Tetsuo Munakata

Onset of oscillatory flow in a Czochralski growth melt and its suppression by magnetic field

Abstract Parameter sensitivity on the onset of oscillatory flow and the effect of magnetic field on such an oscillatory flow in the Czochralski melt are investigated. A defect in the crystal known as growth striations seems to be caused by a macroscopic oscillation of the flow, heat and mass transfer in the melt. An oscillatory flow is observed in a model Czochralski melt under a certain condition. It is due to interaction between natural and forced convection in the rotating container. Similar oscillation of flow and temperature fields is also obtained by numerical simulation. The result reveals that the oscillatory flow in the melt is inherent to the system. The critical Reynolds number for the onset of oscillation and the period of oscillation are decreased with the increasing Prandtl number and Rayleigh number. Further, it is confirmed that the oscillatory flow is possible to occur in the real system and can be suppressed by applying the external magnetic field.

Study on silicon melt convection during the RF-FZ crystal growth process: II. numerical investigation

Silicon melt convection during the floating zone (FZ) crystal growth process under radio-frequency (RF) heating and the effect of the externally applied magnetic field on the RF-FZ silicon melt convection have been investigated numerically. The main purpose of the study is to clarify the characteristics of the silicon melt convection under the RF heating and the effect of externally applied magnetic field on such melt convection. The numerically obtained flow characteristics are almost the same as previously reported experimental results. Further, the fluctuation of melt convection disappears when an external vertical magnetic field is applied. The required minimum magnetic flux density to suppress the convection fluctuation is around 0.2 T.

Flow observation in two immiscible liquid layers subject to a horizontal temperature gradient

Abstract Marangoni convection, driven by an interfacial instability due to a surface tension gradient, has become a significant problem in the crystal growth on the ground or in a microgravity environment. To suppress and control the convection is important for material processing. Especially in the crystal growth by liquid encapsulated czochralski or liquid encapsulated floating zone technique, in which the melt is encapsulated with an immiscible medium, Marangoni convection can occur on the liquid–liquid interface and on the gas–liquid free surface. In the present paper, experiments were carried out with a double liquid layer of silicone oil and fluorinert both in an open-boat system and in an enclosed system. Flow in a cavity subject to a horizontal temperature gradient was observed. An interactive flow near the interface was measured by using particle image velocimetry technique. The measured flow field seemed to agree sufficiently with the numerical prediction.

Lifetime-based measurement of stress using mechanoluminescence of SrAl 2 O 4 :Eu 2+

The stress and loading rate on disks of SrAl2O4:Eu mixed epoxy resin were measured by a lifetime-based method. The concentration of the mechanoluminescence (ML) phosphor and the excitation power did not affect the measured lifetime. The lifetime was proportional to the stress and was inversely proportional to the loading rate. The concentration, the excitation power, the stress, and the loading rate affected the peak intensity of ML, while previous work estimated the stress using the absolute intensity under well-controlled excitation and concentration conditions. The method used here can shorten the measurement time and enhance the practicality of a ML phosphor.

Study on silicon melt convection during the RF-FZ crystal growth process: I. experimental flow visualization

Abstract Silicon melt convection during the floating zone (FZ) crystal growth process under radio-frequency (RF) heating has been observed directly by using an X-ray radiography system with particle tracking velocimetry (PTV) in order to investigate the effect of the RF-induced electromagnetic field on the silicon melt convection. The result reveals that the silicon melt convection is fully affected by the RF induced electromagnetic field and the direction of convection becomes opposite to the natural convection. The obtained maximum velocity was 0.1xa0m/s which was 4–5 times higher than CZ system and the velocity field is fluctuated randomly. This will probably cause strong striation in the crystal.

Suppression of Marangoni convection in the FZ melt by high-frequency magnetic field

The effect of high-frequency magnetic field on the Marangoni convection in the floating zone (FZ) silicon melt has been investigated numerically. The purpose of the study is to clarify the applicability of the high-frequency magnetic field on the suppression of the Marangoni convection. The numerically obtained results reveal that the high-frequency magnetic field has the dumping effect for the Marangoni convection, and is useful to control the melt convection in the space environment. Further, the higher magnetic field frequency is useful to suppress the Marangoni convection due to the skin effect.

Lifetime-based measurement of stress during cyclic elastic deformation using mechanoluminescence of SrAl 2 O 4 :Eu 2+

The present study focused on the rise time and decay times of mechanoluminescence (ML) during cyclic elastic deformation of SrAl₂O₄:Eu²⁺. The time constants during compression and decompression, τup and τdown, respectively, did not change from the 2nd to the 5th cycle. Both τup and τdown were expressed by a linear function of the maximum load and the inverse of the loading rate. τup depended only on the loading time, whereas τdown was affected by the loading time and the rate of change of the strain energy. Measuring τdown may enable evaluation of the loading conditions even under cyclic loading and may enhance the practicality of a ML phosphor.

Preliminary Study of Two Immiscible Liquid Layers Subjected to a Horizontal Temperature Gradient

Marangoni convection, driven by interfacial instability due to a surface tension gradient, presents a significant problem in the crystal growth process. To achieve better materials processing, it is necessary to suppress and control this convection, especially in crystal growth using Liquid Encapsulated Czochralski techniques in which the melt is encapsulated in an immiscible medium. Marangoni convection can occur at the liquid-liquid interface and at the gas-liquid free surface. Buoyancy driven convection can also affect and complicate the flow. The present report studied Marangoni convection in a two-liquid layer system in an open and enclosed cavity. Flow in the cavity was subjected to a horizontal temperature gradient. Interactive flow near the liquid-liquid interface was measured by the Particle Image Velocimetry (PIV) technique. The measured flow field is in good agreement with numerical predictions.

Electrical Initiation of Solidification and Preservation of Supercooled State for Sodium Acetate Trihydrate

Electrical initiation of solidification from supercooled state and preservation of supercooled state of sodium acetate trihydrate solution, which is considered as a promising thermal energy storage material, are experimentally investigated with varying the configuration of electrodes and confirmed that the initiation of solidification and preservation of supercooled state are both possible by using the electric field. Further, effect of crystal growth direction on crystal growth rate is also investigated by using the newly developed electrical nucleation method. The result shows that the crystal growth rate, which growth direction is bottom to top, is slightly decreased compared with the direction of top to bottom at certain supercooling temperature range.Copyright

Flow Characteristics of Two Immiscible Liquid Layers Subjected to a Horizontal Temperature Gradient

Abstract: Marangoni convection, driven by an interfacial instability due to a surface tension gradient, presents a significant problem in crystal growth in normal microgravity environments. It is important to suppress and control the convection phenomenon for better material processing, especially in crystal growth by the liquid encapsulated Czochralski or liquid encapsulated floating zone techniques, in which the melt is encapsulated in an immiscible medium. Marangoni convection can occur on the liquid‐liquid interface and on the gas‐liquid free surface. Buoyancy driven convection can also affect and complicate the flow. In the study we report here, experiments were carried out with two liquid layers, silicone oil and fluorinert, in an open and enclosed rectangular cavity. The flow in the cavity was subjected to a horizontal temperature gradient. The interactive flow near the liquid‐liquid interface was measured by the particle image velocimetry technique. The measured flow field is in agreement with numerical predictions. Free surface fluctuations with several dominant frequencies were also measured.