The Effects of Annealing on the Mechanical Properties of Electrodeposited Nickel

Attempts have been made to clarify the existing experimental evidence of the embrittlement of Watts nickel after heat treatment at temperatures in excess of 600°C. Electrodeposits have been prepared from a ‘purified’ solution maintained at pH 4 at current densities of 21·5, 270 and 540 A/m². It was found with 21·5 A/m² nickel that the ductility (measured at 20°C) was drastically reduced as the annealing temperature (1 h treatment) increased from 600° to 1000°C, whilst the higher current density materials only registered a small reduction in this property after treatment close to 1000°C. The UTS decreased with increasing annealing temperature in all cases. Metallographic observations revealed that the intergranular embrittlement observed in the low current density nickel was due to the presence of grain boundary discontinuities. These were identified as voids by scanning electron microscopy, and confirmed by specific gravity measurements. Grain boundary voids were also observed in the annealed high current density nickel, but to a far lesser degree. The formation of a gaseous phase within the deposit at temperatures above 600°C is thought to be responsible; hence the voids are in fact gas filled bubbles.     

Surface characterization of P3OT thin films by variable temperature scanning force microscopy

In this work variable temperature scanning force microscopy techniques have been used to study poly(3-octylthiophene) (P3OT) thin film samples. Topography images in combination with scanning force spectroscopy have been applied to characterize the morphology and mechanical properties of the P3OT surface. It has been found that at room temperature lamellar islands appears on top of the polymer surface, while at temperatures higher than 35–45 °C these lamellas disappear and the polymer surface becomes homogeneous. This process is reversible and the lamellar structures are recovered when the sample is cooled down. In parallel, local force spectroscopy performed at each temperature shows a marked variation of the mechanical properties at about 30–40 °C, both in the polymer surface as well as in the lamellar islands. This points towards a conformational change in the P3OT molecules which loose planarity disrupting the close packing of the molecules on the lamellas.     

Thermal stability of polyaniline networks in conducting polymer blends

The thermal stability of polyaniline-camphor sulfonic acid (PANI-CSA) networks in blends with poly (methyl methacrylate) (PMMA) and a low molecular weight polyester (PES ) has been studied by transmission electron microscopy (TEM) supplemented with measurements of the optical and electrical properties. The tenuous interpenetrating fibrillar network of PANI-CSA is robust and remains intact at temperatures above the glass transition temperature (T_g) and the melting point (T_m) of the host polymers (T_g~90 °C for PMMA; T_m~60 °C for PES), indicating that the phase-separated network morphology is a thermodynamically stable phase. Although deprotonation of the PANI gradually starts around 100 °C, the network morphology persists (with crystallites of CSA, released by the deprotonation, distributed within the network). After exposure to increasingly higher temperatures, especially above 200 °C, the fibrils of the network coarsen, and the structure becomes more open. Complete deprotonation and degradation of the PANI are observed at temperatures above 200 °C. The conclusions from the TEM micrographs are consistent with thermal gravimetric analysis, spectroscopic data and electrical conductivity measurements.     

Internal chlorination of Ni-based alloys and its relation to volatilization corrosion

The kinetics of internal chlorination of Ni-based alloys between 400°C and 700°C were investigated by optical and scanning electron microscopy. Internal chlorination of Ni-4Cr and Ni-4Cr-0.5Ce alloy occurred by formation of solid precipitates such as CrCl₂, and CeCl₃ which are thermodynamically stable and have low vapor pressures at the temperatures within the alloy matrix. In the lower temperature range, the kinetics of internal chlorination nearly followed a parabolic rate law. The degree of internal chlorination increased with increasing temperature. In the higher temperature range, the internal attack was accompanied by the consumption of the alloy by volatilization. When the rate of internal chlorination equaled the rate of overall metal consumption, the depth of the internal chlorination zone would approach a steady state value. At high temperatures, where vaporization was predominant, the steady state depth of internal attack was even smaller than that at lower temperature. When an alloy specimen was subject to little volatilization, it showed more internal attack than when it was not, and vice versa.     

High-Temperature Corrosion of Nimonic-75 and Various Steels in Gases at Low Partial Pressurest

Abstract

Nimonic-75 has been reacted in low partial pressures of CO₂, H₂O, CO, CH₄, N₂, and various mixtures of these gases at temperatures in the range 750–1000°. Ten different steels have been studied in a fivecomponent gas mixture at temperatures between 500–750° and in a number of (CO + H₂+ H₂O) mixtures at 500° and 600°. No gross effects have been found on any of the materials tested under the various conditions of exposure, and the most significant phenomena in environments of practical importance are decarburisation and/or preferential oxidation of certain alloy constituents.     

