Li2O MgO Research Articles

Influence of zinc-containing compounds on the properties of ceramic materials based on the Li<sub>2</sub>O–MgO–Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub> system

The results of a study the influence of magnesium oxide substitution with zinc oxide in the Li2O–MgO– Al2O3–SiO2 system, as well as the introduction of pre-synthesized ganite ZnAl2O4, on sintering, phase formation and thermal expansion of synthesized materials are presented. It was found that after substitution of 4 % magnesium oxide MgO with zinc oxide ZnO, the ceramic material synthesized at a temperature of 1 150 °C was characterized by higher values of apparent density (not less than 1 835 kg/m3), mechanical compressive strength (300 MPa), and heat resistance (more than 80 thermal cycles), as well as low values of LTEC (–0,25 ∙ 10–6 K–1), which is due to the formation of crystalline phases of spodumene, spinel, forsterite, corundum, ganite and quartz.

Structure and microwave dielectric properties of the Li2O–MgO–TiO2 systems

Structure and microwave dielectric properties of the Li2O–MgO–TiO2 systems

Ultrahigh hardness Li2O–MgO–Al2O3–SiO2 glass–ceramics containing multiphase nanocrystals

AbstractLi2O–Al2O3–SiO2‐based glass–ceramics containing nanocrystals have attracted much attention due to their low expansion coefficient, good mechanical properties, for different applications, such as fire‐safe glass, dental materials, and electronic devices protectors. In current research, ultrahigh hardness Li2O–MgO–Al2O3–SiO2 glass–ceramics were prepared by conventional melt‐quenching and subsequent heat‐treatment method. MgO was introduced via Li2O substitution to change glass crystallization and mechanical properties. The differential scanning calorimetry analysis indicated the glass transition and crystallization temperatures increased with MgO/Li2O ratio increase, for better glass network connectivity from Raman spectra analysis. In addition, the main crystal phase changed from Li2SiO5 and LiAlSi4O10, to the combination of LiAlSi2O6 and MgAl2Si4O12, and finally to MgAl2Si4O12. The Vickers hardness of glass–ceramics was highly dependent on MgO/Li2O ratios in glass components and heat‐treatment temperatures, corresponding with the crystal phases in glass–ceramics. The highest hardness could reach 9.34 GPa, which was much higher than traditional silicate glass–ceramics. The scanning electron microscope images confirmed the crystal diameters that varied from 30 to 100 nm and were determined by MgO content. Transmission electron microscope images and energy‐dispersive spectroscopy mapping also confirmed the precipitation of multiphase nanocrystals in glass matrix. The changes of glass structure, and corresponding crystal combinations in glass–ceramics resulting from MgO introduction, were responsible for the ultrahigh hardness glass.

Effect of MgO/Al2O3 ratio on the crystallization behaviour of Li2O–MgO–Al2O3–SiO2 glass-ceramic and its wettability on Si3N4 ceramic

The composition governs the crystallization ability, the type and content of crystal phases of glass-ceramics. Glass-ceramic joining materials have generated more research interest in recent years. Here, we prepared a novel Li2O–MgO–Al2O3–SiO2 glass-ceramic for the application of joining Si3N4 ceramics. We investigated the influence of the MgO/Al2O3 composition ratio on microstructure and crystallization behaviour. The crystallization kinetics demonstrated that the glasses had excellent crystallization ability and high crystallinity. β-LiAlSi2O6 and Mg2SiO4 were precipitated from the glass-ceramics, and the increase of MgO concentration was conducive to the precipitation of Mg2SiO4. Among the glass-ceramic samples, the thermal expansion coefficient of LMAS2 glass-ceramic was 3.1 × 10−6/°C, which was very close to that of Si3N4 ceramics. The wetting test showed that the final contact angle of the glass droplet on the Si3N4 ceramic surface was 32° and the interface was well bonded.

