Application of automated electrical resistance sensors for measurement of corrosion rate of copper,bronze and iron in model indoor atmospheres containing short-chain volatile carboxylic acids

The corrosion rate of copper and bronze Cu-8 wt.%Sn increased rapidly when the concentration of formic or acetic acid in air reached about 300 ppb at 80% relative humidity (RH) and a temperature of 20 °C. It decreased slowly during the several days after pollutant removal due to the slow rate of pollutant desorption from the metal surfaces. Corrosion of these metals was barely affected by the acids at RH up to 60%. For iron, the critical concentration of formic acid in air which led to surface activation at 80% RH was between 1000 and 1590 ppb.     

Preparation and characterization of tungsten nanopowders from WC scrap in molten salts

Tungsten carbide (WC) scrap was used as a consumable anode to prepare tungsten powder in NaCl–KCl melt at 1023 K for the first time. The electrolysis process was investigated. Results showed that the tungsten component in WC anode was dissolved as W^2 + into the NaCl–KCl melt. The cathode reaction was controlled by the diffusion of tungsten ions. The effect of electrolysis parameters, including the anode–cathode distance, cathode current density and different electrolysis ways (galvanostatic and potentiostatic electrolysis), on the purity and grain size of the cathode deposits was studied. It showed that a large anode–cathode distance was beneficial to the formation of pure tungsten powder at the cathode. With increasing the cathode current density, the tungsten grain size first decreased and then increased. When the cathode current density was 0.125 A cm^− 2, tungsten powder with a diameter of smaller than 100 nm was obtained. Deposits prepared through galvanostatic and potentiostatic electrolysis was compared in the end.     

Synthesis and characterization of low molecular weight photorefractive materials with thioxanthene unit

Two esters of succinic acid containing a thioxanthene unit as an electron-transporting moiety and a 4-dicyanovinylaniline (THEH-DCVA) or 4-nitrovinylaniline unit (THEH-NVA) as an electro-optically (EO) active chromophore were successfully synthesized. The obtained succinates form stable amorphous films at room temperature. These compounds have absorption coefficients of 6.7 and 21.5 cm⁻¹ at 633 nm and glass transition temperatures of 11 and 14 °C for THEH-DCVA and THEH-NVA, respectively. Optical absorption is due to electric charge transfer interaction between an electron-accepting thioxanthene moiety and an electron-donating EO active chromophore. The synthesized compounds without photosensitizers, a plasticizer, and polymer binder showed photorefractivity. A large coupling gain (140 cm⁻¹ at 93 V/μm) was observed for THEH-NVA.     

An investigation on the stabilization of special polyacrylonitrile nanofibers as carbon or activated carbon nanofiber precursor

This paper reports the effect of the conditions of stabilization process on the properties of special polyacrylonitrile nanofibers (SAF) with an average diameter of 467 nm. Stabilization constitutes an important pretreatment for the production of either carbon fibers or activated carbon fibers. It was found that the higher the stabilization temperature, the lower the initial induction time and the total reaction time. Extent of reaction increases with both treatment time and temperature of stabilization process. Crystallinity index and crystal size of stabilized nanofibers decreases as a result of stabilization. Special polyacrylonitrile nanofibers containing itaconic acid shows a higher capability for stabilization process. Potassium permanganate as a catalyst leaves a positive effect on the extent of reaction of stabilization. The diameter of nanofibers decreases by about 20% as a result of stabilization at 250 °C. Thermally stabilized nanofiber shows a wider exothermic peak with a lower height.     

Newly synthesized fused heterocyclic compounds in thin films with semiconductor properties

Temperature-dependent electrical conductivity and thermoelectric power of some recently synthesized fused heterocyclic compounds (nonsymmetrical bisindolizines), are studied. Thin-film samples (d = 0.10–0.20 μm) deposited from dichloromethane solutions onto glass substrates were used. Organic films with reproducible electronic transport properties can be obtained if, after deposition, they are submitted to a heat treatment within temperature range 300–600 K.The studied compounds show typical p-type semiconductor behavior. The activation energy of the electrical conduction ranges between 0.90 and 1.17 eV, while the ratio of charge carrier mobilities was found in the range 0.94–0.97.Some correlations between semiconducting parameters and molecular structure of the organic compounds have been discussed.In the higher temperature range (373–601 K), the electronic transport in examined compounds can be interpreted in terms of the band gap representation model, while in the lower temperature range, the Mott's variable-range hopping conduction model was found to be appropriate.     

