CHARCTERISATION MICROSTRUCTURAL AND MECHANICAL
OF Ni/NiAl 2 O 4 , DEVELOPED BY
MECHANICAL ALLOYING AND REACTIVE SINTERING.
Ali Mameri , Said Azem
Laboratoire Elaboration, Caractérisation des Matériaux et Modélisation (LEC2M)
Université Mouloud MAMMERI de Tizi-Ouzou, PB 17 Hasnaoua 15000, Algérie.
Fares Djematene
Laboratoire Science, Génie Matériaux (LSGM)
Université Houari Boumediene Alger, PB 32 El Alia 16111, Bab Ezzouar 16111, Algérie
Abstract—This study concerns the development of Nickel matrix composite; this composite was obtained after high-energy ball milling for long time of milling. The initial powders mixed are the Nickel oxide and Aluminum, the reduction of Nickel oxide by Aluminum called Aluminothermic reaction. The high energy milling active the aluminothermic reaction and occurred the Nickel-based composite, after milling we obtained powder composite with low density, which it necessary to following this process by reactive sintering. The milling and the sintering was performed under argon atmosphere. The reactive sintering at high temperature allows composite with high density. After sintering at 800 °C we obtained Ni/NiAl2O4.The powders milled and the samples sintering were characterized by X-ray diffraction, scanning electron microscopy, and the grain size of powders milled measured by laser analyzer granulometry. The Nickel aluminate (NiAl2O4) obtained has been applied in numerous fields to its high thermal stability and specific catalytic proprieties.
Keywords—Ni/NiAl2O4, reactive sintering, reactive milling, powder metallurgy, Aluminothermic reaction.
I. INTRODUCTION
High energy ball milling has been known to activate the solid–solid and even solid–liquid chemical reactions during
milling. The high energy ball milling is used to activate chemical reaction; it has been called reactive milling. In reactive milling, plastic deformation and new surfaces were induced by the intensive mechanical treatment of crystalline solids, which causes the chemical reaction activation
The aluminothermic the metal oxides are reduced by more reactive metal to a pure metal. [1]
The aluminothermic reaction in the NiO/Al system is very effective for synthesizing several products like a nanocomposite with intermetallic matrix: NiAl reinforced by Al2O3[2, 3]; ceramic matrix composite: Al2O3 reinforced by metal [4] or intermetallic [5]. One of these reaction applications in industry is the thermite welding which is applied to the rails welding [6].
Metal matrix composite have attractive proprieties as high elastic modulus, wear resistance, which it is promising candidates for applications with several wear abrasive conditions [7]
NiAl2O4 has been applied in numerous fields due to its high thermal stability and specific catalytic properties [8,9]. It has also been proposed as a promising candidate anode for aluminum production because of its high resistance to alkalis and melting aluminum attack [10]
In this study we propose combination of Mechanical Alloying (MA) and reactive sintering to produce metallic matrix composite (Ni/NiAl2O4).
II. EXPERIMENTAL DETAILS
Powders of NiO and Al were mixed in molar ratio: 3/2.
The mixtures were ball-milled in stainless steel container using balls of 8 mm under argon atmosphere. The ball-to- powder weight ratio was10:1, the milling speed was maintained as 300 rpm. The mailing was carried out in planetary mill (RETSH PM400).
The powders milled were sintered at 800 °C under argon atmosphere for 1 h after uniaxial pressure of 376 MPA. Phase identification was performed employing X-ray diffraction using Panatycal diffractometry with filtered Cu alpha radiation of wave length 0.15418 nm. The microscopic observation of powder particles was carried out by SEM type JEOL JSM 6830.
III. RESULTS AND DISCUSSION
Fig 1. Showed the mixture powders after milling and sintering at 800 °C, the reduction of NiO by Al ignited during milling where a quantity of NiO was reacted with Al to form new phases according to equation (1):
3 NiO + 2 Al 3 Ni + 2 Al2O3 (1) At the end of milling the phases formed are: Ni, Al2O3and NiO, Al still remained, it means the aluminothermic reaction is not achieved.
At high temperature (800°c) alumina already formed after milling was reacted with NiO, which leads to form: NiAl2O4
according to equation (2):
NiO +Al2O3 NiAl2O4 (2)
The similar results were obtained after 2 h and 30 h of milling, which the peaks of Ni and NiAl2O4were appeared, it seems formation of Ni-NiAl2O4composite.
It is necessary to notice the peaks of Ni also NiAl2O4after 2h are higher than after 30 h of milling, a decrease in intensity for long milling time is due to the combination of factors as follows: the increase in internal strain, the refinement of crystal size.
Fig 1. XRD pattern of NiO/Al powder mixture ratio (3/2) sintering at 800 °C after different time of milling: 2h and 30 h.
Fig 2. Showed quantitative chemical analysis (EDS- SEM) of samples, where two zones were distinguished: dark zones rich on nickel, aluminum and oxygen probably is NiAl2O4, while other zone was detected less dark than the first contains nickel phase, thus it acts Ni/NiAl2O4composite what in agreement with results XRD presented in fig.1.
The small quantity of iron was revealed it’s due of contamination produced in container during milling.
Figure 2. Plot of the X-ray dispersive energy spectrometer measurement from the NiO/Al (3/2) mixture sintering at 800°C after different time of (MA)
process: 2 h
IV. CONCLUSION
Mechanical alloying followed by sintering process leads to formation of Ni/NiAl2O4composite.
The milling time had a major effect on reduction of NiO by Al, which the reduction increased upon increasing of milling time, the aluminothermic is not achieved after 30 h of milling while it was achieved after sintering at 800 °C. The peaks of Ni and NiAl2O4after 30 h exhibit a broadening and decrease in intensity compared with peaks for 2 hours due to deformation, the presence of iron revealed by EDS indicates the contamination was occurred in container,
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