In situ high-temperature X-ray diffraction studies of reduction of K2CrO4 and the formation of KxCrOy compounds

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.

Download Full-text

Experimental Considerations and Limitations in the Application of Ultra High Temperature (2100°C) X-Ray Diffraction

Advances in X-ray Analysis ◽

10.1154/s0376030800009101 ◽

1991 ◽

Vol 35 (A) ◽

pp. 425-429

Author(s):

Sampath S. Iyengar

Keyword(s):

High Temperature ◽

Crystalline Material ◽

Thermal Treatments ◽

Ceramic Fibers ◽

X Ray Diffraction ◽

X Ray ◽

Controlled Atmospheres ◽

Heat Treated ◽

Multiple Samples

In-situ, high temperature X-ray diffraction (XRD) is an extremely useful tool for studying, monitoring or investigating crystal structure modifications as well as phase transformations in crystalline material during thermal treatments in controlled atmospheres. This technique has been used to investigate the thermal behavior of materials such as carbonate minerals, ceramic fibers, coating pigments, etc. The advantages of such a technique over the conventional practice, where samples are heat treated in a separate oven and then analyzed by XRD include: consistency of sample placement; preservation of high temperature structures to facilitate observation of metastable phases that are unstable upon exposure to outside atmosphere or during cooling; real time monitoring of reactions that occur, and products that are formed at a desired temperature or environment; and need for multiple samples or analysis.

Download Full-text

In-situ High Temperature X-ray Diffraction Study of the Am-O System

MRS Advances ◽

10.1557/adv.2017.200 ◽

2016 ◽

Vol 1 (62) ◽

pp. 4133-4137 ◽

Cited By ~ 1

Author(s):

E. Epifano ◽

R. C. Belin ◽

J-C Richaud ◽

R. Vauchy ◽

M. Strach ◽

...

Keyword(s):

High Temperature ◽

Lattice Parameter ◽

Minor Actinide ◽

Controlled Atmosphere ◽

X Ray Diffraction ◽

X Ray ◽

Binary Phase Diagrams ◽

First Time ◽

O Phase

ABSTRACTIn the frame of minor actinide recycling, (U,Am)O2 are promising transmutation targets. To assess the thermodynamic properties of the U-Am-O system, it is essential to have a thorough knowledge of the binary phase diagrams, which is difficult due to the lack of thermodynamic data on the Am-O system. Nevertheless, an Am-O phase diagram modelling has been recently proposed by Gotcu. Here, we show a recent investigation of the Am-O system using in-situ High Temperature X-ray Diffraction under controlled atmosphere. By coupling our experimental results with the thermodynamic calculations based on the Gotcu model, we propose for the first time a relation between the lattice parameter and the departure from stoichiometry.

Download Full-text

High-temperature X-ray diffraction and thermal expansion of nanocrystalline and coarse-crystalline acanthite α-Ag2S and argentite β-Ag2S

Physical Chemistry Chemical Physics ◽

10.1039/c5cp07224g ◽

2016 ◽

Vol 18 (6) ◽

pp. 4617-4626 ◽

Cited By ~ 37

Author(s):

S. I. Sadovnikov ◽

A. I. Gusev ◽

A. V. Chukin ◽

A. A. Rempel

Keyword(s):

Thermal Expansion ◽

High Temperature ◽

Diffraction Method ◽

Silver Sulfide ◽

X Ray Diffraction ◽

X Ray ◽

First Time

An in situ study of thermal expansion of polymorphic phases of coarse-crystalline and nanocrystalline silver sulfide – monoclinic acanthite α-Ag2S and cubic argentite β-Ag2S – has been carried out for the first time using the high-temperature X-ray diffraction method.

Download Full-text