Isothermal Values Research Articles

Structural and magnetic properties of Mn1.25Fe0.7P0.5Si0.5 alloys prepared by spark plasma sintering using raw materials milled with different lengths of time

Spark plasma sintering (SPS) is an effective method for synthesizing the Fe2P-type alloys due to its fast heating rate and short sintering time. Raw materials in the form of powder are sintered and pressed simultaneously in the preparation. Therefore, the particle size of the powder would have important influences on the structural and magnetic properties of the Fe2P-type alloys. In this work, the structure and magnetic properties of Mn1.25Fe0.7P0.5Si0.5 alloys prepared by SPS using raw materials milled with different lengths of time were investigated. We found that the particle size of the raw materials reduced mainly within milling time of 5 h and only slight difference existed when the milling time exceeded 5 h. Obvious secondary phase of (Mn,Fe)3Si was observed in the alloy prepared with milling time of 1 h. Other alloys prepared with milling time of 2 h, 5 h and 10 h showed similar magnetic properties. Giant isothermal entropy change values of 7.4 ∼ 9.6 J ⋅ kg−1 ⋅ K−1 for a magnetic field change of 1.5 T were obtained near room temperature for the alloys. The results demonstrate that a milling time longer than 2 h is required to obtain such magnetocaloric Mn-Fe-P-Si alloys with excellent magnetic properties using SPS method and the obtained alloys are promising candidates for magnetic refrigeration near room temperature.

Transformation behavior and inverse magnetocaloric effect in Ni45Co5Mn36.7In13.3-xGex melt-spun ribbons

In the present work the influence of Ge doping on crystal structure, microstructure, martensitic transformation (MT) and magnetocaloric effect (MCE) of Heusler-type Ni45Co5Mn36.7In13.3-xGex (x = 0, 2, and 3 at. %) metamagnetic shape memory alloys (MetaMSMAs) have been studied. Melt-spinning was used to prepare ribbons of these alloys since the ribbon shape ensures a high surface-to-volume ratio favoring a high heat exchange rate in a solid-state refrigeration. Furthermore, melt-spinning can induce a specific microstructure and stabilize metastable phases at room temperature. The ribbons were examined by X-ray diffraction at different temperatures, scanning electron microscopy, calorimetry, thermomagnetization, and magnetic field induced adiabatic temperature change measurements carried out across MT. It was found that Ge doping gave rise to enhanced antiferromagnetic interactions, stabilized martensitic phase, increased the MT temperature, causing larger magnetization jumps at MT and making narrower MT hysteresis. The x = 3 ribbon exhibited an inverse MCE at 303 K characterized by the isothermal magnetic entropy change value of |26.9|J/kgK at μ0H = 5 T and an adiabatic temperature change of ǀ1.5ǀ K at μ0H = 1.96 T. These values are comparable with the previously reported data on the Ni–Mn-based metamagnetic shape memory alloys in a bulk form.

Olive industry liquid waste from trash to metal adsorbent for wastewater purification

The development of biobased polymeric materials for wastewater purification has become a demand due to the growing need for water free of hazardous metal ions for safe purposes. The organic components of the OLLW including carbohydrates, phenolics, aromatic acids and others are cost-effective and sustainable choices for this application. This work focuses on a method for turning the organic components of liquid waste from the olive industry (OILW) into a foam-based value-added polymer that has several metal ion binding sites. The process of making the target polymers involved reacting the components of the OILW with hexamethylene diisocyante and 1,4-phnyelene diisocynate to create the polymeric materials LHMIDIC and LPDIC that are in foam forms with urethane linkages, respectively. The adsorption competence of the polymeric foams toward Pb(II) was evaluated as a function of various parameters including adsorbent dose, pH, temperature, initial ion concentration and time. The optimum parameters values that led to a quantitative removal of Pb(II) were identified. The obtained thermodynamic parameters showed that the adsorption by the two foams was spontaneous at room temperature. The isothermal and kinetic values showed that the adsorption by synthesized foams follows a second order kinetic and obeys the Langmuir isothermal model. The foams showed a high tendency for removing multi metal ions present in a real sample of wastewater. The original nature of the starting material used in making the foam, cost and the obtained results showed the potential of using the foam in a large-scale plants of wastewater purification.Graphical

