An Automated Laboratory Apparatus for the Production of Rapidly Solidified Submicron Powders
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AN AUTOMATED LABORATORY APPARATUS FOR THE PRODUCTION OF RAPIDLY SOLIDIFIED SUBMICRON POWDERSt
JULIUS PEREL,
JOHN F. MAHONEY,
Phrasor Scientific,
Inc.,
SCOTT TAYLOR,
ZEF SHANFIELD* AND CARLOS LEVI**
Duarte, California 91010 USA
ABSTRACT The Electrohydrodynamic (EHD) method of spraying fine liquid droplets from a liquid state, in a vacuum environment, was developed and used to produce amorphous, microcrystalline, single crystal, bicrystalline and tricrystalline powders. Studies of these powders have contributed towards increasing the knowledge of extended solubility, nucleation, metastable phases, undercooling effects, etc. Coatings and films have been produced by collecting the liquid droplets before solidification. An automated instrument based upon the EHD method, the Micro-Particle Processor, is computer operated and allows a material scientist not completely acquainted with the EHD process to perform sophisticated experiments on materials of his choosing. Electron transparent powders close to 3pm and large powders up to lOOmm have been collected and observed. 7 Cooling rates above 10 K/s have been achieved. Applications using powders include: new alloy compositions, use as AEM standards, in-situ remelt experiments in the electron microscope, etc. INTRODUCTION A new instrument developed recently, the Micro-Particle Processor, is capable of generating very fine charged liquid droplets for the purpose of producing fine powders and coatings. The droplets are formed by Electrohydrodynamics (EHD) atomization in a vacuum environment so that cooling rates and cleanliness are precisely known or controllable. This process allows a laboratory scientist to prepare small samples for research purposes. EHD processes had been explored previously to produce thrust for space propulsion. The application of EHD as a metallurgical tool was initiated by ARPA when the need for a small laboratory submicron powder generator was recognized by materials scientists. An ONR monitored contract was initiated in 1977 to study the feasibility of the process. It was then extended to include the development of the process and delivery of a table top powder generator which we call the Micro-Particle Processor. EHD GENERATION PROCESS Submicron particles are generated in the Micro-Particle Processor using an electrostatic spray process known as Electrohydrodynamics (EHD)[I]. The EHD process is a method whereby material emission in particulate form (ideal for
* **
This work was sponsored by ARPA and monitored by ONR under Contract No. N00014-77-C-0373 Present address: Northrop Research & Technology, Palos Verdes, CA Present address: Atisa-Atkins, S.A. de C.V., 11300 Mexico, D.F. MEXICO
132 preserving homogeneity in structure) is accomplished by the ejection of charged molten droplets from a conducting liquid surface exposed to intense electric fields. The source and experimental configuration illustrated in Fig.1 are oper5 ated inside a vacuum chamber at a pressure of 10 torr or lower. An applied electric field acts to produce a con
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