Surface modifiers alumina

T. W. Kelley, L. D. Boardman, T. D. Dunbar, D. V. Muyres, M. J. Pellerite, and T. P. Smith, High-performance OTFTs using surface-modified alumina dielectrics, J. Phys. Chem. B 107, 5877 (2003). 

Kelley, T.W. et al.. High-performance OTFTs using surface-modified alumina dielectrics,... 

Alumina tri- hydrate ABS, A, E, N, P, PC, PET, PE, PP, PS, PVA, PVC, UF, UR. Alcan Alcoa AluChem. Climax Custom Grinders Franklin Industrial Georgia Marble R. J. Marshall Solem, Harwick H, FRF, SF UF series C-series, Hydral series AC-series Hydrax ATH series Polyfil series Custom grinds H-series Custom grinds of hydrate carbonate. KC-series A-100 series, A-200 series SB-series surface modified aluminas. Micral series. 

Solem, Harwick SB-series surface-modified aluminas. Micral series... 

Hymod, Surface-modified alumina trihydrate, Huber, J. M., Corp., Engineered Minerals Div. 

Infiltration (67) provides a unique means of fabricating ceramic composites. A ceramic compact is partially sintered to produce a porous body that is subsequently infiltrated with a low viscosity ceramic precursor solution. Advanced ceramic matrix composites such as alumina dispersed in zirconia [1314-23-4] Zr02, can be fabricated using this technique. Complete infiltration produces a homogeneous composite partial infiltration produces a surface modified ceramic composite. 

Due to the formation of Ca/Al mixed oxide on the surface, the Ca -modified alumina has a completely different structure compared to the spinel one This leads to a different type of surface Lewis acid/basic sites, rendering the catalyst 30 times less active. 

Membranes UF membranes consist primarily of polymeric structures (polyethersulfone, regenerated cellulose, polysulfone, polyamide, polyacrylonitrile, or various fluoropolymers) formed by immersion casting on a web or as a composite on a MF membrane. Hydrophobic polymers are surface-modified to render them hydrophilic and thereby reduce fouling, reduce product losses, and increase flux [Cabasso in Vltrafiltration Membranes and Applications, Cooper (ed.). Plenum Press, New York, 1980]. Some inorganic UF membranes (alumina, glass, zirconia) are available but only find use in corrosive applications due to their high cost. 

The abihty to modify the surface of the CdS nanoparticle within the cavity of the w/o microemulsions has been extended for their immobihzation. CdS nanoparticles (e.g., prepared in AOT/isooctane w/o microemulsions) were immobilized onto thiol-modified aluminosihcate particles [218] and thiol-modified alumina [219] by a simple addition of thiol-modified aluminosih-cates and alumina, respectively, in the micellar solution. The resulting CdS nanoparticles-aluminosihcate composites were used as photocatalysts for H2 generation from 2-propanol aqueous solution. 

On the other hand, wet process metal coating method was applied to the surface-modified nylon 12 particles (24). Nylon 12 particles modified by alumina or silica fine particles were given metallic coating by an electroless plating method. 

Catalysts for coal liquefaction require specific properties. Catalysts of higher hydrogenation activity, supported on nonpolar supports, such as tita-nia, carbon, and Ca-modified alumina, are reasonable for the second stage of upgrading, because crude coal liquids contain heavy polar and/or basic polyaromatics, which tend to adsorb strongly on the catalyst surface, leading to coke formation and catalyst deactivation. High dispersion of the catalytic species on the support is very essential in this instance. The catalyst/support interactions need to be better understood. It has been reported that such interactions lead to chemical activation of the substrate 127). This is discussed in more detail in Section XIII. 

The earliest NMR studies of oxide surfaces (362-364) involved wide-line proton NMR of adsorbed organic species. For example, Petrakis and Kiviat (363), who studied the adsorption of pyridine and thiophene on molybdena-modified alumina, found that chemisorbed and physisorbed species can be readily distinguished. When physically adsorbed, both compounds exhibited liquid-like NMR behavior with high molecular mobility even at low temperatures. Chemisorbed pyridine was much more rigidly held with essentially only a rotation about the C2 molecular axis persisting to - 130°C. Pyridine was sorbed both physically and chemically, and pretreatment of the surface was not particularly significant in this respect. By contrast, thiophene was physisorbed only on surfaces previously reduced with hydrogen, and underwent a reaction on calcined but unreduced surfaces. 

The supports used in heterogeneous catalysis are also at a stage where major innovations are on the horizon. Control of pore size and volume, in combination with acidity and high-temperature stability of siuface-modified aluminas, promise years of fertile research. New support materials do not necessarily require a unique bulk phase, because designed surface structures on conventional materials can produce a wide spectrum of novel carriers. By taking advantage of the orementioned features, major advances are expected in this area. 

Figure 3.16 Schematic diagram of a gamma-alumina membrane surface modified by tridecafluro-l,l,2 -ietiahydrooctyM-crichlorosilane (TDFS) [Miller and Koros, 1990]...

Thus alumina membranes surface modified with silanes and sulfone [Shimizu et al. 1987] and with trimethyl chlorosilane TMS [Shimizu et al. 1989] and glass membranes adsorbed with surfactants [Busscher et al. 1987] have been studied this way. The results show that surface treatments alter the zeta potentials. Shimizu et al. [1989] have also demonstrated that under normal operating conditions the zeta potentials of alumina membranes do not change over time even for a period of two to three years. The isoelectric point for alumina particles thus determined is close to 4.00 as determined by direct measurement of membranes. 

The typical high surface area alumina supports employed have acidic sites that accelerate skeletal isomerization, cracking, oligomerization, and polymerization of olefinic materials, and enhance coke formation. Alkalis or alkaline earth metals assist in the control of the acidity. Also, a-alumina supports that have essentially no acidity can be utilized however, the challenge is to obtain high dispersion of platinum on such very low surface area supports. Therefore, acidity must be eliminated by using suitable modifiers. 

The same qualitative conclusions can be drawn from the analysis of curves in Fig.2b. At free pH (pH 6.5 before adsorption), alumina sample represents a moderately-charged hydrophilic substrate because the pH value is close to the pzc. The maximum quantity of adsorption corresponds to the area of 0.52 nm per one adsorbed molecule (cf. 0.35 nm at the water-air interface). For pH 3 surfactant ions achieve a close-packed arrangement in the adsorbed bilayer and the density of bilayer adsorption at the plateau (0.11 nm /molecule) is even less than the air-water interfacial density. At the same time, the cmc is markedly diminished by a decrease in the pH. Both effects can be attributed to the appearance of a non-ionized surfactant species in a solution. The neutral form of the surfactant is less soluble in water and thus exhibits a greater affinity for a hydrophobic surface of alumina modified with grafted aliphatic chains. The decresed repulsion between uncharged heads causes a closer packing of the adsorbate in a mixed surface structure. 

A significant cation effect (with potentials in KCl higher than those in NaCI) in the acidic range is reported in [521], Unusual effects of the nature of 1-1 electrolytes on the electrokinetic behavior of a titania pigment (surface-modified with silica, alumina, and organic groups) are reported in [516]. 

Silica (3% by mass)-Modified Alumina from Akzo Properties BET specific surface area 460 rn /g [1075]. 

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