Crystalline Phase Of Glass-ceramics Research Articles

Effect of thermal poling in sodium tantalum phosphate glass-ceramics

Eu3+-doped sodium tantalum phosphate glass-ceramics containing bronze -like perovskite crystalline phase Na2Ta8O21 were obtained with different crystalline states (degree of crystallinity and average crystallite size) by a suitable control of the heat-treatment time and temperature of the precursor glass. Luminescence properties of Eu3+ in these materials are in agreement with a progressive insertion of the rare earth ions in the sodium tantalate Na2Ta8O21 phase, as probed by a clear decrease of the intensity ratio between transitions [5D0 →] 7F2/7F1 and narrowing of characteristic emission bands. Thermal poling insights were performed on these glassy and glass-ceramic materials and the experimental conditions had to be carefully optimized in the glass-ceramics to avoid electrical sparks and sample break associated with dielectric breakdown of the samples. Suitable and stable thermal poling treatments could be performed at 250 °C and 900 V under N2 atmosphere on both glass and glass-ceramics. These first insights pointed out a lower migration kinetic of sodium ions when compared to the precursor glass as well as a lower content of depleted ions, since part of sodium is supposed to be “frozen” inside the crystalline phase in glass-ceramics. Despite these lower kinetic poling conditions, a poled sodium depleted layer whose thickness depends on the poling time was successfully formed at the anode side. Reflectance infrared spectroscopy was also used to investigate the structural changes in the poled layer. These IR data pointed out that structural changes induced by thermal poling are mainly promoted in the phosphate network rather than tantalate units in both glass and glass-ceramics in agreement with a selective sodium migration from the remaining glassy phase. Macroscopic induced SHG measured by the Maker fringes technique is also consistent with the EFISH model and quantitative simulations of these data allowed to estimate second order nonlinear optical susceptibilities χ(2) ten to twenty times lower in the glass-ceramics than in the precursor glass. Such electric behavior is discussed in terms of dielectric properties of heterogeneous materials and interfacial polarization mechanisms between crystallites and glassy phase.

Monitoring decomposition of Eu3+ doped LaPO4 nanocrystals in glass using Eu3+ as an optical probe for applications in temperature sensing

The methods to directly introduce crystals of known chemistry, size, and optical properties into a glass matrix are useful to circumvent some limitations related to the control of the growth of crystalline phases in glass-ceramics. The emission spectrum of LaPO4:Eu3+ is characteristic for highly symmetrical coordination of Eu3+ and very distinct from the emission spectrum of Eu3+ in amorphous host, which allows for its application as an optical probe. Here, Eu3+ - doped LaPO4 crystals were prepared using solid state reaction and added into various phosphate glass melt before quenching. From the changes in the micro-luminescence spectra, the decomposition occurs along with the diffusion of the Eu3+ ions into the glass confirming that the measurement of the micro-luminescence allows one to precisely track the crystal's decomposition inside the composite. It is demonstrated, for the first time to our knowledge, that the thermometric sensitivity of the Eu3+ ions can be enhanced by adding the LaPO4:Eu3+ crystals into phosphate fluoride glasses due to special separation of the crystallites during the composite preparation and also to the reduction of the self-absorption of the 5D1→7F1 emission. The composite material is promising for applications in temperature sensing.

Study on glass-ceramic prepared by zinc leaching residue and solidification mechanism of heavy metals

Zinc leaching residue is a hazardous solid waste with difficult treatment, high hazard and high yield, and it is a great challenge to treat it efficiently, harmlessly and economically among the various methods available. This paper introduced a micro-crystallization method to process zinc leaching residue into glass-ceramics with excellent performance and high value. The heavy metals in the raw material were well solidified in the glass-ceramics, eliminating the high hazard of heavy metals and other components. The bending strength, compressive strength, and Vickers hardness of the glass-ceramics prepared at the sintering temperature of 950 °C were 69.2 MPa, 434.3 MPa, and 6.66 GPa, respectively, while the water absorption, density, and acid and alkali corrosion resistance were excellent. The relationship between the microstructure and properties of glass-ceramics was investigated using traditional analytical techniques such as XRD, Raman, and SEM, and the mechanism of solidification of heavy metals Pb, Zn and Mn in glass ceramics were innovatively researched by the modified BCR sequential leaching test and XPS analysis. Anorthite and diopside ferrian were the two main crystalline phases in glass-ceramics. The sintering temperature affected the formation and growth of crystals, and determined the crystal size and crystallization rate, thus affecting the properties of glass-ceramics. Part of the heavy metal was solidified in the amorphous phase in the glass-ceramic, and the other major part entered the crystal as an impurity substitution to form a solid solution at a specific location. The zinc leaching residue based glass-ceramic had been studied, which was pioneering and with excellent performance and environmental safety. Thus, the safe and economical treatment of these hazardous wastes promotes the clean, green and efficient development of related industries.

