ES2249985B1 - MECHANICAL DUST GRINDING ACTIVATED BY ULTRAVIOLET RADIATION. - Google Patents

Abstract

Mechanical powder grinding activated by ultraviolet radiation. The present invention aims at mechanical powder grinding activated by ultraviolet radiation, which allows the improvement of the characteristics of powder materials. Specifically, the realization of grinding in the presence of ultraviolet (UV) radiation makes it possible to shorten their duration, with the economic savings that this entails. Furthermore, if they are carried out in the presence of gases, liquids and / or other solids, it enables solid-gas, solid-liquid and / or solid-solid reactions to be carried out, difficult to produce by other methods, and even more at temperatures close to the environment. This allows altering the structure of the material and improving its properties. This process can be applied to all types of materials, regardless of their metallic or non-metallic nature.

Description

Mechanical powder grinding activated by ultraviolet radiation

Object of the invention

The present invention aims at the mechanical powder grinding activated by ultraviolet radiation, what which allows the improvement of the characteristics of materials in form of dust Specifically, the realization of grinding in presence of ultraviolet (UV) radiation allows to shorten the duration of same, with the economic savings that this entails. Also, if performed in the presence of gases, liquids and / or other solids, enables reactions to take place solid-gas, solid-liquid and / or solid-solid, difficult to produce for others methods, and even more at temperatures close to the environment. This allows altering the structure of the material and improving its properties.

This process can be applied to all types of materials, regardless of their metallic character or not metal.

State of the art

The mechanical alloy (AM) is basically a high energy grinding that allows to obtain compound powders with controlled and extremely fine structure. It was developed by John S. Benjamin in 1966, in order to combine the precipitation hardening of the phase and in the super alloys nickel base, and that produced by dispersion of oxides (BENJAMIN, J.S. "Dispersion strengthened superalloys by mechanical alloying "Met. Trans. A-Phys. Met. Mater. Sc., 1 (10); 2943-2951, (1970)).

The AM can, in principle, be applied to a great variety of metals, or mixtures of metals, and particles not metallic In turn, because the mechanical alloy is a process in solid state, which does not require the fusion of materials, can be used to produce alloys from components immiscible in liquid state or with a wide difference between its melting points

During mechanical alloy, the particles of powder are subjected to repetitive processes of deformation, fracture and welding. With the fracture of the material surfaces are created fresh that can react with the grinding atmosphere or with other materials present inside the vessel. The later  welding of the particles through these surfaces allows Change the chemical composition of the material. For example, in the case of grinding of aluminum based powders, this causes the oxide (alumina) films that cover the surface of the particles are fragmented and incorporated into each one of them.

To prevent excessive welding of the powders, and to establish a dynamic balance between the fracture and welding processes, a lubricant, also called the process controlling agent (ACP), is usually added. Following the example of the grinding of aluminum-based powders, and as with alumina, this additive is incorporated into the dust particles, which means, given the generally organic character of this ACP, the inclusion of carbon and oxygen in the material. Thus, during post-milling heating, composite particles of aluminum base with submicroscopic dispersoids, aluminum oxide and aluminum carbide, homogeneously distributed in the matrix are originated.

So that the mechanical alloy process is perform effectively (chemical modification occurs and microstructural of the material), it is necessary that there be a minimum of Energy during grinding. There are numerous factors that affect to the process, among which the type of mill can be highlighted, atmosphere, rotor speed, percentage of agent process controller, ball size and density, ratio Mass balls / powder and feed load. The previous ones factors determine the time needed to complete the grinding [(SCHAFFER, G.B. and McCORMICK, P.G. "Anomalous combustion effects during mechanical alloying "Met. Trans. A-Phys. Met Mater. Sc., 22; 3019-3024, (1991); ZHANG, H. and LIU, X. "Analysis of milling energy in synthesis and formation mechanism of molybdenum disilicide by mechanical alloying "Int. J. Refract. Met Hard Mater., 19; 203-208, (2001)] provoke reactions (SCHAFFER, G.B. and McCORMICK, P.G. "Anomalous combustion effects during mechanical alloying "Met. Trans. A-Phys. Met Mater. Sc., 22; 3019-3024, (1991) or modify the times of reaction, alter the degree of deformation of the material [(SCHAFFER, G.B. and McCORMICK, P.G. "On the kinetics of mechanical alloying "Met. Trans. A-Phys. Met. Mater. Sc., 2. 3; 1285-1290, (1992); SCHAFFER, G.B. and FORRESTER, J.S. "The influence of collision energy and strain accumulation on the kinetics of mechanical alloying "J. Mat. Sci., 32; 3157-3162, (1997)], the rate of powder thickening (RYU, H.J .; HONG, S.H. and BAEK, W.H. "Mechanical alloying process of 93W-5.6Ni-1.4Fe tungsten heavy alloy "J. Mater. Process. Technol., 63; 292-297, (1997). and the amorphization of intermetallic (SAJI, S .; NEISHI, Y .; ARAKI, H .; MINAMINO, Y. and YAMANE, T. "Amorphization promoted by mechanical alloying of aluminum-rich Al-Ti-Fe mixed powders "Met. Trans. A-Phys. Met Mater. Sc., 26 (5); 1305-1307, (1995), among other effects.

