Addition Of Alkali Oxide Research Articles

Analysis of elastic properties of lithium substituted barium vanadate glasses to understand the structural changes

Abstract The elastic moduli of 60V2O5- (40-x) BaO-xLi2O where x = 30, 25, 20, 15, 10 (mol%) glass system was analyzed and correlated with the physical properties of glass-like molar volume and average stretching force constant. This was done to understand how the rigidity of glass is affected by the variation in Li2O content in the glass samples. This study involves the application of Makishima-Mackenzie’s theory to calculate the elastic constants of glass, like Young’s modulus, Bulk modulus, Modulus of rigidity and Poisson’s ratio and correlate them to the structural modifications in the glass with the addition of alkali oxide (Li2O) in the glass system at the expense of alkaline-earth oxide (BaO). This work was done to understand how the variation in the composition of glass affects its rigidity and elastic properties which in turn affects its structure. This study helped to tweak the mechanical properties of the current glass system by varying their chemical composition. It was found that glass with 30% Li2O has the highest value of elastic constants and therefore, maximum mechanical strength.

The influence of pressure on the structural transformation and diffusion mechanism in lithium-silicate melt: Molecular dynamics simulation

The structural transformation and diffusion mechanism of lithium-silicate melt is carried by molecular dynamics method. In order to investigate the nature of the pressure-induced structural transformations, the pair radial distribution function (PRDF), distribution of SiO[Formula: see text], OSi[Formula: see text] and LiO[Formula: see text] coordination units, bond angle distribution (BAD) and bond distance distribution (BDD) are analyzed. The investigation reveals that there is a structural transformation in the structure of lithium-silicate. The addition of alkali oxides results in the formation of nonbridging oxygens (NBOs) by disruption of the Si–O network and it has a slight effect on the topology of SiO[Formula: see text] and OSi[Formula: see text] units. Furthermore, we show that the diffusion of network-former atom in lithium-silicate melt is anomaly and Li atoms have significantly faster diffusion rate than those of oxygen or silicon atoms. Therefore, there is an existence of two diffusion mechanisms in lithium-silicate.

Understanding alkali oxide induced structural modification at different length-scales in tellurite glasses for improved optical properties

Investigating the length-scales of order in glasses is important to understand glass properties and hence, the underlying glass structure. Addition of alkali oxides (M2O) in tellurite glass is well-known to modify its network and alter properties by conversion of its basic structural units of TeO4 → TeO3 and increasing the conversion upon further addition of M2O. In this study, we report results of our Raman and Brillouin scattering investigations on 0.12M2O:0.88TeO2 (M = Li, Na, K, Rb and Cs) glasses with an aim to study the effect of the specific alkali cation (M) at fixed composition, on the resulting network structure that determines their interesting optical properties. The network-polyhedral (TeO3) stretching vibrations exhibits red-shift while the Te–O–Te bending mode blue-shifts as M varies from Li to Cs. The fraction of terminal TeO4 units increase steeply with respect to TeO3 and also at the cost of TeO4 units within the network chains, with increasing size of M, contrary to earlier predictions that at fixed concentration of M2O, only the interactions between alkali cation (M) and anions of structural units change, keeping the network structure unaltered. A reduction in frequency with rising mass of M was observed for the Brillouin modes and the Boson peak. Combining results from these techniques, probing structure at different length-scales, depicts that even though increasing M size lowers the conversion of TeO4 to TeO3 units, still the network disintegrates further since the fraction of TeO4 with non-bridging oxygens (NBOs) enhance. This causes reduction in elastic modulus at a larger length-scale, even though specific intra-molecular interactions become stronger within the glass network. The increasing size of the cation from Li+ to Cs+, while preserving the charge of the alkali ion, helps distribute the same electric charge on larger number of anionic tellurite units of the network, and thus, enlarges the correlation length with M, while simultaneously decreasing the network strength. These observations provide evidence for the structural changes leading to the enhanced densities, increased band gaps, reduced refractive indices and the earlier-reported reduction in non-linear susceptibilities with increasing size and mass of M.

