Papers by Keyword: Impurity Diffusion

Abstract: The objective of this study is to quantify the improvement of diffusion experiments in liquid alloys by using two measurement points of in situ X-ray fluorescence analysis (in situ XRF). The impurity diffusion coefficient of Bi in liquid Sn at 573 K was measured by monitoring the temporal change in the Bi concentration at two fixed points using in situ XRF. In the present study, two XRF measurement points were set in order to determine two unknown parameters that corresponded to the diffusion coefficient and the initial concentration at the measurement point just after complete melting. When only one measurement point is set for in situ XRF, the initial concentration is treated as a variable and the obtained impurity diffusion coefficients of Bi deviated by 20-30% from the reliable reference data. By using two measurement points for in situ XRF, the obtained impurity diffusion coefficient of Bi was (2.44±0.08)×10^-9 m²s^-1 and agreed with the reference data in the reported uncertainty of ±10%.

Abstract: Abstract: The atomic mobilities for impurity diffusion of Al, Au, Co, Cu, Mn, Mo, Nb, Ni, Pt, Sn and Zn in fcc Fe have been critically assessed based on the experimental diffusion coefficient data available in the literature. The impurity diffusion coefficients calculated from the atomic mobilities agree reasonably well with the reliable experimental data. This work provides a helpful guidance for the establishment of a general Fe-based mobility database to design new Fe-based alloys for practical purposes.

Abstract: An experimental approach employing temperature and concentration gradients is presented that is suitable for determining impurity diffusion coefficients in a single experimental cycle. The Al-Cu system is used to illustrate the feasibility of the method. In a single phase α-Al solid solution, concentration gradients are generated by exposing a cylindrical sample to steep temperature gradients and by annealing until the initially formed mushy zone is re-solidified. The annealing is performed such that a symmetric, ramp shaped profile in the form of a roof is generated. The sample is then again exposed to a temperature gradient at somewhat lower temperatures for an extended time period. The symmetric profile then becomes asymmetric due to the varying diffusion coefficient along the sample. Information on the pre-exponential factor D₀ and the activation energy for diffusion Q_D is retrieved from the asymmetry of the resulting concentration profile. The asymmetry becomes increasingly pronounced with longer diffusion times, yielding an increasing accuracy of the diffusion coefficients. The experimental approach is generally applicable to alloy systems with finite solubility.

Abstract: The numerical modeling of melt flow, heat transfer and impurity (phosphorus) diffusion in the double crucible of "Redmet-90M" Cz puller was carried out in an application to a 200 mm diameter Si single crystal growth. The double crucible consists of two coaxial crucibles having different sizes: 490 mm (external) and 300 mm (internal) inner diameters. The bottom of internal crucible has a central hole of Do = 6 and 12 mm diameter for melt inflow from the external crucible. During crystal pulling the granulated Si was added in the external crucible and a melt of the internal crucible was doped by phosphorus. Three-dimensional features of a rotating melt flow affecting on heat transfer and impurity diffusion in the internal crucible were analyzed. In particular, the melt precession and thermal asymmetry near the liquid-solid interface (LSI) in the internal crucible are discussed. It is shown that a significant phosphorus losses caused by its evaporation from a melt surface may be compensated by additional phosphorus doping in the internal crucible.

Abstract: There are a number of well-known empirical relations for diffusion in solids. For example the proportionality between the self-diffusion activation energy and melting point or between the entropy of the diffusion and the ratio of activation energy and the melting point (Zener rule) are perhaps the best known ‘rules of thumb’. We have shown earlier in our Laboratory, that these relations are direct consequences of the similarity of interatomic potentials seen by ions in solids. On the basis of this, similar relations were extended for impurity and self diffusion in binary solid alloys. In this paper, results for binary liquid mixtures will be reviewed. First a minimum derivation of the temperature dependence of the self-diffusion coefficient, D, is presented (minimum derivation in the sense that it states only that the reduced (dimensionless) D should be a universal function of the reduced temperature), using the similarity of interatomic potentials and dimensional analysis. Then the extension of this relation for determination of the pressure and composition dependence of the self-diffusion coefficients is described using pressure and composition dependent scaling parameters (melting point, atomic volume and mass). The obtained universal form (valid for binary liquid alloys) is very useful for the estimation of the temperature, composition and pressure dependence of the self-diffusion coefficients. Finally, the relation for the ratio of the impurity and self-diffusion coefficients is derived.

Abstract: Starting from some fundamentals of solid-state diffusion, we remind the reader to the major techniques for lattice diffusion measurements. Self-diffusion is the most basic diffusion phenomenon in any solid. The paper covers main features of self-diffusion in pure fcc and bcc metals and some important facts about diffusion of substitutional solutes in metals. Binary intermetallics are compounds of two metals or of a metal and a semimetal. Their structures are different from those of the constituents. Some intermetallics are interesting functional materials others have attracted attention as high-temperature structural materials. The paper reviews some results mainly from our laboratory on diffusion in binary intermetallics from the systems Cu-Zn, Ni-Al, Fe-Al, Ni-Ge, Ni-Ga, Fe-Si, Ti-Al, Ni-Mn, Mo-Si and Co-Nb, which have been published in detail elsewhere. Some results for the ternary system Ni-Fe-Al are also mentioned.

Abstract: The solid state diffusion characteristics in the Cu(Al) solid solution phase, was investigated in the temperature range of 1023–1223 K using single phase bulk diffusion couples between pure Cu/Cu- 10 at.% Al. The interdiffusion coefficients, D, were calculated using Boltzmann–Matano method and Hall’s method from the concentration profiles of the couples that were determined using EPMA. The interdiffusion coefficients (D) calculated ranges between 1.39 X 10−14 and 3.97 X 10−13 m2/s in the temperature range of 1023 to 1223 K. The composition and temperature dependence of D were established. The activation energy for interdiffusion varies from 123.1 to 134.2 kJ/mol in the concentration range 1 at. % ≤ CAl ≤ 9 at. %. The impurity diffusion coefficient of Al in Cu is determined by extrapolating the interdiffusion coeffficient values to infinite dilution of the alloy i.e CAl →0 and its temperature dependence was also established. The activation energy for impurity diffusion of Al in Cu was found to be 137.1 kJ/mol.

Abstract: We investigate the influence of sputtered silica as annealing cap on the enhancement of intermixing rate of semiconductor quantum nanostructures. After sputtered silica application and subsequent rapid thermal annealing, we observed bandgap shift of over 200 meV with respect to the bandgap of as-grown material from various GaAs-based quantum well (QW) heterostructures such as GaAs/AlGaAs, InAlGaP/GaAs, and GaAs/AlGaAs systems at significantly lower temperature than the conventional dielectric cap process with plasma enhanced chemical vapor deposition (PECVD). The results suggest that the sputtered silica process is a promising intermixing technique for the monolithic integration of multiple active/passive photonic components on GaAs-based material systems.

Abstract: The diffusion coefficients of 44Ti, 63Ni and 59Fe in γ-TiAl single crystals have been measured by ion-beam sputter-sectioning technique, while those of In have been measured using ion implantation technique and secondary ion mass spectroscopy (SIMS) in order to clarify the diffusion anisotropy: the diffusion perpendicular and parallel to the [001] axis. The diffusion of Ti and In perpendicular to the [001] axis is faster than that parallel to the [001] axis. However, the diffusion anisotropies of Fe and Ni show opposite trend to those of Ti and In, namely the diffusion parallel to the [001] axis is faster than that perpendicular to the axis. The predominant process of diffusion perpendicular to the [001] axis has been discussed from a viewpoint of activation energy using the expression of the diffusion coefficients in L10-ordered alloys.

Abstract: The impurity diffusion coefficients of Cu in Fe have been determined in the temperature range of 1073 - 1163 K by means of Laser Induced Breakdown Spectrometry (LIBS). The volume diffusion coefficients for Cu impurity diffusion in a-iron found in this work are in good agreement with the previously published result. The grain boundary diffusion coefficient gb D s d was also calculated using the volume diffusivity and processing the tails of the measured profiles. The values of the activation energy for volume and grain boundary diffusion were approximately 280 and 161 kJmol-1, respectively. This indicates the possibility of a monovacancy diffusion mechanism in case of volume diffusion. The results for the diffusion coefficients are Dv= 2.2 ×10-2exp(-280 kJmol-1/RT) m2s-1 and gb D s d = 2.6 ×10-11exp(-161 kJmol-1/RT) m3s-1.