Quench Temperature Research Articles

Effect of Salt Additives to Water on the Severity of Vapor Explosions and on the Collapse of Vapor Film

We proposed ultra rapid solidification and atomization technique, CANOPUS (Cooling and Atomizing based on NOble Process Utilizing Steam explosion), using small-scale vapor explosions to make an amorphous metal. The CANOPUS method is suitable for rapid cooling and atomization process, which utilizing sustainable small-scale vapor explosions. In order to apply the CANOPUS method to a high melting point metal, it is necessary to make a small-scale vapor explosion occur at a high temperature of the molten metal. Small-scale experiment is conducted to develop the vapor explosion promotor in which spontaneous vapor explosion can occur at a high temperature of a molten metal. Spontaneous vapor explosion do not occur when water at 80 o C is used as a coolant. However, spontaneous vapor explosion occurs when water at 80 o C with salt additives is used as a coolant. Specifically, lithium chloride solution generates spontaneous vapor explosions at the highest temperature of the molten tin in the experiment. In order to clarify the triggering mechanism of the spontaneous vapor explosion when the promotor is used as a coolant, a high-temperature solid stainless steel sphere is immersed into a coolant. The interfacial temperature of the stainless steel sphere is measured, and the behavior of a vapor film around the stainless steel sphere is observed with a digital video camera. As a result, salt additives resulted in an increase of quench temperature in all salt solutions. The quenching curves of each coolant indicate that the salt additives improve the film boiling heat transfer. The improvement of the film boiling heat transfer causes an unstable formation of the vapor film and a rise of the quench temperature. It is clarified that the salt additives to water promotes a vapor film collapse. Comparing two experiments, the quench temperature of each solution is in close agreement with the upper limit of the molten tin temperature that causes spontaneous vapor explosion. This result suggests that the vapor film collapse triggers spontaneous vapor explosion.

Thermal shock behaviour of a kaolinte refractory prepared using a natural organic binder

The thermal shock resistance of a kaolinite-based refractory prepared with a binder derived from a plant (corchorus olitorius) was investigated. Thermal shock tests employing water-quenching technique were performed at quench temperature differences of between 80 and 580 °C and then the damage parameter, and thermal shock parameters (R, R′, and R′′′) evaluated using measured strength and modulus values. The results showed that R and R′ parameters increased with increasing binder concentrations, an indication that the damage due to crack initiation was progressively impaired with increased binder concentrations. The R′′′ parameter on the other hand decreased with increasing binder concentrations indicating poor resistance of the material to crack propagation. These observations were also matched with thermal shock results which showed that samples plasticized with higher binder concentration had relatively very high strengths before thermal shock, compared to those plasticized with plain water, but they experienced rather large strength losses (over 60% of their initial values) at quench temperature difference (ΔT) exceeding 325 °C. The critical temperature difference (ΔT C) for the samples tested was in the range 250–325 °C. Scanning electron microscope (SEM) micrographs of samples quenched at temperature difference of 580 °C showed that samples plasticized with high binder concentration (0.68) experienced severe cracking of the matrix compared to their counterparts plasticized with plain water, whose microstructures showed an inhibited crack propagation.

Metallic glass formation in the Cu 47Ti 33Zr 11Ni 8Si 1 alloy

Phase formation in the Cu 47Ti 33Zr 11Ni 8Si 1 alloy synthesized by various solidification techniques has been studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) paying, in particular, attention to the TEM sample preparation. While a reduced cooling rate results in a duplex microstructure, consisting of nanocrystals in an amorphous matrix, glass formation is achieved upon employing a faster quenching rate. The difference in composition and quench temperature influence the phase transition upon heating. The essential differences observed in TEM, notwithstanding the ion-milling effects and the different pre-alloy ingots used for metallic glass synthesis, can be linked to differences in the nucleation and growth mechanism which, in turn, is influenced by the chemical short range order (CSRO) obtained upon quenching.

Abnormal thermal shock behavior of Ti3SiC2 and Ti3AlC2

Many layered ternary ceramics displayed unusual thermal shock behavior, i.e., the retained strengths of as-quenched samples increased with increasing quench temperature above a critical quench temperature. However, the causation was not clear even though this phenomenon has been observed for 10 years. In this study, the thermal shock behavior of Ti3SiC2 and Ti3AlC2, two representative members of layered ternary ceramics, was investigated. The results indicated that the formation of surface oxides was responsible for this abnormal phenomenon. These results might contribute to the understanding of this unusual behavior of other layered ternary ceramics.