Electrical characterization of pentacene thin-film transistors with polymeric gate dielectric

Pentacene thin films obtained by thermal evaporation at room temperature have been incorporated as the active layer in bottom-gate thin-film transistors (TFTs). The dielectric was spin-cast polymethyl methacrylate (PMMA) baked at only 170 °C. Crystalline silicon wafers and polyethylenenaphtalate (PEN) polymer foils were used as substrates. These devices were electrically characterised by measuring the output and transfer characteristics at different temperatures. Both the channel conductance and field-effect mobility evidenced similar thermal activation energies around 0.15 eV. These results could indicate that electrical transport is mainly controlled by trapping and thermal release of carriers from localised states.     

Note on the Temperature Stability of Wüstite in Surface Oxide Films on iron

Abstract

Davies et al. have shown that, when iron is oxidised at temperatures above 700°, the oxide film present on flat specimens contains mainly wüstite (FeO), in fact the three oxides FeO, Fe₂O₄ and Fe₂O₄ are all present, approximately in the ratio 95 : 4 : 1. Below 570°, FeO is not stable, as shown by the iron–oxygen equilibrium diagram₂ and Collongues & Chaudron₃ have shown that in vacuo wüstite decomposes to give iron and magnetite at temperatures below 570°. Wüstite formed as an oxide layer on iron oxidised at temperatures above 570° should also become unstable on cooling to room temperature. The following results show how the degree of wüstite breakdown can be easily estimated.     

The Effect of Surface Chemistry and Morphology on the Properties of HVAF PEEK Single Splats

Thermal spray of polymers has had limited investigation due to the narrow processing windows that are inherent to polymer powders, especially their low temperatures of thermal degradation. The polymer poly aryl ether ether ketone (PEEK) has a continuous use temperature of 260 °C, does not suffer significant thermal degradation below 500 °C (Lu et al., Polymer, 37(14):2999-3009, 1996), and has high resistance to alkaline and acidic attack. These properties led to PEEK being selected for investigation. To minimize thermal degradation of the particles, the high velocity air fuel technique was used. To investigate the effect of substrate pretreatment on single splat properties, single splats were collected on aluminum 5052 substrates with six different pretreatments. The single splats collected were imaged by scanning electron microscopy and image analysis was performed with ImageJ, an open source scientific graphics package. On substrates held at 323 °C, it was found that substrate pretreatment had a significant effect on the circularity and area of single splats, and also on the number of splats deposited on the substrates. Increases in splat circularity, area, and the number of splats deposited on the surface were linked to the decrease in chemisorbed water on the substrate surface and the decrease of surface roughness. This proved that surface chemistry and roughness are crucial to forming single splats with good properties, which will lead to coatings of good properties.     

Electrical properties and stability of polypyrrole containing conducting polymer composites

Conducting polymer composites of polyethylene and polypyrrole (PE/PPy), polypropylene and polypyrrole (PP/PPy), and poly (methyl methacrylate) and polypyrrole (PMMA/PPy) were prepared by means of a chemical modification method, resulting in a network-like structure of polypyrrole embedded in the insulating polymer matrix. The content of polypyrrole determined by elemental analysis varied from 0.25 to 17 wt.%. Electrical conductivity of compression-moulded samples depends on the concentration of polypyrrole and reached values from 1 × 10⁻¹¹ to 1 S/cm. The morphology of the composites was investigated by low-voltage scanning electron microscopy (LVSEM). Potential contrast measurements as a function of the acceleration voltage were used to prove the perfection of the PPy network structure. The electrical transport mechanism in PP/PPy composite was studied. The data of the temperature dependence of conductivity were fitted following the function for a charge-energy-limited tunnelling (CELT) model. There is only a small drop in conductivity caused by annealing of PP/ PPy composites in air at temperatures up to 80 °C. A stabilizing effect of PPy on thermal stability of polypropylene is shown by thermogravimetric analysis. The antistatic properties of PE/PPy and PMMA/PPy composites were demonstrated.     

Density compatibility of encapsulation of white inorganic TiO2 particles using dispersion polymerization technique for electrophoretic display

The polymer encapsulated TiO₂ particles with negative charge surface functionality were prepared by a two-stage dispersion polymerization technique for applications in electrophoretic displays (EPDs). In order to give the functionality for inorganic pigment particles in the EPDs, we have investigated the density of the polymer encapsulation of TiO₂ particles with the density of 4.0 g/ml. The density of the polymer encapsulated TiO₂ particles is suitable to 1.7 g/ml, due to density matching with suspending media. In results, the obtained particles showed the average densities in the range 1.5–2.5 g/ml at 25 °C. The polymer encapsulation of TiO₂ particles was confirmed with scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The TGA results showed that the initial weight loss of the encapsulated particles occurred near 400 °C in nitrogen, due to the degradation of the encapsulating polymer of TiO₂ particles.     

