Cordierite Structure Research Articles

Plasma-catalytic Reactor for Decomposition of Chlorinated Hydrocarbons

The conversion of trichloromethane in mixtures with air was investigated under normal pressure in a gliding discharge (GD) reactor operated in both a homogeneous gas system and with a solid catalyst. The Pt catalyst supported by a honey-comb cordierite structure was placed in the reactor below the ends of the electrodes. Cl2 and HCl were the main products of the CHCl3 conversion. The presence of CCl4 was also noted. The influence of the electrode length and the distance between the electrodes in the narrowest section on CHCl3 conversion was examined. The Pt catalyst revealed some activity in the trichloromethane processing. This resulted in an increased overall CHCl3 conversion with the portion of CHCl3 converted to CCl4 smaller than that in the homogeneous system. The effect of temperature on CHCl3 conversion was found to be significant.

Acceptance of the Mineralogical Society of America Roebling Medal for 2007

Thank you, Jerry and Mike, for your generous remarks and for nominating me for this prestigious award. I also wish to thank the 2007 Roebling Medal Committee for selecting me. Jerry and Mike, I am happy to count you among my close friends, both personal and professional. I also want to thank you for organizing the incredible symposium in my honor yesterday (October 29, 2007). The 31 talks presented an exciting retrospective and prospective of many areas of the mineral sciences and made a remarkably positive statement about the health of this field in its broadest definition. What a stroke of luck it was for me to choose to attend Penn State for graduate study in 1965 rather than go to graduate school in inorganic chemistry at the University of North Carolina with Jim Collman, who is now a colleague of mine at Stanford. I also made the correct decision to accompany you, Jerry, from Penn State to Virginia Tech in 1966. I have fond memories of the two of us discussing linear algebra and matrix theory at your home in State College, Pennsylvania, walking to get a milkshake at the local drugstore or a salad at The Greeks in Blacksburg, Virginia, laughing our heads off at the 1967 George C. Scott film The Flim-Flam Man at the only movie theater in Blacksburg at that time, and taking your graduate classes, which were models of clarity and the best classes I ever had. Mike, I remember meeting you for the first time when you came to visit me in the summer of 1976 and we collaborated on the high-temperature crystal structure and thermal expansion of cordierite, and the way you responded to the nickname “Rookie” from my more senior graduate students at Stanford when you joined my research group for …

Dependence of the water content in channels of the cordierite structure on the composition of its Fe-Mg solid solutions

Dependence of the water content in channels of the cordierite structure on the composition of its Fe-Mg solid solutions

Cordierite (2MgO•2Al2O3•5SiO2) synthesis by unconventional methods

The cordierite was synthesized by two unconventional methods: 1) the method which uses hydrosilicate precursors and 2) the method which uses organic precursors. Comparison of these synthesis methods with the classical one is the main subject of the presented paper. The influence of Li2O on the cordierite phase formation was investigated too. The results have suggested that the method which uses hydrosilicate precursors provides the SiO2 linkage as magnesium metasilicate, but is not adequate for the cordierite synthesis. Only in the presence of Li2O considerably amount of the ?-cordierite modification was formed, confirming the mineralizing effect of this oxide. In addition, the results have clearly demonstrated that the method which uses organic precursors is suitable for the cordierite synthesis. Thus, even without mineralizer it can be used for the preparation of the almost pure ?-cordierite at 1200?C. Because of that this method was used to obtain pigments with cordierite structure, in which Al3+ was partially substituted with Cr3+ (pink pale colour), and Mg2+ was partially substituted with Co2+ (blue colour).

Effect of Ni substitution on the microwave dielectric properties of cordierite

Cordierite (Mg 2Al 4Si 5O 18) is one of the silicates with low dielectric constant ( ɛ r), which are expected for good candidate of millimeter wave dielectrics. Microwave dielectric properties of Ni substituted cordierite solid solutions; (Mg 1− x Ni x ) 2Al 4Si 5O 18 have been investigated. (Mg 1− x Ni x ) 2Al 4Si 5O 18 with no secondary phase was obtained in the compositions x range from 0 to 0.1. It was found that a very small amount of Ni substitution was effectively increased of the quality factor ( Qf) value and the highest Qf value of 99,110 GHz was obtained in the composition x = 0.1. No remarkable composition dependence of the temperature coefficient of resonance frequency ( τ f) was observed in the range from x = 0.05 to 0.2, On the other hand, τ f abruptly shifted toward negative value with increasing x from 0.3 to 0.5. The correlation between the crystal structure of cordierite and the microwave dielectric properties, particularly Qf is discussed.

