Lanthanum aluminate

The lanthanum phosphate phosphor is usually prepared by starting with a highly purified coprecipitated oxide of lanthanum, cerium, and terbium blended with a slight excess of the stoichiometric amount of diammonium acid phosphate. Unlike the case of the aluminate phosphor, firing is carried out in an only slightly reducing or a neutral atmosphere of nitrogen at a temperature 1000° C. Also this phosphor is typically made with the addition of a flux,... 

The difference in catalytic activity between the La- and the Ba-based hexa-aluminates results from the following reasons the first difference is the valence of cation in the mirror pleuie between tri-valent lanthanum ion and di-valent barium ion. The second is the crystal structure between magnetoplumbite and P-alumina, which are different in the coordination of ions and concentration of Frenkel-type defect in mirror plane. The redox cycle of transition metal in hexa-aluminate lattice, which closely related with catalytic activity, is affected sensitively with these two factors. 

Ng, M.-F. Cima, M. J. 1997. Fleteroepitaxial growth of lanthanum aluminate films derived from mixed metal nitrates. J. Mat. Res. 12 1306-1314. 

However, the situation becomes already more complicated for ternary single crystals like lanthanum-aluminate (LaAlC>3, er = 23.4). The temperature dependence of the loss tangent depicted in Figure 5.3 exhibits a pronounced peak at about 70 K, which cannot be explained by phonon absorption. Typically, such peaks, which have also been observed at lower frequencies for quartz, can be explained by defect dipole relaxation. The most important relaxation processes with relevance for microwave absorption are local motion of ions on interstitial lattice positions giving rise to double well potentials with activation energies in the 50 to 100 meV range and color-center dipole relaxation with activation energies of about 5 meV. 

Another class of important materials with oxygen ion conduction are perovskites (see Section 2.4.4). Perovskite phases have been, initially, considered as possible electrode materials for SOFCs. The first report of the existence of oxide conductivity in a perovskite material was made using a calcium-doped lanthanum aluminate [98], But the discovery of attractive oxygen conduction properties is rather recent [84],... 

Figure 39 Illustration of a possible lanthanum phosphate-calcium aluminate glass structure for lower LaP04 content in calcium aluminate, derived from Raman and NMR data. For clarity, only a segment of the network is portrayed, with some oxygen atoms removed from the diagram. Taken from Ref. [168].

Lanthanum aluminate. Mechanochemical synthesis of lanthanum aluminate was carried out by the joint grinding of lanthanum oxide La203 with aluminium hydroxide or oxide in a planetary mill [20]. After activation for 120 min, a monophase product LaA103 with a large specific surface area was obtained. However, the formation of LaA103 was not observed when a-AI2O3 was used as an initial reagent. 

The authors [34] proposed to use perovskites ABO3, where A are calcium cations, or a mixture of calcium and lanthanum, and B are iron, cobalt, nickel or manganese cations, or their mixtures. Besides, aluminates, silicates, aluminium sihcates, zirconates and chromates of different types are added as structure-forming components providing strength and stability to thermal shocks [34]. 

Magnified view of lanthanum aluminate crystal MICHAEL W. DAVIDSON, NATIONAL AUDUBON SOCIETY COLLECTION/PHOTO RESEARCHERS, INC. 

What is certain Is that the addition of foreign Ions can lead to new compounds. Nickel aluminate has been shown to be fornied from Che calcination of Ni/Al O catalysts, and the aluminate has been suggested to be responsible, at least in part, for the observed extra stability [19p 19(a)]< Lanthanum aluminate is also known to be formed on calcination of La doped aluminas... 

Figure 5.21. Stacked and contour representations of the A1 MQMAS NMR spectra of lanthanum aluminate gels of (A) low-lanthanum content, in which three resonances assigned to Al, Al and Al can be distinguished, and (B) high-lanthanum content gel, in which only the octahedral and tetrahedral A1 resonances are observed. The solid line indicates the isotropic chemical shift, the dashed line shows the direction of the anisotropic quadrupolar line broadening and the dotted-dashed line indicates the direction of the quadrupolar-induced shift. From luga et al. (1999), by permission of the American Chemical Society.

M.C. Wilding, CJ. Benmore, and P.F. McMillan, A neutron diffraction study of yttrium- and lanthanum-aluminate glasses../. Non-Cryst. Solids 297(2-3), 143-155 (2002). 

