Preparation of machinable bioactive mica diopside-fluoroapatite glass-ceramics

Abstract

A fluorphlogopite based glass powder was added to a bioactive glass-ceramic in the system CaO-MgO-P₂O₅ (Fe₂O₃)-SiO₂ in order to improve its machinability. The sinterability of compacted mixtures, their crystallisation behaviour during sintering and their mechanical properties were evaluated and compared with the extreme ends compounds. According to results, fluoroapatite crystallised as a new phase only in the mixtures of the two glasses, its constituents originated by counter diffusion of two glasses components. Fracture toughness and microhardness of the best sample were higher than twice of the fluorphlogopite glass-ceramic composition. The machinability of samples was evaluated by naked eye observation and determination of brittleness factor.     

Influence of barium oxide on the crystallization, microstructure and mechanical properties of potassium fluorophlogopite glass-ceramics

The influence of barium oxide, heat treatment time and temperature on the crystallization, microstructure and mechanical behavior of the system Ba_x·K_1−2x·Mg₃·Al·Si₃O₁₀·F₂ (where x = 0.0, 0.3 and 0.5) was investigated in order to develop novel, high strength and machinable glass-ceramics. Three glasses were prepared and characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscope (SEM) techniques and some mechanical testing methods.The crystallization kinetics of glass-ceramics was also studied. Activation energy and Avrami exponent calculated for the crystallization peak temperature (T_p) of three different glass batches. The Vickers hardness decreased slightly on formation of the potassium fluorophlogopite and barium fluorophlogopite phases, but decreased significantly on formation of an interconnected ‘house of cards’ microstructure.     

Some studies on nucleation,crystallization, microstructure and mechanical properties of mica glass-ceramics in the system 0.2BaO·0.8K2O·4MgO·Al2O3·6SiO2·2MgF2

The crystallization, microstructure, microhardness and theoretical machinability have been investigated by DTA, XRD, SEM and Microhardness Indenter of resulting glass-ceramics. Two distinct crystallization exotherms in the DTA curve are observed and resolved. The first peak corresponds to the initial formation of potassium fluorophlogopite and the second is due to the formation of barium fluorophlogopite. The activation energy for precipitation of each crystalline phase has been evaluated, and the crystallization mechanism has been studied. DTA analyses were conducted at different heating rates and the activation energy was determined graphically from Kissinger and Ozawa equation. The average activation energy is calculated as 276 KJ/mol for the first and 366 KJ/mol for the second crystallization peak. The Avrami exponent for first and second crystallization peak temperature determined by Augis and Bennett method is found to be 3 and 3.9, respectively. The results indicate that the growth of mica is a two and three dimensional process, controlled by the crystal-glass interface reaction. The Vicker's hardness decreased steadily at intermediate heat treatment temperature with the formation of barium and potassium fluorophlogopite phase, but the decrease in hardness is more rapid at higher temperature with the development of an interconnected ‘house of cards’ microstructure.     

The influence of TiO2 content on the properties of glass ceramics: Crystallization,microstructure and hardness

The effects of compositional variation, crystallization behavior, crystalline phases and microstructure formed in the SiO₂3Al₂O₃3CaO (SAC) glass system using various amounts of TiO₂ as nucleating agent were investigated by Differential Thermal Analysis (DTA), X-ray powder diffraction (XRD), Scanning Electron Microscope (SEM), Energy-dispersive X-ray spectroscopy (EDAX) and Fourier transform infrared spectroscopy (FTIR) techniques. The crystallization kinetics and mechanical properties of SAC glass ceramics were studied using crystallization peak temperature (T_p) of three different glasses as obtained from DTA, the activation energy (E) and Avrami exponent (n) were also determined. The crystallization peak temperature (T_p) and activation energy (E) were found to increase with the increase in TiO₂ content. The major crystalline phases were anorthite and wollastonite along with gehlenite and titanite as the minor crystalline phases present in the glass ceramic system. The studies showed that the three dimensional crystalline structure and the microhardness increased with the increase of TiO₂ content in the glass ceramics system.     