Pd and Pt catalysts supported on carbon-coated monoliths for low-temperature combustion of xylenes

Carbon-coated monoliths were prepared from polyfurfuryl alcohol coated cordierite structures obtained by dip-coating. In this way, thin, homogeneous, consistent and good adhered carbon layers were obtained. The different steps followed in the preparation of these catalyst supports were studied by scanning electron microscopy. Pd and Pt catalysts were prepared by equilibrium impregnation of the monolithic supports with an aqueous solution of the corresponding tetraammine metal (II) nitrates. The catalysts were pretreated in H 2 at 300 °C before their characterization by chemisorption or before testing their catalytic activity. This pretreatment was monitored by temperature programme reduction. Catalytic activities in xylene combustion were evaluated as a function of the reaction temperature as well as against time on stream. The monolithic catalysts were thermally stable during the reaction. The Pt catalysts were more active than the Pd ones. The Pd catalysts with smaller Pd-particle sizes were more active. In the case of Pt catalysts however, the opposite was observed, which might be due to a structure sensitivity effect. Complete xylene combustion was reached in the range between 150 and 180 °C with a total selectivity to CO 2 and H 2O. Combustion of m-xylene was easier than p-xylene over Pt.

Experimental study on incorporation of C-H-O-N fluid components in Mg-cordierite

Experiments on cordierite saturation with “dry” methane, ammonia and the components of H 2 O-CH 4 and H 2 O-NH 3 binary mixtures were performed at 50, 150, 200 MPa in the temperature range from 400 to 800°C to examine the possibility of using Mg-cordierite as an indicator of fluid regime in mineral genesis. We checked that the starting product was free from fluid components at the sensitivity level of the IR and chromatographic methods. Powders with particle size 25–50 μ were used. The run time was 300 h in all the experiments. The typical bands observed in the IR and Raman spectra demonstrate the presence of fluid molecules in the channels. The partition coefficients of CH 4 , NH 3 , and H 2 O between the fluid phase and Mg-cordierite are temperature independent according to the mass spectrometry data. In “dry” systems, small quantities of H 2 O (up to 0.6 mol.%) are formed by reactions between ammonia and the framework oxygen of the cordierite structure. Thus, the occurrence of water in the structural channels of cordierite does not always mean that water is present in the fluid.

Density Functional Calculation on the Structure of Cordierite

Density Functional Calculation on the Structure of Cordierite

Density Functional Calculation on the structure of cordierite

Density functional theory calculations were performed to analyze atomic and electronic structures of cordierite. The most stable configuration of Al and Si atoms in the six-membered ring of a unit cell was decided by geometry optimizations for sixteen different initial structures. A correlation was observed between the number of Al-O-Al bonds in a unit cell and the lattice energy. We concluded that the number of Al-O-Al bonds is a determining factor of the lattice stability. The structural parameters of the most stable crystal structure obtained by geometry optimization agreed well with the experimental observation. According to the distribution of atomic charges and analysis of bond order, the followings were clarified: (i) the covalent bond in a T1 tetrahedron was stronger than that in a T2 tetrahedron, (ii) the covalent bond of a cation in six-membered ring with O atoms in a T1 tetrahedron was the weakest, and (iii) Mg in the cordierite is of ionic nature.

Crystal structure of the Na-, Ca-, Be-cordierite and crystallochemical regularities in the cordierite—sekaninaite series

The crystal structure of the beryllium-rich cordierite [(Na0.28Ca0.19)(H2O)0.92](Mg1.86Fe 0.14 22− ) · { Al3.39Be0.61Si5O18} was established by X-ray diffraction analysis (IPDS Stoe diffractometer, λMoKα radiation, graphite monochromator, 2θmax = 65°, R = 0.0186 for 1378 reflections): a = 16.850(3), b = 9.729(2), and c = 9.298(2) A; V = 1524.3(4) A3, sp. gr. Cccm, Z = 4, and ρcalcd = 2.655 g/cm3. The numbers of Mg and Fe atoms isomorphously occupying the octahedral positions, Al and Be atoms in tetrahedra, and Na and Ca atoms and H2O molecules in the framework cavities are refined. The hydrogen atom is localized and its coordinates and thermal displacement parameters are refined. Based on the comparative crystallochemical analysis of cordierites from different locations and origins, the regularities relating the unit-cell parameters b and c and the distortion index to the features of the chemical composition of the minerals under study are shown.