Among the multiple applications of the alloy mechanic, it deserves to stand out its use to originate, by mechanosynthesis, the formation of second phases, or, for example, reduce oxides, chlorides and sulfides. The use of mechanical alloy as a tool to produce the mechanochemical synthesis of Materials dates from 1989 [(SCHAFFER, G.B. and McCORMICK, P.G. "Combustion synthesis by mechanical alloying" Scr. Metall Mater., 23 (6); 835-838, (1989); McCORMICK, P.G .; WHARTON, V.N. and SCHAFFER, G.B. "Phisical chemistry of powder metals production and processing "ed. Small WM, Warrendale, TMS, (1989)]. Since then, and because of the unique properties of developed materials, the binomial AM-mecanosynthesis is grabbing the attention of Numerous researchers

However, on many occasions, the energy that can be achieved by altering the grinding variables Above mentioned is insufficient to produce reactions. This is mainly critical in the case of grinding in the presence of gases, where it is more complicated to cause the decomposition of gas and the subsequent incorporation of its elementary components to the powder. The importance of the use of gas atmospheres during grinding is that, if the energy is sufficient, the integration of atoms of the chemical elements that make up the gas inside the crystalline structure of the powder that It is grinding, forming supersaturated solid solutions. Subsequently, to obtain pieces with this ground powder, it is it is necessary to submit it to a processing that necessarily includes one or Several hot stages. During this warm-up, and from The solid solution formed, the formation of dispersoids originates which harden considerably the material (HERRERA, E.J; TAPES, J. and RODRIGUEZ, J.A. "Powder nitriding by grinding reactive in the presence of certain nitrogen compounds " Patent Application P2003-01963, August 8 2003

Recently, to solve the problem of lack of energy during grinding, it has been proposed to activate the atmosphere causing electric shocks (CALKA, A and WEXLER, D. "Mechanical milling assisted by electrical discharge" Nature, 419 (2002). This results in rapid fragmentation of the dust particles, believed to be associated with vaporization or local fusion of the material. Which, in turn, is related to its heating by Joule effect and with the tensions caused by grinding and local variations of temperature (CALKA, A; WEXLER, D "Mechanical milling assisted by electrical discharge "Nature, 419; 147-151, (2002).

Currently, the use of radiation ultraviolet is very widespread, and is fundamentally used to purify water [(ANDERSON JEFFREY, J "Water purifier using ultraviolet radiation "Patent US2004004044, (2002); ANDERSON JAMES, L "Ultraviolet water treatment apparatus" Patent US2003218136, (2002)], instrument sterilization [(CORN PRODUCTS "Ultra-violet sterilization apparatus "Patent GB859754, (1957); HWANG KYOOCHEON "Sterilizer using ultraviolet light" Patent WO03094691, (2003)] and polymer curing [(SCHEFFER HERBERT, D "Ultraviolet curing lamp device "Patent US4563589, (1984); GILBERTI JOSEPH, J "Ultraviolet light curing apparatus" Patent US6397491, (2000)]. New uses such as the semiconductor manufacturing (LI YICHENG; SHAO SHOU-QUIAN "Ultraviolet ray assisted processing device for semiconductor processing "Patent EP1381078, (2002). However, there is no evidence of its use as an activator of reactions during the grinding of material.

Description of the invention

One of the main advantages of the employment of mechanical alloy for material mechanosynthesis is that it it can cause, at temperatures close to the environment, the onset of reactions that normally require high temperatures to occur. This phenomenon seems to be promoted by the intimate contact of the reagents that occurs during the grinding, the generation of chemically very active surfaces, the increase in total contact area as a result of the fracture of dust particles, as well as the high density of defects and structural refinement derived from the process of mechanical alloy

In this sense, the application, simultaneous to the grinding process, of ultraviolet (UV) light inside the vessel can further intensify the reactivity of the powder, while, if the appropriate light frequency and power are used, it can cause the dissociation of gas molecules that form the grinding atmosphere. The dissociation of gases, such as nitrogen (N2) or methane (CH4), together with the greater reactivity of the surfaces of the powder itself would significantly favor the formation of solid supersaturated solutions and compounds, which In many cases they cannot be obtained at temperatures close to the environment. The acceleration of these processes, moreover, can result in an attractive reduction of the grinding time and in the reduction of costs of the process that is derived from it. It is also interesting to note that gases such as methane (or nitrogen) are a very cheap source of carbon (nitrogen) to obtain composite materials reinforced by dispersion of carbides (or nitrides). Refractory phases of these types that, thanks to the grinding process, are of nanometric scale and are well distributed in the matrix of the material, allow to significantly improve its mechanical behavior at elevated temperatures. The use of ultraviolet radiation should not be restricted to the grinding of dusts in the presence of gases, but may be used in cryogenic grinding to activate substances in a liquid state, such as N 2 (I).

