Reactivity of aluminum sulfate and silica in molten alkalimetal sulfates in order to prepare mullite

With the aim of preparing mullite, reactions between aluminum sulfate and silica in appropriate proportions and molten sulfate media M2SO4 (M=Na and/or K) were performed at different temperatures. The powders obtained were characterized by XRD, FT-IR, SEM and TEM. The reactivity was the same in Na2SO4 and (K,Na)2SO4 media. The best results in terms of yield (98.3%) and weight of mullite produced (95%) were obtained in Na2SO4 at 950 °C. The mullite phase exhibits an acicular morphology (75×0.75 μm) and a specific surface area close to 20 m2/g. In K2SO4 medium, a potassium alumino silicate is formed as well as mullite

Synthesis of CoAl2O4 by double decomposition reaction between LiAlO2 and molten KCoCl3

Submicronic CoAl2O4 powders were prepared by double decomposition reaction between solid LiAlO2 and molten KCoCl3 at 500 ◦C for 24 h. The reaction mechanism involves the dissolution of LiAlO2 shifted by the precipitation of CoAl2O4 until complete transformation and the reaction leads to powders with a very homogeneous chemical composition. The powders obtained were mainly characterized by XRD, FTIR, ICP, X.EDS, electron microscopy and diffraction and diffuse reflexion. The blue pigments obtained exhibit a high thermic stability allowing their use for the colouring of ceramic tiles

Synthesis of molybdates Zn1-xCoxMoO4 (0 ≤ x ≤ 1), by decomposition of the precursors developed by the glycine-nitrate process (GNP), and their characterization

Nanocrystals of zinc-cobalt molybdate (Zn1-xCoxMoO4) were prepared by the glycine-nitrate process (GNP) route with a glycine/nitrate ratio of 2:3 and compared to the solid state synthesis. The obtained powders were characterized by thermal analysis (TGA-TDA), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The morphology was examined by scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET). The particle size was determined by transmission electron microscopies (TEM). UV–Visible spectroscopy and CIE L*a*b* colorimetric parameters have been used for the colour characterisation and measurement. The compounds obtained present two single-phased domains regardless of the synthesis method. The first domain of blue colour corresponding to a level of cobalt x such as: 0 = x ≤ 0.3, isostructural with α-ZnMoO4 of triclinic symmetry and the second domain of green colour, for cobalt x levels such as: 0.45 = x ≤ 1 isostructural with α-CoMoO4 of monoclinic structure. The Zn0.7Co0.3MoO4 powders obtained at 700 °C by GNP route and synthesized in acidic environment were formed of particles of quasi-spherical morphology, with average size of crystallites estimated between 80 - 140 nm

Influence of temperature and pH on the morphology and the color of the CoAl2O4 prepared by sol gel method

The aim of this study consists in the synthesis of CoAl2O4 spinel by sol gel method using polyacrylic acid as chelating agent, with focusing on the influence of calcination temperature and pH on the morphology and on the color of the powders obtained. The prepared powders have been characterized by X- ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) and colorimetry (L*a*b*). The results obtained show that the spinel phase appears from 500 °C. FTIR spectroscopy reveals oxygen-metal bands characteristic of the spinel structure. The TEM micrographs of powders, synthesized at the temperatures 800°C, 900°C and 1100°C at pH=2,7 and 10, show that these powders are formed of nanometric particle size with a distribution between 20 nm and 90 nm. The colorimetric parameters, measured on powders calcined at 1100 ° C and regardless of the pH values, show an important blueness

Synthesis and physicochemical characterization of pigments based on molybdenum «ZnO-MoO3: Co2+»

International audienceMolybdatesZn1-xCoxMoO4(0≤ x ≤0.3) were elaborated by the Sol-Gel method with pH=3.The results obtained by DRX show a single-phase domain startingfrom 500°C for x ≤ 0.3 isostructural to ZnMoO4.The powder ofZn0.7Co0.3MoO4treated at 500°C and 700°C is formed by nano-sized primary crystallitesof size between 80 and 160nm. The colorimetric parameters (L a* b*) of powders obtained at 700°C present adegree of high bluing

