Mössbauer effect study of the Fe-substituted NASICON

Fe-substituted NASICON was prepared by co-precipitation method and the content of iron at different oxidation states was estimated by Mössbauer spectroscopy (MS). Compounds with different phase composition were obtained depending on the preparation procedure. In the case of samples sintered in reducing atmosphere, NASICON containing di- and trivalent iron was detected. The lattice constants were calculated by Rietveld method. Higher values of the unit cell parameters for Na₃Zr_1−yFe_1−y²⁺Fe_2y³⁺P₃O₁₂ compared to the structural analogue γ-Na₃Fe₂P₃O₁₂ indicated the partial replacement of smaller Fe³⁺ ions by bigger Fe²⁺ and Zr⁴⁺ in the NASICON lattice. The validation of Mössbauer spectroscopy as the useful tool in the calculation of iron content was also performed. The sintering in air led to the multiphase product, which was identified by XRD and MS.     

Reaction mechanism of tin nitride (de)lithiation reaction studied by means of Sn Mössbauer spectroscopy

Tin nitride thin films have been reported as promising negative electrode materials for lithium-ion solid-state microbatteries. However, the reaction mechanism of this material is not yet fully understood. Results on thin film electrodes pointed out that the conversion mechanism of tin nitride most likely differs from the conversion mechanism usually observed for other oxide and nitride conversion electrode materials. The electrochemical data showed that more than six Li per Sn atom can be reversibly exchanged by this material while about four are expected. In order to investigate in more detail the reaction mechanism of tin nitride, thick film electrodes of two compositions (1:1 and 3:4) have been studied. The as-prepared materials were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and ¹¹⁹Sn Mössbauer spectroscopy. Moreover, films (de)lithiated to various extents were analyzed ex situ with Mössbauer spectroscopy. The corresponding results indicate that a more complex reaction mechanism than that generally accepted takes place. During Li-ion insertion, the disappearance of Sn⁴⁺ environments is correlated with the formation of Li-Sn phases, and most likely also of Li₃N. In the case of the SnN_x 1:1 composition films, the formation of various Li-Sn phases is evidenced while only the signature of ‘Li₂₂Sn₅’ is clearly measured for the 3:4 composition. Upon Li-ion extraction, the Li-Sn phases and Li₃N recombine to form octahedrally and tetrahedrally coordinated Sn⁴⁺. The extraction is not fully reversible and the end product consists of a mixture of a tin nitride structure plus a Li_ySn product having the same isomer shift as LiSn but a much higher quadrupole splitting, and most likely some Li₃N.     

Magnetic and Mössbauer behavior of the nanostructured MgFe2O4 spinel obtained at low temperature

This study investigated the solution combustion synthesis technique to obtain the nanostructured magnesioferrite (MgFe₂O₄) spinel powder. The reaction was performed in an electric muffle furnace. Considering the characteristics of the as-synthesized powders, the 30% fuel-deficient formulation was selected for synthesis temperature evaluation. This formulation was synthesized at different furnace temperatures. Powder characterization was carried out by X-ray diffraction (XRD) to evaluate crystallographic analysis and crystallite size; Transmission Electron Microscopy (TEM) was done to assess the morphology and crystallite size; and Mössbauer spectroscopy and vibrational sample magnetometer (VSM) were performed to obtain magnetic measurements. Crystallite sizes estimated from the XRD technique increased with furnace temperature values, which were consistent with the results obtained by TEM. The characterized samples of MgFe₂O₄ had an average crystallite size of 42.8 nm using the DRX method, average saturation magnetization of 25.6 emu/g and coercive field not higher than 11 Oe.     

The relationship between the use of Zijin clay and glaze crackles for Chinese celadon with black body

The celadon with black body is a famous type of ceramic product in ancient China due to its appearance features, black body and crazing glaze, different from regular. For this type of ware, the crazing glaze is a kind of artificial decoration, not production defect. How the glaze crackles were made by ancient potter has always attracted many people's attention. And it has been studied mainly based on chemical composition. In this paper, we aim to provide our discussion and explanation for its sophisticated combinations of crazing glaze and black body. Based on analysis of ancient and modern celadon products, we thought that the difference in quartz content of the fired body is the reason why the celadon with black body is more likely to have crazing glaze than regular. And, the potter could control the expansion coefficient of the body by using Zijin clay with low quartz content as raw material.     

Study on the coloring mechanism of the Ru celadon glaze in the Northern Song Dynasty

The Ru kiln is one of the five most famous kilns in the Chinese Song Dynasty. To clarify the coloring mechanism of the Ru celadon glaze, the celadon samples from the Ru Guan kiln site of Qingliangsi were analyzed by spectrophotometer, X-ray fluorescence spectrum, Raman spectroscopy, scanning electron microscopy and X-ray photoelectron spectrum. The results indicated that the molar ratios of SiO₂/Al₂O₃ and CaO/(CaO + Al₂O₃) affected the formation of micro-bubbles, anorthite crystals and phase separated structures. A large number of bubbles and anorthite crystals formed special glossiness and opacifying effect in the Ru celadon glaze. And then, dense phase separation droplets in the amorphous region were in short-range order, but their diameters (31–46 nm) were too small to form visible structural colors on glaze surfaces. Only “opal effect” was formed by the light scattering, which added the aesthetic feeling for the Ru celadon. Besides, the phase separation droplets intensified the segregation of iron, and thus deepened the chemical color and made the Ru celadon glaze appear green-blue. Due to the neutral to alkaline soil at the Ru Guan kiln site, the water in the soil and its corrosion on the Ru celadon glaze resulted in the formation of Si–OH bond.     

Relaxation dynamics,phase pattern in the vicinity of the Curie temperature,Fe valent state and the Mössbauer effect in PFN ceramics

High-density lead ferroniobate, PbFe_1/2Nb_1/2O₃ (PFN), was prepared by the conventional ceramic technology. Its dielectric properties, phase pattern in the vicinity of transition into the polar phase, and the x-ray electron and Mössbauer spectra were studied. The relaxation dynamics discovered at the temperature exceeding the Curie temperature at the frequencies of 3×10⁻²–10⁵ Hz is described in detail. Near T_C, the following sequence of phase transitions was established: rhombohedral (T<368 K)→pseudocubic (368 K<T<387 K)→cubic (T>387 K). It is shown that in both the ferroelectric and paraelectric phases the Fe ions are, mainly, in a high-spin valent state Fe³⁺ in the octahedral environment.     

In situ Mössbauer spectroscopy of carbon-supported iron catalysts at cryogenic temperatures and in external magnetic fields

A highly dispersed carbon-supported iron catalyst has been studied within situ Mössbauer spectroscopy at temperatures down to 5 K and with external magnetic fields. It is shown that measurements of spectra in the presence of large magnetic fields considerably improves the information obtained from Mössbauer spectra.     

Analysis of the influence of iron source and its occurrence state on the color of celadon glaze

Using different iron sources of industrial iron oxide, loess, slag, and golden soil, iron elements were introduced into the formula respectively, and celadon samples were prepared in a reducing atmosphere. To reveal the influence of iron source on glaze color, the celadon samples were analyzed by Spectrophotometer, X-ray fluorescence spectroscopy, X-ray diffractometer, scanning electron microscope, and X-ray photoelectron spectrometer. The results show that the glaze color of the samples is quite different, samples using iron oxide and golden soil as iron source raw materials are sky-green, the loess sample is olive green, and the slag sample is similar to the bean green. There are many quartz crystals in the glaze of iron oxide samples, and the turbidity is high. The liquid-liquid phase separation size close to the quartz crystal is large, and far away from the crystal is small. Industrial iron oxide is the easiest to reduce, followed by goethite in golden soil, and reduction of hematite in slag and the iron in loess in the form of isomorphic is successively more difficult. The difference in the form of occurrence of iron is the most essential factor that causes the difference in glaze color.     

The mechanism of “flint red” and its relationship with celadon glaze color

"Flint red" is the red narrow band found in the exposed body of porcelain, which is a common phenomenon in ancient porcelain. Some experts believe that flint red is an important symbol for judging the age of ancient ceramics. This paper takes sky-green Yaozhou porcelain as the example, and successfully fired samples of Yaozhou porcelain with flint red, and reveals the formation mechanism of flint red. This study uses XRF (X-ray fluorescence), XRD (X-ray diffraction), SEM (Scanning electron microscope) and non-contact imaging spectrophotometer analysis to discover for the first time that during the reduction process, the iron of the glaze migrates to the body with the melt in the gas phase, and the flint red is a hematite thin film formed on the body after being oxidized for the second time during the cooling process of the kiln. The influence of the redox atmosphere and placement mode of ceramics on flint red were studied. The relationship between flint red and the degree of color reduction of celadon glaze surface was discussed. In addition, the growth method of hematite film is enlightening for the preparation of anticorrosive coatings on steel products, and has broad application prospects.     

粒度对高温色料色度的影响

运用离子呈色理论、晶体场理论,较好地解释了颜色釉的呈色机理,并根据色料的晶体结构及在釉中的存在状态,借助粒度分析仪、色度仪研究了色料的粒度大小对色度的影响规律.     

