Factors Influencing the Stability of Low Temperature Tetragonal ZrO2

Various factors that influence the appearance of a tetragonal (t-) ZrO2 polymorph at room temperature have been extensively investigated. Several proposed models emphasize the role of anionic impurities (SO42-, OH-), crystallite size (surface energy), structural similarities between the starting material and t-ZrO2, lattice strains, water vapor, lattice defects (oxygen vacancies), etc. Our investigations, focused on the stability of low temperature t-ZrO2, showed that, regardless of the structural differences in the starting zirconium materials, their thermal decomposition products crystallized into a metastable t-ZrO2. The t-ZrO2 -> m-ZrO2 transforma-tion occurred during the cooling or further calcination in the pres-ence of air at atmospheric pressure. On the other hand, if these processes are performed in vacuum, the metastable phase is pre-served. These observations indicate that a metastable t-ZrO2 appears at room temperature as a result of stabilization caused by introduction of oxygen vacancies, similarly as in the solid Solutions with aliovalent cations. A decrease in the specific surface area of ZrO2 grains or the presence of the substances that enter into strong surface interactions with ZrO2 (SO42-, Cr2O3) prevents the diffusion of oxygen from the atmosphere into the ZrO2 lattice and due to this fact the metastable t-ZrO2 is stabilized. On the other hand, lattice strain and grain size of metastable t-ZrO2 could not be clearly related to its stability

1968 movements in Belgrad and Mexico City

Die vorliegende Arbeit konzentriert sich auf die Mobilisierungen im Jahr 1968, welche die mekanische und die jugoslawische Gesellschaft erschüttert haben. Der Versuch wird gemacht beide Bewegungen in ihrem historischen Kontext von Entwicklungsländern an der Semiperipherie des Weltsystems zu analysieren, sich entwickelnd durch unterschiedliche, aber konvergierende Sozio-ökonomische Systeme. Mexiko- sich entwickelnd durch ein Importsubstitions-Industrialisierungsmodell einhergehend mit einem politischen Modell mit starken korporartiven Merkmalen, und Jugoslawien- mit seinem Einparteiensystem und der sozialistischen Planwirtschaft kombiniert mit Marktanreizen. Die Entstehung der 1968er Bewegungen in diesen beiden Ländern wird, im Unterschied zu ähnlichen Protesten in den westlichen Metropolen, analysiert vor dem Hintergrund der späten Urbanisierung, der Begrenzungen von staatlich gelenktem wirtschaftlichen Wachstum, starker revolutionärer Diskurse präsent in beiden Ländern, sowie auch der Einflüsse von 1968 als globales Phänomen. Um die politische Orientierung, Forderungen und Errungenschaften dieser beiden Bewegungen zu verstehen, betrachtet die Arbeit Schlüsselbesonderheiten des mexikanischen bürgerlich- korporatistischen Staates und der jugoslawischen Marke des Sozialismus der Selbstverwaltung, und erforscht wie diese Macro-Rahmen die Dynamiken der verschiedenen in ihnen existierenden sozialen Klassen beeinflusst haben. Besondere Aufmerksamkeit wird den Arbeiterbewegungen, der aufsteigenden Mittelschicht und den Diffenzierungen innerhalb der scheinbar monolitischen herrschenden Elite geschenkt. Die 1968er Bewegungen werden gesehen als oberflächliche Ausdrücke tieferer tektonischer Verschiebungen, welche in diesen Gesellschaften unter der autoritären Schale des mexikanischen und des jugoslawischen Staates stattfanden. Die Arbeit stellt außerdem die Annahme eines Zusammenhangs zwischen den 1968er Bewegungen und den späteren profunden Veränderungen, sprich die neolibrale Wende und die politische Liberalisierung in Mexiko, und der Zusammenbruch der Planwirtschaft und des Staatssystems in Jugoslawien, in Frage.This thesis focuses on the mobilizations that shook Mexican and Yugoslav societies in 1968. An attempt will be made to place both movements in the historical context of developing countries on the semi-periphery of the world system, developing through different, but converging socio-economic systems. Mexico, developing through Import Substitution Industrialization model alongside a political system with strong corporatist features, and Yugoslavia, with its one party political system and command socialist economy which included market incentives. The genesis of these 1968 movements, in contrast to similar protests in the Western metropolises, are analyzed against the background of late rapid urbanization, limits of state led economic growth, strong revolutionary discourses present inside both countries as well as the influences of 1968 as a global phenomenon. In order to understand the political outlook, demands and achievements of these two movements, the paper looks at key peculiarities of the Mexican bourgeois corporatist state and the Yugoslav self-management brand of socialism and explores how these macro frames influenced the dynamics of various social classes within them. Special attention is dedicated to the labor movements, the rising middle layers and differentiations taking place within the seemingly monolithic ruling elite. The 1968 movements are considered as surface expressions of deeper tectonic shifts taking place within these societies under the authoritarian façade of the Mexican/Yugoslav state and discover the nature of connections between 1968 movements and the profound changes these systems will go through two decades later- mirrored in the neo-liberal economic turn and political liberalization in Mexico and the breakdown of planned economy and the state system in Yugoslavia. The thesis also re-examines the nature of the often assumed connections between the 1968 movements and the profound changes these two systems would go through in the 1980’s and 1990’s, which are mirrored in the neo-liberal economic turn and political liberalization in Mexico and the breakdown of the planned economy and the unified state in Yugoslavia

Microstructural Analysis of Boehmite Nanoparticles Prepared by Rapid Hydrolysis of Aluminum Sec-butoxide

Microstructural properties of six samples, prepared by rapid hydrolysis of aluminum secbutoxide, were investigated at RT using field emission scanning electron microscopy (FE SEM), X-ray powder diffraction (XRD) and Fourier transform infrared (FT-IR) spectrometry. The results of structural analysis show that, regardless of a significant difference in the processing parameters (pH, temperature, time of synthesis), all products contain boehmite as the only crystal phase present. The results of FE-SEM analysis indicate a significant difference in the morphology of obtained boehmites (plates, needles, granules). The results of line-broadening analysis of powder diffraction patterns (Le Bail method – program GSAS) indicate the presence of very small anisotropic crystal domains (around 1.5 to 7 nm in the direction 010; around 3 to 16 nm in the direction perpendicular to 010). In all cases the parameters that contribute to the strain broadening of diffraction lines decrease to nearly zero, which suggests that the obtained boehmites are almost strain-free. (doi: 10.5562/cca1884

In situ phase analysis of the thermal decomposition products of zirconium salts

X-ray powder diffraction at high temperature was used to determine the phase composition of the thermal decomposition products of two zirconium salts, Zr(SO4)(2). 4H(2)O and ZrO(NO3)(2). 2 H2O, and of a mixture of zirconium nitrates having Zr(OH)(2)(NO3)(2). 4.7 H2O and ZrO(NO3)(2). 2H(2)O as dominant components. Heating of the samples up to 1200 degrees C was performed inside a high-temperature chamber, attached to a diffractometer, at an air pressure of approximate to 2 x 10(-3) Pa. Regardless of the structural differences in the starting salts, thermal decomposition products crystallized to t-ZrO2 which remained stable up to 1200 degrees C. This result indicated that the structural nature of the starting materials was not the most important factor of metastable t-ZrO2 formation. The thermodynamically stable m-ZrO2 appeared after the cooling of the samples to room temperature. If the cooling was performed at low air pressure, the m-ZrO2 content was small. Introduction of air, even at RT, caused a considerable increase of m-ZrO2, which became the dominant phase in all cases. The important role of oxygen in the t-ZrO2 --> m-ZrO2 transition indicates that the lack of oxygen in the zirconia lattice favours the formation of metastable t-ZrO2

In situ phase analysis of the thermal decomposition products of zirconium salts

X-ray powder diffraction at high temperature was used to determine the phase composition of the thermal decomposition products of two zirconium salts, Zr(SO4)2 ⋅ 4 H2O and ZrO(N03)2 ⋅ 2 H2O, and of a mixture of zirconium nitrates having Zr(OH)2(NO3)2 ⋅ 4.7 H2O and ZrO(NO3)2 ⋅ 2 H2O as dominant components. Heating of the samples up to 1200 °C was performed inside a high-temperature chamber, attached to a diffractometer, at an air pressure of ≈ 2 × 10-3 Pa. Regardless of the structural differences in the start-ing salts, thermal decomposition products crystallized to t-ZrO2, which remained stable up to 1200 °C. This result indicated that the structural nature of the starting materials was not the most important factor of metastable t-ZrO2 formation. The thermodynamically stable m-ZrO2 appeared after the cooling of the samples to room temperature. If the cooling was performed at low air pressure, the m-ZrO2 content was small. Introduction of air, even at RT, caused a considerable increase of m-ZrO2, which became the dominant phase in ali cases. The important role of oxygen in the t-ZrO2 → m-ZrO2 transition indicates that the lack of oxygen in the zirconia lattice favours the formation of metastable t-ZrO2

Successful treatment of cardiogenic shock by stenting of the left main coronary artery in acute myocardial infarction

Introduction. Patients with non-ST elevation acute coronary syndromes (NSTE-ACS) are sometimes severely hemodynamicly compromised. Urgent coronary angiography should be performed in these patients in percutaneous coronary intervention (PCI) centers according to the ESC NSTE-ACS guidelines to determine suitabilty for percutaneous or surgical revascularization. Case report. We reported a 62-year-old male with chest pain admitted to the Coronary Care Unit. ST segment depression of 2 mm in leads I, L and V4-6 was revealed at electrocardiogram. After following 6 hours the patient had chest pain and signs of cardiogenic shock despite of the therapy. Chest x-ray showed pulmonary edema. Echocardiographic examination showed dyskinetic medium and apical segments of septum. The patient underwent coronary angiography immediately which revealed 75% stenosis of the left main coronary artery with thrombus. The use of a GPIIb/III inhibitor-tirofiban and stent implantation resulted in TIMI III flow. After that the patient had no chest pain and acute heart failure subsided in the following days Echocardiography done at the fourth day from PCI showed only hypokinesis medium and apical segment of septum. The patient was discharged at day 11 from admission in a stable condition. Conclusion. Stenting of left main coronary artery stenosis in patients with cardiogenic shock and non- ST segment elevation acute coronary syndromes may be a life saving procedure

57Fe Mössbauer, FT-IR and TEM Observations of Oxide Phases Precipitated from Concentrated Fe(NO3)3 Solutions

Concentrated Fe(NO3)3 Solutions (final Fe3+ concentration of 1 M) were completely or partially neutralized by addition of concentrated NaOH solution, and then aged at various temperatures and times. The oxide phases were investigated using Mössbauer spectroscopy, FT-IR spectroscopy and transmission electron microscopy. In a highly alkaline medium, single phase α-FeO(OH) was obtained by the aging of Fe(OH)3 suspension at room temperature (RT) for 135 days. The Mössbauer spectrum of this sample at 298 K showed superposition of the Central quadrupole doublet and a collapsing sextet, while at 80 K a sextet corresponding to α-FeO(OH) was recorded. In the highly alkaline medium, an amorphous material was obtained after heating the Fe(OH)3 suspension at 333 K for 1 day. Spectroscopic investigations provided a certain evidence of the presence of α-Fe2O3 in this material. With prolonged time of heating, α-FeO(OH) appeared at 333 K and its fraction showed a tendency to increase. It was suggested that, in a highly alkaline medium, nucleation and crystallization of α-Fe2O3 occurred inside the amorphous gel, while α-FeOOH crystallized by a dissolution/reprecipitation mechanism. After neutralization of 90% of 1 M Fe(NO3)3 solution, lemon-shaped -Fe2O3 particles were produced at 398 K between 6 and 24 h. Interpretations of the spectroscopic and electron microscopic measurements are given

57Fe Mössbauer, FT-IR and TEM Observations of Oxide Phases Precipitated from Concentrated Fe(NO3)3 Solutions

Concentrated Fe(NO3)3 Solutions (final Fe3+ concentration of 1 M) were completely or partially neutralized by addition of concentrated NaOH solution, and then aged at various temperatures and times. The oxide phases were investigated using Mössbauer spectroscopy, FT-IR spectroscopy and transmission electron microscopy. In a highly alkaline medium, single phase α-FeO(OH) was obtained by the aging of Fe(OH)3 suspension at room temperature (RT) for 135 days. The Mössbauer spectrum of this sample at 298 K showed superposition of the Central quadrupole doublet and a collapsing sextet, while at 80 K a sextet corresponding to α-FeO(OH) was recorded. In the highly alkaline medium, an amorphous material was obtained after heating the Fe(OH)3 suspension at 333 K for 1 day. Spectroscopic investigations provided a certain evidence of the presence of α-Fe2O3 in this material. With prolonged time of heating, α-FeO(OH) appeared at 333 K and its fraction showed a tendency to increase. It was suggested that, in a highly alkaline medium, nucleation and crystallization of α-Fe2O3 occurred inside the amorphous gel, while α-FeOOH crystallized by a dissolution/reprecipitation mechanism. After neutralization of 90% of 1 M Fe(NO3)3 solution, lemon-shaped -Fe2O3 particles were produced at 398 K between 6 and 24 h. Interpretations of the spectroscopic and electron microscopic measurements are given

Formation of ZrO2 by the Thermal Decomposition of Zirconium Salts

Hydrated zirconium salts containing Cl- , NO3- or SO42- anions were thermally treated up to 1300 °C. The thermal decomposition products were investigated using the X-ray diffraction (XRD), Fourier transform IR spectroscopy (FT-IR) and laser Raman spectroscopy. The thermal decomposition products of all three zirconium salts, characterized as amorphous material, showed a maximum of X-ray scattering at -16° and also in the corresponding FT-IR spectra a broad band at 450 cm-1. With an increase of the heating temperature of all three salts (400 °C for ZrOCl2 ∙ 8H2O, 400 °C for ZrO(NO3)2 ∙ 2H2O and 700 °C for Zr(SO4)2 ∙ 4H2O), the metastable f-ZrC>2 was formed, which disappeared on further heating to higher temperatures. The yield of f-ZrC>2, measured by XRD, depended on the nature of the starting salt, and the highest value was obtained for ZrOCl2 ∙ 8H2O salt. The t-ZrO2 phase formed from ZrOCl2 ∙ 8H2O was thermally most unstable, while the presence of a small amount of t-ZrO2 was observed in the thermal decomposition product obtained by heating Zr(SO4)2 ∙ 4H2O even at 1300 °C. Metastable t-ZrO2, generated by the thermal decomposition of ZrOCl2 ∙ 8H2O or ZrO(NO3)2 ∙ 2H2O salt, was highly sensitive to mechanical treatment, while metastable t-ZrO2 formed from Zr(SO4)2 ∙ 4H2O was stable during the same process. The nature of the starting salt influenced the formation of metastable t-ZrO2, however, when t-ZrO2 was once formed, its stability depended on the anionic impurities that remained in the oxide material