Pb Particles Research Articles

Melting Behavior in Granular Metal Thin Films

ABSTRACTGranular metal films consisting of small Sn, Bi, and Pb particles, typically from less than 100 Å to several 1000 Å in size and embedded in a SiO2 matrix, have been fabricated over a range of metal compositions by RF sputter deposition. Two different film geometries have been prepared, homogeneous films and multilayer films consisting of alternating layers of granular metal and SiO2. These films have been characterized by x-ray diffraction and transmission electron microscopy and their melting behavior studied by differential scanning calorimetry. As the concentration of the metal component is decreased, the average particle size decreases and the particle size distribution becomes more narrow. When the solid-liquid transition is studied, the melting temperature has been found to be increasingly depressed as the particle size is reduced. In the smallest particles the relative reduction in the melting temperature is greater than 10 percent. No strong evidence for melting point enhancements, due to pressureeffects arising from the different thermal expansions of the metal particles and the SiO2 matrix, has been observed in either the homogeneous or multilayer films.

In situ transmission electron microscope measurements of solid Al-solid Pb and solid Al-liquid Pb surface-energy anisotropy in rapidly solidified Al-5% Pb (by mass)

Alloys of Al-5% Pb and Al-5% Pb-0.5% Si (by mass) have been manufactured by rapid solidification and then examined by transmission electron microscopy. The rapidly solidified alloy microstructures consist of 5-60 nm Pb particles embedded in an Al matrix. The Pb particles have a cube-cube orientation relation with the Al matrix, and are cub-octahedral in shape, bounded by {100} Al, Pb and {111} Al, Pb facets. The equilibrium Pb particle shape and therefore the anisotropy of solid Al-solid Pb and solid Al-liquid Pb surface energies have been monitored by in situ heating in the transmission electron microscope over the temperature range between room temperature and 550°C. The ani­sotropy of solid Al-solid Pb surface energy is constant between room temperature and the Pb melting point, with a {100} Al, Pb surface energy about 14% greater than the {111} Al, Pb surface energy, in good agreement with geometric near-neighbour bond energy calculations. The {100} AI, Pb facet disappears when the Pb particles melt, and the anisotropy of solid Al-liquid Pb surface energy decreases gradually with increasing temperature above the Pb melting point, until the Pb particles become spherical at about 550°C.

The coarsening of liquid Al-Pb-dispersions

The behaviour of a dispersion with liquid Pb particles moving at their Stokes velocities relative to the liquid Al matrix has been investigated. In order to provide a stable dispersion a special experimental arrangement has been used that minimizes effects due to settling of the heavier Pb droplets. It is shown that the measured stationary droplet size distribution coincides with the authors′ theoretical prediction for Ostwald ripening by convective diffusion.

Superconductivity of (Pb, Sn, Ge)Te Semiconductor Film with a Little Pb Inclusion

The superconductivity (SC) behaviors of PbTe films containing Pb inclusion are observed below Tc of Pb (7.2K) in spite of a small amount of pb precipitate (1 at.%). In these films, random arrays of small Pb particles are considered to be coupled as Josephson junctions through host PbTe. Further a search for enhancement of Tc due to non-phonon mechanism by interactions between superconducting metal particles and excitons of narrow gap semiconductor in Pb1-xSnxTe and (or) Ge-ion motion in Pb1-xGexTe are undertaken. No enhancement of Tc is observed.

X-ray photoemission of Pb and Sn particles supported on carbon

The Pb(4f) and Sn(3d) core-level binding energies in small Pb and Sn particles deposited on carbon are examined as a function of the metal coverage. Both core levels shift toward higher binding energies as the coverage decreases. Since Pb and Sn are sp metals and have lower work functions tha carbon, our results imply that the interpretations of the line-shift based on the changes in the electronic configuration (i.e. changes in the number of valence d electrons) and on the changes in the reference level are incorrect.

鉛入黄銅中の鉛粒子の析出と粗大化

The machinability of leaded brass is well known to be affected by the microstructural properties of its matrix and microconstituents, particularly by the size and distribution of lead particles, and of course, by variation in machining conditions. The behavior of precipitation and coarsening of Pb particles during solidification and subsequent annealing of α- and β-single phase pure leaded brass was initially assessed by conventional metallographic methods. The size distribution was treated by a new statistical method. The results were later extended to α+β phase commercial leaded α+β brasses.The size and distribution of Pb particles were quite different in the two types of brasses. In as-cast conditions, Pb particles in α-brass were much coarser and precipitated mainly on grain boundaries, while the distribution of Pb particles in β phase brass was relatively homogeneous and its size was much smaller.The diffusion path and preferred nucleation sites of Pb atoms such as dislocations, sub-boundaries and grain boundaries were needed to the coarsening of Pb particles.The solid solubility of Pb was likely to be larger in β-phase than in α-phase, and therefore, the distribution of Pb particles in β-phase was more homogeneous than in α-phase.It was concluded that the size and distribution of Pb particles in commercial leaded brass are determined through the change in the grain structure of α and β phases.

