Spark plasma sintering synthesis of Ni1−xZnxFe2O4 ferrites: Mössbauer and catalytic study

Nickel-zinc ferrite nanoparticles, Ni1-xZnxFe2O4 (x ¼ 0, 0.2, 0.5, 0.8, 1.0) were prepared by combination of chemical precipitation and spark plasma sintering (SPS) techniques and conventional thermal treatment of the obtained precursors. The phase composition and structural properties of the obtained materials were investigated by X-ray diffraction and Mössbauer spectroscopy and their catalytic activity in methanol decomposition was tested. A strong effect of reaction medium leading to the transformation of ferrites to a complex mixture of different iron containing phases was detected. A tendency of formation of Fe-carbide was found for the samples synthesized by SPS, while predominantly iron-nickel alloys ware registered in TS obtained samples. The catalytic activity and selectivity in methanol decomposition to CO and methane depended on the current phase composition of the obtained ferrites, which was formed by the influence of the reaction medium

The effect of high energy milling and high-thermal treatment on the structure and thermal decomposition of minerals from natural CaO-SiO2-P2O5 ceramic system

The major issue studied in this paper is a natural mineral aggregate of quartz, calcite, and fluorapatite (the raw material originated from Bulgaria) before and after high energy milling and thermal treatment, in the order to investigate the properties of natural CaO-SiO2-P2O5 ceramic system. The activation effects are monitored by chemical analysis, X-ray powder diffraction, Fourier transformed infrared spectroscopy, and Thermal analysis (TG/DTG). The activation effect study shows: (i) change of chemical bond strength; (ii) deformation of structural polyhedrons with the formation of new isomorphic phases; (iii) the prolonged time of HEM activation leads to lower raw mineral stability and to the formation of new phases; iv) increased SiO2 reactivity resulting in solid-phase crystallization. The obtained results can be used in the study of ceramic and cement materials (ancient and modern), soil conditioners, etc

Treatment of Biogenic Iron-Containing Materials

Biogenic iron oxides could find application in catalysis but their structure and composition should be well characterized. The content of organic rests due to their origin should also be controlled. Samples of natural biomass and biomass obtained after cultivation in Adler’s medium of the Sphaerotilus-Leptothrix group of bacteria were treated by different techniques to reduce or totally remove the organic residues. The aim of the study was to find procedures, which prevent changes in the oxidation state of the iron and of the type of iron-containing compound(s) during treatment. Mössbauer spectroscopy, IRS, DTA, and SEM were used in the study. Chemical treatment with H2O2 or NaOH at room temperature did not significantly change the samples. Thermal treatment in oxidative flow mixture conducted up to 250 °C resulted in a transformation of the iron-containing phases only. The organic matter, which is included in the structure of the particles, cannot easily be affected. DTA revealed that removal of organic rests occurred in the interval of 250–600 °C. However, the transformation of the initial compounds could not be prevented using such a treatment

Experience implementing a mentoring program for incoming students at Faculty of Dentistry

El Objetivo del estudio fue evaluar el desarrollo del proceso de tutoría y el desempeño del docente tutor en un Programa Piloto de tutoría desde la perspectiva del estudiante y docente participante. El diseño de la investigación es pre experimental, aplicativo, cualicuantitativo; la población de estudio es constituida por 61 estudiantes y 12 docentes. El estudio tuvo tres fases, en la primera se realizó capacitación a los docentes tutores y se aperturó una aula virtual. En la segunda se identificó el perfil del estudiante ingresante y se conformó grupos, en la tercera se ejecutó el programa de tutorías y se realizó la evaluación de esta. Resultados: El 44 % de estudiantes asiste con cierta frecuencia y en forma regular a las tutorias, mientras que de los docentes 6 fueron constantes. Los ingresantes y docentes valoraron tres acciones positivas de desempeño del tutor, el establecer objetivos de la tutoria en forma conjunta, el apoyo en el diseño del plan de trabajo según necesidades, generar clima propicio para comunicarse. Mientras que el aspecto negativo señalado es el seguimiento sistemático de las actividades y acuerdos establecidos con el estudiante, lo cual se atribuye a la falta de tiempo en un 90 %, pues no se cuenta con un horario prestablecido en el plan de estudios. La tutoría requiere una decisión política institucional para su implementación, asimismo el trabajo coordinado con las áreas académicas y administrativas, para obtener mayores logros, sin embargo tuvo limitaciones por ser un proyecto piloto. La tutoría permitió evidenciar el esfuerzo del tutor por ayudar al estudiante y potencializar sus habilidades y del tutorado el logro de un empoderamiento con mayor autonomía y capacidad crítica creadora.The purpose of this study was to evaluate the development of mentoring process and performance of the tutor in a mentoring pilot program from the perspective of student and teacher, the research design is pre experimental, application, qualitative and quantitative, the group consisted of 61 students and 12 tutors. This research had three stages; in the first teachers were trained as tutors with e-learning and was opened a virtual classroom. In the second stage was made some groups, the incoming student's profile was identified, in the third stage was performed the mentoring program and was evaluated.Results: 44% of students attend quite frequently and regularly to the tutoring program, while 6 teachers were constant. Students and teachers assessed three positive actions of tutor performance, the goals for the tutoring program were setting together, the support in the design of the plan was according to the needs, it was created a favorable climate for communication. While the negative topic was the systematic monitoring of the activities and agreements with the student, which they attribute to lack of time by 90%, since they have not assigned a schedule in the curriculum. Mentoring requires institutional policy decision for implementation also the work coordinated with the academic and administrative areas,to record greater achievements, but it had limitations because it was a pilot project. Tutoring allows evidence student’s empowerment with more autonomy and a creative criticism and showed tutor’s effort to improve student’s skills

Crystal-Chemical and Thermal Properties of Decorative Cement Composites

The advanced tendencies in building materials development are related to the design of cement composites with a reduced amount of Portland cement, contributing to reduced CO2 emissions, sustainable development of used non-renewal raw materials, and decreased energy consumption. This work deals with water cured for 28 and 120 days cement composites: Sample A—reference (white Portland cement + sand + water); Sample B—white Portland cement + marble powder + water; and Sample C white Portland cement + marble powder + polycarboxylate-based water reducer + water. By powder X-ray diffraction and FTIR spectroscopy, the redistribution of CO32−, SO42−, SiO44−, AlO45−, and OH− (as O-H bond in structural OH− anions and O-H bond belonging to crystal bonded water molecules) from raw minerals to newly formed minerals have been studied, and the scheme of samples hydration has been defined. By thermal analysis, the ranges of the sample’s decomposition mechanisms were distinct: dehydration, dehydroxylation, decarbonation, and desulphuration. Using mass spectroscopic analysis of evolving gases during thermal analysis, the reaction mechanism of samples thermal decomposition has been determined. These results have both practical (architecture and construction) and fundamental (study of archaeological artifacts as ancient mortars) applications