Effect of TiO2 on the sintering temperature and dielectric properties of Li2O–MgO–ZnO–B2O3–SiO2 ceramic composites for LTCC applications

Effect of TiO2 on the sintering temperature and dielectric properties of Li2O–MgO–ZnO–B2O3–SiO2 ceramic composites for LTCC applications

Sintering behavior and properties of Li2O–MgO–ZnO–B2O3–SiO2 ceramic composites for applications in low temperature co-fired ceramic (LTCC) technologies

Herein, the Li2O–MgO–ZnO–B2O3–SiO2 (LMZBS) ceramic with low sintering temperatures were prepared via the traditional solid-state method, and the Mg2SiO4/LMZBS ceramic composite was prepared by adding Mg2SiO4 ceramic, and the results showed that the properties of LMZBS ceramic was improved upon addition of Mg2SiO4 ceramic. The sinterability, microstructure, dielectric properties, mechanical properties and coefficient of thermal expansion (CTE) of composite were determined. The crystal structure was determined using X-ray diffraction, and Mg2SiO4, Mg3B2O6, Mg2B2O5 were the main phase. The 20 wt% Mg2SiO4 ceramic sintered at 900 °C exhibited superior performance: $${\varepsilon }_{\rm{r}}$$ of 6.97, Q value of 1732 at 10 GHz and flexural strength of 206 MPa, and CTE value of 10.06 ppm/°C. The composite was also found to match well with the Ag electrode in an investigational study. These properties have made the Mg2SiO4/LMZBS ceramic composite great candidates in low-temperature co-fired ceramics technology.

Effect of P2O5 and Al2O3 on crystallization, structure, microstructure and properties of Li2O–MgO–Al2O3–SiO2–TiO2–ZrO2 glass ceramics

The structure, microstructure, thermal and mechanical properties of glasses and glass-ceramics in the LMAS (Li2O, MgO, Al2O3, SiO2) system and the effect of P2O5 and Al2O3 additives have been studied. The transition temperatures of both glasses and glass-ceramics increase with the P2O5 and Al2O3 concentration, but at high temperatures the melt viscosity decreases. The main crystalline phases formed are lithium aluminium silicate, enstatite and β-spodumene, being the growth of β-spodumene favoured by fluorine ions, P2O5 and the heat treatment temperature as well. Raman and FT-IR spectroscopies have shown the formation a silica-rich glass phase which acts as a matrix of the crystallites containing Al2O3 and P2O5 in its composition. The shape and aspect ratio of the crystallites depend on the Al2O3 concentration. For low Al2O3 concentration a variety of tubular, granular and plate-like crystals appear, while for high Al2O3 concentration the main shape of the crystals is spherical or globular. Hv, E and CTE properties are related to the crystalline phases formed during the crystallization treatment, and their variations are in accordance with the increase of the crystal aspect ratio. The CTE values of the GCs decrease as the P2O5 content increases up to 3%, while for the Al2O3 concentration of 16% the minimum CTE value is obtained. Hv and E values of the GCs are higher than those corresponding to their respective parent glasses. According to these values, these glasses and glass-ceramics are not appropriate for machining.

Influence of Li2O–MgO–ZnO–B2O3–SiO2 glass doping on the microwave dielectric properties and sintering temperature of Li3Mg2NbO6 ceramics

Li3Mg2NbO6 + x wt% Li2O–MgO–ZnO–B2O3–SiO2 (LMZBS, x = 2, 4, 6, 8, 10) microwave dielectric ceramics with the rock-salt structure were primarily investigated by the traditional solid-state method. The microstructures, microwave dielectric properties, and sintering characteristics were studied systematically according to the doping concentration and sintering temperature. It could be seen that the LMZBS glass effectively lower the sintering temperature of Li3Mg2NbO6 ceramics from 1250 to 925 °C with microwave dielectric properties changing as a function of the amounts of the LMZBS glass. The experimental results showed that 4 wt% LMZBS glass enabled Li3Mg2NbO6 ceramics sintered at 925 °C for 4 h to have excellent microwave dielectric properties: er = 16.02, Q × f = 56,455 GHz, τf = − 18.81 ppm/°C. Therefore, Li3Mg2NbO6 ceramics doped with LMZBS glass meet the requirements of low-temperature co-fired ceramics.

