelletized Y–Ti–Sn oxide mixture and glass precursor at 1200 or 1300°C for 4 h. The metal oxide mixture is prepared by a soft chemistry route. X‐ray diffraction, Raman spectroscopy, and electron microscopy are employed to investigate the formation of pyrochlore GCs and local crystal structures. Near phase pure Ti‐rich pyrochlores are produced with minor phase SnO2 observed for Sn‐rich materials. The cell parameters of the pyrochlore structures refined by Le Bail fitting are in good agreement with the published data and increase linearly with the gradual increment of Sn substitution. With progressively increasing Sn proportion on pyrochlore B‐site, Raman characteristic bands of the pyrochlore structure become sharper and well defined. The Raman A1g peak position and its full width at half‐maximum are linearly progressed with increasing x (Sn). The presence of the melting glass facilitates the pyrochlore formation, with ceramic grain sizes ranging from submicron to microns. Transmission electron microscopy and selected area electron diffraction observations indicate the sample possesses a relatively high crystallographic perfection at the atomic level. This new series of pyrochlore GCs and the method disclosed herein may pave the way for further materials development as potential nuclear waste forms.

Insights into the Iron- and Phosphorus-Induced Structural Rearrangements in Sodium Aluminoborosilicate Glasses and Their Impact on Melt Rheology and Crystallization Behavior

This paper presents an insight into the structural rearrangements induced by Fe2O3 and P2O5 in glasses designed in the Na2O–Al2O3–B2O3–SiO2 quaternary system. A suite of state-of-the-art characterization techniques, including magic angle spinning-nuclear magnetic resonance (MAS NMR) (on both iron-free and iron-containing glasses), Raman, and Mössbauer spectroscopies, have been employed to study the structural evolution of glasses as a function of the Fe2O3/Al2O3 ratio and P2O5 content over a broad composition space. It has been shown that while P2O5 tends to repolymerize the structure of Fe2O3-free glasses, it has a minimal impact on the network connectivity of iron-rich glasses. Further, there seems to exist a strong tetrahedral avoidance between AlO4 and FeO4 units in the glass structure. In P2O5-free glasses, iron tends to preferentially bond with borate and silicate units, while in the presence of P2O5, iron prefers to associate with phosphate (over borate and silicate) units in the glass structure. Finally, an attempt has been made to correlate the underlying structural descriptors with the rheological and crystallization behavior of glasses with an overarching goal to establish the composition–structure–property relationships in the investigated glass system.

LnUO4‐based glass–ceramic composites as waste forms for the immobilization of lanthanide‐bearing uranium wastes

AbstractWe report a comprehensive study on lanthanide monouranate–based glass–ceramic (GC) composites as potential waste forms for the immobilization of the lanthanide actinide fraction waste arising from the reprocessing of spent nuclear fuel (SNF). Although the crystalline LnUO4precursor prepared via a nitrate route can be well stabilized in a sodium aluminoborosilicate glass, the in situ crystallization of EuUO4in glass from oxide precursors (Eu2O3and U3O8) is rather robust with regards to various processing conditions such as waste loadings, ceramic‐to‐glass ratios, and cooling rates. Scanning electron microscopy and transmission electron microscopy investigations revealed the detailed microstructures, where ∼1–5‐μm spheres for NdUO4and EuUO4, and ∼1–5‐μm rectangular crystals for DyUO4and HoUO4were observed in residual glasses. As designed, the pentavalent uranium has been confirmed by diffuse reflectance spectroscopy. Overall, LnUO4‐based GC composite waste forms are chemically durable, offering flexible processing options with wide operating windows for SNF and process waste stream management.

Sodium zirconium phosphate‐based glass‐ceramics as potential wasteforms for the immobilization of nuclear wastes

AbstractA comprehensive study on the development of sodium zirconium phosphate (NZP)‐based glass‐ceramic composites as potential wasteforms for the immobilization of nuclear wastes is reported. Two complementary waste treatment routes, the ex situ and in situ crystallisation of NZP with a sodium aluminoborosilicate glass, were investigated with various processing conditions including sintering temperature, cooling rate and NZP to glass ratios. While the ex situ route with mixing of pre‐made NZP and glass is a robust and reliable means of producing the glass‐ceramic composites, the in situ crystallisation of NZP from an amorphous NZP precursor is a more realistic processing route. The formation of ZrO2 as a minor phase was observed especially for high NZP to glass ratios due to the solubility difference between Zr and P oxides in glass. The addition of extra phosphate can overcome this and yield glass‐ceramic composites with appropriate NZP stoichiometry. Overall, the NZP glass‐ceramic system is versatile offering multiple processing options for nuclear waste management.

