1,721,026 research outputs found
PEROVSKITES. FROM PIGMENTS TO MULTIFERROICS, TO THE DISCOVERY OF THE LOCKED-TILT PEROVSKITES
No full textSuperconductors, non-toxic inorganic pigments, sensitizers in dye-sensitized solar cells (DSSCs), semiconductors, and multiferroics are just a few examples of the broad range of uses for which ceramics with perovskite structure are employed. In its aristotype form the ABO3 perovskite structure is cubic (s.g. Pm-3m) with A cations located at the center of dodecahedral sites defined by a three-dimensional array of corner-sharing BO6 octahedra. This polyhedral arrangement makes the perovskite structure extremely flexible. Indeed, due to changes in the chemical nature of A and B cations as well as on temperature and pressure conditions, the ideal cubic symmetry is often lowered, and the resulting structure is described by a combination of tilts and distortion of the BO6 octahedra (Mitchell, 2002).
In this contribution, a series of case studies on the interplay among structural characterizations, coloration mechanisms, and technological prospects of ceramics with perovskite structure are outlined. Starting from the Crdoped (Y,REE)AlO3 (YAP) case, i.e. the only system manufactured at the industrial scale and currently used as ceramic red pigment (Ardit et al., 2016), the first case study (i.e., a X-ray powder diffraction and electronic absorption spectroscopy combined investigation) is focused on the effects due to the Al↔Cr substitution at the B octahedral site of the YAP structure, which cause a degree of structural relaxation around Cr3+ that, whether compared with other Cr-bearing structures, is relatively low (Cruciani et al., 2009). The concept of crystal field stabilization energy CFSE, closely related with that of structural relaxation (Burns, 1993), will lead to the second case study where in situ high-pressure synchrotron XRD measurements coupled with ab initio simulations of the electronic population of the orthorhombic NdCrO3 perovskite are compared with the compressional feature of NdGaO3 (high-tech ceramics applied as interconnector of solid oxide fuel cells (SOFC), substrate for high-Tc superconductors (HTSC), colossal magnetoresistive (CMR) film epitaxy, and so on). The different electronic configuration of octahedrally coordinated Cr3+ and Ga3+ ions that leads to a redistribution of electrons at the 3d orbitals for Cr3+ allows the CFSE at octahedral sites to act as vehicle of octahedral softening in NdCrO3 or it turns octahedra into rigid units when CFSE is null as in NdGaO3. The third (and last) case study deals with the first finding of a perovskite characterized by absence of changes in the octahedral tilting and a volume reduction with pressure exclusively controlled by an isotropic polyhedral compression (Ardit et al., 2017). A synchrotron structural investigation at high-pressure sets YAl0.25Cr0.75O3 as the prototype of the so-called locked-tilt perovskites. Besides to reveal a new P-T thermodynamic scenario in the world of perovskite compounds, such a freezing of the octahedral rotations offers a new (and antithetic, keeping in mind that oxygen rotations are strongly coupled to the functional properties of perovskite compounds) perspective on the research of new functional materials (e.g., ferroelectrics and multiferroics). For example, the mutual interaction between layers of octahedrally tilted perovskites subjected to an external perturbation can be easily tuned whether one of the layers is a locked-tilt perovskite.
Ardit, M., Cruciani, G., Dondi, M., Zanelli, C. (2016): Pigments based on perovskite. In: “Perovskites and related mixed oxides: Concepts and applications”, P. Granger, V. Parvulescu, S. Kaliaguine, W. Prellier, eds. Wiley-VCH, 259-288.
Ardit, M., Dondi, M., Cruciani, G. (2017): Locked octahedral tilting in orthorhombic perovskites: At the boundary of the general rule predicting phase transitions. Phys. Rev. B, 95, 024110.
Burns, R.G. (1993): Mineralogical application of crystal field theory. 2nd Ed. Cambridge University Press, 551 p.
Cruciani, G., Ardit, M., Dondi, M., Matteucci, F., Blosi, M., Dalconi, M.C., Albonetti, S. (2009): Structural relaxation around Cr3+ in YAlO3-YCrO3 perovskites from electron absorption spectra. J. Phys. Chem. A, 113, 13772-13778.
