Papers by Keyword: Rietveld Method

Abstract: The article investigates the influence of the sintering time with constant temperature on the development of the tricalcium silicate crystallinity using the Scherrer's and Rietveld method.One suitable raw material mixture consisting of only pure CaCO₃ and SiO₂ in their specific ratio of 73.6:26.3 wt.% was selected. This raw material powder was prepared using a wet milling process in the water medium in a PULVERISETTE 6 plan mill. Based on previous research in this area, a firing temperature of 1500 °C was chosen with sintering period of 5, 10, 15 and 20 minutes in an experimental furnace with a manipulator for isothermal sintering of laboratory samples developed by Dr. Chromy. This furnace requires special sample preparation, so a procedure for their preparation was designed and optimized. Thanks to this optimization, it is possible to repeatably prepare identical pellets with the exact parameters for this type of furnace. The resulting pellet weight is 73 mg at a volumetric weight of 2,285 g·cm^-3.The results of the firings with different sintering times and constant temperatures showed that the sintering processes and mineral conversion occur very quickly, since after 5 minutes 30.81 wt.% of the mineral tricalcium silicate was identified and after 20 minutes the raw powder was converted to tricalcium silicate in a significant amount, i.e., 72.02 wt.%. At the same time, the crystallinity was monitored using Scherrer's method and after 20 minutes of sintering, the crystallite size of tricalcium silicate reached 104.889 nm. Thus, there was a relatively rapid development of the crystallinity of Alite.

Abstract: The article investigates the influence of the water content during grinding the raw material mixture on the formation of monoclinic phases M1 and M3 of alite using the Rietveld method. Four identical raw material mixtures were chosen, differing only in the water content for the grinding process. The milling process in a water environment in a PULVERISETTE 6 planetary mill was chosen for the preparation of the raw material mixture. Based on previous research in this area, a firing temperature of 1450 °C with soaking for 60 minutes was chosen. The results showed that the monoclinic M3 phase is predominantly formed. In contrast, the monoclinic M1 phase forms at lower firing temperatures than the M3 phase and with fewer crystallization nuclei due to less fine grinding. The results show that the amount of water used to grind the feedstock does not make any difference in the final amount of monoclinic M1 and M3 phases.

Abstract: The article deals with the laboratory preparation of clinker mineral belite. It monitors the stability of β-C₂S with respect to the firing regime and the effect of the stabilizing additive H₃BO₃. Belite was prepared by high-speed milling using solid-state reaction at 1150, 1250, 1350 and 1450 °C with 30 min soaking. It deals in more detail with the higher temperature 1450 °C where it compares the content of individual phases of belite with samples prepared without the stabilizer H₃BO₃. The results showed a significant stabilizing effect of boron at a higher firing temperature. The effect of the stabilizer is more pronounced in firing regimes, where γ-C₂S is more readily formed, especially at firing temperature 1450 °C with 0, 30, 60 and 90 min soaking. In the samples with the stabilizing additive, double the amount of β-C₂S was identified in comparison with the samples prepared without the stabilizer. At a temperature of 1450 °C and 90 minutes, almost 100% β-C₂S was prepared using a stabilizer H₃BO₃.

Abstract: The article monitors the effect of length of grinding in the process of homogenization of raw material mixture and soaking on the number of monoclinic phases of alite M1 and M3 in the sample using the Rietveld method. The wet grinding process in the water environment in the planetary mill PULVERISETTE 6 was chosen for the preparation of raw material mixture. Based on previous research in this area, two firing temperatures 1450 and 1550 °C with soaking of 30, 60 and 90 minutes were selected. The results showed the monoclinic phase M1 is more readily formed during coarser grinding, during which large crystals of M1 are formed. On the contrary, the monoclinic phase M3 is formed at a higher firing temperature, at a larger amount nuclei and finer grinding. The results show that the grinding time has an important effect on the rate of formation of monoclinic phases.

