MXPA96005486A - Poro production products - Google Patents

Abstract

The present invention relates to a method of manufacturing a porous refractory article, characterized in that it comprises the steps of: a) forming an aqueous dispersion of refractory particles, the dispersion includes a polymerizable monomer component, which generates an exotherm by polymerization; add to step a) a gas generating substance, which thermally decomposes, under conditions of temperature and pressure effective to generate a gas, c) add to step b) a polymerization agent comprising an initiator or a catalyst, thus causing a reaction polymerization to start and produce heat, and d) adjust the temperature or pressure to cause the gas generating substance to generate the gas before or during the polymerization of the monomer component, whereby the gas forms bubbles which, under the heat of the exotherm, are interconnected to form a structure of open pores interconnected

Description

PRODUCTION OF POROUS RTICLES The invention relates to the production of porous articles and is an improvement on, or modification of, the invention described in patent application PCT / TB92 / 01 93, published under number UO 93/04103 on March 4, 1993 Therefore, the entire description of that specification is incorporated in the present. The method described and claimed in the previous application comprises the passage of the formation of a dispersion comprising particles of refractory material in a liquid vehicle, introducing gas into the dispersion and removing the liquid vehicle in order to provide a solid article having pores derived from gas bubbles, characterized in that the critical viscosity of the dispersion is controlled to be 5 inPa.s, (the level below which trapped gas bubbles tend to escape), at 1000 mPa.s ( level above which trapped air bubbles can not be inferred), approximately. The critical viscosity is preferably between 20 rnPa.s to 250 Pa.s, approximately. After the gas is introduced the liquid vehicle is removed, water is typically removed by heat. An optional step is the inclusion of a polymerizable monomer to have an effect when the liquid vehicle is removed, soluble acrylic solvents and acrylarnides are given as suitable additives and are polyesterised with the use of binders and / or heat. There may be a need in certain circumstances for a porous article in which the pores are highly interconnected. This invention is based on the appreciation that, by performing foaming in a defined manner, these articles or articles having predetermined pore structure can be easily formed. According to the invention, in one aspect a method of manufacturing a porous refractory article is provided; the method comprises the steps of: - forming an aqueous dispersion of refractory particles that includes a monomerable polymerizable component that generates an exotherm by polymerization, - addition of a gas generating substance that decomposes thermally. -addition of agents such as initiator- and / or catalyst to cause polymerization. adjusting the temperature and / or pressure so that the gas generating substance generates the gas before or during the initial stage of polymerization of the monomer component whereby the gas forms bubbles which under the heat of the exotherm are interconnected to form a networked open pore structure. The gas generating substance that decomposes thermally under appropriate conditions generates the gas in situ.

The temperature at which the gas is generated depends on the obstacle in question, and the global conditions, for example temperature and pressure. The substance is preferably that which after decomposition does not leave residues that in the context tend to contaminate, decompose at a pH of between 7.5 and 9, and that does not generate free oxygen that could inhibit polymerization. Ammonium carbonate, ammonium bicarbonate, ammonium carbonate and the like are preferred. Metal carbonates can also be used when the presence of residual metal oxide does not have an adverse effect. It is an advantage of this invention that by controlling the temperature and pressure the decomposition rate of the gas generating substance is controlled. The foaming reaction could then be triggered by the increase in temperature associated with the initiation of the polymerization. This firing procedure requires control over the temperature and pressure of the dispersion before the * "Start of polymerization and the use of a catalyst.

Alternatively, the dispersion could be stored at a predetermined temperature and pressure and microwave energy can be used to induce polymerization and decompose the gas generating substance. The particles can be derived from a wide variety of materials such as metals, metal oxides, non-metallic ceramics and mixtures of ceramics and metal. Examples given by illustration and not by limitation, include alumina, cordierite, magnesia, mulite, silica, silicon carbide, aluminum oxide, tungsten nitride, zir-como and the like. In an optional step, foaming is carried out at atmospheric pressure using ammonium carbonate or the like as the gas generating substance, using an initiator that induces polymerization at a higher temperature - at which to operate the ammonium persulfate . Such initiators are well known. The initiator would be selected by type and concentration to delay the start of the polymerization until after the foaming agent has decomposed at 60 ° C at atmospheric pressure. In another option, the composition contains ammonium persulfate or similar initiator and the foaming agent is that which decomposes at a lower temperature from which the persulfate decomposes. Such agents are well known, for example volatile liquids, gases, and halogenated hydrocarbons. Fn another optional step where the gas generating substance that is "thermally decomposed is a halogenated hydrocarbon, the reaction can be carried out under reduced pressure.The porous article formed can be demolded, dried and concreted in a known manner.The article can be put for industrial use." For the invention to be well understood below describes, by way of illustration, with reference to the following examples.

EXAMPLE 1 Alumina (70 g) was mixed, a premix solution (21.27 g), constituted by ammonium acuplate 29.1%, rnetilenbisacplamide 0.9% and the rest of water; and dispersants constituted by ammonium salts of polyacrylate solution (lg), and polyuneacrylate (2g) with deionized water (5g) to form a homogeneous suspension. Then a quantity of the foaming agent (ammonium bicarbonate) was mixed with the suspension and allowed to dissolve). This was followed by the addition of initiator (ammonium persulfate) and finally the foam stabilizing agent (Triton X-100 surfactant). (TRITÓN is a trademark of Union Carbide). The prepared suspension is then transferred to a microwave oven and heated to 70 ~80 ° C in less than 1 minute to dissociate the ammonium carbonate. Several tests were done adjusting the power of nicrobands and the concentrations of initiator and foaming agent. Initiator concentrations were varied between 0.3 and 0.075 g, per sample. The concentration of foaming agent was varied between 1 g and 3 g, per sample. It was found that the addition of the foaming agent does not interfere with the quality of the ceramic suspension. The ammonium bicarbonate crystals mixed in the suspension tend to settle to the bottom of the container. During the application of micronutrients, the crystals at the bottom of the container tend to be placed when the temperature approaches 60 ° C and create a gas cavity at the bottom of the container. The dissolved ammonium bicarbonate in the suspension decomposes and creates small gas bubbles that grow and interconnect with the increase in temperature. After foam production, the foamed samples were dried at room temperature for one day and then at 60 ° C for one day. This was followed by concreting at 1550 ° C for 2 hours. Table 1 shows the concreted and crude densities obtained in the case of some samples.