Characterization of individual particles in the Phoenix urban aerosol, using electron beam instruments

More than 8000 individual particles from the Phoenix aerosol were analyzed by using an analytical scanning electron microscope. The composition of the aerosol were similar at the three sampling locations. Approximately 75% of the coarse particle fraction (>1 ..mu..m) is crustal material, i.e., clays, quartz, feldspars, calcite, etc. The remaining coarse particles consist mainly of biological materials, S compounds, Pb salts from atuomobiles, and other anthropogenic particles. S-bearing particles comprise an estimated 60-80% of the submicron aerosol fraction. Presumably, the most abundant S species is (NH/sub 4/)/sub 2/SO/sub 4/; however, many of the S-bearing particles contain various amounts of other elements such as Zn, Pb, Cu, Na, Ca, As, and K. The remainder of the submicron fraction is composed largely of automobile Pb halides and particles from a variety of anthropogenic sources. Some of the anthropogenic particles have been pinpointed to specific sources, but in most cases to date only possible sources are suggested. 38 references.

Proximity-effect-induced superconductivity in very dilute Pb-Zn composites

Very dilute bulk dispersions of micrometer-sized particles of Pb in Zn show resistive superconducting transitions at up to 3 K, far above that of Zn itself (0.8 K), although the Pb volume fraction is only 0.006. The $I\ensuremath{-}V$ characteristics contain reproducible structure that is not understood. At lower temperatures the samples expel a small, but significant, amount of flux. The superconducting transition can be explained in terms of proximity-effect coupling of the Pb grains through the Zn matrix.

Superconductivity of small particles

The Eliashberg gap equations are used to investigate the contribution of surface-phonon softening to the size dependence of the superconducting transition temperature (${T}_{c}$) of small metallic particles. Because of our limited quantitative knowledge of phonon spectra and electron-phonon coupling in the surface region, the effect cannot be calculated with certainty. Previous calculations which agree with experiment depend on a fortuitous choice of input parameters which cannot be justified at present. For this reason the absence of any observable size effect for ${T}_{c}$ in Pb is especially important. This null effect is obtained in Pb if the electron-phonon coupling strength is the same in the surface region as in the bulk. This assumption can be tested experimentally because it means that the energy gap of Pb should not be independent of particle size but rather should increase significantly with decreasing radius. Hence, measurement of the size dependence of the energy gap for well-characterized small particles of Pb could provide information regarding the importance of the phonon-softening mechanism, at least for Pb.

Effects of impurities and pores on fire-cracking of lead-containing α-nickel silvers

Abstract Work on α-Cu-18Ni-19Zn- Pb alloys showed that fire-cracking sensitivity is caused primarily by impurities and by micropores around Pb particles along grain boundaries. In a certain impurity range, fire cracking depends also on the type of heat treatment preceding cold work. In the case of cyclic heat treatments, only the last cycle is responsible for the fire-cracking behaviour of such alloys. Specimens can thus be sensitized at will for fire cracking. Heat treatment also influences fire cracking through the formation of micro pores which subsequently act as crack initiators. Reversible pore formation must be caused by the variability of the wetting capacity of liquid lead and the matrix. Good wetting, as a result of liquid metal embrittlement, produces many pores around lead particles and conditions an alloy for fire cracking. Furthermore, wettability is influenced by the impurity content. In order to avoid fire cracking, appropriate additions must be made to reduce wettability below a critical ...

Short-term influence of anthropogenic sources on tropospheric baseline lead

ESTIMATING tropospheric baseline lead requires relatively long collection periods using conventional high volume methods because the airborne concentrations are very low in comparison with levels found in urban areas. During such collections, anthropogenic sources of lead may be present for short periods leading to apparently high results, even at remote locations such as the mid-Pacific Ocean1 and Antarctica2. Significant geographical variations in soil-sized Pb particles were also related to anthropogenic sources affecting the distribution of lead in marine atmospheric particulates3,4. We describe here investigations using furnace atomic absorption spectrometry (AAS) of the lead content in the atmosphere around Cape Grim, Tasmania.

