Q3 Species Research Articles

Fe-oxidation state in alkali-trisilicate glasses - A Raman spectroscopic study

This study focuses on analysis of local structural arrangements of ferric and ferrous iron in binary alkali-silicate networks, and the effect of changing Fe2+/Fe3+ ratio on the glass structure, investigated by Raman spectroscopy. Three alkali trisilicate glasses, Li2Si3O7, Na2Si3O7 and K2Si3O7, were synthesized with 4.4–6.0wt% iron oxide, to form three series with the same nominal composition but changing Fe2+/Fe3+ ratio. Structural analyses of the high-wavenumber envelope in Raman spectra of Fe-free alkali-trisilicate analogues have been useful in identifying structural species in the Fe-bearing glasses. Peak fitting of the high-wavenumber region between ca. 820 and 1200cm−1 indicates that the increase in ferric iron content is associated with a considerable increase in the Q2 species while the abundance of Q4- and Q3-decreases. However, the most prominent change with the increase in the ferric content is the rise of the peak centred at ca. 980cm−1 that we identify as related to the vibration of Fe3+-O-Si linkage, regardless of the coordination geometry around ferric cation. We have observed a roughly linear trend in the change of the Fe3+-related Raman peak area with the increase in the ferric iron content for all three alkali trisilicate series, with increasing slope from K to Li. Nonetheless, there are discrete differences in the dependence due to composition of the glass. Based on the results of this study, the obtained linear calibration trend can be used only for an approximate determination and not as a routine quantification of ferric content.

Mixed-modifier effect in (Ca,Mg) metaphosphate glasses

The effect of modifier mixing on structure and properties of (Ca, Mg) metaphosphate glasses is considered across the binary join of xMgO-(1-x)CaO-P2O5. Pronounced extrema in hardness, Young's modulus, local creep and glass transition temperature are related to variations in modifier precipitation. Both alkaline earth species compete for octahedral lattice sites, what leads to an increase in the fraction of [MgO4] tetrahedral units at equimolar mixing. At the same time, the structural backbone of phosphate Q2 species is affected through favorable formation of ring- and chain-like superstructures in the presence of Ca2+ and Mg2+, respectively.

Structural properties of liquid aluminosilicate with varying Al2O3/SiO2 ratios: Insight from analysis and visualization of molecular dynamics data

Molecular dynamics (MD) simulations and visualizations were explored to investigate the changes in structure of liquid aluminosilicates. The models were constructed for four compositions with varying Al2O3/SiO2 ratio. The local structure and network topology was analyzed through the pair of radial distribution functions, bond angle, bond length and coordination number distributions. The results showed that the structure of aluminosilicates mainly consists of the basic structural units TO[Formula: see text] (T is Al or Si; y = 3, 4, 5). Two adjacent units TO[Formula: see text] are linked to each other through common oxygen atoms and form continuous random network of basic structural units TO[Formula: see text]. The bond statistics (corner-, edge- and face- sharing) between two adjacent TO[Formula: see text] units are investigated in detail. The self-diffusion coefficients for three atomic types are affected by the degree of polymerization (DOP) of network characterized by the proportions of nonbridging oxygen (NBO) and Q[Formula: see text] species in the system. It was found that Q4 and Q3 tetrahedral species (tetrahedron with four and three bridging oxygens, respectively) decreases, while Q0 (with four nonbridging oxygen) increase with increasing Al2O3/SiO2 molar ratio, suggesting that a less polymerized network was formed. The structural and dynamical heterogeneities, micro-phase separation and liquid–liquid phase transition are also discussed in this work.

