Fluoride promoted crystallization and mechanical properties of Sr-fluorphlogopite glass

Crystallization, microstructure and mechanical behavior of strontium fluorphlogopite glass-ceramics, SrO·4MgO·Al₂O₃·6SiO₂·2MgF₂, was studied by varying the fluorine content. A number of glass-ceramics of each glass batch with excess MgF₂ [SR0 (0% MgF₂), SR5 (5% MgF₂) and SR10 (10% MgF₂)] were prepared by heating at its respective nucleation temperature followed by at different crystallization temperatures (780–1150 °C). Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Micro Hardness Indenter were used to study the crystallization, microstructure and mechanical behavior of resulting three glass batches. DTA analysis revealed that the peak crystallization (T_p) and glass transition (T_g) temperatures decreased with increasing fluorine content that also lowers down the activation energy (E) as evident from crystallization kinetics. Hardness and fracture toughness values are higher for less fluorine containing glass-ceramics when they are treated isothermally. However, more fluorine based glass-ceramics is found to be more machinable than the less fluorine one.     

Nano-crystal glass-ceramics obtained from high alumina coal fly ash

Glass has been obtained by melting high alumina coal fly ash with fluxing additives. A thermal treatment was employed to convert the obtained glass into nano-crystal glass-ceramics. X-ray diffraction (XRD) patterns show that the main crystalline phases in both the glass-ceramics are anorthite (CaAl₂Si₂O₈) and wollastonite (CaSiO₃). The crystals are homogeneously dispersed within the parent glass. The average crystal size is below 200 nm. Physical and mechanical properties, such as density, thermal expansion coefficient, hardness, and bending strength, of the glass have been examined and the corresponding microstructures are discussed. The results demonstrate that the glass-ceramics have potential for a wide range of construction application.     

Effect of glass fiber surface chemistry on the mechanical properties of glass fiber reinforced, rubber-toughened nylon 6

The mechanical properties of nylon 6 and its blends with maleated ethylene-propylene rubber (EPR-g-MA) plus glass fibers were examined as a function of the chemical functionality of the silane surface treatment applied to the glass fibers. Three reactive silane coupling agents, with anhydride, epoxy, or amine functionality, were used and found to have little effect on the mechanical properties when no EPR-g-MA is present. When 20 wt% EPR-g-MA is used as a rubber toughener, however, the yield strength and Izod impact strength were lowest for the amine functional silane and highest for the anhydride silane, while the epoxy silane fell in-between. These results were attributed to the differences in reactivity of the three reactive silanes. An unreactive silane (octyl groups) was used as a release agent on the glass fibers and compared with the anhydride functional silane. The octyl silane did not improve the ductility of the composite, as may have been speculated, and had poor yield strength and impact resistance when compared to the anhydride silane. Both octyl and anhydride treated glass fibers improve the heat distortion temperature such that most of the high temperature stiffness that is lost on addition of EPR-g-MA is regained by adding glass fibers.     

Microstructural characterization and wear properties of silver and gold nanoparticle doped K-Mg-Al-Si-O-F glass-ceramics

In ascertaining the effects of silver (Ag) and gold (Au) nanoparticles on crystallization of boro-alumino-silicate system; the K₂O-MgO-Al₂O₃-SiO₂-B₂O₃-F glasses doped with/without 0.2?wt% Ag- and Au- content were melt-quenched at 1550?°C. Doping of nanoparticles considerably increased the glass-transition temperature and softening point but decreased the thermal expansion. A sharp crystallization exotherm in differential scanning calorimetry (DSC) is observed at 750?°C (?±?1?°C) for glass without nanoparticle and that broadened to 800–855?°C when contains nanoparticle. Opaque glass-ceramics were derived from the glasses by controlled heat-treatment at 1050?°C with predominant crystalline phase fluorophlogopite (KMg₃AlSi₃O₁₀F₂) mica. Traces of Ag- and Au- particles were also identified from X-ray diffraction (XRD) technique. The activation energy (E_c) of crystallization (344?±?17?kJ/mol) is decreased to 233 (?±?12) and 307 (?±?15) kJ/mol (Kissinger method) on doping with Ag- and Au- nanoparticles, respectively. Compact microstructure (FESEM) composed of rock like and plate-like mica crystals are developed in base glass-ceramic and that gets restructured to interlocked type morphology in presence of Ag- nanoparticle. Significant microstructural change induced by nanoparticle addition caused the decrease in microhardness (4.31–4.66?GPa) and increase in thermal expansion. Friction and wear testing under reciprocative sliding (using WC-Co ball) exposed that the average coefficient of friction (COF) is 0.60?±?0.2 for all glass-ceramics at 20?N load and 10?Hz frequency. At a lower load of 5?N, the average COF value is increased from 0.69 to 0.92 on use of Au-nanoparticle. A Similar trend was also observed at 10?N load as COF increased from 0.62 to 0.78.     

