Phases In Glass-ceramics Research Articles

Effect of Fe2O3 doping on structure, physical-mechanical properties and luminescence performance of magnesium-aluminum-silicon based glass-ceramics

A series of magnesium-aluminum-silicon based glass-ceramics doped with Fe2O3 were prepared by using a high-temperature melting controlled-crystallization method, and the effect of Fe2O3 doping on the structure and performance of the prepared samples was investigated. The obtained results showed that the introduction of Fe2O3 into the MgO–Al2O3–SiO2–B2O3 (MASB) glass samples reduced the crystallization peak temperature, resulting in decreased glass stability. After crystallization, a single α-cordierite crystal phase was precipitated from the MASB glass, and the mechanical strength of the prepared samples clearly increased after Fe2O3 doping. A comparation of the current results with those of our previous works indicated that Fe2O3 doping can provide a single phase and neat micro-morphology of glass-ceramics, and thus it can be applied to the fluorescent material of the light conversion layer of white light-emitting diode (LED) devices.

Characterization of structure and properties of MgO-Al2O3-SiO2-B2O3-Cr2O3 glass-ceramics

MgO-Al2O3-SiO2 (MAS)-based glass-ceramic has excellent properties and is gradually being used in the field of new functional materials. Here, we investigated the crystallization progress (the evolution of crystalline phase and microstructure), luminescence and mechanical properties of MAS-based glass-ceramic with Cr2O3 doped. The obtained results show that the glass stability decreases gradually with increasing Cr2O3 content. Structurally, the predominant phase in glass-ceramics varies from α-cordierite to spinel, mullite and sapphirine-2 M. The analysis of crystal field parameters confirms that the added Cr3+ ions located in a strong crystal environment and explains the appearance of the sharp peak at 690 cm−1 and long decay time. The prepared sample with 0.15 mol% Cr2O3 has low bulk density and high mechanical performances. We therefore show that a few Cr2O3 dopants have positive effects on both luminescence and physical behavior, which is great importance for tuning MgO-Al2O3-SiO2 based glass-ceramics in optical device applications.

Effects of waste glass particle size on improving the property and environmental safety of fired brick containing electroplating sludge

The introduction of industrial solid waste in fired clay brick is a promising way to consume this waste, however, physical and mechanical properties were seriously impacted due to the incorporation of these solid waste. In current study, various particle diameters of waste glass powder (WGP) were introduced in the preparation process of brick to examine the difference in improving physical and mechanical performances of products, and to obtain the optimal particle size of waste glass for applying in the preparation of fired brick. Results showed the incorporation of WGP in larger particle size (100 and 300 meshes) can effectively improve properties, like bulk density, water absorption and compressive strength, but decrease thermal conductivity slightly. XRD and SEM analysis revealed that WGP with particles size of 100 and 300 meshes would become glass–ceramic phase or form albite, which can improve effectively physical and mechanical properties. However, part of WGP with particle size of 600 and 800 meshes might melt and crystalize into quartz at high temperature. The addition of WGP in particle size of 100 and 300 meshes can decrease much leachability of heavy metals from fired bricks and promote environment safety comparing with WGP with particle size of 600 and 800 meshes. Above results suggested that there is no necessary to grind WGP in much smaller particle size during introduction of waste glass for improving fired brick property. The conclusions from this research give some useful information for the incorporation of WGP in the preparation of fired brick.

Influence of Ho2O3 on Optimizing Nanostructured Ln2Te6O15Anti‐Glass Phases to Attain Transparent TeO2‐Based Glass‐Ceramics for Mid‐IR Photonic Applications

The transparent TeO2‐based glass‐ceramics (GCs) have yet to achieve the breakthrough in photonic technologies, because of poor understanding in optimizing the growth of nanostructured crystalline phases. In the present investigation, the size effect of phase‐separation‐induced, nanostructured Ln2Te6O15‐based (Ln: Gd, Ho) “anti‐glass” phase in Ho2O3‐modified TeO2‐based TTLG (in mol%, 80TeO210TiO25La2O35Gd2O3) glass has considered to achieve transparent GCs. Raman study of TTLG glass reveals the presence of TeO3, TeO3 + 1, and TeO4 units with average TeO coordination number as 3.49. The formation of nanostructured Ln2Te6O15 phases in GCs is confirmed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. Furthermore, TEM analysis confirms that an increase of Ho2O3 concentration has reduced the size of phase‐separated domains in nanoscale with superstructure formation to attain transparent GCs. The superiority of this obtained transparent GCs as photonic material for near‐IR (NIR) to mid‐IR (MIR) range has been established by the realization of enhanced luminescence intensities and bandwidth at ≈2900 nm (Ho3+: 5I6 → 5I7) and ≈2050 nm (Ho3+: 5I7 → 5I8). This study offers an opportunity to fabricate the various accessible lanthanide ions‐doped and/or co‐doped TTLG glass with control over nanostructure, to design a series of GCs which are transparent from visible to MIR range.

