Heat Capacity Of Metals Research Articles

Determination of Activation Energy of Surface Diffusion Based on Thermal Oscillations of Atoms

This paper covers calculations of the activation energy of surface diffusion of ad-atoms on the substrate surface from the point of view of thermal oscillations of substrate atoms and ad-atoms. The main characteristic of oscillations of atoms and geometric mean frequency was calculated based on statistical approximation of the Debye model using the reference values of entropy and heat capacity of metals. The basic principle of the model of activation energy calculation presented in the paper is the formation of potential wells and barriers during oscillations of atoms localized in the sites of the lattice. Oscillations of atoms were considered in the framework of quasiclassical quantum approximation as the oscillations of harmonic oscillators in the potential parabolic wells. Dimensions of the negative part of values of the potential well energy were determined by the amplitude of thermal oscillations of atoms. Positive values constituted a significant part of the potential well energy values. Barriers were formed owing to interaction of positive values of the energy of parabolic wells of adjacent atoms. Therefore, in order to make the ad-atom jump, it is necessary to get out of the potential well having the negative values, and to overcome the potential barrier. The energy required for the ad-atom jump on the substrate surface was the activation energy of surface diffusion. The results obtained in this paper agree satisfactorily with the results of another method, which is based on determining the energy of ad-atom binding with the substrate atoms.

TEMPERATURE DEPENDENCE OF HEAT CAPACITY OF ALUMINIUM, COPPER, SILICON, MAGNESIUM AND ZINC AND COMPARISON WITH DEBYE THEORY

The results of comparison of heat capacity of aluminum, copper, silicon, magnesium and zinc with Debye's theory depending on temperature are given in the paper. It was revealed that the main components of the heat capacity of metals are the lattice component; is a component due to thermal expansion and is an electronic contribution. It is proposed that when creating the theory of heat capacity, it is necessary to take into account the anharmonicity of the oscillations of atoms in the nodes of the crystal lattice and the change in Debye temperature.

Detection of Ash Fouling in Thermal Power Plant

Ash fouling is one of the significant problems in thermal power plant. It degrades the thermal performance of heat transfer surfaces; hence, soot blowers are initiated in a pre-defined sequence and scheduled to clean the surfaces. Frequent soot blow operation leads to waste of steam, increased maintenance cost and tube erosion. This study aims in developing a simplified method to detect economizer fouling based on the assessment of cleanliness factor. Economizer model that includes the heat capacity of metal between flue gas and feed water is simulated and validated using power plant data. The decrease in efficiency and cleanliness factor with effect of fouling is analyzed. It is observed that a 3% decrease in cleanliness factor in the economizer leads to a 2% loss in its efficiency.

Atomic epn(ep) Spin Models and Spectral Lines

We confirmed that how many kinds of epn spins the atoms have by calculating heat capacity of metals according to energy levels in the previous reference. To know more the spin models of epn of hydrogen and helium are imagined and their line spectra are counted. And the explanation of interference is discussed. Gas atoms make line spectra by optical interference. Solid atoms make them by exciting the lowest epns of their cluster first. They all make s, p energy orbit. One axis is composed of two epns. 1s or 2s of atoms except for lithium generally makes the symmetric axis. When each energy level is filled up by epns, these are symmetrically paired first. The atoms which fit the number of line spectra correctly by optical interference are hydrogen and helium. By counting the number of alignments of epns spins within the cluster, the atoms which fit the number of line spectra correctly are lithium, beryllium and phosphorus. The number of line spectra of the rest atoms which we have counted approaches the experimented numbers approximately, not correctly.

Possible mechanisms of increase in heat capacity of nanostructured metals

The problem of anomalously high experimental values of the heat capacity of metallic nanoclusters has been analyzed in terms of the thermodynamics of the surfaces, as well as based on the data of computer experiment. The heat capacity of ideal face-centered cubic (fcc) palladium clusters with a diameter of 6 nm in the temperature range of 150–300 K has been investigated using the molecular dynamics method with several tight-binding potentials. It has been found that, at a temperature T = 150 K, the heat capacity of a Pd nanoparticle exceeds the heat capacity of the bulk material by 12–16%. Based on the results of the theoretical treatment, computer simulation, and analysis of experimental data, it has been concluded that an increase in the heat capacity of the compacted nanomaterial is not determined by the high heat capacity of individual clusters. Apparently, the significant increase in the heat capacity of compact nanomaterials can be explained either by their disordered state or by the high content of different types of impurities, mainly hydrogen.

A Simple Experimental Procedure for the Approximate Determination of the Heat Capacity of Metals in a Natural Convection Environment under the Premises of a Lumped Model

A method is presented of measuring the specific heat capacity, Cp, of pure metals and alloys in an undergraduate thermofluids laboratory using simple concepts of unsteady heat conduction in solids and natural convection in fluids taken from textbooks on heat transfer. A simple experiment was developed in which a small-diameter metallic sphere at ambient temperature (∼20° C) is suddenly immersed in a tank containing quiescent ice water at 0° C. The metallic sphere was suspended by the lead wire of a thermocouple and the temperature-time evolution was recorded. A first-order differential equation descriptive of a lumped model was used. Although the equation is nonlinear, a variable transformation converted it into the Bernoulli form, which allows an analytic solution. Introduction of two measured temperatures at two distinct times into the analytic solution allows the specific heat capacity of a metallic material to be determined by means of an algebraic procedure.

