Pb-Sb Alloys Research Articles

Lead Hardening by Oxide Dispersion

Lead hardened through oxide scattering is investigated as raw materials for the fabrication of the support gratings of lead accumulators in order to increase their life service. For the preparation of lead powder hardened through oxide scattering we used air jet pulverisation, a technique specific to powder metallurgy. Two research approaches are presented in the paper: one in which the oxide was introduced through oxidised lead powder, and the other in which additional lead oxide was introduced. Oxide dispersion into metallic matrix was achieved by pronounced deformation through extrusion of the powder. During extrusion, the particles are compelled to pass through the mould calibration zone and consequently they are considerably deformed. As an effect of this deformation, the particles of fragile oxide which cover the lead powder particles are crashed and carried away to the material flowing through the matrix longitudinally on the extruded semiproduct. The content of oxide introduced in matrix by the oxidised lead powder depends on the powder particle size. This paper presents the effect of the powder particle size and oxide phase dispersion in the metallic matrix on the mechanical, chemical and electrical properties of the extruded semi-products. The semi-products made from lead powder belonging to the grain size class of < 40 µm and oxide particles allowance have the highest mechanical resistance and the best corrosion behaviour. Using controlled oxidised lead powder better extruded semi-products are obtained in terms of mechanical resistance, corrosion behaviour and electrical conductivity as compared with lead and Pb-Sb alloy. A higher electrical conductivity represents an important advantage especially for the starting accumulators where the voltage fall should be as low as possible.

Impression creep behavior of cast Pb–Sb alloys

Creep behavior of the cast the Pb–1.25%Sb and Pb–4.5%Sb alloys was studied by impression testing. The tests were carried out under constant stress in the range of 40–135 MPa and at temperatures in the range of 300–420 K. Assuming a power law relationship between the impression velocity and stress, power law stress exponents of 3.3 and 12.5 were obtained for Pb–1.25%Sb at low and high stresses, respectively. These stress exponents for the Pb–4.5%Sb alloy were found to be 4 and 19 in the similar stress and temperature ranges. Analysis of the data showed that for all loads and temperatures, the activation energy for both materials was stress-independent with an average value of 63 kJ mol −1. Based on the obtained stress exponents and activation energy data, which is very close to 65.6 kJ mol −1 for Pb diffusion in the Pb grain boundaries, it is proposed that in the low stress regime the operative creep mechanism is grain boundary diffusion. This behavior is in contrast to the high stress regime in which, the stress exponents of 12.5 and 19 are indicative of a dislocation creep mechanism in both alloys.

Cellular growth during transient directional solidification of Pb–Sb alloys

Cellular spacings and solidification thermal variables were determined for three dilute Pb–Sb alloys, which were solidified under unsteady-state heat flow conditions. The experiments have been carried out by using a casting assembly, which was designed in such way that the heat was extracted only through the water-cooled system at the casting bottom, promoting vertical upward directional solidification. An experimental approach, based on thermal readings collected at six different positions from the casting surface, was used in order to quantitatively determine the solidification thermal variables: tip growth rate and cooling rate of Pb–0.3 wt%Sb, Pb–0.85 wt%Sb and Pb–1.9 wt%Sb alloys castings. After grinding, polishing and etching procedures, both longitudinal and transverse sections of the castings were characterized by a typical cellular microstructure which prevailed along the entire casting. The cell spacing variation with cooling rate and tip growth rate was characterized by −0.55 and −1.1 experimental power laws, respectively. The experimental cell spacings were compared with the theoretical predictions furnished by cellular growth models.

