Aerodynamic Levitation Research Articles

Optical temperature sensing performance of Er3+/Yb3+ co-doped TiO2–ZrO2–La2O3 glasses

Er3+/Yb3+ co-doped TiO2–ZrO2–La2O3 glasses were prepared by aerodynamic levitation method. The transmittance spectrum shows that the transmittance of the glass before and after irradiation decreases from 75.46% to 71.13% in visible and near-infrared bands. The absorption and emission cross sections of the glasses at 525 nm were studied. The glasses were thermally treated at various temperatures and then investigated by x-ray diffraction, Scanning Electron Microscope and Transmission Electron Microscope. Optical spectra were measured as a function of temperature in the range of 298–498 K. The maximum relative sensitivity was determined to be 1.47% K−1 at 298 K. These results imply that the obtained glass may have the potential to be the matrix material for temperature sensing that requires to employed in a complex environment.

A tale of two cooling curves: Measuring heat capacity using aerodynamic levitation

Multiple-gas cooling method for aerodynamic levitation allows simultaneous solving of emissivity and heat capacity for liquid metals.

Multiple-gas cooling method for constant-pressure heat capacity measurement of liquid metals using aerodynamic levitator.

Until now, heat capacity measurements performed with levitation techniques have required accurate knowledge of the sample's emissivity beforehand. For a sample levitated using an aerodynamic levitator, it experiences both radiative and forced convective heat loss. The sample's emissivity only allows for the calculation of the radiative heat loss term, and a model has yet to be developed to accurately describe the total combined heat loss for aerodynamic levitation (ADL). In this study, we will introduce a novel multiple-gas cooling method for heat capacity measurement for ADL where two types of inert levitation gases (Ar and Kr) with different thermal conductivities were used to generate two cooling curves for the same sample. For samples being cooled at different cooling rates, the total heat loss is the same. The radiative heat loss was expressed using Stefan-Boltzmann's law, and the convective heat loss using Ranz-Marshall's equation. The two independent parameters (i.e., emissivity and heat capacity) of one given sample could then be solved using the two independent cooling curves. The heat capacities of gold, copper, nickel, iron, and palladium around the melting pointwere measured using this method. The multiple-gas cooling method for heat capacity measurement introduced in this study is the first heat capacity measurement method available for ADL and can be performed for materials with unknown emissivity. This newly developed method is important for the study of the thermophysical properties of high-temperature liquids, especially molten oxides with low electrical conductivity.

Luminescent properties of Er3+-doped La2O3–Ga2O3 glass prepared by aerodynamic levitation technique

Although silicon photonics has made great progress, there are still challenges to realization of modules or devices such as integrated light sources and amplifiers because of the indirect band gap nature of silicon. In this paper, we report a high concentration Er3+-doped La2O3–Ga2O3 glass for Er3+-doped waveguide amplifier (EDWA). The results show the xEr2O3–44La2O3-(56-x)Ga2O3 glasses prepared by the aerodynamic levitation (ADL) technique have high glass transition temperatures (Tg > 1000 K) and microhardness (HV ≥ 6.9 GPa), which means the glasses have high thermal stability and damage resistance. The Er3+ concentration in Er2O3–44La2O3-55Ga2O3 glass is as high as ~2.5 × 1020 cm−3, and the luminous intensity at NIR (~1550 nm) is ~10–100 times that of up-conversion and MIR. The small branching ratio β of the 4I11/2 → 4I13/2 transition (20.1 %), large radiative transition probabilities Arad for 4I13/2 → 4I15/2 transition (190.39 s−1), and low temperature sensitivity of luminescence make the glass an idea material for EDWA using in NIR band.

Glass forming regions, structure and properties of lanthanum barium germanate and gallate glasses

Glass forming regions in the system GaO3/2 – GeO2 – LaO3/2 – BaO have been explored using aerodynamic levitation coupled to laser heating synthesis technique. Structure property relationships have been established between the thermal and optical properties of the resulting glass thanks to Raman and Infrared vibrational spectroscopies. The germano-gallate glass networks are mainly made of three-dimensional interconnected corner shared GeO4 and GaO4 tetrahedra forming Ge – O – Ge and Ga – O− – Ge bridges in which gallium tetrahedral GaO4 units are charged-compensated by barium and lanthanum cations. In GeO2-rich compositions, the excess of positive charges produces mainly non-bridging oxygens on germanate moieties, leading to a depolymerization of the glass network. In the case of gallium rich compositions, the infrared cut-off is red-shifted as compared to the germanate glasses, in accordance with the disappearance of germanium associated entities such as germanium and gallium bridges or germanium sites with non-bridging oxygen both vibrating at higher wavenumber.

