Borosilicate Glass Matrix Composites Research Articles

Synthesis, Characterization and Bioactivity of Fluoride Containing Borosilicate Glass Matrix Composite

Fluoride containing borosilicates find interesting applications in biomedical transplants and dentistry, wherein calcium and magnesium play pivotal role in human bone formation. In the present work, calcium and magnesium fluoride containing borosilicate glass matrix composites were synthesized via sol-gel route. The as synthesized and heat-treated samples were characterized using various techniques such as X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). and Scanning Electron Microscopy-Energy dispersive spectroscopy (SEM-EDS). The samples were stabilized at suitable temperature based on the thermogravimetric analysis (TGA). The XRD patterns of as prepared samples showed various crystalline phases with varied degree of crystallinity. Heat-treated samples were tested for their in–vitro bioactivity. Interaction at sample-SBF interface was investigated by dipping the samples in simulated body fluid (SBF) at 37 °C. The analysis of the samples dipped in SBF and that of the residual SBF was carried out using various characterization techniques. Increasing the ageing time, the samples exhibited better in-vitro bioactivity.

Preparation and Dynamic Mechanical Properties at Elevated Temperatures of a Tungsten/Glass Composite

Experiments were conducted to prepare a borosilicate glass matrix composite containing 50 vol.% tungsten and examine its dynamic compressive behavior at elevated temperatures in the range of 450-775 °C. The results show that the homogenous microstructure of the tungsten/glass composite with relative density of ~ 97% can be obtained by hot-pressing sintering at 800 °C for 1 h under pressure of 30 MPa. Dynamic compressive testing was carried out by a separate Hopkinson pressure bar system with a synchronous device. The results show that the peak stress decreases and the composite transforms from brittle to ductile in nature with testing temperature increasing from 450 to 750 °C. The brittle–ductile transition temperature is about 500 °C. Over 775 °C, the composite loses load-bearing capacity totally because of the excessive softening of the glass phase. In addition, the deformation and failure mechanism were analyzed.

Comparison of hot pressing and spark plasma sintering in the densification behavior of indium tin oxide‐borosilicate glass composites

AbstractThe goal of this study was to fabricate borosilicate glass matrix composites with high optical transmittance and high conductivity by forming percolated segregated networks of indium tin oxide (ITO) in the microstructure. ITO nanoparticles and borosilicate glass microspheres were mechanically mixed with ITO concentrations varying from 0 to 2.99 vol%. The mixes were then consolidated using either hot pressing (HP) or spark plasma sintering (SPS). The effects of changing sintering methods, along with varying other processing parameters such as heating rate, maximum temperature, and applied pressure, had surprising and unanticipated effects. Ac impedance spectroscopy (IS), SEM, and EDS results indicated the successful formation of a grain‐like microstructure of the sintered glass using both HP and SPS processing, with the ITO particles segregated to the boundary regions in all samples. IS results indicated percolation threshold values between 0.154 and 0.307 vol% ITO in the HP samples and between 0.307 and 0.764 vol% ITO in the SPS samples, with resistivities as low as 29 (Ω·cm) at 2.99 vol% ITO. Optical properties were dominated by impurities and light scattering at defects such as pores. Contrary to conventional belief, it was found that samples made using SPS required far higher temperatures to fully densify, with all other processing conditions being the same, compared with HP. This behavior was confirmed through repeat tests using different SPS equipment and a wide range of processing conditions.

Percolation in Borosilicate Glass Matrix Composites Containing Antimony-Doped Tin Oxide Segregated Networks. Part II: Examination of Electrical Behavior Using Impedance Spectroscopy

Glass nanocomposites, fabricated using borosilicate glass microspheres and antimony tin oxide (ATO) nanoparticles, were previously reported to have formed segregated networks at the boundaries of the glass particles. This resulted in an electrically conducting composite at low volume fractions (~0.5–0.8 vol%) of ATO nanoparticles. The wide range of electrical response in these borosilicate glass composites containing networks of varying concentration of ATO was examined using impedance spectroscopy. The electrical resistance of these composites varied over a range of around 12 orders of magnitude and exhibited several different types of insulator and conductor behavior. The formation of the ATO network was identified and tracked by scanning electron microscopy images and energy dispersive X-ray spectroscopy (EDS) scans. Detailed impedance spectroscopy analysis using all of the dielectric functions (impedance, permittivity, electric modulus, and admittance) was found to be an excellent method for detecting the development of the network and the effect that processing variables can have on its formation and the overall electrical properties of the nanocomposites.