Mitchell, R.H. (2002): Perovskites: Modern and Ancient. Almaz Press., Thunder Bay, Ontario, 316 p
PEROVSKITES. FROM PIGMENTS TO MULTIFERROICS, TO THE DISCOVERY OF THE LOCKED-TILT PEROVSKITES
No full textSuperconductors, non-toxic inorganic pigments, sensitizers in dye-sensitized solar cells (DSSCs), semiconductors, and multiferroics are just a few examples of the broad range of uses for which ceramics with perovskite structure are employed. In its aristotype form the ABO3 perovskite structure is cubic (s.g. Pm-3m) with A cations located at the center of dodecahedral sites defined by a three-dimensional array of corner-sharing BO6 octahedra. This polyhedral arrangement makes the perovskite structure extremely flexible. Indeed, due to changes in the chemical nature of A and B cations as well as on temperature and pressure conditions, the ideal cubic symmetry is often lowered, and the resulting structure is described by a combination of tilts and distortion of the BO6 octahedra (Mitchell, 2002).
In this contribution, a series of case studies on the interplay among structural characterizations, coloration mechanisms, and technological prospects of ceramics with perovskite structure are outlined. Starting from the Crdoped (Y,REE)AlO3 (YAP) case, i.e. the only system manufactured at the industrial scale and currently used as ceramic red pigment (Ardit et al., 2016), the first case study (i.e., a X-ray powder diffraction and electronic absorption spectroscopy combined investigation) is focused on the effects due to the Al↔Cr substitution at the B octahedral site of the YAP structure, which cause a degree of structural relaxation around Cr3+ that, whether compared with other Cr-bearing structures, is relatively low (Cruciani et al., 2009). The concept of crystal field stabilization energy CFSE, closely related with that of structural relaxation (Burns, 1993), will lead to the second case study where in situ high-pressure synchrotron XRD measurements coupled with ab initio simulations of the electronic population of the orthorhombic NdCrO3 perovskite are compared with the compressional feature of NdGaO3 (high-tech ceramics applied as interconnector of solid oxide fuel cells (SOFC), substrate for high-Tc superconductors (HTSC), colossal magnetoresistive (CMR) film epitaxy, and so on). The different electronic configuration of octahedrally coordinated Cr3+ and Ga3+ ions that leads to a redistribution of electrons at the 3d orbitals for Cr3+ allows the CFSE at octahedral sites to act as vehicle of octahedral softening in NdCrO3 or it turns octahedra into rigid units when CFSE is null as in NdGaO3. The third (and last) case study deals with the first finding of a perovskite characterized by absence of changes in the octahedral tilting and a volume reduction with pressure exclusively controlled by an isotropic polyhedral compression (Ardit et al., 2017). A synchrotron structural investigation at high-pressure sets YAl0.25Cr0.75O3 as the prototype of the so-called locked-tilt perovskites. Besides to reveal a new P-T thermodynamic scenario in the world of perovskite compounds, such a freezing of the octahedral rotations offers a new (and antithetic, keeping in mind that oxygen rotations are strongly coupled to the functional properties of perovskite compounds) perspective on the research of new functional materials (e.g., ferroelectrics and multiferroics). For example, the mutual interaction between layers of octahedrally tilted perovskites subjected to an external perturbation can be easily tuned whether one of the layers is a locked-tilt perovskite.
Ardit, M., Cruciani, G., Dondi, M., Zanelli, C. (2016): Pigments based on perovskite. In: “Perovskites and related mixed oxides: Concepts and applications”, P. Granger, V. Parvulescu, S. Kaliaguine, W. Prellier, eds. Wiley-VCH, 259-288.
Ardit, M., Dondi, M., Cruciani, G. (2017): Locked octahedral tilting in orthorhombic perovskites: At the boundary of the general rule predicting phase transitions. Phys. Rev. B, 95, 024110.
Burns, R.G. (1993): Mineralogical application of crystal field theory. 2nd Ed. Cambridge University Press, 551 p.
Cruciani, G., Ardit, M., Dondi, M., Matteucci, F., Blosi, M., Dalconi, M.C., Albonetti, S. (2009): Structural relaxation around Cr3+ in YAlO3-YCrO3 perovskites from electron absorption spectra. J. Phys. Chem. A, 113, 13772-13778.
