Process for producing tin sintered bodies and coatings

Details Process for producing tin sintered bodies and coatings Process for producing tin sintered bodies and coatings

1996-05-06

1998-05-12

Utech, Benjamin

Coating processes

Particles, flakes, or granules coated or encapsulated

Solid encapsulation process utilizing an emulsion or...

427215, 427375, 427384, B05D 700

Patent

active

057501939

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a process for producing sintered bodies or coatings of titanium nitride (TiN) using a suspension of surface-modified TiN particles in the nanoscale range.
2. Discussion of the Background
In the following "particles in the nanoscale range" are to denote particles whose average size is not higher than 100 nm, particularly not higher than 50 nm, and particularly preferred not higher than 30 nm.
In the processing of nanodisperse materials (particles, powders), there are essentially two problems, i.e.:
(a) control of particle agglomeration in the processing of said materials; and
(b) production of processable ceramic compositions having a high solids content.
Regarding problem (a) it is to be noted that when going from ceramic powders in the sub-micron range to those in the nanoscale range, an increase in agglomeration is generally observed. This is due to the fact that with decreasing particle size, weak interactive forces such as van der Waals forces gain significant importance and dominate, respectively. Additionally, there are always functional groups, i.e., groups capable of undergoing condensation, on the particle surface. With conventional sub-micron powders, said forces are only of importance as far as they may be used as centers of interaction for necessary organic processing aids (dispersing aids, binders, etc.). Due to the high surface to volume ratio in nanodisperse materials, said surface groups are, however, also of great importance in another respect. On the one hand, they can also serve as reaction centers for organic processing aids. However, by condensation reactions between individual particles they can also result in the formation of hard agglomerates. Said particles are then connected to each other quasi by "sinter necks". Therefore, it is desirable to develop processes with which the agglomeration can be controlled such that agglomerated powders can be obtained in a controlled manner. Further, it would be favorable if by said process the reactive surface could be shielded outwardly, thus preventing a condensation between particles.
As regards the above problem (b) it may be noted that the production of ceramic compositions having high solids contents and processing properties adapted to a molding process causes severe difficulties. In order to avoid agglomerates which may result in serious defects both in the green and sintered bodies, the operation is usually carried out in suspension. For stabilizing the suspension, dispersion aids are added which dispersion aids have the function of preventing agglomeration and imparting the required processing properties to the suspension. In the stabilization of the suspension there are two different basic possibilities, i.e., electrostatic and steric stabilization.
The electrostatic stabilization is disadvantageous in that due to the high hydrodynamic radius of the suspended particles only low solids contents may be realized. In contrast thereto, the steric stabilization on principle offers the possibility of preparing suspensions of high solids contents from materials in the nanoscale range since in this case the hydrodynamic particle radius is much smaller.
The advantages of steric stabilization have already been demonstrated with nanodisperse SiO.sub.2 as example. In this case, non-ionic organic polymers (e.g., polymethyl methacrylate) which become adsorbed onto the particle surface have generally been employed. The disadvantage of such a stabilization is that even therewith only solids contents of at the most about 20 to 30% by volume may be realized and that said stabilization can be applied to systems different from SiO.sub.2 only with considerable restrictions. The reason therefor mainly is that the chemical properties relating to the surface (e.g., acidic/basic properties) specific for a particular material cannot be taken into account.
Thus, it is desirable to provide a process which makes it possible to modify the particle surface by corresponding chemic

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