Evolution Of Crystalline Phases Research Articles

Sol–gel grown Fe-doped ZnO nanoparticles: antibacterial and structural behaviors

Bacterial resistance to antibiotic treatment is an attractive issue. The discovery of new antibiotics often does not respond to the rapidly increasing bacterial resistance and needs innovative approaches to combat bacterial infections. The NPs size-dependent strong anti-bactericidal effect of Zn1−x Fe x O is inspected. Iron (Fe)-doped zinc-oxide (ZnO) nanoparticles (NPs) with composition Zn1−x Fe x O, where x = 0.0, 0.01, 0.03, and 0.05 are synthesized by sol–gel method from nitrate precursors and gelatin at fixed calcination temperature of 650 °C maintained for 2 h. The effects of Fe contents on the antibacterial and structural features of these NPs are inspected. XRD patterns display the single-crystalline nature of samples that exist in hexagonal wurtzite phase. SEM images reveal the existence of nearly spherical-shaped single-crystalline NPs. The observed broadening in the X-ray peaks confirms the evolution of crystalline phases in Zn1−x Fe x O NPs. A quantitative analysis of the size-dependent strain effects is performed through Williamson–Hall and size–strain plot, and its impact of strain on peak broadening is demonstrated. The values of strain, stress, and energy density are calculated. The estimated NPs mean size from FESEM and size–strain plot (SSP) is found to be in close agreement. ZnO NPs in the presence of Fe show some inhibition toward E. coli bacterial growth. Fe acting as impurity in the ZnO nanostructure enhances the power oxidation of ZnO resulting in an augmentation of antimicrobial activity.

Effect of annealing temperature on the structural and magnetic properties of CTAB-capped SrFe12O19 platelets

The use of surfactant such as cetyl-trimethyl ammonium bromide (CTAB) in producing highly coercive SrFe12O19 platelets is presented in this study. The synthesis of SrFe12O19 was accomplished by co-precipitation in presence of 1wt% CTAB. The CTAB-coated precipitant thus obtained was subjected to annealing at different temperatures: 700, 800, 900 and 1000°C. The annealed counterparts were characterized with respect to their structural and magnetic properties and the results are compared with that of those processed without CTAB. Thermogravimetry analysis was employed to study the thermo-chemical behavior for the SrFe12O19 samples. The evolution of crystalline phases as a function of annealing temperature was studied using x-ray diffraction. For the SrFe12O19 samples without CTAB, formation of α-Fe2O3 secondary phases are noticed at annealing temperatures of 700 and 800°C; while such a secondary phase formation is not evident for the CTAB-capped SrFe12O19. Fourier transform infrared spectroscopy of the samples annealed at 1000°C showed deformation in the structure due to the splitting of the bands. Both morphology and composition of the samples were examined by a field-emission scanning electron microscope attached with energy dispersive x-ray analysis. The morphology of CTAB-capped SrFe12O19 samples showed the presence of hexagonal platelets at higher annealing temperatures. The magnetic parameters such as saturation magnetization, MS and coercivity, HC were evaluated from the magnetic hysteresis loops obtained by vibrating sample magnetometer. Maximum values of HC (6.3kOe) and MS (42.7emu/g) were obtained for the CTAB-capped SrFe12O19 samples annealed at 900°C. The possible mechanism on the formation of M-type hexagonal phase with platelet morphology using minimal amount of CTAB (1wt%) in achieving high the HC values for the SrFe12O19 is discussed.

Hydrogen production by methane reforming with H2S using Mo,Cr/ZrO2–SBA15 and Mo,Cr/ZrO2–La2O3 catalysts

A series of supported catalysts based on ceramic type supports (ZrO2–SBA15 and ZrO2–La2O3) and refractory metals (Mo,Cr) were prepared and tested in the methane reforming with hydrogen sulfide (H2S). The main products of the reaction were hydrogen (H2) and carbon disulfide (CS2). The physicochemical properties of these catalysts were characterized by XRD, STEM and N2-BET methods mainly. The evolution of crystalline phases along the reaction led to formation of sulfides and carbides, i.e., MoS2, ZrS2 and the carbides MoC, Mo3C2, which could be the active phases. At high temperatures (1073 K–1123 K) the SBA-15 structure collapses while formation of mixed phases occurs i.e., ZrSiO4; the CH4 and H2S conversion rates were dependent on temperature and catalysts composition, however, the evolution of crystalline phases at high temperatures seems essential for achieving high activity and selectivity.

