Embrittlement of Armco iron by indium at high temperatures

We determined the relative elongation () and ultimate strength (_u) of hollow Armco iron specimens and Armco iron specimens filled with indium at high temperatures in a vacuum. It was shown that indium embrittles Armco iron in the temperature range 850–950°C. The lowest values of were obtained at a temperature of 925°C, where a small amount of the -phase is observed in the structure of strained specimens. The high-temperature liquid metal embrittlement of Armco iron is caused by an indiummelt-induced decrease in the flow stress, which localizes strains in the -phase and initiates its premature cracking. On the basis of metallographic investigations, we made the conclusion that corrosion is not responsible for the high-temperature liquid metal embrittlement of Armco iron.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 6, pp. 41–45, November–December, 1993.     

Amplified on-chip fluorescence detection of DNA hybridization by surface-initiated enzymatic polymerization

We describe the incorporation of multiple fluorophores into a single stranded DNA (ssDNA) chain using terminal deoxynucleotidyl transferase (TdT), a template-independent DNA polymerase that catalyzes the sequential addition of deoxynucleotides (dNTPs) at the 3'-OH group of an oligonucleotide primer; we term this methodology surface initiated enzymatic polymerization (SIEP) of DNA. We found that long (>1 Kb) ssDNA homopolymer can be grown by SIEP, and that the length of the ssDNA product is determined by the monomer to oligonucleotide initiator ratio. We observed efficient initiation (≥50%) and narrow polydispersity of the extended product when fluorescently labeled nucleotides are incorporated. TdT's ability to incorporate fluorescent dNTPs into a ssDNA chain was characterized by examining the effect of the molar ratios of fluorescent dNTP to natural dNTP on the degree of fluorophore incorporation and the length of the polymerized DNA strand. These experiments allowed us to optimize the polymerization conditions to incorporate up to ~50 fluorescent Cy3-labeled dNTPs per kilobase into a ssDNA chain. With the goal of using TdT as an on-chip labeling method, we also quantified TdT mediated signal amplification on the surface by immobilizing ssDNA oligonucleotide initiators on a glass surface followed by SIEP of DNA. The incorporation of multiple fluorophores into the extended DNA chain by SIEP translated to a ~45 fold signal amplification compared to the incorporation of a single fluorophore. SIEP was then employed to detect hybridization of DNA, by the posthybridization, on-chip polymerization of fluorescently labeled ssDNA that was grown from the 3'-OH of target strands that hybridized to DNA probes that were printed on a surface. A dose-response curve for detection of DNA hybridization by SIEP was generated, with a ~1 pM limit of detection and a linear dynamic range of 2 logs.     

Thermophysical property measurement at high temperatures by laser-produced plasmas

Excitation by a high-power laser pulse of a material surface generates a sequence of plasma, fluid flow, and acoustic events. These are well separated in time, and their detection and analysis can lead to determination of material properties of the condensed phase target. We have developed a new methodology for real-time determination of molten metal composition by time-resolved spectroscopy of laser-produced plasmas (LPP). If the laser pulse is shaped in such a way that the movement of the bulk surface due to evaporation is kept in pace with the thermal diffusion front advancing into the interior of the target, the LPP plume becomes representative of the bulk in elemental composition. In addition, the mass loss due to LPP ablation is very well correlated with the thermal diffusivity of the target matter. For several elemental solid specimens, we show that the product of the ablation thickness and heat of formation is proportional to the thermal diffusivity per unit molecular weight. Such measurements can be extended to molten metal specimens if the mass loss by ablation, density, heat of formation, and molecular weight can be determined simultaneously. The results from the solid specimen study and the progress with a levitation-assisted molten metal experiment are presented.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Sulphidation of cobalt at high temperatures

The kinetics and mechanism of cobalt sulphidation have been studied as a function of temperature (773–1023 K) and sulphur partial pressure (1–104 Pa) by means of thermogravimetric, SEM and X-ray techniques, and also using inert-marker and ratio-tracer methods. It has been shown that the sulphidation process is diffusion controlled, the rate-determining step being the outward volume diffusion of cations. According to the phase diagram of the Co–S system, the sulphide scale on cobalt is heterogeneous. At sulphur pressures higher than the dissociation pressure of the CoS2 phase, the sulphidation rate is pressure independent, and at lower pressures it increases with rising pressure, in agreement with theoretical predictions. The apparent activation energy of sulphidation is considerably higher for multilayer than for double-layer scale formation, because the main part of multilayer scale is growing at the dissociation pressure of the CoS2 phase, which increases with increasing temperature. Over the whole temperature and pressure range studied, the rate of cobalt sulphidation is more than three orders of magnitude higher than the oxidation rate of this metal. Rapid degradation of cobalt in a sulphur atmosphere results mainly from a very high defect concentration in Co1-yS and Co9S8 sulphides, participating in comparable amounts in the scale formation on this metal at T>900 K. The only sulphide of cobalt in which the defect concentration may be very low is CoS2, the growth rate of this sulphide layer being more than two orders of magnitude lower than that of other cobalt sulphides. © 1998 Chapman & Hall     