Effect of LMZBS glass on the microstructure and microwave dielectric properties of monocelsian ceramics

BaAl2Si2O8–Li2O–MgO–ZnO–B2O3–SiO2 (BAS-LMZBS) glass ceramics were prepared through the solid-state route. The phase transformation, microstructure, bulk density and microwave dielectric properties of (1-x)BaAl2Si2O8-xLMZBS(x = 0.1–0.4) the glass ceramics were examined. The effects of the LMZBS additive as a mineralizer on the hexagonal-to-monoclinic transformation were investigated by X-ray diffraction and scanning electron microscope. All of the hexagonal phases were converted into monoclinic phases when x = 0.1, and it was found that LMZBS glass affected the densification of the ceramic samples. Monocelsian was successfully prepared, and its sintering temperature was reduced from above 1400 °C–870 °C by adding LMZBS glass. Excellent microwave dielectric properties (εr = 7.31, Q × f = 48,926 GHz and τƒ = −48 ppm/°C) were obtained at 870 °C. This sample shows great chemical compatibility with Ag electrodes and can be a promising candidate for practical applications of low-temperature, co-fired ceramics.

Microwave dielectric properties of low-temperature-fired MgNb2O6 ceramics for LTCC applications.

MgNb2O6 ceramics doped with (Li2O–MgO–ZnO–B2O3–SiO2) glass were synthesized by the traditional solid phase reaction route. The effects of LMZBS addition on microwave dielectric properties, grain growth, phase composition and morphology of MgNb2O6 ceramics were studied. The SEM results show dense and homogeneous microstructure with grain size of 1.72 μm. Raman spectra and XRD patterns indicate the pure phase MgNb2O6 ceramic. The experimental results show that LMZBS glass can markedly decrease the sintering temperature from 1300 °C to 925 °C. Higher density and lower porosity make ceramics have better dielectric properties. The MgNb2O6 ceramic doped with 1 wt% LMZBS glass sintered at 925 °C for 5 h, possessed excellent dielectric properties: εr = 19.7, Q·f = 67 839 GHz, τf = −41.01 ppm °C−1. Moreover, the favorable chemical compatibility of the MgNb2O6 ceramic with silver electrodes makes it as promising material for low temperature co-fired ceramic (LTCC) applications.

Structural investigation of hydrous phosphate glasses

Dissolved water has major impact on the physical and chemical properties of phosphate glasses. In the present study we have investigated the structural response to water incorporation for glasses in the system Li2O–MgO–Al2O3–P2O5. Glasses containing 0–8 wt% H2O were synthesised at 500 MPa confining pressure in internally heated gas pressure vessels at 1323 K (LMP, Al-poor glass) and 1423 K (LMAP, Al-enriched glass). Water contents of glasses were determined by pyrolysis and subsequent Karl-Fischer titration (KFT) and/or by infrared spectroscopy. Density varies nonlinearly with water content implying large structural changes when adding up to 2 wt% H2O to the dry glass. Glass Transition temperatures measured by differential thermal analysis (DTA) continuously decrease with water content. The trend can be explained by depolymerisation of the phosphate network. Near-infrared spectroscopy shows that even in Al poor glasses only a minority of dissolved water is present as H2O molecules, but the largest amount is present as OH Groups formed by hydrolysis of P–O–P bonds. The network is stabilised by aluminium which is predominantly six-coordinated in these glasses as shown by 27Al MAS NMR spectroscopy. With increase of Al in the glasses, breaking up of the Phosphate network through hydrolysis is depressed, i.e. much lower OH Contents are formed at same total water content. Network depolymerisation upon addition of H2O is evident also from 31P MAS NMR spectroscopy. While Phosphate tetraheda are crosslinked by two to three bridging oxygen in dry glasses, diphosphate Groups are dominant in glasses containing 8 wt% H2O.

