A PROCEDURE FOR THE PREPARATION OF NON-FIBROUS ALKALINE TITANATES WITH SPECIFIC SURFACE AREA AND POROSITY

Abstract

A process for the preparation of non-fibrous alkali titanates comprising the steps of: melting alkali titanate in a furnace at a temperature ranging from 1300 °C to 1500 °C to form a molten product; cooling said molten product by bringing it into contact with a material having a temperature equal to or less than 15 °C.

Description

A PROCEDURE FOR THE PREPARATION OF NON-FIBROUS ALKALINE TITANATES WITH SPECIFIC SURFACE AREA AND POROSITY DESCRIPTIVE MEMORANDUM The present invention relates to a process for the preparation of non-fibrous alkali titanates with high specific surface area and porosity. Alkali titanates can be used in brake pads, brake linings, clutch linings for automobiles, trucks, train cars, airplanes and various industrial machines and for welding electrodes. The harm and health risks of asbestos are well known to everyone. Starting in the 1990s, asbestos was banned in the United States and Europe. Since then, other materials have been tested and used, including potassium and sodium titanates. Among others, potassium and sodium titanates have shown a considerable improvement in the stability of the coefficient of friction with reduction or cancellation of the deterioration of phenolic resin that induces the slippage of the discs without braking, Fading in slang, a dangerous phenomenon, for example, in the use of brake pads. Friction materials are used to control the deceleration of many vehicles of various types, such as industrial equipment, cars, airplanes, bicycles, and motorcycles. In particular, in the field of friction materials, some titanium-based compounds have been studied and used, such as potassium hexatitanate, sodium hexatitanate, and potassium octatitanate. Potassium and sodium are characterized by elongated fibers and have shown suitable behavior for use in the aforementioned sector. However, fibers of this type have also recently been considered as potential health risks, and the EU and the US have set maximum size limits for the fibers that can be used. For example, Commission Regulation (EC) No 761 / 2009 of 23 July 2009 defines crystals with a diameter / length ratio equal to or greater than 1:3 as fibers and requires that all materials with a content of such fibers greater than 0.1% be defined as fibrous and classified under risk level Car 2 (possibly carcinogenic). Thus, crystals with a ratio less than 1:3 are not considered fibers and, therefore, can be used without specific precautions. However, products obtained in accordance with the prior art comprise titanates in the form of fibers which, even when mixed with resins in various uses as described, present a potential problem and are considered unsuitable because they are potentially hazardous and therefore subject to specific regulations. The objective of the present invention is to provide a process for the preparation of alkali titanates that result in a non-fibrous powder material. An additional objective is to provide a procedure that results in crystals with a diameter / length ratio less than 1:3. An additional objective is to provide a procedure that results in crystals with a specific surface and porosity. According to the present invention, these and even other objectives are achieved by a process for the preparation of non-fibrous alkali titanates comprising the steps of: melting alkali titanate in a furnace at a temperature ranging from 1300 °C to 1500 °C to form a molten product; cooling said molten product by bringing it into contact with a material having a temperature equal to or less than 15 °C. These objectives are further achieved by means of an alkali titanate powder with the formula AzTixChx+i, where A is an alkali metal included in the group comprising Na, K, L1, Rb, and x represents any number between 2 and 6; where said powder comprises particles having a diameter / length ratio less than 1:3 and a specific surface area greater than 10 m2 / g. Additional features of the invention are described in the dependent claims. The solution offers several advantages over solutions of the known technique. The process yields alkali titanates, particularly potassium titanate and sodium titanate, which have substantially rounded crystals, lacking the fibrous structures defined above, and are extremely porous with a high specific surface area and high porosity. These characteristics give them a more pronounced reactivity compared to phenolic resin when used in braking systems. The resulting product can be used as a component of high fraction coefficient materials, in plastic materials, in paints, in heat-resistant materials, and in lubricants. The features and advantages of the present invention will become apparent from the following detailed description of a practical embodiment thereof, illustrated by non-limiting examples in the accompanying drawings, in which: Figure 1 shows an X-ray crystallography (XRD) of the product obtained, in accordance with the present invention, which shows, from the 2 ñor / nm ίζηζ / ε / γίΛΐ position theta of the peaks, that it belongs to the monoclinic structure, therefore identical to that of fibrous titanate; Figure 2 shows an X-ray crystallography (XRD) of a commercial product of potassium hexatitanate in fibrous form; Figures 3 to 7 show electron microscope photographs of the product obtained, at different magnifications, in accordance with the present invention, demonstrating that it does not have a fibrous form, highlighting its spongy morphology and high specific surface area. Alkali titanates are represented by the generic formula AzTixOzx+i where A is an alkali metal such as Na, K, Li, Rb and x represents any quantity between 2 and 6. The procedure for the preparation of alkali titanates, in particular potassium and sodium titanates, involves the use of TiCh as synthetic rutile or anatase, or also natural rutile with a minimum concentration of 90% in TiCh in the form of flour or sand, or also the mineral leucoxene. Potassium or sodium carbonates and / or potassium hydroxide or sodium hydroxide can be used as starting reagents, or other organic derivatives of alkali metals can also be used, although this represents an increase in costs. If the mineral rutile or leucoxene, or mixtures of these, are used as raw materials, cups of different oxides may be present as impurities. For example, Ca, Mg, Si, Zr, Al, V, Mη, P and S oxides may be present, as well as traces of various oxides. Although impurities