G. Venturello

Grain growth and secondary recrystallization in iron

The effect of impurities and of slight deformations as factors modifying the kinetics of normal grain growth after primary recrystallization in pure iron is investigated. Samples of pure iron and Armco iron, each with or without a content of precipitated oxides, were examined.Inclusions inhibit grain growth up to high temperatures, whilst the influence of strain depends on its amount: very low deformations (∼2%) generally block grain growth; for deformations around 5%, secondary recrystallization takes place; higher deformations (∼10%) accelerate the early stages of growth, leading to not very large final grain dimensions. 2.0% elongation has been found to be, in our conditions, the critical strain limit for secondary recrystallization.

Surface rehydration of variously dehydrated eta-alumina

Abstract The surface dehydration and rehydration of well-characterized eta-alumina have been investigated by means of gas adsorption microcalorimetry and infrared spectroscopy. Dehydration shows a multiplicity of surface hydroxyl species, some of which are not reformed on water adsorption at room temperature. The creation of an undissociated water phase takes place from the earliest stages of rehydration. Differential heats steeply decrease with surface coverage, while the adsorption energy distribution does not seem to depend on the dehydration degree.

Energetics of adsorption in the alumina—water system microcalorimetric study on the influence of adsorption temperature on surface processes

Abstract The interaction of water vapor with highly dehydroxylated η-alumina has been investigated at four adsorption temperatures (25, 100, 150, 200°C) by means of a microcalorimetric-volumetric technique. A part of the water molecules irreversibly chemisorbed at room temperature became reversibly adsorbed at the higher temperatures. Three types of adsorption mechanisms were noted: physisorption, only at the lowest temperature, coordination of molecular water on the dehydroxylated surface, and dissociative adsorption, within a wide energy spectrum. The molecular process appeared to be instantaneous, while thermokinetic data showed that dissociative adsorption was always activated. Increasing temperature resulted in greater filling up of the more energetic sites in the first stages of adsorption. In particular, from 150°C on the molecules appear to possess sufficient energy to obtain the most ordered surface occupation. The equilibrium between the two chemisorbed species was displaced toward dissociation by a temperature increase: Sites available for reversible adsorption were reduced, and the total heat released at high coverage decreased. These findings are interpreted on the basis of classical thermodynamic considerations.

Surface characterization of various silicas: a tentative correlation between the energies of adsorption sites and the different biological activities

In order to correlate the biological activity of silica to its surface properties, the analysis of surface sites on three kinds of silicas of different origins and textures has been performed by adsorption calorimetry.Mechanically micronized quartz (5.2 m2g−1), an amorphous silica of low surface area (“Porasil F”; 16.1 m2g−1) and a high surface area silica obtained by ignition (“Aerosil”; 380 m2g−1) have been considered.The heat and mechanism of interaction of water vapour on the surface of quartz reveal a few highly reactive sites not present in the amorphous specimens. The surface behaviour of the latter two specimens is the same, in spite of the large difference in surface area.Radicals produced in quartz by mechanical grinding account for its reactivity and are correlated here to the fibrotic activity of quartz, as opposed to the non-fibrogenicity of amorphous silicas.The heats of interaction of amorphous and crystalline forms with proline also point to a reactivity on quartz that is absent from amorphous silica.ZusammenfassungAn drei Siliciumdioxidproben verschiedener Herkunft und Textur wurden Oberflächenzentren adsorptionskalorimetrisch mit dem Ziel untersucht, die biologische Aktivität von Siliciumdioxid mit dessen Oberflächeneigenschaften in Beziehung zu setzen. In die Untersuchung wurden mechanisch zerkleinerter Quarz (5.2 m2 g−1), ein amorphes SiO2 mit kleiner Oberfläche (“Porasil F”; 16.1 m2 g−1) und ein auf dem Verbrennungsweg erhaltenes Siliciumdioxid mit grosser Oberfläche (“Aerosil”; 380 m2 g−1) einbezogen. Wärme und Mechanismus der Wechselwirkung zwischen Wasser und der Quarzoberfläche weisen auf das Vorliegen einiger hochaktiver Zentren hin, die in den amorphen Proben nicht nachzuweisen sind. Das Oberflächen verhalten der amorphen Proben ist trotz des grossen Unterschiedes in der Oberflächengrösse gleich. Die in Quarz durch Zerkleinerung gebildeten Radikale bedingen dessen Reaktivität und werden mit der fibrotischen Aktivität des Quarzes in Beziehung gebracht, der sich darin von den keine fibrotische Aktivität aufweisenden amorphen Siliciumdioxidproben unterscheidet.РезюмеС целью нахождения ко релляции между биологической актив ностью двуокиси кремния и его поверхн остными свойствами, п роведен адсорбционный калор иметрический анализ поверхностны х участков трех типов двуокиси кремния различного п роисхождения и текстуры. Были рассм отрены механически микронизированный к варц (5,2 m2g−1), аморфная двуокись кр емния с низкой площад ью поверхности (“Пораси л Ф”; 16,1 m2 g−1) и прокаленная двуоки сь кремния с высокой п лощадью поверхности (“Аэроси л”; 380 m2 g−1). Теплота и механиз м взаимодействий пар ов воды на поверхности кварц а показывают нескольк о высокореакционных участков, не представленных в амо рфных образцах. Свойства по верхностей двух друг их образцов одинаковые, несмотря на большое различие их площадей поверхности. Радикал ы, получаемые при механ ическом размалывани и кварца, обусловливаю т его реакционную способность и коррел ируются с фиброидной активностью кварца, в противоположность а морфной двуокиси кремния, не о бладающей такой активностью. Те плоты взаимодействи я кристаллической и ам орфной форм двуокиси кремния с пр опиленом также указы вают на реакционную способн ость кварца.

