JPH0577622B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a refractory shaped article containing a stable acidic aqueous colloidal zirconia sol. A well-known method, namely mixing a binder and a gelling agent with a refractory material, chemically solidifying or gelling the mixture to form a bond, and then firing the object, is used to manufacture ceramic objects. It has been traditionally used in Typically, many structures have been fabricated using sodium silicate, potassium silicate, colloidal silica, and hydrolyzed ethyl silicate as binders. However, to obtain objects with maximum fire resistance, binders that leave more refractory oxides are preferred. For example, alumina and zirconia create a high temperature bond for refractory materials. US Pat. No. 4,025,350 shows the use of an aqueous solution of a zirconium salt together with a gel inducing and retarding agent and a refractory powder to form a refractory article. This composition requires additional gelling agents to limit cost increases and limit problems. Also, by-products of zirconium salt gelation may need to be eliminated during firing.
Also, the cost of zirconium salt versus oxide is added. US Pat. No. 4,201,594 describes bonding refractories with zirconium salts and incorporating gelling agents and gel retarders. For the same reason, these compositions are less desirable. US Pat. No. 2,984,576 describes green mixtures of refractories bound with zirconia or hafnia sols in which the percentage of solids in the dispersed phase is at least 30%. This patent does not describe any particular refractory materials useful for use with the stable acidic zirconia sols of the present invention, only binders for various refractory materials. U.S. Pat. No. 3,758,316 describes a method for making refractories from a refractory powder and a binder precursor, and the binder pre-drive material includes colloidal zirconia, but also requires the addition of a gelling agent. . The basic principle of the invention is to create a refractory mixture consisting of a refractory material and a stable acidic zirconia sol with fine particle size and acidic PH. The refractory material is comprised of an active portion and, optionally, a relatively inert portion. Highly refractory materials will be relatively inert to zirconia sol. However, a number of refractory materials are not completely inert to the zirconia sol and actually react with it, causing it to gel. Very fast or slow gels can be produced depending on the specific type of active refractory material, its particle size distribution, and its distribution in the refractory mixture. Some examples of active refractories that gel with zirconia sols are alkali metal and alkaline earth metal aluminates, silicates, zirconates, stannates, titanates, silicates of zirconium. and oxides. Specific examples are: calcined magnesium oxide,
Electrolytically fused magnesium oxide, calcium oxide, electrically fused calcium oxide, monocalcium aluminate, calcium aluminate cement, fused akinite, high alkali glass, magnesium aluminate, magnesium aluminum silicate, magnesium zirconate , magnesium silicate, magnesium zirconium silicate, magnesium ferrite, magnesium titanate, magnesium stannate, calcium zirconate, calcium silicate, calcium zirconium silicate, calcium titanate, calcium stannate, barium zirconium, barium aluminum silicate, Barium aluminate, barium zirconium silicate, barium stannate, barium titanate, barium silicate, strontium zirconate, strontium stannate, strontium zirconium silicate, strontium silicate, strontium aluminum silicate, strontium titanate, electrically Fused calcium oxide stabilized zirconia, electrofused magnesium oxide stabilized zirconia, iron chromite, Zeolex 23, wollastonite, bentonite, strontium aluminate, phorsterite, calcium aluminum silicate, fluorspar, fluorite Fluorbarite, lithium zirconate, lithium aluminate, lithium silicate, lithium aluminum silicate, lithium titanate, lithium zirconium silicate, and other refractory materials that are reactive with zirconia sols. Some relatively non-reactive refractory materials are: monoclinic zirconia, hafnia, alumina,
Bauxite, mullite, sillimanite, zircon, ceria, thoria, silicon nitride, silica and other substances that do not contain large amounts of impurities in their structure that can react with oxides of alkali metals and alkaline earth metals or with zirconium sols. This system can also be used as a binder for various fibers made from aluminosilicate, low alkali glass, alumina, zirconia, silica, and various organic fibers, such as silk, rayon, nylon, and other synthetic fibers. . The aqueous zirconia sols used in the examples described herein are acidic, with a pH ranging from about 0.3 to 6.0. The particle size of zirconia particles is generally small, on the order of 25 millimicrons or less. The sol is stabilized with acids such as nitric acid, hydrochloric acid, acetic acid, etc.
The sol-forming effect of the “active” refractory material on the sol is believed to be due to the reaction between the acid and the “active” refractory material to form a “salt”, and this reaction increases the pH, thereby stabilizing the sol. decrease. The salt formed also catalyzes the gelation of the sol. This gelling reaction binds the refractory material into a strong object. Several factors govern the properties of the zirconia sol bonded refractory body. Examples of such factors are the type of acid in the sol, the particle size and age of the sol, the percentage of zirconia sol in the sol, the percentage and type of "active" refractory in the mixture, its particle size distribution, temperature, and This is a mixed condition. Listing potential "active" refractories often indicates oxides of alkali metals or alkaline earth metals in the structure of the refractory, or indicates that "active" refractories react with acids. It plays the role of reacting with sol. The presence of such "active" refractories will not only cause gelation, but will also serve as a sintering aid for certain refractory systems.
The relative scratch hardness of the bonded refractory material after firing is
It serves as a measure of the sintering effect of the "active" refractory material. One procedure utilizing the present invention is to produce cast refractory shapes by mixing a zirconia sol with at least one "active" refractory material. The remainder of the refractory material can include a relatively inert refractory material. In some cases, depending on the nature of the active refractory material, the total refractory material can be of the active type. In other cases, the "active" refractory material can be a very small portion of the total refractory material in the mixture. The particle size distribution and chemistry of the active refractory material are two of the primary factors that determine the amount of "active" refractory component. Various refractory shapes can be cast according to the present invention to produce practical products such as metal melting crucibles, ports,
tundish, injection ladle, injection tip, tube,
We can manufacture rods, slabs, bricks, sheaths, furnace accessories, furnace car tops, open hearth door exteriors, furnace parts, injection nozzles, furnace liners, etc. Such mixtures can also be used to cast metal casting tooth and jewelry molds. In particular, some of these mixtures are particularly suitable for casting molds of superalloys, stainless steel, niobium, tantalum, titanium and molybdenum. By choosing refractories that are inert at high temperatures or "active" refractories with low activity, such as zirconia, hafnia, ceria, alumina, ittria, lantana, they have very high PEC values and are free from the aforementioned reactive metals. Templates can be made that have low activity against some of the following. If desired, a pressing mixture can be prepared that "sets" or "gels" at a predetermined time in order to produce a refractory shaped article by pressing and subsequent solidification or gelation. Thin or thick films can be made from mixtures that can be cast onto a belt or mold and then gelled or solidified. The coating can be applied by dipping or spraying onto the mold or shape and then allowed to gel. The mixture according to the invention can be formed into profiled bricks by injection molding. Current ceramic injection molding techniques typically require various temporary bonding materials for the refractory body to facilitate molding. Examples include expensive waxes, resins, and plastics. These organic materials burn away leaving behind a hot binder and shrinkage occurs while the organic material is lost. The present invention provides a "green" bond and a fired bond in the refractory body. This technology is used to form various complex objects such as spindles, nozzles, ceramic cores for metal casting, ceramic turbine blades, shell mold parts for metal casting, and various other objects as required. Can be used for The primary application of this invention is to make cast refractory objects that solidify or gel in a controlled amount of time. The proportion of "active" refractory material can be adjusted according to the setting time required for the mass. This percentage is