Effect of MPEG on MPEG-grafted EAA membrane formation via thermally induced phase separation

By grafting reaction of poly(ethylene glycol monomethyl ether) (MPEG) and poly(ethylene-co-acrylic acid) (EAA), the MPEG-grafted EAA (EAA-g-MPEG) was obtained. The effect of MPEG on the phase diagram of EAA-g-MPEG/MPEG/di- n-octyl phthalate (DOP) system was investigated by varying the composition of MPEG and DOP via thermally induced phase separation (TIPS). The binodal temperature originally shifted to lower temperature as the proportion of MPEG increased, then increased remarkably when the ratio of MPEG to DOP was more than 1/6. The domain growth kinetics of EAA/DOP, EAA-g-MPEG/DOP and EAA-g-MPEG/MPEG/DOP systems was studied by light scattering method. It was found that the domain growth rate of EAA-g-MPEG/MPEG/DOP system was lower than EAA/DOP and EAA-g-MPEG/DOP systems at a certain quench temperature. Moreover, the membrane morphologies were compared, indicating that the pore size became smaller when MPEG was added as a component of diluent. Furthermore, the distribution of the grafted MPEG chains on the imitated interphase was investigated by energy-dispersive X-ray (EDX) analysis. Results showed that more hydrophilic MPEG chains existed on the interphase when MPEG was contained in the solvent.

Effect of Cooling History on Cladding Ductility under LOCA Conditions

In a Loss-of-Coolant Accident of LWRs, heated and oxidized fuel cladding is slowly cooled and then quenched by re-flooding water. Effects of cooling rate during the slow-cooling process and quench temperature were investigated on post-quench ductility of the oxidized cladding. Unirradiated Zircaloy-4 cladding specimens were oxidized in steam at 1,373 or 1,473 K, cooled at a rate from 2 to 7 K/s, and finally quenched from temperatures ranging 1,073 to 1,373 K. Post-quench ductility was evaluated by ring-compression test, and microscopic properties were examined by metallurgical examination, hardness test, and oxygen analysis. Morphology of oxygen-rich α phase in the metallic prior-β phase layer changed depending on the cooling history. Area fraction of α phase region in the cross section obviously increased and post-quench ductility reduced with decrease in the quenching temperature. Since α phase region with low ductility can be preferential path for crack propagation, increase in area fraction of α phase region possibly decreases resistance for fracture, which results in ductility reduction. On the other hand, the area fraction was nearly constant irrespective of the rate of the slow cooling, and consequently, effect of the cooling rate on the post-quench ductility was negligible.

Internal friction peaks associated with the behaviour of hydrogen in Zr and Zr–2.5Nb

The origins/mechanisms of internal friction peaks P 2 and P 3 in specimens of solid δ-hydride ZrH 1.5, Zr–2.5Nb + 60 at.% H, Zr + 18 at.% H, etc. have been studied. Both peaks occur in a specimen of Zr + 18 at.% H, and the height of P 3 increases with the quench temperature but peak P 2 does not vary with quenching. However, in specimens of ZrH 1.5 and Zr–2.5Nb + 60 at.% H, only peak P 2 is observed, except for a small shoulder in ZrH 1.5 denoted as P′, which does not vary with quenching either, even though quenching reduces Young's modulus. The height of P 2 is proportional to the square of the H concentration. From this dependence, the mechanism of peak P 2 is proposed to be the stress-induced redistribution of H atom-pairs within the fcc lattice of δ-hydride. The height of P 3 depends on the content of quench-induced hydride particles. The relaxation mechanism responsible for peak P 3 is proposed to be stress-induced motion of H atoms across the interface between the hcp lattice of α-Zr and the fct (or fcc) lattice of the quench-induced hydrides.

