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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on K2Cr2O7 by Materials Project

K2Cr2O7 crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of two K2Cr2O7 sheets oriented in the (1, 0, 0) direction. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a rectangular see-saw-like geometry to four O2- atoms. There are a spread of K–O bond distances ranging from 2.63–2.95 Å. In the second K1+ site, K1+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of K–O bond distances ranging from 2.59–2.72 Å. There are two inequivalent Cr6+ sites. In the first Cr6+ site, Cr6+ is bonded to four O2- atoms to form corner-sharing CrO4 tetrahedra. There are a spread of Cr–O bond distances ranging from 1.63–1.77 Å. In the second Cr6+ site, Cr6+ is bonded to four O2- atoms to form corner-sharing CrO4 tetrahedra. There are a spread of Cr–O bond distances ranging from 1.68–1.90 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to one K1+ and one Cr6+ atom. In the second O2- site, O2- is bonded in a linear geometry to two Cr6+ atoms. In the third O2- site, O2- is bonded in a distorted single-bond geometry to one K1+ and one Cr6+ atom. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to two K1+ and one Cr6+ atom. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to two K1+ and one Cr6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2Cr2O7 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗
NASA NTRS1978

Determination of carbon by the oxidation reduction reaction with chromium

Free carbon was determined in silicon and boron carbides in ash, oxides, and other materials by oxidation to carbon dioxide with a mixture of K2Cr2O7 + H2SO4. The determination was made from the amount of CR(6) consumed, by adding excess Mohr's salt and titrating with a standard solution of KMnO4. The amount of Cr(6) self reduced was determined in a blank test. Optimum oxidation and conditions were achieved when the volumes of 5% k2Cr2Oz and H2SO4 were equal. The mixture was boiled for 1-2 hours using a reflex condenser. The volume should not be reduced, in order to avoid an increase in the sulfuric acid concentration. The relative error was 4-7% for 0.005-0.04 g C and less than or equal to 3.5% for 0.1 g C.

Mashkovich, L.↗
NASA NTRS1983

Interatomic Auger transitions in maximal valent V and Cr compounds

The sensitivity of the intensities of the L(3)M(23)M(45) and L(3)M(45)M(45) Auger transitions toward the 3d character in the valence band has been demonstrated by using argon ion bombardment as a means of in situ reduction for the valence state of V and Cr in their maximal valent compounds. The selected V(5+) and Cr(6+) compounds were V2O5, NH4VO3, K2Cr2O7, K2CrO4, and CrO3. Auger and X-ray photoelectron spectra of fresh samples were obtained, and the samples were then subjected to ion bombardment of various durations. The subsequent spectra were recorded to monitor possible alterations due to the reduction of the cation valence state. The interatomic to intraatomic transitions of the Auger spectra transitions of the Auger spectra were observed dynamically and in situ. In particular, the intensity of the cation L(3)M(23)N(45) transitions was observed to increase dramatically with ion bombardment. The correlation between the interatomic Auger transition and covalency as well as the movements of the 3d electrons are discussed.

Yin, L. I.↗