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In this work, the reduction mechanism of potassium chromate (K2CrO4) was investigated via in situ high-temperature X-ray diffraction coupled with Fourier transform infrared spectroscopy. During the hydrogen reduction of K2CrO4, the formation of K3CrO4, KCrO2, and KxCrO2 were detected for the first time. The study discovered that K2CrO4 was firstly reduced to K3CrO4 and an amorphous Cr(III) intermediate product at low temperature (400–500 °C). Moreover, the K3CrO4 was the only crystalline material at this stage. As the temperature increased, a stabilized amorphous CrOOH was formed. At a high temperature (550–700 °C), KCrO2 was generated. Interestingly, a portion of KCrO2 was spontaneously decomposed during the hydrogen reduction, accompanying by the formation of K0.7CrO2. Finally, the results clearly illustrated the reduction mechanism of K2CrO4: K2CrO4 → K3CrO4 → amorphous intermediate → KCrO2.

Convergent-beam electron diffraction (CBED) is one of the most popular techniques to measure crystal thickness. The traditional measurement involves linear fitting of several fringes across the CBED disc, but for a thin crystal with fewer than three fringes the usefulness of this method will be limited. CBED Tools, a free plugin for the DigitalMicrograph software, provides a fast (∼1–2 min) and accurate algorithm to measure the crystal thickness on the basis of the linear fitting method, but it is also capable of determining the crystal thickness when it is very thin and only one fringe or part of the first fringe is recorded. CBED Tools can also be utilized to handle the severely distorted CBED pattern obtained when the zero-order Laue zone Kikuchi lines overlap with the fringes.

Molten salt synthesis (MSS), due to the high reactivity of salts, small diffusion distance and high mobility of species in molten salt, can not only reduce the synthesis temperature but also shorten the reaction time. Herein, MSS method was employed to synthesize δ-CaCr2O4 powder by using CaO, Cr2O3 as raw materials and CaCl2 which has a high solubility of CaO as molten salt. The influence of reaction time was investigated and δ-CaCr2O4 with platelet morphology was obtained after reaction for 2 h at 900 °C. Pure rod-like β-CaCr2O4 was further prepared by simply annealing the as-synthesized δ-CaCr2O4 in argon atmosphere for 3 h at 1100 °C. The magnetization and its corresponding reciprocal susceptibility of δ-CaCr2O4 and β-CaCr2O4 samples was also measured and calculated, which indicated a paramagnetic arrangement and an antiferromagnetic arrangement during the test temperature range 2–250 K, respectively.

In this study, Cr2O3 green pigments were prepared using two types of CrOOH, alpha-CrOOH and gamma-CrOOH, and the resulting pigments were characterised. The thermal decomposition behaviours of the two types of synthesised CrOOH were discussed. The resulting Cr2O3 pigments were characterised using X-ray diffraction (XRD), scanning electron microscope (SEM), International Commission on Illumination (CIE-L*a*b*) and ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS). The key factors and mechanism that influenced the preparation of the Cr2O3 green pigments were studied. The results revealed that gamma-CrOOH produces Cr2O3 that is more homogeneous, has a uniform size of 200-400 nm and a yellowish-green colour compared to alpha-CrOOH, which produces Cr2O3 with non-uniform sizes and a brownish-green colour. In addition to the different particle morphologies and sizes, the change in the crystal field, which leads to a shift in the (4)A(2g) -> T-4(1g) and (4)A(2g) -> T-2(2g) transition, also affects the colour of the pigment. Lastly, a series of Cr2O3 green pigments displaying a wide range of colours were prepared by calcining mixtures of alpha-CrOOH and gamma-CrOOH with different compositions. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Cr2O3 green pigment was prepared through the thermal decomposition of chromium hydroxide precursor, which was precipitated by Cr(NO3)(3) and NaOH solutions. The color performance of as-prepared Cr2O3 is comparable to the commercial pigment when the precursor was precipitated from 025 mol/L Cr(NO3)(3) solution. When increasing the concentration of Cr(NO3)(3) solution, the color of Cr2O3 becomes more reddish and much darker. The structure and morphology of different precursors and Cr2O3 samples were characterized. Amorphous precursor with non-agglomerated particles, which could be obtained by controlling the concentration of Cr(NO3)(3) solution, was found to be a prerequisite for preparing Cr2O3 pigment with good color performance. (C) 2013 Elsevier B.V. All rights reserved

We report a quick and easy method for a random selected area electron diffraction (SAED) pattern without rotating and tilting the specimen to perform phase identification and unit cell determination by combined with the XRD softwares. If your TEM is well aligned and camera length is carefully corrected, two-dimensional (2D)-SAED pattern can be directly transformed to 1D-profile after the center determination of pattern, this profile is then imported to XRD analysis packages. Finally, phase identification and unit cell determination can be performed after peak search or precise peak position determined by profile fitting. Two examples, flaky-like TiO2 nanomaterial and TiO2 nanotubes precipitated by the silver nanoparticles, were tested and verified for the validation of phase identification and unit cell determination using this method; the successful crystallographic analysis of one single gold nanocrystal indicates it is still validate for the nanocrystals with the smaller diffraction volume, but need two or more random tilt SAED patterns. This method could be further used in the quantitative phase analysis, structure determination and Rietveld refinement for the nanomaterials if the reliable integrated intensity can be extracted. Microsc. Res. Tech. 76:641647, 2013. (c) 2013 Wiley Periodicals, Inc.

In order to reduce greenhouse gas emission and urban heat island mitigation, pure and titanium(Ti)-doped Cr 2 O 3 cool pigments were prepared via the thermal decomposition of CrOOH. The result reveals that the pure Cr 2 O 3 pigment presents both a high near-infrared reflectance and excellent yellowish-green color. Meanwhile, titanium was doped to improve the NIR reflectance and strengthen the color. The color of the designed pigments was brighter, and most importantly, the NIR reflectance increased from 84.04% to 91.25% with increasing Ti content from 0 to 0.006% (mole fraction). However, excessive doping of Ti 4+ for Cr 3+ in Cr 2 O 3 ( x (Ti)≤0.008%) decreased the NIR reflectance. One possible reason is that the conductivity type of the Cr 2− x Ti x O 3+ δ changed from p-type conduction to n-type conduction with increasing Ti content, accompanied by the change of the electrical resistivity and the NIR reflectance. The prepared yellowish-green Cr 2 O 3 pigments have a great potential for extensive applications in construction and military.

We report a quick and easy method for a random selected area electron diffraction (SAED) pattern without rotating and tilting the specimen to perform phase identification and unit cell determination by combined with the XRD softwares. If your TEM is well aligned and camera length is carefully corrected, two-dimensional (2D)-SAED pattern can be directly transformed to 1D-profile after the center determination of pattern, this profile is then imported to XRD analysis packages. Finally, phase identification and unit cell determination can be performed after peak search or precise peak position determined by profile fitting. Two examples, flaky-like TiO2 nanomaterial and TiO2 nanotubes precipitated by the silver nanoparticles, were tested and verified for the validation of phase identification and unit cell determination using this method; the successful crystallographic analysis of one single gold nanocrystal indicates it is still validate for the nanocrystals with the smaller diffraction volume, but need two or more random tilt SAED patterns. This method could be further used in the quantitative phase analysis, structure determination and Rietveld refinement for the nanomaterials if the reliable integrated intensity can be extracted.