Microanalysis of Glass Containing Alkali Ions

 The common problems connected with alkali ion migration during EPMA were studied on glasses containing nearly all possible alkali ions (Na, K, Rb, Cs). Binary silica glasses were prepared by melting from a very pure batch in Pt crucible. The glasses were carefully polished using alcohol to prevent surface corrosion by water and they were stored in vacuum. The specimens were coated with carbon layers approximately 30-nm thick and exposed to a 50- keV electron beam of 100 μm diameter. It was found that all alkali ions migrate under the electron beam, but the rate of the migration depends on the current density. The decay curves (characteristic X-ray intensity versus time) are similar in shape in all cases. The decay curve shows two transport regimes, the first being linear-like, the second being the exponential-like. The first transport regime busts into the rapid alkali migration after a time known as the incubation period. The period is in general longer for the larger-alkali ions size. It was found that even large rubidium and caesium ions migrate inside the glass with the same mechanism as sodium and potassium ions. While for K, Rb, and Cs ions the incubation periods were observed under the suitable experimental conditions, binary glass containing Na exhibits no observable incubation period. Except for the binary Na₂O + SiO₂ glass, the suitable experimental conditions for reliable quantitative EPMA can be found.     

Relaxation of Alkali Glass Exposed to an Electron Beam

Binary potassium and rubidium silicate glasses were irradiated with high-energy electrons. The changes induced in the glasses were observed as a decay of alkali X-ray signals with time. The decay curves displayed incubation periods, connected with changes of the transport mechanism. The electron exposures were interrupted relative to the incubation periods, next the glasses were annealed to enable easier relaxations, and successively irradiated again to finish the decay curve. Relaxation, which depends on the point of the decay curve at which exposure is interrupted, is calculated for the glasses. Relaxation was found to depend strongly on the interruption point with regard to the incubation period. The longer irradiation causes worse recovery of the structure during annealing, especially if the irradiation lasts longer than the incubation time. The larger ions and lower concentration also inhibit relaxation.     

Changes in the activity of Ru/Fe2O3 catalysts modified with alkali metal salts in the water-gas shift reaction

A study was undertaken to determine the activity of ruthenium catalysts, obtained by deposition of Ru₃(CO)₁₂ on products of iron oxide-hydroxide calcination modified with alkali metals, in the water-gas shift reaction. The activity depends on the kind of starting iron support, the ruthenium precursor and the amount of alkali metal salts. The most active were the catalysts obtained by deposition of Ru₃(CO)₁₂ on calcination products of σ-FeOOH, both modified and unmodified with alkali metal salts, and of α-FeOOH modified with alkali metal salts.     

Alkalized borazine: A simple recipe to design closed‐shell superalkalis

Superalkalis are hypervalent species, possessing smaller ionization energy (IE) than alkali metal. These species are typically designed by electronegative atoms with excess electropositive ligands. Typical examples include FLi₂, OLi₃, NLi₄, etc. Herein, we study successive alkali metal substitution at H atoms in borazine (B₃N₃H₆). Our B3LYP and MP2 calculations demonstrate that the vertical ionization energy (VIE) of B₃N₃H_6‐xLi_x decreases with the increase in x for x = 1–6. For x ≥ 4, the VIE of B₃N₃H_6‐xLi_x becomes lower than that of Li atom, thereby indicating their superalkali nature. More interestingly, all these species are planar with closed‐shell structure such that the NICS_zz value at the ring's center is reduced. We have also studied B₃N₃M₆ (M = Li, Na, and K) species and found that the VIE is further reduced in case of Na and K substitutions. These findings should suggest a simple yet effective route to the design of species with lower ionization energies than alkali metal.     

Thermal Intercalation of Alkali Halides into Kaolinite

Solid state intercalation of alkali halides into kaolinite takes place by heating pressed disks of dimethylsulfoxide (DMSO)-kaolinite complex ground in different alkali halides. This reaction involves diffusion of the DMSO outside the interlayer space and the alkali halide into the interlayer space. IR and Raman spectroscopy reveal two types of intercalation complexes: (i) almost non-hydrous, obtained during thermal treatment of the DMSO complex; and (ii) hydrated, obtained by regrinding the disk in air. The strength of the hydrogen bonds between intercalated water or halide anions and the inner surface hydroxyls decreases in the order Cl⁻>Br⁻>I⁻. Chlorides penetrate the ditrigonal holes and form hydrogen bonds with the inner OH groups. This revised version was published online in August 2006 with corrections to the Cover Date.     

