Wetting contact angles of certain systems

The wetting contact angles of a number of systems are determined experimentally. The measurements are carried out in air at temperatures of 20–70°C by a variety of methods.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 6, pp. 1000–1003, June, 1977.     

Wetting behavior of liquid Fe–C–Ti alloys on sapphire

Wetting behavior in the (Fe–C–Ti)/sapphire system was studied at 1823 K. The wetting angle between sapphire and Fe–C alloys is higher than 90° (93° and 105° for the alloys with 1.4 and 3.6 at.% C, respectively). The presence of Ti improves the wetting of the iron–carbon alloys, especially for the alloys with carbon content of 3.6 at.%. The addition of 5 at.% Ti to Fe–3.6 at.% C provides a contact angle of about 30°, while the same addition to Fe–1.4 at.% C decreases the wetting angle to 70° only. It was established that the wetting in the systems is controlled by the formation of a titanium oxicarbide layer at the interface, which composition and thickness depend on C and Ti contents in the melt. The experimental observations are well accounted for by a thermodynamic analysis of the Fe–Ti–Al–O–C system.     

Interaction of some pollutant oxides on durability of silicon carbide as a material for diesel vehicle filters

The short-term interaction of SiC and some single pollutant oxides (Na2O, PbO and V2O5) was investigated as a function of temperature by X-ray diffraction (XRD) and Fourier transform infrared (F.T–i.r.) analysis. Sodium oxide dissolves the protective silica layer forming glassy sodium silicates at a temperature of 550°C. V2O5 accelerates SiC oxidation, leading to the formation of large amounts of silica at temperatures above 750°C. PbO begins to react with silica film at 600°C forming Pb2SiO4. Degradation becomes highly destructive at higher temperatures. Given the presence of Na2O, PbO and V2O5 in diesel particulates and the temperatures that filters must tolerate, SiC appears to have insufficient thermal and chemical resistance for this application.     

Corrosion of alumina ceramics in acidic aqueous solutions at high temperatures and pressures

Alumina is resistant against corrosive aqueous solutions and could be used as a reactor material in the Supercritical Water Oxidation (SCWO) process. For this reason, the corrosion resistance of alumina and zirconia toughened alumina (ZTA) ceramics was investigated in aqueous solutions containing 0.1 mol/kg H₂SO₄, H₃PO₄ or HCl at T = 240°C–500°C at p = 27 MPa. In sulfuric acid, the solubility of alumina and its corrosion products was high at temperatures of 240°C–290°C. The corrosion rate was still high at higher temperatures (340°C–500°C), but the corrosion products were less soluble and formed a non-protecting scale on the samples. Phosphoric acid was less corrosive due to the formation of berlinite (AlPO₄) on the surface of the specimens. In hydrochloric acid, the dissolution of the alumina grains was the predominant corrosion phenomenon at temperatures of 240°C–290°C. At higher temperatures, intergranular corrosion was observed, but a dissolution of the grains did not occur.     

Crystallization of an amorphous B–C–N precursor with a Li–B–N catalyst at high pressures and temperatures

An orthorhombic B–C–N compound was synthesized using an amorphous B–C–N precursor and a Li–B–N catalyst at 6 GPa and 1773 K. The results of energy dispersive spectrometry and electronic energy loss spectrometry suggest a stoichiometry of B:C:N = 1:3.3:1. In addition, the Li–B–N catalyst improves the crystallizations of the B–C–N compound, graphite and BN and therefore might be a profitable catalyst in ultrahigh pressure experiments.     

Optimization of annealing temperature for YBa2Cu3O7 thin films post-annealed at a low oxygen partial pressure

Post-annealing of YBa₂Cu₃O₇ (YBCO) thin films is usually performed at 850–900°C in atmospheric-pressure oxygen. In this study, coevaporated YBCO films on LaAlO₃ were post-annealed in an oxygen partial pressure of 29 Pa at temperatures in the range 700–825°C. Zero resistance transition temperatures were 89–90 K. Both d.c. (room-temperature resistance and critical-current density) and a.c. parameters (extracted from eddy-current response measurements at 25 MHz) were monitored. The optimum temperature is close to 750°C, which is on the YBCO thermodynamic stability line at this low oxygen partial pressure.     

