Production and characterisation of iron-chromium pigments and their interactions with transparent glazes

In this study, production and characterisation of pigments by using less expensive raw materials such as limonite and chromite was undertaken. The resulting pigments were characterised by using X-ray diffraction (XRD) and UV-Vis spectrophotometer. The colour of glazed tiles containing 3 wt.% pigment change from dark brown to light brown depending on the calcination temperature and limonite content. With pigments prepared with 50% limonite content calcined at 1250 °C, the chocolate brown colour was obtained corresponding to the commercial brown pigments. An iron-chromium black pigment was synthesised from a mixture of pure chromium (III) oxide (Cr₂O₃) and iron (III) oxide (Fe₂O₃) powders and was used to determine possible interactions between a pigment and a transparent glaze. The interactions were studied using a scanning electron microscope (SEM) attached with an energy dispersive X-ray spectrometer (EDX). The results showed that black pigment particles give brown colour to the glaze. EDX analysis on pigment crystals embedded in the glaze clearly showed that Zn and Mg diffused into pigment crystals and caused a change of colour from black to brown.     

Stability of (Cr)CaO.SnO2.SiO2 pink pigment in ceramic frits

Abstract

Incorporation of the (Cr) CaO.SnO₂.SiO₂ pigment in ceramic glazes yields colours with a red component the hue of which depends on the nature of the frits used to produce the glazes. Several samples were prepared by adding this pigment to different frits commonly used in the manufacture of glazed ceramic tiles, each sample subsequently being fired at the appropriate maturing temperature. A study of the resulting glazes shows that variations in colour arise as a result of the three possible phenomena which may develop in firing depending on the frit composition used. These three phenomena are pigment dissolution in the glassy phase, devitrification of crystalline phases whose nature differs from that of the pigment, and immiscible glassy phase separation.     

Production of brown pigments for porcelain insulator applications

In this study, production of brown pigment for the ceramic insulator applications by using inexpensive natural raw materials or waste materials was undertaken. Different pigment compositions were designed, synthesised and examined. As a source of chromium, chromite, Cr₂O₃ and ferrochrome were used. Limonite, grinding waste, flotation waste and iron oxide scale were used as an iron source whereas manganese oxide and ferromanganese were used as a manganese source. The colour of glazed insulator bodies change from dark brown to light brown depending on the pigment composition. The pigments prepared with ferrochrome, manganese oxide, flotation waste (C6) or iron oxide scale (D4) and calcined at 1300 °C have a darker brown colour and possess suitable L*a*b* values as 30.1, 2.7, 1.6 for C6 and 30.9, 2.1, 0.3 for D4, which are closer to the L*a*b* values (30.1, 2.9, 0.1) of commercial MnFeCr pigments. The results indicate that waste materials containing iron can be used to produce brown pigments to be used in the insulator application in ceramic industry and as a result of this waste material can be converted into a value-added product. Also, ferrochrome can be used successfully as chromium source and help to reduce the cost of the pigment.     

Combination of ACO-artificial neural network method for modeling of manganese and cobalt extraction onto nanometer SiO2 from water samples

In this study, modeling based on ant-colony optimization – artificial neural network have been employed to develop the model for simulation and optimization of nanometer SiO₂ for the extraction of manganese and cobalt from water samples. The pH, time, amount of SiO₂ nanoparticles and concentration of 1-(2-pyridylazo)-2-naphthol (PAN) were the input variables, while the extraction% of analytes was the output. Under the optimum conditions, the detection limits were 0.52 and 0.7 μg L^?1, for manganese and cobalt, respectively. The method was applied to the extraction of manganese and cobalt from water samples and one certified reference material.     

Magnesium-cobalt (II) — Aluminium spinels for pigments

Magnesium, cobalt (II) and aluminium hydroxides coprecipitated from a single solution have been sintered at 400–1200°C for 0.5 to 8 hours. A series of spinels of a general formula Mg_1?nCo_nAl₂O₄ have been obtained. Within the entire range of compositions the colour of the products sintered above 900°C varied from white to dark blue. The formation of these spinels and variation of their colours were analyzed in the trichromatic system.     

