Gerhard Neumann

Monovacancies and divacancies in copper: Reanalysis of experimental data

Abstract The vacancy concentrations c v in copper measured by means of the absolute technique (Hehenkamp et al., Phys. Rev. B 45 (1992) 1998) and those derived from positron lifetime studies (Kluin, Philos. Mag A 65 (1992) 1263) are reanalysed. Taking into account the results of quenching and annealing investigations the best fit to the temperature function of c v is described by H F 1v =1.03xa0eV and S F 1v / k =1.1 for the monovacancy formation enthalpy and entropy and a divacancy binding enthalpy and entropy of H B 2v =−0.23xa0eV (attractive interaction) and S B 2v / k =2.8, respectively. Accordingly, the divacancy concentration amounts to 1.5×10 −4 at the melting temperature.

Diffusion of Manganese, Chromium, and Titanium in Single Crystalline Copper

The diffusion of Mn, Cr, and Ti in single crystalline copper was investigated in the temperature range between 582 and 800 K, 639 and 829 It and 621 and 747 K, respectively. Ion beam sputtering in combination with secondary ion mass spectrometry (SIMS) was used to measure concentration depth profiles. The temperature dependence of the diffusion coefficients of Mn, Cr, and Ti in copper can be described by D-Mn = (0.43(-0.20)(+0.37)) x 10(-4) exp(-2.01 +/- 0.035 eV/kT) m(2) s(-1) D-Cr = (0.26(-0.06)(+0.09)) X 10(-4) exp (-1.99 +/- 0.02 eV/kT) m(2) s(-1) and D-Ti = (0.37(-0.03)(+1.60)) x 10(-4) exp (-1.99 +/- 0.10 eV/kT) m(2) s(-1) These results are compatible with earlier high temperature data. The combination of them with the present diffusion coefficients reveals a curvature in the corresponding Arrhenius plots, which is ascribed to the contribution of divacancies at higher temperature. The temperature dependence of the diffusion coefficients of Mn, Cr and Ti in copper can be described with the aid of the modified electrostatic model of impurity diffusion, assuming effective values for the charge difference between host atom and impurity.

Interstitial impurity diffusion in metals; the apparent size effect

It is demonstrated that the abnormally fast impurity diffusion in Pb and α-Ti, which is interstitial-dominated, mainly depends on the solubility. With decreasing solubility, the fraction of interstitially dissolved impurities increases. This leads to a drastic increase of the diffusivity. In the case of small solubilities, the solubility depends on the atomic radius of the solute. This effect erroneously suggests a direct correlation between diffusivity and atomic size (size effect).

New Characterization of Setting Times of Alkali Containing Calcium Phosphate Cements by Using an Automatically Working Device According to Gillmore Needle Test

This paper presents equipment for the measurement of initial as well as final setting times of calcium phosphate cements containing alkali to achieve higher solubility. Until now, the selfsetting process of cements also if alkali is integrated has been tested by using the “standard test method for time of setting of hydraulic-cement paste by Gillmore needles” in accordance to ASTM C 266 – 99. This procedure needs high man power and, furthermore, the results have been markedly influenced by individual experiences that are incorporated in the criterion “without appreciable indentation”.

On the impurity diffusion in β-Ti

Abstract The impurity-diffusion data in β-Ti are reanalysed on the basis of the assumption that the vacancy-migration enthalpy H 1v M as well as the vacancy-formation enthalpy H 1v F depend on temperature. A simple linear temperature dependence in the form of H(T)=H(T 0 )+αk(T−T 0 ) is used. The results of the analysis show that the impurity-diffusion energy Q 2 increases linearly with α 2 , i.e. Q 2 (T m )≈Q 0 (T m )+8(α 2 −α 0 ) with Q in kJ/mol. Q 0 and α 0 describe the self-diffusion.

Application of the modified electrostatic model to the impurity diffusion in cobalt

The modified electrostatic model (Neumann and Tolle 1995) is applied to the impurity diffusion in nickel.Z0 = 0.4 is used for the effective charge of the nickel ion.

A modified thermodynamic model for the impurity diffusion via nearest- and next-nearest neighbour jumps in body-centred cubic metals of the groups V and VI

Abstract A modified thermodynamic model ( T m -model) for the impurity diffusion in group V and VI metals is developed, which takes into account nearest-(NN) and next-nearest (NNN) neighbour monovacancy jumps. The correlation factor f is separately calculated with the aid of Monte-Carlo simulation. The calculation of f is based on a nineteen-frequency model for mixed NN and NNN jumps. The comparison of calculated and experimental diffusion coefficients reveals good agreement for several systems. On the other hand, it becomes obvious that the T m -model is not applicable to the diffusion of group VIII metals in metals of the groups V and VI.

On the diffusion of scandium and hafnium in tungsten

The modified thermodynamic model of impurity diffusion in BCC metals, which is based on the assumption that monovacancy jumps to nearest and next-nearest neighbour positions are responsible for the transport, is applied to the diffusion of Sc and Hf in tungsten. The agreement with experimental data reveals that the applicability of the model is not restricted to impurities of the groups V to VII of the periodic system.

Application of the thermodynamic model to the diffusion of substitutionally dissolved impurities in lead

Abstract The thermodynamic model ( T m -model) is applied to substitutionally dissolved impurities in lead. For Tl, Sn, Na, Cs and with some restrictions also for Hg, good agreement is found between calculated and experimental diffusion coefficients. Although Hg and Cd exclusively diffuse via vacancies, the diffusion behaviour of Cd cannot be explained in terms of the T m -model.