CaCO3 Crystallite Evolution during CaO Carbonation: Critical Crystallite Size and Rate Constant Measurement by In-Situ Synchrotron Radiation X-ray Powder Diffraction

In this work, the evolution of the CaCO3 crystalline phase during the CaO–CO2 reaction was investigated by means of in situ synchrotron radiation X-ray powder diffraction performed at the Advanced Photon Source (APS) facilities of the Argonne National Laboratory. CO2 absorption experiments were carried out in a high temperature reaction capillary with a controlled atmosphere of pure carbon dioxide (CO2 partial pressure of 1 bar) and in the temperature range between 450 and 750 °C, using CaO-based sorbents obtained by calcination of commercial calcium carbonate. The Rietveld refinement method was applied to estimate the average size of the CaCO3 crystallites formed during a carbonation time of 20 min, as a function of the carbonation temperature and of the initial calcination conditions. Local maxima were observed in the CaCO3 crystallite size versus time curves and were identified as the critical CaCO3 crystallite sizes, marking the transition between the first fast carbonation stage and the second reacti...

Development of barium boron aluminosilicate glass sealants using a sol–gel route for solid oxide fuel cell applications

A key problem in the fabrication of planar solid oxide fuel cells is the sealing of the metallic interconnect to the ceramic electrolyte. The sealing material must be gas-tight, stable in different atmospheres at high temperature, chemically compatible with the other cell components and resistant to thermal stresses. Glass–ceramic sealants are good candidates because of their high mechanical properties and the possibility to use a wide range of chemical compositions to control some physical properties like viscosity or coefficient of thermal expansion (CTE). In this work, glass sealants were synthesized using a sol–gel route, which generally allows to obtain both homogeneity at a nanoscale and reduction of the processing temperature. The studied glasses were based on the system BaO–B2O3–Al2O3–SiO2 with varying amounts of CaO and MgO additions. Dilatometry, differential thermal analysis and hot-stage microscopy were the techniques used to determine optimal thermal treatment for sealing operation (880 °C with a dwell time of 10 h). The thermomechanical properties of the sealants were improved after sealing by a thermal treatment transferring the sealant into a favourable partially polycrystalline state. Gas-tightness tests performed after joining and 100 h ageing treatment at 800 °C under air of steel-sealant-steel assemblies highlighted that 4 of the selected glass chemical compositions remained impermeable. Joining degradations, crystalline phases evolution and CTE of these glasses were analysed. Electrical resistivities were larger than 105 Ω cm at 700 °C. On the basis of these results, four glasses were identified as promising candidates for this application.

Synergistic effect of zero-dimensional spherical carbon nanoparticles and one-dimensional carbon nanotubes on properties of cement-based ceramic matrix: microstructural perspectives and crystallization investigations

In the present investigation, hybrid effect of spherical carbon nanoparticles and carbon nanotubes as zero- and one-dimensional entities, respectively (synthesized by novel CVD route), on properties of cement ceramic matrix was studied. Ceramic matrix composites were fabricated using different dosages (% by wt. of cement) of as-synthesized nanoadditive (labeled as rCNTs) and tested for their resistance to compression at increasing hydration curing times of 7, 14, and 28 days. Evolution of different inorganic crystalline phases in composites was examined using X-ray diffraction (XRD). Improvement in mechanical behavior of composites was explained on the basis of microstructural observations using field emission scanning electron microscopy (FE-SEM). Electrical behavior was evaluated using four-probe method and it was observed that addition of nanoadditive had a semiconducting influence on ceramic matrix composites. Thermal behavior of composites was investigated using thermogravimetric analysis (TGA) and compared with that of unreinforced counterpart. All the properties of rCNT composites were compared with carbon black (pCB) cement mortar nanocomposites. Obtained results indicated a maximum improvement of 13.5% in strength in case of 0.125% rCNT cement mortar composite. Electrical and thermal properties were improved with incorporation of rCNTs indicating significant potential for the practical application of low-cost novel rCNT in the preparation of cement-based materials of high strength and smart functionality.

