JPS58217468A - Silicon nitride bonded silicon carbide article and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a silicon tinide bonded silicon carbide shaped article and a method for producing the same.

Products made of silicon nitride-bonded silicon carbide have excellent strength at high temperatures and also have excellent thermal shock resistance. An example of the manufacture of silicon-bonded silicon carbide shapes, which represents a significant advantage over conventional porcelain-bonded silicon carbide shapes, is disclosed in U.S. Pat. No. 2,752,258. As disclosed in the patent specification, the titanide bonded shaped product is made of sized silicon carbide coarse particles, metal silicon fine powder,
Manufactured from batches consisting of clay and temporary binder.

After drying, this model was heated to 1650 to 14
Heat treatment at a temperature of 00'C for 12 hours. Depending on the amount of silicon metal powder in the batch, the shaped article will have an increase in weight of about 5-6%. This means that the silicon metal in the raw batch has been virtually completely converted to silicon nitride.Silicon carbide shaped articles have the excellent properties mentioned above--but the downward slope of the blast furnace shaft The downwardly sloping lining is exposed to slag. The slag in this area is at high temperature and is one of the most corrosive blast furnace slags. The lining of the downward slope shall be highly fire resistant. In the unlikely event that
If there is a tendency to react with slag, the downslope lining must have low gas permeability and low porosity.

Traditionally, downslope linings have been lined with oxide ceramic bricks, carbon black and silicon carbide bricks, and other exotic materials.

Because of the extremely high temperatures it is subjected to, downslope linings are almost always water cooled. Protecting the water cooling system from the contents of the downslope is, to say the least, an essential requirement; the presence of silicon carbide bricks used in the downslope lining of blast furnaces as well as alkaline fumes and alkali oxide-containing slags. Silicon carbide bricks used in other applications are alkali resistant. Must be υ-sexual.

If a small amount of carbon or a carbon-producing material is mixed into the six pieces of silicon-bonded silicon carbide shaped articles before oxidation, the characteristics of the fused shaped articles (1+ll, alkali slag resistance)
was found to be dramatically improved. Even if the amount of carbon added to the batch is as small as f70.15 wt%, the porosity is reduced, the strength is increased both at room temperature and high temperature, and the alkali resistance is also increased. If the amount of carbon added is increased slightly (for example,
0.6 wt%), the properties would be further improved dramatically. Accordingly, the present invention comprises silicon-bonded silicon carbide shaped articles produced from batches containing small amounts of carbon or carbon-producing materials, which bonded shaped articles do not contain silicon oxytide when analyzed by X-ray diffraction. ,
The bonding matrix of a silicon carbide shaped article is a homogeneous mixture of silicon nitride, silicon carbide, and, if present, free graphite or carbon. In a preferred embodiment, the binding matrix does not contain free graphite or carbon.

The molded product of the present invention essentially consists of silicon carbide coarse particles, metal silicon fine powder, and carbon or a batch of 0.1 to 5 w.
This batch is produced by preparing a batch of carbon producing material yielding t% of carbon, mixed with a temporary binder, kneaded and then subjected to conventional brick making or shaping, such as for example in a pressure press. Create a shaped product using product manufacturing technology. After drying, the shaped article is heated in a nitriding atmosphere to cause the silicon metal to react with the nitrogen. The resulting shaped article not only has excellent alkali resistance, but also has other excellent properties.

According to the present invention, approximately o, is ~ 2.5
Preferably, the carbon or carbon-producing material is formulated to provide a wt% amount of carbon. Is the finished object substantially equivalent to a similar object without the addition of carbon?
Alternatively, about 0.1
Most preferably, the carbon or carbon producing material is formulated to provide an amount of 5 to Q, 6 wt% carbon.

Silica, clays and other aluminum silicates and Anovena-producing materials should not be added to the fines portion of the raw batch because they have the effect of introducing silica, alumina and oxygen into the matrix. do not have. Traditionally, small amounts of clay have been added to silicon carbide brick production batches to make the batch plastic and make it easier to press. Although clay is desirable as a press forming aid, it cannot be used in the present invention. However, the addition of small amounts of carbon or graphite has the beneficial effect of facilitating press forming. And, in fact, batches made by press molding have greater density during press molding.Other features, objects and effects of the present invention will become apparent from the following description and accompanying drawings.

A series of silicon carbide brick making batches were made from silicon carbide aggregates of a particle size that passed through a 6 mesh sieve and very fine silicon metal powder. The silicon carbide to silicon metal weight ratio was 87:16 in Sochi; no carbon was added to the control batch, Example CI. Carbon black as shown in Table 1 was added to the remaining pieces (Examples 1 to 6). Mix this mixture and add 4 wt% 50150 dextrin solution (
Temporary binder) and press-formable powder (temporary binder) were kneaded together with enough water to prepare a press-formable powder. Therefore, only Example 6 had 1 wt% water added, whereas all other batches had Q. This batch with 5 wt% water was pressed into a shaped article to obtain a press density of approximately 160 pcf (pounds per cubic foot).

