123,228 research outputs found
Cancrinite-group minerals ([CAN]-framework type) at non-ambient conditions
No full textAll the isotypic minerals of the cancrinite-group share the [CAN]-framework type, built up by layers of single six-membered rings of tetrahedra centered in an “A” or “B” position, according to the ABAB stacking sequence. The resulting framework has the following secondary building units: 12-membered ring channels parallel to the [0001] axis, bound by columns of base-sharing cages, and the so-called can units. A large chemical variability is shown by both natural and non-natural isotypic compounds. Among the natural species, the majority shows an alumino-silicate framework (Al6Si6O24), and two subgroups can be identified according to the extraframework content of the can units: the cancrinite- and the davyne-subgroups, showing Na-H2O and Ca-Cl chains, respectively. Several cations, anionic and/or molecular groups lie in the channels.
The description of the phase-stability fields and the of the thermo-elastic behavior of the cancrinite-group minerals play a key role in the study of the natural and industrial processes where these compounds are primary constituents (a short summary of which is in [1,2]).
We aim to model the thermo-elastic behavior and (P,T)-induced structure evolution of these isotypic compounds, with a focus on the influence played by the different extraframework constituents on the structure deformation mechanisms. The study is restricted to the chemical compositions commonly occurring in Nature, delimited by the (CO3)-rich and (SO4)-rich end-members within the two aforementioned subgroup: cancrinite {[(Na,Ca)6(CO3)1.2-1.7][Na2(H2O)2][Al6Si6O24]} and vishnevite {[(Na,Ca,K)6(SO4)][Na2(H2O)2][Al6Si6O24]}, balliranoite {[(Na,Ca)6(CO3)1.2-1.7][Ca2Cl2][Al6Si6O24]} and davyne {[(Na,Ca,K)6((SO4),Cl)][Ca2Cl2][Al6Si6O24]}, respectively. The high-pressure and low-temperature (T < 293 K) studies of the carbonate end-members (i.e. cancrinite and balliranoite) have been performed by means of in situ single-crystal X-ray diffraction. The results [1-4] show that, though sharing a similar volume compressibility and thermal expansivity, these minerals have a different thermo-elastic anisotropy, being more pronounced in cancrinite. This is due to different (P,T)-induced structure deformation mechanisms, likely governed by the different coordination environment of the cage population. An in situ high-temperature (293 ≤ T(K) ≤ 823(7)) single-crystal X-ray diffraction study of cancrinite, allowed the description of thermo-elastic behavior and anisotropy. An irreversible dehydration process takes place at 748(7) K. Preliminary results of the high-pressure studies of the sulfatic end-members (i.e. vishnevite and davyne) are available. A clear change of the elastic behavior of vishnevite, with an increase of compressibility, is shown between 2.47(2)-3.83(2) GPa. A similar increase of compressibility was also reported for cancrinite at 4.62-5.00(2) GPa.
References. [1] Lotti, P., Gatta, G.D., Rotiroti, N., Cámara, F. (2012): Am. Mineral., 97, 872-882; [2] Gatta, G.D., Lotti, P., Kahlenberg, V. (2013): Micropor. Mesopor. Mater., 174, 44-53; [3] Gatta, G.D., Lotti, P., Kahlenberg, V., Haefeker, U. (2012): Miner. Mag., 76, 933-948; [4] Lotti, P., Gatta, G.D., Rotiroti, N., Cámara, F., Harlow, G.E. (2013): Z. Kristallogr., in press
Cancrinite-group minerals at non-ambient conditions: vishnevite and davyne