Enhanced stability of poly(3-hexylthiophene) transistors with optimally cured poly(methyl methacrylate) dielectric layers

Poly(3-hexylthiophene)-based organic field-effect transistors (OFETs) have been fabricated on poly(methyl methacrylate) (PMMA) gate dielectric layers under different process conditions, resulting in very different device stability in ambient air. The dielectric layers were prepared by spin coating and subsequently curing at various temperatures (120, 150, and 180 °C) or by ultraviolet light (UV) exposure. With respect to the variations of the on/off current ratio and the threshold voltage, dramatically enhanced stability of the OFETs with the PMMA layer cured at 150 °C has been demonstrated when compared to those cured at different temperatures. The devices cured by UV exposure showed even more superior stability, with reliable performance in ambient air for more than 10 days. The differences in the film surface morphology were analyzed and possible mechanisms for the enhanced stability are discussed.     

Precipitates and hydrogen permeation in HSLA steel produced by TMCP

Abstract

The precipitates and hydrogen permeation behaviour were investigated in high strength low alloy steel produced by thermomechanical controlled processing with air/water cooling after finishing rolling, and the water cooled specimens were further tempered at various temperatures. Two types of precipitates have been found in the specimens. One is TiN with the size ranging from 50 to 300 nm, and the other one is fine NbC. The cooling and tempering treatment conditions affect the precipitation behaviour of NbC particles in α-Fe, leading to the difference in hydrogen permeation. The apparent hydrogen diffusivity in the air cooled specimen is lower than that in the specimen quenched and subsequently tempered at 300°C when the charging current density is 10 mA cm^?2. Increasing the tempering temperature to 500°C leads to the decrease of apparent hydrogen diffusivity; but the value is still higher than that in the air cooled specimen. However, the apparent hydrogen diffusivity slightly increases with further increasing tempering temperature from 500 to 650°C.     

Oxidation Behavior of Carbon Steel: Effect of Formation Temperature and pH of the Environment

The nature of surface oxide formed on carbon steel piping used in nuclear power plants affects flow-accelerated corrosion. In this investigation, carbon steel specimens were oxidized in an autoclave using demineralized water at various temperatures (150-300 °C) and at pH levels (neutral, 9.5). At low temperatures (< 240 °C), weight loss of specimens due to dissolution of iron in water occurred to a greater extent than weight gain due to oxide formation. With the increase in temperature, the extent of iron dissolution reduced and weight gain due to oxide formation increased. A similar trend was observed with the increase in pH as was observed with the increase in temperature. XRD and Raman spectroscopy confirmed the formation of magnetite. The oxide film formed by precipitation process was negligible at temperatures from 150 to 240 °C compared to that at higher temperatures (> 240 °C) as confirmed by scanning electron microscopy. Electrochemical impedance measurement followed by Mott–Schottky analysis indicated an increase in defect density with exposure duration at 150 °C at neutral pH but a low and stable defect density in alkaline environment. The defect density of the oxide formed at neutral pH at 150-300 °C was always higher than that formed in alkaline environment as reported in the literature.     

Preparation and sintering properties of zirconia-mullite-corundum composites using fly ash and zircon

Zirconia-mullite-corundum composites were successfully prepared from fly ash,zircon and alumina powder by a reaction sintering process.The phase and microstructure evolutions of the composite synthesized at desired temperatures of 1 400,1 500 and 1 600°C for 4 h were characterized by X-ray diffractometry and scanning electronic microscopy,respectively.The influences of sintering temperature on shrinkage ratio,apparent porosity and bulk density of the synthesized composite were investigated.The formation process of the composites was discussed in detail.The results show that the zirconia-mullite-corundum composites with good sintering properties can be prepared at 1 600°C for 4 h.Zirconia particles can be homogeneously distributed in mullite matrix,and the zirconia particles are around 5μm.The formation process of zirconia-mullite-corundum composites consists of decomposition of zircon and mullitization process.     

