Alkaline Earth Compounds Research Articles

Measurement of Strontium Monoxide in Methane-Air Flames.

The spectroscopy of alkaline earth metal compounds is stimulated by the use of these compounds in practical areas ranging from technology to medicine. Applications in the field of pyrotechnics were the motivation for a series of flame emission spectroscopy experiments with strontium-containing compounds. Specifically, strontium monoxide (SrO) was studied as a candidate radiator for the diagnosis of methane-air flames. Strontium monoxide emissions have been observed in flames with temperatures in the range 1200 K to 1600 K for two compounds: strontium hydroxide and strontium chloride. Comparisons are made of the measured SrO spectra to simulated spectra in the near-infrared region of 700 nm to 900 nm.

Failure of Density Functional Dispersion Correction in Metallic Systems and Its Possible Solution Using a Modified Many-Body Dispersion Correction.

Previous density functional dispersion corrections to density functional theory lead to an unphysical description of metallic systems, as exemplified by alkali and alkaline earth compounds. We demonstrate that it is possible to remedy this limitation by including screening effects into the form of interacting smeared-out dipoles in the many-body expansion of the interaction. Our new approach, called the coupled fluctuating smeared dipole model, describes equally well noncovalent systems, such as molecular pairs and crystals, and metallic systems.

Topological nodal-line semimetals in alkaline-earth stannides, germanides, and silicides

Based on first-principles calculations and an effective Hamiltonian analysis, we systematically investigate the electronic and topological properties of alkaline-earth compounds $AX_2$ ($A$=Ca, Sr, Ba; $X$=Si, Ge, Sn). Taking BaSn$_2$ as an example, we find that when spin-orbit coupling is ignored, these materials are three-dimensional topological nodal-line semimetals characterized by a snake-like nodal loop in three-dimensional momentum space. Drumhead-like surface states emerge either inside or outside the loop circle on the (001) surface depending on surface termination, while complicated double-drumhead-like surface states appear on the (010) surface. When spin-orbit coupling is included, the nodal line is gapped and the system becomes a topological insulator with Z$_2$ topological invariants (1;001). Since spin-orbit coupling effects are weak in light elements, the nodal-line semimetal phase is expected to be achievable in some alkaline-earth germanides and silicides.

Mechanism Switching of Ammonia Synthesis Over Ru-Loaded Electride Catalyst at Metal-Insulator Transition.

The substitution of electrons for O(2-) anions in the crystallographic cages of [Ca24Al28O64](4+)(O(2-))2 was investigated to clarify the correlation between the electronic properties and catalytic activity for ammonia synthesis in Ru-loaded [Ca24Al28O64](4+)(O(2-))2-x(e(-))2x (0 ≤ x ≤ 2). This catalyst has low catalytic performance with an electron concentration (Ne) lower than 1 × 10(21) cm(-3) and a high apparent activation energy (Ea) for ammonia synthesis comparable to that for conventional Ru-based catalysts with a basic promoter such as alkali or alkaline earth compounds. Replacement of more than half of the cage O(2-) anions with electrons (Ne ≈ 1 × 10(21) cm(-3)) significantly changes the reaction mechanism to yield a catalytic activity that is an order higher and with half the Ea. The metal-insulator transition of [Ca24Al28O64](4+)(O(2-))2-x(e(-))2x also occurs at Ne ≈ 1 × 10(21) cm(-3) and is triggered by structural relaxation of the crystallographic cage induced by the replacement of O(2-) anions with electrons. These observations indicate that the metal-insulator transition point is a boundary in the catalysis between Ru-loaded [Ca24Al28O64](4+)(O(2-))2 and [Ca24Al28O64](4+)(e(-))4. It is thus demonstrated that whole electronic properties of the support material dominate catalysis for ammonia synthesis.

Influence of dust and mud on the optical, chemical, and mechanical properties of a pv protective glass.

Recent developments in climate change have increased the frequency of dust storms in the Middle East. Dust storms significantly influence the performances of solar energy harvesting systems, particularly (photovoltaic) PV systems. The characteristics of the dust and the mud formed from this dust are examined using various analytical tools, including optical, scanning electron, and atomic force microscopies, X-ray diffraction, energy spectroscopy, and Fourier transform infrared spectroscopy. The adhesion, cohesion and frictional forces present during the removal of dry mud from the glass surface are determined using a microtribometer. Alkali and alkaline earth metal compounds in the dust dissolve in water to form a chemically active solution at the glass surface. This solution modifies the texture of the glass surface, thereby increasing the microhardness and decreasing the transmittance of the incident optical radiation. The force required to remove the dry mud from the glass surface is high due to the cohesive forces that result from the dried mud solution at the interface between the mud and the glass. The ability altering the characteristics of the glass surface could address the dust/mud-related limitations of protective surfaces and has implications for efficiency enhancements in solar energy systems.

