Powder mixtures compaction behavior can be quantitatively expressed by densification equations that describe the relationship between densities - applied pressure during the compaction stages, using correction factors. The modelling of one phase (metal/ceramic) powders or two-phase metal-ceramic powder composites was studied by many researchers, using the most commonly compression equations (Balshin, Heckel, Cooper and Eaton, Kawakita and Lüdde) or relative new ones (Panelli - Ambrózio Filho, Castagnet-Falcão- Leal Neto, Ge Rong-de, Parilák and Dudrová, Gerdemann and Jablonski. Also, for a better understanding of the consolidation process by compressing powder blends and for better prediction of compaction behavior, it's necessary the modeling and simulation of the powder pressing process by computer numerical simulation. In this paper are presented the effect of ceramic particles additions in metallic matrix on the compressibility of composites made by P/M route, taking into account (a) the some of above mentioned powder compression equations and also (b) the compaction behavior modeling through finite element method (FEM) and discrete element modeling (DEM) or combined finite/ discrete element (FE/DE) method.
Over the last few decades, researchers has been focused on the study of processing using different methods of new biocompatible and/or biodegradable materials such as permanent or temporary medical implants in reconstructive surgery. The advantages of obtaining biomedical implants by Powder Metallurgy (P/M) techniques are (i) obtaining the near-net-shaped with complex forms, (ii) making materials with controlled porosity or (iii) making mechanically resistant sintered metallic materials used as reinforcing elements for ceramic/polymeric biocompatible materials. In this first part of the 2-part review, the most used and newest metallic biomaterials obtained by P/M methods are presented, along with their compaction and sintering behavior and the properties of the porous biomaterials studied in correlation with the biomedical domain of application.
In order to determine the optimum geometry of the ingot mold format (the format of ingot mold with a diameter per height ratio H / D <3 and the conicity of minimum 7%) was analyzed by mathematical modeling of solidification and segregation of the carbon and sulfur in it.
It was considered 205Cr115 steel type (according with , STAS 3611 - Romanian stardandization) and known also as X210Cr12 steel type (according with European standard). It has been considered an element of volume of coordinates x, y, z in the solidifying ingot and have made the following assumptions: (i) the equilibrium distribution ratio K, is applied to the solid-liquid interface; (ii) solid diffusion is negligible during solidification; and (iii) the solid density is constant during solidification. In carrying out the simulation of segregation mechanisms are resolved heat transfer equation, that simulating the solidification process and are are solved the interdendritic fluid equation of motion.
The basic purpose of compaction is to obtain a green compact with sufficient strength to withstand further handling operations. The strength of green compact is influenced by the characteristics of the powders (apparent density, particle size and shape, internal pores etc.), the processing parameters (applied force, pressing type, and temperature) and testing conditions (strain rate etc.) Successful powder cold compaction is determined by the densification and structural transformations of powders (metallic powders, ceramic powders and metal-ceramic powder mixtures) during the compaction stages. In this paper, for understanding the factors that determine a required strength of compacted metal-ceramic powder mixtures, we present the densification mechanisms of different mixtures according to densification theories of compaction, the elastic-plastic deformations of mixture powders, the stressstrain relations and the relaxation behavior of compacted metal-ceramic composite parts and the particularities of each of them.
This paper presents the most used processes for the synthesis of hydroxyapatite from aqueous solutions: chemical precipitation, the hydrothermal process and the sol-gel method. The experimental part includes the synthesis of hydroxyapatite by chemical precipitation. The obtained results confirm the obtaining of a ceramic with a high purity and a high degree of crystallization.
A microfluidic device designated for measurement of fluidic flows with different viscosity, necessary within trapping/realising of cells/particles system has been developed. We use a new concept as Microfluidic Pulse Width Modulation (MPWM) for controlling transport of a single cell/particle. The image processing helped the nano-hydraulic volumes/flow rates measurement, through tracking inovative methods with the purpose to build a flow sensor. The device open an unique opportunitie for single cell study with applications in biomedical devices, tools for biochemistry or analytical systems.
In this presentation are evidenced instrumental characterization by Electronic Scanning Microscopy (SEM) equipped with EDS / WDS of aluminum alloys such 2024 alloy with multiple synergistic purposes as: acquisition of new knowledge, increase the amount of information obtainable about the material, increasing the efficiency and the quality of the tests, characterization of special destination alloys and assessing their conformity with the specified requirements. In this direction, it requires both the knowledge the test methods (theoretical basis, test method, procedure relating to the method, quality assurance testing) as well material characteristics investigated. These aspects are necessary for test system design, and preliminary interpretation of experimental results.
This paper presents solutions and the equipment for preheating combustion air from scrap aluminum melting furnaces through flue gas heat recovery. For sizing convection pre-heaters, there has been developed a mathematical model which has been transcribed into a computer program in C + +. A constructive version of the pre-heater was drawn up and a recovery heat exchanger was manufactured and mounted on an aluminum melting furnace. Both the functional parameters values and the reasons causing the pre-heater worning out, as well as the steps taken for sizing and the achievement of a new air pre-heater able to bear the operating conditions of the aluminum melting furnace are shown.
The aim of the paper was to develop a device (“pin-on-disc” type) for the measurement of friction in plane friction couplings with sliding movement. On tribometric device (made in our laboratory) we can measure the friction force, friction coefficient and wear, for different loading conditions, speeds, time and material coupling.
For the measurement of the frictional force as well as of the coefficients of friction, mainly the method with a resistive tensiometric transducer is used. With a DataQ DI 245 data acquisition board it is possible to record up to 2 kHz frequencies in the range of -10 ÷ +10 mV with a resolution of 13 bits. To test the functionality of the device, a preliminary test was carried out for a steel pin- on- cast iron disc, for different values of the normal pushing force. The device was calibrated and the measurement results were recorded and processed on the computer.
Autophagy, a homeostatic process involved in nutrient regeneration and immune responses, may be involved in intracellular killing of M. tuberculosis. Several studies linked variation in autophagy genes with susceptibility to pulmonary tuberculosis, but others did not confirm these findings.
We genotyped single nucleotide polymorphisms (SNPs) in the ATG5 (rs2245214, c.574-12777G>C) and NOD2 (rs2066844, c.2104C>T) genes for 256 pulmonary tuberculosis patients and 330 unrelated healthy controls in Romania. Both SNPs have been reported as relevant for the autophagy process and potentially for susceptibility to active pulmonary tuberculosis.
In our study, the polymorphisms in ATG5 and NOD2 were not associated with tuberculosis. This suggests that the two genetic variants we focused on are not related to the risk for developing active TB in a Romanian population.