Formation mechanism of a multihollow structure within submicron-sized styrene/methacrylic acid copolymer particles by the stepwise acid/alkali method

 The formation mechanism of a multihollow structure within submicron-sized styrene/methacrylic acid copolymer particles by the stepwise alkali/acid method, which we proposed in 1990, was discussed thermodynamically from the viewpoint of interfacial free energy. Received: 6 March 2001 Accepted: 17 May 2001     

煤催化气化工艺中碱金属腐蚀刚玉质耐火材料的实验研究

针对煤催化气化反应器设计中遇到的材料问题,采用碳酸钾及催化气化工况富含碱金属气化灰渣为实验原料,进行了碱金属腐蚀刚玉质耐火材料的实验研究。着重考察了有氧空气气氛和无氧还原性气氛、反应温度、反应时间、碱金属存在形态对腐蚀行为的影响,并结合SEM-EDX、XRD、核磁Al谱等表征手段,研究了反应前后碱金属和刚玉质耐火材料的成分、物相及结构变化。结果表明,碱金属对耐火材料腐蚀行为受反应的温度、气氛、时间及碱金属存在形态等因素影响较大。分析表明,有氧空气气氛下腐蚀尤为严重的原因是,原料中存在的钾与刚玉耐火材料发生化学反应生成新的钾的铝酸盐物相,且其含量随温度升高、反应时间延长而增加。     

How anomalous are the anomalous properties of fluorine? Ionization energy and electron affinity revisited

It is well established that atomic fluorine has a miserly high ionization energy and avariciously high electron affinity. Yet, as was shown some 30 years ago, the latter value is anomalously low-linear extrapolation shows the value to be some 110 kJ/mol less than expected by comparison to the heavier halogens. Related literature investigation extended this anomaly to nitrogen and oxygen and their (valence) isoelectronic congeners. We extend it to related cationic species and thereby the noble gases and alkali metals, and the aforementioned species are better understood. We thus ask if the ionization energy/electron affinity anomaly of fluorine remains an anomaly.     

Effect of molecular weight on the production of multi-hollow polymer particles by the alkali/cooling method

 The effects of molecular weight, particle diameter and cooling condition on the formation of multi-hollow structure formed within submicron-sized styrene-methacrylic acid copolymer particles by the “alkali/cooling method” proposed by the authors were examined and the formation mechanism was proposed. The original particles were produced by emulsion copolymerization in the presence of n-octyl mercaptan as a chain transfer agent. Received: 29 March 1996 Accepted: 19 June 1996     

DFT studies and AIM analysis of intramolecular N–H···O hydrogen bonds in 3-aminomethylene-2 methoxy-5,6-dimethyl-2-oxo-2,3-dihydro-2λ5-[1,2]oxaphosphinin-4-one and its derivatives

The intramolecular N–H···O hydrogen bonds in 3-aminomethylene-2 methoxy-5,6-dimethyl-2-oxo-2,3-dihydro-2λ⁵-[1,2]oxaphosphinin-4-one and its derivatives (F, H, Li, -BeH) were studied by DFT (density functional theory) methods. The results of calculations were obtained at B3LYP/6-311++G(d,p) level on model species, with the resonance-assisted hydrogen bonds (RAHB). Topological parameters such an electron density, its Laplacian, kinetic electron energy density, potential electron energy density, and total electron energy density at the bond critical points (BCP) of H···O/N–H contact bonds from Bader’s ‘Atoms in molecules’ (AIM) theory were analyzed in details. The energy of the N–H···O interactions studied here was found rather weak (E _HB = 2.53–12.08 kcal/mol). The results of AIM ellipticity indicated π-delocalization over all six atoms within ring.     

New type of compounds based on s-and d-block metal trimethylacetates

Heterometallic compounds based on alkali (Li, Na, K, Rb, or Cs) trimethylacetates and transition metal (Cu or Co) trimethylacetates were synthesized. These compounds are characterized by a larger number of s-block atoms compared to d-block atoms. An excess alkali metal trimethylacetate in the reaction system leads to the formation of unusual polymeric systems containing alternating s-and d-block atoms. Dedicated to Academician O. M. Nefedov on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1863–1874, November, 2006.     

