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Popescu G.,Polytechnic University of Bucharest | Vladutiu L.M.,Polytechnic University of Bucharest | Soare V.,National Institute of Research and Development for Non Ferrous and Rare Metals | Mitrica D.,National Institute of Research and Development for Non Ferrous and Rare Metals | And 2 more authors.
Metalurgia International | Year: 2011

This paper presents the results of researches carried out in order to obtain nanostructured Al-Mn master alloys, by mechanical alloying in high-energy mill. Mechanical alloying (MA) is a solid-state powder processing technique that involve repeated welding, fracturing and rewelding of powder particles. It is also a complex process that involves optimization of a great number of variables in order to achive the desired product phase or microstructures. Among these parametres are: type of mill, milling container, speed and time, type and size of grinding medium, ball-to-powder ratio, milling atmosphere, process control agent and/or temperature of milling. Planetary mills have been often used for powders studies.Powder mixtures of Al-65%wt.Mn and respectively Al-75%wt.Mn were milled in a medium of petroleum ether or phenyl methane at a mill speed of 300 rpm, with a ball to powder ratio of 10:1, using different milling times. The Al-Mn master alloys obtained were investigated by SEM and XRD analysis. The results indicate that by milling of Al and Mn ultrafine powders in a high-energy mill and varing the milling time and milling medium were obtained nanocrystalline structures with grains sizes in the range of 20 to 100 nm, that leads to superior properties of aluminum alloys. Source


Usurelu-Cristea A.,Polytechnic University of Bucharest | Popescu G.,Polytechnic University of Bucharest | Dumitru M.,National Institute of Research and Development for Non Ferrous and Rare Metals | Soare V.,National Institute of Research and Development for Non Ferrous and Rare Metals | Buzatu M.,Polytechnic University of Bucharest
Metalurgia International | Year: 2013

Al-Mg wrought alloys have high mechanical resistance associated with a good ductility high corrosion resistance and good weldability. Also, these alloys can be easily plastic cold deformed. Mechanical and corrosion properties of these alloys can be improved by alloying with Mn and Cr. It was obtained AlMg4.5Mn0.7Cr0.15 alloy by alloying with nanostructured AlMn master alloy. This alloy was grain refined with nanostructured AlTi5B1 master alloy, as ribbons obtained by melt spinning. This improved the AlMg4.5Mn0.7Cr0.15 alloy structure and also mechanical properties. Source


Onisei S.,Polytechnic University of Bucharest | Onisei S.,Catholic University of Leuven | Pontikes Y.,Catholic University of Leuven | Van Gerven T.,Catholic University of Leuven | And 4 more authors.
Journal of Hazardous Materials | Year: 2012

The present work reports on the synthesis and properties of inorganic polymers (" geopolymers" ) made of 100% fly ash from lignite's combustion, 100% primary lead slag and mixtures of the two. In the inorganic polymers with both fly ash and lead slag the main crystalline phases detected are wüstite, magnetite, sodium zinc silicate, quartz, anorthite, and gehlenite; litharge partially dissolves. FTIR analysis in these samples revealed that the main peaks and bands of end members also exist, along with a new amorphous reaction product. In terms of microstructure, both fly ash and lead slag dissolve and contribute in the binding phase whereas the larger particles act as aggregates. For an increasing lead slag in the composition, the binding phase is changing in chemistry and reaches PbO values higher than 50. wt.% for the 100% lead slag inorganic polymer. Regarding the properties of fly ash and lead slag inorganic polymers, compressive strength is higher than 35. MPa in all cases and water absorption diminishes as the lead slag content increases. A comparison of leaching results before and after polymerisation reveals that pH is an important factor as Pb is immobilised in the binding phase, unlike Zn and As. © 2011 Elsevier B.V. Source


Ghita M.,National Institute of Research and Development for Non Ferrous and Rare Metals | Stoiciu F.,National Institute of Research and Development for Non Ferrous and Rare Metals | Badilita V.,National Institute of Research and Development for Non Ferrous and Rare Metals | Enache L.,National Institute of Research and Development for Non Ferrous and Rare Metals | And 2 more authors.
11th International Multidisciplinary Scientific Geoconference and EXPO - Modern Management of Mine Producing, Geology and Environmental Protection, SGEM 2011 | Year: 2011

The hydrometallurgical process for obtaining alumina by Bayer process bauxite is getting significant amounts of red mud (0.8 - 2 t/t Al2O3). It is deposited in dumps which can cause danger for environment mainly due to the alkali content (pH = 8-13) and small dimensisons of particles (less than 60 microns). Chemical and mineralogical composition of red mud bauxite is closely related to type of the bauxite used as raw material and processing conditions determined by some peculiarities of applied technology (pressure, temperature, etc.). In Romania, a producer of alumina and aluminum tradition for over 50 years, have been processed in time many varieties of bauxite of internal origin and imported bauxites. Red mud is stored entirely in dump type deposits. This paper presents the results of the mineralogical study (x-ray diffraction, scanning electronic microscopy, optical microscopy) and chemical analysis of different sorts of red mud. © SGEM2011 All Rights Reserved by the International Multidisciplinary Scientific GeoConference SGEM. Source


Marinescu C.,Institute of Physical Chemistry Ilie Murgulescu | Sofronia A.,Institute of Physical Chemistry Ilie Murgulescu | Rusti C.,National Institute of Research and Development for Non Ferrous and Rare Metals | Piticescu R.,National Institute of Research and Development for Non Ferrous and Rare Metals | And 4 more authors.
Journal of Thermal Analysis and Calorimetry | Year: 2011

The aim of the article is to investigate the influence of particle size on titanium dioxide phase transformations. Nanocrystalline titanium dioxide powder was obtained through a hydrothermal procedure in an aqueous media at high pressure (in the range 25-100 atm) and low temperature (≤200 °C). The as-prepared samples were characterized with respect to their composition by ICP (inductive coupled plasma), structure and morphology by XRD (X-ray diffraction), and TEM (transmission electron microscopy), thermal behavior by TG (thermogravimetry) coupled with DSC (differential scanning calorimetry). Thermal behavior of nanostructured TiO2 was compared with three commercial TiO2 samples. The sequence of brookite-anatase-rutile phase transformation in TiO2 samples was investigated. The heat capacity of anatase and rutile in a large temperature range are reported. © 2010 Akadémiai Kiadó, Budapest, Hungary. Source

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