The effect of sulfur evolution on the properties of high-temperature carbons—II. The addition of Fe2O3

A thianthrene-anthracene mixture has been used to study the influence of Fe₂O₃ addition in suppressing the volume expansion of carbons due to sulfur release on heat treatment. For undoped carbons, the particle density began to decrease above about 1200°C and continued to 2500°C. There was an accompanying sharp reduction in sulfur content between 1400–1600°C. With Fe₂O₃ addition, the sulfur content was higher over the whole temperature range studied. Between 1200–1600°C the carbon density increased slightly, while from 1600–2500°C the density continuously decreased. Below 1600°C, iron sulfide was detected in the cooled reaction mixture, consistent with the presence of an iron-sulfur liquid phase during heat treatment. The liquid phase appears to influence density changes through modifying the mechanisms for sulfur release. Although FeS was no longer evident at higher temperatures, the presence of iron compounds appeared to have an influence in reducing expansion.The addition of Fe₂O₃ did not affect crystal growth and development of structural order during graphitization. Density decreases for doped and undoped carbons are attributed to disruption of crystallite alignment. Porosity measurements showed that the increase in pore volume is due to the formation of pores smaller than 200 nm diameter.     

The nickel hydroxide electrode; the effect of ageing—II. Changes in electrochemical behaviour

Polarization curves for the anodic oxidation and cathodic reduction of Ni(OH)₂ electrodes at constant current have been obtained, and also Tafel curves for the anodic process. A comparison is made between the electrochemical behaviour of freshly prepared and of recrystallized Ni(OH)₂ layers, and the extent to which the differences may be correlated with structural charges in the solid phase is discussed.     

The influence of preparation method on the physicochemical properties of titania–silica aerogels: Part two

Titania–silica aerogels with different titania content were prepared. Four preparation methods differing mainly in approach to precursors hydrolysis were applied, while only three of them allowed total hydrolysis of silica precursor before titania precursor was added. The preparation of mixed products of titania and silica hydrolysis precursors containing gels was followed by high temperature supercritical drying (HTSCD) and thermal treatment at 500 °C. Obtained mixed oxides in form of aerogels were characterized by BET surface areas up to 1000 m²/g, mesopore volumes up to 1.6 cm³/g and bulk densities as low as 0.04 g/cm³. Even 18 h lasting aging did not allow to produce narrow diameter range mesoporous materials, their broad pore diameter distributions resulted in average pore sizes varying from 10 to nearly 30 nm. XRD measurements proved the presence of anatase crystalline form of titania, while silica was present in amorphous form. SEM studies indicated presence of isolated titania particles on titania–silica surface while joint hydrolysis method was applied. Titania–silica aerogels obtained by the simultaneous hydrolysis of precursors and the impregnation method showed high photocatalytic activity in degradation of salicylic acid in water. Activities of these mesoporous photocatalysts were higher than commercial P25 Degussa TiO₂. Comparison of activity of pure TiO₂ (P25 Degussa) and aerogels indicates higher utilization of titania present in mesoporous mixed oxides.     

Experimental investigation on explosion characteristics of nano-aluminum powder—air mixtures

Explosion characteristics of nano-aluminum powders with particle sizes of 35, 75, and 100 nm are investigated in a 20-liters spherical explosion chamber. Results show that the maximum explosion pressure and the maximum rate of pressure rise mainly depend on the dust concentration. For dust concentrations below 1000 g/m³, the maximum explosion pressure increases gradually to a maximum value with increasing dust concentration. After the dust concentration increases above 1250 g/m³, the maximum explosion pressure starts to decrease. The trends of the maximum rate of pressure rise follow the same pattern with increasing dust concentration. The lower explosion concentration limits of nano-aluminum powders with sizes of 35, 75, and 100 nm are found to be 5, 10, and 10 g/m³, respectively, while the lower explosion concentration limit of ordinary aluminum powders is about 50 g/m³.     