Electron densities over Si and O atoms of tetrahedra and their impact on Raman stretching frequencies and Si-NBO force constants

Systematics of SiO Raman stretching frequencies in the range 800–1200cm−1, and Si 2p and O 1s XPS binding energies (BE) are examined for a large number of alkali and alkaline earth silicate glasses, melts, and crystals. Several relationships in the Raman and X-ray Photoelectron spectral (XPS) data lead to new insights concerning charge delocalization over Si tetrahedra and to recognition of controls on both Raman stretching frequencies, and Si 2p and O 1s XPS chemical shifts. The Raman stretching frequencies of the five Q species and the Si 2p and O 1s XPS chemical shifts, vary linearly with the alkali and alkaline-earth content of glasses over the range 0–50mol% counter oxide (M2O or MO). The relationships demonstrate that the frequencies and chemical shifts are controlled by the same property, the valence band electron densities on the atoms of silicate tetrahedra. Specifically, where M-O ion interactions are strongly ionic, the number of NBO's attached to the central Si atom most affects the electron density of Si and O in tetrahedra, and is the major control on Raman symmetric stretching frequencies. Also, the Raman stretching frequency of individual Q species are effectively independent of the mass of the alkali counter cation (MNa, K, Rb, Cs).Addition of alkali oxides to vitreous SiO2 produces Si 2p and O 1s XPS chemical shifts. The magnitude of the chemical shifts increase with counter oxide abundance through transfer of valence ‘s’ electrons from alkali atoms to NBO of tetrahedra. The negative charge acquired by the NBO is redistributed (delocalized) over all atoms of the tetrahedron via SiO bonds thereby increasing valence band electron densities over the constituent Si and O atoms. The greater the number of NBOs associated with a tetrahedron the greater the enhancement of electron density on all atoms of the tetrahedron, thus explaining the Si 2p and O 1s XPS chemical shifts. With respect to Raman spectra, the increased valence electron density causes the central Si atom to become appreciably less positive, which diminishes the strength of Coulombic interactions between Si and O atoms, and weakens SiO force constants. In turn, the weakened force constants result in decreases to SiO stretching frequencies. The weakening of force constants and decrease in stretching frequencies occur in a stepwise manner and relate directly to the number of NBO attached to the tetrahedra. The SiO force constant for the Q4 species is much larger than the force constant for the Q0 species, causing their stretching frequencies to decrease (stepwise) from ~1200cm−1 to ~850cm−1. The mathematical relationships among alkali oxide compositions, Raman stretching frequencies and XPS chemical shifts are quantified.

Modifier constraint in alkali borophosphate glasses using topological constraint theory

In recent years, composition-dependent properties of glasses have been successfully predicted using the topological constraint theory. The constraints of the glass network are derived from two main parts: network formers and network modifiers. The constraints of the network formers can be calculated on the basis of the topological structure of the glass. However, the latter cannot be accurately calculated in this way, because of the existing of ionic bonds. In this paper, the constraints of the modifier ions in phosphate glasses were thoroughly investigated using the topological constraint theory. The results show that the constraints of the modifier ions are gradually increased with the addition of alkali oxides. Furthermore, an improved topological constraint theory for borophosphate glasses is proposed by taking the composition-dependent constraints of the network modifiers into consideration. The proposed theory is subsequently evaluated by analyzing the composition dependence of the glass transition temperature in alkali borophosphate glasses. This method is supposed to be extended to other similar glass systems containing alkali ions.

Effects of Ion Exchange on the Mechanical Properties of Basaltic Glass Fibers

Basaltic glass fibers with different lithium oxide (6–14 mol%) and sodium oxide (2–14 mol%) contents were prepared. The influence of Li2O and Na2O content on the process of fiber manufacturing was investigated. Addition of alkali oxides reduced the forming temperature and substantially expanded the fiber‐forming temperature ranges. The obtained thermal data from differential thermal analysis revealed a decline in glass transition temperature (Tg) of fibers against the compositional changes. The inclusion of Li2O and Na2O in the glass network led to a reduction in its thermal stability. The obtained X‐ray diffraction patterns and IR spectra of Li‐rich and Na‐rich basaltic glass fibers confirmed the formation of highly polymerized structures such as LiAl(Si2O6) and (Na,K)(AlSiO4), respectively, and relatively depolymerized silicate anions. The effects of potassium–lithium and potassium–sodium ion exchange on the mechanical properties of basaltic glass fibers were investigated. As‐received Li‐rich and Na‐rich basaltic glass fibers were ion‐exchanged in potassium nitrate for different exchange times, and their mechanical properties were measured before and after chemical tempering. The measured tensile strength and Young's modulus values of the fibers showed an increase after treatment in molten salt.