X-ray powder reference patterns for magnetoplumbite-like compounds, (BaxSr1−x)Ti6Co6O19(x= 0.2, 0.4, 0.6, 0.8)

X-ray reference powder patterns and crystal structures have been determined for a series of titanium- and cobalt-containing layered alkaline-earth compounds with nominal formula (BaxSr1−x)Ti6Co6O19(x= 0.2, 0.4, 0.6, 0.8). Structural isomorphism of the title compounds with the hexagonal ferrite BaFe12O19and magnetoplumbite (PbFe12O19), was confirmed. The (BaxSr1−x)Ti6Co6O19series crystallize in the space group ofP63/mmc(No. 194) andZ= 2. The lattice parameters range froma= 5.90729(6) Å,c= 23.2378(3) Å, andV= 702.27(2) Å3forx= 0.2 toa= 5.914 93(9),c= 23.3391(5) Å, andV= 707.15(2) Å3withx= 0.8. The structure consists of alternating spinel S-block and R-blocks. The tetrahedral sites within the spinel S-blocks are occupied with only Co2+, while Ti4+is mainly located in the octahedral sites of the spinel S-blocks and in the face-sharing octahedral site of the R-blocks. A bipyramidal mixed Co/Ti site was confirmed in the R-block of the structure. Powder X-ray diffraction patterns of this series of compounds have been submitted to be included in the Powder Diffraction File.

Computational mechanistic elucidation of the intramolecular aminoalkene hydroamination catalysed by iminoanilide alkaline-earth compounds.

A comprehensive computational exploration of plausible alternative mechanistic pathways for the intramolecular hydroamination (HA) of aminoalkenes by a recently reported class of kinetically stabilised iminoanilide alkaline-earth silylamido compounds [{N^N}Ae{N(SiMe3)2}⋅(thf)n] ({N^N} = iminoanilide; Ae = Ca, Sr, Ba) is presented. On the one hand, a proton-assisted concerted N-C/C-H bond-forming pathway to afford the cycloamine in a single step can be invoked and on the other hand, a stepwise σ-insertive pathway that involves a fast, reversible migratory olefin 1,2-insertion step linked to a less rapid, irreversible metal-C azacycle tether σ-bond aminolysis. Notably, these alternative mechanistic avenues are equally consistent with reported key experimental features. The present study, which employs a thoroughly benchmarked and reliable DFT methodology, supports the prevailing mechanism to be a stepwise σ-insertive pathway that sees an initial conversion of the {N^N}Ae silylamido into the catalytically competent {N^N}Ae amidoalkene compound and involves thereafter facile and reversible insertive N-C bond-forming ring closure, linked to irreversible intramolecular Ae-C tether σ-bond aminolysis at the transient {N^N}Ae alkyl intermediate. Turnover-limiting protonolysis accounts for the substantial primary kinetic isotope effect observed; its DFT-derived barrier satisfactorily matches the empirically determined Eyring parameter and predicts the decrease in rate observed across the series Ca>Sr>Ba correctly. Non-competitive kinetic demands militate against the operation of the concerted proton-assisted pathway, which describes N-C bond-forming ring closure triggered by concomitant amino proton delivery at the C=C linkage evolving through a multi-centre TS structure. Valuable insights into the catalytic structure-activity relationships are unveiled by a detailed comparison of [{N^N}Ae(NHR)] catalysts. Moreover, the intriguingly opposite trends in reactivity observed in intramolecular (Ca>Sr>Ba) and intermolecular (Ca<Sr<Ba) HA catalysis for the studied family of iminoanilide alkaline-earth amido catalysts are rationalised.

Kinetic and economic analysis of reactive capture of dilute carbon dioxide with Grignard reagents.

