Initial Stage Of Heat Treatment Research Articles

Exogenous Threonine-Induced Conversion of Threonine-Xylose Amadori Compound to Heyns Compound for Efficiently Promoting the Formation of Pyrazines.

The involvement of exogenous threonine during the degradation of l-threonine-d-xylose Amadori rearrangement product (Thr-ARP) was found to promote the formation of pyrazines. A model including Thr-ARP and 15N-labeled l-threonine was applied to reveal the role of free threonine in Thr-ARP conversion to pyrazines. Quantitative analyses of pyrazines in the model of Thr-ARP/15N-labeled threonine showed a precedence of the endogenous threonine (formed by the degradation of Thr-ARP) over the exogenous threonine in pyrazines formation, and the ratio of 15N to 14N content in pyrazines increased significantly over time. According to the observed occurrence of the Heyns rearrangement products (HRP) derived from 15N-threonine, as well as the sharp decrease of 15N-threonine content and a rapid increase of 14N endogenous threonine at the initial stage of heat treatment, it was proposed that aldimine condensation between exogenous threonine and Thr-ARP followed by the hydrolysis led to the endogenous threonine and the generation of HRP. Then, the HRP underwent dehydration followed by hydrolysis to form exogenous threonine and deoxyxyosones, and the dehydration and hydrolysis of deoxyxyosones to form organic acids was inhibited, but the retro-aldolization of deoxyxyosones was promoted, facilitating the generation of reactive α-dicarbonyl compounds. In this way, exogenous threonine accelerated the release of endogenous threonine and α-dicarbonyl compounds and the pH decline was slowed down, which was favorable for the formation of pyrazines.

The formation mechanism of Cd–S–Se quantum dots with CdSe/CdS core–shell structure within silicate glass

AbstractThe formation mechanism of Cd–S–Se quantum dots (QDs) with a CdS/CdSe core–shell structure within a silicate glass system was investigated by monitoring the change in the first excitonic absorption peak of CdSe, CdS, and Cd–S–Se QDs as a function of the heat‐treatment (HT) duration. When a silicate glass containing QD formation components for CdSe or CdS single‐phased QDs was heat‐treated, CdSe QDs grew via Ostwald ripening, whereas CdS QDs hardly formed within the given silicate glass matrix. When the glass, including CdO, ZnSe, and ZnS, was utilized for the synthesis of Cd–S–Se QDs within the glass matrix, Cd–S–Se QDs were successfully formed and exhibited similar growth behavior to CdSe QDs during the initial stage of HT. The structural changes in the QD‐embedded glasses during HT were also monitored by Raman spectroscopy and discussed, and a possible formation mechanism of CdSe/CdS core–shell‐structured QDs within silicate glasses is suggested.

Thermoelectric properties of Zn-Sb compound semiconductor

The article discusses the results obtained in the study of the thermoelectric properties of the semiconducting Zn-Sb polycrystalline structure obtained by powder technology. Studies show that thermal processing stages and temperature changes significantly affect its thermoelectric properties. At the initial stages of heat treatment, with an increase in temperature, the Seebeck coefficient (α), thermal conductivity (λ) and thermoelectric index (ZT) first decrease, then increase, and decrease again with an increase in temperature. From the fourth stage of heat treatment, all parameters increase with temperature. The research results were explained on the basis of the formation of intergranular boundary areas and its physical properties. The first stage of thermal treatment is the initial stage of ZnSb particle fusion, and the supplied thermal energy Q is not enough for ZnSb particle fusion. In the next stage of heat treatment, the atoms of the crystal lattice, which consists of a broken bond or defect between the pressed particles, are forced together or condensed. As the temperature increases, the phases of the crystal lattice atoms change and their reactivity increases. This leads to the formation of a ZnSb semiconductor with a polycrystalline structure. As the temperature increases, the localized traps with Ein energy level are ionized and electron-hole pairs are formed in the two adjoining boundary areas. Charges created in area A move to area V, which has a relatively low temperature, along the Ein energy levels. As a result, the total λ increases at the same time as the thermal conductivity of these two adjacent areas.

