Process for manufacturing a β-SiAlON-based ceramic powder by carbonitriding porcelain residues

Abstract

The invention relates to a process for manufacturing a β-SiAlON-based ceramic powder suitable for the sintering production of ceramic parts with a density greater than 90%, characterized in that it comprises the following successive steps: (1) grinding at least one porcelain waste based on a mixture of kaolin, quartz and feldspar having the following composition: (a) 20 to 30 wt% Al2O3; (b) 60 to 70 wt% SiO2; (c) 1 to 10 wt% K2O; (d) 0.1 to 10 wt% Fe2O3; (e) 0.1 to 10 wt% MgO; (f) 0.1 to 10 wt% Na2O; (g) 0.1 to 10 wt% CaO; (h) 0.01 to 5 wt% of TiO2, for 100 wt% of (a) + (b) + (c) + (d) + (e) + (f) + (g) + (h), until a powder is obtained with an average particle size less than or equal to 2 μm; (2) mixing of the powder obtained in (1) with powdered carbon;(3) carbonitriding heat treatment of the powder obtained in (2), at a temperature T between 1525 and 1625°C for a time period t of 3 to 6 h, under nitrogen purging.;

Description

Title of the invention: Process for manufacturing a ceramic powder based on p-SiAlON by carbonitriding of porcelain residues

[0001] The present invention relates to the manufacture of a ceramic powder based on [3-SiAlON], suitable for the production by sintering of ceramic parts with a density greater than 98%.

[0002] The ceramic phase [3-SiAlON] is sought after because it has promising physicochemical properties, such as high rigidity and high hardness, promising resistance under a high temperature oxidizing environment, and very good resistance to friction.

[0003] These interesting properties lead to the use of this ceramic being considered in numerous application sectors, such as the steel industry, for example for manufacturing pipes and bags for transporting liquid metals or alloys, probe sheaths such as immersion heaters, the abrasives industry, the civil or military transport industry, for example for manufacturing turbojet parts for aeronautics such as spark plugs or ball bearings for electric vehicles.

[0004] Seeking also to valorize the porcelain residues, resulting from the heat treatment of degourdi, the present inventors have surprisingly discovered that by converting by carbonitriding the porcelain residues once ground, a ceramic powder is obtained comprising a majority phase of [3-SiA10N, a corundum phase, and a / -SiAlON phase and capable of undergoing a heat treatment to densify it into a ceramic part having a density of at least 90% and good mechanical properties. In certain cases, during sintering, the corundum phase - which is a sintering aid - can advantageously decrease, or even disappear in favor of the other two phases, thus leading to a part based on [3-SiAlON] which is very dense and has good mechanical properties. It is then possible to carry out direct sintering of the powder obtained, without having to add a sintering aid.

[0005] The present invention therefore relates to a method for manufacturing a ceramic powder based on [3-SiA10N] suitable for the production by sintering of ceramic parts with a density greater than 90%, characterized in that it comprises the following successive steps:

[0006] (1) grinding of at least one porcelain waste based on a mixture of kaolin, quartz and feldspar having the following composition: a. 20 to 30% by weight of Al2O3 b. 60 to 70% by weight of SiO2 c. 1 to 10% by weight of K2O d. 0.1 to 10% by weight of Fe2O3 e. 0.1 to 10% by weight of MgO f. 0.1 to 10% by weight of Na2O g. 0.1 to 10% by weight of CaO h. 0.01 to 5% by weight of TiO2

[0007] for 100% by weight of (a) + (b) + (c) + (d) + (e) + (f) + (g) + (h), until a powder is obtained whose average particle size is less than or equal to 2 qm;

[0008] (2) mixing the powder obtained in (1) with powdered carbon;

[0009] (3) carbonitriding heat treatment of the powder obtained in (2), at a temperature temperature T between 1525 and 1625°C for a period of time t of 3 to 6 hours, under a nitrogen flush.

[0010] Porcelain scraps may be scraps from the so-called dégourdi firing, which, during the manufacture of porcelain pieces, follows the production of raw pieces by casting or by calibrating or by pressing, from pastes based on kaolin, quartz and feldspar.

