Refractory product having improved flow

Abstract

An unshaped product including a particulate mixture containing: a coarse fraction, representing >50%<91% of particulate mixture, in mass percentage, and containing particles size 50 m, coarse particles, and matrix fraction, forming remainder up to 100% of particulate mixture, and containing particles sizes <50 m, product having chemical analysis, in mass percentage based on oxides of product, such: 45%<Al.sub.2O.sub.3, 7.5%<SiO.sub.2<35%, 0%ZrO.sub.2<33%, providing 10%<SiO.sub.2+ZrO.sub.2<54%, 0.15%<B.sub.2O.sub.3<8%, other oxides: <6%, Al.sub.2O.sub.3 forming remainder up to 100%, coarse fraction including more than 15% coarse particles having size >1 mm, in mass percentage based on particulate mixture, matrix fraction having a chemical analysis, in mass percentage based on oxides of matrix fraction, such: Al.sub.2O.sub.3+SiO.sub.2+ZrO.sub.2>86%, providing 35%<Al.sub.2O.sub.3.

Claims

1. An unshaped product comprising a particulate mixture consisting of: a coarse fraction, representing more than 50% and less than 91% of the particulate mixture, as weight percentage, and consisting of the particles having a size greater than or equal to 50 m, referred to as coarse particles, and a matrix fraction, forming the remainder up to 100% of the particulate mixture, and consisting of the particles having a size less than 50 m, referred to as matrix particles, the product having a chemical analysis, as weight percentage on the basis of the oxides of the product, such that: 45%<Al.sub.2O.sub.3, 7.5%<SiO.sub.2<35% and 0%ZrO.sub.2<33%, provided that 10%<SiO.sub.2+ZrO.sub.2<54%, 0.15%<B.sub.2O.sub.3<8%, other oxides: <6%, Al.sub.2O.sub.3 constituting the remainder up to 100%, said coarse fraction comprising more than 15% of coarse particles having a size greater than 1 mm, as weight percentage on the basis of the particulate mixture, said matrix fraction having a chemical analysis, as weight percentage on the basis of the oxides of the matrix fraction, such that: Al.sub.2O.sub.3+SiO.sub.2+ZrO.sub.2>86%, provided that 35%<Al.sub.2O.sub.3, said unshaped product comprising particles comprising boron.

2. The unshaped product as claimed in claim 1, wherein 0.2%<B.sub.2O.sub.3<6.5% and/or the content of other oxides is less than 5%.

3. The unshaped product as claimed in claim 2, wherein 0.75%<B.sub.2O.sub.3<4.5% and/or the content of other oxides is less than 2%.

4. The unshaped product as claimed in claim 3, wherein B.sub.2O.sub.3<2.6%.

5. The unshaped product as claimed in claim 1, wherein the particles comprising boron are selected from the group consisting of boron carbide, boron oxides, boric acid, colemanite, sodium borate, compounds comprising silica and boron oxide, SiB.sub.6, alumina borates, AlB.sub.3 and mixtures thereof.

6. The unshaped product as claimed in claim 1, wherein the matrix fraction, other than the particles comprising boron, consists, for more than 80% of its weight, of alumina particles and/or silica particles and/or mullite particles and/or mullite-zirconia particles and/or particles of a silicoaluminous material having an alumina content greater than 50%.

7. The unshaped product as claimed in claim 1, wherein more than 50% of the particles comprising boron are matrix particles, as weight percentage on the basis of the oxides.

8. The unshaped product as claimed in claim 1, wherein Al.sub.2O.sub.3+SiO.sub.2>83% or Al.sub.2O.sub.3+SiO.sub.2+ZrO.sub.2>92% or 15%<SiO.sub.2+ZrO.sub.2<50% or SiO.sub.2>10%.

9. The unshaped product as claimed in claim 8, wherein Al.sub.2O.sub.3+SiO.sub.2>90% or 20%<SiO.sub.2+ZrO.sub.2<40% or SiO.sub.2>13%.

10. The unshaped product as claimed in claim 1, wherein, if the silica content in the matrix fraction is greater than 10%, as weight percentage on the basis of the oxide phases of the matrix fraction, said matrix fraction has an alumina/silica ratio greater than 2 and less than 10.

