The structural evolution and optical properties of Mg1-xZnxAl1.8Cr0.2O4 pink ceramic pigments

In this work, pink ceramic pigments based on the composition of Mg_1-xZn_xAl_1.8Cr_0.2O₄(x = 0.0,0.3,0.5,0.7,1.0) were synthesized by using a gel polymerization method. We focused on studying the effect of A-site ion doping on the random cation distribution, microstructure and optical absorption performance. Field Scanning electron microscopy (FESEM), X-ray diffraction (XRD) and the Rietveld refinement method with a GSAS program were applied for micromorphology and cation distribution analyses. The optical performance of the pigments was studied by UV–vis and CIE L*a*b* spectrophotometry. All samples had a single spinel phase within the calcination temperature range of 800 °C–1400 °C and the primary grain size of the synthesized pigments were approximately 0.5–1 μm. The ion distribution in the tetrahedron and octahedron was largely dependent upon the calcining temperature and composition. The oxygen parameter, cell parameter, and T-O and M-O band lengths also varied with the cation distribution, leading to a change in the spinel structure and octahedron crystal field parameter and ultimately changing the optical absorption properties of the synthetic pigments. This study lays the foundation for subsequent studies of colour modification in ceramics.     

Synthesis and characterization of (Pr,Ce)-ZrSiO4 ceramic pigments: The properties of the pigments and the effect of Ce

A series of (Pr, Ce)-ZrSiO₄ ceramic pigments were synthesized and characterized using XRD, SEM, EDS, XPS, XRF, colorimeter, and a UV-VIS-NIR spectrometer. The prepared pigments were mainly composed of the zircon phase and were well crystallized. Only a specific amount of Pr was incorporated into the ZrSiO₄ lattice. Compared with Pr, Ce was almost completely incorporated into the ZrSiO₄ lattice and was homogeneously distributed within the pigment particles. The dopant Ce reduced the amount of Pr dissolved in the ZrSiO₄ lattice and thus caused the b* values of the samples to decrease slightly. Meanwhile, the presence of Ce induced an apparent increase in red tone in the samples. The enhanced red tone resulted primarily from an increase in the absorption of light with wavelengths between 500 and 565 nm. High-temperature stability analysis demonstrated that it is feasible to improve the tone of Pr-ZrSiO₄ pigment by doping with Ce.     

Effect of phase composition of natural quartz raw material on characterization of microfiltration ceramic membranes

The results of development of multi-layer ceramic membranes on the basis of natural quartz raw material from Mongolia are presented. The influence of the phase composition and temperature of calcination on the porosity, morphology and mechanical strength of large-porous ceramic support obtained by the method of isostatic pressing was studied. It was established that multi-layer ceramic membranes obtained by the application of water suspension of high-disperse quartz sand of Mongolia and alumosilicate binder with the addition of 15–35 wt% of quartz are characterized by optimal properties. The developed tubular ceramic membranes with the average pore size 5.3 µm, coefficient of air permeability (4.17–4.41)×10⁻¹³ m², productivity by water 46.3–48.0 m³/(h×m²×bar) and mechanical strength 2.27–2.53 MPa are perspective for wide use in microfiltration processes.     

Synthesis and characterization of yttrium iron garnet nanoparticles doped with cobalt

In this work, we have synthesized and characterized yttrium iron garnet nanoparticles doped with cobalt. The X-ray diffraction data showed a single phase, belonging to the cubic structure of Y₃Fe₅O₁₂. Rietveld refinement revealed variation of the angles and interionic distances (Fe³⁺(a)-O^2-Y³⁺(c) and Fe³⁺(d)-O^2--Y³⁺(c) when Fe³⁺ ions are replaced by Co³⁺ ions in the tetrahedral (d) and octahedral (a) sites of YIG. In addition, the lattice parameter a, decreases from 12.3846?Å to 12.3830?Å with the increasing of cobalt concentration. The analysis by Infrared and Raman spectroscopies has shown a slight stretching at lower wave numbers as the dopant concentration increased. The magnetic measurements confirm the substitution of Fe³⁺ by Co³⁺ in the a-sites and d-sites with the reduction of the saturation magnetization from 26.63?emu/g to 24.92?emu/g, for 0.000?≤?y?≤?0.030. Changes in the coercive field varying the dopant concentration were related to the particle size and pinning centers existence.     

