Paul Mccormick

Human Skin Penetration of Sunscreen Nanoparticles: In-vitro Assessment of a Novel Micronized Zinc Oxide Formulation

The extent to which topically applied solid nanoparticles can penetrate the stratum corneum and access the underlying viable epidermis and the rest of the body is a great potential safety concern. Therefore, human epidermal penetration of a novel, transparent, nanoparticulate zinc oxide sunscreen formulation was determined using Franz-type diffusion cells, 24-hour exposure and an electron microscopy to verify the location of nanoparticles in exposed membranes. Less than 0.03% of the applied zinc content penetrated the epidermis (not significantly more than the zinc detected in receptor phase following application of a placebo formulation). No particles could be detected in the lower stratum corneum or viable epidermis by electron microscopy, suggesting that minimal nanoparticle penetration occurs through the human epidermis.

Displacement reactions during mechanical alloying

The occurrence of simple solid-state displacement reactions during mechanical alloying has been investigated. The reduction of cupric oxide to pure copper metal by a variety of metallic reducing agents was studied, and the powders were examined by X-ray diffractometry and electron microscopy. When milled with a liquid process control agent, the reaction progressed gradually with time, whereas an unstable combustion reaction occurred when no such control agent was employed. A minimum adiabatic temperature of 1300 K is necessary for combustion to occur in these systems. The reaction enthalpy is an important factor in determining the precombustion period. The as-milled powders consisted of finely divided, nanometer-sized crystallites with an extremely high defect density. It is proposed that the increased reactivity of the system arises through the unique conditions prevailing during mechanical alloying.

Thermodynamic analysis of the martensitic transformation in NiTi. II: Effect of transformation cycling

Abstract The effect of transformation cycling, with and without applied stress, on the martensitic transformation in NiTi has been studied. Changes in transformation temperatures resulting from cycling are interpreted in terms of changes to the elastic strain energy and the irreversible energy associated with the transformation. It is found that the main effect of thermal cycling under zero stress is to increase the elastic strain energy. With pseudoelastic cycling and extensive thermal cycling under stress the elastic strain energy decreases with increasing cycling due to the development of a directional internal stress field associated with the formation of aligned variants.

Reduction of metal oxides by mechanical alloying

The chemical reduction of metal oxides by mechanical alloying with a strong reducing element has been investigated. Using x‐ray diffraction to follow the reaction it was found that the mechanical alloying of CuO and Ca using toluene as a processing lubricant resulted in the formation of Cu. The mechanical alloying of CuO and ZnO together with Ca resulted in the formation of β’ brass.

Nanopowders synthesized by Mechanochemical Processing

The activation of chemical reactions by milling reactants in a ball mill is presented here as a novel, low cost method for the synthesis of wide range of nanopowders with mean particle sizes as small as 4 nm. The factors controlling such mechanochemical reactions are discussed with respect to their influence on particle size, size distribution, and dispersion.

MECHANOCHEMICAL SYNTHESIS OF ULTRAFINE FE POWDER

Ultrafine Fe powders were synthesized by mechanochemical solid‐state reduction of FeCl3 by Na and subsequent removal of the reaction by‐products. X‐ray diffraction, Mossbauer spectroscopy, and transmission electron microscopy measurements showed that Fe particles with a relatively uniform particle size ∼10 nm were formed during the mechanical milling process. The powders exhibited coercivity values of 350–550 Oe, consistent with that expected for separated nanosized particles. This study demonstrates that mechanochemical processing has significant potential for the synthesis of ultrafine metal powders in an economic and efficient way.

Mechanically alloyed nanocomposite magnets (invited)

Nanocomposites, consisting of a hard magnetic rare earth–transition metal phase exchange coupled to soft magnetic α-Fe or α-(Fe,Co), exhibit enhancement of the remanent magnetization due to exchange coupling across interfaces between grains. Modeling studies have shown that crystallite sizes of less than 20 nm are generally required for significant remanence enhancement and values of remanent magnetization equal to 70%–80% of saturation magnetization have been reported in mechanically alloyed two phase mixtures of α-Fe and a hard magnetic phase, such as Nd2Fe14B. Studies of microstructural evolution during mechanical alloying have shown that as-milled structures consist of a magnetically soft two phase mixture of α-Fe and an amorphous phase. Similar microstructures are observed regardless of whether mechanical milling or mechanical alloying has been carried out. Heat treatment above a critical temperature is required to crystallize grains of the hard magnetic phase. The formation of metastable intermediat...

On the kinetics of mechanical alloying

The kinetics of solid-state displacement reactions during mechanical alloying have been investigated. The effects of charge ratio and ball size on the progress of the reaction between CuO and Fe have been evaluated from measurements of ignition temperature, combustion time, and crystallite size. The reaction kinetics are shown to increase with charge ratio. This is rationalized in terms of the effect of charge ratio on the number of ball/particle collisions. Ball size influences reaction kinetics through both the particle collision frequency and collision energy.

The morphology of Portevin-Le Chatelier bands: Finite element simulation for Al-Mg-Si

Abstract A constitutive model for dynamic strain ageing together with a three-dimensional finite element analysis were used to simulate discontinuous yielding behaviour associated with the Portevin–Le Chatelier effect. The deformation behaviour of both flat and round specimens of a dynamically strain ageing material was simulated, utilizing constitutive parameters for an Al–Mg–Si alloy. Finite element simulations showed the occurrence of propagative zones of localized deformation and provided insight into the strain rate distribution in the zones, characterized by a sharp strain rate peak. The localized deformation zones in round specimens were found to have a diffuse double cone morphology. Propagative deformation bands in flat strip specimens were planar and inclined with respect to the tensile axis by approximately 35°. The dependence of the morphology of the localized deformation zones on specimen geometry and deformation conditions, as well as the serrated stress–time curves obtained, are in good agreement with experimental measurements in Al–Mg–Si.

High-coercivity ferrite magnets prepared by mechanical alloying

Abstract Nanocrystalline hexaferrite (BaFe 12 O 19 or SrFe 12 O 19 ) and mixed Fe,Co-ferrite ((Fe x Co 1− x )Fe 2 O 4 with x =0–1) materials have been prepared by mechanical alloying and subsequent annealing. High coercivities were obtained in these nanocrystalline materials, 6–7 kOe for hexaferrite and ∼3 kOe for Co-ferrite. Hexaferrite powders prepared by mechanical alloying have been used as the starting material for high-coercivity bonded magnets. Hot-pressed anisotropic hexaferrite magnets have been produced with high values of coercivity and remanence. High magnetic performance was also achieved in some mixed Fe,Co-ferrites after magnetic annealing.