The electrocatalytic oxidation of ascorbic acid on polyaniline film synthesized in the presence of ferrocenesulfonic acid

The catalytic oxidation of ascorbic acid on the two kinds of polyaniline electrodes (PAn and PAnFc films) has been carried out by cyclic voltammetry, constant potential and constant current methods. PAnFc and PAn films were synthesized in the presence and absence of ferrocenesulfonic acid, respectively. For the electrolysis of ascorbic acid at pH 5.64, the anodic peak potential of ascorbic acid shifts from 0.32 V (vs. SCE) on the bare platinum electrode to 0.05 V on both PAn and PAnFc electrodes. The oxidation current of ascorbic acid on the PAnFc electrode is 31 times as high as on the bare platinum electrode at the electrolysis of the constant potential. The exchange current density is 1.3 mA cm⁻² on the PAnFc electrode and 1.0 mA cm⁻² on the PAn electrode. The catalytic effect is caused by polyaniline itself. Ferrocenesulfonic acid doped in polyaniline plays an important role in enhancing the catalytic activity of polyaniline in the solution of pH >5.     

SEM/STM studies on the surface structure of a novel carbon fiber from lyocell

The surface structure and strengths of two types of cellulose-based carbon fibers, rayon-based carbon fiber (RCF) and lyocell-based carbon fiber (LCF), were investigated through scanning electronic microscopy (SEM) and scanning tunneling microscopy (STM). SEM delineated much smoother surface for LCF, while rougher surface with obvious cracks and grooves for RCF. It is believed that the difference of surface structure between these two carbon fibers results in a decrease in tensile strength for RCF. It can be found from the image of STM (500 nm × 500 nm) that the surfaces of LCF are characterized by bulk structure. Furthermore, it is proven that the bulk structure is composed of the smaller slug-like microstructures, each of which has a width of about 25 nm and length of 150 nm aligned with an angle at 45° to fiber axis when the observation scales down to 50 nm × 50 nm. The distance between two adjacent carbon atoms of LCF estimated by section analysis of STM reveals that no hexagonal carbon ring is formed on the surface of LCF examined.     

High temperature EMAT design for scanning or fixed point operation on magnetite coated steel

Bulk thickness measurements were performed at elevated temperatures on magnetite coated low carbon steel pipe and aluminium samples, using a permanent magnet electromagnetic acoustic transducer (EMAT). The design presented here exploits the non-contact nature of EMATs to allow continuous operation at elevated temperatures without physical coupling, sample preparation (in the form of oxide scale removal), or active cooling of the EMAT. A non-linear change in signal amplitude was recorded as the magnetite coated sample was heated in a furnace, whereas a steady decrease in amplitude was observed in aluminium. For a magnetite coated pipe sample, after a dwell time of 3 h, a SNR of 33.4 dB was measured at 450 °C, whilst a SNR of 33.0 dB was found at 25 °C. No significant EMAT performance loss was observed after one month of continuous exposure to 450 °C. EMAT-sample lift-off performance was investigated at elevated temperature on magnetite coated steel; a single-shot SNR of 31 dB for 3.0 mm lift-off was recorded at 450 °C, highlighting the suitability of this design for scanning or continuous fixed point inspection at high temperature.     

