Mirror Furnace Research Articles

Analysis of the melting and solidification process of aluminum in a mirror furnace using Fiber-Bragg-Grating and numerical models

In the search of an adequate real time strain measurement method in aluminum casting, the use of Fiber-Bragg-Grating (FBG) is being investigated with great interest. In order to do so, the behaviour of glass fiber sensors in a liquid aluminium alloy at temperatures up to 750°C is experimentally analysed in a laboratory environment. For better process understanding a simulation of the fiber alloy composite is conducted. FBG is an optical measurement method, which uses engraved Bragg reflectors in a 125 µm in diameter thick glass fiber. This reflector transmits most of the wavelengths but only reflects one specific wavelength. This specific wavelength can be measured and changes due to the axial strain on the grating by the fluid alloy reaction and by the changes in temperature. Using a so-called mirror furnace, several experiments with the fiber alloy composite are evaluated. These measurements are also the basis for the further understanding of hot tearing. The data gathered during the measurement campaign - both numerical and experimental - is used to parameterize a simulation. As a result, the understanding of the fiber alloy composite behaviour is expanded and a digital twin is modeled with MATLAB’s partial differential equation toolbox.

Effect of synthesis method on the structural behavior of CaFeO2.5 compound

CaFeO2.5 samples were synthesized by solid solution, mirror furnace and Sol-gel methods. The effect of the synthesis method on the behavior structure was investigated. Phase structures are comparatively characterized and studied by means of X-ray powder diffraction. Experimental results have revealed that the synthesis method has a strong influence on the structure of the studied compounds. All samples obtained by the three methods are crystallized in the Pnma orthorhombic system. We obtained the best results in the case of the Sol-gel technique. In the Sol-gel method, the lattice parameters obtained are a=5.41631 Å, b= 14.73899 Å and c=5.58790 Å. Also, the value of the average crystallite size D=52.03 nm and the dislocation density δ=3.69x1010/cm². Since the values ​​of the lattice parameters in this method were the smallest of the three methods, which exhibiting a weak shrink of the volume compared to the solid solution and mirror furnace one. This shrinking is a natural result of the decrease in the value of the average crystallite size and the increase of dislocation density, with a reason for the inverse relationship between them. This allows us to conclude the importance of the Sol-gel method for obtaining CaFeO2.5 nanoscale compound.

A Method for Characterising the Influence of Casting Parameters on the Metallurgical Bonding of Copper and Steel Bimetals.

Traditional casting technology offers two mayor drawbacks towards research activities. On the one hand, time and resources needed for every casting are rather high. The mould has to be able to withstand the high temperatures introduced by the melt and provide cooling for the cast part. Preparation and installation of measuring equipment therefore takes time. Additionally, due to the high mass of the mould when compared to the cast part, parameter variations are rather limited in their resulting effect on the temperature-time profile being one of the most prominent factors regarding cast quality. Especially when pouring by hand, variations in casting times and rates superimpose effects created intentionally. Therefore, a different process was advanced and evaluated, allowing to minimise some of the drawbacks mentioned before. The key idea is to drastically reduce casting size to the dimensions of one specimen and to apply a highly automated production route. As such, a mirror furnace was modified as to allow the processing of melt. Due to the specimens size, an adaption of mechanical testing equipment was performed and evaluated. As an example, copper-iron bimetal specimens were examined by light microscopy, micro hardness testing, nanoindentation as well as tensile and torsion testing. As the results were consistent, the newly introduced method can be applied successfully in casting research. This allows for highly reproducible results, reducing the uncertainty of temperature measurements of a specimen due to the distance between them. The possibility of separating influencing variables like maximum temperature and cooling rate allows an analysis of the casting process, which would require different moulds to do so in traditional casting methods. The next steps will be directed at a broader variety of metals processed and at a direct comparison between the new process route and traditional casting technology.