Cordierite IV: structural heterogeneity and energetics of Mg?Fe solid solutions

The local structural heterogeneity and energetic properties of 22 natural Mg-Fe cordierites, ideal formula (Mg,Fe)(2)Al4Si5O18.x(H2O,CO2), were investigated at length scales given by powder infrared spectroscopy (IR) and also by published electronic absorption spectra. The studied samples have iron mole fractions from X-Fe = 0.06 to 0.82 and cover most of the Mg-Fe cordierite binary. Variations in wavenumbers and line widths of the IR bands were determined as a function of composition. Most modes shift linearly to lower wavenumbers with increasing X-Fe, except those at high wavenumbers located between 900 and 1,200 cm(-1). They are vibrations that have a large internal (Si,Al)O-4 character and are not greatly affected by Mg-Fe exchange on the octahedral site. The lower wavenumber modes can be best characterized as lattice vibrations having mixed character. The systematics of the wavenumber shifts suggest small continuous variations in the 'average' cordierite structure with Mg-Fe exchange and are consistent with an ideal volume of mixing, DeltaV(mix)= 0, behavior (Boberski and Schreyer 1990). IR line broadening was measured using the autocorrelation function for three wavenumber regions in order to determine the range of structural heterogeneity between roughly 2 and 100 Angstrom (0.2-10.0 nm) in the solid solution. In order to do this, an empirical correction was first made to account for the effect that small amounts of channel Na have on the phonon systematics. The results show that between 1,200 and 540 cm(-1) the line widths of the IR bands broaden slightly and linearly with increasing X-Fe. Between 350 and 125 cm(-1) nonlinear behavior was observed and it may be related to dynamic effects. These results suggest minimal excess elastic enthalpies of mixing for Mg-Fe cordierite solid solutions. Channel Na should affect measurably the thermodynamic properties of natural cordierites as evidenced by variations in the IR spectra of Na-containing samples. Occluded H2O (Class I) and CO2 should have little interaction with the framework and can be considered nearly 'free' molecules. They should not give rise to measurable structural heterogeneity in the framework. The contribution of the crystal field stabilization energy (CFSE) of octahedral Fe2+ to the energetics of Mg-Fe cordierites was also investigated using published electronic absorption spectra (Khomenko et al. 2001). Two bands are observed between 8,000 and 10,500 cm(-1) and they represent electronic dd-excitations of octahedral Fe2+ derived from the T-5(2g) --> E-5(g) transition. They shift to higher wavenumbers with increasing X-Mg in cordierite. An analysis gives slightly asymmetric excess -DeltaCFSE across the Mg-Fe cordierite join with a maximum of about -550 J/mole towards iron-rich compositions.

Zr budgets for metamorphic reactions, and the formation of zircon from garnet breakdown

AbstractThe construction of zirconium (Zr) budgets for metamorphic reactions in high-grade rocks provides new insight into zircon growth during metamorphism. In this study we target reactions involving garnet, as they enable zircon growth to be related to known pressure and temperature conditions. Two reactions involving the breakdown of Zr-bearing garnet from Rogaland, SW Norway have been investigated in detail, showing contrasting behaviour of Zr, with zircon formation being subject to the solubility of Zr in product phases. In the decompression reaction garnet + sillimanite + quartz → cordierite, Zr released during garnet breakdown cannot be incorporated into the cordierite structure, resulting in zircon nucleation and growth. In contrast, for the reaction garnet + biotite + sillimanite + quartz → osumilite + orthopyroxene + spinel + magnetite, no new zircon growth takes place, despite the garnet involved containing more than double the Zr concentration of the former reaction. In the latter case, all the Zr released by garnet breakdown can be detected in the product phases osumilite and orthopyroxene, thereby preventing growth of new metamorphic zircon. This study highlights the potential for high resolution geochronology in metamorphic rocks by relating zircon growth to specific metamorphic reactions.

Cordierite honeycomb structures formed by reduction extrusion processing

Cordierite honeycomb structures formed by reduction extrusion processing

Aliphatic hydrocarbons in structural channels of cordierite; a first evidence from polarized single-crystal IR-absorption spectroscopy