Quenching and partitioning martensite—A novel steel heat treatment

A novel concept for the heat treatment of martensite, different to customary quenching and tempering, is described. This involves quenching to below the martensite-start temperature and directly ageing, either at, or above, the initial quench temperature. If competing reactions, principally carbide precipitation, are suppressed by appropriate alloying, the carbon partitions from the supersaturated martensite phase to the untransformed austenite phase, thereby increasing the stability of the residual austenite upon subsequent cooling to room temperature. This novel treatment has been termed ‘quenching and partitioning’ (Q&P), to distinguish it from quenching and tempering, and can be used to generate microstructures with martensite/austenite combinations giving attractive properties. Another approach that has been used to produce austenite-containing microstructures is by alloying to suppress carbide precipitation during the formation of bainitic structures, and interesting comparisons can be made between the two approaches. Moreover, formation of carbide-free bainite during the Q&P partitioning treatment may be a reaction competing for carbon, although this could also be used constructively as an additional stage of Q&P partitioning to form part of the final microstructure. Amongst the ferrous alloys examined so far are medium carbon bar steels and low carbon formable TRIP-assisted sheet steels.

Thermal Shock Behaviour of Open-Cell Cordierite Foams

Open-cell ceramic foams are being considered for a variety of applications owing to their high permeability and low weight, including molten metal filters, catalytic substrates and radiant burners. In these applications, foams are exposed to high temperatures and thermal gradients and thus the materials used require resistance to severe thermal stresses during service. Unfortunately, little is known about the thermal shock behaviour of cordierite foams when subjected to sudden changes in temperature. The objective of the present study was to investigate the thermal shock behaviour of two kinds of cordierite-based ceramic foams manufactured by the replication process. Thermal shock experiments were carried out by rapidly transferring the heated samples from a resistance furnace to a quenching bath containing distilled water followed by measuring of the retained flexural strength. Unlike dense cordierite samples that showed a sudden decrease in flexural strength at quench temperature differences above 325 K, the strength retained after thermal shock by open-cell cordierite foams decreased gradually with increasing quench temperatures. This suggests a cumulative damage mechanism reflecting an increase in damage throughout the material rather than sudden failure owing to propagation of pre-existing cracks.

Quench rate and temperature effects on framework ordering in aluminosilicate melts

The effect of temperature on the structure of LiAlSiO4 and NaAlSiO4 liquids has been studied by 17O 3QMAS NMR spectroscopy using glass samples prepared with different fictive temperatures. The abundance of Al-O-Al and Si-O-Si bridging O linkages increases with increasing fictive temperature, indicating that the reaction 2 Al-O-Si ↔ Al-O-Al + Si-O-Si shifts to the right with increasing temperature in the liquid. The observed temperature dependence of Al-O-Al species abundance allows us to estimate the ΔH of this reaction to be 28.8 ± 11.3 kJ/mol for NaAlSiO4 glasses and 31.7 ± 13.3 kJ/mol for LiAlSiO4 glasses. Extrapolating our results to higher temperature, we estimate that 13.18% of the bridging O atoms occur as Al-O-Al in NaAlSiO4 and 15.25% in LiAlSiO4 at ~2000 K, as compared to 25% Al-O-Al predicted by a statistically random bridging O distribution in compositions with an Al/Si ratio of 1. Using the experimental data to estimate the contribution to configurational heat capacity from Al/Si disordering in NaAlSiO4 liquid, we find that redistribution of bridging O species with increasing temperature produces a negative dCP/dT above the glass transition and therefore cannot account for the observed positive dCP/dT. We discuss a generalized mechanism for structural rearrangement characterized by a small initial species concentration at Tg and a large ΔH, which produces a positive dCP/dT.

Studies on melt spinning process of hollow polyethylene terephthalate fibers

AbstractDimensional change and profile development in the melt spinning process of polyethylene terephthalate hollow fibers were studied through the numerical simulations and experimental results. The simulation predicts the final dimensions and profiles development of the hollow fibers at various positions from the die. Experimental results show that the melt extruded from the spinneret coalesces initially to form a hollow inner core and the cross‐sectional shape holds for over the whole spinline with only variation in the hollow portion. Analysis of the effect of spinning parameters on hollow portion shows that the spinning temperature, mass throughput rate, and take‐up speed are the most critical variables in controlling the hollow portion followed by quench air velocity. The quench air temperature has relatively less effect than the other variables. As the mass throughput rate and quench air velocity increase and the take‐up speed and spinning temperature decrease, the hollow portion increases. To investigate the effect of die geometry, die having a different ratio of inner to outer diameter was used. The effect of change of process variables decreases as the die gap becomes narrow. POLYM. ENG. SCI. 46:609–616, 2006. © 2006 Society of Plastics Engineers

