CN1237564A - A Porous Ceramic Extrusion Molding Method Adopting Macromolecular Polymerization Crosslinking and Solidification - Google Patents

Abstract

The present invention adopts the porous ceramic extrusion molding method of polymer polymerization cross-linking and solidification, based on the current extrusion molding method, and is characterized in that acrylamide (AM) and N, N'-methylene bis The organic monomer composed of acrylamide (MBAM) and its initiator are extruded and heated to polymerize and cross-link the organic monomer in the wet billet; with this method, the drying process of the wet billet is easy to control, which can avoid deformation and Cracks and other defects can shorten the drying time; the green body has high strength and is convenient for machining; it can improve the quality of products and increase the rate of finished products.

Description

A Porous Ceramic Extrusion Molding Method Adopting Macromolecular Polymerization Crosslinking and Solidification

The invention belongs to the technical field of ceramic forming technology.

"Fundamentals of Inorganic Membrane Science and Technology" ("Fundamentals of Inorganic Membrane Science and Technology", edited by A.J.Burggraaf and L.Cot, Elsevier Science B.V. Press, 1996) pp. 119-123 published in the Netherlands and "Desalination" magazine published in the UK (Desalination, 70 (1988) 395-404) has reported that single-channel and multi-channel porous ceramics have been prepared by extrusion molding. The basic procedures include weighing and mixing of raw materials, vacuum mud refining, homogenization to form billets, Medium extrusion molding, drying and firing. The main defect of above-mentioned existing extrusion molding method is:

(1) The drying process of extruded wet billet parts is not easy to control, and deformation and cracks are easy to occur, especially for honeycomb multi-channel products. Its reason is just as George W. Sherer (George W. Sherer) publishs in " American ceramic society journal " (J.Am.Ceram.Soc., 73 (1) 3-14 (1990) in " drying theory " article It is pointed out that since the drying properties depend on the composition of the billet, the control of the ingredients in the current extrusion molding process is often based on experience, and the drying properties are often deteriorated due to improper control;

(2), the adhesive used in the current technology is a thermosetting organic polymer compound, such as cellulose and starch, etc., the bonding strength of this type of adhesive is not high, so the dry body strength of the adhesive alone is not high. High, prone to damage during post-machining processing;

(3) Since the wet blank is easily deformed during the drying process, and the dry blank after drying has low strength and is not easy to process, it is difficult to ensure the dimensional accuracy, which reduces the yield.

The object of the present invention is to propose a porous ceramic extrusion molding method using macromolecular polymerization cross-linking and solidification to overcome the above-mentioned defects in the prior art.

This porous ceramic extrusion molding method using polymer polymerization cross-linking and solidification is based on the current extrusion molding method, including weighing, mixing, vacuum mud refining, homogenization, forming wet billets, and vacuum extrusion of ceramic body raw materials. Pressing, drying and firing; it is characterized in that organic monomers and their initiators are added during the production of the wet billet, heated to 40-100°C after extrusion molding, and kept for 2 minutes to 2 hours.

The raw materials of the ceramic body include ceramic powder, deflocculating agent, binder, pore forming agent, lubricant and water;

The ceramic powder can be alumina, zirconia, mullite, silicon carbide, cordierite, silicon oxide, composite oxide functional ceramic powder or a mixture thereof;

The deflocculant can be selected from polymethacrylic acid, polyacrylic acid and its soluble salts, polyvinyl alcohol, polyethylene glycol, and the dosage is 0.5-1.5% of the weight of the ceramic powder;

The binder can be selected from starch, methylcellulose, carboxymethylcellulose, and hydroxypropylcellulose, and the amount is 5-15% of the weight of the ceramic powder;

The pore-forming agent is an organic compound that is solid within the range of room temperature to 100°C and burns without residue, including carbon powder, polyethylene powder, and starch; the dosage is 5-20% of the weight of the ceramic powder; if used The pore-forming agent is non-water-soluble, and its particle size is preferably smaller than that of the ceramic powder to avoid uneven microstructure;

The lubricant is selected from stearic acid and its soluble salts and glycerin, and the dosage is 0.5-1% of the weight of the ceramic powder;

The organic monomer is composed of acrylamide (AM) and N,N'-methylenebisacrylamide (MBAM) at a ratio of 20-40 wt% of MBAM/AM; the weight concentration of the organic monomer solution is 10-30 %; the amount of organic monomer solution accounts for 25-40% of the billet weight;

The initiator is ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ )) or potassium persulfate (K ₂ S ₂ O ₈ ), and the amount of the initiator is generally 0.1-1% of the weight of the organic monomer; preferably Ammonium persulfate, because it can be completely decomposed during heat treatment without residue;

The homogenization is to place the blank after vacuum refining at room temperature for no less than 1 day;

The drying temperature generally ranges from room temperature to 110°C; using hot air or microwave heating can speed up the drying speed; using freeze-drying below room temperature is more beneficial to the product.