Polarized IR-absorption spectra were measured on inclusion-free spots, 50 μm in diameter of (100)-, (010)-, and (001)-oriented single-crystal plates of orthorhombic cordierites extracted from anatectic granitoids and their pegmatite from the western part of the Ukrainian shield. In the range 3100-2700 cm -1 , the spectra display four weak (α lin ≤ ca. 7 cm -1 ) and sharp (∆ν 1/2 ≅ 20 cm -1 ) bands typical of the antisymmetric and symmetric stretching modes of CH 3 - and -CHH 2 - groups of aliphatic hydrocarbons, C n H 2n+2 (ν as,CH₃ at 2951-2959 cm -1 , ν as,CH₂ at 2920-2923 cm -1 , ν sym,CH₃ at 2871-2874 cm -1 , ν sym,CH₂ at 2850-2851). All bands are polarized in the ac-plane of orthorhombic cordierite. In the temperature range 123 ≤T (K) ≤573, the degree of polarization decreases as temperature increases. The band polarizations and their temperature dependence ensure that the hydrocarbons are incorporated in the cordierite matrix, i.e., in the ca. 5.8 Å wide cavities of the c-parallel channels of the crystal structure. The concentrations of alkanes, C n H 2n+2 from band intensities, are between about 20 and about 100 ppm, corresponding to about 0.7·10 -3 and about 2.3·10 -3 molecules per formula unit cordieriite. Evaluation of the averaged intensities of the antisymmetric as well as symmetric C-H stretching vibrations of either species, CH 3 - and -CH 2 - , yields a ratio of 1:1 between them consistent with n = 4 only, realized in butane C 4 H 10 or in a butane-rich mixture with n = 4 on average and concentrations between 0.7 × 10 -3 to 2.3 × 10 -3 molecule pfu. Polarizations as well as molecular and cordierite-cavity sizes are consistent with an allocation of butane molecules in the channel cavities of the cordierite structure, with the molecular axes of butane predominantly parallel to b.

New hypotheses on the mechanism of the deterioration of cordierite diesel filters in the presence of metal oxides

It is well known that the durability of the honeycomb structures made of cordierite, used as filters for diesel exhaust emissions, is affected by some components of the soot which can react with cordierite during regeneration cycles at high temperature (up to 1000 °C). Amongst all the components of the soot, sodium is particularly dangerous because of its destructive effect on the cordierite structure. The interaction between sodium carbonate and cordierite has been studied by means of FTIR spectroscopy and the following statements can be made: even if very slowly, the attack on cordierite has already begun at 500 °C and proceeds very quickly onwards from 600 °C; an amorphous phase is formed at 700 °C; at higher temperature, the amorphous phase crystallizes releasing sodium which, during cooling, reacts with carbon dioxide, yielding again sodium carbonate; this carbonate will act as sodium source in the following thermal regeneration cycles. During this study it has also been shown that the first attack is not determined by the sodium ion diffusion into the pseudo-zeolitic channels of the cordierite lattice.

Synthesis and structural characterization of Cu I and Cu II-doped cordierites

The possible diffusion and localization of copper in hexagonal cordierite structure, either by Cu 1 insertion within the hexagonal channels or by Cu II substitution for Mg in octahedral sites have been studied. Limited amounts of Cu I (about 30% of theoretical values) can be inserted within the cordierite channels in statistically occupied 4e sites (0, 0, z with z = 0.06 and 0.10 respectively for Cu 0.5Mg 2Al 4.5Si 4.5O 18 and CuMg 2Al 5Si 4O 18). Cu 2+/Mg 2+ substitution is limited by the competitive formation of mullite and spinel phases.