Study on silica coated chrome oxide green pigment and its performance

In this study, sodium silicate (Na₂SiO₃) was used as the precursor of SiO₂ to prepare Cr₂O₃/SiO₂ composite pigments. First, using cetyltrimethylammonium bromide to surface modification of the chromium oxide green pigment to make the surface of the particles positively charged. The negatively charged SiO₂ sol coats the surface of the pigment particles through electrostatic attraction. Then use HCl solution acid to precipitate SiO₂, and finally get Cr₂O₃/SiO₂ composite pigment. The structure of the modified pigment was analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size distribution analysis, and X-ray diffraction (XRD) characterization. The influence of silica coating on the tinting strength, dispersibility of pigment in water, and hiding power of the chromium oxide green pigment were further investigated. The results demonstrate that SEM, TEM, and particle size analysis shows that this experimental method can obtain a good silica coating. When the coating quantity is 30%, the full coating of chromium oxide green by silica is achieved. According to the XRD analysis before and after the chromium oxide green coating, as the reaction temperature increases, the intensity of the SiO₂ diffraction peak becomes larger and the crystallization effect becomes better. In the test of pigment performance, it can be concluded that the coloring power, hiding power, and dispersibility of Cr₂O₃/SiO₂ composite pigments are better than those of uncoated chromium oxide green pigments.     

A Highly Active and Selective Manganese Oxide Promoted Cobalt-on-Silica Fischer�CTropsch Catalyst

A highly active and selective manganese oxide-promoted silica-supported cobalt catalyst for the Fischer?CTropsch reaction is reported. Co/MnO/SiO₂ catalysts were prepared via impregnation of a cobalt nitrate and manganese nitrate precursor, followed by drying and calcination in an NO/He flow. The catalysts were studied with STEM?CEELS, infrared spectroscopy measurements of adsorbed CO and Steady-State Isotopic Transient Kinetic Analysis experiments. Based on those experiments, a relation between C₅₊-selectivity and surface-coverages of CH _x -intermediates on cobalt was found.     

Melting Relations of CaO-Manganese Oxide and MgO-Manganese Oxide Mixtures in Air

Melting relations in the systems CaO-manganese oxide and MgO-manganese oxide in air have been determined at temperatures up to 1705°C. In the system CaO-manganese oxide four crystalline phases have stable existence in equilibrium with liquids: lime (approximate composition CaO-MnO), spinel (approximate composition Mn₃O₄-CaMn₂O₄), and two ternary solid solution phases in which Ca/Mn ratios as well as oxygen contents vary over considerable ranges. One of these ternary solid solution phases may for the sake of simplicity be represented approximately by the formula CaMnO₃ and the other by the formula CaMn₂O₄. Three isobaric invariant situations exist, with temperatures and phase assemblages as follows: At 1588°± 10°C the two crystalline phases lime and CaMnO₃ coexist in equilibrium with liquid (40 wt% CaO, 60 wt% manganese oxide) in a peritectic situation. Another peritectic at 1455°± 5°C is characterized by the equilibrium coexistence of CaMnO₃, CaMn₂O₄, and liquid (25 wt% CaO, 75 wt% manganese oxide). A eutectic situation exists at 1439°± 5°C with CaMn₂O₄, spinel, and liquid (18 wt% CaO, 82 wt% manganese oxide) present together in equilibrium. In the system MgO-manganese oxide in air periclase-manganosite solid solution (approximate composition MgO-MnO) and spinel (approximate composition Mn₃O₄-MgMn₂O₄) are the only crystalline phases present in equilibrium with liquids. Liquidus and solidus temperatures increase with increasing MgO content. A peritectic situation exists at 1587°± 10°C, with the two crystalline phases coexisting in equilibrium with liquid (1 wt% MgO, 99 wt% manganese oxide).     

