EP2632874A1

EP2632874A1 - Fused ceramic particle

Info

Publication number: EP2632874A1
Application number: EP11781657.9A
Authority: EP
Inventors: Samuel Marlin; Michela Valentini
Original assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Current assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Priority date: 2010-10-29
Filing date: 2011-10-28
Publication date: 2013-09-04
Also published as: CN103180265B; FR2966824B1; FR2966824A1; WO2012056420A1; US20130263523A1; CN103180265A

Abstract

The present invention relates to a fused ceramic particle having the following chemical composition, as weight percentages based on the oxides, and for a total of 100%: ZrO₂+HfO₂: balance to 100%; 5.0% < SiO₂ < 32.0%; 2.0% < La₂O₃ < 15.0%; 2.5% < Y₂O₃ < 11.0%; 0.5% < Al₂O₃ < 8.0%; and less than 1.0% of other oxides. Use in particular as a grinding agent, an agent for dispersion in a wet medium, a supporting agent, a heat-exchange agent, or for the treatment of surfaces.

Description

Melted ceramic particle

Technical area

The present invention relates to new melted ceramic particles, in particular in the form of beads, to a process for producing these beads, and to the use of these particles as grinding agents, dispersants in a wet medium or for the treatment of surfaces.

State of the art

The mineral industry uses particles for the fine grinding of materials that may be dry-milled by conventional methods, in particular for calcium carbonate, titanium oxide, gypsum, kaolin and iron ore.

The paints, inks, dyes, magnetic lakes and agrochemicals industries use particles for the dispersion and homogenization of the various liquid and solid constituents.

The surface treatment industry finally uses particles, especially for cleaning metal molds (for making bottles for example), deburring parts, descaling, preparing a support for a coating, the treatment of pre-constraints ("shot peening"), the forming of parts ("peen forming") ...

The particles are conventionally substantially spherical and of a size of 0.005 to 4 mm in order to serve all the markets described above. For them to be used in these three types of applications, they must in particular have good resistance to wear.

On the market, there are different types of particles, particularly beads, especially in the microbrinding field:

■ Rounded sand, such as OTTAWA sand, is a natural, inexpensive product that is not suitable for modern, pressurized, high-volume mills. Indeed, the sand is not very resistant, of low density, variable in quality and abrasive for the material.

^■ Glass beads, widely used, have better strength, lower abrasiveness and availability in a wider range of diameters.

^■ Metallic balls, especially of steel, have insufficient inertia with respect to the treated products, in particular causing pollution of the mineral and a graying of the paints, and too high a density requiring special grinders involving in particular a high energy consumption, a significant heating and a high mechanical stress of the equipment.

Ceramic balls are also known. These beads have better strength than glass beads, higher density and excellent chemical inertness. We can distinguish :

^■ sintered ceramic beads, obtained by cold forming of a ceramic powder, then consolidation by baking at high temperature, and

^■ so-called "fused" ceramic beads, generally obtained by melting ceramic components, forming spherical drops from the melt, then solidifying said drops.

The vast majority of the fused beads have a composition of the zirconia-silica type (Zr0 ₂ -SiO ₂ ) in which the zirconia is crystallized in monoclinic form and / or partially stabilized in quadratic form (by suitable additions), and the silica as well as some of the optional additives form a glassy phase which binds the zirconia crystals. The fused ceramic beads provide optimum properties for grinding, ie good mechanical strength, high density, low chemical inertness and abrasiveness to the grinding material.

Molten zirconia-based ceramic beads and their use for grinding and dispersing are for example described in FR 2,320,276 (US 4,106,947) and EP 0,662,461 (US 5,502,012). These documents describe the influence of SiO ₂ , Al ₂ O ₃ , MgO, CaO, Y ₂ O ₃ , CeO ₂ , and Na ₂ 0 on the main properties, in particular on the properties of crush resistance and resistance to abrasion.

Although the fused ceramic beads of the prior art are of good quality, the industry still needs even better quality products. Indeed, the grinding conditions are always more demanding and it is necessary, in order to reduce operating costs, to increase the yields of the devices used. In particular, it is desirable to reduce the periods of unavailability of these devices.