Mitchell, R.H. (2002): Perovskites: Modern and Ancient. Almaz Press., Thunder Bay, Ontario, 316 p
The ferroelastic phase transition in ZSM-5 zeolites: chemistry vs. thermodynamic
No full textNo abstract availabl
Micronization of ceramic pigments: the mineralogist’s viewpoint on comminution rate and amorphisation
No full textNo abstract availabl
The ferroelastic phase transition in ZSM-5 zeolites: chemistry vs. thermodynamic
No full textNo abstract availabl
Micronization of ceramic pigments: the mineralogist’s viewpoint on comminution rate and amorphisation
No full textNo abstract availabl
Micronization of ceramic colorants. From understanding to energy efficiency of the process
No full textWith over 16 billion m2 worldwide, in 2020 the ceramic industry marked a new record in tile production (Baraldi, 2021). Similarly, the global demand for ceramic pigments and dyes (ceramic colorants), driven by the ceramic tile industry, has also grown rapidly in the last decades leading to a growing need for raw materials and energy.
Nowadays, inkjet printing (IJP) with micronized inks has become the decoration technology par excellence for ceramic tile (Molinari et al., 2020). Through this technology, the finished product is no longer a powdered colorant, but a micronized colorant dispersed in a carrier, i.e., an ink that undergoes a high-energy stirring milling process where particles must have a median size (d50) of 300 nm to fulfill IJP requirements (Hutchings, 2010).
Being mainly dependent on the specific energy input (i.e., the energy supplied to the grinding chamber per mass of product), pigment micronization down to the requested particle size proves to be the most energy-consuming comminution process per unit weight of product (Wang & Forssberg, 2007). It follows that comminution of ceramic colorants is a key issue for ink production, which has strong repercussions on color strength, mechanical properties and resistance to amorphization of the colorants' crystal structure, as well as on the energy management of the entire process. On the other hand, a deep understanding of the comminution dependence on many of these aspects is still lacking.
In this contribution, the micronization effects on a set of five industrial ceramic colorants are thoughtfully investigated through a simulation of the industrial process at a pilot plant, where particle size distribution and energy consumption are monitored during the comminution process.
The combined analytical approach (i.e., X-ray diffraction, scanning electron microscopy, and diffuse reflectance spectroscopy) aided by a physical/semiempirical modelling of the colorants' elastic features versus the energy response of the particle reduction has yielded details on the nature of the micronization-induced microstructural changes in ceramic colorants.
The results obtained represent a fundamental development towards the optimization of the comminution process. A proper energy modulation allows to limit harmful emissions and save raw materials.
Baraldi L. 2021. World production and consumption of ceramic tiles. Ceram. World Rev., 143, 26-40.
Hutchings I. 2010. Ink-jet printing for the decoration of ceramic tiles: technology and opportunities. Proc. 12th World Congress on Ceramic Tile Quality, QUALICER, 1-16.
Molinari C., Conte S., Zanelli C., Ardit M., Cruciani G., & Dondi M. 2020. Ceramic pigments and dyes beyond the inkjet revolution: From technological requirements to constraints in colorant design. Ceram. Int., 46, 21839-21872.