Varies with certain “active” refractories. The resulting refractory mixture is then mixed with an appropriate amount of zirconia sol to a high pouring consistency and poured or cast into a mold;
It can be solidified. The particle size distribution of the refractory mixture can be varied according to the desired result, strength, settling in the mold and gelling time. It is usually advantageous to allow a suitable amount of time to thoroughly mix the refractory material before pouring it into the mold. This depends on the size of the mold and the equipment handling the mixture.
When using small volume manual mixing, mixing can usually be carried out within a very short time, for example within 1-2 minutes, and the mixture can then be prepared to gel or solidify very quickly. A relatively fast gelling time of 5 to 30 minutes is preferred for relatively fast shaped article production. It may be desirable to remove foam from the mixture and incorporate suitable wetting agents and defoamers to create a relatively foam and void free mass. It takes time to completely wet the mass and degas it before casting. Ideally, gelation should occur as soon as possible after injection. To illustrate the present invention, the data in Table 1 shows that when mixed with an inert refractory material, e.g., platy alumina,
Indicates the percentage of active refractory material that can produce a specific setting or gelling time. fireproof material,
Mix with zirconia sol containing 20% Zro ₂ and having a PH of 0.6. The alumina part is 50%
Small plate alumina of 325 mesh or less and 50%
(obtained from Alcoa). The percentage of active refractory is calculated based on the total amount of refractory used in the final mixture. All the samples shown in Table 1 have excellent green strength, and separately
(982.2℃), 2000〓(1093℃) and 2500〓
When fired at (1371°C), it had extremely excellent firing strength. A series of experiments similar to those in Table 1 were carried out according to Table 2, where the plate-like alumina refractory substrate was 25%
It consisted of small items of 325 meshes or less, and 75% of small items of 60 meshes or less. This table shows gel times for various mixtures with activated refractory materials. These were mixed with the same zirconia sol used in Table 1.
After gelling, these samples had excellent green strength, and after firing to the same temperature conditions, they had excellent fired strength. In all cases, the strength at 2500〓 (1371℃) is 2500〓
(1371℃) than those fired at a lower temperature. Several unique properties were observed for the compositions listed in Table 1. A series of specimens, approximately 1 inch (2.54 cm) thick, 1 inch (2.54 cm) wide and 2.375 inches (6.033 cm) long, were prepared in a mold using the same composition as prepared in Table 1. did. They were gelled and solidified for 30 minutes and then removed from the mold. After removal from the mold, the specimens were air dried in air overnight, then oven dried at 120° C. for 4 hours to remove all water from the shapes, and then placed in a desiccator for cooling. It was then removed and measured immediately. All test pieces were found to have shrunk by approximately 0.5 to 1% from the mold dimensions. After the specimens are dry, heat them to 1200
(648.9°C), maintained at that temperature for 2 hours, then allowed to cool to room temperature and remeasured. After measurement,
The specimens were reheated to 1800°C (982.2°C), held at that temperature for 2 hours, cooled, and then remeasured.
This same heating is done separately to 2000〓(1093℃) and
2500㎓ (1371°C), and then the specimens were measured. It was observed that many of the specimens experienced very small to significant measurable permanent expansion after cooling. As the data in Table 2 shows, permanent expansion was obtained for a certain number of cast specimens. Negative values indicate contraction. The remainder of the numbers indicate permanent expansion. As observed from this table, some substantial expansion occurs for certain samples. These expansions are not necessarily related to the proportion of active refractory material, but are clearly due to the presence of active refractory material. Each composition likely acts in a different manner and produces different reaction products that govern the amount of swelling obtained. This minimizes shrinkage during firing of the refractory body using this zirconia sol bonded system. Typically, when significant sintering occurs during firing of the refractory material to high temperatures, significant shrinkage occurs with sintering. Some compositions in the table below are 2500〓
It is observed that even when fired at (1371°C) it exhibits relatively low shrinkage. Table 3 shows 25% of 325
Test specimens were tested using plate alumina containing sub-mesh particles and 75% sub-60 mesh particles, along with a corresponding "active" refractory material. A similar series of measurements is shown. The following examples are examples of other refractories used with acid stabilized zirconia sols and demonstrate the use of "active" refractories. EXAMPLE Composition: Electro-fused calcium oxide stabilized zirconium oxide -325 mesh 30g Fused magnesium oxide -325 mesh
1 g Plate alumina 60 meshes or less 150 g Plate alumina −28+48 mesh 120 g This refractory composition was mixed with 35 ml of acid stabilized zirconia sol containing 20% Zro ₂ . Then,
They were poured into rubber molds. Gel time was determined to be approximately 5 minutes. After 30 minutes, the samples were removed from the mold and cut with a diamond saw into specimens for determination of the modulus of rupture. The green strength of this mixture was approximately 57 psi.
The sample was fired to 2500°C (1371°C), held for 2 hours, cooled to room temperature, and the modulus of rupture was determined to be 575psi. A similar firing to 2700°C (1482°C) for 2 hours followed by cooling resulted in a rupture modulus of 910psi. After firing for 2 hours at 2900° C. (1593° C.) and cooling, a rupture modulus of 1888 psi was obtained. EXAMPLE Composition: 240 g of platelet alumina-325 mesh 2 g of electrically fused magnesium oxide This was mixed with 45 ml of the same zirconia sol as in the example. Gel time for this mixture was approximately 4.5 minutes. Although raw modulus of rupture was not measured, specimens fired to 2000°C (1093°C) for 2 hours and cooled exhibited a modulus of rupture of 234 psi. After firing for 2 hours at 2500°C (1371°C) and cooling, the modulus of rupture was 1164 psi. 2700〓
(1482℃) for 2 hours and cooled to 2995psi.
The rupture coefficient was obtained. Specimens fired at 2900° C. (1593° C.) for 2 hours exhibited a modulus of rupture of 5674 psi. Examples Composition: EF zirconium oxide, calcium stabilized, −325 mesh 170 g −50+100 mesh −325 mesh 160 g −12+35 mesh −325 mesh 80 g This refractory composition was mixed with 30 ml of the zirconia sol used in the example. did. The gelation time was 8 minutes. After the specimen is fired to a certain temperature for 2 hours and tested after cooling, the modulus of rupture is as follows: Modulus of rupture, psi Unfired 278 2000〓 (1093℃) 479 2500〓 (1371℃) 1888 2700〓 (1482℃) 2019 2900〓(1593℃) 2623 Examples, and the test pieces from
Measurements before firing and after each firing gave the following percentages of permanent expansion (+) or contraction (-):