EXAMPLE II Alumina, premix solution and dispersants were mixed as in Example 1. The re-blowing agent (Ammonium carbonate) is ground to form a fine powder and mixed in the suspension. This was followed by the addition of initiator (ammonium persulfate) 1.2 g. The foam stabilizing agent (surfactant) is then mixed with the suspension and finally an amount of catalyst (tet rametiletiiendiamia) 0.05 rnl is added. The suspension is transferred to a vacuum desiccator at room temperature. Or a reduced pressure of about 60 mrn Hg, the suspension began to decompose, which resulted in foam formation. This behavior was completely unexpected and it seems that ammonium carbonate decomposes and generates gas.

At the time of polymerization the foam expands even after the temperature of the gas increases. This requires that the pressure inside the vacuum chamber be increased to compensate for the expansion of the foam. After a few minutes the polymerization is complete and the pressure inside the chamber is reduced to atmospheric pressure and the poly-bristled foam is removed from the chamber. The result is a ceramic foam with an extremely open pore structure and low density. The samples with foam are dried at room temperature for 1 day and then at 60 ° C for 1 day. This is then followed by concretion at 1550 ° C for 2 hours. Table 2 shows the specific and crude density obtained for a sample.

EXAMPLE III Alumina (75 g) was mixed with a pre-fermentation solution (21.27 g) constituted by ammonium acplate (29.19 g), metiienbisacplamide (0.9%) and the rest of water, and dispersants comprising ammonium salts of pol acplato solution ( lg) and pol unetacri lato (2g) with deionized water (0.73 g) to form a homogeneous suspension. To this suspension is added sodium dodecylsulfate (0.15 g) and ammonium persulfate (0.1 g). The mixture was stirred for 10 minutes. A fluorocarbon was added, FORONE 141 B DGX; (FORANE is a brand of EIF) (8g), with a substance of P5tal > Gas lye, TERGITOL TMN 10 (0.15g) (TERG1ÍOL a brand of Union Carbide). The mixture was stirred by immute and then placed in a microwave oven. The applied nanocropon energy causes the fluorocarbon composition to decompose at about 32 ° C resulting in the formation of foam in the suspension. While the temperature continues to rise, the ammonium persulfate is activated to cause polymerization of the foam suspension. After a few minutes the foam suspension becomes rigid enough to be demolded. The concreted and raw density is shown in Table III.

EXAMPLE IV It was repeated to Example III except that 3g of the fluorocarbon composition was used. The concrete and crude density are also shown in Table 3. The content of the gas generating substance is a factor that controls the density of the product formed.

TABLE I SAMPLE DENSITY IN RAW CONCRETE DENSITY (g / c? N3) (g / crn3) 1 0.55 0.86 2 0.62 0.97 3 0.41 0.64 TABLE II Ex. II 0.19 0.29 TABLE III Ex. III 0.59 0.92 Ex. IV 1.50 2.35

Claims (9)

NOVELTY OF LR INVENTION CLAIMS

1. - A method of manufacturing a porous refractory arc, the method comprises the steps of: forming an aqueous dispersion of refractive particles Those which include a non-combustible polymer component that generates an exotherm by polymerization; addition of a gas generating substance that is thermally decomposed; addition of agents such as initiator and / or catalyst- to cause polymerization; adjusting the temperature and / or pressure so that the gas-generating substance generates the gas before or during the initial polymerization step of the monomer component, whereby the gas forms bubbles which, under the heat of the exotherm, They are connected to form a structure of open, interconnected odors.

2. A method according to claim 1, further characterized in that the gas generating substance is one that, after decomposition, leaves no waste that in the context tends to pollute, which decomposes at a pH of between 7.5 and 9, and that does not generate free oxygen.

3. A method according to claim 2, further characterized in that the gas generating substance is ammonium carbonate, ammonium bicarbonate, ammonium carbonate and the like.

4. - A method according to any of the preceding claims further characterized in that both the temperature and the pressure are controlled to control the rate of decomposition of the gas generating substance.

5. A method according to any of the foregoing claims further characterized in that the dispersion is stored at a predetermined temperature and pressure and microwave energy is used to induce polymerization and decomposition of the gas generating substance.

6. A method according to any of the preceding claims further characterized in that the gas generating substance is a halogenated hydrocarbon and the decomposition is carried out under reduced pressure.

7. A method according to any of claims 1 to 5, further characterized in that the foaming is carried out at atmospheric pressure using ammonium carbonate or the like or the gas generating substance, using an initiator that induces polymerization at a higher temperature at which the ammonium per-sulfate operates.

8. A method according to any of claims 1 to 6, further characterized in that the dispersion contains ammonium persulfate or the like initiator and the foaming agent is that which decomposes at a temperature lower than that which persulfate decomposes.

9. - A method according to any of the preceding claims, further characterized in that the refractory particles are metals, metal oxides, non-metallic ceramics and mixtures of ceramic and metal.