Viscoelasticity of ceramics at high temperatures

The dependence of the fracture toughness, K _IC, on the loading rate has been calculated. On the basis of linear elastic fracture mechanics (LEFM) a strong dependence of the fracture toughness on the loading rate is obtained if subcritical crack growth is taken into account. If the subcritical crack growth parameters n and B are sufficiently small, which correspond to a high velocity of crack extension, the fracture toughness should decrease at lower loading rates. This behaviour is similar to the well-known decrease of bending strength. The experimental results for alumina containing glassy phase as a model material, however, show a maximum in a certain regime of loading rates. A model is established, which combines LEFM and the viscoelasticity, and leads to a maximum of K _IC at a certain loading rate dependent on the viscosity of the glassy phase.     

Theory of superconductivity at high temperatures

Superconductivity is generally explained by an electron-lattice interaction which results in the pairing of electrons and the condensation of these pairs into a state of lower entropy. In high-temperature superconductivity the pairs consist of hybrids in which the top of the oxygen band of the crowded perovskite layer is mixed with the bottom of unoccupiedd- orf-bands from monoxide layers in the crystal. Only electrons and phonons with low quasi-momentum (k) values participate. This makes it possible to localize the lattice perturbation into broad regions in which the van der Waals forces are reduced and the perovskite planes are contracted. The low entropy state associated with superconductivity manifests itself as the formation of a superlattice of lattice distortions which is in actual motion in the current-carrying states. The observability of this superlattice is discussed.     

Thermal cycling of siliconized-SiC at high temperatures

Thermal cycling (between 1340 °C and 1480 °C) experiments were conducted using two types of reaction-bonded (siliconized) silicon carbide. A commercial material (Crystar^TM) and various silicon carbide pieces that had been joined together using electrophoretic deposition (EPD) followed by reaction bonding were evaluated. During the thermal cycling, residual free silicon metal rapidly vaporized from the Crystar^TM and cracks developed within its large SiC grains. In contrast, the EPD/reaction-bonded silicon carbide joints did not lose an observable amount of their residual silicon nor develop cracks. The reduced loss was attributed to reduced silicon content with the silicon residing largely in closed pores of the EPD layer. Reduced vaporization of the silicon that resided in surface-connected pores was engineered by applying a thick SiC surface coating. The morphology of the resulting coating was microscopically evaluated and two sequential growth mechanisms were postulated. An implication of this research is that hermetic (gas-tight) joints could be formed using EPD-derived SiC as a filler material.     

Thermal diffusivity of iron at high temperatures

The results of the thermal diffusivity measurements for pure iron within the temperature range from 830 K up to 1820 K obtained in automated mode by the dynamic plane temperature wave method have been presented.     

Thermophysical properties of cobalt at high temperatures

Measured values of the thermal conductivity, total hemispherical and spectral (λ=0.65 μ) emittances, resistivity, and coefficient of linear expansion of cobalt are presented.     

Specific heat of rhenium at high temperatures

The results of measurements of the specific heat of a wire sample of rhenium in the temperature interval 1600–2400°K and also data on the electrical resistivity and the integrated degree of blackness are reported.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 2, pp. 292–296, February, 1977.     

Thermophysical properties of lanthanides at high temperatures

Results of measurements of heat capacity, thermal diffusivity, and thermal conductivity of yttrium, gadolinium, holmium, and lutecium in the temperature range 1100–2100°K are presented. The behavior of the thermophysical properties with phase transitions is discussed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 6, pp. 1010–1012, December.     

Solution crystallization of polyethylene at high temperatures

Single crystals of polyethylene have been grown from solution in various solvents at temperatures between 70 and 120° C. This represents an overlap in crystallization conditions with those used for melt growth, where substantial isothermal thickening is known to occur during growth. The crystal thicknesses have been measured by Raman spectroscopy. Values of the equilibrium dissolution temperature and fold surface free energy are calculated for each solvent and the results analysed using the kinetic theory. Variations in crystal properties with time of crystallization are also investigated. A specific dependence of fold length on supercooling has been found to apply over the whole temperature range, consistent with predictions by the kinetic theories of crystallization in spite of changes in morphology which are incompatible with assumptions underlying the theoretical model. No evidence for isothermal thickening has been observed, except possibly for a small marginal effect at the highest temperature of 120° C investigated, over the same temperature range where melt crystallized material shows the effect prominently. Crystals grown at all temperatures displayed a rise in dissolution temperature with time which could be associated with an increase in surface perfection. All these findings have wider implications for our picture of polymer crystallization and crystal structure which are discussed here. A further, explicit, correlation with melt crystallization is deferred to a subsequent publication.