11. The unshaped product as claimed in claim 10, wherein said ratio is less than 5.

12. The unshaped product as claimed in claim 1, wherein more than 80% by weight of the coarse particles have a size greater than 200 m and less than 25 mm.

13. The unshaped product as claimed in claim 1, wherein the coarse fraction consists, for more than 80% of its weight, of alumina particles and/or mullite particles and/or mullite-zirconia particles and/or particles of a silicoaluminous material having an alumina content greater than 50%.

14. The unshaped product as claimed in claim 1, having a chemical analysis such that: Al.sub.2O.sub.3: remainder up to 100%, (21%SiO.sub.225% and ZrO.sub.2<1%) or (14%<SiO.sub.2<17% and 26%<ZrO.sub.2<32%), 0.2%<B.sub.2O.sub.3<2.6%, other oxides: <3%, and a matrix fraction having a chemical analysis such that Al.sub.2O.sub.3+SiO.sub.2+ZrO.sub.2+B.sub.2O.sub.3>90%, and an amount of matrix particles between 20% and 35% of the weight of the particulate mixture, and more than 15% of coarse particles having a size greater than 1 mm, the contents of the chemical analysis being expressed as weight percentages on the basis of the oxides.

15. A process for manufacturing a sintered part, comprising the following steps: A) preparing of a starting charge from an unshaped product according to claim 1; B) forming of said starting charge so as to form a preform; C) sintering of said preform so as to obtain a sintered product having a microstructure consisting of grains bonded by a matrix, and having a chemical analysis such that, as weight percentages on the basis of the oxides and for a total of 100%: 45%<Al.sub.2O.sub.3, 7.5%<SiO.sub.2<37% and 0%ZrO.sub.2<35%, provided that 10%<SiO.sub.2+ZrO.sub.2<54.3%, 0.1%<B.sub.2O.sub.3<2.5%, other oxides: <6.4%, Al.sub.2O.sub.3 constituting the remainder up to 100%, the boron being distributed in the body of said sintered product, and more than 15% of grains having an equivalent diameter greater than 1 mm.

16. A process according to claim 15, wherein 0.25%<B.sub.2O.sub.3<1% in the sintered product.

17. A process according to claim 15, wherein the boron is distributed in the matrix substantially homogeneously.

18. A process according to claim 15, wherein the aggregate consists, for more than 80% by number, of alumina grains and/or mullite grains and/or mullite-zirconia grains.

19. A process according to claim 15, wherein 20%<SiO.sub.2+ZrO.sub.2<40% in the sintered product.

20. A process according to claim 15, wherein Al.sub.2O.sub.3<85% in the sintered product.

21. A process according to claim 15, wherein said sintered product has a chemical analysis such that: Al.sub.2O.sub.3: remainder up to 100%, (21%SiO.sub.225% and ZrO.sub.2<1%) or (14%<SiO.sub.2<17% and 26%<ZrO.sub.2<32%), 0.25%<B.sub.2O.sub.3<1%, other oxides: <3%, and more than 15% of grains having an equivalent diameter greater than 1 mm, the contents of the chemical analysis being expressed as weight percentages on the basis of the oxides.

22. A process for manufacturing a glass furnace, wherein a sintered product is manufactured according to claim 15, and used to make said glass furnace.

23. A process as claimed in claim 22, wherein said sintered product is included in a region which is not capable of coming into contact with molten glass.

24. A process as claimed in claimed in claim 23, wherein said sintered product is included in a superstructure of said furnace.

25. A process as claimed in claimed in claim 24 wherein said sintered product is included in a crown of said furnace.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other characteristics and advantages of the invention will further emerge on examining the drawing, provided by way of nonlimiting illustration, in which FIG. 1 diagrammatically represents a device that can be used to measure the creep resistance, and FIG. 2 diagrammatically represents the deformation of the small bar after a creep test.

DETAILED DESCRIPTION

(2) An unshaped product according to the invention may be advantageously used for producing a sintered product having an aggregate bonded by a bonding matrix. To this effect, a process comprising steps A) to C) described above may be carried out.

(3) In step A), a particulate mixture is mixed in a solvent, conventionally water. The sources of raw materials are determined according to the composition and the particle size distribution that are desired.

