Short Heating Time Research Articles

Short-time heat treatment of press hardened steel for laser assisted clinching

Clinching of high strength steels is currently difficult due to their relative low ductility. Hence a new method has been developed to clinch these steel grades. This could be achieved by heating the sheets locally at the joint by a laser during the clinching process. The short-time tempering behaviour of the press hardened steel 22MnB5 has been investigated by dilatometry respectively calorimetry experiments. Different stages of the tempering process have been identified depending on heating rates up to 1000 K s−1. Characteristic tempering reactions were shifted to higher temperatures with increasing heating rate. Based on these results, suitable short-time heat treatment parameters have been selected and transferred to the clinching process. Thereby the press hardened steel 22MnB5 has been successfully clinched with laser assistance for the very first time. The laser assisted clinched joint has been characterised by metallographic analysis and hardness testing. It could be shown, that in the clinching joint only a slight strength loss occurs due to the introduced laser heat.

Tin Oxide Modifed LiNi0.8Co0.2O2 Cathode Material for Lithium-ION Batteries

Since the commercialization of lithium secondary batteries in the early of 1990s, their development has been rapid. It is a well known fact that lithium ion battery technology’s future depends on mostly improvements in electrode materials. Sol–gel production method is a promising way to prepare electrode materials due to their evident advantages over traditional methods, for example, homogeneous mixing at the atomic or molecular level, lower synthesis temperature, shorter heating time, better crystallinity, uniform particle distribution and smaller particle size at nanometer level. This study focused on the production of a cathode material ‘LiNi0.8Co0.2O2’ improved with a metal oxide ‘SnO2 surface modification’ for obtain improved cycling and better electrochemical performance lithium ion battery. ‘LiNi0.8Co0.2O2’ sub-micron sized powders are produced by using sol-gel production method, with using 3 different chealating agents ( citric acid, oxalic acid, adipic acid), various different calcination temperature (600, 700, 800, 900°C) and durations (5, 10, 15 hours). Following to that, by mechanical mixing and by using sol-gel technique, tin oxide modifcations with different molarities obtained on chosen powders. XRD and SEM analyses performed for obtained bare and modificated powders. These Powders with different characteristics laminated on alumunium foils with an automatic laminaton system and punched as a cathode material to use in coin cells. BET analysis, XRD and SEM studies showed that chealating agent and process parameters effect the powder crystallinity and morphology, and related to these specifications, electrochemical performance is directly effected. Electrochemical results also showed that, SnO2 modificated cathode materials (sol-gel modification) showed better cycle life and capacity retention (above 140mAh/gr) until 50 th cycle due to reducing the electrolyte–cathode interactions.

Experimental and theoretical study of Ti20Zr20Hf20Nb20X20 (X = V or Cr) refractory high-entropy alloys

We investigated the microstructure and mechanical properties of Ti20Zr20Hf20Nb20X20 (X=V or Cr) high-entropy alloys (HEA), produced by induction melting and casting in inert atmosphere. The structures of these alloys were studied via X-ray diffractometry and scanning electron microscopy. Results show that Ti20Zr20Hf20Nb20V20 has mainly the body centered cubic (BCC) structure, whereas the BCC matrix of Ti20Zr20Hf20Nb20Cr20 contains small amount of Cr2Nb and Cr2Hf intermetallic compounds. Ti20Zr20Hf20Nb20V20 alloy shows the high strength and the homogeneous deformation under compression at room temperature. The strength and hardness of Ti20Zr20Hf20Nb20Cr20 alloy are further enhanced by the Cr-containing Laves phases segregated during casting. The structural and mechanical properties remained almost unchanged after a short time (10min) heat treatment at 573, 773, 973 and 1173K indicating the resistance to working temperature peaks for these two alloys. Ab initio calculations predict ductile behavior for these and similar refractory HEAs. The theoretically calculated Young's modulus E is in good agreement with the experimental ones.

