Short Heating Period Research Articles

Oxidation behaviour of Al‐alloyed ductile cast irons at elevated temperature

AbstractThe oxidation resistance of ductile irons alloyed with aluminium in the range from 0.08 to 6.16 wt.% has been investigated by heating at 550°C for periods up to 1270 h. Examination by light and SEM microscopy and EPMA indicated that two quite distinguishable layers of oxide were established at the surface. It was found that, in alloys containing aluminium, a very thin and adherent film of aluminium oxide is produced after a short period of heating, which protects the bulk of the alloy from further attack. It is believed that the oxidation resistance can be improved by increasing the aluminium content: an increase in aluminium content led to a decrease in the average thickness of the iron‐rich oxide layer. It was also found that the Al addition improved decarburization resistance; after long times at 550°C a nodular iron with a 6.16% Al content was free of decarburization. Copyright © 2004 John Wiley & Sons, Ltd.

Heat-induced apoptosis of mouse meiotic cells is suppressed by ectopic expression of testis-specific calpastatin.

Calpastatin is a naturally occurring inhibitor of calpain, a protease involved in apoptotic cell death. A testis-specific isoform of calpastatin (tCAST) has been identified that is transcribed in haploid germ cells but not in spermatocytes. To investigate the possible function(s) of tCAST, we tested the hypothesis that the ectopic expression of calpastatin in spermatocytes would suppress the death of these cells in response to an apoptosis-inducing stimulus in vivo. To this end, the 5'-flanking region of the mouse ldhc gene was linked to tCAST, and transgenic mice were generated. Immunohistochemical analysis revealed that, in contrast to control sections in which the signal for tCAST was seen in round spermatids, intense staining was visualized in pachytene spermatocytes in the transgenic animals, indicating that the strategy we used to generate the transgenic animals resulted in the ectopic expression of tCAST in spermatocytes. We then tested the effect of a short period of heating on germ cell apoptosis in the testes of wild-type and transgenic mice. Pachytene spermatocytes were the major germ cell type seen to undergo apoptosis after heat treatment. There were no differences in the number of apoptotic germ cells per seminiferous tubule between wild-type and tCAST transgenic control mice; thus, there was no apparent effect of the transgene on normal apoptosis. Heating resulted in increased numbers of TUNEL-positive germ cells in both wild-type and tCAST transgenic mice, as well as increased testicular DNA fragmentation. Heating the tCAST transgenic mouse testes resulted in significantly fewer apoptotic cells per seminiferous tubule than in wild-type mice at both 8 and 24 hours after treatment. Thus, as hypothesized, the ectopic expression of tCAST in pachytene spermatocytes suppressed germ cell apoptosis.

Nanosize LiNiyMn2 ? yO4 (0 < y ? 0.5) spinels synthesized by a sucrose-aided combustion method. Characterization and electrochemical performance

Nanosize crystalline cathode materials of LiNiyMn2 − yO4 (0 < y ≤ 0.5) composition and spinel-type structure have been obtained by a single-step sucrose-aided self-combustion method. The as-prepared samples contained some amorphous organic impurities that were removed after a short period of heating at 500 °C. The pure single-phase spinels have been characterized by X-ray diffraction, transmission electron microscopy, chemical analysis, and nitrogen sorption isotherms. The samples consist of particles (ca. 24 nm size) that are aggregated in clusters (ca. 1 µm size) in which mesopores (10–80 nm size) appear among the particles. Additional heating at 800° and 1000 °C produces a slight increase in the cubic lattice parameter and a pronounced increase in particle size (>100 nm). Electrical conductivity decreases as the Ni content increases in accordance with an electron hopping mechanism between Mn3+ and Mn4+ ions. The 500 °C- and 800 °C-heated LiNi0.5Mn1.5O4 samples show good electrochemical behaviour at 4.7 V as cathode materials. The capacity (132.7 mA h g−1) found is close to the nominal capacity (146.7 mA h g−1) and remains constant for current densities in the range C/24–2C (where C = 2.6 mA cm−2). At higher current densities (2C–10C) the capacity decreases progressively. The cyclability at the C current density is ca. 99.7% for both samples.