X-ray photoelectron spectroscopy study of passive layers formed on Pb-Sn and Pb-Sb alloys

In this article, passivated Pb-Sn and Pb-Sb alloys with different compositions were studied by X-ray photoelectron spectroscopy (XPS). The passive films were found to have a double-layer structure. Both Sn and Sb were found to play an important role during the growth of passive film, which resulted in different compositions of passive films. The Pb oxides, Pb sulfate, Sn/Sb oxides, and Pb-Sn/Sb complex oxides (PbOx·Sn1−xO2, PbSb2O6) were present in the passive films. Both Sn and Sb facilitated PbOx (1<x<2) formation, which was considered to be very helpful to optimize the conductivity of passive films. It was also shown that the positions of peak signals of alloying Sn/Sb, Pb, and O were almost fixed, even though the contents of alloying Sn/Sb oxides were quite different in different specimens.

Investigation of stress exponent in the power-law creep of Pb–Sb alloys

Abstract The power-law creep behavior of Pb–1.25 Sb and Pb–4.5 Sb alloys was investigated at room temperature. Stress exponent values for these alloys were determined by indentation creep, conventional creep and uniaxial tension tests in order to evaluate the correspondence of indentation creep results with conventional tests. In all cases, the stress exponent values of 8–11 and 5–6, depending on the antimony content, obtained by different indentation methods were very similar. Also, it was observed that the indentation results were in good agreement with the results of the tensile and conventional creep tests. Within limits, the indentation tests are thus considered useful to acquire information on the creep behavior of antimonial lead alloys at room temperature.

Room temperature indentation creep of cast Pb–Sb alloys

Creep behaviour of cast Pb–Sb alloys with antimony contents in the range of 1.25–4.5% was studied by indentation methods at room temperature. Stress exponent values have been determined through different methods of analysis and in all cases, the calculated exponents are in good agreement. The stress exponent values in the range of 13–15.5, 18–20 and 29–30, depending on the antimony content, indicate that dislocation movement is the possible mechanism during creep deformation of these alloys.

Quenching media and temperature dependence of structural and stress–strain characteristics of deformed Pb-2 at% Sb alloy during transformation

The hardening behavior of Pb–Sb alloys let them have important role in industrial applications especially as suitable materials for battery grids in the acidic accumulators manufacturing. Three different cooling techniques were used to prepare samples of Pb-2 at%Sb alloy with different grain size. Transmission electron microscope examination showed that slowly cooled samples have the largest grain diameter, while the samples quenched in liquid nitrogen (fast cooling rate) have the smallest grain size. The stress–strain characteristics were studied in the temperature range from 433 to 503 K. The yield stress σ y, the fracture stress σ f and the coefficient of logarithmic work hardening χ decreased with increasing the test temperature while the fracture strain ε f increased. All these parameters showed two temperature stages around the transformation temperature 473 K. The X-ray diffraction technique was used to investigate the microstructure of the samples after the tensile test. The lattice parameter showed maximum value at 463 K for samples quenched in cold water.

Directional solidification and convection in small diameter crucibles

Pb–2.2 wt.% Sb alloy was directionally solidified in 1, 2, 3 and 7 mm diameter crucibles. Pb–Sb alloy presents a solutally unstable case. Under plane–front conditions, the resulting macrosegregation along the solidified length indicates that convection persists even in the 1 mm diameter crucible. Al–2 wt.% Cu alloy was directionally solidified because this alloy was expected to be stable with respect to convection. Nevertheless, the resulting macrosegregation pattern and the microstructure in solidified examples indicated the presence of convection. Simulations performed for both alloys show that convection persists for crucibles as small as 0.6 mm of diameter. For the solutally stable alloy, Al–2 wt.% Cu, the simulations indicate that the convection arises from a lateral temperature gradient.

Modeling dendritic growth of a binary alloy

A two-dimensional model for simulation of the directional solidification of dendritic alloys is presented. It solves the transient energy and solute conservation equations using finite element discretizations. The energy equation is solved in a fixed mesh of bilinear elements in which the interface is tracked; the solute conservation equation is solved in an independent, variable mesh of quadratic triangular elements in the liquid phase only. The triangular mesh is regenerated at each time step to accommodate the changes in the interface position using a Delaunay triangulation. The model is tested in a variety of situations of differing degrees of difficulty, including the directional solidification of Pb–Sb alloys.

