Silicon-rich Particles Research Articles

Hydrogen trapping on non metallic inclusions in cr-mo low alloy steels

The behavior of non metallic inclusions was investigated on undeformed and plastically deformed ferritic steels. Damaging of non metallic particles increases with strain level. Extensive cracking of the inclusions is generated by cathodic charging at a high current density. High resolution tritium autoradiography shows that manganese sulphides containing iron, silicon-rich particles and titanium nitrides are preferential trapping sites for hydrogen. The decrease in the hydrogen diffusivity, the larger amount of diffusible hydrogen observed when the sulphur content increases and the full outgassing of hydrogen at 523 K are representative of a moderate binding energy of hydrogen with sulphide compounds.

Effects of squeeze casting on the wide freezing range binary alloys

The application and effects of squeeze casting were investigated on the density, Brinell hardness, tensile strength and fracture elongation values of the wide freezing range Zn27%Al, Al20%Si, Al7%Si, Al10%Mg, Al5%Mg, Al4.5%Cu0.5%Bi and Fe3%CSi alloys. It was found that these alloys as a group were suitable for the squeeze casting practice. Sharp increases could be achieved in all mechanical properties due to the reductions in porosity levels. In general, higher squeezing pressures provided better mechanical properties. The trend in the Al20%Si alloy however, was sporadic and cracking occurred in the vicinity of silicon rich primary particles above 100 MPa pressure. An optimum melt, and die and punch temperatures were found as 1500 °C and 1150 °C, respectively to suppress white cast iron formation in the Fe3%C2%Si alloy. The Al10%Mg and Al4.5%Cu0.5%Bi alloys suffered microsegregation in addition to microporosity. Their squeeze cast samples showed higher hardness and tensile properties after annealing them. The machinabilities of the two alloys however, were degraded due to squeeze casting.

The morphology of particles of minor phases in a commercial Al-7.12wt% Si alloy

The morphology of particles of minor phases was monitored in an Al-7.12 wt% Si alloy in three different states: as-cast, hot isostatically pressed (HIPed) and heat-treated. In all of these states, the minor phases existing in this alloy were secondary silicon-rich particles and those which are iron-containing-Al12Fe3Si and (FeAl6) Si. The major phase was primary silicon-rich particles. The HIPed and heat-treated materials contained an additional phase, the iron-containing particles Al9Fe2Si2. It was found that secondary silicon-rich particles in the as-cast material were plate-like, spherical or fibrous. On the other hand, the few iron-containing particles in the as-cast material were needle-like. During HIPing or heat treatment, the iron-containing particles which precipitated also had a needle-like morphology. Most of the non-spherical secondary silicon-rich particles tended to spheroidize during HIPing or heat treatment. Fibrous secondary silicon-rich particles were not present in the HIPed or heat-treated materials.

Metals in airborne particulate matter in rural Switzerland

Weekly samples of aerosol in nine size fractions were taken in the period October 1985 to September 1986, and were analyzed for Na, V, Mn, Cu, Zn, As, Cd and Pb. Sampling locations were south of Berne, Switzerland, at elevations of 515, 750, 940 and 1550 m above sea level. The results indicate that the particulate matter concentration decreases with increasing elevation, but the extent of this decrease depends on atmospheric conditions, and is more pronounced during fall and winter when frequent inversion situations occur. During a few weeks in February 1986 unusually high aerosol concentrations were observed with atypical As to Zn ratios. The meteorological situation indicated transport from Eastern Europe. Principal component analysis revealed two to three factors in every size fraction, which were considered to be an ‘anthropogenic’, a ‘soil’ and a ‘large particle’ sodium component. Single particle analysis of one summer and one winter sample (particle size 2–4 μm) provided a variety of particles previously described in the literature as well as nickel and silicon rich particles of unknown origin (summer sample).

Machined surface flaws on the high strength aluminium alloys 7075 and 2024

Conventionally turned surfaces on two high-strength aluminium alloys have been examined using scanning electron microscopy and microanalysis. New mechanisms for machined surface flaw formation, based on the interaction of micro-constituents with the tool, are proposed. These mechanisms are suggested by the proximity to the flaws of iron-rich and silicon-rich particles, and by the similarity of the distributions of the particles and flaws. The new mechanisms are compared with the traditional machined surface flaw formation mechanisms, which are based on the formation of built-up edges. The inadequacy of conventional profilometry and of conventional surface roughness parameters in detecting this type of flaw is discussed.

Isolation and characterization of fly ash from rat lung tissue.

Inhaled fly ash may be leached by lung fluids, making potentially toxic trace elements in the fly ash bioavailable. We studied the composition and morphology of fly ash particles recovered from lungs of rats exposed to fly ash from a power plant burning pulverized eastern coal. Animals were sacrificed 1, 3, 6, and 12 mo after the commencement of the 4-wk exposures. Particles isolated from lungs of exposed animals, control fly ash samples, and samples recovered from control lungs spiked with fly ash were characterized by computer-controlled scanning electron microscopy (CCSEM) and thin window energy dispersive X-ray spectroscopy (EDS). EDS spectra of fly ash and ashed lung residues were distinct. Thus, fly ash particles could be distinguished from ashed lung residues. A majority of the fly ash particles recovered from lungs of exposed animals had similar morphology and composition to the exposure material. However, the number of silicon-rich particles decreased with time. After 6 mo, about 1% by number of the particles had been transformed, producing numerous "needles" associated with residues of fly ash particles. Particles that looked like diatoms were observed. This demonstrated that the sample preparation procedures used did not destroy delicate structures. Fly ash particles from a spiked control lung subjected to the same separation procedures did not have these structures. The structures may be the result of leaching of particles by lung fluids, which suggests that the glassy matrix components of fly ash particles may be bioavailable.

Particle characterization and cavity nucleation during superplastic deformation in Al-Li-based alloys

The role of intermetallic particles on the cavity formation during superplastic deformation has been studied in two aluminium-lithium-based alloys of identical chemical composition. They were, however, manufactured by two different routes — one by ingot metallurgy (IM) and the other by rapid solidification powder metallurgy (PM). A large number of particles of different shapes and sizes were found in both the alloys. In the IM alloy, particles were aligned in stringers in the direction of rolling. Iron and silicon, which were present as impurity elements, formed intermetallic phases in the IM alloy whereas only silicon-rich particles were found in the PM alloy. The particles of the PM alloy were of smaller size and were rather uniformly distributed in comparison to the IM alloy. During superplastic deformation, cavities first nucleated at the interface of large particles. The cavities of the IM alloy formed around the aligned stringers of large particles, whereas in the PM alloy they were uniformly distributed. It is shown that because both alloys contained particles of varying sizes, cavity nucleation occurred continuously during superplastic deformation.

Composition and size of individual particles from a gold mine atmosphere

Airborne dust particles were collected in a return airway of a South African gold mine using a 7-stage, single-orifice cascade impactor. Between 70 and 130 individual particles were analysed on each stage using automated electron-probe x-ray microanalysis (EPXMA). Particle size and shape parameters are given for different classes of particles sorted by elemental composition. Silicon-rich particles are the most abundant overall, while chlorine-rich particles dominate (up to 80%) in the range 0.2–1.0 μm. It is shown that EPXMA characterisation of particles can be used to infer relative contributions of various particle sources and dust generating processes to the total dust concentrations in mine atmospheres. An understanding of the nature and source of particles is essential for any source control strategy. We conclude that the EPXMA technique merits inclusion in the repertoire of techniques used for characterising underground dust.