Effect of the method for producing $$\hbox {}$$–$$\hbox {Cr}_{3}\hbox {C}_{2}$$Cr3C2 bulk composites on the structure and properties

Copper–chromium carbide composites containing a carbide phase of 20–30 vol% were obtained with the use of solid- and liquid-phase mechanosyntheses, followed by magnetic pulse compaction (MPC) and spark plasma sintering. The morphology, structural-phase composition, density, hardness and electrical conductivity of the composites were investigated. The structure of composites obtained by MPC represents regions of copper matrix hardened by superfine carbide precipitates surrounded by a layer of chromium carbide. In the composites obtained by spark plasma sintering, the copper matrix hardened by superfine carbide precipitates was divided into areas surrounded by a copper–chromium layer. A composite obtained by the MPC of the powders synthesized using solid-phase mechanosynthesis (MS) (copper, chromium and graphite) had the highest values of Vickers microhardness (4.6 GPa) and Rockwell hardness (HRA 69). The best value of electrical conductivity (36% IACS) was achieved using liquid-phase MS (copper, chromium and xylene) and spark plasma sintering. Liquid-phase MS is the only way to synthesize the powder with a small amount of the carbide phase and without contamination.     

Crystal structure,thermal behaviour,vibrational spectroscopy and optical properties of new compounds K$$_{}$$Ca(HAsO$$_{4}$$4)$$_{}\cdot $$·H$$_{}$$O with kröhnkite-type chain

The new kröhnkite compound called potassium calcium-bis-hydrogen arsenate dihydrate K\(_{2}\)Ca(HAsO\(_{4})_{2}\cdot \)2H\(_{2}\)O was obtained by hydrothermal method and characterized by X-ray diffraction, infrared spectroscopy, Raman scattering, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis and optical (photoluminescence and absorption) properties. It crystallizes in the triclinic space group P\(\bar{1}\) and unit cell parameters \(a = 5.971(3)\) Å, \(b =6.634(3)\) Å, \(c = 7.856(4)\) Å, \(\alpha =104.532(9)\) \(^{\circ }\), \(\beta = 105.464(9)\) \(^{\circ }\) and \(\gamma = 109.698(9)\) \(^{\circ }\). The structure of K\(_{2}\)Ca(HAsO\(_{4})_{2}\cdot \)2H\(_{2}\)O built up from this infinite, (Ca(HAsO\(_{4})_{2}\)(H\(_{2}\)O)\(_{2})^{2+}\), was oriented along an axis resulting from the association of CaO\(_{6}\) octahedra alternating with each two HAsO\(_{4}\) tetrahedra by sharing corners. Each potassium atom links two adjacent chains by three oxygen atoms of HAsO\(_{4}\) tetrahedra. TGA and DSC have shown the absence of phase transition. The existence of vibrational modes corresponding to the kröhnkite is identified by the IR and Raman spectroscopies in the frequency ranges of 400–4000 and 20–4000 cm\(^{-1}\), respectively. The photoluminescence measurement show one peak at 507 nm, which is attributed to band–band (free electron–hole transitions) and (bound electron–hole transitions) emissions within the AsO\(_{4}\) inorganic part.     

Thermodynamic Investigation of the Eutectic Mixture of the $$\hbox {LiNO}_{3}$$–$$\hbox {NaNO}_{3}$$NaNO3–$$\hbox {KNO}_{3}$$KNO3–$$\hbox {Ca}(\hbox {NO}_{3})_{2}$$Ca(NO3)2 System