Structure-property relations of caesium silicate glasses from room temperature to 1400 K: Implications from density and Raman spectroscopy

This study investigated a series of caesium bearing silicate glasses with compositions ranging from 5 to 35mol. % Cs2O using Raman spectroscopy. The proportions of 4- and 3-fold SiO4 rings are estimated by using the relative intensities of the D1 and D2 vibrational bands in each spectra. An increase in the abundance of 3-fold SiO4 rings is apparent and confirms previous studies which proposed such a mechanism to be present with increasing alkali content in alkali silicate glasses. The behaviour of the D1 and D2 bands correlates with the density measurements lending credence to the importance of the formation 3-fold SiO4 rings with increasing molar volume in silicate glasses. The high frequency envelopes (∼800–1300cm−1) were modeled using Gaussian lineshapes in order to isolate the separate contributions to the convoluted peak shape. These Gaussian bands are interpreted as being representative of the Qn species and are linked to the depolymerization reaction. We observe an increase in Q2 species coupled with a decrease in Q4 species with increasing Cs2O content. We propose that proximity to modifier cations drastically changes the vibrational character of the different Qn species and due to this effect we have assigned our curve-fit bands to both Qn and QnM species. High-temperature measurements were also conducted to investigate pre-melting and melting effects on the structure of these glasses. We observed similar changes in the high frequency envelope and Qn species distribution with increasing temperature as we did for increasing alkali content. The creation of Q2 species above the melting point leads us to conclude that depolymerization occurs at the solid-liquid transition.

Bridging oxygen speciation and free oxygen (O2 −) in K-silicate glasses: Implications for spectroscopic studies and glass structure

O 1s X-ray Photoelectron Spectroscopic (XPS) results for K-silicate glasses near the K-disilicate composition indicate the presence of at least two, and likely three, types of Bridging Oxygen (BO), which are distinguished by the number of K ions coordinated to BO (BO-K moieites). The relative abundances of these moieties cannot be accurately determined from XPS spectra, but based on crystalline K-disilicate, they are likely to be BO, BO-K1 and BO-K2 or BO-K1, BO-K2 and BO-K3 (subscript indicates the number of K+ coordinated to BO). The presence of three BO moieties is consistent with crystallographic results for crystalline K-disilicate (K2Si2SiO5) and their presence in K-silicate glass may be assessed using high quality molecular dynamics studies. The binding energy (BE) separating each BO-K peak is ~40 to ~70kJ and sufficient to affect stretching frequencies in Raman and IR spectra, and to effect the electronic properties of O and Si atoms in 17O and 29Si NMR spectra. The BO moieties may give rise to separate signals or they may coalesce to produce a broad, asymmetric band in Raman, 29Si NMR and 17O NMR spectra, just as they do in O 1s XPS spectra.The O 1s XPS and previously published 17O NMR spectra of glasses containing ~20 and ~35mol% K2O are well resolved. Both types of spectra yield the same NBO and BO abundances within experimental uncertainty. For 20mol% K2O glass, the O 1s XPS results yield ~21.5mol% NBO and ~78.5% BO whereas the 17O MAS NMR results are ~22.2% NBO and 77.8% BO. The 35mol% K2O glass yields similarly close agreement between O 1s XPS and 17O MAS NMR spectral fits. Both techniques can provide accurate oxygen species abundances provided the spectra are of high resolution, and provided complete fits are performed on the spectra.A 2D 29Si MAF NMR spectrum of K-disilicate glass indicates that two Q4 contributions are present in the spectrum, as previously observed in highly siliceous K-silicate glasses. One explanation for two peaks is that one Q4 signal represents Q4 tetrahedra attached to Q3 tetrahedra and the second peak represents Q4 attached to other Q4 species. An alternative explanation is offered based on these findings. The two Q4 signals may result from different types of BO-K moieties bonded to Si centers of Q4 species. K+, located in the second coordination sphere of BO, modifies the electronic (valence band) properties of the BO and Si atoms of the tetrahedron, thereby producing two Q4 signals. The 2D 29Si MAF NMR, 17O NMR and O 1s XPS spectra indicate ~2 (±1) mol% O2− in the K-disilicate glass. These three types of spectra yield remarkably similar results when high resolution spectra are collected and complete fitting of the spectra are performed.

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.