Microstructure and dielectric properties of BaxSr1−xTiO3 ceramics prepared by direct current arc discharge technique

A direct current arc discharge technique has been employed to prepare BaxSr1−xTiO3 ceramics. The effect of sintering temperature and dwell time on the crystalline structure, phase and morphology evolution are briefly studied. The results show that with the increase of sintering temperature and dwell time, the structure becomes more homogeneous, but a small amount of BaTi4O9 phase can still be traced. We also present data on dielectric permittivity measurements made in the temperature range from −165 to 200 °C with frequencies from 0.1 to 100 kHz. Except for Curie temperature (Tc) for BaxSr1−xTiO3 ceramics, a new phase transition for BaTi4O9 can be detected.

Directly patternable high refractive index ferroelectric sol–gel resist

The development of a ferroelectric negative tone sol–gel resist for Ultraviolet (UV) and Electron Beam (EB) lithography is presented. A new system based on Lead Zirconate Titanate (PZT, with formula PbZr0.52Ti0.48O3) was synthesized by sol–gel method. The lithographic performances were investigated and several structures spanning from the micron range down to less than 50 nm have been achieved by UV and EB lithography. The system interaction with UV light and Electron beam was thoroughly characterized by FT-IT spectroscopy. The exposed PZT was annealed at high temperatures in order to study the crystalline phase evolution, the optical constants values and stability of patterned structures. After exposure and annealing, the refractive index of the material can vary from 1.68 up to 2.33 (@400 nm), while the ferroelectric behaviour seems to be maintained after high temperature annealing. These results suggest a possible application of PZT resist not only as ferroelectric but also as nanopatternable high refractive index material. Moreover, direct nanopatterning by means of Focused Ion Beam (FIB) lithography was verified and the potentiality for the preparation of high aspect ratio hollow nanostructures will be presented.

Study of the Evolution of Phase Calcium Aluminate through the Method for Polymeric Precursors C<sub>12</sub>A<sub>7</sub>

The synthesis of ceramic materials from polymeric precursors has been the subject of numerous studies due to lower energy cost compared to conventional processing. The study aims to research and develop synthesis of calcium aluminate powders via the polymeric precursor method, in order to obtain the pure phase of hepta-aluminate dodecálcio (C12A7) with mayenita mineral name, since it has applications like: special cements and components for high temperature fuel cells. A study of the evolution of crystalline phases by X-ray diffraction was performed, the vibrational modes of atomic location in crystalline phases were studied by micro-Raman spectroscopy was also performed and images from scanning electron microscopy. From the characterizations carried out on the material can be seen that the sintering temperature of 1200°C was obtained pure phase, so the choice of synthesis shown to be effective due to the complexity of obtaining this phase pure.

Real time observation of phase formations by XRD during Ga-rich or In-rich Cu(In, Ga)Se2 growth by co-evaporation

Solar cells with Cu(In, Ga)Se2 absorbers rely on the three-stage co-evaporation process with Cu-poor/Cu-rich/Cu-poor absorber deposition conditions for highest efficiency devices. During the three-stage process, the formation and evolution of different selenide phases with changing compositions throughout the process crucially determine the final absorber quality. In this contribution, we monitor the evolution of crystalline phases in real-time with an X-ray diffraction (XRD) line detector setup implemented into an evaporation setup. Using the common three-stage process, we prepare and compare samples covering the full alloying range from CuInSe2 to CuGaSe2. The in situ XRD allows the detection of the crystalline phases present at all times of the process as well as an advanced analysis of the phase evolution through a closer look at peak shifts and the full width at half maximum. For samples with a Ga/(Ga + In) ratio (GGI) < 0.5, distinct phase transitions associated with the transition to the reported vacancy compounds Cu(In,Ga)5Se8 and Cu(In, Ga)3Se5 are observed. No such indication was found for samples with a GGI > 0.5. For Ga-rich Cu(In, Ga)Se2 phases with a GGI of 0.55, the XRD analysis evidenced a Ga-rich phase segregation before the stoichiometric point was reached. The above findings are discussed in view of their implication on wide gap solar cell performances.

