A study of the surface of carbon fiber by means of X-ray photoelectron spectroscopy—III

This paper reports a study of the surface composition of carbon fibers treated by various methods by means of X-ray photoelectron spectroscopy (SPS). C_1S X-ray photoelectron spectra showed that after the surface treatment of carbon fibers, the carbon atoms in the hydrocarbon were changed into

etc. oxygen-containing groups, that is, the results of surface oxidation and concentration increased with time but finally reached a constant level. Comparing experimental results for the treatments used, we found that all of these methods resulted in concentrations of oxygen groups on the surface in the order:

.Evidence was found for the formation of lactone groups

during treatment in an oxygen or nitrogen plasma, but not during treatment by nitric acid or anodic oxidation.     

Adsorption isotherms of helium on activated charcoal

Adsorption of helium on activated charcoal has been measured in the pressure range 1–30 atm¹ and in the temperature range 15–70 K. A Clapeyron like law (InP_s = A + B/T) for fictitious saturation vapour pressure P_s above T_cr is deduced experimentally from the measurements. This law leads to a fairly good generalized correlation for all experimental data in the framework of Dubinin theory:

     

Regulation of cell fate by near infrared-responsive telomerase activity

Here we develop a strategy using near infrared (NIR) modulation of telomerase activity based on gold nanocage@smart polymer system. Using this biocompatible design, we can regulate cellular behavior. This system has been used in vivo by taking advantages of NIR. This is the first example for optical modulation of telomerase activity in living cells and tissues.

     

Synthesis of anion exchange adsorbent particles by surface functionalization of polystyrene-divinylbenzene based spherical porous matrices

The replacement of Br⁻ by trimethylamine for the synthesis of anion exchange adsorbent particles by surface functionalization of polystyrene-divinylbenzene based spherical porous particles was studied experimentally and theoretically. The calculated values of the kinetic parameters indicate that the net rate of the replacement of Br⁻ by trimethylamine is dominated by the kinetic mechanism involving the formation and opening of an epoxide,

where P represents the polymeric backbone. The theoretical results obtained from the solution of the equations of the mathematical model that describes the dynamic behavior of the kinetic mechanisms, clearly indicate that the highest concentration of the desired product,

on the surface of the pores of the particles, is obtained when the initial concentration of trimethylamine is highest. The equilibrium adsorption of bovine serum albumin (BSA) into the anion exchange adsorbent particles produced in this work was also studied, and the results indicate that the maximum value of the concentration of BSA in the adsorbed phase is a weak function of the concentration of the desired product,

, on the surface of the pores of the particles.     

Etude de l'intensification des échanges de chaleur par convection dans des canaux de section triangulaire et rectangulaireStudy on the increase of convective heat exchange in channels of triangular and rectangular section

Most of the research work applied to the intensification of heat transfer through convection in turbulent flow, has been devoted to local heat flow and local friction losses. Intensification is obtained by means of turbulators inside smooth channels (fins, steps).In the re-sticking zone of the boundary layer, the heat transfer is maximum and the friction factor is minimum, the latter being maximum in the free flow zone. Maximum values are more than ten times higher than those observed in an undisturbed analogous stream.As early as 1958, those results have been applied to the construction of heat exchangers by which the heat transfer coefficient rises faster than the hydraulic resistance (discovery No 242).Such heat exchangers (water-air) are built from ribbed fin-plates and cross-tubes. The ribs act as turbulators inside the channels which are allowed between plates and tubes.The present paper deals with the influence of geometrical shape and distribution of the turbulator on thermal and hydraulic efficiencies of heat transfer surfaces.The results are presented as graphs

where:Nu,Nu_R = Nusselt number for channels with and respectively, without, turbulators; ε,ε_R=friction loss factor for channels with, and respectively, without, turbulators; l'/d = pitch of trottling=ratio between the length of smooth piece l' and its hydraulic diameter d; d1/d=rate of throttling=ratio between hydraulic diameter of the throttled section d1, and that of the smooth piece d.Experimentations have been performed with 16 different combinations of l'/d and d1/d, in channels of the same triangular section and Reynolds number varying between 400 and 5500; in channels with different triangular sections; in channels with rectangular sections.Main results are: the heat transfer intensification depends on the parameters l'/d and d1/d; the maximum intensification depends on the shape of the channel section, the highest values being obtained with triangular shaped channels; the most efficient turbulators