Passivation phenomenon of low antimony alloys in deep discharge conditions of lead–acid batteries

The effects of the low antimony content and polarisation time on passivation of lead–antimony alloys under deep discharge conditions of the lead–acid batteries were investigated at a potential of +0.7 V versus Hg ∣ Hg 2SO 4 ∣ K 2SO 4sat., in a 0.5 M H 2SO 4 solution. Electrochemical techniques and metallographic analyses revealed that the antimony level controls the electric passivation of Pb–Sb alloys, used as positive grid alloys. For low antimony alloys (Sb<0.75 wt.%), this passivation phenomenon is due to the formation of α-PbO, acting as an electric barrier at the grid surface, and growing through a solid-state diffusion process of O 2− anions in a local electric field. Thickness measurements and monitoring of PbO growth by electrochemical impedance spectroscopy have demonstrated, by computation of the diffusion coefficient and the diffusion resistance of O 2− anions, that antimony incorporated into the oxide acts as a doping element for its growth. At higher antimony levels, the two-phase alloys (lead matrix+Sb precipitates) promote the formation of a very thin layer of a Sb-rich oxide inhibiting the PbO growth.

Primary dendrite distribution and disorder during directional solidification of Pb-Sb alloys

Pb-2.2 wt pct Sb and Pb-5.8 wt pct Sb alloys have been directionally solidified from a single-crystal seed with its [100] orientation parallel to the growth direction, to examine the primary dendrite distribution and disorder of the dendrite arrays. The dendrite distribution and ordering have been investigated using analysis techniques such as the Gauss-amplitude fit to the frequency distribution of nearest and higher-order spacings, minimum spanning tree (MST), Voronoi polygon, and Fourier transform (FT) of the dendrite centers. Since the arrangement of dendrites is driven by the requirement to accommodate side-branch growth along the 〈100〉 directions, the FT images of the fully developed dendrite centers contain spots which indicate this preferred alignment. A directional solidification distance of about three mushy-zone lengths is sufficient to ensure a steady-state dendritic array, in terms of reaching a constant mean primary spacing. However, local dendrite ordering continues throughout the directional solidification process. The interdendritic convection not only decreases the mean primary spacing, it also makes the dendrite array more disordered and reduces the ratio of the upper and lower spacing limits, as defined by the largest 5 pct and the smallest 5 pct of the population.

Effect of growth rate on macrosegregation during directional solidification of a Pb-Sb alloy

Directional solidification experiments on Pb-5.8 wt% Sb alloy have been carried out over growth rates varying from 0.8 to 20 μm s−1 in a positive temperature gradient of 140 Kcm−1. The microstructural examination of this alloy composition indicated cellular to dendritic transition at a growth rate of 1.5 μm s−1. The primary arm spacing was observed to decrease with growth rate in dendritic solidification regime. The maximum primary arm spacing occurred at the growth rate corresponding to the cellular to dendritic transition. Chemical analysis data revealed large amounts of macrosegregation in the longitudinal section of the alloy. A decrease in growth rate resulted in an increased degree of macrosegregation. These effects are discussed in light of thermo-solutal convection in the melt ahead of the solid-liquid interface during directional solidification of this alloy. A parameter ke is used to represent the extent of convection in the melt and the consequent degree of macrosegregation of the alloy with varying growth rates for solidification with a cellular-dendritic interface in the same way as it has been earlier used for the planar-front solidification condition.

Electrochemical characteristics of Pb–Sb alloys in sulfuric acid solutions

Lead–antimony alloys with a wide range of Sb contents, pure Pb and pure Sb were subjected to sulfuric acid solutions to elucidate their electrochemical characteristics by cyclic voltammetry and corrosion potential measurements. A corrosion test with a Pb/Sb galvanic couple was also done. For Pb-rich α-phase alloys (<0.3 wt.% Sb), their electrochemical behavior was similar to that of pure Pb. On the other hand, for α+β phase alloys (>0.3 wt.% Sb) their behavior was quite different from those of α-phase alloys; (i) dissolution current of Sb was proportional to Sb contents; (ii) hydrogen overvoltage was decreased remarkably with increasing the Sb contents; (iii) the corrosion potential shifted and approached that of pure Sb with time. It is confirmed that the electrochemical behavior of Pb–Sb alloys is related to the electrochemical property of the individual phase involved in the internal galvanic couples formed.

