Martin Castillo

Development of Hot-Disk Sensor for Molten Metal, and the Thermal Conductivity Measurement of Molten Bismuth and Tin using Hot-Disk Method

The thermal conductivities of molten bismuth and tin were measured using the hot-disk method. A hot-disk sensor was made of molybdenum foil (thickness, 20 µm; radius of sensor region, 3.05 mm) cut in a conducting pattern and placed between two aluminum nitride plates (plate thickness, 0.05 mm). Aluminum nitride did not corrode because of its contact with a molten metal and thus the molybdenum foil was protected from the molten metal. The thermal conductivities of molten bismuth and tin were measured during a short-duration of microgravity using a 10 m drop tower, to confirm the thermal convection effect during the measurement. The thermal conductivities measured in normal gravity were found to be approximately equal to those measured during the microgravity (during microgravity, thermal convection is suppressed), up to 977 K. Moreover, at 1083 K, normal gravity results were found to be higher than microgravity results.

Combustion Products of Bulk Aluminum Rods Burning in High-Pressure Oxygen

Characterization of the combustion products released during the burning of commonly used engineering metallic materials may aid in material selection and risk assessment for the design of oxygen systems. The characterization of combustion products in regards to size distribution and morphology gives useful information for systems addressing fire detection. Aluminum rods (3.2-mm diameter cylinders) were vertically mounted inside a combustion chamber and ignited in pressurized oxygen by resistively heating an aluminum/palladium igniter wire attached to the bottom of the test sample. This paper describes the experimental work conducted to establish the particle size distribution and morphology of the resultant combustion products collected after the burning was completed and subsequently analyzed. In general, the combustion products consisted of a re-solidified oxidized slag and many small hollow spheres of size ranging from about 500 nm to 1000 µm in diameter, surfaced with quenched dendritic and grain-like structures. The combustion products were characterized using optical and scanning electron microscopy.

Effect of microgravity and magnetic field on the metallic and crystalline structure of magnetostrictive SmFe2 synthesized by unidirectional solidification.

Abstract:  The Sm‐2Fe molten alloy with 1:2 molar ratio was unidirectionally solidified in both microgravity and normal gravity in concurrence with a magnetic flux (0–0.12 T). The compound SmFe2 was produced by the unidirectional solidification in microgravity with a magnetic flux of 0T and exhibited a lamellar microstructure. The average lamellar thickness was 30 μm and each lamella possessed a <111> crystallographic alignment along major axis aligned in the direction of cooling. Unidirectional solidification in microgravity with a magnetic field of 0.04 T produced crystalline SmFe2 and Fe phases. The microstructure of this product was lamellar with an average lamellar thickness of 17 μm and no crystalline alignment. Unidirectional solidification in microgravity with a magnetic flux ranging from 0.06 to 0.12 T and in normal gravity with a magnetic flux ranging from 0 to 0.12 T produced crystalline Sm2Fe17 and Fe. During unidirectional solidification in microgravity without a magnetic flux, few nucleation sites were formed and rapid crystal growth occurred, consequently forming large‐grain SmFe2. The produced SmFe2 had a lamellar structure with a dominant <111> crystallographic alignment in the direction of cooling. Convection in the molten state and where a magnetic flux was present caused homogeneous nucleation, forming Sm2Fe17 with a disordered structure and crystalline alignment coinciding with the formation of the dendritic Fe.

Synthesis of Structure Controlled Magnetostrictive Materials by Use of Microgravity and Magnetic Fields

Tb-2Fe and Sm-2Fe molten alloys with a 1:2 molar ratio were unidirectionally solidified separately in microgravity and normal gravity in concurrence with a magnetic flux (0-0.12T). The Tb-2Fe molten alloy was solidified unidirectionally in microgravity with a 0.1T magnetic flux and the solidification product, TbFe2, had dominant [111] crystallographic alignment and the microstructure was lamellar with an average lamellar thickness of 30μm oriented along the solidification direction. The single phase SmFe2 was synthesized by unidirectional solidification in microgravity with a magnetic flux of 0T, and the microstructure was lamellar. The average SmFe2 lamella thickness was 30μm and each lamella possessed a <111> crystallographic alignment along the direction of cooling. The unidirectional solidification of Sm-2Fe molten alloys in normal gravity or in microgravity with a magnetic field resulted in Sm2Fe17 and Fe crystalline phases. The magnetostriction of TbFe2 solidified unidirectionally in microgravity with a 0.1T magnetic flux was 4,500ppm with an external 1.6T static magnetic flux. In TbFe2 solidified in normal gravity, the maximum magnetostriction remained at 2,000ppm with an external 1.6T static magnetic flux. The magnetostriction of single phase SmFe2 solidified unidirectionally in microgravity with a magnetic flux of 0T was -3,200ppm with an external 0.09T static magnetic flux.