Phases In Glass-ceramics Research Articles

Ordering of fluorite-type phases in erbium-doped oxyfluoride glass ceramics

In this study, novel transparent Er3+ doped glass ceramics were prepared from melt-quenched oxyfluoride glasses with general composition of Na2O-NaF-BaF2-YbF3-Al2O3-SiO2. The crystallization of fluorite (BaF2, BaF2-YbF3, NaF-BaF2-YbF3 and Na0.5-xYb0.5+xF2+2x) and distorted fluorite (rhombohedral Ba4Yb3F17 and tetragonal NaF-BaF2-YbF3) phases was analysed in glass ceramics with different BaF2 and YbF3 ratio. The phase composition and microstructure were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Intense red upconversion luminescence (UCL) was detected under near-infrared excitation resulting from three photon upconversion followed by cross-relaxation between Er3+ and Yb3+ ions.The local environment of Er3+ ions in fluorite and distorted phases was analysed using site-selective spectroscopy. The Er3+ ions were found to act as nucleation centres in the glass ceramics containing BaF2. The phase transition from metastable fluorite to rhombohedrally and tetragonally distorted fluorite phases was detected using Er3+ ions as a probe.

Destructive and non-destructive behavior of nickel oxide doped bioactive glass and glass-ceramic

Nickel oxide substituted bioactive glasses (45S5) have been prepared by melting and annealing techniques. The doping of Ni2+ ion from 0 to 1.65 mol% of NiO was done to replace Si4+ ion and yield a charge balanced (CB) bioactive glass. The Ni2+ ion would enter into [SiO4]4− network as [NiO4]2− tetrahedra due similar charge/size ratio, but depending upon oxygen environment, it may act as modifier also in octahedral coordination in the glass. Polycrystalline bioactive glass-ceramics were prepared through controlled heat treatment. The glass and glass-ceramic structure was evaluated using FTIR and XRD techniques. The crystalline phases in bioactive glass-ceramics were identified using X-ray difractometry. The SEM micrographs of the samples after chemical treatment with simulated body fluid (SBF) for definite time of 15 days had shown the formation of hydroxyl carbonate apatite (HCP) layer on their surface which indicated that NiO had no opposite effect on the overall bioactivity. The destructive tests like microhardness, compressive, flexural strengths, and the non-destructive tests of elastic moduli were carried out. Both the results indicated that substitution of nickel oxide by silica in 45S5 bioactive glass and glass-ceramic influenced the structure and enhanced its density, compressive, flexural strength, micro hardness, and elastic properties.

Preparation of Glass Ceramics by Reactive Crystallization with Waste Glass and Spinel

Magnesium silicate glass ceramics were prepared by reactive crystallization with mixed powder of waste glass and spinel. The effects of spinel content and sintering temperature and holding time on the crystal phase and morphology of magnesium silicate glass ceramics were investigated. The reactive crystallizing behavior between waste glass powder and spinel was studied using energy dispersive spectrdmeter during the holding process. The result show that the optimum preparation conditions were as follows: the addition of 30 wt% spinel used as crystallization promoting agent, sintering temperature of 900 oC and holding time of 2 h. The magnesium silicate and alumina crystals were formed via an interaction between glass powder and spinel instead of direct precipitation from the parent glass. With increasing of the holding time, the Al and Mg element contents of the glass were increased, on the contrary, that Si element content was decreased in the glass phase. It shows that the Si element is diffused from glass into spinel phase and subsequently magnesium silicate crystals are formed.

Study on ZrSiO4-aluminosilicate glass coating with high infrared emissivity and anti-oxidation properties

A multicomponent coating composed of ZrSiO4 and aluminosilicate glass was designed and prepared by slurry dipping and subsequent sintering on the surface of SiC substrate to improve the anti-oxidation ability of substrate. At appropriate temperature, the molten aluminosilicate glass carrying the stable ZrSiO4 particles will spread over the substrate’s surface to form a dense and stable coating. Among them, the flowing aluminosilicate glass will fill the crack and micro-pores of ZrSiO4, which inform a dense coating. Glass phase and ceramic phase could inhibit the propagation of the cracks together. This coating shows high infrared emissivity at broad bands, reaching more than 0.93. Wonderfully, the coating was endowed high oxidation resistance performance at high temperature in the air, which was mainly attributed to the compact and stable structure of coating, coupled with the high thermal expansion coefficient.

