A Metallografic study of the homogeneization quenching of copper

During homogeneization quenching the dislocation density in copper grows up to saturation and the dislocation structure becomes stabilized. This process is realized on quenching into gases and liquids, i.e. at both lower and higher quenching rates. Grain growth is also observed. The dislocation structure formed by cold-working is removed by annealing at temperatures near to the melting point in a time interval shorter than 30 minutes and the dislocation density reaches a stable value, growing with decreasing thickness of the specimen.The authors would like to thank Dr. K. Míek, CSc. (Institute of Solid State Physics, Czechosl. Acad. Sci., Prague) for his comments, Dr. J. Kuera CSc. and Dr. P. Luká, CSc. (Institute of Metallurgy, Czechosl. Acad. Sci., Brno) for critical remarks on the paper and Mrs. J. Zoubková for assistance with the experiments.     

Dislocation density growth in copper during homogeneization quenching

In this paper it has been experimentally proved that the dislocation density of annealed copper ribbons grows up to saturation during repeated quenching. The effect is explained on the basis of a simple idea: During each annealing a certain part of the excessive dislocation density is removed and during each quenching a constant increase in dislocation density is generated.     

The electrical resistance of platinum at repeated quenching

The reversible change in electrical resistance of platinum after quenching from high temperatures is studied by the repeated quenching method. The values measured for three different radii of the wire specimens are used to determine the quench temperature at which the concentration of quenched-in vacancies does not depend on the quenching rate or on the diameter of the specimen. The value (1070±50)°K, i.e. (0·53±0·02)T _m, was found for it, indicating a high stacking fault energy of platinum.     

The electrical resistance of platinum at repeated quenching

It is shown how the irreversible change in electrical resistance of platinum is related to the irreversible change in resistivity and dimensional changes of the samples. A preliminary interpretation is also given of the component connected with resistivity on the basis of the scattering of conduction electrons on defect formations produced mainly from the vacancies and stabilized by impurities, primarily oxygen.     

A dilatometric study of platinum during repeated quenching

The increase in length of platinum of 99.9% purity has been examined during repeated quenching in air.In the initial region of thermal fatigue at constant quenching temperature, the total and irreversible component were found to be linear functions of the number of quenchings and the reversible part remained constant. The activation enthalpy of vacancy formation determined from thermal fatigue characteristics (i.e. from the dependence of the total increase in length on the quench number) wasH _v ^f =(1.41±0.04) eV.     

Lattice contraction due to quenching in vacancies in platinum and gold

Combined measurements of lattice parameter and electrical resistivity change of platinum and gold after quenching were performed. The lattice contraction due to vacancies could be determined.     

On the homogeneization of transverse gas discharges by preionization

Detailed data of the minimum preionization electron density (MPED)n ₀ necessary to initiate a homogeneous discharge mode in transverse gas discharges are computed. An upper limit for the inductance of the discharge circuit is set by the power balance during breakdown. The results are presented as functions of generalized parameters. Applicability of the computations is proved by experimental observations.     

Electrical resistance of platinum wires during annealing and quenching in air and helium

Electrical resistance of platinum wires annealed and quenched in air and helium was measured. No irreversible changes of the electrical resistance were observed in specimens treated in helium, however, these changes were appreciable in specimens treated in air. By measurement at two temperatures the total change was divided into the change of the electrical resistivity and the change of geometrical dimensions. The changes of geometrical dimensions were interpreted in terms of the oxidation of platinum and the activation energy of oxidation of platinum was determined asE=(1.79±0.04) eV.     

The measurement of the quenching rate

In this paper the methods of measuring the quenching rate are described, which enable us to determine either the temperature or the resistance of the specimen as a function of time during quenching. A simple calculation of the initial quenching rate for wires having different diameters is presented and its validity checked for exponential quenches in different gases. The methods for measuring the quenching rates are compared and the error in the quenching rate determination is estimated.The author is indebted to Ing. J. Steiner for realization of the transistorized electronic equipment, to Mr. V. Zita and Ing. P. Vaek for assistance in the measurements, and to other collaborators of the Metal Physics Department for critical remarks and help.     

The recovery of thermal-neutron-irradiated platinum

The dose-dependence of the recovery substages I_A to I_E in stage I and of the substages at 35 K and 120 K in stage II and of the stage between 300 K and 400 K, is presented. The 120 K stage is investigated especially carefully, in order to determine whether this stage is due to impurities.     

The resistivity of fine platinum wires

We have measured the resistivity of pure platinum wires ranging in diameter from 16 mil to 0.3 mil in the temperature range 1.2 to 4.2°K, and observed size-dependent deviations from Matthiessen’s rule. The temperature dependent portion of the resistivity is dominated in this temperature range by a term of the formAT ², whereA increases from about 12×10^?12 Ω cm/°K² for the thickest wires to 18×10^?12 Ω cm/°K² for the thinnest ones. There is an additional resistivity contribution which appears to increase more rapidly thanT ⁵, and which also evidences some increase with decreasing wire diameter. The observed deviations from Matthiessen’s rule display temperature and size variations consistent with the theory ofBlatt andSatz, and the magnitude of the deviations can be accounted for by this theory taking into account only that portion of the electrical resistivity produced by electron-phonon scattering. Thus the data are consistent with arguments suggesting that interband electron-electron scattering does not lead to size-dependent deviations from Matthiessen’s rule.     