In1-xGa1+xO3(ZnO)0.5: Synthesis, structure and cation distribution

Crystals of the quaternary compound In1-xGa1+xO3(ZnO)0.5 were grown by the optical floating-zone method using a mirror furnace with halogen lamps as heat source. X-ray diffraction (XRD) and electron diffraction yielded a hexagonal crystal system and the space group P63/mmc (No. 194). Structure refinement from single crystal XRD data at −90 °C (a ​= ​3.3137(1) Å; c ​= ​29.523(1) Å; wR2: 0.054) revealed a structure isotypic to YbFeO3(FeO)0.5 and consists of three different alternating layers: (i) layer of edge-sharing InO6 octahedra, (ii) a pair of two layers of corner-sharing (Ga/Zn)O4 tetrahedra corresponding to wurtzite structure type, and (iii) a layer of GaO5 trigonal-bipyramids (tbp). The polyhedra of layers (ii) and (iii) share corners with the InO6 octahedra, resulting in inverted orientations of the two (Ga/Zn)O4 layers in the wurtzite type region. Additionally, atomic resolution imaging in the electron microscope proves a perfect periodic stacking of the atomic layers. The analysis of individual crystals revealed an excess of Ga expressed by the composition range In1-xGa1+xO3(ZnO)0.5 with 0.20 ​≤ ​x ≤ 0.82, determined by energy dispersive X-ray spectroscopy (EDXS). Consequently, the octahedral site is occupied with In and Ga in a ratio of In:Ga ​= ​0.80:0.20 to 0.18:0.82, assuming that the tbp sites are only occupied by Ga. The transparent crystals as-received from floating-zone growth had a blueish color and became colorless after annealing at 1000 ​°C for 10 ​h in air. The as-prepared crystals are oxygen deficient and contain unpaired electrons (color centers) at vacant oxide sites proven by electron paramagnetic resonance with g-value of ca. 2.

Single crystal growth of BaZrO3 from the melt at 2700 °C using optical floating zone technique and growth prospects from BaB2O4 flux at 1350 °C

Growth of BaZrO3 crystals at 2700 °C in a mirror furnace and growth prospects at 1350 °C using BaB2O4 flux are reported.

Radiation induced luminescence properties of Ce-doped Y2O3-Al2O3-SiO2 glass prepared using floating zone furnace

We synthesized Y2O3-Al2O3-SiO2 glasses doped with various concentrations of Ce (0, 0.03%, 0.10%, 0.30%, and 1.00%). The glasses were obtained by melt-quenching using an IR mirror furnace, and then they were studied in terms of their optical, dosimetric and scintillation properties. The obtained samples indicated photoluminescence (PL) and scintillation due to the 5d–4f transitions of Ce3+ characterized as a broad emission peaking around 350 nm. The PL and scintillation decay times were 35.4–38.1 ns and 47–109 ns, respectively. The 0.10% Ce-doped sample showed the highest PL quantum yield (20%) among the synthesized samples. The quantum yield was well-correlated with the decay time of PL and scintillation. Thermally- and optically-stimulated luminescence were observed after the irradiation of X-rays (10 Gy). The thermally- and optically-stimulated luminescence spectra were confirmed that the luminescence was due to the 5d–4f transitions of Ce3+ in the 0.03% and 0.10% Ce-doped samples. Overall, the samples showed sensitive response of thermally-stimulated luminescence, and it was the highest for the 0.10% and 0.30% Ce-doped samples, having the dynamic range from 0.01 mGy to 1 Gy.

<i>In Situ</i> Synchrotron X-Ray Topography Observation of Double-Ended Frank-Read Sources in PVT-Grown 4H-SiC Wafers

We present in-situ observations of the dynamical operation of multiple double-ended Frank-Read dislocation sources in a PVT-grown 4H-SiC wafer under thermal gradient stresses. The nucleation of these sources is facilitated by a specific configuration consisting of one basal plane dislocation (BPD) segment pinned by two threading edge dislocations (TEDs). This configuration is formed during PVT crystal growth by deflection of TEDs on to the basal planes by macrosteps and re-deflection of resulting BPDs back into TEDs. Under the influence of thermal gradient stresses induced by heating inside a double ellipsoidal mirror furnace, the pinned BPD segment glides and activates dislocation multiplication by the double Frank-Read source mechanism. A more intricate mechanism of swapping of TED pinning points between Frank-Read sources lying on same basal plane is identified, enabling one dislocation loop to effectively “pass through” the other dislocations on same basal plane.

