The Crystal Data of Ternary Rare Earth Borides, RCo_2B_2

Compounds with the composition of RCo_2B_2 (R=La, Nd, Sm, Gd, Tb, Dy, and Y) were prepared by arc-melting methods. Their crystal structure was investigated by means of X-ray diffraction. These ternary rare earth borides crystallize in the tetragonal lattice. The lattice parameters are a=3.616±0.003 A and c=10.215±0.005 A for LaCo_2B_2 and a=3.561±0.002 A and c=9.358±0.005 A for YCo_2B_2. The good agreement between the X-ray diffraction intensities observed and those calculated shows that the ternary borides, LaCo_2B_2 and YCo_2-B_2, crystallize in the ThCr_2Si_2-type structure. The crystallographic data obtained for LaCo_2B_2 and YCo_2B_2 are as follows : space group 14/mmm (D^_); R in 2(a), 4Co in 4(d), and 4B in 4(e) with z～3/8. The boron atoms in this structure are situated at the center of a trigonal prism formed by four rare earth atoms and two cobalt atoms. We also found the RCo_2B_2 compounds to be isostructural with LaCo_2B_2 and YCo_2B_2, where R=Nd, Sm, Gd, Tb, and Dy. However, efforts to prepare CeCo_2B_2 and ErCo_2B_2 by arc-melting were unsuccessful

Chemical Vapour-Deposited Silicon Nitride : Part 1. Preparation and Some Properties

Pyrolytic Si_3N_4 has been deposited on a graphite substrate, using a mixture of SiCl_4, NH_3 and H_2. The pyrolysis is performed with deposition temperatures of 1100 to 1500℃, total gas pressures of 5 to 300 Torr, and flow rates of H_2=700, NH_3=60 and SiCl_4 (1iq.)=0.8 cm^3 min^. Massive amorphous and crystalline pyrolytic forms of Si_3N_4 are prepared at a maximum thickness of 4.6 mm. The effects of deposition conditions on some properties of the deposited products and the dependence of formation of amorphous or crystalline deposits on deposition temperature and total pressure were investigated. The surface and cross-sectional structures show growth cones and oriented crystals which are strongly dependent on the deposition conditions. The thin deposits are translucent ; the thick deposits vary in colour from white to black. The silicon content is close to the theoretical composition and independent of the deposition conditions, while the oxygen content increases with decreasing deposition temperature and total pressure. No segregation of silicon and nitrogen at cone boundaries was found

The Preparation and Crystal Structure of Ternary Rare Earth Borides, RCo_3B_2

In the ternary system of rare earth-cobalt-boron, RCo_3B_2 compounds (R=rare earth elements) were prepared by arc-melting methods. Their crystal structure was investigated by X-ray diffraction methods. These ternary borides, RCo_3B_2, crystallize in a hexagonal lattice. The lattice parameters are a=5.020±0.002A and c=3.027±0.002 A for YCo_3B_2 and a=5.066±0.003 A and c=3.022±0.002 A for GdCo_3B_2. The good agreement between the X-ray diffraction intensities observed and calculated shows that the ternary borides, YCo_3B_2 and GdCo_3B_2, crystallize in the CaZn_5-type structure. The space group and atomic positions are as follows : P6/mmm (D^1_), 1R in 1(a), 3Co in 3(g), and 2B in 2(c). It can be seen from these results that the ternary borides, RCo_3B_2, have a superstructure in which two Co atoms in the 2(c) site of intermetallic compounds, RCo_5, with the CaZn_5-type structure are replaced by two B atoms. The B atoms in this structure are situated at the center of a trigonal prism formed by six Co atoms. The interatomic distances between B and the six Co atoms are 2.11-2.10 A and are fairly constant, although the radii of the rare earth atoms are changed according to the lanthanide contraction. We have also found RCo_3B_2 compounds to be isostructural with YCo_3B_2 and GdCo_3B_2, where R=Ce, Sm, Tb, Dy, Ho, and Er. Efforts to prepare LaCo_3B_2, PrCo_3B_2, and NdCo_3B_2 by arc-melting were unsuccessful

The Crystal Structure and Nonstoichiometry of Rare Earth Oxyfluoride

Oxyfluoride phases for the rare earth Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Y have been prepared by heating a mixture of lanthanon fluorides, LnF_3, and lanthanon oxides, Ln_2O_3. Three phases were identified. The rhombohedral phases, LnOF, have a stoichiometric composition, and the tetragonal phases, Ln_4O_3F_6, have a comparatively large nonstoichiometric composition range. The third cubic phase, with a fluorite-type structure, was observed in the SmOF-Sm_4O_3F_6 region after quenching from a high temperature. This establishes that both the rhombohedral SmOF and the tetragonal Sm_4O_3F_6 transform to the cubic phase and form a complete solid solution in the high-temperature range. It is postulated that the rhombohedral and tetragonal phases are pseudocubic from the fact that the diffraction patterns of these two phases are closely similar to that of the fluorite type

Chemical Vapor-Deposited Amorphous Silicon Nitride

Chemical vapor-deposited amorphous Si_3N_4 (CVD-amorphous Si_3N_4) up to 4.2mm in thickness has been prepared from a gaseous mixture of NH_3 and H_2-carried SiCl_4 under various deposition conditions. The formation of the CVD-amorphous Si_3N_4 depended strongly on the deposition temperature, total gas pressure and gas flow rate. The CVD-amorphous Si_3N_4 prepared at 1100-1300℃ does not crystallize by heating at each deposition temperature. Their density and deposition rate are markedly dependent on deposition conditions and have maximum values of 3.00g/cm^3 (94% of the theoretical density of α-Si_3N_4) and 0.36mm/hr, respectively. The Vickers microhardness of the CVD-amorphous Si_3N_4 at room temperature varies between 2200 and 3200kg/mm^2 according to its deposition conditions. The hardness at 1300℃ is 1200～1300 kg/mm^2. The thermal conductivity was 0.010cal/cm/sec/℃ at 20℃ and 0.012cal/cm/sec/℃ at 1300℃. The thermal expansion coefficient at 20～1200℃ is 2.99±0.05/℃. The formation mechanism and the effect of gas flow patterns on the deposition rate of the CVD-amorphous Si_3N_4 are also discussed

Changes of cytokines in mouse skeletal muscle and plasma by a single bout of endurance exercise.