Confined self-assembly of cellulose nanocrystals in a shrinking droplet

We have studied how cellulose nanocrystals (CNC) self-assemble into liquid crystalline phases in shrinking, isolated droplets. By adjusting the water dissolution rate of an aqueous CNC droplet immersed in a binary toluene-ethanol mixture we can control the final morphology of the consolidated microbead. At low ethanol concentration in the surrounding fluid dense microbeads of spherical morphology are produced while collapsed core-shell particles are obtained at high ethanol concentration. Polarized light microscopy was used to follow the spatial evolution and coalescence of birefringent spheroids during droplet shrinkage. Electron microscopy reveals the resultant nematic microstructure. This method of confined CNC assembly provides thus the possibility to prepare ordered microbeads, which can be useful as templates or for their optical properties.

Hydration and carbonation reactions of calcium oxide by weathering: Kinetics and changes in the nanostructure

The weathering reactions of hydration and carbonation of nanostructured calcium oxide with atmospheric moisture and carbon dioxide have been characterized. This work is the first-to-date combined kinetic and nanostructural research on CaO oriented to two key processes for different systems, i.e. hardening of construction materials and carbon mineral sequestration. The evolution of the precipitated crystalline phases was monitored by X-ray diffraction and thermogravimetry, along with structural characterization by nitrogen physisorption, electron microscopy and small-angle scattering. Complete hydration of the samples was always found prior to the onset of carbon sequestration, which depended on the nanostructure of the samples. Hence, carbonation started after 300h of weathering for samples with a specific surface area of 40m2/g, whereas carbonation of the samples with 20m2/g occurred after 550h. Full carbonation from atmospheric CO2 (100% efficiency) was obtained in all cases. This combined research was completed by developing an empirical description of the weathering reactions in terms of a two-process Random Pore Model. Finally, this work aimed to determine the role of the nanostructure of samples based on industrial wastes as one of the most important factors for developing efficient carbon sequestration technologies.

Synthesis temperature effect on Na-Mica-4 crystallinity and heteroatom distribution

The discovery of swelling brittle mica, Na-Mica-4, has been one of the most significant advances in the pursuit for a material with high ion-exchange capacity. For technical applications, the control of the phase evolution during the synthesis is crucial. The main aim of this study was to investigate the effect of Na-Mica-4 synthesis temperature on the crystalline phase evolution, Si–Al distribution in the tetrahedral sheet, the Al occupancy between tetrahedral and octahedral sites and their effects on the interlayer space composition. The synthesis temperature range between 600°C and 900°C was explored. At low temperature (600°C), the precursors were transformed in a low-charged swelling 2:1 phyllosilicate, saponite type, which was progressively aluminum enriched with temperature. The high-charged swelling mica was completely formed at 700°C, although a minor anhydrous contribution remained up to 850°C. Up to 800°C, silicates and fluorides secondary phases were detected as a minor contribution.

Quantitative firing transformations of a triaxial ceramic by X-ray diffraction methods

The firing transformations of traditional (clay based) ceramics are of technological and archeological interest, and are usually reported qualitatively or semiquantitatively. These kinds of systems present an important complexity, especially for X-ray diffraction techniques, due to the presence of fully crystalline, low crystalline and amorphous phases. In this article we present the results of a qualitative and quantitative X-ray diffraction Rietveld analysis of the fully crystalline (kaolinite, quartz, cristobalite, feldspars and/or mullite), the low crystalline (metakaolinite and/or spinel type pre-mullite) and glassy phases evolution of a triaxial (clay-quartz-feldspar) ceramic fired in a wide temperature range between 900 and 1300 ºC. The employed methodology to determine low crystalline and glassy phase abundances is based in a combination of the internal standard method and the use of a nanocrystalline model where the long-range order is lost, respectively. A preliminary sintering characterization was carried out by contraction, density and porosity evolution with the firing temperature. Simultaneous thermo-gravimetric and differential thermal analysis was carried out to elucidate the actual temperature at which the chemical changes occur. Finally, the quantitative analysis based on the Rietveld refinement of the X-ray diffraction patterns was performed. The kaolinite decomposition into metakaolinite was determined quantitatively; the intermediate (980 ºC) spinel type alumino-silicate formation was also quantified; the incongruent fusion of the potash feldspar was observed and quantified together with the final mullitization and the amorphous (glassy) phase formation.The methodology used to analyze the X-ray diffraction patterns proved to be suitable to evaluate quantitatively the thermal transformations that occur in a complex system like the triaxial ceramics. The evaluated phases can be easily correlated with the processing variables and materials properties. These correlations can be employed for materials characterization, design and processing control.