RESPONSES OF ALVEOLAR MACROPHAGE TO METALLIC FUME

Alveolar macrophage was lavaged from lungs of rats exposed to inhalation of the particles of Sb, Pb, Cd, CaCO3 or poly vinyl chloride (PVC) and its number and 14C-leucine incorporating activity were studied. The number of free cell lavaged from the lung decreased remarkably by the exposure to Sb or Cd fume, while by the exposure to Pb fume, CaCO3 or PVC particles the number of lavaged cells did not change from that of control group breathing air in the exposure chamber. There was found a linear correlation 1 hr after inhalation between 14C-leucine in-corporation value for total cell and the number of lavaged cell in all the experi-mental groups except unrestrained (bred freely under normal condition) group and Sb group. That is, the incorporation value per cell in all the experimental groups except Sb group and unrestrained group was almost equal. In the case of Sb group and unrestained group the incorporation value per cell was lower than those of the other groups. Although the incorporation of 14C-leucine into cell in control group decreased by level of unrestrained group 21 hr after inhalation, in the Pb, CaCO3 or PVC group 14C-leucine incorporation into cell 21th hour did not change from that 1 hr after inhalation. 14C-leucine incorporation per cell in Sb group 21 hr after inhalation remarkably increased. This tendency was also seen in Cd group.The effects of the particles used in the inhalation experiment on the macrophage in vitro were also studied. The Sb fume was the most effective of all the samples and followed by Cd fume and then by Pb fume. The particles of CaCO3 or PVC were practically inert to the macrophage.

Condensation and evaporation of metallic aerosols

The heat-pulse cloud chamber has been used to study the condensation of metallic aerosols in the presence of purified argon. Multiplication, growth and evaporation of Ca, Cd, Pb and Zn particles vary with the background temperature in the chamber. The volatile Cd and Zn resemble the alkali halides in that growth occurs readily in suspension when a sufficient vapour pressure is maintained, and particles are formed that settle out at appreciable speeds. These particles fall from the cloud independently.

Powder segregation during die filling

A study of powder segregation during die filling with two-component mixes of Pb particles has shown that: (1) Segregation occurs by fines filtering down through the moving powder mass. This effect builds up an inner mound of fines-rich material on the bottom of the die and an excess of coarse particles in the periphery of the die cavity. This is termed normal segregation. (2) For a particular size of large component, reducing the size of the small component increases segregation up to the point at which the average relative size difference between coarse and fine is 0.7. When the fines are smaller than this their flow is restricted and so segregation is reduced. (3) Particle shape and density in the mixtures studied have little effect upon segregation. (4) Increasing the rate of die filling decreases opportunity for segregation. (5) Increasing the height from which the powder falls into the die causes mixing and decreases segregation. (6) Inverse segregation, which is an excess of fines in the periphery of the die cavity, occurs in coarse particle systems containing a high percentage of fines. This is because the relatively few coarse particles are Lindered from flowing within the matrix of fines towards the rim of the die cavity.

Metal polymers based on �D-5 epoxy-diane resin and colloidal lead

1. The authors establish the conditions of formation of metal polymers based on ED-5 epoxy-diane resin and colloidal lead. 2. They have established by infrared spectroscopy that epoxy resin reacts via its polar groups with the surface of the colloidal Pb particles as they form on the cathode, thereby forming chemically bound adsorption compounds on the surface of these particles. 3. It is found that hardening of the resin is greatly promoted by the presence of colloidal lead.

亜鉛電解における浮遊物質の挙動に関する研究 (第2報)

It has been generally considered that major substances suspended in zinc electrolyte are lead compounds such as PbO2, PbO, PbSO4, Pb and manganese dioxide particles. The experiments, were -made on various properties of these particles in the solution, i. e., the variations of coagulation, electrophoresis, settling rate of suspension, pH value etc. From theabove experiments, it was considered that lead peroxide particles, which aremost harmful in zinc deposit, are positively charged by absorbing hydrogen ion in zinc electrolyte, and deposited on the cathode with zinc by the electrophoresis, but this hydrogenion is exchanged by the presence of manganese dioxide particle and the deposition of lead peroxide on the cathode is prevented.Next, the preventive phenomenon to deposit of lead peroxide particle on the cathode was compared with regard to manganese dioxide and ion exchange resins. From this experimental results, it was considered that the properties of manganese dioxide particle has a, selective ion exchange to hydrogen ion on lead peroxide particle.