No full textIsotypic minerals of the cancrinite-group share the [CAN]-framework type, built up by layers of single six-membered rings of tetrahedra centered in an “A” or “B” position, according to the ABAB stacking sequence. In order to describe a model for the thermo-elastic behavior of these isotypic compounds, we have recently investigated the high-pressure (up to ca. 8 GPa) and low-temperature (100 ≤ T (K) ≤ 293) characteristics of the (CO3)-rich end-members cancrinite {[(Na,Ca)6(CO3)1.2-1.7][Na2(H2O)2][Al6Si6O24]} and balliranoite {[(Na,Ca)6(CO3)1.2-1.7][Ca2Cl2][Al6Si6O24]}, by means of in situ single crystal X-ray diffraction. The results [1-4] showed that, though sharing a similar volume compressibility and thermal expansivity, these minerals have a different thermo-elastic anisotropy, being more pronounced in cancrinite. This is due to different (P,T)-induced structure deformation mechanisms, governed by the different coordination environment of the extraframework population within the cages. We are extending our investigation on (SO4)-rich members of the group, and in particular on vishnevite {[(Na,Ca,K)6(SO4)][Na2(H2O)2][Al6Si6O24], analogue of cancrinite} and davyne {[(Na,Ca,K)6(SO4,Cl)][Ca2Cl2][Al6Si6O24], analogue of balliranoite}. High-pressure and low-temperature in situ single-crystal X-ray diffraction experiments are currently in progress. A preliminary analysis allowed an early description of their high-pressure behavior. Vishnevite, which is apparently stable up to 7.40(2) GPa, shows a change of the compressional behavior, with an increase of compressibility, between 2.47(2)-3.83(2) GPa. Experimental data within the range 0.0001-2.47(2) GPa have been fitted with a II-order Birch-Murnaghan equation of state (II-BM EoS, K' = 4), giving the following refined elastic parameters: V0 = 733.5(4) Å3, KV0 = 51(1) GPa; a0 = 12.762(2) Å, Ka0 = 59.8(9) GPa; c0 = 5.2013(9) Å, Kc0 = 38.0(6) GPa. A III-BM EoS fit of the experimental data within the range 3.83(2)-7.40(2) gave: V0 = 757(6) Å3, KV0 = 30(3) GPa KV' = 2.6(5); a0 = 12.84(2) Å, Ka0 = 40(3) GPa, Ka' = 1.8(4); c0 = 5.33(4) Å, Kc0 = 16(3) GPa, Kc' = 3.6(5). A re-arrangement of the extra-framework population within the channels appear to control the observed change of the compressional behavior. A significantly less pronounced increase of compressibility was observed for cancrinite at 4.62(2)-5.00(2) GPa [2]. Davyne does not show any loss of crystallinity nor a change of compressional behavior up to 7.18(2) GPa. Experimental data have been fitted with a III-BM Eos, leading to the following refined parameters: V0 = 761.6(4) Å3, KV0 = 46.8(9) GPa, KV' = 3.6(3); a0 = 12.815(2) Å, Ka0 = 50.3(9) GPa, Ka' = 4.0(3); c0 = 5.355(1) Å, Kc0 = 41.6(9) GPa, Kc' = 2.9(2), showing a strong similarity with the elastic behavior of balliranoite at high pressure[4].
[1] G.D. Gatta, P. Lotti, V. Kahlenberg, U. Haefeker Miner. Mag. 2012, 76, 933.
[2] P. Lotti, G.D. Gatta, N. Rotiroti, F. Cámara Am. Mineral. 2012, 97, 872.
[3] G.D. Gatta, P. Lotti, V. Kahlenberg, Micropor. Mesopor. Mater. 2013, 174, 44.
[4] P. Lotti, G.D. Gatta, N. Rotiroti, F. Cámara, G.E. Harlow Z. Kristallogr. 2013 (in press)
Comparative thermo-elastic behaviour of the isotypic cancrinite and balliranoite
No full textThe high-pressure behaviour and the P-induced structure evolution of a natural cancrinite from
Cameroun (Na6.59Ca0.93[Si6.12Al5.88O24](CO3)1.04F0.41•2H2O, a = 12.5976(6) Å, c =5 .1168(2) Å,
space group: P63) were investigated by in situ single-crystal X-ray diffraction under hydrostatic
conditions up to 6.63(2) GPa with a diamond anvil cell[1]. The P-V data were fitted with an
isothermal Birch-Murnaghan-type equation of state (BM EoS) truncated to the 3rd-order, giving
the following elastic parameters: V0 = 702.0(7) Å3, KV0 = 51(2) GPa and KV' = 2.9(4). Linearized
BM EoS was used to fit the a-P and c-P data, giving the following parameters: a0 = 12.593(5) Å,
Ka0 = 64(4) GPa, Ka' = 4.5(9), and c0 = 5.112(3) Å, Kc0 = 36(1) GPa, Kc' = 1.9(3). A subtle change
of the elastic behaviour appears to occur at P > 4.62 GPa, and so the elastic behaviour was also
described on the basis of BM EoS valid between 0.0001 – 4.62 and 5.00 – 6.63 GPa, respectively.