Heat capacity, entropy, configurational entropy, and viscosity of magnesium silicate glasses and liquids

In this work, five Mg-silicate glasses with compositions between MgSiO_3 and Mg_2SiO_4 were synthesized by aerodynamic levitation combined with laser melting. Low-temperature heat capacity (C_p) was measured (by relaxation calorimetry in the range 2–310 K) for all of them, with the resulting vibrational entropies at T = 298.15 K: sample MG50 with composition Mg_{0.996}SiO_{2.996} and entropy 72.88 J mol^{-1} K^{-1}; MG54 Mg_{1.174}SiO_{3.174} 78.54; MG58 Mg_{1.364}SiO_{3.364} 85.05; MG62 Mg_{1.611}SiO_{3.611} 91.40; and MG67 Mg_{1.907}SiO_{3.907} 102.75. Heat capacity of the glasses is higher than that of the corresponding crystal mixtures below 200 K but plunges below the C_{p,mathrm{crystal}} at higher temperatures. High-temperature C_p was measured (by differential scanning calorimetry in the range 300–970 K) for MG50 and MG67 up to approx 1000 K. Using our C_p data, selected data for entropies of fusion, C_p of crystals, and fictive temperatures, the configurational entropy (S_mathrm{conf}) at glass transition temperature (T_mathrm{g}) were calculated. For the near-forsterite glass MG67, the S_mathrm{conf} is 1.9 J mol^{-1} K^{-1} at T_mathrm{g} = 1040 K. As this small value is a difference of several large numbers, its uncertainty is relatively high; we consider a conservative estimate of 15 J mol^{-1} K^{-1}. Using the expression log eta = A + B/[T S_mathrm{conf}(T)], the available experimental viscosities (eta ) and the temperature-dependent configurational entropy from our work, we refined the parameters A = -2.34 and B = 76,500 for this equation, with S_mathrm{conf} (T) = 1.90+(83.7 ln (T/1040)). The configurational entropy for the enstatitic MG50 glass is 16.8 J mol^{-1} K^{-1} at T_mathrm{g} = 1063 K. The presented data can be combined with enthalpies of formation and thermophysical properties of Mg-silicate glasses for models that could elucidate geological and geophysical observations in the crust and mantle of the Earth.

On the phenomena of partial crystallization of highly undercooled magnesium silicate molten droplets

The present work reports real-time observations of the phenomena of partial crystallization of one of the glass-forming materials, namely enstatite (MgSiO3) from its supercooled liquid droplet. Initially, the molten droplet has been held under purely non-contact conditions using the aerodynamic levitation technique. The desired levels of undercooling have been achieved by deliberately making the levitated molten droplet touch a thin molybdenum wire and hence to initiate heterogeneous nucleation from the point of contact. Influence of thermal parameters like undercooling, cooling rates and recalescence on the process of crystallization is investigated. To understand and report the morphological properties and extent of crystallinity, the solidified enstatite samples have been characterized using optical/scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively, which confirmed the formation of partially crystallized enstatite spherules and fully glass spherules. XRD showed sharp peaks of enstatite, which confirm crystallinity and a halo profile confirms the amorphous phase of enstatite. Based on the observations of several experiments, we propose the effect of thermal parameters such as levels of undercooling and recalescence on the partial crystallization, as well as partial glass formation from the initially molten droplets of enstatite composition.

In situ synchrotron XRD measurements during solidification of a melt in the CaO–SiO2 system using an aerodynamic levitation system

Phase formation and evolution was investigated in the CaO–SiO2 system in the range of 70–80 mol% CaO. The samples were container-less processed in an aerodynamic levitation system and crystallization was followed in situ by synchrotron x-ray diffraction at the beamline P21.1 at the German electron synchrotron (DESY). Modification changes of di- and tricalcium silicate were observed and occurred at lower temperatures than under equilibrium conditions. Despite deep sample undercooling, no metastable phase formation was observed within the measurement timescale of 1 s. For the given cooling rates ranging from 300 K s−1 to about 1 K s−1, no decomposition of tricalcium silicate was observed. No differences in phase evolution were observed between reducing and oxidizing conditions imposed by the levitation gas (Ar and Ar + O2). We demonstrate that this setup has great potential to follow crystallization in refractory oxide liquids in situ. For sub-second primary phase formation faster detection and for polymorph detection adjustments in resolution have to be implemented.

