Site Heterogeneous Catalysts: Strategies, Methods, Structures, and Activities Christophe Copeŕet,*,† Aleix Comas-Vives,† Matthew P. Conley,† Deven P. Estes,† Alexey Fedorov,† Victor Mougel,† Haruki Nagae,†,‡ Francisco Nuñ́ez-Zarur,† and Pavel A. Zhizhko†,§ †Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 1−5, CH-8093 Zürich, Switzerland ‡Department of Chemistry, Graduate School of Engineering Science, Osaka University, CREST, Toyonaka, Osaka 560-8531, Japan A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov str. 28, 119991 Moscow, Russia

Surface Organometallic and Coordination Chemistry toward Single-Site Heterogeneous Catalysts: Strategies, Methods, Structures, and Activities

A review of the mechanisms of set-retardation in portland cement pastes containing organic admixtures

Wettability of silica by gold, silicon, and lead has been determined by the sessile-drop method. The contact angle, θ, and the work of adhesion, W, have been found to be 143° and 227 mJ·m−2 for gold at 1353 K, 87° and 869 mJ·m−2 for silicon at 1723 K, and 120° and 203 mJ·m−2 for lead at 1000 K. Thermodynamic adhesion between silica and nonreactive pure metals has been analyzed using models for metal-oxide bonds. Models based on the assumption that only van der Waals interactions and/or metal-oxygen chemical bonds exist at the metal-oxide interface are unsuited for explaining the relative variations in the W values. A valid model can be accomplished by using an empirical equation which takes into account both metal-oxygen and metal-oxide chemical bonds. It appears that chemical bonds exist at the interface even for nonreactive metal-ionocovalent oxide systems.

Wettability and Work of Adhesion of Nonreactive Liquid Metals on Silica

Interactions of polymers and organic admixtures on portland cement hydration

Precision molded articles, such as die cavities, pertaining to the field of powder metallurgy, and having high hardness and impact resistance, are made by combining granules of refractory and granules of a first metal or alloy which has a homogeneous crystalline appearance at a temperature below its melting point and a lower Rockwell Hardness than the refractory, mixing the granules with organic binder, molding the granule-binder mixture into a green molded preform, thermally degrading and removing the binder to form a skeletal preform, and infiltrating the preform with a second metal or alloy which will wet the first metal or alloy and has a lower Rockwell Hardness than the first metal or alloy, thereby forming a molded article having refractory granules fully enveloped within a single skeleton of the first metal or alloy, the refractory granules and skeleton being surrounded by layers or matrices of softer metals.

Infiltrated powdered metal composite article.

In an attempt to verify theories on the effect of admixtures on portland cement, the adsorption isotherms for calcium lignosulfonate and salicylic acid on cement have been determined. The adsorption isotherms for these compounds on 3CaO·SiO2, 2CaO·SiO2, 3CaO·Al2O3, and 4CaO·Al2O3·Fe2O3 and on a mixture of these components in the ratio 60/25/5/10 have also been determined. Adsorption isotherms were determined at 24°C by a spectrophotometric method, using a Beckman DU spectrophotometer. As a check on the method, previous work of Ernsberger and France on the adsorption of lignosulfonates on portland cement was repeated and their results were confirmed. Results indicate that in aqueous solution the constituents of portland cement mainly responsible for the adsorption of the two compounds studied are the hydration products of 3CaO·Al2O3 and 4CaO·Al2O3·Fe2O3. Salicylic acid adsorption on cement compounds does not fit the Langmuir form. However, adsorption of salicylic acid on type I portland cement, for equilibrium concentrations above 0.005%, fits the form. Calcium lignosulfonate adsorption on type I portland cement, 3CaO·SiO2, 2CaO·SiO2, and partly on 4CaO·Al2O3·Fe2O3 fits the Langmuir form. Adsorption isotherms of salicylic acid on the major cement compounds were determined from ethyl alcohol solution to eliminate the hydration of the compounds occurring in aqueous solution. The adsorption of salicylic acid on the materials studied was found to be in the order: 



The effect of water on the adsorption of salicylic acid from ethyl alcohol solution was studied. It was found that the smaller the amount of water present, above a minimum value, the greater was the adsorption on 3CaO·Al2O3, 2CaO·SiO2, and 3CaO·SiO2. In the case of 4CaO·Al2O3·Fe2O3 the adsorption of salicylic acid was proportional to the amount of water present at all concentrations studied. It is observed in certain cases that it is probably not surface adsorption but a compound formation with salicylic acid.

Adsorption of Admixtures on Portland Cement

Contact angles, surface free energies, and work of adhesion were determined by a sessile drop technique for the wetting of MgO, Al2O3, and SiO2 by In, Ga, and Sn at 10-10 torr. The surface free energies of In, Ga, and Sn were 540, 632, and 573 ergs/cm2 (±5%), respectively, at their melting points. Works of adhesion and equilibrium contact angles for wetting of MgO by In are 172 ergs/cm2 and 133° by Ga, 356 ergs/cm2 and 116° by Sn, 278 ergs/cm2 and 121°. For wetting of Al2O3 by In, they are 237 ergs/cm2 and 124° by Ga, 226 ergs/cm2 and 130° by Sn, 257 ergs/cm2 and 123°. For wetting of SiO2 by In, they are 208 ergs/cm2 and 128° by Ga, 260 ergs/cm2 and 126° by Sn, 252 ergs/cm2 and 124°.

Wetting of Ceramic Oxides by Molten Metals Under Ultrahigh Vacuum

The adsorption of calcium lignosulfonate and salicylic acid was studied on the hydration products of the four principal components of portland cement. To investigate the adsorption as a function of development of hydration product, the determinations were made after varying hydration times. The times allowed were from 5 min to 24 hr for tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF) and from 1 hr to 28 days for β-dicalcium silicate (β-C2S) and tricalcium silicate (C3S). Samples were characterized with respect to surface area and poresize distribution. The effect of gypsum on the adsorption was also investigated. The results indicate that the amounts of salicylic acid and calcium lignosulfonate adsorbed on the hydration products of C3A, and of calcium

Adsorption of Admixtures on Portland Cement Hydration Products

The surface states of silica in the forms quartz, cristobalite, and silicic acid were studied by investigating the kinetics of para-ortho hydrogen conversion and of hydrogen-deuterium equilibration from 93° to 773°K. The products of conversion were analyzed by microthermal conductivity, and those of equilibration by mass spectrometry. The results are discussed in terms of the reaction mechanisms. The active sites for low-temperature conversion are thought to be stable free radicals produced by the thermal removal of hydroxyl groups from the surfaces. Reactivity at high temperatures depends on thermal activation procedure and time. The order of reactivity for equilibration at all temperatures is: quartz > cristobalite > silicic acid. For conversion at low temperatures the order is: quartz > cristobalite > silicic acid; at high temperatures, cristobalite > quartz > silicic acid.

D. R. Rossington

Papers

Adsorption of Admixtures on Portland Cement

Wetting of Ceramic Oxides by Molten Metals Under Ultrahigh Vacuum

Adsorption of Admixtures on Portland Cement Hydration Products

Comparison of Surface States of Quartz, Cristobalite, and Silicic Acid