Obtaining granular semiconductor intermetallic compound Zn-Sb and some of its electrical properties

The article discusses the microstructure of the ZnSb intermetallic compound obtained by powder technology and the results of the study of charge transfer processes in it. Also, the article proposes a method of preparing a Zn-Sb intermetallic compound with a stem-shaped polycrystalline structure using powder technology. Semiconductor Zn-Sb polycrystalline structure preparation method is carried out by pressing Zn-Sb particles together, followed by thermal treatment in several stages. It was found that the stages and temperature of heat treatment have a significant effect on its electrophysical properties. Electrical conductivity (σ), charge carrier concentration (n) suddenly decreases with temperature increase at the initial stage of heat treatment. Such a process is not observed in the subsequent stages of heat treatment. At all stages of heat treatment, the mobility of charge carriers (μ) decreases. In this case, the residence time of charge carriers in the crystal lattice is π~1,52÷1,1·10-12 sec. was determined to change between The results of the study were explained on the basis of the influence of intergranular boundary areas on charge transfer processes. Studies show that at T=300÷700 K, the potential barrier height (φ) in the intergranular boundary areas increases linearly with temperature. For example, φ~0,436 eV at the initial stages of thermal treatment at T=300 K, and φ~0,469 eV at later stages, and at T=700 K, it increases to φ~0,92 eV in all cases. It was shown that it depends on the amount of charges trapped in the localized traps in the intergranular boundary regions.

Study on Low-Damage Cutting of Alfalfa Stalks by Self-Sharpening Blades of Gradient Material with Carbon-Nitron-Boronized Heat-Treatment

The work aims to realize low-damage cutting of Alfalfa stalk. The self-sharpening blades of gradient material were prepared by 40 Cr steel, then heat-treating the flank surface by carbon-nitron-boronized with a rare elements catalysis technique. The biological characteristics of Alfalfa incision self-healing and regeneration process were analyzed in order to compare the cutting effects of different blades. After treatment with carbon-nitron-boronized with rare elements catalysis, the flank surface and tip point of blades were coated by boride layer and carbonitriding layer. The composition, microstructure and properties of the carbon-nitron-boronized layer demonstrated a gradient distribution state, and had good wear resistance. A kinetic model for the formation of the carbon-nitron-boronized layer was proposed. The initial stage of heat-treatment was mainly a carbonitriding process. When continuous and compact boride was formed on the surface, it was mainly boridized. The results of field experiment indicated that compared with the commercial blades, the self-sharpening blades have excellent properties as wear resistance and long service life. In addition, the cut damage caused by the self-sharpening blades was less, the self-healing and regeneration process of Alfalfa stalk was normal, and the regeneration duration was greatly shortened. The blades with carbon-nitron-boronized heat-treatment could form the self-sharpening characteristics, always maintaining the cutting sharpness, and realized the low-damage cutting of Alfalfa stalk.

Synergistic effects of Cd, Si and Cr additions on precipitation strengthening and thermal stability of dispersoids in AA3003 alloy

The thermally stable Mn-rich dispersoids in Al alloys were recently reported to have a significant dispersion strengthening effect. Further improvements in the dispersion strengthening and thermal stability of Mn-rich dispersoids are required to achieve satisfactory mechanical properties for elevated temperature applications. This study reports that, with minor additions of Cd, Cr and increased Si content, the yield strength of the modified AA3003 alloy is increased by 39% compared to the base alloy subjected to the same heat treatment. Moreover, the thermal stability of the modified alloy when exposed to a long-term thermal holding up to 1000 h at 400 °C is greatly improved. Microstructural characterizations reveal that the dispersoids in the modified alloy are greatly refined, and their distribution is more homogeneous compared to the base alloy. It is observed that the Cd-rich clusters/nanoparticles formed in the initial stage of heat treatment, can effectively “attract” dispersoid-forming atoms (e.g. Mn, Si and Cr) and subsequently lead to a heterogeneous nucleation of dispersoids on them, which is responsible for the enhanced dispersoid precipitation and dispersion strengthening in the modified alloy. The partitioning of the low-diffusivity peritectic element Cr into dispersoids can improve the thermal stability and increase the number density of dispersoids in the centre of dendrite arms, which also contributes to the promising mechanical properties of the modified alloy.