Quench propagation properties analysis of high-temperature superconductors using finite element method

Quench propagation property is an important issue in stability of high-temperature superconductor for practical application. There are many factors inducing quench, such as external disturbance, operating temperature, transport current and magnetic field. Quench propagation velocity and minimum quench energy (MQE) are two important parameters to the stability and protection issues of superconducting magnet. This paper presents some analytical results about quench propagation properties of Bi-2223/Ag superconducting multifilament tape using finite element method (FEM). The results show that the temperature transition behaviors from superconducting-state to normal-state in the process of quench propagation can be conveniently simulated through establishing a suitable thermal analysis model. The simulation results of quench temperature–time traces of different location on Bi-2223/Ag superconducting tape are basically coincident with the former experimental results. These results are significant to the application of high-temperature superconductor.

Amylose Crystallization from Concentrated Aqueous Solution

Maize amylose, separated from granular starch by means of an aqueous leaching process, was used to investigate spherulite formation from concentrated mixtures of starch in water. Amylose (10-20%, w/w) was found to form a spherulitic semicrystalline morphology over a wide range of cooling rates (1-250 degrees C/min), provided it was first heated to >170 degrees C. This is explained through the effect of temperature on chain conformation. A maximum quench temperature of approximately 70 degrees C was required to produce spherulitic morphology. Quench temperatures between 70 and 110 degrees C produced a gel-like morphology. This is explained on the basis of the relative kinetics of liquid-liquid phase separation vis-à-vis crystallization. The possibility of the presence of a liquid crystalline phase affecting the process of spherulite formation is discussed.

Grain shapes and growth kinetics during self‐assembly of block copolymers

AbstractWith block copolymer equilibrium phase behavior becoming increasingly better understood, a more detailed description of ordering kinetics is feasible. This article highlights recent experimental observations that provide new insight into ordering kinetics and grain structures when a block copolymer liquid is first cooled below the order–disorder transition. Measurements have been made on several concentrated poly(styrene‐b‐isoprene) solutions, with concentrations and temperatures adjusted to access the cylinder, lamellar, and gyroid phases. A diverse set of grain types were observed using polarized optical microscopy (POM). Cylinder grains were either oblate ellipsoids or spherulites, whereas the lamellar phase formed prolate ellipsoidal grains, twinned ellipsoidal grains, twofold twinned grains, and spherulites. The orientation of the cylinders and lamellae within the grains were unambiguously identified. The shapes of the ellipsoidal and twinned grains were dictated by the relative interfacial tensions of the available growth surfaces with respect to the disordered state. Grain growth front velocities were also quantified before grain impingement, and consistent values were obtained among different grains for a given sample and quench temperature. The experimental growth velocities were compared to an expression derived by Goveas and Milner. There was good agreement in terms of the temperature dependence, and the absolute magnitude was predicted with some success. The rates of nucleation and overall conversion to the ordered phase were also determined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 481–491, 2006

Physical Aging of Starch, Maltodextrin, and Maltose

The physical aging of low water content, amorphous starch/water, maltodextrin/water, and maltose/water mixtures in the glassy state was examined using mechanical testing and calorimetry. Stress relaxation measurements showed that upon storage of the glassy materials there was a time-dependent increase in both flexural modulus and mechanical relaxation time. The mechanical relaxation time increased with depth of quench below the calorimetric glass transition temperature and with aging time at the quench temperature. Calorimetry of the aged materials showed an overshoot in heat capacity in the vicinity of the glass transition. The logarithm of the mechanical relaxation time showed a simple linear relationship with the size of the overshoot expressed as an enthalpy change. The calorimetric behavior could be modeled using the Tool-Narayanaswamy-Moynihan method.

Domain growth in Ising systems with quenched disorder

We present results from extensive Monte Carlo (MC) simulations of domain growth in ferromagnets and binary mixtures with quenched disorder. These are modeled by the random-bond Ising model and the dilute Ising model with either nonconserved (Glauber) spin-flip kinetics or conserved (Kawasaki) spin-exchange kinetics. In all cases, our MC results are consistent with power-law growth with an exponent theta(T, epsilon) which depends on the quench temperature T and the disorder amplitude epsilon. Such exponents arise naturally when the coarsening domains are trapped by energy barriers that grow logarithmically with the domain size. Our MC results show excellent agreement with the predicted dependence of theta(T, epsilon).