After press molding, this shaped article was dried. The shaped article was then heated in a nitrogen atmosphere in a conventional manner. That is, the maximum temperature is 26. [It was 100F.

This temperature was quite sufficient to completely react the silicon metal with the nitrogen within a residence time of less than about 10 hours. The conversion process was the same for all (Sochi).

The physical and chemical properties of the molded product are shown in Table 1 below. Example No. 1 2 3 Added amount of carbon black (wt%): 5 2-1
/2 Bulk density at 1-1/4 press, pcf: 158 1
61 162 Bulk density, pcf:
166 168 170 Apparent porosity (%
): 14,0 13.9
15.8 Room temperature crushing strength (psi) (average of 2 pieces) 6,830
8,850 12.54E rupture coefficient (psi)
: ・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・1×1× Room temperature: 2620 4840 454 [J
・・・・・・・・・2X2X9 test piece・・・・・・・・・
...at 2000°F: 33
50 4590 4900 at 2700'F
: 2410 3130
3690 Ni (N) 1%: 4.4
5.4 5.9 Free carbon (C) 9%:
2,97 1.33 0.6
X-ray diffraction analysis phase other than ESiC αSi N αS r 3N4 αSr 3
1'4 4 5 6
C10,630,310,15- 164163162161 171174172168 13,712,612,316,0 i 20,475 Roro, 070
Ro2,140 24.0006 Test piece...
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・－・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・7380 791
5 8080 72851XIX9 "Test piece...2X2X9" Test piece...lXlX
9"2x2x9"5520 4950 5
7505570 53504140 4860
55205290 46107.0 7
．． 0 7.2 7.4i 0.
56 0.42 0.37 0.58J
ctsiN ctsiN αsiN
α5I3N44 34
34 34J4 β513N4 β
S l 3 N4 β513N4 β513N4 not present) Carbon black was found in electron microscopy (SEM) analysis of the chemical products of Example 1, but carbon black was found in the chemical products of Examples 4 and 5. No pump racks were found in the analysis.The shaped articles listed in Table 1 were then tested and quantitatively compared for alkali resistance at elevated temperatures. In this test, the destructive environment that would be encountered during service (e.g., the destructive environment on the downward slope of a blast furnace shaft) could, within a short period of time, Promote demonstration.

This model is encapsulated in potassium carbonate powder, and
Heat to 1700°F (927°C) in a reducing atmosphere. The shaped product was heated twice to the maximum temperature, then allowed to cool, and immersed in hot water for 24 hours. The results of the alkaline test are shown in Table 2 below.

Example No. 12 Percentage loss (%) of alkaline specimen test exposed twice to 1700'F (average value of two times): 1.9 1
．． 2 range: 1.5-230.8-1.5 2゜MOR reduction rate: 57.8 51.
4 Destruction coefficient after alkali test (psi): 1105 2ro50
:I 2.2 1-2.2 27, 6 5285 4670 4755 3125
Drawing 4310 is a graph illustrating the effect of carbon addition on three types of physical properties and alkali resistance as measured by rancidity rate. As is clear from this graph, the alkali resistance can be dramatically improved by adding a very small amount of carbon. Furthermore, as is clear from this graph, even if a small amount of carbon is added, there is no adverse effect on the physical properties, but rather the effect of increasing the bulk density and lowering the porosity can be obtained.

Addition of small amounts of carbon appears to lubricate the mixture and increase bulk density during press forming. Thus, even if the amount of carbon added is less than about 1.3 wt%, the porosity will be significantly reduced. However, the decrease in porosity is not the reason for the improvement in alkali resistance. If the amount of carbon added is increased slightly, the alkali resistance will improve and the apparent porosity will also increase.

The reason why the shaped articles produced according to the present invention have excellent alkali resistance has not been completely elucidated.

However, as the amount of finely divided carbon in the batch increases, some effects become clearly visible. If only very small amounts of carbon are added, no silicon oxytide, which is sometimes found in the matrix of silicon apricot silicon carbide shaped articles, is detected by X-ray diffraction analysis. #If the amount of powdered carbon added is too large, graphite σ),
Traces are detected by servants. As the amount of carbon added to the batch increases, the amount of nitrogen taken up by the silicon metal decreases. Therefore, the finely divided carbon reacts with the surface silica of the silicon metal and the silicon carbide grains and the entrained silica accompanied by the incompletely reacted silicon carbide grains, so that during the tinning process, the silica is removed from the shaped article. It should be thought that it is. If the free carbon present in the raw material silicon carbide is sufficiently finely powdered, it will also exhibit a similar effect.

The actual composition of the bonding matrix produced by oxidizing silicon in the presence of carbon has excellent alkali resistance, as evidenced by the data presented herein.