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.     

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.     

Effect of composition and sintering process on mechanical properties of glass ceramics from solid waste

Sintered diopside glass ceramics were successfully prepared from mixtures of blast furnace slag, fly ash and mining tailing. Results showed that sample C2 with relatively low iron oxides and mass ratio of CaO/SiO₂ possessed the highest bending strength value among samples. A low content of iron oxide enhanced densification degree because pores were developed by reduction of ferric oxide into ferrous oxide. Moreover, a low CaO/SiO₂ mass ratio also greatly promoted the densification process by prolonging the sintering time and delaying the crystallisation. In addition, sample C1 developed by one-stage sintering had a worse mechanical performance than that obtained by two-stage sintering although they had the same crystals. For all samples, despite of different compositions and sintering processes, the main crystal phases are augite and diopside ferrian.     

Effects of doping Al-metal powder on thermal,mechanical and dielectric properties of AlN ceramics

In this work, the influence of Al-metal powder addition upon that thermal, mechanical and dielectric properties of aluminium nitride (AlN) ceramic was studied. The findings show that adding Al-metal powder improves not only the mechanical and thermal properties of the AlN ceramic but also has no negative impact on its dielectric properties. Based on Y₂O₃ as sintering aid, the AlN ceramic with 1.0 wt% Al doping were 14.35% higher thermal conductivity, 11.73% higher flexural strength and 59.50% higher fracture toughness than those doped without Al, respectively. This study showed that the addition of Al-metal powder may favor the purifying of the AlN lattice and the formation of homogenous and isolated second phase, which would increase the AlN–AlN interfaces and improve the thermal conductivity. Furthermore, the grain boundaries of AlN ceramics might be strengthened by the isolated second phases due to the thermal mismatch between the second phases and AlN grains, thus strengthening and toughening the AlN ceramic doped with Al. However, the large additive amount of Al powder (>1.0 wt%) was not help the isolation and homogenization of the second phase, giving a deterioration in an AlN ceramic's mechanical and thermal properties. These results suggest that the introduction of an appropriate dose of aluminium metal powder is a simple method that can be used to improve the AlN ceramic's mechanical and thermal properties simultaneously.     

Microstructure evolution and mechanical properties of YAG/YAG joint using bismuth-borate glass

Joining of Y₃Al₅O₁₂ garnet single crystal (YAG) was achieved by using a bismuth-borate based glass filler. The thermal properties of glass filler were experimentally determined and the wettability of molten glass on YAG was investigated. The YAG reacted with glass to form ZnAl₂O₄ particles and Y₂O₃ nanowires successively as joining temperature is above 625℃. ZnAl₂O₄ preferentially nucleated and grew on Y₂O₃ nanowires. The cooperative growth of the two phases accelerated YAG decomposition, which in turn led to cluster growth of Y₂O₃ nanowires and aggregation of ZnAl₂O₄ particles at elevated temperature. The microstructure evolution and reaction mechanism were studied. The highest shear strength of 29.6 ± 5.2 MPa was obtained for the joint brazed at 650℃. The fracture morphology demonstrated that the dispersive strengthening of ZnAl₂O₄ and stress relief by Y₂O₃ nanowire network contributed to the superior mechanical performance.     

Pressureless sintering and mechanical properties of 3Y-TZP-reinforced LZAS glass-ceramic composites

LZAS glass-ceramic composites toughened by 5, 10, 15 and 20 vol% 3-mol%-Y₂O₃-tetragonal-ZrO₂-polycrystal (3Y-TZP) were prepared via pressureless sintering. Sinterability of composites was investigated in the temperature range of 520–720 °C using soaking time of 30 min. The sintered specimens were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. The results revealed that during sintering 3Y-TZP particles agglomerated between the glass powders and were not dissolved by glass-matrix. Mechanical properties of the sintered samples such as bending strength, Vickers micro-hardness and fracture toughness were also investigated. Measurements showed that the relative density of the samples decreased with increasing 3Y-TZP content. The composite containing 15 vol% 3Y-TZP has a best mechanical properties and it would be the optimum composition. It can be confirmed that crack deflection and transformation toughening are the dominant mechanisms for improving mechanical properties of the composites.     

