WO2006010780A1

WO2006010780A1 - Ultraviolet-radiation-activated mechanical powder grinding

Info

Publication number: WO2006010780A1
Application number: PCT/ES2005/000343
Authority: WO
Inventors: Juan Manuel Montes Martos; Jesús CINTAS FÍSICO; Francisco de Paula GÓMEZ CUEVAS; José Antonio RODRÍGUEZ ORTIZ; Enrique Juan Herrera Luque
Original assignee: Universidad De Sevilla
Priority date: 2004-06-25
Filing date: 2005-06-17
Publication date: 2006-02-02
Also published as: ES2249985A1; ES2249985B1

Abstract

The invention relates to a mechanical powder-grinding process which is activated by ultraviolet radiation and which can be used to improve the characteristics of materials in powder form. When performed in the presence of ultraviolet radiation (UV), the duration of the grinding process can be reduced, thereby generating a saving in terms of cost. In addition, when performed in the presence of gases, liquids and/or other solids, it is possible to produce solid/gas, solid/liquid and/or solid/solid reactions which are difficult to obtain with other methods and, furthermore, at temperatures close to ambient temperature. In this way, the structure of the material can be altered and the properties thereof improved. The inventive process is suitable for use with any type of material, regardless of the metallic or non-metallic nature thereof.

Description

TITLE

Mechanical powder grinding activated by ultraviolet radiation.

OBJECT OF THE INVENTION

The present invention has as its object the mechanical powder grinding activated by ultraviolet radiation, which allows the improvement of the characteristics of powder materials prepared by grinding. 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. In addition, 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 so. 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.

STATE OF THE TECHNIQUE

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

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

During mechanical alloy, the dust particles are subjected to repetitive deformation, fracture and welding processes. With the fracture of the material, fresh surfaces are created that can react with the grinding atmosphere or

SUBSTITUTE SHEET (RULE 26) with other materials present inside the vessel. The subsequent welding of the particles through these surfaces allows changing the chemical composition of the material. For example, in the case of the grinding of aluminum-based powders, this causes the oxide (alumina) films that cover the surface of the particles to be fragmented and incorporated into each of them.

To prevent excessive welding of the powders, and 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, given the generally organic character of this ACP, implies inclusion of carbon and oxygen in the material. In this way, during the post-milling heating, particles composed of aluminum base with submicroscopic dispersoids, aluminum oxide and aluminum carbide, homogeneously distributed in the matrix are originated.

In order for the mechanical alloy process to be carried out effectively (the chemical and microstructural modification of the material occurs), it is necessary that there be a minimum of energy during the grinding. There are numerous factors that affect the process, among which the type of mill, atmosphere, speed of rotation of the rotor, percentage of process controlling agent, size and density of the balls, mass ratio balls / dust and load can be highlighted of feeding. The above factors determine the time required to complete the grinding [(SCHAFFER, GB and McCORMICK, PG "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)] elicit reactions (SCHAFFER, GB and McCORMICK, PG "Anomalous combustion effects during mechanical alloying" Met. Trans. A-Phys. Met. Mater. Sc, 22; 3019-3024, (1991) or modify reaction times, alter the degree of deformation of the material [(SCHAFFER, GB and McCORMICK, PG "On the kinetics of mechanical alloying" Met. Trans. A-Phys. Met. Mater. Sc, 23; 1285-1290, (1992); SCHAFFER, GB and FORRESTER, JS "The influence of collusion energy and strain accumulation on the kinetics of mechanical alloying" J. Mat. ScL, 32; 3157-3162, (1997)] , The rate of thickening of the powders (RYU, HJ. ; HONG, S.H.

SUBSTITUTE SHEET (RULE 26) and BAEK, WH "Mechanical alloying process of 93W-5.6Ni-1.4Fe tungsten heavy alloy" J. Mater. Process Technol., 63; 292-297, (1997). and the amortization of intermetallic (SAJI ₁ 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 mechanical alloy, its use deserves to be highlighted to cause, by means of mechanosynthesis, the formation of second phases, or, for example, reduce oxides, chlorides and sulphides. The use of the mechanical alloy as a tool to produce the mechanochemical synthesis of materials dates from 1989 [(SCHAFFER, GB and McCORMICK, PG "Combustion synthesis by mechanical alloying" Ser. Metall. Mater., 23 (6); 835-838, (1989); McCORMICK, PG; WHARTON, VN and SCHAFFER, GB "Phisical chemistry of powder metais production and processing" ed. Small WM, Warrendale, TMS, (1989)]. Since then, and because of the unique properties of developed materials, the AM-mechanosynthesis binomial is attracting the attention of numerous researchers.

