Production of Fine Aluminum Powder from

Production of Fine Aluminum Powder from Metallic Aluminum

Hnin Yu Khaing Department of Chemical Engineering, Mandalay Technological University

Room-63, Mann Thazin Hostel, Mandalay Technological University, Mandalay, Myanmar eMail: [email protected]

Tint Tint Kywe Department of Chemical Engineering, Mandalay Technological University

Mandalay Technological University, Mandalay, Myanmar eMail: [email protected]

Abstract- This paper intend to produce fine aluminum powder from metallic aluminum by using hybrid atomization technique. The hybrid atomization system used in this experiment has three main parts: melting unit, hybrid atomization and powder collector. The characteristics of aluminum metal were analyzed by X-ray Diffraction (XRD) and wet assay method. Experiments were carried out at different gas pressures (0.5, 0.6, 0.7 MPa) and temperatures (710ºC, 750ºC, 800ºC). Aluminum powder with a mean particle size of under 75 microns were obtained from these experiments. The morphologies of product aluminum powder were determined by SEM and crystallization phase structures were studied by XRD. The product aluminum nano-particles with the size range from 50 to 80 nm were observed at 800ºC and 0.6 MPa.

Keywords- Aluminum Powder, Hybrid Atomization, Melting Unit, Scanning Electron Microscope

I. INTRODUCTION Aluminum is found in many rock

minerals, usually combined with silicon and oxygen in compounds called alumino-silicates. When such deposits are rich in alumina, they comprise the mineral bauxite. Aluminum is a lightweight, durable metal. It is silvery in appearance when freshly cut, is a good conductor of heat and electricity and is

easily shaped by moulding and extruding. [1].Many uses have been purposed for various application of the aluminum, such as aerospace, architectural construction and marine industries. Aluminum materials can be produced by a variety of manufacturing routes [2]. Atomization process is one of the popular processes for making powder metal [3]. The main advantage of gas atomization is due to totally inert processing conditions and the spherical the product homogeneity and the absence of contamination shape of the product powder. [4]. A new powdermaking technique, hybrid atomization was invented and developed recently to produce very fine spherical powders economically. This technology combines low-pressure gas atomization with centrifugal atomization effectively [5]. As an advantage of this method, the powder with low content oxygen can be easily produced because the powder is produced in an inert gas atmosphere [6]. This method is easy to control the powder particle size, particle size distribution, powder shape and other characteristics by detail investigation of the relation between the metal physical properties and the rotational speed of the rotary disk [7]. The suitable metals that can be melted and is used commercially for powder production are tin, lead, zinc and aluminum [8]. The primary aim of this paper was to apply for the production of solid rocket propellant. The objectives were carried out: to examine the characteristics of

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Hnin Yu Khaing and Tint Tint Kywe

raw aluminum sample, to fabricate the hybrid atomization structure and to explore aluminum powder by using hybrid atomization technique.

II. MATERIALS AND METHOD

A. Analysis of Raw Material In this paper, the raw material

aluminum metal wires were collected from a local market. The crystalline phase structure and composition of aluminum metal shown in Fig.1 and Table.1 were analyzed by XRD and wet assay. On viewing the XRD pattern of aluminum, the detailed peaks were clearly identified for the amount of aluminum in the aluminum metal wire.

Fig. 1 X-ray Diffraction Pattern of Raw Aluminum

metal

TABLE 1 COMPOSITION OF ALUMINUM METAL

B. Specification of Melting Unit The dimensions of melting unit used

in this study were described in Table. 2. TABLE 2

SPECIFICATION OF MELTING UNIT

C. Specification of Atomizer Design The dimensions of atomizer used in

this study were described in Table. 3. TABLE 3

SPECIFICATION OF ATOMIZER DESIGN

In this paper, confined type nozzle

was chosen to produce aluminum metal powder.