High-temperature strength of bulk single crystals of III-V nitrides

A Vickers indentation method was used to determine the hardness of AlN and GaN, grown by the hydride vapor phase epitaxy technique, in the temperature range 20–1400 °C. At room temperature, the hardnesses of GaN and AlN are 10.2 and 17.7 GPa, respectively. The hardness of GaN and AlN shows a gradual decrease from RT and then a steep decrease from around 1000 °C. AlN is harder than GaN but softer than SiC. The steep decrease of the hardness means the beginning of macroscopic dislocation motion and plastic deformation. The mechanical strength of bulk single-crystal GaN is investigated at elevated temperatures directly by means of compressive deformation. The yield stress of GaN in the temperature range 900–1000 °C is around 100–200 MPa, i.e., similar to that of 6H-SiC and much higher than those of Si, Ge, GaAs.     

Glass Formation in the GeS2–EuS System

Crystalline and glassy alloys in one of the highest temperature glass-forming systems GeS₂–EuS are studied by differential thermal analysis, x-ray diffraction, chemical analysis, and IR spectroscopy. The glass-transition, crystallization, and melting temperatures of the alloys are determined with a high accuracy. The results indicate that, with increasing EuS content, the glass-transition temperature decreases from 492 to 448°C. The most homogeneous glasses can be prepared at EuS contents below 15 mol %. To obtain homogeneous glasses in the range 25–30 mol % EuS, an increased cooling rate is needed: 20–30°C/s.     

Solid-state deformation of polytetrafluoroethylene powder

Polytetrafluoroethylene (PTFE) powder of a high molecular weight (~ 10⁷) was drawn by solid-state extrusion in the temperature range 100–340°C, which covers the glass transition temperature (125°C) and the ambient melting point (334°C). Draw was attainable only above 100°C. The maximum achievable extrusion draw ratio (EDR_max) was almost constant, ~ 10, from 100–280°C, yet increased rapidly with further increasing temperature, reaching a maximum of 60 at 330–340°C. At yet higher temperatures, the drawability was lost due to melting. The structure and properties of drawn products were found to be complexely affected by extrusion temperature and EDR. For extrusion at 330–340°C, near the melting point, an effective and high draw was achieved. The crystalline chain orientation function, crystallite sizes, both along and perpendicular to the chain axis, differential scanning calorimetry heat of fusion, and flexural modulus increased with EDR and approached a maximum at EDR of 30–40, depending on the extrusion temperatures. Above a specific EDR, the efficiency of draw decreased due to the formation of flaws. The highly oriented PTFE consisted of microfibrils of a significantly large lateral dimension (~ 45 nm) compared to those (6–20 nm) generally found in oriented polymers. The modulus of a drawn PTFE was sensitive to the test temperatures, reflecting the reversible crystal/crystal transitions at ~ 19 and 30°C. The optimization of the extrusion conditions resulted in the maximum achieved flexural modulus at 24°C of 20 GPa at an EDR 40 for extrusion at 340°C.     

Effect of Temperature on the Tensile Strength and Failure Modes of Angle Ply Aramid Fibre (KRP) Tubes Under Hoop Loading

A comprehensive study was undertaken to characterise Kevlar reinforced plastic (KRP) angle ply filament wound tubes at different temperatures. Quasi-static burst tests were performed on tubes of 25°, 55° and 75° winding angle. The tubes were burst under internal radial pressure with minimum end constraints. An experimental rig and two conditioning tanks were designed and built to test the specimens at three temperatures; –46°C (low temperature) and +20°C (room temperature) and +70°C (high temperature). For each test the internal pressure and the strains in both circumferential and longitudinal directions were recorded on suitable digital processing equipment.For a particular batch of tubes tested at three different temperatures, an increase in ultimate hoop strain and a decrease in hoop modulus of the 55° tubes with increasing temperatures was recorded; the temperature effect was less pronounced on the corresponding properties of 25° and 75° tubes. The use of a non-structural thin liner during the tests led to a higher ultimate strength of 55° tubes but had negligible effect on the behaviour of 25° and 75° tubes. The 75° tubes failed in a catastrophic fibre fracture under all test conditions. The mode of failure of 55° changed from weeping at 70°C to fibre fracture at –46°C. The 25° tubes failed by weeping with matrix cracking. The matrix cracking was particularly severe when a liner was used.     

Influence of high temperature exposure on the mechanical behavior and microstructure of 17-4 PH stainless steel

The mechanical behavior and microstructural evolution of 17-4 PH stainless steels in three conditions, i.e. unaged (Condition A), peak-aged (H900) and overaged (H1150), exposed at temperatures ranging from 200 to 700°C were investigated. The high-temperature yield strength of each condition decreased with an increase in temperature from 200 to 400°C except for Condition A at 400°C with a longer hold time where a precipitation-hardening effect occurred. At temperatures from 500–700°C, the decrease in after-exposure hardness of Condition A and H900 at longer exposure times was caused by a coarsening effect of copper-rich precipitates. A Similar microstructural change was also responsible for the hardness of H1150 exposed at 700°C decreasing with increasing exposure time. Scanning electron microscopy (SEM) observations indicated that the matrix structures of Condition A and H900, when exposed at 600°C and above, exhibited lamellar recrystallized -ferrite in the tempered martensite and the size and quantity of these lamellar ferrite phases increased with exposure time. X-ray diffraction (XRD) analyses showed that the reverted austenite phase in H1150 that formed during the over-aging treatment was stable and hardly affected by deformation at temperatures of 200–400°C.     

