Structure and electrical conductivity of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The temperature-concentration dependence of the electrical conductivity of glasses in the Na₂SO₄-NaPO₃ and Na₂O-P₂O₅ systems has been investigated. Based on the obtained experimental data (IR spectra, density, microhardness, sound velocity, and paper chromatography), it has been demonstrated that SO₄²⁻ ions form terminal groups through the incorporation into polyphosphate fragments of the structure of glasses in the Na₂SO₄-NaPO₃ system. An increase in the electrical conductivity of glasses in this system by a factor of ∼1000 (as compared to NaPO₃) at 25°C and a decrease in the activation energy for electrical conduction from 1.40 to 1.10 eV have been interpreted from the viewpoint of the decrease in the dissociation energy E _d of polar sulfate phosphate structural chemical fragments formed in the glass bulk upon introduction into sodium metaphosphate Na₂SO₄. This leads to an increase in the number of dissociated sodium ions, which are charge carriers, and to a decrease in the energy (E _a) of their activation shift in the sublattice formed by sulfate phosphate fragments of the structure.     

Structure of Glasses in the Na2SO4–P2O5–H2O System

The structure of sulfate–phosphate glasses is investigated by high-resolution ³¹P solid-state nuclear magnetic resonance with magic-angle sample spinning (³¹P MAS NMR spectroscopy). The structure parameters that account for the number of different types of phosphorus–oxygen structural units involved in the glass network are determined, and the main structural units of the glasses under investigation are revealed. The role of H₂O and Na₂SO₄ as modifiers of the structural network of sulfate–phosphate glasses is clarified.     

Electrical Properties and the Structure of Glasses in the Li2SO4–LiPO3 System

Electrical characteristics, namely, the temperature–concentration dependence of the electrical conductivity and the concentration dependence of the transport numbers of lithium ions (determined with the use of the Tubandt method) are investigated for glasses in the Li₂SO₄–LiPO₃ system. It is revealed that only lithium ions are involved in charge transfer. The IR absorption spectra, density, microhardness, and ultrasonic velocity are measured. An analysis of the experimental results obtained demonstrates that SO^2- ₄ ions form terminal groups and can be incorporated into polyphosphate structural fragments. An increase in the electrical conductivity and a decrease in the activation energy for electrical conduction are interpreted in the framework of a crossover of the migration mechanism. In lithium metaphosphate, lithium ions predominantly migrate through the interstitial mechanism. However, an increase in the lithium sulfate content in the initial glass leads to an increase in the fraction of charge carriers that migrate according to the vacancy mechanism.     

Synthesis and Properties of Glasses in the NaF–ZnSO4 System

The glass-forming ability is studied in the NaF–ZnSO₄ system. It is revealed that, when melts are cooled at a rate of 10³ K/s, the glass formation is observed in the concentration range 35–70 mol % ZnSO₄. The characteristic temperatures are determined by differential thermal analysis. According to these temperatures, fluorosulfate glasses can be assigned to low-melting glasses. The density of glasses is measured by hydrostatic weighing. The experimental data obtained are used to calculate the molar volume and the thermal stability parameters of fluorosulfate glasses.     

Glass Formation in the ZrF4–LaF3–BaF2–NaF System

The glass formation in the ternary ZrF₄–LaF₃–BaF₂and quaternary ZrF₄–LaF₃–BaF₂–NaF systems at a zirconium fluoride content of 50–60 mol % is investigated. The glass formation region in the ternary system has the shape of a petal and lies along the LaF₃–BaZr₂F₁₀join. The glass formation regions in the quaternary system are either localized or continuous depending on the zirconium fluoride content. The glass transition temperatures T _gfall in the range 180–290°C, and the temperatures of the onset of crystallization lie in the range 250–340°C. Glasses crystallize in one, two, or three stages. The melting temperature varies in the range from 390 to 650°C. The microhardness of glasses is measured. The compositions of the most stable glasses are determined.     