consist of two dimensioned surfaces generated along the channel radius.New radiators for farm tractor-engines have been developed. Their volume and weight are half those of conventional radiators. Their construction does not require any significant modification of the traditional manufacturing technique of such type of equipment and their utilization in dusty environments does not raise any particular difficulty.     

Thkrmotropic liquid crystalline compounds with lateral long-chain substituents. Part VI. Liquid crystalline oxime bmzoates with lateral long-chain substituents

The synthesis and liquid crystalline properties of several series of oxime benzoates with long-chain lateral substituents of the general formulae R¹

are reported and discussed from the view point of molecular statistical theories.     

Characterization of single and discretely-stepped electro-composite coatings of nickel-alumina

Electrodeposition from a sulfamate bath has been used to produce single layer and discretely stepped electro-composites consisting of a metallic nickel matrix with second phase alumina (-Al₂O₃) particles. Light optical microscopy (LOM), scanning electron microscopy (SEM), quantitative image analysis (QIA), and micro-indentation techniques were used to characterize the deposits. As previously seen, an increase in bath particle loading and decrease in plating current density increased the volume percent of alumina incorporated into the coating, with a maximum of 40 vol % being attained. For samples deposited above 1 A/dm², a direct relationship between the alumina volume percent and coating hardness was seen due in part to the related decrease in interparticle spacing (IPS) at the higher vol %. However, the strengthening mechanism of the electro-composites may be more complex with both the metallic nickel grain structure and IPS being factors, as seen for samples deposited at 0.5 A/dm². The incorporation of alumina into the electrodeposited nickel was also observed to affect the as-plated surface structure of the coating. Due to the particles inhibiting the formation of pyramidal features found on the surface of pure nickel electrodeposits, the electro-composite surfaces were observed to be relatively flat. Also, structure within the metallic nickel matrix appeared due to rapid growth of the nickel coating around the inert particles when plated at high current densities. In addition, discretely layered functionally graded materials were produced without alterations to the original deposition procedure of the single layer deposits. It was found that the various processing stages needed to produce the stepped coatings did not affect the structure or properties of the individual layers, when compared to that of the corresponding single-layered electro-composites.     

Coatings on graphite crucibles used in melting uranium

Standard coatings for graphite crucibles used for melting uranium have generally been zirconia based and have been applied as a paint or by flame spraying. These coatings do not provide adequate protection at the temperatures normally required for melting uranium alloys. Yttria provides superior protection above 1300°C but becomes less satisfactory above 1450°C when applied directly on graphite. The utilization of a protective niobium/zirconia bilayer coating between the yttria and the graphite results in improved performance at 1500°C. Yttria has been satisfactorily applied both by plasma spraying and by brush applying a stable suspension. When the protective niobium layer is used, coating adherence after melting is excellent and multiple use of coatings is practical. The coatings adhere to graphite with a high coefficient of thermal expansion (CTE) (≈7 μm m^-1 °C^-1) much better than to standard crucible grade graphite (≈4μm m^-1 °C^-1). A single Nb/Y₂O₃-coated high CTE graphite crucible has been used for seven melts at 1450°C without repair or increased carbon contamination.The yttria paint coating is cost effective when compared with flame- or plasma-sprayed zirconia.     