TABLE The occurrence of some permanent expansion may help eliminate or minimize settling and drying shrinkage for certain compositions, thereby increasing dimensional accuracy in the build. The following is an example of a typical Schiermolt system with which the present invention can be used: Composition: 2000g electrically fused calcium oxide stabilized zirconium oxide Zirconia sol containing 20% Zro ₂
500g concentrated hydrochloric acid 17ml wetting agent - 15 drops of SteroxN J This slurry was prepared to have a viscosity of 34 seconds as measured by a Zahn #4 cup. A sheet of wax, approximately 1/8 inch (0.318 cm) thick x 2.5 inches (6.35 cm) wide x 5.5 inches (13.97 cm) long, was immersed in this slurry and used in this slurry. −50 of the same composition
While the +100 mesh zirconia is wet,
Applied immediately. After dipping several specimens, this slurry was diluted with zirconia sol to a viscosity of 15 seconds, and after the first dip was dried overnight,
Additional soaking was applied. While the second coating was still wet, it was applied with a -12+35 mesh of relatively coarse zirconia granules of the same composition as the material in the slurry. Repeat this for additional coatings,
A final sealing coat was then applied, forming a total of 6 stucco layers and 7 slurry layers. Two daily dips were applied with the final dip. The soaked test piece was then dried for two days to melt the wax. The specimens were then cut to 1 inch (2.54 cm) widths, dried, and then tested for green strength. Six specimens were tested and an average modulus of rupture value of 500 psi was obtained. Add additional specimens to 2000〓(1093
The samples were baked for 2 hours at various temperatures starting at 30°F (°C), returned to room temperature, and tested. After firing to 2000°C (1093°C), the MOR was 220psi. 2200〓(1204℃)
After calcination and cooling to room temperature, the MOR was 300 psi. After firing at 2500〓(1371℃), MOR is
Increased to 1200psi. As shown by this,
Substantial strength has been obtained for shell mold compositions utilizing the present invention.