Structural evolution and microwave dielectric properties of a novel Li3Mg2−x/3Nb1−2x/3TixO6 system with a rock salt structure

Phase transition from an orthorhombic superstructure to a cubic subcell structure has splendid advantages in dielectric properties of Li2O–MgO–Nb2O5–TiO2 quaternary solid solutions.

Coupled experimental phase diagram study and thermodynamic optimization of the Li2O–MgO–SiO2 system

AbstractA coupled key phase diagram study and critical evaluation and optimization of all available experimental data of the Li2O–MgO–SiO2 system was performed to obtain a set of Gibbs energy functions to reproduce all the reliable phase equilibria and thermodynamic data. Differential scanning calorimetry measurements and equilibration/quenching experiments were performed in the Li2SiO3–MgO and Li4SiO4–Mg2SiO4 sections, respectively, using sealed Pt capsules to prevent the volatile loss of Li. According to the present experimental results, Li2MgSiO4 is the only compound present in the Li4SiO4–Mg2SiO4 isopleth, which shows a peritectic melting at 1465 ± 6°C (1738 ± 6 K). The Modified Quasichemical Model, which considers short‐range ordering in the melt, was employed to describe the thermodynamic properties of the liquid phase. The Li4SiO4–Li2MgSiO4 and Mg2SiO4‐rich solid solutions were modeled using the Compound Energy Formalism.

Sintering behavior, phase structure and adjustable microwave dielectric properties of Li2O–MgO–nTiO2 ceramics (1 ≤ n ≤ 5)

Li2O–MgO–nTiO2 (1 ≤ n ≤ 5) ceramics were prepared by a solid state reaction method. The sintering behavior, phase evolution, microstructure and microwave dielectric properties of ceramics were investigated. With increasing n value, the microstructure of ceramics changed from a porous structure to the compact structure. Bulk density, relative permittivity (er) and temperature coefficient of resonator frequency (τf) firstly increased, reached a max value and then decreased with increasing n values. Q × f value first decreased, then increased and finally decreased again. When n = 2, Li2O–MgO–2TiO2 systems presented good microwave dielectric properties with Q × f value of 44,914 GHz, er of 20.8 and τf of −10.15 ppm/oC and low density of 3.33 g/cm3. When n = 3, Li2O–MgO–3TiO2 systems showed better comprehensive performances with sintering temperature of 1050 °C, Q × f value of 48,513 GHz, er of 25.5, τf of 1.6 ppm/oC and low density of 3.40 g/cm3.

Pseudo Phase Diagram and Microwave Dielectric Properties of Li2O–MgO–TiO2 Ternary System

Li2O–MgO–TiO2 ternary system is an important microwave dielectric ceramic material with excellent properties and prospect in both scientific research and application. A phase diagram of the Li2O–MgO–TiO2 ternary system was established in this article, based on earlier research results and our present work. Microwave dielectric properties with compositions in different regions of the phase diagram have been analyzed. We found that the 0.33 Li2MgTi3O8–0.67 Li2TiO3 ceramics sintered at 1200°C exhibited excellent dielectric properties: Q × f value = 80 476 GHz (at 7.681 GHz), εr = 24.7, τf = +3.2 ppm/°C. We also designed two ceramic systems in the Li‐rich region of the Li2O–MgO–TiO2 ternary system, which received little attention in the past decades, because many excellent single‐phase ceramics, such as Li2MgTiO4, Li2MgTi3O8 and MgTiO3, have been found in the Ti‐rich region. The ceramic systems have low sintering temperatures but also relatively poor dielectric properties.

Correlations between crystal structure and dielectric properties of high-Q materials in rock-salt structure Li2O–MgO–BO2(B = Ti, Sn, Zr) systems at microwave frequency

A series of ultra-low loss microwave dielectric materials Li2O–MgO–BO2(B = Ti, Sn, Zr) were prepared by the conventional solid-state method.

