Superconducting Phase Diagram of Rh17S15

We report on measurements of the magnetization up to 7 T, of the specific heat and electrical resistivity in fields up to 14 T, and of the magnetic susceptibility in fields up to 20 T of a polycrystalline sample of Rh₁₇S₁₅. Our data allow us to complement the superconducting phase diagram. The existence of narrow 4d-band states (and thus of strong electronic correlations that seem not to provide magnetic correlations) is supported by the moderately high electronic contribution to the specific heat of about 107 mJ/molK², favoring the existence of a strong superconducting interaction. This fact, and the remarkably high upper critical field (exceeding the simple Pauli limit by a factor of two), give evidence of the uncommon nature of the superconductivity in Rh₁₇S₁₅.     

Heat capacity measurements on a thin ribbon sample of Zr0.55Al0.10Ni0.05Cu0.30 glassy alloy and Apiezon N high vacuum grease using a Quantum Design Physical Property Measurement System

We measured the heat capacity of a thin ribbon sample of Zr_0.55Al_0.10Ni_0.05Cu_0.30 glassy alloy using a Heat Capacity option of Quantum Design’s Physical Property Measurement System (PPMS) between 1.9 K and 310 K. The cut ribbon pieces were piled up to form a block, where each ribbon layer was adhered to one another with Apiezon N grease (ANG), and the heat capacity of the block was measured. In order to obtain the heat capacity of the sample, the heat capacity of ANG was subtracted from the block heat capacity. We report how we measured the heat capacity of a thin ribbon sample, and in this connection, we also reviewed the ANG heat capacity previously reported.     

‘Heat from Above’ Heat Capacity Measurements in Liquid 4He

We have made heat capacity measurements of superfluid ⁴He at temperatures very close to the lambda point, T _λ, in a constant heat flux, Q, when the helium sample is heated from above. In this configuration the helium enters a self-organized (SOC) heat transport state at a temperature T _soc(Q), which for Q≥100 nW/cm² lies below T _λ. At low Q we observe little or no deviation from the Q=0 heat capacity up to T _SOC(Q); beyond this temperature the heat capacity appears to be sharply depressed, deviating dramatically from its bulk behaviour. This marks the formation and propagation of a SOC/superfluid two phase state, which we confirm with a simple model. The excellent agreement between data and model serves as an independent confirmation, of the existence of the SOC state. As Q is increased (up to 6 µW/cm²) we observe a Q dependent depression in the heat capacity that occurs just below T _SOC(Q), when the entire sample is still superfluid, This is due to the emergence of a large thermal resistance in the sample, which we have measured and used to model the observed heat capacity depression. Our measurements of the superfluid thermal resistivity are a factor of ten larger than previous measurements by Baddar et al.     

Estimation and experimental study of the density and specific heat for alumina nanofluid

This study analyses the density and specific heat of alumina (Al₂O₃)/water nanofluid to determine the feasibility of relative calculations. The Al₂O₃/water nanofluid was produced by the direct-synthesis method with cationic chitosan dispersant served as the experimental sample, and was dispersed into three concentrations of 0.5, 1.0 and 1.5?wt.%. This experiment measures the density and specific heat of nanofluid with weight fractions and sample temperatures with a liquid density meter and a differential scanning calorimeter (DSC). To assess the availability of these equations, it then compares the experimental data with the calculated results according to the concepts of mixing theory and statistical mechanism. Comparing the calculated results of density and specific heat with the experimental data, the deviation of density fell within the range of ?1.50% to 0.06% and 0.25% to 2.53%, whereas the deviation of specific heat fell within the range of ?0.07% to 5.88% and ?0.35% to 4.94%, respectively. Calculated results of density and specific heat show a trend of greater deviation with an increased concentration of nanofluid. However, two kinds of density and specific heat of the calculated results fall within an acceptable deviation range in this study.     

Implications of Tc-Variation in UBe13 for a Possible Fulde–Ferrell–Larkin–Ovchinnikov Phase

We measure the heat capacity of a UBe₁₃ sample with an unusually low T _c for a polycrystal. We find an upturn in the upper critical field H _c2(T) below about T _c/2, much as for higher-T _c samples. Comparing the critical fields in our sample and in samples with higher T _c's shows that the low temperature limit of H _c2 is proportional to T _c(H = 0), as expected if the upturn comes from an FFLO phase and strong coupling.     