(4) The Andrasen or Fuller-Bolomey compaction models may be used to adapt the particle size distribution to the apparent density desired for the sintered products. Such compaction models are in particular described in the work entitled Trait de cramique et matriaux minraux [Treatise on ceramics and mineral materials], C. A. Jouenne, Editions Septima. Paris (1984), pages 403 to 405. In particular, this adaptation advantageously makes it possible to produce a sintered refractory product having an apparent density of between 2.3 g/cm.sup.3 and 3.5 g/cm.sup.3, preferably of between 2.5 g/cm.sup.3 and 3.2 g/cm.sup.3.

(5) The boron compound may be added in solid form, for example in the form of a powder, and/or in liquid form, for example diluted in water. The boron may for example be provided in the form of a B.sub.4C powder.

(6) In one advantageous embodiment, the boron is provided in liquid form, preferably during the preparation of the starting charge, preferably at the time the mixture is prepared in step A), for example by dissolving and/or sprinkling. Advantageously, the boron compound is well dispersed in the starting charge.

(7) Preferably, the starting charge contains a forming additive, preferably introduced in a dry form, preferably in an amount greater than 0.1% and less than 7%, preferably less than 5%, preferably less than 3%, or even less than 2%, as weight percentage on the basis of the weight of the particulate mixture.

(8) The forming additive may in particular be chosen from the group consisting of: clays; plasticizers, for instance polyethylene glycol (or PEG) or polyvinyl alcohol (or PVA); cements, preferably with a high alumina content; hydratable aluminas, for instance boehmite; phosphates, preferably alumina phosphates; sodium and/or potassium silicates; geopolymers; binders, including organic temporary binders such as organic resins, lignosulfonates, carboxymethylcellulose, dextrin and alginates; deflocculants, such as alkali metal polyphosphates, alkali metal polyacrylates, or polycarboxylates; mixtures of these products.

(9) Preferably, the forming additive is chosen from the group consisting of cements, deflocculants, clays, lignosulfonates, PVA and mixtures thereof.

(10) When the boron or the additive is provided in the form of particles, these particles are of course part of the particulate mixture.

(11) The unshaped product may be provided ready-to-use. Preferably, it is dry and contains the forming additive. It is then sufficient to mix it with a solvent, preferably water, in order to prepare the starting charge.

(12) The amount of solvent depends on the technology used in step B).

(13) In the case of forming by cold pressing, addition of an amount of water of between 1.5% and 4%, as weight percentage on the basis of the particulate mixture, is preferred. In the case of forming involving hydraulic bonding, for example pouring, addition of an amount of water of between 3% and 7%, as weight percentage on the basis of the particulate mixture, is preferred.

(14) In step B), the starting charge may be poured into a mold, in order to be formed and converted into a preform according to conventional techniques, for example by pressing.

(15) After step B) and before step C), the preform may undergo a drying step, in order to remove a part of the water having been used for the forming. Such a step is perfectly known to those skilled in the art.

(16) In step C), the sintering conditions, and in particular the sintering temperature, depend on the composition of the preform. Those skilled in the art may readily control the quality of the sintering and optionally adjust the temperature accordingly. Usually, a sintering temperature of between 1350 C. and 1850 C., preferably of between 1500 C. and 1750 C., is very suitable. The sintering may be carried out in situ, i.e. after the preform has been placed in its working position, in particular in a crown of a glass furnace.

(17) At the end of step C), a sintered refractory product according to the invention, having a substantially homogeneous distribution of the boron element, preferably in the matrix of said refractory product, is obtained.

(18) The properties of this sintered product make it particularly well suited to use in a glass furnace, in particular in a glass furnace crown.

EXAMPLES

(19) The following examples are given for illustrative purposes and do not limit the invention.

(20) The content of boron and of elements of which the amount does not exceed 0.5% is determined by Inductively Coupled Plasma or ICP.

(21) The content of other elements is determined by X-ray fluorescence.

(22) The creep resistance is determined by means of the following method: a small bar 2 of the product to be tested, having a length equal to 200 mm, a width equal to 25 mm and a height equal to 15 mm, is placed on blocks 10 made of dense sintered alumina, said blocks being placed at each of the ends of the small bar such that the scope (in other words the length of the small bar not supported between the blocks) is equal to x=180 mm. A refractory brick 12 having a weight equal to 2670 g is placed at the center of the small bar on blocks 14 made of dense sintered alumina, separated from one another by y=40 mm, said brick having a length approximately equal to 110 mm, a width approximately equal to 75 mm and a height approximately equal to 200 mm (see FIG. 1). The center of the brick is approximately aligned with the center of the small bar to be tested. This assembly is then placed in an electric furnace and the following heat cycle is applied: Increase from 20 C. to 1600 C. at 100 C./h Stationary phase of 50 hours at 1600 C. Decrease at 100 C./h.