Influence du milieu fondu Na2SO4, sur la décomposition de gels précurseurs de la mullite

Nous avons préparé des gels de mullite par neutralisation de solutions de sulfate d’aluminium et de silicate de sodium dans un rapport A1203/Si02 = 1,5. Les gels obtenus ont été séchés à 120°C pendant 12 heures, puis décomposés, d’une part par calcination à l’air à 950°C pendant 6 heures et d’autre part, par traitement thermique dans un bain fondu de sulfate de sodium toujours à 950°C pendant 6 heures. Les différentes poudres obtenues ont été caractérisées par diffraction de rayons X, par spectrométrie infrarouge à transformée de Fourrier (FTIR) et par microscopies à balayage (MEB) et à transmission (MET). L’étude de paramètres tels que la nature du traitement thermique et le pH montre que le processus de mullitisation est favorisé quand les précurseurs sont traités en milieu sel fondu et à pH acide

Molten Salt Synthesis and Characterization of CuIn(1-x)GaxS2 (x ≤0.3) Nanoparticles.

Solid solutions CuIn(1-x)GaxS2 (x ≤ 0.3)were synthesized, with a yield of 70%, by reaction in molten KSCN at 400°C for 24h of CuCl2, InCl3 and GaCl3 with a ratio KSCN/Cu=15. The homogeneous solid solutions obtained are formed of nano-sized grains (70–100nm), with a specific surface area of 6.5 m2/g and a band gap between 1.5 and 1.8 eV

Preparation and characterisation of green nano-sized ceramic pigments with the spinel structure AB2O4 (A = Co, Ni and B = Cr, Al)

Inorganic pigments based on AB2O4 (A = Co, Ni; B = Cr, Al) spinel structures with green colour were successfully synthesised by the polymeric route. The effect of the substitution of trivalent and divalent cations on the structural, optical and morphological properties of the pigments was investigated. The synthesised nanopowders were examined using thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller analysis (BET), UV–vis diffuse reflectance measurements, and CIEL*a*b* colorimetric analyses. The results show that the CoCr2O4 spinel and the spinels substituted by nickel and aluminium cations were obtained with a single phase after heat treatment at 900 °C. The produced powders present shades of the green colour with improvement in morphology for the substituted samples. The Ni0·5Co0·5CrAlO4 nanoparticles consisted of grains of quasi-spherical shape with sizes between 50 and 75 nm. This powder was used in small quantities with glazes for colouring tests on the surfaces of ceramic substrate

Sol–gel synthesis and sintering of submicronic copper molybdate (α-CuMoO4) powders

A sol–gel method was proposed to prepare copper II molybdate α-CuMoO4 powders. A gel was first obtained via the polymerizable complex method, using citric acid as complexing and polymerizing agent, dried at 120 °C and decomposed at 300 °C. A calcination in the temperature range 400–500 °C for 2 h led to the pure phase α-CuMoO4. The different powders obtained were characterized by X ray diffraction analysis and by transmission (TEM) and scanning (SEM) electron microscopies. Ceramics were prepared using conventional sintering and spark plasma sintering (SPS) techniques. A maximal relative density of 94.8% was reached after conventional sintering at 520 °C for 2 h. In the case of SPS, the densification was optimized by varying the temperature, the time and the applied pressure. Higher densities, up to 98.7%, were obtained at very low temperature, i.e., 300 °C, for 5 min only under a pressure of 225 MPa

Structural and microstructural characterization of CuMo(1-x)WxO4 (x ≤ 0.12) ceramics sintered by spark plasma sintering

Cupric molybdate CuMoO4is an interesting material due to their rich electrical, optical and magnetic properties. In this work, Solid solutions CuMo(1-x)WxO4(x≤0.12) were obtained by pyrolysis at 400 -700°C for 2 hours of a polymeric precursors elaborated by polymerizable complex method. For x ≤ 0.075, they were isostructural with α-CuMoO4 and for 0.075<x≤0.12, they were isostructural with γ-CuMoO4. Spark Plasma Sintering (SPS) at 300°C for 5 min under an applied pressure of 200 MPa led to variety CuMoO4-III for tungsten contents in the range 0.075-0.12