Evidence from 29Si Solid-State Nuclear Magnetic Resonance of Dissolution Reactions of Forsterite

We have used solid-state nuclear magnetic resonance (NMR) of 29Si to monitor the reaction of forsterite (Mg2SiO4) with isotopically enriched 13CO2. Fate of silicon that comes from dissolution of forsterite in the presence of water or NaCl brine was monitored as a function of depth in a packed bed reactor, which used elevated-temperature and -pressure conditions to mimic underground geological sequestration conditions. Silicon provides an important window into the reaction since the precipitation of amorphous silica can affect forsterite dissolution, and solid-state magic-angle spinning NMR can readily distinguish between 29Si in forsterite and amorphous silica. Furthermore, differences between Q3 and Q4 species of amorphous silica were observed as a function of depth. Results differed between water- and brine-based reactions, with enhanced dissolution of forsterite observed in the brine.

Insights into structural characterisation and thermal properties of compositionally equivalent vapour-condensed and melt-quenched glasses

Physical vapour deposition of Phosphate-based glasses enables their application onto load bearing implant surfaces for their potential to enhance osseointegration by leaching therapeutic ions at the bone/implant interface. Structural understanding with respect to processing parameters will prove useful in the on-going production of multi-functional coatings for antibacterial ion release and osseous tissue integration. This study highlights significant differences in short-range structural variation between vapour condensed and conventional melt-quenched phosphate glasses, via 31P MAS-NMR, XPS, FTIR and DTA. Three coating compositions containing P2O5 - 32.5, 34 and 37mol% showed greater bulk network polymerisation based on the presence of (23% to 45% Q2 species) versus (9% to 32% Q2 species) in melt-quenched glasses as determined by NMR. The proportion of P-O-P bridging oxygens as suggested by XPS on the surface of coatings remained consistent at (34% to 35%) forming (PO3)− metaphosphates (Q2), whilst P‐O‐P bonding in melt-quenched glasses increased from (12% to 18%) and were found to form (PO4)3− orthophosphates (Q0) and (P2O7)4− pyrophosphates (Q1). AFM analysis of the coating surfaces showed nano-topographical changes due to etch pitting, which led to Ra increases from 19nm to 167nm, which correlated to an increased deposition rate and therefore bombardment energy.

Pressure-induced metastable phase transformations of calcium metasilicate (CaSiO3): A Raman spectroscopic study

Pressure-induced phase transformations of two kinds of calcium metasilicate (chain-type wollastonite-2M and ring-type pseudowollastonite) were characterized by in-situ Raman spectroscopy at room temperature. Wollastonite transforms to two high-pressure polymorphs, i.e., wollastonite Ha and Hb at ca. 8.5 and 19 GPa, respectively and then slowly changes into amorphous phase above 26 GPa. Pseudowollastonite transforms to its high-pressure polymorph (pseudowollastonite II) at ca. 10 GPa, and then rapidly vitrifies at ca. 22–23 GPa. The three polymorphic transformations of wollastonite and pseudowollastonite at pressures are all reversible, but the amorphization of both wollastonite Hb and pseudowollastonite II are irreversible. A Raman analysis on the samples recovered from high pressure shows that the pressure-induced amorphs of wollastonite and pseudowollastonite are alike, but have different structures from the melt-derived CaSiO3 glasses regardless of compression treatment, i.e., far more Q2 but less Q3 species. The presence of the non-Q2 species in both wollastonite- and pseudowollastonite-derived amorphous phases indicates that disproportional polymerization and depolymerization of silicate chains and rings at the expense of the Q2 species characteristic to the two crystalline phases occurred during pressure-induced amorphization. Pressure-induced disproportionation also occurs in the melt-derived CaSiO3 glass under compression to show less Q3 yet more Q1 species after pressure release.

Structure, thermal behavior, and chemical durability of lead–calcium–phosphate glasses

ABSTRACTStructure and physical properties of 25CaO–xPbO–(75–x)P2O5 (0≤x≤35) glasses are investigated in this paper. Substitution of PbO for P2O5 in the binary 25CaO–75P2O5 glass was found to increase the density and to decrease the molar volume. Fourier transform infrared (FTIR) and Raman spectroscopies show the evolution of the phosphate skeleton when the PbO content increases: Q3 to Q2 species (0<x≤25) and Q2 phosphate network (x = 25) to short phosphate groups (x > 25) such as (P4O136−) (x = 35). The glass transition temperature first decreases with x, then increases for x values larger than 10%. The evolution of the glass transition temperatures is interpreted from the structural data: the minimum point observed in Tg is attributed to the transition of the ultraphosphate network from the network containing the modifying cations at isolated sites to a network with modifier sub-structure sharing terminal oxygens. At higher PbO content, the large increase in Tg is due to the reticulation of the phosphate network by PbO4 groups.