Characterization of electrodeposited thin layers of magnetic alloys by Mössbauer spectroscopy

Rare earth and transition metal alloys are interesting magnetic materials for applications in the field of magnetooptical memories. We describe the preparation of Dy/Fe alloys by electrodeposition using a pulsed galvanostatic process. Samples were characterized by Mössbauer spectroscopy. Thin layers obtained with short electrolysis pulses (0.1 s) give a Mössbauer spectrum analysed as the sum of two subspectra: the first corresponds to a spectrum originating from very small sized particles of Fe and the second is attributed to a Dy/Fe phase. Longer electrolysis pulses (1 s) give samples whose spectrum is also the sum of two subspectra: the first is attributed to metallic Fe with an extended particle-size distribution while the second is attributed to a Fe/Dy alloy. Mössbauer spectroscopy was found useful in determining the best electrolysis parameters leading to domains of uniform magnetization with high coercive fields.     

Interaction between ammonium sulfate-iron oxide shown by ESR and Mössbauer spectroscopy

The ammonium sulfate-iron oxide system treated at different temperatures has been characterized by ESR, IR and Mössbauer spectroscopy. Results show that during the heat treatment some interaction between ammonium sulfate and iron oxide takes place. As a result of this interaction a surface sulfato complex of iron is formed. The complex is involved in the sites responsible for activity for acid catalytic esterification. Above 573 K, the sulfato complex will gradually decompose with a further increase in temperature. A new structure scheme of the sulfato complex is proposed.     

Mössbauer spectroscopy and neutron activation analysis of ancient Chinese glazes

The optical spectra of the glaze of Ru porcelain made in the Chinese Northern Song Dynasty (AD 960–1126) were measured by the chromatometer to determine the relations between glaze color and its dominant wavelength (λ_D). The concentrations of 30 coloring elements in the glaze were determined by neutron activation analysis (NAA). Iron was the dominant coloring element. Mössbauer spectroscopy detected that iron existed in the state of structural Fe²⁺ and Fe³⁺ ions. A relationship between λ_D of various colored glazes and the Fe²⁺/Fe³⁺ ratio was established. As the Fe²⁺/Fe³⁺ ratio gradually increases, the glaze color of Ru porcelain will gradually change from pea green to sky green. All the Ru porcelains were fired in a reducing atmosphere. The sky green Ru porcelain was fired in the most reducing atmosphere and at the highest temperature, the powder green in a more reducing atmosphere and at a lower temperature and the pea green in a lightly reducing atmosphere and at the lowest temperature.     

Olefin selective carbon-supported K-Fe-Mn CO hydrogenation catalysts: A kinetic,calorimetric, chemisorption,infrared and Mössbauer spectroscopic investigation

Carbon-supported Fe, Fe-Mn, and K-Fe-Mn catalysts derived from stoichiometric mixed-metal carbonyl clusters were pretreated at either 473 K or 673 K in hydrogen. Chemisorption and kinetic measurements were conducted following these pretreatments. The iron remained highly dispersed at all times except after high temperature reductions when potassium was present. The single promotion by either Mn or K increases the olefin/paraffin ratio, while the doubly promoted catalyst gave very high selectivities for light olefins. Isothermal, integral heats of adsorption of CO were determined at 300 K, and they increased from 15 kcal/mole for Fe₃/C to nearly 17 kcal/mole for both the singly promoted Fe₂Mn/C and KFe₃/C catalysts to 21 kcal/mole for the doubly promoted KFe₂Mn/C sample. A model of the decomposition of these carbonyl clusters is proposed based on calorimetric, Mössbauer effect spectroscopic and diffuse reflectance Fourier transform infrared spectroscopic studies. The state of the MnO_x and K phases on the iron surface, as well as the Fe crystallite size, appears to play a dominant role in determining the catalytic behavior.     

Some physical properties of anhydrous and hydrated Brownmillerite doped with NaF

Different samples of Brownmillerite (the ferrite phase of cement clinker) doped with 0, 1 or 3 wt.% NaF were prepared. At first, the oxide mixture of Brownmillerite was prepared according to the following composition: 4 mol CaO, 1 mol Al₂O₃ and 1 mol Fe₂O₃ in addition to 1 or 3 wt.% NaF. Each mixture was mixed very well, introduced into an electric furnace at 1300 °C for 1 h in a platinum crucible, and then quenched in air. The product was divided into four portions mixed with 40 wt.% distilled water to form Brownmillerite paste, except for one portion which was left dry. Each paste was molded into two molds; after 24 h, they were immersed in a distilled water and withdrawn after 1 or 3 days of hydration, respectively. The pastes were ground again. The anhydrous powders of Brownmillerites and the hydrated samples were prepared for a.c. conduction measurements by pressing it to be in pellets form. The two surfaces of each pellet were coated with silver paste. The a.c. conductivity and dielectric constant for different samples were measured using four-probe method. The data was collected from 320 up to 670 K. Mössbauer spectra and X-ray diffraction patterns were measured for each sample (anhydrous and hydrated) to confirm the formation of Brownmillerite, identify the iron states and the magnetic properties. The results showed that NaF addition to Brownmillerite expedites the hydration reaction rate. The superparamagnetic relaxation, which appeared in the anhydrous Brownmillerite spectra due to the small particle size, decreases with increasing the hydration time. Also, the Fe³⁺(Oh) state increases while Fe³⁺(Td) decreases with the time of hydration. The a.c. conductivity value at fixed frequency for anhydrous and hydrated samples was found to increase with NaF addition. The a.c. conductivity and Mössbauer measurements can be used as good tools to verify the purity of Brownmillerite phase and, accordingly, the purity of cement.     