Bioactive glass-ceramics prepared by powder sintering and crystallization of polyphosphate glass containing strontium

Melt-quenching method was employed for obtaining a glass-ceramic with the following composition 42P₂O₅·40CaO·5SrO·10Na₂O·3TiO₂ (mol%) glass. The crystallization and sintering behavior of glass have been studied by using DTA, HSM, XRD, FTIR and SEM methods. It was determined that the surface and volume crystallization mechanisms act simultaneously in bulk glass samples. The comparison of DTA and HSM data revealed that the sintering and crystallization processes are independent. The sintered calcium phosphate glass-ceramic which contained bioactive β-Ca₃(PO₄)₂ and β-Ca₂P₂O₇ phases was successfully prepared. It was determined that during crystallization the primary phase in the precipitate was β-Ca(PO₃)_2. Other phases appearing in the resulting glass-ceramic were: α-Ca₂P₂O₇, γ-Ca₂P₂O₇, Ca₄P₆O₁₉ and CaHPO₄(H₂O)₂. Crystalline phases containing Sr and Ti were not detected. SEM analysis of the glass-ceramic microstructure revealed surface crystallization of glass particles and plate-like morphology of crystal growth. The result of the in vitro bioactivity showed that no apatite layer was formed on the surface of the as-prepared glass-ceramic samples after immersion in the simulated body fluid (SBF).     

Enhanced energy storage and discharge-charge performance by changing glass phase content in potassium sodium niobate glass-ceramics

(1-x) (K₂O–Na₂O–2Nb₂O₅)-x (2BaO–Nb₂O₅–2SiO₂) glass-ceramics with x = 0.10, 0.15, 0.20, 0.25 have been successfully prepared by traditional melting method. XRD and microstructure analysis demonstrate that all glass-ceramics are crystallized into uniform Na_0.9K_0.1NbO₃ and K₂(NbO)₂(Si₄O₁₂) ferroelectric crystalline phase. Increasing x promotes the formation of Ba₂NaNb₅O₁₅ phase with a tungsten bronze structure. Raman and complex impedance data confirmed that Ba²⁺ is introduced to repair the disruption of the glass network and make carrier migration difficult when x = 0.15. Thus, the x = 0.15 glass-ceramic sample possesses a maximum calculated energy storage density of 2.32 J/cm³ under 820 kV/cm because of a high degree of polymerization (DOP) glass network structure. Moreover, the pulsed discharge-charge tests are carried out to evaluate actual energy storage performance.     

Optical transmittance and energy storage properties of potassium sodium niobate glass-ceramics

In this work, 0.8(K₂O-Na₂O-2Nb₂O₅)?0.2((1-x)B₂O₃-xP₂O₅) (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) glass-ceramics have been fabricated. The effects of P₂O₅ on the microstructure and properties of the glass-ceramics were comprehensively studied. The addition of P₂O₅ promotes the transition of the glass network structure from a negatively charged [B?₄]^- tetrahedron to an electrically neutral [BP?₄] tetrahedron. With the increase of P₂O₅ content, the formation of K₂B₄O₇ is inhibited, with major phase of Na_0.9K_0.1NbO₃ and minor phase of K₂B₄O₇. It is found that the band gap width of the glass-ceramics increases from 3.34 eV to 3.52 eV firstly and then decreases to 3.43 eV. The grain size of the glass-ceramics decreases from 150 nm to 50 nm. High optical transmittance (63%), large discharge energy density (4.58 J/cm³) and large energy storage efficiency (98%) have been simultaneously obtained for K₂O-Na₂O-Nb₂O₅-B₂O₃-P₂O₅ glass-ceramics, which are potential for the applications of the transparent pulse capacitors.     

Influence of phosphorus pentoxide on crystallisation,microstructure and mechanical properties of potassium fluorophlogopite glass ceramics

Abstract

Potassium fluorophlogopite glass ceramics were prepared. Differential thermal analysis showed that there were two exothermic peaks at ～750 and 950°C, corresponding to the Avrami exponent ～1·5 and 2·0. Spherical particles were found using a scanning electron microscope when the glass ceramics were heat treated at 750 and 800°C. With the increase in heat treatment temperature, a kind of lamellar crystals was gradually formed, and the shape of crystals changed from spherical to lamellar when the Avrami exponent changed from 1·5 to 2·0. Mechanical tests showed that material cutting and bending strength increased, while the Vickers hardness decreased with the increasing of P₂O₅ content and heat treatment temperature.     

High breakdown strength and enhanced energy storage performance of niobate-based glass-ceramics via glass phase structure optimization

The dielectric capacitors with excellent energy storage characteristics, high power density and temperature stability are strongly desired in modern pulse power system and electronic industry. Thus, BKNAS-xPbO glass-ceramics were designed and prepared. Free oxygen in the glass phase which weakens the glass network structure can be adsorbed by trace Pb²⁺, thus improving the breakdown strength (BDS) of BKNAS glass-ceramics. Extremely high BDS (~2089 kV/cm) and excellent energy storage density (~17.62 J/cm³) were achieved in 0.6 mol% PbO doped BKNAS glass-ceramics. Moreover, the permittivity variance of BKNAS-0.6PbO glass-ceramics was less than 4.39% in the ultrawide temperature range (−80–300 °C), suggesting excellent temperature stability. The single layer capacitor made by BKNAS-0.6PbO glass-ceramics also exhibited excellent charge-discharge performance, in which the underdamped discharge power density reached 133.69 MW/cm³ as well as the overdamped discharge power density reached 146.89 MW/cm³ with ultrashort discharge time (<18 ns). The above results show that BKNAS-0.6PbO glass-ceramics possesses great potentiality for pulse capacitors owning to excellent energy storage property, temperature stability and charge-discharge performance.     

