Borosilicate glasses and glass ceramics in the system 30Na 2O-2Al 2O 3-25SiO 2-xFe 2O 3(43-x)B 2O 3 (x = 0 - 20 mol%) have been prepared and studied by distinguished techniques. X-ray diffraction (XRD), transmission electron microscope (TEM), electron diffraction pattern (EDP) and SEM experiments are applied to explore the induced structural changes. Nanometer-sized species of polycrystalline structure are formed particularly in low Fe 2O 3 containing glasses. The size of the crystallites is found to depend on Fe 2O 3 concentrations. It is ranged from 10 to 33 nanometers. Structurally, these materials are suggested to contain different components, crystalline component and an interfacial component which situated between the crystallized domains. Presence of these components affects the atomic arrangement without short- or long-range order. An intermediate range ordered structure is dominant in glass ceramics of Fe 2O 3 < 8 mol%. Less ordered structure is dominated in glasses of higher Fe 2O 3 concentration, since more disordered structure of lower size is present. These structural changes are found to be connected with the role of Fe 2O 3 and Na 2O in glasses. Na 2O is the strong glass modifier in the studied composition region, while Fe 2O 3 is consumed also as a modifier in composition of < 8 mol%. Glass forming character of Fe 2O 3 is mainly dominant in the composition region of higher iron oxide concentration (8 - 20 mol%).
Glasses and glass ceramics containing metal oxide have a wide variety in most of industrial and technical applications [
The changes in microstructure of borosilicate glasses were found to depend on their own building species such Qn [SiO4], [BO3] and [BO4] units in borosilicate network. In miscibility region of borate and silicate network structure, the oxygen atoms can be bonded to boron and silicon atoms and have a Na+ ion as a charge compensator [
The arrangement of the modifier oxide between silicate and borate network depends on two structural factors namely R and K. Generally R is the ratios of Na2O/B2O3 and K is the ratio of SiO2/B2O3 [
The present paper aims to make use of our recent published work which based on NMR and FTIR spectroscopy [
The glasses were prepared from raw materials graded SiO2, H3BO3, Na2CO3, Al2O3 and Fe2O3. The sodium borosilicate glasses were prepared by melting batches in alumna crucibles at a temperature ranging from 1250˚C to 1520˚C depending on composition. Then the melt was frequently swirled to make the material free from air bubbles and to enhance homogeneity of the melt. Then, the melt has been quenched by pouring it over a stainless steel plate.
XRD measurements were carried out using a Brucker Axs-D8 technique. CuKα radiation source (λCuKα = 0.1540600 nm) has been utalized. Data was accumulated steeply with an interval of 0.02˚, over a 2θ range of 4˚ - 65˚ using a dwell time of 0.4 seconds. The obtained experimental patterns were compared to standards compiled by Joint Committee on Powder Diffraction and Standards (JCDPS).
Transmission Electron Microscopy (TEM) is a common technique used to evaluate the shape, size, and morphology of the bulk of the material. TEM investigations were carried out using a JEOL-JEM-2100, with an acceleration voltage of 200 kV. During this technique, a high energy beam of electrons is transmitted through a very thin specimen, causing interactions between the electrons and the atoms and producing the TEM images.
SEM micrograph were obtained with a JEOL JSM 6400 scanning electron microscope equipped with a Link analytical system. The electron energy used was 20 keV. The SEM and EDX analysis were carried out for some selected samples.
The structure of some of the investigated glasses may offers neither long-range order (like crystals) nor short-range order like glasses. It possess polycrystalline structure with intermediate range order. XRD patterns of some selected glass compositions are presented in
the patterns of the glass containing 0, 1, 3 and 5 mol% Fe2O3. These diffractions are centered at 2θ = 18.5, 25.2, 30, and 60 degree, revealing precipitation of some ordered Na2SiO3 species in these glasses [Card No. 16-818]. Formation of polycrystalline cluster from Na2SiO3 is accessible in these glasses, since network is enriched with NBO atoms. The total modifier content from both Na2O and Fe2O3 is extremely high in these glasses [
In initial glasses (0 - 5 mol% Fe2O3), part of modifier oxide (Na2O and Fe2O3) is consumed to produce NBO in silicate, the other portion can be consumed to modify the borate network and the rest is distributed as accumulated polycrystalline clustered species containing Na and Fe ions. The extra modifier oxide are forced to form some nano-size crystallites or clusters from its own. As a direct result, Na2SiO3 are the main species which are simply to be formed. The angular position of the diffraction lines in the XRD peaks closely match the Na2SiO [card nu.78-1713C]. On the other hand, diffraction peaks disappear for all glasses of Fe2O3 > 5 mol%. Only a broad hump arises revealing of less ordered glassy matrix containing poly crystalline species of extra small size. As can be seen from
Absence of sharp diffraction peaks in Fe2O3 rich glasses reveals that Fe2O3 inter the network as glass former [
Evidences based on XRD data are in a good agreement with that obtained from TEM and EDP, Figures 2-6. Both confirmed that well-formed structural species are constructed in its amorphous state in glasses of high concentration Fe2O3 (≥ 6 mol%). Samples of 10 & 20 mol% Fe2O3 are presented as examples,
confirms that iron has high ability to withdraw NBO from the silicate and plays the role of a glass former [
As shown in
reduces the content and the size of the well-formed clusters.
It can be observed from TEM and EDP that the disorder of the aggregated species increases with increasing Fe2O3 concentration. The interconnection between different species drops down on further increase in Fe2O3 concentration and becomes almost indistinguishable from the background at around 20 mol% % Fe2O3, see
Same observation is observed from SEM micrographs
The concentration of the aggregated species is shown to be more higher in sample containing 3 mol% Fe2O3 (
of polycrystalline species (Na2SiO3) should be decreased as presented from both SEM and TEM micrographs.
Elemental analysis of samples containing 3 and 10 mol% Fe2O3 has been also done using EDEX spectroscopy. The spectra of glass of low Fe2O3 content (3 mol%) contains only Na, Si and O elements,
X-ray diffraction (XRD), transmission electron microscope (TEM), electron diffraction pattern (EDP) and SEM experiments are applied to analyze the structural changes. Species of polycrystalline structure are formed in low Fe2O3 containing glasses. The obtained size is ranged from 10 to 33 nanometers. An intermediate range ordered structure is dominant in glass ceramics of Fe2O3 < 8 mol%. Less ordered structure is a feature of glasses of higher Fe2O3 concentration. The type of range order is found to be connected with the role of Fe2O3 and Na2O in glasses. Na2O is the strong glass modifier in the studied composition region, while Fe2O3 is consumed also as a modifier in composition of < 8 mol%. Fe2O3 is consumed as a network former in the composition region of higher iron oxide concentration (≥8 mol%).
El-Damrawi, G., Hassan, A.M. and El-Jadal, S. (2017) Morphological and Structural Investigations on Iron Borosilicate Glasses. New Journal of Glass and Ceramics, 7, 13-21. https://doi.org/10.4236/njgc.2017.72002