Thermal Stability Of Pigments Research Articles

Encapsulation of carotenoids with sucrose by co-crystallization: Physicochemical properties, characterization and thermal stability of pigments

Natural pigment carotenoids specifically β-carotene present in carrots is very sensitive to heat and light. The present work studied the co-crystallization as a process to increase the stability of the carotenoids extracted from carrots. Carotenoids encapsulated co-crystals were evaluated for their encapsulation efficiency, antioxidant activity, thermal behavior, physicochemical, and structural properties. Co-crystallization of the carotenoids with sucrose showed an encapsulation efficiency of 77.58% and an antioxidant activity of 68% towards DPPH free radicals. DSC thermogram confirmed the thermal stability of carotenoids encapsulated co-crystals by indicating the endothermic peaks at 190 °C. XRD pattern and FTIR spectra revealed that the crystal nature of sucrose and functional groups remained the same even after co-crystallization. SEM results revealed the irregular cavities in well-defined cubic crystals of sucrose which suggested the better entrapment of carotenoids into sucrose. Hence, co-crystallization significantly improved the overall stability of the carotenoids, and these co-crystals can be used as a natural colorant, sweetener, and antioxidant.

Engineering the crystal structure of γ-[Li]-Ce2S3 red pigments for enhanced thermal stability

The search for high thermal stability, environmentally-friendly, and low-cost red pigments for glazes remains a significant challenge in ceramic research. Here, we report a simple gas-solid reaction method to synthesis red inorganic pigments, namely γ-[Li]-Ce2S3. The effects of different molar ratio of lithium to cerium nLi/Ce (nLi/Ce ​= ​0.05, 0.10, 0.15, 0.20, 0.25, 0.30) on the phase composition, crystal structure, chromatic properties and thermal stability of pigments were systematically studied. The XRD and XPS characterization combined with Rietveled structural refinement showed that Li+ entered into the γ-Ce2S3 lattice structure to form γ-[Li]-Ce2S3 solid solutions. The two different nearest-neighbors Ce–S bond lengths in the γ-[Li]-Ce2S3 and the lattice parameters decreased with the content of nLi/Ce, while these values displayed a constant beyond nLi/Ce ​= ​0.20, indicating that the vacancies in the lattice were fully filled and Li+ no longer entered the lattice. The substitution of Li+ for Ce3+ and the elimination of the cationic vacancies in γ-[Li]-Ce2S3 led to an increase in the band gap from 1.95 to 2.00 ​eV, corresponding to a slight change in the red hue. Furthermore, from Raman spectra, a trace of cerium polysulfide as an impurity phase was found in the pigments, which was responsible for the observed dark red color of as-prepared γ-[Li]-Ce2S3. In addition, the thermal stability was evaluated by TG-DSC and the thermal stable temperature of γ-[Li]-Ce2S3 can be raised to 450 ​°C when nLi/Ce was equal to 0.20, showing that the stability of the pigments can be improved by adjusting the structural parameters.

Study of Bi2O3 doped by rare-earth element

A series of novel environmentally inorganic pigments based on Bi2O3 doped by metal ion Dy3+ has been developed and characterized using methods of thermal analysis, X-ray powder diffraction and by reflectance spectral data. The new pigments have been synthesized from mixtures containing Bi2O3 and Dy2O3 by traditional solid-state route. The incorporation of Dy3+ into crystal lattice Bi2O3 changes the colour from yellow-orange to orange. The band gap of phases with formula Bi2−xDyxO3, where x = 0.8, increases from 2.30 to 2.38 eV with growth of calcination temperature. The pigment Bi1.2Dy0.8O3 was also evaluated from the standpoint of influence of milling time on the colour properties and particle size. The simultaneous TG–DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. The results confirm the positive effect of lanthanide ions into Bi2O3 on thermal stability of prepared phases.

Thermal stability and colour properties of new pigments based on BiREO3

A series of novel environmentally inorganic pigments based on Bi2O3 doped by rare-earth elements RE (Er, Ho, La, Nd, Dy, Lu and Y) have been developed and characterized using methods of thermal analysis, X-ray powder diffraction and by reflectance spectral data. The new pigments have been synthesized from mixtures containing Bi2O3 and RE2O3 by traditional solid-state route. The incorporation of RE3+ into crystal lattice Bi2O3 changes the colour from yellow, yellow-orange to orange. The simultaneous TG–DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. The results confirm the positive effect of rare-earth ions doped into Bi2O3 that contribute to a growth of thermal stability of prepared pigments.

Thermal study of the Ce0.9Tb0.1O2 pigment prepared by different synthesis

The inorganic ceramic compounds based on the CeO2 belong into the group of high-temperature pigments. The pigments have been prepared by the classical dry process (i.e. solid-state reaction) in the temperature range from 1,300 to 1,600 °C and by the coprecipitation at the three different temperatures: 400, 600 and 1,100 °C. The principal of these pigments makes the host lattice of the CeO2, which is doped by terbium ions. This incorporation of the doped ions leads to obtaining of the interesting dark orange colour after application into ceramic glaze. The aim of our research was to improve and optimize the synthesis conditions of these pigments. The samples were submitted to thermal analysis (TG–DTA) for determination of the temperature interval of the pigment formation and the thermal stability of pigments. The compounds were also measured from the point of view of their colouring, structure and particle size distribution.