Preparation and optical properties of Er3+: Na2O-Al2O3-SiO2 transparent glass-ceramics

Na2O-Al2O3-SiO2 glass-ceramics doped with Er3+ ions were synthesized by the conventional melt quenching technique at a low melting temperature. The samples were characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis-NIR scanning spectrophotometry, and fluorescence spectrometry. The results show that the main crystalline phase of glass-ceramics is nepheline.The best heat-treatment process is at 520 °C for 2 h. Because the up-conversion luminescence and near infrared luminescence properties of glass doped with Eu3+ are studied in detail.

Assessment of nickel oxide substituted bioactive glass-ceramic on in vitro bioactivity and mechanical properties

Many type of oxide substituted glass-ceramics like strontium, cobalt, barium and titanium have shown bioactivity with improved mechanical properties. The present work reports the in vitro bioactivity and mechanical properties of nickel oxide substituted in bioactive glass-ceramic and results were compared with 45S5 bioactive glass-ceramic. Bioactive glass ceramics were processed through controlled crystallization of their respective bioactive glasses. The formed crystalline phases in bioactive glass-ceramics were identified using X-ray diffraction (XRD) analysis. The formation of HA layer was assessed by immersing them in the simulated body fluid (SBF) for different soaking periods. The formation of hydroxyapatite was confirmed by FTIR spectrometry, SEM and pH measurement. Densities and mechanical properties of the samples were found to increase considerably with an increasing the concentration of nickel oxide. A decrease in glass transition temperature (Tg) with NiO addition showed that the nickel oxide had acted as an intermediate in smaller quantities in the bioactive glass. The cell culture studies demonstrated that the samples containing low concentration of NiO from 0 to 1.65mol% were non-cytotoxic against osteoblast cells. Finally, this investigation clearly concluded that NiO doped bioactive glass would be potential biomaterials for biomedical applications.

Preparation of Glass-Ceramics by Reactive Crystallization with Waste Glass and Mullite

Diopside glass-ceramics were prepared by reactive crystallization with mixed powder of waste glass and mullite. The effects of mullite content and sintering temperature and holding time on the crystal phase and morphology of diopside glass-ceramics were investigated. The reactive crystallizing behavior between waste glass powder and mullite was studied using energy dispersive spectrdmeter during the sintering and holding process. The result show that the optimum preparation conditions were as follows: the addition of 30 wt% mullite used as crystallization promoting agent, sintering temperature of 900 °C and holding time of 2h. The main difference between reactive crystallization method and the traditional method of preparing diopside glass-ceramics was the reactive crystallization mechanism. The diopside and corundum crystals were formed via an interaction between glass powder and mullite instead of direct precipitation from the parent glass during the calcining and holding process. With the increasing of sintering temperature and holding time, the Ca and Mg element concents of the glass were increased, on the contrary, that Si element concent was decreased in the mullite. It shows that the Si element diffused from mullite to glass and precipitated diopside crystals.

Studies of the spectroscopic properties of lead–gallium oxyfluoride (LGOF) glasses and glass–ceramics activated by Pr3+ ions