D. Fabrication of Hybrid Atomization The required units for hybrid

atomization structure were constructed in the local workshop and fabricated at laboratory of Department of Chemical Engineering in Mandalay Technological University.

The design of this structure has three parts of units as shown in Fig. 2. The first process of this structure is preparation of the material and then was fabricated based on drawing design. The melting unit is the upper part of this system. Atomizer, disk and gas supply system are the middle parts also. The lower parts of this system are a high speed motor, an air cleaner and powder collector. The dimensions of the laboratory scale hybrid atomizer are 45.7cm (width) × 65cm (length) × 118.1cm (height).

In the upper part of the system, the melting unit was made of fire brick, fire clay, and asbestos. The crucible was placed into the furnace. Moreover, there was a temperature controller (0-1300ºC) inside the crucible to indicate the temperature of liquid metal. At the bottom of the crucible, feed tube was attached. The end of the tube was extended into an atomizing nozzle. The diameter of nozzle was 3mm. In this system, confined type nozzle was used.

In the middle part of the system, disk actually was a basic element in the centrifugal atomization process. The disk was made of stainless steel. Disk was

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attached with flexible wire from the high speed motor. The motor rotating speed was up to 23000 rpm. The spray distance was 100mm and the atomizing gas (nitrogen) entered the furnace and atomizer. Nitrogen gas was used as an atomizing medium.

This gas can be adjusted by using a pressure regulator. The function of this gas was to prevent the oxidation on the particle. The atomizing chamber was divided by two sides, a glass chamber at the upper side and zinc chamber at the bottom side.

The lower part of the atomizer involved an air cleaner and powder collector.

Fig.2 Schematic Diagram of Hybrid Atomization

III. EXPERIMENTAL DESIGN PROCEDURE

A. Experimental Procedure Experimental procedure of aluminum

powder was shown in Fig. 3. Twenty grams of aluminum metal wire was weighed and placed in a crucible for the primary three experiments. Six grams of aluminum metal wire was used for other experiments. Then, the crucible was placed into the furnace and heated for 30 min at (710ºC, 750ºC and 800ºC). The melt was atomized by a gas atomizer into coarse liquid droplets. After that, the thin liquid film was centrifuged at 23000 rpm. The solidified powders were collected by a powder collector. The products at different gas pressures and temperatures were weighed for particle size distribution analysis and analyzed by SEM for investigation of morphologies of product aluminum powder.

Fig. 3 Flow Diagram of Powder Production Procedure

B. Experimental Parameters Hybrid atomization was carried out

with different gas pressures: 0.5, 0.6, and 0.7 MPa and melting temperatures: 710ºC, 750ºC, 800ºC. Other parameters were disk diameter: 100mm, rotational speed: 23000rpm and spray distance: 100 mm which were kept constant in this study.

IV.RESULTS AND DISCUSSION

A. Particle Size Distribution of Aluminum Powder

According to the experimental parameters, the data of particle size distribution were given in Tables 4, 5, 6, 7, 8, 9, 10, 11 and 12. The results of particle size distribution were shown in Figs 4, 5 and 6.

TABLE 4 PARTICLE SIZE DISTRIBUTION AT GAS

PRESSURE 0.5 MPA AND TEMPERATURE 710ºC


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TABLE 6

PARTICLE SIZE DISTRIBUTION AT GAS PRESSURE 0.7 MPA AND TEMPERATURE 710ºC

TABLE 7


TABLE 8




TABLE 10


TABLE 11


TABLE 12



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Fig. 4 Particle size distribution of powders under

different gas pressures and melting temperature 710ºC

Fig. 5 Particle size distribution of powders under


Fig. 6 Particle Size Distribution of Powders under


For the particle size less than 75 μm, the yield of aluminum powder at 0.7 MPa is more than that at other two pressures. According to the experiment 1, yield of aluminum powder under 75μm was found to be 20.6%. As for experiment 3, although it gave 44.5% of yield, it had larger particle size than experiment 2. In experiment 2, product yield was lower than that of experiment 3. When the metal temperature reached a melt temperature (800ºC ±5), yield of powders was more than at that other conditions. Table.13 summarizes the total yield percent of aluminum powder obtained during the present experiment work. The result shows that pressure and temperature variables have a strong influence on weight of grams. By viewing from this experiments, it was found that total yield percent of

aluminum powder (97.6%) at gas pressure (0.7MPa)and temperature (800ºC) was higher than that at other two conditions.

TABLE 13 YIELD PERCENT OF ALUMINUM POWDER

B. Aluminum Powder Morphology

The shape and microstructures of the powders were observed by a scanning electron microscope (SEM)(SEM JEOL JSL-5610). Scanning electron microscope images of the produced powders were shown in Figs 7. Most of the powder particles were nearly spherical. Few particles were dumbbelled shape or granular. According to the Figs, the powder particles were more nearly spherical at gas pressure 0.6 MPa and temperature 800ºC than that at other conditions.

Fig.7 SEM Analysis of Aluminum Powder at Gas

Pressure (0.5, 0.6, 0.7 MPa) and Temperature 800ºC

C. Analysis of Obtained Aluminum Powder The crystal structure of the aluminum

powder was characterized by XRD (RIGAKU model RINT 2000) diffractometer using Cu/K α radiation (λ=1.54056 Aº with 40kV, 40mA), scan speed of 4º/min, in the 2θ range of 10º to 70º. The XRD patterns of aluminum powder were observed at 2θ angles of 38.720º (111), 45.020º (200), 65.420º (220). The typical XRD pattern of product aluminum powder was shown in Fig. 8. The sizes of the particles were estimated by calculation using Scherrer’s equation. The


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Scherrer constant (K=1.33) was calculated for spherical powder. The result shows that the distribution size is narrowest at 800ºC with the minimum size of 50nm and maximum of 80nm.

Fig. 8 X-ray Diffraction Pattern of Aluminum Powder

IV. CONCLUSIONS In this research, hybrid atomization

unit for producing aluminum powder was fabricated. By using the hybrid atomization method, it can be produced fine, nearly spherical aluminum powder with high yields. Aluminum powders with the particle size of under 75 μm were obtained.These atomization experiments confirm the strong influence of two processing variables (gas pressure and melting temperature) on particle size distribution.The smallest size of 50nm was obtained from powder synthesize at 800ºC. The product total yield (97.6%) can be obtained at gas pressure 0.7 MPa and temperature 800ºC.

REFERENCES [1] S. K. Grjotheim and B. J. Welch, “Aluminum

smelter technology- a pure and applied approach,” 1988, pp. 1-10.

[2] J. B. Verlinden and L. Froyen, “Aluminum powder metallurgy,” 1994, pp. 1-26.

[3] S. E. Klar and J. W. Fesko, “ Gas and water atomization,” ASM Handbook , ASM International, USA, 1984, pp.25–39.

[4] J. J. Dunkley, “Atomization, powder metal technologies and applications,” ASM Handbook, ASM International, Ohio, 1998, pp. 35-52.

[5] Y.Z. LIU, K. Minagawa, H. Kakisawa and H. Halada “Melt film formation and disintregation

during novel atomization process,” vol.17, pp.1276-1281, September 2007.

[6] K. Minagawa, H. Kakisawa, H. Halada, Y. Osawa and S. Takamori, “Production of fine spherical lead-free solder powders by hybrid atomization,” pp. 325-329, July 2005.

[7] K. Minagawa, H. Kakisawa, H. Halada, Y. Osawa and S. Takamori, “Hybrid atomization method suitable for production of fine spherical lead-free solder powder,” pp. 83–88, December 2005.

[8] H. Lubanska, “ Correlation of spray ring data for gas atomization of liquid metal,”. pp.45-49, 1970.


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Production of Fine Aluminum Powder from