Ceramic material and method for its preparing

FIELD: ceramic industry.

SUBSTANCE: invention relates to the development of ceramic material for heat regenerative oxidants not subjecting to volume changes during heat cycles. Ceramic material is prepared by using ceramic components that comprise, wt.-%: spodumene, 5-20 by weight, and from 40 to 95 other ceramics-forming components comprising 50-95 of clay and 5-50 of feldspar. Proposed material shows decreased shrinkage in annealing and improved physical properties.

EFFECT: improved preparing method, valuable properties of material.

6 cl, 2 ex

Prerequisites to the creation of inventions

The present invention relates to the creation of a ceramic material, in particular material useful in the processes of mass transfer when the material is subjected to repeated thermodynamic (heat) cycles. An important example of the use of this advanced material is a regenerative thermal oxidizers (RTOs). Normal material when exposed to thermal cycles undergoes a volume change during thermal cycles, which can lead to the weakening or even loss of physical integrity, especially when exposed to abrasive forces or static forces from the load of material in thermal oxidizer or in other industrial column. Therefore, a material with a reduced sensitivity to dimensional changes during thermal cycles has a great attraction.

Another problem of conventional ceramic materials is that they inherently have large volumetric change during firing. Such materials are usually obtained by mixing suitable forming of ceramics raw materials, such as clay, feldspar, talc, wollastonite, zircon sand and other minerals. Then from this mixture get moldable mixture is formed into a so-called "raw", which has the shape (configuration) desirable Coeur is chemical products, but other physical properties, and then convert the raw to the desired material by firing raw at elevated temperatures. During firing components interact through a combination of mechanisms of solid state sintering, liquid phase and vapor phase, resulting in getting the desired ceramic material. The problem is that when firing the shaped raw usually changes the volume, which can easily reach 25-35%. The firing in the kiln, which has a limited volume. Thus, the oven allows the volume of the ceramic product, which ranges from 3/4 to 2/3 of the volume loaded raw, which makes the process very inefficient.

For example, JP 56109869 discloses a mixture for the production of ceramic material containing 50-95% glass (SiO₂68,5, Al₂About₃19,8, Li₂O 3,7, TiO₂, 1,9, ZrO₂2.0 and P₂About₅1,2%), 3-30% kaolin clay and 2-30% feldspar, which is fired at a temperature of 1100-1300°C.

In accordance with this invention proposes a ceramic composition and the process of firing, which allow to obtain ceramics with small volume changes or with a small deterioration in physical properties due to exposure to thermal cycles, and reduce or eliminate the performance degradation due to the decline in selling the KTA during firing.

The invention

In accordance with this invention features a ceramic material obtained by firing a raw material formed of a mixture which contains from 5 to 20 wt.%, and from 80 to 95 other forming a ceramic component containing from 50 to 95 wt.% clay and 5 to 50 wt.% feldspar, and this material has a linear shrinkage of less than 2.5%, in comparison with the size before firing.

Spodumene this material contains from to 7.25 to 7.75% wt. lithium in terms of oxide of lithium.

In accordance with the present invention a method of manufacturing a ceramic material, which includes the following operations:

(a) forming from a mixture which contains from 5 to 20 wt.% spodumene and from 80 to 95 wt.% other forming a ceramic component containing from 50 to 95 wt.% clay and 5 to 50 wt.% feldspar, crude, having a desired shape (configuration); and

b) the firing of raw sugar at a temperature of from 1100 to 1300°to obtain a ceramic material (product, product);

and forming a ceramic components is chosen so that after firing the linear dimensions of raw sugar was reduced by more than 2.5%.

Spodumene is a naturally occurring mineral that is formed from a mixture of aluminosilicates lithium and sodium, and two standard mineralogists "kunzite and hiddenite", with the generic name "triptan". Preferred main mineral is aluminosilicate lithium with lithium content in the mineral, measured as the oxide of lithium, in the range approximately from of 7.25 and 7.75% by weight.

