Mica Glass-ceramics Research Articles

Crystallization, structure and properties of mica glass-ceramics based on the substitution of MgO by Fe2O3

In this paper, the effect of partially substituting MgO with Fe2O3 in mica glass-ceramics was investigated. The results showed that with the increase of Fe2O3 content and the decrease of MgO content, the glass transition and crystallization peak temperatures both initially declined, followed by an increase. A small amount of Fe2O3 can effectively reduce the crystallization activation energy, but adding too much Fe2O3 will quickly raise the nucleation barrier of the glasses. After the introduction of Fe2O3, some Fe3+ was reduced to Fe2+, resulting in the precipitated mica crystal phase containing fluorophlogopite and biotite. With the increase of Fe2O3 content, the crystallinity and grain size initially increase and then decrease. The related physical and chemical properties also show corresponding trends. This work provides a reference for the development of new mica-based materials.

Effect of MnO content on the crystallization, physicochemical and dielectric properties of mica glass-ceramics

This paper has concentrated on the effect of partial substitution of MnO for MgO on the crystallization, physicochemical and dielectric properties of mica glass-ceramics. The results showed that MnO acted as a network modifier to diminish the network integrity. Fluorphlogopite (KMg3(Si3AlO10) F2) phase, as the dominant crystal phase, suggested that Mn2+ ions did not participate in forming the mica phase. The crystallinity achieved the maximum (67.96%) at a MnO doping of 4 mol%. From SEM images, the conclusion that appropriate MnO doping could promote the formation of nuclei and refine the grains can be obtained. When the doping of MnO was 4 mol%, the Vickers hardness (4.59 GPa) of mica glass-ceramics was the lowest, while the bending strength (136.84 MPa) and chemical stability reached the best. The dielectric constant was about 7–8 at 1 MHz, and the dielectric loss remained relatively low.

Effect of silica on the crystallization behavior and microstructure of mica glass-ceramics in the system SrO·4MgO·Al2O3·6SiO2·2MgF2

Effect of silica on the crystallization behavior and microstructure of mica glass-ceramics in the system SrO·4MgO·Al2O3·6SiO2·2MgF2

Effects of B2O3 substitution for Al2O3 on the crystallization and properties of translucent mica glass-ceramics

The effects of substituting Al2O3 with B2O3 on the structure, crystallization, mechanical properties, thermal properties and optical properties of translucent mica glass-ceramics were thoroughly investigated. The results demonstrated that the addition of 0.5 wt% B2O3 was optimum for glass precipitation, which increases the crystallinity of glass-ceramics and provides good translucency. When the content of B2O3 was greater than 0.5 wt%, both crystallinity and translucency decreased noticeably. The replacement of B2O3 for Al2O3 had no influence on the type of crystal phase and the precipitation of tetrasilicic fluoromica with non-stoichiometric ratio, while it did have an effect on the crystallinity and structure. The crystal sizes of glass-ceramics were in the nanoscale range and the transmittance test results indicated that they exhibit excellent translucency.

Influence of nucleating agents on crystallization and electrical properties of SiO2–MgO–MgF2–K2O mica glass-ceramics

The effects of adding ZrO2 and TiO2 at the expense of MgF2 on the crystallization, microstructure, mechanical properties, thermal properties and electrical properties of mica glass-ceramics based on the SiO2–MgO–MgF2–K2O system were investigated by the differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), microhardness tester and resistivity tester. The electrical properties were discussed emphatically. The results showed that the additions of ZrO2 and/or TiO2 at the expense of MgF2 effectively increase the viscosity, the glass transition temperatures (Tg) and the crystallization temperatures (Tp) of the glasses. The crystallization activation energy (Ec) of the amorphous glasses varied with the nucleating agents was discussed in depth. It was discovered that the nucleating agents had no effect on the crystal phase type but had a certain effect on the crystallinity and microstructure. Tetrasilicic fluoromica and enstatite were precipitated at different crystallization temperatures. Due to the non-stoichiometric ratio of tetrasilicic fluoromica crystal, the prepared glass-ceramics had high dielectric constant (24.4–34.3) and volume resistivity (>2 × 1011 Ω cm) at 25 °C, and the dielectric loss was almost zero.