Abstract: In this work it was investigated the influence of CTAB surfactant concentration on the synthesis of the compound Mn_0.75Zn_0.25Fe₂O₄ by the coprecipitation method. It was also compared the influence of hydrothermal treatment on the synthesized materials. The magnetic properties were characterized by AC susceptometry for the determination of the magnetic susceptibility and magnetic density energy. The phases, crystal structure and morphology of the nanoferrites were determined by Rietveld analysis of X-ray diffraction data. It was found the presence of two phases: Franklinite and Akaganeite and it was shown that the samples synthesized only by coprecipitation presented the tendency to increasing the crystallite sizes of the akaganeite phase and decreasing of crystallite sizes of the Franklinite phase as a function of CTAB concentration. The samples submitted to subsequent hydrothermal treatment presented a tendency to decreasing the crystallite sizes of both phases and increasing in Franklinite phase fraction, compared to the samples synthesized only by coprecipitation, suggesting that the hydrothermal treatment was effective in obtaining nanostructured materials of smaller particles.

Abstract: Silicon dioxide is the most common silicon compound and a major constituent of the Earth’s crust. Silicon dioxide, also known as silica, is a chemical compound that is an oxide of silicon with the chemical formula SiO₂. Silica is most commonly found in nature as quartz. Quartz exists in natural and synthetic forms. More specifically α-quartz is a widely known material, which is stable at low temperatures and pressures. The α-quartz is considered competent material because over the past many years it has attracted wide attention due to its unique characteristics. The article presents the research results from comparison between one of the morphological varieties of quartz – vein quartz of shungite rocks from Zazhogino deposit of Karelia – and a reference quartz sample. Via the Rietveld method, the values of the lattice parameters are determined. Apparent coherent length for vein quartz samples having contacts with various minerals are determined by the approximation method.

Abstract: In this study, phosphocalcic coatings on titanium alloy Ti6Al4V substrate are elaborated using Electrodeposition (ELD) by adding optimized amount of hydrogen peroxide H₂O₂ into the electrolyte. Structural analysis is performed by X Rays Diffraction and the data are treated using the RIETVELD method. The characterization of the coatings elaborated by ELD showed that the H₂O₂ amount variation has an influence on the morphology, the crystal size and the chemical composition (monophasic or biphasic) of the coatings.

Abstract: For cement-matrix materials, the microstructure plays a vital important role in the research. Recently, quantitative phase analysis of cementitious materials can be performed using the Rietveld method by fitting the calculated X-ray diffraction (XRD) profile with the observed one. The aim of this paper is to further perform the quantitative analysis by the Rietveld method and discuss the influence of testing factors on the Rietveld quantitative phase analysis. The factors included the collection range of pattern, step size and the scan time of per step. In this study, the chemical composition of the samples was determined by X-ray fluorescence (XRF) spectrometry. And their phase composition was calculated by X-ray powder diffraction and Rietveld analysis. The results showed that the collection range of pattern depended on the tested materials , and the scanning range should include the main diffraction peak of the sample. Smaller step size and longer scan time of each step made the fitting factor smaller, also the calculated pattern coincided with the measured pattern, better enhance the precision of the analyses.

Abstract: TheAl₂O₃-YAG biphasic composite has been extensively studied since this system has important properties such as high resistance to corrosion and creep in harsh environments. This material system is potentially very attractive for high temperatures applications. In this work, the precursor powders of Al₂O₃ and Y₂O₃, were homogenized in planetary ball mill for 2h, dried in oven at 120oC for 48h, sieved and deagglomerated. It was performed a series of heat treatments over the powder for verification of the YAG phase formation, using1100, 1200, 1300°C and 1400 °C for 3.0 h time. The powders of the starting mixture after grinding and calcinations were characterized for phase quantification using the Rietveld method. The complete formation of the YAG phase in the composite was determined at1300°C after 3h.

Abstract: Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) is used for dental prosthodontics, however, it can present accelerated tetragonal to monoclinic phase transformation in oral environment. The aim of this study was to compare the behavior of a Y-TZP synthesized in laboratory by the coprecipitation method to a commercial Y-TZP, after hydrothermal aging in pressurized reactor (150°C/ 35 hours). The discs were sintered at 1520°C for two hours. The kinetics curve of phase transformation was determined through the data collect by XRD diffractograms treated by the Rietveld method. The experimental and commercial control groups did not present monoclinic phase. After 35 hours of aging, the experimental group presented 69% of monoclinic phase compared to 67% for the commercial group. Scanning electron microscopy and atomic force microscopy images suggested that the commercial group presented heterogeneity of grain size and that the experimental group was more homogeneous. All groups presented superficial degradation process.