The invention aims to meet these needs by providing melted ceramic particles which have excellent resistance to breakage and wear, especially in basic medium. Summary of the invention

The invention relates to a novel fused ceramic particle, preferably in the form of a ball, having the following chemical composition, in percentages by weight on the basis of the oxides and for a total of 100%:

Zr0 ₂ + Hf0 ₂ : 100% complement;

15.0% <SiO ₂ <32.0%;

2.0% <La ₂ 0 ₃ <15.0%;

2.5% <Y ₂ 0 ₃ <1 1, 0%;

0.5% <Al ₂ O ₃ <8.0%; and

less than 1.0% other oxides.

The inventors have unexpectedly found that the presence of lanthanum oxide (La ₃ O ₃ ) and yttrium oxide (Y ₂ O ₃ ) in the abovementioned proportions significantly improves the properties of the melted ceramic particles, in particular compared to the particles described in FR 2,320,276.

The particles according to the invention are thus particularly well suited to wet dispersion, micro grinding and surface treatment applications. In the grinding application, the particles according to the invention have improved breaking resistance during start-up and in use.

The invention also relates to a particle powder comprising more than

90%, preferably more than 95%, preferably substantially 100%, in percentages by weight, of particles according to the invention.

The invention also relates to a process for producing melted particles according to the invention, in particular melted balls, comprising the following successive steps:

a) mixing raw materials to form a feedstock;

b) melting the feedstock to obtain a melt, c) dispersing said melt in the form of liquid droplets and solidifying these liquid droplets in the form of particles (especially beads).

According to the invention, the raw materials are chosen in step a) so that the particles obtained in step c) are in accordance with the invention. Preferably, oxides of lanthanum, yttrium and aluminum and / or one or more precursors of these oxides are added voluntarily and systematically into the feedstock, preferably in the oxide form, so as to ensure this conformity.

The invention finally relates to the use of a powder of particles, in particular beads, according to the invention, in particular manufactured according to a process according to the invention, as grinding agents; dispersants in a humid environment; propping agents, in particular to prevent the closure of deep geological fractures created in the walls of an extraction well, in particular of oil; heat exchange agents for example for fluidized bed; or for the treatment of surfaces.

Definitions

By "particle" is meant a solid product individualized in a powder.

"Ball" means a particle having a sphericity, that is to say a ratio between its smallest diameter and its largest diameter, greater than 0.6, whatever the way in which this sphericity has been obtained. Preferably, the balls according to the invention have a sphericity greater than 0.7.

The "size" of a ball (or particle) is the average of its largest dimension dM and its smallest dimension dm: (dM + dm) / 2.

By "fused ball", or more broadly "melted particle" is meant a solid ball (or particle) obtained by solidification by cooling of a molten material. A "molten material" is a liquid mass that may contain some solid particles, but in an amount insufficient for them to structure said mass. To maintain its shape, a molten material must be contained in a container.

By "impurities" is meant the inevitable constituents, necessarily introduced with the raw materials. In particular, in one embodiment, the compounds forming part of the group of oxides, nitrides, oxynitrides, carbides, oxycarbides, carbonitrides and metallic species of sodium and other alkalis, iron, vanadium and chromium are impurities. By way of examples, mention may be made of MgO, CaO, Fe ₂ O ₃ , TiO ₂ or Na ₂ O. The residual carbon is one of the impurities of the composition of the particles according to the invention.

When reference is made to zirconia or Zr0 ₂ , it is necessary to understand (Zr0 ₂ + Hf0 ₂ ), that is to say Zr0 ₂ and traces of Hf0 ₂ . Indeed, a little Hf0 ₂ , chemically indissociable Zr0 ₂ in a fusion process and having similar properties, is still naturally present in zirconia sources at levels generally below 2%. Hafnium oxide is not considered an impurity.

By "precursor" of an oxide is meant a constituent capable of supplying said oxide during the manufacture of a particle according to the invention.

All percentages of the present description are percentages by weight based on the oxides unless otherwise indicated.

Brief description of the figures

Other characteristics and advantages will become apparent on reading the following detailed description and on examining the appended drawing in which:

FIG. 1 represents a snapshot of the reference product of the examples, and

FIG. 2 represents a snapshot of the product of example 8.

detailed description

Process

To manufacture a product according to one embodiment of the invention, it is possible to proceed according to the steps a) to c) mentioned above.