Mechanical Properties of CaO–Al2O3–SiO2 Glass-Ceramics Precipitating Hexagonal CaAl2Si2O8 Crystals

Fracture behavior via a flexural test for a newly found CaO–Al2O3–SiO2 (CAS) glass-ceramic (GC) was compared with that of enstatite GC and mica GC, which are well-known GCs with high-fracture toughness and machinability, respectively. By focusing on the nonelastic load–displacement curves, CAS GC was characterized as a less brittle material similar to machinable mica GC, compared with enstatite GC, which showed higher fracture toughness, KIC. The microcrack toughening mechanism in CAS GC was supported by the nondestructive observation of microcracks around the Vickers indentation using the X-ray microcomputed tomography technique. The CAS GC also showed higher transparency than mica GC due to its low crystallinity. Moreover, the precursor glass had easy formability due to its low-liquidus temperature.

Machinability of Zirconia Toughened Mica Glass Ceramics for Dental Restorations

Objective: For a dental material to be machinable for CAD/CAM technology, it must offer convenient machining, under a given set of cutting conditions. Quantitative evaluation of machinability has been assessed in literature through various parameters such as tool wear, penetration rates, surface roughness, cutting force and power. A machinable ceramic will typically demonstrate a higher tool penetration rate with signs of reduced diamond tool wear and edge chipping. The purpose of this in vitro study was to evaluate the feasibility of machining an experimental ceramic, 20 wt.% zirconia reinforced mica glass ceramics (G20Z) for indirect dental restorations and compare the tool penetration rates of G20Z to commercially available dental ceramics, Presintered Zirconia (PSZ) and IPS emax CAD. Material and Methods: Precursors of base glass (SiO2 -Al2O3 -K2O -MgO-B2O3 -F) were melted at 15000C for 2 h in a platinum crucible and quenched in deionised water. The glass frit was ball milled with 20 wt. % YSZ (G20Z) and subject to two stage heat treatment in a muffle furnace. Specimens of G20Z (12 X 2 mm) were evaluated for their feasibility of machining under varying spindle speed, depth of cut, and feed rates. Influence of depth of cut, spindle speed and feed rate (vc=8000-16000 rpm, d=0.4-0.8 mm, f=0.1- 0.3 mm/tooth) on cutting forces, material response, surface roughness and tool wear were investigated. Tool penetration rates, tool wear and margin chipping were also evaluated and compared with Pre-sintered Zirconia (PSZ) and e.max CAD in a custom dental milling surveyor at 30,000 rpm with a load of 0.98 N under water lubrication for 6 min. Tool penetration rates were calculated as the ratio of length of cut and milling time with a measuring microscope and scanning electron microscope was used for tool wear and edge chipping. ANOVA and Tukey Kramer tests were used for statistically comparing the means of each group. Results: Spindle speed and feed rate play a significant role in influencing surface roughness, thrust force, cutting forces and tool wear. Penetration rates of G20Z (0.32 ±0.12 mm/min) was significantly greater than PSZ (0.26 ±0.06 mm/min) and IPS e.max CAD (0.21 ±0.05 mm/min). SEM observations reveal tool abrasion and edge chipping regardless of the ceramic type. Conclusion: High spindle speeds delivers low cutting forces with an average surface roughness of 1.61 µm, with abrasive wear of the tool insert and brittle fracture of zirconia mica glass ceramic composites. G20Z with its machinable nature demonstrates greater tool penetration rates than PSZ and IPS e.max CAD. Tool wear and edge chipping is seen in all the investigated ceramics. Keywords Machinability, Dental Ceramics, Mica Glass-Ceramics, Dental Zirconia, Tool penetration rates.

Tribology, mechanical properties and coloration of a mica glass-ceramic

The research employed pigments, Fe2O3 and CeO2, into the glass frit for adjustable mechanical properties and coloration. Disc samples were prepared to determine microstructures and mechanical properties in terms of tribology and nano-indentation hardness as well as biaxial flexural strength. The glass system presented the crystalline phases, by XRD, of phlogopite Ca-mica, fluorapatite, stishovite, anorthite and strontium apatite. Furthermore, SEM micrographs revealed rod-like microstructures and parent glass phase in all specimens 1) GC, 2) GC + 1wt% CeO2, 3) GC + 0.1wt% Fe2O3 and 4) GC + 1wt% CeO2 + 0.1wt% Fe2O3. For the tribology test, specimens were tested by a pin-on-disc tribometer with 10 N load and 1,000 wear cycles. The obtained values of wear rate and friction coefficient of GCF were better than those of others. The nano- indentation hardness results showed that GC exhibited 3.2 GPa which lower than those of GCC, GCF and GCCF, respectively. The addition of pigments affected reddish yellow color. After crystallization, the contrast ratio is around 0.72 for GC and decreases to 58-75% for the mica glass-ceramics that contain the pigments. The values of biaxial flexural strength of all were acceptable (≥100 MPa) according to ISO 6872:2015.