Synthesis of bactericidal polymer coatings by sequential plasma-induced polymerization of 4-vinyl pyridine and gas-phase quaternization of poly-4-vinyl pyridine

Plasma-based technology is an alternative to produce universal polymer coatings with the appropriate requirements of robustness and stability for antibacterial applications. Here, we proposed a sequential two-step alternative to synthesize antibacterial polymer coatings. A non-isothermal plasma reactor, operated at atmospheric pressure (P_atm) and room temperature (T_room), was used to induce free radical polymerization of 4-vinyl pyridine (4VP) on high-density polyethylene (PE). In a subsequent step, the poly-4VP (P4VP) films were treated with a bromoethane/He gas stream to produce quaternized P4VP (P4VPQ) films. Chemical structure of polymer films was validated by infrared and UV–visible spectroscopy, and morphology was evaluated by optical and atomic force microscopy; scanning electron microscopy was used to determine films thickness, which was then used to estimate the surface charge density. The bactericidal capacity was determined with a standard test by using Escherichia coli. Both types of films had an estimated charge density in the order of 10¹⁶ positive charges per cm²; P4VP films removed about 95–99% of bacteria, whereas 4PVPQ films eliminated 100%. The methodology proposed for the synthesis of antibacterial polymer coatings is simpler, faster, and more environmentally friendly than other plasma-based methods; operation at T_room and P_atm may also have a significant effect on the economics and the ease of implementation of the process at commercial scale. The suggested approach may facilitate the development of new universal coatings, and operating plasma conditions could be extrapolated for engineering antibacterial coatings in industrial areas where bacterial attachment is of concern.     

Very high thermal stability with excellent dielectric,and non-ohmics properties of Mg-doped CaCu<Subscript>3</Subscript>Ti<Subscript>4.2</Subscript>O<Subscript>12</Subscript> ceramics

In this work, the nominal CaCu_3?xMg_xTi_4.2O₁₂ (0.00, 0.05 and 0.10) ceramics were prepared by sintering pellets of their precursor powders obtained by a polymer pyrolysis solution method at 1100 °C for different sintering time of 8 and 12 h. Very low loss tangent (tanδ)?<?0.009–0.014 and giant dielectric constant (ε′) ～?1.1?×?10⁴–1.8?×?10⁴ with excellent temperature coefficient (Δε′) less than ±?15% in a temperature range of ??60 to 210 °C were achieved. These excellent performances suggested a potent application of the ceramics for high temperature X8R and X9R capacitors. It was found that tanδ values decreased with increasing Mg²⁺ dopants due to the increase of grain boundary resistance (R_gb) caused by the very high density of grain, resulting from the substitution of small ionic radius Mg²⁺ dopants in the structure. In addition, CaCu_3?xMg_xTi_4.2O₁₂ ceramics displayed non-linear characteristics with the significant enhancements of a non-linear coefficient (α) and a breakdown field (E_b) due to Mg²⁺doping. The high values of ε′ (14012), α (13.64) and E_b (5977.02 V/cm) with very low tanδ value (0.009) were obtained in a CaCu_2.90Mg_0.10Ti_4.2O₁₂ ceramic sintered at 1100 °C for 8 h.     

About the allotropic transformations of PbSnF4

Microcalorimetric and dilatometric studies of PbSnF₄ give evidence of several allotropic forms for PbSnF₄. The complex thermal behaviour may be summarized as follows :

.The crystallographic data of the detected allotropic forms have been determined by investigations on single crystals. All structures derive from the fluorite-type. The obtained results confirm a previous work of the authors, new more precise techniques bringing further information.     

Diaphyseal fractures treated by polylactide and hydroxyapatite pins. Experimental study in rat

Hydroxyapatite (HAp) coatings were deposited onto substrates of metal biomaterials (Ti, Ti6Al4V, and 316L stainless steel) by electrophoretic deposition (EPD). Only ultra-high surface area HAp powder, prepared by the metathesis method 10Ca(NO₃)₂ + 6(NH₄)₂HPO₄ + 8NH₄OH), could produce dense coatings when sintered at 875–1000°C. Single EPD coatings cracked during sintering owing to the 15–18% sintering shrinkage, but the HAp did not decompose. The use of dual coatings (coat, sinter, coat, sinter) resolved the cracking problem. Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) inspection revealed that the second coating filled in the valleys in the cracks of the first coating. The interfacial shear strength of the dual coatings was found, by ASTM F1044-87, to be 12 MPa on a titanium substrate and 22 MPa on 316L stainless steel, comparing quite favorably with the 34 MPa benchmark (the shear strength of bovine cortical bone was found to be 34 MPa). Stainless steel gave the better result since -316L (20.5 m mK^-1) > -HAp (14 m mK^-1), resulting in residual compressive stresses in the coating, whereas -titanium (10.3 m mK^-1) < -HAp, resulting in residual tensile stresses in the coating. © 1999 Kluwer Academic Publishers     