Molten nitrate salt is usually employed as heat transfer or energy storage medium in concentrating solar power systems to improve the overall efficiency of thermoelectric conversion. In the present work, the liquidus curves of the \(\hbox {LiNO}_{3}\)–\(\hbox {NaNO}_{3}\)–\(\hbox {KNO}_{3}\)–\(\hbox {Ca}(\hbox {NO}_{3})_{2}\) system is determined by conformal ionic solution theory according to the solid–liquid equilibrium state of the binary mixture. The calculated eutectic temperature of the mixture is \(93.17\,{^{\circ }}\hbox {C}\), which is close to the experimental value of \(93.22\,{^{\circ }}\hbox {C}\) obtained from differential scanning calorimetry (DSC). Visualization observation experiments reveal that the quaternary eutectic mixture begins to partially melt when the temperature reaches \(50\,{^{\circ }}\hbox {C}\), and the degree of melting increases with temperature. The mixture is completely melted at \(\hbox {130}\,{^{\circ }}\hbox {C}\). The observed changes in the dissolved state at different temperatures correlate well with the DSC heat flow curve fluctuations.     

Enhanced infrared transmission characteristics of microwave-sintered $$\hbox {Y}_{2}\hbox {O}_{3}$$–$$\hbox {MgO}$$MgO nanocomposite

Infrared (IR) transparent ceramics are found to have applications in demanding defence and space missions. In this work, \(\hbox {Y}_{2}\hbox {O}_{3}\)–\(\hbox {MgO}\) nanocomposites were synthesised by a modified single-step combustion technique. The characterisation of the as-prepared powder by X-ray diffraction and transmission electron microscopy revealed the presence of cubic phases of ultra-fine nanostructured \(\hbox {Y}_{2}\hbox {O}_{3 }\) and MgO, with an average crystallite size of \({\sim }19 \hbox { nm}\). For the first time the resistive and microwave heatings were effectively coupled for sintering the sample, and it was found that the sintering temperature and soaking time were reduced considerably. The pellets were sintered to 99.2% of the theoretical density at \(1430{^{\circ }}\hbox {C}\) for a soaking duration of 20 min. The well-sintered pellets with an average grain size of \({\sim }200 \hbox { nm}\) showed better transmittance properties relative to pure yttria. The promising percentage transmission of 80% in the UV–visible region and 82% in the mid-IR region shown by \(\hbox {Y}_{2}\hbox {O}_{3}\)–\(\hbox {MgO}\) nanocomposites can be tailored and made cost-effective to fabricate high-quality IR windows for strategic defence and space missions.     

Synthesis and luminescence in sol–gel auto-combustion-synthesized $$\hbox {CaSnO}_{3}{:}\hbox {Eu}^{3+}$$ phosphor

Undoped and Eu-doped \(\hbox {CaSnO}_{3}\) nanopowders were prepared by a facile sol–gel auto-combustion method calcined at \(800{^{\circ }}\hbox {C}\) for 1 h. The samples are found to be well-crystallized pure orthorhombic \(\hbox {CaSnO}_{3}\) structure. Photoluminescence (PL) measurements indicated that the undoped sample exhibits a broad blue emission at about 420–440 nm, which can be recognized from an intrinsic centre or centres in \(\hbox {CaSnO}_{3}\). Eu-doped \(\hbox {CaSnO}_{3}\) showed broad blue emission centred about 434 nm, a weak peak at 465 nm and a sharp intense yellow emission line at 592 nm. The emission situated at 592 nm was assigned to the f–f transition of \(^{5}\hbox {D}_{0}\rightarrow ^{7}\hbox {F}_{1}\) in \(\hbox {Eu}^{3+}\) ions. The afterglow emission and PL decay results in Eu-doped \(\hbox {CaSnO}_{3}\) phosphor, which revealed that there are at least two different traps in this phosphor. From the obtained results, \(\hbox {Eu}^{3+}\)-doped \(\hbox {CaSnO}_{3}\) phosphor could be proposed as a potential white luminescent optical material.     