Luminescence characteristics of Li2O–MgO–B2O3 doped with Dy3+ as a solid TL detector

Abstract Enhancing the luminescence characteristics of rare earth doped borate glasses is the key issue in achieving an accurate dosimeter. Series of lithium and magnesium oxide modified borate glasses of compositions 20Li2O–(70−x)B2O3–10MgO–xDy2O3, where 0.3≤x≤1 mol% are prepared using melt-quenching method. Synthesized samples are further activated with different concentration of Dy3+ and subjected to different doses by using a 60Co source. Effects of Dy3+ concentrations on luminescence behavior are examined. XRD patterns confirm the amorphous nature of all samples. A simple glow curve exhibits a peak at 190 °C and optimum intensity for 0.5 mol% of Dy3+ ions. Thermoluminescence (TL) properties including dose response and effective atomic number are determined. A good linearity in the dose response with correlation coefficient ~0.9977 and a tissue equivalent Zeff~8.71 is achieved. The room temperature photoluminescence (PL) spectra of these glasses under 350 nm laser excitations reveal two enhanced peaks centered at 480 nm (blue) and 573 nm (yellow). The mechanism for the TL and PL enhancements are discussed and understood. These attractive luminescence features of prepared glasses may contribute towards the advancement of dosimetry.

Siliconizing of iron and molybdenum by electrochemical reduction of silicon in molten SiO2–Li2O–MgO

Electrochemical reduction of silicon on metal electrodes in molten silicate was studied. An iron sheet was immersed in SiO2–Li2O–MgO at 1273K, and the electrode potential was controlled for 1h. Formation on the iron of a Si-containing layer about 10–30μm thick was observed after the electrolysis, depending on the potential. When a molybdenum electrode was used, α-MoSi2 layer about 5μm thick was formed on the surface. The results suggest the applicability of molten oxide electrolysis as a synthesis method of Si-containing alloy layers.

A Multi-interlayer LMAS Joint of C/C–SiC Composites and LAS Glass Ceramics

Porous C/C–SiC composites were prepared through a two-step chemical vapor infiltration process, and a multi-interlayer joint of Li2O–MgO–Al2O3–SiO2 (LMAS) was applied to join C/C–SiC composites and lithium aluminum silicate (LAS) glass ceramics by means of a vacuum hot-pressing technique. Plenty of SiC whiskers were generated in the pores of low-density C/C composites during chemical vapor deposition process, which is essential to form a zigzag interface structure between C/C–SiC substrate and the LMAS interlayer. The average shear strength of the LMAS joint was improved from 12.17 to 19.91 MPa after changing the composites from high-density C/C composites (1.75 g/cm3) with a CVD-SiC coating to the C/C–SiC composites with a low density (1.48 g/cm3). The improvement of the joint strength is mainly attributed to the formation of the inlay structure at the SiC–C/C and SiC–LMAS interfaces.

Effect of SiC nanowires on the thermal shock resistance of joint between carbon/carbon composites and Li2O–Al2O3–SiO2 glass ceramics

Abstract In order to improve the bonding property of joint between SiC modified carbon/carbon (C/C) composites and Li2O–Al2O3–SiO2 (LAS) glass ceramics, SiC nanowires were attempted as the reinforcement materials in the interface region of SiC transition layer and Li2O–MgO–Al2O3–SiO2 (LMAS) gradient joining interlayer. The C/C–LAS joint with SiC nanowire-reinforced interface layer was prepared by a three-step technique of pack cementation, in situ reaction and hot-pressing. The microstructure and thermal shock resistance of the as-prepared joints were examined. The average shear strength of the joined samples with SiC nanowires increased from 24.9 MPa to 31.6 MPa after 40 thermal cycles between 1000 °C and room temperature, while that of the joined samples without SiC nanowires dropped from 21.4 MPa to 8.3 MPa. The increase of thermal shock resistance of the C/C–LAS joints was mainly attributed to the toughening mechanism of SiC nanowires by pullout, bridging and crack deflection.