The effect of the surface nanostructure and composition on the antiwear properties of zirconia–titania coatings

This study describes the preparation, surface imaging and tribological properties of titania coatings modified by zirconia nanoparticles agglomerated in the form of island-like structures on the titania surface. Titania coatings and titania coatings with embedded zirconia nanoparticles were prepared by the sol–gel spin coating process on silicon wafers. After deposition the coatings were heat-treated at 500 °C or 1000 °C. The natural tendency of nanoparticles to form agglomerates was used to build separated island-like structures unevenly distributed over the titania surface having the size of 1.0–1.2 μm. Surface characterization of coatings before and after frictional tests was performed by atomic force microscopy (AFM) and optical microscopy. Zirconia nanoparticles were imaged with the use of transmission electron microscopy (TEM). The tribological properties were evaluated with the use of microtribometer operating in ambient air at technical dry friction conditions under normal load of 80 mN. It was found that nanocomposite coatings exhibit lower coefficient of friction (CoF) and considerably lower wear compared to titania coating without nanoparticles. The lowering of CoF is about 40% for coatings heated at 500 °C and 33% for the coatings heated at 1000 °C. For nanocomposites the wear stability was enhanced by a factor of 100 as compared to pure titania coatings. We claim that enhanced tribological properties are closely related to the reduction of the real contact area, lowering of the adhesive forces in frictional contacts and increasing of the composite hardness. The changes in materials composition in frictional contact has secondary effect.     

Use of the Weibull model on sizing thickeners—Part II: Methods of thickener sizing

Among several methods employed for sizing thickeners available in the literature, the Kynch, Biscaia Jr., Talmadge and Fitch, Roberts, Coe and Clevenger, and Oltmann methods use experimental data from sedimentation curves and graphical approaches. By using the Weibull distribution, it is possible to represent sedimentation curves with algebraic equations, which does not require the use of graphical approaches and provides more accuracy and speed for sizing calculations. In the present work, the main objective is the development of a set of equations for sizing continuous thickeners, for six conventional methods found in the literature, using the Weibull model. A comparative analysis of calculated and literature diameters for each graphical method presented variations between 0.73% and 8.93%. The use of the Weibull model presented the best accuracy for the Biscaia Jr. method, with a 0.73% average absolute error.     

The mechanism of mass transfer of solutes across liquid-liquid interfaces: Part II.—The transfer of organic solutes between solvent and aqueous phases

“Overall” transfer coefficients were determined for a number of organic ternary systems and the results compared with the values predicted assuming zero interfacial resistance and using individual transfer coefficients calculated from the correlation derived in the preceding paper. Although good agreement was obtained in many cases, some systems, notably ethyl acetate-water with acetone, gave larger transfer rates than predicted, whilst others, especially toluene-water systems gave lower results. The faster rates were found to be associated with interfacial turbulence.The low results are ascribed to slow heterogeneous reactions at the interface, and a method is devised for deriving the rate constants. Experiments were carried out at different temperatures in order to obtain the energies of activation. The probable reason for the slow step is discussed.     

The application of x-ray powder diffraction for the analysis of synthetic organic pigments. Part 2: artists’ paints

This paper presents x-ray powder diffraction data for over 200 synthetic organic pigments. These pigments, most manufactured in the last 130 years, are frequently found in modern works of art. Their identification is of interest in the field of art conservation for the purposes of dating works of art as well as making conservators and curators aware of issues with lightfastness and solubility. Most classes of these pigments, including β-naphthol, Naphthol AS, mono- and di-arylide yellows, quinacridones, copper phthalocyanines, benzimidazolones, and perylenes give good diffraction data. Some pigments, including certain triarylcarbonium and some other metal containing pigments, especially aluminum containing pigments, were found not to diffract. X-ray powder diffraction is of great use in distinguishing polymorphs of pigments such as quinacridones and copper phthalocyanines.     

The effect of axial diffusion processes on the optimum yield of tubular reactors—II: Variable temperatures,simple reversible reaction A@rlhar2:C

The one-dimensional model of an isothermal continuous flow tubular reactor with axial diffusion, considered in part I, is extended to deal with variable temperatures. A differential equation is deduced which allows the optimum yields and optimum temperature distributions to be determined. Some numerical results are obtained for a reactor with first order reversible reaction A @rlhar2: C, in which the activation energy of the reverse reaction is twice that of the forward reaction.     