Crystallization characteristics, microstructural evolution, and Cr migration mechanism of glass-ceramics synthesized entirely from low-carbon ferrochromium slag and waste glass

The disposal and large-scale reutilization of industrial solid waste in construction materials have been gaining considerable interest. Herein, the synthesis of glass-ceramics from low-carbon ferrochromium slag (FCS) and waste glass is reported. The crystallization characteristics, microstructural evolution, and Cr migration mechanisms of the glass-ceramics were investigated through offline quenching experiments. The physical properties and Cr ion leaching performance were tested and evaluated. As the low-carbon FCS content was increased, glass network depolymerization was promoted and the crystallization ability was effectively improved. When 50 wt% low-carbon FCS was added, the compressive strength and Vickers hardness of the glass-ceramics reached maximum values of 160.26 MPa and 736 Hv, respectively. Simultaneously, the dominant crystalline phase in glass-ceramics was transformed from diopside and wollastonite into gehlenite when the low-carbon FCS content was further increased to 60 wt%, thereby reducing the mechanical properties. Cr2O3 primarily existed as a [CrO6] octahedron and Cr-containing spinel in the parent glass, resulting in composition segregation. On combining the growth orientation of diopside and spinel, the resulting specific crystal coating structure improved the Cr ion leaching performance. Considering the physical properties and risk of Cr leaching, the optimal FCS content in glass-ceramics is 40–50 wt%. These findings indicate that the production of glass-ceramics from low-carbon FCS and waste glass is an effective and environment-friendly method for co-utilizing these two solid wastes.

Comparison of hot pressing sintering and conventional powder-sintering in preparation of CaO-Al2O3-SiO2-Fe3O4-R2O glass ceramics

The influences of different alkali metal oxides, sintering methods, process conditions on the crystallization behavior and densification of CaO-Al2O3-SiO2-Fe3O4-R2O (R=Na, K) glass ceramics were investigated. It can be concluded that the initial crystallization temperature and crystallization peak temperature of glass containing K2O were higher than those of glass containing Na2O, respectively. The increase of sintering temperature promoted the precipitation of crystalline phase in glass ceramics, meanwhile, the crystalline phases transformed from single magnetite to magnetite and CaFeSi2O6. The glass ceramics obtained by powder-sintering showed a low degree of densification. The fully dense glass ceramics containing Na2O can be obtained by hot pressing sintering above 680 °C for 2 h. However, due to the high viscosity of the glass containing K2O, the degree of densification of K2O containing glass ceramics was relatively low even after the hot pressing sintering. Magnetite based glass ceramics can be used as candidates for magnetic materials.

Frequency-related viscoelastic properties in high translucent CAD-CAM resin-based composites

ObjectiveThe study aims to quantify the viscoelastic properties of representative dental CAD/CAM resin-based composites (RBC) and to determine the effects of loading frequencies on the viscoelastic material response in comparison to clinically established CAD/CAM glass ceramics. MethodsEight RBCs, one leucite-reinforced, and one lithium disilicate glass-ceramics were selected. The quasi-static (indentation hardness HIT, indentation modulus, EIT) and viscoelastic (storage modulus E′, loss modulus E″, loss factor tan δ) material behavior was monitored by a depth-sensing indentation test equipped with a DMA module. A low-magnitude oscillating force was therefore superimposed onto a quasi-static force (Fmax = 1000 mN) at 20 different frequencies in the range 1–50 Hz. One and multiple-way analysis of variance (ANOVA), the Tukey honestly significant difference (HSD) post-hoc tests (α = 0.05), and a Pearson correlation analysis were used for data analysis. ResultsThe quasi-static parameters increased with the crystalline phase in glass ceramics and with the amount of inorganic filler in RBCs. The tan δ, which is related to the damping capacity of a material, increased with the increasing amount of glass phase in glass ceramics or with the amount of organic phase in RBCs. A pronounced influence of the frequency on the measured parameters and their patterns of variation was observed. HIT was up to ten time higher in glass ceramics compared to RBCs and highest at the lowest frequency (1 Hz). Parameters EIT and E′ differ less and were lowest at the lowest frequency. E″ distinguished three different patterns of variation with frequency. The tan δ decreased rapidly with frequency in glass ceramics, while the decrease in RBCs was gradually. Frequency influenced stronger tan δ (p < 0.001, ηP2 = 0.85), followed by E′ (p < 0.001, ηP2 = 0.773), EIT (p < 0.001, ηP2 = 0.772), and E″ (p < 0.001, ηP2 = 0.714), and less HIT (p < 0.001, ηP2 = 0.384). ConclusionsAll materials sowed viscoelastic behavior related to their microstructure and the internal friction created by grain or interphase boundary relaxation. RBCs have better damping capabilities over a wider frequency range. The deviations from the ideal elasticity were significantly lower in the glass ceramics than in the RBCs.

Preparation and characterization of glass-ceramics from oil shale ash: Effect of basicity and sintering temperature on crystallization behavior, properties, and environmental risk

Oil shale ash is an inorganic by-product generated from the combustion and refinement of oil shale. In this study, it was used as main raw material to produce glass-ceramics. The crystalline phases, crystallization mechanism, bulk density, compressive strength and microstructure of glass-ceramics were studied. Specifically, the leaching characteristics and ecological risk assessment of heavy metals in glass-ceramics were emphasized. The results showed that the increase of basicity reduced the crystallization activation energy, but the surface crystallization mechanism of different samples has not changed. Anorthite and diopside were identified as the main crystalline phases in glass-ceramics despite varying basicity and sintering temperatures. The compressive strength and bulk density increased with the increase of sintering temperature. The compressive strength of VS2 (basicity = 0.3) was higher than that of VS1 (basicity = 0.2) for the same sintering temperature due to more crystals and denser microstructure. Independent of the basicity, a higher sintering temperature promoted the sintering and densification of products. The highest compressive strengths of VS1 and VS2 were 219.14 ± 12.8 and 255.57 ± 15.6 MPa, respectively. In addition, the reliable stability and low potential ecological risk index of heavy metals in the final products make it to be a competitive eco-friendly construction material.

Concurrent sinter-crystallization and microwave dielectric characterization of CaO-MgO-TiO2-SiO2 glass-ceramics

ABSTRACT The present work aims to clarify sinter-crystallization behavior and microwave dielectric features of CaO-MgO-TiO2-SiO2 glass-ceramics fabricated via one-step sintering procedure at 800–950°C for 4 h. In this regard, starting glasses were obtained from a conventional melt quenching technique, then subjected to the sinter-crystallization heat treatment. The crystallization behavior of sintered glass-ceramics was studied using X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). On the basis of the obtained results, diopside (CaMgSi2O6) precipitated as the main crystalline phase in all sintered glass-ceramics; however titanite (CaTiSiO5) was found as the secondary crystalline phase in glass-ceramics containing high TiO2 content. The degrees of crystallization of the glass-ceramics prepared procedures were also characterized. Optimized glass-ceramics sintered at 800°C for 4 h showed the maximum relative density of 99%. Further increase of sintering temperature led to gradual decrease of density. The most promising microwave dielectric properties of the sintered glass-ceramics were as εr = 6.8–9.4 and Q × f = 3,735–41,359 GHz.

Sinthesis and Properties of Marble-Like Glass-Ceramics Using of Ash from Thermal Power Plants

Color marble-like glass-ceramic materials were obtained through thermal treatment of glasses of the system CaO-Al2O3-SiO2 by using natural materials with the introduction of waste materials - ash from thermal power plants (TPP). The melting of the glass batch was in corundum crucibles at 1450oC with an isothermal hold of 60 min. The glasses obtained was fritted in distilled water and dried for 6 hours at 100oC, then completely crushed and divided into fractions with grain size of 0.8 mm, 1.0 mm, 2 mm, 2.5 mm and over 2.5 mm. It was found that the use of ash from TPP lead to higher values of degree of transformation (crystallization) than using base composition. Values of Avramy parameter’s in the range n=1,0 ÷ 1,6 are showed that crystallization of the glass frit is largely heterogeneous and crystal growing starts from the surface. The introduction of ash from TPP to native glasses carry out to significant reduction of energy of crystallization by Ес=289 kJ/mol to Ec=221 kJ/mol. The glass-ceramic materials were obtained through a one stage crystallization - 1050÷1070оС and an isothermal hold of 60 min., colored white, yellow brown to dark brown. The main crystalline phase in glass-ceramics is β-vollastonite with needle habit, size of crystals - ĺ = 40 ÷ 120 μm and d &lt;5 μm in quantities 37 ÷ 42%. As secondary phases depending on the amount of ash have been identified - the anorthite, gehlenite and α-quartz with prismatic habit were appeared. The obtained glass-ceramic materials have a marble-like effect and technical parameters compared with natural granite and marble and have higher values of density, micro hardness, speed grinding, bending strength and chemical resistance. That’s why they can be used in construction such as lining materials.

Eu3+ ion distribution in oxyfluoride glass nanocomposites

Assessment of activator distribution in lanthanide doped nanocomposites is an important and challenging task. Oxyfluoride glass ceramics have been chosen as a model system to characterize incorporation efficiency of Eu3+ ions in CaF2 nanocrystals using a combination of X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) techniques. Lattice constant changes induced by size mismatch of Eu3+ and Ca2+ ions have been used to evaluate Eu3+ content in CaF2. The distortion of CaF2 lattice due to incorporation of europium ions can be detected from EPR investigations via Gd3+ paramagnetic probe spectra. It is shown that ratio of different symmetry CaF2:Gd3+ centres and linewidth of EPR transitions can be used to monitor europium content in the crystalline phase of glass ceramics.

Evaluation of Wear Resistance of Dental Chairside CAD/CAM Glass Ceramics Reinforced by Different Crystalline Phases

The mechanical properties of crystalline phase of glass ceramics are critical. This study aimed to evaluate wear resistance of different crystalline-reinforced dental chairside computer-aided design/computer-aided manufacturing (CAD/CAM) glass ceramics. Materials of feldspar (Vita Mark II, VM), leucite (IPS Empress CAD, EC), lithium disilicate (IPS e.max CAD, EX), lithium disilicate enriched with zirconia (Vita Suprinity, VS), and enamel were embedded, grounded, and polished, respectively. Samples were indented with a Vickers hardness tester to test the fracture resistance (KIC). Two-body wear tests were performed in a reciprocal ball-on-flat configuration under artificial saliva. The parameters of load force (50 N), reciprocating amplitude (500 μm), frequency (2 Hz), and the test cycle (10,000 cycles) were selected. Specimen microstructure, indentation morphology, and wear scars were observed by scanning electron microscope (SEM), optical microscopy, and three-dimensional profile microscopy. EX, VS, and EC demonstrated significantly higher KIC values than the enamel, while ceramic materials showed smaller wear depth results. Cracks, massive delamination, and shallow plow were seen on the enamel worn scar. Long deep plow, delamination, and brittle cracks are more common for VM and EC, and short shallow plow and smooth subsurface are the characteristics of EX and VS. Greater fracture toughness values indicated higher wear resistances of the materials for the test glass ceramics. The CAD/CAM glass ceramics performed greater wear resistance than enamel. Feldspar- and leucite-reinforced glass ceramics illustrated better wear resistance similar to enamel than lithium disilicate glass ceramics, providing amicable matching with the opposite teeth.

Crystalline phase detection in glass ceramics by EPR spectroscopy

The advances of EPR spectroscopy for the detection of activators as well as determining their local structure in the crystalline phase of glass ceramics is considered. The feasibility of d-element (Mn2+, Cu2+) and f-element (Gd3+, Eu2+) ion probes for the investigation of glass ceramics is discussed. In the case of Mn2+, the information is obtained from the EPR spectrum superhyperfine structure, for Gd3+ and Eu2+ probes—from the EPR spectrum fine structure, whereas for Cu2+ ions the changes in the EPR spectrum shape could be useful. The examples of EPR spectra of the above-mentioned probes in oxyfluoride glass ceramics are illustrated.

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.

Synergistic Effect of K&lt;sub&gt;2&lt;/sub&gt;O and Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3 &lt;/sub&gt;on&lt;sub&gt; &lt;/sub&gt;the Crystallization and Structure of Na&lt;sub&gt;2&lt;/sub&gt;O-CaO-SiO&lt;sub&gt;2&lt;/sub&gt;-MgO-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-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...