Stability of Capsaicinoid Content at Raised Temperatures

Capsaicinoids, found in the fruits of Capsicum species, contribute to the spiciness of foods. However, the fruits are often subjected to heat, particularly during food preparation and in other high temperature operations, and possible changes in the capsaicinoid content have not been systematically reported. Therefore, this investigation focused on the effects of initial concentration, temperature, time and pH on the final capsaicinoid content in a model system. With higher initial concentrations (200-1000 ppm) of capsaicinoids to start with, the reduction rates were slower as the heating time increased. Under a constant initial capsaicinoid concentration (200 ppm), neutral pH had a lower rate of change in capsaicinoid content than that of both alkaline and acidic conditions. Also, alkaline conditions were more stable than acidic. The rate of reduction was generally much faster at higher temperatures, no matter what the initial concentration. Apparently, to retain a high content of capsaicinoids at the end of heating at high temperature, a high initial concentration is necessary, as well as maintaining at neutral pH and having a short heating time.

Softening of High-Strength Steel for Laser Assisted Clinching

The conventional clinching of steels is currently limited to tensile strength less than 800 N/mm2 and to elongation at fracture more than 14 %. To realise the clinching of high-strength steels, the sheet can be heated locally at the joint, to improve ductility. Thereby the material characteristics outside the joint should be maintained. This could be achieved by means of short-time laser heating. The short-time tempering behaviour of press hardened steel 22MnB5 has been analysed. The mechanical properties during a short-time heat treatment were investigated by thermo-mechanical analysis in a deformation dilatometer. Thereby laser-assisted clinching shall be established and an efficient form-closed and force-closed connection shall be produced. As a result, the press hardened steel 22MnB5 could be clinched by laser assistance for the very first time.

Review on the explosive consolidation methods to fabricate tungsten based PFMs

Tungsten is one of the best candidates for plasma-facing materials in the fusion reactors, owing to its many unique properties. In the development of tungsten-based Plasma Facing Materials/Components (PFMs/PFCs), materials scientists have explored many different, innovative preparation and processing routes to meet the requirement of International Thermonuclear Experimental Reactor (ITER). Some explosive consolidation technology intrinsic characteristics, which make it suitable for powder metallurgy (powders consolidation) and PFMs production, are the high pressure processing, highly short heating time and can be considered as a highly competitive green technology. In this work, an overview of explosive consolidation techniques applied to fabricate tungsten-based PFMs is presented. Emphasis is given to describe the main characteristics and potentialities of the explosive sintering, explosive consolidation techniques. The aspects presented and discussed in this paper indicate the explosive consolidation processes as a promising and competitive technology for tungsten-based PFMs processing.

Influence of the Process Temperature on the Properties of Friction Stir Welded Blanks Made of Mild Steel and Aluminum

Hybrid components made of steel and aluminum sheet metal are a promising approach for weight reduction for automotive applications. However, lightweight components made of steel and aluminum require suitable joining technologies, particularly if forming operations follow after the welding process. Friction Stir Welding (FSW) is a promising solid-state welding technology for producing dissimilar joints of steel and aluminum. Within this work dissimilar butt joints were produced using sheet metals of mild steel DC04 and the aluminum alloy AA6016 with a thickness of about 1 mm. The FSW joints show approximately 85 % of the tensile strength of the aluminum base material. In metallographic investigations of the produced FSW blanks it was found that the microstructure in the area of the weld seam changes in the aluminum alloy due to the process temperature and plastic deformation. Due to temperature dependent changes of precipitations of the aluminum alloy, temperature measurements have been carried out during the welding process. To find an explanation of the reduction in tensile strength of the FSW joints, short time heat treatment experiments in the temperature range between 250 °C and 450 °C were performed using the aluminum base material. Heat treatments in the temperature range of the measured process temperature result in a reduction of the tensile strength of about 20 % regardless the annealing time.

Formation of Al‐enriched surface layers through reaction at the Mg‐substrate/Al‐powder interface

Al‐enriched surface layers containing a Mg17Al12 intermetallic phase and a solid solution of Al in Mg were fabricated by heating Mg specimens in contact with Al powder in a vacuum furnace. The layer formation process proceeded through partial melting at the Mg‐substrate/Al‐powder interface. The test results suggest that a good contact between the Al powder and the Mg substrate is required during heat treatment. In this study, a pressure of 1 MPa was applied to improve the contact of the Al powder with the Mg specimen. When the powder was pressed down during heating, it was possible to reduce the process temperature from 450 °C to 440 °C. The layers produced at 440 °C in a short heating time (40 min) were thick, continuous and uniform. The microhardness of the Al‐enriched layers was much higher than that of the Mg substrate. The results of the electrochemical corrosion tests indicated that the Mg specimens with an Al‐enriched surface layer had better corrosion resistance than the bare Mg. Copyright © 2014 John Wiley & Sons, Ltd.