Improving hardness and tribological characteristics of nanocrystalline Cr–C films obtained from Cr(III) plating bath using pulsed electrodeposition

Effect of pulsed electrodepostion on the nanocrystal size, composition, hardness, coefficient of friction and wear resistance was investigated for the Cr–C electrodeposits obtained from a trivalent chromium bath. The electrodeposits were shown to contain about 9% of carbon. Pulsed electrodeposition does not virtually affect the carbon content. At the same time, an increase in the off time duration leads to a decrease in the nanocrystals size. The hardness and wear parameters of the electrodeposits may be sufficiently improved when using pulsed current. For instance, at t_on = t_off = 1 s, the hardness reaches the values of ~ 1200 ÷ 1300 HV (meanwhile, it is close to 850 ÷ 950 HV at a steady-state electrolysis).     

Ions transport and self-doping in layer-by-layer conducting polymer films

The self-doping mechanism for charge transport is investigated in layer-by-layer (LBL) films from two conducting polymers, namely poly(o-methoxyaniline) (POMA) and poly(3-thiophene acetic acid) (PTAA). The efficiency of charge intercalation, defined as the ratio between the charge and the mass change, is twice for the POMA/PTAA LBL film in comparison with a cast POMA film. This is attributed to differences in the diffusion-controlled charge and mass transport, where distinct ionic species participate in the LBL films, as demonstrated with experiments using a quartz crystal microbalance. The doping efficiency for LBL film is the same, i.e., 3.93 × 10⁻⁴ and 3.56 × 10⁻⁴ g/C for the Li⁺ and (C₂H₅)₄N⁺ doped films, and is different for the cast POMA film, i.e., 11.3 × 10⁻⁴ for Li⁺ and 6.45 × 10⁻⁴ g/C for (C₂H₅)₄N⁺. Therefore, once no significant differences in the intercalation mechanism are observed when different cations, Li⁺ or (C₂H₅)₄N⁺, are used with the LBL films, this indicates that the self-doping mechanism is controlled by the exchange of anions.     

Oxidation behavior of sulfidation processed TiAl–2 at.%X (X=Si,Mn, Ni,Ge, Y,Zr, La,and Ta) alloys at 1173 K in air

The oxidation behavior of sulfidation processed TiAl–2 at.%X (X=Si, Mn, Ni, Ge, Y, Zr, La, and Ta) alloys was investigated at 1173 K in air for up to 630 ks under a heat-cycle condition between 1173 K and room temperature. During the sulfidation processing the TiAl–2 at.%Ta alloy formed Ta-aluminides on the TiAl₃ layer, while the alloys containing Mn, Ni, Y, and Zr formed a TiAl₃ (TiAl₂ included) layer including a small amount of the third element, like the TiAl binary alloy. The cross-sectional microstructure of the TiAl–2 at.%Ta alloy shows the sequence: oxide scale/TiAlTa/TiAl₂/alloy substrate; and the cross sections of the alloys containing Mn, Ni, Y, and Zr are: oxide scale/Ti₃Al/alloy substrate. The TiAl–2 at.%Ta alloy showed some scale exfoliation at the initial stage of oxidation, but very little exfoliation after long oxidation times, whereas alloys containing other third elements such as Si and Ge showed little exfoliation at the first several cycles and then tended to exfoliate significantly, resulting in very rapid oxidation. The TiAlTa/TiAl₂ layers formed by the reaction between the Ta-aluminide and TiAl₃ improve the oxidation properties of the TiAl–2 at.%Ta alloy.     

Variation of temperature at the bottom surface of a hole during drilling and its effect on tool wear

The temperature at the bottom surface of a hole being drilled is measured by using an infrared-radiation pyrometer equipped with two optical fibers. One of the optical fibers is inserted into the oil hole of an internal coolant carbide drill and passes through the machine-tool spindle. This optical fiber is connected to another optical fiber at the end of the spindle. Infrared rays radiating from the bottom surface of the hole being drilled are accepted and transmitted to the pyrometer by the two optical fibers. Temperature increases as drilling progresses, and it increases considerably near the bottom surface of the workpiece. In case of a 10-mm-thick carbon–steel workpiece, temperature reaches 190, 250, and 340 °C at drilling depths of 6, 8, and 10 mm, respectively. To investigate the effect of the increase in temperature on drill wear, a series of 10-mm-deep blind holes are drilled in workpieces with thicknesses of 10 and 25 mm. Tool wear is greater when the drill cuts a hole at the bottom of a 10-mm workpiece than that when the drill cuts a hole at the mid-depth of a 25-mm workpiece. This indicates that the rapid increase in temperature near the bottom of the workpiece effects the progress of drill wear.     