Microstructural investigation of plastically deformed Pb(1−x)Snxalloys: an X-ray profile-fitting approach

A detailed X-ray line-profile analysis is presented on five compositions of Pb–Sn alloys in the face-centred cubic (f.c.c.) α phase. Analysis has been performed within the framework of the Warren–Averbach method and the Williamson–Hall method through a profile-fitting algorithm assuming a pseudo-Voigt (pV) profile shape function convoluted with an asymmetric function. The effect of cold-working on the alloys is analysed in terms of defect-related parameters and defect distribution. The alloys decompose beyond the composition Pb–13.2 at.% Sn. Cold-working produces very weak structural broadening in Pb–Sn alloys, along with negligible incidence of deformation-fault probability. However, the presence of the Sn-rich β phase enhances the fault probability. The plot of \ln \langle \varepsilon^2\rangle^{1/2}versus\ln L is a straight line and the slope is around −0.26 to −0.43, indicating that the strain-broadened profile is intermediate between a Gaussian and a Lorentzian profile. The origin of the `hook' effect in the size Fourier plot is attributed to non-Gaussian strain distribution or strain gradients in the diffracting columns. The effect of recovery is noticeable and is probably due to polygonization. Furthermore, the rate of recovery is greater in Pb–Sn alloys compared to Pb–Sb alloys for identical solute concentrations.

Macrosegregation caused by thermosolutal convection during directional solidification of Pb-Sb alloys

Pb-2.2 and 5.8 wt pct Sb alloys were directionally solidified with a positive thermal gradient of 140 K cm−1 at growth speeds ranging from 0.8 to 30 µm s−1, and then quenched to retain the mushyzone morphology. Chemical analysis along the length of the directionally solidified portion and in the quenched melt ahead of the dendritic array showed extensive longitudinal macrosegregation. Cellular morphologies growing at smaller growth speeds are associated with larger amounts of macrosegregation as compared with the dendrities growing at higher growth speeds. Convection is caused, mainly, by the density inversion in the overlying melt ahead of the cellular/dendritic array because of the antimony enrichment at the array tip. Mixing of the interdendritic and bulk melt during directional solidification is responsible for the observed longitudinal macrosegregation.

Strain distributions in cold-worked-α-PbSb alloys from X-ray line profile analysis

A detailed X-ray profile-fitting study of cold-worked Pb–Sb alloy in the α-phase is presented using a Pseudo-Voigt profile shape-function. Warren–Averbach's line-profile analysis reveals that the deformation process has a minimal effect on the microstructure, characterised by large coherent domain size (∼800–1000 Å), small microstrains, negligible planar fault probability. Interpretation of the variation of column strains in terms of local strains and strain derivatives show that dislocation arrangement and also the Sb precipitates (if any) modifies the mean-square strain derivatives. The dislocation densities are of the order of 1010 cm/cm3. The effect of recovery is noticed and the possible mode of recovery appears to be polygonization of the dislocation.

Effect of antimony on premature capacity loss of lead/acid batteries

Lead/acid batteries with antimony-free positive grids have a tendency to lose discharge capacity early indeep-discharge cycling. In this study, the effect of antimony in positive active-material (PAM) on the performance of batteries with Pb-Ca-Snalloy grids is investigated. The corrosion layer of Pb-Ca-Sn positive grids with conventional leady oxide discharges before the PAMdischarges. With Pb-1 wt.%Sb leady oxide, however, the corrosion layer of positive grids of the same composition does not discharge somuch, and antimony is observed in the corrosion layer. These results suggest that the antimony-containing corrosion layerdischarges with difficulty and, thus, the active material discharges more readily than the corrosion layer and a passivation layer does not format the grid/active-material interface. This suggestion is also supported by parallel discharge tests of anodic corrosionlayers on lead and Pb-Sb alloys in dilute sulfuric acid. The corrosion layer of the Pb-Sb alloy has a tendency to discharge after that of pureleads in a parallel circuit.