Evolução da resistência mecânica e dos produtos de hidratação de um cimento de aluminato de cálcio, visando sua aplicação em endodontia

Atualmente o agregado trióxido mineral (MTA) é o cimento mais utilizado para retrobturação em endodontia. Porém, apesar de sua composição ser semelhante a do cimento Portland convencional, seu elevado custo, longo tempo de endurecimento e baixa resistência mecânica tem motivado a busca por materiais alternativos para esta aplicação. Baseado nisto, neste trabalho foi avaliado a evolução da resistência mecânica e das fases cristalinas durante a hidratação de um cimento de aluminato de cálcio (CAC), visando seu uso em tratamentos endodônticos. Para isto, amostras do cimento Secar 71 foram preparadas e mantidas em contato com água ou SBF (simulated body fluid) ao longo de 15 dias a 37 ºC. Ensaios de compressão uniaxial, porosidade aparente, difração de raios X e termogravimetria foram utilizados na avaliação dos corpos de prova após 1, 3, 7 e 15 dias de cura. Verificou-se que as principais fases formadas foram CAH10, C2AH8, C3AH6 e AH3. Quando em presença de SBF, devido ao seu efeito retardador algumas mudanças na quantidade dos produtos de hidratação do CAC foram observadas, causando efeitos na resistência mecânica do mesmo. Além disso, o presente estudo aponta que a antecipação ou retardamento da formação de algumas fases pode induzir alterações nas propriedades dos cimentos.

Crystallization Behaviors of CaO-SiO2-Al2O3-Na2O-CaF2-(Li2O-B2O3) Mold Fluxes

The effects of basicity (CaO/SiO2), B2O3, and Li2O addition on the crystallization behaviors of lime-silica-based mold fluxes have been investigated by non-isothermal differential scanning calorimetry (DSC), field emission scanning electron microscopy, X-ray diffraction (XRD), and single hot thermocouple technique. It was found that the crystallization temperature of cuspidine increased with increasing the basicity of mold fluxes. The crystallization of wollastonite was suppressed with increasing the mold flux basicity due to the enhancement of cuspidine crystallization. The addition of B2O3 suppresses the crystallization of mold flux. The crystallization temperature of mold flux decreases with Li2O addition. The size of cuspidine increases, while the number of cuspidine decreases with increasing mold flux basicity. The morphology of cuspidine in mold fluxes with lower basicity is largely dendritic. The dendritic cuspidine in mold fluxes is composed of many fine cuspidine crystals. On the contrary, in mold fluxes with higher basicity, the cuspidine crystals are larger in size with mainly faceted morphology. The crystalline phase evolution was also calculated using a thermodynamic database, and compared with the experimental results determined by DSC and XRD. The results of thermodynamic calculation of crystalline phase formation are in accordance with the results determined by DSC and XRD.

Non-isothermal crystallization kinetics of a Si–Ca–P–Mg bioactive glass

In this work, the crystallization process of a SiO2–3CaO·P2O5–MgO glass was studied by non-isothermal measurements using differential thermal analysis carried out at various heating rates. X-ray diffraction at room and high temperature was used to identify and follow the evolution of crystalline phases with temperature. The activation energy associated with glass transition, (E g), the activation energy for the crystallization of the primary crystalline phase (E c), and the Avrami exponent (n) were determined under non-isothermal conditions using different equations, namely from Kissinger, Matusita & Sakka, and Osawa. A complex crystallization process was observed with associated activation energies reflecting the change of behavior during in situ crystal precipitation. It was found that the crystallization process was affected by the fraction of crystallization, (x), giving rise to decreasing activation energy values, E c(x), with the increase of x. Values ranging from about 580 kJ mol−1 for the lower crystallized volume fraction to about 480 kJ mol−1 for volume fractions higher than 80 % were found. The Avrami exponents, calculated for the crystallization process at a constant heating rate of 10 °C min−1, increased with the crystallized fraction, from 1.6 to 2, indicating that the number of nucleant sites is temperature dependent and that crystals grow as near needle-like structures.

