Abstract: Samples of 316L austenitic steel were submitted to a thermochemical treatment which implies surface diffusion of Al and Ti. The technique of pack cementation with NH4Cl as activator was employed. The powder mixture was made of aluminium, titanium, aluminium oxide and ammonium chloride. The same ratio of Al : Ti = 1 : 5 was used in all experiments. The variables were temperature and time. As a function of these parameters, diffusion layers of different thicknesses were obtained. The samples were analyzed by optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX), X-ray diffraction and Vickers microhardness trials. All layers were formed by diffusion with reaction and present two zones with different structures and compositions and therefore different properties. The Ti3NiAl2N compound was identified by X-ray diffraction. The presence of this compound in the diffusion coatings increases the superficial hardness of the samples.
Abstract: In this work we give heed especially to the dominating process which is the solid metal A dissolving in the melt B. During the dissolving, the melt B saturates with the metal A and the process is influenced by convections which are characteristic for the given experimental configuration. A theoretical description of the kinetics of the solid phase dissolving in melt will be presented for the case of planar and cylindrical dissolving. The aim is to derive a relation for the interface boundary (t) movement in dependence on time and a time course of growth of the element A concentration in the melt B. There are problems with an accurate determination of the interface boundary movement after certain heating times of specimens, when it is observed experimentally, since intermetallic phases create in the original A metal at both the diffusion and cooling and some phases segregate at the solidifying melt cooling. The rate constant is a fundamental parameter characterizing the dissolving rate at a certain configuration. We present a theoretical description of dissolving of a long metallic cylinder submerged into a melt column and relations for the rate constant determination from the time of the whole metallic cylinder dissolution are derived. In our experiments were performed in which Cu was dissolving in the Sn melt for a Cu cylinder (wire) diameters 0.8÷2.5 mm and the rate constant K (T = 350°C) was determined. Relationships between the solid phase dissolving rate, i.e. the solid phase interface boundary movement (t) in the melt and rates of growth of intermetallic phases in the metal A will be observed. This procedure enables to create surface and subsurface layers of regulated thickness in metallic materials by means of reactive diffusion.
Abstract: A formula for quick calculation of thermal characteristics of materials used for thermal protection is proposed. The mode of heating of the sample external surface (subjected to thermal exposure) is approximated by two regions, which differ by corresponding boundary conditions on the heating surface: T_f=cτ (linear growing with time) and T_f=const (with permanent temperature of destruction). That approximation permits to obtain an analytical solution in integral form. In order to simplify and accelerate data treatment, a simple empirical formula is proposed. A contribution of each thermal region is proportional to the regime duration. A good agreement with an analytical solution is shown.
Abstract: The impact behavior of a liquid droplet on solid surface is a complex phenomenon and yet is a basic component of various industrial processes particularly in the pharmaceutical industry. In this industry, film coating technique is used in tablet coating, in which coating uniformity is important especially if the coating is for functional purposes. Coating uniformity on a tablet could be affected by several factors, one of which is the impingements of droplets on its surface. In this work, the maximum spreading diameter and the initial impact behavior of a single droplet on pharmaceutical tablet surfaces and metal surfaces having different surface properties are investigated. A Charged-Coupled-Device (CCD) high-speed camera with framing rate of 2,000, attached to a 10X microscope, was used to capture the phenomena. The results show that the initial impact behavior of a droplet is not affected by the porosity of a surface. The results on the pharmaceutical tablets, stainless steel and etched silicon surfaces show that the rougher the surface the lower the spreading factor. The droplets on all surfaces demonstrate that a droplet that produces higher spreading factor gives a lower bouncing factor.
Abstract: It has been proven that HA coatings on implant materials treated with silver exhibited excellent antibacterial effects. Silver (Ag) ions were successfully incorporated into HA structure with the precipitation method. Although this method was pretty much suitable for the synthesis in powder form, it is not applicable to in-situ coating processes. The aim of the current study is to synthesize Ag ion incorporating HA via the decomposition of EDTA Chelate. For this reason, Ag doped crystalline-sodium and carbonate-containing HA solutions will be prepared using calcium-EDTA in a sodium phosphate solution, hydrogen peroxide and silver nitrate. As the source of Ag ions, silver nitrate was added into the solution in the desired proportions. Then, the samples were sintered at temperatures from 800oC to 1100oC and characterized with XRD and SEM.
Abstract: In this paper, we present the results of complex thermo-mechanical analysis (CTMA). In the technical point of view CTMA contains both thermovision camera and tensile machine which are in a perpendicular position. We have measured the cooling curve of the sample after its tensile deformation. On the basis of an exponential model of cooling body with respect to Biot number Bi value it is possible to calculate the specific heat capacity , thermal diffusivity and thermal conductivity . The method has been tested on a variety of materials and the results have been compared to those in charts or obtained by reference independent experiments. We obtained a very good agreement of all gathered experimental results with those of comparative ones. We also measured mechanical properties of materials such as yield stress, tensile strength, Young´s modulus of elasticity and ductility.
Abstract: After hydrogen desorption from hydrides based on crystal and partly amorphous CeNi3 compounds samples were obtained with a composition CeNi3Нx (x = 0.5, 0.9). All samples were investigated by X-ray diffraction under the usual conditions. It was revealed that samples after hydrogen desorption have hexagonal and orthorhombic structure of the metallic matrix with cell parameters close to the initial alloy CeNi3. Such structural behavior under hydrogen desorption is determined by the desorption conditions and depends on different hydrogen diffusion in the lattice.
Abstract: Glycolic acid ethoxylate 4-tert-butylphenyl ether was used as investigated anionic surfactants in this experimental work. A built up rig with ratio of pipe length to diameter (L/D) is equal to 59 was used to achieve the purpose of this work which is to investigate the drag reduction in turbulent flow with different flow rates and concentration of additive. In the present study, the concentrations (ppm) of additive were analyzed starting from 200, 300, 400, 500 and 600, respectively. The flow rates (Re) of the solution were from 11235, 22470, 33705, 44940, 56175, 67410 and 78645, respectively. It was found that glycolic acid ethoxylate 4-tert-butylphenyl ether is capable to reduce the drag less than 10 %. The highest drag reduction is 8 % was achieved in 600 ppm of solution for turbulent flow with Re within the range 44940 to 56175. The results of experimental work shows that this anionic surfactant perform as a poor drag reducing agent due to its drag reduction values increases only 1 to 3 % even though the concentration of solution was added about 100 ppm. This occurred probably because of the formation of micelle in the solution which is not in a fully threadlike forms and the micelle networks are not fully established in solution to surpassed the degree of turbulent flow.