Electrically conductive PANi multifilaments spun by a wet-spinning process

Electrically conductive polyaniline (PANi) filaments were successfully spun from a spinning solution prepared from the PANi protonated with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) in dichloroacedic acid (DCA) as a solvent by a wet-spinning process. The conductivity of the fibre is in a range of 145 (±35) Scm^–1 to 1440 (±300) Scm^–1, which depends on the orientation of polymer chains. The fibre has a Young's modulus about 3.2 GPa, and a tensile strength about 0.23 GPa. Thermal analysis by TGA and DSC show that the fibre has five major weight losses at around 100 °C, 165 °C, 215 °C, 315 °C and 465 °C which are associated with the removal of moisture, residual solvent, the decompositions of the AMPSA, and the degradation of the PANi, respectively. The AMPSA in doped PANi performs two-stage thermal decompositions. The conductivity of the fibre was adversely affected by the thermal ageing due to the evaporation of the residual solvent at the temperatures lower than 100 °C and the decompositions of the dopant AMPSA at the temperatures above 100°C. The temperature dependent conductivity of both aged and unaged fibres is thermally activated at the temperatures between 15 K and 295 K. A negative temperature coefficient was observed in the temperature range of 240 K to 270 K for the unaged fibres. This disappeared when the fibres were thermally aged at 100 °C for 24 hours in vacuum. These results indicate that the residual solvent trapped inside the fibre enhances the electrical conductivity of the fibres, and possibly affects the negative temperature coefficient at the temperatures around 260 K.     

Characterisation of K, Na, and Li birnessites prepared by oxidation with H2O2 in a basic medium. Ion exchange properties and study of the calcined products

Birnessites containing Na, K or Li in the interlayer have been prepared by oxidation of Mn(II) cations with H₂O₂ in a basic medium with different alkaline cation/Mn molar ratios. The solids prepared have been characterised by elemental chemical analysis, powder X-ray diffraction, thermal analyses (differential thermal analysis and thermogravimetric analysis), FT-IR spectroscopy and surface texture assessment by adsorption of N₂ at –196°C. Crystalline birnessites are obtained for A/Mn ratios (A = K, Li) larger than 3.4, but MnO(OH) has been also identificed when such a ratio is smaller than 3.4. Ion exchange is topotactic, but is not complete for exchanging Na, K, or Mg for pre-existing Li. The solids are stable up to 400°C, and formation of spinels and solids with tunnel structures is observed at this temperature. Li-containing birnessites are transformed to LiMn₂O₄ spinel at 400°C, and co-crystallization of bixbyte (Mn₂O₃) is observed at higher temperatures. Bixbyte and cryptomelane are formed at 500°C for the K-containing birnessites.     

Effects of age heat treatment and thermomechanical processing on microstructure and mechanical behavior of LAZ1010 Mg alloy

An Mg–Li–Al–Zn (designated as LAZ1010) alloy containing about 10 wt% of Li has been prepared by melting and solidification in a carbon steel crucible, and extruded at a billet preheating temperature of 200 °C with an extrusion ratio of approximately 29. Effects of age heat treatments and thermomechanical processing on microstructures and mechanical properties were performed in this study. Hardness, optical microscopy, X-ray diffraction studies, and tensile testes were carried out to explore the variations in microstructures and mechanical behaviors during processing. The results showed that LAZ1010 alloy presented age hardening effect at temperatures below 50 °C. Rapid decrease in hardness with aging temperature at intermediate temperatures should be resulted from the transformation of θ phase into the equilibrium phase AlLi. Kocks–Mecking type plots were used to illustrate different stages of work hardening of the cold rolled specimens. The results indicated that cold rolled LAZ1010 alloy showed stage III and stage IV work hardening behaviors.     

Viscosity and thermal conductivity of binary eutectics of alkali metals in the vapor phase

Values calculated for the dynamic viscosity and thermal conductivity are presented for vapors of binary eutectics of the alkali metals at temperatures from 800 to 1500 K and at pressures from 100 to 8×10⁵ Pa. Data are presented for the vapors of the systems Li + Na, Na + Rb, Na + Cs, K + Rb, K + Cs, Na + K, and Rb + Cs. The values of the concentrations of the five components in the vapor phase of each binary eutectic are also presented. The accuracy of the calculated viscosities is estimated to be within 4–5% and the accuracy of the calculated thermal conductivities is estimated to be within 8–10%.     