(23) After heat treatment, the deformation F of the small bar is determined using a ruler, according to FIG. 2. The smaller the deformation of the small bar, the higher the creep resistance.

(24) The method used to determine the amount of grains of equivalent diameter greater than 1 mm in a sintered product according to the invention is the following: three samples of said sintered product are taken randomly. Each sample is then coated with a resin, for example an epoxy resin, and then polished. Each polishing is then immersed for one minute in a solution of hydrofluoric acid at 10% by weight at ambient temperature so as to reveal the grain boundaries. Each polishing is then rinsed with water and then dried. Images of the polished area are taken using an optical microscope, each image making it possible to observe at least one area equal to 8 mm by 5 mm. The area of the images taken that is occupied by grains having an equivalent diameter greater than 1 mm may be evaluated using image processing software, for instance ImageJ.

(25) The particle size distribution of the powders was determined using a laser particle size analyzer for the particles having a size less than 2 mm and by sieving using sieves with square meshes having an opening greater than 2 mm for the particles having a size greater than 2 mm.

(26) The apparent density and the open porosity were measured according to standard ISO5017.

(27) The following raw materials were used for the examples: mullite powders such that D.sub.99.5<3 mm, a powder of fumed silica consisting essentially of vitreous silica microspheres such that D.sub.90<4 m, with D.sub.50=0.5 m. It has a B.E.T. specific surface area of 14 m.sup.2/g, a silica weight content of 93.5%, an Al.sub.2O.sub.3 content of 3.5% and a content of ZrO.sub.2+HfO.sub.2 of 2.4%; an alumina powder having an alumina content greater than 99.75% and a D.sub.50 equal to 5 m; the following forming additives: a clay containing 40% of alumina, a calcium lignosulfate, a water-soluble nonionic cellulose ether.

(28) The boron compound used is:

(29) for examples 2 and 5 to 8, a powder of boron carbide B.sub.4C having a median diameter D.sub.50 equal to 4.6 m,

(30) for example 3, a powder of boron oxide B.sub.2O.sub.3, sold by the company Borax,

(31) for example 4, a powder of boric acid H.sub.3BO.sub.3, sold by the company Borax under the name Optibor TG, having an H.sub.3BO.sub.3 content greater than 99.9%.

(32) The silica, alumina and mullite powders are mixed with 1% of clay, as weight percentage on the basis of the particulate mixture. The boron compound, the calcium lignosulfate and the cellulose ether diluted in the water required for the forming are then introduced. The amount of water is equal to 2.8% and the total amount of additive, including clay, is equal to 1.7%, as percentages on the basis of the particulate mixture.

(33) The wet mixture obtained is then pressed in the form of bricks having the dimensions 23011464 mm.sup.3 on a single-acting mechanical press at a pressure of 720 kg/cm.sup.2.

(34) The bricks obtained are oven-dried for 24 hours at 110 C.

(35) These bricks were then sintered at a stationary-phase temperature of 1700 C., the duration of the stationary phase being 5 hours, the temperature increase rate being 50 C./h. After the temperature stationary phase, the temperature is decreased, the temperature decrease rate being 50 C./h, down to 800 C., the temperature decrease then being free down to ambient temperature.

(36) Table 1 below summarizes the tests and the results obtained, the percentages being weight percentages unless indicated.