Effect of graphite intercalation compounds in the interfacial zone on the mechanical and thermal properties of unidirectional carbon fiber reinforced spodumene composite

The interface in unidirectional carbon-fiber-reinforced β-spodumene matrix composite (UD-Cf/β-spodumene) significantly affected the thermal conductivity characteristics and mechanical properties due to the presence of a multi-layer interface. The mechanical and thermal properties of UD-Cf/β-spodumene composites with and without a multi-layer interface have been studied. The measured thermal conductivities, flexural strength and fracture toughness of composites with a multi-layer interface were much better than those composites with a clear interface. Interfacial layers with a multi-layer morphology originated from the diffusion of lithium from the β-spodumene matrix to the surface of the carbon fiber, which led to the formation of graphite intercalation compounds. The mechanical properties and thermal conductivity of UD-Cf/β-spodumene hot pressed at 1350 and 1400 °C were enhanced due to the textured interfacial microstructure and high thermal conductivity of graphite intercalation compounds. The textured interface decomposed at 1450 °C, resulting in the formation of a “strong” interface. Inevitably, the mechanical properties and thermal conductivity decreased.     

Electron transport properties of some newly synthesized nonsymmetrical bisindolizines in thin films

In this work, temperature dependences of electrical conductivity and thermoelectric power, for some recently synthesized nonsymmetrical bisindolizines, are studied. Thin-film samples (d = 0.10–0.30 μm) spin-coated from dichloromethane solutions onto glass substrates were used. Organic films with reproducible electronic transport properties can be obtained if, after deposition, they are subjected to a heat treatment within the temperature range of 301–541 K.The studied organic compounds show typical p-type semiconductor behavior. The activation energy of electrical conduction was found in the range 1.00–1.26 eV, while the ratio of charge carrier mobilities ranged between 0.90 and 0.97.The correlations between determined semiconducting parameters and specific features of molecular structure of the compounds have been discussed.In the higher temperature range (363–541 K), the electronic transport in actual compounds can be interpreted by using the band gap representation model, while for lower temperatures, Mott's variable-range hopping conduction model was found to be appropriate.     

On the electronic transport properties of pyrrolo[1,2-a][1,10]phenanthroline derivatives in thin films

The temperature dependences of electrical conductivity, σ, and Seebeck coefficient, S, for six new synthesized pyrrolo[1,2-a][1,10]phenanthroline compounds, have been investigated. Thin film samples (d = 0.05–0.66 μm) deposited by an immersion method (with dimethylformamide as solvent) onto glass were used.The crystalline structure of as-prepared organic films was investigated by XRD. The sample surface was examined by means of AFM and optical microscopy techniques.The ln σ = f(10³/T) and S = f(10³/T) experimental curves are quite typical for polycrystalline semiconducting materials. The examined organic compounds show a p-type electrical conduction. The activation energy of electrical conduction ranged between 1.42 and 2.04 eV, while the ratio of charge carrier mobilities was in the range 0.76–0.90.The study of optical absorption evidenced direct bandgaps ranged between 4.06 and 4.11 eV, as well bandgaps of 2.69–3.58 eV for amorphous phases.Some relationships between materials parameters and molecular structure of the compounds are established. The model based on band gap representation is suitable for the explanation of charge transport in the studied compounds.     