Multiple steps during the formation of beta-lactoglobulin fibrils.

In this study, the heat induced fibrilar aggregation of the whey protein beta-lactoglobulin is investigated at low pH and at low ionic strength. Under these circumstances, tapping mode atomic force microscopy results indicate that the fibrils formed have a periodic structure with a period of about 25 nm and a thickness of one or two protein monomers. Fibril formation is followed in situ using light scattering and proton NMR techniques. The dynamic light scattering results show that the fibrils that form after short heating periods (up to a few hours) disintegrate upon slow cooling, whereas fibrils that form during long heating periods do not disintegrate upon subsequent slow cooling. The NMR results show that even after prolonged heating an appreciable fraction of the protein molecules is incorporated into fibrils only when the beta-lactoglobulin concentration is above approximately 2.5 wt %. The data imply multiple steps during the heat induced formation of beta-lactoglobulin fibrils at low pH and at low ionic strength: (partly) denatured protein monomers are either incorporated into fibrils or form instead a low molecular weight complex that is incapable of forming fibrils. Fibril formation itself also involves (at least) two steps: the reversible formation of linear aggregates, followed by a slow process of "consolidation" after which the fibrils no longer disintegrate upon slow cooling.

A new approach to modelling of single droplet drying

A model was developed to predict the change in droplet mass and temperature when it is exposed to hot air, as in spray drying of droplets containing solids. The droplet was assumed first to undergo sensible rapid heating with no mass change. Then the droplet experiences some shrinkage, with no temperature change but rapid mass losses, followed by a period of crust formation with a significant change in droplet mass and temperature and finally a short period of sensible heating of the dried particle. The model, unlike previous models, accounts for shrinkage and for the temperature distribution in the droplet. It provided a good prediction for the change in droplet temperature and mass for some of the experimental measurements available in the literatures.

LiMn 2O 4 cathode doped with excess lithium and synthesized by co-precipitation for Li-ion batteries

LiMn 2O 4 exhibits lower cost, acceptable environmental characteristics, and better safety properties than other positive-electrode (cathode) materials for lithium-ion batteries. In this study, excess Li doped Li 1+ x Mn 2O 4 is synthesized by a well-mixed co-precipitation method with LiOH utilized as both the reactant and co-precipitation agent. The precursor is calcined for various heating times and temperatures to form a fine powder of a single spinel phase with different particle sizes, size distributions, and morphology. The minimum heating temperature is around 400 °C. For short heating periods, Mn 2O 3 impurity is observed, but disappears after longer heating times. The average particle size is in the range 2–8 μm for powders calcined between 700 and 870 °C. The lattice parameter increases with increase in heating temperature. The electrochemical behavior of LiMn 2O 4 powder is examined by using test cells which consist of a cathode, a metallic lithium anode, and an electrolyte of 1 M LiPF 6 in a 1:1 (volume ratio) mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). Cells with cathodes of LiMn 2O 4, Li 1.08Mn 2O 4 and Li 1.1Mn 2O 4 give a capacity of 85, 109 and 126 mAh g −1, respectively. The introduction of excess Li in LiMn 2O 4 apparently increases the capacity, and decreases significantly the rate of capacity degradation on charge–discharge cycling.

Tin soaps in emulsion PVC heat stabilization

AbstractIn this study, the effect of a liquid stabilizer based on organotins on PVC heat stability is investigated. Control and films with tin soap heat stabilizer Sn500K were prepared by solvent casting and they were heated at 160 and 180°C for different time periods. X‐ray fluorescence spectroscopy analysis showed that tin was present in Sn500K and it was lead‐free. DSC analysis showed that glass‐transition temperature of films with Sn500K increased from 67 to 75–85°C by heating for 15 min at 180°C. IR spectroscopy indicated that concentration of carboxylate groups of Sn500K decreased with heating. Films with Sn500K did not degrade for short heating periods; however, degradation occurred in long heating times. Low concentration of Sn500K was recommended, since at high levels incompatibility with PVC and acceleration of degradation was observed. In the high temperature range, control and stabilized samples degraded in the same manner in two steps. © 2002 John Wiley &amp; Sons, Inc. Adv Polym Techn 21: 65–73, 2002; DOI 10.1002/adv.10008

Influence of temperature and time on thermally induced forces in corneal collagen and the effect on laser thermokeratoplasty

Purpose To investigate thermomechanical aspects of corneal collagen denaturation as a function of temperature and time and the effect of the induced forces on refractive changes with laser thermokeratoplasty (LTK). Setting Medical Laser Center Lübeck, Lübeck, Germany. Methods In a material-test setup, porcine corneal strips were denatured in paraffin oil at various constant temperatures for 10 and 500 seconds, and the temporal course of the contractive forces was studied under isometric conditions. Typical LTK lesions were performed in porcine eyes in vitro with a continuous-wave infrared laser diode at a wavelength of 1.87 μm for 10 and 60 seconds. The laser power was chosen to achieve comparable denatured volumes at both irradiation times. The refractive changes were measured and analyzed by histologic evaluations and temperature calculations. Results The time course of the induced forces was characterized by a maximal force, which increased almost linearly with temperature, and a residual lower force. After 500 seconds of heating, the highest force was achieved with a temperature of 75°C. With a limited heating period of only 10 seconds, the forces steadily increased with temperature over the entire observation period. Laser thermokeratoplasty produced less refractive change after 10 seconds of irradiation than after 60 seconds, although the laser power was 25% higher in the short heating period. Polarization light microscopy of LTK lesions revealed different stages of thermal damage. Conclusion The course of the contractive forces during and after heating is a complicated function of the spatial time/temperature profile. Laser thermokeratoplasty lesions produced with 2 irradiation times showed different stages of denaturation and induced refractive change.

Determination of the kinetic data of the thermal decomposition of energetic plasticizers and binders by adiabatic self heating

The thermal decomposition behaviour of the following plasticizers and uncured binders (diols for PUR-type elastomer binders) was investigated in solutions of toluene (with 10 mass% contents) by adiabatic self heating with an `accelerating rate calorimeter' (ARC ™): uncured GAP (poly-glycidylazide) from two manufacturers, polyGLYN (poly-glycidylnitrate) mixture (58.8/41.2 in mass%) N-methyl-/ N-ethyl-NENA (NENA = N-(2-nitratoethyl)-nitramine), DANPE (1,5-diazido-3-nitraza-pentane), GAPA (short chain GAP but with azido end groups), EGBAA (ethylene glycol-bis-(α-azidoacetate), octylazide (not for use in explosives), GAP-AA-2000 (normal GAP, but OH-end groups as esters of α-azidoacetic acid), GAP-AA-500 (short chain GAP, but OH-end groups as esters of α-azidoacetic acid). Three types of energetic groups are represented with these compounds: the organic nitric acid ester group, the nitramine group and the organic azido group. The closed measuring system prevents the solutions from evaporating and gives a good adiabaticity. The amount of the solution weighed-in was about 6 g, the measuring cells used are made from titanium with one inch in diameter. All named energetic substances would deflagrate after a short period of controllable self heating with the weighed-in amount of energetic substance. The advantage of the investigation of the solutions is that the decomposition of the energetic substances can be followed in a fully controlled way. With the self heat rate curves one can distinguish the plasticizers and binders with respect to the decomposition temperature range, the heat generation and the heat generation rate. The Arrhenius parameters and the released heats of reaction have been determined from the self heat rate curves, which have been described well with reactions of first order. The self heat rate curves have been scaled to the thermal inertia equal to one, which corresponds to (1) the measurement on a solution without measuring cell and to (2) the measurement on the energetic substance alone without solvent and measuring cell. The procedures of the scaling and of the data evaluation are described.

The redox behaviour of thermally pretreated, highly disrupted, states of platinum surfaces in aqueous media

Subjecting platinum wire electrodes to short periods (10 to 25 s) of intense heating ( T>ca. 1200°C) in an inert gas atmosphere leads to considerable changes in the surface microstructure of the metal; metastable active states become frozen-in as the temperature of the thermally excited sample drops rapidly to ambient values. Unusual redox responses and, in particular, enhanced premonolayer oxidation peaks in the positive sweep, were observed when such wires were subsequently immersed in aqueous media and investigated using cyclic voltammetry. These unusual responses, which are similar to those reported earlier following prolonged electrochemical activation of platinum (the thermal procedure is much shorter and the behaviour more consistent), were further enhanced by subsequently polarizing the thermally treated samples at low potentials. For a number of reactions and, in particular, methanol oxidation which is important from a fuel cell viewpoint, the electrocatalytic activity of platinum at low potentials was greatly enhanced. However, for other processes, e.g. hydrazine oxidation, thermal pretreatment resulted in a decrease in electrocatalytic activity; it appears that in some cases the active sites become overoxidised. A synopsis is given of the active site behaviour of platinum surfaces in aqueous media and a comparison is made between the present results and those reported elsewhere for platinum single crystal electrodes where similar thermal pretreatment is frequently employed.

Oxidation of alloys of the system Ni−Ta. I. Oxidation of the intermetallic Ni3Ta

Oxidation kinetics for the intermetallic Ni3Ta in air at 600–1000°C are studied by a thermogravimetric method. The alloy has an ordered crystal structure (D132h-Pmmn) with rhombic lattice parameters a=0.512 nm, b=0.423 nm, and c=0.452 nm. The kinetic isotherms of Ni3Ta oxidation are described by a parabolic equation. With t≤800°C there is a periodic increase in the rate constant of parabolic oxidation, but with t>800°C there is a periodic decrease of it. In the range 850–875°C the alloy oxidation rate decreases as a result of scale sintering. Oxygen diffusion slows down in the compact scale. X-ray and metallographic analysis of the scale that forms on Ni3Ta indicates that it contains NiO, NiO·Ta2O5, Ta2O5 and also Ni and the solid solution Ni(Ta). These phase components are distributed in layers of the scale: NiO (first), NiO+NiO·Ta2O5 (second), NiO·Ta2O5+Ni+Ta2O5 (third), Ta2O5+Ni(Ta) (fourth). With a low temperature and short periods of heating there is no Nio·Ta2O5 or Ni(Ta) in the scale. Oxidation of Ni3Ta is controlled by oxygen diffusion in the scale over the direction towards the alloy. With t>850°C this mechanism changes. By analogy with oxidation of tantalum it is assumed that structural changes in the Ta2O5 lattice may be responsible for this.

The thermostability of purified isoperoxidases from Brassica oleracea VAR. gemmifera

The thermostabilities of four previously purified isoperoxidases from Brussels sprouts ( Brassica oleracea VAR. gemmifera.)have been determined. The heating time periods selected (10 s – 0.5 min intervals) are comparable to those used during commercial blanching. Non-linear regression (NLR) equation fitting, using common goodness of fit criteria (low chi-squared value, high regression coefficient and low residuals) points to a mechanism of peroxidase heat inactivation involving two consecutive reactions during the initial periods of heating. In the consecutive model, native peroxidase ( E 0) is converted into a partially active from ( E 1) and then into the inactivated enzyme ( E 2) during short periods of heating. The order of calculated decimal reduction times for the two anionic (A1 and A2) and two cationic (C1 and C2) Brussels sprouts isoperoxidases was A1⩾ C1> A2> C2. Calculated concentration changes for E 0, E 1 and E 2 during heat inactivation were quite different for the four isoperoxidase preparations and indicated the generation of more stable forms of partially denatured peroxidases. The anionic isoenzymes showed greater regeneration of enzymatic activity after heat treatment and this could have been due to their greater ability to regain previously liberated haem. ©

The effect of cold deformation on grain refinement of heavy metals

Rapid heating experiments, of the order of seconds, were performed on a 90%W–7%Ni–3%Fe alloy, which was cold worked by rotary swaging to 50 and 82% reduction in diameter. It was found that even very short periods of heating above the melting temperature of the matrix causes the partition of the elongated tungsten grains into small round ones. The higher the degree of deformation, the shorter the period of heating for the partition of the tungsten grains. The grain refining process is carried out by the penetration of the molten matrix into the subgrain boundaries of the tungsten grains.

Experimental Investigation on Pulsating Horizontal Heating of a Water-Filled Enclosure

Experimental results of the natural convection generated by the time periodic horizontal heating of a square cross-section enclosure filled with water are reported. A pulsating (on/off) heat flux is delivered to the heating wall of the enclosure, with the opposite wall cooled by a high thermal capacitance system. All other surfaces are insulated. Heating periods from 32 to 1600 seconds and cycle-averaged heat-flux based Rayleigh numbers from 2.5 × 108 to 1.0 × 109 are considered. Results presented in terms of time series, phase-plane portraits, and cyclic evolution of surface-averaged cooling and heating wall temperatures illustrate the main characteristics of the evolution to periodic regime. Also presented are the cycle-averaged heat transfer coefficient versus heating period, and the corresponding average Nusselt number versus Rayleigh number for various heating frequencies. These results, which support published theoretical and numerical analysis, indicate that by tuning the heating period properly, the heat transfer across an enclosure can be enhanced. The results also reveal that short heating periods hinder the convection within the enclosure, in general (e.g., for Ra = 7.5 × 108 and a period of 32 s the heat transfer coefficient is 13 percent smaller than the steady heating value). The sensitivity of the transport phenomenon to pulsating heat is shown to depend strongly on Ra. Finally, a correlation for estimating the maximum heat transfer coefficient, derived from the experimental results, is presented.

The radicular dentine temperature during laser irradiation: a numerical modeling.

The boundary element method is well adjusted to the numerical resolution of thermal diffusion problems existing in complex volumes such as teeth. This technique is used to determine the temperatures in the bulk and on the surface of a tooth illuminated by a CO2 laser beam. The parameters taken into account in calculations include power absorbed by the tooth, laser irradiation time, and diameter of the beam on the tooth. In each case, a very fast and short heating period is observed on the tooth surface; then, the temperature decreases slowly. Inside the tooth, temperature variations are small or nonexistent. Temperature increases due to a laser beam remain concentrated at the impact region. Results are in reasonable agreement with experimental results.

Auger Depth Profiling and Diffusion Measurements in Electrolytic Tinplate

Electrolytic tinplate of low tin coating has been subjected to a diffusion heat treatment typical of that employed in commercial tinplate. Diffusion profiles were obtained by means of Auger electron spectroscopy in conjunction with ion sputtering. The diffusion coefficients were calculated for temperatures from 150 to 240 °C. A preliminary study of both the diffusion-controlled growth of the FeSn 2 layer and the penetration curves indicates that the interdiffusion coefficient is dependent on the concentration of Sn. The interdiffusion coefficients were determined on either side of the interface alloy layer and for distances corresponding to the concentration ranges of 0-81 wt.% Sn and 0-19 wt.% Fe. A short heating period during flow melting in the electrolytic manufacturing process results in a very thin layer of the FeSn 2 intermetallic phase at the Fe/Sn interface.