The oxidation behaviour of layered Al-Ni coating at high-temperature heating

The aim of the work is to study of the structure and phase composition of an oxide film formed on the surface of the layered coating of the Al-Ni system during high-temperature heating. It was experimentally established that at the initial stages of heat treatment, as a result of the interaction of the Al-Ni system layered coating with air oxygen, individual sections of Al2O3 oxide are formed on its surface, which are agglomerates of nanometre-thick plate crystals, which increase and grow into a continuous oxide film with increasing exposure time. Along with stable α-modification, transitional metastable δ- and θ-modifications are present in the film. An increase in the heating temperature leads to an intensification of the oxidation processes and the formation of a complex oxide film of Al2O3 and spinel NiAl2O4, 1–3 μm thick.

STUDY OF THE STRUCTURE AND PHASE COMPOSITION OF THE OXIDE FILM ON THE SURFACE OF A LAYERED COATING OF THE Al-Ni SYSTEM

This work is aimed to the study of the structure and phase composition of the oxide film formed on the surface of the layered coating of the Al-Ni system during high-temperature heating. It was experimentally established that at the initial stages of heat treatment, as a result of the interaction of the Al-Ni system layered coating with atmospheric oxygen, separate sections of Al2O3 oxide are formed on its surface, which are agglomerates of plate crystals of α-modification of nanometer thickness, which increase and grow together with increasing exposure time continuous protective oxide film. An increase in the heating temperature leads to an intensification of oxidation processes and the formation of a complex oxide film of AlO and spinel NiAlO.

Reducing Dust Emission During the Sintering of Iron Ores by Using the Energy of an Acoustic Field

One of the main sources of dust-bearing emissions in the metallurgical industry is the sintering machine. An acoustic field was formed during the initial stage of heat treatment of a sintering-machine charge by using an acoustic radiator in the form of a Hartmann whistle installed in the vacuum chambers of the machine. The acoustic field covers 15–20% of the sintering area and has an acoustic power of 1.0–1.2 kW/m2. Use of the field has increased the productivity of the sintering machine 3.2–8.3%, reduced the amount of carbon monoxide formed by 26.7–33.4%, and reduced the entrainment of dust by the gas by 29.2–36.2%. When an acoustic field with a power of 0.3–0.4 W/m3 is created inside the flue-gas collection main, dust emissions can be cut by at least 20–25% of the original value.

Effects of extended heat treatment on carbide evolution in Cr-Mo steels

Cr and Mo are known to be effective steel alloying elements for high-temperature applications, and they affect steel mechanical properties via carbide formation. Mechanical properties of Cr-Mo steels affected by the carbide evolution were investigated by performing heat treatments, and the treatment duration was determined by the Larson-Miller parameter fitting. The hardness value decreased after heat treatment at 690°C for 10h with the decomposition of the bainitic microstructure. The quantified chemical composition results for the carbides were plotted on the Fe-Cr-Mo ternary and Fe-Cr binary composition diagrams to classify the types of carbides formed. Most of the carbides were identified as Fe-rich M3C-type carbides at the initial stage of heat treatment. The Fe fraction in the carbides decreased with time while the Cr and Mo fractions increased. The Cr- and Mo-rich carbides were identified as M23C6- and M2C-type, respectively. An increase in the Cr and Mo fractions in the carbides resulted in the decrease in the alloying element concentration in the matrix, which in turn resulted in the deterioration of the solid solution strengthening. Further, it was determined that coarse carbides, observed on the grain boundaries after extended heat treatment, deteriorated the mechanical properties of the alloy.