[0011] The grinding of step (1) can be carried out by carrying out the following successive operations: • pre-crushing to reduce porcelain waste from a size ranging from cm to tens of cm to a size of 1 mm to 0.1 mm with multimodal distribution, said pre-crushing being able to be carried out in particular in a jaw crusher or an impact crusher; • a grinding process to adjust the particle size, allowing the pre-ground porcelain waste to be reduced to an average particle size of between 2 and 30 qm with a bimodal distribution of the particles, said grinding being able to be carried out in particular in a planetary mill; • finishing grinding by attrition, allowing the particles to pass to an average dimension less than or equal to 1.5 qm, with a monomodal distribution of these.

[0012] The powdered carbon may be selected from carbon black, carbon black, charcoal and activated carbon.

[0013] In step (2), Fe2O3 may be added as an agent promoting the conversion to [3-SiAlON], in particular in an amount of up to 0.5 parts by weight per 100 parts by weight of the powder obtained in step (1), in particular from 0.1 to 0.5 parts by weight per 100 parts by weight of the powder obtained in step (1).

[0014] In mixing step (2), 19 to 22 parts by weight of powdered carbon can be used per 100 parts by weight of the powder obtained in (1).

[0015] The reaction followed during the carbonitriding process of the porcelain residue can therefore be that of formation of the [3-SiA10N] phase from a mixture of feldspar and metakaolin:

[0016] K2O, 6SiO2, A12O3 + 9C + 3N2 -> Si4Al2O2N6 + 2SiO2 + K2O + 9CO

[0017] Carbonitriding can be carried out under a nitrogen flush at a flow rate of 50 to 75 L / h.

[0018] Carbonitriding can be carried out on a powder in direct contact with the heat treatment atmosphere, which makes it possible to promote the escape of the volatile phases produced during the carbonitriding reaction, the kinetics of formation of the [3-SiA10N] phase being thus promoted.

[0019] The heat treatment of step (3) may include a prior increase in temperature of the mixture of step (2) up to temperature T.

[0020] Carbonitriding can be carried out on a powder in the open air.

[0021] According to the invention, a ceramic powder having the following composition can be obtained: • 60 to 87% by weight of [3-SiAlON; • 11 to 30% by weight of a-Al2O3; • 2 to 8% by weight of / -SiAlON; • 0 to 5% by weight of mullite.

[0022] The following Examples illustrate the present invention without, however, limiting its scope.

[0023] Example 1 (according to the invention): Manufacture of a ceramic powder based on [3-SiAlON

[0024] (1) Obtaining a powdery raw material

[0025] A porcelain scrap was used, consisting of "solids" of casting porcelain, calibration porcelain and pressing porcelain having undergone a heat treatment step of deglazing at 980°C. The size of the solids varies from 10 to 1 cm. The composition of these solids was as follows: a. 28.23% by weight of Al2O3 b. 64.13% by weight of SiO2 c. 5.69% by weight of K2O d. 0.48% by weight of Fe2O3 e. 0.547% by weight of MgO f. 0.474% by weight of Na2O g. 0.358 wt% CaO h. 0.091 wt% TiO2

[0026] for 100% by weight of (a) + (b) + (c) + (d) + (e) + (f) + (g) + (h)

[0027] Pre-crushing in an impact crusher

[0028] The masses were crushed in the FRITSCH PUL-VERISETTE 1 compact jaw crusher to reduce them from a size ranging from cm to tens of cm to particles with a size of 1 mm to 0.1 mm with a multimodal distribution, the crushing being ensured here with the aid of a strong pressure exerted by a fixed jaw and a movable jaw in the closed crushing chamber, the crushing plates being first in position 3 to standardize the size of the scrap, then in position 10.

[0029] The powder obtained is multimodal.

[0030] Grinding to adjust the final particle size

[0031] The raw materials thus crushed were then ground in the PULVERISETTE 6 planetary mill, with 50 grinding balls of 1 cm diameter in the grinding jar, the rotation speed of the jar in the mill being set at 490 rpm with a holding time of 10 minutes of grinding, without pause. This planetary grinding step makes it possible to obtain a micrometric powder with a bimodal distribution, two types of population being generated in fine, namely agglomerates of particles which still remain after this grinding treatment, and isolated particles. The bimodal distribution has a first peak at 2.27 pm with a volume fraction of 9.9% and a second peak at 29.9 pm with a volume fraction of 1.8%. The average particle diameter is 2.5 pm.