The Precise Measurement of Vapor–Liquid Equilibrium Properties of the CO$$_{}$$/Isopentane Binary Mixture,and Fitted Parameters for a Helmholtz Energy Mixture Model

Natural working fluid mixtures, including combinations of CO\(_{2}\), hydrocarbons, water, and ammonia, are expected to have applications in energy conversion processes such as heat pumps and organic Rankine cycles. However, the available literature data, much of which were published between 1975 and 1992, do not incorporate the recommendations of the Guide to the Expression of Uncertainty in Measurement. Therefore, new and more reliable thermodynamic property measurements obtained with state-of-the-art technology are required. The goal of the present study was to obtain accurate vapor–liquid equilibrium (VLE) properties for complex mixtures based on two different gases with significant variations in their boiling points. Precise VLE data were measured with a recirculation-type apparatus with a 380 cm\(^{3}\) equilibration cell and two windows allowing observation of the phase behavior. This cell was equipped with recirculating and expansion loops that were immersed in temperature-controlled liquid and air baths, respectively. Following equilibration, the composition of the sample in each loop was ascertained by gas chromatography. VLE data were acquired for CO\(_{2}\)/ethanol and CO\(_{2}\)/isopentane binary mixtures within the temperature range from 300 K to 330 K and at pressures up to 7 MPa. These data were used to fit interaction parameters in a Helmholtz energy mixture model. Comparisons were made with the available literature data and values calculated by thermodynamic property models.     

Thermal Properties of Jojoba Oil Between $$20\,{^{\circ }}\hbox {C}$$ and $$45\,{^{\circ }}\hbox {C}$$45∘C

Vegetable oils have been widely studied as biofuel candidates. Among these oils, jojoba (Simmondsia chinensis) oil has attracted interest because it is composed almost entirely of wax esters that are liquid at room temperature. Consequently, it is widely used in the cosmetic and pharmaceutical industries. To date, research on S. chinensis oil has focused on to its use as a fuel and its thermal stability, and information about its thermal properties is scarce. In the present study, the thermal effusivity and conductivity of jojoba oil between \(20\,{^{\circ }}\hbox {C}\) and \(45\,{^{\circ }}\hbox {C}\) were obtained using the inverse photopyroelectric and hot-ball techniques. The feasibility of an inverse photopyroelectric method and a hot-ball technique to monitor the thermal conductivity, and the thermal effusivity of the S. chinensis is demonstrated. The thermal effusivity decreased from 538 \(\hbox {W}\cdot \,\hbox {s}^{1/2}\cdot \,\hbox {m}^{-2}\cdot \,\hbox {K}^{-1}\) to 378 \(\hbox {W}\cdot \,\hbox {s}^{1/2}\cdot \,\hbox {m}^{-2}\cdot \,\hbox {K}^{-1}\) as the temperature increased, whereas the thermal conductivity remained the same over the temperature range investigated in this study. The obtained results provide insight into the thermal properties of S. chinensis oil between \(20\,{^{\circ }}\hbox {C}\) and \(45\,{^{\circ }}\hbox {C}\).     

Dissociation reaction of the 1/3$$ \left\langle {\bar{1}101} \right\rangle $$ edge dislocation in α-Al2O3

It has been reported that dislocations with 1/3\( \left\langle {\bar{1}101} \right\rangle \) edge component of the Burgers vector are formed in {1\( \bar{1} \)04}/\( \left\langle {11\bar{2}0} \right\rangle \) low-angle grain boundaries of alumina (α-Al₂O₃). These dislocations dissociate into two partial dislocations with a stacking fault on the (0001) plane (Tochigi et al. in J Mater Sci 46:4428–4433, 2011). However, the dissociation reaction of these dislocations has not been determined so far. In this study, the structures of the dissociated dislocations and the (0001) stacking fault were investigated by transmission electron microscopy and theoretical calculations. It was revealed that the dissociated dislocations were generated from the 1/3\( \left\langle {\bar{1}101} \right\rangle \) perfect edge dislocation by the reaction of 1/3\( \left\langle {\bar{1}101} \right\rangle \) → 1/18\( \left\langle {\bar{4}223} \right\rangle \) + 1/18\( \left\langle {\bar{2}4\bar{2}3} \right\rangle \). Furthermore, electron energy loss spectroscopy analysis was performed to examine the atomic/electronic structure of the (0001) stacking fault. In the observed spectra, a chemical shift and intensity decrease were found at the oxygen K-edge. Theoretical spectrum analysis using first-principles calculations revealed that the characteristic features of the spectra are originated from the local atomic configurations of the (0001) stacking fault.     

