SK288815B6 - Method for preparation of nano-crystalline powder mixture Cu – Al2O3 – MgO - Google Patents

Abstract

The preparation of nano-crystalline powdered Cu containing various volume ratio of secondary phases Al2O3 and MgO is realized by means of phase changes - in situ method, and by mechanical grinding. The secondary phases –Al2O3 and MgO nanoparticles having size below 50 nm are obtained by means of thermochemical transformations of the precursors Al(NO3)3 . 9H2O and Mg(HCO3)2 , and the nano-crystalline powdered matrix of Cu is obtained by chemical reduction of CuO precursor. The grinding processes applied provide homogenous distribution of secondary phases and making the structure of the copper finer, resulting in temperature stable nano-crystalline structure of powdered mixture Cu – Al2O3 – MgO.

Description

S K 288815 B6

Technical field

The invention belongs to the field of powder metallurgy (PM) and relates to a process for the preparation of dispersion-strengthened copper-based powder mixtures containing different proportions of Al 2 O 3 and MgO nanoparticles. The object of the invention is to obtain temperature-stable Cu-AhOs-MgO powder mixtures containing a nanocrystalline copper matrix in which fine oxide particles of a reinforcing phase are evenly dispersed, not only under laboratory conditions but also in operating volumes.

Prior art

In electrical engineering practice, materials characterized by high strength characteristics and high electrical, resp. thermal conductivity even at elevated temperatures. However, a combination of these properties is very difficult to obtain with conventional materials such as pure coarse copper, solid copper solution or precipitation hardened copper. For this reason, research into nanocrystalline, dispersion-strengthened copper-based alloys prepared by powder metallurgy technologies is gaining prominence. Oxidally dispersed reinforced materials are characterized by very good durability, excellent thermal stability of the structure, improved strength at elevated temperatures and only low degradation of electrical and thermal conductivity compared to pure copper. The main requirement for ensuring the mechanism of oxidic dispersion strengthening is the homogeneous dispersion of fine, thermodynamically stable oxides - dispersoids into the copper matrix. Secondary particles with a size below 50 nm prevent the growth of grain due to the thermal loading of the material, thus maintaining its strength characteristics to high temperatures. A significant increase in strength compared to coarse conventional Cu can be achieved by preparing a copper matrix with a nanocrystalline structure, ie. with a crystallite / grain size below 100 nm.

Properties of powder compact materials, resp. products are predetermined by the structure that is formed at the very beginning, in the formation of powder particles. Depending on the choice of input phases and the chosen preparation technology, the setting of conditions depends on the formation of the initial structure and its further development during the subsequent compaction of the powder, which takes place at high temperatures and pressures. Monophase nanozymes are significantly unstable, so nanomaterials have excellent strength properties at ambient temperatures, but as the temperature increases, they immediately coarse the grain and thus degrade the properties. The greatest possibilities for the practical use of nanotechnologies are opened by research that will ensure perfect compaction of the material without degrading the nanocrystalline structure of the powder particles. Therefore, it is very important to create a temperature stable structure already in the powder itself. From this point of view, dispersion-reinforced systems come to the fore as very promising materials, suitable for the use of a large number of high-temperature applications in the electrical, automotive and aerospace industries. Oxide-reinforced copper-based composites are among the materials to which continuous knowledge is devoted.

The essence of the invention

The subject of the invention is an original method of preparation of nanocrystalline powder mixture Cu-AhOs-MgO having copper crystal size in the range from 20 nm to 30 nm and uniform distribution of secondary particles Al2O3 and MgO with sizes below 50 nm. in situ and mechanical grinding as follows:

MgO powder with an average particle size of less than 0.5 .mu.m is poured into water and CO2 gas is introduced under pressure to form magnesium bicarbonate Mg (HCO3) 2, which is stable in a supersaturated aqueous solution of CO2 and readily soluble in water. This solution is poured into powdered CuO and mixed thoroughly. During the subsequent drying and annealing at 550 ° C for 1 hour, a phase change takes place and an ultrafine solidifying phase MgO is formed directly in the QrO powder. The CuO-MgO powder mixture is then ground in an attritor with a frequency of 20 Hz for 30 min. The next step is to form the second reinforcing phase γ-AhOj by dissolving the crystalline aluminum nitrate A1 (NO3) 3.9 H2O in water and pouring the solution into the ground CuO-MgO powder. Subsequent addition of aqueous ammonia forms precipitates of alumina hydrate in the form of an amorphous hydrogel as a precursor of the γ-AhCl 2 phase. The mixed mixture was dried at 120 ° C and stirred in a wet atrator for 30 min. The ground powder mixture was annealed in an induction furnace at 500 ° C for 1 h and then chemically reduced in a stream of hydrogen at 150 ° C for 1 h to the resulting ultrafine Cu-AhCh-MgO system. The final operation of the preparation is dynamic grinding in a vibrating mill with a frequency of 30 Hz and a grinding time of 12 minutes to obtain a homogeneous distribution of secondary particles Al2O3 and MgO and refinement of the copper matrix structure to the nanometric level.