Effect of water washing pre-treatment on the properties of glass-ceramics from incinerator fly ash using electronic arc furnace

Production of glass-ceramics by sintering the molten slag obtained from electric arc furnace treatment of fly ash was investigated. The effect of washing pretreatment prior to melting the fly ash on the microstructure and properties of the glass-ceramics was examined. The results show that washing pretreatment of fly ash can decrease alkali metal chloride and increase network former in fly ash, which results in the increase of peak crystallization temperature of parent glass and strengthening of properties of bending strength and chemical stability of the glass-ceramics. The optimal heat treatment temperature for parent glass of washed fly ash is 1 173 K, at which the crystalline phase of glass-ceramics is composed of gelignite (Ca2Al2SiO7) and akermanite (Ca2MgSi2O7). Glass-ceramics produced at optimal heat treatment temperature are excellent in term of the physical and chemical properties and leaching characteristics, indicating attractive potential as substitute of nature materials.

NMR Studies of Strontium Zinc Silicate Based Glass/Glass-Ceramic Sealants for High Temperature Applications

Glass having composition 40SrO-10ZnO-40SiO2-2B2O3-2Al2O3-2TiO2-2Cr2O3-2Y2O3 (mol%) was prepared by melt-quench technique and converted into glass-ceramics by controlled crystallization. Formed crystalline phases in glass-ceramics were identified using powder XRD. MAS-NMR spectroscopy shows the presence of mainly Q1 and Q2 silicate structural units and BO3 structural units of boron in the glass network. It is inferred from 29Si NMR and XRD that glass-ceramics have high crystallinity and during crystallization initially Sr2ZnSi2O7 crystalline phase is formed and later SrSiO3 crystalline phase is crystallized. 11B and 27Al MAS-NMR of glass-ceramics depict an increase in the BO4 and AlO4 structural units with the crystallization. In accordance with XRD, NMR results also suggest the formation of solid solution of Sr2ZnSi2O7 phase with substitution of Zn/Si tetrahedral sites with B/Al.

Influence Of Zro2 on The Physicochemical Properties of Phosphate-Based Glasses and Glass Ceramics

Phosphate-based bioactive glasses and their glass ceramics for 47P2O5– (30.5)CaO–(22.5 − x)Na2O–xZrO2 for different ZrO2 contents (x = 0, 1.5, 3.0, 4.5, and 6.0 mol%) were prepared through melt quenching and controlled heat treatment procedures. The amorphous nature of glasses and the presence of crystalline phases in glass ceramics were studied by means of X-ray diffraction (XRD) studies. The density, molar volume, ultrasonic velocities, attenuation, elastic constants, and microhardness of glass and glass ceramics were used to study the structural changes. The formation of hydroxyapatite layer on the surface of glasses and glass ceramics after immersion in simulated body fluid (SBF) was explored through XRD, Fourier transform infrared (FTIR), and scanning electron microscopy (SEM) analyses. The results indicate that the added ZrO2 increases the crosslink density of glasses, resulting in network stability, and also induces the formation of an apatite layer on the surface of glasses. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Study of PbO-SrO-TiO2-B2O3 glass and glass ceramics

The glasses with composition (50−X)PbO–XSrO-25TiO2-25B2O3 (where X=0, 5, 10 and 15mol%) were prepared using conventional quenching technique. The Tg, Tc, density and CTE of the glass samples were measured. The Tg observed to increase with increasing concentration of SrO, while the Tc first decreased and then increased. The glass samples were converted to glass ceramics by following two stage heat treatment schedule. The glass ceramic samples were characterized by XRD, SEM and dielectric measurements. The XRD results revealed the formation of ferroelectric lead titanate as a major crystalline phase in glass ceramics. Additional phases observed include Sr2B2O5 and PbB2O4. The room temperature (RT) dielectric constant of glass and glass ceramics are in the range of 100–120 which is promising for capacitor application.

Precipitation of ZnO in Al 2O 3-doped zinc borate glass ceramics

Crystallization behavior of the oxide semiconductor ZnO in zinc borate glass was investigated. The precipitated crystalline phase of glass ceramics containing a small amount of Al 2O 3 was α-Zn 3B 2O 6 whereas that of the glass ceramics containing a large amount of Al 2O 3 was ZnO. It was found that the c-oriented precipitation of ZnO in a glass ceramic was brought about by the in-plane crystal growth of needle-like ZnO crystallites along the a-axis. Amount of Al 2O 3 that can make glass network affected the coordination state of B 2O 3 in the glass, and a three-coordinated BO 3 unit was preferentially formed in the glass containing a higher amount of Al 2O 3. The present results suggest that crystallization of ZnO from multi-component glass is dominated by the local coordination state of the mother glass.