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Previous studies have shown that exposure of carbon black nanoparticles to nanosecond pulsed near-infrared laser causes intracellular delivery of molecules through hypothesized transient breaks in the cell membrane. The goal of this study is to determine the underlying mechanisms of sequential energy transfer from laser light to nanoparticle to fluid medium to cell. We found that laser pulses on a timescale of 10 ns rapidly heat carbon nanoparticles to temperatures on the order of 1200 K. Heat is transferred from the nanoparticles to the surrounding aqueous medium on a similar timescale, causing vaporization of the surrounding water and generation of acoustic emissions. Nearby cells can be impacted thermally by the hot bubbles and mechanically by fluid mechanical forces to transiently increase cell membrane permeability. The experimental and theoretical results indicate that transfer of momentum and/or heat from the bubbles to the cells are the dominant mechanisms of energy transfer that results in intracellular uptake of molecules. We further conclude that neither thermal expansion of the nanoparticles nor a carbon-steam chemical reaction play a significant role in the observed effects on cells, and that acoustic pressure appears to be concurrent with, but not essential to, the observed bioeffects.

The jet formed from the high velocity collision of metal plates have proven both scientifically unique and of potential interest, although the underlying deformation mechanism remains less firmly established. In this study, oblique collision of titanium and stainless steel observed by high-speed camera is discussed. The nature of jet, its velocity and its existence at low velocity are all discussed and theoretical developments are connected. Microstructural studies are done on the sample welded using gas gun and a comparison with explosive welded sample is made.

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Two-phase TiB2+Al2O3ceramics with an interconnected or dispersed TiB2(minor)-phase microstructure can be produced by variations in processing parameters. A standard method of quantitative characterization of the microstructural bias, i.e., the degree of TiB2phase connectivity relative to its dispersion, is necessary to comprehend the mechanism(s) controlling the evolution of microstructure during processing. In this work, techniques derived from stereology were used to quantitatively characterize the microstructural bias on the basis of the connectivity and dispersion of the minor phase (TiB2), in addition to the size of the TiB2- and Al2O3-phase regions. The mean integral curvature calculated using the area particle-countand area tangent-countmethods was determined to quantitatively describe the connectivity of the TiB2minor phase around the Al2O3major phase. The results illustrate that, in spite of partial and mixed bias, integral curvature measurements (particularly those based on the area tangent-count method) provide a reliable and reproducible means for quantitative characterization of the two-phase biased microstructure.

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Chemical reactions occurring in Mo + 2Si powder mixtures under “shock-induced” (during the high-pressure shock state) and “shock-assisted” (due to bulk temperature increases subsequent to unloading from the shock state) conditions were investigated using shock recovery experiments performed under a range of loading conditions. Cylindrical implosion geometry experiments showed fully reacted mixed-phase eutectic microstructure (MoSi2and Mo5Si3) in axial regions and a partially reacted region (containing MoSi2spherules surrounding molybdenum particles in melted and resolidified silicon matrix) in outer peripheral areas of the compact cross sections. Planar-pressure geometry experiments showed a single-phase MoSi2microstructure in almost the entire compact. Calculations of the peak shock pressure and maximum mean bulk temperature in the different regions of the compacts and their correlation with the observed microstructures suggest that the formation of the mixed-phase and partially reacted products in the implosion geometry samples is due to “thermally initiated” liquid-liquid or solid-liquid reactions. In contrast, formation of the single-phase product in the planar-pressure geometry experiments is due to solid-state “pressure-initiated” reactions. The “thermally initiated” reactions are a result of large increases in shock-generated bulk temperatures, produced in time scales of thermal equilibration following unloading from the high-pressure state; hence, these are referred to as “shock-assisted” chemical reactions. However, the pressure-initiated reactions occur during the rise to the peak pressure and in time scales of pressure equilibration; hence, these are referred to as “shock-induced” chemical reactions.

Spherically shaped, microcrystalline NiTi alloy powder with both nonhomogeneous particle-size distribution (2 to 60µm diameter) and chemical composition, was consolidated with a shock input energy of 316 kJ kg-1. Upon shock compaction, the two-phase NiTi powder particles (containing 45wt% Ti and 65 wt% Ti) were bonded together, generally by interparticle melting and subsequent welding. The melted material at interparticle regions was observed to have rapidly solidified to largely amorphous and/or microcrystalline phases. Particle interiors were also subjected to extensive plastic deformation which resulted in deformation twinning, grain elongation and some recrystallization to defect-free grains. Unique microstructural modifications occurring due to inhomogeneous thermal and mechanical processing during the dynamic consolidation process, are reported here.

