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Minerals of base metals
Published in Francis P. Gudyanga, Minerals in Africa, 2020
Nickel (Ni) is sufficiently reactive with oxygen which means that elemental nickel rarely exists in nature except in combination with iron thought to be the product of supernova nucleosynthesis [556] such as alloys kamacite and taenite. Limonite ((Fe,Ni)O(OH)), garnierite ((Ni,Mg)3Si2O5(OH)4) which are laterites and pentlandite ((Ni,Fe)9S8), a magnetic sulphide deposit, are the most important commercial sources of nickel. Other minerals in which nickel is found are millerite, nickeline, nickel galena. Like iron, cobalt and gadolinium, nickel is ferromagnetic around room temperature [557] but non-magnetic above its Currie temperature of 355° C [558].
The native metals
Published in R. F. Tylecote, The Prehistory of Metallurgy in the British Isles, 2017
Therefore, if the nickel content is over 4% there is a good chance of meteoric origin. Most of the meteorites with less than about 6% Ni are known as hexahedrites and show little structure and therefore may be difficult to distinguish microscopically from pure irons.49 Meteorites with a nickel content between 7 and 13% are mainly octahedrites which have a very characteristic Widmanstätten structure consisting of a network of bands of a low nickel constituent known as kamacite, bordered by a higher nickel constituent taenite. These bands intersect in three or four directions. Filling the angular interstices are fields containing plessite, a mixture of the above two constituents. There is a third group which is almost structureless known as ataxites. These fall into two compositional groups: up to 7% and between about 12 and 20%.
Investigation of the reduction roasting of saprolite ores in the Caron process: microstructure evolution and phase transformations
Published in Mineral Processing and Extractive Metallurgy, 2021
Figure 3 shows the X-ray diffraction patterns of the ore samples after reduction at temperatures in the range 500°C to 800°C for 15 min in 15%H2, 85% N2. The diffraction patterns indicate, in the original ore sample, the presence of serpentine (lizardite), and small quantities of magnetite. With the increase of the reduction temperature, the lizardite diffraction peaks decrease in intensity and have completely disappeared for samples reduced at 600°C; up to 600°C, there is no indication of the formation of any other crystalline phases – however the increase in background intensity indicates the presence of amorphous material. In the temperature range from 600°C to 800°C diffraction peaks characteristic of the olivine phase ((Mg, Fe, Ni)2SiO4) appear and increase in intensity with increasing temperature. At 800°C only olivine diffraction peaks are observed. Neither the taenite (Fe-Ni alloy) nor quartz (SiO2) could be detected in this analysis.
A review of processing techniques for Fe-Ni soft magnetic materials
Published in Materials and Manufacturing Processes, 2019
Powder metallurgy is a near-net shape technique to produce mini parts and complex shape soft magnetic components. The powder metallurgy technique has both design flexibility and economic benefits for electromagnetic applications.[116,117,118] The magnetic materials produced by powder metallurgy are categorized into two generations. The first-generation materials are produced by normal density technology (NDT) or high-density technology (HDT). The second-generation materials are comprised of insulated powders, amorphous and nanocrystalline materials.[119–121] The NDT uses conventional Press-Sinter process involving 600–800 MPa compaction pressure, 1120–1250°C sintering temperature and gives 92–94% sintered density of the wrought material. As mentioned earlier that saturation induction is a linear function of density. Thus, HDT is a relavent process that involves compaction pressure exceeding 800 MPa, 1250–1300°C sintering temperature and gives 95–98% sintered density of the wrought material.[119,122] Hanejko et al.[32] analyzed the effect of processing parameters on magnetic performance of Fe-Ni alloys. The green samples were compacted uni-axially and sintered at 1260°C in dissociated ammonia. In order to achieve high magnetic performance, the sintered parts were also annealed at 1070°C followed by low cooling rate. The maximum permeability of 8910 was reported in the samples having the highest density of 91%. Rodrigues et al.[123] analyzed the effect of compaction on density and microstructure. The green compacts having density of 6.5 g/cc were produced by the uniaxial press. After sintering in vacuum at 1220°C, XRD revealed the complete austenite phase formation. The sintering temperature was increased to 1350°C to study its effect on densification.[124] After repressing and heat treatment process, the density was improved up to 7.65 g/cc and it was analyzed that the acquired dilatometer data were in accordance with the models of densification and grain growth.[125] Sing et al. fabricated the Fe-Ni alloys with varying Ni content from 10,20,30,40, to 50 wt% by powder metallurgy.[126] The temperature and composition effect on the evolution of α-kamacite phase, γ-taenite phase, and microstructure was investigated. The Ni content from 10% to 50% enhanced the taenite phase formation that is a soft phase as compare to kamacite. Higher sintering temperature increased the taenite phase formation which leads to enhanced densification. The highest wear resistance was achieved in Fe-30Ni alloy due to the presence of both taenite and kamacite phases. Neera et al.[127] analyzed the effect of sintering temperature on various properties of Fe-30Ni alloys for advanced industrial applications. The green specimens were sintered at 1000°C, 1200°C, and 1250°C with 1 h dwell time. The sintering temperature of 1200°C was optimized for good combination of hardness, wear resistance and densification.