Papers by Keyword: Diffusion

Abstract: The proposed balance logic-statistical model of the blast furnace process is based on the use of material and thermal balances along with calculations of heat- and mass exchange taking into account the non-uniformity of gas and burden distribution on the radius of the furnace and influence of the basic metallurgical characteristics of iron ore raw materials and coke on the indices of blast furnace operation. As a check of the applicability of the model, calculations on the most critical parameters of the blast furnace process – the smelting of ferromanganese and iron nickel with a graphical representation of heat- and mass exchange processes, dynamics of oxides reduction on the height and radius of the blast furnace have been carried out.

Abstract: Metals with a bcc crystalline structure such as Ti-13V-11Cr-3Al alloys have their physical properties significantly changed through the addition of interstitial elements such as oxygen and nitrogen. These metals can dissolve substantial amounts of interstitial elements forming solid solutions. Mechanical spectroscopy measurements constitute a powerful tool for studying interactions of these interstitial elements with other elements that make up the alloy. From these measurements, it is possible to obtain information regarding diffusion, interstitial concentration, interaction between interstitials, and other imperfections of the crystalline lattice. In this paper, Ti-13V-11Cr-3Al alloys with several amount of nitrogen, in a solid solution, were studied using mechanical spectroscopy (internal friction) measurements. The results presented complex internal friction spectra which were resolved in a series of constituent Debye peaks corresponding to different interactions and interstitial diffusion coefficients. Pre-exponential factors and activation energies were calculated for nitrogen in theses alloys.

Abstract: Titanium alloys are excellent implant materials for orthopedic applications due to their desirable properties, such as good corrosion resistance, low elasticity modulus, and excellent biocompatibility. The presence of interstitial elements (such as oxygen and nitrogen) causes strong changes in the material’s mechanical properties, mainly in its elastic properties. Study of the interaction among interstitial elements present in metals began with Snoek’s postulate, that a stress-induced ordering of interstitials gives rise to a peak in the mechanical relaxation (internal friction) spectra. In the mechanical relaxation spectra, each species of interstitial solute atom gives rise to a distinct Snoek’s peak, whose temperature and position depend on the measurement frequency. This effect is very interesting because its peculiar parameters are directly related to the diffusion coefficient (D) for the interstitial solute. This paper presents a study of diffusion of heavy interstitial elements in Ti-35Nb-7Zr-5Ta alloys using mechanical spectroscopy. Pre-exponential factors and activation energies are calculated for oxygen and nitrogen in theses alloys.

Abstract: In this paper, we review the recent developed method based around lattice-based random walks and the Monte Carlo method. This method, which is now called the Lattice Monte Carlo method, permits complex phenomenological problems in diffusion, thermal conductivity and elasticity to be addressed. It is shown how the effective mass diffusivity, thermal diffusivity/thermal conductivity and the bulk modulus in composites can be calculated and also how concentration profiles and temperature profiles can be determined in situations where the diffusivity depends on position and concentration and the thermal conductivity depends on position and temperature respectively.

Abstract: The presence of atomic oxygen at internal metal-ceramic oxide interfaces signi¯- cantly affects the physical properties of the interfaces which in turn affects the bulk properties of the material. The application of numerical tools such as the ¯nite element method requires some conceptional considerations if results from different finite element meshes of methods should be comparable. This paper summarises some of these thoughts in order to provide the right basis for comparative investigations.

Abstract: Depth profiles of ion-implantation induced defect centers have been investigated by cross-sectional CL measurements in the energy range from visible to near infrared. CL observation has shown that point defects diffused out from implanted region to ~10 µm depth during activation annealing. Annealing temperature dependence of the depth distribution of CL intensity of these defects has suggested that structural transformation of point defects proceeds as “silicon vacancy (VSi) → carbon vacancy-antisite pair (VC-CSi ; UD2) → antisite pair (CSi-SiC ; DI)”.

Abstract: In this work the analysis of thermal diffusion of boron carried out from vapor phase was performed. Two-branch diffusion associated with kick-out and substitution mechanisms was observed. The activation energy and prefactor were calculated from Arrhenius plot for each diffusion branch. It has been established that the surface layer of diffused boron mostly consists of shallow boron acceptors, while the tail of the diffusion profile has mostly deep level D centers.

Abstract: In this article, the liquid-solid interface solidification stability of dilute binary alloy systems during unidirectional (z) solidification was investigated. A new quantitative approach is proposed with (z-δ) as a variable to solve the equation of solute diffusion in the liquid, where δ is the real diffusion layer thickness.

Abstract: Classically a master curve as Dorn's equation is applied for elucidating stationary creep behaviour within high temperature range (T > 0.6 Tm). As the diffusion of both 63Ni and 44Ti have been measured in an equiatomic NiTi, an effective choice of creep-relevant diffusion coefficient D may be possible. Moreover, creep measurements in the same temperature range performed can be found in the literature. The correlation does not permit to establish precisely what D coefficient to integrate in the Dorn's equation.

Abstract: The mechanism of slow positron annihilation in ion-implanted Si has been discussed in terms of the Diffusion-Trapping model (DTM). The trapping of positron has been considered in native vacancies (monovacancies) and ion induced vacancies i.e. vacancy clusters. The model has been used to calculate the Doppler broadening line shape parameter (S-parameter) as a function of incident positron energy for different ion-implanted Si. It has been found that at lower energies the monovacancies and vacancy clusters both contribute to the S-parameter while, with the increase in positron energy the vacancy clusters are reduced. The S-parameter is found to be dependent on the fluency of the implanted ions.