Influence of Phase Transformations on Crystal Growth of Stoichiometric Brownmillerite Oxides: Sr2ScGaO5 and Ca2Fe2O5

High quality stoichiometric brownmillerite-type oxide single crystals have been successfully grown by the floating zone method using a mirror furnace. We report here on the growth conditions and structural characterization of two model compounds: Ca2Fe2O5 and Sr2ScGaO5. Both show oxygen deficiency with respect to the average perovskite structure, and are promising candidates for oxygen ion conductivity at moderate temperatures. While Sr2ScGaO5 single crystals were obtained in the cubic oxygen-deficient perovskite structure, Ca2Fe2O5 crystallizes in the brownmillerite framework. Having no cubic parent high temperature counterpart, Ca2Fe2O5 crystals were found to be not twinned. We report on structural characterization of the as-grown single crystals by neutron and X-ray diffraction, as well as scanning electron microscopy (SEM) coupled with EDX (Energy Dispersive X-Ray Spectroscopy) analysis and isotope exchange experiments.

Si1−xGex crystal growth by the floating zone method starting from SPS sintered feed rods – A segregation study

The availability of suitable feed rods for Si–Ge bulk crystal growth is known to be a limiting factor in floating zone growth and other growth techniques. In this work, three Si-rich SiGe single crystals were crystallized by an optical floating zone technique in a double ellipsoid mirror furnace. The feed rods were prepared by pre-synthesis in the Spark Plasma Sintering (SPS) process starting with powders of different compositions. In a detailed section the preparation method of consolidation by mechanical alloyed powders to feed rods will be given. Results from two growth experiments starting with uniform compositions with 11at% and 20at% germanium as well as a zone leveling experiment with a segmented feed rod consisting of a starting zone with 32at% Ge will be discussed. The latter experiment resulted in a crystal with nearly no axial segregation.

In Situ Study of the Influence of Nickel on the Phase Transformation Kinetics in Austempered Ductile Iron

Phase fractions and austenite carbon contents in austempered ductile iron samples with three different nickel contents were determined by in situ neutron diffraction. The samples were austenitized at 1178 K (905 °C) for 30 minutes and austempered for 3.5 hours at temperatures between 523 K and 723 K (250 °C and 450 °C) using a mirror furnace. Based on the in situ neutron diffraction studies, plateau times were derived, which determine the end of stage I reaction. The austenite contents increase for higher austempering temperatures when the austempering times are selected properly, considering the accelerated phase transformation at higher temperature. Appropriate austempering times were derived for austempering temperatures between 523 K and 723 K (250 °C and 450 °C). Increased nickel contents lead to higher austenite phase fractions. Moreover the retarding effect of nickel on the phase transformation was quantified. The plateau values of phase fraction and the according austempering times were converted to TTT diagrams. The evolution of the austenite carbon content shows a maximum at 623 K (350 °C) austempering temperature. This can be explained by temperature-dependent carbide precipitation and carbon diffusion into lattice defects. Fine carbides within the ferrite could be found by preliminary APT analysis.

Magneto-crystalline Anisotropy and non-Fermi-liquid Behavior in CeNi1-xCoxGe2

We present results of magnetization, AC susceptibility and heat capacity measurements on polycrystalline CeNi1-xCoxGe2 samples (x = 0, 0.025, 0.05, 1) which were prepared by arc melting and on crystal CeNiGe2 grown by optical floating zone method in four mirror furnace. The parent compound CeNiGe2 is an antiferromagnetic Kondo system that orders magnetically at TN = 3.8K and undergoes a spin structure rearrangement at T1 = 3.2K while CeCoGe2 is a nonmagnetic heavy-fermion Kondo compound with j = 5/2 ground state and large Kondo temperature TK > 200K. Our measurements showed that the phase transition from the paramagnetic to the antiferromagnetic state was suppressed to lower temperatures with an increasing concentration of dopant.