Synthesis of $$\hbox {Ag}_{2}\hbox {Se}$$–graphene–$$\hbox {TiO}_{2} $$TiO2 nanocomposite and analysis of photocatalytic activity of $$\hbox {CO}_{2}$$CO2 reduction to $$\hbox {CH}_{3}\hbox {OH}$$CH3OH

The present work deals with the development of a new ternary composite, \(\hbox {Ag}_{2}\hbox {Se}\)–\(\hbox {G}\)–\(\hbox {TiO}_{2}\), using ultrasonic techniques as well as X-ray diffraction (XRD), scanning electron microscopy (SEM), high transmission electron microscopy (HTEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and UV–Vis diffuse reflectance spectra (DRS) analyses. The photocatalytic potential of nanocomposites is examined for \(\hbox {CO}_{2}\) reduction to methanol under ultraviolet (UV) and visible light irradiation. \(\hbox {Ag}_{2}\hbox {Se}\)–\(\hbox {TiO}_{2}\) with an optimum loading graphene of 10 wt% exhibited the maximum photoactivity, obtaining a total \(\hbox {CH}_{3}\hbox {OH}\) yield of 3.52 \(\upmu \hbox {mol}\,\hbox {g}^{-1}\,\hbox {h}^{-1}\) after 48 h. This outstanding photoreduction activity is due to the positive synergistic relation between \(\hbox {Ag}_{2}\hbox {Se}\) and graphene components in our heterogeneous system.     

Radiative Properties of Ceramic $$\hbox {Al}_{2}\hbox {O}_{3}$$, AlN and $$\hbox {Si}_{3}\hbox {N}_{4}$$Si3N4—II: Modeling

In Part I of this study (Cheng et al. in Int J Thermophys 37: 62, 2016), the reflectance and transmittance of dense ceramic plates were measured at wavelengths from 0.4 \(\upmu \hbox {m}\) to about 20 \(\upmu \hbox {m}\). The samples of \(\hbox {Al}_{2}\hbox {O}_{3}\) and AlN are semitransparent in the wavelength region from 0.4 \(\upmu \hbox {m}\) to about 7 \(\upmu \hbox {m}\), where volume scattering dominates the absorption and scattering behaviors. On the other hand, the \(\hbox {Si}_{3}\hbox {N}_{4}\) plate is opaque in the whole wavelength region. In the mid-infrared region, all samples show phonon vibration bands and surface reflection appears to be strong. The present study focuses on modeling the radiative properties and uses an inverse method to obtain the scattering and absorption coefficients of \(\hbox {Al}_{2}\hbox {O}_{3}\) and AlN in the semitransparent region from the measured directional-hemispherical reflectance and transmittance. The scattering coefficient is also predicted using Mie theory for comparison. The Lorentz oscillator model is applied to fit the reflectance spectra of AlN and \(\hbox {Si}_{3}\hbox {N}_{4}\) from 1.6 \(\upmu \hbox {m}\) to 20 \(\upmu \hbox {m}\) in order to obtain their optical constants. It is found that the phonon modes for \(\hbox {Si}_{3}\hbox {N}_{4}\) are much stronger in the polycrystalline sample studied here than in amorphous films reported previously.     