However, in many cases, the energy that can be achieved by altering the aforementioned milling variables 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 the 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 being ground is achieved, forming solid supersaturated solutions. Subsequently, to obtain pieces with this ground powder, it is necessary to subject it to a processing that necessarily includes one or several hot stages. During this heating, and from the solid solution formed, the formation of dispersoids that harden the material considerably (HERRERA, EJ; CINTAS, J. and RODRÍGUEZ, JA "Powder nitriding by reactive grinding in the presence of certain nitrogen compounds) "Patent Application P2003-01963, August 8, 2003.

Recently, to solve the problem of lack of energy during milling, it has been proposed to activate the atmosphere causing electric shocks

SUBSTITUTE SHEET (RULE 26) (CALKA, A and WEXLER ₁ D. "Mechanical milling assisted by electrical discharge"

Nature, 419 (2002). This results in rapid fragmentation of the dust particles, which is believed to be associated with the vaporization or local fusion of the material. Which, in turn, is related to its heating by Joule effect and to the tensions caused by grinding and by local temperature variations (CALKA, A; WEXLER, D "Mechanical milling assisted by electrical discharge" Nature, 419; 147-151, (2002).

At present, the use of ultraviolet radiation is 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 semiconductor manufacturing (Ll YICHENG; SHAO SHOU-QUIAN "Ultraviolet ray assisted processing device for semiconductor processing" Patent EP1381078, (2002). However, there is no evidence of its use as a reaction activator during the grinding of mat wasteland

DESCRIPTION OF THE INVENTION

One of the main advantages of using the mechanical alloy for the mecanosynthesis of materials is that 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 grinding, the generation of chemically very active surfaces, the increase of the total contact surface as a result of the fracture of the dust particles, as well as the high Density density and structural refinement derived from the mechanical alloy process.

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 light frequency and power are used

SUBSTITUTE SHEET (RULE 26) suitable, can cause the dissociation of the molecules of the gases that form the grinding atmosphere. The dissociation of gases, such as, for example, nitrogen (N ₂ ) or methane (CH ₄ ), together with the greater reactivity of the surfaces of the powder itself would greatly favor the formation of solid supersaturated solutions and compounds, which in many cases do not They can be obtained at temperatures close to the environment. The acceleration of said processes, in addition, 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 a 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 powders 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 ultraviolet radiation as an extra source of energy during milling, has several advantages over activation by electric shocks. In the first place, it is not necessary to use mills with vessels and / or conductive balls, which in many cases present serious problems of dust contamination during milling. In addition, it is a clean process that does not leave any type of combustion residue, and from which it is possible to regulate its power with great precision. To all this must be added that, the adaptation of the grinding equipment to be able to make use of this technique does not require, in most cases, to make any modification in them.

Although in the experiences carried out in our laboratory, the ultraviolet light has been applied directly inside the grinding vessel (activation in situ), it is also possible to perform the activation of the atmosphere in a lung external to 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 atmospheres,

SUBSTITUTE SHEET (RULE 26) confined air and methane, 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 (within the vessel itself or in the external lung with recirculation of the atmosphere) has been called photomechanosynthesis.

AN EXAMPLE OF PRACTICAL REALIZATION

In a high-energy mill, the aluminum powder is introduced together with 3% EBS wax. This lubricant acts as the controlling agent 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 used is connected, so that the frequency of the radiation is sufficiently energetic to cleave the CH ₄ molecule. The UV radiation is channeled into the grinding vessel, and after that, the grinding of the aluminum powder begins. The grinding can be carried out in any type of mill, it being advisable that it be of high energy and that the walls of the vessel be reflective. In the case of performing it in a vertical attritor type mill, the operating conditions indicated in Table 1 could be used. Any change in some or some of these operating variables will affect the rest of the variables. So, for example, if the rotor is rotated at 300 rpm instead of 500 rpm, the grinding time should be longer than 5 hours. The mechanical characteristics of the powder obtained can be modified by changing the percentage of EBS wax and the frequency of the UV radiation used.

The ground powder, a metal-ceramic aluminum base compound powder is consolidated by uniaxial cold pressing, 850 MPa, and sintering in vacuum at 650 ⁰ C for 1 hour. However, any other hot consolidation method, such as pressing and extrusion, hot pressing, electric resistance sintering, etc. can be used.

SUBSTITUTE SHEET (RULE 26) Table 1. Grinding conditions.

SUBSTITUTE SHEET (RULE 26)

Claims

1. Procedure for obtaining powder-shaped material by grinding in a high-energy mill, 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 material according to claims 1 and 2, characterized in that in addition, a process controlling agent is added, such as, for example, the EBS wax (ethylene-bis-stearamide).

4. Procedure for obtaining powder material according to claims 1-3, characterized in that the milling 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).

SUBSTITUTE SHEET (RULE 26)

8. Material in powder form, characterized in that it is obtained with the procedure described in claims 1-7.

9. Parts manufactured from the powders obtained in claim 8, by hot forming processes, such as cold pressing and sintering, hot pressing and extrusion, hot pressing, sintering by electrical resistance, etc.

SUBSTITUTE SHEET (RULE 26)