The PbO 2 agglomerate-of-spheres: investigation of four grid materials

During the past decade, the agglomerate-of-spheres (AOS) model has been developed to describe the behaviour of the PbO 2 electrode during cycling. In the model, the formation of the AOS is described as an electro-metasomatic process that creates the so-called ‘electroformative’ force (EFF). This force causes an enlargement of the entire volume of the formed PbO 2. PbO 2 electrodes are investigated in a special electrochemical cell that is integrated into a tension testing machine. With this arrangement, the positive electrode can be cycled with simultaneous measurement of the EFF and the solid-state resistance (SSR) between the grid and the active material during formation, charge and discharge. From a technological point of view, it is of interest to investigate the influence of the grid alloy on the AOS parameters of the PbO 2 electrode. Investigations have been performed on pure lead and Pb-Sb, Pb-Ca-Sn and Pb-Ca-Sn-Ag alloys. A very small amount of additive can greatly influence the mechanical, corrosive and electrochemical properties. The corrosion behaviour depends mainly on the properties of the corrosion layer (i.e., on its mechanical, electronic, and electrochemical characteristics) rather than on the properties of the alloy itself. The components of the grid alloys appear to influence the EFF, the highest values are observed for the Pb-Sb alloy. This alloy exhibits the smallest corrosion region of the tested materials. The rupture plane after 15 cycles for all four materials is located in the active material close to the ‘grid’. The tensile strength differs markedly between the different materials. A very high tensile strength is displayed by the Pb-Ca-Sn-Ag alloy. This demonstrates the influence of silver on the behaviour of the active material, although the tin content is about 35% larger, too. Theoretical consideration is given to the formation of the corrosion layer. It is concluded that no significant layer of PbO exists between grid metal and the active material.

Influence of antimony on the properties of the anodic oxide layer formed on Pb-Sb alloys

Electric and dielectric properties, changes in structure and kinetics of formation and reduction of anodic phase layers on Pb and Pb-Sb electrodes in H 2SO 4 have been studied by means of electrochemical and structure characterizing impedance spectroscopy methods. The results obtained were discussed with respect to the effectiveness of Sb on the solid-state PbO → PbO n and PbO n → PbO 2 transformations. It is found that Sb facilitates the appearance of a potential region in which non-stoichiometric mixed oxides are formed; it has a catalytic effect on the PbO into the PbO n transformation. The formation of the mixed oxide leads to a shift in the potential of the oxidation of PbSO 4 to PbO 2 of about 200 mV in comparison with the pure-Pb electrode. It seems that the observed effects could explain why Sb prolongs the positive plate cycle life. It was shown that the electrochemical impedance spectroscopy is a very sensitive and suitable method for in situ investigation of solid-state processes in the positive lead/acid battery plate.

リサイクリング 鉛のリサイクル

Because of the steady increase in car population and the mounting of enviromental concern, lead consumption ratio for lead-acid batteries is tending to gradually increase. As a result of this fact, itis important to establish new reliable collection, treatment, and recycling system of used lead-acidbatteries that would not to be effected by the fluctuation of lead prices and the exchange rate. Andlead-acid batteries made of lead, dilute sulfuric acid and polypropylene have to be treated withoutcausing any enviromental problem.In Japan, in October 1994, the battery manufacturing industry started the a “lead recyling system”.As maintenance-free batteries using no Pb-Sb alloy as grid arewidely used, demand for secondary Pb-Sb alloy has decreased.To maintain the usage amount of secondary lead as lead-acid battery, primary smelters were asked toparticipate in this recycle system.Afterthe introduction of this system, recyclig ratio for lead-acid batteries has risen to about 90%contributing to stabilized recycling ratios.