1,721,127 research outputs found
Composizione di croste nere da differenti siti di interesse storico.
No full textNell’ambito di un progetto finalizzato allo studio delle diverse tipologie di degrado causate dall’inquinamento atmosferico a carico del patrimonio culturale costruito, in questo lavoro sono state prelevate croste nere in 4 differenti siti (3 europei e 1 nord africano) e caratterizzate mediante cromatografia ionica e spettroscopia a emissione atomica e di massa. I risultati ottenuti mostrano come in tutti i luoghi oggetto di studio, l’SO2 abbia un ruolo prioritario nella formazione delle croste nere. É stato inoltre identificato l’impatto di fonti inquinanti locali antropiche e di sorgenti naturali sul degrado degli edifici considerati, come le emissioni da combustione di carbone e da trasporto, sia ferroviario che veicolare, nel sito di Colonia, l’aerosol marino nei siti costieri di Salè ed Oslo, i sali disgelanti ad Oslo e precedenti trattamenti di restauro nel sito di Firenze
Lattice parameters and composition limits of mixed Mg-Al hydroxy structures - a discussion.
No full textThe differences in lattice parameters and the limiting values of composition between synthetic hydroxy carbonates of Mg,Al (M.A. 80-1593) and synthetic hydroxide structures of Mg,Al (M.A. 80-3117) earlier noted (M.A. 81-1331) may be due to the presence of Na in the hydroxy carbonates.R.A.H
A study on the reactivity of C4An . H2O with aqueous solutions
No full textThe reaction products obtained by treating C 4A•nH 2O with various inorganic salts and acid-containing solutions were characterized. The anions taken into consideration were carbonate, chloride, nitrate, sulfate and acetate. As counter-cation H +, NH 4 +, Na + and Ca 2+ were chosen, thus obtaining different pH values according to the specific solution utilized. C 4A•nH 2O gives place to two competing and reversible reactions: exchange of the interlayer OH anions according to the following selectively sequence: CO 3 2-?SO 4 2-> Cl -> NO 3 -> CH 3COO - and an antacid behaviour towards aqueous solutions containing less selective anions
The Action of Heavy Oil Combustion Products On Aluminosilicate Refractories
No full textAluminosilicate refractory bricks exposed for a long period to the action of heavy oil combustion products were analysed. The bricks located in zones characterized by higher working temperatures are mainly degraded by Na2O and V2O5, while SO3 represents the most important contaminant at lower working temperatures. Two series of different mixtures were prepared, taking into account the significant increase in the contaminant contents of the refractory bricks exposed to fuel oil products. V2O5, Na2O and SO3 were added to as-received aluminosilicate refractory and to a mullite-cristobalite mixture. These mixtures, in pelletized form, were thermally treated at temperatures ranging between 600 and 1300°C. The results enable the differences between the data obtained in laboratory and those observed in refractory bricks employed in combustion chambers to be explained. In this last case, in fact, preferential contact between impurities and refractory material may be expected in microzones of the brick characterized by the presence of cracks and pores in which the fuel oil impurities might concentrate
Discrimination between synthetic MgAl double hydroxides and related carbonate phases
No full textPure mixed MgAl double hydroxides were utilized for the preparation of the corresponding MgAl hydroxycarbonates. Three different modes of carbonation were adopted: CO 2 was bubbled through MgAl double hydroxides or these compounds underwent exchange with NaHCO 3 or Na 2CO 3 in aqueous solution. The resulting carbonated phases were investigated by X-ray, DTA, TG, and analysed chemically, and the results compared with those of mixed MgAl double hydroxides. © 1980
Characterization of the Hydrogenated Species In Li2ti4o9.nh2o By Isothermal Weight-change Determination
No full textIsothermal weight-change determination was used to characterize the nature of the hydrogenated species (OH -, H 2O, H 3O +) present in Li 2Ti 4O 9•H 2O. This product contains two OH - groups and five H 2O molecules per unit formula and may be formulated as Li 2Ti 4(OH) 2O 8•5H 2O
Thermal stability of Mg,Al double hydroxides modified by anionic exchange
No full textMetastable phases in the MgO-Al//2O//3-H//2O system below 200 degree C have been studied. Mixtures of alumina gel and MgO were used as starting materials and submitted to hydrothermal treatment at different temperatures. Extensive solid solutions of Mg-doped gibbsite, Mg-doped boehmite and Al-doped brucite have been obtained
On permeation effects of aqueous solutions through non-mature pastes of portland-pozzolana cement
No full text• Portland-pozzolana cement pastes hydrated at 1,2 and 3 days were investigated for permeability tests. They were carried out with distilled water or lime-saturated solutions. Significant differences in flow rates, depending on the period of curing of cement pastes and on the type of testing solution, have been observed. Among the effects that influence the permeation process, an osmotic pressure that originates when distilled water is forced through disk-shaped specimen, has been considered
Destruction of asbestos fibres by sintering asbestos-volcanic tuff mixtures
No full textA new method for the disposal of hazardous asbestos bearing wastes is described; it is based on low temperature sintering of asbestos fibres-unzeolitized tuffs quarry dusts mixtures. Ceramic products similar to gres employable as floor covering both in public and industrial installations, have been produced. Mixtures containing up to 50 wt% asbestos fibres were prepared and moulded by dry grinding and pressing. In spite of the low moisture content, the presence of the fibres produces high strength moulded green bodies which were, without drying, fired at temperatures ranging from 1060 to 1180°C
Uno studio sulla permeabilità di paste non mature di cemento pozzolanico.
No full textIn questo articolo viene riportato uni studio sulla messa a punto di un dispositivo per la misura della permeabilità, un parametro caratterizzante la durabilità di manufatti di cemento.
L’apparecchiatura è stata utilizzata per la determinazione della permeabilità di paste non mature di cemento pozzolanico. Le misure sono state effettuate impiegando come liquido permeante acqua distillata o soluzione satura di Ca(OH)2 .
Vengono discussi i dati sulla riproducibilità della misura e le differenze connesse alle velocità di flusso in funzione delle differenti soluzioni di permeazione
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