Effect of vanadium on the precipitation strengthening upon tempering of a high-strength pipe steel with different initial structure

Methods of metallography, scanning electron, and transmission electron microscopies were used to study the structure of two pipe steels (without vanadium and with 0.03% vanadium) subjected to γ → α isothermal transformation at temperatures of 400–600°C (initial structure) and tempering at 600–650°C. It has been found that the addition of 0.03% vanadium intensifies the process of the precipitation of ferrite and contributes to the formation of a granular structure. It has been shown that, in high-strength pipe steels with 0.03% vanadium, which have bainitic granular-type structures, the effect of the precipitation strengthening is effected upon subsequent high-temperature tempering at 600–630°; the addition of vanadium leads to an increase in the hardness by 16 HV. In the presence of bainite of the lath type in the initial structure, the subsequent tempering leads to a softening associated with the processes of the recovery, polygonization, and initial stages of recrystallization in situ, which develops at temperatures above 640°C. It has been found that the hardness of the steel without vanadium upon additional tempering decreases regardless of the morphology of structural constituents in the initial structure.     

Thermal undoping in poly(3-alkylthiophenes)

Thin solid films of doped poly(3-hexylthiophene) and poly(3-decylthiophene) undergo rapid conductivity degradation at elevated temperatures (110 °C). We have followed the changes in the electronic structure during thermal treatment by optical spectroscopy. We have also studied thin films of the materials, before and after heat treatment, by means of infrared and X-ray photoelectron spectroscopy. The results show that the materials are undoped by thermal treatment. Comparative studies on poly(3-methylthiophene) show that this polymer also undergoes thermal undoping, but at a much slower rate.     

Electrochemical studies of hot corrosion of type 347H stainless steel

Abstract

Electrochemical studies of the hot corrosion of AISI SA 213 TP 347H stainless steel have been carried out in a mixture of 80 wt-% V₂O₅ + 20 wt-% Na₂SO₄. The range of temperatures was 540–680°C at intervals of 20 K and the techniques employed included corrosion potential, Tafel polarisation, and electrochemical noise measurements. At 620°C the corrosion potential, measured against a platinum reference electrode (PRE), decreases from ?350 mV to ?480 mV and remains at this level during the first 8 h. Using Tafel polarisation, it was found that, with change in the temperature from 540 to 680°C, the corrosion potential decreased on initial heating to 600°C and then increased again at higher temperatures, the corrosion rate increasing continuously with increasing temperature. However, at constant temperature (620°C) the corrosion rate increased with time during the first 8 h, after which it decreased and reached a steady state after 27 h, probably owing to the formation of a surface film. Electrochemical noise measurements, of both voltage and current noise, indicated a combination of general corrosion, probably owing to the formation of a surface layer, and localised corrosion in the grain boundaries.     

The Zn-Rich Corner of the Zn-Fe-V-Sb Quaternary Systems at 450 and 600 °C

In this paper, the isothermal sections of the Zn-Fe-V-Sb quaternary system at 450 and 600 °C with Zn fixed at 93 at.% have been determined experimentally by means of scanning electron microscopy coupled with energy dispersive x-ray spectroscopy and x-ray diffraction. Four four-phase regions and three four-phase regions have been inferred from experimental data in the isothermal section at 450 and 600 °C, respectively. Furthermore, no new ternary and quaternary compounds have been found at those two temperatures.     

Influence of polymerization temperature on the characteristics of polythiophene films

Characteristics of polythiophene (PT) films prepared by electrochemical polymerization at different temperature (5°C, 25°C and 40°C) have been investigated, mainly based on spectroscopic observations such as optical absorption and infrared transmission. Emphasis is put on clarifying the origin of the “inferior” characteristics of PT films prepared at higher temperatures. It has been suggested from comparison with those films prepared at the lowest possible temperature that the effective spatial extension of the π-conjugation in a PT ‘chain’ is much shortened and that fragments consisting of crosslinked thiophene rings prevail in the whole polymer skeletons.     

Volatilization kinetics of chromium oxide,manganese oxide,and manganese chromium spinel at high temperatures in environments containing water vapor

Performance degradation of solid oxide fuel cells due to chromium volatilization is a well‐investigated issue in the literature. Therefore, retention coatings were developed to distinctly reduce the chromium volatilization. One approach was by alloying with manganese to ferritic steels to form manganese chromium spinel which is reported to decrease chromium volatilization by 61–75%. In the present paper, the volatilization rates of pure manganese chromium spinel ceramics were examined as well as those of the two oxides forming this spinel—pure chromium oxide and pure manganese oxide—in synthetic air containing 10% water vapor (high p(O₂)) and argon/hydrogen containing 10% water vapor (low p(O₂)) at 850°C, 950°C, and 1,050°C. Chromium oxide showed higher volatilization rates in high p(O₂), whereas manganese oxide demonstrated higher volatilization rates in low p(O₂). Contradictory to the literature, manganese chromium spinel displayed the highest volatilization rates in both atmospheres and nonlinear kinetics behavior. This deviation from linear behavior can be attributed to diffusion‐controlled volatilization in high p(O₂).