Spreading of Cobalt Phase and Silicate Formation in Co/SiO2 Model Catalyst

The electron microscopy technique was used to characterize the cobalt–silica interaction in a model catalyst at high temperature in air. The samples were in the form of thin cobalt films (1 and 4 nm thick) supported on an amorphous layer of SiO₂. It was concluded that cobalt loading determines the evolution of the microstructure, morphology and phase composition. The spreading of the cobalt oxide phase and formation of cobalt silicate was established.     

Synthesis of CoAl2O4/Al2O3 nanoparticles for ceramic blue pigments

The demand for pigments for industrial ceramic ink-jet printing is increasing steadily. The main challenge is the availability of ceramic pigments comprised of small-sized particles in order to avoid clogging of the printer head nozzle. This work presents a novel way to prepare ceramic blue pigment as a shell/core structure of CoAl₂O₄/Al₂O₃ nanoparticles through a simple and low-cost process. In this process, the colour tone of nano-pigment can be tuned by the selection of the cobalt precursor/Al₂O₃ ratio and calcining temperature.     

Synthesis,phase composition and characterization of Co-diopside ceramic pigments

Ceramic pigments in the system CaO – CoO – MgO – 2SiO₂ were synthesized through solid-state high temperature sintering at 1000, 1100 and 1200 °C. The starting compositions were determined from the stoichiometric mineral diopside, following the expression CaO.xCoO.(1-x)MgO·2SiO₂, where x = 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.5, 0.7 and 0.9. The effect of sintering temperature and initial cobalt concentration on the phase composition and colour were studied by powder X-ray diffraction analysis, scanning electron microscopy (SEM), infrared (FT-IR), ultraviolet–visible - (UV–Vis) and electron paramagnetic resonance (EPR) spectroscopy. Poly-phase ceramics were obtained depending on synthesis parameters, which in addition to Co-diopside, may contain wollastonite, Co-åckermanite – Ca₂(Co, Mg)Si₂O₇, Co-olivine – CoMgSiO₄, Co-monticellite – Ca(Mg, Co) SiO₄, and cristobalite. Quantitative ratios of detected mineral phases and the degree of cobalt isomorphic substitution were determined by applying Rietveld refinement approach. Trends and consistencies were outlined revealing that concentration of cobalt in the initial synthesis batch and its isomorphous incorporation in the crystal structure of diopside affect the structural perfection of the cation polyhedra. This fact obviously plays a key role in controlling the amount of the main constituent phase in the run-product. Ceramics of highest diopside content and lowest measured degree of structural distortion were only formed at 1200 °C and initial cobalt concentration in the range x = 0.2–0.3. These samples are pink in colour and have the highest value of red coordinate in the CIELab system due to Co²⁺ ions in octahedral coordination in diopside structure.     

Potentiostatically deposited polypyrrole/graphene decorated nano-manganese oxide ternary film for supercapacitors

A simple method based on potentiostatic polymerization was developed for the preparation of ternary manganese oxide-based nanocomposite films. The ternary nanocomposites, which were characterized using x-ray diffraction spectroscopy and x-ray photoelectron spectroscopy, showed that the manganese oxide within the film consisted of MnO₂ and Mn₂O₃. Electrochemical measurements showed that the ternary nanocomposite electrode exhibited high specific capacitance (up to 320.6 F/g), which was attributed to the morphology of a polypyrrole/graphene/manganese-oxide (PPy/GR/MnO_x) ternary nanocomposite. The experimental approach maximized the pseudocapacitive contribution from redox-active manganese oxide (MnO_x) and polypyrrole (PPy), as well as the electrochemical double layer capacitive (EDLC) characteristic from graphene (GR) sheets. Long cyclic measurements indicated that the specific capacitance of the ternary nanocomposite film could retain 93% of its initial value over 1000 charge/discharge cycles, in the potential range of −0.2 to 0.7 V versus silver/silver chloride electrode (Ag/AgCl).     