The role of substitutional transition elements on recrystallization processes in dilute iron solid solutions

Abstract A study of the effect of substitutional solute elements of the 4th period on recrystallization of highpurity iron (99.998 %) has been carried out. Specimens of iron alloys containing Ti, V, Cr, Mn, Co, Ni, Cu, Ga and Ge in concentrations ranging from 10 to 5000 at. × 10 −6 , deformed by cold rolling (85 per cent), were subjected to isochronal anneals at increasing temperatures and then examined by X-ray, optical microscopy and mechanical tests. The dependence of half-recrystallization temperature upon the concentration of the added element may be described by a curve with a maximum, since the greatest effect is reached for an intermediate concentration (about 50–200 at. × 10 −6 ). The dependence of the effect of solutes on their position in the periodic table was checked and found to fit two different patterns respectively at very low and at higher concentrations. In both ranges transition and non-transition elements behave as two separate groups. The hypothesis that two distinct mechanisms of interaction between grain boundaries and solute atoms may act in different concentration ranges is discussed, together with the relative importance of size and electron factors.

Recrystallization and stored energy of dilute copper solid solutions with substitutional transition elements of the 4th period

Abstract A study of the effect of substitutional solute elements of the fourth period on recrystallization and stored energy of pure copper (99.999%) has been carried out. Specimens of copper alloys containing Mn. Fe, Ni, Zn. Ge in concentrations ranging from 10 at . × 10 −6 to 1.5%, deformed by cold rolling (85%), were submitted to heating at a constant rate in a Differential Scanning Calorimeter. The foreign elements act in different ways according to the concentration range considered: small amounts enhance recrystallization rate and stored energy content, further additions always retard recrystallization, while stored energy is increased or lowered according to the type of solute. The dependence of the effect of foreign atoms on their position in the periodic table was checked and found to fit two different patterns at very low and at higher concentrations. The effect of the first additions seems to be related to their atomic volume as displayed in solid solution, while free binding energy of the solute with boundary is to be considered the prime factor conditioning the behaviour of the alloys at higher contents.

Effect of transition elements (Ti, V, Cr, Mn, Co, Ni) oh thermal stability of Fe-B metallic glasses Part II: Crystallization temperature

Abstract The thermal stability against crystallization of iron-boron-based metallic glasses is investigated. The effect of small additions of transition elements on the crystallization temperature is shown, and a steric factor associated with the different substitutional atoms is pointed out to explain the results. Some analogies with the effect of substitutional elements on the primary recrystallization of iron-based cold-yorked solid solutions are suggested.