MATHEMATICAL MODELING OF THE THERMO-STRESSED CONDITION IN THE COLD WORK ROLLS DURING FAST HEATING IN THE CHAMBER FURNACE

A physical-and-mathematical pattern of calculation of the thermo-stressed condition of the cold work roll, being heated in the chamber fast (gradient) heating furnace for hardening of the working layer of the certain depth, has been demonstrated. The heating furnace consists of two sliding halves and is connected with the spraying unit. A roll subjected to heating runs on rollers and rotates during heating and hardening. Two heating conditions: forced one and more rational one, under which a speed of the roll heating is limited at the initial stage, have been compared. The authors have offered a steptype schedule of increasing the heating medium temperature during roll heating at which the maximum tensile stress does not exceed an acceptable value of 300 MPa. It is recommended to limit a heating speed at the initial stage of heat treatment to reduce the thermal stress.

Microstructure evolution during isothermal forging and subsequent heat treatment of Ti-17 alloy with a lamellar colony structure

The effect of isothermal forging and subsequent heat treatment on microstructure evolution was investigated for Ti-17 alloy with a lamellar colony structure. For this purpose, Ti-17 alloy was isothermally forged at 820°C or 860°C and subsequently heat treated for times ranging from 10min to 8h. The principal features of microstructure evolution were found to be strain and temperature dependent. Microstructure evolution during deformation included the rotation of alpha lamellae toward the metal flow direction. The orientation distribution of alpha lamellae changed from the two symmetrical peaks to the single one with the increasing strain. The angle (θ) in the single peak position was about 90°. Additionally, length of the lamellar alpha decreased with strain and deformation temperature. Thickness of the lamellar alpha increased with deformation temperature but was independent on strain. During heat treatment, microstructure observations suggested that the process of evolution can be divided into two stages. The first included segmentation of the lamellae in the initial stage of heat treatment, whereas microstructure coarsening characterized the second one during prolonged heat treatment. Furthermore, the segmentation and coarsening processes could be accelerated by the increasing prestrain and temperature.

Static globularization kinetics for Ti-17 alloy with initial lamellar microstructure

The kinetics of static globularization of the hot worked Ti-17 alloy with initial lamellar microstructure was investigated. For this purpose, Ti-17 alloy was isothermally forged to different height reductions at 820°C or 860°C and subsequently heat treated for times ranging from 10min to 8h at 820°C or 860°C. Microstructure evolution during static heat treatment was quantitatively analyzed. Microstructure observations indicate that both boundary splitting and microstructure coarsening promote static globularization process. Boundary splitting plays an important role in the initial stage of static heat treatment. Microstructure coarsening occurs throughout heat treatment process, but it is more significant during prolonged static heat treatment. The static globularization kinetics is sensitive to the amount of strain prior to heat treatment, heat treatment temperature and time. Globularization process is accelerated with the amount of strain and heat treatment temperature increase. Globularization fraction increases fast at first and then slow down with the increase of heat treatment time. The amount of strain prior to heat treatment mainly influences the initial stage of heat treatment and plays a supporting role in the latter stage. Heat treatment temperature has an important role during the whole heat treatment process. Static globularization kinetics is found to be less dependent on deformation temperature. Higher deformation temperature is conducive to static globularization when strain prior to heat treatment is lower and heat treatment time is shorter. However, difference caused by deformation temperature disappears with the increase of strain and heat treatment time. To model the static globularization behavior, the theoretical models of boundary splitting and termination migration were proposed. A comparison of experimental observations and model predictions indicate that the theoretical models can provide a reasonable prediction of time for finishing static globularization.