Physico-mechanical behaviour of alkali and alkaline earth metal-containing mica glass–ceramics: a comparative evaluation

Mica glass–ceramics are known for their superior mechanical strength, fracture toughness and machinability. Crystallization, microstructure and mechanical behaviour of alkali and alkaline earth metal-containing mica glasses based on K2O/SrO/BaO·4MgO·Al2O3·6SiO2·2MgF2 composition were investigated by differential thermal analysis, X-ray diffraction, scanning electron microscopy and microhardness indenter. A distinct crystallization exotherm was observed in the differential thermal analysis curve.The crystallization peak corresponded to the formation of K-fluorphlogopite for K-glass, Sr-fluorphlogopite for Sr-glass, and Ba-fluorphlogopite for Ba-glass. XRD results revealed that the above-mentioned formations were the major phases, while alpha hexacelsian, enstatite, and mullite were the minor phases in K-, Sr-, and Ba-glass–ceramics. SEM results indicated that the “house of cards” microstructure appeared in Sr-glass–ceramics at lower crystallization temperature than in the K- and Ba-glass–ceramics. The physico-mechanical properties of Ba- and Sr-glass–ceramics were compared with K-glass ceramics, and it was found that Ba-glass–ceramics possessed superior crystallization, microstructure and mechanical strength than the other two glass ceramics.

Study of Fracture Mechanism of Machinable Mica Glass-Ceramics under Quasi-Static Conditions

In order to study the deformation and fracture mechanism of machinable mica glass ceramics under different loading modes, quasi-static uniaxial tensile and compression experiments are designed and analyzed based on the obtained quasi-static stress-strain curves at different strain rates, the macroscopic and microscopic fracture morphology of the samples and the nano-indentation experiment. The results show that mica glass ceramics are basically elastic brittle bodies. A very short “softening” section before the compression fracture is observed. There is a significant SD (tensile and compressive strength difference) effect, and the ratio of compressive to tensile strength is 14. The fracture mechanism of mica glass ceramics is related to the loading mode. The fracture mechanism is normal tensile fracture perpendicular to the loading axis under tensile loading. Under compressive loading, there is a mixed mode of distensile splitting and local shear failure. The microcrack is preferentially nucleated and extends to the weak interface at the junction of two phases, and the critical nucleation load is about 20 mN. The energy consumption mechanism of crack initiation and propagation at the weak interface and cleavage steps are the reason for the softening of the compression end curve.

Effect of the crystallisation time and metal oxide pigments on translucency and the mechanical and physical properties of mica glass-ceramics

Mica glass-ceramics tend to be opaque making them less desirable, from an aesthetic point of view, for dental materials. This research focuses on the development of a mica glass-ceramic for use as a restorative dental material with improved translucency. A ceria-based pigment and a zircon-based pigment consisting of Pr-ZrSiO4 and Fe-ZrSiO4 were added to glass-ceramic and the effect on translucency, phase development and morphology, strength, thermal expansion and chemical solubility were studied. The addition had no effect on the level of crystallinity obtained, the morphology of the crystals formed or the strength. The use of the pigments allowed for the control of the translucency and values of the translucency parameter similar to natural teeth were produced. The characteristic strength values and chemical solubility obtained to make these materials acceptable as dental ceramics type II class 2, for single-unit anterior or posterior prostheses adhesively cemented, according to ISO 6872.

Zirconia toughened mica glass ceramics for dental restorations: Wear, thermal, optical and cytocompatibility properties

BackgroundIn an effort to design novel zirconia reinforced mica glass ceramics for dental restorations, clinically relevant properties such as wear, coefficient of thermal expansion, optical transmittance, and cytocompatibility with human gingival fibroblast cell lines were investigated in the present study. Materials & MethodsMicrostructure analysis of two body wear of heat treated mica glass ceramic ceramics (47.2 SiO2–16.7 Al2O3–9.5 K2O–14.5 MgO–8.5 B2O3–6.3F wt.%) reinforced with 20wt.% YSZ, were evaluated against a steatite antagonist in a chewing simulator following Willytec Munich method. In addition, Coefficient of thermal expansion (CTE), total transmittance, scattering coefficient and cytocompatibility on human gingival fibroblast cell lines were performed and compared to the commercially available dental ceramic systems. ResultsThe experimental mica glass ceramic demonstrate micro-ploughing, pull out and debris formation along the cutting surface, indicating abrasive wear mechanism. Thermal expansion of mica glass ceramic composite was recorded as 5×10−6/°C, which is lower than the thermal expansion of commercially available core and veneering ceramics. Further, significant differences of transmittance and scattering coefficient of mica glass ceramics with 20wt.% YSZ with commercial dental ceramics was found and extensive fibroblast cell spreading with filopodial extension, cell-to-cell bridges and proliferation with human gingival fibroblast cell lines. ConclusionWith acceptable cytocompatibility with human gingival fibroblast cells and better wear properties with respect to commercial IPS emax Press, the mica glass ceramic composites (47.2 SiO2–16.7Al2O3–9.5 K2O–14.5 MgO–8.5 B2O3–6.3F wt.%) with 20wt.% YSZ have the potential for dental restorative applications as machinable veneering ceramics.