Percolation in Borosilicate Glass Matrix Composites Containing Antimony‐Doped Tin Oxide Segregated Networks. Part I: Fabrication of Segregated Networks

The percolation threshold in a composite depends on the processing conditions used to fabricate it along with the size and shape of the filler and the matrix. In this study, borosilicate glass microspheres were used as the matrix material, and nanosized antimony tin oxide (ATO) particles were used as the filler. The glass microsphere/ATO composites were fabricated by hot pressing at temperatures in the range between the glass transition temperature and the softening temperature of the glass to control the viscosity. The pressure and temperature applied allowed the ATO to be confined to the spaces between certain glass particles, forming percolating networks at low volume fractions of the ATO. The viscous flow of the glass allowed for the composite to have near full densities, while allowing for the nanoparticle segregation to occur. Even though apparently similar microstructures were made using different heating schedules, the percolation behavior and electrical conductivity showed noticeable differences. The percolation threshold ranged from 0.1 to 2.5 phr (parts per hundred glass) and the change in electrical conductivity was around seven to nine orders of magnitude. The differences were attributed to the interaction of the segregated ATO particles with one another. The electrical properties were examined using ac impedance spectroscopy along with current atomic force microscopy (C‐AFM), which allowed for valuable insights in the structure–property–processing relationships in these materials.

Sol–gel route to carbon nanotube borosilicate glass composites

Dense borosilicate glass matrix composites containing up to 3 wt% of multiwalled carbon nanotubes were produced by a sol–gel process. The three different silicate precursors employed (tetramethylsilane (TMOS), methyltriethoxysilane (MTES) and methyltrimethoxysilane (MTMS)) yielded transparent xerogels which were subsequently crushed and densified by hot pressing at 800 °C. The dispersion of the carbon nanotubes was aided by using an organic–inorganic binder (3-aminopropyl triethoxysilane) which limited flocculation of the CNTs in the silica sol. After densification, the borosilicate glass composites containing up to 2 wt% CNTs showed significant improvements in hardness and compression strength, as well as thermal conductivity, whilst percolation effects lead to a dramatic increase in electrical conductivity above 1 wt%. This simple approach to disperse CNTs into a technical silicate glass matrix via the sol–gel process focusses specifically on the borosilicate system, but the procedure can be applied to produce other inorganic matrix composites containing CNTs.

Viscous Sintering in a Glass-Alumina System

The densification during sintering of borosilicate glass matrix composites with 25 vol. % alumina (Al2O3) particles was investigated. The powder compacts, isostatically pressed at 200 MPa, were sintered at a temperature within the range 800-1000º C and maintained at this temperature during various times. The sintering behaviour of the composites was investigated by density measurement and by axial and radial shrinkage measurements. The crystalline phases present in the sintered composites were identified by XRD and the microstructure was analyzed by SEM. For temperatures up to 900 °C, the relative density of the composites increased continuously with sintering temperature and sintering time, while for higher temperatures, the density increased rapidly and then slowed down to achieve a nearly constant value after sintering the composites for 30 minutes. The composites exhibited isotropic shrinkage behaviour when sintered at 800 °C and 850 °C, but at higher temperatures slightly higher axial shrinkage than radial shrinkage was observed. The shrinkage behaviour and microstructural characteristics of the composites indicate that densification during sintering can be attributed to the viscous flow of the borosilicate glass.

Toughening effects quantification in glass matrix composite reinforced by alumina platelets

A borosilicate glass matrix composite containing alumina platelets was considered to investigate toughening mechanisms and crack tip behavior in dispersion reinforced brittle matrix composites. Fracture toughness was determined by applying the chevron notched specimen technique, and fractographic analysis was employed to reveal the active toughening mechanisms with increasing content of reinforcement. A roughness-induced shielding effect has been quantified to prove the relation between fracture toughness and fracture surface roughness. Theoretical calculations of the fracture toughness enhancement based on a modified crack deflection model developed by Faber and Evans, combined with the influence of the increase in Young’s modulus, were found to be in good agreement with experimental data. An effect of residual stresses upon toughening of the investigated composite is discussed.

Mechanical and electrical properties of hot-pressed borosilicate glass matrix composites containing multi-wall carbon nanotubes

Borosilicate glass matrix composites reinforced with 10 wt% multiwall carbon nanotubes (CNTs) were fabricated using a conventional powder processing route and uniaxial hot pressing. The microstructure of the composites contained aggregates of CNTs which had not been infiltrated by the viscous glass during hot-pressing leaving a ∼9% residual porosity. As a result, the mechanical properties (hardness, elastic modulus, fracture toughness and fracture strength) were not improved in comparison to those of the monolithic glass matrix. However the brittleness index (B), which is the ratio of hardness to fracture toughness, decreased with addition of CNTs, which indicates that the composites should exhibit improved contact damage and wear resistance. Electrical resistivity measurements revealed that the addition of 10 wt% CNTs to the normally insulating borosilicate glass decreased its resistivity to 13 Ω cm in comparison to the high value (1015 Ω cm) of the monolithic glass.