Wang Y. & Forssberg E. 2007. Enhancement of energy efficiency for mechanical production of fine and ultra-fine particles in comminution. China Particuol., 5, 193-201
Polytypism of AlPO4•2H2O variscite
No full textVariscite (orthorhombic), a hydrated aluminophosphate with formula Al(PO4)•2H2O, and metavariscite (the monoclinic polymorph) are uncommon secondary minerals that are relevant in environmental applications and particularly in technological applications when synthesized in a dehydrated form. Although two orthorhombic modifications are known (so-called "Lucin-type" and "Messbach-type"), the fine-grained nature of the "Messbach-type" variscite has hampered determination of its crystal structure.In this contribution, the crystal structure of the latter (a natural specimen from Tooele County, Utah) has been solved and refined using X-ray powder diffraction data via ab initio charge-flipping methods and the Rietveld method. Our results, structural interpretations, and topological analysis demonstrate that the two orthorhombic structural modifications are polytypes, and we refer to them as variscite1O ("Lucin-type") and as variscite2O ("Messbach-type"), to be consistent with modern polytype terminology. The structure of variscite2O is similar to that of the 1O polymorph, with a doubling of the b unit-cell parameter. The variscite2O crystal structure contains two crystallographically independent Al3+ cations coordinated by two H2O molecules and four oxygen atoms of the PO4 groups. Two crystallographically independent PO4 tetrahedra share their corners with four adjacent AlO4(OH2)2 octahedra. Both orthorhombic polymorphs belong to the family of framework 3D MT structures in which octahedra (M) and tetrahedra (T) are linked by bridging O atoms, and topological analysis suggests that these two structures may be considered polytypes. Similarities between these polytypes, along with observed broadening of diffraction peaks of the Tooele material, suggest that interstratifications of the two forms may exist in nature. Besides the long-range characterization of the crystal structure by X-ray diffraction, information on the short-range structural properties of this mineral have been gained through 31P and 27Al MAS/NMR measurements. Results from NMR corroborate the crystal structure determination and they show distinct signals for each of the two independent P and Al positions in variscite2O. In addition, high-temperature XRD, thermal analyses, and NMR measurements clarified the nature of the transformation of variscite2O to the derivative AlPO4 structure. The crystal structure of this new anhydrous AlPO4 phase (AlPO4-variscite2O in analogy to its parent structure) can be described as a 3D framework of alternating AlO4 and PO4 tetrahedra linked by bridging O atoms. Thermogravimetric analyses revealed almost complete dehydration above ~450K, and NMR results were consistent with Al and P atoms located at tetrahedral sites
Micronization of ceramic colorants. From understanding to energy efficiency of the process.
No full textWith over 16 billion m2 worldwide, in 2020 the ceramic industry marked a new record in tile production (Baraldi, 2021). Similarly, the global demand for ceramic pigments and dyes (ceramic colorants), driven by the ceramic tile industry, has also grown rapidly in the last decades leading to a growing need for raw materials and energy.
Nowadays, inkjet printing (IJP) with micronized inks has become the decoration technology par excellence for ceramic tile (Molinari et al., 2020). Through this technology, the finished product is no longer a powdered colorant, but a micronized colorant dispersed in a carrier, i.e., an ink that undergoes a high-energy stirring milling process where particles must have a median size (d50) of 300 nm to fulfill IJP requirements (Hutchings, 2010).
Being mainly dependent on the specific energy input (i.e., the energy supplied to the grinding chamber per mass of product), pigment micronization down to the requested particle size proves to be the most energy-consuming comminution process per unit weight of product (Wang & Forssberg, 2007). It follows that comminution of ceramic colorants is a key issue for ink production, which has strong repercussions on color strength, mechanical properties and resistance to amorphization of the colorants' crystal structure, as well as on the energy management of the entire process. On the other hand, a deep understanding of the comminution dependence on many of these aspects is still lacking.
In this contribution, the micronization effects on a set of five industrial ceramic colorants are thoughtfully investigated through a simulation of the industrial process at a pilot plant, where particle size distribution and energy consumption are monitored during the comminution process.
The combined analytical approach (i.e., X-ray diffraction, scanning electron microscopy, and diffuse reflectance spectroscopy) aided by a physical/semiempirical modelling of the colorants' elastic features versus the energy response of the particle reduction has yielded details on the nature of the micronization-induced microstructural changes in ceramic colorants.
The results obtained represent a fundamental development towards the optimization of the comminution process. A proper energy modulation allows to limit harmful emissions and save raw materials.
Baraldi L. 2021. World production and consumption of ceramic tiles. Ceram. World Rev., 143, 26-40.
Hutchings I. 2010. Ink-jet printing for the decoration of ceramic tiles: technology and opportunities. Proc. 12th World Congress on Ceramic Tile Quality, QUALICER, 1-16.
Molinari C., Conte S., Zanelli C., Ardit M., Cruciani G., & Dondi M. 2020. Ceramic pigments and dyes beyond the inkjet revolution: From technological requirements to constraints in colorant design. Ceram. Int., 46, 21839-21872.
Wang Y. & Forssberg E. 2007. Enhancement of energy efficiency for mechanical production of fine and ultra-fine particles in comminution. China Particuol., 5, 193-201
Metallic spherules in silica glass from the Ries-Steinheim impact crater area: sign of the impactor?
No full textRiassunto presentato al V Forum italiano di Scienze della Terra, Geoitalia 2005, Spoleto, 21-23 settembre 2005
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