These steps are conventional except for the composition of the feedstock, and those skilled in the art can adapt them according to the intended application.

A preferred embodiment of this method is now described.

In step a), the feedstock is formed of the indicated oxides or precursors thereof. Preferably, ZrSiO ₄ natural zircon sand containing about 66% ZrO ₂ and 33% SiO ₂ , plus impurities is used. The addition of Zr0 ₂ and Si0 ₂ in the form of zircon is indeed much more economical than an addition in the form of free zirconia and silica.

The compositions may be adjusted by addition of pure oxides, mixtures of oxides or mixtures of precursors of these oxides, in particular by addition of Zr0 ₂ , Si0 ₂ , La ₂ 0 ₃ , Y ₂ 0 ₃ , and Al ₂ 0 ₃ .

According to the invention, those skilled in the art adjust the composition of the feedstock so as to obtain, after step c), particles in accordance with the invention. The chemical analysis of the melted ceramic particles according to the invention is generally substantially identical to that of the feedstock. In addition, where appropriate, for example to take account of the presence of volatile oxides, or to account of the loss of Si0 ₂ when the melting is performed under reducing conditions, the skilled person knows how to adapt the composition of the feedstock accordingly.

Preferably, no raw materials other than those providing Zr0 ₂ + Hf0 ₂ , Si0 ₂ , La ₂ 0 ₃ , Al ₂ 0 ₃ , Y ₂ 0 ₃ and their precursors are deliberately introduced into the feedstock, the other oxides present being impurities.

In step b), the feedstock is melted, preferably in an electric arc furnace. Electrofusion makes it possible to manufacture large quantities of particles (preferably in the form of beads) with interesting yields. But all known furnaces are conceivable, such as an induction furnace or a plasma furnace, provided they allow to melt substantially completely the charge.

In step c), a stream of the molten liquid is dispersed in small liquid droplets which, as a result of the surface tension, take, for the majority of them, a substantially spherical shape. This dispersion can be performed by blowing, especially with air and / or steam and / or nitrogen, or by any other method of atomizing a molten material, known from the skilled in the art. A fused ceramic particle of a size of 0.005 to 4 mm can thus be produced.

The cooling resulting from the dispersion leads to the solidification of the liquid droplets. Molten particles, in particular melted balls, according to the invention are then obtained.

Any conventional method for producing melted particles, especially molten beads, may be implemented, provided that the composition of the feedstock makes it possible to obtain particles having a composition in accordance with that of the particles according to the invention. For example, it is possible to manufacture a melted and cast block, then to grind it and, if necessary, to make a granulometric selection.

particles

A fused ceramic particle according to the invention has the following chemical composition, in percentages by weight on the basis of the oxides and for a total of 100%:

Zr0 ₂ + Hf0 ₂ : 100% complement;

15.0% <SiO ₂ <32.0%; 2.0% <La ₂ 0 ₃ <15.0%;

2.5% <Y ₂ 0 ₃ <1 1, 0%;

0.5% <Al ₂ O ₃ <8.0%; and

less than 1.0% other oxides. A fused ceramic particle according to the invention preferably has a mass content of La ₂ 0 ₃ greater than 2.5%, greater than 3.0%, greater than 4.0%, or even greater than 5.0%.

Preferably, the mass content of La ₂ 0 ₃ is less than 14.0%, less than 12.0%, less than 10.0%, less than 9.5%, and even less than 9.0%.

In one embodiment, the mass content of yttrium oxide Y ₂ O ₃ is greater than 3.0%, greater than 3.5%, greater than 4.0%, or even greater than 4.5%, and / or less than 10.0%, less than 9.0%, less than 8.5%, or even less than 8.0%, less than 7.5%, less than 7.0%.

Likewise, a fused ceramic particle according to the invention preferably has a mass content of Al ₂ O ₃ greater than 0.8%, preferably greater than 1.0%, greater than 1.2%, greater than 1.5% by weight. %, greater than 1, 6% or even greater than 1, 8%.