An example of the first approach (matrix assimilation) would be to match the acid content in the standards with the acid content in the samples. Matrix assimilation is only effective provided that the interference is not severe and the sample matrix is relatively simple. For more marked interferences, a second cation can act as a release agent. As an example, lanthanum [as La(N03)3] can be added to solutions in which Ca is to be determined in the presence of P04 , silicate or aluminate in an air/C2H2 flame. An example of the third approach would be to add a strong complexing agent (such as EDTA) to both samples and standards. Many metals have an appreciable tendency to hydrolyse in aqueous media moreover the hydroxides can be sparingly soluble yet precipitates can be difficidt to detect visually in dilute solutions. To limit this process, samples are customarily prepared in acidic media. 

P-aluminate amount is increased. The stabilizing effect of lanthanum was assumed to result from the formation of intermediate X-ray amorphous compounds with the transient AI2O3 forms [2],... 

The influence of lanthanum aluminate, LaA103, on the thermal stability of both alumina and platinum supported alumina catalysts is investigated. 

The addition of LaA103, is shown to increase both the dispersion and the resistance to sintering of the platinum supported alumina catalyst. Moreover, lanthanum hexa-aluminate (La-p-A C ) is present in the platinum catalyst fired at 1150°C. 

Examination of the XRD patterns of Y-AI2O3 and 5% La-Al203 both fired in air at 1150°C (12 hours) shows the transformation of pure Y-AI2O3 to corundum. However, in the latter case y-A1203 is transformed to 8-AI2O3 (Refill) and well crystallized lanthanum aluminate is also detected (Ref. 12). 

Comparison of Fig. 6 with the diffraction pattern of pure LaA103 (Fig.4) shows that the framework obtained could represent a three-fold superstructure of lanthanum aluminate (3X-LaA103). The formation of such a superstructure normally requires reaction at high temperature because of the high activation energy of these... 

These results are in good agreement with those of Schaper et al. who invoked surface diffusion to account for the sintering mechanism of active alumina, the effect of lanthanum being interpreted as a surface interaction (Ref. 5, 6). Our work confirms that lanthanum aluminate LaA103 is the lanthanum active species, and suggests a model for the thermal stabilization of alumina which takes into account the structural interface between lanthanum aluminate and 5-alumina. 

The results presented in Table 2 and Fig. 2 show that the presence of lanthanum aluminate increases the initial dispersion and the resistance to sintering of supported platinum. It thus confirms that an interfacial interaction proceeds between lanthanum aluminate and 8-AI2O3. ... 

Sapphire substrates, for II-Vl or III-V applications, can be found through the 100 mm range. Whereas, ZnSe, ZnTe, and GaN are found in the 1 cm range in research quantities. Efforts on ZnSe and related substrates increased with the demonstration of blue lasers in this material system. However, those efforts are foreshadowed by the blue LED and laser results in GaN. Presently there are several major research efforts underway to produce large area GaN substrates. The nitride substrate development effort also is motivated by high power, temperature and frequency device applications. For superconductors, lanthanum aluminate, strontium titanate, magnesium oxide, and other related substrates are found in the few to tens of square centimeter ranges. 

There are a few catalytic applications in which other mixed oxide structures are cited. Among them are pyrochlore compounds such as La2Zr207, spinels such as AB2O4, and lanthanum beta aluminates, all of them with well-defined crystalline structures. There are also a few examples of oxide solid solutions made up of a rare-earth oxide and a transition-metal oxide. 

KAI(S04)2 3H20 POTASSIUM ALUMIN. SULFATE 3-HYDRATE 884 LaAs04 LANTHANUM ARSENATE 927... 

KAI(S04)2 12H20 POTASSIUM ALUMIN. SULFATE 12-HYDR. 885 LaBr3 LANTHANUM BROMIDE 927... 

We previously proposed an interpretation of thermal stabilization of supported catalysts by rare-earth elements [10, 11, 18] by means of interfacial structural coherence between alumina and rare-earth aluminates. This model, developped for lanthanum and neodymium, can be easily extended to cerium since LaAlOs, NdAlOs and CeAlOs are iso-structural mixed oxides with identical lattice parameters (a = 7.6 A). 

The influence of the reduction temperature on the metal support interaction and particle agglomeration occurs frequently on supported catalysts and will be illustrated for nickel-supported catalysts. It depends on the support, the metal concentration, the calcination temperature, the reducing agent, the Hi concentration, and the presence of water. When promoted with potassium, lanthanum, or any other promoter, the reducibility and the metallic distribution improve. After calcination, nickel is converted as oxide (NiO), also as suboxide (NiiOs) and as aluminate form. 

The first peak is associated to the reduction of NiO with low interaction with the support, while the second and third peaks, which are partially superimposed, are associated to the reduction of NiO interacting with the support, thus, to the reduction of nickel aluminates. The reduction degree was 100% and the particle sizes of 200 A. XRD data confirmed the existence of metallic Ni, aluminates and lanthanum aluminates in this sample after reduction. 

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