Structure of levitated Si–Ge melts studied by high-energy x-ray diffraction in combination with reverse Monte Carlo simulations

The short-range order in liquid Si, Ge and binary Si x –Ge1−x alloys (x = 0.25, 0.50, 0.75) was studied by x-ray diffraction and reverse Monte Carlo simulations. Experiments were performed in the normal and supercooled liquid states by using the containerless technique of aerodynamic levitation with CO2 laser heating, enabling deeper supercooling of liquid Si and Si–Ge alloys than previously reported. The local atomic structure of liquid Si and Ge resembles the β-tin structure. The first coordination numbers of about 6 for all compositions are found to be independent of temperature indicating the supercooled liquids studied retain this high-density liquid (HDL) structure. However, there is evidence of developing local tetrahedral ordering, as manifested by a shoulder on the right side of the first peak in S(Q) which becomes more prominent with increasing supercooling. This result is potentially indicative of a continuous transition from the stable HDL β-tin (high pressure) phase, towards a metastable low-density liquid phase, reminiscent of the diamond (ambient pressure) structure.

Experimental investigation of elemental and isotopic evaporation processes by laser heating in an aerodynamic levitation furnace

Experimental investigation of elemental and isotopic evaporation processes by laser heating in an aerodynamic levitation furnace

Novel Method for Surface Tension Measurement: the Drop-Bounce Method

The surface tension of liquids at high temperatures is generally measured with the well-established oscillating drop method in a contactless environment. However, technical difficulties in surface tension measurements make it hard to apply the oscillating drop method to the aerodynamic levitation (ADL) system, the most reliable levitation technique for liquids with low electrical conductivity. In this study, we developed a novel drop–bounce method that can be used within an ADL system to measure the surface tension of liquids. A levitated molten sample was first dropped onto an inert substrate through a splittable nozzle. The rebounded sample’s oscillatory motion behaved as it would under microgravity conditions during its free-fall, and oscillations were obtained only in the l=2, m=0 mode. Fourier transformation of the oscillation pattern provided resonant frequency of the l=2, m=0 mode and enabled the calculation of the surface tension of the sample under knowledge of its mass. Furthermore, a short experimental duration of less than 50 ms significantly reduced the possibility of surface evaporation in the sample. Our measured surface tension data from 1354 K to 1827 K for gold exhibited a standard deviation of 13.4 mJ/m2 and were consistent with the data published by Egry et al. under microgravity conditions, with a maximum deviation of 1.5% between the two fitted linear equations.

Anti-corrosion LaO3/2-GaO3/2-ZrO2 infrared glasses with high refractive index and low dispersion prepared by aerodynamic levitation

LaO3/2-GaO3/2-ZrO2 ternary glasses have been prepared by aerodynamic levitation technique. The highest refractive index of glass system is 1.976 and the Abbe number of glass system reaches 49.9 for 30LaO3/2-62.5GaO3/2-7.5ZrO2 glass. Glasses have high transmittance of over 80% from ultraviolet light to the middle infrared light region. The maximum of infrared cutoff wavelength reaches to 10.6 μm. After ZrO2 doping, the acid corrosion resistance of glass is increased and the hardness of glass is improved from 7.14 GPa to 7.72 GPa ZrO2 adding increases the transforming temperature and crystallization temperature of glasses and improves the thermal stability of the glasses. The proper amount of ZrO2 doping improves the corrosion resistance, hardness, thermal and optical properties of the glass at the same time, which indicates that LaO3/2-GaO3/2-ZrO2 ternary glasses may have the potential to be used in a variety of endoscopes, especially those that need to be used in harsh environments.