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.

Effect of CeO2 and Nd2O3 on phases, microstructure and aqueous chemical durability of borosilicate glass-ceramics for nuclear waste immobilization

The borosilicate glass-ceramics containing zirconolite phase were prepared successfully and the effect of cerium and neodymium on their phases, microstructure and aqueous chemical durability has been investigated in detail. The results show that zirconolite is the main crystalline phase in borosilicate glass-ceramics. With increasing the contents of CeO2 and Nd2O3 to 15 wt%, the transformation from zirconolite-2M to zirconolite-4M occurs, which leads to accommodating larger amounts of rare-earth ions compared with those without the phase transformation. Oxyapatite phase appears in the glass-ceramics while increasing the contents of CeO2 and Nd2O3 to 40 wt%, which insignificantly influences the chemical durability of final glass-ceramics. After 28 leaching days, normalized leaching rates of Ca, Si and Nd are in order of 10−3, 10−3, 10−4 g m−2 d−1 from MCC-1 test respectively, which shows the good chemical durability of glass-ceramics. The obtained conclusions suggest that the glass-ceramic containing zirconolite as main crystalline phase is a potential candidate for immobilizing high-level nuclear wastes, which are rich in lanthanides and actinides.

Effects of pyrochlore content on the phase, structure, and properties of uranium-rich glass ceramics

In this study, the effects of the pyrochlore content on the phase, structure, and properties of uranium-rich glass ceramics were studied by modifying the mass ratio of the uranium pyrochlore in the glass ceramics. The results indicate that U has a high occupancy rate of approximately 0.7 f.u. at the A position of pyrochlore, and the crystal pyrochlore phase in the glass matrix can increase or decrease according to the U amount in the waste. Specifically, at a high occupancy rate and crystallization amount, the U loads reach 20 wt% in the sample, which exceeds the reported 16 wt% maximal U loads of pyrochlore-based glass ceramics. Furthermore, all the samples have excellent mechanical properties and chemical stabilities. The bulk density of each sample is more than 90% the theoretical density, which is 10–20% higher than those of the glass ceramics prepared by pressure sintering. Moreover, the Vickers hardness values of all samples exceed 6 GPa, and the U leaching rate after 21 days is only 6.7 × 10−5 g m−2 d−1, which is an order of magnitude lower than those of brannerite glass ceramics under equal leaching conditions.

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 <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.

Low Li2O content study in Li2O-Al2O3-SiO2 glass-ceramics

The price of lithium-containing minerals and other chemical materials continues to increase, resulting in an increase in the production cost of Li2O-Al2O3-SiO2 (LAS) system glass-ceramics. In the LAS glass-ceramics component, the reduction in the amount of Li2O used can reduce the cost of the product. It is worthwhile to study whether it is possible to prepare glass-ceramics with low expansion properties under low Li2O content. The effect of Li2O content on the glass-ceramics of LAS system was studied. In this paper, spodumene was used as the main raw material, and TiO2 and ZrO2 were added as crystal nucleating agents to prepare transparent glass-ceramics with low expansion coefficient. The effects of the change of Li2O content on the crystal phase and microstructure of glass-ceramics were investigated by XRD, DSC, FTIR and SEM. The results show that the main crystalline phase of the low expansion transparent glass-ceramics is β-quartz solid solution. When Li2O content is in the range of 2.99 wt% to 4.13 wt%, low expansion glass ceramics can be prepared by an appropriate method. With the increase of Li2O content, the average coefficient of thermal expansion (CTE) in the temperature range of 30 °C–300 °C shows a decreasing trend. When Li2O content is in the range of 3.51 wt% to 4.13 wt%, the thermal expansion coefficient of the glass ceramics is extremely small, and even a negative expansion coefficient occurs.

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.