The method of the invention contemplates a very large number of brick and shaped manufacturing operations. Therefore, the temporary binder may be a dextrin solution, a mixture of rigenin solution and water, or other temporary binder. The mixture can be made, for example, by pressing or impact pressing at pressures up to about 18,000 psi. The brick can be fired in the presence of nitrogen at a temperature of about 2600'F with a residence time of at least 4 hours. Brick-making mixtures must be sized. For example, about 7-20 wt% is 10
Approximately 23-36 wt% passes through a mesh sieve, about 10 mesh, and the remainder passes through a 28 mesh sieve, about 15 wt%.
~19 wt% passes through a 28 mesh sieve, and the remainder passes through a 65 mesh sieve, approximately 7-1 [1 wt% passes through a 65 mesh sieve, and the remainder passes through a 200 mesh sieve, and approximately The wt% is sized so that it passes through a 200 mesh sieve. The sieve mentioned above is a standard Silkworm Tyler sieve. All silicon metal must be present in the -625 mesh portion of the batch. The preferred average particle size of silicon metal is less than about 10 microns.

The smaller the particle size of the silicon metal, the more rapidly it reacts in the formation process.

Raw materials useful in the practice of this invention must be relatively pure and substantially free of silica, anovena and other materials that would introduce oxides into the binding matrix. Must be. For example, a suitable silicon metal useful in the present invention is silicon that is greater than 99% pure. The silicon carbide refractory aggregates suitable for this invention are about 9
It must be composed of at least 5% silicon carbide and free carbon, and the amount of free carbon must be less than about 1%. Suitable silicon carbide condensates useful in the present invention are shown in the table below. ) The weight ratio of particulate silicon metal to silicon carbide aggregates in the hollow can vary from about 5:95 to 20:80.

silicon carbide aggregate Al2030.4% maximum 'L"i02'Q, 1% maximum Fe2030.6% maximum Ca0 0.2% maximum.

MgO0.02% maximum MnQ 0.1% maximum Na,,
0 K2O0,03% most dog I20 free carbon 1,0% maximum free silicon
2.0% max silicon carbide
95.0% Maximum The carbon added according to the present invention must be finely divided (e.g. -200 mesos). Examples 7 and C2 were prepared identically and were substantially identical to Examples 1-6. In Example C2, -6 mesh graphite was added instead of carbon powder. The test results of Example 7 and C2 are shown in the following table (■).

Table ■ Example number: Addition amount (wt%) Graphite (-6 mesh): carbon plaque powder Bulk density during breath (pcf): Bulk density (pcf): Apparent porosity (%): Cold crush strength (psi): Modulus of rupture (psi) of lXlX9" test piece at room temperature: At 2000’F: At 2700°F: Nitrogen (N (%): X-ray diffraction analysis of materials other than SiC phase (strength decrease) Alkaline Specimen Test, 2 exposures to 1700°F.

3,4 K2 C03/test piece weight loss percentage C27 5.0% - -5.0% 158 166 161 16614.6 - 11.860 3850 2760-
2890 2740 31207, 0
4・1Si3N4
5i3N412, 1 1.
6 The amount of nitrogen absorbed by the shaped article of Example C2 was almost the same as for the composition with no added carbon (Example C), and the alkali resistance was also approximately the same.

As used herein, the term "carbon material" means carbon in the form of carbon black, graphite or amorphous carbon. Similarly, as used herein,
The term ``carbon-producing materials'' refers to materials such as pitch, resins, tars, or other carbonaceous sources that produce carbon residues when heated below the temperature at which silicon metal begins to react with nitrogen. material.

[Brief explanation of drawings]

The figures illustrate the effect on certain physical properties and alkali resistance of increasing the amount of carbon added to a batch of silicon-bonded silicon carbide bricks.

Claims (1)

[Scope of Claims] (1) A silicon oxide-bonded silicon carbide shaped article, which does not contain silicon oxytide when analyzed by X-ray diffraction; The product is manufactured from batches containing a small but effective amount of carbon or carbon-producing material such that the product has excellent alkali resistance. (2) A method for producing a silicon carbide shaped article bonded to silicon carbide, wherein the shaped article has no silicon oxytide when analyzed by X-ray diffraction; Although in small quantities, it has an excellent alkaline property.
(3) characterized in that an effective amount of carbon or carbon producing material is added to the batch (3) a) silicon carbide coarse grains, silicon metal fine grains and carbon or about 0.15 carbon to the batch;
producing a batch consisting essentially of a carbon-producing material such as to provide an amount of carbon in an amount of ~5 wt%; b) mixing this batch with a temporary binder [2 and forming into a shaped article; C) forming the batch into a shaped article; d) recovering a bonded shaped article having excellent alkali resistance; method of manufacturing the product. (4) Add 0.15 to Q, 6 w of carbon or carbon-producing material so that the shaped article has physical properties substantially equal to or better than similar shaped articles to which no carbon is added.
The method according to claim 3, which comprises blending t%. (5) About 0.15 to 2.5 wt% of carbon or a carbon-producing material is mixed so that when the shaped article is collected and analyzed by X-ray diffraction, no silicon oxynitride or graphite is contained in the bonding matrix. 7. A method according to claim 6, comprising: