Structure and Magnetic Properties of RFe6−xGa6+x (R=rare earth)

The crystal structures and magnetic properties of RFe6−xGa6+x (R=Ce, Pr, Nd, Sm, and Gd) alloys have been investigated by x-ray powder diffraction and magnetic measurement. A ternary intermetallic compound with an orthorhombic ScFe6Ga6 type structure is found in these alloys. The lattice parameter contraction is observed when the higher atomic number lanthanides are substituted into the intermetallic. In each unit cell, there are six nonequivalent crystal positions, i.e., 2a, 4e, 4f, 4g, 4h, and 8k, which are occupied by 2R, 4GaI, 4(FeI,Ga), 4GaII, 4GaIII, and 8FeII, respectively. The RFe6−xGa6+x alloys have ferromagnetic ordering but the magnetic transitions have been found in Nd based alloy. The RFe6−xGa6+x alloys show a soft magnetic behavior but the magnetization hysteresis loops have been observed in the Nd and Sm alloys at 5 K. The saturated magnetic moments per molecule tend to increase from Ce to Nd. However, a drastic decrease of magnetic moment in GdFe6Ga6 alloy is observed and is likely due to the Gd spin alignment being antiparallel to Fe spin. The saturation magnetic moments of these alloys are calculated and agree with the experimental values

Magnetic and Electronic Transport Properties of YbxCa1−xMnO3 Compounds

The polycrystalline YbxCa1−xMnO3 (x=0.1,0.2) were studied by x-ray powder diffraction, magnetic, and electrical resistivity measurements. The YbxCa1−xMnO3 crystallizes in an orthogonally distorted perovskite structure, and shows the ferromagnetic ordering with TC more than 110 K. However, the field dependence of magnetization and electrical resistivity exhibits very complicated behavior. A magnetic field induced insulator–metal transition has been found in the Yb0.2Ca0.8MnO3 compound. In addition, the large asymmetry in magnetization and resistivity hysteresis loops has been observed in this compound at 10 K, which might be due to the charge ordering and magnetocrystalline anisotropy

Metakaolin particle size reduction and geopolymer composite modeling for higher strength

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Drying shrinkage behavior of metakaolin-based and bamboo fiber reinforced geopolymers

This Brazil-USA collaborative research uses bamboo cultivated in the Amazon region and metakaolin attained from calcined Amazonian kaolin. The durability of sustainable geopolymer materials is studied by means of the drying shrinkage aging behavior. Scanning electron microscopy and energy dispersive x-ray fluorescence were used to investigate the microstructure of the composite materials. X-ray diffraction was used to confirm the formation of geopolymer. The water treated geopolymer matrix (GP) samples dried at room conditions for the periods of 3-7-14-21-28-56-112 days showed very close and increasing weight and length changes. The GP reinforced with bamboo fiber (GPBF) treated samples weight and length changes increased from the 3-day sample up to the 21-day, then it dropped down to the 112-day. The GP water treated samples dried at room conditions for the aging periods showed increasing flexural strength (MOR) and modulus of elasticity (E). The GPBF treated samples MOR were higher and very close to each other

Strength and elastic behavior of metakaolin-based and bamboo fiber reinforced geopolymers

Amazonian metakaolin-based and bamboo fiber reinforced geopolymers were studied by means of the strength and elastic aging behaviors for construction materials applications. Scanning electron microscopy and energy dispersive x-ray fluorescence were used to investigate the microstructure of the composite materials. X-ray diffraction was used to confirm the reliability of the samples as being geopolymers. The geopolymer matrix (GP) and the GP reinforced with bamboo fiber (GPBF) samples were aged-dried at room conditions for the periods of 1-7-28 days. The GP and GPBF ultimate compressive stress increased with age from 1-day to 28-day, while elastic modulus decreased with age. The GPBF samples ultimate compressive stresses and elastic moduli were lower than the GP samples values, but still can be suitable as sustainable construction materials