The SrB4O7:Sm2+ optical sensor and the pressure homogeneization through thermal cycles in diamond anvil cells

Abstract

Preliminary results, up to 550 kbar, on a thermal-cycling relaxation process of the 4.Methanol-1.Ethanol pressure-transmitting medium, are presented. The homogeneization is monitored by linewidth measurements of the ⁵D₀-⁷F₀ emission line of SrB₄O₇:Sm²⁺, recently proposed as an “almost ideal” high pressure calibrant. Above 100 kbar at 20°C, the line broadens linearly with increaisng pressure. Upon heating, at a fixed pressure, the linewidth is reduced to a minimum (“hydrostatic”) value provided a sufficient temperature is reached and this narrowing is irreversible upon cooling. For T=300°C this relaxation is observed for P (250 kbar, incomplete at 340 kbar and not observed at 550 kbar.     

The effects of collisional quenching on degenerate four-wave mixing

We report a theoretical and experimental investigation of the effects of collisional quenching on resonant degenerate four-wave mixing (DFWM). Using single-mode laser radiation, peak signal intensity measurements were performed on an isolated line in the A – X transition of NO. By using appropriate mixtures of N₂ and CO₂ as buffer gases, we varied the collisional quenching rate over several orders of magnitude while maintaining a fixed total collisional dephasing rate. The mixtures had approximately 100 Torr total pressure and were at room temperature. For I/I _sat approximately equal to 0.02, DFWM intensities were found to be less affected by variations in quench rate than were laser-induced fluorescence (LIF) intensities (I and I _sat are the pump laser and one-photon saturation intensities, respectively). Moreover, for I/I _sat roughly equal to 0.5, DFWM intensities were observed to be nearly independent of quench rate. The results are compared to two theoretical predictions, with good agreement observed. Both theories indicate that the minimum sensitivity of DFWM to quenching occurs near I/I _sat1.     

The loss of single vacancies in metals during quenching

The Lomer equation, describing the rate of change of single vacancy concentration in a metal specimen during exponential quenching, was numerically solved for different quenching temperatures and different quenching rates. A relation has been found between the constantb, which characterizes the initial quenching rate, and the quenching temperature leading to the same percentual loss of vacancies. This relation enables us to determine the conditions of quenching, yielding the predetermined percentage of retained vacancies.The possibility is discussed of applying the above results in measurements of the formation energyEf^F, to estimate the migration energyE ^M and to determine the change of the mean number of jumps during quenching.The author would like to express his gratitude to Dr. K. Míek, head of the Metal Physics Department, for his interest and useful comments.     

The heat of adsorption of hydrogen on platinum

The heat of adsorption (q) of hydrogen on clean polycrystalline platinum filaments has been determined as a function of the coverage (θ), temperature and method of preadsorption using UHV adiabatic calorimetric techniques. Adsorption at 273 °K results in a stepped shape q-θ curve with q (θ=0)= 24.7 kcalmole^?1. At 77 °K, the form of the curve depends on the temperature of preadsorption. The relative roles of a priori and induced heterogeneity are discussed and while both must play a part, the temperature dependence of the form of the q-θ curves suggest that the latter is the more important of the two in these experiments.     

The characteristics of platinum diffusion in n-type GaN

The electrical and optical characteristics of platinum (Pt) diffusion in n-type gallium nitride (GaN) film are investigated. The diffusion extent was characterized by the SIMS technique. The temperature-dependent diffusion coefficients of Pt in n-GaN are 4.158 × 10⁻¹⁴, 1.572 × 10⁻¹³ and 3.216 × 10⁻¹³ cm²/s at a temperature of 650, 750 and 850 °C, respectively. The Pt diffusion constant and activation energy in GaN are 6.627 × 10⁻⁹ cm²/s and 0.914 eV, respectively. These results indicate that the major diffusion mechanism of Pt in GaN is possibly an interstitial diffusion. In addition, it is also observed that the Pt atom may be a donor because the carrier concentration in Pt-diffused GaN is higher than that in un-diffused GaN. The optical property is studied by temperature-dependent photoluminescence (PL) measurement. The thermal quenching of the PL spectra for Pt-diffused GaN samples is also examined.     

The bonding of water molecules to platinum surfaces

Using high resolution electron energy loss spectroscopy in ultra-high vacuum we have studied the vibrational spectrum of submonolayer and multilayer quantities of water adsorbed on platinum (100) surfaces. For adsorbed multilayers the spectrum resembles the spectrum of ice I. For submonolayer quantities of H₂O we find three different OH stretching vibrations, 2850, 3380, and 3670 cm^?1. The highest frequency is attributed to free OH groups. The vibration around 3380 cm^?1 indicates H bonding between oxygen atoms. It is therefore concluded that the water molecules cluster even at low coverage. The lowest OH stretching frequency is attributed to H bonding to platinum. We find also evidence for additional oxygen lone pair orbital bonding to the surface which disappears however when the first monolayer is completed. The relation to currently considered models in electrochemistry of aqueous solutions is discussed.