Method for preparing non-fibrous alkali metal titanates having large specific surface area and high porosity

Abstract

A method for preparing a non-fibrous alkali metal titanate, comprising the steps of melting an alkali metal titanate in a furnace at a temperature in the range of 1300°C to 1500°C to form a molten product, and cooling the molten product by contacting the molten product with a material having a temperature of 15°C or less.

Description

[Technical field]

[0001] explanation The present invention relates to a method for preparing non-fibrous alkali metal titanates having a large specific surface area and high porosity.

[0002] The alkali metal titanates can be used for brake pads, brake linings, clutch linings, and welding electrodes for automobiles, trucks, rail vehicles, aircraft, and various industrial machines.

[0003] The hazards and health risks of asbestos are well known to everyone.

[0004] Since the 1990s, asbestos has been banned in the United States and Europe.

[0005] Since then, various other materials have been tested and used, including potassium titanate and sodium titanate.

[0006] In particular, potassium titanate and sodium titanate show a significant improvement in the stability of the friction coefficient, together with a reduction or elimination of the degradation of the phenolic resin, which, for example, in the use of brake pads, induces the sliding of the disk without braking, a dangerous phenomenon known in the technical term as "fade".

[0007] Friction materials are used to control the deceleration of many different types of vehicles, such as industrial equipment, automobiles, aircraft, bicycles and motorcycles.

[0008] In particular, in the field of friction materials, several titanium-based compounds, such as potassium hexatitanate, sodium hexatitanate, and potassium octatitanate, have been studied and used.

[0009] Potassium and sodium are characterized by elongated fibers and exhibit behavior suitable for use in the above mentioned fields.

[0010] However, these types of fibers have recently been viewed as a potential health hazard, and the EU and US have established maximum size limits for the fibers that can be used.

[0011] For example, the Commission's EU (EC) Regulation No. 761 / 2009 of 23 July 2009 defines as fibres crystals with a diameter / length ratio of 1:3 or greater and requires that all materials with a content of these fibres greater than 0.1% be defined as "fibrous" and classified as having hazard level Car 2 (possible carcinogen).

[0012] Thus, crystals having a ratio less than 1:3 are not considered fibers and therefore can be used without special precautions.

[0013] However, the products obtained by the known techniques contain titanates in the form of fibers, which, even when mixed with resins or utilized in different applications as described, present potential problems and are potentially dangerous and therefore subject to specific regulations and are therefore not considered suitable.

[0014] It is an object of the present invention to provide a method for the preparation of alkali metal titanates which results in a non-fibrous powder material.

[0015] A further object is to provide a method which results in crystals having a diameter / length ratio of less than 1:3.

[0016] A further object is to provide a method which leads to crystals with a large specific surface and high porosity.

[0017] In accordance with the present invention, these and other objects are further achieved by the following method for preparing a non-fibrous alkali metal titanate, comprising the steps of melting an alkali metal titanate in a furnace at a temperature in the range of 1300°C to 1500°C to form a molten product, and cooling the molten product by contacting the molten product with a material having a temperature of 15°C or less.

[0018] These objectives are further achieved by the formula A2Ti x O 2x+1 where A is an alkali metal from the group including Na, K, Li, Rb, and x is any number between 2 and 6, the powder having a diameter / length ratio of less than 1:3 and a surface area of ​​less than 10 m 2 / g.

[0019] Further features of the invention are set out in the dependent claims.

[0020] This solution offers various advantages over known art solutions.

[0021] This method provides alkali metal titanates, especially potassium and sodium titanates, which have extremely spongy crystals that are substantially round in shape, do not contain fibrous structures as defined above, and further have a very large specific surface area and high porosity, properties that give them a greater reactivity towards phenolic resins when used in braking systems.

[0022] The resulting products can be used as high coefficient of friction material components in plastic materials, coatings, heat-resistant materials and lubricants.

[0023] The characteristics and advantages of the present invention will become apparent from the following detailed description of practical embodiments of the invention, and illustrated by way of non-limiting examples in the accompanying drawings, which are described below. [Brief description of the drawings]

[0024] [Figure 1] In accordance with the present invention, the X-ray crystal structure analysis (XRD) of the product obtained from the 2θ positions of the peaks shows that the product belongs to a monoclinic structure and is therefore identical to the structure of the fibrous titanate. [Diagram 2] The X-ray crystal structure analysis (XRD) of commercially available fibrous potassium hexatitanate is shown. [Diagram 3] Electron micrographs of the product obtained according to the invention are shown at different magnifications, demonstrating that the product is not fibrous, highlighting its spongy morphology and its large specific surface area. [Figure 4] Electron micrographs of the product obtained according to the invention are shown at different magnifications, demonstrating that the product is not fibrous, highlighting its spongy morphology and its large specific surface area. [Diagram 5] Electron micrographs of the product obtained according to the invention are shown at different magnifications, demonstrating that the product is not fibrous, highlighting its spongy morphology and its large specific surface area. [Figure 6] Electron micrographs of the product obtained according to the invention are shown at different magnifications, demonstrating that the product is not fibrous, highlighting its spongy morphology and its large specific surface area. [Figure 7] Electron micrographs of the product obtained according to the invention are shown at different magnifications, demonstrating that the product is not fibrous, highlighting its spongy morphology and its large specific surface area.