Recent Developments in CTE-Matched Composite Thermal Materials

A surprisingly large number of engineered materials are available to the module and system packaging engineer that have been designed for a target coefficient of thermal expansion (CTE, stated both at room temperature and across a specified range of temperatures) and possessing bulk thermal conductivity values useful for device heat dissipation. There are continuing research and development programs for new forms and variations of such materials, intended to meet continuing demands for improvement on a spectrum of requirements. These requirements include higher bulk isothermal conductivity values, lower cost, lower CTE values, reduced density and weight, and, for certain types of applications, a target CTE and highly anisotropic property. This discussion seeks to identify both existing and common materials (for comparison purposes) and new developments that are being brought to market and/or are in production today. The purpose is to add to the design engineer’s tool kit for available materials of these types. In addition, high temperature effects on selected materials are illustrated.

Ho6FeSb2: Potential magnetic refrigerant with improved magnetocaloric effect

The magnetic and magnetocaloric characteristics of Ho6FeSb2 have been investigated. The compound crystallizes in Fe2P type hexagonal crystal structure (P6‾2m) with lattice parameters a, b = 8.1046 Å and c = 4.1470 Å. There are 2 second-order ferromagnetic transitions occurring at temperatures T1 = 56 K and T2 = 34 K. The occurrence of subsequent second-order transitions opens the door to hysteresis-free magnetocaloric effect across wide temperature span. The study utilizes different magnetocaloric figures of merit, including isothermal magnetic entropy change, relative cooling power, and temperature-averaged entropy change. The alloy has a maximum relative cooling power of 710 J/kg in 0–5 T, with the temperature-averaged entropy change value being close to the isothermal magnetic entropy change value, making it suitable for hysteresis-free magnetocaloric applications. We have studied the electrical transport properties of the alloy and estimated a maximum magnetoresistance of −9% around T1.

Comparison of Isothermal and Adiabatic Elasticity Characteristics of the Single Crystal Nickel-Based Superalloy CMSX-4 in the Temperature Range Between Room Temperature and 1300°C

Based on the results of performed thermophysical measurements and available experimental data for adiabatic elastic stiffnesses, isothermal elastic characteristics of the single crystal nickel-based superalloy CMSX-4 have been calculated for a wide temperature range, from room temperature to 1300°C. According to the results obtained, the adiabatic and isothermal values of such elastic characteristics as elastic stiffnesses {{c}_{{11}}}, {{c}_{{12}}} and bulk modulus of elasticity B differ significantly at high temperatures. The reasons for this are significant changes in the thermophysical properties of the alloy with temperature and a temperature increase of its Poisson’s ratio approaching the limiting value for cubic crystals, equal to 0.5. It is shown that the use of adiabatic elastic constants instead of isothermal ones in engineering calculations affects the relationship between the volumetric strain and hydrostatic stress, and this effect is similar to introducing a field of thermal dilatation into the analyzed object. At low temperatures, this effect is small, but at high temperatures, typical for the service conditions of the blade material of aircraft gas turbine engines, it increases many times.

Polytropic Behavior in the Structures of Interplanetary Coronal Mass Ejections

The polytropic process characterizes the thermodynamics of space plasma particle populations. The polytropic index, γ, is particularly important as it describes the thermodynamic behavior of the system by quantifying the changes in temperature as the system is compressed or expanded. Using Wind spacecraft plasma and magnetic field data during 1995 February–2015 December, we investigate the thermodynamic evolution in 336 interplanetary coronal mass ejection (ICME) events. For each event, we derive the index γ in the sheath and magnetic ejecta structures, along with the pre- and post-event regions. We then examine the distributions of all γ indices in these four regions and derive the entropic gradient of each, which is indicative of the ambient heating. We find that in the ICME sheath region, where wave turbulence is expected to be highest, the thermodynamics takes longest to recover into the original quasi-adiabatic process, while it recovers faster in the quieter ejecta region. This pattern creates a thermodynamic cycle, featuring a near adiabatic value γ ∼ γ a (=5/3) upstream of the ICMEs, γ a − γ ∼ 0.26 in the sheaths, γ a − γ ∼ 0.13 in the ICME ejecta, and recovers again to γ ∼ γ a after the passage of the ICME. These results expose the turbulent heating rates in the ICME plasma: the lower the polytropic index from its adiabatic value and closer to its isothermal value, the larger the entropic gradient, and thus, the rate of turbulent heating that heats the ICME plasma.