Deterioration of cordierite honeycomb structure for diesel emissions control

The durability of cordierite honeycomb structure for automotive emissions control is strongly affected by the presence of some pollutants on the trap walls during the high temperature step of filter regeneration. The short-term interaction between cordierite and some single pollutant oxides (Na 2 O, CaO, ZnO, PbO, Fe 2 O 3 , V 2 O 5 ) has been investigated by differential dilatometry, XRD, IR spectroscopy and SEM. There is evidence that the pollutant ions diffuse into the cordierite lattice. The formation of new phases and surface etching have often been observed; the appearance of new phases having a thermal expansion coefficient different to that of the pure cordierite is responsible of a diffuse microcracking, particularly in the sample polluted by sodium oxide. At 900°C all the pollutants except Fe 2 O 3 strongly etch the cordierite; particularly dangerous is the presence of sodium or lead oxides which are able to completely destroy the cordierite structure. Die Beständigkeit der zellenförmigen Struktur von Cordierit-Filtern, die für die Kontrolle der Abgase von Vergasermotoren verwendet werden, ist von der Gegenwart verschiedener Verunreinigungen beeinflußt, welche sich an den Wänden des Filters absetzen und mit ihnen bei den hohen Temperaturen der Regenerierung des Filters reagiren. Die kurzfristige Wechselwirkung zwischen Cordierit und einphasigen Verunreinigungen (Na 2 O, CaO, ZnO, PbO, Fe 2 O 3 , V 2 O 5 ) wurde durch Differenzialdehnungsmessung, Infrarotspektroskopie und Rasterelektronenmikroskopie untersucht. Die Untersuchung zeigt vor allem die Oberflächen-Angriffserscheinungen des Filters, aber auch die Diffusion der Verunreinigungsione in das Gitter des reinen Cordierit und die Bildung neuer Kristallinphasen. Nachdem die letzteren einen anderen Wärmeausdehnungskoeffizent haben als der Cordierit sind sie für die verbreiteten Mikrorisse verantwortlich, dies wird ganz besonders deutlich bei Na 2 O-verunreinigten Strukturen. Es wurde beobachtet, daß alle Verunreiniger außer Fe 2 O 3 von 900°C an den Cordierit mit Sicherheit angreifen. Die gefährlichsten Verunreiniger sind jedoch Na 2 O und PbO, weil sìe zur vollkommenen Zerstörung der Cordieritstruktur führen. La durabilité de la structure à nid d'abeille à base de cordiérite utilisée pour le contrôle des émissions automobiles est affectée par la présence sur les parois du filtre des différents polluants, pendant les cycles thérmiques de régénération à haute température. L'interaction à court terme entre la cordiérite et chaque pollutant (Na 2 O, CaO, ZnO, PbO, Fe 2 O 3 , V 2 O 5 ) a été étudiée par dilatomètrie differentielle, diffraction des rayons X, spectroscopie IR et MEB. La diffusion des ions polluants dans le réseau de la cordiérite a été mise en évidence; la formation de phases nouvelles et phénomènes d'attaque superficielle ont été observés. Les nouvelles phases ayant un coefficient de dilatation thermique different de la cordiérite pure sont responsable de la microfissuration diffuse, surtout evidente dans l'échantillon pollué par l'oxyde de sodium. A l'exception du Fe 2 O 3 , à partir de 900°C, tous les polluants attaquent fortement la cordiérite; particulièrement dangereux sont l'oxyde de sodium et l'oxyde de plomb, qui détruisent completement la structure de la cordierite.

Influence of the size of the alkali ion on the thermal expansion of alkali-doped cordierites: A powder neutron diffraction study

Abstract The crystal structure of hexagonal cordierite with the formula Cs0·5Mg2Al4·5Si4·5O18 has been determined at 20, 275, 550 and 825°C by powder neutron diffraction. The mechanism of thermal expansion has been analysed and compared to that of its potassium homologue. The substitution of Cs for K results logically in an increase of the unit cell volume but in a decrease of the distortion and of the volume of the T(1)O4 tetrahedra, and therefore in an opposite response of the tetrahedral network to the thermal expansion of the MgO6 octahedra. As a consequence, the compensation of the increase in the a-parameter by a decrease in the c-parameter, observed for pure and K-doped cordierites, is no longer observed with the Cs0·5-cordierite.

Fluid inclusions in granulite-facies metapelites of the Hercynian ancient lower crust of the Serre, Calabria, Southern Italy

Investigations of fluid inclusions in granulitefacies metapelites of southern Calabria enable characterization of the fluid composition of these lower crustal rocks, and constrain the petrologically deduced retrograde P-T path characterized by isothermal uplift prior to isobaric cooling in middle crustal levels. Fluid inclusions in cordierite, garnet and sillimanite have a CO2-rich composition. Inclusions in cordierite rarely contain minor amounts of N2 and H2O, and in garnets some CO2−CH4−N2 inclusions have been analyzed by Raman microprobe. Quartz reveals the most complex fluid melusion compositions (1) CO2-rich, (2) CO2−CH4−N2, (3) CH4−N2, (4) H2O−MgCl2−CaCl2−NaCl, (5) H2O−NaCl and (6) H2O−CO2. The earliest fluid inclusions after peak metamorphism are rich in CO2 with minor amounts of N2 and H2O. An early CO2−(H2O−N2) fluid composition has been confirmed by detection of CO2, H2O and N2 in the channels of the cordierite structure. Most of the early CO2-rich fluid inclusions were modified during the uplift from the lower to the middle crustal level, resulting in a density decrease with CO2 still dominant. The subsequent isobaric cooling led to further modifications of the fluid inclusions. High-density inclusions around implosion textures or scattered amongst lower-density ones must have formed during this cooling episode. Aqueous inclusions in quartz are mostly formed late and are consistent with trapping during retrograde rehydration.

Pigments having a cordierite type structure

Pigments having a cordierite type structure