Special Thermal Treatment Research Articles

Cellular magnetic domains in Fe–Ga alloys

A peculiar magnetic domain pattern (so-called cellular domain structure) was recently observed in Fe–Ga alloys, which was claimed to be responsible for desirable hysteresis-free and isotropic magnetization behaviors and to be associated with the reported non-Joulian magnetism [H. D. Chopra and M. Wuttig, Nature 521, 340 (2015)]. So far, such cellular domain phenomenon is observed only in Fe–Ga single crystal specimens of thin disk shape and with special thermal history. In this Letter, we report that the cellular domain structure is also observed in as-cast polycrystalline Fe–Ga alloys that are simply synthesized by arc-melting without special thermal treatment. For comparison, the cellular domains observed in an Fe–Ga single crystal specimen of rectangular prism shape are also presented. The cellular domain structure is discussed in light of a surface domain phenomenon and is found to be well interpreted by the Stephan model [Von W. Stephan, Exp. Tech. Phys. 4, 153 (1956)] based on classical domain theory, contrary to the Chopra–Wuttig model relying on the hypothesized charge density wave theory.

Thermo-Economic Optimization of Solar Thermal Devices by Coherent Integration of Technologies

Radiation is a form of energy where the angular variable of the direction of its photons has a primary importance, particularly for radiation concentration processes, which are essential tools to reach high temperatures from radiation beams (as the solar ones) with moderate intensities. Solar radiation cannot be used directly to feed thermodynamic cycles, and optical concentration must be applied to that goal. In general, reflection from mirrors is preferred to refraction by lenses in this case, because they have less optical aberrations. Concentration conveys very high temperatures in the receiver. However, the higher the temperature, the lower the efficiency of the solar thermal apparatus. Besides that, economy also suffers quite a lot when going to very high concentration factors, which is one of the main burdens in the development of Solar Thermal Energy. A new configuration of solar radiation concentrator is presented. It includes a salient innovation in the way the mirrors are given the right curvature by mechanical forces. Those mirrors are originally flat and do not need any special thermal treatment for this purpose. The whole device concept has been guided by the principle of thermoeconomic coherence, which requires similar efforts in all degrees of freedom that have strong influence in the performance and cost of the system. The paper shows the decision tree that has oriented the project, following the principle of equilibrium in efforts, which leads to a design window of moderate values in the main variables. The prototype of this new configuration has already been built, and the first stage of research is considered to be finished, because the prototype has shown excellent conditions to include selected (fitting) technologies at a very low cost.

FERROELECTRIC NANOCOMPOSITES WITH GOVERNED INTERFACE ON BASE OF MAGNETIC POROUS GLASSES

Two-phase (nonporous) magnetic alkali borosilicate glasses have been produced by induction melting. Their macroscopic properties and crystal structure have been studied and it is shown that in the silica skeleton there are the agglomerates of Fe3O4. These agglomerates are formed by monodomain nanoparticles of magnetite and demonstrate the superparamagnetic properties. After special thermal treatment (liquation process) and chemical etching the nanoporous matrices with random dendrite pore structure and magnetic properties have been produced. The channels (porous space) were filled by ferroelectric materials KH2PO4 (KDP), KH2PO4+(NH4)H2PO4 (KDP-ADP or KADP), and NaNO2 and the effect of applied magnetic fields on phase transitions in these nanocomposite have been studied. It has also been established that a restricted geometry changed essentially the phase diagram of KADP.

Synthesis and characterization of core-shell HgO/C colloids and hollow carbon nanospheres by chemical vapor deposition and investigation of its conductivity properties

In this study, interested core-shell structures of HgO/C nanocomposite were synthesized by chemical vapor deposition (CVD) process. These structures contain a rhombohedral-HgO as core and a hexagonal C as shell. In special thermal treatment, the HgO-cores are removed from core-shell composite and the hollow carbon Nanospheres (HCNSs) remain. The properties of these new core-shell structures and the HCNSs were characterized by TEM, SAED, SEM, XRD, AFM, FT-IR and TGA. The electronic structure and conductivity properties of the hollow carbon nanospheres were also investigated via scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) technique. The local currents images on the surface of HCNSs was recorded by STM and the differential conductance (dI/dV) measurements of the synthesized hollow carbon nanospheres was carried out using an improved method by STS. The HCNSs I-V curve follows from the quantum behavior. It was observed that the HCNSs had acceptable conductivity properties.