Microstructure and dielectric properties of glass/Al2O3 composites with various low softening point borosilicate glasses

The effects of various low softening point borosilicate glasses on both the sintering behavior and dielectric properties of glass/Al2O3 composites were investigated by FTIR, DSC, XRD, SEM and EDS. Results show that the addition of alkali oxides and PbO can decrease the glass softening temperature. While, the addition of Al2O3 and more SiO2 content in the glass can increase the continuity of glass network and further increase the glass softening temperature of samples. Glass with lower softening temperature has more time to flow to finish the densification of samples, and that can contribute to get better sintered composites. By contrast, CaO–PbO–B2O3–SiO2–Na2O–K2O glass/Al2O3 composites sintered at 875 °C for 15 min exhibit better properties of a bulk density of 3.06 g/cm3, a porosity of 0.17 %, a λ value of 2.47 W/m K, a er value of 8.05 and a tan δ value of 8.8 × 10−4 at 10 MHz.

Effect of Additives on the Refractive Index of B2O3-SiO2-Al2O3 Glasses for Photolithographic Process in Electronic Micro Devices

In fabricating plasma display panels, the photolithographic process is used to form patterns of barrier ribs with high accuracy and high aspect ratio. It is important in the photolithographic process to control the refractive index of the photosensitive paste. The composition of this paste for photolithography is based on the B2O3-SiO2-Al2O3 glass system, including additives of alkali oxides and rare earth oxides. In this work, we investigated the density, structure and refractive index of glasses based on the B2O3-SiO2-Al2O3 system with the addition of Li2O, K2O, Na2O, CaO, SrO, and MgO. The refractive index of the glasses containing K2O, Na2O and CaO was similar to that of the [BO3] fraction while that of the SrO, MgO and Li2O containing glasses were not correlated with the coordination fraction. The coordination number of the boron atoms was measured by MAS NMR. The refractive index increased with a decrease of molar volume due to the increase in the number of non-bridging oxygen atoms and the polarizability. The lowest refractive index (1.485) in this study was that of the B2O3-SiO2-Al2O3-K2O glass system due to the larger ionic radius of K+. Based on our results, it has been determined that the refractive index of the B2O3-SiO2-Al2O3 system should be controlled by the addition of alkali oxides and alkali earth oxides for proper formation of the photosensitive paste.

Effect of Alkali Oxides on Crystallization in CaO–SiO2–CaF2 Glasses

In the initial solidification stage in continuous steel casting, controlled crystallinity of the slag film is essential for regulating the horizontal heat flux from the strand to the mold. The effects of alkali oxides on the formation of cuspidine 13CaO·2SiO 2 ·CaF 2 ), which is the primary crystalline phase in the flux film in CaO-SiO 2 -CaF 2 -M 2 O glasses (M=Li, Na, K), were investigated in both isothermal and heating conditions. Addition of alkali oxides enhances crystallization of cuspidine by lowering the glass transition temperature and lowering the apparent activation energy of crystal growth. However, single excess addition of alkaline oxide (M 2 O) hinders the formation of cuspidine as CaF 2 is substituted by M 2 O.

O K-edge XANES studies of alkali germanophosphate glasses

Alkali germanophosphate glasses exhibit a ‘germanate anomaly’, which is a maximum or minimum in their density profiles with the addition of alkali oxide. Several structural mechanisms have previously been recognized to affect the density behavior of these glasses: (1) depolymerization of the PO 4 tetrahedral network; (2) conversion of 4- to 3-membered GeO 4 rings and (3) depolymerization of the GeO 4 network through the formation of non-bridging oxygens. A coordination change from 4- to 5-fold Ge has been detected in alkali germanate glasses, which also exhibit the germanate anomaly. In this study, oxygen K-edge XANES of alkali germanophosphate glasses is used to investigate the coordination change of Ge with increasing alkali content and at various Ge to P ratios. The dominant peak at ∼538 eV in the spectra undergoes a shift to lower energy of ∼0.4 eV, indicating the formation of 5-fold Ge similar to previous studies on alkali germanate glasses. However, the formation of 5-fold Ge does not correlate with the density anomaly compositions of these glasses suggesting that the appearance of higher-coordinated Ge species is not controlling the anomaly behavior.

Chemical stability of Ni-enriched nanodomains in alkali borate glasses

The stability of Ni nanodomains observed in low alkali borate glasses (10 mol% alkali oxide) has been investigated at higher alkali contents using Ni K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. EXAFS data indicate that the Ni nanodomains disappear progressively when adding alkali oxide, whatever the nature of the alkali. This medium range reorganization around Ni is associated with a change of the local site from 6- to 5-fold coordination at 27–30 mol% alkali oxide and 4-fold coordination at higher alkali oxide content. Ni–Ni connections are still present for [5]Ni but no second neighbors are observed for [4]Ni in the EXAFS signal. The changes at both the local and medium range around Ni are likely associated to the disappearance of the large, rigid borate groups with the addition of alkali oxide.