Glass–Ceramic Foams from Borosilicate Glass Waste

In this study, we reported the studies on a glass–ceramic foam with wollastonite and cristobalite micrometric crystals prepared by sintering a borosilicate glass waste with organic binder as foaming agent. The waste glass, coming from the dismantling of washing machine, was characterized by high CaO content and low‐temperature sinterability. The effect of the temperature on the sinter‐crystallization ability of the borosilicate glass waste was followed with thermal analysis, heating microscopy, and electron scanning microscopy (ESEM) observations. Additionally, the effect of temperature on the evolution of crystalline phases and density variation was monitored with XRD and density measurements. The softening started at 800°C and crystallization at 845°C to be completed at 900°C with a linear expansion of 38–40% in the range 850–900°C. Wollastonite and cristobalite were identified as crystalline phases in variable proportions dependently upon temperature. No crack evidence was found at high ESEM magnification even though cristobalite crystals were present. The final products showed a total porosity around 78–79% and an apparent density of about 0.5 g/cm3, in line with common porous closed‐cell glass foams used for thermal insulation.

Incinerator Bottom Ash and Ladle Slag for Geopolymers Preparation

Ladle slag (LS) and urban incineration bottom ash (BA) are two types of non hazardous inorganic wastes which do not contain significant amounts of pollutants such as heavy metals and organics. Nowadays they are necessarily disposed of with little attention placed for re-use or recycling. Considering their chemical composition, rich in silica and alumina with substantial levels of lime and iron oxides, these residues can be suitable for generating new alkali activated materials. A safe reuse of these residues in high percentages (60–70 wt%) is presented in this study for mortar production. The final room-temperature consolidated materials, also known as geopolymers, have been characterized in terms of thermogravimetric analysis, morphology, porosity, and crystalline phases evolution. When incinerator BA is used, the morphology of the resulting geopolymer is very close to that of pure metakaolinic pastes, whereas for LS based geopolymers calcium presence promotes the formation of calcium–aluminate–silicate–hydrate phase. This investigation also demonstrated that the content of reactive fraction of BA is of primary importance to assess its possible use in alkaline activation process.

Thermal and mechanical stability of lanthanide-containing glass–ceramic sealants for solid oxide fuel cells

Thermal stability of lanthanide (Ln = La, Nd, Gd, Yb) containing glass and glass–ceramics (GCs) was characterized for their application as sealants for solid oxide fuel cells (SOFCs). X-ray diffraction (XRD) in conjunction with the Rietveld-RIR and solid-state NMR techniques was employed to quantify the crystalline and amorphous fractions in the glasses sintered/heat treated at 850 °C in air for 1–1000 h. The structure and crystalline phase evolution of Ln containing aluminosilicate glasses depend markedly on the Ln3+ cation field strength over both short and intermediate length scales. Along with diopside, Ln containing silicate apatites, with general formula Ln9.33+2x(Si1−xAlxO4)6O2 (Ln = La, Nd and Gd; with x varying between 0 and 0.33), were observed in the GCs after the heat treatment periods of 1 to 1000 h at 850 °C, leading to moderately higher electrical conductivity. The substantial amount of the remaining glassy phase in Gd2O3-containing GC after 1000 h at 850 °C is likely to confer self-healing properties to this composition, in accord with the oxygen leakage measurements on thermal cycling. 29Si, 27Al and 11B magic-angle spinning (MAS) NMR spectra confirmed the results of the XRD RIR analysis. The values of Weibull characteristic strength and of average flexural strengths for all the GCs are higher than those reported for G-18 commercial glass (51 MPa), with Weibull modulus varying in the range 11.6–34.4 towards good mechanical reliability. Thermal shock resistance of model electrochemical cells made of yttria-stabilized zirconia (YSZ) was evaluated employing quenching from 800 °C in air and water. All the GC seals bonded well to YSZ and Sanergy HT metallic interconnects without gap formation. Suitable thermal expansion coefficient (9.7–11.1 × 10−6 K−1), mechanical reliability, high electrical resistivity, strong adhesion to Sanergy HT interconnects and YSZ, and sufficient thermal shock resistance indicate good suitability of the lanthanide-containing sealants for SOFC applications.