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Powder-Preparation Method

IP.com Disclosure Number: IPCOM000099880D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 164K

Publishing Venue

IBM

Related People

Takamori, T: AUTHOR

Abstract

The powder-preparation method described herein will be highly useful for certain electronic applications such as phosphor preparation for CRT screens. The powder prepared by this method will be well-crystallized, nearly mono-sized. The method can be applied to the powder preparation of various inorganic compounds including oxides (such as alumina, zirconia, garnets, tungstates, niobates, etc.) and some chalcogenides.

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Powder-Preparation Method

       The powder-preparation method described herein will be
highly useful for certain electronic applications such as phosphor
preparation for CRT screens.  The powder prepared by this method will
be well-crystallized, nearly mono-sized. The method can be applied to
the powder preparation of various inorganic compounds including
oxides (such as alumina, zirconia, garnets, tungstates, niobates,
etc.) and some chalcogenides.

      In view of the status of the current technology, a completely
satisfactory method for preparing powders consisting of
well-crystallized, fine, and nearly mono-sized particles of a micron
or larger size has not been established to date.  Such a powder, once
prepared, will have many useful applications, such as CRT phosphor
screens, in which the resolution and the brightness will be
significantly improved.  The purpose of this disclosure is to present
a significant breakthrough for this problem by providing a powder
consisting of fine and nearly mono-sized stress-free single crystals.

      A method for preparing a powder consisting of fine and nearly
mono-sized stress-free single crystals by hydrothermal crystal growth
under controlled nucleation density will now be described.  The
hydrothermal method for growing single crystals has been used for
decades. Sometimes the method has also been used to prepare powders.
However, the method has never been used to prepare powders under
controlled nucleation density, which is actually crucial for
obtaining near mono- sized particles.  In all the previous works on
the use of the hydrothermal methods for the preparation of powders,
only spontaneous nucleation density is actually crucial for obtaining
near mono-sized particles.  In all the previous works on the use of
the hydrothermal methods for the preparation of powders, only
spontaneous nucleation was induced by the addition of "mineralizers",
and no one has ever conceived of the positive control of nucleation
density.  How one can control the nucleation density when the
hydrothermal method is used for preparing well-crystallized powders
will be described.

      The present powder-preparation method consists of (1)
preparation of crystalline seeds for the controlled nucleation, (2)
uniform dispersion of the seeds in the starting materials, and (3)
crystal growth in the hydrothermal condition.  The hydrothermal
method generally is known to be of advantage on growing a single
crystal with minimal stress and much less defects over many other
fusion techniques.  In a given temperature and pressure condition,
nutrients, or the starting materials for the crystal growth, in the
system dissolve into the fluid which is mainly water, and precipitate
on the seed crystal which is hanging in the space where the
temperature is set to be a little lower in the same system.  There is
no reason why one cannot have more than one seed crystal on the
hydrothermal growth.  This method exte...