Aluminum compositional model

Desorption isotherms for the hydrides of LaNi eAlo,] and LaNij sAlo.s are presented and values for the enthalpy and entropy changes of the hydriding reactions are calculated from the vant Hoff plots of log P vs, i/T. A crystallographic model of LaNij Al is shown and consideration of the nearest neighbor atom distribution leads to a rationalization of the observed linear relationship between the enthalpy change, aH, and the aluminum composition. Brief discussions of methods to predict dissociation pressures or interstitial site occupation are included. The cubic and hexagonal ABs phases are compared and, finally, the application of these alloys in chemical heat pump systems is noted. 

Armarego EJA, Katta RK (1997) Predictive cutting model for forces and powers in self-propelled rotary tool turning operation. CIRP Ann 46(1) 19-24 Chen P, Hoshi T (1992) High-performance machining of SiC whisker-reinforced aluminum composite by self-propelled rotary tools. CIRP Ann 41(l) 59-62... 

As an example of this problem, Hayes and Fritz have studied the velocity of explosively driven Aluminum plates using their magnetic probe technique. The velocity as a function of time for 5 cm of Composition B shocking 0.6295 cm of Aluminum is shown in Figure 5.2. Also shown is the velocity-time history calculated with the Aluminum fluid model that does not include elastic-plastic or spall behavior. Not only is the velocity pull-back not observed experimentally, but at first glance one would conclude that a second shock is not received by the metal from the explosive products ... 

The Beckstead-Derr-Price model (Fig. 1) considers both the gas-phase and condensed-phase reactions. It assumes heat release from the condensed phase, an oxidizer flame, a primary diffusion flame between the fuel and oxidizer decomposition products, and a final diffusion flame between the fuel decomposition products and the products of the oxidizer flame. Examination of the physical phenomena reveals an irregular surface on top of the unheated bulk of the propellant that consists of the binder undergoing pyrolysis, decomposing oxidizer particles, and an agglomeration of metallic particles. The oxidizer and fuel decomposition products mix and react exothermically in the three-dimensional zone above the surface for a distance that depends on the propellant composition, its microstmcture, and the ambient pressure and gas velocity. If aluminum is present, additional heat is subsequently produced at a comparatively large distance from the surface. Only small aluminum particles ignite and bum close enough to the surface to influence the propellant bum rate. The temperature of the surface is ca 500 to 1000°C compared to ca 300°C for double-base propellants. 

An important appHcation of MMCs in the automotive area is in diesel piston crowns (53). This appHcation involves incorporation of short fibers of alumina or alumina—siHca in the crown of the piston. The conventional diesel engine piston has an Al—Si casting alloy with a crown made of a nickel cast iron. The replacement of the nickel cast iron by aluminum matrix composite results in a lighter, more abrasion resistant, and cheaper product. Another appHcation in the automotive sector involves the use of carbon fiber and alumina particles in an aluminum matrix for use as cylinder liners in the Prelude model of Honda Motor Co. 

To demonstrate nonuniqueness, we pose here three problems in geochemical modeling that each have two physically realistic solutions. In the first example, based on data from an aluminum solubility experiment, we assume equilibrium with an alumina mineral to fix the pH of a fluid of otherwise known composition. Setting pH by mineral equilibrium is a widespread practice in modeling the chemistry of... 

Our initial work on the TEMPO / Mg(N03)2 / NBS system was inspired by the work reported by Yamaguchi and Mizuno (20) on the aerobic oxidation of the alcohols over aluminum supported ruthenium catalyst and by our own work on a highly efficient TEMP0-[Fe(N03)2/ bipyridine] / KBr system, reported earlier (22). On the basis of these two systems, we reasoned that a supported ruthenium catalyst combined with either TEMPO alone or promoted by some less elaborate nitrate and bromide source would produce a more powerful and partially recyclable catalyst composition. The initial screening was done using hexan-l-ol as a model substrate with MeO-TEMPO as a catalyst (T.lmol %) and 5%Ru/C as a co-catalyst (0.3 mol% Ru) in acetic acid solvent. As shown in Table 1, the binary composition under the standard test conditions did not show any activity (entry 1). When either N-bromosuccinimide (NBS) or Mg(N03)2 (MNT) was added, a moderate increase in the rate of oxidation was seen especially with the addition of MNT (entries 2 and 3). 

The difference between the compound energy model and the simple two-sublattice model can be illustrated with two ternary intermetallic phases from the Al-Mg-Zn system. One of these two phases is known to contain a constant composition of 54.5 atomic percent magnesium and an extended homogeneity range of aluminum and zinc, corresponding to the formula Mg6(Al,Zn)5. However, no crystallographic data is available for this phase. Therefore, it is appropriately thermodynamically modeled by two sublattices, in which one sublattice is exclusively occupied by Mg, while A1 and Zn are allowed to randomly mix on the second sublattice (Liang et al., 1998). 

Alkylaluminoxanes, or alkylalumoxanes as they are often called, contain at least one oxide bridge between two or more aluminum centers that contain an organic substituent. Alkylaluminoxanes are most commonly obtained by partial hydrolysis of aluminum triaUcyls under controlled conditions, but many other preparative routes have been described in the literature and in patents. The structures and compositions of most alkylaluminoxanes are the subject of much debate. Often referred to as black box materials, proposed stmctures previously focused on cyclic or polymeric structures as described in an excellent review by Pasynkiewicz. New structural models for aUcylaluminoxane have emerged over the past 15 years. 

The refractory condensate model has fallen out of favor, including with Lewis (1988). Nevertheless, it is a useful end-member case. Goettel (1988) calculated the composition of the silicate portion of an ultrarefractory Mercury (Table 2, column 2). This model composition contains no FeO or volatiles, and has large concentrations of the refractory elements—aluminum, calcium, and magnesium. We calculated the thorium and uranium contents of such refractory condensates by assuming chondritic Al/Th and Al/U ratios. A surface of this composition will contain many of the phases in calcium-aluminum-rich inclusions (CAls), such as forsterite, anorthite, spinel, perovskite, hibonite, and melilite. 

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