Towards more ecological ceramic pigments: Study of the influence of glass composition on the colour stability of a pink chromium-doped ceramic pigment

This paper describes the study of a pink ceramic pigment based on the optical properties of Cr-doped structures, having into account environmental considerations. The research is focused on the optimisation of the synthesis parameters in order to minimise the amount of pollutant Cr(VI) in the washing liquids and enhance chromatic coordinates. In a first stage, the Al_2−xCr_xO₃ solid solution was studied. Nevertheless, the observation that ZnO was required in the frit to stabilise the pink colour after glazing made us to conduct the research towards the optimisation of the ZnAl_2−xCr_xO₄ system. X-ray diffraction (XRD) indicates a solid solution formation based on the gahnite structure; moreover, no Cr(VI) and B contents were found in the analysis of the washing liquids. Thus, this research enabled us to produce a pink pigment with low environmental impact and good chromatic coordinates. Further study of the pigment applied in a glaze showed evidence of the importance of the glaze composition for the colour development and stability of the ceramic pigments.     

Investigation of the microstructure,cation distribution and optical properties of nanoscale NixMg1-xAl2O4 spinel pigments

Nanoscale Ni_xMg_1-xAl₂O₄ spinel pigments were synthesized by a citric acid precursor combined with the gel-casting method. The microstructure, cation distribution and optical properties as a function of calcining temperature and nickel content were investigated by the X-ray diffraction (XRD) Rietveld refinement, transmission/field emission scanning electron microscopy (TEM/FESEM), X-ray photoelectron spectroscopy (XPS), colour measurement and UV–vis–NIR spectrophotometry. Upon increasing the calcining temperature, both Ni²⁺ and Mg²⁺ hindered the migration of Al³⁺ to octahedral sites. When the Ni content increased, the cation site percentage of Ni²⁺ in the tetrahedral and octahedral sites varied slightly while that of Al³⁺ and Mg²⁺ change substantially. The cation exchange resulted in an increase in the inversion parameters and a decrease in the lattice parameters with increasing temperature or Ni content. Furthermore, Rietveld refinement also showed a shrinkage of the tetrahedra and an expansion of the distorted octahedra in the spinel structure. Short-range information based on optical spectra suggests that variation in the splitting energy of tetrahedra and octahedra caused the change in the spectral absorption. This study may deepen the understanding of the structural-optical property relationship of Ni_xMg_1-xAl₂O₄ spinel, which is vital to the further colour modification of ceramics and glazes.     

Advances and challenges of ceramic pigments for inkjet printing

In the last decades, the development of new ceramic pigments has been a very pursuit goal, mainly since the emergence of the inkjet technology applied to ceramic tiles. The digital decoration of industrial ceramics has contributed to a notable reduction of pigment consumption and an aesthetical decoration improvement, which makes more flexible the production processes, enhancing the reproducibility and cost savings. The nanopigment requirements of the inkjet technology demand submicronic particle size, ink rheology, stability, drop resolution, etc. Although the up-down procedure by micromilling contributed firstly to the particle size reduction of existing pigments, novel approaches are developed to obtain directly high-quality particles of suitable size with the aim of providing a higher optical efficiency. Thus, in this work, a comprehensive review about the existing crystalline structures, novel compositions, and synthesis methods as well as new coloring mechanisms is addressed, giving an overview of all these advances while considering the four-color process required for inkjet technology. The inkjet technology has the challenge of evolving towards a sustainable technology by eliminating the use of critical raw materials, removing the use of synthesis aid fluxes, and reducing the energy consumption, to approximate to a circular economy which is predominant in this sector.     

Comparison of blue pigments prepared by two different methods

The color efficiency of ceramic glaze blue pigments obtained by synthesis methods was compared. the fired pigments and enameled samples were characterized by XRD, UV-vis-NIR spectroscopy, CIE-L^*a^*b^* color-measurements, and SEM. The pigments obtained by the Pechini method presented a better solubility in the molten glazes than the pigments obtained by the mechanical mixture of the oxide precursors. The pigments obtained by the Pechini method also developed a bluer color hue than the pigments obtained by the mechanical mixture of the oxide method.     