Lead–gallium glasses, due to the absence of typical glass-forming components, are characterized by an increased tendency to crystallization. Despite this, they are interesting materials due to a shift of IR absorption edge up to 6 and 7μm. The paper studies thermal stability, the UV–vis and IR transmission and luminescence spectroscopy of the lead–gallium glass. The base lead–gallium glass 0.65PbO·0.20Ga2O3·0.15SiO2 was modified by the addition of 2mol% BaF2 and 1mol% Pr6O11. DTA/DSC data showed that the glasses are characterized by the multi-stage crystallization. Unusual luminescence excitation spectra confronted with emission spectra, measured for glass (as made) and glass ceramic (annealed) phase, have been tentatively interpreted by means of single configuration coordinate diagrams. It seems that in both phases the praseodymium ions occur in two sites: lower- and higher-field environment. We propose the fluorine-affected sites as the lower field sites and purely oxide sites as the higher field sites. It seems likely that O–Pr–O sites can be treated as the higher filed sites whereas the fluorine affected sites, i.e. F–Pr–F and/or O–Pr–F sites, as the lower field sites.

Final flotation waste kinetics of sintering at different heating regimes

In the copper extraction, especially during the process of flotation enrichment and the pyrometallurgical processing, the waste materials that represent huge polluters of environment are being generated. In order to examine the application of Final flotation waste (FFW) in the manufacturing of new materials from the glass-ceramic group phase and mineral composition were examined as well as thermal properties. FFW kinetics of sintering has been tested at different dyamics (1?C/min, 29?C/min and 43?C/min), in order to find the optimum conditions for sintering with a minimum amount of energy and time consumption. The samples were examined using: X-ray diffraction, X-ray fluorescence analysis, SEM (Scanning Electron Microscopy) and thermal microscopy. The best results for the production of glass ceramic materials were obtained during the sintering at heating regime of 29?C/min.

Synthesis of 60 (wt.)%SiO<sub>2</sub>-40 (wt.)%CaO Sol-Gel Derived Glass-Ceramic and <i>In Vitro</i> Bioactivity Assessment in SBF Solution

The objective of this study is to determine the bioactive property of compacted and crystallized glass-ceramic based on 60 (wt.)%SiO2-40 (wt.)%CaO by immersion in simulated body fluid (SBF) for various times. The powder of this phosphate-free glasses based on binary SiO2-CaO system was synthesized via an acid catalyzed sol-gel route prior to powder compaction for the bioactivity assessment. The main chemical precursors used for synthesis the glass powder were tetraethylorthosilicate (TEOS) and calcium nitrate tetrahydrate reagent whereas nitric acid was used as the catalyst during the sol-gel process. The obtained hydrogels were dried, heat treated and grounded into powders before being pressed into rounded shape compacts. The initial compacted glass then sintered at 1000°C for 4 hours in typical muffle furnace to obtain crystallized glass-ceramic phase. Precipitation of apatite structures on the glass-ceramic surface were observed by immersion of the compacted pellets into SBF solution from one to 21 days. All the test results obtained from X-Ray Diffraction (XRD), Fourier Transform-Infrared (FT-IR), Field Emission-Scanning Electron Microscopy (FE-SEM) and Energy Dispersive Spectroscopy (EDS) indicates that the sintered glass-ceramic showed an actively bioactivity property. Precipitation of apatite was detected on the surface of the compacted glass-ceramic within the first 24 hours after being immersed in SBF. The development of apatite structures were continuously increased and progressively growth into coral-like structure and has particularly found to crystallize into carbonated apatite (HCA) layer after 14 days of immersion in SBF.

Reducing the reaction between boron-containing sealing glass-ceramics and lanthanum-containing cathode: Effect of La2O3

The volatile boron species from sealing glass-ceramics have a significant poisoning effect on the electrochemical activity of Solid Oxide Fuel Cell (SOFC) cathodes. The reaction between boron-containing sealing glass-ceramics and cathodes thus presents a challenge for the development of SOFC. Here we report for the first time that the addition of La2O3 can significantly reduce the boron volatility from sealing glass-ceramics and consequently the formation of LaBO3 in reaction couple between glass and (La,Sr)(Co,Fe)O3 (LSCF) cathode. In particular, the boron volatility can be reduced by about 6 times with the addition of 4mol.% La2O3 (3.7×10−3 vs. 0.6×10−3%). The addition of La2O3 condenses the structure of glasses and glass-ceramics, contributing to the decrease in boron volatility from glass-ceramics. In addition, La2O3 dopant favors the formation of boron-containing phase (La5SiBO13) in glass-ceramics, which dramatically reduces the boron volatility. The reported results provide an effective approach for solving the sealing challenge.