Effect of Bi-doping and Mg-excess on the thermoelectric properties of Mg2Si materials

In this work, Bi-doped magnesium silicide compounds were prepared by applying a combination of both, short-time ball milling and heating treatment. The effect of Mg excess was also studied, aiming towards further improvement in thermoelectric properties. The structural modifications of all materials were followed by Powder X-ray diffraction and Scanning Electron Microscopy. Highly dense pellets of Mg2Si1−xBix (0≤x≤0.035) and Mg2+δSi0.975Bi0.025 (δ=0.04, 0.06 and 0.12) were fabricated via hot pressing and studied in terms of Seebeck coefficient, electrical and thermal conductivities and free carrier concentration. Their thermoelectric performance, at high temperature range, is presented and the maximum value of the dimensionless-figure-of-merit (ZT) is found to be 0.68 at 810K, for Mg2Si0.97Bi0.03.

C60 three-dimensional polymerization by impulse heating effect

Impulse laser heating combined with a quick sample cooling in a diamond anvil cell provides unique conditions for the 3D polymerization reaction of C60. The reaction proceeds under the 8–10 GPa pressure and 2700 K temperature in the case of heating-cooling cycle time around 0.1 μs. Such a short heating time permits to increase the maximal temperature of the fullerite sample by 1700 K on conditions that C60 are still surviving. As a result, the pressure of the phase transition to 3D polymerized fullerite phase with 519 GPa bulk modulus was essentially decreased. Furthermore, the transition has proceeded at quasi-hydrostatic conditions without activation by applying a plastic deformation.

Cold column trapping-cloud point extraction coupled to high performance liquid chromatography for preconcentration and determination of curcumin in human urine

A cold column trapping-cloud point extraction (CCT-CPE) method coupled to high performance liquid chromatography (HPLC) was developed for preconcentration and determination of curcumin in human urine. A nonionic surfactant, Triton X-100, was used as the extraction medium. In the proposed method, a low surfactant concentration of 0.4% v/v and a short heating time of only 2min at 70°C were sufficient for quantitative extraction of the analyte. For the separation of the extraction phase, the resulted cloudy solution was passed through a packed trapping column that was cooled to 0 °C. The temperature of the CCT column was then increased to 25°C and the surfactant rich phase was desorbed with 400μL ethanol to be directly injected into HPLC for the analysis. The effects of different variables such as pH, surfactant concentration, cloud point temperature and time were investigated and optimum conditions were established by a central composite design (response surface) method. A limit of detection of 0.066mgL−1 curcumin and a linear range of 0.22–100mgL−1 with a determination coefficient of 0.9998 were obtained for the method. The average recovery and relative standard deviation for six replicated analysis were 101.0% and 2.77%, respectively. The CCT-CPE technique was faster than a conventional CPE method requiring a lower concentration of the surfactant and lower temperatures with no need for the centrifugation. The proposed method was successfully applied to the analysis of curcumin in human urine samples.

Comparison of bacterial inactivation with novel agitating retort and static retort after mild heat treatments

Lower thermal load on foods is desirable for food producers and consumers as the food gets higher quality. With reduced thermal load, the investigation of food safety is of importance. In this study, microbial inactivation efficacy of a new retort process with high frequency longitudinal agitation was compared to static retort process which was used as a benchmark. As a model, fish soup samples, inoculated with approximately 108 cells/ml Listeria innocua, was exposed to mild heat treatments at 62, 65 and 68 °C. Results clearly demonstrated that agitating mode can provide equivalent lethality to the model organism L. innocua within significantly shorter heating times compared to static mode. Bacteria were not detected on TSA-YE plates after 11.5, 6.8 and 5.5 min processing in agitating mode; 77, 67 and 52 min processing in static mode at 62, 65 and 68 °C respectively. Bacterial inactivation in agitating mode was generally correlated with estimated inactivation based on product core temperature, D- and z-values for L. innocua. This may indicate that distribution of the heat load over the soup was enhanced through agitation. Results showed that utilization of high frequency longitudinal agitation mechanism in retorts is promising for reducing the thermal load on food products without compromising on food safety related to non-spore forming pathogens.

