JPS6121961A - Glass coated ceramic particle - 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 (Field of Industrial Application) The present invention relates to glass-coated ceramic particles and a method for producing the same.

The increased use of ceramics has led to research into techniques that maintain the electrical properties and heat resistance of ceramics while at the same time reducing their tendency to fracture under a given load strip 41.

BACKGROUND OF THE INVENTION One of the conventional techniques for manufacturing many ceramic articles, preferably alumina ceramic articles, is slip casting.

In order to obtain a rheologically stable suspension using this method, a wide distribution of particle sizes is required.

This is easily achieved by controlling the particle size distribution and flocculant performance requirements in a single phase suspension. however,
A second particulate phase may be added to change the properties of the product. Unfortunately, however, the addition of such a second phase results in surface charge effects, solubility differences, and changes in particle size distribution resulting in a rheologically unstable slip. The complexity of the suspension increases due to the overpowering components of the suspension. Even in rheologically stable systems, these competing effects do not favor homogeneous mixing. On the contrary, it results in an increase in the final ceramic microstructure containing a range of separate secondary and tertiary phases which inherently reduces agglomeration, pore distribution and material properties.

Published December 26, 967 by Edward J., Smoke and Nicholas H. Snyder.
H.

5nyder> [Prereacting technology of raw materials to obtain high performance ceramics (Prereacting R
aw Material Technique for
Attaining High Quality C
U.S. Pat. No. 3,360, entitled
No. 203 describes a new method for producing a high quality alumina ceramic material with a true density close to 100% by pulverizing and removing hoyts in the material by a method that utilizes fine particles and fine particle distribution. In this process, each particle is essentially of the same composition, and any compositional discontinuities are well dispersed when mixed by milling and then batch-formed. Even in this prior art it is possible to add minerals such as talc and clay within the composition range which do not form two or more phases.

PROBLEMS SOLVED BY THE INVENTION Methods for manufacturing glass and ceramic mixtures by casting are known and are described, for example, in US Pat. No. 3,706,582@ to Meyer. However, in this type of product the glass phase is located at the grain boundaries.

Therefore, a crack growth reaction occurs along the glass phase. Therefore, in order to increase the strength of the material, it is desirable to maintain the low temperature adhesion properties of the glass while at the same time obtaining strong internal ceramic particle bonding.

(Means for Solving the Problems) An object of the present invention is to create a new composite particle of glass and ceramic in which the ceramic part of most of the particles in the composition is partially coated with glass having a homogeneous composition. The goal is to provide materials. Most particles have at least the ceramic portion covered by glass, but not all of it. The novel material of the present invention is produced by dry mixing ceramic and glass frits in which a homogeneous mixture is suspended in an aqueous slurry and then sieving to produce particles of a predetermined size range, preferably about 5 to 15
Mesh particles are obtained and molded.

These particles are dried, heated to a temperature of about 925°C to about 1600°C, and soaked at a slightly lower temperature.
L/, cool to room temperature. Particles consisting of agglomerates of ceramic coated with glass (of course with some alumina dissolved in the glass) are reduced in particle size, preferably successively with water in a jaw crusher and ball mill.
A suspension of fine particles of about 5-10 microns is obtained, which is then sieved and dried. These particles expose glass and ceramic surfaces and form glass/glass, ceramic/ceramic and ceramic/glass bonds.

After that, they are successively cast and fired. The firing temperature is about 950 to about 1500°C, preferably about 1120 to about 14°C.
It is 00℃. Products obtained in this way have greater bending strength than products obtained by conventional methods.

It is an object of the present invention to provide a new composite ceramic material and method for its production that involves the addition of second phase particles to fine alumina particles. U.S. Patent No. 3.360,2
No. 03 describes an improvement and modification of the pre-reaction method in which second phase glass particles are added to alumina or other ceramic materials to create a composite material with superior properties that can be applied to slurry casting and other ceramic materials. It can be molded by a molding method.

