scholarly journals The fascinating world of mayenite (Ca12Al14O33) and its derivatives

2021 ◽  
Author(s):  
Adriano Intiso ◽  
Federico Rossi ◽  
Antonio Proto ◽  
Raffaele Cucciniello
Keyword(s):  
Aluminum Oxide ◽  
Crystalline Structure ◽  
Electric Charge ◽  
Ammonia Synthesis ◽  
Unit Cell ◽  
Environmental Sensors ◽  
Free Oxygen ◽  
Sorbent Materials ◽  
Oxygen Substitution ◽  
Oxide Ions

AbstractMayenite (12CaO·7Al2O3) is a mesoporous calcium aluminum oxide, with a characteristic crystalline structure. The framework of mayenite is composed of interconnected cages with a positive electric charge per unit cell that includes two molecules [Ca24Al28O64]4+, and the remaining two oxide ions O2−, often labelled “free oxygen”, are trapped in the cages defined by the framework. Starting from mayenite structure several derivatives have been prepared through advanced synthetic protocols by free oxygen substitution with various anions. Mayenite and its derivates have been intensively investigated in many applications which include catalysis (oxidation and reduction, ammonia synthesis, pinacol coupling), environmental sensors and CO2 sorbent materials. In this review, we summarize our recent results on the main applications of mayenite and its derivatives.

scholarly journals The structure of polychloroprene

1942 ◽  
Vol 180 (980) ◽  
pp. 100-107 ◽  
Keyword(s):  
Physical Properties ◽  
Crystalline Structure ◽  
Light Treatment ◽  
Unit Cell ◽  
Cross Linking ◽  
Chain Molecules ◽  
X Ray ◽  
Before And After ◽  
Ray Methods ◽  
Long Chain

Specimens of polychloroprene before and after light treatment have been examined by X -ray methods. There is no change in the crystalline structure, although there are differences in the physical properties ascribed to cross-linking of the long-chain molecules. The unit cell is possibly ortho­rhombic: a = 8·90 A , b = 4·70 A, c = 12·21 A, and contains four chloroprene (C 4 H 5 Cl) units.

Crystalline structure of Ba2YCu0.25W0.75O6: A member of the new set of Ba2YzCuxW1−xO6 solid solutions

1996 ◽  
Vol 11 (1) ◽  
pp. 42-44 ◽  
Author(s):  
Bokhimi ◽  
A. Morales ◽  
A. Garci´a-Ruiz
Keyword(s):  
Solid Solution ◽  
Crystalline Structure ◽  
Solid Solutions ◽  
Local Environment ◽  
Unit Cell ◽  
Ordered Structure ◽  
Space Group ◽  
First Approximation ◽  
And Tungsten

A model for the crystalline structure of Ba2YCu0.25W0.75O6 solid solution is given. The model proposed a perovskite ordered structure, with a cubic unit cell made from eight perovskite-like units and having a symmetry described by the space group Fm3m. The crystalline structure was refined by the Rietveld technique, giving RF=0.048 for 82 reflections. The solid solution was characterized by the following parameters: Z=4, Mr=613.2, a=8.43630(8) Å, V=600.42(1) Å3, Dx=6.78 g cm−3, μ=209.04 mm−1, and F(000)=1047. The model assumed that copper and tungsten atoms, which were ordered with Y atoms, had the same local environment. Therefore, it was only a first approximation to the crystalline structure.

The Structure of Polychloroprene

1942 ◽  
Vol 15 (4) ◽  
pp. 847-853
Author(s):  
C. J. Birkett Clews
Keyword(s):  
Physical Properties ◽  
Crystalline Structure ◽  
Spatial Configuration ◽  
Unit Cell ◽  
Cross Linking ◽  
X Ray ◽  
Ray Density ◽  
Pass Through ◽  
Ray Methods ◽  
Identity Period

Abstract Specimens of polychloroprene and light-treated polychloroprene have been examined by x-ray methods. There is evidently no change in the crystalline structure of the two substances, although there are differences in physical properties which are ascribed to cross-linking of the long polychloroprene chains. This conclusion is confirmed by the x-ray work. The unit cell of polychloroprene is probably orthorhombic, with dimensions a=8.90 A.U., b=4.70 A.U., c=12.21 A.U. From the experimentally determined density of 1.086 g. per cc, it is deduced that there are four chloroprene units in the cell. The x-ray density (for the stretched material) is 1.14 g. per cc. The long chains lie parallel to the b-axis (the direction of stretching), and four of these chains pass through the unit cell. It is concluded, from the identity period, that the chain is not planar and a possible spatial configuration is given.

Iodo-oxyapatite, the first example from a new class of modulated apatites

1999 ◽  
Vol 55 (2) ◽  
pp. 165-169 ◽  
Author(s):  
Peter Alberius Henning ◽  
Sven Lidin ◽  
Vačlav Petříček
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Unit Cell ◽  
Apatite Structure ◽  
Flux Method ◽  
Space Group ◽  
X Ray ◽  
New Class ◽  
Oxide Ions

Iodo-oxyapatite [pentadecacalcium iodide oxide nonaphosphate, Ca15(PO4)9IO] was synthesized by a flux method and the structure was solved from single-crystal X-ray data. The crystal structure was refined in the space group P63/m [a = 9.567 (1), c = 20.754 (2) Å and Z = 2] to wR on F of 0.0459. Iodo-oxyapatite has a typical hexagonal apatite structure but the unit cell is tripled along the hexad owing to ordering of the iodide and oxide ions along this direction.

scholarly journals The crystalline structure of benzene

1932 ◽  
Vol 135 (827) ◽  
pp. 491-498 ◽  
Keyword(s):  
Benzene Ring ◽  
Crystalline Structure ◽  
Unit Cell ◽  
Space Group ◽  
Preliminary Results ◽  
Amount Of Information ◽  
Previous Communication ◽  
Cell Dimensions

In a previous communication the writer gave the preliminary results of an investigation on the structure of solid benzene. It may be recalled that the unit cell was found to have the following dimensions at —22° C. ; a = 7·44, b = 9·65, c = 6·81 Å. U., while the space-group was determined as Q h 15 (orthorhombic bipyramidal). The unit cell contains four molecules, the molecules being centro-symmetrical. Since the publication of these results a certain amount of information has been obtained by other investigators. Bruni and Natta took powder photographs of benzene which confirmed the above values of the cell-dimensions; this is very satisfactory, since previous workers (Broomé and Eastman) had obtained axial ratios which did not agree particularly well with each other’s or with the writer’s. Mrs. Lonsdale has shown that in hexamethylbenzene the benzene ring is planar, the diameter of the atoms being 1·42 Å. U. More recently she has examined hexachlorobenzene, and although in this case the investigation did not yield quite such definite results, it was shown that if the ring is planar then again the diameter of the atoms must be 1·42 Å. U.

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