Vapor Explosion of Coolant Jet When Penetrating a Hot Molten Metal

The vapor explosion phenomenon is investigated experimentally for a geometrical arrangement in which a cold liquid (water) jet is injected into a hot liquid surface (tin). Medium-scale experiments using 1 kg of molten tin were performed in an open geometry experiment system. In the first phase of the research, the influence of the injection mass flow rate on the likelihood of vapor explosion was investigated in order to map the various relevant regimes. In the second phase, the influence of some selected parameters on the interaction was studied to characterize the relevant parameters of the vapor explosion phenomenon.The range of the initial tin and water temperatures that leads to vapor explosion has been determined in order to define the thermal interaction zone. It is noticed that vapor explosion can occur at high water temperatures even near the saturation point. The delay time for the explosion to occur and the degree of the interaction violence were correlated with the initial tin and water temperatures. We also clarified the triggering point and noted a correlation between the quench temperature and the likelihood of the vapor explosion occurrence.

Spherulitic Crystallization in Starch as a Model for Starch Granule Initiation

The influence of cooling rate and quench temperature on the formation of spherulitic morphology in heated mung bean starch is reported. Spherulites were obtained for a wide range of cooling rates (2.5-250 degrees C/min), provided the system was heated to 180 degrees C and then cooled below 65 degrees C. Branched crystalline structures were also observed, as was a gellike morphology. The dissolution temperature for spherulitic material ranged between 100 and 130 degrees C. A second dissolution endotherm was observed between 130 and 150 degrees C in systems containing gellike material. Spherulites revealed B-type X-ray diffraction patterns. Spherulitic crystallization of starch following phase separation is proposed as a model for starch granule initiation in vivo.

Microstructural evolution at the initial stages of continuous annealing of cold rolled dual-phase steel

Abstract The performance of cold rolled dual-phase (DP) steels depends on their microstructure, which results from the thermomechanical processing conditions, involving hot rolling, cold rolling, and continuous annealing. The knowledge on the influence of each annealing stage on the microstructure formation is essential for manufacturing high-quality DP steels. In the present work, the effects of some intercritical annealing parameters (heating rate, soaking temperature, soaking time, and quench temperature) on the microstructure and mechanical properties of a cold rolled DP steel (0.08% C–1.91% Mn) were studied. The microstructure of specimens quenched after each annealing stage, simulated on a Gleeble, was analyzed using optical, scanning, and transmission electron microscopy. The tensile properties, determined for specimens submitted to complete annealing cycles, are influenced by the volume fractions of martensite, bainite, martensite/austenite (MA) constituent, and carbides, which depend on annealing processing parameters. The results obtained showed that the yield strength (YS) increase and the ultimate tensile strength (UTS) decrease with the increasing intercritical temperature. This can be explained by the increased formation of granular bainite associated with the increased volume fraction of austenite formed at the higher temperatures. The experimental data also showed that, for the annealing cycles carried out, UTS values in excess of 600 MPa could be obtained with the steel investigated.

The structure and mechanical properties of Fe2AlMn single crystals

The microstructure and mechanical properties of off-stoichiometric single-crystal Fe2AlMn have been investigated. After casting, the alloy contained two sets of thermal antiphase boundaries, (a/4)⟨111⟩ and (a/2)⟨100⟩, which are attributed to the fact that the compound solidifies into a bcc structure and subsequently orders to a B2 structure and then a L21 structure respectively upon further cooling. Crystals strained under tension at room temperature in air at 1s−1 showed 6% elongation, whereas specimens strained at 1 × 10−5 s−1 showed no elongation, indicating that the compound is sensitive to the testing environment. Fracture occurred on {100} in both cases. Compression tests showed that a yield anomaly was present at intermediate temperatures, with the peak yield strength occurring at about 800 K, which is slightly below the L21–B2 transition temperature of 898 K. The slip systems were found to be ⟨111⟩{110} at room temperature and 800 K. Transmission electron microscopy observations showed fourfold-dissociated ⟨111⟩ dislocations in specimens strained at room temperature but only paired ⟨111⟩ dislocations in specimens strained at the peak temperature. The room-temperature yield strength of quenched specimens increased with increasing quench temperatures from 700 to 1100 K.