Properties and microstructure of eco‐cement produced from co‐sintered washed fly ash and waste sludge

This study investigated the possibility of recycling washed fly ash, limestone sludge, stone sludge, and iron‐oxide sludge in raw meal for producing Portland cement clinker. All of the major phase components of ordinary Portland cement (OPC)—C3S, C2S, C3A, and C4AF—were identified in each eco‐cement clinker. The compressive strength development showed that the eco‐cement pastes no contained washed fly ash was similar to commercial OPC products. The exothermic peak at 105°C to 440°C corresponded to the coordination change of C‐S‐H gel in the pastes during curing time. The TG/DTA curves showed that the weight loss of the eco‐cement pastes no contained washed fly ash was higher than that of the eco‐cement pastes contained 1% washed fly ash. The Q0 (−70 ppm) species shifted to the Q1 (−80 ppm) and Q2 (−87 ppm) species during curing time. The degrees of hydration of the eco‐cement pastes contained 2 to 4% washed fly ash were lower than that of the eco‐cement pastes no contained washed fly ash. The results of the physicomechanical tests showed that adding the limestone sludge, stone sludge, and iron‐oxide sludge did not negatively affect the quality of the produced cement. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 764–771, 2016

In situ structural changes of amorphous diopside (CaMgSi2O6) up to 20 GPa: A Raman and O K-edge X-ray Raman spectroscopic study

Diopside, CaMgSi2O6, is an important analogue for depolymerized silicate melts. We have used the complimentary spectroscopies, X-ray Raman Scattering (XRS), X-ray absorption near edge structure (XANES) and Raman, to investigate diopside glass in situ to 20GPa. We observe a stark change in behavior of CaMgSi2O6 near 4GPa that corresponds to a major change in the rate of inter-tetrahedral angle (∠Si–O–Si) closure. Below 4GPa, the ∠Si–O–Si closes rapidly at 2–3°/GPa whereas above 4GPa it decreases by ∼1°/GPa. A distinct shift to higher wavenumbers of the 870 and 905cm−1 Raman bands are observed at 1.3GPa suggesting that Q0 species have been completely converted to Q1 or higher Qn species.XRS measurements at the O K-edge suggest that [5]Si is formed by 3GPa. This formation is accompanied by a rapid decrease in the ∠Si–O–Si and a decrease in Q0 species. A linear increase in the geometric mean of the high frequency envelope, the χb value, from 999 to 1018cm−1 suggests that the conversion of NBO to BO is continuous up to 14GPa. Above 14GPa, the Raman spectra show an obvious negative shift in both, the high frequency peak maximum, and the χb position. Simultaneously, the low frequency envelope looses its asymmetry at 14GPa. This may be explained by either a loss of a vibrational mode in the range 1000–1200cm−1 and/or the formation of [6]Si. The structural evolution of CaMgSi2O6 correlates well with a major change in the compressibility and diffusivity around 5GPa.

Calcium/strontium substituted phosphate based glasses for orthopaedic applications