(Example) Ceramics including the field of the present invention have approximately 500 to 200
All inorganic, non-metallic substances having a crystalline structure that are solid in the 0°C range are included. Furthermore, the term "glass" as used herein includes a solid, at least 500 to
It also broadly contains amorphous inorganic materials that have essentially no flow properties in the temperature range of 2000°C. For those skilled in the art:
It will be appreciated that many substances belong to both of the above categories.

The most commonly used ceramics include several forms of alumina. The ceramic need not be chemically pure for this invention.

For those skilled in the art of ceramics, common purity specifications of the material are applicable here. This descriptive example was carried out with pure alumina because pure alumina is readily available and its properties are easy to chemically measure.

However, this purity should not be considered as limiting the invention in any way. Conventional charring ceramic materials can also be used.

Similarly, with respect to glasses, those skilled in the art are well aware of the compositions of available glasses and the properties associated with various glass compositions. It is an object of the present invention to effectively use the present invention with glasses that provide suitable end product properties. In particular, the glass used includes fused silica,
Includes borosilicates, soda lime silica, germanium glasses, lead glasses, and halide glasses.

This specification is intended to be comprehensive but not limiting. In fact, for ease of scientific measurements, the preferred embodiments of the present invention use silica-based glasses containing about 45-100% by weight silica, preferably about 70% by weight. It was carried out. Similarly, it contains about 5.5% to about 25% by weight of boron oxide, about 5% to about 25% by weight of calcium oxide, and about 3.5% to about 25% by weight of sodium oxide. Furthermore, it will be clear to a person skilled in the art that it is consistent with the end result conditions that the glass used in the present invention contains 0 to 100% by weight of silica. The thermal expansion coefficient of the glass is approximately 4.75-13, 75X 10'
cm-1. However, from the point of view of convenience,
In the present invention, it is possible to use glasses having a wide range of softening points, but in reality, glasses having a transition temperature of 1000° C. or lower were used. This ensures that the glass softens and flows below that temperature of the ceramic component of the mixture.

In a preferred embodiment of the present invention, an alumina composition consisting of various amounts of alumina and glass frit powder was first dried at a temperature above 300° C., but below the softening point of the glass, for 1 hour or more. These powders were dry mixed in a set of shell mixers for 0.5 to 2 hours, preferably for 1 hour to form a mixed composition. A mixed composition of 95-50% by weight alumina and the balance glass frit is preferred. More preferably, the alumina content is 75 to 95% by weight, more preferably 80 to 90% by weight. The ratio of Al2O3 or Iya ceramic to glass frit is not particularly critical, but is indicative of the range used. It should be noted that this ratio can be varied greatly depending on the desired firing temperature and desired resulting properties. After the materials are dry mixed, immediately in a Muller" or other type mixer, from about 1 to about 5% by weight, preferably about 3% by weight.
Wet mix with about 10 to about 30% by weight water, preferably about 20% by weight water containing a water retention agent to form a wet mixture suitable for sieving.

Sodium alginate is a water-retaining agent.

This wet mixture was sieved to obtain particles of 6 to 12 meshes. When more water is added to the above mixture, the
It was found that it could be extruded into small rods with a size of ~12 meshes. These particles were then collected in an alumina or sagger and dried.

A sagger containing agglomerated alumina or other ceramic/glass particles is placed in an electric furnace or other furnace, and
00 to 500°C/hour, preferably about 300°C/hour, depending on the composition, about 925 to about 160°C.
The temperature was increased to a soaking temperature of 0°C. The soaking temperature is about 100°C lower than the temperature at which the final product formed by the slurry casting process is fired, preferably about 900°C to about 15°C.
It's oo'c. . The temperature at which the final product is fired is referred to as the final firing temperature. Table A shows the relationship between the final firing temperature and the composition expressed as the percentage of glass added to the composition in a preferred embodiment.

11)! They were kept at soaking temperature for 2 hours. 500 furnaces
The mixture was cooled to room temperature at a temperature decreasing rate of °C/hour.

Once the particulate material had cooled, it was immediately removed from the furnace.

Because the glass frit softens at temperatures lower than those used in the pre-reaction, pre-baking soaking, the alumina and glass particles tend to bond together.

