Spinels aluminate

The transition from non-protective internal oxidation to the formation of a protective external alumina layer on nickel aluminium alloys at 1 000-1 300°C was studied by Hindam and Smeltzer . Addition of 2% A1 led to an increase in the oxidation rate compared with pure nickel, and the development of a duplex scale of aluminium-doped nickel oxide and the nickel aluminate spinel with rod-like internal oxide of alumina. During the early stages of oxidation of a 6% A1 alloy somewhat irreproducible behaviour was observed while the a-alumina layer developed by the coalescence of the rodlike internal precipitates and lateral diffusion of aluminium. At a lower temperature (800°C) Stott and Wood observed that the rate of oxidation was reduced by the addition of 0-5-4% A1 which they attributed to the blocking action of internal precipitates accumulating at the scale/alloy interface. At higher temperatures up to 1 200°C, however, an increase in the oxidation rate was observed due to aluminium doping of the nickel oxide and the inability to establish a healing layer of alumina. 

It is for this reason that we write the solid state diffusion reaction for the magnesium aluminate spinel as follows ... 

In these soak (300°C)-ramp (up to 900°C) /min) mode tests, a O.lOg of sulfated DESOX sample—the leading catalyst based on magnesium aluminate spinel with an excess MgO catalyzed with Ce and V oxides [9]—was allowed to react with either Hj (5%)/Ar (50 ml/min), undiluted H (70 ml/min) or CH (14 ml/min). 

Grabowska et al [112] reported methylation of 2-hydroxypyridine with methanol over hydrothermally synthesized zinc aluminate spinels. N-methyl-2-pyridone was formed selectively (95%) and 100% 2-hydroxy pyridine conversion was achieved at 340°C. During the experiment the activity of the catalyst was shown to be stable and catalyst can be regenerated repeatedly without any significant loss of activity by passing air through the catalyst bed at 500°C. 

Liermann H.P. and Ganguly J. (2002) Diffusion kinetics of Fe + and Mg in aluminous spinel experimental determination and applications. Geochim. Cosmochim. Acta 66, 2903-2913. 

Tanaka et al. reported that gasoline POX over Rh, Pt, and Pt-Rh is promoted by alkali (Li) and alkaline earth metals (Ba, Ca, K) supported on magnesium aluminate spinel. The catalysts were tested isothermally at 800°C at an air to fuel ratio of 5.1 and GHSV 50,000 h Li, Mg and MgLi promoters were added to Pt supported on MgAl204 spinel. All catalysts produced similar H2 and CO reformate concentrations of 23 and 25 vol%, respectively. There was a discernable difference in the carbon deposition. The unpromoted Pt catalyst showed carbon levels of 0.02 wt% carbon, where the alkali and alkaline earth promoted Pt catalysts had carbon levels of 0.01 wt%. 

The low-pressure methanol synthesis process utilizes ternary catalysts based on copper, zinc oxide, and another oxide, such as alumina or chromia, prepared by coprecipitation. Cu-Zn0-Al203 and Cu-Zn0-Cr203 are usually the most important industrial catalysts. A significant advance was made when a two-stage precipitation was suggested in which ZnAl2C>4, a crystalline zinc aluminate spinel, was prepared prior to the main precipitation of copper-zinc species.372 This alteration resulted in an increase in catalyst stability for long-term performance with respect to deactivation. Catalyst lifetimes industrially are typically about 2 years. 

Kiviat and Petrakis (80) found the infrared specta for adsorbed pyridine on NiMo/Al to be only slightly different than that on CoMo/Al. Both showed evidence of Lewis and Brpnsted acid sites, but the Ni catalyst had a somewhat higher Brpnsted-to-Lewis acidity ratio. Similar results were reported by Mone and Moscu (75), who also found that higher calcination temperatures produced more nickel aluminate spinel. 

Peigney, A., Rul, S., Lefevre-Schlick, F. and Laurent, Ch., Densification during hot-pressing of carbon nanotube-metal-magnesium aluminate spinel composites , to be submitted, 2006. 

Ting, C.-J. and Lu, H.-Y., Hot-pressing of magnesium aluminate spinel-I. Kinetics and densification mechanism , Acta. Mater., 1999, 47, 817-830. 

It is reported1 that fracture toughness and hardness values of sintered magnesium aluminate spinel are in the ranges of 1.9-2.7 MPa m1/2 and 9.3-... 

Dal Maschio, R., Fabbri, B. and Fiori, C., Industrial applications of refractories containing magnesium aluminate spinel , Industrial Ceramics, 1988 8(3) 121-6. 

Carbone, T.J., Characterization and refractory properties of magnesium aluminate spinel raw materials , Interceram. Spec. Issue, 1985 91-4. 

Aksel, C., Davidge, R.W., Knott, P. and Riley, F.L., Mechanical properties of magnesia-magnesium aluminate spinel composites , in III Ceramic Congress Proceedings Book, Engineering Ceramics, Istanbul, Turkey, 2, 172-9, 1996. 

C02 Reforming of Methane to Syngas Deactivation Behavior of Nickel Aluminate Spinel Catalysts... 

Beale AM, Sankar G. Understanding the crystallization of nanosized cobalt aluminate spinel from ion-exchanged zeolites using combined in situ QEXAFS/XRD. Chemistry of Materials. 2005 18(2) 263-272. 

Shortly after the condensation of the first minerals to form within the Solar System, thermal processing of refractory inclusions began. The overall processing of these materials into igneous rocks was short-lived, perhaps only 100000 years (Bizzarro et al. 2007). The critical constraints on the thermal histories of these objects is essentially limited to Type-B CAIs (Connolly Desch 2004), which have been generated by the experimental reproduction of these objects in the laboratory. Type-B CAIs are composed mostly of melilite, anorthite, aluminous spinel, and a titanium-rich pyroxene known in the parlance as fassaite (for a summary of minerals common to the Solar System see Appendix 1). The general consensus is... 

N. Wang, Z. Wang, and G. C. Weatherly, Formation of Magnesium Aluminate (Spinel) in Cast SiC Particulate-Reinforced A1 (A356) Metal Matrix Composites, Metall. Trans., 23A[5], 1423-1430 (1992). 

Preparation and Characterization of Magnesium Aluminate Spinel for SOx Abatement in Fluid Catalytic Cracking... 

Recent studies have demonstrated that cerium containing magnesium aluminate spinels such as MgAl204 and Mg2Al205 are very effective SOx reduction catalysts for FCC units. These magnesium aluminate spinels can be prepared by three different techniques (i) thermal co-condensation... 

Designing a catalyst for effective removal of SOx (S02 + S03) in a fluid catalyst cracking unit regenerator is a challenging problem. One must come up with a particle having physical properties similar to FCC catalysts which will 1) oxidize S02 to S03, 2) chemisorb the S03/ and 3) be able to release it as H2S as it enters the reactor side of the unit. A cerium containing magnesium aluminate spinel was found to be very effective for this purpose (1). The preparation methods and characterization techniques utilized for this spinel catalyst and how the SOx abatement activity of this catalyst is related to the preparative route used are discussed in this paper. 

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