Event Abstract Back to Event Calcium/strontium substituted phosphate based glasses for orthopaedic applications Uresha Patel1*, Kazi Md Zakir Hossain1, Andrew Kennedy1, Alex Hannon2, Emma Barney1 and Ifty Ahmed1 1 University of Nottingham, Faculty of Engineering,, United Kingdom 2 Rutherford Appleton Laboratory, ISIS Facility, United Kingdom Introduction: Phosphate based glasses (PBGs) are an ideal material to act as “carriers” of therapeutic ions such as strontium (Sr), since their degradation rate can be tailored to range over orders of magnitude [1] by altering the glass composition. Sr substitution is of particular interest for orthopaedic applications due to the dual effect of Sr on bone metabolism: osteoblast activation and osteoclast inhibition[2]. This study aims to investigate the effect of the substitution of CaO with SrO in a PBG system with a fixed glass former content of 40mol%. By investigating the glass structure at an atomic level the inter-relationship between glass composition, structure and durability can be understood, enabling optimisation of an ideal therapeutic glass with controlled release rates. Materials and Methods: SrO was substituted for CaO in a series of PBGs (mol%(P2O5)40 (CaO)16-x (MgO)24 (Na2O)20 (SrO)x where x= 0, 4, 8, 12 and 16, denoted P40, Sr4, Sr8, Sr12 & Sr16 respectively). All glass samples were fabricated via a melt quench route involving drying of precursors at 350ºC for 30min, followed by melting at 1150ºC for 1.5h. Structural characterisation was carried out using 31P NMR (spectra obtained at the EPSRC UK National Solid-state NMR Service, Durham) and neutron diffraction (ND) studies (GEM diffractometer at ISIS spallation neutron source, Rutherford Appleton Laboratory, UK). The ND results were interpreted using fitting and simulation techniques. Dissolution studies were conducted in distilled water at 37ºC for 28d. Results and Discussion: The ND study revealed that CaO substitution with SrO had little effect on the well-ordered, short range structure of the glasses. This is thought to be due to the similarities in charge and field strength of Ca2+ and Sr2+ ions. The coordination numbers (CN) derived from ND showed that all P atoms are 4-coordinated (Table 1) which is consistent with previous studies[3]. The modifier environments for each glass composition also did not vary considerably as shown in Figure 1A & B. Solid state 31P NMR indicated little change in Qi­­ species for all compositions except for Sr16. These glasses showed an approximate 1:1 ratio of Q1:Q2 species, suggesting a network connectivity (number of bridging oxygens (BO) per network forming tetrahedral) of around 1.5. From these results it can be assumed the glass network consists of an average chain length of 4 tetrahedral units. The larger increase in Q1 species for Sr16 indicated that Q1 units may also be present as dimers i.e. pyrophosphates. Dissolution studies showed that Sr free glasses degraded at a faster rate than those with Sr, which contradicted previous studies [4][5]. In addition, no significant difference was observed between the Sr containing glasses (p>0.05) suggesting it may be possible to deliver varying concentrations of Sr without affecting the rate of the glass degradation. Conclusion: Replacing CaO with SrO exerted little effect on the overall glass structure. A consistent Qi distribution and network connectivity was observed along with little change in modifier environments (CN and percentage of BO). The dissolution studies showed that the Sr content had an insignificant effect on degradation rate, hence controlled release of a suited amount of Sr may be delivered posing these glasses beneficial for therapeutic use in bone related diseases such as osteoporosis. Funding body: Science and Technology Facilities Council (STFC ref. no. ST/L502583/1); EPSRC UK National Solid-state NMR Service at Durham

Dynamic Structural Changes of SiO2 Supported Pt–Ni Bimetallic Catalysts over Redox Treatments Revealed by NMR and EPR

SiO2 supported Pt–Ni bimetallic catalysts with different nickel loadings were prepared and their structural changes after redox treatments were studied by XRD, NMR, and EPR. It is found that the paramagnetic Ni species are mainly located on the surface of silica lattice. The relaxation of detected 29Si nuclei in our samples is mainly governed by a spin-diffusion mechanism. The paramagnetic effects are reflected in the spin–lattice relaxation of Q4 species, with the oxidized samples presenting faster relaxation rates than the corresponding reduced ones. Meanwhile the Q3 species, which are in close contact with the paramagnetic nickel centers, are “spectrally invisible”. In reducing atmosphere Ni gradually diffuses into Pt NPs to form PtNi alloys. While under oxidization treatment, the alloyed Ni atoms migrate outward from the core of Pt NPs and are oxidized. The main EPR spectrum results from reduced nickel species, and the reduced samples show stronger EPR signal than the corresponding oxidized ones. Howe...