Application of physical and numerical simulations for interpretation of peripheral coarse grain structure during hot extrusion of AA7020 aluminum alloy

In this research, hot compression test is used to simulate the metallurgical phenomena occurring in the peripheral part of AA7020 aluminum alloy extrudates during hot extrusion and leading to the formation of the peripheral coarse grain (PCG) structure. The temperature profiles at a tracking point in the peripheral part of extrudates are predicted using finite element method (FEM). A special thermal treatment representing the predicted thermal profiles during extrusion is designed and applied to specimens after hot-compression testing. The effects of deformation conditions, i.e., temperature and strain rate, and the subsequent special thermal treatment on the formation of coarse grains in the AA7020 alloy are investigated. The as-deformed microstructures of specimens as well as the microstructures of specimens after the special thermal treatment are examined and the average grain size and homogeneity of grain size distribution determined. It is observed that with increasing deformation temperature or decreasing strain rate, the average recrystallized grain size increases. A fine and homogenous grain structure is obtained by increasing strain rate. According to the results of this investigation, formation of coarse grains at the periphery of the extrudate is attributed to high temperatures raised during extrusion rather than high strain rates.

Investigations of Temperatures of Phase Transformations of Low-Alloyed Reinforcing Steel within the Heat Treatment Temperature Range

AbstractThe paper presents the results of DSC analysis of steel B500SP produced in the process of continuous casting, which is intended for the production reinforcement rods with high ductility. Studies were carried out in the temperature range below 1000°C in a protective atmosphere of helium during samples heating program. The main objective of the study was to determine the temperature range of austenite structure formation during heating. As a result of performed experiments:Ac1s,Ac1f– temperatures of the beginning and finish of the eutectoid transformation,Ac2– Curie temperature of the ferrite magnetic transformation and the temperature Ac3of transformation of proeutectoid ferrite into austenite were elaborated. Experimental determination of phase transformations temperatures of steel B500SP has great importance for production technology of reinforcement rods, because good mechanical properties of rods are formed by the special thermal treatment in Tempcore process.

First principles molecular dynamics studies of elastic constants, ideal tensile strength, chemistry of crack initiation, and surface and cohesive energies in amorphous silicon

First principles Kohn–Sham density functional theory (DFT)-based molecular dynamics (MD) is employed to investigate some physical and mechanical properties of amorphous Si (a-Si) samples, as-quenched and annealed containing dangling and floating bonds as well as distorted tetrahedral bonds. The total energy and true stress as functions of the engineering strain for a-Si samples subjected to uniaxial tensile stress as well as uniaxial extension are obtained. It is well-known that the electron density of the state of matters can be determined via ab initio DFT-based MD with high accuracy. Using this technique, such inherent properties as the elastic constants, ideal tensile strength, ultimate tensile strength, and surface and cohesive energies will be calculated. Since the employed ab initio MD, in contrast to the empirical potentials simulations, is capable of providing the evolution of the electronic charge distribution, we can afford to study the chemistry of crack initiation and reconstructed surfaces at final rupture. The calculated cohesive and surface energies are compared with the available theoretical and experimental results; Tyson’s empirical relation and universal binding energy relations (UBERs) are also examined. The calculated elastic constants using the symmetry-general scheme satisfy well the isotropic relation . To date, the ab initio MD samples of a-Si generated from the completely melted scheme were all free of three-fold-coordinated Si. In contrast, as we will show, by implementing special thermal treatments, generation of all inherent structural defects is possible. Based on the electronic charge distribution, dative bonds and trigonal prisms for, respectively, floating and dangling bonds have been observed.

Amorphous soft-magnetic ribbons studied by ultra-small-angle polarized neutron scattering

When we investigated the magnetic structure of a variety of soft-magnetic amorphous ribbons by means of ultra-small-angle neutron scattering (USANSPOL) we were confronted with one particularly interesting Fe65.7Co18Si0.8B15.5 ribbon, provided by VAC Hanau. Due to a special thermal treatment during production a field- and stress-induced transverse domain texture was expected. Although the USANSPOL technique encountered its resolution limits during the investigation of this specific sample ribbon, such a texture could indeed be verified.