Jaw crush this material
er) to give a material of 6 to 12 meshes.

For alumina or other ceramic/glass compositions to be used in slurry casting processes, the 6-12 mesh particles must be further reduced to particles averaging 5-10 microns. This particle size reduction was achieved by whole milling.

A high alumina pebble mill with a capacity of 3 gallons (11.4 liters) or less was used. The grinding body consists of 96% alumina pulled into three different sizes. The mill insert consisted of 60% by volume of 1.5 inch balls, 25% by volume of 1 inch balls, and 15% by volume of 0.5 inch balls. Place the pulverized body into the mill with a capacity of 172
~578 inserted. The alumina/glass composition was added to a 3 gallon (11.4 liter) mill based on a water soluble solids content of 78% solids by weight and a volume of 1750 cm3 of water. It is preferred to use substances such as sodium hexametaphosphate and tetrasodium pyrophosphate as dispersants.

The grinding time depends on the percentage of glass present, but 36-4
8 hours or until the specific gravity of the suspension was at least 76% solids by weight of 325 mesh or less.

The resulting suspension was sieved through a 325 mesh stainless steel sieve, dried and stored until slurry casting. The resulting pre-reacted ceramic composition material is sufficiently homogeneous that it behaves rheologically like a single material, ie, a single surface charge. Flocculation problems resulting from the dissolution of various glasses in water are reduced and/or eliminated when alumina is incorporated into the glass. Pre-reacted alumina or other ceramics form homogeneous materials with less controlled particle size distribution than composites. Since the reaction between the alumina and the glass is essentially complete in the first firing step, the second firing step allows the glass to be more intimately dispersed into the alumina particles, resulting in a roughly uniform material.

The incorporation of one or more glasses from one or more raw materials according to the present invention results in the production of a highly homogeneous composition. A detailed and complete reaction is possible when glass touches alumina particles at high temperatures. However, the control parameters are limited or, once they are established, the resulting materials exhibit high reproducibility.

These high-performance materials are applied in ceramic composite sets ranging from macro to micro, such as electrical components, ceramic seals, ceramic engine parts, and ceramic fibers. The increased reactivity of the glass phase lends itself well to aluminum metal bonding at low temperatures.

Example 1 Pre-reaction of Alumina/Glass Composite In the pre-reaction step, alumina/glass composite consisting of 1.95% to 50% by weight of Al2O3 and various glass frits, in a proportion within the system.
The glass composition was dried in an oven at 300°C for 3 hours. The properties of these materials are shown in Tables 1, 2 and 3 below.

These powders were cooled to room temperature and mixed with a shell mixer (
Dry mixing was performed on a shelf m1xer for 1 hour. These materials were thoroughly dry mixed and then wet mixed with a 20% by weight aqueous solution of sodium alginate in a Muller type mixer for 30 minutes.

This mixture was sieved to obtain 2-12 mesh particles. These particles are dried in an alumina cage and then
Firing was carried out in a bottom load shifting rotary furnace with a volume of 12 ft3 (339,89). The furnace temperature was increased at a rate of about 300° C./hour and held at about 1 oo'c below the final firing temperature for 2 hours. Table 4 shows the pre-soaking reaction temperatures used for various alumina/glass composites. The furnace was cooled at a rate of 500°C/hour. The pre-reacted material was removed from the sagger and stored in double polyethylene bags. The glass frit is heated at a temperature lower than the temperature treated in the pre-reaction step.
It was sufficiently softened that sometimes the alumina/glass particles were found to form large agglomerates. The aggregated particles were crushed with a jaw crusher to obtain a material of 6 to 18 meshes.

It was necessary to reduce the particle size of the material to an average particle size of 5-10 μm. The particle size was reduced using a ball mill. For this purpose, the ball mill was equipped with a Lumard high alumina pebble mill (peb) with a capacity of 3 gallons (11,40>
ble m1ll) was used. The grinding body consists of 96% alumina pebbles of three different sizes. Mill inserts are 60% by volume for 1.5 inch (3,81 cm) balls, 25% by volume for 1 inch (2,54 cn+) holes, and 15% by volume for 0.5 inch (1°27 cm) holes.
Consists of. 172 to 5/8 of the capacity of the grinding body was inserted into the mill.