The effect of solute concentration on fluidity and structure in aqueous solutions of electrolytes—II. Alkaline earth chlorides,cupric chloride and ferric chloride

An examination has been made of the effect of concentration on the temperature dependence of fluid flow in solutions of alkaline earth chlorides, cupric chloride and ferric chloride. From the way in which the Arrhenius and Eyring parameters for fluid flow vary with concentration in these solutions it is tentatively suggested that Mg²⁺ in concentrations up to 0·05 m enhances the intrinsic structural properties of water, but Mg²⁺ above this concentration, the remaining alkaline earth cations, Cu²⁺ and the ferric chloride complex destroy water structure; in the ferric-chloride—water system above 0·25 m water structure is not only destroyed with rising concentration but there are imposed upon the system new and entirely different fluid hydrate structures. It is also concluded that a common mechanism, which depends on the hydration properties of the cation, is responsible for the flow characteristics of these solutions.     

Generalized aged-adjusted effective modulus method for creep in composite beam structures. Part II — Application

The generalized age-adjusted effective modulus method for creep in composite beams is compared to the original age-adjusted effective modulus method, and various examples comparing the accuracy of the solution under the assumption of a linear aging creep law are given. It is shown that the use of the classical aging coefficient χ always leads to an underestimation of creep effects in a composite beam structure, as compared to the exact solution of the integral equations for creep in the cross section. The underestimation is sometimes very small, sometimes larger, depending on the type of the compliance function assumed. For the CEB compliance function the difference from the exact solution is larger than it is for the ACl compliance function. On the basis of the generalized age-adjsted effective modulus method, a new aging parameter χ_F is introduced, and it is shown that its use either slightly overestimates the creep effects or predicts them accurately in some special cases. Parameter χ_F depends not only the type of compliance functions of the materials interacting within the composite cross section, but also on the geometrical properties of the cross section.     

The Effect of Bauxite Substitution on High Temperature Strength Properties of Zirconia—corundum Mullite Material

Investigations on the effect of bauxite substi-tution for industrial alumina on high temperature strength and thermal shock resistance of reaction-sintered zirconia-corundum-mullite material(ZrO2 15%) have indicated that bauxite substitution would lead to increase in modulus of rupture at 1000-1400℃ as well as improvement in thermal shock resistance,Hot strength value reaches a maximum at 15% buxite addition.The mecha-nism of mechanical behavior at elevated tempera-tures is discussed in association with changes in mi-crostructural characteristics.     

The effect of heat treatment conditions on the textural and catalytic properties of nickel–titania composite aerogel catalysts

Highly dispersed nickel–titania composite aerogel catalysts have been prepared by CO₂ supercritical drying of alcogels obtained by the sol–gel process. The effect of heat treatment conditions on the textural and structural properties of the resulting aerogels was investigated by nitrogen adsorption–desorption, TG/DTA, XRD and TEM. The nickel–titania composite aerogel calcined and reduced under carefully controlled conditions exhibited an excellent catalytic performance for the liquid-phase hydrogenation of benzophenone to benzhydrol.     

Impedance and formation characteristics of electrolytically generated silver oxides—II. photo-effects

Photo-effects in the anodic oxidation of silver electrodes have been examined by means of potentiodynamic and ac impedance-following techniques. A primary photo-effect arises in the formation of Ag₂O after the oxide has formed a film appreciably thicker than a monolayer. Secondary photo-effects arise in the formation of AgO and in its reduction due to changes of amount of Ag₂O formed in the prior stage of oxidation of the electrode surface. A second region of primary photo-effect occurs prior to reduction of Ag₂O in the cathodic direction of potential sweep. Rise times of the photo-effect have been determined.Mechanisms of the photo-effect are discussed in terms of electron promotion from Ag⁺ interstitial sites in the oxide in relation to the semi-conducting properties of the oxides and local fields in the oxide film and its interfaces. Secondary effects in AgO formation from Ag₂O also arise because of changes of the nucleation rate, which controls the initial stages of the kinetics of AgO formation. Similar effects are associated with nucleation of Ag formation in reduction of Ag₂O in the cathodic cycle.     