A comparative study of Sr1−xKxFe2As2 and SmFeAsO1−xFx superconducting tapes by magneto-optical imaging

Using the magneto-optical imaging (MOI) technique, the intergranular critical current density Jc at various temperatures and the homogeneity of the local structure of the superconducting cores for the powder-in-tube (PIT) Sr1−xKxFe2As2 and SmFeAsO1−xFx tapes are systemically investigated. These two tapes have large transport Jc over 104 A cm−2 in self-field at 20 K and 4.2 K, respectively, but the Jc of the SmFeAsO1−xFx tape decreases rapidly with increasing magnetic field. The MOI characterization indicates large bulk currents circulating through the whole sample for both Sr1−xKxFe2As2 and SmFeAsO1−xFx tapes, but also reveals the inhomogeneity inside the SmFeAsO1−xFx sample. The results obtained from the MO measurements can be confirmed by the magnetic hysteresis measurements M(H) and the SEM examination. The weak high-field performance of the SmFeAsO1−xFx tape may be ascribed to its short-time heat treatment.

Understanding Disk Carbon Loss Kinetics for Heat Assisted Magnetic Recording

An optical pump-probe set-up that allowed short dwell time ( ~ 500 μs) heating with a high-temperature ramp rate ( ~ 106 K/s) was used to detect the magnetization change in heat assisted magnetic recording (HAMR) media. The temperature of the media was monitored by observing the Kerr signal. The pump power at zero magnetization allowed the determination of the power needed to attain the Curie temperature of the media (the Curie temperature was determined with a high-temperature magnetometer before the pump-probe experiments). HAMR media was then irradiated with a pump power to obtain 480°C for increasing exposure times. Atomic force microscopy (AFM) of these media surfaces revealed depressions or holes in the media surface [within the carbon overcoat (COC) layer] that increased in extent with cumulative exposure time. Media surfaces exposed to somewhat lower temperatures (450°C) and for shorter times had a swollen region that surrounded a much smaller depression. High-spatial resolution Raman spectroscopy was used to analyze these irradiated areas. An increased D-band was observed within the swollen portion of the media surface, while the overall Raman signal intensity decreased within the small depressed area. Using time and temperature irradiations along with AFM analysis of the depressions the activation energy for COC loss was determined to be 0.6 eV. These observations were attributed to COC failure through graphitization and oxidation. The failure mechanism leading to these observed changes and the possible relationship of the present results to the HAMR media COC thermal stability are discussed.

Microwave-Assisted Synthesis and Gas-Sensing Performance of Hollow-Spherical WO<sub>3</sub> Nanocrystals

Hollow-spherical WO3 nanocrystals were obtained by calcining an organic-inorganic W-C precursor containing C and W in a microwave oven or in a conventional muffle furnace, and the W-C precursor hybrid precursor was synthesized via a hydrothermal method. The samples were characterized by XRD, TG-DTA, FTIR and SEM. The morphologies of the WO3 samples obtained by conventionally heating (C-WO3) and microwave-assisted heating (M-WO3) were compared. The average diameter and shell thickness of C-WO3 hollow spheres is about 450 and 200 nm, respectively. The average diameter and shell thickness of M-WO3 hollow spheres is about 500 and 50 nm, respectively. The M-WO3 has a loose and multilayered shell, and their nanoparticles are smaller than those of C-WO3. The improved structure of M-WO3 is due to shorter heating time and the unique heating style in a microwave oven. The gas-sensing performances of the WO3 sensors were investigated. The M-WO3 sensor has better response to ethanol vapors than the C-WO3.

A comparative study of ZnNb2O6 nanoceramics synthesized by high energy ball milling and subsequent conventional and microwave annealing

Ball-milling and subsequent conventional and microwave assisted heating processes have been applied to synthesize ZnNb2O6 nanoceramic. X-ray diffraction, simultaneous thermal analysis, scanning electron microscope (SEM), transmission electron microscope (TEM) and BET techniques were utilized to characterize the as-milled and annealed samples. Characterization of synthesized powders revealed that in spite of the very short heating time in the microwave process without soaking time, the powder heated at 550 A degrees C had all physical properties similar to powders synthesized in conventional heating at the 650 A degrees C temperature with a heating rate of 10 A degrees C/min and a soaking time of 1 h. In addition, SEM, TEM and BET observations of synthesized powders showed that the particle size of powders lies in the nano meter range.