Alumina/glass composition with a volume of 3 gallons (11°=l)
The solution was added to a mill based on a solids content of 78% by weight based on the aqueous solution. Approximately 0.02% by weight of tetrasodium pyrophosphate was added as a dispersant (based on solids content).

It was ground for 72 to 76 hours depending on the percentage of glass involved. The resulting suspension was sieved through a 325 mesh stainless steel sieve and stored.

Table 1 A-163G Nominal chemical analysis substance name for alumina
Weight (%) △1203 99.5+ Na2O0,08 SlOz O,03 Fe203 0.01 (Left below) Table 3 Thermal expansion temperature range of alumina and five types of glass Thermal expansion coefficient TG Purchasing name (℃) ) (10-8/”C)(
°C) Glass A 100-400 4.75
440 Glass B 100-500 7.
96 565 Glass C100-5009,6055
0 glass D 100-500 9.75
495 Glass E 100-500 13
．． 75 525 Alumina 100-900
9.10 - Table 4 Pre-Reaction Soaking Temperature Alumina in Composite Temperature A suspension of 78% weight was obtained. The apparent viscosity was adjusted to 150-18° O centipoise using 1% tetrasodium pyrophosphate solution. The amount of slurry to be poured was passed through a 20 mesh sieve to remove bubbles generated during the previous step.

Slime Casting Step The alumina/glass suspension was rheologically adjusted and a pressure casting system was immediately assembled as shown in Figures 18 and 9. Assembly includes pre-wetting the plaster batts, evenly tightening the bolts, and finally pressure testing the system. If a leak could not be clearly detected, the alumina/glass suspension was injected through the two slip ports. The population was then covered with a perforated brass stopper and pressurized through the air inlet. 30Ωb/in2 (
Pure N2 at a pressure of pSi > (2,1 kMcm2)
A gas called . Cast molding was performed for 30 to 60 minutes, depending on the molding composition and conditions. Immediately after casting was completed, the pressure was released and the molding cavity was taken out from the slip inlet.

Remove the top plate and retaining bolts, disassemble the plaster butt and steel retaining structure, and set the molded body. For example, the compact could be easily separated from the steel holding structure due to shrinkage of the compact. The compact tile was allowed to dry until it could be easily removed from the plaster batt.

A method for obtaining a stable suspension of alumina and glass is shown below. Alumina 75% aqueous suspension and glass flin 1
-5% aqueous suspensions were prepared separately. Suspend the alumina in dilute HCQ solution and add the glass frit to Darvan No.

7). Immediately after suspension, each material was mixed in a high shear mixer for 30 minutes and then aged for 1 hour. The pH of each suspension was monitored and maintained between 4 and 5. The alumina and glass suspensions were added together and allowed to stand for 30 minutes. If necessary, Durban No. 7 (Durban No. 7,
7> to increase the slip viscosity to 150-200 centipo2
I adjusted it to the size. Prior to casting, the composite slip was sieved to 325 mesh or less.

] composite bending strength 95% by weight as a function of forming method
The bending strength of an alumina/glass C composite of 70% by weight was measured. Table 6 shows the flexural strength of dry pressed, non-pre-reacted slurry casting and pre-reacted composites. Table 5 shows the statistical differences between methods. As seen before, there were two strong domains in terms of alumina proportion. Although not obvious, the first domain of 95-75% by weight alumina is distinct from the second or lesser percentage domain of alumina. For 95% alumina composites, the maximum flexural strength of dry-pressed and non-pre-reacted slurry cast bi-molded composites is 2550 atm [3
7 Kpsi (255 MPa)] and 4350 atmospheres [63 Kpsi (435 MPa>]).

The two increases compared to the bending strength of the pre-reacted material are
A similar observation was made in the dry pressed composite.

The bending strength as a function of alumina content is shown in Table 5 and Figure 5.

