DE1646666C - Process for the production of silicon nitndformkorpern - Google Patents

Description

From British patent specification 1054 631, working temperatures prevail can be used. You let

Process for the production of silicon nitride molds with rubbing or sliding loads up to

bodies known, either from silicon · to temperatures of over 600 C, otherwise up to

nitride powder of undefined modification, use this at 135O ° C. The special economical one

with the help of a temporary and hydraulic binding interest of these products lies in the field

by means of the desired shaped body and the gas turbines, in Rootes pumps, fuel pumps

then subjected to a ceramic fire. This uses 6 ° p _{en and} servo motors, as well as turbine

the hydraulic binding agent, which is primarily used for shoveling, guide vanes and the like for extremely hot conditions

Ethyl silicate or magnesium oxychloride or oxy machines.

sulfate, decomposes to the refractory oxide. In the For the implementation of the fire-proofing according to the invention Molded body should then drive the proportion of this, preferably magnesium oxide. One can refractory oxide at least 2 percent by weight, but also 65 use magnesium carbonate, which preferably 5 to 15 percent by weight. One at the temperature of hot pressing to the oxide A modification of this known process consists of decomposition. Taking into account this in the fact that one starts out from silicon powder and this setting is the required amount of magnesium

to calculate carbonate. The release of carbon dioxide does not affect the production of the molded bodies. When selecting the magnesium compounds, it is only necessary to ensure that none are used which is able to form a gas which has an adverse effect on the desired product.

The hot pressing of the powder mixture of silicon nitride and magnesium oxide takes place in graphite molds. It is preferred that the surfaces of the mold that come into contact with the powder mixture to be coated with boron nitride or some other substance that causes a reaction between the silicon nitride and the graphite prevented.

The invention is explained in more detail using the following example: ^T 5

example

Commercially available silicon powder (98%) was in a furnace atmosphere containing 90 percent by volume Nitrogen and 10 percent by volume hydrogen, heated to 1280 ° C. The heating took place in 72 hours. The crystallographic examination of the silicon nitride powder obtained revealed that only the α-modification Template.

The silicon nitride powder was then mixed with no more than 1 weight percent magnesium oxide, namely by wet grinding for 72 hours in butanol or down to a grain size of 95% <2 μΐη. The powder mixture was now in a graphite mold with a boron nitride protective layer at a temperature not exceeding 1650 ° C under a pressing pressure formed by 280 bar. The crystallographic examination showed that a conversion of the α-modification into the ^ modification.

The molded body made of silicon nitride has an extremely low porosity down to about 0 and a breaking strength of 74 kg / mm ² .

Comparative experiments

To the superiority of the products according to the invention over the products of the British To show patent specification 970 639, test specimens were produced in the sense of the above procedural measures and the properties determined. These are compiled in the following table.

25th

According to the invention Known procedure proceedings hü. Si powder Si powder 3 [im oven the atmosphere N ₂ + 10% H ₂ N ₂ Nitriding 1280 ° C, 1360 ° C, 72 hours 48 hours Pressing. ... 280 bar, 210 bar, 10 mins 10 mins at 165O ⁰ C at 1850 ⁰ C Modulus of rupture
at 20 ° C ... 84 kg / mm ² 63 kg / mm ² 1200 ° C 47 kg / mm ² 30 kg / mm ² MgO 1% 5% porosity 0 <0.5% Thermal shock factor*) at 20 ° C ... 52.5 28.7 at 1200 ⁰ C 30.2 20.8

35 *) Thermal shock factor R =

/. Thermal conductivity.

B modulus of rupture.

E modulus of elasticity.

η coefficient of thermal expansion.

En

Claims (1)

in situ in a nitrogen atmosphere to form silicon nitride γ, _tt u converts or starts from silicon carbide and Claim: Tses mU hooves of a metal powder with a stick Process for the production of silicon nitride carriers in molded bodies made of silicon powder by heating 5 binding agent to form silicon oxide aminium carb in a nitrogen-containing atmosphere in the presence of silicon dioxide and various intermediate compounds of magnesium oxide and subsequent hot fertilization. ,, ·,. _R , ..,
pressing, due to the fact that the disadvantage of this process is that one should be careful in a nitrogen atmosphere with 5 to 25, in which crystal modification the lum percent hydrogen silicon powder is converted to a silicon nitride powder the production; the kerarm temperature is not heated above 1300 ° C., the body is seen in this way. The firing conditions indicate that the α-silicon nitride powder formed with MgO or that the silicon nitride that is present during the rock fire is a mixture of the α - and /? - phase sem bond mixes in such an amount that must.,,
Magnesium oxide in an amount of 0.25 to .5 It was found, however, that the percent by weight, based on silicon nitride, is present in the mechanical properties of a phase mixture, and that the powder mixture is worse than that for silicon nitride from building a temperature not above 1650 ⁰ C presses. substances that have been manufactured exclusively from an α-phase silicon nitride powder. The invention thus relates to a method for production of silicon nitride molded bodies made of silicon powder by heating in a nitrogenous atmosphere in the presence of magnesium oxide and subsequent hot pressing and is characterized in that 25 one the silicon powder in a 5 to 25 volume percent The invention relates to a process for the production of a nitrogen atmosphere containing hydrogen on silicon nitride moldings from silicon powder heated to a temperature of not more than 1300 C, which by heating "in a nitrogen-containing atmosphere in n-silicon nitride powder thus formed with magnesium presence of magnesium oxide and subsequent oxide or one of the Pressing conditions Magne hot pressing. As a starting material, a silicon oxide-producing compound is used in such a silicon powder, which mixes as high an amount as possible that a molding has 0.25 to 1 Ge proportion of α-modification. * Weight percent magnesium oxide, based on silicon From British patent specification 970 639 a nitride is present and the mixed powder in a process for the production of dense silicon nitride does not ^{press above 1650 0} C,
molded bodies by hot-pressing a powder mixture 35 An essential aspect of the invention is known from silicon nitride and a "flux". method according lies in that the silicon powder The silicon nitride powder is not produced by transesterification is heated over 1300 ⁰ C. If silicon powder is placed in a nitrogen-containing temperature below 1300 ° C, n-silicon nitride is obtained, over 1300 ° C atmosphere to silicon nitride, this reaction would result in a mixture of α- and /? - phase between 1300 and 1650 ° C takes place. It was found that better, in particular denser silicon nitride, various products are obtained when additives such as oxides of iron, aluminum, calcium are not present in the silicon nitride powder. If n-silicon nitride in a mixture of about 5% is incorporated according to the invention or magnesium or magnesium nitride, in amounts according to the method, and the powder mixture is then pressed with magnesium oxide at 1650 ° C., it is pressed at the highest possible temperature. According to the 45 man molded body with a breaking strength of roughly known processes, the properties are 74 kg / mm ² . The higher the press temperature, the better the finished products. It was found that the products produced according to the invention rature is. Magnesium products have the best properties which are nitride-containing bodies, but the difference in the traded British patent is superior, Rupture modulus at 20 ° C and in the heat, i.e. around 50, and this applies to the high-temperature strength 1200 ⁰ C, very large. The porosity is remarkable and thermal shock resistance, and thus also the resistance to temperature changes. The moldings according to the invention are for not yet fully satisfactory. · A wide variety of fields of application where high