Introduction: Exercise influences some cytokine levels, which is considered the body’s reaction against endogenous stress. Previous human studies demonstrated that high intensity exercise contributes to a dramatic increase of plasma cytokines like Interleukin-6 (IL-6) and Interleukin-1 receptor antagonist (IL-1ra) immediately after exercise. Recently, it has been identified that skeletal muscle produces cytokines and peptides and they exert both paracrine and endocrine effects. However, the sequential changes of cytokine production according to exercise conditions such as intensity, types and working time are still unclear. In this study, we identified the sequential changes of cytokines in both skeletal muscle and plasma after acute endurance exercise. Methods: Male C57BL/6 mice (n=35) were randomized to a sedentary or a treadmill running group (25m/min, 0% grade). To examine the sequential changes of cytokines, the exercise group was divided into 3 groups and each group was sacrificed at different time points (Post-exercise 0, 2, and 6 hours). Skeletal muscle and plasma were taken and real-time PCR and ELISA were conducted. The mRNA expression of IL-6, IL-7, IL-15, Myostatin, Irisin, Leukaemia inhibitory factor (LIF), IL-1ra and IL-1beta in skeletal muscle was identified by real-time PCR. The protein concentrations of IL-6, IL-1ra, Monocyte chemotactic protein 1 (MCP-1), and Myeloperoxidase (MPO) in plasma were investigated by ELISA. Also, IL-6 protein concentration in skeletal muscle was measured by ELISA. Results: IL-6 mRNA expression in skeletal muscle increased at 6 hrs post-exercise compared with pre-exercise, immediately post-exercise and 2 hrs post-exercise. In contrast, IL-6 protein concentration in skeletal muscle was decreased significantly 2 and 6 hrs post-exercise compared with pre-exercise and immediately post-exercise. However, there was no significant change in IL-6 protein levels in plasma. Also, there were no significant changes in IL-7, IL-15, Myostatin, Irisin, LIF, IL-1ra and IL-1beta mRNA levels at each time point. Conclusions: A single bout of endurance exercise in mice altered IL-6 mRNA and protein expression in skeletal muscle in a delayed onset manner. However, there has no effect on IL-7, IL-15, Myostatin, Irisin, LIF, IL-1ra and IL-1beta mRNA expression in skeletal muscle and the plasma concentrations of IL-6, IL-1ra, MCP-1, and MPO

Densely Packed Linear Assembles of Carbon Nanotube Bundles in Polysiloxane-Based Nanocomposite Films

Linear assemblies of carbon nanotubes (LACNTs) were fabricated and controlled in polysiloxane-based nanocomposite films and the effects of the LACNTs on the thermal and electrical properties of the films were investigated. CNTs were dispersed by mechanical stirring and sonication in a prepolymer of polysiloxane. Homogeneous suspensions were cast on polyamide spacers and oriented by linear-assembly by applying DC and switching DC electric fields before the mixture became cross-linked. Densely packed LACNTs that fixed the composite film surfaces were fabricated with various structures and thicknesses that depended on the DC and switching DC conditions. Polymer nanocomposites with different LACNT densities exhibited enhanced thermal and electrical conductivities and high optical transmittances. They are considered promising structural materials for electronic sectors in automotive and aerospace applications

Surface engineering alumina armour ceramics with laser shock peening

Laser shock peening (LSP) of Al 2 O 3 armour ceramics is reported for the first-time. A 10 J, 8 ns, pulsed Nd:YAG laser with a 532 nm wavelength was employed. The hardness, K Ic , fracture morphology, topography, surface residual stresses and microstructures were investigated. The results showed an increase in the surface hardness by 10% which was confirmed by a reduction in Vickers indentations size by 5%. The respective flaw sizes of the Vickers indentations were also reduced (10.5%) and inherently increased the K Ic (12%). Residual stress state by X-ray diffraction method showed an average stress of − 64 MPa after LSP, whilst the untreated surface stress measured + 219 MPa. Further verification with the fluorescence method revealed surface relaxation with a maximum compressive stress of − 172 MPa induced after LSP within the Al 2 O 3 armour ceramic. These findings are attributed to a microstructural refinement, grain size reduction and an induction of compressive stress that was relaxing the top/near surface layer (post LSP) from the pre-existing tensile stresses. Further process refinement/optimization will provide better control of the surface properties and will act as a strengthening technique to improve the performance of armour ceramics to stop bullets for a longer period of time and protect the end-users

The Preparation and Nonstoichiometry of Samarium Hexaboride

Samarium hexaboride was prepared by the borothermal reaction ; 2Sm_2O_3+(6+4x)B=4SmB_x+3B_2O_2. The residual oxygen content amounted to less than 0.03 w/o under optimum reaction conditions heating at 1650℃ for 2 hr under a high vacuum. It was found by X-ray intensity and density measurements that the samarium hexaboride stayed stable over a large nonstoichiometric region from Sm_B_6 to SmB_6. These extensive nonstoichiometric properties of samarium hexaboride can be explained in terms of the required electron numbers of the SmB_6 network in hexaboride