The bending strength of other composites was measured according to the above method. The results are shown in Table 6 and in Figure 7.

(Margin below) Table 5 Table 6

[Brief explanation of the drawing]

FIG. 1 is a flowchart of a conventional manufacturing method consisting of dry mixing and dry pressing ceramic and glass frits. FIG. 2 is another prior art flowchart showing slit casting of alumina and glass frit. FIG. 3 is a flowchart illustrating the formation of pre-reacted composites and slurry casting according to the method of the present invention. FIG. 4 is a graph showing the aging temperature of the alumina and glass composite material after slurry casting as the weight percentage of alumina is varied. FIG. 5 is a graph showing the bending strength of alumina-glass composites fired by the methods of FIGS. 1, 2, and 3. FIG. 6 is a bar graph showing the flexural strength of prior art materials in light shading and the flexural strength of pre-reacted materials according to the invention in black shading. FIG. 7 is a diagram showing the bending strength of an alumina-glass composite prepared by the method of the present invention. FIG. 8 is a representative side view of an experimental pressure casting system for slurry casting compositions used in the present invention. 9 is a perspective view of a steel retaining structure for the apparatus of FIG. 8; FIG. 1...Air supply, 2...Slip inlet, 3.
...Bolt, 4...Top plate, 5...Gasket,
6... Steel frame, 7... Plaster batt,
8...Bottom plate, 9...Adjustment bolt. Patent Applicant Rutgarth the State University Agent Patent Attorney Murase -*=2゜To 55 Saryu FIG, 4 ioo 90 80 70
60 507 WAf (*t') FIG, 5 γ1Vmij-('l!t%nFIG, 7 7 LeE-j(%n to meeting 4)

Claims (15)

[Claims] (1) A composite particle material made of glass and ceramics, in which the ceramic portion of most of the particles in the composition is partially coated with glass of homogeneous composition. (2) Material according to claim 1, characterized in that the glass component consists of at least 45% by weight of silica. (3) A material according to claim 2, characterized in that the ceramic accounts for 50 to 95% by weight of the composition. (4) A material according to claim 2, characterized in that the ceramic accounts for 75-95% by weight of the composition. (5) A material according to claim 2, characterized in that the ceramic accounts for 80-90% by weight of the composition. (6) The material according to claim 2, wherein the ceramic material is alumina. (7) Glass is approximately 4.75 x 100^-^6~13.7
Material according to claim 2, characterized in that it has a coefficient of thermal expansion of 5 x 10^-^6 cm^-^1. (8) The glass composition includes about 45 to about 100% by weight silica, about 5.5 to about 25% by weight boron oxide, about 5 to about 2% by weight
3. The material of claim 2, comprising 5% by weight of calcium oxide and from about 3.5 to about 25% by weight of sodium oxide. (9) A product obtained from slurry casting the material of claim 2 and aging at a temperature of about 950 to about 1500C. (10) A product obtained according to claim 9, characterized in that the ripening temperature is from about 1120 to about 1400°C. (11) (a) dry mixing the ceramic and glass frit; (b) preparing an aqueous slurry of the mixture; (c) sieving the mixture to obtain particles of about 5-15 mesh; (d) collecting and drying the particles; (e) soaking the particles at a temperature of about 900 to about 1500°C; and (f) cooling the particles and reducing the particle size to about 5 to about 10 microns. A method for producing a composite particle material consisting of glass and ceramics, comprising partially coating the ceramic portion of most of the particles in a composition with glass having a homogeneous composition. (12) The particle size is reduced by a continuous process of crushing in a jaw crusher and then in a ball mill in a water/dispersant medium.
The method described in Section 1. (13) The method according to claim 11, wherein the ceramic is alumina. 14. A method according to claim 11, characterized in that the glass of the glass frit consists of at least 45% by weight silica. (15) The glass composition includes about 45 to about 100% by weight silica, about 5.5 to about 25% by weight boron oxide, about 5 to about 25% by weight calcium oxide, and about 3.5 to about 25% by weight
12. Process according to claim 11, characterized in that it consists of % by weight of sodium oxide.