Effects of Al2O3 addition on microstructure and luminescence of transparent germanosilicate glass-ceramics with incorporated spinel Ga-oxide nanocrystals

Ga-oxide spinel nanocrystals are wide band gap systems, which can be incorporated in a glass matrix by phase separation mechanisms. In suitable conditions, this kind of processes can give rise to transparent nanostructured glass-ceramics with UV excitation and luminescence properties potentially interesting in several technological areas. Nanophase size dispersion and volume fraction have been demonstrated to be controllable, at some extent, by suitable thermal treatments for nucleation and nano-crystallization in low-alkali gallium germanosilicate system. Here we report the results on the role of Al₂O₃ additions on the microstructure and optical response of the glass-ceramics fabricated in this system. Data of differential scanning calorimetry, X-ray diffraction, transmission electron microscopy, absorption and fluorescence spectroscopy show that Al₂O₃ addition, up to 4.5 mol%, turns out to have a considerable impact on the size and number density of precipitated nanocrystals, which are solid solutions of γ-Ga_2-xAl_xO₃ resulting from the partial incorporation of Al³⁺ ions into the crystalline phase. We show that the use of Al₂O₃ as an additive in the composition of gallium germanosilicates facilitates glass melting and leads to glass-ceramics with significantly modified photoluminescence characteristics such as decay lifetime and integrated intensity of light emission. The possible reasons are discussed.     

PMMA composite bone cement containing bioactive and ferrimagnetic glass-ceramic particles: Effect of temperature and of the additional phase on some physical and mechanical properties

In this work, PMMA-based composite bone cements, embedding bioactive and ferrimagnetic glass-ceramic particles, have been prepared and characterized. Bioactivity, wettability, density, curing parameters, viscoelastic behaviour, bending strengths and creep have been investigated at 37 °C. The growth of a layer of HA on the samples surface after immersion in SBF has been confirmed. The presence of glass-ceramic particles improved the wetting behaviour of the composite cements. Shorter curing times and lower maximum temperatures for the three composite cements, in comparison to the plain one, have been detected. Almost unaffected mechanical properties of the composite bone cements have been found in comparison to those of the plain commercial cement both at room and at 37 °C. A little increase of the viscous flow has been evidenced in the composite samples at 37 °C. Radiographic imaging confirmed the intrinsic radiopacity of the composite cements.     

Influence of molybdenum addition on the microstructure and mechanical properties of TiC-based cermets with nano-TiN modification

Effect of Mo addition on the microstructure and mechanical properties of TiC–TiN(nm)–WC–Co–Ni–C system cermets was studied in the work. Specimens were fabricated by conventional powder metallurgy techniques. The microstructure was investigated using transmission electron microscope (TEM) and the scanning electron microscope (SEM). Chemical compositions of different phases such as ceramic phase with core/rim structure [the core being TiC and rim being (Ti,W,Mo)(C,N)] and metallic phase were analyzed quantitatively by EDX. Mechanical properties such as flexural strength, fracture toughness and hardness were also measured. Results show that flexural strength and fracture toughness have a trend to decline with increasing Mo addition, but the change of hardness is not apparent with the increase of Mo addition. Results also reveal that finer microstructure and thicker rim phase will be obtained with the increase of Mo addition. The optimal addition of Mo can be estimated to be 4 wt.% with respect to TiC–10TiN(nm)–15WC–5Co–Mo–5Ni–1C system cermets. Fracture micrographs show that main failure mode of the cermets is a mixed one, i.e., trans-granular and inter-granular fractures both exist.     

Effect of sintering temperature on microstructure and mechanical properties of zirconia-toughened alumina machinable dental ceramics