Carbon Dioxide Utilisation (CDU) processes face significant challenges, especially in the energetic cost of carbon capture from flue gas and the uphill energy gradient for CO2 reduction. Both of these stumbling blocks can be addressed by using alkaline earth metal compounds, such as Grignard reagents, as sacrificial capture agents. We have investigated the performance of these reagents in their ability to both capture and activate CO2 directly from dried flue gas (essentially avoiding the costly capture process entirely) at room temperature and ambient pressures with high yield and selectivity. Naturally, to make the process sustainable, these reagents must then be recycled and regenerated. This would potentially be carried out using existing industrial processes and renewable electricity. This offers the possibility of creating a closed loop system whereby alcohols and certain hydrocarbons may be carboxylated with CO2 and renewable electricity to create higher-value products containing captured carbon. A preliminary Techno-Economic Analysis (TEA) of an example looped process has been carried out to identify the electrical and raw material supply demands and hence determine production costs. These have compared broadly favourably with existing market values.

Study on biomass tar reduction by ash and fluidizing medium in a heterogeneous reaction

Since fossil energy resources are exhaustible in the world, renewable biomass is considered as one of the useful future resources for energy and materials. In addition, when the biomass grows, it can contribute to the prevention of global warming by circularly absorbing CO 2 . There are different biomass utilization technologies such as the pyrolysis and gasifi cation, fermentation and combustion. For example, gaseous components are used as chemical products and used for energy production; these can be produced by the pyrolysis or synthesized by gasifi cation. However, there is the problem that condensable organic compounds, so-called ‘tar’ will also be generated during the pyrolysis and gasifi cation processes. Most of the tar components are present as gases at higher temperature inside of the reactors. However, a black oily liquid will be formed, leading to the equipment failure when the temperature is cooled down lower than their boiling points. Therefore, appropriate processing is required. As a processing method, catalytic decomposition of tar has been widely studied. In the present study, it was carried out for the thermal decomposition of cellulose in the experimental apparatus connecting two reaction tubes. Tar and gases generated by the thermal decomposition of cellulose in the fi rst reactor can be pyrolyzed with catalytic cracking in the second reactor. Tar contents were fi rstly cooled and collected. At the same time, the amount of gases was measured by a gas chromatograph with a fl ame ionization detector and a gas chromatograph with a thermal conductivity detector. Then, K and Ca were selected as the catalyst of alkali metals and alkaline earth metals contained in the waste biomass, which were present in the state of oxide or carbonate during the pyrolysis and gasifi cation. The amount of condensable products was decreased by installing catalytic contents of K 2 CO 3 and Ca(OH) 2 . Additionally, the amount of gaseous products was increased. It can be concluded that an alkali metal compound (K 2 CO 3 ) and an alkaline earth compound (CaO) have a catalytic effect to decompose tar contents, which can enhance gaseous production in the secondary reaction.

Synthesis and Crystal Structure of Three Alkaline Earth Coordination Compounds Based on 1,2,5-Thiadiazole-3,4-Dicarboxylic Acid Ligand

1,2,5-thiadiazole-3,4-dicarboxylic acid (H2 tdzdc) ligand has been used to construct three coordination compounds [Mg(tdzdc)(H2O)4](1), [Ca(tdzdc)(H2O)2]n(2) and [Sr(tdzdc)(H2O)3]n(3) by the solvothermal reaction. Single-crystal structure analyses reveal a mononuclear coordination structure for compound 1 and two dimensional coordination structure both for compound 2 and 3. Furthermore, all of these three compounds comprise any amount of hydrogen bond interactions, which extends their crystal structure into three dimensional (3D) frameworks. Different crystal structure of compounds 1–3 reveals diversified coordination modes of H2 tdzdc ligand toward alkaline earth metal ions, depending mainly on the radius and the electron shell number of metal ions used. Based on 1,2,5-thiadiazole-3,4-dicarboxylic acid (H2 tdzdc) ligand, three new alkaline earth metal compound were synthesized with different structure.

A kinetic study on the effects of alkaline earth and alkali metal compounds for catalytic pyrolysis of microalgae using thermogravimetry

In this paper, thermogravimetric (TG) analysis and kinetic modeling are applied to study the effects of alkaline earth and alkali metal compounds on catalytic thermal decomposition of microalgae. When alkaline earth and alkali metal compounds are added, the initial thermal degradation temperatures increased by about 3.2–10.2 K, and the final temperatures reduced by about 3.5–9.4 K. The results show that CaO, MgO, K2CO3, BaCO3 and Na2CO3 may shorten the time of pyrolysis, implying that alkaline earth and alkali metal compounds may promote the process of thermal degradation of organic matters. The first maximum weight loss rate is in the order of Na2CO3 > CaO > K2CO3 > BaCO3 > MgO > no additive. Em (weight means activation energy) varies from 99.60 to 134.05 kJ mol−1, which implies ignorable overall activation energies (Em) after alkaline earth and alkali metal compounds are added.

