Design,preparation and properties of online-joints of C/SiC–C/SiC with pins

This work is aimed at providing a new joining technology for C/SiC composites and investigating the influence of drilling holes, hole distribution (including ratios of edge distance to diameter (E/D), width to diameter (W/D) and hole distance to diameter (H/D)) and the number of applied pins on the mechanical properties of C/SiC substrates and joints. The mechanical testing results show that drilling holes and hole distribution greatly affects the mechanical properties of C/SiC substrates but when adopting an optimized design principle (E/D ⩾ 3, W/D ⩾ 3 and H/D ⩾ 3) the effect could be neglected. 1D C/SiC pins with higher shearing strength (107.2 MPa) are more suitable to join the substrates. With the increase of pins (1, 2 and 4), the bearing loads of the joints increase almost linearly, and the reliability of joints is also improved in that the fracture mode changes from the interlayer damage to the substrate rupture. Besides, the joining process generates uniform and dense joining layer (composition of ZrC and SiC) and a strong bonding without obvious interface.     

Boron implantation effects in CdS thin films grown by chemical synthesis

CdS thin films grown on ITO/glass substrates by using chemical bath (CB) were boron-implanted employing 100 keV beam of boron ions (B⁺) with fluences in the range 1.0×10¹⁵–1.0×10¹⁶ ions/cm². The B doping was successfully carried out, as was proved by the major carrier density introduced in the range 0.8×10¹⁸–5.4×10¹⁸ cm⁻³, which was calculated from thermo power measurements. Raman spectroscopy results support the assumption that triply ionized boron (B³⁺) enters into the CdS lattice occupying Cd²⁺ sites, which create shallow donor levels in the forbidden energy band gap.     

Tribological properties of pulsed laser deposited DLC/TM (TM=Cr,Ag, Ti and Ni) multilayers

Tribological and scratch resistance properties of pulsed laser deposited Diamond-Like Carbon (DLC) coatings with transition metal interlayers (TM=Cr, Ag, Ti and Ni) are studied. Remarkably high scratch resistance property is found when DLC is deposited with Ni and Ti transition metal interlayer. Transformation of I(D)/I(G) ratio from a higher value on the surface to a lower value in the wear track of DLC indicates formation of graphitized/amorphized tribofilm during sliding. These tribofilms and formation of carbonaceous transfer layer is a characteristic of easy in-plane sliding which provides low friction coefficient for the system of DLC/Ni and DLC/Ti multilayer.     

Surface reactivity of graphite materials and their surface passivation during the first electrochemical lithium insertion

The surface passivation of TIMREX^® SLX50 graphite powder was studied as received and after heat treatment at 2500 °C in an inert gas atmosphere by differential electrochemical mass spectrometry in electrochemical lithium half-cells. 1 M LiPF₆ in ethylene carbonate and either a dimethyl carbonate, propylene carbonate or 1-fluoro ethylene carbonate co-solvent was used as electrolyte systems in these half-cells. The SEI-film formation properties of both graphite materials were correlated with their active surface area (ASA), being responsible for the interactions between the carbon and the electrolyte system. The active surface area was determined from the amount of CO and CO₂ gas desorbed at temperatures up to 950 °C from the graphite material surface after chemisorption of oxygen at 300 °C. The structural ordering at the graphite surface increased significantly during the heat treatment of the SLX50 graphite material as indicated by the significant decrease of the ASA value. The increased surface crystallinity was confirmed by krypton gas adsorption, Raman spectroscopy as well as temperature-programmed desorption. This increased structural ordering seemed to be the parameter being responsible for a hindered passivation of the heat-treated SLX50 causing partial exfoliation of the graphite structure during the first electrochemical lithium insertion in the ethylene carbonate/dimethyl carbonate electrolyte. In the case of the ethylene carbonate/1-fluoro ethylene carbonate electrolyte system, primarily the fluoro compound is responsible for the graphite passivation. In this electrolyte system, pristine SLX50 and the less reactive, heat-treated SLX50 graphite showed significantly different SEI-film formation mechanisms. In contrast, no difference in the passivation mechanism could be identified for different graphite surfaces in the ethylene carbonate electrolyte system with propylene carbonate as co-solvent.     