Shock-compression was used to make Si3N4powder compacts (80–85% theoretical density) in order to investigate its effect on the α–βphase transformation occurring during post-shock thermal treatments. Crystallite size reduction to half of the starting powder size was attained, and residual strains in crystallites in excess of 10−3–10−2, corresponding to dislocation densities of the order of 1015–1017cm−2, were generated due to shock compression. Transmission electron microscopy showed evidence of defects in the form of irregular striations (fringes), hexagonal dislocation arrays, sub-grains, and vacancy clusters in the interiors of the individual crystallites, with contrast-free amorphous regions along interparticle boundaries. Upon subsequent annealing (sintering) of the shock-densified compacts, the α–βphase transformation was observed to occur at temperatures of ≈200°C below that in unshocked powders, with no obvious change in density. The amount of α–βphase transformation increased with increasing temperature and time, with up to 87% conversion to β-phase in the compact heated for 5 h at 1650°C. The apparent activation energy for the α–βphase transformation in the shock-compressed silicon nitride powder compacts was determined based on the measured fraction transformed as a function of time and temperature, and was found to be in the range of 154–286 kJ mol−1. The results provide evidence that shock compression activates and enhances the reactivity of Si3N4powders, by creating defect sites for heterogeneous nucleation of the β-phase, and thereby causing the α–βphase transformation to occur in the solid state and at reduced temperatures.

Shock compression was used to make dense compacts of Ti and C elemental powder mixtures for subsequent reaction sintering in near-net form. The reaction sintering experiments were performed in an induction-heated hot press at temperatures below the melting point of Ti, with hold times of less than a few hours. The unique combination of defect states and packing characteristics introduced during shock compression results in significant enhancement in the solid-state chemical reactivity of the powder mixtures. Consequently, the reaction behavior of the powders is altered, and the reaction mechanism is dominated by solid-state diffusion, resulting in a microstructure reminiscent of solid-state processes. Reaction-sintered TiCxcompacts, with bulk density in the range of 3.9 to 4.2 g/cm3(80 to 85 pct TMD of TiC), were produced in near-net form. The compacts had a highly refined microstructure (<6-μm grain size) and microhardness in the range of 1360 to 1934 KHN. In this article, reaction sintering mechanisms involving solid-state diffusion in Ti + C powder mixture compacts will be described, along with characteristics of the titanium carbide produced by the com-bined shock modification and reaction sintering approach.

The effect of shock compression on the solid-state chemical reactivity of titanium and carbon powder mixtures was investigated with the objective of forming net-shaped TiC ceramics with a fine-grain microstructure. The combination of defect states and intimate interparticle contacts introduced during shock compression results in significant enhancement of the otherwise sluggish solid-state diffusion of Ti and C through the TiCxboundary layer. The apparent activation energy for TiCxformation was determined using solid-state reaction kinetics models, and was found to be reduced by four-to-six times that of diffusion of Ti into TiCxand two-to-three times that of diffusion of C in TiCx. As a result, net-shaped sections of shock-densified compacts (˜85% dense) were reaction synthesized via solid-state diffusion, producing microstructures with grain size <6 μm and microhardness of ˜2000 kg/mm2, in contrast to statically pressed powder compacts which reacted by a combustion process resulting in a highly porous product.

Exposure of carbon‐black (CB) nanoparticles to near‐infrared nanosecond‐pulsed laser energy can cause efficient intracellular delivery of molecules by photoporation. Here, cellular bioeffects of multi‐walled carbon nanotubes (MWCNTs) and single‐walled carbon nanotubes (SWCNTs) are compared to those of CB nanoparticles. In DU145 prostate‐cancer cells, photoporation using CB nanoparticles transitions from (i) cells with molecular uptake to (ii) nonviable cells to (iii) fragmented cells with increasing laser fluence, as seen previously. In contrast, photoporation with MWCNTs causes uptake and, at higher fluence, fragmentation, but does not generate nonviable cells, and SWCNTs show little evidence of bioeffects, except at extreme laser conditions, which generate nonviable cells and fragmentation, but no significant uptake. These different behaviors cannot be explained by photoacoustic pressure output from the particles. All particle types emit a single, ≈100 ns, mostly positive‐pressure pulse that increases in amplitude with laser fluence. Different particle types emit different peak pressures, which are highest for SWCNTs, followed by CB nanoparticles and then MWCNTs, which does not correlate with cellular bioeffects between different particle types. This study concludes that cellular bioeffects depend strongly on the type of carbon nanoparticle used during photoporation and that photoacoustic pressure is unlikely to play a direct mechanistic role in the observed bioeffects. Cellular bioeffects of photoporationdepend on laser energy and carbon nanoparticle type. Nanosecond‐pulsed laser irradiation yields different cellular bioeffects for carbon‐black nanoparticles, multi‐walled carbon nanotubes, or single‐walled carbon nanotubes. Energy mechanisms associated with multi‐walled nanotubes produce the highest intracellular uptake with high cell viability. Lack of bioeffects correlation with photoacoustic pressure suggests it may not play a mechanistic role.

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