Kinetics of a non-catalytic gas-solid chemical reaction under SHS-like conditions

Nitration of metallic tantalum under self-propagating high-temperature synthesis (SHS) conditions (i.e. rapid heating rates 2000–3000 Ks−1, and short heating periods 2–100 s) has been studied. Phase analysis and microstructural characterization have been performed. A two-phase mixture region of solid solution TaNx and tantalum subnitride, namely Ta2N, was observed in the nitrided tantalum at temperatures of 1600–2600 K and a partial nitrogen pressure of 0.1–0.8 MPa. It was also found that tantalum subnitride phase formed before the formation of Ta-N solid solution throughout the sample during nitration. A theoretical study was conducted in order to determine the intrinsic reaction kinetics of a typical combustion synthesis reaction. A new model was developed to explain all experimental observations. The computer simulation results are in good agreement with experimental data. The results indicate that at sufficiently large heating rates the product layer does not necessarily act as a diffusion barrier that prevents further uptake of nitrogen. The results are helpful in developing an understanding of the mechanism of powder-based SHS.

Increasing the Soil Temperature to Study Global Warming Effects on the Soil Nitrogen Cycle in Agroecosystems

According to the GCMs air temperature will in- crease 3-5?C above ambient in Central Europe. As one consequence the element turnover in terrestrial ecosystems should change; in particular, the large soil carbon and nitrogen pools are crucial because of their potential to further 'pollute' the globe with liquid and gaseous compounds. According to the goals of the International Geosphere-Biosphere Pro- gramme (IGBP) an ecosystem manipulation was carried out to increase the temperature of the top soil in an agroecosystem No changes in the soluble nitrogen pools could be measured at the end of the investigation, probably because of the short heating period and the high spatial variability. However, N20-N emissions were much higher in the unheated plot (0.233 kg ha-1) compared with the heated one (0.058 kg ha - 1). This effect could be caused by more frequent freezing- thawing cycles in the unheated plots, which showed the highest emission rates. The importance of the reduced water content in the heated plot could not be evaluated in this investigation. Based on the experiences of this study a sched- ule for intensified field experiments was developed.

Drying of Solid Furl Particlbs in Hot Gases

ABSTRACT Drying of solid fuel particles in hot gases ( 50–200c) is studied both theoretically and experimentally. The measurements are carried out by using a thermobalance reactor constructed for drying and pyrolysis studies of particles up to 30 mm by diameter. The model is based on the solution of the conservation equations for mass and energy. The drying is considered to consist of three successive periods: a short initial heating period, period of constant rate of drying and period of falling rate of drying. It is assumed that the particle moisture distribution is uniform during the constant rate of drying. Shrinking core model is assumed for the falling rate period. esides fuel particles, the model is applicable also for other solid particle drying processes. Model calculations are compared to measurements for wood chips. The model can predict the efFect of the main parameters reasonably well. These main parameters affecting the drying rate are: particle size, particle shape, initial particle moistur...

Heat shock-induced prompt glycosylation. Identification of P-SG67 as calreticulin.

Acute heat shock initiates the phenomenon of "prompt" glycosylation, which is characterized by selective glycosylation of specific cellular proteins called the prompt stress glycoproteins (P-SG). Prompt glycosylation rapidly occurs even during short heating periods, e.g. 10 min at 45 degrees C, and is not affected by the presence of cycloheximide (Henle, K. J., Kaushal, G. P., Nagle, W. A., and Nolen, G. T. (1993) Exp. Cell Res. 207, 245-251). The major P-SG in Chinese hamster ovary cells, P-SG67, was characterized by an M(r) of 67,000 and a pI = 5.1. In the present study, we purified P-SG67 by sequential gel filtration, anion exchange, affinity chromatography with concanavalin A-Sepharose, and two-dimensional isoelectric focusing/SDS-polyacrylamide gel electrophoresis. The purified protein was digested and partially characterized by microsequencing of three major peptide fragments. The fragments, comprising a total of 46 amino acid residues, had an almost 100% sequence homology with calreticulin and partial homology with calnexin. Calcium binding studies with 45Ca2+ overlay confirmed that P-SG67 is a Ca(2+)-binding protein. These observations support the notion that P-SG67 is identical to calreticulin and that the glycosylation status of calreticulin can respond to environmental stress conditions.