Machinability of fluormica glass-ceramics of high mica volume fraction

The high Machinability of Mica glass-ceramics is due to its unique microstructure. This study investigated barium fluormica glass-ceramics, with reference to parameters, which determine the microstructure that governs Hardness and machinability and explore the validity of Baik’s model for high mica Volume Fractions. Barium fluormica glasses were synthesized and casted into rods then heat-treated at 1175 °C and 1200 °C for various times. Glass-ceramics were characterized using DSC, SEM, Vickers microhardness and machinability test. “House of Cards” microstructure was successfully obtained upon heat treatment and was associated with an increase in Volume Fraction and Aspect Ratio of crystals. The Volume Fraction was almost identical for all the samples. However, crystal length and width increased with increasing holding time. Hardness and machinability forces decreased with increasing the Aspect Ratio and Effective Crystallinity. Hardness and Machinability data agreed well with Baik’s data and extend the validity of Baik’s model to much higher Volume Fractions.

Fracture toughness of experimental mica-based glass-ceramics and four commercial glass-ceramics restorative dental materials.

The mica-based glass-ceramics were prepared in the SiO2-Al2O3-MgO-MgF2-SrCO3-CaCO3-CaF2-P2O5 glass system. There were four mica-based glass-ceramics produced in this study according to the pigment added (CeO2 or Pr-ZrSiO4/Fe-ZrSiO4) and crystallization time (5-35 min). Four dental glass-ceramics, which were leucite-based, lithium disilicate-based and two zirconia reinforced lithium silicate ceramics, were also tested. The phase identification of mica-based glass-ceramics was performed using an X-ray diffractometer. The fracture toughness (KIC) was determined using the fractographic analysis approach. The one-way ANOVA was used to analyze the significant differences among the obtained KIC values at a=0.05. The results from the phase analysis showed that the mica glassceramics consisted of calcium-mica, fluorapatite and strontiumapatite. The KIC of mica-based glass-ceramics ranged between 1.36 to 1.53 MPa•m1/2 which were superior to only that of a leucite-based glass-ceramic. The shade and translucency of mica-based glassceramics appeared to be acceptable for dental application when compared with other dental glass-ceramics.

Catalytic, kinetic and thermodynamic properties of free and immobilized caseinase on mica glass-ceramics

Bacillus megaterium 314 strain was able to utilize agricultural and industrial wastes for metallo-protease production. Orange peel and wheat bran were found as the most suitable carbon and nitrogen sources, respectively. Optimized production process enhanced the enzyme production by 5.1-folds. Glass and glass-ceramic with different particle sizes based on mica were used as inorganic carrier. Protease enzyme was immobilized by covalent bonding and physical adsorption methods on nanoparticle supports. Enzyme physically adsorbed on glass ceramic (particle size 0.71–1.0 mm) had the highest residual activity and the highest immobilization yield. Glass-ceramic was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Immobilized enzyme exhibited activation energy (Ea) and deactivation rate constant at 60 °C (kd) about 1.29 and 1.46-times, respectively lower than free enzyme. Moreover, adsorbed enzyme had higher energy for denaturation (Ed), half-life (t1/2), and decimal reduction time (D). The thermodynamic parameters of irreversible thermal denaturation for the protease enzyme indicate that immobilized enzyme had higher enthalpy (ΔH°), free energy (ΔG°), and entropy (ΔS°) than free one. There was a significant improvement in the maximum reaction velocity Vmax (2.5-fold), Michaelis constant Km (1.9-fold), and catalytic efficiency Vmax/Km (4.7-fold) values after immobilization indicating the efficiency and effectiveness of immobilization approach.