can reach considerable quantities, they are not taken into consideration; they are absent if pure raw materials are used and do not influence the effectiveness of the product in any way. The materials are mixed in a mixer of any type and then placed in an oven of any type, electric or induction or open flame, in which case fuels, diesel, methane gas or LPG (liquid propane gas) can be used. The material can be baked in batches or continuously. Oven operating temperatures range from 700°C to 1000°C and the duration ranges from 2 to 8 hours, or is otherwise based on the quantity of material in the process and the ease with which the oven reaches the desired temperature. The material produced in this way, in powder form after cooling, is appropriately ground, for example, in a ball mill, where the type of balls and coating are chosen based on the particle size requirements of the finished product. ñor / nm ίζηζ / ε / γίΛΐ The alkali titanates produced in this way are fibrous. These titanates are used as raw material for the subsequent final treatment that will make them non-fibrous. The same result can be obtained by starting from raw materials in a direct procedure, without going through the step described above. The same result can be obtained by starting from raw materials in a direct process. Alkaline titanates or the respective raw materials are melted in a crucible or in smelting furnaces by means of batch procedures, i.e., discontinuous procedures, or in specific furnaces that allow continuous production of the same types described above. If starting with the respective raw materials, melting must be continued until all the titanium dioxide has melted due to the alkali salt, which melts first. If pre-produced titanates are used as raw materials, it is sufficient that they reach a melting point between 1300 and 1500 °C. The molten product is poured extremely quickly or allowed to drip into basins of water, at well temperature (12-15 °C), preferably under agitation to promote heat exchange, or poured onto surfaces, preferably below 15 °C, or compressed between cylinders, preferably cooled below 15 °C, which simultaneously cools and compresses the material, rapidly bringing it to its solid state, or dripped into a liquid nitrogen bath. In any case, the molten product is brought into contact with a material (solid or liquid) at a temperature equal to or greater than 15 °C. Rapid cooling and the sudden transition from a liquid to a solid state are fundamental steps in the invention. The faster the cooling, the better the resulting product. The transition from the reaction temperature (1400 °C) to room temperature or lower (if liquid nitrogen is used) takes place in fractions of a second. In accordance with the cooling method used, the product is dried in the case of liquid cooling and then ground with any type of mill that is determined to be suitable for the particle size required by the market of use. Alkali titanates produced in this way result in 99.9% non-fibrous crystals. The starting materials used for the production of potassium titanate are rutile ore powder in an amount between 60% and 90% of the total weight, and reagent (e.g., potassium carbonate) in an amount between 40% and 10% of the total weight. In one example of the method, the starting materials are loaded into the mixer, in an amount of 100 kg of K2CO3 and 350 kg of rutile for each batch, mixed until they are completely mixed, and the material is loaded into a tank with a valve at the bottom for loading into the furnace. The total amount of material loaded into the kiln for each batch is 450 kg, and the theoretical amount of end product is 415 kg per batch, because the material typically dispersed in the vapors is approximately 15–20 kg for each batch. The kiln uses LPG. Each batch is reacted for three hours at a temperature of 1000 °C. At the end of the reaction, the batch is poured onto a flat steel surface that has a preferred temperature below 15 °C, and is placed at room temperature and dispersed on the same surface. At this point, the material has the appearance of granular agglomerates whose dimensions range from a few millimeters to several centimeters, and is fibrous. At this point, it can be placed, still hot, or boiling, or cold, in a melting furnace and brought to melting, after which the furnace is opened and the molten material is poured into a tank filled with water at a temperature less than or equal to 15 °C, so that the thermal shock prevents crystal growth. If water is used for cooling, it is then separated from the water and dried, but it can also be ground wet. Alternatively, it can be dried in a dryer and then ground dry. It can be used as is, ground in a hammer mill, for example, of the Danioni type with a 50 kW electric motor, with a yield of 100 kg / h. Optionally, the ground material can be strained through a 1 mm mesh strainer. At the end of the milling process, the material is collected and packaged according to its use and destination, for example, in bags. The percentage analysis of the material produced is given in Table 1. An X-ray diffractometry of the obtained product is shown in Figure 1, where on the X axis we have the position measured in 2 theta and on the Y axis we have the intensity measured in CPS (counts per second). A diffractometry of a commercial product of potassium hexatitanate in fibrous form is shown in Figure 2. A very marked difference in the relative intensity of the peaks clearly shows that the planes on which the crystals lie are extremely different from those of fibrous materials, confirming that the non-fibrous structure of the material produced is an intrinsic feature of the crystal. Figures 2 to 7 show the FESEM electron microscope photographs at different magnifications (2000-17000) of the product obtained, from which the absence of fibers can be seen, emphasizing the sponge morphology with very high specific surface and very high porosity. The product obtained (powder) has a specific surface area greater than 10 m2 / g, where the specific surface area (sometimes also defined as a specific surface area) is the surface area of ​​the granules of a given material, per unit mass, usually expressed in square meters / grams (m2 / g). The resulting product has a black color due to the non-stoichiometric oxidation state of titanium. ñor / nm ίζηζ / ε / γίΛΐ TABLE 1 Element % K2O 15.569 T1O2 79.232 ZrO2 + HfO2 1.686 S1O2 1.601 Fe2O3 0.843 CaO 0.101 MgO 0.025 Al2O3 0.480 V 205 0.430 MnO 0.008 P 0.017 S 0.008 NOVELTY OF THE INVENTION