[Table] Mu

[Table] Metsuyu

【table】

【table】

Claims (1)

[Scope of Claims] 1. An acid-stabilized aqueous colloidal zirconia sol is mixed with a refractory material, where the refractory material consists of an active refractory material capable of gelling the sol, and wherein the refractory material comprises an active refractory material capable of gelling the sol. A method for producing a green refractory shaped article, which is present in a sufficient amount and is characterized in that, before gelling, the mixture is formed into a shaped article and the sol is gelled. 2. The method according to claim 1, wherein when mixing the acid-stabilized zirconia sol and the active refractory material, an inert refractory material is also present and mixed together. 3. Claims in which the active refractory material is selected from the group consisting of alkali metal and alkaline earth metal aluminates, silicates, zirconates, stannates, titanates, silicates and oxides of zirconium. The method described in Scope 1. 4. The mixture has a pourable consistency, and the object is formed by pouring the mixture into a mold, curing the mixture, and removing the cured object from the mold. The method described in section. 5. Claims for bringing the mixture to a consistency suitable for injection molding, then adding the mixture to an injection molding device, thereby injecting the mixture into a closed mold, gelling the mixture, and removing the shaped article from the mold. 1st
The method described in section. 6. The method according to claim 1, wherein the mixture is placed in a mold, the mixture is formed into a final shaped article, the mixture is gelled, and the gelled refractory shaped article is removed from the mold. 7. The method according to claim 1, wherein the refractory shaped article is a refractory core. 8. The method according to claim 1, wherein the refractory shaped article is of a refractory type. 9 The active refractory material is calcined magnesium oxide, electrically fused magnesium oxide, calcium oxide,
electrically fused calcium oxide, monocalcium aluminate, calcium aluminate cement,
Fused akinite, high alkali glass, magnesium aluminate, magnesium aluminum silicate, magnesium zirconate, magnesium silicate, magnesium zirconium silicate, magnesium ferrite, magnesium titanate, magnesium stannate, calcium zirconate,
Calcium silicate, calcium zirconium silicate, calcium titanate, calcium stannate, barium zirconium, barium aluminum silicate, barium aluminate, barium zirconium silicate, barium stannate, barium titanate, barium silicate, strontium zirconate,
Strontium stannate, strontium zirconium silicate, strontium silicate, strontium aluminum silicate, strontium titanate, electrically fused calcium oxide stabilized zirconia, electrically fused magnesium oxide stabilized zirconia, iron chromite, wollastonite , bentonite, strontium aluminate,
selected from the group consisting of forsterite, calcium aluminum silicate, fluorspar, fluorbarite, lithium zirconate, lithium aluminate, lithium silicate, lithium aluminum silicate, lithium titanate, lithium zirconium silicate, A method according to claim 1.