Luminescent properties of doped amorphous and polycrystalline Y3Al5O12‐Al2O3

AbstractTransparent polycrystalline ceramics (TPCs) are crystalline materials with single‐crystal‐like transparency, which, however, have to rely on fabrication processes with a relatively high cost. Here, we produced lab‐scale TPCs based on the typical refractory Y2O3‐Al2O3 system, through full congruent crystallization of the parent glass prepared by aerodynamic levitation melting method. Doping of the glass and TPCs by rare‐earth (RE) ions (Ce3+, Tb3+, Nd3+, and Yb3+) and transition‐metal (TM) ions (Cr3+) results in strong visible and near‐infrared (NIR) photoluminescence with high quantum yield. The dominance of Stark splitting of the emission band for RE and TM ions in the TPCs as compared with that of the glass confirms crystallization of the parent glasses.

Morphological transition of silicate crystals solidified from highly undercooled aerodynamically levitated melt droplets

The present work reports the morphological transition during solidification of a non-metallic system. Pure magnesium silicate (Mg2SiO4) is chosen as the model material and the solidification experiments have been conducted under purely non-contact conditions using the principles of aerodynamic levitation. The influence of the undercooling and cooling rates on the surface features observed in the solidified samples is investigated. Levitation experiments have been performed for different samples, which are solidified for a range of undercooling levels between 360 to 1100° C. In order to understand and report the morphological transitions, solidified samples have been observed using scanning electron microscopy, which showed the formation of highly branched faceted microstructure for an undercooling regime of 360–800° C, and non-dendritic microstructure for even higher undercooling regime of 800–1100° C. Further experiments performed on this non-metallic system for different cooling rates also suggested that, regardless of the cooling rate, lower undercooling leads to branched faceted features, whereas higher undercooling results into unbranched facets. The methodology and instrumentation provide unique capabilities to probe the behavior of materials at high temperatures.

In situ pair distribution function analysis of crystallizing Fe-silicate melts

The structures of a series of Na2O–FeO–Fe2O3–SiO2 melts with Si/Fe = 1, 2, or 3 have been characterized via synchrotron X-ray total scattering using aerodynamic levitation, a containerless technique, paired with laser heating. The melt structure has been simulated using empirical potential structure refinement (EPSR) based on X-ray scattering data and molecular dynamics (MD) simulations with effective partial charge potentials. Pair distribution functions and coordination numbers of cations in the melt were obtained from the data refinement and from the MD simulations. Iron redox and accompanying density were modeled for each composition assuming either (1) oxidized (all Fe3+) or (2) reduced (some Fe2+) to the level predicted for the Ar levitator environment from a literature model. The actual redox of the melts appears to be intermediate, with some Fe2+ but not as much as assumed from the literature model of redox. Comparison of EPSR and MD models at the same redox conditions indicates generally good agreement, and precise values of coordination numbers depend sensitively on the assumptions for cutoff lengths. Stepwise cooling of each melt in the series resulted in formation of magnetite on the free surface of the sample, but no silica-containing crystalline phases were observed. This study provides a comprehensive assessment of coupled factors (composition, redox, density) needed to assess high-temperature in situ structural measurements of simplified iron silicates.

Development of a new method to measure surface tension of molten oxides

Physical properties of molten oxides such as viscosity and surface tension are important in various fields. However, it is very difficult to measure the properties of molten oxides owing to their high melting points, high reactivity, and high vapor pressure. Hence, the physical properties of molten oxides are scarcely reported. Therefore, we developed a new method, termed the �impingement method,� for measuring the surface tension of molten oxides in a very short time, using the aerodynamic levitation technique. In this work, we developed an apparatus for measuring the surface tension of molten Al2O3 and compared the value with that of other methods, considered as reference values. Results showed that the surface tension of molten Al2O3 was approximately 0.72 N/m at around 2500 K, which is close to the reference value; moreover, the measurements could be obtained in a very short time (approximately 80 ms). Thus, it is expected that the surface tension of molten materials with high vapor pressures such as ZrO2 and UO2 can be measured using this method.