Suspension high velocity oxy-fuel spraying of TiO2: A quantitative approach to phase composition

A range of coatings from a water based suspension of anatase has been prepared by suspension high velocity oxy-fuel spraying with the aim to study effects of heat power of the flame on phase composition, microstructure and surface topography. Three most commonly used approaches of quantitative phase analysis have been scrutinized with respect to their applicability and as some of the coatings showed presence of preferred orientation and it was argued that quantitative Rietveld refinement is the most accurate method for phase composition determination. Coatings had a layered duplex anatase/rutile microstructure with fraction of rutile increasing exponentially with heat power. Spraying at the lower heat power led to a lower surface roughness and higher power resulted in surfaces with pronounced humps, which were distributed homogeneously on the surface. The emergence of humps is related to an increase in macroscopic surface area of up to 30% with respect to the flat coating.     

Physico-chemical properties of ceramic pigments for high-temperature application

Heat resistant coatings are required primarily for stacks, exhaust pipes, reactors, space crafts and similar equipments that are permanently or occasionally exposed to elevated temperatures. High-temperature coatings are generally based on silicone resin with ceramic and metallic pigments. In this study, iron oxide, cobalt oxide (thermo chromic compound) and aluminum oxide are used for the preparation of four new types of coloured pigments. The thermal resistant characteristics of these ceramic pigments were studied by differential thermal analysis, thermo gravimetric analysis and differential scanning calorimetric analysis. These ceramic pigments are found to be thermally stable up to 400 °C.     

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.     

Colour measurement as a proxy method for estimation of changes in phase and chemical composition of fly ash formed by combustion of coal

Influence of technology on colour changes of fly ashes was studied in relationships with their chemical and phase composition. Dry bottom boilers at the Detmarovice Power Plant (the Czech Republic) were selected for this study. Combustion tests were performed using mixture of coal and mineral oil residues at the minimum and maximum output of the power plant. Fly ashes for chemical analysis, phase analysis and colour measurements were sampled from the four sections of electrostatic fly ash precipitator. Colour parameters indicate relationships with concentrations of elements which are preferentially bound in silicate matrix. The maximum output of power plant increases the concentration of glass which has decisive influence on values of colour parameters. The changes of colour parameters can indicate the conditions of the technological process. Relationships between colour and constituents of the fly ash are expressed by CIE Lab colour parameters.     

Ceramic pigments with sphene structure obtained by both spray- and freeze-drying techniques

The present study is focused on the procedure of spray- and freeze-drying techniques for the preparation of Cr-doped sphene pigments (CaSn_0.98Cr_0.02SiO₅, CaTi_0.98Cr_0.02SiO₅) from an aqueous solution of precursor salts, followed by calcinations of the resulting powders in absence of additives. The evolution of the present crystalline phases with applied thermal treatments was studied by X-ray powder diffraction and thermal analysis. The powder morphology was analysed by scanning electronic microscopy. The behaviour of the chromium ion was clarified by ultraviolet and visible spectroscopy. The colour efficiency of pigments was evaluated by colourimetric analysis (CIE L?a?b? system).     

Red-brown ceramic pigments based on chromium doped ferrian armalcolite,effect of mineralizers

