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Pyrometallurgy
Published in C. K. Gupta, Extractive Metallurgy of Molybdenum, 2017
Liquid phase diffusion (dipping) normally is carried out by dipping molybdenum into a molten bath, such as an aluminum silicon alloy bath. As a typical example, mention may be made of coatings given to molybdenum gas turbine blades by dipping into an aluminum-30 silicon alloy bath at 1100°C for 30 s. This treatment produces a 0.012-in. thick coating. The latter is then converted to sillimanite by heating in air at 800 to 1000°C. The blades are next coated with a paste of 95% silicon and 5% alumina in carbon tetrachloride. This goes off with heating and at 1600°C the oxide mixture fuses to a glaze. It is feasible to chromium-coat molybdenum by desolutionizing during immersion in molten chromium-tin or chromium-copper baths. The main limitation of the process arises from the melting point of the molten bath, which must be relatively low to avoid affecting the shape and the structure of molybdenum parts.
Metamorphic rocks
Published in W.S. MacKenzie, A.E. Adams, K.H. Brodie, Rocks and Minerals in Thin Section, 2017
W.S. MacKenzie, A.E. Adams, K.H. Brodie
Sillimanite is one of the three polymorphs of composition Al2SiO5 (the other two are shown in kyanite and andalusite) and is the highest temperature form. It occurs as prismatic crystals, diamond-shaped in cross-section, and also as needle-like acicular crystals. Sillimanite occupies most of the field of view of Figure 223 & 224 where high relief elongate prismatic crystals with no cleavage and middle order orange- blue interference colours are present in the bottom part and square or diamond shaped basal sections, with a characteristic diagonal cleavage (Figure 223) and low grey interference colours (224) are seen in the top part of the image. An opaque mineral and minor feldspar are also seen.
Metamorphic Rocks
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
Sillimanite (p. 79), kyanite (p. 79) and andalusite (p. 79) are metamorphic minerals of great value to the refractory industry. Porcelain containing these minerals is endowed with the ability to withstand very high temperatures and exhibit little expansion. Commercial concentrations of these minerals occur in Kenya, the Appalachians, California, India, S. Africa and Western Australia: all are associated with schists.
Physico-chemical characterization of detrital sillimanite and garnet: Insights into REE elements, crystal structure and morphology
Published in Marine Georesources & Geotechnology, 2022
Rajan Girija Rejith, Mayappan Sundararajan, Sreekantaiyer Ramaswamy, Abdul Azeez Peer Mohamed, Manavalan Satyanarayanan
Sillimanite is an aluminosilicate with the chemical formula of Al2SiO5 having the orthorhombic structure formed by A1O6 octahedra connecting SiO4 and AlO4 tetrahedra (Winter and Ghose 1979). The Raman modes, their symmetry, and assignments of sillimanite recovered from the present study area are clearly shown in Figure 2(a) and Table 1. The vibration modes are represented by Γ = 13 Ag+8 B1g+ 13 B2g+8 B3g+ l l Au +16 B1u +11 B2u +16 B3u where the free SiO4 tetrahedron of Si-O(c) is responsible for high Raman modes such as v3 vibrations (Salje and Werneke 1982). The Al-O displacements cause Raman vibrations at mid-wave numbers, whereas the vibrations caused by silicate and aluminate tetrahedra are hard to discriminate in this region (McMillan and Piriou 1982). The Raman modes of sillimanite are relatively sharp and show clear discrimination from other A12SiO5 polymorphs such as andalusite and kyanite (Sundararajan et al. 2021). The sharp peaks also suggest low A1/Si disorder levels (Mernagh and Liu 1991).
Effects of flake-shape and content of nano-mullite on mechanical properties and fracture process of corundum composite ceramics
Published in Journal of Asian Ceramic Societies, 2021
Wei Lian, Yan Liu, Wenjie Wang, Yangtao Dong, Sheng Wang, Rui Zhu, Nan Xie, Yueqin Wang, Zhenying Liu, Yin Liu, Ling Bing Kong
Figure 4 shows XRD patterns of the mullite and MTA35 powders after sintering at different temperatures. As demonstrated in Figure 4(a), the diffraction peaks of mullite are much weaker than those of corundum, which is the main reason why mullite is not detected in the sintered samples (Figure 3). In addition, the peak intensity of the quartz is decreased, indicating that the quartz was involved in the formation of mullite. As observed in Figure 4(b), corundum grains grow with increasing sintering temperature. Mullite transforms into dialuminium silicate oxide (Al2(SiO4)O, PDF#89-0890; Al2SiO5, PDF#88-0893; Al2SiO5, PDF#74-1976) and sillimanite (Al2SiO5, PDF#88-0892) at 1300°C, and dialuminium silicate oxide into sillimanite with the increase of temperature and stabilizes at 1500°C
Raman-XPS spectroscopy, REE chemistry, and surface morphology of Fe-Ti oxide heavy mineral sands: a case study from Varkala-Kovalam coast, south-west India
Published in Applied Earth Science, 2021
R. G. Rejith, M. Sundararajan, A. Peer Mohamed, M. Satyanarayanan
Most of the beaches in India are bestowed with a high concentration of strategic minerals such as ilmenite (FeTiO3), monazite, rutile (TiO2), zircon (ZrSiO4), sillimanite (Al2SiO5), garnet (almandine- Fe3Al2(SiO4)3), etc. (Gayathri et al. 2017). The important placer deposits in India are Chavara (Kerala), Ratnagiri (Maharashtra), Chatrapur (Orissa), Bhimunipatnam (Andhra Pradesh), and Manavalakurichi (Tamil Nadu) (Ali et al. 2001). The ilmenite from Chavara in Kerala is industrially important for high TiO2 of about 60%, and ferrous oxide ranges from 2.32% to 14.22% (Nair et al. 2009). Many researchers have completed detailed studies, including depositional environment, mineralogy, and geochemical characterisation of these placer deposits (Behera 2003; Nair et al. 2009; Valsangkar and Fernandes 2011). Apart from these major deposits, other beach placer deposits like the Kanyakumari coast (Sajimol et al. 2017), Cuddalore coast (Viveganandan et al. 2013), Thiruchendur coast (Rajganapathi et al. 2013), Valapatanam-Azhikode coast in Kerala (Sundararajan et al. 2010), etc. were also studied in detail. All these minerals are deemed as ‘critical’ on the basis of their wide range of applications in diverse areas (Gupta et al. 2016; Rao et al. 2005). The minerals are recovered from beach sands using a combination of different magnetic, electrostatic, and physical separation units (Rejith and Sundararajan 2018). In India, the rutile and upgraded ilmenite (synthetic rutile) are used for the production of Titania products such as pigment, metal, etc. (Sundararajan et al. 2009b). Monazite is processed by leaching, solvent extraction, precipitation, etc., for the recovery of rare earth metals (Kumari et al. 2015). Zircon is used in ceramics and also for the extraction of high purity zirconia(Sinha 1992). Sillimanite, as such or processed into synthetic mullite is used for refractory applications and garnet as an abrasive material for glass polishing (Banerjee 1998). The potential applications of all these minerals truly depend on the quality of minerals, and it is determined using the advanced characterisation of crystal structure and chemical composition.