Chromium and vanadium incorporation in sulfate-containing sodium aluminoborosilicate glass

In the composition space for Hanford low-activity nuclear waste glass, the waste loading of some formulations is limited by poor incorporation of sulfate. In particular, certain elements identified in previous studies tend to raise or lower sulfate solubility in borosilicate glass. The aim of the current study is to understand how vanadium and chromium each affect a sulfate-containing sodium aluminoborosilicate glass structure. Glass transition temperature, mass density, visible absorption, and Raman scattering were measured to investigate changes in the glass structure. Both Cr6+ (CrO42−) and Cr3+ were found in the chromium-containing glasses while vanadium primarily existed in the 5+ oxidation state in the vanadium-containing glasses. Electron probe microanalysis determined elemental compositions to assess retention of components. Increasing Cr2O3 caused saturation of Cr concentration within the glass and formation of crystalline eskolaite (Cr2O3). On the other hand, all the targeted V was incorporated into the glass. A fraction of batched S was not incorporated in any glass, presumably due to volatilization during melting. Apparently, the details of incorporation of Cr, and to an extent V, are different depending on whether sulfur is added as in this study or in oversaturated conditions as described in the literature, where Cr partitions to a sulfate-containing salt phase.

Effect of composition on structural evolution and NMR parameters of quadrupolar nuclides in sodium borate and aluminoborosilicate glasses: a view from high-resolution 11B, 27Al, and 17O solid-state NMR

In this study, using 11B, 27Al, and 17O 3QMAS NMR spectroscopy, we investigated the compositional effect on the structures (particularly, topological evolution of boron species and their spatial proximity) and the NMR parameters of B, Al, and O configurations in binary sodium borate and sodium aluminoborosilicate glasses in NaBSiO4–NaAlSiO4 and NaBSi3O8–NaAlSi3O8 joins. Noble structural findings of the current study include the two distinct [4]B species in sodium borate glasses with low alkali content and the presence of Na–O–B peak in NaAl0.25B0.75SiO4 glasses. The proximity between [3]B and [4]B in NaAlSiO4-NaBSiO4 glasses was revealed via 11B double quantum MAS NMR. The changes in quadrupolar coupling constants and isotropic chemical shift for diverse coordination B and Al environments and oxygen clusters provide improved insights in the effect of composition on the changes in the 2nd nearest neighbors environments and the extent of topological distortion.

Hot Isostatically Pressed (HIPed) fluorite glass‐ceramic wasteforms for fluoride molten salt wastes

AbstractMolten pyroprocessing salts can be used to dissolve used nuclear fuel from a reactor allowing recovery of the actinides. Previously, ANSTO have demonstrated hot isostatically pressed (HIPed) sodalite glass‐ceramic wasteforms for eutectic (Li,K)Cl salts containing fission products, but this system cannot be used for the analogous molten alkali fluoride salts (eg, FLiNaK), which have utility in the application of the next generation of nuclear reactors. In this work, a novel glass‐ceramic composite wasteform has been prepared by HIPing, as a candidate for the immobilization of fission product‐bearing FLiNaK salts. The wasteform has been tailored to immobilize the high fluoride content of the waste within fluorite, whereas the waste alkali elements are incorporated in a durable sodium aluminoborosilicate glass, with total waste loadings of ~17‐21 wt% achieved. It was also demonstrated that the speciation of Mo‐ and Sb‐simulated fission products was altered by adding Ti metal due to a controlled redox environment. The resulting candidate wasteform has been studied by X‐ray diffraction and scanning electron microscopy, including the HIP canister‐wasteform interaction zone, and its performance assessed via leaching studies using the PCT and ASTM C1220 leaching protocols. Dr Vance very much enjoyed the challenge of wasteform design for problematic nuclear wastes, for which fission product‐bearing FLiNaK salts are a clear example. His ability to hone in on a wasteform solution with viable waste loadings that meet performance requirements was testament to his nearly 40 years experience in nuclear waste immobilization. The samples discussed in this work represent the last wasteform materials that he prepared.

Pyrochlore glass‐ceramics fabricated via both sintering and hot isostatic pressing for minor actinide immobilization

AbstractPyrochlore glass‐ceramics (GCs) have been investigated with samples fabricated via both sintering and hot isostatic pressing (HIPing) of a mixed oxide precursor. It has been demonstrated that sintering at 1200°C in air is necessary to obtain well‐crystallized pyrochlore crystals in a sodium aluminoborosilicate glass through a one‐step controlled cooling. The crystallization, structure, and microstructure of Eu2Ti2O7 pyrochlore as the major phases in residual glass were confirmed with X‐ray diffraction (XRD), scanning electron microscopy‐energy dispersive spectroscopy, transmission electron microscopy, and Raman spectroscopy. The structures of major Eu2Ti2O7 pyrochlore and minor [Eu4.67O(SiO4)3] apatite in both sintered and HIPed samples were refined using synchrotron XRD data. While the processing atmosphere did not appear to affect the cell parameter of the main pyrochlore phase, very small volume expansion (~0.3%) was observed for the minor apatite phase in the HIPed sample. In addition, static leaching of the HIPed sample confirmed that pyrochlore GCs are chemically durable. Overall, pyrochlore GCs prepared via both sintering and HIPing with the Eu partitioning factor of ~23 between ceramics and the residual glass are suitable waste forms for minor actinides with processing chemicals.

An insight into the corrosion of alkali aluminoborosilicate glasses in acidic environments.

The majority of the literature on glass corrosion focuses on understanding the dissolution kinetics and mechanisms of silicate glass chemistries in the neutral-to-alkaline aqueous regime owing to its relevance in the fields of nuclear waste immobilization and biomaterials. However, understanding the corrosion of silicate-based glass chemistries over a broad composition space in the acidic pH regime is essential for glass packaging and touch screen electronic display industries. A thorough literature review on this topic reveals only a handful of studies that discuss acid corrosion of silicate glasses and their derivatives-these include only a narrow set of silicate-based glass chemistries. Although the current literature successfully explains the dissolution kinetics of glasses based upon classically understood aqueous corrosion mechanisms, more recent advancements in atomic-scale characterization techniques, have enabled a better understanding of reactions taking place directly at the pristine glass-fluid interface which has facilitated the development of a unifying model describing corrosion behavior of silicate glasses. Based on the corrosion mechanisms described and the questions raised in preceding literature, the present study focuses on understanding the corrosion mechanisms governing metaluminous (Na/Al = 1) sodium aluminoborosilicate glasses in acidic environments across a wide composition-space (ranging from SiO2-rich to B2O3-rich compositions), with particular emphasis on understanding the reactions taking place near the glass-fluid interface. Using state-of-the-art characterization techniques including nuclear magnetic resonance (NMR) spectroscopy, Rutherford backscattering, X-ray photoelectron spectroscopy (XPS) and elastic recoil detection analysis (ERDA), it has been shown that stepwise B2O3 substitutions into nepheline (NaAlSiO4) glass, although causing non-linear changes in glass structure network structural features, leads to strikingly linear increases in the forward dissolution rate at pH = 2. While the glasses undergo congruent dissolution in the forward rate regime, the residual rate regime displays evidence of preferential extraction near the glass surface (i.e., enrichment in aluminum content upon corrosion through AlO4→ Al(OH)3 evolution) implying that dissolution-re-precipitation processes may occur at the glass-fluid interface in both B2O3-rich and SiO2-rich glass compositions-albeit with vastly dissimilar reaction kinetics.

Indentation cracking and deformation mechanism of sodium aluminoborosilicate glasses

AbstractDeveloping less brittle oxide glasses is a grand challenge in the field of glass science and technology, as it would pave the way toward new glass applications and limit the overall raw material usage and energy consumption. However, in order to achieve this goal, more insight into the correlation between the chemical composition and material properties is required. In this work, we focus on the mechanical properties of quaternary sodium aluminoborosilicate glasses, wherein systematic changes in glass chemistry yield different resistances to indentation crack initiation. We discuss the origin of the composition dependence of indentation cracking based on an evaluation of the deformation mechanism taking place during the indentation event. To this end, we use a simple metric, the extent of indent side length recovery upon annealing, to quantify the extent of reversible volume deformation. Finally, we also compare the compositional trend in crack initiation resistance to that in crack growth resistance (fracture toughness), showing no simple correlation among the two.

Network polymerization and cation coordination environments in boron-bearing rhyolitic melts: Insights from 17O, 11B, and 27Al solid-state NMR of sodium aluminoborosilicate glasses with varying boron content

Despite the geochemical implications for the dissolution behaviors of nuclear waste glasses and the properties of boron-bearing rhyolitic melts, a detailed atomic-level understanding of the overall effect of boron content on the structural characteristics of boron-bearing silicate glasses remains elusive. Herein, we explore the effects of B/Al and Si/B ratios on the local configurations around cations and the degree of network polymerization of Na2O-Al2O3-B2O3-SiO2 glasses in nepheline (NaAlSiO4) – malinkoite (NaBSiO4) and albite (NaAlSi3O8) – reedmergnerite (NaBSi3O8) joins using multi-nuclear magnetic resonance (NMR). The 11B NMR results confirmed an increase in the B coordination numbers from 3 ([3]B) to 4 ([4]B) as B/Al and Si/B ratios increase. The 27Al NMR spectra show that the Al is mainly four coordinated, except in NaAl0.25B0.75SiO4 glasses, with a minor amount of [5]Al species, revealing a more prominent control of Si over that of B on the Al coordination environments. The 17O NMR spectra resolve distinct bridging (BO, Si−O−Al, Al−O−Al, Si−O−Si, B−O−B, and Si−O−B) and non-bridging oxygens (NBO, Na−O−Si). In contrast, the absence of B−O−Al species confirmed the separation between B and Al and prevalent melt depolymerization exclusively in silicate-networks. The fractions of B−O−B and Na−NBO increase as B/Al ratio increases, accounting for a drastic enhancement in the dissolution rate of glasses. A dramatic increase also indicates an enhanced connectivity of relatively weaker bonds such as B−O−B and Na−O−Si as composition reached a certain boron content. This is linked to a decrease in the melt viscosity with increasing B2O3 component. Based on the measured fractions of [3,4]B in 11B NMR spectra with varying composition, the trend of the evolution of boron isotope composition in sodium aluminoborosilicate melts was estimated, confirming the preferential enrichment of 10B into rhyolitic melts with increasing boron content. The decreased fraction of [3]B species with increasing Si/B may partly explain the reduction in δ11B in boron-bearing volcanic rocks at deeper depths in the subduction zone. The results suggest that composition-induced changes in the atomic structures should be constrained to precisely interpret the melt viscosity, boron isotope composition of arc volcanic lavas, and the dissolution rates of nuclear waste glasses.

Monte Carlo simulation of the corrosion of irradiated simplified nuclear waste glasses

Ballistic effects due to recoil nuclei will be the predominant mode of long-term radiation damage of nuclear waste glass in disposal facilities. While these ballistic effects are known to modify the glass structure in ways that have been quantified using molecular dynamics (MD) simulations, the effect of irradiation-induced structural changes on glass corrosion is not understood. Monte Carlo (MC) simulations were therefore performed to quantify the effects of structural changes determined from MD simulations on the corrosion of simplified nuclear waste glasses, namely sodium borosilicate and sodium alumino-borosilicate glasses. MC simulations were first performed to determine separately the effects of irradiation-induced changes in boron coordination, the number and nature of Qn species, and the angular distribution of SiOSi linkages, that is, changes to the short-range order of the glass. Generally, the MC simulations showed the resulting effects on the kinetics (B release rate) and extent (B leached thickness) of corrosion were correlated to the extent of depolymerization of the glass network introduced by these local structural changes. The combined effects of these structural changes, as parameterized using the results of MD simulations, were then determined using a glass composition for which relevant experimental data were available for comparison. Here, the combined effect of local changes was lower than the increase in alteration depth observed upon irradiation. This insight from the MC simulations highlighted the need to consider changes in the medium-range order to completely account for experimental observations.

