Determination of the Oxide Layer Thickness on Beryllium Metal Particles

Abstract

The hypothesis was tested that beryllium metal particles have a uniformly thick surface coating of beryllium oxide and that smaller particles should have a higher oxide fraction by mass because they have a higher surface to volume ratio. The mass fraction of oxygen, physical density, and specific surface area were determined for size-fractionated samples of respirable beryllium metal particles. The largest particles analyzed (count median diameter 4.6 microns with geometric standard deviation 1.6) contained 7% +/- 1% beryllium oxide by mass; had a physical density of 1.90 +/- 0.02 g/cm3; and had a specific surface area of 4.0 +/- 0.3 m2/g. The smallest particles analyzed (count median diameter 0.4 micron with geometric standard deviation 1.8) contained 31% +/- 3% beryllium oxide by mass; had a physical density of 2.00 +/- 0.17 g/cm3; and had a specific surface area of 20.8 +/- 2.1 m2/g. These shifts in density and oxide content with size and surface area are consistent with a beryllium metal core of density 1.84 +/- 0.02 g/cm3 (1.848 g/cm3 is theoretical); a beryllium oxide layer of density of 2.53 +/- 0.16 g/cm3 (3.025 g/cm3 is the perfect crystalline density); and an oxide layer thickness of 49 +/- 4 A for all particle sizes. These results indicate that the inhalation toxicity of beryllium metal particles may be similar to that of beryllium oxide formed at low temperatures.

Dissolution of the metal sensitizers Ni, Be, Cr in artificial sweat to improve estimates of dermal bioaccessibility

“…2). For example, in the case of Be metal, the oxide species are loosely organized because they were not heat-treated to form regularly ordered crystalline species 19 and hence susceptible to dissolution. 30 In addition to surface reactivity with ambient oxygen, another parameter which influences dissolution of metals such as Ni is the presence of alloying compounds in the material.…”

“…18 The Be metal powder was obtained from a primary production facility. 19 Chemical properties of the bulk powders were characterized using Auger spectroscopy to determine the surface elemental composition (outer 50-75 Å layer) and powder X-ray diffraction (XRD) to identify crystalline constituents. Physical properties were characterized using transmission or scanning electron microscopy to evaluate the morphology and size; helium pycnometry to determine the density; and nitrogen gas adsorption to determine the surface area using the Brunauer, Emmett, and Teller (BET) method.…”

“…In this protocol, 0.01 M hydrochloric acid is used to dissolve the soluble beryllium fraction followed by increasingly more aggressive acid-assisted digestions to dissolve poorly soluble beryllium metal, oxide, and silicate compounds. Prior to our experimental studies, we performed a pilot study in which three samples of a mixture of beryllium sulfate tetrahydrate salt >99.99% (Sigma-Aldrich, St Louis, MO), beryllium metal powder, 19 and beryllium oxide powder (NIST SRM® 1877: beryllium oxide powder) were accurately weighed to within 0.01 mg using a microbalance (Model AX-205, Mettler-Toledo, Switzerland) in a temperature- and humidity-controlled room. Ten milliliters of 0.01 M hydrochloric acid were added to each sample and the suspensions were subjected to ultrasonic agitation for 5 minutes at room temperature (20 °C), filtered, diluted to 20 mL using deionized water, and quantified for soluble Be using inductively coupled plasma-optical emission spectroscopy (ICP-OES).…”