Plastic and nonmetallic article shaping or treating: processes – Including step of generating heat by friction
Patent
1983-07-19
1984-04-17
Parrish, John
Plastic and nonmetallic article shaping or treating: processes
Including step of generating heat by friction
501 97, 264 66, C04B 3550
Patent
active
044433948
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to the technology of making a heat fused silicon nitride comprising body from the following system: Si.sub.3 N.sub.4, SiO.sub.2, Y.sub.2 O.sub.3 and Al.sub.2 O.sub.3.
BACKGROUND OF THE INVENTION AND PRIOR ART STATEMENT
The use of the component system of Si.sub.3 N.sub.4, SiO.sub.2, Y.sub.2 O.sub.3 and Al.sub.2 O.sub.3 for making a silicon nitride comprising product is relatively new in the art. Such component system has been processed by hot pressing to obtain a densified product (see U.S. Pat. Nos. 3,969,125; 2,264,550; 4,264,548). But such component system has not been successfully processed to a densified product by sintering.
It is known that it is not possible to sinter the single component of Si.sub.3 N.sub.4 under ambient conditions. To achieve some degree of satisfactory densification, oxides must be added to the Si.sub.3 N.sub.4, extremely high temperatures must be employed (above the sublimation point of Si.sub.3 N.sub.4), and over-pressures as well as blankets must be used to contain the sublimation (see U.S. Pat. No. 4,285,895 by Mangels). This procedure does not achieve optimum economy and efficiency of processing. In an effort to eliminate the necessity for over-pressure during sintering, U.S. Pat. No. 4,354,990 discloses a method by which larger than usual amounts of oxides are added, while still using a packing blanket to contain sublimation at excessively high sintering temperatures. Again, this processing technique lacks economy and efficiency. Neither of these last two patents employ the Si.sub.3 N.sub.4 /Y.sub.2 O.sub.3 /SiO.sub.2 /Al.sub.2 O.sub.3 component system (which may afford enhanced strength characteristics) and thus fail to recognize the solubility enhancing characteristics of such system under sintering conditions.
SUMMARY OF THE INVENTION
The invention is a method of making a silicon nitride comprising product by heat fusion without the necessity for special atmospheres or packing mediums which will hinder efficiency.
The method comprises (a) fabricating a unitary, porous, reaction bonded silicon nitride/yttrium silicon oxynitride/alumino-silicate comprising object, the yttrium silicon oxynitride being formed from an SiO.sub.2 component and being present in an amount of 5-17% by weight of the object, the silicate being present in an amount of up to 3% by weight of the object; (b) heating the object in an ambient atmosphere to a temperature level below the sublimation temperature of the silicon nitride and for a period of time sufficient to substantially fully densify the object as a result of dissolution of said silicon nitride into liquified yttrium silicon oxynitride. The object is preferably in direct contact with the ambient atmosphere during heating.
It is preferable that the yttrium silicon oxynitride consist of at least 75% of the Y.sub.10 Si.sub.6 O.sub.24 N.sub.2 phase, and that the alumino-silicate is amorphous and resides as a thin coating on the grains of the silicon nitride and yttrium silicon oxynitride. The silicon nitride may have an alpha/beta ratio in the range of 1:10 to 20:1.
The object is preferably fabricated by compacting silicon and reactive oxygen carrying agents under ambient conditions to a density level of about 1.2 gm/cm.sup.3, and nitriding the compact to a density level at least 1.9 gm/cm.sup.3. The oxygen carrying agents preferably consist essentially of 4-12% Y.sub.2 O.sub.3, 1-4.0% SiO.sub.2 (SiO.sub.2 being usually present as a layer on the silicon metal particles), and 0.75-4.0% Al.sub.2 O.sub.3 (all percentages based on silicon normalized to Si.sub.3 N.sub.4). The nitriding is preferably carried out in the temperature range of 1090.degree.-1430.degree. C. for a period of time sufficient to (a) form the desired amount of yttrium silicon oxynitride, and (b) provide at least 99.5% conversion of the silicon to silicon nitride.
It is preferable that the fusion heating be carried out at a temperature level of 1650.degree.-1750.degree. C. over a period of time of 0.5-12 hours and without the use of me
REFERENCES:
patent: 3969125 (1976-07-01), Komeya
patent: 4264548 (1981-04-01), Ezis
patent: 4264550 (1981-04-01), Ezis
patent: 4285895 (1981-08-01), Mangels
patent: 4354990 (1982-10-01), Martininyo
Ford Motor Company
Johnson Olin B.
Malleck Joseph W.
Parrish John
LandOfFree
Method of making a silicon nitride body from the Y.sub.2 O.sub.3 does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of making a silicon nitride body from the Y.sub.2 O.sub.3, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of making a silicon nitride body from the Y.sub.2 O.sub.3 will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-94944