Integrated analysis and design optimization of germanium purification process using zone-refining technique

Germanium (Ge) is a preferred material in the fabrication of high-performance gamma radiation detector for spectroscopy in nuclear physics. To maintain an intrinsic region in which electrons and holes reach the contacts to produce a spectroscopic signal, germanium crystals are usually doped with lithium (Li) ions. Consequently, hyperpure germanium (HPGe) should be prepared before the doping process to eliminate the interference of unexpected impurities in the Li dopant. Zone-refining technique, widely used in purification of ultra-pure materials, is chosen as one of the purification steps during detector-grade germanium production. In the paper, numerical analysis has been conducted to analyze heat transfer, melt flow and impurity segregation during a multi-pass zone-refining process of germanium in a Cyberstar mirror furnace. By modifying the effective redistribution coefficients, axial segregations of various impurities are investigated. Marangoni convection is found dominant in the melt. It affects the purification process through modifying the boundary layer thickness. Impurity distributions along the ingot are obtained with different conditions, such as pass number, zone travel rate, initial impurity concentration, segregation coefficient, and hot-zone length. Based on the analysis, optimization of the purification process design is proposed.

A Mirror Furnace for <i>In Situ</i> Residual Stress Measurements by Neutron Diffraction

A mirror furnace for in situ residual stress measurements by neutron diffraction is designed. Bulk and stick sample can be in situ heated up to 1000 degrees centigrade. The stability of the temperature is better than ±1 degree centigrade. This furnace is designed mainly for residual stress neutron diffraction experiments. And also it can be applied to some other neutron instruments such as neutron texture diffractometer, neutron powder diffractometer and triple axis spectrometer.

In-situ measurement of phase transformation kinetics in austempered ductile iron

Austempered ductile iron (ADI) alloyed with 0.42% Mn and 0.72% Cu was heat treated in a mirror furnace and the phase transitions were studied in-situ by neutron diffraction. The heat treatment consisted of austenitisation at 920°C and isothermal austempering at 400°C, 350°C and 300°C, respectively. Due to the growth of ferrite platelets, the austenite content decreases rapidly at all temperatures within the first 15–20min and reaches a stable plateau after 35min (400°C) to 80min (300°C).The carbon content of the residual austenite, which was monitored and characterised by the change of the lattice parameter, increases up to 1.6wt.% caused by redistribution from the newly formed ferrite. While at higher austempering temperatures this takes place almost parallel to the phase transformation, at 300°C the redistribution of carbon to austenite lags behind considerably.Furthermore the neutron data revealed an austenite peak asymmetry during austempering which is attributed to successive phase transformation. It results temporarily in two fractions of austenite, an initial low-carbon and an enriched high-carbon modification.

ChemInform Abstract: Fergusonite‐Type CeNbO4+δ: Single Crystal Growth, Symmetry Revision and Conductivity.

AbstractCrystals of CeNbO4 are prepared in a floating zone mirror furnace under air or Ar atmospheres using stoichiometric amounts of CeO2 and NbO2 (calcined at 1000 °C, 12 h).

Fergusonite-type CeNbO4+: Single crystal growth, symmetry revision and conductivity

Large fergusonite-type ( AB O 4 , A =Ce, B =Nb) oxide crystals, a prototype electrolyte composition for solid oxide fuel cells (SOFC), were prepared for the first time in a floating zone mirror furnace under air or argon atmospheres. While CeNbO 4 grown in air contained CeNbO 4.08 as a minor impurity that compromised structural analysis, the argon atmosphere yielded a single phase crystal of monoclinic CeNbO 4 , as confirmed by selected area electron diffraction, powder and single crystal X-ray diffraction. The structure was determined in the standard space group setting C 12/ c 1 (No. 15), rather than the commonly adopted I 12/ a 1. AC impedance spectroscopy conducted under argon found that stoichiometric CeNbO 4 single crystals showed lower conductivity compared to CeNbO 4+ δ confirming interstitial oxygen can penetrate through fergusonite and is responsible for the higher conductivity associated with these oxides. Large fergusonite-type CeNbO 4 crystals were prepared for the first time in a floating zone mirror furnace. Crystal growth in an argon atmosphere yielded a single phase monoclinic CeNbO4, as confirmed by selected area electron diffraction, powder and single crystal X-ray diffraction. The structure was determined in the standard space group setting C12/c1 (No. 15), rather than the commonly adopted I12/a1. AC impedance spectroscopy found CeNbO 4 single crystals showed lower conductivity compared to CeNbO 4+δ confirming interstitial oxygen can penetrate through fergusonite and is responsible for the higher conductivity associated with these oxides. • Preparation of single crystals of CeNbO 4 using a floating zone mirror furnace. • Correction to the crystal symmetry of the monoclinic form of CeNbO 4 . • Report the conductivity of a single crystal of CeNbO 4 .