This study investigated the effect of sintering temperature on the microstructure and mechanical properties of dental zirconia-toughened alumina (ZTA) machinable ceramics. Six groups of gelcast ZTA ceramic samples sintered at temperatures between 1100 °C and 1450 °C were prepared. The microstructure was investigated by mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. The mechanical properties were characterized by flexural strength, fracture toughness, Vickers hardness, and machinability. Overall, with increasing temperature, the relative density, flexural strength, fracture toughness, and Vickers hardness values increased and more tetragonal ZrO₂ transformed into monoclinic ZrO₂; on the other hand, the porosity and pore size decreased. Significantly lower brittleness indexes were observed in groups sintered below 1300 °C, and the lowest values were observed at 1200 °C. The highest flexural strength and fracture toughness of ceramics reached 348.27 MPa and 5.23 MPa m^1/2 when sintered at 1450 °C, respectively. By considering the various properties of gelcast ZTA that varied with the sintering temperature, the optimal temperature for excellent machinability was determined to be approximately 1200–1250 °C, and in this range, a low brittleness index and moderate strength of 0.74–1.19 µm^−1/2 and 46.89–120.15 MPa, respectively, were realized.     

Effects of nitrogen and fluorine on crystallisation of Ca-Si-Al-O-N-F glasses

The effect of nitrogen and fluorine substitution on the crystallisation of a new generation of oxyfluoronitride glasses in the Ca-Si-Al-O-N-F system has been studied. Glasses were nucleated for 5 h at the nucleation temperature of Tg + 50 °C and crystallised for 10 h at the maximum crystallisation temperature (900-1050 °C depending on the glass composition) determined from differential thermal analysis. For the oxide glass, crystallisation results in formation of wollastonite (CaSiO₃), gehlenite (Ca₂Al₂SiO₇) and anorthite (CaAl₂Si₂O₈) along with a small amount of residual glass. For crystallisation of oxyfluoride glasses (0 equiv.% N), when fluorine content increases, cuspidine (Ca₄Si₂O₇F₂) is the major crystalline phase at the expense of gehlenite while in oxyfluoronitride glasses containing 20 equiv.% N, gehlenite is always the dominant crystalline phase at different fluorine contents. At constant fluorine content (5 equiv.%), an increase in nitrogen content favours the formation of gehlenite rather than anorthite or wollastonite suggesting that this phase may be able to accommodate N into its crystal structure. While a small amount of nitrogen substitution for oxygen can be assumed in the gehlenite structure, the residual glass in the glass-ceramic is expected to be very N-rich. In terms of properties, hardness is shown to be more sensitive to changes in microstructure, phase morphology and crystal size compared with elastic modulus which is related to the amounts of constituent phases present.     

Microstructural evolution and mechanical performances of SiC/SiC composites by polymer impregnation/microwave pyrolysis (PIMP) process

SiC/SiC composites were prepared by polymer impregnation/microwave pyrolysis (PIMP) process, and their microstructural evolution and the mechanical performances were characterized. Using non-coated Tyranno SA fiber preforms as reinforcement and impregnation with only allylperhydropolycarbosilane (AHPCS) into the preforms, Tyranno SA/SiC composite (TSA/SiC) with higher density was obtained. While using carbon-coated Tyranno SA fiber preforms, Tyranno SA/C/SiC composite (TSA/C/SiC) with lower density were also fabricated. In this composite, SiC particulate was loaded with polymer precursor (AHPCS) in the first cycle impregnation. Microstructural observation revealed that pore and crack formation was affected by processing conditions. Bending strength was also dependent on the microstructural evolution of the samples. In TSA/SiC composite, relatively strong interfaces contribute to effective load transfer so that higher bending strength could be reached. In the TSA/C/SiC composite, weak interfaces provide a relatively lower strength. Meanwhile, different microstructural evolution and interfacial properties of the composites lead to the variation of the fracture behaviors.     

Growth behavior,morphology and properties of lithium aluminosilicate glass ceramics with different amount of CaO,MgO and TiO2 additive

Li₂O–Al₂O₃–SiO₂ glass with CaO, MgO and TiO₂ additive were investigated. With more CaO + MgO addition, the crystallization temperature (T_p) and the value of Avrami constant (n) decreased, the activation energy (E) increased. The mechanism of crystallization of the glass ceramics changed from bulk crystallization to surface crystallization. With more TiO₂ addition, the crystallization temperature decreased, E and n had a little change. The crystallization of the glass ceramics changed from surface crystallization to two-dimensional crystallization. Plate-like, high mechanical properties spodumene-diopside glass ceramics were obtained. The mechanical properties related with crystallization and morphology of glass ceramics.     