The effect of rippled graphene sheet roughness on the adhesive characteristics of a collagen–graphene system

A great amount of effort has been made in order to reach a more precise understanding of the adhesion phenomenon that happens as a vital component of several biological systems. Therefore, a firm understanding of the important factors that influence this phenomenon is of special importance in triggering the adhesive characteristics of different biological, bio-inspired and synthetic materials in fields such as tissue engineering.In this study the adhesive characteristics of a multi-material system consisting of the frequently used synthetic material, graphene, in the form of armchair-configuration sheets, and an important biological filament which is type 1 Collagen consisting of 3 alpha helices, has been studied in detail. The main emphasis of this study is placed on understanding the effects of the roughness characteristics of the inorganic elements which are the graphene sheets on the overall adhesive features of the system which are quantified within the framework of two main criteria: adhesion energy and peeling force. At first, the methodology used in order to obtain graphene sheets with various roughness values is described in detail. The abovementioned criteria are then evaluated through Molecular Dynamics (MD) modeling of the system in the NAMD simulation software environment and various simulation scenarios are studied.     

The effect of sulfur evolution on the properties of high-temperature carbons—I. Thianthrene and thianthrene-anthracene precursors

The carbonization (525°C) and graphitization (up to 2500°C) of thianthrene, anthracene and a 17% wt thianthrene-83% wt anthracene mixture were investigated. The thianthrene carbons were found to be non-graphitizable and of low density. Upon heat-treatment from 1200–2500°C sulfur was evolved continuously and there was a further decrease in density due to an increase in closed porosity. The carbons produced from the mixture were found to be graphitizable and possessed similar crystal parameters to those carbons derived from anthracene after heat treatment to the same temperature. In contrast to the anthracene carbons, the mixed carbons showed a sharp decrease in density with heat treatment temperature. The principal reduction in sulfur content occurred between 1400–1600°C. The density change appears to be produced through the disruption of crystallite alignment which substantially increases the open pore volume for pores of less than 200 nm diameter. The behavior of the mixed carbon is similar to that reported for high sulfur petroleum cokes which can undergo an irreversible expansion (puffing) during graphitization.     

The effect of diffusion and bulk gas flow on the thermal oxidation of porous carbons—II. Diffusional effects in graphite at high temperatures

The variation with temperature and oxygen concentration of the oxidation rate of large tubular specimens of graphite exposed to oxidising gas on the bore surface has been examined. Temperatures in the range 550–675°C and oxygen concentrations between 2.5 and 20.8 per cent were studied. Under these conditions the overall rate of reaction is controlled by the rate of in pore mass transport. A previously reported mathematical model is extended to interpret these results. The experimental results yield an apparent energy of activation of 25.0 kcal/g atom and an apparent order of 0.81. Calculations based on the extended model give a true energy of activation for the graphite—oxygen reaction of 48.6 k cal/g atom and an order of reaction of 0.62.     

Analytical models of adhesively bonded joints—Part II: Comparative study

The literature survey presented in Part I describes the major analytical models for adhesively bonded joints, especially for single lap joints. By consulting the summary table given in Part I, the designer can choose from a wide range of models which is the best for a particular situation. However, the information given in the summary table is not sufficient for a proper selection. The designer also needs to know the time required for setting up an analysis and solving it. Another important factor is the accuracy of strength prediction. Therefore, models of increasing complexity were selected from the summary table and a comparative study was made in terms of time requirements and failure prediction for various cases. Three main situations were considered: elastic adherends and adhesive, elastic adherends with nonlinear adhesive, and nonlinear analyses for both adherends and adhesive. The adherends were both isotropic (metals) and anisotropic (composites). The effects of the overlap length and the adhesive thickness were also considered.     

Inhibition effect of zinc on the cathodic deposition of cobalt—II. Potentiodynamic and intensiodynamic curves in chloride solutions

Polarization curves obtained with the potentiodynamic and intensiodynamic methods (linear variation with time of cathodic potential or current imposed by a potentiostat) have been established in buffered chloride solutions of cobalt with a gold cathode, adding different proportions of more electronegative cations and keeping the anion concentration constant.Among all the more electronegative cations added (Cal²⁺, Ba ²⁺, Sr²⁺, Mg²⁺, Zn²⁺) only Zn²⁺ produced a particular change in the shape of the curves, similar to that obtained in anodic passivation.This specific effect of cathodic inhibition, blocking the discharge reaction of cobalt, has been studied in function of the Zn²⁺/Col²⁺ ratio and the temperature at pH 4, buffered with boric acid and in a more acid solution.The results support the hypothesis of the production of a zinc hydroxide film, favoured by specific adsorption of the zinc cations.