Bifunctional ternary manganese oxide/vanadium oxide/reduced graphene oxide as electrochromic asymmetric supercapacitor

A bifunctional ternary manganese oxide/vanadium oxide/reduced graphene oxide (MnO₂/V₂O₅/rGO) was developed for asymmetric electrochromic supercapacitor (EC-SC) application. The elemental mapping revealed uniformly distributed MnO₂, V₂O₅ and rGO, depicting homogenous synthesis of the hybrid composite. The phase composition, vibration modes and valance state of the ternary composite were analyzed via X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis, respectively. Interestingly, the as-prepared MnO₂/V₂O₅/rGO composite disclosed tremendous C_sp of 1403.5 F/g, which was higher compared to MnO₂/V₂O₅ (801.1 F/g), V₂O₅ (613.1 F/g), MnO₂ (126.7 F/g) and rGO (60.7 F/g). MnO₂/V₂O₅/rGO that appeared in dark green switched its visual color to orange at the charged state, confirming the electrochromic property. The bifunctional manganese oxide/vanadium oxide/reduced graphene oxide//copper-based metal-organic framework/reduced graphene oxide (MnO₂/V₂O₅/rGO//MrGO) asymmetrical EC-SC device revealed outstanding cycling stability (90.3% charge retention over 5000 cycles), tremendous specific capacitance (652.7 F/g) and maximum specific energy (60.4 Wh/kg). MnO₂/V₂O₅/rGO//MrGO asymmetrical EC-SC device demonstrated reversible color changes from dark green to orange at the discharged and charged states, respectively. The significantly great electrochromic and supercapacitive performance revealed that MnO₂/V₂O₅/rGO//MrGO is an outstanding electroactive candidate for the next generation of electrochromic supercapacitors.     

The effects of Al and Ba on the colour performance of chromic oxide green pigment

On the basis of the novel hydrogen reduction of chromite ore, an activated sintering method was devised to prepare chromic oxide green pigment. Using XRD, SEM, EDX, ICP-AES, UV and reflectance colorimetry it was found that the colour performance of the synthesized pigment was markedly improved by adding Al and Ba, which resulted in the formation of an Al₂O₃–Cr₂O₃ solid solution and a secondary BaCr₂O₄ phase, respectively, within the pigment. The colour performance of the chromic oxide green pigment doped with 0.1% Al and 0.55% Ba conformed to commercial pigment standards.     

Selective epoxidation of styrene with air catalyzed by CoOx and CoOx/SiO2 without any reductant

Cobalt oxide (CoOx) prepared by a direct calcination of cobalt nitrate was considerably active for the epoxidation of styrene with air in DMF under mild conditions. A substrate conversion of 75.8 mol% with an epoxide selectivity of 82.1% was achieved at 353 K over 10 mg of cobalt oxide catalyst. Once CoOx was loaded on the support SiO₂ through a simple procedure consisting of wet impregnation, drying and calcination, the as-prepared catalyst presented higher catalytic activity and epoxide selectivity than cobalt oxide itself. Over the optimized catalyst CoOx/SiO₂ (1.0 wt% Co), 85.7 mol% of styrene was effectively converted at 363 K within 4 h, with a high epoxide selectivity up to 86.0%. The results showed that many factors influenced the performance of the catalyst, such as the Co loading, the support, the temperature and the atmosphere, etc. The leaching of cobalt from the catalyst CoOx/SiO₂ was negligible, indicating the applicability of the catalyst CoOx/SiO₂ as a true heterogeneous catalyst. The control test and UV–vis spectra revealed a synergic interaction among solvent, oxygen and substrate over CoOx/SiO₂.     