The effect of barium content on the crystallization and microhardness of barium fluormica glass-ceramics

Mica glass-ceramics are easily machined due to their “House-of-Cards” microstructure. Barium fluormica glass-ceramics were developed and indicated good mechanical properties. This work studies the effect of varying barium content on the crystallization and microhardness of mica glass-ceramics. Four glasses were produced with different baria contents, then converted to mica glass-ceramics using a two-step heat treatment. They were characterized using Differential Scanning Calorimetry [DSC], X-ray Diffraction [XRD], Scanning electron microscopy [SEM] and Vickers microhardness. DSC showed some formulations indicated bulk crystallisation as the dominant mechanism. XRD showed the crystallization of Barium fluorphlogopite in all the compositions with minor secondary phases. SEM showed the formation of “House-of-Cards” microstructures and with an increase in BaO content, a decrease in contrast was observed in back scattered mode. Exceptionally low hardness values (<2 GPa) were obtained for longer heat treatments/holding times and are related to the well-developed house-of-cards microstructures formed.

Mica glass ceramics for dental restorations

ABSTRACTCeramics are popular as dental restorative materials for missing teeth due to their esthetics, chemical durability and ease of fabrication. Glass ceramics are commonly used for the fabrication of dental inlays, veneers, dental crowns and bridges. Mica containing glass ceramics (SiO2-Al2O3-MgO-K2O-B2O3-F) are one of the potential materials due to their machinability, bioactivity and resemblance to tooth colour. The review aims to provide an overview of dental ceramics with emphasis on mica glass ceramics, and their strengthening mechanisms with nucleating agents. The review discusses the clinically relevant properties of various mica based glass ceramic compositions such as fracture toughness, hardness, bending strength, machinability, wear, translucency and provides recommendations for their biocompatibility testing.

Comparison of shear bond strengths between a mica-based glass-ceramic and human dentin using three different resin cements

Three resin cements, RelyX™ Ultimate, Panavia F2.0 and RelyX™ U200, were evaluated for their bond strengths between a mica glass-ceramic and human dentin. This research shows that a self-etch dental cement resin system, Panavia F2.0 provided the best bond strength. The glass-ceramic was produced and phases analysed. Biaxial flexural strength and hardness were measured and found to be comparable to that of human enamel and dentin. Bond strength was measured before and after thermocycling. Thermocycling was found to reduce the bond strength. Thermocycling reduced the shear bond strengths of all adhesives by 50–60%. The two-way ANOVA test was used to analyse the data (p = 0.05). Failure modes were analysed, showing failure predominately at the cement/glass-ceramic and dentin/resin cement interfaces. Failure modes changed after thermocycling. The resin cement bond between the dentin and mica glass-ceramics interfaces was examined for failure by optical microscopy (OM) and scanning electron microscopy (SEM).

Zirconia toughened mica glass ceramics for dental restorations

ObjectiveThe objective of the present study is to understand the role of yttria stabilized zirconia (YSZ) in achieving the desired spectrum of clinically relevant mechanical properties (hardness, elastic modulus, fracture toughness and brittleness index) and chemical solubility of mica glass ceramics. MethodsThe glass–zirconia mixtures with varying amounts of YSZ (0, 5, 10, 15 and 20wt.%) were ball milled, compacted and sintered to obtain pellets of glass ceramic-YSZ composites. Phase analysis was carried out using X-ray diffraction and microstructural characterization with SEM revealed the crystal morphology of the composites. Mechanical properties such as Vickers hardness, elastic modulus, indentation fracture toughness and chemical solubility were assessed. ResultsPhase analysis of sintered pellets of glass ceramic-YSZ composites revealed the characteristic peaks of fluorophlogopite (FPP) and tetragonal zirconia. Microstructural investigation showed plate and lath-like interlocking mica crystals with embedded zirconia. Vickers hardness of 9.2GPa, elastic modulus of 125GPa, indentation toughness of 3.6MPa·m1/2, and chemical solubility of 30μg/cm2 (well below the permissible limit) were recorded with mica glass ceramics containing 20wt.% YSZ. SignificanceAn increase in hardness and toughness of the glass ceramic-YSZ composites with no compromise on their brittleness index and chemical solubility has been observed. Such spectrum of properties can be utilised for developing a machinable ceramic for low stress bearing inlays, onlays and veneers.

Boron Promoted on Crystallization and Microstructure of Strontium Containing Mica Glass-Ceramics

Boron Promoted on Crystallization and Microstructure of Strontium Containing Mica Glass-Ceramics