Solidification of NaCl–LiF–$$\hbox {CaF}_{2}$$ ternary composites

The purpose of this work is to refine the microstructure of eutectic halides, candidates to polaritonic metamaterials, through the directional solidification of ternary compositions. NaCl–LiF–\(\hbox {CaF}_{2}\) ternary composites have been solidified using Bridgman and micro-pulling-down techniques at pulling rates from 3 to 300 mm/h for the first time. The interparticle spacing is 12% smaller for this composition than for the binary fibrous NaCl–LiF eutectic. Conditions for solidification and growth in order to generate ternary aligned microstructures are discussed. The very small amount of melt remaining in the mixtures until \(580\,^{\circ }\hbox {C}\) is probably the consequence of solid solubility of LiCl in NaCl and the formation of the reciprocal salt pairs, as in NaCl–LiF. However, it does not prevent the solidification of homogenous ternary microstructures.     

Reversibility of the $$\beta \rightleftharpoons \alpha $$ phase transformations in a Pd–Cu solid solution

Thin samples (about 4 μm in thickness) of membrane foil of a Pd–Cu solid solution have been grown on the surface of a SiO₂/Si heterostructure by magnetron sputtering. The key features of \(\beta \rightleftharpoons \alpha \) phase transformations have been identified using X-ray diffraction, Auger electron spectroscopy, energy dispersive X-ray microanalysis, and resistivity measurements during a heating–cooling cycle. The results demonstrate that the phase transformations are reversible only in solid solutions containing an excess of copper in the concentration range corresponding to limiting temperatures near the temperature stability limit of the β-phase. Thermal conditions of membrane element operation have been found that ensure stability of the ordered atomic structure of the foil and, accordingly, its high performance. The \(\beta \rightleftharpoons \alpha \) phase transformation has been shown to be reversible after holding the foil at t = 830°C, in a state with a disordered atomic structure, which ensures restoration of its high hydrogen permeability after diffusion bonding to the case of a membrane element.     

Cavitation Bubbles Generated by Vibrating Quartz Tuning Fork in Liquid $$^$$He Close to the $$\lambda $$λ-Transition

We report direct optical observation of cavitation bubbles in liquid helium, both in classical viscous He I and in superfluid He II, close to the \(\lambda \)-transition. Heterogenous cavitation due to the fast-flowing liquid over the rough surface of prongs of a quartz tuning fork oscillating at its fundamental resonant frequency of \(4\,\mathrm {kHz}\) occurs in the form of a cluster of small bubbles rapidly changing its size and position. In accord with previous investigators, we find the cavitation threshold lower in He I than in He II. In He I, the detached bubbles last longer than one camera frame (10 ms), while in He II the cavitation bubbles do not tear off from the surface of the fork up to the highest attainable drive.     

Process optimization of dye-sensitized solar cells using $$\hbox {TiO}_{2}$$–graphene nanocomposites

\(\hbox {TiO}_{2}\)–graphene (TGR) nanocomposites with varying concentrations of graphene from 0 to 1 wt% were prepared by direct mix method. X-ray diffraction (XRD) spectra confirmed the incorporation of graphene in photoanode material, which was further supported by field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX). The UV–visible spectrum of these nanocomposites shifted towards higher wavelength region as compared to pure \(\hbox {TiO}_{2}\) that indicated a reduced band gap and hence, enhanced absorption bandwidth. Significant reduction in electron–hole recombination was confirmed from photoluminescence spectroscopy. These TGR nanocomposite films after tethering with black dye were employed as photoanodes in dye-sensitized solar cells (DSSCs). The efficiency of solar cells at varying concentrations of graphene (in photoandes) was also investigated. TGR 0.25 wt% nanocomposite showed the highest photocurrent density (\(J_{\mathrm{SC}}\)) of \(18.4\,\hbox {mA}\,\hbox {cm}^{-2}\) and efficiency (\(\eta \)) of 4.69%.     

Momentum Distribution of Liquid $$^{}$$He Across the Normal–Superfluid Phase Transition

We have carried out a study of the momentum distribution and of the spectrum of elementary excitations of liquid \(^4\)He across the normal–superfluid transition temperature, using the path integral Monte Carlo method. Our results for the momentum distribution in the superfluid regime show that a kink is present in the range of momenta corresponding to the roton excitation. This effect disappears when crossing the transition temperature to the normal fluid, in a behavior currently unexplained by theory.     