Interactions between oxides and compounds in the ZrO2-Al2O3-SiO2 system and a glass melt

Conclusions The interaction between ZrO₂, Al₂O₃, ZrSiO₄, and 3Al₂O₃·2SiO₂ with alkali silicate glasses of three compositions has been studied. It is shown that the greatest resistance to the effect of a molten glass is found in ZrO₂ and Al₂O₃. Therefore, the most promising compositions in the ZrO₂-Al₂O₃-SiO₂ system are those which contain baddeleyite and corundum as the crystal phases with the minimum amount of silica.The most aggresive oxide in the composition of the glasses used in this experiment is K₂O whose interaction with the refractory leads to the formation of low-melting compounds.The dissolution of corundum in the glass and the associated change in the properties of the glass have been studied. It is established that the dissolution of Al₂O₃ is the result of its interaction with the melt and the formation of low-melting compounds (alkali aluminosilicates of the feldspar type) while the emergence of a more viscous contact zone in the glass around the corundum grains lowers the rate of dissolution of Al₂O₃.Translated from Ogneupory, No. 2, pp. 50–53, February, 1980.     

Effects of SO2 on the alkane activity of three-way catalysts

Over current Pt-Rh/CeO₂-Al₂O₃ catalysts, the conversion of alkanes occurs by two principal mechanisms: direct oxidation (HC + O₂) and steam reforming (HC+H₂O). Sulphur dioxide can influence both these mechanisms. Direct oxidation, which predominates when the exhaust-gas is fuel-lean, ispromoted by the adsorption of SO_x species by the support. Under fuel-rich atmospheres, the presence of SO₂ severelyinhibits steam reforming. The poisoning is associated with the formation of S^2– on the platinum and of SO ₄ ^2– on the support, but there is no indication of S-species being retained by the rhodium. It is proposed that each of the two mechanisms is sensitive to a different type of interaction at the metal-support interface. Direct oxidation is enhanced by the transfer of electrons from the precious metal to the support; steam reforming occurs at interfacial sites, which can be blocked by adsorbed SO_x species.     

Kinetics and Mechanism of the Interaction of Alkali Calcium Silicate Glasses with Salt Melts in the KNO3–Pb(NO3)2 System

The interaction of alkali calcium silicate glasses with salt melts in the KNO₃–Pb(NO₃)₂ system is investigated at temperatures of 420–520°C. The chemical composition of crystalline coatings formed upon treatment contains both components of the initial glass (SiO₂, 9–12 wt %; CaO, 0.8–1.2 wt %) and components of the salt melt (PbO, 82–89 wt %). The treatment temperature is the main factor affecting the structure of the modified surface layer. The mechanism of the interaction of alkali calcium silicate glasses with salt melts is analyzed. According to this mechanism, the interaction involves the ion exchange (with the participation of Na⁺, K⁺, Ca²⁺, and Pb²⁺ ions), crystallization of modified surface layers, and incorporation of Pb _x O _y nanoparticles (formed in the salt melt) into the coating structure.     

First In Situ Raman Study of Vanadium Oxide Based SO2 Oxidation Supported Molten Salt Catalysts

In situ Raman spectroscopy at temperatures up to 500°C is used for the first time to identify vanadium species on the surface of a vanadium oxide based supported molten salt catalyst during SO₂ oxidation. Vanadia/silica catalysts impregnated with Cs₂SO₄ were exposed to various SO₂/O₂/SO₃ atmospheres and in situ Raman spectra were obtained and compared to Raman spectra of unsupported model V₂O₅–Cs₂SO₄ and V₂O₅–Cs₂S₂O₇ molten salts. The data indicate that (1) the V^V complex V^VO₂(SO₄)₂ ^3– (with characteristic bands at 1034 cm^–1 due to (V=O) and 940 cm^–1 due to sulfate) and Cs₂SO₄ dominate the catalyst surface after calcination; (2) upon admission of SO₃/O₂ the excess sulfate is converted to pyrosulfate and the V^V dimer (V^VO)₂O(SO₄)₄ ^4– (with characteristic bands at 1046 cm^–1 due to (V=O), 830 cm^–1 due to bridging S–O along S–O–V and 770 cm^–1 due to V–O–V) is formed and (3) admission of SO₂ causes reduction of V^V to V^IV (with the (V=O) shifting to 1024 cm^–1) and to V^IV precipitation below 420°C.     