Interfacial bond strength of electrophoretically deposited hydroxyapatite coatings on metals

Hydroxyapatite (HAp) coatings were deposited onto substrates of metal biomaterials (Ti, Ti6Al4V, and 316L stainless steel) by electrophoretic deposition (EPD). Only ultra-high surface area HAp powder, prepared by the metathesis method 10Ca(NO₃)₂ + 6(NH₄)₂HPO₄ + 8NH₄OH), could produce dense coatings when sintered at 875–1000°C. Single EPD coatings cracked during sintering owing to the 15–18% sintering shrinkage, but the HAp did not decompose. The use of dual coatings (coat, sinter, coat, sinter) resolved the cracking problem. Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) inspection revealed that the second coating filled in the valleys in the cracks of the first coating. The interfacial shear strength of the dual coatings was found, by ASTM F1044-87, to be 12 MPa on a titanium substrate and 22 MPa on 316L stainless steel, comparing quite favorably with the 34 MPa benchmark (the shear strength of bovine cortical bone was found to be 34 MPa). Stainless steel gave the better result since -316L (20.5 m mK^-1) > -HAp (14 m mK^-1), resulting in residual compressive stresses in the coating, whereas -titanium (10.3 m mK^-1) < -HAp, resulting in residual tensile stresses in the coating. © 1999 Kluwer Academic Publishers     

Critical Behavior of La<Subscript>0.67</Subscript>Ba<Subscript>0.33</Subscript>Mn<Subscript>0.95</Subscript>Fe<Subscript>0.05</Subscript>O<Subscript>3</Subscript> Manganite

The critical behavior of perovskite manganite La_0.67Ba_0.33Mn_0.95Fe_0.05O₃ at the ferromagnetic–paramagnetic has been analyzed. The results show that the sample exhibited the second-order magnetic phase transition. The estimated critical exponents derived from the magnetic data using various such as modified d’Arrott plot Kouvel–Fisher method and critical magnetization M(T _C, H). The critical exponents values for the La_0.67Ba_0.33Mn_0.95Fe_0.05O₃ are close to those expected from the mean field model β = 0.504 ± 0.01 with T _C = 275661 ± 0.447 (from the temperature dependence of the spontaneous magnetization below T _C ), γ = 1.013 ± 0.017 with T _C = 276132 ± 0.452 (from the temperature dependence of the inverse initial susceptibility above T _C ), and δ = 3.0403 ± 0.0003. Moreover, the critical exponents also obey the single scaling equation of M(H, ε) = |ε| ^β f _±(H/|ε| ^β+γ ).     

Deposition of TiN/CrN hard superlattices by reactive d.c. magnetron sputtering

Multilayer superlattice coatings of TiN/CrN were deposited on silicon substrates using a reactive d.c. magnetron sputtering process. Superlattice period, also known as modulation wavelength (A), was controlled by controlling the dwell time of the substrate underneath Ti and Cr targets. X-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) were used to characterize the films. The XRD data showed 1st and 2nd order satellite reflections along the principal reflection for films having 132 Å > Å > 84 Å, thus confirming the formation of superlattice. The multilayer coatings exhibited hardness(H) as high as 3200 kg/mm², which is 2 times the rule-of-mixtures value (i.e.)H _TiN = 2200 kg/mm² andH _CrN = 1000 kg/mm²). Detailed investigations on the effects of various process parameters indicated that hardness of the superlattice coatings was affected not only by modulation wavelength but also by nitrogen partial pressure and ion bombardment during deposition.     

