Kinds Of Unit Cells Research Articles

Damage Simulation for 3D Braided Composites by Homogenization Method

In order to study the failure patterns and strength of 3D braided composites from the microscopic view, the damage propagation under tensile loading steps in three kinds of unit cells is simulated. The homogenization formula of micro-stress and the solving approach of finite element method are given firstly. A criterion is presented to determine the damage and its pattern of each element, and then the stiffness degradation method based on Murakami's geometric damage theory is used to simulate the status of damage under tensile loading steps for three kinds of unit cells. It can be seen that the damage percentage and damage pattern of damaged unit cell are totally different for different kind of unit cells. More damaged elements are observed for face cell and corner cell than that for body cell. It is also observed that the damage firstly occurs at the area of face cell, which agrees well with experimental results. It is verified that considering the effects of face and corner cells are important for the damage and strength analysis of 3D braided composites.

Reaction of Fully Indium-Exchanged Zeolite A with Hydrogen Sulfide. Crystal Structures of Indium-Exchanged Zeolite A Containing In2S, InSH, Sorbed H2S, and (In5)7+

Four single crystals of fully dehydrated, fully indium-exchanged zeolite A (Inca. 10−Si12Al12O48 or Inca. 10-A, colorless) were exposed to 0.5 atm of H2S for 3 h at 298, 373, 423, and 573 K for crystals 1 to 4, respectively. After evacuation at temperature followed by cooling to 294(2) K, the crystals were red, brown, yellow, and yellow, respectively. Their structures were determined by single-crystal X-ray diffraction techniques in the cubic space group Pm3m at 294(2) K (a = 12.083(3), 12.076(2), 12.094(2), and 12.094(2) A; R1 = 0.069, 0.063, 0.065, and 0.060; R2 = 0.062, 0.058, 0.064, and 0.060 for crystals 1 to 4, respectively). The structures differ in the degree of sorption and/or reaction with H2S. Crystal 1 (In9.5H0.5−A(InSH)0.5(H2S)2.5) may be viewed as being an equimolar mixture of two kinds of unit cells with compositions In9−A(H2S)3 and In10H−A(InSH)(H2S)2. Unit cell 1 contains three H2S molecules stabilized as [(In)2(H2S)3]2+ in the large cavity and a tetrahedral (In5)n+ cluster in the sodali...

Crystal Structures of Encapsulates within Zeolites. 3. Xenon in Zeolite A

The positions of Xe atoms encapsulated in the cavities of fully dehydrated zeolite A of unit-cell composition Cs3Na8HSi12Al12O48 (Cs3-A) have been determined. Cs3-A was exposed to 255 atm of xenon at 400 °C for 7 days, followed by cooling at pressure to encapsulate Xe atoms; a second crystal was treated similarly at 450 atm, and a third at 1020 atm. The resulting crystal structures of Cs3-A(2.5Xe) (crystal 1, a = 12.245(2) Å, R1 = 0.056, R2 = 0.059), Cs3-A(4.5Xe) (crystal 2, a = 12.258(2) Å, R1 = 0.061, R2 = 0.058), and Cs3-A(5.25Xe) (crystal 3, a = 12.236(2) Å, R1 = 0.061, R2 = 0.057) were determined by single-crystal X-ray diffraction techniques in the cubic space group Pm3m at 21(1) °C and 1 atm. The approximately 2.5, 4.5, and 5.25 Xe atoms per unit cell, respectively, are distributed over three crystallographically distinct positions. At the center of each sodalite unit in crystals 1, 2, and 3, respectively, are 0.5, 0.75, and 0.75 Xe atoms at Xe(1); in addition, off center in crystal 3 are 0.25 Xe atoms at Xe(4), opposite a six-ring in the sodalite unit. Opposite four-rings in the large cavity at Xe(2) are 1, 2, and 2.25 Xe atoms, respectively, for the three crystals. Opposite six-rings in the large cavity at Xe(3) are 1, 1.75, and 2 Xe atoms, respectively. Relatively strong interactions of Xe(3) atoms with six-ring Na+ ions are observed: Na−Xe(3) = 3.18(2), 3.22(2), and 3.38(2) Å, respectively. In Cs3-A(2.5Xe), two Xe atoms are found in each large cavity: Xe2 with a 4.54(4) Å distance may exist. Cs3-A(4.5Xe) may be viewed as a mixture of two kinds of unit cells: in most of their large cavities, four Xe atoms form a rhombus with Xe(2)−Xe(3) = 4.51(3) Å and Xe(2)−Xe(3)−Xe(2) = 95.1(5)°. Cs3-A(5.25Xe) may also be viewed as having two kinds of large cavities: 75% contain a rhombus of four Xe atoms, Xe(2)−Xe(3) = 4.45(2) Å and Xe(2)−Xe(3)−Xe(2) = 97.3(4)°. The remaining 25% have five Xe atoms arranged trigonal-bipyramidally with three Xe(2)'s equatorial and two Xe(3)'s axial (Xe(2)−Xe(3) = 4.45(2) Å). These arrangements of encapsulated Xe atoms in the large cavity are stabilized by alternating dipoles induced on Xe(2) and Xe(3) atoms by four-ring oxygens and six-ring Na+ ions, respectively.

Synthesis and characterization of (Bi, AE)MnO 3 (AE=Ca, Sr) system

The effects of electron lone pairs of trivalent bismuth ions on the crystal structure and magnetic properties were examined in Bi 1− x AE x MnO 3 (AE=Ca, Sr). Polycrystalline perovskite manganites Bi 1− x AE x MnO 3 were synthesized by using a conventional ceramic technique and a high-pressure technique (4 GPa). Perovskites with triclinic, monoclinic, and tetragonal distortions were found in Bi 1− x Sr x MnO 3 from X-ray powder diffraction. In particular superlattice reflections were found in BiMnO 3 by electron diffraction which revealed two kinds of unit cell, i.e. polymorphism. The bismuth lone pair character was reflected in these structures. Both Bi 1− x Ca x MnO 3 and La 1− x Ca x MnO 3 showed the same crystal symmetry and weak ferromagnetism in the Ca-rich region. However, the magnetic moment of Bi 1− x Ca x MnO 3 was larger than that of La 1− x Ca x MnO 3 with the same x value. Their ferromagnetism was suppressed by charge ordering with further substitution of trivalent cations, although the charge ordering temperature of the La-system is higher than that of the Bi system. The difference is probably associated with the Bi lone pair.

The crystal structure of barium lead hexaaluminate phase II

A refinement was performed on the average crystal structure of barium lead hexaaluminate phase II ((Ba 0.8Pb 0.2) 2.34Al 21.0O 33.84) using single crystal X-ray diffraction data, giving a final R value of 0.030 with space group symmetry P 6m2 . The structure is essentially of a β-alumina type, but contains a lot of defects and interstitials. Inside the spinel block were found Ba(Pb) ions at 12-coordinated polyhedral sites, formed by complex defects, including triple Reidinger defects, in the same unit cell. Barium lead hexaaluminate phase II was found to consist of two kinds of unit cells with formulae “(BaPb) 3.0Al 20.0O 35.0” and “Ba 2.0Al 22.0O 34.0” in a 1 : 2 ratio; these three cells combine to form an a√3 × a√3 superstructure.