Surface Space‐Charge Potential and Oxygen Surface Exchange Coefficient of SrTiO3: The Effect of Surface Orientation

Abstract18O2/16O2 exchange experiments on terminated (100), (110), and (111) oriented samples of single‐crystal SrTiO3 are used to study the effect of surface orientation on the oxygen surface exchange coefficient and the surface space‐charge potential Φ0. Isotope exchanges are carried out at temperatures 922 < T/K < 1073 at an oxygen activity aO2 = 0.2 in dry conditions (aH2O < 10−7.7); isotope profiles are measured subsequently by secondary ion mass spectrometry. Isothermal values are found to vary by less than one order of magnitude, with . All data are consistent with a change in the activation enthalpy of surface exchange from 3.0 eV at high temperatures to 1.8 eV at lower temperatures. The transition is attributed to a change from a charge‐transfer mechanism at high temperatures to a mechanism involving surface OH species. The transition temperature depends on the surface orientation, Ttr(111) ≈ Ttr(110) > Ttr(100). Values of Φ0 obtained varied between 0.50 V and 0.37 V, with isothermal values obeying Φ0(111) ≈ Φ0(110) < Φ0(100). Φ0 data is analysed to obtain the OH− surface coverage for the low‐temperature regime. Similarities between the behavior of Φ0 and that of are highlighted.

Changes in elements and magnetic properties of Sendai Bay sediments caused by the 2011 Tohoku‐oki tsunami

AbstractNearshore marine sediments deposited along island arcs can preserve evidence of past disaster events, such as tsunamis. Evidence of a tsunami that occurred off the Pacific coast of Tohoku, Japan, on March 11, 2011, was likely preserved in marine sediments. Using geochemical and rock magnetic analyses, this study aimed to investigate tsunami records preserved in marine sediments in Sendai Bay, located west of the epicenter of the 2011 Tohoku earthquake. We collected sediment samples at five stations (S‐1, S‐2, S‐3, S‐4, and S‐5) in Sendai Bay from 2002 to 2014. We compared the samples collected before and after the tsunami. We established that the silt component increased, while that of fine sand decreased at stations S‐3, S‐4, and S‐5 in the 2011 sediment sample. Notably, the concentrations of terrestrial and industrial metallic elements (Cu, Zn, and Pb) and total nitrogen, carbon, and sulfur amounts increased, while the magnetic susceptibility and isothermal remanent magnetization values decreased after the tsunami. We also found that Ti‐poor magnetite increased in the 2011 samples, indicating tsunami‐mediated changes. The study area experienced a large typhoon 6 months after the tsunami, leading to flooding. The elevation in the total organic carbon and total nitrogen ratio in the 2012 sample suggested that terrestrial organic matter was supplied by the flood.

Isokinetic analysis of reaction onsets

Kinetic studies of chemical reactions typically assume a constant fractional conversion of reactants to products, α, at a particular time, t, or temperature, T, during the reaction. This constant (iso) conversion approach cannot provide both Ea and A of the Arrhenius rate constant, k = A exp[-Ea/RT], without specifying an algebraic model or value for the reaction mechanism, f(α), or its integral F(α), which are rarely known a priori. A new isoconversion rate approach eliminates the reaction model from consideration by specifying f(α) =1 at the reaction onset, so that the rate of conversion, dα/dt = k, is the same in isothermal and nonisothermal experiments. This equal (iso) kinetic approach reduces the kinetic problem to the relationship between time and temperature at the reaction onset, and allows for the determination of Ea and A for the initial step of a potentially complex chemical reaction by measuring the change in the onset temperature Tonset with heating rate, β = dT/dt, in nonisothermal experiments, or the change in onset time tonset with temperature in isothermal experiments. In a test of the new theory, oxidation onset times of the reaction of hydrocarbons with oxygen at constant temperature (tonset) were calculated for a wide range of materials and experimental conditions using isothermal and nonisothermal values for Ea and A, and found to be in quantitative agreement with experimental values of the oxidation induction (onset) time (OIT).

Assessing the thermal and fungal behavior of eco-friendly epoxy thermosets derived from vegetable oils for wood protective coatings

The paper deals with the study of the obtaining, characterization and thermal and fungal behavior of a green thermoset based on epoxidized soybean oil (ESO), castor oil maleic anhydride adduct (COMA) and methyl nadic anhydride (MNA). By varying the MNA/COMA crosslinking agent ratio, resins with different degree of stiffness can be obtained suitable for green thermosets coatings. Differential scanning calorimetry (DSC) and a simultaneous TG/FT-IR/MS coupling were used to establish the crosslinking behavior, evolved gases analysis and thermal decomposition mechanisms associated with their corresponding kinetic parameters. The non–isothermal global kinetic parameters values (activation energy and pre–exponential factor) were calculated with the aid of the Friedman and Flynn–Wall–Ozawa isoconversional methods. The curves shape of the variation of activation energy versus conversion degree and first derivative (DTG) curves shapes suggest that the thermal degradation processes occurred in multi-step kinetics. Using a multivariate linear regression method the most probable thermal decomposition and crosslinking kinetic models were established. A good concordance between experimental and simulated data was obtained, confirming the correct description of the thermal mechanisms. The main identified gaseous fragments were water, carbon dioxide, saturated and unsaturated hydrocarbons and carboxylic derivatives. The decay resistance against two wood decaying strains, P. chrysogenum and A. brasiliensis was also evaluated.

High-pressure phase equilibrium and volumetric properties of pseudo-binary mixtures of stock tank oil + methane up to 463K

High-pressure phase equilibrium and volumetric properties of highly asymmetric mixtures related to reservoir fluids are critical to the development of high-pressure and high-temperature (HPHT) reservoirs. However, there is a lack of the relevant data and accurate modeling tools. In this work, we prepared asymmetric pseudo-binary mixtures of methane (CH4) + stock tank oil (STO) and systematically measured their phase equilibrium and densities at temperatures from (298.15 to 463.15) K and pressures up to 140 MPa. The methane mole fraction in these mixtures range from 0.20 to 0.61 for the density measurement, and from 0.20 to 0.81 for the phase equilibrium measurement. From the experimental densities, the isothermal compressibility values, as well as the pseudo-excess volumes, were determined. Moreover, phase envelopes, relative volumes, and liquid volume fractions below the saturation point were also measured. These data are valuable for evaluating and improving thermodynamic models for HPHT reservoir fluids. The experimental results were modeled by the Soave-Redlich-Kwong (SRK) equation of state (EoS), the Peng-Robinson (PR) equation of state, their volume translated versions SRK-VT and PR-VT, and the Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT). For density, SRK and PR gave large deviations of ~18% and ~8%, respectively, as compared with ~3% for PC-SAFT. Inclusion of volume translation reduced their deviations to the same level as that for PC-SAFT. For isothermal compressibility, all the models gave deviations of 20-30%, with PC-SAFT, SRK-VT and PR-VT being slightly better. The excess volumes calculated by SRK, PR and PC-SAFT were similar and close to the experimental values. The deviations in the calculated excess volumes resulted in only ~1% deviations in the calculated densities if the experimentally determined STO densities were used. It was illustrated that the small deviations could be utilized in the excess volume method to accurately estimate the high-pressure live oil densities from the high-pressure STO densities. This excess volume method gave ~1% density deviation on average for all the models, with PC-SAFT giving the smallest maximum deviation. The deviations in calculated saturation pressures were ~5% for all the models with the overall deviation for PC-SAFT being slightly smaller.

Hysteresis, latent heat and cycling effects on the magnetocaloric response of (NiMnSi)0.66(Fe2Ge)0.34 alloy

In this work, we further analyze the promising magnetocaloric (NiMnSi)0.66(Fe2Ge)0.34 alloy, which presents isothermal entropy change values as large as 29 J kg−1 K−1 for 2 T at room temperature. It undergoes a magnetostructural transition accompanied by large thermal/magnetic hysteresis, which remains up to high magnetic fields (corroborated by the elaboration of an experimental magnetic phase diagram). We illustrate that this huge hysteretic behavior (i.e. different responses when magnetizing or demagnetizing) can lead to erroneous interpretation of the order of the phase transition by applying the conventional Banerjee's criterion or the recently developed field dependence analysis of the magnetocaloric effect. Additionally, the cyclability of the response is characterized, showing that after several measurements the magnetocaloric response is significantly reduced (by ≈ 40%) due to sample breaking. These dependences together with the large latent heat of the transition (15.0 kJ kg−1) lead to relatively small values of the adiabatic temperature change for powdered samples at moderate field changes, reaching around 0.6 K for 1.75 T by direct measurement methods.

Characterization of the Quality Factor Due to the Static Prestress in Classical Caputo and Caputo-Fabrizio Fractional Thermoelastic Silicon Microbeam.

The thermal quality factor is the most significant parameter of the micro/nanobeam resonator. Less energy is released by vibration and low damping, which results in greater efficiency. Thus, for a simply supported microbeam resonator made of silicon (Si), a thermal analysis of the thermal quality factor was introduced. A force due to static prestress was considered. The governing equations were constructed in a unified system. This system generates six different models of heat conduction; the traditional Lord–Shulman, Lord–Shulman based on classical Caputo fractional derivative, Lord–Shulman based on the Caputo–Fabrizio fractional derivative, traditional Tzou, Tzou based on the classical Caputo fractional derivative, and Tzou based on the Caputo–Fabrizio fractional derivative. The results show that the force due to static prestress, the fractional order parameter, the isothermal value of natural frequency, and the beam’s length significantly affect the thermal quality factor. The two types of fractional derivatives applied have different and significant effects on the thermal quality factor.

Method of Determining the Elastic Characteristics of Graphene and Other 2D Nanoallotropes

To calculate and design nanoelectronic and nanophotonic devices, in which graphenes and graphene-like 2D nanoallotropes of carbon, silicon, and binary III–V compounds are used, knowledge of the elastic characteristics and piezoelectric, photoelastic, and other properties of 2D materials, which depend on them, is of great significance. In this work, a simple method suitable for engineering calculations of determining the isothermal values of the force constants, elastic rigidities, Young’s modulus, and Poisson coefficient for 2D nanoallotropes of elements of Group IV of the periodic table and binary III–V compounds is proposed. The method is based on the Harrison method of bonding orbitals modified by S.Yu. Davydov and the R. Keating model for describing the elastic properties of such materials. It is shown that the method makes it possible to perform evaluative calculations of the elastic properties for known synthesized 2D crystal structures as well as for structures “constructed” theoretically. It is established that single-layer hexagonal boron nitride and other binary III–V compounds in the form of 2D nanoallotropes of various types of symmetry, which are piezoelectrics in addition, can be promising materials for nanoelectronics along with graphene. This extends the spectrum of the possible practical applications of the studied 2D materials (C, Si, BN, AlN, GaN, AlP, and GaP) both with a graphene-like and more complex structure. The results of this work can be used when developing the acoustic delay lines of the terahertz-frequency range, piezoelectric transducers for exciting and receiving elastic waves in nanoscale 2D acoustic lines, as well as piezoelectric sensors.

Relation between excess volume, excess free energy and isothermal compressibility in liquid alloys

Excess volume data of 32 liquid alloys were reviewed and plotted versus their excess free energies. It is hereby found that all combinations of the signs of EV and EG are possible. The excess volume data split into two different curves which are monotonous in EG. For one of these curves the signs of EV and EG are equal and they are opposite for the other.We improved our previously developed model and found that there is an unspecified sign which can be chosen either + or -, depending on the system. This explains why there are two curves corresponding to the experimental finding. The model relates excess volume, excess free energy and isothermal compressibility with each other whereby the concept of internal pressure is used.The model can also predict the excess volume as function of the excess free energy, when the correct sign, either + or -, is known and a reasonable assumption is made for the effective isothermal compressibility. In the present work, the latter has been estimated as an average from the isothermal compressibility values over the involved pure elements. Good qualitative and quantitative agreement with the experimental data is obtained for the systems investigated. The model is valid at least for -3RT < EG < +1RT.