Claims

1. A process for the preparation of non-fibrous alkali titanates comprising the steps of: melting alkali titanate in a furnace at a temperature ranging from 1300 °C to 1500 °C to form a molten product; cooling said molten product by putting it in contact with a material having a temperature equal to or less than 15 °C.

2. The process according to claim 1, further characterized in that said alkali titanate thus obtained has a non-fibrous structure and is obtained by mixing titanium dioxide sources with reactive material or is obtained from fibrous titanates.

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

4. The process according to claim 1, further characterized in that said step of cooling said molten product comprises the step of cooling, by means of water, or by surfaces below 15 °C or by means of cylinders cooled below 15 °C or by means of liquid nitrogen.

5. The process according to claim 2, further characterized in that said titanium dioxide source comprises synthetic rutile and / or natural rutile and / or anatase and / or leucoxene.

6. The process according to claim 2, further characterized in that said titanium dioxide is used in quantities ranging from 60% to 90% of the total weight and said reagent is used in an amount ranging from 40% to 10% of the total weight. 7.- An alkali titanate powder with the formula A2TkO2x+i, wherein A is an alkali metal belonging to the group comprising Na, K, L1, Rb, and x represents any number between 2 and 6; wherein said powder comprises particles having a diameter / length ratio less than 1:3 and a specific surface area greater than 10 m2 / g.

8. The alkali titanate powder according to claim 7 further characterized in that one of said alkali titanates has the formula K2T16O13 or Na2T16O13.

9. The alkali titanate powder according to claim 7 further characterized in that it is black.