WO2008012673A2

WO2008012673A2 - Process for the preparation of metal titanates

Info

Publication number: WO2008012673A2
Application number: PCT/IB2007/002177
Authority: WO
Inventors: Mario Terruzzi
Original assignee: Immi Industria Macinazioni Minerali S.R.L.
Priority date: 2006-07-28
Filing date: 2007-07-27
Publication date: 2008-01-31
Also published as: WO2008012673A3; WO2008012851A1

Abstract

Method for the preparation of metal titanates, in particular potassium hexatitanate and its use as a component in materials having a high friction coefficient, in plastic materials, paints, heat resistent materials, and lubricants.

Description

"PROCESS FOR THE PREPARATION OF METAL TITANATES "

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OBJECT OF THE INVENTION The present invention relates to a method for the preparation of metal titanates, in particular potassium titanate, as well as the titanate thus obtained, and its use as a component of materials with a high friction coefficient, in plastic materials, paints, heat resistant materials and in lubricants.

PRIOR ART Materials with a high friction coefficient are used to control the acceleration/deceleration of a wide range of vehicles of various types such as automobiles, planes, bicycles, motorcycles, and also in industrial equipment. Until a few years ago, the main component in almost all high friction coefficient materials was asbestos fibre, also sometimes combined with other reinforcing fibres in lesser quantities. Asbestos was widely used mainly for its fibrous structure, because it was easily available and for its low cost. Asbestos was widely used in textiles, as a thermal and accoustic insulant, and in the field of civil and industrial construction. However large numbers of asbestos-based products were revealed to be rather highly perishable, resulting in the consequential release of an amount of fibres in the environment proportional to the degradation. Mineral fibres released in this way are potentially inhalable, and once they are in the lungs can provoke even very serious damage such as asbestosis, mesothelioma and lung cancer. For the reasons described above, asbestos was abandoned several years ago, and therefore it was necessary to search for alternative materials for the aforesaid applications.

In particular in the field of materials with a high friction coefficient, certain metallic compounds with a titanium base have been researched and used, such as potassium hexatitanate and potassium octatitanate for example, that have long fibres and that have resulted as being suitable for use in the

i aforesaid sector. The typical size of the fibres of these titanate based materials relates to a length of at least 5μm and a diameter up to 3μm. However, fibres of this type have also been found to be inhalable and potentially dangerous for health. In particular, each country has established the size limits for fibres used to replace asbestos according to the end products the fibres are used in, and therefore there is a rather strong need for providing new products, especially in the field of materials with a high friction coefficient; products which will not present the problems described above, and that are manufactured using materials that are within the specification limits of all countries.

For example, US 5,891,933 describes a material with a high friction coefficient that comprises an alkaline metal titanate or alkaline earth metal titanate, such as potassium titanate for example, and a physical or chemical type binder for said titanate, such as for example a phenolic resin. On the other hand, US 2003/0049427 describes a material with a high friction coefficient which must possess a porosity between 8 and 20% and that comprises a fibrous base free of fibres having a length of at least 5μm and a diameter up to 3μm, such as for example potassium titanate, and a binder composed of a resin with specific characteristics. However, the products obtained according to prior art are composed of titanates in the form of fibrous particles which, even when mixed with the resins as described, represent a potential problem and which are still considered as unsuitable because they are dangerous.

OBJECTS OF THE INVENTION Therefore the object of the present invention is to provide a method for the preparation of metal titanates, in particular potassium titanate, which is able to form a product characterised by the rounded shape of the particles, and which is practically free of particles having an elongated form with a fibrous structure. Another object of the invention to provide a method for the preparation of metal titanates, in particular potassium titanate, which is performed in solid phase and which leads to the creation of a product with round-shaped particles, and practically free of any elongated particles with a fibrous structure.

Another object of the present invention is to provide a metal titanate, in particular potassium titanate, characterised by round-shaped particles, and practically free of any elongated particles with a fibrous structure. A further object of the present invention is to provide metal titanate, in particular potassium titanate, characterised by round-shaped particles, and practically free of any elongated particles with a fibrous structure that can be used in particular to create materials with a high friction coefficient.

DESCRIPTION

These and other further objects and relative advantages which will be described more clearly further on, are achieved by a method for the preparation of metal titanates that includes the reaction in solid state, at a temperature between 855⁰C and 1200 ⁰C, between at least a carbonate, or hydroxide or oxide of an alkaline metal or alkaline-earth metal and a source of TiO₂. In particular, said carbonate, hydroxide or oxide is preferably chosen in the form of potassium carbonate, and said source of TiO₂ is rutile, a mineral composed of titanium dioxide. According to the present invention, the metal titanate thus obtained is potassium titanate, in particular potassium hexatitanate in the formula K₂Ti₆Oi₃.

In general, all metal titanates, in particular, potassium titanates having the general formula

produced using methods according to known techniques, are characterised by an elongated crystal structure, in the form of needles and/or fibres. On the other hand, the method according to the present invention permits the formation of a metal titanate, in particular potassium hexatitanate in the formula K₂Ti₆Oi₃ (1 (K₂O)6(TiO₂) characterised in that it possesses almost no elongated crystals in needle and/or fibre form. The particles of potassium hexatitanate obtained according to the method of the invention have a rounded, almost spherical form (and are therefore defined as rounded spherical particles) presenting a ratio between length and diameter which is less than 3.

According to a variant of the method of the invention, metal titanate, in particular potassium titanate, obtained as a raw reaction product does not contain particles with a length less than 2 μm, apart from extremely small percentages formed accidentally.

As stated previously, the particles obtained in this manner have a spherical and/or rounded ellipsoid shape, and as well as not having an elongated and therefore fibrous form, they are not flat or lenticular, and possess parameters very far from those imposed by the limits established by national and international standards. This means that the spherical and/or rounded ellipsoid form of the particle is able to guarantee that the metal titanate, and in particular, the potassium titanate according to the invention, can be considered a valid alternative to products currently on the market, and can remain in use without restraint even if the limits currently applied for the use of fibrous substances are restricted even further in the future.

Therefore metal titanate, in particular potassium hexatitanate according to the invention, can be advantageously used in materials with a high friction coefficient or other materials for example, since the rounded spherical form of its particles, and the almost complete absence of elongated fibrous particles, whether in needle, flat or lenticular form, frees the materials in which they are used from the limits and restrictions imposed by a large number of European and international standards, thus making the material in question suitable for safe and widespread application. The method for the preparation of metal titanates, in particular potassium titanate, according to one of the aspects of the present invention, provides for the use of rutile in powder form and potassium carbonate or potassium hydroxide as an initial reagent. Rutile powder has a nominal fineness of 325 mesh but other sizes , including sand, can be used, and this has a ΗO₂ content of approximately 95%. The potassium carbonate employed is obtained synthetically, and can therefore be considered as pure. The initial reagents are mixed for a sufficient time in a paddle mixer, and are then sent into a hopper for loading directly or indirectly into a free-fired rotating furnace using diesel, methane gas or Viquid propane gas as fuel. The material can be fired continuously or in batches. Furnace temperatures range between 855°C and 1200⁰C, preferably between 1000⁰C and 1200⁰C, and more preferably, the ideal conditions for furnace operation are at 1000⁰C.

The method of preparation of metal titanates, particularly potassium titanate, according to the present invention, provides, as we have already stated, for the advantageous use of a rotating furnace that makes it possible to obtain a uniform product and considerably decreases production time.

The rotating furnace used according to the invention, is associated with equipment including a movable trolley that can, for example, be driven on rails in the direction parallel to the length of the furnace and that is positioned frontally with respect to the furnace outlet. This trolley supports a projecting rod of suitable length, for example made of ceramic material or special steel suitable for high temperatures, that can rotate on its axis and is fitted on the end with a scraper-type scraper of adequate size and shape with respect to the size and shape of the furnace, also made, for example, of ceramic material or special steel suitable for high temperatures. The scraper-type scraper, when at rest, is preferably kept in a vertical position.

Periodically, with a frequency that depends on the parameters of furnace operation, the burner is shut down and moved away from the mouth of the furnace and the trolley, driven by a suitable system, proceeds towards the furnace opening.

When the scraper has been completely introduced in the furnace, the trolley stops and the scraper is made to rotate, so as to adhere to the wall of the furnace . The rotating motion of the furnace is not interrupted, so that the scraper scrapes the stratified encrustation from the furnace wall.