Phase Relationships in the NaPO3–Al2O3 Glass-Forming System

The phase formation is studied in the NaPO₃–Al₂O₃ system (0–25 mol % Al₂O₃). It is shown that two individual compounds, namely, Na₆Al₂(P₂O₇)₃ and Na₃Al₂(PO₄)₃, exist along the studied join. The phase diagram of the NaPO₃–Al₂O₃ system (0–25 mol % Al₂O₃) is constructed. The phase separation phenomena are revealed in the melt.     

Electrochemical supercapacitors based on industrial carbon blacks in aqueous H2SO4

It is shown that industrial carbon blacks (CBs) are interesting materials for electrochemical supercapacitors (ECSCs). The specific areas A _s ranged from 28 to 1690 m² g^–1. The highest values were realized through activation in CO₂ at 1100 °C. Precompacted carbon black electrodes with 5–10 wt% PTFE as a binder in the pellet in 10–12 M H₂SO₄ were characterized by constant current cycling, CCC, j = 20–50 mA cm^–2. Voltage–time curves showed nearly pure capacitive behaviour. Specific capacitance of single electrodes, C _s,1, could be derived therefrom. A plot of C _s,1 against A _s shows a linear behavior according to C _s,1 = C _A,DL A _s, where C _A,DL is the Helmholtz double layer capacitance per atomic surface area. Best fit was obtained with C _A,DL = 16 F cm^–2. The highest experimental values, C _s,1 = 250 F g^–1, are due to 60% of the theoretical maximum, which corresponds to an A _s calculated from both faces of isolated graphene layers. Only marginal pseudocapacitances are observed. Model cells for ECSCs (with microporous Celgard^TM separators) could be extensively cycled (CCC). A monopolar cell endured Z > 2000 cycles. Bipolar cells (5 units) allowed 700 cycles. Practical problems such as the development of electrode holders and of carbon black filled polypropylene composites for current collectors are discussed. It is concluded that entirely metal-free ECSCs with low cost can be produced.     

Structural characterization of a layered double salt Mn3(OH)2(SO4)2(H2O)2 · K2SO4

The title layered double salt Mn₃(OH)₂(SO₄)₂(H₂O)₂ · K₂SO₄ (1) was obtained from a simple hydrothermal reaction of CdSO₄ · 8/3H₂O, MnCl₂ · 4H₂O, α-aminopyridine (apy) and KI. X-ray analysis reveals that the two-dimensional (2-D) sheet of 1 is built up of the dimers of edge-sharing Mn(1) octahedral, extended by the apices of Mn(2) octahedral together with μ₃ and μ₄ SO₄ groups. With free K⁺ ion as guest species, the 2-D sheets are further self-assembled into a 3-D supramolecular network with 1-D channels through the Ow-H ⋯ O hydrogen-bonded interactions. The magnetic property of 1 was investigated, and a classical behavior is observed with an antiferromagnetic order below 12.5 K.     

Glass Formation and Vibrational Spectra of Glasses in the SrSO4–KPO3–Na2B4O7 System

The glass formation region in the SrSO₄–Na₂B₄O₇–KPO₃ system is determined for the first time. This region occupies 31.8% of the concentration triangle predominantly in the polyphosphate region. The boundary of the glass formation lies along the binary line connecting the sodium tetraborate and potassium metaphosphate regions and reaches compositions with 40 mol % SrSO₄. Along the line connecting the potassium phosphate and sodium tetraborate regions, the glass formation at 10 mol % SrSO₄ is bounded by the 0.1SrSO₄–xNa₂B₄O₇–(0.9 – x)KPO₃ join (the Na₂B₄O₇–KPO₃ binary join is vitrified completely). From analyzing the IR and Raman spectra, it is assumed that the structure of the glasses under investigation is formed by lattices of two types, namely, the sulfate phosphate and borate lattices.     

Review of SO2-4/MxOy solid superacid catalysts

Some metal oxides modified with sulfate ions form highly acidic or superacidic catalysts. SO₂₋⁴/M _x O _y solid superacid catalysts, play a vital role in more and more fields such as organic synthesis, fine chemicals, pharmaceuticals, and means for strengthening environmental safeguards. This review highlights the recent development of solid superacid catalysts based on SO₂₋⁴/M _x O _y , including synthesis method, characterization of acid sites and acid strength, and applications.     