燃煤过程中碱金属迁移规律的模拟研究与预测分析

基于ASPEN PLUS 平台,对燃煤过程中碱金属迁移规律进行了模拟研究和预测。模拟结果表明,在850K~1650K气态碱金属物质随反应温度的升高而增加;1400K以下,气相中以NaCl、KCl为主,Na2SO4蒸气量明显高于K2SO4;1500K以下,气态碱金属释放量随着煤中氯质量分数的增加而增加;一定温度下,气态碱金属质量分数随压力的升高而降低;常压下煤中氯的质量分数0.1%,温度降到972K时气态碱金属的质量分数可降到2.4×10－8;而当氯的质量分数分别为0.05%和0.01%时,为达到同样的气态碱金属质量分数,温度需分别降到990K和1025K。模拟结果为燃煤联合循环发电系统的设计和优化提供了参考依据。     

Facile Synthesis of Unsolvated Alkali Metal Octahydrotriborate Salts MB3H8 (M=K,Rb, and Cs), Mechanisms of Formation,and the Crystal Structure of KB3H8

A facile synthesis of heavy alkali metal octahydrotriborates (MB₃H₈; M=K, Rb, and Cs) has been developed. It is simply based on reactions of the pure alkali metals with THF?BH₃, does not require the use of electron carriers or the addition of other reaction media such as mercury, silica gel, or inert salts as for previous procedures, and delivers the desired products at room temperature in very high yields. However, no reactions were observed when pure Li or Na was used. The reaction mechanisms for the heavy alkali metals were investigated both experimentally and computationally. The low sublimation energies of K, Rb, and Cs were found to be key for initiation of the reactions. The syntheses can be carried out at room temperature because all of the elementary reaction steps have low energy barriers, whereas reactions of LiBH₄/NaBH₄ with THF?BH₃ have to be carried out under reflux. The high stability and solubility of KB₃H₈ were examined, and a crystal structure thereof was obtained for the first time.     

Diatomic potential well depths from analyses of high-resolution electron energy spectra for autoionizing collision complexes

High-resolution energy spectra of electrons released in Penning ionization collisions of metastable rare gas atoms Rg*(ns) (Rg = He, Ne, Ar, Kr, Xe) with several open-shell and closed-shell atoms are analyzed to determine the well depth of the potential energy curve which describes the respective autoionizing collision complex. We thereby elucidate trends in the chemical interaction of Rg* with closed-shell target atoms A(ns ²) and establish a basis for detailed comparison with the respective interactions involving open-shell, ground state alkali atoms A(ns). From electron energy spectra due to␣associative ionization (RgH⁺ formation) in Rg* + H(1s) collisions, we determine binding energies for the RgH⁺(¹Σ) ground state potential (Rg = Ne, Ar, Kr, Xe) with uncertainties around 0.03 eV. Received: 30 June 1998 / Accepted: 5 August 1998 / Published online: 28 October 1998     

Inorganic electrides

Inorganic electrides are a novel kind of ionic compounds in which the anions are electrons confined in a complex array of cavities or channels and the cations are nanoscale arrays of alkali metal ions that provide charge balance. In electrides the donated electron behaves like a low-density correlated electron gas, whereby the dimensionality of the electron gas and its electronic and magnetic properties are determined by the topology of the cavities in the host matrix. Unlike traditional electrides, in which alkali cations are encapsulated within an organic cage, inorganic electrides are thermally stable. The current inorganic electrides based on alkali metal loaded zeolites can be designed as useful reduced-dimensionality materials. Inorganic electrides are powerful reducing agents, and they are able to reduce small aromatic molecules to the radical anions within the channels of the zeolite.     

Old acid,new chemistry. Negative metal anions generated from alkali metal oxalates and others

A brief search in Sci Finder for oxalic acid and oxalates will reward the researcher with a staggering 129,280 hits. However, the generation of alkali metal and silver anions via collision-induced dissociation of the metal oxalate anion has not been previously been reported, though Tian and coworkers recently investigated the dissociation of lithium oxalate [18]. The exothermic decomposition of alkali metal oxalate anion to carbon dioxide in the collision cell of a triple quadrupole mass spectrometer leaves no place for the electron to reside, resulting in a double electron-transfer reaction to produce an alkali metal anion. This reaction is facilitated by the negative electron affinity of carbon dioxide and, as such, the authors believe that metal oxalates are potentially unique in this respect. The observed dissociation reactions for collision with argon gas (1.7−1.8 × 10⁻³ mbar) for oxalic acid and various alkali metal oxalates are discussed and summarized. Silver oxalate is also included to demonstrate the propensity of this system to generate transition-metal anions, as well.     

污泥与醋糟共热解特性及碱金属迁移规律

分别采用热重分析仪、真空固定床反应器和原子吸收光谱研究了污泥与醋糟共热解过程中反应动力学、产物分布和碱金属迁移行为,探究了协同效应及碱金属迁移规律。结果表明,两者共热解过程中存在明显协同效应;与理论计算相比,混合物分解所需的活化能下降了35.38%～29.49%,脱挥发指数比计算低3.5×10-8。协同效应导致气体产率增加,生物炭、液体产率降低;醋糟的存在加速了污泥的脱挥发分析出,提高了气体产物中合成气含量,加大了生物炭中大芳香环的裂解反应,使生物油中酚类和酯类物质含量明显增加;热解终止时,碱金属元素析出量达到79.19%～86.73%。     

DFT studies and AIM analysis of AlN-polycycles

The structure and properties of AlN-polycycles were studied by DFT (density functional theory) method. The results of calculations were obtained at B3LYP/6-311G(d, p) level on model species. Topological parameters such as electron density, its Laplacian, kinetic electron energy density, potential electron energy density, and total electron energy density at the ring critical points (RCP) from Bader’s ‘Atoms in molecules’ (AIM) theory were analyzed in detail. These results indicate a good correlation between ρ(3, +1), G(r), H(r), and V(r) averaged values and hardness of AlN-polycycles. The aromaticity of all molecules has been studied by nucleus-independent chemical shift. There is a linear correlation between ΣNICS(0.0)_molecule values and polarizability.     

Electron free energy levels in oxidic solutions: relating oxidation potentials in aqueous and non-aqueous systems

We provide background to the problem of describing the state of redox couples in different types of solvent media ranging from acidic aqueous solutions to high temperature molten silicates, pointing out the essential similarity between these solvent media in Lewis acid–base terms. We review the adaptation of the Gurney proton energy level diagram approach to the case of electron transfer processes. Using data from various spectroscopic and analytical chemistry sources, we review the construction of electron free energy level diagrams for redox couples in aqueous and non-aqueous systems using, as a common reference, the potential of the oxygen gas (1 atm)/oxide ion couple in the solution of interest. We emphasize the anomalous effect of “oxide ion activity” (mean ionic activity of alkali oxide) on the state of equilibrium and interpret this in terms of oxide ion transfers that accompany electron transfers. After showing the essential agreement between recent direct electrochemical assessments of the energy levels and those deduced in our original analysis of oxidic melts of different glass formers, we provide an interpretation of the apparent “oxide ion transfer” in terms of the differential medium polarization by the two redox species involved in the equilibrium. We anticipate the extension of these ideas to redox chemistry in the currently burgeoning field of “ionic liquids” in its recent ambient temperature liquid incarnation. Dedicated to the 85th birthday of John O’M. Bockris.

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Equilibrium Constant Studies for Complexation between Ammonium Ions and 18-Crown-6 in Aqueous Solutions at 298.15 K

Osmotic vapor pressure and density measurements have been carried out for binary aqueous and ternary aqueous solutions containing a fixed concentration of 18-crown-6 (0.2 mol⋅kg⁻¹) and ammonium chloride or ammonium bromide at 298.15 K. The concentration of the ammonium salts was varied between 0.02 to 0.5 mol⋅kg⁻¹. The measured water activities were used to obtain the activity coefficient of water and the mean molal activity coefficient of the ions in binary as well as ternary solutions. Using the method developed by Patil and Dagade reported earlier in this journal and the McMillan-Meyer pair and triplet Gibbs energy interaction parameters, the thermodynamic equilibrium constant (K) for the 18-crown-6:NH₄ ⁺ complexes were determined. It is observed that the nature and polarizability of anions play important roles in imparting stability to the complexed species. The log₁₀ K values for the 18-crown-6:NH₄ ⁺ complexed species are lower than for the complexes involving alkali metal ions such as K⁺. The volume of complexation for the studied systems obtained from the apparent molar volumes of ammonium halides in ternary solutions are positive and of smaller magnitude than those reported for complexation with alkali ions. The results are further discussed in terms of water structural effects, complex formation, the role of counter anions and hydrophobic interactions.