Electrochemical behaviors of silicon based anode material

Mixed silicon–graphite anode materials have been prepared by means of simple mechanical milling process. Research reveals that the microstructural changes, accompanying the electrochemical alloying/de-alloying operations, lead to a macrostructural deformation of the anodes. The key step for improving of such composites therefore could be sought in alternative electrode configurations or textures, preserving the electrodes from the detrimental effect of silicon hosts volume variations.     

Magnetic moments and exchange interaction in Sm(Co, Fe)5 from first-principles

The electronic structure, magnetization and exchange interaction in Sm(Co_1?xFe_x)₅ with x = 0–1 are studied from a first-principles density functional calculation. The dependence of the magnetization on Fe content shows a 3d-like Slater–Pauling relationship in these alloys. As the Fe content x increases from 0 to 1.0, the magnetization increases from 7.8 μ_B to 10.6 μ_B (x = 0.8) and then decreases to 10.0 μ_B (x = 1). The effective exchange interaction parameters show a peak value around x = 0.6, which is ascribed to the exchange parameters between Fe and Co being larger than those for Co–Co and Fe–Fe pairs. The estimated T_C from the calculated exchange parameters range between 890 K and 1357 K in Sm(Co_1?xFe_x)₅ using a multi-sublattices mean field model.     

The dynamic storage capacity of a periodically heated slab

The well-known problem of evaluating the dynamic heat storage capacity of a 1D slab is analysed extending the results to the more general case of periodic excitation profiles of any form. Equations in time and frequency domain to calculate the storage capacity are obtained and applied to some cases, showing that harmonic heating is not the most efficient way to store energy in finite and semi-infinite slabs. Quantitative comparisons show that, for slab of finite thickness, intermittent heating may yield up to 40% more heat storage capacity (and up to 52% for semi-infinite slab) than harmonic heating.     

Synthesis and characterisation of rare earth oxysulphide phosphors. I. Studies on the preparation of Gd2O2S:Tb phosphor by the flux method

Terbium activated gadolinium oxysulphide phosphor (Gd₂O₂S:Tb) shows bright green luminescence and high efficiency under X-ray excitation. Phosphor utilisation depends on powder characteristics and luminescence properties that are regulated during the synthesis stage. The paper presents some of our new results on the synthesis of Gd₂O₂S:Tb phosphor by solid-state reaction route from oxide precursors. Efficient luminescent powders utilisable in the manufacture of X-ray intensifying screens for medical diagnosis were prepared from optimised synthesis mixtures containing oxide precursors, alkaline carbonate based flux, alkaline phosphate based mineralising additives and sulphur suppliers.     

Mechanochemical synthesis of hybrid electrolytes from the Li2S–P2S5 glasses and polyethers

Novel hybrid solid electrolytes were prepared by mechanochemistry using the Li⁺ conductive Li₂S–P₂S₅ glasses and –OH terminated oligomers. The P–O–C bonds were observed in FT-IR spectra for the obtained electrolytes, suggesting that the molecular level hybrid materials were synthesized. The addition of small amounts of oligomers into the glass successfully enhanced the conductivity of hybrid electrolytes by lowering glass transition temperature. The hybrid electrolyte with 2 mol% of 1,4-butanediol exhibited the ambient temperature conductivity of 9.7 × 10⁻⁵ S cm⁻¹, which is 1.5 times as large as the conductivity of the pristine glass. The hybrid with a polyether showed lower conductivity than the hybrid with 1,4-butanediol. Incorporating oligomer blocks into glass network is a new approach to enhance the conductivity of glass-based solid electrolytes.     

New conjugated materials containing cyano substituents for light-emitting diodes

New electroluminescent cyano-substituted phenylenevinylene (PV) monomeric and oligomeric chromophores, 1–3, were synthesized by Knoevenagel condensation and investigated in terms of their photoluminescence (PL) and electroluminescence (EL) behavior. All show PL emission maxima between 463 and 471 nm in solution with quantum efficiencies of 0.65, 0.46 and 0.68, respectively. EL maxima in an LED configuration ITO/PEDOT–PSS/1–3/Ca–Al were 507, 518 and 551 nm with luminance efficiencies 0.01, 0.05 and 0.02 cd/A, respectively.