Synthesis and Characterization of CuNi Magnetic Nanoparticles by Mechano-Thermal Route

In the present investigation, Cu_0.5Ni_0.5 nanoparticles were synthesized using high energy ball milling of a mixture of Cu₂O, NiO, and graphite powders. The mixture of powders was milled up to 50 h. The 30 h milled sample was heat treated at various temperatures for 1 h in a vacuum tube furnace. The effects of milling time and heat treatment temperature on the powder particle characteristics were studied employing X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), differential thermal analysis (DTA), and vibrating sample magnetometer (VSM) techniques. XRD results indicated incomplete formation of Cu_0.5Ni_0.5 after 30 h of milling. Further heat treatment at 500 ^°C led to the formation of a single phase Cu_0.5Ni_0.5 powder. FESEM and TEM images of the heat treated sample showed spherical Cu_0.5Ni_0.5 nanoparticles with a mean particle size of 15 nm. Magnetic properties data measured by VSM of the above sample are correlated well with the XRD results. Coercivity and saturation magnetization have been approximately achieved at 25 Oe and 18 emu/g, respectively.     

Experiments with 4He Heated from Above, Very Near the Lambda Point

We report on new transport phenomena observed within a column of ⁴He heated from above and close to its transition to superfluidity. In this configuration the helium sample will self-organize to a state where the temperature gradient across the column remains equal to the pressure-induced gradient of T _λ (1.273 µK/cm) even as the heat flux is varied by a factor of about a thousand. On this self-organized state we have observed a new temperature-entropy wave that propagates opposite to the direction of a steady heat flux Q. This propagating mode is due to a non-linear temperature dependence of the thermoconductance of the helium near criticality. Such a mode had been predicted to exist in this state for Q less than about 100 nW/cm². We confirm that this mode exists in this regime, however we also observe that it propagates at higher values of Q, even when the helium is pushed away from the self-organized state into the normal state.     

Implications of T c-Variation in UBe13 for a Possible Fulde–Ferrell–Larkin–Ovchinnikov Phase

We measure the heat capacity of a UBe₁₃ sample with an unusually low T _c for a polycrystal. We find an upturn in the upper critical field H _c2(T) below about T _c/2, much as for higher-T _c samples. Comparing the critical fields in our sample and in samples with higher T _c's shows that the low temperature limit of H _c2 is proportional to T _c(H = 0), as expected if the upturn comes from an FFLO phase and strong coupling.     

Effect of two-step heat treatment on the phase formation of MgAlB14

Functional ceramics MgAlB₁₄ disks were prepared by a two-step heat treatment. In the first step, Mg₆AlB₁₄ disks were fabricated through composition of uniformly mixed Mg, Al, and B powders in the form of pressed disks heated at 850 °C in closed argon atmosphere. And in the second step, target MgAlB₁₄ disks were obtained by decomposition of the Mg₆AlB₁₄ disks sintered in vacuum. It has been found that the main peaks of MgAlB₁₄ were sharp except the common impurity-MgAl₂O₄ according to X-ray diffractions (XRD). The nano-hardness of the sample was about 11 GPa. And the heat treatment effects in the second step on the phase formation of MgAlB₁₄ were also studied.     

Specific heat of YBa2Cu3O7

Specific heat measurements, including measurements in magnetic fields and at both low temperatures and nearT _c , on a number of YBa₂Cu₃O₇ samples have revealed several correlations among strongly sample-dependent parameters. These correlations suggest that the sample dependence of the parameters reflects a sample dependence of the volume fraction of superconductivity, which is in turn correlated with a low concentration of Cu²⁺ moments. The correlations give a criterion for recognizing the values of the parameters characteristic of the fully superconducting material. Preliminary results on the effects of sample heat treatment are reported. New data on the “linear term” is presented and discussed.     