Synthesis of homogeneous Ca 0.5Sr 0.5FeO 2.5+ δ compound using a mirror furnace method

A new synthesis method using melting zone technique via the double mirror furnace around 1600 °C is used to obtain homogenous brownmillerite compounds Ca 1− x Sr x FeO 2.5+ δ in the range 0.3 ≤ x ≤ 0.7. These compounds play important role in understanding the mystery of the oxygen diffusion in the perovskite-related oxides. We have successfully solved the miscibility gap problem by synthesizing a good quality of homogenous powder samples of Ca 0.5Sr 0.5FeO 2.5+ δ compound. Our result was confirmed by X-rays diffraction, Raman spectroscopy and energy dispersive spectroscopy analysis. Thermal treatment was also applied until 800 °C under vacuum to confirm again the homogeneity of powder samples, improve its quality and show that no decomposition or return to form Ca- and Sr-enriched microdomains takes place as a result of phase separation.

Crystal growth and magnetic property of MCo 2V 2O 8 (M=Sr and Ba)

We report, for the first time, the crystal growth of SrCo 2V 2O 8 and BaCo 2V 2O 8 compounds using floating zone technique in a mirror furnace under air. We have grown the single crystals of both compounds, with typical dimensions of 3 mm diameter and 5 cm long, which exhibit phase decomposition at about 820 °C. The magnetic susceptibility of both SrCo 2V 2O 8 and BaCo 2V 2O 8 compounds has similar temperature dependences and exhibit AFM ordering with a Néel temperature of 5 and 6 K, respectively.

Hot crack formation during peritectic reaction in steels

Hot crack formation during solidification was investigated during the peritectic reaction in steels. A series of in situ solidification experiments was performed using a MTS tensile testing machine combined with a mirror furnace. Sample temperature and force change were measured during the solidification process. The force measurements showed a sudden drop during the solidification of samples, which occurred around the peritectic temperature of the alloy, were accompanied by cracks or refilled cracks in the microstructure. Furthermore, the peritectic reaction types were studied theoretically and experimentally to understand their effects on the force change during solidification. The theoretical analyses showed that the volume change due to the peritectic transformation is one of the reasons for crack formation. In addition, when the peritectic reaction occurs in a diffusionless (partition less) manner in an alloy with sufficiently high primary precipitation, crack formation is more probable.

Dislocation generation related to micro-cracks in Si wafers: High temperature in situ study with white beam X-ray topography

The generation and propagation of dislocations in Si at high temperature is observed in situ with white beam X-ray topography. For the heating experiments a double ellipsoidal mirror furnace was installed at the Topo–Tomo beamline of the ANKA synchrotron light source, Research Centre Karlsruhe, Germany. Details of the experimental set-up and the first results on the occurrence of dislocations are presented. Artificial damage was generated in commercial (1 0 0) Si wafers using a nanoindenter with various loads. The applied forces for each set of indents were varied from 100 to 500 mN, respectively. After heating to approx. 790 °C large area transmission topographs were taken every 30 min which were then compared to room temperature topographs before and after heating. At the outset straight 60°-dislocations with b = a/2〈1 1 0〉 originate from the 500 mN indents into the direction of the strongest temperature gradient. After 60 min at constant temperature an increase in the length and number of the dislocations in other directions is also observed. As a result of the continual thermal stressing dislocations develop from the 100 mN indents too.