Strontium- and calcium-containing, titanium-stabilised phosphate-based glasses with prolonged degradation for orthopaedic tissue engineering.

Strontium- and calcium-releasing, titanium-stabilised phosphate-based glasses with a controlled degradation rate are currently under development for orthopaedic tissue engineering applications. Ca and/or Sr were incorporated at varying concentrations in quaternary phosphate-based glasses, in order to promote osteoinduction. Ti was incorporated at a fixed concentration in order to prolong degradation. Glasses of the general formula (P2O5)–(Na2O)–(TiO2)–(CaO)–(SrO) were prepared via the melt-quench technique. The materials were characterised by energy-dispersive X-ray spectroscopy, X-ray diffraction, 31P magic angle spinning nuclear magnetic resonance, Fourier transform infrared spectroscopy, differential thermal analysis and density determination. The dissolution rate in distilled water was determined by measuring mass loss, ion release and pH change over a two-week period. In addition, the cytocompatibility and alkaline phosphatase activity of an osteoblast-like cell line cultured on the surface of glass discs was assessed. The glasses were shown to be amorphous and contained Q1, Q2 and Q3 species. Fourier transform infrared spectroscopy revealed small changes in the glass structure as Ca was substituted with Sr and differential thermal analysis confirmed a decrease in crystallisation temperature with increasing Sr content. Degradation and ion release studies also showed that mass loss was positively correlated with Sr content. These results were attributed to the lower electronegativity of Sr in comparison to Ca favouring the formation of phosphate-based mineral phases. All compositions supported cell proliferation and survival and induced at least 2.3-fold alkaline phosphatase activity relative to the control. Glass containing 17.5 mol% Sr had 3.6-fold greater alkaline phosphatase activity than the control. The gradual release of Ca and Sr supported osteoinduction, indicating their potential suitability in orthopaedic tissue engineering applications.

Effect of Zn- and Ca-oxides on the structure and chemical durability of simulant alkali borosilicate glasses for immobilisation of UK high level wastes

Compositional modification of United Kingdom high level nuclear waste (HLW) glasses was investigated with the aim of understanding the impact of adopting a ZnO/CaO modified base glass on the vitrified product phase assemblage, glass structure, processing characteristics and dissolution kinetics. Crystalline spinel phases were identified in the vitrified products derived from the Na2O/Li2O and the ZnO/CaO modified base glass compositions; the volume fraction of the spinel crystallites increased with increasing waste loading from 15 to 20wt%. The spinel composition was influenced by the base glass components; in the vitrified product obtained with the ZnO/CaO modified base glass, the spinel phase contained a greater proportion of Zn, with a nominal composition of (Zn0.60Ni0.20Mg0.20)(Cr1.37Fe0.63)O4. The addition of ZnO and CaO to the base glass was also found to significantly alter the glass structure, with changes identified in both borate and silicate glass networks using Raman spectroscopy. In particular, these glasses were characterised by a significantly higher Q3 species, which we attribute to Si–O–Zn linkages; addition of ZnO and CaO to the glass composition therefore enhanced glass network polymerisation. The increase in network polymerisation, and the presence of spinel crystallites, were found to increase the glass viscosity of the ZnO/CaO modified base glass; however, the viscosities were within the accepted range for nuclear waste glass processing. The ZnO/CaO modified glass compositions were observed to be significantly more durable than the Na2O/Li2O base glass up to 28days, due to a combination of the enhanced network polymerisation and the formation of Ca/Si containing alteration layers.

Exploration of metaphosphate glasses dispersed with Eu-doped SiAlON for white LED applications

Ca-α-SiAlON:Eu2+ oxynitride phosphors are typical luminescent materials with a high thermal tolerance. A series of metaphosphate glass samples (50MO–50P2O5; mol%, M=Zn, Ca, and Ba) were prepared in order to investigate their ability to disperse Ca-α-SiAlON:Eu2+ phosphor powders. The glass structures of all of the samples were formed using Q2 species and composed in long chain networks by investigation of the NMR and Raman spectra. In the glass samples, SiAlON was dispersed until reaching 5 or 6mass%. The color due to irradiation by a blue LED (wavelength of 450nm) depended on the glass composition, concentration of SiAlON, and thickness of the composite. Regarding the glass formation and quantum efficiency, the BaP glass with between 3 and 4mass% SiAlON composite was determined to be the most suitable for use as a host material for white LEDs.