Properties and Crystallization Phenomena in Li2Si2O5–Ca5(PO4)3F and Li2Si2O5–Sr5(PO4)3F Glass–Ceramics Via Twofold Internal Crystallization

The combination of specific mechanical, esthetic, and chemical properties is decisive for the application of materials in prosthodontics. Controlled twofold crystallization provides a powerful tool to produce special property combinations for glass–ceramic materials. The present study outlines the potential of precipitating Ca5(PO4)3F as well as Sr5(PO4)3F as minor crystal phases in Li2Si2O5 glass–ceramics. Base glasses with different contents of CaO/SrO, P2O5, and F− were prepared within the glasses of the SiO2–Li2O–K2O–CaO/SrO–Al2O3–P2O5–F system. Preliminary studies of nucleation by means of XRD and scanning electron microscopy (SEM) of the nucleated base glasses revealed X-ray amorphous phase separation phenomena. Qualitative and quantitative crystal phase analyses after crystallization were conducted using XRD in combination with Rietveld refinement. As a main result, a direct proportional relationship between the content of apatite-forming components in the base glasses and the content of apatite in the glass–ceramics was established. The microstructures of the glass–ceramics were investigated using SEM. Microstructural and mechanical properties were found to be dominated by Li2Si2O5 crystals and quite independent of the content of the apatite present in the glass–ceramics. Biaxial strengths of up to 540 MPa were detected. Ca5(PO4)3F and Sr5(PO4)3F influence the translucency of the glass–ceramics and, hence, help to precisely tailor the properties of Li2Si2O5 glass–ceramics. The authors conclude that the twofold crystallization of Li2Si2O5–Ca5(PO4)3F or Li2Si2O5–Sr5(PO4)3F glass–ceramics involves independent solid-state reactions, which can be controlled via the chemical composition of the base glasses. The influence of the minor apatite phase on the optical properties helps to achieve new combinations of features of the glass–ceramics and, hence, displays new potential for dental applications.

Synergistic Effect of K<sub>2</sub>O and Al<sub>2</sub>O<sub>3 </sub>on<sub> </sub>the Crystallization and Structure of Na<sub>2</sub>O-CaO-SiO<sub>2</sub>-MgO-Al<sub>2</sub>O<sub>3</sub>-ZnO of Glass-Ceramics

The Na2O-CaO-SiO2-MgO-Al2O3-ZnO glass-ceramics was prepared from the phosphorus slag as main primary raw materials by melt quenching technique. The effects of K2O and Al2O3 on crystallization behavior and structure of glass-ceramics were investigated by DSC, XRD and SEM. It is shown that the main crystalline phase is combeite (Na4Ca4(Si6O18)) in glass-ceramics. K2O and Al2O3 do not change the main crystalline phase of glass-ceramics, but K2O increases the crystallization temperature, Al2O3 increases the crystallization temperature, obviously decreases the grain size. The K2O isometric replaces Na2O at the same time the Al2O3 isometric to replace SiO2, reduced the grain size.

Influence of Strontium Oxide on Structural Transformations in Diopside-Based Glass-Ceramics Assessed by Diverse Structural Tools

A full understanding of the structural glass variations and of the nucleation and growth of crystalline phases in glass-ceramics (GCs) induced by compositional changes is highly relevant for applications such as sealants for solid oxide fuel cells, bio- and dental materials, and photonics. Systematic substitution of Ca with Sr in diopside (Di-CaMgSi2O6) has a significant impact on the crystalline-phase assemblage after heat treating at 850 °C for 500 h. A high percentage of Di crystallized from Sr-free glass; however, with increasing Sr content the tendency toward crystallization decreased, and Sr-akermanite (Sr-Ak) was preferentially crystallized. In this study, the structural transformations in the Di-based-GC system upon the substitution of calcium with strontium have been examined by X-ray powder diffraction (XRD), 29Si and 27Al magic angle spinning (MAS)-nuclear magnetic resonance (NMR), and Raman spectroscopies. XRD Rietveld refinement results indicate that up to a maximum of ∼25 at. % of Sr occupie...