A new red-brown ceramic pigment based on chromium-doped ferrian armalcolite have been synthesized and characterized. (MgFe)(Cr_xTi_3−xFe)O₁₀ powders (x=0–0.3) fired at 1200 °C crystallize ferrian armalcolite as the only crystalline phase detected. Samples fired at 1000 °C show red-brown shades in glazes that darken and bluish (b* turns to negative values) at 1200 °C. The x=0.2 sample fired at 1000 °C shows the best red colour (L*a*b*=49.5/15.2/10.3). Assignment of bands in the UV–Vis–NIR spectra is difficult due to the overlapping of Cr³⁺, Cr⁴⁺ and Fe³⁺ absorptions in octahedral coordination. Analysis of UV–Vis–NIR spectra of powders shows that these spectra are dominated by the strong absorption associated to Fe³⁺ ions in octahedral sites. In contrast, an intense band at 520 nm dominates the UV–Vis–NIR spectra of glazed samples, which should be associated to Cr⁴⁺ in octahedral coordination. This absorption increases when the amount of chromium increases, indicating that chromium is the real chromophore of the system. Finally, the weak shoulder at 600 nm and the double weak band at 700 nm, detected more evidently when chromium amount in sample increases, indicate the progressive presence of Cr³⁺ in octahedral sites. The entrance of Cr⁴⁺ in x=0.1 sample shrinks the crystalline cell, but when chromium amount in the samples increases, both Cr⁴⁺ and Cr³⁺enter simultaneously and the unit cell remains practically stable. The microstructure of the powders analysed by SEM microscopy indicates aggregates of 6–10 fine particles of 200–400 nm of diameter. The addition of mineralizers (boric acid, sodium perborate, NaF and a mixture BaF₂.4MgF₂) does not modify significantly the reactivity of the system; at 1000 °C hematite and rutile remain as residual crystalline phases, except in NaF additions where the crystallization of NaFeTi₃O₈ is detected. SEM-EDX mapping analyses of pigment powders confirm in all cases a homogeneous distribution of ions in the particles.     

Phase evolution,structure, and electrochemical performance of Al-, Ga- and Ta- substituted Li7La3Zr2O12 ceramic electrolytes by a modified wet chemical route

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is one of the most promising solid-state electrolytes (SSEs) for advanced solid-state lithium batteries (SSLBs). In this work, Li_6.25Al_0.25La₃Zr₂O₁₂, Li_6.4Ga_0.2La₃Zr₂O₁₂, and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ ceramics are prepared by a modified wet chemical route. The composition of the black mixtures derived from the precursors is ascertained. The phase evolution and structural properties from the ceramic mother powders to the final ceramic electrolytes are discussed in detail. The characteristic of cubic LLZO with the space group I-43d arises in the Li_6.4Ga_0.2La₃Zr₂O₁₂ ceramic electrolyte pellet after the secondary higher-temperature (1200 °C) sintering. The Rietveld refinement reveals the roles of Al³⁺ substitution at the Li⁺ sites and Ta⁵⁺ substitution at the Zr⁴⁺ sites to adjust crystal structure. In addition, the electrochemical performance of the ceramic pellets is also investigated. Remarkably, the Li_6.4La₃Zr_1.4Ta_0.6O₁₂ ceramic electrolyte has the most outstanding electrochemical performance, showing the high ionic conductivity of 6.88 × 10^?4 S cm^?1 (25 °C), the low activation energy of 0.42 eV and an extremely low electronic conductivity of 1.77 × 10^?8 S cm^?1 (25 °C). Overall, it is supposed that this work may help to achieve high-quality modified LLZO ceramic electrolytes, especially using the wet chemical strategy.     

Synthesis of Pure Hydroxyapatite and the Effect of Synthesis Conditions on its Yield,Crystallinity, Morphology and Mean Particle Size

Abstract

Hydroxyapatite (HAP) is a calcium phosphate compound with the chemical formula Ca₅(PO₄)₃OH. This compound is especially significant in biomedical applications since it resembles the mineral constituents of the hard tissue in the human body. Its biocompatibility, castability, and sinterability make it a very attractive material for simulating bones and therefore for implantations. The objective of this study was to produce HAP with a high purity and to determine quantitatively the exact percentage of HAP in the synthesized powder. Hydrothermal methods have been used to produce HAP. In the present work, Hydroxyapatite powder was produced using the chemical precipitation method in a batch and semi‐batch modes of operation. The effect of temperature, pH, and reactant addition rates on the mean particle size was studied. Results showed a maximum in the mean particle size at pH 9, while a minimum was observed at around 45°C. As the reactant addition rate increased the mean particle size increased as well. The purity of the obtained powder was characterized using both quantitative and qualitative techniques. The quantitative results were performed using the powerful Rietveld refinement method. The quantitative results were obtained for three samples. Results showed that pure HAP was produced at a temperature of 85°C, pH 9 and reactant addition rate of 1.3 mL/min.     