Clays are mixtures of aluminum oxide and silicon dioxide, and include materials such as kaolin, ball clay, fire clay, etc. Preferred clays are highly plastic clay such as ball clay and fire clay. Particularly preferred clays contain methylene blue index ("MBI"), in the amount of approximately from 11 to 13 meq/100 g

Methylene index is a measure of the absorption of clay methylene blue dye and measured the standard method for methylene blue index of clay S-99 (2003).

The term "feldspar" is used here to denote a silicate of alumina and soda, potash and lime.

Other components, such as quartz, zircon sand, feldspar, clay, montmorillonite, nepheline syenite, etc. may also be present in small quantities in other forming ceramics components of the compositions in accordance with the present invention, provided that the resulting compositions meet the above requirements resizing.

Components that are fired jointly to p the receipt of ceramic products in accordance with the present invention, mainly injected into the mixture in the form of fine powders and molded mixture by adding water and/or extrusion additives. The shape can be made by molding, however, economic considerations forced to use the initial extrusion process, followed by cutting the extrudate is perpendicular to the direction of extrusion into pieces of the desired length.

Sintered ceramic material has an apparent open porosity, comprising less than 8% by volume, and mostly less than 4% by volume. The amount of absorbed water is less than 4% by weight, and mostly less than 2% by weight.

The process, in accordance with which can be made of ceramic material includes mixing the components with medium agitation, such as water, and receiving from a mixture of raw desirable shape, for example, by extrusion or molding, followed by drying raw at a temperature sufficient to remove bound water, over time, mostly amounting to several hours. This is necessary in order to avoid the destruction of the weak structure of the raw material and the drying is usually carried out at a temperature below approximately 120°and often below approximately 70°With, in the course of time of about 5 hours. Dried raw then calcined at elevated temp is the temperature, for example, from 1100 to 1300°to which come gradually over time from approximately 3 to 20 hours, and is usually kept in the course of time from 1 to 5 hours earlier gradual cooling to ambient temperature.

Ceramic material in accordance with the present invention may be in the form of monoliths with multiple through holes, however, this material mainly has the appearance of random packings, having the form of rings, cylinders, spheres, granules, etc. Products this form is placed in the heat exchanger randomly (in bulk), so as to accommodate the available space.

Ceramic material in accordance with the present invention has an additional unexpected advantage associated with the fact that he usually loses less than 10% resistance to crushing, and mostly less than 5% resistance to crushing, after a temperature cycle 800°C. In fact, often such ceramic material seems to even increase its resistance to crushing.

Description of the preferred variants of the present invention

Hereinafter the invention will be described with reference to the following Examples serve only to illustrate the present invention and are not restrictive. In the Examples, the following materials were used:

CH is us:

Ball clay, which is supplied by the company Unimin Co. or ..Clay Co., as "highly plastic clay. In any case, it contains methylene blue index (MBI) in an amount of about 11 to 13 meq/100 g Clay takes the form of a powder with particles, 90% by weight are smaller than 10 microns.

Fire clay, which is supplied by the firm Cedar Heights Clay Co. It contains MBI in the amount of approximately from 7 to 8 meq/100 g and has a particle size in the range from 0.5 μm to 20 μm with an average particle size of approximately from 3 to 4 microns.

Spodumene:

The spodumene concentrate is supplied by the firm Gwalia Co. or Tantalum Mining Co., in the form of a powder having a particle size in the range from approximately 20 to 200 microns, with an average particle size of approximately from 85 to 95 μm, and the lithium content, measured as lithium oxide constituting from to 7.25 to 7.75% by weight.

Other minerals:

Feldspar

a) 30 mesh, treated fraction with a particle size of at least 10% larger than 40 mesh, and at least 70% larger than 100 mesh. The full content of sodium and potassium, as measured by the content of their oxides is at least 10% by weight;

b) 200 mesh sodium feldspar, in which the content of sodium oxide is 6.5% by weight, and the content of potassium oxide is about 4.1% by weight;

c) feldspathic conglomerate;

d) the nepheline syenite.