The trolley resumes its motion so that the scraper travels the entire length of the inside of the furnace, automatically "cleaning" the wall along the entire length of the furnace.

When it reaches the end of the furnace, the trolley automatically reverses the direction of motion, moving away from the oven entrance. At the end of this "return trip" the scraper resumes its vertical position so as to be able to exit the furnace. At this point the burner is returned to its normal position and lit, and heating resumes as required.

For the entire duration of this operation, the furnace never stops rotating and can therefore ensure the uniformity of the products it contains, as well as the product in the process of formation or also the finished product.

The advantage of the equipment described above, that combines a rotating furnace with an automatic "mixing" system to detach the encrustation from the inner surface of the furnace, is readily apparent. According to the prior art, reactions at such high temperatures are achieved typically in crucibles or in suitable furnaces of the static type.

In the case of crucibles, the first problem is represented by the fact that these systems have a capacity between 5 and 20 kg that, from the industrial viewpoint, is very limited. Moreover, typically, the use of crucibles requires that they be filled with materials already perfectly ground and blended together as, during the heating stage, it is not possible to perform any further blending of the material contained. If the material loaded is not perfectly ground and blended, the end product will not be perfectly uniform, with negative consequences. Once prepared and filled, the crucible is placed in a furnace and heated. At the end of the reaction, the crucible is removed from the furnace and allowed to cool partially before being handled to unload the material, as the process of emptying the crucible as soon as the heating stage ends is not readily feasible at the industrial level and involves serious hazards for the operators. Since the process according to the present invention provides for a stage of rapid cooling of the incandescent material at the end of the heating stage, the use of the crucible is not possible, as it would be necessary to wait too long before unloading the material, and rapid cooling would thus no longer be possible.

To resolve these problems, the method according to the invention provides for the use of a rotating furnace, that offers the advantage of guaranteeing a much higher capacity compared to the capacity of crucibles traditionally used according to the prior art. Moreover, the combination of the rotating furnace and the equipment for "mixing" represented by the trolley, the automated arm or rod and scraper-scraper, with reference to programming of furnace operation, makes it possible to maintain the material for reaction, as well as the finished product, continuously in motion, preventing the formation of encrustation on the inner walls of furnace and ensuring a uniform finished product of good quality, with a procedure that results in very little waste and processing residue. A further advantage of the use of the rotating furnace is represented by the fact that the incandescent material, after the reaction has terminated, can be discharged from the furnace immediately without any danger whatsoever for the operator and without waiting for it to cool partially, as would be necessary if the reaction were obtained in a crucible. In this way, the incandescent material discharged from the furnace according to the invention, can be advantageously subjected to rapid cooling, with the advantages already (Illustrated.

Once again, according to the method of the present invention, the rutile is advantageously used in quantities that are higher than stechiometric levels. Thus, after cooling as rapidly as possible, the material produced is ground appropriately, for example in a ball grinder, where the choice of the type of ball and the coating is made according to the purity requirements for the finished product. This also applies to the choice of the appropriate granulometric range according to the requirements of the markets where the end products are destined. The production of rounded spherical particles of potassium titanate according to the aforesaid method reaches and exceeds 99%.

Yet again, according to the present invention, it has been noted that the addition of a titanate of the formula XTiO₃, or one of its precursors to the reaction mixture, where x represents an alkaline earth metal, chosen from Mg, Ca, Sr, or Ba, for example, permits the production of an end product characterised by 100% spherical and/or ellipsoid, and/or rounded ellipsoid particles. It was noted that the best results were obtained by adding CaTiO₃ or the reagents that lead to its formation, to the reaction mixture. In this case the molar ratio of the end mixture CaTiO₃/ K₂Ti₆O₁₃ ranges between 0.25/1 and 1.5/1.

In the case where CaTiO₃ or the reagents that lead to its formation, are added to the reaction mixture, the method according to the invention involves a mechanism which provokes the formation of a cubic structure of a calcium titanate crystal, around which a growth of micro-crystals, also monoclinic, is formed, but which is, in any case, large enough to lead the formation of end product spherical particles, in particular potassium hexatitanate in the case described above and provided as an example.

The aforesaid description will be illustrated in detail purely as a non-limiting example of the present invention. EXAMPLE 1

The installation equipment for the production of metal titanates, in particular potassium and sodium titanates, comprises the following:

- mixer

- rotating furnace - grinder

- packaging

The raw materials used for the production of potassium titanate are: rutile and potassium carbonate mineral powder.

