Mobility Of Mg Research Articles

Monolayer α-beryllene as an anode material for magnesium ion batteries with high capacity and low diffusion energy barrier.

High specific capacity and fast charge/discharge rate are important indicators for the development of next-generation ion batteries. Compared with conventional monovalent ion batteries like lithium-ion batteries and sodium-ion batteries, multivalent ion batteries have attracted extensive attention owing to their high energy densities. Here, we systematically explore the interactions between Mg atoms and α-beryllene monolayers by means of density functional theory calculations. Mg atoms can be adsorbed stably on α-beryllene monolayers with the adsorption energy of -0.24 eV. The low diffusion energy barriers (0.099/0.101 eV) indicate the rapid mobility of Mg during the charge/discharge process. Moreover, the α-beryllene monolayer exhibits an ultra-high theoretical specific capacity of 5956 mA h g-1 for Mg, a low average open-circuit voltage of 0.24 V, and a tiny volume change of -1.08%. Finally, the constructed h-BN/α-beryllene heterostructure shows that h-BN can serve as a protective cover to preserve pristine α-beryllene in respect of metallicity, Mg adsorption capability, and fast ionic mobility. The above mentioned outstanding results make α-beryllene a promising anode material for magnesium-ion batteries.

Magnesiothermic Reduction of Natural Quartz

In the current work, the metallothermic reduction of natural quartz by magnesium has been studied at 1373 K under different reaction conditions, i.e. quartz type, quartz particle size, Mg:SiO2 mole ratio and reaction time. The microstructure of reaction products was studied to illustrate the reaction progression through scanning and transmission electron microscopy techniques. X-ray diffraction analysis with Rietveld phase quantification was used to calculate the change in the amount of phases at different reaction conditions. The results showed that the Mg:SiO2 mole ratio strongly affects reaction mechanism and product characteristics such as phase content and microstructure. At lower Mg:SiO2 mole ratios, the reaction rate is fast at the beginning and the formation of a product layer consisting of different phases such as MgO, Si, Mg2Si, Mg2SiO4 and MgSiO3 around quartz particles limits the Mg diffusion. This phenomenon is more noticeable for larger quartz particle sizes where Mg should diffuse longer distance towards the quartz core to react with it. At higher Mg:SiO2 mole ratios, a significant amount of Si–Mg liquid alloy is formed during reaction where the high mobility of Mg in this liquid phase and cracking of quartz particles result in significantly higher reaction rate. Here the formation of intermediate phases is not significant and the products would be the mixture of MgO, Mg2Si, and either Si or Mg phases.

The mechanism of Mg diffusion in forsterite and the controls on its anisotropy

Mg diffusion is important for explaining many properties of forsterite but its mechanism is unknown. This makes it hard to predict how it will behave in different circumstances. In this study we used Density Functional Theory (DFT) and a Kinetic Monte Carlo (KMC) method to calculate the diffusivity of Mg vacancies and interstitials in forsterite and thus the diffusion rate of Mg in forsterite. We predict vacancy diffusion to be highly anisotropic with considerably faster diffusion in the [001] direction while interstitial diffusion is predicted to be more isotropic. Thus we predict that a combination of interstitial and vacancy diffusion is required to reproduce experimentally derived anisotropies. Interstitial diffusion is predicted to be highly pressure dependant such that with increasing pressure the anisotropy of Mg diffusion decreases while temperature has little effect on this anisotropy. Impurities like Fe and water likely cause increases in Mg diffusion rate through the creation of extrinsic Mg vacancies and we predict that without modifications to the inherent mobility of Mg vacancies these cause small increases to diffusional anisotropy at 1300 and 1600 K but very large increases at 1000 K. The activation volume of Mg self diffusion is also predicted to decrease with increasing extrinsic vacancy concentration.

Nonisothermal dissolution kinetics on Mg17Al12 intermetallic in Mg-Al alloys

In this work, nonisothermal dissolution of intermetallic Mg17Al12 in Mg-Al alloy has been firstly studied via Differential Scanning Calorimetry-DSC, X-Ray Diffraction-XRD and Scanning Electron Microscope-SEM as well as CALPHAD_based dissolution models and molecular dynamics simulation. The size and volume fraction of Mg17Al12 phase could be predicted via the present kinetic dissolution model and agree well with experimental results. Also, the data-driven screening calculation shows that there is a range of temperature for significantly dissolving Mg17Al12 phase, which could be increased with the increase of heating rate. The evolution of structural order for Mg17Al12 phase has also been performed via molecular dynamics simulation with LAMMPS. The simulated results indicate that the structural order of Mg17Al12 phase during heating is mainly affected by the Al-contained atomic pairs (Al-Al and Al-Mg), suggested that Mg atoms are thermodynamically and kinetically more active than Al atoms in Mg17Al12 phase during heating, which has also been approved via the calculated atomic mobility of Mg and Al atoms in Mg17Al12 phase in this work. Therefore, the atomic mobility of Mg atoms is mainly attributed to the interdiffusion coefficient of Mg17Al12 phase which determines the dissolution of Mg17Al12 phase during heating. The fundamental principle in this work could be used for other intermetallics and offers the greatly valuable information for optimizing the thermal processing in application of metal structural materials.

Nonisothermal Dissolution Kinetics on Mg17Al12 Intermetallic in Mg-Al Alloys

In this work, nonisothermal dissolution of intermetallic Mg17Al12 in Mg-Al alloy has been firstly studied via Differential Scanning Calorimetry-DSC, X-Ray Diffraction-XRD and Scanning Electron Microscope-SEM as well as CALPHAD_based dissolution models and molecular dynamics simulation. The size and volume fraction of Mg17Al12 phase could be predicted via the present kinetic dissolution model and agree well with experimental results. Also, the data-driven screening calculation shows that there is a range of temperature for significantly dissolving Mg17Al12 phase, which could be increased with the increase of heating rate. The evolution of structural order for Mg17Al12 phase has also been performed via molecular dynamics simulation with LAMMPS. The simulated results indicate that the structural order of Mg17Al12 phase during heating is mainly affected by the Al-contained atomic pairs (Al-Al and Al-Mg), suggested that Mg atoms are thermodynamically and kinetically more active than Al atoms in Mg17Al12 phase during heating, which has also been approved via the calculated atomic mobility of Mg and Al atoms in Mg17Al12 phase in this work. Therefore, the atomic mobility of Mg atoms is mainly attributed to the interdiffusion coefficient of Mg17Al12 phase which determines the dissolution of Mg17Al12 phase during heating. The fundamental principle in this work could be used for other intermetallics and offers the greatly valuable information for optimizing the thermal processing in application of metal structural materials.

Magnesium Deficiency Triggers SGR-Mediated Chlorophyll Degradation for Magnesium Remobilization.

Magnesium (Mg) is a relatively mobile element that is remobilized in plants under Mg-limited conditions through transport from old to young tissues. However, the physiological and molecular mechanisms underlying Mg remobilization in plants remain poorly understood. In this study, we investigated Mg remobilization in rice (Oryza sativa) as facilitated through a Mg dechelatase gene involved in chlorophyll degradation, STAY-GREEN (OsSGR). We first observed that mid-aged leaves of rice are more susceptible to Mg deficiency. Expression of OsSGR was specifically upregulated by Mg deficiency, and the response was more pronounced in mid-aged leaves. Knockout of OsSGR exhibited the stay-green phenotype, which hindered the mobility of Mg from mid-aged leaves to young developing leaves. This decline in Mg mobility was associated with inhibited growth of developing leaves in mutants under Mg-limited conditions. Furthermore, Mg deficiency enhanced reactive oxygen species (ROS) generation in mid-aged leaves. ROS levels, particularly hydrogen peroxide, in turn, positively regulated OsSGR expression, probably through chloroplast-to-nucleus signaling, which triggers chlorophyll degradation to protect mid-aged leaves from photodamage. Taken together, these results show that OsSGR-mediated chlorophyll degradation contributes to not only internal remobilization of Mg from mid-aged leaves to developing leaves, but also photooxidative protection of mid-aged leaves under Mg-limited conditions. ROS appear to act as feedback regulators of OsSGR expression to precisely govern chlorophyll degradation in mid-aged leaves where Mg and photosynthetic capacities are relatively high.

Unveil the Chemistry of Olivine FePO4 as Magnesium Battery Cathode.

Despite growing interest in magnesium batteries, it is still a challenge to find a cathode that fulfills requirements such as high capacity and good cyclability. Because of their positions in the periodic table and the similar ionic sizes of lithium and magnesium, it was naturally postulated that a classical intercalation-type Li-ion battery cathode may also accommodate the intercalation of Mg. On the contrary, many Li-ion battery cathodes performed very poorly in Mg cells, although the mechanism behind such phenomena is still unclear. Here we provide first-hand evidence about the chemistry of olivine FePO4 as Mg battery cathode using a combined theoretical and experimental approach. Although LiFePO4 is a commercial cathode with extraordinary good performance in Li-ion batteries, the measured capacity of FePO4 in nonaqueous Mg cell was only ∼13 mAh/g. Density functional theory calculations predicted sufficient mobility of Mg(2+) in FePO4 lattice to support the insertion of Mg at a reasonable rate, suggesting the poor performance cannot be simply attributed to the limitation of Mg(2+) diffusion. Instead, the recorded low capacity was the result of surface amorphorization that prohibited the electrochemical reaction from penetrating deeply into the bulk phase. The amorphorization had a thermodynamic origin from the instability of intercalated product, which was predicted from DFT calculations and supported by the failure to synthesize magnesiated FePO4 in the solid state reaction route. These results highlighted the importance of a thermodynamically preferred intercalation in order to achieve successful Mg battery cathode.

Surface water chemistry at Torfajökull, Iceland—Quantification of boiling, mixing, oxidation and water–rock interaction and reconstruction of reservoir fluid composition

The surface geothermal water chemistry and alteration mineralogy associated with rhyolitic rocks at Torfajökull central volcano, Iceland was studied. The geothermal waters ranged in pH and temperature from 2.33 to 9.77 and 6–98°C, respectively, and was characterized by variable alteration products including amorphous silica, quartz, hematite, goethite, kaolinite, elemental sulfur, pyrite, anatase, montmorillonite. alunite, amorphous iron silicates, pyrite, goethite, hematite and illite. The chemical composition of these waters and the associated mineralogy is influenced by several processes occurring from the geothermal reservoir to the surface including boiling, mixing, degassing, oxidation and water–rock interaction. In order to quantify these processes and explain the observed geothermal surface water composition and mineralogy, a geochemical model was applied that involved three steps: (i) defining the composition of the end-member fluid types present in the system, (ii) applying a mixing model based on conservation of non-reactive elements and enthalpy (temperature) and (iii) quantifying the process of progressive fluid–rock interaction and secondary mineral formation in the surface zone. The model may be applied to any geothermal system. Geothermal waters at Torfajökull represent either a mixture of non-thermal water and condensed steam with insignificant fraction of boiled reservoir water or boiled reservoir water that has been mixed. Two types of steam-heated waters were observed, acid and carbonate rich, the difference thought to be related to the boiling process. Steam-heated carbonate waters are formed from <10% steam originated by boiling and phase segregation at >200°C followed by mixing with non-thermal water at shallow depth whereas steam-heated acid waters are formed upon extensive boiling and steam condensation and mixing with non-thermal surface in the surface zone. The surface alteration mineralogy and associated elemental mobility is largely influenced by the formation mechanism and chemistry of the geothermal surface water in the surface zone. At acid pH and under oxidized conditions Na, K, Mg and Ca were observed to be mobile and leached out whereas Fe, Ti and to a less extent Si, were retained in the alteration product forming amarphous silica, kaolinite, anatase and pyrite as well as some smectites and sulfates. For steam-heated carbonate waters, Na and K were observed to be mobile whereas Fe and Si are retained in amorphous silica, ferrihydrites and iron rich silicates. Carbonates were not calculated or observed to form associated with carbonate springs. Magnesium, Ca and K were observed to be mobile at pH<6 whereas they are quantitatively retained into smectites and eventually also zeolites and carbonates with increasing pH. As a consequence, the mobility of Mg and K and to a less extent Ca and Na are greatly reduced under alkaline conditions. Based on the above, the key factors controlling the fluid–rhyolite interaction under surface geothermal conditions (∼100°C) are acid supply, oxidation state and extent of reaction. The surface geochemical exploration methods developed and applied here are suitable for any geothermal system in order to explore geochemical processes occurring in active geothermal systems including boiling and fluid mixing, fluid and elemental sources, reservoir fluid properties and when applied before and during geothermal exploitation and utilization how these may have changed in nature with time.

Magnesium mobility in soils as a challenge for soil and plant analysis, magnesium fertilization and root uptake under adverse growth conditions

BackgroundDue to its unique chemistry magnesium (Mg) is subject to various cycling processes in agricultural ecosystems. This high mobility of Mg needs to be considered for crop nutrition in sustainable agricultural systems. The Mg mobility in soils and plants and its consequences for crop nutrition are understood, but recent findings in crop Mg uptake, translocation and physiology particularly under adverse growth conditions give new insights into the importance of Mg in crop production.ScopeThe aim of this review is to combine the knowledge on the origin and mobility of Mg in soils with the role of Mg in plant stress physiology and recent evidence on the principles of crop Mg uptake. The question is addressed whether the progress made in Mg research, particularly on the role of Mg in stress physiology, makes a revision of the development of Mg fertilization recommendations necessary.ConclusionsNew insights into Mg uptake and utilization but particularly into the role of Mg in increasing crop tolerance to various stresses indicate changes in the crop Mg demand under adverse growth conditions. Future work should incorporate these findings in optimization of site-specific balanced fertilization programs particularly under stress conditions.

Origin of sulfide replacement textures in lunar breccias. Implications for vapor element transport in the lunar crust

Lunar samples 67016,294, 67915,150, and 67016,297 represent clasts of Mg-suite and ferroan anorthosite lithologies that have interacted with a S-rich vapor. Numerous studies have speculated on the composition and source of these “fluids”, their capability for the transport of vapor-mobilized elements, and the scale and environment under which these types of process occurred. These models all assumed a Moon with a very “dry” mantle, crust, and surface. The olivine in these lithologies is partially to totally replaced by troilite and low-Ca pyroxene. The troilite makes up 30–54vol% of the troilite+low-Ca pyroxene pseudomorphs after olivine. Other silicates and oxides in the assemblages have experienced post-magmatic reequilibration (pyroxene exsolution, recrystallization, “exsolution” of ilmenite in spinel). The troilite also occurs in veins cross cutting individual phases and metamorphic textures. The sulfide veining and replacement features are restricted to individual clasts and do not cut across the matrix surrounding the clasts, and thus predate the breccia-forming event. The proportion of troilite to low-Ca pyroxene and silicate chemistries indicate that simple reactions (such as olivine+S2↔low-Ca pyroxene+troilite+O2) do not adequately represent the replacement process. The sulfides have compositions that are similar to those found in mare basalts. In particular, the sulfides generally are enriched in Co relative to Ni. Exsolution of Ni–Co–Cu in the sulfides is distinctly different between the breccias and mare basalts and suggests a different cooling or crystallization (melt versus vapor) history. The sulfur isotopic composition of the vein and replacement troilite ranges from approximately δ34S=−1.0‰ to −3.3‰.Based on our observations, it appears that the model suggested by Norman et al. (1995) is the most appropriate for the origin of the troilite veining and troilite–pyroxene pseudomorphs after olivine. Our data add significant definition to this model. This process occurs in the relatively shallow lunar crust on a scale that involves vapor interaction with multiple plutonic lithologies of various ages and compositions. These reactions occur at distinct conditions of fS2, fO2, and temperature. The reacting vapor is S-rich, and perhaps low in H. The reduction of the oxides in the clasts was not a product of H-streaming as has been suggested for similar textures in lunar rocks, but more likely related to “S-streaming”. These vapors had the capability to transport chalcophile–siderophile elements. However, a proportion of the minor elements making up the troilite (Fe, Ni, Co) did come directly from the olivine being replaced. Further, there is evidence to suggest minor mobility of Mg from the olivine pseudomorphs into the adjacent pyroxene. One of the heat sources driving the transport of elements is closely tied to the emplacement of magmas into the shallow lunar crust. These intrusions were either the source for the S or provided heat to remobilized troilite already in the lunar crust. The process that drove the derivation of the S-rich volatiles was instrumental in fractionating the isotopic composition of S. The enrichment of S32 in the vapor phase may be attributed to either the stable S species during degassing (COS, S2 and CS2) or the high-temperature partial breakdown of troilite in the shallow crust.

Some features of thermo‐activated structural transformation of biogenic and synthetic Mg‐containing apatite with β‐tricalcium‐magnesium phosphate formation

AbstractTemperature transformation of biogenic and synthetic Mg‐containing apatite with β‐tricalcium‐magnesium phosphate (β‐TCMP) formation was investigated by X‐ray diffraction. Samples were annealed in air at the temperature range from 600 to 1200 °C at intervals 100 °C and cooled down to room temperature. The appearance of β‐TCMP was ascertained in samples annealed at 800 °C. As revealed, the relative amount of β‐TCMP increases and Mg concentration in this phase decreases as the annealing temperature is raised. While this, the replacement degree of Ca by Mg in the β‐TCMP lattice is the annealing temperature function and does not depend either on sample origin (biogenic/synthetic) or on initial Mg concentration. The results of present work together with other investigation data testify to a high thermally activated mobility of Mg both in structure of Mg‐containing apatites and in the structure of β‐TCMP formed after thermal decomposition. Obtained data can be used for new biomaterials design with varied prolongation of Mg released into the living biological tissue. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A Theoretical Study of Initial Deposition Processes of Mg on MgO: A Novel Quantum Chemical Molecular Dynamics Approach

Initial deposition processes of Mg on MgO were studied using our novel quantum chemical molecular dynamics (QCMD) simulator. This novel simulator was developed on the basis of our tight-binding quantum chemical molecular dynamics (TB-QCMD) simulator and our molecular dynamics simulator. The justification of the novel QCMD simulator was shown by the excellent agreement of the QCMD result with the first-principles results and experimental results for the physicochemical properties of the MgO crystal. Dynamic behaviors of Mg atom deposited on the MgO(001) and (111) surfaces were simulated by the novel QCMD method. It was shown that the mobility of Mg deposited on the MgO(001) surface was larger than that on the (111) surface, which suggests the difference between the interaction of the deposited Mg atom with the MgO(111) surface and that with the MgO(001) surface.

Measurements of the mobility of alkaline earth ions in liquid xenon

The mobility of alkaline earth ions, Mg+, Ca+, Sr+ and Ba+, in liquid xenon is measured for the first time. The mobility of Tl+ is also determined for comparison with a measurement by other researchers. The Atkins cluster model for positive ions in non-polar liquids, based on the electrostriction effect, gives general agreement with the magnitude of the mobility values. This is some evidence that the positive ions form a snowball rather than a bubble structure in liquid xenon. However, the temperature dependence of the mobility does not match well with the Atkins theory, so there are still open theoretical questions on the nature of the environment of alkaline earth ions in liquid xenon. The lower mobility of Mg+ and Ba+ may be explained by a better size match to interstitial and substitutional sites, respectively, in solid Xe. These measurements are motivated by the development of a new technique to search for neutrino masses through 0νββ decay of 136Xe. A key component of one version of the proposed experiment is tagging of 136Ba+ daughter ions in liquid 136Xe by laser-induced fluorescence.

Advances in Magnesium Electrochemistry — A Challenge for Nanomaterials

AbstractFor Abstract see ChemInform Abstract in Full Text.

Preparation and electrochemical magnesium insertion behaviors of Mg 0.5+ y(Me yTi 1− y) 2(PO 4) 3 (Me = Cr, Fe)

A series of transition metal phosphates, Mg 0.5+ y (Fe y Ti 1− y ) 2(PO 4) 3 (MFTP) and Mg 0.5+ y (Cr y Ti 1− y ) 2(PO 4) 3 (MCTP), modified from Mg 0.5Ti 2(PO 4) 3 (MTP) were prepared by sol–gel method and evaluated as a possible cathode material for magnesium cells. The lattice structures of MFTP and MCTP at 0≤ y≤0.5 were identical with that of MTP, while their unit cell volumes were smaller than that of MTP due to the increased amount of Mg 2+ ions. Electrochemical magnesium insertion into MFTP and MCTP was found to be possible as observed for MTP. However, the limiting extent of magnesium insertion into MFTP at 0.1≤ y≤0.5 was small compared with MTP and remarkably dependent on the discharge current density during discharge. These facts suggested that the insertion limit is determined not by the number of available sites for Mg 2+ or electrons but by the mobility of Mg 2+ in these host materials correlating with decrease in the unit cell volume.

Electrochemical insertion of magnesium to Mg 0.5Ti 2(PO 4) 3

Mg 0.5Ti 2(PO 4) 3 having NASICON-lattice was prepared by sol–gel method and evaluated as a cathode material for magnesium cells. The crystalline phase could be successfully obtained after heating at 600°C. Electrochemical magnesium insertion from a propylene carbonate solution into this host was found possible and one Mg 2+ ion could be accommodated per unit formula. However, the magnesium insertion process was under kinetic control of Mg 2+ diffusion due to the low mobility of Mg 2+ in this host.

Magnesium insertion into Mg 0.5+ y(Fe yTi 1− y) 2(PO 4) 3

A series of transition metal phosphates, Mg 0.5+ y (Fe y Ti 1− y ) 2(PO 4) 3 (MFTP), modified from Mg 0.5Ti 2(PO 4) 3 (MTP) were prepared by sol–gel method and evaluated as cathode materials for rechargeable magnesium cells. The crystal structure of MFTP at 0≤ y≤0.5 was identical to that of MTP, while their unit cell volumes were smaller than that of MTP due to introduced Mg 2+ ions. Electrochemical magnesium insertion into MFTP was found possible as observed for MTP. However, the limiting extent of magnesium insertion into MFTP at 0.1≤ y≤0.5 was small compared with MTP and remarkably dependent on the current density during discharge, suggesting that the insertion limit is determined not by the number of available sites for Mg 2+ or electrons but by the mobility of Mg 2+ in the host varying with the unit cell volume.

Partition coefficients for iron between plagioclase and basalt as a function of oxygen fugacity: Implications for Archean and lunar anorthosites

Experimental studies were undertaken to determine D for FeO T between plagioclase and melt as a function of oxygen fugacity for a basaltic composition that occurs as matrices for plagioclase megacrysts that are similar to those in calcic anorthosites. At liquidus conditions, the D for FeO T between calcic plagioclase and tholeiitic basalt changes very little, from 0.030 to 0.044, between the very low ƒ o 2 of the iron-wustite buffer and that of the quartz-fayalite-magnetite (QFM) buffer. At fugacities above QFM the value for D increases rapidly to 0.14 at the magnetite-hematite buffer and 0.36 in air. The increase in D results from the fact that nearly all of the Fe is in the Fe 2+ state at ƒ o 2 below QFM, and the Fe 3+ Fe 2+ ratio in the melt increases rapidly above QFM causing more Fe to enter the plagioclase which accepts Fe 3+ more readily than Fe 2+. There is essentially no change in values of D over cooling rates that vary by two orders of magnitude. The D for FeO T of 0.030 at iron-wustite is in good agreement with earlier studies at low ƒ o 2 . Terrestrial calcic plagioclase-matrix pairs display Ds of about 0.043, in excellent agreement with the experimental value of 0.044 at QFM which is the accepted fugacity for terrestrial tholeiitic basalts. Application of the Ds for FeO T and other components to terrestrial calcic anorthosites indicates that the anorthosites were in equilibrium with nearby coeval tholeiitic basalts at QFM, as was expected. Lunar anorthosites, however, have anomalously low contents of FeO T as well as MgO and would be in equilibrium with melts that are several times lower in these components than expected. The low values of FeO T and MgO in the plagioclase of lunar anorthosites are a result of subsolidus reequilibration with pyroxene, olivine, and other Fe-Mg-bearing phases during high-temperature metamorphism, as is the case in terrestrial anorthosites that have undergone granulite-grade metamorphism. The Ds for K 2O, MgO, and TiO 2 were determined as 0.21, 0.044, and 0.033, respectively, and show no variation with ƒ o 2 . The value for K 2O is in good agreement with natural assemblages. The values for MgO and TiO 2, however, are lower in natural assemblages; but the high degree of mobility of Mg and the very low contents of TiO 2 in plagioclase makes the reliability of the natural values rather low. Also, the D for TiO 2 may be affected by rate of cooling. Attempts to determine the D for Cr 2O 3 as a function of ƒ o 2 were made difficult by the low levels of Cr 2O 3 (300 to 500 ppm) in the melt when saturation with a Cr spinel occurred. Because the Cr concentrations in plagioclase are nearly 100 times less than those in the melt, it was not possible to obtain reliable analyses for plagioclase. These uncertainties constrain the D for Cr to be less than 0.07 at the QFM buffer.

Behaviour of alkaline earth metals and silver perchlorates and their complexes with some crown ethers in propylene carbonate

The conductance behaviour of magnesium, calcium, strontium, barium and silver perchlorates and their complexes with 18-crown-6 (18C6) and also, the com dibenzo-18-crown-6 (DB18C6) and dicyclohexano-18-crown-6 (DCH18C6) have been studied in propylene carbonate (PC) at 25°C. In addition, a potentiometr was undertaken by using a silver indicator electrode in conjunction with a Hg/HgCl 2(s) reference electrode in PC to compare the results with those agreement with each other. The complexation study indicates 1 : 1 complex formation between the metal ion and the crown ether. The order of the formati Sr 2+ > Ba 2+. The mobility of Mg 2+ is found to be greater than those of 18C6-Mg 2+, DB18C6-Mg 2+ and DCH18C6-Mg 2+, whereas it is l 2+ and Ba 2+ are somewhat lower than those of their respective 18C6 complexes, indicating that the moving entity of the metal ion is larger than

119Sn Mössbauer and X-ray photoelectron studies of novel tin oxide pillared laponite formed under ambient conditions from aryltin precursors. Rapid intercalation reactions using microwave heating

119Sn Mössbauer spectroscopy studies have shown that attempts to intercalate three aryltin compounds [Ph 3SnCl, (Ph 3Sn) 2O, Ph 2SnCl 2] into the synthetic smectite clay laponite under ambient conditions result in the formation of tin(IV) oxide pillared clays. The Mössbauer data indicate that the effectiveness of conversion to tin oxide pillars is in the order: Ph 3SnCl > (Ph 3Sn) 2O, Ph 2SnCl 2. The organic product of the pillaring reaction is benzene and has been identified by 13C MASNMR spectroscopy as trapped in the pillared lattice. The new materials are novel since the pillaring was achieved via neutral precursors rather than by sacrificial reaction of the exchanged cation. The intercalation/pillaring reactions are much more rapid (5 min) when carried out in Teflon containers in a simple domestic microwave oven. Combined 119Sn Mössbauer and X-ray photoelectron spectroscopic studies (XPS) suggest that, in the microwave experiments, Ph 3SnCl has a higher initial affinity for the clay surface than (Ph 3Sn) 2O but that the chloride undergoes hydrolysis on the surface once sorbed. Evidence for the considerable mobility of Mg 2+ within the laponite lattice during microwave heating is presented.