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Raw runner type peanuts were dried to moisture levels of 4.24 and 6.62 g/100g. Each batch was oil roasted at 160°C in pure peanut oil for the amount of time determined to produce a surface color of 48 on the Hunter L scale. The surfaces of the cotyledons were examined by scanning electron microscopy. Escaping steam caused ruptures in the surfaces during the roasting process. The principal differences found were that the higher moisture samples had more complex tears to the outer surface as a result of higher amounts of steam escaping from the interior. The interior cell components were found to be more distorted and compacted at the lower moisture. Although it was found that in peanuts, shorter heating times were required to reach the desired color at the higher moisture, the large amount of escaping steam resulted in more surface cell destruction than at the lower moisture, where as the lower moisture samples appeared to have more interior cell damage. This may have an effect on the retention of oil by the peanuts during storage.

Synthesis and electrochemical characterization of duo doped spinels (zinc and praseodymium) for use in lithium rechargeable batteries

LiMn2O4 and LiZnxPryMn2−x−yO4 (x = 0.10–0.24; y = 0.01–0.10) powders have been synthesized by sol–gel method using palmitic acid as chelating agent. The synthesized samples have been subjected to thermo gravimetric and differential thermal analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX). The sol–gel route bestows low calcination temperature, shorter heating time, high purity, good control over stoichiometry, small particle size, high surface area, good surface morphology and better homogeneity, The XRD patterns reveal high degree of crystallinity and better phase purity. SEM and TEM images exhibit nano-sized nature particles with good agglomeration. EDAX peaks of Zn, Pr, Mn and O have been confirmed in actual compositions of LiMn2O4 and LiZnxPryMn2−x−yO4. Charge–discharge studies of pristine spinel LiMn2O4 heated at 850 °C delivers discharge capacity of 132 mA h g−1 corresponding to columbic efficiency of 73 % during the first cycle. At the end of 10th cycles, it delivers maximum discharge capacity of 112 mA h g−1 with columbic efficiency of 70 % and capacity fade of 0.15 mA h g−1 cycle−1 over the investigated 10 cycles. Inter alia, all dopants concentrations, LiZn0.10Pr0.10Mn1.80O4 exhibits the better cycling performance (1st cycle discharge capacity: 130 mA h g−1 comparing to undoped spinel 132 mA h g−1) corresponding to columbic efficiency of 73 % with capacity fade of 0.12 mA h g−1 cycle−1.

Luminescence properties of YAG:Nd 3+ nano-sized ceramic powders via co-microemulsion and microwave heating

Nano-sized ceramic powders with weaker aggregation of Nd 3 +-doped yttrium aluminum garnet (YAG:Nd 3 +) were synthesized via co-microemulsion and microwave heating. This method provides a limited small space in a micelle for the formation of nano-sized precursors. It also requires a very short heating time, thus reducing energy consumption in comparison with conventional solid-state sintering processes. As a result, small-sized particles with narrow size distribution, weaker aggregation and high purity were obtained. Powder X-ray diffraction results revealed that the structure of pure YAG:Nd 3 +nanoparticles was cubic garnet. Transmission electron microscopy results indicated that the synthesized particles were almost spherical with average diameters of 40 and 80 nm. The luminescent properties of YAG:Nd 3 +were investigated through PL. Under excitation at 488 nm, YAG:Nd 3 +nano-sized ceramic powders showed main emission bands of 1045–1080 nm because of 4 F 3/2 → 4 I 11/2 transitions that are identical to those observed for a single YAG:Nd 3 +crystal.

Preparation and characterization of nano-NaX zeolite by microwave assisted hydrothermal method

In the present work, nano-NaX zeolite crystals were synthesized via microwave and conventional hydrothermal methods. The effects of reaction time, temperature and heating method on the characteristics of zeolite nanoparticles such as particle size, crystallinity, morphology, size distribution and surface area were investigated. The prepared NaX zeolite nanoparticles were characterized by the XRD, SEM, DLS, BET and XRF analysis. The results showed that both heating methods produced the NaX zeolite crystals with nano-in size. The microwave heating produced smaller zeolite nanoparticles with relatively narrower particle size distribution, required much shorter heating times and did not significantly change composition or crystallinity, compared with the conventional heating method. It was also observed that the time and temperature of microwave heating had significant effects on the prepared zeolite particles and the pure zeolite X nanoparticles or a mixture of zeolite X and A can be synthesized using the microwave heating method by control of the crystallization time and temperature.