The Al ₂ 0 ₃ mass content is preferably less than 7.0%, less than 6.5%, less than 6.0%, less than 3.5%.

The contents of zirconia and silica also influence the performance of a particle according to the invention.

Preferably, a fused ceramic particle according to the invention comprises a mass content of Zr0 ₂ greater than 50.0%, greater than 51.0%, greater than 52.0%, and even greater than 53.0%. Preferably, this mass content is less than 70.0%, less than 65.0%, preferably less than 63.0%, or even less than 60.0% or less than 58.0%.

Preferably, a melted ceramic particle according to the invention comprises a mass content of SiO ₂ greater than 16.0%, greater than 18.0%, preferably greater than 20.0%, more preferably greater than 22.0. %, preferably greater than 24.0%. Preferably, this mass content is less than 31.0%, less than 30.0%, less than 29.0%, preferably less than 28.0%.

Preferably, a melted ceramic particle according to the invention has a ratio of the mass percentages Zr0 ₂ / SiO ₂ greater than 1, 5, or even greater than 1, 8, or even greater than 2.0 or greater than 2.1, and / or less than 4.0, less than 3.0, preferably less than 2.5.

Preferably, a fused ceramic particle according to the invention has a ratio of Al ₂ 0 ₃ / SiO ₂ mass percentages greater than 0.05, and / or less than 0.25, less than 0.20, preferably less than 0. 15.

The "other oxides" are preferably present only in the form of impurities. It is considered that a total content of "other oxides" of less than 1.0% does not substantially modify the results obtained. However, preferably, the "other oxides" content, as a weight percentage based on the oxides, is less than 0.6%, preferably less than 0.5%, preferably less than 0.45%.

Still preferably, the oxide content of a particle according to the invention represents more than 99.5%, preferably more than 99.9%, and more preferably substantially 100% of the total mass of said particle.

A particle according to the preferred invention has the following chemical composition, in percentages by mass on the basis of the oxides and for a total of 100%:

Zr0 ₂ + Hf0 ₂ : complement to 100%, preferably 51.0% <Zr0 ₂ + Hf0 ₂ <63.0%; 20.0% <SiO ₂ <30.0%;

2.5% <La ₂ 0 ₃ <10.0%;

3.0% <Y ₂ 0 ₃ <7.5%;

1, 5% <Al ₂ O ₃ <5.5%; and

less than 1.0% other oxides.

Zr0 ₂ + Hf0 ₂ : complement to 100%, preferably 52.0% <Zr0 ₂ + Hf0 ₂ <63.0%; 22.0% <SiO ₂ <28.0%;

3.0% <La ₂ 0 ₃ <10.0%;

4.0% <Y ₂ 0 ₃ <7.5%;

1.8% <Al ₂ O ₃ <3.5%; and

less than 1.0% other oxides. A fused ceramic particle according to the invention may in particular have a size of less than 4 mm and / or greater than 0.005 mm.

Other forms than those of "balls" are possible according to the invention, but the substantially spherical shape is preferred. The melted ceramic particles according to the invention are very resistant to wear.

In the case of stress in a strongly basic medium, that is to say for pH> 8, for example for the grinding of calcium carbonate suspensions, such particles are particularly well suited because they exhibit resistance to high wear coupled with good resistance to chemical attack of the medium in which grinding is carried out.

The melted ceramic particles according to the invention are particularly well suited as grinding agents or as dispersing agents in a wet medium, as well as for the treatment of surfaces. The invention therefore also relates to the use of a plurality of particles, in particular beads according to the invention, or beads made according to a process according to the invention, as grinding agents, or dispersion agents in a medium. wet.

It may be noted, however, that the properties of the beads, in particular their strength, their density, as well as their ease of production, may make them suitable for other applications, especially as proppants or heat exchange agents or for the treatment of surfaces.

The invention therefore also relates to a device selected from a suspension, a grinder, a surface treatment apparatus and a heat exchanger, said device comprising a particle powder according to the invention.

Examples

The following nonlimiting examples are given for the purpose of illustrating the invention.

Measurement protocols

The following methods have been used to determine certain properties of different mixtures of fused ceramic beads. They allow an excellent simulation of the actual service behavior in the grinding application.

