Temperature Time Intervals Research Articles

Зависимость теплофизических характеристик белковых продуктов от их компонентного состава

Food additives and substitutes make it possible to model the sensory profile of foods and regulate their nutritional value. As a result, the range of food products grows while their cost goes down. Dairy protein and fat are inherent components of cheese production, which makes them vulnerable to counterfeiting. New food additives must be provided with various objective control methods to determine their actual composition. A thermophysical analysis of protein-fat dairy products, e.g., cheese, determines whether the actual component composition corresponds with the label. The method of two temperature-time intervals is a complex and express analysis that defines the thermophysical properties of cheese. It takes 30 min and processes the data automatically with an error of ≤ 1 %.

REGULATIONS OF THE FORMATION OF BAINETIC COMPONENT MATRIX IN ECONOMY ALLOYED CHROMO-MANGANESE ALLOYS

Purpose. The purpose of the investigation is to establish the regularities of the kinetics of supercooled austenite decomposition in the bainite temperature range (400−200 °C) in chromium-manganese cast iron for the development of thermal hardening regimes that increase the service life of products. Methodology. The object of the study are samples of research and industrial smelting of chrome-manganese cast iron containing 3,1 % carbon, 13,1 % chromium, and 15,75 % manganese. The study of the supercooled austenite decomposition kinetics was carried out by the dilatometric method in the temperature range of 400−200 °C, the study of the microstructure, phase composition, as well as the measurement of microhardness and hardness was carried out according to standard methods. Scientific novelty. The peculiarities of the supercooled austenite decomposition kinetics in the bainite temperature range (400−200 °С) in chromium-manganese cast iron were determined, the structure of the cast iron after aging consists of eutectic carbides Me (Cr, Mn, Fe)7C3, products of austenite decomposition, secondary carbides Me (Cr, Mn, Fe)7C3, Me (Cr, Mn, Fe)3C, as well as untransformed austenite in the amount of 70...75 %. The maximum hardness of the experimental cast iron was established during isothermal exposure at 350 °C for 35 hours. Practical value. The established regularities of the chromium-manganese cast iron structure formation and the determined and optimized temperature-time intervals of the supercooled austenite isothermal decomposition in cast iron are the basis for the development of heat treatment regimes to increase the strength, wear resistance of the material and the service life of its products.

Approaches to stabilization of heat-resistant polymers by the example of polyphenylene sulfi de and polymer composite materials based on it

The article analyzes the general patterns of thermooxidative destruction of heat-resistant polymers in the temperature-time interval of processing and operation of polymer composite materials based on them and suggests optimal approaches to their stabilization.

Dolomite recrystallization revealed by Δ47/U-Pb thermochronometry in the Upper Jurassic Arab Formation, United Arab Emirates

Abstract The process of recrystallization affecting dolomitic successions remains a longstanding enigma in carbonate research. Recrystallization influences the accuracy of genetic dolomitization models as well as the prediction of porosity and permeability distribution within dolomitic reservoirs. We investigate early-formed dolomites of the Upper Jurassic Arab Formation reservoir (Arabian Platform, United Arab Emirates), where recrystallization is not easily ascertained based on petrographic and O-C-Sr isotope analyses. Conversely, the application of Δ47/U-Pb thermochronometry revealed the occurrence of burial recrystallization over a temperature-time interval of ~45 °C/45 m.y. during the Early and Late Cretaceous. The process was initially driven by Late Jurassic mixed marine-meteoric fluids, which evolved during burial in a closed hydrologic system and remained in thermal equilibrium with the host rocks. Recrystallization was a stepwise process affecting the succession heterogeneously, so that samples only few meters apart presently record different temperature-time stages of the process that stopped when hydrocarbons migrated into the reservoir. Our results illustrate how Δ47/U-Pb thermochronometry may provide a novel approach to unravel dolomite recrystallization and to precisely determine the timing and physicochemical conditions (temperature and δ18Ow) that characterized the process. Therefore, this study paves the way for better appraisal of recrystallization in dolomitic reservoirs.

In situ phase formation during high-temperature synthesis in clad mechanocomposites based on the Ti-Al system.

An in situ synchrotron experimental study of phase formation dynamics in clad mechanocomposites of Ti-Al systems during high-temperature synthesis was performed. Cladding of the obtained mechanocomposites was carried out with an SiO2 target, with a deposition time of 40 min. The high-temperature synthesis was performed using the thermal explosion method based on a microwave induction heater in the in situ mode on an experimental setup adapted to synchrotron radiation time-resolved diffractometry. The influence of the cladding on the macrokinetic parameters of synthesis in situ was investigated experimentally. It was found that for an ignition temperature Tig = 650 ± 10°C, the maximum synthesis temperatures were in the range Tmax = 1380-1465°C. The characteristic heating speed was 525 K min-1. The sequence and temperature-time interval of phase formation are determined. The formation of the TiAl, TiAl3 and Ti3Al compounds begins at T = 661°C. At Tmax = 1465.6°C, the synthesis product is multiphase, the structures of the formed TiAl3 (content about 70%) and TiAl (content about 25%) have a nonequilibrium state. At the stage of system annealing with T = 1384.9°C, the reaction of the components occurs with the formation of almost monophase TiAl (content of more than 90%); Ti occupies the rest.