The raw materials are loaded into the mixer in the following proportions: 100 Kg of K₂CO₃ and 350 Kg of rutile for each batch, mixed until they are completely homogeneous, then unloaded into a tank with a valve at the bottom which is then loaded into the furnace. The total amount of material loaded into the furnace for each batch is 450 Kg and the theoretical amount of end product is 415 Kg for each batch. The amount of material normally dispersed in fumes is about 15-20 Kg for each batch. The furnace is run on LPG.

Each batch is left to react for 3 hours at a temperature of 1100⁰C. At the end of the reaction, the batch is unloaded into an iron container, however it is not left to cool in these conditions, but poured onto a flat surface and spread as finely as possible so that cooling can occur very rapidly. When the material is cool it is ground in a hammer mill, such as a "Danioni" type, equipped with an electric 50 kw motor, producing a yield of 100 Kg/h. If necessary, after the method described above, another stage can be added, passing the material through a sifter with a 1 mm mesh. After grinding, the material is collected and packaged for example in bags, according to use and final destination.

The material percentage analysis is as follows:

K₂O 18,5 +/- 1.5% TiO₂ 76 +/- 1.5%

Fe₂O₃ 1.5 % max

AI₂O₃ 1%max

SiO₂ 2%max

ZrO₂ 2%max

Na₂O 1%max

S 0.03 %max

P 0.03 % max

H₂O 1% max

Claims

1. Method for the preparation of metal titanates that comprises the reaction in solid phase at a temperature between 855°C and 1200 ⁰C, between at least a carbonate, a hydroxide, or an oxide of an alkaline metal or an alkaline earth metal and a source of TiO₂.

2. Method according to claim 1 , characterised in that said carbonate is potassium carbonate and said source of TiO₂ is rutile.

3. Method according to claim 1 , characterised in that said metal titanate is potassium titanate.

4. Method according to claim 3, characterised in that said potassium titanate is potassium hexatitanate in the formula K₂TΪ₆O₁₃.

5. Method according to claim 1 , characterised in that it comprises the following stages:

- mixing of initial reagents to obtain a mixture - loading of said mixture into a rotating furnace

- reaction in the furnace of said mixture to obtain an end material

- cooling of said end material

- grinding of said material after cooling

- packaging of said ground material.

6. Method according to claim 5, characterised in that said reaction in rotating furnace is performed in combination with an operation of mixing inside said furnace obtained using equipment consisting of a movable trolley, at least a rod of suitable length, at least a ploughshare-scraper.

7. Method according to claim 5, characterised in that said reaction in the furnace occurs at a temperature between 855°C and 1200⁰C, preferably between 1000⁰C and 1200°C.

8. Method according to claim 6, characterised in that said reaction in the furnace occurs at a temperature of 1000⁰C.

9. Method according to claim 5, characterised in that said cooling action is performed rapidly.

10. Method according to claim 1 , characterised in that said rutile is employed in greater quantities than the stechiometric quantity.

11. Method according to claim 1 , characterised in that said reaction in solid phase also comprises a titanate in the formula xTiθ₃, or of reagents that result in said titanate, where x is an alkaline earth metal chosen among Mg, Ca, Sr, and Ba.

12. Method according to claim 10, characterised in that said titanate of the formula XTiO₃ is CaTiO₃.

13. Method according to claim 10, characterised in that the molar ratio of the end mixture XTiO₃ / end product ranges between 0.25/1 and 1.5/1.

14. Metal titanate which can be obtained according to the method described in the previous claims.

15. Potassium hexatitanate in the formula KaTJeOi₃ that can be obtained as described in claims 1 to 12.

16. Potassium hexatitanate according to claim 14, characterised in that it is composed of particles having rounded, spherical and/or ellipsoid shape.

17. Potassium hexatitanate according to claim 15, characterised in that said particles have a ratio less than 3 between their length and the diameter.

18. The use of potassium hexatitanate as described in the previous claims in materials with a high friction coefficient, in plastic materials, paints, heat resistant materials, and lubricants.

19. Materials with a high friction coefficient that comprise potassium hexatitanate as described in the previous claims.