[0032] Finishing grinding by attrition

[0033] An attrition step of the powder thus obtained was then carried out in a Netzsch Labstar attritioner with 550g of zirconia balls with a diameter of 0.8 mm with 110g of powder in the grinding jar then 250g of water containing 0.05% by weight of the dispersant-deflocculant marketed by the CERADEL Company under the name Dolaflux, the rotation speed being set at 1000 rpm for a period of 2h30, without a break. A monomodal distribution centered on an average particle size of 1 pm was obtained.

[0034] 12) Mixing the powdered material with carbon

[0035] The powdered raw material obtained in (1) was mixed with carbon black marketed by the company Alfa Aesar under the name “39724 Carbon black, acetylene, 50% compressed, 99.9+%” in a mass proportion of 21%.

[0036] For this purpose, the mixture was placed in a cylindrical grinding bowl with a sintered corundum cover of the SODIPRO brand. The mixing was carried out using a Fritsch PULVERISETTE 6 planetary mill with 50 grinding balls of 1 cm diameter in the grinding jar for a period of 10 minutes at a rotation speed of 490 rpm.

[0037] 13) Carbonitriding

[0038] A carbonitriding heat treatment was carried out, without a cover on the crucible containing the reaction mixture, the thermal cycle being composed of: • a temperature rise of up to 1550°C; • maintained for 4 hours at this temperature under a nitrogen sweep, at a flow rate of 75L / h.

[0039] The arrangement without a cover on the crucible containing the mixture makes it possible to promote the escape of the volatile phases produced during the carbonitriding reaction. The kinetics of formation of the [3-SiA10N] phase is thus promoted.

[0040] After this carbonitriding heat treatment step, the composition of the reaction product is as follows: [3-SiA10N 82% by weight A12O3 (corundum) 15% by weight / -SiAlON 3% by weight 100% by weight

[0041] Example 2 (application example): Sintering of the powder obtained in Example 1

[0042] Flash sintering (SPS) of the powder obtained in Example 1 was carried out. In this sintering technique, heating is ensured by the passage of a pulsed direct electric current. A quantity of the order of 3g of carbonitrided powder is weighed and introduced into a 20mm diameter graphite SPS sintering die. Pre-compaction of the powder contained in the SPS sintering die is carried out using a manual Atlas 15011 1 ton pellet press. The thermomechanical cycle applied consists of a temperature rise with a speed of 100°C / min up to 1450°C then a maintenance of 5 minutes at this temperature. Cooling is ensured with the same speed, namely 100°C / min. A uniaxial load of 50 MPa is applied throughout the thermal cycle.

[0043] It was thus possible to obtain a part with a relative density of 90.63% with a [3-SiAlON] phase of 73% by weight, a [ / -SiAlON] phase of 19% by weight, a 15R-SiA10N phase of 6% by weight and a mullite phase of 2% by weight.

[0044] The mechanical performances of Vickers Ho I hardness of 15.4 ± 1 Gpa and Young's Modulus of 238 ± 10 Gpa make these ceramic parts, produced from porcelain scrap, comparable to commercial ceramic parts based on [3-SiA10N.

[0045] Example of application (according to the invention) 3

[0046] The procedure was as in Examples 1 and 2, adding 18% of carbon black and carrying out the carbonitriding step at 1625°C.

[0047] The results are shown in the following table.

[0048] Example of application (according to the invention) 4

[0049] The procedure was as in Examples 1 and 2, adding 0.5% of Fe2O3 to the carbonitriding step.

[0050] The results are shown in the following table.

[0051] Comparative example 5

[0052] The procedure was carried out as in Examples 1 and 2, carrying out the carbonitriding step at 1650°C.