Synthesis and characterization of clinopyroxene based glasses and glass-ceramics along diopside (CaMgSi2O6)-jadeite (NaAlSi2O6) join

The crystallization behavior and mechanical characterization of glasses based upon the compositions along diopside (CaMgSi₂O₆)-jadeite (NaAlSi₂O₆) join has been investigated. Six glasses were obtained by the melt-quenching technique. Structural and thermal behaviors of these glasses were investigated by density and molar volume, infrared spectroscopy (FTIR) and dilatometry. The crystallization behavior of glasses was investigated by using differential scanning calorimetry (DSC). Sintering and crystallization behavior of the glass-ceramics were investigated under non-isothermal heating conditions up to temperatures of 850 °C. Mechanical characterization of glasses was investigated by using the measurement of Vickers indentation hardness and elastic constants such as Young's modulus (E), shear modulus (G), bulk modulus (K) and Poisson's ratio (ν). These data of the glasses were correlated with the structure of glasses, nature and role played by glass forming cations.     

Infiltration of Al2O3/Y2O3 mix into SiC ceramic preforms

Silicon carbide ceramics are very interesting materials to engineering applications because of their properties. These ceramics are produced by liquid phase sintering (LPS), where elevated temperature and time are necessary, and generally form volatile products that promote defects and damage their mechanical properties. In this work was studied the infiltration process to produce SiC ceramics, using shorter time and temperature than LPS, thereby reducing the undesirable chemical reactions. SiC powder was pressed at 300 MPa and pre-sintered at 1550 °C for 30 min. Unidirectional and spontaneous infiltration of this preform by Al₂O₃/Y₂O₃ liquid was done at 1850 °C for 5, 10, 30 and 60 min. The kinetics of infiltration was studied, and the infiltration equilibrium happened when the liquid infiltrated 12 mm into perform. The microstructures show grains of the SiC surrounded by infiltrated additives. The hardness and fracture toughness are similar to conventional SiC ceramics obtained by LPS.     

Low-temperature preparation and microwave dielectric properties of cold sintered Li2Mg3TiO6 nanocrystalline ceramics

This study aims to fabricate Li₂Mg₃TiO₆ ceramics with ultrafine grains using a novel cold sintering process combined with a post-annealing treatment at a temperature <?950?°C. In this study, phase composition, sintering behavior, microstructure evolution, and microwave dielectric properties of the resultant nanocrystalline ceramics were investigated for the first time. The as-compacted green pellets at 180?°C yielded a high relative density of ~ 90% and the ceramics that were post-sintered over a broad temperature range (800–950?°C) possessed highly dense microstructure with a relative density of ~ 96%. The average grain size varied from 100 to 1200?nm for the samples sintered at 800–950?°C. Furthermore, the quality (Q × f) values of the obtained specimens exhibited a strong positive dependency on the grain size, which increased from 17,790 to 47,960?GHz for grain sizes ranging between 100 and 1200?nm, while the dielectric permittivity (ε_r) and temperature coefficient of the resonant frequency (τ_f) values did not undergo any significant changes over this range of grain size.     

Technological properties of celsian reinforced glass matrix composites

Monoclinic celsian derived from an innovative route, i.e. cation exchanged zeolites heat-treated at low temperature, was added at different contents (10, 20, 30 wt%) to a glass matrix, in order to improve its mechanical and electrical performances. The effect of the celsian reinforcement was evaluated by testing several properties of the composite materials, such as the elastic modulus, abrasion resistance, flexural strength and electrical insulation. The results so far obtained suggest that the addition of the monoclinic celsian to the glass matrix may produce low-cost particulate composites with interesting technological properties.     

