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Synthesis of Solids
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Elaine A. Moore, Lesley E. Smart
The original hydrothermal method involves heating the reactants in a closed vessel, an autoclave, with water (Figure 3.6). An autoclave is usually constructed from thick stainless steel to withstand the high pressures and is fitted with safety valves; it may be lined with nonreactive materials, such as the noble metals, quartz, or Teflon. The autoclave is heated, the pressure increases, and the water remains liquid above its normal boiling temperature of 100°C, so-called ‘superheated water’. These conditions, in which the pressure is raised above atmospheric pressure and the temperature is raised above the boiling temperature of water but not to as high a temperature as used in the methods described previously, are known as hydrothermal conditions. Hydrothermal conditions exist in nature, and numerous minerals including naturally occurring zeolites and gemstones, are formed by this process. The term has been extended to other systems with moderately raised pressures and temperatures lower than those typically used in ceramic and sol–gel syntheses. The lower temperatures used are one of the advantages of this method. Others include the preparation of compounds in unusual oxidation states or phases, which are stabilised by the raised temperature and pressure. It is used industrially to prepare large crystals of quartz and synthetic gemstones. It is useful in metal oxide systems, where the oxides are not soluble in water at atmospheric pressure but dissolve in the superheated water of the hydrothermal setup. Where even these temperatures and pressures are insufficient to dissolve the starting materials, alkali or metal salts as mineralisers can be added, whose anions form complexes with the solid and render it soluble. Methods using solvents other than water are known as solvothermal methods.
Thermal efficiency enhancement using a ceramic coating on the cylinder liner and the piston head of the IC engine
Published in International Journal of Ambient Energy, 2021
P. Anand, D. Rajesh, M. Shunmugasundaram, I. Saranraj
Zirconium dioxide (ZrO2), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite (Alkidas 1989). A dopant stabilised cubic structured zirconia, cubic zirconia, is synthesised in various colours for use as a gemstone and a diamond simulant. Zirconia can be found in three crystal structures and it can be seen in Figure 2. These are monolithic (m), tetragonal (t) and cubic (c) structures. The monolithic structure is stable between room temperature and 1170°C while it turns to a tetragonal structure above 1170°C. The tetragonal structure is stable up to 2379°C and above this temperature, the structure turns to cubic structure (Assanis et al. 1991).
Materials-to-product potentials for sustainable development in Nigeria
Published in International Journal of Sustainable Engineering, 2021
Adewale George Adeniyi, Joshua O Ighalo, Comfort Abidemi Adeyanju
Besides the oil and gas resources, Nigeria is also endowed with solid minerals (Adekoya, Kehinde-Phillips, and Odukoya 2011). These minerals include gold, coal, bitumen, talc, gypsum, iron ore, rock salt, kaolin, gemstone (NHC 2020), limestone, tin ore, columbite and zinc/lead sulphates (Alison-Madueke 2009) and a host of others (see Figure 4). Not less than 75% of solid minerals are of great relevance in the industry by the Nigerian Geological Survey Association. Solid minerals are divided into the following; energy minerals (coal, lignite, atomic minerals), major industrial metals (base metals, ferrous metals), specialist metals (tin, wolfram, tantalum), precious metals (gold, silver, platinum), gemstones (precious and semi-precious), and Industrial minerals and construction materials. Over 3 billion metric tonnes deposits of iron ore were estimated to be in Enugu, Kogi, Niger, Lagos, and Federal Capital Territory. The deposits of talc in Osun, Niger, Ogun, Kaduna and Kogi States are over 40 million tonnes. Located in Taraba and Bauchi States barite which is over 7.5 million tonnes (Jack, Nkwocha, and Odubo 2016).
Photocatalytic mechanism of tourmaline/BiVO4 composites with different ratios
Published in Inorganic and Nano-Metal Chemistry, 2020
Shuyan Qi, Yadong Zhao, Ninglong Ma, Huanyan Xu
Tourmaline is a kind of natural nonmetallic ore with electrode property.[16] Specially, the tourmaline can release negative ions,[17] which has the advantages of piezoelectricity, infrared radiation and so on. At present, brightly colored tourmaline is used as a gemstone mineral, and the component of some technological equiptments. However, many tourmalines are not very ornamental, which are regarded as mine waste and have not been properly developed and utilized.[18] The spontaneous polarization characteristic of tourmaline is the most widely application. The film of tourmaline and TiO2 can effectively reduce the forbidden band width of TiO2. Moreover, the spontaneous polarization characteristics of tourmaline can effectively separate the TiO2 electron-hole pairs, reducing the recombination ratio, and finally improving the photocatalytic effect of TiO2[19] in this work, in order to solve the high ratio recombination of electrons and holes tourmaline/BiVO4 with different ratios were prepared by sol-gel method, and the effect of different tourmaline incorporation on the photocatalytic mechanism of BiVO4 was observed.