DE3119424A1 - Production of nitride-bonded refractory materials - Google Patents

Abstract

A means for producing nitride-bonded refractory materials in situ by mixing an aluminium metal powder, relatively pure silicate mass, raw clay and a refractory aggregate, by pressing these mixtures in moulds and firing them at elevated temperature in a nitriding atmosphere in order to lead to bonding.

Description

Manufacture of nitride-bonded refractory bodies

The invention relates to a means for producing nitride-bound Refractories in situ by mixing aluminum metal powder, proportionately pure silica, raw clay and a refractory aggregate or aggregate.

Silicon nitride, aluminum nitride and aluminum oxide can be used in fine powder form, if mixed thoroughly and uniformly at appropriate proportions and at increased temperature, ceramic products with favorable high-temperature properties result that are applicable at temperatures above 140000 q nitride compounds that are summarized under the term SIALON, by mixing alpha and / or beta silicon nitride synthesized with alpha or gamma aluminum oxide powder.

SIALON generally means an intimate dispersion of aluminum oxide through the entire silicon nitride matrix.

It is believed that after sintering, the mass becomes a solid solution of aluminum oxide in silicon nitride. The letters which form the expression SIALON, represent a sequence of chemical symbols, namely of silicon, aluminum, oxygen (oxygen) and nitrogen (nitrogen).

Considerable effort has been put into the development of ceramic products directed that 80% or more silicon nitride, silicon oxide nitride and / or sialon contain. These products mainly consist of single-phase Nitrides and show advantageous thermal shock resistance, strength as well Corrosion resistance. Little information is available on how to use these Nitride phases as binders in conventional refractory bodies. Several factors which delay the further development on a large scale of nitride-bonded ones Refractories have led to the high costs of purchasing silicon nitride, the instability of certain oxide nitrides at high temperatures and the tendency for hydrolyzing any starting materials such as aluminum nitride and magnesium nitride back, To overcome the aforementioned shortcomings, it would be advantageous to use nitride phases Form in situ by adding a single metal powder that is mixed with the gaseous Nitrogen reacts to form a crystalline nitride phase, so that a ceramic Binding is achieved with relatively inexpensive refractory grains. By such a Initially, the cost of the nitride products is significantly reduced, and the individual benefits of the nitride compounds are made with the existing advantages of conventional refractory grains connected.

It is the object of the invention to create nitride-bonded refractory bodies, those created by adding two or more reactive metal powders Refractories have better physical properties.

In addition, sialon and other nitride phases with conventional Refractory grains are connected to the typically by oxides which can be easily decomposed by certain metals Properties such as non-wettability due to molten metal, resistance to chlorine attack and to give low thermal expansion.

According to the invention, nitride-bonded refractory bodies are also created, which have improved porosity and relatively good resistance to room and possess at high temperatures.

According to the invention, a method for producing nitride-bonded Refractories created in situ. A mixture is set up that consists of about 1 to 25 wt.% aluminum metal powder, about 1 to 25 wt.% essentially pure Silica mass, about 1 to 5% by weight of raw clay and the remainder from a classified refractory aggregate or aggregate. This mixture is pressed into refractory molds and at elevated temperatures in a nitriding atmosphere to form the nitride bond burned.

In a preferred embodiment of the invention is Share of aluminum about 3 to 13% by weight, that of the practically pure silica mass about 4 to 13% by weight and that of raw clay about 1 to 2% by weight of the mixture.

The shaped bodies are preferably at a temperature between about 10900C and 17500C., The nitriding atmosphere being made up of either gaseous Nitrogen, industrial furnace gases or gaseous ammonia.

The refractory aggregate is preferred in its composition chosen from fired clay, mullite melt, synthetic alumina and Magnesia spinel.

Reduced in a nitrogen atmosphere at elevated temperatures Aluminum makes the silica mass by adding silicon, aluminum oxide, aluminum nitride and gamma-aluminum oxide nitride are formed. With additional treatment at elevated temperature, silicon is nitrided, to form beta silicon nitride and aluminum oxide, the aluminum nitride and Aluminum oxide nitride enters the silicon nitride structure as a solid solution, to beta1-sialon (beta prime sialon) to form. During the fire it is always possible that minor Oxygen content can get into the chamber enclosing the refractory body. In such a case, the formation of a pure Beta1 sialon is hindered and so-called "X", "J" or aluminum nitride poly types can also form.

During nitriding, a gas-metal reaction occurs in the metal phase, whereby the smallest crystals form 9 which enclose the metal core. If kept up the dwell time during the fire ensures that the metal is removed from the core through the pores of the crystalline mass flows off, causing it to become an additional Nitridization of the metal occurs.

At the end of the dwell, a real ceramic bond is created achieved with the coarse refractory bodies due to their solubility in the nitride phases.

In order to achieve a successful nitriding as well as an economical one Setting up fire schedule should preferably make the starting metal powder as fine as to be possible. In general, the aluminum powder should have an average Particle diameters of about 34 microns with 90 of the particles finer than 70 microns should be. The silica used in the mixtures may have one or more particle size range. As an example, can an extremely fine sllica mass can be used, which is one particle diameter below about 1 micron. However, ingesting large amounts of these is extremely beneficial fine mass to the refractory mixture often leads to difficulties in pressing.

It is advantageous to use the very fine silica in a coarser form of silica to get the large amounts of silica needed for a mixture. The raw clay should be kept between coarse and fine grain size.

Likewise, the reaction mass should preferably be economical Reasons not to exceed about 20% of the mixture, because larger amounts do not lead to products with significantly improved physical properties.

In the following examples shown below, was Aluminum powder with a silica mass, raw clay and either burnt fire clay, Mullite melt, synthetic aluminum oxide or mixed with magnesia spinel. It became a dextrin solution and / or lignin and water as a temporary binder used.

The mixtures were pressed into shapes at about 1265.58 kgf / cm2 (18,000 psi).

The refractory bricks were then poured in the presence of Nitrogen at a temperature of about 26,000 F and a residence time of about Burned for four hours. Mixtures have also been prepared that combine both aluminum and silicon metal powders shown. The overall results indicated that the mixtures produced with only a single addition of metal were put together, more stable and less porous at elevated temperatures were as mixtures with two metal admixtures. Below are also the different ones Binding phases listed in Table 1.

T A B E L L E I MIXTURE 1 2 3 4 5 6 7 Mullite melt 72% 92% - - - - 96.5 Fired clay - - 72% 69% - - -synthetic aluminum oxide - - - - 72% - -Magneiospinell 5 - - - - - 72% silica, less than 1 micron 6 4 6 6 6 6 1.5 aluminum 13 3 13 13 13 13 1.0 Raw clay 2 1 2 - 2 2 1.0 Silicon 10 - - - 5 - - -Silica - 100 Mesh size 7 - 7 7 7 7 - Apparent porosity% 20.4 18.3 21.1 22.2 19.8 17.9 19.0 Modulus of rupture at room temperature 4130 2360 3340 2320 1970 3060 1800 Modulus of rupture psi at 1092 ° C 3340 - 2790 2480 2570 3890 - main binding phase (beta'- magnesium silicon Prime # Sialon Oxynitride Sialon) Poytyp In the case of the above Mixed the classification of the refractory aggregate was shown that about 7 to 20% of the mesh size 10, about 23 to 36% of that of -10 +28, about 15 to 1 of that of -28 +65, about 7 to 10% that of -65 + 200 and about 30 to 35% of one mesh size over 200 corresponded (this is based on the mesh sizes of the Tyler scale).

In the raw materials used above, it was aluminum powder pure aluminum metal and the silica content was over 98% SiO2.

The refractory aggregate used in the examples has the following approximate proportions, which are those in the below in the Table II are listed.

TABLE II Fired Raw Mullite Synth. Magnesian fire clay melt Aluminum spinel oxide SiO2 47.3% 62.9% 22.9 0.1% 0.2% Al203 49.2 33.5 76.4 99.6 69.0 TiO2 2.4 2.1 0.1 0.01 0.04 Fe2O3 1.0 1.0 0.3 0.2 0.09 CaO 0.02 0.2 - 0.04 0.54 MgO 0.04 0.3 - 0.04 30.1 Alk. 0.08 0.5 0.35 0.05 all chemical content information are based on an oxide analysis.

Claims (9)

Claims; i} Process for the production of nitride-bonded Refractories in situ not shown by mixing approx 1 to 25% by weight of aluminum, about 1 to 15% by weight of essentially pure silica mass, about 1 to 5 wt. yv raw tuna and the rest from a classified refractory aggregate for the production of refractory bricks, by compression molding these mixtures and by Firing of shaped bodies in a nitriding atmosphere at an elevated temperature for a period of time sufficient for the nitride bond to form. 2. The method according to claim 1, d a d u r c h g e -k e n n z e i c h n e t that the refractory aggregate is chosen from a group to the fired clay, molten mullite, synthetic alumina and magnesia spinel belong. 3. The method of claim 1, d a d u r c h g e -k e n n z e i c h n e t that the aluminum content is 3 to 13 wt.%, the proportion of the practically pure Slicamasse at about 4 to 13 wt.% And the raw clay content at about 1 to 2 wt.% Of the Mixture lies. 4. The method according to claim 1, d a d u r c h g e -k e n n z e i c h n e t that the refractory body is between about 1090 and 175ob G lying Temperature to be fired. 5. The method of claim 1, d a d u r c h g e -k e n n z e i c h n e t that the nitriding atmosphere is selected from a group including the gaseous Include nitrogen, industrial furnace gases, and ammonia gas. 6. Nitride-bonded refractory bodies d a d u r c h ek e n n z e i c h n e t that it consists of an offset consisting essentially of about 1 to 25 % By weight of aluminum, about 1 to 25% by weight of practically pure silica, about 1 to 5% by weight raw clay and the remainder from a refractory aggregate is made. 7. Refractory body according to claim 6, d a d u r c h g ek e n n z e i c h n e t that the refractory aggregate is selected from a group to which Fired clay, molten mullite, synthetic aluminum oxide and magnesia spinel belong. 8. Refractory body according to claim 6, d a d u r c h g e k e n n z e i c h n e t that the proportions of aluminum at about 3 to 13 wt.%, practically purer Silica at about 4 to 13% by weight and of raw clay at about 1 to 2% by weight of the batch lie. 9. Refractory body according to claim 6, d a d u r c h g e k e n n z e i c h n e t that the nitride bond is at least one bond selected from a group is, to the beta '- sialon (beta prime sialon), silicon oxide nitride, beta silicon nitride, Alpha silicon nitride and magnesia sialon include.