Microstructure observations on butt joint composed of Nb3Sn CIC conductors

To precisely evaluate a butt joint technology for the JT-60SA CS coils, microstructure observations on the butt joint composed of Nb₃Sn CIC conductors were conducted using a FE-SEM. As a sample for the observations, the butt joint sample utilized in the joint resistance measurement was used. During the sample fabrication, the butt joint sample was heated up to about 920 K from room temperature for diffusion bonding after heat treatment for Nb₃Sn production. Then, the sample was subjected to the cycles of electromagnetic force in the joint measurement.The observation results indicated that Nb₃Sn strands and a copper sheet were butted properly at the interface of the butt joint. In addition, there were hairline cracks in the Nb₃Sn layers of the strands near the interface. To investigate a cause of the crack initiation, the stresses generated in the butt joint under same conditions were analyzed using a simple model. As a result, the cracks would occur with an axial compressive stress generated by the butt joint fabrication.     

A sample-saving method for heat capacity measurements on powders using relaxation calorimetry

An experimental method is described for determining the low-temperature heat capacity (C_p) of mg-sized powder samples using the Quantum Design “Physical Properties Measurement System” (PPMS). The powder is contained in an Al pan as an ∼1 mm thick compressed layer. The sample is not mixed with Apiezon N grease, as compared to other methods. Thus, it is not contaminated and can be used for further study. This is necessary for samples that are only available in tiny amounts. To demonstrate the method various samples, all insulating in nature, were studied including benzoic acid, sapphire and different silicate minerals. The measurements show that the method has an accuracy in C_p to better than 1% at T above 30–50 K and ±3–5% up to ±10% below. The experimental procedure is based on three independent PPMS and three independent differential scanning calorimetry (DSC) measurements. The DSC C_p data are used to slightly adjust the PPMS C_p data by a factor . This is done because heat capacities measured with a DSC device are more accurate around ambient T (?0.6%) than PPMS values and is possible because the deviation of PPMS heat capacities from reference values is nearly constant between about 50 K and 300 K. The resulting standard entropies agree with published reference values within 0.21% for the silicates, by 0.34% for corundum, and by 0.9% for powdered benzoic acid. The method thus allows entropy determinations on powders with an accuracy of better than 1%. The advantage of our method compared to other experimental techniques is that the sample powder is not contaminated with grease and that heat capacity values show less scatter at high temperatures.     

Heat capacity and pressure at phase separation and solidification of3He in hcp4He

We have measured heat capacity and pressure of 0.45% and 0.9%³He-⁴He mixtures at pressures between 25 bar and 33 bar and temperatures between 20 mK and 250 mK. The data show the latent heats and the pressure changes associated with the phase separation (or remixing) and with the liquification (or solidification) of the resulting droplets in the hcp matrix. Above about 31 bar, the phase separation and the liquid-solid phase transition are separately observable. From these data, as well as from the heat capacity of the liquid droplets, we conclude that the droplets are filled with almost pure³He showing bulk behavior and that only a part of the separated³He is liquified. The amount of the liquid depends on the history of the sample. The phase separation is reproducible and lasted for many hours. In the pressure range of the hcp-L₁-L₂ univariant the sample moves along the univariant for a limited temperature range.     

The stability of Nb3Sn-composite conductors cooled by normal and superfluid helium

The stability of Nb₃Sn superconductors, which were additionally stabilized by soldering copper to the prereacted cable, was investigated. Cooling channels in a sample coil provided access to LHe in the 4.2 K and the 1.85 K temperature range. The measurements show that a heat flow rate of 0.6 W cm^?2 at 4.2 K in the Nb₃Sn composite conductor guarantees a stable operation even at local heat inputs of about 0.5 J onto the surface of the conductor. In superfluid helium, recovery up to the take-off values of current in magnetic fields between 8 T and 13 T was found. A theoretical analysis was performed to explain the experimental results with respect to the cooling channel geometry, magnetic fields, and the local energy inputs to initiate a normal conducting region.     

Bulk nanocrystalline Al85Ni10La5 alloy fabricated by spark plasma sintering of atomized amorphous powders

Amorphous Al₈₅Ni₁₀La₅ powders were consolidated to cylindrical samples by spark plasma sintering (SPS), and their microstructures and mechanical properties were investigated. When the powders were consolidated below the crystallization temperature, an amorphous phase was retained in the consolidated sample. Sintering above the crystallization temperature caused full crystallization. The Vickers hardness of the amorphous-containing sample was about 350 HV in the as-sintered state and increased up to 450 HV by a subsequent heat treatment just below the crystallization temperature. The highest hardness was achieved in a nanocrystalline microstructure. Compression tests revealed the brittle nature of the consolidated samples although the fracture and yield strength was higher than 1 GPa. The brittleness is due to the low relative density of the amorphous-containing samples and the presence of a large amount of intermetallic compounds in the fully crystallized sample.     

Ortho-para conversion of hydrogen in copper as origin of time-dependent heat leaks

It is shown that H₂ precipitated into bubbles in copper undergoes ortho-para conversion. This conversion, at a rate of about 2%/h, and the hydrogen content are detected quantitatively by the time-dependent heat release associated with them. The heating is comparable to the time-dependent heat leak observed in copper nuclear refrigerators. The amount of H₂ necessary to explain the data lies between 10 and 100 ppm. Due to its much smaller conversion rate and the smaller energy conversion, the heat released from D₂ in copper is essentially time independent fort<100 h and is up to two orders of magnitude smaller than the one for H₂.     

A Novel Method for Heat Capacity Measurements near 2K

We have constructed a calorimeter of novel design for high resolution heat capacity measurements near 2K. This device resembles high resolution paramagnetic salt thermometers used in previous heat capacity measurements on the ⁴ He-Vycor system. ² However, we have modified this thermometer so that our signal is no longer directly proportional to the temperature of the sample, but rather to the change in temperature with respect to time. We demonstrate the technique by measuring the heat capacity of paramagnetic gadolinium trichloride (GdCl ₃ ) salt near its critical temperature of 2.21K.     

Synthesis and Characterization of Cubic Omega-3-coated Cobalt Ferrite Nanoparticles

This research focuses on the synthesis and characterization of novel nanocomposite containing CoFe₂O₄ nanoparticles coated with omega-3. The omega-3 shell is a completely biocompatible. In this paper, cubic magnetic nanoparticles were synthesized by a simple one-step wet chemical method at room temperature. The product was characterized using standard techniques: X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and vibrating sample magnetometry (VSM). The results obtained from FTIR and TGA indicate that omega-3 was adsorbed onto the surface of the magnetic nanoparticles. With respect to the heat generation mechanisms such as relaxation and hysteresis, cobalt ferrite single-domain nanoparticles exhibit much larger specific power losses than superparamagnetic particles due to the high anisotropy constant. The synthesized nanocomposite has a saturation magnetization and a coercive field about 31.5 Am² kg^?1 and 1.2 × 10⁵ A m^?1, respectively. The coercivity of as-prepared nanocomposites is higher than that reported in previous works, so they are suitable for the aforementioned heat generation mechanism.     

Improvement of magnetic properties of nanostructured Ni79Fe16Mo5 alloyed powders by a suitable heat treatment

The supermalloy (Ni₇₉Fe₁₆Mo₅) nanostructured powder with average crystallite size of about 8 nm was prepared by high energy milling. The obtained powders were characterized by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry and vibration sample magnetometer. The results showed that the coercivity and the saturation magnetization reach about 8 Oe and 75 emu/g at 96 h and become approximately 1 Oe and 85 emu/g after a suitable heat treatment, respectively. The magnetic measurements confirmed that the supermalloy soft magnetic nanostructure powder was produced by mechanical alloying followed by a post heat treatment. The results revealed that a small amount of Mo element remain in the system up to 96 h due to (i) high fusion temperature, T_f = 2893 K, (ii) high mechanical hardness, (iii) low solubility of Mo into Ni at low temperatures in mechanical alloying conditions.     

A short note on the effect of sample size on the estimation error in Cp

Process capability indices such as C_p are used extensively in manufacturing industries to assess processes in order to decide about purchasing. In practice, the parameter for calculating C_p is rarely known and is frequently replaced with estimates from an in-control reference sample. This article explores the optimal sample size required to achieve a desired error of estimation using absolute percentage error of different C_p estimates. Moreover, some practical tools are created to allow practitioners to find sample size in different situations.