Effect of manganese on Cu/SiO2 catalysts for the dehydrogenation of cyclohexanol to cyclohexanone

The effect of the addition of manganese to Cu/SiO₂ catalysts for cyclohexanol dehydrogenation reaction was investigated. At reaction temperature of 250 °C, the conversion and the selectivity to cyclohexanone were both increased with the addition of manganese to Cu/SiO₂ catalyst. However, as the reaction temperature was further increased, higher loading of manganese in Cu/SiO₂ catalyst led to a decrease in the conversion of cyclohexanol. Manganese in Cu/ SiO₂ catalyst decreased the reduction temperature of copper oxide, increased the dispersion of copper metal, and decreased the selectivity to cyclohexene. It was found that the dehydration of cyclohexanol to cyclohexene occurred on the intermediate acid sites of catalyst. At high Mn loading, catalyst surface was more enriched with manganese in used catalyst compared to that in freshly calcined or reduced catalyst, which may account for the sharp decrease of the conversion at high temperature of 390 °C. Upon reduction, copper manganate on silica was decomposed into fine particles of copper metal and manganese oxide (Mn₃O₄).     

A Study of the Acid–Base Properties of Melts in the Na2O–B2O3–SiO2System: I. Composition Joins with a Na2O Content of Less Than 20 mol %

Three composition joins in the Na₂O–B₂O₃–SiO₂system at constant Na₂O contents of 5, 10, and 15 mol % are studied by the high-temperature method of determining oxygen ion exponents pO for oxide melts. It is found that the basicity of melts increases in going from the binary sodium borate system to the sodium silicate system. The acid–base properties of ternary melts are simulated under the assumption that their basicity is determined by the interaction in pseudobinary systems. It is shown that the basicity of the studied melts is governed, to a large extent, by the formation of the Na₂O · B₂O₃· 2SiO₂ternary compound.     

Moist expansion of ceramic materials

It is demonstrated that introduction of wollastonite in the composition of ceramic mixtures promotes an increase in the RO content, a decrease in the ratio of Al₂O₃ + SiO₂:RO, and neutralizes the negative effect of R₂O on the moist expansion of ceramic tiles. Likewise pyrophyllite can contribute to a decrease in the expansion of tiles but is less efficient than wollastonite.     

Multi-micro analytical studies of blue-and-white porcelain (Ming dynasty) excavated from Shuangchuan island

Shangchuan Island lies in the southern part of the Guangdong Province in China. Historically it is considered as an important berthing wharf of the South China Sea for the Maritime Silk Roads, witnessing the early Sino-Portuguese trades. Related research on the cultural relics in the region has attracted significant attention from archaeologists. In this study, blue-and-white porcelains excavated from Shangchuan Island were analyzed by multi-micro analytical techniques. In-glaze decoration and under-glaze decoration processes were suggested for the glaze painting process, as revealed by digital microscopy. Silica-aluminum system with flux agents of calcium, potassium and sodium, as well as the main elements of blue pigment with iron, manganese, cobalt and nickel, were found by analysis of micro X-ray fluorescence spectrometry. By calculating the discriminate functions (F) for the chemical compositions of porcelains body, as well as the S_i value for porcelain glaze, the origin of these blue-and-white porcelains were identified with the origin of the Jingdezhen kiln in the Ming dynasty. Anorthite (CaAl₂Si₂O₈) crystals were observed in glaze layer of porcelain by micro-Raman spectroscopy, as well as α-quartz (SiO₂) and calcite. These archeological evidences not only helped to understand the history of the early Sino-Portuguese relations, but also proved the important historical status of Shangchuan Island and contributed to the study of the history of Chinese ancient Maritime Ceramic Road.     

Metallo-organic deposition of tungsten oxide films from alkylammonium tungstate solutions

This paper describes a simple and inexpensive metallo-organic deposition (MOD) process for forming electrochromic tungsten oxide (WO₃) films on glass. The thin films of WO₃ were made by air firing (500–700°C) films from xylene/2-propanol solutions of bis-(di-n-octylammonium) tetratungstate, [(n-C₈H₁₇)₂NH₂]₂[W₄O₁₃]. The process coats glass with undoped films ranging in colour from faint yellow to dark brown, and can be used to make gradients of these colours. The colour is determined by the firing parameters and results from residual carbon and tungsten suboxides in the film due to incomplete firing. Increased firing temperatures or longer firing times removes the carbon and produces films with higher crystallinity. Electrochemical doping with acid (H⁺) switches the colour gradient films to a uniformly blue colour.