A Near-Surface Layer Heat Treatment of Die Casting Dies by Means of Electron-Beam Technology

Increasing the service life of die casting dies is an important goal of the foundry industry. Approaches are either material- or process-related. Despite new material concepts, hot work steels such as H11 are still predominantly used in the uncoated condition for die casting dies. In order to withstand the stresses that occur, this steel is used exclusively in the quenched and tempered condition. Required properties such as high high-temperature strength and high hardness combined with high toughness are, in principle, contradictory and can only be adjusted consistently over the entire die by furnace-based heat treatment. However, the results of various investigations have shown that improvements in the thermal shock resistance and wear resistance of hot work tool steels can be achieved by thermally influencing the microstructure near the surface. Based on these studies and related findings, an approach to surface heat treatment using the electron beam was developed. Due to the particle character of the radiation and the associated possibility of high-frequency beam deflection, the electron beam offers significantly greater flexibility in energy input into the workpiece surface compared with lasers or induction. The overall technological concept envisages replacing furnace-based heat treatment in the production of casting dies by localized and demand-oriented boundary layer heat treatment with the electron beam. The experiments include, on the one hand, the experimental determination of a suitable temperature–time interval with a focus on short-term austenitization. On the other hand, a simulation-based approach of boundary layer heat treatment with validation of a suitable heat source is investigated. Regarding short-term austenitization, the corresponding temperature and time range could be narrowed down more precisely. Some of these parameter combinations seem to be very suitable for practical use. The test specimens show a hard surface layer with a depth of at least up to 6 mm and a very tough buffer layer. Numerical simulation is used to estimate the resulting metallurgical microstructure and the achievable hardness as a function of the temperature–time interval. In addition, the results provided show the possibility of determining and optimizing the material properties by means of a simulation-based approach within the framework of a purely digital process planning and subsequently transferring them into a process planning. In the technical implementation, a temperature control was first established by means of a two-color pyrometer. In the further course of research, the pyrometer will be supplemented by an internally installed infrared camera, which will allow the reproducible setting of specified temperature profiles even for complex, large-area contours in the future.

Effect of phase transformation temperature on evolution of physical contact structure of titanium OT4-1 alloy permanent joints in samples "bushing—shaft"

The patterns in changes of microstructure, microhardness, distribution of alloying elements, dislocation density are studied during the cold tight interference fi t of 450 microns and subsequent thermal heating in the temperature range of phase α→β-transformation in the contact area of the permanent joint of the "bushing —shaft" samples made of OT4-1 alloy . The temperature-time interval of the phase pre-transformation of accelerated diffusion processes for the formation of diffusion OT4-1 alloy permanent joint corresponding to heating in autovacuum at temperature of 975...1000 °C with exposure time of 20 to 60 minutes is revealed.

Magnetometric research of bainite transformation in Cr-Ni-Mo steels

In this work, Cr-Ni-Mo steel, additionally alloyed with aluminum and silicon, was investigated. Magnetometric research of the decomposition kinetics of supercooled austenite during bainitic transformation was carried out. The temperature-time interval of bainitic transformation of specified steels is determined. The C-curves of the intermediate transformation are constructed. The volume of retained austenite at all temperatures was measured. It was shown that the content of retained austenite increases with increasing temperature of the isothermal transformation. The influence of aluminum and silicon on the position of the region of the intermediate transformation is revealed. The temperature of the onset of martensitic and bainitic transformation was calculated taking into account the influence of aluminum and silicon. The calculated data showed a good correlation with the data obtained experimentally.