A Review of Thermal Co-Conversion of Coal and Biomass/Waste

Biomass is relatively cleaner than coal and is the only renewable carbon resource that can be directly converted into fuel. Biomass can significantly contribute to the world’s energy needs if harnessed sustainably. However, there are also problems associated with the thermal conversion of biomass. This paper investigates and discusses issues associated with the thermal conversion of coal and biomass as a blend. Most notable topics reviewed are slagging and fouling caused by the relatively reactive alkali and alkaline earth compounds (K2O, Na2O and CaO) found in biomass ash. The alkali and alkaline earth metals (AAEM) present and dispersed in biomass fuels induce catalytic activity during co-conversion with coal. The catalytic activity is most noticeable when blended with high rank coals. The synergy during co-conversion is still controversial although it has been theorized that biomass acts like a hydrogen donor in liquefaction. Published literature also shows that coal and biomass exhibit different mechanisms, depending on the operating conditions, for the formation of nitrogen (N) and sulfur species. Utilization aspects of fly ash from blending coal and biomass are discussed. Recommendations are made on pretreatment options to increase the energy density of biomass fuels through pelletization, torrefaction and flash pyrolysis to reduce transportation costs.

Thermodynamical Stability of Complex Transition Metal Hydrides M2FeH6

The thermodynamical stability of complex transition metal hydrides M2FeH6 is investigated by first-principles density-functional calculations. In addition to the reported alkaline-earth compounds (...

Magnesium and Cadmium in Covalently‐Bonded Lonsdaleite Networks: Synthesis, Structure, and Bonding of AETMg2 and SrTCd2 (AE = Ca, Sr; T = Pd, Ag, Pt, Au)

AbstractThe alkaline earth metal compounds AETMg2 and AETCd2 (AE = Ca, Sr; T = Pd, Ag, Pt, Au) were synthesized by induction‐melting (or in muffle furnaces) of the elements in sealed niobium ampoules. The new phases were characterized by powder X‐ray diffraction. The structures of SrPdMg2 and SrPdCd2 were investigated by X‐ray diffraction on single crystals: MgCuAl2 type, Cmcm, a = 436.42(4), b = 1130.1(1), c = 820.54(7) pm, wR2 = 0.0115, 511 F2 values for SrPdMg2 and a = 443.5(2), b = 1063.0(2), c = 810.2(2) pm, wR2 = 0.0296, 386 F2 values for SrPdCd2 with 16 variables for each refinement. The magnesium and cadmium atoms build up [TMg2] and [TCd2] polyanionic networks, which leave cavities for the calcium and strontium atoms. The bonding variations within the polyanions, which are mainly influenced by the length of the b axis are discussed. Ab initio calculations of electronic structure, charge densities, and chemical bonding, characterize SrPdMg2 with a larger cohesive energy than SrPdCd2. This is illustrated by larger bonding Pd–Mg interactions, opposite to compensating Pd–Cd between bonding and antibonding states.

Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae = Ca, Sr, Ba, as thermoelectric materials

We present a detailed theoretical study of three alkaline earth compounds Ca2Pb, Sr2Pb and Ba2Pb, which have undergone little previous study, calculating electronic band structures and Boltzmann transport and bulk moduli using density functional theory. We also study the corresponding tin compounds Ca2Sn, Sr2Sn and Ba2Sn. We find that these are all narrow band gap semiconductors with an electronic structure favorable for thermoelectric performance, with substantial thermopowers for the lead compounds at temperature ranges from 300 to 800 K. For the lead compounds, we further find very low calculated bulk moduli—roughly half of the values for the lead chalcogenides, suggestive of soft phonons and hence low lattice thermal conductivity. All these facts indicate that these materials merit experimental investigation as potential high performance thermoelectrics. We find good potential for thermoelectric performance in the environmentally friendly stannide materials, particularly at high temperature.