Study on the Five dynasty sky-green glaze from Yaozhou kiln and its coloring mechanism

This work takes the Five dynasty sky-green glaze of Yaozhou kiln as the major study object. Based on the analysis of XRF, XRD, XPS and SEM/EDS, the chemical compositions, firing technique and microstructure of the sky-green glaze were investigated. A possible coloring mechanism was proposed to explain the variation of glaze appearance. The results indicated that the Five dynasty sky-green glaze had relatively high contents of CaO and K₂O, which led to the better gloss and transparency than others. Besides that, the chemical coloring of Fe₂O₃ and the scattering of phyical structures also affected the color saturation and opacity of glaze surface. The high Fe²⁺/Fe³⁺ ratio and phase separation droplets of forming structural color by the amorphous photons and Rayleigh scattering contributed to increasing the blue tone of sky-green glaze. In addition, the residual crystals decreased the transparency of glaze surfaces.     

Colouring mechanism and firing process of celadon from the Xiangzhou kiln in Anyang,China, from the 5th-7th century

The Xiangzhou kiln was the largest celadon kiln site in northern China from the Northern and Southern Dynasties to the Sui Dynasty (5th-7th centuries). In order to investigate the colouring mechanisms and firing process of two types of celadon (yellow-green and earthen-yellow glazes) from the Xiangzhou kiln, samples were tested and analysed using OM, ED-XRF, TD, SEM-EDS, LRS, XPS and UV-Vis-NIR. The study results show that most of the samples in the two enamels have different formulations. The celadon glaze of the Xiangzhou kiln contains a small amount of quartz, anorthite and other crystals. The yellow-green glaze is fired in a reducing atmosphere and the earthy yellow glaze is fired in an oxidising atmosphere. The colouring mechanism of the Xiangzhou kiln celadon is mainly dominated by the chemical colouring of ionic colouring and aided by structural colouring caused by the microstructure (bubbles, various crystals, fractal structures, etc.).     

Carbon monoxide hydrogenation on Fe2O3/ZrO2 catalysts

Fe₂O₃/ZrO₂ catalysts prepared by impregnation and coprecipitation methods were used for catalytic hydrogenation of CO. It was shown that the structure, reduction behavior of iron species, and catalytic properties of the catalysts were obviously affected by the preparation methods. For the Fe₂O₃/ZrO₂ catalyst prepared by the impregnation method, the Fischer-Tropsch catalytic activity and the selectivity to light olefins were much higher than those of the corresponding catalyst prepared by the coprecipitation method, the formation of methane was suppressed and the selectivity to light olefins was enhanced. Various intermediates formed during the successive steps of reduction of the catalysts were studied by using temperature-programmed reduction combined with in situ Mössbauer spectroscopy. The role of zirconia in the catalysts was discussed.     

Data-driven research on chemical features of Jingdezhen and Longquan celadon by energy dispersive X-ray fluorescence

The energy dispersive X-ray fluorescence (EDXRF) is used to determine the chemical composition of celadon body and glaze in Longquan kiln (at Dayao County) and Jingdezhen kiln. Forty typical shards in four cultural eras were selected to investigate the raw materials and firing technology. Random forests, a relatively new statistical technique, has been adopted to identify chemical elements that are strongest explanatory variables to classify samples into different cultural eras and kilns. The results indicated that the contents of Na₂O, Fe₂O₃, TiO₂, SiO₂ and CaO vary in celadon bodies from Longquan and Jingdezhen, which implies that local clay was used to manufacture celadon bodies in Jingdezhen kiln. By comparing the chemical composition in glaze, we find that the chemical elements and firing technology of Jingdezhen kiln are very similar to those in Longquan kiln, especially for Ming dynasty. This study reveals the inheritance between Jingdezhen kiln and Longquan kiln, and explains the differences between two kilns.