Example 1

Three parties ceramic then SKOV were prepared from a mixture of powders of 30 mesh refractory clay, 20 mesh feldspar and spodumene. The first batch, which in this Example is called "standard", contains 408 g refractory clay (60%wt.) and 272 g of feldspar (40 wt.%). The second batch, which is 11.8% spodumene contains 408 g refractory clay (60 wt.%), 192 g of feldspar (28.2 wt.%) and 80 g of spodumene (11.8 wt.%). Third party, which is 17.6% spodumene contains 408 g refractory clay (60 wt.%), 152 g of feldspar (22.4 wt.%) and 120 g of spodumene (17.6 wt.%).

The components of each batch were mixed together in a high-speed stirrer for 1 minute. Then added 120 g of deionized water (17.65% wt. in terms of dry weight) and stirring continued until a homogeneous consistency. Then each batch of the mixture was applied in a laboratory single-screw extruder and was extrudible through the rectangular head of the extruder with the sides of the cross section 16.5 mm and 13.5 mm Extruded raw each batch cut perpendicular to the direction of extrusion into pieces with a length of 25 mm After undergoing a complete drying of the obtained pieces of raw and each piece was measured over the long side of the cross-section. Then the samples were subjected to firing, the temperature was increased with a speed of 3°C per minute to a maximum temperature of 1170°C, aged at 1170°C for 2 hours. After firing again measured the size of the specified Bo is its long side and was calculated by linear shrinkage. For a standard party, party with 11.8% spodumene and party with 17.6% spodumene received 2.35 respectively, and 2.44 2.71% linear shrinkage. Then, in accordance with ASTM C-373 determined the percentage of water absorption, which for a standard party, party with 11.8% spodumene and party with 17.6% spodumene, respectively 6.03, 2.37, and 1.63 percent. This shows that at approximately the same linear shrinkage additive spodumene can reduce the percentage of water absorption.

Several annealed samples were subjected to thermal shock due to heating up to 700°and rapid cooling in 19 liters of water at room temperature. Measured the resistance to crushing of the samples subjected to thermal shock, and compared with the resistance to crushing for samples not subjected to thermal shock, for each of the tested composition. Slices (perpendicular to the direction of extrusion) pieces with a length of 25 mm were subjected to mechanical processing to achieve their flatness. Then measured the resistance to crushing in the direction of extrusion of the individual samples, mounted in a spherical seat silicon nitride, using machine brand "Instron" with a maximum load of 10,000 kg, and the sample was placed between parallel steel plates and the plates were mixed at a speed of 25 mm/min When the destruction is of brazza readings machine "Instron" fell sharply. The maximal value corresponds to the resistance to crushing. The average resistance to crushing for samples standard party, party with 11.8% spodumene and party with 17.6% spodumene, which has not been hardened, respectively 167 MPa, 254 MPa and 272 MPa. The average resistance to crushing for samples standard party, party with 11.8% spodumene and party with 17.6% spodumene, which were hardening, respectively 137, 215 and 256 MPa. It displays the retention of resistance to crushing for samples standard party, party with 11.8% spodumene and party with 17.6% spodumene, constituting, respectively, 82, 85, and 94%.

Example 2

Three parties ceramic powders were prepared from a mixture of powders of 30 mesh refractory clay, 20 mesh feldspar and spodumene. The first batch, which in this Example is called "standard", contains 408 g refractory clay (60%wt.) and 272 g of feldspar (40 wt.%). The second batch, which has a 5% spodumene, also contains 387.6 g fireclay 30 mesh (57 wt.%), 258.4 g feldspar (38 wt.%) and 34 g of spodumene (5 wt.%). Third party, which has 20% spodumene, also contains 326.4 g fireclay 30 mesh (48 wt.%), 217.6 g of feldspar (32 wt.%) and 136 g of spodumene (20 wt.%).

Components of a standard party mixed together in a high-speed stirrer for 1 minute. Then added 120 g deion tirovannoj water (17.65% wt. in terms of dry weight) and stirring continued until a homogeneous consistency. For parties with 5% spodumene and 20% spodumene, refractory clay and feldspar mixed together in a high-speed stirrer for 1 minute. Spodumene was pre-dispersed in water using a high speed stirrer. Then a solution of spodumene was added to the other components in the mixer, and mixing was continued at high speed until homogenous.