Effect of M xO (M=Li, K, Ca) on the solubility of Ag 2O in borate glass

The variation of Ag 2O solubility under air atmosphere with the chemical potential of Ag was measured for the M x O–B 2O 3–Al 2O 3 system by equilibrating with Ag–Au alloy of various Ag contents at 1273 and 1373 K. It was found that in this system the regular solution model is not valid for estimating the activity coefficient over a wide composition range. The activity coefficient of Ag 2O in B 2O 3 at infinite dilution and first-order Gibbs energy interaction coefficients of Ag 2O, Al 2O 3, and Na 2O on Ag 2O were determined from the Ag 2O solubility data without assuming a regular solution. The increase of the Al 2O 3 solubility by addition of alkali oxide suggested that the glass melts were equilibrated with 2Al 2O 3·9B 2O 3 and not Al 2O 3 and the activity was considered to increase by the addition of alkali oxide. A good correlation was found between the activity coefficient of Ag 2O and the optical basicity.

Network structure of M 2O–TeO 2 (M=Li, Na, Li 0.62Na 0.38) glasses

The network structures of xM 2O–(100− x)TeO 2 (M=Li, Na, Li 0.62Na 0.38) ( x=10, 25, 33 mol%) glasses prepared by melt quenching were studied by X-ray and neutron diffraction. The partial correlation functions for network frameworks have been calculated using the Reverse Monte Carlo (RMC) method. As a result, it was found that Te–Te correlation does not change with increasing alkali content. The RMC result supports recent reported observation that the units of TeO 4 trigonal bipyramid decrease by addition of alkali oxide, while the units of TeO 3 trigonal pyramid increase.

Structural anomaly in sodium germanate glasses by molecular dynamics simulation

The structures of GeO 2–Na 2O glasses with different Na 2O contents, from 0–30 mol%, have been simulated by molecular dynamics (MD) and were found to be in good agreement with the existing experimental results. The Ge–O coordination number was found to increase initially with the addition of alkali oxide. The results indicate that this increase in coordination number was due to the conversion of some of the tetrahedral germanate units into 5-fold coordinated trigonal bipyramidal units. Further additions of alkali oxide, beyond the glass composition range where maxima (or minima) in certain physical properties are experimentally observed (∼18 mol% Na 2O), led to the formation of non-bridging oxygen (NBO) atoms and to a decrease of the average Ge–O coordination number. The reconversion to tetrahedral geometry was found to be responsible for the observed decrease in Ge–O coordination. A simple scheme was used to analyse the populations of various structural entities present in the glass system. It is shown that the conversion of 4-fold to 5-fold coordinated units and their back-conversion, with increasing alkali oxide contents, are feasible and consistent.

Raman Spectra of Potassium and Sodium Selenite Glasses

The vitrification range and Raman spectra of binary KO1/2-SeO2 and NaO1/2-SeO2 systems were investigated. Addition of alkali oxide results in cleavage of Se-O-Se linkages in (SeO2)n chains. Glass structural fragments are discussed.

Raman spectroscopy study of the structure of lithium and sodium ultraphosphate glasses

Anhydrous binary phosphate glasses containing from 0 to 50 mol% Li 2O or Na 2O have been prepared and examined by Raman scattering spectroscopy. The unpolarized Raman spectrum of vitreous P 2O 5 has intense bands near 640 cm −1, attributed to the symmetric stretching mode of POP bridging oxygens, (POP) sym, between Q 3 phosphate tetrahedra, and at 1390 cm −1 due to the symmetric stretch of the PO terminal oxygens, (PO) sym. With the addition of alkali oxide to P 2O 5, a new feature appears in the Raman spectra near 1160 cm −1 indicating the formation of Q 2 phosphate tetrahedra with two bridging and two non-bridging oxygens. The increase in relative amplitude of this new (PO 2) sym band with increasing modifier content is consistent with a simple depolymerization of the phosphate network. From 20 to 50 mol% alkali oxide, the position of the (PO) sym Raman band decreases by ∼ 130 cm −1 whereas the frequency of the (POP) sym band increases by ∼ 60 cm −1. These frequency shifts are the result of π-bond delocalization on Q 3 species that effectively lengthens the PO terminal oxygen bond and strengthens the POP linkages with increasing alkali oxide content. The compositional dependence of the π-bond delocalization on Q 3 tetrahedra is described by considering the interconnections between neighboring Q 3 and Q 2 tetrahedra. The onset of π-bond delocalization on Q 3 species corresponds with the anomalous T g minimum at 20 mol% alkali oxide in alkali ultraphosphate glasses. The increase in T g between 20 and 50 mol% alkali oxide is attributed to the increased ionic interconnection of what becomes a chain-like phosphate network at higher alkali contents. Finally, the Raman spectra of several alkali ultraphosphate glasses show high frequency shoulders on the Raman bands attributed to the (PO 2) sym and (PO 2) asym vibrational modes. These shoulders represent the presence of strained structural units, possibly three- or four-membered rings.