The volume fraction (vol.%) Of secondary phases Al2O3 and MgO can be modified by the mentioned method of preparation depending on the required properties of the final product, high temperature stability can be achieved

S K 288815 B6 structure of Cu-AhCh-MgO nanocrystalline powder, up to temperatures close to the melting point of the Cu matrix and to obtain larger amounts of Cu-AhCh-MgO powder mixture (semi-operational or operating volumes).

Examples of embodiments of the invention

Preparation of Cu-2 powder mixture vol. % AI2O3-I vol. % MgO:

5.15 g of MgO powder with an average particle size of 0.5 .mu.m are poured into water and CO2 gas is introduced under pressure. The action of CO2 produces magnesium bicarbonate Mg (HCO3) 2, which is stable in a supersaturated aqueous solution of CO2 and readily soluble in water. This solution is poured into 625.88 g of powdered CuO and mixed thoroughly. During the subsequent drying and annealing at 550 ° C for 1 h, a phase change and ultrafine MgO are formed directly in the CuO powder. The CuO-MgO powder mixture is then ground in an attritor with a frequency of 20 Hz for 30 min. in the presence of steel balls with a diameter of 5 mm In the ground CuO-MgO mixture, a second phase of γ-AhO is formed in situ? as follows: 37.93 g of crystalline aluminum nitrate A1 (NO3) 3.9 H2O is dissolved in water, the solution is poured into CuO-MgO powder and subsequent treatment with aqueous ammonia forms precipitates of aluminum oxide hydrate in the form of an amorphous hydrogel as a precursor of AhCh. After drying at 120 ° C, the mixed mixture is wet-milled in a trap (in methyl alcohol) using 5 mm diameter steel balls for 30 minutes. with a frequency of 20 Hz. The powder mixture is annealed in an induction furnace at 500 ° C for 1 h and then chemically reduced in a stream of hydrogen at 150 ° C for 1 h to the resulting ultrafine Cu-2 vol. % AI2O3- 1 vol. % MgO. The final operation of the preparation of the given powder is dynamic grinding in a vibrating mill with balls with a diameter of 7 mm, with a frequency of 30 Hz for 12 minutes, in order to obtain a homogeneous distribution of both secondary phases and refinement of the copper matrix structure.

Industrial applicability

Oxidally dispersed reinforced materials based on nanocrystalline copper can be used for the production of a large number of high temperature applications in the electrical industry, e.g. for the production of electrical contacts and conductors, motor brushes, as well as electrodes for spot resistance welding, because such a composite is characterized by very good material life, excellent thermal stability of the structure, improved strength at elevated temperatures and only low degradation of electrical and thermal conductivity compared to pure copper.

Claims (1)

S K 288815 B6 PATENT CLAIMS Process for the preparation of a nanocrystalline Cu powder mixture containing simultaneously Al 2 O 3 and MgO nanoparticles, characterized in that the CuO powder is thoroughly mixed with an aqueous solution of Mg (HCO 3) 2, 5 then dried, the powder mixture is annealed in air for 1 hour at 550 ° C and ground, the ground mixture is mixed with aqueous solution of Α1 (Νθ3) 3.9Η2θ and then with aqueous ammonia solution, dried at 120 ° C, ground and annealed in air at 500 ° C for 1 hour, CuO is chemically reduced in a stream of hydrogen at 150 ° C and the mixture is then ground to obtain a temperature stable Cu-AhOs-MgO powder having a copper crystallite size in the range of 20 nm to 30 nm and a uniform distribution of 10 Al 2 O 3 and MgO secondary particles with sizes <50 nm. 15 __________________________ End of document