The high-pressure structure refinements allowed the description of the main deformation
mechanisms responsible for the anisotropic compression of cancrinite. The low-temperature
structure evolution of the same natural cancrinite was also investigated by means of in-situ single-crystal
X-ray diffraction[2]. The V-T data exhibit a trend without any evident thermoelastic
anomaly, with a thermal expansion coefficient αV = 38(7) •10^(-6) K^(-1) (between 100 and 293 K).
Seven structure refinements showed that the same mechanisms observed at high pressure, mainly
govern the low-T structure evolution.
A study of a natural sample of balliranoite
(Na4.47Ca2.86K0.10[Si5.96Al6.04O24](CO3)0.62(SO4)0.33Cl2.03, a = 12.680(1) Å, c = 5.3141(5) Å, S.G.:
P63) at high pressure and low temperature is in progress. Preliminary P-V data up to 4.93 GPa
were fitted with a BM EoS truncated to the 2nd order (II-BM EoS), giving the following refined
parameters: V0 = 735.6(9) Å3, KV0 = 48.0(14) GPa. A fit with a II-BM EoS, applied to the P-V
data of cancrinite within the range 0.0001-4.62 GPa, gave the following parameters: V0 = 702.5(5)
Å3, KV0 = 48.8(6) GPa, showing similar volume compressibility. However, a different elastic
anisotropy is observed (Ka0:Kc0 = 2.14:1 in cancrinite; Ka0:Kc0 = 1.40:1 in balliranoite). Structure
refinements of balliranoite from high pressure and low temperature diffraction data will lead to
the description of the P/T-induced structure evolution, allowing a comparative crystal-chemistry
analysis of this class of materials.
References
1.P. Lotti, G.D. Gatta, N. Rotiroti, F. Càmara Am. Mineral. (2012), 97, 872−882.
2.G.D. Gatta, P. Lotti, V. Kahlenberg, U. Haefeker Mineral Mag. (2012, in press)
Commento dell'art. 583 quater Cod. pen. (Lesioni personali gravi o gravissime a un pubblico ufficiale in servizio di ordine pubblico in occasione di manifestazioni sportive)
No full textCommento della circostanza aggravante prevista dall'art. 583 quater c.p., inserito con l. n. 8/2007, per l'ipotesi di lesioni personali gravi o gravissime a un pubblico ufficiale in servizio di ordine pubblico in occasione di manifestazioni sportive
Commento dell'art. 61 nn. 11 bis - 11 quinquies Cod. pen. (Circostanze aggravanti comuni)
No full textCommento delle seguenti circostanze aggravanti comuni previste dall'art. 61 del codice penale: aggravante della clandestinità (n. 11 bis); delitto contro la persona a danno di un minore commesso all'interno o nelle vicinanze di istituti di istruzione o formazione (11 ter); delitto non colposo commesso durante l'esecuzione di una misura alternativa alla detenzione in carcere (n. 11 quater); delitto non colposo commesso in presenza o in danno di un minorenne o di una donna in stato di gravidanza (11 quinquies)
Commento dell'art. 224 bis del Codice della Strada (Sanzione amministrativa accessoria del lavoro di pubblica utilità in caso di condanna per un delitto colposo commesso con violazione delle norme del codice della strada)
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Commento dell'art. 648 quater Cod. pen. (Confisca speciale in tema di riciclaggio, autoriciclaggio e impiego di denaro, beni o utilità di provenienza illecita)
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Commento dell'art. 81, co. 4 Cod. pen. (Disciplina del concorso formale di reati e del reato continuato in ipotesi di recidiva reiterata)
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Commento dell'art. 727 bis Cod. pen. (Uccisione, distruzione, cattura, prelievo, detenzione di esemplari di specie animali o vegetali selvatiche protette)
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Commento dell'art. 590 bis Cod. pen. (Disciplina derogatoria al giudizio di bilanciamento ex art. 69 c.p. per le circostanze di cui agli artt. 589, co.3 e 590, co. 3, secondo periodo, relative ai delitti di omicidio colposo e di lesioni personali colpose realizzati da conducente di veicolo in stato di ebbrezza o sotto l'effetto di stupefacenti)
No full textCommento della disciplina prevista dall'art. 590 bis c.p., inserito dalla l. n. 125/2008, che deroga l'art. 69 c.p. in relazione alle circostanze di cui agli artt. 589, co.3 e 590, co. 3, secondo periodo, quando i delitti di omicidio colposo e di lesioni personali colpose siano realizzati dal conducente di un veicolo che si trovi in grave stato di ebbrezza o sotto l'effetto di sostanze stupefacenti o psicotrope
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