Prediction of new additives for galvanizing process by the properties of their constituent chemical elements

Chemical element properties are generally classified in six groups: size, atomic number, electrochemical factor, valence-electron, cohesive energy, and angular valence-orbital. It is well known that some bulk properties of materials, like electrical conductivity and heat capacity of metals, may be interpreted in principle based on their constituent chemical element properties. In this study, effects of additives in galvanizing have been correlated to the chemical element properties of the additives. By screening all chemical elements (in the periodic table of elements) with this model, new additives, like Ca, Sc, Ge, Sr, and Y, have been predicted to reduce the steel weight loss in galvanizing. This model may also help to design new alloys as additives.

Measurements of thermophysical properties in high temperature melts

The levitated drop method has been used to measure the surface tensions, densities and enthalpies of liquid metals and alloys. Undercoolings of 300 °C were recorded for pure metals but only 50 °C could be obtained for austenitic stainless steels. Surface tensions for the undercooled state of pure Fe, Ni and Au were found to be linear extrapolations of the data obtained for the liquid phase. Densities for the liquid state of Fe, Ni and commercial alloys were found to be within ±2% of accepted values. A levitated drop calorimeter has been constructed for the measurement of enthalpies and heat capacities of metals and alloys to an accuracy of ±1%. Measurements of the densities and enthalpies for the liquid and undercooled states of metals and commercial alloys will be carried out in the near future.

Of heat capacity at homologous temperatures for metals showing h.c.p. ⇄ b.c.c. transformation

Some interesting aspects of the temperature dependence of the Planck’s functionφ and heat capacities of metals exhibiting the h.c.p. ⇄ b.c.c. transformation have been brought to light by the use of reduced temperature (T*) and Planck’s function (-φ T*). It has been shown that tangents drawn to the -φ T* vsT* plots of these metals at any chosen value ofT* intersect at a point whose coordinates are defined by the slope and intercept ofφ vs entropy plots at any homologous temperature and the selectedT* value. A generalized expression obtained for the temperature dependence ofφ has been used to demonstrate that the heat capacity of these metals may be visualized to have structural and material components.

Calculation of dissociation energies in interatomic pair potentials and review of the relationship between coefficients of thermal expansion and heat capacities of simple metals

Dissociation energies for a two-term inverse power type of interatomic pair potential have been calculated for several metals by considering all interatomic interactions in the solid and using the experimental values of the cohesive energies. The results are then employed to calculate the ratio of thermal expansion coefficients and heat capacities of metals. It is found that the calculated values are in much better agreement with the experimental observations compared to an earlier work.

The heat capacity of metals: A physical chemistry experiment

Improvements on an earlier procedure result in heat capacities of metals within 10% of literature values.

Changes in Atomic Heat Capacity of Metals During Polymorphic Phase Transitions

Changes in Atomic Heat Capacity of Metals During Polymorphic Phase Transitions

An apparatus for the measurement of thermal diffusivity and electrical resistivity at elevated temperatures on a single sample

An apparatus for measuring the thermal diffusivity, electrical resistivity and heat capacity of metals is described. All measurements are performed on the same cylin- drical sample, which is kept in high vacuum and externally heated to the desired temperature Thermal diffusivity is determined from the phase relation of a propagating heat wave created at the ends of the sample by two miniature furnaces. Heat capacity is determined from the rate of temperature rise while the sample is ohmically heated. Electrical resistivity is determined from the voltage drop along the sample, produced by known direct current. The measurements yield accurate values for the determination of the Wiedemann-Franz ratio. (loo-900°C).

Experiments in the use of thermistors lor low pressure-measurements

Experiments investigating the use of thermistors for low pressure-measurements were carried out. It is shown that bead thermistors may be used only in the pressure range from 1 ÷ 10−3 mm Hg. On the contrary thermistor-systems consisting of bead thermistors fixed to thin metallic foils take advantage not only of the high temperature coefficient of thermistors but also of the low radiation emissivity and heat capacity of metals. These samples allow precise measurements down to 10−6 mm Hg.

The Specific Heat of Molybdenum From 250°C to -40°C

By the use of a long covered tube in the calorimeter proper of an ordinary Richards adiabatic calorimeter, values for the heat capacities of metals from high temperatures may be obtained, even when the falling body is not protected from radiation losses by a metal jacket. The experimental procedure for such a determination is given. A calorimeter arrangement in which the metal was first partially cooled in the calorimeter and then allowed to come in contact with the water of the calorimeter proved unsuitable as is shown. The specific heats of molybdenum between the temperatures of -30\ifmmode^\circ\else\textdegree\fi{}C and 300\ifmmode^\circ\else\textdegree\fi{}C are given by the following equation with an accuracy of about one percent. ${C}_{p}=0.0593+0.000013(T+40)\ensuremath{-}\frac{0.0265}{{(T+40)}^{1.06}}$ Stern's equation, which is linear agrees with the values given between 50\ifmmode^\circ\else\textdegree\fi{}C and 300\ifmmode^\circ\else\textdegree\fi{}C. Below 50\ifmmode^\circ\else\textdegree\fi{}C the curve shows a decided bend.

Heat capacity of metals and metallic compounds: H. Schimpff. ( Zeit. Phys. Chem., lxxi, 257.)

Heat capacity of metals and metallic compounds: H. Schimpff. ( Zeit. Phys. Chem., lxxi, 257.)