[0025] Alkali metal titanates have the general formula A2Ti x O 2x+1 In the formula, A is an alkali metal such as Na, K, Li, or Rb, and x is an arbitrary number from 2 to 6.

[0026] The process for the preparation of alkali metal titanates, particularly potassium and sodium titanates, involves the use of TiO2 as synthetic rutile or anatase, or natural rutile at a minimum concentration of 90% in TiO2 in the form of powder or sand, or the mineral leucoxene, either alone or in admixture therewith.

[0027] Potassium or sodium carbonate and / or potassium or sodium hydroxide can be used as starting reagents or other organic derivatives of the alkali metals, but this represents an increase in cost.

[0028] When the minerals rutile or leucoxene are used as raw materials or mixtures thereof, trace amounts of different oxides may be present as impurities.

[0029] For example, oxides of Ca, Mg, Si, Zr, Al, V, Mn, P, and S may be present, as well as trace amounts of different oxides.

[0030] Impurities can be significant but are not taken into account: when pure raw materials are used, impurities are not present and have no effect on the effectiveness of the product.

[0031] The materials are mixed in any type of mixer and then placed in any type of furnace, electric or induction flame or open flame, in the case of open flame, fuels such as diesel, methane gas or LPG (liquefied propane gas) can be used.

[0032] Materials can be fired in batches or continuously. Furnace operating temperatures range from 700°C to 1000°C, with durations ranging from 2 to 8 hours, or other ranges based on the amount of material being processed and the ease with which the furnace can reach the desired temperature.

[0033] The material thus produced is in powder form after cooling and is then suitably ground, for example in a ball mill, the type of balls and coating being selected based on the particle size distribution requirements of the final product.

[0034] The alkali metal titanate thus produced is in the form of fibers.

[0035] The titanates are used as raw material for subsequent final processing to render them non-fibrous.

[0036] Similar results can be obtained by starting from the raw material in a direct process without going through the steps mentioned above.

[0037] The same result can be achieved by starting with the raw material in the direct process.

[0038] The metal titanate or the respective raw material is melted in a crucible or melting furnace in a batch process, i.e. a discontinuous process, or in specific furnaces that allow the same type of continuous production as above.

[0039] When starting from the respective raw material, the melting must be maintained until all the titanium dioxide has been melted by the alkali salt which melts first. When "pre-fabricated" titanates are used as raw materials, melting is reached sufficiently at 1300-1500 °C.

[0040] The molten product is poured very rapidly or dropwise into water (preferably under stirring to facilitate heat exchange) at well temperature (12-15°C), or poured onto a surface preferably below 15°C, or compressed between cylinders cooled preferably below 15°C to simultaneously cool and compress the material and rapidly return it to a solid state, or dripped into a liquid nitrogen bath.

[0041] In either case, the molten product is placed in contact with a material (solid or liquid) at a temperature below 15°C.

[0042] The rapid cooling and sudden passage from the liquid state to the solid state is a fundamental step in the present invention. The faster the cooling, the better the product obtained.

[0043] The passage from reaction temperature (1400° C.) to subambient temperature (if liquid nitrogen is used) occurs in a fraction of a second.

[0044] Depending on the cooling method used, the product is dried when cooled in a liquid and then ground in any type of mill deemed suitable for the particle size distribution required by the market of use.

[0045] The alkali metal titanate thus produced yields 99.9% non-fibrous crystals.

[0046] The starting materials used in the production of potassium titanate are rutile mineral powder in an amount of 60% to 90% by weight, and a reagent (eg, potassium carbonate) in an amount of 40% to 10% by weight.

[0047] In one example embodiment, the starting materials are charged into a mixer in the amount of 100 Kg KCO and 350 Kg rutile for each batch, mixed until thoroughly mixed, and then the materials are charged into a tank with a valve at the bottom for loading into the furnace.

[0048] The total amount of material loaded into the furnace for each batch is 450Kg and the theoretical amount of final product is 415Kg per batch, because the material normally dispersed in the fumes is about 15-20kg for each batch. The furnace is operated on LPG.