Mechanical properties of oxide-fiber reinforced glass matrix composites with BN or SnO 2 interfaces

With the aim of developing optomechanical inorganic materials, boron nitride-coated Nextel™ 440 fibers and tin oxide-coated ZenTron™ glass fibers were used for manufacturing continuous and short fiber reinforced borosilicate glass matrix composites. No evident loss in tensile strength occurred for the BN-coated Nextel™ fibers whereas coating the ZenTron™ fiber with tin oxide caused a significant strength decrease. Composites with ≤12 vol% of short or continuous fibers were fabricated by a standard slurry infiltration and hot-pressing process. The mechanical properties of the composites were investigated by uni- and biaxial flexural strength tests. Nextel™ 440 short fiber reinforced composites with boron nitride interfaces demonstrated “quasi”-ductile fracture behaviour under biaxial stress loading with biaxial fracture strength values of up to 88 MPa. The boron nitride layers caused fiber pull-out during fracture of long fiber reinforced composites, leading to a fracture toughness ( K ic) value of 3.3 MPa m 1/2. In contrast to this, the ZenTron™ glass fiber reinforced glass matrix composites with SnO 2 interface exhibited brittle fracture behaviour.

Joining of SiC fibre reinforced borosilicate glass matrix composites to molybdenum by metal and silicate brazing

The brazing of SiC fibre reinforced borosilicate glass matrix composites with Mo plates has been investigated. Molybdenum was chosen as the metallic partner under consideration of system requirements, e.g. thermomechanical stability at temperatures of interest (500–750∘C), and physical properties, e.g. coefficient of thermal expansion close to that of the glass matrix composite. Two brazing filler materials were investigated: a glass braze (Schott G018-174) and an active filler metal (Incusil ABA, brazing temperature = 740∘C). When using the glass braze the surface of the metal had to be roughened to ensure a bond of significant strength. Vacuum brazing with the active filler metal resulted in joints with high strength, which allows to fully utilise the mechanical competence of the glass matrix composite when the joint configuration is adapted to the relevant loading conditions. A novel design of a tool for hot glassware handling, made of glass matrix composite/Mo joints, is presented.

Mechanical performance and fracture behaviour of glass–matrix composites reinforced with molybdenum particles

A borosilicate glass–matrix composite has been fabricated by addition of molybdenum particles in various volume fractions. In order to systematically investigate the effect of metallic particulate reinforcement on the overall composite mechanical behaviour, a FEM based numerical model was prepared. The study focused on the global elastic and fracture response of the composites. By studying crack propagation patterns, toughening mechanisms such as crack deflection and load transfer were detected, thus enabling to assess the influence of second phase volume fraction on composite fracture toughness. Microscopy observations of fracture surfaces were performed to support the numerical results.

Characterisation of borosilicate glass matrix composites reinforced with SiC or ZrO2

Abstract Two kinds of glass/ceramic composites were prepared. The first contained borosilicate glass with SiC ceramic: batches designated SG10, SG20, SG30 and SG40 consisted of 10 : 90, 20 : 80, 30 : 70 and 40 : 60 SiC/glass (wt-%) respectively. The second contained borosilicate glass with ZrO2: batches designated ZG5, ZG10, ZG20 and ZG40 consisted respectively of 5 : 95, 10 : 90, 20 : 80, 40 : 60 ZrO2/glass (wt-%). The densification parameters (bulk density and apparent porosity) were measured by the Archimedes method. Scanning electron microscopy and X-ray diffraction were used to investigate the microstructure and phase composition of the prepared composites. Cold crushing strength was also measured. The results reveal that in composites containing SiC, apparent porosity increases with increasing SiC content, while with increasing firing temperature from 800 to 1000°C, apparent porosity decreases to a minimum at 875°C before increasing again. As SiC content increases, the inhibition of cristobalite for...

Effect of compaction on the sintering of borosilicate glass/alumina composites

Abstract The effect of initial compaction on the sintering of borosilicate glass matrix composites reinforced with 25 vol.% alumina (Al 2 O 3 ) particles has been studied using powder compacts that were uniaxially pressed at 74, 200 and 370 MPa. The sintering behaviour of the samples heated in the temperature range 850–1150 °C was investigated by density measurement, axial and radial shrinkage measurement and microstructural observation. The density of the sintered composites increased continuously with temperature for compacts pressed at 74 MPa, while for compacts pressed at 200 and 370 MPa it reached the maximum value at 1050 °C and at higher temperatures it decreased slightly due to swelling. The results showed anisotropic shrinkage behaviour for all the samples, which exhibited an axial shrinkage higher than the radial shrinkage, and the anisotropic character increased with the initial compaction pressure.