The influence of excess alkalis on the viscosity of a haplogranitic melt

The effect of the addition of 5, 10, and 20 wt% of the alkali oxides on the viscosity of a haplogranitic melt composition has been investigated at I atm and in the temperature range of 400-1650 0c. The high-temperature viscosity data were obtained with concentric cylinder viscometry and the low-temperature viscosity data using micropenetration viscometry. The combined data sets for low- and high-temperature viscosities have been fitted for each composition using the Tamann-Vogel-Fulcher (TVF) equation. The effect of alkali oxide on the viscosity of a haplogranite melt is extreme. The viscosity decreases with added alkali oxide content in a nonlinear fashion. The first few mole percent of alkali oxide added decreases viscosity several orders of magnitude, whereas subsequent addition of alkali oxide has a much smaller effect. The effects of each of the alkalis are broadly similar, implying that the structural role of the alkalis is common to all. In detail however, the viscosity of the strongly peralkaline melts investigated here increases with the size of the added alkali cation in the order Li < Na < K,Rb,Cs. This trend probably reflects a minor influence ofthe alkali-O bond strengths on the melt viscosity. This distinction of a dominant depolymerizing influence and a minor alkali specific bond-strength influence has important implications for the comparison of these data with those for the addition of other depolymerizing agents on the viscosity ofhaplogranitic melt (e.g., H20, F20-1).

The influence of MgO, K2O, Na2O and gas pressure on slag foaming behaviour under reducing conditions

Using a photoelectric measuring technique to determine the foaming behaviour of iron oxide‐containing slag, investigations were carried out into the influences of magnesium oxide and the alkali oxides K2O and Na2O on melt foaming behaviour under reducing conditions. An MgO content of just a few percent intensifies the foaming action of acidic and self‐fluxing melts. This behaviour is also induced by a relatively low addition of alkali oxide. If the magnesium oxide and alkali oxide addition is further increased, slag volume growth during foaming declines. With basic compositions, both the magnesium oxide and the alkali oxides may reduce the volume increase of the foaming slag. Overall, melts undergo maximum foaming under conditions of medium basicity and in the medium temperature range. Alkali oxides promote the phenomenon of melt resolidification often observed in the tests. Tests with different furnace gas pressures up to max. 3 bar reveal that foaming volume of the melt increases with rising gas pressures.

Spectroscopic Analysis of the Structure and Properties of Alkali Tellurite Glasses

Structural development of tellurite glasses with the addition of Li2O and Na2O has been studied using infrared, Raman, and X‐ray photoelectron spectroscopies. The increase in intensity of the peak at 755 cm−1 in the infrared spectra as compared to the peak at 620 cm −1 suggests the transformation of TeO4 building units to TeO3 pyramids with the addition of alkali oxide. Proposed structural change is further supported by the strong compositional dependence of the 755‐cm−1 peak in the Raman spectra as well as by the formation of a shoulder in the O 1s peak of X‐ray photoelectron spectra. In contrast to alkali silicate glasses, formation of nonbridging oxygens with the addition of alkali oxide is not observed.

Borate glass structure by Raman and infrared spectroscopies

Raman and infrared spectroscopies have been employed to probe the continuous evolution of borate glass structures as a function of the nature and concentration of alkali oxide modifier. At relatively low alkali contents, the glasses contain covalent networks consisting of interconnected units bearing BO − 4 tetrahedra. Further addition of alkali oxide causes the progressive depolymerization of the network as a result of the formation of non-bridging oxygen atoms. Eventually, complete network disruption into small and highly charged borate units results in “ionic” glasses. The nature of the alkali cation determines the structure of these glasses by affecting several high- temperature isomerization or disproportionation equilibria.