Maziar Sahba Yaghmaee

An Absolute Scale for the Cohesion Energy of Pure Metals

Cohesion energy is a basic energetic property of metals, determ ining the majority of their other physical properties. The reasons why the sublimation energy of metals cannot be a proper estimation for their absolute cohesion energy values are discussed. It i shown that cohesion energy is proportional to the melting point of metals. The absolute slope of t his correlation is found from the experimental surface tension value for liquid gold, and our recent t h ory between the surface tension and the cohesion energy of liquid metals. Based on that, a ta ble for the absolute values of the cohesion energy of metals has been prepared.

Stability of SiC in Al-Rich Corner of Liquid Al-Si-Mg System

The thermodynamic analysis of the SiC/Al-Si-Mg system has been performed in order to find the conditions to produce SiC/Al-Si-Mg composite materials with the stable SiC/alloy interface (for both a-SiC and b-SiC) and with the solidification of primary a-Al solid solution. The conditions to avoid the formation of Al4C3 are expressed as function of temperature, and the silicon and magnesium content of the liquid aluminium alloy. It has been shown that to ensure stabilization of (the more stable) b-SiC, lower Si-content is needed and higher working temperature is allowed, compared to the requirements to stabilize (the less stable) a-SiC.

Equilibria in the Ternary Fe-Al-N System

The model of an ideally associated mixture has been applied to describe equilibria in the Fe-rich corner of the ternary Fe-Al-N system. It has been found that when the molar ratio of aluminum to nitrogen is higher than 2.5, more than 90 % of N is complexed into AlN molecules (associates) at a temperature of 1873 K. The phase boundaries between liquid iron and N 2 gas on the one hand, and between liquid iron and solid AlN on the other hand have been determined The solubility of N 2 gas increases with increasing concentration of aluminum in the liquid. The concentration dependence of the solubility of A1N considerably differs from that predicted by the concept of the solubility product, due to the strong complex (A1N) formation in the system.

In the Search of Fundamental Inner Bond Strength of Solid Elements

In order to understand the physics behind the surface properties and nano-scale phenomena, we are motivated first to investigate the inner bond strengths as well as the effect of number of neighboring atoms and their relative distance in addition to space positions (crystallography). Therefore, in order to study the effect of the nature of metallic bond on their physico-chemical properties, we first tried to investigate and introduce a mathematical model for transforming the bulk molar cohesion energy into microscopic bond strengths between atoms. Then an algorithm for estimating the nature of bond type including the materials properties and lattice scale “cutoff” has been proposed. This leads to a new fundamental energy scale free from the crystallography and number of atoms. The results of our model in case of fundamental energy scale of metals not only perfectly describe the inter relation between binding and melting phenomena but also adequately reproduce the bond strength for different bond types with respect to other estimations reported in literatures. The generalized algorithm and calculation methodology introduced here by us are suggested to be used for developing energy scale of bulk crystal materials to explain or predict any particular materials properties related to bond strengths of metallic elements.

Comparison of wetting models and geometrical analysis in describing the effect of cavity number, size, and position on apparent contact angle

Abstract A critical subject of surface science is whether contact area or the triple-phase contact line (TPCL) directly affects the apparent contact angle (APCA). On this premise, effect of cavity size and position on APCA is studied. Cavities were created using a laser machining process. Optimal conditions for laser patterning were obtained via trial and error. It was impossible to deposit a droplet that could rest on all of the cavities for about 0.16 mm distance between the edge of the patterns and the drop’s perimeter. Neither Wenzel nor Cassie–Baxter models can fully explain the acquired data from static contact angle measurements. Revised Cassie–Baxter equation also fails, while a simple geometrical analysis based on Spherical Cap assumption shows a better agreement with the data as long as the cavities are sufficiently far from TPCL. Based on our results, we believe that theoretical analyses regarding wetting models are not in line with engineering aspects of wetting which should be focused on TPCL.

DC-EPD of nanoceramic particles accelerated via anodic dissolution in organic media

Abstract This paper presents the fabrication of nanoceramic layers by electrophoretic deposition. Suspensions containing TiO2 nanoparticles were prepared in different organic solvents, such as ethanol, methanol, acetone, and acetylacetone. During electrophoretic deposition, the color of organic media at around 200 V cm−1 began to change. This phenomenon is related to the anodic dissolution, which may assist deposition processes in some cases. Deviation from Hamakers equation was observed upon measuring the deposited mass using different anode electrodes. Atomic absorption spectroscopy was used to measure concentrations of chemical elements liberated in the suspension due to the dissolution of anodes. These results show that anodic dissolution directly affects deposition rate. We observed this event even in the absence of powder and additives. Therefore, this is advantageous if anodic contaminants are not effective or influential.

MODELING OF THE SURFACE TENSION OF COLLOIDAL SUSPENSIONS

Surface tension is one of the fundamental properties of the colloids, which can be altered by concentration and size of colloidal particles. In the current work, modeling of the surface tension of suspension as it would be analyzed by maximum bubble pressure method has been performed. A new modified equation to correlate the surface tension with the bubble pressure is derived by applying fundamental thermodynamic relation considering the presence of particles in suspension and curvature of the interface between the particles and bubbles inside liquid. Moreover, the change of particles concentration in air–water interface due to capillary force is also considered. The predicted surface tension using the developed model has been verified by numerous experimental data with deviation less than 5% in most of cases. It was found that the calculated surface tension is altered by contact angle and particle radius as well as particle concentration. The obtained model may have potential application to predict the surface tension of colloidal suspension.