[0053] Table 1 shows the results obtained

[0054] [Tables 1] Example 2 (invention) 3 (invention) 4 (invention) 5 (comparative) Composition of basic porcelain scrap (% by weight) A12O3 28.23 28.23 28.23 28.23 SiO2 64.13 64.13 64.13 64.13 k2o 5.69 5.69 5.69 5.69 Fe2O3 0.48 0.48 0.48 0.48 MgO 0.547 0.547 0.547 0.547 Na2O 0.474 0.474 0.474 0.474 CaO 0.358 0.358 0.358 0.358 TiO2 0.091 0.091 0.091 0.091 Mixture with carbon black % of carbon black 21 18 21 21 % of Fe2O3 - - 0.5 - Carbonitriding T(°C) 1550 1625 1550 1650 t(h) 4 4 4 4 Nitrogen (L / h) 75 75 75 75 Composition after carbonitriding (% by weight) [3-SiAlON 76 61 82 59 a-Al2O3 18 26 15 9 X-SiAlON 5 8 3 - 15R-SiA10N - - - 32 Mullite 1 5 - - Composition after Flash sintering at 1450°C for 5 minutes (% by weight) [3-SiA10N 73 62 88 56 a-A12O3 19 15 7 27 X-SiAlON 6 15 5 17 15R-SiA10N - - - - Mullite 2 8 - - Density 90.63 96.74 98.34 79.18

Claims

Claims

1. - Method for manufacturing a ceramic powder based on [3-SiA10N suitable for the production by sintering of ceramic parts with a density greater than 90%, characterized by the fact that it comprises the following successive stages: (1) grinding of at least one porcelain waste based on a mixture of kaolin, quartz and feldspar having the following composition: a. 20 to 30% by weight of Al2O3 b. 60 to 70% by weight of SiO2 c. 1 to 10% by weight of K2O d. 0.1 to 10% by weight of Fe2O3 e. 0.1 to 10% by weight of MgO f. 0.1 to 10% by weight of Na2O g. 0.1 to 10% by weight of CaO h. 0.01 to 5% by weight of TiO2 for 100% by weight of (a) + (b) + (c) + (d) + (e) + (f) + (g) + (h), until a powder is obtained whose average particle size is less than or equal to 2 pm; (2) mixing the powder obtained in (1) with powdered carbon; (3) carbonitriding heat treatment of the powder obtained in (2), at a temperature T between 1525 and 1625°C for a period of time t of 3 to 6 h, under a nitrogen sweep.

2. - Method according to claim 1, characterized in that the porcelain waste is waste from the so-called dégourdi firing, which, during the manufacture of porcelain pieces, follows the production of raw pieces by casting or by calibration or by pressing, from pastes based on kaolin, quartz and feldspar.

3. - Method according to one of claims 1 and 2, characterized in that the grinding of step (1) is carried out by carrying out the following successive operations: • pre-grinding making it possible to reduce the pig wool waste from a dimension ranging from cm to tens of cm to a dimension of 1 mm to 0.1 mm with a multi-modal distribution, said pre-grinding being able in particular to be carried out in a jaw crusher or an impact crusher; • a grinding process for adjusting the particle size, allowing the pre-ground porcelain waste to be reduced to an average particle size of between 2 and 30 pm with a bimodal distribution of the particles, said grinding being able in particular to be carried out in a planetary mill; • a finishing grinding process by attrition, allowing the particles to be reduced to an average size of less than or equal to 1.5 pm, with a monomodal distribution thereof.

4. - Method according to one of claims 1 to 3, characterized in that the powdered carbon is chosen from carbon black, carbon black, coal and activated carbon.

5. - Method according to one of claims 1 to 4, characterized in that in step (2), Fe2O3 is added as an agent promoting the conversion to [3-SiAlON, in particular in an amount of up to 0.5 parts by weight per 100 parts by weight of the powder obtained in step (1), in particular from 0.1 to 0.5 parts by weight per 100 parts by weight of the powder obtained in step (1).

6. - Method according to one of claims 1 to 5, characterized in that in the mixing step (2), 19 to 22 parts by weight of powdered carbon are used per 100 parts by weight of the powder obtained in (1).

7. - Method according to one of claims 1 to 6, characterized in that the carbonitriding is carried out under a nitrogen sweep at a flow rate of 50 to 75 L / h.

8. - Method according to one of claims 1 to 7, characterized by the heat treatment of step (3) comprising a prior increase in temperature of the mixture of step (2) up to temperature T.

9. - Method according to one of claims 1 to 8, characterized in that the carbonitriding is carried out on a powder in the open air.

10. - Method according to one of claims 1 to 9, characterized in that a ceramic powder is obtained having the following composition: • 60 to 87% by weight of [3-SiAlON; • 11 to 30% by weight of a-Al2O3; • 2 to 8% by weight of / -SiAlON; • 0 to 5% by weight of mullite.