Review on structural, thermal, optical and spectroscopic properties of tellurium oxide based glasses for fibre optic and waveguide applications

This review focuses on the engineering of the structural, thermal, optical and spectroscopic properties of tellurium oxide (TeO2) glasses for their applications in fibre optic and waveguide devices. Unlike silica optical fibres, tellurium oxide glass fibres and light waveguides support propagation of light beyond ∼2 μm, where silica fibres become opaque. Silica fibres also have limited solubility for rare earth oxides due to silica’s structure, which is where tellurium oxide fibres and light waveguides can offer significant opportunities to engineer novel lasers and amplifiers for integrated optics. In this review, we compare the structural properties of TeO2 based glasses, modified by incorporating alkali, alkaline earth, and other oxide compounds. Based on Raman, UV, visible and infrared spectroscopic data, the structural aspects of tellurite glasses are discussed. The effects of compositional modification on the thermal and viscous flow properties are also compared and related with the resistance against devitrification. The significance of glass to crystal phase transformation during cooling and heating is explained in the context of preform and fibre fabrication. The review also reports on the characterisation of OH− impurities in tellurite glasses. Recent developments in tellurite fibre lasers and femtosecond laser inscribed waveguide fabrication are discussed.

RAPID DISTILLATION COUPLED WITH ION CHROMATOGRAPHY FOR THE DETERMINATION OF SIX ALKYLAMINES IN COSMETICS

A rapid distillation method coupled with ion chromatography was developed for simultaneous determination of methylamine, ethylamine, dimethylamine, trimethylamine, propylamine, and butylamine in cosmetics. The distillation system was designed professionally to achieve rapid distillation in less than 3 min and eliminate the interferences of alkali metals, alkaline earth, and organic compounds effectively. Samples were distilled using vapor stream under alkaline conditions and the distilled products were absorbed in acetic acid solution prior to detection. The linear ranges of alkylamines were within 0.1–18 mg/L and the detection limits ranged from 0.045 mg/L to 0.075 mg/L. The method was successfully utilized to determine the amount of alkylamines in commercial cosmetics without need for tedious pretreatments. Average recoveries ranged from 84.4% to 108.5% with relative standard deviations (RSD) in the range of 0.7–7.6%. Validation results indicated that the method was simple, accurate, precise, selective, and suitable for the determination of alkylamines in cosmetics.

The Kinetics and Inhibition of Chloride Hydrolysis in Canadian Bitumen

Chloride salts in heavy oils can cause significant corrosion and fouling of refinery equipment, because desalting is not completely effective. The kinetics of the reaction of chloride salts with steam in diluted bitumen at 250°C was affected by reaction and diffusion in the solid salt particles. Four inhibitors based on alkaline–earth compounds were effective in reducing the initial rate of hydrolysis, thereby offering potential protection to refinery equipment. Chlorides were retained by the inhibitors even at 550°C. The physical association between salt particles and the inhibitors suspended in the crude oil was important for effective trapping of released chloride.

TGA and Drop Tube Furnace Investigation of Alkali and Alkaline Earth Metal Compounds as Coal Combustion Additives

Even though alkali and alkaline earth metal compounds are well-known catalysts for the combustion of coal, there has been no significant investigation into the importance of the anion across a broa...

Mechanistic elucidation of the yttrium(iii)-catalysed intramolecular aminoalkene hydroamination: DFT favours a stepwise σ-insertive mechanism

A comprehensive computational mechanistic study regarding intramolecular hydroamination (HA) of aminoalkenes mediated by a recently reported class of highly active cyclopentadienyl-bis(oxazolinyl)borate {Cpo}Y(III) alkyl compounds is presented. Two distinct mechanistic pathways of catalytic HA mediated by rare earth and alkaline earth compounds have emerged over the years, describing amidoalkene → cycloamine conversion proceeding through a stepwise σ-insertive mechanism or a concerted non-insertive N-C/C-H bond forming pathway. Notably, both mechanisms account equally for reported distinct process features. Non-competitive kinetic demands revealed for the concerted amino proton transfer associated with N-C ring closure, which commences from a {Cpo(M)}Y(NHR)·(NH(2)R) substrate adduct and evolves through a six-centre TS structure, militates against a proton-triggered non-insertive pathway to promote HA for the rare earth catalyst at hand. A stepwise σ-insertive pathway, featuring rapid and reversible olefin insertion into the Y-N amido σ-bond, linked to a less facile and irreversible intramolecular Y-C azacycle tether aminolysis, is found to prevail energetically. The assessed effective barrier for turnover-limiting aminolysis matches the empirically determined Eyring parameter well and the computationally estimated primary KIE is close to the observed values. A recent computational study revealed a similar scenario for an analogous tris(oxazolinyl)borate {To(M)}Mg system. Valuable insights into the catalytic structure-reactivity relationships have been unveiled by a comparison of {Cpo(M)}Y(NHR)- and {To(M)}Mg(NHR)-catalysed hydroaminations.