Then each batch of the mixture was applied in a laboratory single-screw extruder and was extrudible through the rectangular head of the extruder with the sides of the cross section 16.5 mm and 13.5 mm Extruded raw each batch cut perpendicular to the direction of extrusion into pieces with a length of 25 mm After undergoing a complete drying of the obtained pieces of raw and each piece was measured over the long side of the cross-section. Then (5×3) samples of each batch were subjected to firing, the temperature was increased with a speed of 3°C per minute to a maximum temperature of 1140°S, 1170°and 1200°With exposure time at the maximum temperature for 2 hours. After firing again measured the size of the specified longer sides and calculated linear shrinkage. For a standard party, party with 5% spodumene and party with 20% spodumene, who fired at 1140°received 3.72 respectively, 4.35 and 3.99 percent linear shrinkage. For mill artney party, party with 5% spodumene and party with 20% spodumene, who were firing at 1170°received respectively 4.13, 4.01, and 2.60 percent linear shrinkage. For a standard party, party with 5% spodumene and party with 20% spodumene, who were firing at 1200°received 4.27 respectively, 4.18 percent linear shrinkage and is 3.46 percent linear expansion. This shows that the party with 20% pre-dispersed spodumene linear shrinkage is reduced in the case of annealing at 1170°and 1200°compared with a standard party.

Then determined the percentage of water absorption, which for samples standard party, party with 5% spodumene and party with 20% spodumene, who fired at 1140°With, respectively 4.97, 3.34 and 0.12 percent. The percentage of water absorption for samples standard party, party with 5% spodumene and party with 20% spodumene, who were firing at 1170°With, respectively 3.47, 0.81 and 0.03 percent. The percentage of water absorption for samples standard party, party with 5% spodumene and party with 20% spodumene, who were firing at 1200°amounted to 2.63 respectively, 0.02 and 0.23 percent. This shows that the addition of 5% and 20% pre-dispersed spodumene reduces the rate of water absorption for samples who were fired at 1140°S, 1170°and 1200°With, in comparison with a standard party.

This study shows the AET, due to the additive 5 wt.% pre-dispersed spodumene possible to obtain samples with a linear shrinkage of 4.0% to 4.5%. This study also shows that you can get the percentage of water absorption for these samples from 3.34% for firing at 1140°With up to 0.81% for firing at 1170°and up to 0.02% for firing at 1200°C.

This study shows that due to the additive 20 wt.% pre-dispersed spodumene you can get the percentage of water absorption for the respective samples, constituting less than 0.25%. This study also shows that it is possible to obtain samples with a linear shrinkage of 3.99% for firing at 1140°With up to 2.60% for firing at 1170°and a linear expansion - 3.46% for firing at 1200°C.

1. Ceramic material obtained by firing a raw material formed of a mixture which contains from 5 to 20 wt.% spodumene and from 80 to 95 wt.% other forming ceramic components, which contain from 50 to 95 wt.% clay and 5 to 50 wt.% feldspar, and this material has a linear shrinkage upon firing temperature of 1100 to 1300°With less than 2.5%, in comparison with the dimensions of the raw before passing firing.

2. The ceramic material according to claim 1, wherein the clay has a methylene blue index MBI from 11 to 13 meq/100 g

3. The ceramic material under item 1, in which the spodumene contains about which of 7.25 to 7.75% wt. lithium measured as the oxide of lithium.

4. The ceramic material according to any one of claims 1 to 3, characterized in that the retention rate for the resistance to crushing of at least 85%, and mostly at least 98%, from thermal shock applied using a heat treatment using a sharp drop in the temperature range from 400 to 800°C.

5. A method of manufacturing a ceramic material which provides

a) formation of a mixture which contains from 5 to 20 wt.% spodumene and from 80 to 95 wt.% other forming ceramic components, which contain from 50 to 95 wt.% clay and 5 to 50 wt.% feldspar, crude, having a desired shape;

b) the firing of raw sugar at a temperature of from 1100 to 1300°obtaining a ceramic material, and forming a ceramic components is chosen so that after firing the linear dimensions of raw sugar was reduced by more than 2.5%.

6. The method according to claim 5, in which the processes of molding and firing, ensuring the increase in the linear dimensions of the raw obtaining the net volume expansion.