The dielectric, thermal properties and crystallization mechanism of Li–Al – B–Si – O glass – Ceramic systems as a new ULTCC material

Abstract Li–Al–B–Si–O (LABS) glass-ceramics with a sintering temperature of 600 °C were studied for ultra-low temperature co-fired ceramics (ULTCC) applications. The crystal phase of LABS glass-ceramics is dendritic β-spodumene. The permittivity and dielectric loss of LABS glass-ceramics are e r = 5.8 and tg δ = 1.3 × 10 −3 at 10 MHz, respectively. The coefficient of thermal expansion (CTE) of LABS glass-ceramics is 3.23 ppm/°C, which is close to that of silicon. The dielectric and thermal properties of LABS glass-ceramics are closely correlated to the degree of its crystallization. The permittivity decreases continually while the dielectric loss decreases first and slightly increases with the increasing of crystallization of β-spodumene. The CTE of LABS glass-ceramics decreases as β-spodumene crystallized from LABS glass. The crystallization kinetic and mechanism of LABS glass-ceramics indicate that the β-spodumene crystallizes in a two-dimensional interfacial growth mechanism due to the migration of Li-ions. The diffusion coefficients derived from energy-dispersive X-ray spectroscopy (EDS) results indicated that both Al and Ag electrodes have good compatibilities with ULTCC tapes, which could reduce the cost of multilayer electro-ceramic devices dramatically by using the ULTCC and base metallization.

Effect of TiO2 doping on crystallization, microstructure and dielectric properties of CBS glass-ceramics

In this study, calcium borosilicate (CaO-B2O3-SiO2, CBS) glass-ceramics were fabricated using chemically pure CaO, SiO2, and B2O3 as raw materials. Differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and electrical measurements were conducted to explore the effect of titanium dioxide (TiO2) doping on crystallization, microstructure, and dielectric properties of CBS glass-ceramics. Furthermore, the influence of sintering temperature and sintering schemes on crystalline phases of CBS glass-ceramics was systematically investigated. Results showed that the increase of TiO2 content led to the reduction in sintering temperature of CBS glass-ceramics and promoted the precipitation of wollastonite crystal phase. For instance, with the increase of content of TiO2 from 0 to 3 wt%, transition temperature and crystallization temperature were reduced by 12.9 and 27.6 °C, respectively. However, excessive TiO2 affected the precipitation of wollastonite crystal phase, destroyed crystal structure, and damaged close arrangement of crystal grains. Moreover, higher TiO2 content was found to weaken dielectric properties of CBS glass-ceramics. In this study, the best molar ratio of ingredients, meeting that of ideal target material, is n(Ca): n(Si): n(B) = 1:1:0.6, with doping mass fraction of 2 wt% of TiO2. After optimal sintering procedure, dielectric constant of the best sample was found to be 1.4 (1 MHz), 1.3 (10 MHz), and dielectric loss was 3.9 × 10−3 (1 MHz) and 3.8 × 10−3 (10 MHz).

Effect of nickel doping on structure and suppressing boron volatility of borosilicate glass sealants in solid oxide fuel cells

The high volatility of boron from borosilicate glass sealants often leads to boron deposition and poisoning of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode, presenting a challenge for the development of reliable solid oxide fuel cells (SOFCs). In this paper, we report that boron volatilization from borosilicate glass at 700 °C can be significantly suppressed by appropriate NiO dopant, mainly due to the increase of Si-O-B linkages in the combining B-O− and Si-O− network. Also, the formation of boron-containing phase in NiO-doping glass-ceramics has been studied, which suppresses the reaction between glass and LSCF cathode after heat treatment at 700 °C for 1000 h. Moreover, the change of crystalline phases leads to an improvement in thermal and electrical properties. We believe that our findings will open a new way for the design and development of the reliable sealing glass for SOFCs applications.

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.

Effect of TiO2 on the crystallization and properties of MgO-Al2O3-SiO2 glass-ceramics prepared by an "one-step" method from laterite ore