Nucleation rates of spherulites in natural rhyolitic lava

The rates of nucleation and crystal growth from silicate melt are difficult to measure because the temperature–time path of magma is often unknown. We use geochemical gradients around spherulites in obsidian glass to estimate the temperature–time interval of spherulite crystallization. This information is used in conjunction with new high-resolution X-ray computed tomography (HRXCT) data on the size distributions of spherulites in six samples of rhyolite obsidian lava to infer spherulite nucleation rates. A large data set of geochemical profiles indicate that the lavas cooled at rates of 10 −2.2 to 10 −1.2 °C/h, and that the spherulites grew at rates that decreased exponentially with time, with values of 10 −0.70 to 10 0.30 μm/h at 600 °C. Spherulites are estimated to have begun nucleating when undercooling [Δ T , = liquidus T (≈800 °C) minus nucleation T ] reached 100–277 °C, and stopped when Δ T = 203–365 °C, with exact values dependent on assumed cooling and growth rates. Regardless of rates, we find that spherulites nucleated within a ~88–113 °C temperature interval and, hence, began when Δ T ≈ 0.65–0.88 × T L , peaking when Δ T ≈ 0.59–0.80 × T L . A peak rate of nucleation of 0.072 ± 0.049 cm −3 h −1 occurred at 533 ± 14 °C, using cooling and growth rates that best fit the data set of geochemical profiles. While our inferred values for Δ T overlap those from experimental studies, our nucleation rates are much lower. That difference likely results from experimental studies using hydrous melts; the natural spherulites grew in nearly anhydrous glass.

Studying the denaturation of bovine serum albumin by a novel approach of difference-UV analysis

A novel approach in the analysis of difference-UV spectrophotometric data for determining the heat denaturation degree of bovine serum albumin (BSA) was assessed. Five different parameters of difference-UV spectra were obtained by subtracting spectra of unheated and denatured protein solutions at different temperature-time combinations. BSA was found to exhibit a maximum degree of heat denaturation of about 17% compared to the complete unfolding caused by 6M guanidine hydrochloride. This low degree of heat denaturation is probably caused by the aggregation of the initially unfolded protein molecules. The kinetic analysis exhibited discontinuities in the Arrhenius plots, distinguishing the unfolding and aggregation phases of the denaturation process, whereas such a discrimination could not be obtained by differential scanning calorimetry analyses. The proposed method is accurate, fast, simple and sensitive enough to detect changes in the protein heat denaturation even at short temperature-time intervals.

Study of multicomponent segregation at interfaces in high-strength skelp steel

Rolled plates of high-strength skelp steel 05G2NDMFBT with a thickness of 30.9 mm and a strength rating of X70 were studied after two-stage thermomechanical treatment with accelerated cooling. Auger electron spectroscopy was used to study the temperature-time intervals associated with the segregation of carbon, nitrogen, sulfur, and phosphorus in specimens cut out from the surface and mid-thickness of the plates. Electron spectra were recorded after certain time intervals during isothermal holds (ranging from 300 to 8000 sec in duration). The article presents diagrams describing the isothermal segregation of carbon, nitrogen, sulfur, and phosphorus at 120, 200, 300, 355, 400, and 600°C and the main temperature-time intervals in which these elements tend to segregate in the grain boundaries of the steel.

Thermal deformation of a polymer heat-shielding material on the trajectory of descent

The thermal deformation of a heat-shielding coating of polymer composite material with a phenol-formaldehyde matrix under conditions simulating the temperature-time interval of descent of a spacecraft from orbit is considered. It is shown that in the plane of reinforcing of the composite the maximum thermal deformations occur in a direction 45° to the base of the fabric of the filler and with an increase in heating rate there is a significant reduction in the amplitude of its dilatometric values. The residual relative thermal deformation of the heat-shielding material tested to a program of descent from a trajectory may reach 2% and more.

Explosive crystallization phenomena in SOI structures

Using the double pulse technique with two synchronized lasers, we studied the conditions of ignition and evolution of explosive crystallization. The structure of the resulting crystallized layers is analyzed by TEM. Results of calculations are reported describing the development of the two phase fronts: amorphous/molten and molten/crystalline. It is shown that the system takes more than 500 ns to reach the steady state. The experimental results support the model of creating first a melt nucleus in the amorphous layer followed by the formation of the crystalline nucleus in the molten sphere. Competitive solid phase nucleation and growth in the amorphous layer limit the temperature-time interval of melt nucleation. Defined explosively crystallized areas in laterally structured SOI layers are presented.

Service properties of Cr?Mo?V steels in different structural conditions

1. In the whole investigated temperature-time interval (540–630°C, 104–2·105 h) Cr−Mo−V steel with a bainitic structure has the maximum stress-rupture strength. With an increase in temperature and test base there is a decrease in the difference in the stress-rupture strengths of 15K1M1F steel with different structures. 2. Variations in heat analysis within specification limits do not have a marked influence on the stress-rupture strength of 15Kh1M1F steel in the investigated temperature-time interval but do significantly influence its long-term plasticity. The higher the stress-rupture strength of the material, the stronger this influence.

Thermophysical properties of some thermite and intermetallic systems

Data is presented on thermal conductivity and thermal diffusivity of a number of thermite and intermetallic systems having differing dilutions by reaction products, densities and component forms and dispersities. The thermophysical parameters were determined by the high-speed two temperature-time interval method. The dependence of thermophysical parameters on size of the particles of various forms must be considered specifically.