Experiments to understand crystallization of levitated high temperature silicate melt droplets under low vacuum conditions

We report experiments on crystallization of highly undercooled forsterite melt droplets under atmospheric and sub-atmospheric pressure conditions. Experiments have been conducted under non-contact conditions using the principles of aero-dynamic levitation. Real time dynamics of solidification, along with the transient evolution of surface textures, have been recorded using high speed camera for three cooling rates. These images have been matched with the time-tagged temperature data to understand the effect of pressure conditions and cooling rates on the crystallization dynamics. Compared to normal pressure, relatively higher levels of undercooling could be achieved under sub-atmospheric conditions. Results showed a strong dependence of surface textures on pressure conditions. For any externally employed cooling rate, relatively small length scale morphological textures were observed under sub-atmospheric conditions, in comparison to those achieved under ambient conditions. The observed trends have been explained on the basis of influence of pressure conditions on recalescence phenomenon and the rate at which latent heat of crystallization gets dissipated from the volume of the molten droplet. Sub-atmospheric experiments have also been performed to reproduce one of the classical chondrule textures, namely the rim + dendrite double structure. Possible formation conditions of this double structure have been discussed vis-à-vis those reported in the limited literature. To the best of our knowledge, the reported study is one of the first attempts to reproduce chondrules-like textures from highly undercooled forsterite melt droplets under sub-atmospheric non-contact conditions.

Redox-structure dependence of molten iron oxides

The atomic structural arrangements of liquid iron oxides affect the thermophysical and thermodynamic properties associated with the steelmaking process and magma flows. Here, the structures of stable and supercooled iron oxide melts have been investigated as a function of oxygen fugacity and temperature, using x-ray diffraction and aerodynamic levitation with laser heating. Total x-ray structure factors and their corresponding pair distribution functions were measured for temperatures ranging from 1973 K in the stable melt, to 1573 K in the deeply supercooled liquid region, over a wide range of oxygen partial pressures. Empirical potential structure refinement yields average Fe–O coordination numbers ranging from ~4.5 to ~5 over the region FeO to Fe2O3, significantly lower than most existing reports. Ferric iron is dominated by FeO4, FeO5 and FeO6 units in the oxygen rich melt. For ferrous iron under reducing conditions FeO4 and FeO5 units dominate, in stark contrast to crystalline FeO.

Optical properties and luminescence of Er3+/Yb3+ co-doped La2O3–Nb2O5–Ga2O3 glasses prepared by aerodynamic levitation method

40La2O3–20Nb2O5–40Ga2O3 and xYb2O3–5Er2O3–(35-x) La2O3–20Nb2O5–40Ga2O3 (x = 0, 1, 5, 10) spherical transparent glasses were prepared by aerodynamic levitation method. Upconversion and near-infrared luminescence characteristics have been studied. Moreover, the thermal, mechanical, refractive index, transmittance properties of the glasses have also been discussed. Hardness and density of the glasses increase with the increase of Yb3+ concentration. The hardness of all samples are above 8.4 GPa, and density increase from 5.2504 g/cm3 to 5.817 g/cm3. The blank LNG glass has a refractive index of 2.0217 and Abbe number of 88.84, which is an excellent glass with high refractive index and low dispersion. Through DTA analysis, it is found that this series of glasses has excellent thermal stability. The glasses transition temperature (Tg) is about 800 °C. With the increase of Yb3+ concentration, Tg does not change obviously, but the crystallization initial temperature To and △T (△T = To−Tg) increase at first and then decrease. Upconversion fluorescence spectra show that green and red emission bands of 551 nm, 558 nm and 674 nm are obtained under the pump of 980 nm laser, which are two-photon emission processes. And in the near infrared region, the near-infrared emission with the emission center at 1559 nm is obtained, which corresponds to the transition from 4I13/2–4I15/2 of Er3+. The full width at half maximum (FWHM) of the prepared samples is about 120 nm, which is larger than that of ordinary glass. At the same time, with the increase of Yb3+ concentration, the change trend of fluorescence lifetime is consistent with that of near-infrared emission intensity.

Synthesis and crystallization kinetics of Y2CaAl4SiO12 garnet-type glass-ceramic

Y2CaAl4SiO12 garnet-type glass-ceramic was obtained by heat-treatment of the bulk glass with corresponding composition, which fabricated by aerodynamic levitation coupled with a laser heating system. The crystallization kinetics of the glass was investigated via Differential Scanning Calorimetry (DSC). The effects of heat-treatment temperature on the phase, microstructure, mechanical and optical properties of the Y2CaAl4SiO12 garnet-type glass-ceramic were also systemically studied. The crystallization mechanism of this Y2CaAl4SiO12 glass is three-dimensional growth followed with surface and inner nucleation. With the increasing of heat-treatment temperature, the density and hardness increased, while transparency declined as a result of rapid grain growth.