(37) TABLE-US-00001 TABLE 1 Example 1* 2 3 4 5 6 7 8 Particulate mixture Nature of the coarse particles mullite mullite mullite mullite mullite mullite mullite mullite Amount of coarse particles on the basis of 70.3 70.3 69.9 69.4 70.1 69.9 69.4 68.5 the weight of the particulate mixture (%) Amount of coarse particles of size > 1 mm, on the 39 39 39 39 39 39 39 41 basis of the weight of the particulate mixture (%) silica, silica, silica, silica, silica, silica, silica, silica, alumina, alumina, alumina, alumina, alumina, alumina, alumina, alumina, Nature of the matrix particles mullite mullite, mullite, mullite, mullite, mullite, mullite, mullite, boron boron boron boron boron boron boron compound compound compound compound compound compound compound Al.sub.2O.sub.3 (%) 75.47 75.28 75.10 75.05 74.91 74.54 73.62 71.82 SiO.sub.2 (%) 23.97 23.90 23.85 23.83 23.78 23.67 23.37 22.80 ZrO.sub.2 (%) 0.18 0.18 0.18 0.18 0.18 0.17 0.17 0.17 B.sub.2O.sub.3 (%) 0.25 0.50 0.56 0.75 1.24 2.46 4.85 Other oxides (%) 0.38 0.39 0.37 0.38 0.38 0.38 0.38 0.36 Al.sub.2O.sub.3 + SiO.sub.2 + ZrO.sub.2 (%) 99.62 99.36 99.13 99.06 98.87 98.38 97.16 94.79 SiO2 + ZrO2 (%) 24.15 24.08 24.03 24.01 23.96 23.84 23.54 22.97 Al.sub.2O.sub.3 as weight % on the 76.12 75.48 74.86 74.69 74.23 73.02 70.15 65.02 basis of the oxides of the matrix fraction Al.sub.2O.sub.3 + SiO.sub.2 + ZrO.sub.2 99.43 98.59 97.78 97.55 96.95 95.37 91.62 84.93 as weight % on the basis of the oxides of the matrix fraction Silica content in the matrix fraction, as weight % 22.68 22.49 22.31 22.25 22.12 21.76 20.90 19.37 on the basis of the oxide phases of the matrix fraction Alumina/silica in the matrix fraction 3.36 3.36 3.36 3.36 3.36 3.36 3.36 3.36 Nature of the boron compound B.sub.4C B.sub.2O.sub.3 H.sub.3BO.sub.3 B.sub.4C B.sub.4C B.sub.4C B.sub.4C Amount of boron compound (%) 0.1 0.5 1 0.3 0.5 1 2 Sintered product Al.sub.2O.sub.3 (%) 75.79 75.28 75.87 75.11 75.04 74.88 74.9 74.54 SiO.sub.2 (%) 23.57 23.47 23.23 24.05 23.54 23.53 23.59 23.58 Al.sub.2O.sub.3 + SiO.sub.2 (%) 99.36 98.75 99.1 99.16 98.58 98.41 98.49 98.12 B.sub.2O.sub.3 (%) 0 0.13 0.24 0.19 0.26 0.65 0.71 1.41 Others (%) 0.64 1.12 0.66 0.65 1.16 0.94 0.8 0.47 Grains having an equivalent diameter > 1 mm, 36 38 35 37 35 40 37 34 as surface percentage Apparent density (g/cm.sup.3) 2.69 2.66 2.65 2.65 2.71 2.69 2.69 2.69 Open porosity (%) 13.5 14.2 14.2 13.7 11.8 12.7 12 9.9 Deformation F after creep test (mm) 4.68 1.67 1.84 1.27 1.02 0.22 0.61 1.57

(38) It is considered that a product exhibits a considerable improvement in its creep resistance when it exhibits, with the test used, a deformation F measured after test of less than 4 mm, that is to say an improvement of at least 15% compared with the product of example 1 outside of the invention, normally used in a glass furnace crown.

(39) A comparison of example 1 outside the invention and of examples 2 to 8 according to the invention shows the effectiveness of the addition of a boron compound on the improvement in the creep resistance.

(40) A comparison of examples 2 to 8 according to the invention further shows that: the creep resistance (which corresponds to a minimal measured deformation F) is at a maximum for boron contents in the particulate mixture such that 0.75%B.sub.2O.sub.32.46%, a boron content in the particulate mixture equal to 4.85% makes it possible to improve the creep resistance of the sintered product, but to a lesser extent.

(41) The particulate mixture according to example 6 is the preferred example.

(42) The sintered product obtained from the particulate mixture of example 6 is the preferred sintered product.

(43) As clearly presently emerges, the invention provides a refractory product which has an excellent creep resistance at high temperature, and also resistance to corrosion, resistance to heat cycling and mechanical strength which make it perfectly suitable for the intended application.

(44) Of course, the invention is not limited to the embodiments described, provided by way of nonlimiting illustration.