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Steam Reforming
Published in Martyn V. Twigg, Catalyst Handbook, 2018
For many years nickel has been recognized as the most suitable metal for steam reforming of hydrocarbons. Other metals can be used; for example cobalt, platinum, palladium, iridium, ruthenium and rhodium. Although some precious metals are considerably more active per unit weight than nickel, nickel is much cheaper and sufficiently active to enable suitable catalysts to be produced economically. The reforming reaction takes place on the nickel surface, so the catalyst must be manufactured in a form which produces the maximum stable nickel surface area available to the reactants. This is done by dispersing the nickel as small crystallites on a refractory support which must be sufficiently porous to allow access by the gas to the nickel surface. This is usually achieved by precipitating nickel as an insoluble compound, from a soluble salt, in the presence of a refractory support such as mixtures of aluminium oxide, magnesium oxide, calcium oxide and calcium aluminate cement. Alternatively, the nickel can be incorporated by impregnating a preformed catalyst support, such as alumina or an aluminate, with a solution of a nickel salt which is subsequently decomposed by heating to the oxide. In either case the nickel oxide is reduced to the metal by hydrogen supplied from another plant, or by cracking a suitable reactant gas (e.g. ammonia) over the catalyst as the reformer is being started up (see Section 5.8.7.1). In some instances process gas itself is used to reduce the nickel oxide to metal as the reformer is gradually brought on-line.
Lime, cement and concrete
Published in Arthur Lyons, Materials for Architects and Builders, 2019
Calcium aluminate cement (CAC), also known as high alumina cement, is manufactured from limestone and bauxite (aluminium oxide). The ores, in roughly equal proportions, are charged together into a vertical furnace that is heated to approximately 1600°C (Fig. 3.5). The mixture melts and is continuously run off into trays, where it cools to produce the clinker, which is then milled, producing calcium aluminate cement to BS EN 14647: 2005. The dark grey cement composition differs from that of Portland cement as it is based on calcium aluminates rather than calcium silicates. Although calcium aluminate cement can be produced over a wide range of compositions, the standard product has 40% alumina content.
Material properties
Published in Charles E. Reynolds, James C. Steedman, Anthony J. Threlfall, Reynolds's Reinforced Concrete Designer's Handbook, 2007
Charles E. Reynolds, James C. Steedman, Anthony J. Threlfall
As well as cement for general use (which used to be known as ordinary Portland cement), cements for rapid hardening, for protection against attack by freezing and thawing, or by chemicals, and white cement for architectural finishes are also made. The cements contain the same active compounds, but in different proportions. By incorporating other materials during manufacture, an even wider range of cements is made, including air-entraining cement and combinations of Portland cement with mineral additions. Materials, other than those in Portland cements, are used in cements for special purposes: for example, calcium aluminate cement is used for refractory concrete.
Facile auto-combustion synthesis of calcium aluminate nanoparticles for efficient removal of Ni(II) and As(III) ions from wastewater
Published in Environmental Technology, 2023
Hossam S. Jahin, Magdy I. Kandil, Mostafa Y. Nassar
Calcium aluminate (CA) is widely used in different applications such as cement and steel industry because of its relatively low density, hardness, straightness, etc. [24–27]. Calcium aluminate (CA) was also used as a material for bone graft application owing to its singular combination of physical and mechanical, bioactive, and biocompatible properties [28,29]. It is also utilized as optical ceramics, catalyst support, flame detectors, dental cement, and advanced ceramics [30–37]. Calcium aluminates (CA) powders were synthesized via different methods like solid-state reactions [38], sol–gel [39], polymeric precursor processes [40], and high-energy ball milling [41], spray-drying [42], Pechini method [43,44], and combustion method [45,46]. It is worth mentioning that the auto-combustion method can be employed for the synthesis of simple and complex inorganic materials [47,48]. This is owing to the simplicity, scalability, low cost, short time, and energy saving of the auto-combustion synthesis. Recently, calcium aluminate nanoparticles were used for the removal of dyes and pigments from industrial effluents and wastewater by the adsorption process [49,50]. To the best of our knowledge, no such research was reported on the preparation of monoclinic CaAl2O4 using a simple auto-combustion method, followed by the application of monoclinic CaAl2O4 as an adsorbent for the removal of heavy metals from wastewater.