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  • Author: Ileana Nicoleta Popescu x
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Ileana Nicoleta Popescu and Ruxandra Vidu

Abstract

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.

Open access

Vasile Bratu and Ileana Nicoleta Popescu

Abstract

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.

Open access

Ileana Nicoleta Popescu, Ruxandra Vidu and Vasile Bratu

Abstract

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.

Open access

Ileana Nicoleta Popescu and Ruxandra Vidu

Abstract

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.

Open access

Aurel Gaba, Vasile Bratu, Dorian Musat, Ileana Nicoleta Popescu and Maria Cristiana Enescu

Abstract

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.

Open access

Mihai Gabriel Cucu, Ioana Streața, Anca Lelia Riza, Alina Liliana Cimpoeru, Simona Șerban-Șoșoi, Adela Ciocoiu, Răzvan Mihail Pleșea, Elena Leocadia Popescu, Ștefania Dorobanțu, Andreea Anghel, Aida Maria Stroe, Andreea Nicoleta Ștefan, Ramona Cioboată, Ileana Băzăvan, Marius Sorin Ciontea, Iulia Căpitănescu, Mihai Olteanu, Mimi Nițu, Florin Burada, Tiberiu Tătaru, Mihai Netea, Reinout van Crevel, Marian Olaru, Francisc Mixich and Mihai Ioana

Abstract

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.