In the current paper, we proposed a novel, "one-step" method to simultaneously prepare MgO-Al2O3-SiO2 glass-ceramics and Ni-Fe alloy from laterite ore with the addition of TiO2. The "one-step" method makes full use of the thermal energy of the molten slag so that the energy consumption for the production of the glass-ceramics is much lower than that in a more conventional method. Moreover, the slag utilization rate can reach 100%. In this method, 0–4 g of TiO2 as a nucleating agent was added into laterite ore to control the phase composition and microstructure of glass-ceramics. The effects of the addition of different amounts of TiO2 on the crystallization behaviour, major crystalline phase, microstructure and various properties of glass-ceramics were investigated by XRD, SEM, EDS and a Vickers hardness tester. The results show that with an increase in the amount of TiO2 added (0–3 g), the μ-cordierite gradually precipitated and became the main crystalline phase of the glass-ceramics. Meanwhile, the crystallinity, grain size and acid/alkali resistance were all enhanced with increased TiO2 addition. The micro-hardness increased from 6.699 GPa to 9.156 GPa. However, as the amount of TiO2 added increased up to 4 g, a large amount of sapphirine ((Mg4Al4)(Al4Si2)O20) precipitated in the glass-ceramics. The major crystalline phase of the glass-ceramics begins to change from μ-cordierite to sapphirine, accompanied by a decrease of its density, acid/alkali resistance and micro-hardness. This study is helpful for extending the "one-step" method of simultaneously preparing glass-ceramics and metals to other low-grade ores and not just laterite ore.

Controlling Selective Doping and Energy Transfer between Transition Metal and Rare Earth Ions in Nanostructured Glassy Solids

AbstractSelective doping of optically active ions into the nanocrystalline phase(s) of glass ceramics is of interest for photoluminescence (PL) applications to control the energy transfer (ET) processes between dopants on the nanometer length scale. Here, the focus is on explaining the essential knowledge of the distribution of two groups of active ions: transition metal (Ni2+ and Cr3+) and rare earth (Yb3+ and Er3+) ions, which are doped into i) single‐phase Ga2O3 and ii) dual‐phase Ga2O3 and YF3 nanocrystals (NCs). These NCs are obtained by thermally crystallizing ternary silicate‐ and quinary fluorosilicate‐based glasses, respectively. It is found that the two types of active ions can successfully be doped into Ga2O3 NCs, resulting in enhanced ET between the dopants because of the small separation distance of, e.g., <10 Å, whereas ET is significantly suppressed when Ga2O3 and YF3 NCs are coprecipitated. In this case, the studied rare earth ions have a high propensity for being selectively doped in YF3 NCs. The studied transition‐metal ions can always be found in Ga2O3 NCs irrespective of the presence of the fluoride phase. The selective doping and the ET between the two types of active ions can be controlled simultaneously on annealing. This may allow for the achievement of diverse PL properties, such as ultrabroadband near‐infrared and upconversion‐mediated Stokes emissions.

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.

Mechanical milling assisted synthesis of novel LiTi2(PO4)3-glass-ceramic nanocomposites

In order to enhance the ionic conductivity in Li+ ion NASICONs, LiTi2(PO4)3 (LTP), novel LTP-glass–ceramic composites have been prepared by mechanical ball milling assisted synthesis route. Composites were prepared using Li+ ion oxide glassy system (Li2SO4)x-(LiPO3)100−x where x = 30 mol% and 60 mol%. The glass content in composite was fixed to 20 wt%. Structural, thermal and electrical properties of the novel composites reveal interesting results. X-ray diffraction and differential scanning calorimetry confirm the formation of LTP-glass–ceramic composite. FESEM investigations performed on the samples suggest that LTP-glass–ceramics contain LTP grains of nano size with an appreciable homogeneity. In-grain (bulk) and grain boundary conductivity exhibit significant increase in the composites. A tentative mechanism of electrical transport has been proposed according to which glass–ceramic phase creates amorphous ‘Li+ ion rich regions’ at the grain boundaries/interface. Concentration of Li+ ions at the interface of LTP grains possibly leads to the enhanced electrical transport.

Braunite phase embedded Y2O3/MnO2-Al2O3-CaO-SiO2 glass ceramics and their properties

Glass series (20-x)Y2O3-xMnO2-20Al2O3-40SiO2-20CaO (x=5, 10, 15 and 20, mol%) have been synthesized by melt quench technique followed by sintering at 850°C. The optical band gap of the samples is in wide semiconductor range and increased with MnO2 content. Photoluminescence study exhibits emission in Mn2+ d-states. On the other hand, hardness decreases with MnO2 content except for 10mol% MnO2 containing glasses (YM10). The formation of braunite phase in glass ceramics induces capacitive losses. In lower temperature region, the conductivity behaviour of samples follows superlinear power law. In higher temperature region, it follows the universal law of conduction. The dielectric constant for the sintered glasses is constant with respect to temperature, approximately upto 350°C and 1MHz frequency. Above 350°C, the ionic conduction dominates in all the sintered glasses. The anomaly in properties is observed when the ratio of Y2O3/MnO2 is 1:1.