Synthesis and characterization of ceramic - polymer composites containing bioactive synthetic hydroxyapatite for biomedical applications

Presented research involved preparation of hydroxyapatite and synthesis of composites based on gelatin, albumin and polyvinylpyrrolidone (PVP) modified with the obtained compound. Hydroxyapatite was attained as a product of two-stage processing of pig bones. Applied procedure involved hydrolysis of the raw material in acidic environment and double calcination. Molar ratio Ca/P of hydroxyapatite has been determined and its chemical structure has been characterized using X-ray diffraction and FT-IR spectroscopy. Ratio Ca/P calculated on the basis of conducted research was 1.50?±?0.05. Thus prepared material met the ISO requirements, which assume that the Ca/P ratio should be in the range 1.5–2.0, which qualifies the material for further studies. Next, series of polymer matrix on the basis of gelatin, albumin and polyvinylpyrrolidone (PVP) has been synthesized and subjected to some analyzes. On the basis of the conducted studies, matrixes with the most favorable features such as desirable strength, flexibility and crosslinking degree were modified with previously prepared hydroxyapatite. Surface morphology and elemental composition of the composites have been analyzed using SEM-EDS method. Additionally, sorption capacity of modified composites and their behavior in simulated body fluids have been determined. Based on the conducted research it can be concluded that pig bones represent a good material for preparation of hydroxyapatite. Furthermore, composites based on proteins of natural origin modified with attained hydroxyapatite constitute a promising material that can be used for biomedical purposes.     

Glass–ceramic frits for porcelain stoneware bodies: Effects on sintering,phase composition and technological properties

In the present work, the effects of glass–ceramic frits (10 wt.%) added to a porcelain stoneware body in replacement of non-plastic raw materials were evaluated simulating the tile-making process. Each glass–ceramic frit plays its own peculiar effect on the compositional properties and only some precursors behave as real glass–ceramic materials. The positive influence of glass–ceramic precursors in promoting the sintering stands out when temperature onset densification and sintering rate are considered: both of them are improved with respect to the reference body. The presence of glass–ceramic frits allows to preserve good technological properties, complying with the latest requirements of the industrial practice.     

Microstructural characterization and phase analysis of new pyrochlore-type mixed metal oxides RESmTi2O7 (RE = Gd,Er) by X-ray powder diffraction using Rietveld refinement method and spectroscopic studies

Two new RESmTi₂O₇ mixed metal oxides were prepared by mixing Sm₂O₃, RE₂O₃ (RE = Gd, Er) and TiO₂ using a modified solid state method which gives the target pyrochlores with excellent phase purity. SmGdTi₂O₇ and SmErTi₂O₇ samples were characterized using PXRD, SEM, EDS, FT-IR and Raman spectroscopy. Rietveld refinement was employed to obtain crystallographic parameters using MAUD software. The qualitative phase analysis showed that the mixed metal oxides were crystallized in a cubic crystal system with the Fd3m space group with small shifting in Bragg positions due to the effect of RE cationic radius on the lattice structure. The quantitative phase analysis using Rietveld refinement method illustrated the relation between crystallographic parameters, structural factors and ionic radii of RE atoms, during which, the sensitivity of the pyrochlores for cationic radius variations of RE atoms, and the extraordinary effect of the RE on the crystal structure of pyrochlores were confirmed.     

Synthesis, through pyrolysis of aerosols, of YIn1−xMnxO3 blue pigments and their efficiency for colouring glazes

Mn-doped YInO₃ blue pigments have been synthesised at a much lower temperature (1100 °C) than that required by the traditional solid state method (1400 °C). The developed procedure, which is based on the pyrolysis at 600 °C of aerosols generated from aqueous solutions of Y, In and Mn nitrates followed by an annealing treatment at 1100 °C, yields spherical pigments particles with heterogeneous size in the optimum range required for ceramic applications (<10 μm). The amount of Mn introduced in the YInO₃ matrix has been systematically varied in order to evaluate the effects of the Mn content on the colour properties of the pigments. It has been found that the optimum pigment composition (bluer colour with the lowest Mn content) is given by the formula YIn_0.90Mn_0.10O₃. The technological performance of these YIn_1−xMn_xO₃ blue pigments has also been evaluated by testing their efficiency for colouring ceramic glazes of different composition (boracic and plumbic) and properties, aiming to find a less toxic alternative for the Co-based pigments commonly used by the ceramic industry.