Optimization of the liquid–liquid interfacial precipitation method for the synthesis of $$\hbox {C}_{60}$$ nanotubes

Tubular fullerene nanowhiskers called ‘fullerene nanotubes’ are composed of \(\hbox {C}_{60}\) fullerene molecules (\(\hbox {C}_{60}\) NTs) are synthesized at room temperature using the liquid–liquid interfacial precipitation method in the pyridine and isopropyl alcohol (IPA) system. The growth control of fullerene nanotubes is important for their chemical and physical properties as well as for their future applications. In the present study, we investigated the effect of light, water, solvent ratio and temperature on the synthesis of \(\hbox {C}_{60}\) nanotubes. A marked development in the yield of \(\hbox {C}_{60}\) NTs was achieved using dehydrated solvents, a solution with a volume ratio of 1:9 for pyridine: IPA, a growth temperature equal to \(5{^{\circ }}\hbox {C}\) and by illuminating the \(\hbox {C}_{60}\)-pyridine solution with ultraviolet light (wavelength 302 nm) for 102 h. The synthesized fullerene nanotubes were characterized by different analytical techniques including Raman and Fourier transform infrared spectroscopy, optical microscopy, focussed ion beam scanning electron microscopy and transmission electron microscopy.     

Photoacoustic Spectroscopic Study of Optical Properties of $$\hbox {Cu}_{2}\hbox {GeTe}_{3}$$ in Temperature Range from 80 K to 300 K

We used photoacoustic spectroscopy to investigate the optical properties of \(\hbox {Cu}_{2}\hbox {GeTe}_{3}\). The temperature dependence of the bandgap energy was evaluated from optical absorption spectra obtained in the photon energy range of 0.76 eV to 0.81 eV between 80 K and 300 K. We used the empirical and semi-empirical models of Varshni, Viña, and Pässler to describe the observed bandgap shrinkage in this compound. The Debye temperature and effective phonon temperature of the compound were estimated to be approximately 227.4 K and 151.6 K, respectively. Thus, the temperature dependence of the bandgap is mediated by acoustic phonons.     

Hysteresis and Instability in Some IPRT Sensors Within Temperature Ranges Extending from $$-196\,^{\circ }\hbox {C}$$ to $$150\,^{\circ }\hbox {C}$$150∘C

Industrial platinum resistance thermometer (IPRT) sensors or probes suffer from some instability on cycling over significant ranges of temperature and, specifically, from hysteresis in which the resistance tends to follow different paths for increasing temperatures compared with decreasing temperatures. The effect is well known, and cases of quite large hysteresis have been reported in the literature. Therefore, in establishing calibration and measurement capabilities for IPRT calibrations it is important to include an assessment of the performance which can be expected of a ‘typical good’ IPRT and to include this in the overall uncertainty which the laboratory can expect to achieve in such calibrations, even though the effect itself is outside the laboratory’s control. This paper presents results which have been obtained in cycling IPRT probes from four sources within various temperature ranges of current interest at NPL, between \(-196\,^{\circ }\hbox {C}\) and \(150\,^{\circ }\hbox {C}\), to see what levels of hysteresis may be expected. The cycles were carried out quite quickly in order to detect the hysteresis before it was mitigated by relaxation effects, but the time dependence was not itself studied. In most cases, hysteresis was \({<}0.0025\,^{\circ }\hbox {C}\) between \(0\,^{\circ }\hbox {C}\) and \(100\,^{\circ }\hbox {C}\), and \({<}0.0035\,^{\circ }\hbox {C}\) when the range extended down to \(-80\,^{\circ }\hbox {C}\) or up to \(150\,^{\circ }\hbox {C}\). Greater instability occurred when the sensors were cooled to \(-196\,^{\circ }\hbox {C}\).