Process integrating two-stage hydrocracking and a hydrotreatment process

Excess volume data of 32 liquid alloys were reviewed and plotted versus their excess free energies. It is hereby found that all combinations of the signs of EV and EG are possible. The excess volume data split into two different curves which are monotonous in EG. For one of these curves the signs of EV and EG are equal and they are opposite for the other.We improved our previously developed model and found that there is an unspecified sign which can be chosen either + or -, depending on the system. This explains why there are two curves corresponding to the experimental finding. The model relates excess volume, excess free energy and isothermal compressibility with each other whereby the concept of internal pressure is used.The model can also predict the excess volume as function of the excess free energy, when the correct sign, either + or -, is known and a reasonable assumption is made for the effective isothermal compressibility. In the present work, the latter has been estimated as an average from the isothermal compressibility values over the involved pure elements. Good qualitative and quantitative agreement with the experimental data is obtained for the systems investigated. The model is valid at least for -3RT < EG < +1RT.

Pressure-induced structural transition and metallization in MnSe2

The high-pressure behavior of manganese diselenide MnSe2 was investigated by synchrotron angle-dispersive X-ray diffraction (ADXRD) and infrared reflection spectroscopy equipped with a diamond-anvil cell. It was found that MnSe2 with a pyrite-type structure undergoes a transformation into a disordered intermediate phase at ~ 12.5 GPa, with a ground state composed of an arsenopyrite-type structure, as confirmed by laser-heating treatment. The pyrite to arsenopyrite phase transition was found to be coupled to a large collapse in the unit-cell volume (∆V ~ 19%) and an electronic transition from a high-spin to low-spin state for manganese cations (Mn2+). With a fixed value for the pressure derivation of the bulk modulus K' = 4, fitting of the pressure–volume data to a second-order Birch–Murnaghan equation of state yielded isothermal bulk modulus values of K0 = 56.1(9) GPa and K0 = 93.1(4) GPa for the pyrite-type and arsenopyrite-type phases, respectively. The measured infrared reflectivity (Rsd) for MnSe2 showed a drastic increase at pressures between 13 and 20 GPa, but became insensitive to pressure under further compression, implying a pressure-induced transition from an insulator to metallic state.

Influence of the Static Pre-Stress in Micro-Viscothermoelastic Resonators Based on Dual-Phase-Lagging Heat Conduction

Thermal and mechanical relaxation times play vital roles in the values of the quality factor of micro/nanoresonators. They can control the energy dissipation across the coupling of mechanical and thermal behavior. In this paper, we introduce an analytical model that considers a pre-stress in a micro-viscothermoelastic resonator to modify the thermal and mechanical relaxation times and thus higher the quality factor. The impacts of length scale and static pre-stress on the quality factor have been discussed. The model expects that significant improvement in terms of quality factors is possible by tuning the pre-stress and the thermal and mechanical relaxation times parameters, and the isothermal value of frequency have significant effects on the thermal quality factor of the resonators.

Characterization of the thermal quality factor of two-temperature micro-viscothermoelastic resonator due to static-pre-stress based on dual-phase-lagging heat conduction

Thermal and mechanical relaxation times play essential roles in the thermal quality factor Q-factorof the micro-resonators, where controls the energy damping through the coupling of thermal and mechanical behavior. In this work, we developed an analytical mathematical model that assumed a pre-stress in a two-temperature micro-viscothermoelastic resonator of silicon to modify the thermal and mechanical relaxation times and thus increase the thermal quality factor. The impacts of length-scale and pre-stress on the thermal quality factor have been discussed. The present model predicts that significant enhancement in terms of thermal quality factors is enabled by tuning the static-pre-stress, the thermal and mechanical relaxation times parameters. The isothermal value of frequency and the two-temperature parameter have impact effects on the thermal quality factor of the micro-resonators.