Pathogen-mimicking nanocomplexes: self-stimulating oxidative stress in tumor microenvironment for chemo-immunotherapy

A novel drug-loaded pathogen-mimicking nanocomplex (MSN-DOX-SP-LPS) has been constructed for synergistic chemo-immunotherapy.

     

Influence of Nd doping on microwave dielectric properties of SrTiO<Subscript>3</Subscript> ceramics

Sr_1?x Nd _x TiO₃ (x?=?0.08–0.14) ceramics were prepared by conventional solid-state methods. The analysis of crystal structure suggested Sr_1?x Nd _x TiO₃ ceramics appeared to form tetragonal perovskite structure. The relationship between charge compensation mechanism, microstructure feature and microwave dielectric properties were investigated. Trivalent Nd³⁺ substituting Sr²⁺ could effectively decrease oxygen vacancies. This reduction and relative density were critical to improve Q?×?f values of Sr_1?x Nd _x TiO₃ ceramics. For ε _r values, incorporation of Nd could restrain the rattling of Ti⁴⁺ cations and led to the reduction of dielectric constant. The τ _f values were strongly influenced by tilting of oxygen octahedral. The τ _f values decreased from 883 to 650 ppm/°C with x increasing from 0.08 to 0.14. A better microwave dielectric property was achieved for composition Sr_0.92Nd_0.08TiO₃ at 1460 °C: ε _r ?=?160, Q?×?f?=?6602 GHz, τ _f ?=?883 ppm/°C.     

Strength and deformation properties of compositions with plasma-sprayed coatings

Results, which make it possible to compare the strength properties of the group of compositions investigated with plasma-sprayed coatings, are obtained. It is established that the deformability characteristic _cr ^c correlates better with strength characteristics as compared with the universally adopted deformability characteristic _cr ^b . It is demonstrated that based on the set of parameters determined, compositions with a thin dysprosium oxide coating and compositions with a thick yttrium oxide exhibit the best mechanical characteristics of the coatings compared.Translated from Problemy Prochnosti, No. 6, pp. 57–60, November–December, 1966.     

Structure of CN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 0.5) deposited by arc sputtering of graphite

The structure of a-C and CN _x coatings 1–3 μ thick deposited on metal substrates by arc-pulse sputtering of graphite target in nitrogen background at P = (10^?2 ?5) Pa was studied by transmission electron microscopy and scanning electron microscopy. Concentration and depth distribution of nitrogen in CN _x depend on progressive saturation of graphite target. Nitrogen-free coatings (x = 0) consist of amorphous matrix with multiwalled nanotubes. Structure of carbon nitride coatings depends on nitrogen concentration. Over the range of C_N/C_C < 0.15 and C_N/C_C > 0.4 CN _x coatings are amorphous. The structure of CN_0.15<x<0.4 is a mixture of two types of amorphous domains, one of which is decorated by microcrystalline inclusions. The same structured inclusions were found on graphite target modified by electric arc. The obtained results allow understanding the dependence of the CN_0≤x≤0.5 coatings properties on nitrogen concentration.     

Effect of Ni<Superscript>2+</Superscript> substitution on crystal structure and microwave dielectric properties for MgZrNb<Subscript>2</Subscript>O<Subscript>8</Subscript> ceramics

Monoclinic structured Mg_1?xNi_xZrNb₂O₈ (0?≤?x?≤?0.12) ceramics were synthesized for the first time through traditional solid-state reaction process and pure phase were obtained in all range. Rietveld refinement was used to analyze the crystal structure. With the increase of Ni²⁺ substitution amount, ε _r decreased, Q?×?f rose first then fell, τ _f shifted for the positive direction. Bond ionicity, lattice energy and bond energy were separately calculated to investigate the correlations with microwave dielectric properties. Typically, ceramics samples with the composition of Mg_0.92Ni_0.08ZrNb₂O₈ sintered at 1280 °C for 4 h exhibited the optimum microwave dielectric properties: ε _r ?=?24.58, Q?×?f?=?74534.1 GHz, τ _f ?=???49.11 ppm/°C, which could be a promising material for application.