Thermal analysis of the (Bi2O3)1−x (Lu2O3) x compounds

New inorganic compounds having the general formula (Bi2O3)1−x(Lu2O3)x (x ranges from 0.1 to 0.5) displaying orange colours have been synthesized by traditional solid-state route, as viable alternatives to lead, cadmium and chromium based yellow toxic inorganic pigments. The host lattice of these pigments is Bi2O3 that is doped by Lu3+ ions. The goal was to develop conditions for the synthesis of these compounds and to determine the influence of calcination temperature and lutetium content on their colouring effects. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. The pigments were also evaluated from the standpoint of their structure and particle sizes.

Thermal analysis of the Ce1−x Tb x O2 pigments

Compounds based on CeO2 were synthesized as high-temperature environment-friendly inorganic pigments with interesting hues. The pigments have been synthesized by using the solid state reaction in the temperature range from 1,300 to 1,600 °C. The host lattice of these pigments is CeO2 that is doped by terbium ions. The incorporation of doped ions provides interesting orange colours after application into ceramic glaze. The goal was to develop conditions for the synthesis of these compounds and to determine the influence of calcination temperature on their colouring effects. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. The pigments were also evaluated from the standpoint of their structure and particle sizes.

Thermal analysis of the Bi2O3-Y2O3-ZrO2 pigments

The synthesis of new compounds based on Bi2O3 is investigated because they can be used as new colour inorganic pigments. Chemical compounds of the Bi2-xYx/2Zr3x/8O3 type were synthetised. The host lattice of these pigments is Bi2O3 that is doped by Y3+ and Zr4+ ions. The incorporation of doped ions provides interesting colours and contributes to a growth of the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. This paper also contains the results of the pigment characterization by X-ray powder diffraction and their colour properties.

Thermal analysis of the Bi2O3-Er2O3-Zro2 pigments

The synthesis of new compounds based on Bi2O3 is investigated because they can be used as new colour inorganic pigments. Chemical compounds of the Bi2-xYx/2Zr3x/8O3 type were synthetised. The host lattice of these pigments is Bi2O3 that is doped by Y3+ and Zr4+ ions. The incorporation of doped ions provides interesting colours and contributes to a growth of the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. This paper also contains the results of the pigment characterization by X-ray powder diffraction and their colour properties.

Thermal analysis of the (Bi2O3)1−x(Y2O3)x pigments

The synthesis of new compounds based on Bi2O3 is investigated because they can be used as new ecological inorganic pigments. Chemical compounds of the (Bi2O3)1−x(Y2O3)x type were synthesized. The host lattice of these pigments is Bi2O3 that is doped by Y3+ ions. The incorporation of doped ions provides the interesting colours and contributes to a growth of the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. This paper also contains the results of the pigment characterization by X-ray powder diffraction and their colour properties.

Thermal synthesis of the (Bi2O3)1–x(Er2O3)x pigments

The synthesis of new compounds based on Bi2O3 is investigated because they can be used as new environmentally friendly inorganic pigments. Chemical compounds of the (Bi2O3)1–x(Er2O3)x type were synthetized. The host lattice of these pigments is Bi2O3 that is doped by Er3+ ions. The incorporation of doped ions provides interesting colours and contributes to an increase in the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments.

Preparation and practical application of spinel pigment Co0.46Zn0.55(Ti0.064Cr0.91)2O4

Synthesis of the green spinel pigment Co0.46Zn0.55(Ti0.064Cr0.91)2O4 by a novel two-step method of preparation have been investigated. Inorganic pigments are almost always prepared by a solid state reaction. It is classical ceramic method which used oxides, hydroxides or carbonates as precursors. The reaction is performed at temperature higher than 1300°C and an agent of mineralization is usually present. The presented novel method of preparation decreases the calcining temperature necessary for reaching of bright and clear hue of the pigments prepared. Main attention was focused on the influence of two types of titanium raw materials on the temperature region of the spinel structure formation and on the colour properties of the pigments. The mixture of precursors with TiO2 gives a one-phase system when calcining at 1100°C but the colour properties are more interesting at 1150°C. Thermal stability of this pigment is limited by temperature 1300°C. This temperature is connected with partial oxidation of Cr(III) to Cr(VI). Thermal analysis provided the first information about the temperature region of the pigment formation and determined the thermal stability of pigment.

Thermal analysis of pigments based on Bi2O3

The synthesis of new pigments based on Bi2O3 is investigated because they give interesting orange hues and can substitute the pigments problematic from the environmental point of view. Chemical compounds of the Bi2–xZr3x/4O3 type were synthesized. The host lattice of these pigments is Bi2O3 that is doped by Zr4+ ions. The area of ZrO2 solubility in Bi2O3 at 800°C forming solid solution of both oxides was studied. The incorporation of doped ions provides interesting colours and contributes to a growth of the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments.