BaO Content Research Articles

The carbonate fraction in carbonatitic Italian lamprophyres

Alkaline and ultramafic lamprophyres represent the majority of pre-Pleistocene alkaline mafic magmatic activity in Italy and have been described from several localities. The age of magmatism ranges from Triassic to Lower Oligocene. Some contain appreciable amounts of carbonate. The primary carbonate of the Italian carbonatitic lamprophyres is mainly Sr- or Mn-rich calcite that occurs mostly as immiscible ocelli or as groundmass. Its textural occurrence, composition, and relationship with co-precipitating silicate phases is taken as evidence of an igneous origin. Low BaO and REE contents in the carbonate are explained by early crystallization of essential mica and subordinate apatite. Whole rock analyses and isotopic data (Rukhlov, A.S., Bell, K., Vichi, G., Stoppa, F., submitted for publication. The heterogeneous deep mantle: the Sr, Pb and Nd isotopic evidence from Early Cretaceous alkaline lamprophyres of Southern Tuscany, Italy. Lithos.) suggest a mantle origin for these rocks and rule out contamination in either high or low pressure regimes. The bulk compositions of the carbonatitic lamprophyres have high HFSE / LILE and LREE / HREE ratios and although the abundances of these elements are generally lower than for carbonatites s.s., they are comparable with the abundances in other ‘carbonate-free’ Italian lamprophyres and Italian carbonatites, suggesting similar mantle sources. Moreover, the age of the Italian lamprophyres, ranging from Middle Triassic to Lower Oligocene, is much greater than the Pleistocene age of Italian carbonatites and indicates that the source remained similar over a long time span.

Effect of Barium Content and Sample Size of BaO2−MgO Oxygen Acceptor on Reaction Rate

The BaO−BaO2 reaction cycle was investigated in a range of temperatures from 973 to 1123 K and oxygen pressures from 0 to 0.2 MPa using the BaO2−MgO oxygen acceptor of different barium content and sample size prepared with barium peroxide and magnesium oxide. The rates of the oxidation of barium oxide and the reduction of barium peroxide by the BaO2−MgO oxygen acceptor during repeated cycling were little influenced by pellet sizes smaller than 16 mm in diameter, and an increase in the barium content of the sample led to a decrease in the reaction rate, while oxygen loading of the oxygen acceptor increased. In addition, fairly high reaction rates were obtained for the BaO2/MgO at ratios up to 1:1.4 (mol). The application of the BaO−BaO2 reaction cycle to oxygen production or enrichment with regard to operation mode and conditions was also investigated using the BaO2−MgO oxygen acceptor.

PELLETIZATION OF HETEROGENEOUS IRON CONCENTRATES FOR BLAST FURNACE OPERATIONS

High barite iron ore of the El-Gedida region (eastern desert in Egypt) contains a high BaO content even after beneficiation. The high BaO content of such anore limits its use as a blast furnace feed charge. Blending this oxidized iron ore with another heterogeneous iron concentrate containing less BaO content for blast furnace operations was the objective of this investigation. The effect of such blending on the productivity and mechanical properties of green, dried and fired pellets formed from such mixtures was investigated. The effect of blending on the chemical composition, total porosity, reducibility and kinetics of reduction of these pellets was also studied. The results indicated that pellets formed from a feed charge of high barite hematitic iron concentrate partially replaced with 30% reduced Wadi Kareem iron concentrate showed acceptable mechanical properties with an appropriate chemical composition. The kinetics study revealed that the mechanism of reduction was controlled by a mixed mechanism for 50% reduction degree changing to chemical reaction control mechanism for 80% reduction degree.Le minerai de fer, à haute teneur en baryte, de la région de El-Gedida (désert oriental, en Égypte) a une teneur élevée en BaO même après concentration. La teneur élevée en BaO d’un tel minerai limite son utilisation comme charge d’alimentation du haut-fourneau. L’objectif de cette investigation consistait à mélanger ce minerai de fer oxydé avec un autre concentré de fer hétérogène contenant moins de BaO pour opérations de haut-fourneau. On a évalué l’effet d’un tel mélange sur la productivité et les propriétés mécaniques de boulettes crues, séchées et cuites, formées à partir de tels mélanges. On a également étudié l’effet du mélange sur la composition chimique, la porosité totale, la réductibilité et la cinétique de réduction de ces boulettes. Les résultats indiquaient que les boulettes formées à partir d’une charge d’alimentation de concentré de fer hématitique à haute teneur en baryte partiellement remplacé par 30% de concentré de fer réduit de Wadi Kareem montraient des propriétés mécaniques acceptables avec une composition chimique appropriée. L’étude cinétique a révélé que le mécanisme de réduction était contrôlé par un mécanisme mixte avec un degré de réduction de 50% se changeant en un mécanisme de contrôle de la réaction chimique avec un degré de réduction de 80%.

Compositional dependence of ultraviolet fluorescence intensity of Ce3+ in silicate, borate, and phosphate glasses

Fluorescence spectra of Ce3+ ions in silicate, borate, and phosphate glasses melted in Ar were measured. The relative fluorescence intensity of Ce3+ in the ultraviolet region increased in the order of R=Ba, Ca, Sr, and Mg in the 20Li2O–20RO–60SiO2 glass samples and with decreasing BaO content in the BaO–B2O3 glass samples, respectively. In contrast, the relative fluorescence intensity of Ce3+ did not change with varying the glass composition in phosphate glass samples. The compositional dependence of the relative fluorescence intensity of Ce3+ is discussed in terms of redox reaction of Ce3+–Ce4+ in oxide glasses.

Ionic conductivity of Li 2O–BaO–Bi 2O 3 glasses

Dc and ac conductivities of Li 2O–BaO–Bi 2O 3 glasses have been studied in a temperature range of 263–523 K and a frequency range of 10 Hz–2 MHz and have been compared with those of binary Li 2O–Bi 2O 3 glasses. The frequency dependent conductivity has been studied employing both the modulus and conductivity formalisms. We have observed small changes in the dc conductivity and its activation energy from those of the binary glass when content of BaO is small. However we have observed noticeable changes in the conductivity and the activation energy when BaO content is large. The significant changes in the values of the non-exponential parameter and the power-law exponent of the ac electrical properties have been observed due to introduction of BaO in the lithium bismuthate glasses. The existing relation between the power-law exponent and the non-exponential parameter was also violated in the present glass compositions.

Role of Pt-precursor on the performance of Pt/BaCO3/Al2O3·NOx storage catalysts

Monolith Pt/BaCO 3 /Al 2 O 3 NO x storage catalysts were prepared using one of the following platinum precursors for each catalyst: (i) hexachloroplatinic acid [H 2 Pt(Cl) 6 ], (ii) tetraammineplatinum hydroxide [Pt(NH 3 ) 4 (OH) 2 ], (iii) diammineplatinum nitrite [Pt(NH 3 ) 2 (NO 2 ) 2 ] and (iv) platinum nitrate [Pt(NO 3 ) 2 ]. The Pt dispersion is strongly affected by the interaction between the Pt complex and the BaCO 3 /γ-Al 2 O 3 surface during the Pt impregnation. The influence of the choice of platinum precursor on the catalytic performance of Pt/BaCO 3 /Al 2 O 3 NO x storage catalysts was studied. The precursors used in the preparation of the catalysts were: (i) hexachloroplatinic acid [H 2 Pt(Cl) 6 ], (ii) tetraammineplatinum hydroxide [Pt(NH 3 ) 4 (OH) 2 ], (iii) diammineplatinum nitrite [Pt(NH 3 ) 2 (NO 2 ) 2 ] and (iv) platinum nitrate [Pt(NO 3 ) 2 ]. The catalytic activity of the prepared catalysts was tested for continuous lean NO x reduction with C 3 H 6 , NO x storage and reduction, and NO 2 dissociation in a flow reactor. The reactor experiments show that the sample prepared using platinum nitrate is the most active catalyst followed by the catalyst prepared from tetraammineplatinum hydroxide. The catalyst prepared from hexachloroplatinic acid is more active for continuous NO x reduction, and NO x storage and reduction than the catalyst prepared from diammineplatinum nitrite, but deactivates faster during NO 2 dissociation than the catalyst prepared using diammineplatinum nitrite. In order to be able to predict mechanisms for the interaction between the platinum precursors and the BaCO 3 /Al 2 O 3 surface during the platinum impregnation, powder samples of γ-Al 2 O 3 , BaCO 3 and BaCO 3 precipitated on γ-Al 2 O 3 were studied using FTIR and zeta potential measurements. Additionally, XRD measurements were performed to verify the transformation of the barium precursor to BaCO 3 . The results from these studies show that up to 18% BaO content, the BaCO 3 /Al 2 O 3 surfaces contain domains of both BaCO 3 and Al 2 O 3 .

The morphology and chemistry of K-feldspar megacrysts from Ikizdere Pluton: evidence for acid and basic magma interactions in granitoid rocks, NE–Turkey

Ikizdere Pluton consists of granite, granodiorite, tonalite, monzonite, quartz monzonite containing pinkish colored K-feldspar megacrysts (KFMs). The crystal sizes of the KFMs range from 1 to 4 cm. The lath-shaped megacrysts are uniformly (i.e., randomly) distributed in the host plutonic rocks and have mafic and felsic inclusions whose crystal sizes are smaller than 1 mm. The crystal inclusions are biotite, slightly annitic in composition with X Mg[=Fe tot/(Fe tot+Mg)]=0.50–0.58, amphibole (magnesio-hornblende, X Mg[=Mg/(Mg+Fe tot)]=0.70–0.79), iron-titanium oxide (low titanium magnetit and ilmenite), plagioclase (Ab 75−25An 65−35) and as minor quartz. The compositions of the KFMs range from Or 95Ab 5An 0 to Or 82Ab 17An 1. BaO contents of the megacrysts increase from core to rim. The mafic and felsic inclusions are compositionally similar those of the host rocks. The chemical and textural features of K-feldspar are typical for megacrysts that grew as phenocrysts in dynamic granitoidic magma systems. The overgrowth of KFMs and mafic magma injections (magma mixing) may be related to temperature, pressure and compositional fluctuations in the magma chamber. Remnant of earlier formed K-feldspar crystals remain in the felsic magma system, while the mafic injection can decompose some earlier precipitated KFMs. The remnant of K-feldspar remaining after mafic injection are overgrown by rapid diffusion of Ba, K and Na elements in liquid phase, during the later stages of crystallization of the host magma.

Effect of Cation Nonstoichiometry on the Properties of Solid Electrolyte BaxCe0.97Nd0.03O3 – (0.90 x 1.10)

The effect of the cation nonstoichiometry on the electroconduction, electrotransfer, and stability in humid air of solid proton-conducting electrolyte Ba x Ce0.97Nd0.03O3 - δ (0.90 ≤ x ≤ 1.10) is studied. The electroconduction is found to decrease with decreasing content of BaO (x ≤ 1.0) and weakly depend on the BaO excess (x> 1.0). Ceramics of a stoichiometric composition (x = 1) and with lack of barium is stable when stored in humid air at room temperature, as opposed to the ceramics with barium excess, which rapidly decomposes in these conditions. The conduction of materials under study in oxidizing environment is ion-hole and in reducing media, ionic (proton + oxygen). The cation nonstoichiometry barely affects the nature of the ion transfer. An analysis of possible models for the formation of defects shows oxygen vacancies to be always present in Ba x Ce0.97Nd0.03O3 - δ, even at the CeO2 excess exceeding the content of neodymium.

Modelling of NO x adsorption over NO x adsorbers

Modelling of the phenomena involved during the adsorption of NO x on NO x trap catalysts was developed. The aim of the model is the prediction of the quantity of stocked barium nitrate as well as the emissions of NO and NO 2, as a function of time and temperature. The mechanism of the process is sounded on the adsorption of gas species (NO, NO 2, O 2) on platinum sites, equilibrium reaction between adsorbed species followed by the formation of Ba(NO 3) 2. This formation of barium nitrate is limited by the thermal decomposition reaction which liberates NO in the gas phase. The kinetic constant of decomposition of barium nitrate was determined by temperature programmed thermogravimetry on pure Ba(NO 3) 2, using the method of Freeman and Carroll. Other kinetic constants bound to the mechanism were estimated by fitting the results of the model to experimental results. The mechanism was validated for various values of the molar fraction of O 2, the molar fraction of NO and various values of the NO/NO 2 ratio in the gas entering the reactor. It was also tested with different catalyst compositions (variation of the platinum and BaO concentrations). The importance of oxygen in the process was clearly demonstrated as well as the promoting role of NO 2.

Barium-rich sanidine megacrysts from the West Eifel (Germany)

Sanidine megacrysts are erupted together with syenitic and phonolitic debris in a Quaternary carbonatite diatreme located within the West Eifel volcanic field (Germany). The sanidines have a limited compositional range (Or 7 0 - 8 0 ), which overlaps with that of sanidine phenocrysts from syenite and phonolite xenoliths from the same diatreme. The sanidines have BaO contents of c. 1 wt.%, low total REE, but large positive Eu anomalies (Eu/Eu* = 7.5-9.2). A contrast in xenocryst population between the carbonatite-phonolite diatreme and a neighbouring nephelinite volcano provides an insight into mineral stability regions. The key difference is sanidine from the carbonatite-phonolite diatreme and phlogopite from the nephelinite volcano. Both minerals are major potassic phases and have a significant Ba content. A subsolidus transition from phlogopite to feldspar stability is known to occur at around 25 kbar, indicating a maximum depth for the felsic rocks. Isotopically the felsic rocks are distinct from the nephelinite and carbonatite rocks and preclude a cogenetic relationship. Therefore the felsic rocks are thought to be derived either by interaction between lower crustal rocks and nephelinite, or they represent the crystallisation products of exotic silicic melts in the upper mantle.

DC conductivity and hopping mechanism in V2O5–B2O3–BaO glasses

The dc electrical conductivity of 60 V 2 O 5 -(40 - x)B 2 O 3 -xBaO (x = 15, 20, 25, 30 and 40 mol%) glasses is reported in the temperature range 300-523 K. The physical and transport properties such as density, number of ions per unit volume, hopping distance, polaron radius and activation energy are reported. The electrical data are analysed in the light of the models of polaronic hopping conduction. The analysis shows that the high-temperature conductivity is well explained by polaronic models. The methods suggested by Holstein and by Sayer and Mansingh are applied to the determination of adiabatic or nonadiabatic hopping conduction. It is observed that in this system nonadiabatic hopping conduction is present. The hopping distance evaluated as 3.479-3.831 A increases with decreasing BaO content. The values of the decay constant and the density of states are reasonable for the localized states.

Electrical Conductivity in Mixed Calcium and Barium Iron Phosphate Glasses

The electrical properties of xCaO–(20 — x)BaO–20Fe2O3–60P2O5 glasses with x = 0, 5, 10, 15 and 20 mol% have been studied in the frequency range 400 Hz–200 kHz and over a temperature range 323–593 K. The ac conductivity as a function of temperature was divided into two domains, one where the absolute magnitude of the ac conductivity was close to the dc conductivity and another where it was larger than the dc conductivity. At the same temperature, the dc conductivity varied only slightly in glasses with different CaO and BaO content. It is concluded that the conductivity in these mixed CaO and BaO iron phosphate glasses is electronic and depends upon the Fe2+/(Fe2+ + Fe3+) ratio. In the high-temperature region above θD/2 (where θD is the Debye temperature) the Mott model of small polaron hopping (SPH) between nearest neighbours is consistent with the conductivity data, while at low temperature (below θD) the Greaves intermediate variable-range hopping (VRH) model is found to be appropriate. The electrical conduction of the glasses is confirmed to be non-adiabatic SPH. Mössbauer spectral analysis indicates the presence of both Fe2+ and Fe3+ ions.

Resistência química de vitro-cerâmicos pertencentes a sistemas Li2O-ZrO2-BaO-SiO2 frente ao tratamento com soluções ácidas e básicas

The chemical durability of the Li2O-ZrO2-BaO-SiO2 system was examined by determination of the Vickers hardness. The dependence of hardness and of the chemical resistance with BaO addition was investigated. The experimental results indicate that the hardness increases with the BaO content. The samples surface's morphology submitted to the chemical treatment in acidic (H2SO4) and basic (KOH) solution was accompanied by scanning electron microscopy. The chemical durability of the materials with BaO showed better than the glass ceramic without this content. These materials treated with H2SO4 solution showed a preferential attack to the silica rich sites.

Structure of (45− x)Na 2O– xBaO–5ZnO–50P 2O 5 glasses studied by DSC and infrared spectroscopy

The properties and structure of (45− x)Na 2O– xBaO–5ZnO–50P 2O 5 (0≤ x≤45 mol%) glasses were investigated. These properties include density, molar volume and glass transition temperature. The increase of density of glasses with increasing BaO content can be interpreted by differences of masses. The variation in the molar volume of these glasses is small. The glass transition temperature increases as the BaO is substituted for Na 2O. This behavior indicates that the replacement of Na 2O by BaO improves the strength of the cross-links between the phosphate chains of the glasses. The analysis of the infrared spectra of the studied glasses reveals that the increase of BaO content decreases the formation of end groups [(PO 3) n] n− .

Crystallization Mechanism and Kinetics of BaO-Li2O-ZrO2-SiO2 Glasses

Differential thermal analysis and scanning electron microscopy were used to determine the influence of the addition of BaO on the crystallization mechanism of Li2O-ZrO2-SiO2 systems. As the concentration of BaO in the samples increased, a transition occurred in the predominant crystallization mechanism, which passed from superficial to volumetric. To determine the maximum nucleation rate, the crystallization kinetics of the sample containing 20 mole % BaO, which showed the most uniform crystallization, was studied by counting the nuclei with an image analyzer. The first nuclei appeared at the first endothermic inflection point (at the start of Tg, at 440 °C), while the maximum number of nuclei was counted at the midpoint of the glass transition region (446 °C). These results are similar to those observed for other materials that crystallize in volume, and confirm scanning electron microscopy data.

Dielectric relaxation and a.c. conductivity of titanium-substituted iron in boron-based glasses

The a.c. conductivity and dielectric properties of the glass system B2O3-BaO-Pb3O4-Fe2O3-TiO2 have been investigated for different Fe2O3-TiO2 ratios, while the content of B2O3, BaO, and Pb3O4 were kept constant and equal to 60, 20, and 5 mol %, respectively. The results of the a.c. conductivity could be explained in terms of the correlated barrier hopping and the overlapping large-polaron tunneling models. The dielectric properties have also been investigated considering the dipolar relaxation model. A good agreement between the experimental data and the Cole–Cole equation have been obtained. The addition of small amounts of TiO2 strongly affected the dielectric properties of the glasses under investigation.

Heptane Dehydrocyclization Over Pt/KL Catalysts Doped with Barium or Lanthanum

Several 1 wt% Pt/KL catalysts doped with different concentrations of either BaO or La2O3 were prepared by successive impregnation of a zeolite KL and then characterized by H2-O2 titration, TPR, CO–FTIR, TEM-XEDS and XPS. Catalytic activity measurements in the hydroconversion of n-heptane showed that barium highly enhances the aromatization activity of Pt/KL, the more so the higher the barium concentration. The yield to aromatics increases to a lesser degree by adding 1 wt% La, but it is little modified at higher La concentrations. The CO–FTIR results suggest that the promoter effect of barium is related to an electron enrichment of Pt produced by the BaO → Pt0 interaction which, according to the TEM–XEDS and XPS results, is more favored than the La2O3 → Pt interaction.

Synthesis of Glass-Ceramic Materials in the BaO–PbO–B2O3–Al2O3–TiO2 System

The influence of PbO, B2O3, and Al2O3 additives on the glass formation and crystallization of glasses with a high total content of BaO and TiO2 (65–75 wt % or 76–86 mol %) is investigated. It is shown that glasses of the compositions (wt %) 31–35 BaO, 12–17 PbO, 34–42 TiO2, 10–13 Al2O3, and 2–3 B2O3 are promising materials for use in preparing glass-ceramic ferroelectrics based on the melting–molding–crystallization technology. These compounds are characterized by a relatively low melting temperature (1450°C), the absence of spontaneous crystallization during molding, and the possibility of controlling the phase composition of the material through the appropriate choice of the crystallization temperature.

Effects of BaO on the glass formation of the PbO-B2O3-TiO2-BaO system in relation to transition temperatures

The variation of the BaO content on the quaternary PbO-B2O3-TiO2-BaO system's glass formation tendency was investigated in relation to transition temperatures, such as melt temperature (T f), liquidus temperature (T l), crystallization temperature (T c) and glass transition temperature (T g). Compositions were melted between 800°C and 1300°C. In order to obtain bulk glass samples, glass formation was carried out using a preheated cylindrical brass mould without forcing the cooling rate to increase. Glass formation tendency increased with increasing the temperature ratios of T g/T l and T c/T l and with decreasing T g/T c. Eutectic compositions preferentially formed glasses from melts due to their low melting temperatures.

Mineral chemistry of barium- and titanium-bearing biotites in calc-alkaline volcanic rocks from the Mezitler area (Balikesir-Dursunbey), western Turkey.

Barium- and titanium-bearing biotites from Miocene volcanic rocks of Mezitler area, eastern Balikesir, western Turkey are studied. The chemical composition of volcanic rocks range from andesite to rhyodacite. The iron-enrichment index of micas (average I.E. = 0.40) is intermediate between annite and phlogopite. The biotite phenocrysts contain up to 1.72 wt.% BaO and 5.90 wt.% TiO2, with the average formulae (K0.807Na0.131Ca0.036Ba0.027) (Mg1.404Fe2+0.800 Fe3+0.131 Ti0.303Al0.056Mn0.023) (Si2.832Al1.167)O10[(OH)1.976Cl0.024]. The BaO content of electron-microprobe micas is positively correlated with the Al2O3, TiO2, and FeO contents, and with the I.E., and is negatively correlated with the SiO2, K2O, and MgO contents. Ba- and Ti-rich micas are generally found in potassic igneous rocks, in subalkaline and alkaline gabbroic rocks and in contact metamorphic rocks, whereas Ba- and Ti-bearing micas in this study occur in calc-alkaline volcanic rocks that hosted manganese-oxide and barite deposits. Most of the phenocrysts analyzed have deficiencies in their octahedral and partly interlayer sites. Deficiencies in the octahedral sites may arise from the Ti-vacancy and partly the Ti-tschermakite substitution. On the other hand, deficiencies in the interlayer-site are due to the replacement of K by Ba. The substitution mechanism in the Mezitler micas is characterized by Ba + 2Ti + 3Al = (K + Na + Ca) + 3(Mg + Fe + Mn) + 3Si, with an excellent correlation coefficient. In terms of aluminum and titanium contents, micas from the Mezitler area lie on a similar trend parallel to that for metasomatic phlogopites from Canary Island xenoliths, which overlap the field for micas from the Ilha da Trindade xenolith, South Atlantic. Biotite compositions from the Mezitler area fall between the quartz-fayalite-magnetite (QFM) and nickel-nickel oxide (NNO) oxygen fugacity buffers. All these show that Mezitler micas with low to moderate Ba- and Ti-contents may be formed from magmas in a subduction-enriched sub-continental lithospheric mantle environment.