Development of nanostructured materials by mechanical alloying and/or rapid solidification

AbstractThe knowledge of thermal behaviour of materials is important in order to control their structure and properties. In nanocrystalline materials obtained from amorphous alloys, the knowledge of the crystallization kinetics permits to design special thermal treatments to develop materials with specific microstructure. The milling of melt‐spun ribbons is a two‐steps procedure to develop new nanostructured materials. Two, Co and Fe rich, melt‐spun alloys were obtained and mechanically alloyed in low energy milling conditions, and their structure and thermal behaviour was analyzed. The thermal study was performed by means of differential scanning calorimetry. All experimental curves are derived from non‐isothermal calorimetric experiments. Good agreement is observed between the transformation curves and the experimental data, which verifies the reliability of the approach and the validity of the rate constant model description. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Impact of Instant Controlled Pressure Drop Treatment on Moisture Adsorption Isotherm of Cork Granules

Some special thermal and mechanical treatments may completely modify the composition, and the structure of organic material changes its interaction with water. In the case of the instant controlled pressure drop (DIC) technique, the main modification, which is structure expansion and high porosity, allows the product to generally reduce moisture activity. In the special case of cork granules, the impact of DIC in terms of porosity is completely absent and expansion is linked to a tear effect obtained from only the large size granules. In order to characterize this type of treatment, we considered natural and DIC-treated cork granules and determined moisture adsorption isotherms at three different temperatures (25, 40, and 60°C) and different water activity levels ranging from 0.05 to 0.9 using the static gravimetric method. We used three samples of the same cork variety with 0.5–1 mm, 2–4 mm, and 4–6 mm as granule diameter. The adsorption isotherms of both natural untreated and DIC-treated cork whatever granules display a sigmoid form type II isotherm, with equilibrium moisture contents at constant water activity decreasing when temperature increases. The impact of DIC treatment depends of cork shape; the larger the shape, the lower the water activity for the same water content. Such a result is linked to the modification of structure. Thus, for the smallest shape, DIC implying only low thermal effect without any structure modification allows cork to lightly increase its water activity compared to the untreated samples. With higher shape cork granules, as DIC treatment induces a tear effect and some expansion, activity of water is lower for the same water content. For describing the experimental data of adsorption isotherms, we used GAB, BET, and Henderson models. We found the GAB to be the most suitable model with predicted values higher than those obtained using the BET model. We note that monolayer moisture content values increase in the case of big shape cork granules after having been treated by DIC.

Thermal conductivity of exfoliated graphite nanocomposites

Abstract Since the late 1990’s, research has been reported where intercalated, expanded, and/or exfoliated graphite nanoflakes could also be used as reinforcements in polymer systems. The key point to utilizing graphite as a platelet nanoreinforcement is in the ability to exfoliate graphite using Graphite Intercalated Compounds (GICs). Natural graphite is still abundant and its cost is quite low compared to the other nano–size carbon materials, the cost of producing graphite nanoplatelets is expected to be ~$5/lb. This is significantly less expensive than single wall nanotubes (SWNT) (>$45000/lb) or vapor grown carbon fiber (VGCF) ($40–50/lb), yet the mechanical, electrical, and thermal properties of crystalline graphite flakes are comparable to those of SWNT and VGCF. The use of exfoliated graphite flakes (xGnP) opens up many new applications where electromagnetic shielding, high thermal conductivity, gas barrier resistance or low flammability are required. A special thermal treatment was developed to e...

Effect of the sintering temperature on the Ba(Zn 1/3Ta 2/3)O 3 dielectric properties

Preparation of dielectric materials with optimal properties for wireless applications requires special thermal treatments due to the difficult control of the cationic ordering. The BZT samples prepared by solid-state reaction were sintered at temperatures in the range 1400–1600 °C for 4 h. For compositional, structural and morphological characterization, XRD, SEM and EDX were employed. The order–disorder transition of the BZT material was analyzed. With the increase of the sintering temperature, a long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was observed. The dielectric parameters were measured in the microwave range and were correlated with morphological and structural properties. In order to improve the microwave properties, annealing treatment at 1400 °C for 10 h was performed. Sintering temperatures greater than 1550 °C are required for undoped BZT compositions, in order to obtain low microwave loss ( Qf > 100,000).

CARPENTER GLASS SEALING 42-6

Abstract Carpenter Glass Sealing 42-6 alloy has been used for sealing to Corning 0120 glass. A special thermal treatment develops a tightly adherent oxide beneficial to obtaining hermetic seals. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on high temperature performance and corrosion resistance as well as forming and heat treating. Filing Code: FE-137. Producer or source: Carpenter Technology Corporation.

Stress-dependent magnetoimpedance in Co-based amorphous wires with induced axial anisotropy for tunable microwave composites

A remarkably strong dependence of magnetoimpedance (MI) on tensile stress has been observed in the microwave frequency range for thin CoMnSiB glass-coated microwires exposed to a special thermal treatment. The MI ratio runs into more than 100% at 0.5-1.5 GHz when the tensile stress of 600 MPa is applied to the wire. It was demonstrated that a large MI change at such high frequencies is related predominantly with the dc magnetization orientation. A host of such microwires incorporated into a dielectric matrix may constitute a new sensing medium that is characterized by the stress-dependent effective permittivity. Such medium can be used for the microwave visualization of the stress distribution inside of a composite structure or on its surface.

Testing Laminated Glass for Impact Resistance

Comparative testing of laminated glass made up by different combinations for impact resistance has been performed. The testing corroborates the possibility of using glass subjected to special thermal treatment (STT) in the production of impact-resistant laminated glass. Glasses based on STT glass satisfy the impact resistance requirements of GOST R 51136–98, and their thickness and weight are a factor of 1.5 less.

Controlled growth of Sb2O5nanoparticles and their use as polymer electrolyte fillers

Antimony pentoxide nanocrystals with controlled sizes (4–400 nm) and shapes (spheres, sheets and cubes) have been synthesized hydrothermally. The growth process of the crystals observed by transmission electron microscopy (TEM) obeys Ostwald ripening theory. Upon annealing, the composites of the Sb2O5 nanoparticles with PEO–LiClO4 polymer electrolyte exhibit significantly enhanced ionic conductivities and these enhanced conductivities have long-term stability at ambient temperature. The conductivity variation after special thermal treatment and the impedance evolution with time of the PEO–Sb2O5–LiClO4 films have direct relationships with the sizes and shapes of the Sb2O5 fillers. Such performance of the composite solid polymer electrolytes can be interpreted by dipole–dipole interactions between the PEO macromolecules, lithium salt and the Sb2O5 dopants.

Dielectric properties of (100) textured thick Pb(ZrxTi1−x)O3 films with different Zr/Ti atom ratios

Near 4-μm-thick Pb(ZrxTi1−x)O3 (PZT) films with Zr/Ti ratios of 60/40, 52/48, and 45/55 were coated onto platinized silicon substrates by using 2-methoxyethanol based sol-gel spin-on techniques with a special thermal treatment process. The scanning electron microscopy observations show the columnar growth of grains. The analysis of x-ray diffraction data indicates that all PZT films exhibit (100) texture. The dielectric constants and dissipation factors of the films were measured at elevated temperatures and frequencies. It is found that Curie points of 60/40, 52/48, and 45/55 films are at 350, 375, and 422 °C, respectively. All these films exhibit high dielectric constants and remnant polarizations. A permittivity of 1658 and remnant polarization of 35 μC/cm2 had been achieved for the 60/40 films. No enhancement of the dielectric constant was observed in films with a Zr/Ti ratio close to morphotropic phase boundary. The high dielectric constant observed in films with the higher Zr content was explained by the concept of domain engineering.

Testing Of Laminated Glass for Bullet-Proof Capacity

The results of comparative testing of laminated glass fired at using a Makarov pistol are given. It is demonstrated that the use of glass sheets after special thermal treatment in laminated glass articles makes it possible to reduce their weight and the energy consumption and to improve the light transmission.

Epitaxial CoSi 2 by solid phase reaction of Co/Ti and Co/Hf bilayers on Si(001)

TEM and RBS studies of the solid phase reaction of Co/Ti- and Co/Hf/Si(001) layer systems are reported. In addition to conventional annealing procedures a special thermal treatment was applied to investigate the intermediate stages of the reaction during heating up. With rising temperature a complex Co–Si-phase sequence was observed which finally results in the growth of epitaxial CoSi 2. The emerging silicide phases were proved to grow with preferred orientation relations to the substrate. The observed growth behaviour is compared for both the systems and discussed considering aspects of energy minimization and material supply under the conditions of a thin film reaction.

Peculiarities of the glow-peak 5a of LiF:Mg,Ti

The glow-peak 5a of LiF:Mg,Ti is a glow-peak, with peak maximum temperature between those of glow-peaks 5 and 6. This glow-peak is not seen in the usual glow-curve, resulting after normal annealing at 400°C for 1 h and at 100°C for 2 h. However, its existence is confirmed first experimentally and then as the necessity to achieve a very good glow-curve fitting. In the present work it is found that the glow-peak 5a can be very well isolated from its neighbouring glow-peaks, after special thermal treatment between 140°C and 160°C. The isolation permits the study of its individual behaviour, which was found to have the following peculiarities. (i) This glow-peak is clearly seen only after thermal treatment between 140°C and 160°C. (ii) It appears with the same properties after both pre-irradiation and post-irradiation annealing in the above temperature region. (iii) Its activation energy was found to be above 3 eV and its frequency factor above 1030 s−1. These values are extremely high and outside the physically accepted limits.