High-temperature interaction of uranium and zirconium with water vapor

We analyze physicochemical processes of interaction between uranium, zirconium, and its alloy (with 1% Nb) with water vapor at temperatures up to 1500°K and study mechanisms and kinetics of these processes. It is shown that, up to 700°K, the kinetics of the process of oxidation of uranium is described by a linear function of time; at temperatures higher than 900°K, this dependence becomes parabolic. Our interpretation of the mechanism of the process of oxidation of uranium takes into account the influence of structural defects and electrochemical properties of uranium oxides formed in the course of this process. The process of oxidation of zirconium and its alloy with 1% Nb by water vapor obeys a cubic law in the temperature range 900–1200°K and a parabolic law in the range 1300–1500°K. The comparative analysis demonstrates that the hydrogen release rate in the process of uranium oxidation is about twice as high as in the process of vapor-zirconium reaction.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 3, pp. 36–43, May–June 1995.     

Effect of heat treatment on the infrared absorption spectra of Sr-Na borosilicate glass

Internal modes of vibrations are studied here at different temperatures (27–800°C) and in the frequency range 200–4000 cm^–1 through heat treatment. The baseline method was used. The strong bands of SiO₄ tetrahedra in this glass show an increase in absorbance at high temperature (600–800°C). The deformation of SiO₄ tetrahedra is investigated. This is found to depend on the ionic radius of the divalent metal oxide introduced, and the coordination number of the cation. Also from a study of the temperature dependence of the relative integrated intensity of the modes 600–800 and 850–1450 cm^–1, the relaxation time and rotational energy barrier of the glasses selected indicate that the glassy phases are transformed to crystalline phases at 500°C.     

Thermal stability of a PCS-derived SiC fibre with a low oxygen content (Hi-Nicalon)

The oxygen free Si–C fibre (Hi-Nicalon) consists of -SiC nanocrystals (5nm) and stacked carbon layers of 2–3nm in extension, in the form of carbon network along the fibre. This microstructure gives rise to a high density, tensile strength, stiffness and electrical conductivity. With respect to a Si–C–O fibre (Nicalon NL202), the Si–C fibres have a much greater thermal stability owing to the absence of the unstable SiOxCy phase. Despite its high chemical stability, it is nevertheless subject to a slight structural evolution at high temperatures of both SiC and free carbon phases, beginning at pyrolysis temperatures in the range 1200–1400°C and improving with increasing pyrolysis temperature and annealing time. A moderate superficial decomposition is also observed beyond 1400°C, in the form of a carbon enriched layer whose thickness increases as the pyrolysis temperature and annealing time are raised. The strength reduction at ambient for pyrolysis temperatures below 1600°C could be caused by SiC coarsening or superficial degradation. Si–C fibres have a good oxidation resistance up to 1400°C, due to the formation of a protective silica layer.     

On the thermoelectric properties of CdxHg1−xSe alloys

The thermal and electrical conductivity, Hall and Seebeck coefficients have been measured as a function of temperature for various undoped alloys up to x=0.50. The Hall coefficient and the thermoelectric power remained negative for all samples at all temperatures in the investigated range (77 to 450° K).The alloys with x=0.10 provided the optimum figure of merit, which reached a maximum of 0.9 × 10^–3 deg^–1 at 400° K. This represents an improvement of at least 50% over the best values for n-type Ge-Si alloys below 700° K.     

Low-temperature cyclic crack-growth resistance of hydrogenated welds

We study the influence of chemical and phase composition on the cyclic crack-growth resistance of non-hydrogenated and hydrogenated welded joints in low-alloy steel at normal and low (–70°C) temperatures. It was discovered that the increase in the nickel content from 0.06% to 3.27% induces an increase in impact toughness and cyclic crack-growth resistance at low temperatures which can be explained by the increase in the content of needle ferrite and by the substitution of uniformly distributed residual austenite for the pearlitic component in the zone characterized by the columnar structure of heat treated beads. Hydrogen saturation of the weld metal leads to a decrease in its cyclic crack-growth resistance at normal temperatures and produces almost no effect on this parameter at low temperatures (–70°C). The presence of the second austenitic phase in the low-alloy weld metal decreases its susceptibility to hydrogen embrittlement in the case where finely divided austenite is uniformly distributed over the weld.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 2, pp. 62–68, March – April, 1995.