Principles of crystal phase formation in Ivoclar Vivadent glass-ceramics for dental restorations

This article describes the main principles that are involved in the development of glass-ceramics for restorative dental products. These principles include the controlled nucleation and crystallization of crystal phases in glass-ceramics. The aim of these liquid-to-solid state reactions is to produce glass-ceramics with different crystal phases, such as lithium disilicate, which feature special microstructures and crystal phase contents in order to influence the properties of the resulting material. Two fundamentally different nucleation and crystallization mechanisms have been identified in this respect: firstly, internal nucleation and crystallization by heterogeneous, amorphous or nano-crystalline phases to precipitate, e.g. lithium disilicate (Li2Si2O5) and secondly, surface nucleation and crystallization by means of controlled surface activation to precipitate, e.g. leucite (KAlSi2O6). The authors show methods for developing also glass-ceramics of fluorapatite type (Ca5(PO4)3F) and glass-ceramics with high ZrO2 content. The use of the principles mentioned allows Ivoclar Vivadent AG to develop glass-ceramics with e.g. high mechanical strength, chemical durability and good optical properties, which are suitable for use in restorative dentistry. Metal-free and metal-supported dental restorations such as crowns, inlays, veneers and bridges are presented as examples of typical applications.

Fabrication and characterization of Er+3 doped SiO2/SnO2 glass-ceramic thin films for planar waveguide applications

Glass-ceramics are a kind of two-phase materials constituted by nanocrystals embedded in a glass matrix and the respective volume fractions of crystalline and amorphous phase determine the properties of the glass-ceramics. Among these properties transparency is crucial in particular when confined structures, such as, dielectric optical waveguides, are considered. Moreover, the segregation of dopant rare-earth ions, like erbium, in low phonon energy crystalline medium makes these structures more promising in the development of waveguide amplifiers. Here we are proposing a new class of low phonon energy tin oxide semiconductor medium doped silicate based planar waveguides. Er3+ doped (100-x) SiO2-xSnO2 (x= 10, 20, 25 and 30mol%), glass-ceramic planar waveguide thin films were fabricated by a simple sol-gel processing and dip coating technique. XRD and HRTEM studies indicates the glass-ceramic phase of the film and the dispersion of ~4nm diameter of tin oxide nanocrystals in the amorphous phase of silica. The spectroscopic assessment indicates the distribution of the dopant erbium ions in the crystalline medium of tin oxide. The observed low losses, 0.5±0.2 dB/cm, at 1.54 μm communication wavelength makes them a quite promising material for the development of high gain integrated optical amplifiers.

Synthesis and Analysis of Optical Properties of Cordierite Nanopowder Prepared by the Pechini Method

In this research, the amorphous-type cordierite (2Mg.2Al2O3.5SiO2) was synthesized by the Pechini method. After calcination at 800°C, the powder was pressed to form disk pellets which were sintered at 1200, 1250 and 1300°C. The structural information of the synthesized glass ceramic cordierite phases have been obtained by X-ray diffraction (XRD) when the sintering processes performed by increasing the temperature. The SEM-micrographs of the glass ceramic showed a uniform distribution of particles in the structure. The sizes of the produced nanocrystallite grains were found to be in the range of 27-100nm. Furthermore, we determined refractive index (n), extinction coefficient (k), real and imaginary dielectric coefficients as a function of wavenumber (K) by using Kramers-Kronig dispersion transformations.