To determine the so-called "planetary" wear resistance, 20 ml (volume measured using a graduated test piece) of test balls of size between 0.8 and 1 mm are weighed (mass m ₀ ). and introduced into one of the 4 bowls coated with dense sintered alumina, with a capacity of 125 ml, a RETSCH type PM400 fast planetary mill. Are added in the same bowl already containing the beads, 2.2 g of Presi brand silicon carbide (having a median size D50 of 23 μηη) and 40 ml of water. The bowl is closed and rotated (planetary motion) at 400 rpm with reversal of the direction of rotation every minute for 1 hour 30 minutes. The contents of the bowl are then washed on a sieve of 100 μηη so as to remove the residual silicon carbide and tearing material due to wear during grinding. After sieving through a sieve of 100 μηη, the particles are dried in an oven at 100 ° C. for 3 h and then weighed (mass m).

The planetary wear is expressed as a percentage (%) and is equal to the mass loss of the balls reduced to the initial mass of the balls, ie: 100 (m ₀ -m) / (m ₀ ); the UP result is given in Table 1.

The results are considered to be particularly satisfactory if the products exhibit an improvement in the resistance to planetary wear (UP) of at least 20% compared to that of Example Ref. 1.

To determine the so-called wear resistance "in basic medium", that is to say in media having a pH greater than 8, a batch of balls to be tested is sieved between 0.6 and 0.8 mm. square mesh screens. An apparent volume of 1.04 liters of beads is weighed (mass m ' ₀ ). The balls are then introduced into a Netzsch LME1 type horizontal mill (useful volume of 1.2 L) with eccentric steel discs. An aqueous suspension of calcium carbonate CaCO ₃ having a pH equal to 8.2, containing 70% of dry matter and of which 40% of the grains by volume are smaller than 1 μηη, passes continuously through the mill, with a flow rate of 4 liters per hour. The mill is started gradually until reaching a linear speed at the end of 10 m / s disks. The mill is kept in operation for a time t, between 16 and 24 hours, then stopped. The beads are rinsed with water, carefully removed from the mill and then washed and dried. They are then weighed (mass m '). The wear rate V in grams / hour is determined as follows: V = (me-m ') / t.

The bead load is taken up and supplemented with (me-m ') grams of new beads so as to repeat the grinding operation as many times as necessary (n times) so that the cumulative grinding time is at least 100 hours and that the difference between the wear speed calculated in step n and in step n-1 is less than 15% in relative. Wear in a basic medium is the rate of wear measured in this stabilized situation (typically beyond 120 hours). The result UB is given in Table 1. It is considered that the results are particularly satisfactory if the products have an improvement in the base wear resistance (UB) of at least 20% compared with that of Example Ref. 1. Manufacturing protocol

In the examples, a zircon composition is used for the feedstock, and lanthanum oxide, yttrium oxide and aluminum oxide are added. This feedstock is melted in an electric Herault type arc furnace. The molten material is then dispersed into balls by blowing compressed air.

Several melting / casting cycles are carried out, in particular by adjusting the contents of oxides of lanthanum, yttrium and aluminum.

Results

The results obtained are summarized in Table 1 below.

Table 1

ND: Not determined

^* : example outside the invention

The impurities represent, for each example, less than 1%.

The reference beads of the example "Ref. 1 ", outside the invention, are beads commonly used in grinding applications.

The examples show that, surprisingly, the balls according to the invention tested have remarkable performances compared to the reference beads. The comparison of Example 4 with Example 1 1 outside the invention shows the synergistic effect from the addition of yttrium oxide and lanthanum oxide.

Scanning electron microscopy structure analyzes were performed on the reference sample (Figures 1a and 1b) as well as for Example 8 (Figure 2a and 2b). The largest white areas correspond to the dentrites of zirconia, the rest is the silicate phase with the silica in black. It is observed that the silicate phase of the product according to the invention is very different from that of the reference product. The silicate phase of the product of the example according to the invention consists in fact of a continuous network of small crystals comprising Zr0 ₂ , La ₂ 0 ₃ , Y ₂ O ₃ and Al ₂ O _3, whereas that of the reference product contains only small zirconia crystals dispersed discontinuously.