[0049] Each batch is reacted for 3 hours at a temperature of 1000° C. At the end of the reaction, the batches are transferred onto a flat steel surface, preferably having a temperature below 15° C., placed at ambient temperature and spread over the same surface.

[0050] At this point the material has the appearance of granular agglomerates with dimensions ranging from a few millimeters to a few centimeters and is fibrous.

[0051] At this point the material, either still hot, scorched or cold, can be placed into a melting furnace to be melted, after which the furnace is opened and the molten material poured into a tank filled with water at a temperature of 15°C or less so that thermal shock prevents crystal growth.

[0052] If water is used for cooling, the material is then separated from the water and dried, although it may be ground while wet.

[0053] Alternatively, the material can be dried in a desiccator and then milled dry.

[0054] The material can be ground in a hammer mill, for example of the "Danioni" type, equipped with a 50 Kw electric motor, with a yield of 100 kg / h and used as is.

[0055] Optionally, the ground material can be sieved through a 1 mm mesh sieve.

[0056] At the end of the grinding, the material is collected and depending on the use and destination, it is packaged, e.g., bagged. The percentage analysis of the produced material is shown in Table 1.

[0057] The X-ray diffraction measurement of the obtained product is shown in FIG. 1, where the X-axis is the position measured in 2θ and the Y-axis is the intensity measured in CPS (counts per second).

[0058] Figure 2 shows the X-ray diffraction measurement of a commercially available fibrous potassium hexatitanate.

[0059] The very significant difference in the relative intensities of the peaks clearly indicates that the planes on which the crystals reside are significantly different from those of the fibrous material, confirming that the non-fibrous structure of the produced material is an inherent property of the crystals.

[0060] Figures 2 to 7 show FESEM electron micrographs at various magnifications (2000 to 17000) of the products obtained, from which the absence of fibres can be seen and a spongy morphology with a very large specific surface and very high porosity is prominent.

[0061] The resulting product (powder) was 2 / g, and the specific surface (sometimes also defined as specific surface area) is generally expressed in square meters per gram (m 2 is the surface area of ​​a granule of a given material per unit of mass, expressed as 1 / g.

[0062] The resulting product has a black color due to the unusual non-stoichiometric oxidation state of titanium.

[0063] [Table 1]

Claims

1. 1. A method for preparing a non-fibrous alkali metal titanate comprising melting an alkali metal titanate in a furnace at a temperature in the range of 1300° C. to 1500° C. to form a molten product, and cooling the molten product by contacting the molten product with a material having a temperature of 15° C. or less, The method of claim 1, wherein the non-fibrous alkali metal titanate is 99.9% non-fibrous crystals of an alkali metal titanate having the formula A2TixO2x+1, where A is an alkali metal from the group including Na, K, Li, Rb, and x is any number from 2 to 6, and the non-fibrous alkali metal titanate comprises particles having a diameter / length ratio of less than 1:3 and a specific surface area of ​​greater than 10 m2 / g.

2. 2. The method according to claim 1, characterized in that the alkali metal titanate thus obtained has a non-fibrous structure and is obtained by mixing a titanium dioxide source with a reagent material or is obtained from a fibrous titanate.

3. 3. The method according to claim 2, characterized in that the reagent material is included in the group comprising potassium carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide or other organic derivatives of alkali metals.

4. 2. The method of claim 1, wherein the step of cooling the molten product comprises cooling with water, or with a surface below 15°C, or with a cylinder cooled to below 15°C, or with liquid nitrogen.

5. 3. The method of claim 2, characterized in that the titanium dioxide source comprises synthetic rutile and / or natural rutile and / or anatase and / or leucoxene.

6. 3. The method according to claim 2, characterized in that the titanium dioxide is used in an amount ranging from 60% to 90% of the total weight and the reagent is used in an amount ranging from 40% to 10% of the total weight.

7. Formula A ２ Ti ｘ O ２ｘ＋１ wherein A is an alkali metal selected from the group consisting of Na, K, Li, Rb, and x is any number from 2 to 6, said powder being of 99.9% non-fibrous crystallinity, said powder having a diameter / length ratio of less than 1:3 and a diameter / length ratio of less than 10 m 2 7. A powder of alkali metal titanate comprising particles having a specific surface area greater than 100 nm / g, obtainable by the method according to claim 1.

8. One of the alkali metal titanates is of the formula K ２ Ti ６ O １３ Or Na ２ Ti ６ O １３ The alkali metal titanate powder according to claim 7, characterized in that it has the following formula:

9. 8. The alkali metal titanate powder according to claim 7, characterized in that it is black in color.

Images