Nano-imaging confirms improved apatite precipitation for high phosphate/silicate ratio bioactive glasses

Bioactive glasses convert to a biomimetic apatite when in contact with physiological solutions; however, the number and type of phases precipitating depends on glass composition and reactivity. This process is typically followed by X-ray diffraction and infrared spectroscopy. Here, we visualise surface mineralisation in a series of sodium-free bioactive glasses, using transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDXS) and X-ray nano-computed tomography (nano-CT). In the glasses, the phosphate content was increased while adding stoichiometric amounts of calcium to maintain phosphate in an orthophosphate environment in the glass. Calcium fluoride was added to keep the melting temperature low. TEM brought to light the presence of phosphate clustering and nearly crystalline calcium fluoride environments in the glasses. A combination of analytical methods, including solid-state NMR, shows how with increasing phosphate content in the glass, precipitation of calcium fluoride during immersion is superseded by fluorapatite precipitation. Nano-CT gives insight into bioactive glass particle morphology after immersion, while TEM illustrates how compositional changes in the glass affect microstructure at a sub-micron to nanometre-level.

A Gas-Particle Analogue to the Richtmyer-Meshkov Instability: Comparing Multiphase Simulations to Shock Tube Experiments

A research area emerging in the multiphase flow community is the study of Shock-Driven Multi-phase Instability (SDMI), a gas-particle analog of the traditional fluid-fluid Richtmyer-Meshkov instability (RMI). In this work, we study the interaction of planar air shocks with corrugated glass particle curtains through the use of numerical simulations with an Eulerian-Lagrangian approach. This approach has simulations track computational particle trajectories in a Lagrangian framework while evolving the surrounding fluid flow on a fixed Eulerian mesh. In addition to observing the evolution of the perturbed particle curtain in the simulations, we also observe the evolution of the curtain of gas which is initially trapped inside of the particle curtain as the simulation progresses. The objective of this study is to compare the evolving simulation curtains (both particle and gas) to a comparable set of shock tube experiments performed to analyze traditional fluid RMI evolution. The simulations are set to match the experimental shock Mach numbers and perturbation wavelengths (3.6 and 7.2 mm) while matching the Atwood number of the experiments to the multiphase Atwood number of the simulations. However, multiple particle diameters are tested in the simulations to get a view into the impact of the particle diameter on the evolution of the particle curtain. This simulation setup allows for a one-to-one comparison between RMI and SDMI under comparable conditions while also allowing for a separate study into the validity of the use of both the multiphase Atwood number and the fluid-only Atwood number to compare the single-phase and multiphase instabilities. In particular, we show that this validity is at least partly dependent on the diameters of the particles in the curtain (thus, dependent on the Stokes number of the flow). We also analyze the effect of the multiphase terms of the vorticity evolution equation on the vorticity deposition in SDMI. Also discussed is the effect of the particle diameter on the multiphase generation terms as well as in the baroclinic vorticity generation term in SDMI as the shock passes over the curtain.

Finite element modeling of glass particle reinforced epoxy composites under uniaxial compression and sliding wear

In this study, the failure mechanism of glass particle epoxy composites was investigated under compression and sliding wear. Random fiber distribution with minimum interfiber distance was modeled by representative volume elements (RVEs). Spherical and platelet type glass particles were used for the reinforcements. A numerical simulation of the elastic properties of composites was performed for a perfectly bonded interface, and the results were compared using the Mori Tanaka mean field approach. The elastic stiffness results indicated that the platelet reinforced composites bore more load than spherical ones because of the aspect ratio effects. The separation distance based cohesive zone model was applied to modeling the failure zone at the particle matrix interfaces to establish sliding wear. The effect of the perfectly bonded interface and the cohesive zone interface on overall stiffness and elasto-plastic behavior were discussed. The cohesive zone interface was found to be effective at the interface in terms of the strength and debonding characteristics of the composites. The results were compared with the sliding wear test results of glass particle reinforced composites. The numerical and sliding wear experimental results indicated that matrix yield stress, plastic strain, particle penetration at the contact interface and particle stress are found to be effective parameters for the debonding mechanism.

Influence of ultrasonic excitation on microhardness of glass ionomer cement

BACKGROUND: Numerous researchers have attempted to improve the mechanical properties of glass ionomer cement since 1972. In this study, ultrasonic curing treatment was introduced during the mixing of glass ionomer cement (GC Fuji IX) to facilitate intimate mixing, compaction and adaptation of residual glass particle which consequently improves densification of the material. OBJECTIVE: To assess the influence of ultrasonic treatment on the microhardness of glass ionomer cement (GC Fuji IX) and compare it with the conventionally cured method. METHODS: A total of 40 specimens (2 × 2 mm) were fabricated and equally divided into two groups: Group I (conventional curing method) and Group II (ultrasonically cured). For Group II, an ultrasonic scaler was used which provides energy to ensure proper mixing of material without leaving any air bubbles or unmixed particles. Vicker’s hardness test was employed to generate the average microhardness values by making three indentations at different points on each specimen. Statistical Package for Social Sciences (SPSS) Version 17 was used, employing independent samples T test to compare the difference in microhardness values between two curing groups. RESULTS: The average surface hardness value for conventional cured GIC was 62.21 ± 13.61 while ultrasonically cured GIC exhibited a higher mean microhardness value of 66.37 ± 12.83. Additionally, the average microhardness values produced by the two groups showed statistically significant differences (p value < 0.035). CONCLUSION: Ultrasonic excitation treatment leads to intimate mixing and accelerated hardening of glass ionomer cement thereby enhancing its microhardness and reducing early weakness.