In the present invention, the extruded wet body is heated to a temperature of 40-100° C., and the holding time is 2 minutes to 2 hours, so that the organic monomer in the wet body is polymerized and cross-linked.

Compared with the existing extrusion molding method, since the method of the present invention adopts the polymerization reaction crosslinking of organic monomers to form a three-dimensional network structure, the ceramic powder and additives in the wet billet are firmly combined, thereby improving the strength of the wet billet and making the wet billet The drying process is easy to control, the green body is not easy to crack and deform, and the drying time is shortened; the dried green body has high strength, and can be machined according to the required shape and precision before burning, thereby improving the quality of the product and improving the quality of the finished product. rate; the organic monomer completely dispersed in the blank has a plasticizing effect on the binder, thereby improving the rheological properties of the blank; when the organic monomer is polymerized and cross-linked into a polymer compound, it acts as a pore-forming agent, so the amount of other pore-forming agents can be reduced; at the same time, the organic monomer is a water-soluble system, which avoids the pollution of the environment by the use of organic solvents; using the method of the present invention, the single-channel or multi-channel wet tube blank can be vacuum extruded. The porosity is greater than 30%, the average pore diameter is adjustable in the range of 0.1-15 microns, and the single-channel or honeycomb multi-channel porous ceramics with uniform microstructure and high strength are obtained.

Example 1: Take 5000g of alumina powder with an average particle size d ₅₀ =60μm, 750g of carbon powder, 250g of acrylamide, 50g of N,N'-methylenebisacrylamide, 500g of carboxymethylcellulose, and 3.0g of polyacrylic acid , 25g of stearic acid, 1570ml of distilled water, 1.5g of ammonium persulfate, mixed in a blender; then practice mud in a vacuum mud mill to obtain a plastic billet; place it airtightly at room temperature for 1 day; in a vacuum extruder Extrude to obtain single-channel and 7-channel tubular wet billets; heat in an oven to 60°C and cure for 20 minutes; then dry at 80°C for 5 hours; place the dried billet in a high-temperature furnace and heat up from room temperature to 1700°C , kept warm for 5 hours, then cooled with the furnace to obtain single-channel and 7-channel tubular alumina porous ceramics; the porosity was 43% measured by the Archimedes drainage method; measured by the bubble point method (nitrogen as the working gas) The average pore diameter is 15 μm.

Example 2: Take 5000g of cordierite powder (d ₅₀ =0.3μm), 500g of melamine powder, 50g of sodium stearate, 3.5g of polyethylene glycol, 300g of acrylamide, and 120g of N,N'-methylenebisacrylamide , 750g of starch, 2500ml of distilled water, 1.0g of potassium persulfate, mixed in a mixer, and muddled in a vacuum mud mill to obtain a plastic billet; placed in a sealed place at room temperature for 2 days, extruded in a vacuum extruder The obtained wet billet was solidified at 90°C for 15 minutes, then cooled to room temperature, and air-dried for 9 hours; the dried billet was placed in a high-temperature furnace, heated from room temperature to 1280°C, kept for 3 hours, and then cooled with the furnace to obtain Cordierite porous ceramics; the porosity measured by the method described in Example 1 is 45%, and the average pore diameter is 0.15 μm.

Example 3: Take 5000g of zirconia powder (d ₅₀ =4μm), 750g of polypropylene powder, 25g of glycerin, 250g of acrylamide, 25g of N,N'-methylenebisacrylamide, 500g of methylcellulose, and 2500ml of distilled water. Ammonium persulfate 0.3g was mixed in a mixer, and the vacuum smelting was carried out to obtain a plastic billet; it was airtightly placed at room temperature for 1 day; extruded in a vacuum extruder; the obtained wet billet was solidified at 50°C for 60 minutes, Then dry at 60°C for 7 hours; place the dried green body in a high-temperature furnace, raise the temperature from room temperature to 1600°C, keep it warm for 10 hours, and then cool with the furnace; obtain zirconia with a porosity of 44% and an average pore size of 1.0 μm porous ceramics.

Claims (1)

1, a kind of porous ceramics extrinsion pressing that adopts high molecular polymerization crosslinking stateization based on existing extrinsion pressing, comprises the taking by weighing of ceramic body raw material, mixing, vacuum pugging, homogenizing, formation wet blank, vacuum extrusion, drying and burns till; It is characterized in that adding organic monomer and initiator thereof when wet base is made, the extrusion molding post-heating is incubated 2 minutes to 2 hours to 40-100 ℃; Described organic monomer is by acrylamide (AM) and N, and N '-methylene-bisacrylamide (MBAM) is that 20-40wt% forms by the ratio of MBAM/AM; The weight concentration of organic monomer solution is 10-30%; The organic monomer solution usage accounts for the 25-40% of billet weight; Described initiator is selected ammonium persulphate ((NH for use ₄) ₂S ₂O ₈)) or Potassium Persulphate (K ₂S ₂O ₈).