UNIQUE MICROSTRUCTURE OF GLASS-METAL COMPOSITES OBTAINED BY MICROWAVE ASSISTED HEAT-TREATMENTS

The present study deals with the computer-aided simulation of the microwave heating of metal/glass composites in single mode applicator and the rapid densification of borosilicate glass matrix composites containing molybdenum particle inclusions. The selective and penetrating microwave heating led to a layered porous structure of the samples. They consisted of a highly porous core containing spherical pores and a relatively dense outer shell. Pores in the central region were formed in the molten glass phase due to gas evolution and entrapment. The outer region of the sample remained at lower temperature and it sintered by viscous flow with minimal distortion.

Preliminary Investigation of the Wear Behaviour of Self-lubricating Carbon Fibre Reinforced Glass Matrix Composites in Vacuum

The self-lubricating wear behaviour of a C-fibre reinforced borosilicate glass matrix composite was investigated using a vane-stator configuration resembling a rotating vacuum pump. The vanes were made of the composite material and the stator was of cast iron. Tests were carried out under varying loads in the range 3.8 to 5.8 N. Rotational velocities varied between 5.5 and 7.8 m/s. Fibre fracture and glass matrix particle detachment were the damage mechanisms observed by scanning electron microscopy. Composite wear was accompanied by material transfer onto the stator surface. The formation of isle-type and continuous graphitic films on the counter-body surface was observed. These films provide adequate lubrication during friction, leading to a relatively low wear of the composite under the conditions investigated.

Fracture surface roughness and toughness of Al2O3-platelet reinforced glass matrix composites

The correlation between fracture surface roughness and fracture toughness of alumina platelet reinforced borosilicate glass matrix composites was investigated. With increasing volume fraction of platelets both fracture toughness and fracture surface roughness increase. The fracture roughness parameter Ra was determined by the profilometric technique. A linear correlation was found between the fracture toughness and the Ra values of the composites. Scanning electron microscopy observation of fracture surfaces confirmed that surface roughness is related to a crack deflection process. Crack deflection is thus one of the toughening mechanisms acting in these composites.

Determining the fracture resistance of fibre-reinforced glass matrix composites by means of the chevron-notch flexural technique

Results on fracture toughness determination on SiC (Nicalon®) fibre-reinforced borosilicate glass matrix composites after thermal cycling and thermal shock are presented. The thermal shock tests involved quenching the samples from high temperatures (600–650°C) in a water bath at room temperature. For the thermal cycling tests, the samples were alternated between a furnace at high temperature (700°C) and room temperature for up to 1000 cycles in air. Fracture toughness and work of fracture were measured using the chevron-notched specimen technique. Supported by fracture surface observations, the results were used to assess the microstructural damage in the material after thermal loading. To detect the onset of unstable microcracking during the chevron-notch experiments, an acoustic emission technique was used. The fracture toughness values measured were in the range 18–26 MPam 1/2, in agreement with literature reports, and they were little affected under the thermal shock and thermal cycling conditions investigated (for low number of cycles). The present results were shown to be in agreement with data of previous studies in which other techniques (Young's modulus and internal friction determination, fibre push-out test) were used to assess damage development under similar thermal loading conditions. The overall finding is that, for these conditions, no major degradation of the fibre–matrix interfaces occurred, and therefore the material retains its apparent fracture toughness and flaw tolerant behaviour. However, for a high number of thermal cycles in air (>800), severe microstructural damage occurred in the form of porosity development and interfacial oxidation. Under these conditions, the material showed also macroscopic delamination, which made impossible the use of the chevron-notch test.

Thermal shock resistant Al2TiO5-glass matrix composite

In this study, a thermal shock resistant soda borosilicate glass matrix composite has been developed by incorporation of aluminum titanate, Al 2 TiO 5 , particles.

ランダム配向不連続炭素繊維強化ガラス基複合材料の破壊メカニズム

Fracture mechanisms in randomly oriented discontinuous carbon fiber reinforced borosilicate glass matrix composites are experimentally characterized. Two types of composite specimens with identical constituents but different microstructure were produced. The first type shows the three-stage behavior in the tensile stress-strain curve. In the second type which has the initial cracks, the stress-strain response is almost linear, but the initial Young's modulus is lower than that of the first type. Monotonic and static cyclic tensile and four point bend tests are conducted on those two specimens to measure the microcrack density, Young's modulus and Poisson's ratio as a function of applied strain. The experimentally determined crack density is used to estimate the interfacial shear stress. In the bend tests, evolution of microcracking on the tensile surface and through the thickness has been studied. Acoustic emission (AE) during the tests is monitored to understand the fracture mechanisms. It is proved that the difference in fracture mode between the two specimens is due to the difference in microstructure and the presence of initial defects. The AE behavior shows good correlation with the evolution of microcracking and can explain the fracture processes. Young's modulus can be a damage parameter to estimate the microcrack density. Microcracking during the flexural tests begins on the tensile surface and the cracks progress gradually towards the neutral axis.