In one embodiment, a particle according to the invention thus has a microstructure comprising zirconia dendrites, preferably longer than 2 μηη, greater than 3 μηη, or greater than 5 μηη, embedded in a silicate phase comprising crystals of Zr0 ₂ , La ₂ 0 ₃ , Y ₂ 0 ₃ and Al ₂ 0 ₃ having a length of less than 0.3 μηη, less than 0.2 μηη, and even less than 0.1 μηη. Preferably, the crystals of Zr0 ₂ , La ₂ 0 ₃ , Y ₂ 0 ₃ and Al ₂ 0 ₃ are distributed within the silicate phase so as to form a continuous network. Preferably, more than 50%, more than 70%, or even more than 80% of these crystals are in contact with other crystals.

Of course, the present invention is not limited to the embodiments described or represented, provided by way of illustrative examples.

Claims

1. Melted ceramic particle having the following chemical composition, in percentages by mass on the basis of the oxides and for a total of 100%:

Zr0 ₂ + Hf0 ₂ : 100% complement;

15.0% <SiO ₂ <32.0%;

2.0% <La ₂ 0 ₃ <15.0%;

2.5% <Y ₂ 0 ₃ <1 1, 0%;

0.5% <Al ₂ O ₃ <8.0%; and

less than 1.0% other oxides. 2. Particle according to the preceding claim, wherein

₂ 0 ₃ <10.0%.

3. Particle according to any one of the preceding claims, wherein

Y ₂ 0 _3> 3.0%.

Particle according to any one of the preceding claims, wherein

Y ₂ O ₃ <10.0%.

5. Particle according to the preceding claim, wherein

Y ₂ 0 ₃ <7.5%.

The particle of any one of the preceding claims, wherein

Al ₂ 0 ₃ > 1, 5% 7. Particle according to any one of the preceding claims, wherein Al ₂ 0 ₃ <7.0%

8. Particle according to the preceding claim, in which Al ₂ 0 ₃ <6.0%

Particle according to any one of the preceding claims, wherein

ZrO ₂ > 52.0%

Particle according to any one of the preceding claims, wherein

SiO ₂ > 20.0%.

1 1. Particle according to any one of the preceding claims, having the following chemical composition, in percentages by weight on the basis of the oxides and for a total of 100%:

Zr0 ₂ + Hf0 ₂ : 100% complement;

20.0% <SiO ₂ <30.0%;

2.5% <La ₂ 0 ₃ <10.0%;

3.0% <Y ₂ 0 ₃ <7.5%;

1, 5% <Al ₂ O ₃ <5.5%; and

less than 1.0% other oxides.

Particle according to any one of the preceding claims, wherein

2.5> Zr0 ₂ / SiO ₂ > 1.5.

13. Particle according to any one of the preceding claims, wherein

La ₂ 0 _3> 3.0%.

14. Particle according to any one of the preceding claims, wherein

Y ₂ 0 ₃ > 3.5%.

15. Particle according to the preceding claim, wherein

Y ₂ 0 ₃ > 4.5%.

Particle according to any one of the preceding claims, wherein

Al ₂ 0 ₃ <3.5% 17. Particle according to any one of the preceding claims, wherein

2.5> Zr0 ₂ / Si0 ₂ > 2.0.

18. Particle according to any one of the preceding claims, wherein

SiO ₂ > 22.0%.

19. A method of manufacturing a particle powder according to any one of the preceding claims, comprising the following successive steps:

a) mixing raw materials to form a feedstock;

b) melting the feedstock to obtain a melt, c) dispersing said melt in the form of liquid droplets and solidifying these liquid droplets as solid particles, process in which the raw materials are selected in step a) so that the particles obtained in step c) are in accordance with any one of the preceding claims, oxides of lanthanum, yttrium and aluminum and / or one or more precursors of these oxides being added voluntarily and systematically into the feedstock.

20. Use of a particle powder according to any one of claims 1 to 18 or manufactured according to a method according to the preceding claim, as grinding agent, dispersing agent in a humid medium.

Use of a particle powder according to any one of claims 1 to 18 or made by a process according to claim 19 as a proppant, heat exchange agent, or for surface treatment. .