Adsorption of hydrogen on zinc oxide. Energy of interaction and related mechanisms

The heat of adsorption of hydrogen on zinc oxide (Kadox 25) has been measured at room temperature using a Calvet microcalorimeter.Two main forms of adsorbed hydrogen have been found, coinciding with the literature types I and II. Both always occur simultaneously (although with different kinetics) and a clear-cut separation between the two forms is not achieved on the basis of their reversibility. Differential heats of adsorption decrease with coverage from 60 to 14 kJ mol–1. Apart from the lowest coverages, where a real heterogeneity in site energies is present, the decrease is basically due to the simultaneous adsorption of type I (ca. 40 kJ mol–1) and type II (ca. 14 kJ mol–1), the latter prevailing at increasing coverage. The surprising feature that the ‘irreversible’ type II has a lower adsorption heat than the reversible type I is interpreted as evidence for diffusion of the adsorbate into the bulk, in agreement with kinetic observations.

Surface amorphous and crystalline structures in laser glazed Fe-Ni-P-B and Fe-Ni-Cr-P-B alloys

Traitement par laser des alliages Fe 40 Ni 40 P 14 B 6 et Fe 36 Ni 36 Cr 14 P 12 B 6 prepares par frittage ou fusion des melanges de poudres. Etude par microscopie electronique des surfaces des alliages apres traitement

Physico-chemical aspects in silicosis

Abstract Silicosis is a pulmonary disease which afflicts persons who inhale over long periods of time freshly-ground silica-containig dust. Its mechanism of action at the molecular level is not yet understood. The majority of crystalline SiO 2 forms are pathogenic whereas the amorphous silicas are largely inactive. The primary cause of silicosis has thus to be sought in the structural and surface characteristics of the SiO 2 particles. Recent biological work envisages in the engulfment of the SiO 2 particles into a macrophage the first step ending up with the formation of the silicotic nodule in the lung [1–3]. Intermediate stages of the process are illustrated in Fig. 1. Any silica particle exhibits a membranolytic action on the phagolysosome, probably related to the surface hydroxyls configuration, with consequent release of lytic enzymes into the cytoplasm, death of the macrophage and release of the free SiO 2 particle in the lung tissue where it can be phagocytosed by another macrophage. This does not imply any fibrotic action per se . If the process takes place with fresh ground, crystalline SiO 2 , namely quartz, tridymite and cristobalite, within the phagolysosome a fibrogenic factor is also formed, which, when released in the lung tissue, stimulates fibroblasts to an abnormal production of collagen, and hence the formation of the silicotic nodule. Membranolysis can be reduced or blocked by chemical modification of the surface, however the intimate cause of silicosis relies on the catalytic role of crystalline SiO 2 in the production of the ‘factor’. Virtually any difference in surface properties between amorphous and crystalline silicas may account for their different biological activities. We have investigated, so far, the formation of free radicals at the crushed surface (E.S.R.), the heat of interaction with water molecules (adsorption microcalorimetry) and the kinetics and energy of interaction with some aminoacids (immersion calorimetry) on amorphous and crystalline silicas of comparable size [4]. Free radicals are produced by mechanical grinding of quartz, and readily react with various atmospheric components yielding paramagnetic species such as SiO • 2 and SiCO • 2 , possible intermediates in the formation of the fibrogenic factor. Water vapour reacts with silicas in various ways depending on the dehydration degree of the surface. The heat of adsorption on micronized quartz (∼ 5 M 2 g −1 ), low and high surface area amorphous silicas (porasil ∼ 16 m 2 g −1 ), (aerosil ∼ 380 m 2 g −1 all out-gassed in vacuo below 423 K (in order to prevent elimination of silanols), are reported in Fig. 2 as a function of water uptake. Micronized quartz exhibits at low coverages an interaction energy (∼ 210 kJ mol −1 ) which is much higher than corresponding one on the two amorphous silicas (∼ 125 kJ mol −1 ). Crystalline structure rather than particle size thus dictates the binding energy of surface sites. Aminoacids are adsorbed at the quartz surface [5] but when the process occurs from aqueous solution their interaction energy is competitive with water itself. In the case of proline, however, a specific interaction with quartz was observed: in that case the heat released upon contact with quartz was 30 times higher than on amorphous silica and the interaction lasted many hours indicating an activated process, possibly the oxidation to hydroxyproline specifically catalyzed by the quartz surface. All these findings may be regarded as a first step in the investigation of the particular reactivity of crystalline SiO 2 within the cells.