Structural characteristics and spectral properties of novel transparent lithium aluminosilicate glass-ceramics containing (Er,Yb)NbO4 nanocrystals

Transparent lithium aluminosilicate glass-ceramics based on nanosized crystals of β-quartz solid solutions and Er,Yb orthoniobates are prepared for the first time, to our knowledge. According to X-ray diffraction analysis, parent Er,Yb-codoped glass contains (Er,Yb)NbO4 nanocrystals with the defected fluorite structure while the single Yb-doped glass is X-ray amorphous. The Er,Yb orthoniobates with the tetragonal structure crystallize under heat-treatments at 800–900°C; and at 1000°C the transformation to a monoclinic form begins. β-quartz solid solutions are the main crystalline phase of glass-ceramics prepared in the temperature range of 800–1000°C. These structural transformations are confirmed by Raman spectroscopy. The structure evolution is illustrated by the TEM study of the Yb-doped glass and glass-ceramics. The spectral-luminescent properties of glass-ceramics are directly linked to their structure; an appearance of the monoclinic phase has a crucial effect on these properties. Glass-ceramics with tetragonal (Er,Yb)NbO4 nanophase are characterized by the high efficiency of Yb3+→Er3+ energy transfer (85%), strong absorption in the vicinity of 0.98μm and shorter lifetime of 4I13/2 state (as compared with the parent glass), so they look promising for laser operation in the eye-safe region around 1.53μm.

Reducing the reaction between boron-containing sealing glass-ceramics and lanthanum-containing cathode: Effect of Bi2O3

The volatile boron species from sealing glass-ceramics have a significant poisoning effect on the electrochemical activity of Solid Oxide Fuel Cell (SOFC) cathodes. The reaction between boron-containing sealing glass-ceramics and cathodes thus presents a challenge for the development of SOFC. Here we report for the first time that the addition of La2O3 can significantly reduce the boron volatility from sealing glass-ceramics and consequently the formation of LaBO3 in reaction couple between glass and (La,Sr)(Co,Fe)O3 (LSCF) cathode. In particular, the boron volatility can be reduced by about 6 times with the addition of 4 mol.% La2O3 (3.7 × 10−3 vs. 0.6 × 10−3%). The addition of La2O3 condenses the structure of glasses and glass-ceramics, contributing to the decrease in boron volatility from glass-ceramics. In addition, La2O3 dopant favors the formation of boron-containing phase (La5SiBO13) in glass-ceramics, which dramatically reduces the boron volatility. The reported results provide an effective approach for solving the sealing challenge.

Studies on the use of microwave for enhanced properties of glass-ceramics produced from sewage sludge pyrolysis residues (SSPR)

SSPR (sewage sludge pyrolysis residues) were reused as main raw materials (up to 80%) for glass-ceramics. In the present work, glass-ceramics were synthesized by microwave and conventional processes with an objective of investigating the function of microwave radiation on enhancement in the properties and crystallization mechanisms of the two heating styles. The heat treatment schedule of the microwave glass (M-G) and conventional glass (C-G) was decided on the basis of differential scanning calorimetry (DSC) results. A control study of microwave glass (CM-G) was carried out following identical heat treatment schedule as was adopted by M-G under conventional heating process. X-ray diffraction (XRD) analysis revealed that the main crystalline phase of microwave glass-ceramics (M-GC) was anorthite (CaAl2Si2O8), and the main crystalline phases of both conventional glass-ceramics (C-GC) and control microwave glass-ceramics (CM-GC) were wollastonite (CaSiO3) and anorthite (CaAl2Si2O8). The difference of the main crystalline phase between the two heating styles was attributed to the improved ionic interdiffusion caused by microwave radiation. Scanning electron microscopy (SEM) analysis clearly indicated that M-GC possess finer and uniform microstructure. M-GC exhibited excellent properties in comparison to C-GC and CM-GC. The kinetics study indicates that microwave radiation decreased Ea about 76kJmol−1. The n values of M-G and C-G were in the range of 3.03–3.43 and 1.73–1.95, representing the crystallization mechanism of bulk nucleation and surface nucleation, respectively.