Electronic transport properties of some new monoquaternary salts of 4,4′-bipyridine in thin films

The dc electrical conductivity and thermoelectric power of some recently synthesized monoquaternary salts of 4,4′-bipyridine in thin films have been investigated as a function of temperature. Thin-film samples (d = 0.30–0.95 μm) were deposited from dimethylformamide solutions, by an immersion technique, onto glass. Their heat treatment within temperature range of 291–617 K leads to stable structure and reproducible electronic transport properties.The crystalline structure of organic samples was investigated by XRD, while AFM technique, corroborated to optical microscopy, was used for the examination of surface morphology.The temperature dependences of the electrical conductivity and thermoelectric power are typical for n-type polycrystalline semiconductors. The activation energy of electrical conduction ranges between 1.56 and 1.86 eV, while the ratio of charge carrier mobilities lies in the range of 1.08–1.33.Some correlations between semiconducting parameters and molecular structure of the compounds were established. In the higher temperature range (415–617 K), the model based on band gap representation is suitable for the explanation of electronic transfer in investigated compounds. The examined compounds are also promising for thermistor applications.     

Effect of surface ablation products on the ablation resistance of C/C–SiC composites under oxyacetylene torch

Single and cyclic ablations under oxyacetylene torch with 2380 ± 10% kW/m² heat flux were performed to evaluate the effect of ablation products on the ablation resistance of carbon/carbon – silicon carbide (C/C–SiC) composites separately. As a result of the accumulation of noncrystalline SiO₂ enwrapped SiC, ablation resistance of prepared composites was enhanced with time prolonging under single ablation while it was improved more significantly under cyclic ablation. The ablation products played several key roles during ablation: decreasing surface temperature, acting a barrier to oxidizing species attack and conglutinating defective ablated carbon fibers.     

Microstructure and oxidation resistance of Si–Mo–B coating for C/SiC coated carbon/carbon composites

A self-sealing Si–Mo–B oxidation resistance coating was prepared on C/SiC coated carbon/carbon (C/C) composites by slurry and high temperature treatment method. The oxidation resistance of the coating increases at 1173 K and first increases then decreases at 1873 K with the increase of B content from 0 to 20 wt.%. The C/SiC/gradient Si–Mo–B multilayer coating can protect C/C composite from oxidation for 100 h at 1173 K and 125 h at 1873 K. The good oxidation resistance of the coating in broad temperature range could be attributed to its good self-sealing property.     

Immobilization of urease in conducting thiophene-capped poly(methyl methacrylate)/pyrrole matrices

Urease was immobilized in conducting polypyrrole and block copolymers of thiophene-capped poly(methyl methacrylate) matrices by electropolymerization. Immobilization of the enzyme was achieved by application of 1.0 V constant potential in a solution of 0.02 M pyrrole, 2 mg/ml urease, 0.5 mg/ml supporting electrolyte. The optimum immobilization conditions, electrolysis time, electrolysis medium, enzyme concentration during electrolysis, type of supporting electrolyte were determined. The kinetic behaviors of free and immobilized urease were determined.     

EPR study of charge transfer in polyaniline highly doped by p-toluenesulfonic acid

Magnetic, relaxation and electronic dynamic parameters of paramagnetic centers in crystalline domains of polyaniline highly doped by p-toluenesulfonic acid (PANI-PTSA) as well as PANI-PTSA dispersed in poly(methyl methacrylate) were studied by the 3 cm (9.7 GHz) and 2 mm (140 GHz) wavebands EPR. These centers demonstrate the Lorentzian single line with the Dysonian contribution at both wavebands indicating intrinsic conductivity of metal-like domains near 1500–4000 S/cm at room temperature. Effective conductivity of the polymer is defined by Q3D delocalization of charge carriers within such domains and their Mott variable range hopping between the domains dominating its micro- and macroscopic conductivity. It was shown that the interaction of the charge carriers with the lattice phonons governs intradomain charge transfer at high temperatures. Reversible dipolare interaction of paramagnetic centers with oxygen was revealed. This interaction depends on electron precession frequency and/or on the PANI-PTSA dispersion in an insulating matrix. Charge transfer in PANI-PTSA was analyzed to be non-correlated with spin relaxation and dynamics that evidences the formation of Q3D metal-like domains contrary to the “single conducting chain” model.