Elasticity, hardness, and fracture toughness of sodium aluminoborosilicate glasses

AbstractDue to an increasing demand for oxide glasses with a better mechanical performance, there is a need to improve our understanding of the composition‐structure‐mechanical property relations in these brittle materials. At present, some properties such as Young's modulus can to a large extent be predicted based on the chemical composition, while others—in particular fracture‐related properties—are typically optimized based on a trial‐and‐error approach. In this work, we study the mechanical properties of a series of 20 glasses in the quartenary Na2O–Al2O3–B2O3–SiO2 system with fixed soda content, thus accessing different structural domains. Ultrasonic echography is used to determine the elastic moduli and Poisson's ratio, while Vickers indentation is used to determine hardness. Furthermore, the single‐edge precracked beam method is used to estimate the fracture toughness (KIc) for some compositions of interest. The compositional evolutions of Vickers hardness and Young's modulus are in good agreement with those predicted from models based on bond constraint density and strength. Although there is a larger deviation, the overall compositional trend in KIc can also be predicted by a model based on the strength of the bonds assumed to be involved in the fracture process.

Molecular dynamics simulation of ballistic effects in simplified nuclear waste glasses

Ballistic effects in simple sodium borosilicate (Na2OB2O3=1) and sodium alumino-borosilicate glasses (Na2O−Al2O3B2O3=1) were investigated using molecular dynamics simulations. Specifically, the glasses were irradiated with heavy projectiles that caused atomic displacements by elastic collisions (displacement cascades) and progressively damaged the bulk glass. The accumulated pressure and internal energy inside the glass were found to saturate with deposited energy. Furthermore, structural analysis of the irradiated glasses revealed several important ballistic effects including a decrease in glass density, depolymerization of the borosilicate network, and increase in chemical mixing, short range and intermediate disorder. The magnitude of radiation damage was found to depend on the glass composition and, in general, alumino-borosilicate glasses were found to be slightly less damaged, after irradiation, as compared to borosilicate glasses.

Effects of boron on structure of lanthanum and sodium aluminoborosilicate glasses studied by X-ray diffraction, transmission electron microscopy and infrared spectrometry

Study of glasses with a high content of rare earth elements has a particular interest due to their use in nuclear waste storage. New glass matrices are required to immobilize even higher concentrations of high-level waste in comparison to borosilicate glasses already used. We study the effect of aluminum/boron substitution on the structure of peraluminous lanthanum-rich sodium aluminoborosilicate glasses of 55SiO2-(25-x)Al2O3-xB2O3-15Na2O-5La2O3 composition, where lanthanum simulate all the lanthanides as well as the minor actinides typical for the high-level waste. We have here chosen a chemical composition of a model glass that can accept the presence of minor actinides among the fission products generated by the new reactors of the fourth generation.Transmission Electron Microscopy, Differential Scanning Calorimetry, X-ray diffraction and Infrared spectroscopy showed the existence of phase separation at high boron oxide concentrations, and finely characterized the structure of the major vitreous network.

Phase evolution and microstructure analysis of CaZrTi2O7 zirconolite in glass

The internal crystallization of CaZrTi2O7 zirconolite in a sodium alumino-borosilicate glass has been investigated with powder X-ray diffraction (XRD), scanning electron microscopy and energy dispersion spectroscopy (SEM-EDS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) techniques. The samples have been prepared using a soft chemistry route and ceramic phase evolution has been observed with sintering time. Zirconolite as the dominant phase at 1h sintering gradually changes to baddeleyite structured materials for longer sintering times. XRD shows that one dominant phase belongs to zirconolite at 3h sintering, however, SEM-EDS reveals that the dominant ceramic phase is actually baddeleyite phase, which is enclosed by zirconolite phase. TEM and SAED patterns also confirm the crystallization of zirconolite phase in glass. The addition of CaO enhances the formation of zirconolite (i.e. impedes baddeleyite phase) with CaO to glass weight ratio ≤ 35:100.