Suppressing the effect of cullet composition on the formation and properties of foamed glass

The process of foaming glass is very dependent on the chemical composition of the glass. In this study we used a foaming-agent/oxidizing-agent couple and a crystallization inhibitor to foam cullets of flat, container and CRT-panel glass. Foamed glass with a density of 110–120?kg?m^–3, a thermal conductivity of 50–52?mW?m^–1 K^–1 and a homogeneous pore structure was obtained from a mixture of panel glass, 0.33?wt% carbon and 4.45?wt% Fe₂O₃. We also showed that it is possible to fabricate foamed glass with the same density or pore structure as mentioned above by adding up to 50?wt% container cullet or 70?wt% flat glass to the mixture. In the foamed samples with a low content of panel glass, crystals form, resulting in an increased open porosity, density and inhomogeneous pore structure. The crystallization can, however, be inhibited by adding calcium phosphate, so enabling the preparation of high-quality foamed glass from flat glass or flat/container-glass mixture. The pore gas is predominantly CO₂ and the pressure inside the pores is 0.36–0.47?bar. The reduced effect of the composition on the foaming process suggests that there is a great potential for stabilizing the production of foamed glass and ensuring the product's quality.     

Cellular glass obtained from non-powder preforms by foaming with steam

Cellular glass, or foamed glass, has been obtained as a result of the heating (to 700–800 °C) of heavy and strong preforms formed due to the binding properties of the silicate additives. Durability of the preforms reached 6 MPa at the density of 1.8 g/cm³. The main expanding agent in the composition is steam, which can also be a carbon oxidizer and increase the amount of the evolved gases and decrease the density of the foamed glass obtained. As a result of changing the initial composition structure, the density of the obtained foamed glass varied from 0.14 to 0.6 g/cm³, its breaking strength - from 0.6 to 5.0 MPa. and heat conductivity – from 0.045 to 0.15 W/(m·К), respectively. The speed of expansion of the preforms had an extreme character with the induction period typical for topochemical reactions. The obtained cellular materials possessed a distinct crystalline structure. The experiments showed the possibility of obtaining cellular materials with acceptable properties from different types of glass for the solution of environmental tasks. Various technological methods of obtaining cellular material blocks from preforms of various forms were tested to use them for thermal insulation and facing materials.     

Influence of brick pattern interface structure on mechanical properties of continuous carbon fiber reinforced lithium aluminosilicate glass-ceramics matrix composites

Continuous carbon fiber reinforced lithium aluminosilicate glass-ceramic matrix composites have been fabricated by sol-gel process and hot pressing technique. The results show that the Cf/β-eucryptite composites hot pressed at 1300 °C and Cf/β-spodumene composites hot pressed at 1400 °C form weak interface with brick pattern characteristics, leading to high mechanical performance. The maximum flexural strength and fracture toughness reach 571 ± 32 MPa and 9.8 ± 0.6 MPa m^1/2 for Cf/β-eucryptite composites and 640 ± 72 MPa and 19.9 ± 1.8 MPa m^1/2 for Cf/β-spodumene composites. On increasing the hot pressing temperature, the active chemical diffusion consumes brick pattern interface layer, which leads to the formation of strong bonding between carbon fiber and the matrix. As a result, the composites exhibit brittle fracture behavior and the mechanical properties decrease significantly.     

SiO2/Al2O3 ratio dependence of microstructures and dielectric properties in barium strontium titanate glass ceramics

(Ba, Sr)TiO₃-Al₂O₃-SiO₂ glass ceramic system with various SiO₂/Al₂O₃ ratios was investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), dielectric spectroscopy and impedance spectroscopy. The XRD results demonstrated that the proper SiO₂/Al₂O₃ ratio could promote the crystallization of the major crystalline phase from the glass matrix. The dielectric property investigations showed that the dielectric constant passes through a maximum value while the dielectric breakdown strength has a minimum value with increasing SiO₂/Al₂O₃ ratio. Meanwhile, the complex impedance analyses suggest the resistance of the glass-crystal interface rapidly decreases and the capacitance of the crystal slightly decreases with the increase of SiO₂/Al₂O₃ ratio. The relaxation mechanisms of the (Ba, Sr)TiO₃ glass ceramics changed from localized relaxation to long range conductivity as the SiO₂/Al₂O₃ ratio was increased from 1.43 to 1.83. The variations in the dielectric response and the activation energy of the glass-crystal interface in the (Ba, Sr)TiO₃ glass ceramics with the ratio of 2.40 could be attributed to the crystallization of fresnoite phase.