INVESTIGATION OF CARBOTHERMAL REDUCTION OF MECHANICALLY ACTIVATED CHROMITE WITH THERMAL ANALYSIS

Ferrochromium is one of the important alloying materials used in the production of stainless and high-alloy ferritic steels. The carbothermal reduction of chromite with graphite under argon atmosphere was studied by differential thermal analysis up to 1350 degrees C and the effects of mechanical activation on the chromite structure was investigated using of X-ray diffraction analysis and scanning electron microscopy. The results showed that the carbothermal reduction temperatures of reducible oxides in the chromite spinel were decreased after mechanical activation, due to structural disordering in chromite spinel

Effect of mechanical activation on manganese extraction from manganese carbonate ore in acidic media

215-219<span style="font-size:9.0pt;mso-bidi-font-size: 12.0pt;mso-ansi-language:EN-US" lang="EN-US">A manganese carbonate ore has been mechanically activated at different milling times and the effect of mechanical activation on the ore structure is analyzed by X-ray diffraction, scanning electron microscopy and particle size analysis. The activation procedure leads to amorphisation and structural disordering of the ore structure. Sulfuric acid leaching of the non-activated and activated manganese carbonate ore has been studied at different temperatures, durations, and acid concentrations. The results show that dissolution of manganese increases from 69% to 100% in acidic leaching with 1 M H2SO4 at 70°C after 30 min of mechanical activation, due to amorphisation in structure and creating more surface area. </span

Effect of mechanical activation on manganese extraction from manganese carbonate ore in acidic media

A manganese carbonate ore has been mechanically activated at different milling times and the effect of mechanical activation on the ore structure is analyzed by X-ray diffraction, scanning electron microscopy and particle size analysis. The activation procedure leads to amorphisation and structural disordering of the ore structure. Sulfuric acid leaching of the non-activated and activated manganese carbonate ore has been studied at different temperatures, durations, and acid concentrations. The results show that dissolution of manganese increases from 69\% to 100\% in acidic leaching with 1 M H2SO4 at 70 degrees C after 30 min of mechanical activation, due to amorphisation in structure and creating more surface area

Low temperature formation of barium titanate in solid state reaction by mechanical activation of BaCO3 and TiO2

In this study, the effects of mechanical activation on BaTiO3 formation from BaCO3 and TiO2 powders were investigated. Differential thermal analysis (DTA), high-temperature x-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) studies were performed following the mechanical activation of the powder mixture to reveal the phase formation and structural changes. In addition, the powder mixtures were sintered at 1350 degrees C for 3 h. Structural differences between the non-activated and activated samples were observed with scanning electron microscopy (SEM), and their electrical properties were measured to study the effects of mechanical activation. It was observed that mechanical activation increased the chemical reactivity of BaCO3 and TiO2 powders, causing amorphization and structural disorder in their structures. These were confirmed with XRD and FT-IR analysis. The 120-min activation of a mixture of barium carbonate and titania caused a decrease in the formation temperature of the Ba2TiO4 phase from 815 degrees C to 640 degrees C, while the formation temperature of the BaTiO3 phase decreased from 1095 degrees C to 890 degrees C. It was observed that the dielectric constants of the samples were increased by increasing the mechanical activation time

Formation of SrTiO3 in mechanically activated SrCO3-TiO2 system

In this study, mechanical activation process was used for intimate mixing as well as producing finely ground particles, increased surface area and improved chemical reactivity of milled materials for producing SrTiO3 from commercially pure strontium carbonate and TiO2 as a contributive process. Characterization of milled powder mixture by X-ray diffraction analysis showed that disappearing, decreasing and/or shifting of the patterns occurred with mechanical activation that means amorphization was taken place. Amorphization was also demonstrated by FT-IR analysis where shift of band centers as well as the decrement of transmittance related to CO3 was observed. Advantage of amorphization was established with high-temperature XRD analysis which showed 1300 A degrees C was not enough for non-activated mixture to form SrTiO3, whereas structure only composed of SrTiO3 at 1000 A degrees C for activated ones. The reason for this phenomenon was investigated by DTA-TG analysis, and it was based on energy accumulation originated from mechanical activation that corresponds to peak temperature shifting to the lower temperatures and CO2 liberation at mechanical activation step arising from local temperature rising at the vial during high-energy milling that was understood from peak temperature, and area decrement of endothermic peak corresponds to decomposition of SrCO3

Malperfusion Remains the Major Cause of Mortality in Proximal Aortic Operations

WOS: 000293244200014PubMed ID: 21507058Background: This study was undertaken to identify the incremental risk factors for early mortality in operations for proximal aortic pathologies. Methods: Between September 2000 and May 2010, 240 consecutive patients underwent replacement of various portions of the proximal aorta. Mean age was 56 +/- 13 years (range 18 to 84) and female/male ratio was 3/7. Operations were performed emergently in 97, urgently in 21, and electively in 122 patients. Thirty-four patients had previous cardiac or aortic operations. Etiology was acute dissection in 102, chronic dissection in 41, degenerative aneurysm in 61, and other factors (endocarditis, pseudoaneurysm, aortitis, etc.) in 36 patients. The ascending aorta was replaced in all patients. In addition, the aortic arch was replaced in 20 and the root was replaced in 106 patients. Results: The in-hospital mortality rate was 10.4% in the overall group (25/240), 21.6% in emergent cases (21/97), 9.5% in urgent cases (2/21), and 1.6% in elective cases (2/122). Morbidity rates were as follows: stroke 2.7%, temporary neurological dysfunction 13.3%, nonoliguric renal failure 3%, dialysis 5.4%, tracheostomy 3.3%, bleeding requiring revision 3.3%. In multivariate analysis, the presence of malperfusion in patients with acute aortic dissection emerged as the incremental risk factor for mortality (p < 0.0001, odds ratio = 10.37). There was no variable associated with stroke. Emergency/urgency of operation did not emerge as incremental risk factors for mortality. Conclusion: Immediate outcomes of elective aortic operations for proximal aortic pathologies are excellent. Complicated acute dissections with malperfusion remain the major cause of early mortality. doi: 10.1111/j.1540-8191.2011.01250.x (J Card Surg 2011; 26: 393-396