The effect of lithium fluoride on the thermal stability and thermoluminescence properties of borosilicate glass and glass-ceramics

The oxyfluoride glass and glass-ceramics from the LiF-B₂O₃-SiO₂ system are developed. The stable glass can be produced in the range of 20–40 mol% LiF. The effect of LiF admixture on the thermal stability of the glass as well as the thermoluminescence (TL) properties such as glow curves shape is studied. The results show that the increase of lithium fluoride content in the borosilicate glass causes efficiency enhancement of the thermoluminescence signal. We have clearly stated that the process of controlled crystallization of the oxyfluoride glasses can lead again to increased intensity of the TL process. The glass-ceramics with 40 mol% LiF reveals similar level of TL signal to commercially used doped LiF material and can be considered as active material for alpha and beta radiation detectors.     

Enhanced mechanical properties of glass fibre epoxy composites by 2D exfoliated graphene oxide filler

Graphene oxide (GO) received a significant attention in the scientific community due to their excellent mechanical properties identifying themselves as an alternative and combinatory to various other metals and composites. Though GO possess excellent strength, it was observed from the literature that graphene oxide consisting of hydroxyl group elements ensue in poor bonding. Thus reduced functional group density (rFGD) graphene is preferred which has an advantage of good bonding, alongside very small quantity as a filler is required to achieve the enhancement equivalent to graphene oxide which forms the novelty of the current work. In current case, 3, 6 and 9 wt% of rFGD is dispersed into E-glass fibre reinforced composite by traditional hand layup technique. The obtained results revealed that, the tensile, flexural and impact strength have shown superior enhancement with 3 and 6 wt% of rGO than neat E-glass epoxy (0 wt% rGO), whereas an asymptotic decrement is noticed at 9 wt% when tested with ASTM standards except for impact strength. The microstructural studies also indicated the proper adhesion and alignment of fibres without any agglomerations corroborate the enhancement of properties. These overall finding supports the suitability of the developed laminates for potential use in structural applications in aerospace industry.     

Crystallization process and some properties of novel transparent machinable calcium-mica glass-ceramics

Bulk glass having a calcium-mica composition (Ca_0.5Mg₃AlSi₃O₁₀F₂) is homogeneous glass. The crystallization mechanism of the mica is surface crystallization and transparency is lost completely when crystallization occurs on the surface. In this study, by decreasing SiO₂ and increasing CaO and Al₂O₃ from the chemical composition of Ca_0.5Mg₃AlSi₃O₁₀F₂, and moreover by replacing a small amount of K₂O instead of CaO, the phase separation appears in the glasses. Because of this phase separation, the mica begins to be crystallized not only on the surface but also in the bulk at lower temperatures. Consequently, the novel transparent machinable mica glass-ceramic can be obtained by heating the glasses having the chemical composition of Ca_0.6Mg₃Al_1.2Si_2.8O₁₀F₂ and K_0.01Ca_0.595Mg₃Al_1.2Si_2.8O₁₀F₂. As a larger amount of calcium-mica is separated, the bending strength decreases and the fracture toughness increases. Furthermore, by replacing K⁺ ion instead of Ca²⁺ ion in the interlayer of calcium-mica, the interlayer bonding strength becomes high, resulting in the increase of the bending strength.     

玻璃纤维增强回收聚对苯二甲酸乙二醇酯复合材料的力学性能

用熔融共混制备了玻璃纤维（GF）增强的回收聚对苯二甲酸乙二醇酯（rPET）复合材料,研究了复合材料的力学性能并进一步利用Halpin-Tsai模型、Krenchel-COX模型和Kelly-Tyson模型探讨了GF的近程和远程结构与复合材料性能间的关系。结果表明,GF对rPET具有较为显著的增强、增韧效果。当玻璃纤维含量为30 %(质量分数,下同)时,复合材料的冲击强度、拉伸强度以及弯曲强度分别提高了245 %、113 %以及84 %;长径比和取向度是影响GF改性rPET复合材料性能的重要结构参数;Halpin-Tsai方程能够较好地描述rPET/GF复合材料中GF的有效长径比;而相比于Krenchel-COX方程,由Kelly-Tyson方程获得的GF的取向度更接近实验结果。