Phase evolution of Ag sheathed Bi-2223 tapes during heat treatment before the formation of Bi-2223 phases

The phase evolution of Ag sheathed Bi-2223 tapes during heat treatment at a temperature below the formation temperature of Bi-2223 phase has been investigated. During the mechanical deformation stage of powder in tube process, the Bi-2212 grains were crushed into small fragments. XRD results show that with increasing temperature, the amorphous/nano-crystalline background decreases, and the peaks from the Bi-2212 phase become stronger. XRD rocking curve reveals that the FWHM value decreases, and towards a nearly constant preferential orientation value with increasing temperature. This indicates that the texture becomes better as the temperature increasing. During the stage of heat treatment under constant temperature, the FWHM value increases within the initial stage of heat treatment under constant temperature and the FWHM value decreases with prolonged time. It is suggested that these results are related to the recrystallization and grain growth of Bi-2212 phase.

Preparation and Characterization of Methylsilsesquioxane Thin Film Containing Tris(ethylenediamine)cobalt(III) Chloride as a Photobase Generator

Porous methylsilsesquioxane thin films were prepared using the sol−gel process, with tris(ethylenediamine)cobalt(III) chloride (Co(en)3Cl3) as a photobase generator and polypropylene glycol (PPG) as a template. The generation of amines was confirmed for more than 2 min of ultraviolet (UV) irradiation. The prepared film with the UV irradiation and subsequent heat treatment showed a low refractive index of n = 1.35. Subsequent field-emission scanning electron microscopy (FE-SEM) observations confirmed that shrinkage of the film with the heat treatment was suppressed in the film with UV irradiation. The photogenerated amines from Co(en)3Cl3 worked as a catalyst for the condensation reaction in the gel films during the initial stage of heat treatment. A porous structure was obtained using the thermal decomposition of PPG without collapse of the gel network.

KINETICS AND THERMAL ACTIVATION/INACTIVATION OF STARKING APPLE POLYPHENOL OXIDASE

ABSTRACT The objective of this study was to evaluate the activity, kinetic behavior and thermal inactivation kinetics of apple polyphenol oxidase (PPO). PPO was extracted from an apple (cv. Starking Delicious), and enzyme activity was measured with 4-methyl catechol and pyrogallol. Optimum pH of the enzyme was found as 5.5 with 4-methyl catechol and 7.2 with pyrogallol. The kinetics of PPO catalyzed oxidation obeyed Michaelis–Menten model with both substrates. Apple PPO had a higher affinity to 4-methyl catechol than pyrogallol having Km values of 2.24 mM and 8.04 mM, respectively. Thermal inactivation of apple PPO was studied at temperatures from 45C to 75C with different exposure times. When remaining enzyme activity was measured with pyrogallol, PPO activity initially increased and then decreased which shows activation of apple PPO at initial stages of heat treatment at 45, 55 and 65C. In apple extract there were both soluble and latent PPO with different substrate affinities and thermal stabilities. Activation energies of soluble and latent PPO were found as 12.85 kcal/mol and 7.89 kcal/mol, respectively (T < 75C). Soluble PPO was more heat stable than latent PPO. Heat treatment at 75C for 10 min resulted in 46% inactivation of soluble PPO where latent PPO was 62% inactivated at the same condition. PRACTICAL APPLICATIONS Color is an important quality attribute of food. PPO catalyzes the oxidation of phenols to colored quinones. These quinones are further polymerized to form brown pigments which are generally considered to be detrimental to food quality from both organoleptic and nutritional points of view. The most effective method to inactivate PPO is heat treatment. Thermal stability of apple PPO has been investigated by many researchers and it was found that each variety has different characteristics and thermal stabilities. This research demonstrates that the characterization of the Starking PPO is necessary to control enzymatic browning of this apple. This study shows that Starking apple has both soluble and latent PPO with different thermal stabilities and the enzyme can be activated with mild heating. To control enzymatic browning of this apple variety, heat treatment must be applied with temperature greater than 75C.