On the other hand, the use of radiation ultraviolet as an extra source of energy during grinding, It has several advantages over download activation electric. First, it is not necessary to use mills with vessels and / or conductive balls, which often present Serious problems of dust contamination during grinding. In addition, it is a clean process, which does not leave any residue of combustion, and from which it is possible to regulate its power with great precision. To all this must be added that, the adaptation of grinding equipment to be able to use this technique not requires, in most cases, make modification Some in them.

Although in the experiences carried out in our laboratory, ultraviolet light has been applied directly inside the grinding vessel ( on-site activation), it is also possible to activate the atmosphere in a lung outside the vessel ( ex situ activation ). A recirculation system would drive the activated gas into the vessel, and vice versa. Said lung could also be used to apply electric shocks that would collaborate in the activation of the atmosphere.

The present invention aims at high energy grinding using attritor- type mills, with elemental aluminum powder in vacuum, confined air and methane atmospheres, and with application, in situ , of ultraviolet (UV) radiation. In all cases, an improvement in the mechanical properties of the parts manufactured from the powders resulting from the grinding has been observed. This powder grinding process, in the presence or absence of gases, and with simultaneous application of ultraviolet radiation (inside the vessel itself or in external lung with recirculation of the atmosphere) has been called photomechanosynthesis .

An example of practical realization

In a high energy mill, the Aluminum powder together with 3% EBS wax. This lubricant makes The controlling agent function of the grinding process.

After extracting the air inside the mill, by means of a vacuum equipment, the grinding vessel is filled with CH 4 gas.

The ultraviolet generator is connected employed, so that the radiation frequency is Energy enough to cleave the CH4 molecule. UV radiation is channeled into the vessel of grinding, and after that, the grinding of the powder of aluminum.

The grinding can be carried out in any type of mill, it is advisable that it be of high energy and that the walls of the vessel are reflective. In the case of performing it in a vertical attritor type mill, the operating conditions indicated in the

Table 1. Any change in any or some of These operational variables will affect the rest of the variables. So that, for example, if the rotor is rotated at 300 rpm instead of at 500 rpm, the grinding time should be more than 5 hours. The mechanical characteristics of the obtained powder can be modified changing the percentage of EBS wax and the frequency of radiation UV used.

The ground powder, which is a compound powder ceramic-metallic aluminum base, consolidates by cold uniaxial pressing, at 850 MPa, and sintering, in vacuum, at 650 ° C for 1 hour. However, it can be used any other hot consolidation method, such as pressing and extrusion, hot pressing, sintering by electrical resistance, etc.

TABLE 1 Grinding conditions

Kind of windmill Vertical attrittor Reason loading = dough balls / dough powder 50: 1 Balls used Bearing steel Rotor speed 500 rpm Refrigeration Water at 28ºC Grinding time 5 h

Claims (9)

1. Procedure for obtaining powder-shaped material by grinding, characterized in that the grinding is carried out with the application of ultraviolet radiation inside the grinding vessel. 2. Procedure for obtaining powder material according to claim 1, characterized in that the grinding is carried out in a high energy mill. 3. Procedure for obtaining powder-shaped material according to claims 1 and 2, characterized in that in addition, a process controlling agent, such as EBS wax (ethylene bis-stearamide), is added in the milling process. 4. Procedure for obtaining powder material according to claims 1-3, characterized in that the grinding is carried out in the presence of gases (grinding atmosphere). 5. Procedure for obtaining powder material according to claims 1-4, characterized in that the activation of the grinding atmosphere is carried out in an external lung and not in the grinding vessel itself. A recirculation system conducts the activated atmosphere from the lung into the vessel, and vice versa. 6. Procedure for obtaining powder material according to claims 1-5, characterized in that electric discharges are applied to contribute to the activation of the grinding atmosphere. 7. Procedure for obtaining powder material according to claims 1-6, characterized in that the grinding is carried out in the presence of substances in a liquid state (at any temperature, even cryogenic). 8. Material in powder form, characterized in that it is obtained with the procedure described in claims 1-7. 9. Parts made from powders obtained in claim 8, by forming processes hot, such as cold pressing and sintering, pressing and hot extrusion, hot pressing, sintering electrical resistance, etc.