Understanding the composition–structure–bioactivity relationships in diopside (CaO·MgO·2SiO2)–tricalcium phosphate (3CaO·P2O5) glass system

The present work is an amalgamation of computation and experimental approach to gain an insight into composition–structure–bioactivity relationships of alkali-free bioactive glasses in the CaO–MgO–SiO2–P2O5 system. The glasses have been designed in the diopside (CaO·MgO·2SiO2; Di)–tricalcium phosphate (3CaO·P2O5; TCP) binary join by varying the Di/TCP ratio. The melt-quenched glasses have been investigated for their structure by molecular dynamic (MD) simulations as well as by nuclear magnetic resonance spectroscopy (NMR). In all the investigated glasses silicate and phosphate components are dominated by Q2 (Si) and Q0 (P) species, respectively. The apatite forming ability of the glasses was investigated using X-ray diffraction (XRD), infrared spectroscopy after immersion of glass powders in simulated body fluid (SBF) for time durations varying between 1h and 14days, while their chemical degradation has been studied in Tris–HCl in accordance with ISO 10993-14. All the investigated glasses showed good bioactivity without any substantial variation. A significant statistical increase in metabolic activity of human mesenchymal stem cells (hMSCs) when compared to the control was observed for Di-60 and Di-70 glass compositions under both basal and osteogenic conditions.

Hydration of Portland Cement in the Presence of Highly Reactive Metakaolin

The degree of conversion of highly reactive metakaolin in Portland cement metakaolin paste at different ages as well as the influence of metakaolin on the degree of hydration of Portland cement and composition of C-S-H is investigated by 27Al- and 29Si-MAS NMR spectroscopy. At the age of 7 days, in the paste with 10% of metakaolin, the additive is completely consumed. In the 30% substituted cement paste, the content of metakaolin remains quite high (about 40% of the initial amount) even after 3 months of hydration. At the age of 1 - 3 months, the degree of Portland cement hydration in the presence of metakaolin is of 15% - 20% less than without it, probably, due to deficit of water or spatial restrictions. After 7 days of hydration, about half of C-S-H consists of material derived from metakaolin. Metakaolin mainly contributes to Q2 and Q2 (1Al) species, whereas PC does to Q1. After 1 day of hydration, an amount of ettringite in cement paste with high dosage of metakaolin is higher than in pure PC paste.

Developing nano-bonded refractory castables with enhanced green mechanical properties

Applying colloidal silica suspensions as a binder source for refractory castables has been of great interest in recent years. Nevertheless, the resultant low green mechanical strength of these castables has hindered their application in relevant areas. The current paper provides a novel engineering route to improve the mechanical properties of colloidal silica bonded castables before firing. In order to attain this target, small amounts of calcium aluminate cement (CAC) and/or hydratable alumina (HA) were used as gelling agents. A splitting tensile test showed that although using HA resulted in a more significant increase in the modulus of rupture of the samples when compared to CAC, mixing both (CAC+HA) had the most positive impact on the green mechanical properties of the castables, leading to strength levels as high as the reference cement-bonded system (CAC-Ref). XRD and DTG tests were carried out to evaluate the hydration behavior of the selected additives. The results indicated that CAC enhanced the hydration of HA based on the accelerated dissolution of the gel layer formed on HA particles, which was induced by the Al(OH)4− common ion effect. The proposed mechanism was confirmed by a specific conductivity test. Additionally, 29Si solid state NMR spectroscopy was used to determine the effect of the dual additive system (HA+CAC) on the siloxane bond formation. Quantification of Q2, Q3 and Q4 species in alumina–colloidal silica suspensions containing HA, CAC or HA+CAC highlighted that the improved green strength is mainly related to a more effective hydration of HA. Based on the NMR and XHR SEM analyses, HA can be considered as an alternative gelling agent for nano-bonded refractory castables.