Grain growth and mechanical properties of electrodeposited nanocrystalline nickel–4.4mass% phosphorus alloy

The relationship between microstructural evolution and mechanical properties in Ni–4.4mass% P alloy was systematically examined. As-electrodeposited Ni–4.4mass% P alloy consists of grains having an average grain size of 37 nm and texture strongly oriented to (1 1 1). Phosphorus is entirely in solid solution. Heat treatment induces precipitation of Ni 3P phase. Rapid grain growth occurs only at the initial stage of heat treatment, and saturated at all the annealing temperatures, even at temperatures higher than 873 K (0.51 T m). Grain growth exponents n in Ni and Ni 3P phases were found to be 4.5–5.9 and 4.9–5.4, respectively. These values are close to those for grain boundary diffusion-controlled growth. Activation energies for grain growth in Ni and Ni 3P phases were estimated as 210 and 180 kJ mol −1, respectively. The nanocrystalline and ultrafine-grained specimens (about 40–400 nm) fractured prior to yielding, while the larger grained specimens (>400 nm) showed plastic deformation. Fracture strength and fracture strain depend not only on grain size but also on connectivity of Ni 3P grains, where cracks were preferentially nucleated.

Early stages of oxygen clustering in hydrogenated Cz-Si: IR absorption studies

The formation kinetics of small oxygen clusters in hydrogenated Si has been studied by means of infrared absorption measurements. Hydrogen was introduced into the crystals by in-diffusion from H 2 gas at 1200–1300°C. The samples were heated at temperatures in the range of 280–370°C for different durations. At initial stages of heat-treatment, enormous generation rates of the oxygen dimer have been observed in hydrogenated samples. This indicates highly enhanced diffusion of the interstitial oxygen atoms. The maximum achievable concentration of the dimers is found to be limited by their dissociation rate even at temperatures of about 300°C, while in as-grown crystals the capture processes are known to be dominant in this temperature region. An explanation of this phenomenon is presented.

Deactivation of steam reforming catalysts by sintering: experiments and simulation

Sintering of coprecipitated Ni/Al 2O 3 catalysts was studied in a microreactor at 500 and 800°C under steam reforming reaction. Changes in microstructure (crystalline phases, average metal crystallite sizes and size distributions) were investigated by temperature programmed reduction (TPR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Differences between particle size distributions determined by XRD and TEM are discussed in view of their specific limitations. Low temperature calcination of unpromoted catalysts may have a beneficial stabilizing effect upon reduction. The rate of sintering of small nickel crystallites increases as a result of the combined action of steam and high temperature, particularly for narrow initial crystallite size distributions and high initial dispersions. This behavior suggests a shift, from crystallite migration in the initial stages of heat treatment, to atomic migration in the latter stages. The lanthanum promoter seems to inhibit metal crystallite growth under reduction and reaction conditions. Predictions of a developed Monte Carlo based model are in good qualitative agreement with experimental observations.

Infrared spectroscopic study of SiOx film formation and decomposition of vinyl silane derivative by heat treatment. I. On KBr and gold surface

The free-radical copolymerization of vinyltrimethoxysilane (VTS) with vinylimidazole (VI) was carried out in benzene at 68°C. Thermooxidative degradation and the SiOx film-formation mechanism of poly(VI-co-VTS) both on gold and KBr were studied with Fourier transform infrared (FTIR) spectroscopy. Reflection-absorption (R-A) spectra on gold were compared with transmission spectra on KBr. In the initial stage of heat treatment, the Si—O—Si bond formation was caused mainly by the residual water in the copolymer film. As heating time increased, however, both the water resulting from the thermal decomposition of the copolymer and the water vapor in air began to participate in the hydrolysis of the Si—O—CH3 group followed by the condensation reaction. The structure of the SiOx film became closer to the structure of SiO2 with increasing heating temperature. In addition, the differences between the transmission spectra and R-A spectra were observed at the peaks related to Si—O—Si stretching due to the optical effect. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:775–784, 1998