Measurements on the temperature dependence of the cationic polymerization of styrene in CH2Cl2 with CF3SO3H as catalyst

Summary The cationic polymerization of styrene in CH₂Cl₂ with CF₃SO₃H as catalyst and at low monomer concentrations shows, at –15°C, –45°C and –60°C, the same formal dependence on monomer concentration. The dependence on the catalyst concentration is approximately but not exactly of a third order.The unimodal molecular weight distributions at [M]_o<0.2 mol·1^–1 become broader with decreasing polymerization temperature and increasing monomer concentration and change to bimodal or trimodal distributions at [m]_o>0.2 mol·1^–1. The addition of (Bu)₄N⁺CF₃SO₃ ^– to the polymerization system shows that the two higher molecular peaks are produced by free ions. The activation energy of the total reaction is found to be 3.5 kcal·mol^–1.I thank Prof. G. V. Schulz for interesting discussions and the possibility to work in his group, G. Greschner for a computer program and the Alexander von Humboldt Stiftung for their financial help.     

Polymerization of Vinyl Acetate Initiated by a Copper Alginate Coordination Polymer Film/Na2SO3/H2O System

A hydrophobic film of copper alginate coordination polymer was prepared by soaking a sodium alginate film in a 13% CuCl₂ aqueous solution at room temperature for more than 24 h. The composition, structure, and property of copper alginate as a coordination catalyst were studied by ESR, IR, XPS, and electric conductivity methods. It was shown that a low-spin copper complex was formed as a result of the acceptance by dsp² hybrid orbitals of nonpaired electrons transferred from oxygen atoms of two carbonyl hydroxyl groups and negatively charged oxygen atoms of two deprotonated carbonyl hydroxyl groups of two alginate chains. The coordination number of the central Cu²⁺ ions in copper alginate is 4. It can be concluded that the vacant site on the active catalysis resulted from the distorted tetragonal configuration that was caused by a crimped chain of the alginate molecule. HSO ₃ ^– produced primary free-radical hydrogen by a coordination catalysis mechanism and vinyl acetate (VAc) polymerization by a free-radical mechanism that is different from polymerization initiated by a CuCl₂–Na₂SO₃–H₂O oxidation–reduction system. The induction period for VAc polymerization is 90 s and the yield is 82%. The M _w, M _n, and M _w/M _n of poly(vinyl acetate) (PVAc) were found to be 1.23×10⁶, 2.27×10⁵, and 4.51, respectively.     

Structure and Physicochemical Properties of Glasses in the Li2S–LiPO3 System

The temperature–concentration dependence of the electrical conductivity of glasses in the Li₂O–LiPO₃ and Li₂S–LiPO₃ systems is investigated. With the use of the Tubandt method, it is demonstrated that the electric current in glasses of these systems is provided by migration of lithium ions. The concentration dependence of the electrical conductivity is interpreted using the obtained data on the IR absorption spectra, density, microhardness, ultrasonic velocity, etc. It is found that the electrical conductivity of glasses in the Li₂S–LiPO₃ system is more than 10³ times higher than that in pure LiPO₃. The observed increase in the electrical conductivity is explained by the formation of sulfur-containing polar structural–chemical groupings of the Li⁺[S^–PO_3/2] type, whose dissociation energy is lower than that of similar oxide polar structural fragments. This results in an increase in the number of lithium ions involved in the electricity transport due to an increase in the degree of dissociation of polar structural–chemical units.     

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.     

Synthesis and Properties of Glasses in the (Sb2S3)1 – x (PbBr2) x System

The glass formation region, refractive index, and optical transmission in the IR spectral range are investigated for glasses in the (Sb₂S₃)_{1 – x} (PbBr₂) _x system. It is noted that these glasses are moisture resistant and hold considerable promise for use in practice.     

Corrosion behavior of Ti3AlC2 in NaOH and H2SO4

Passivation behavior, corrosion kinetics and film formation mechanism of Ti₃AlC₂ in 1 M NaOH and 1 M H₂SO₄ solutions were investigated by linear potential scan, electrochemical impedance spectroscopy, cyclic voltammetry, SEM and XPS. The corrosion resistance mainly depended on the formation of passivating films on Ti₃AlC₂ in 1 M NaOH and 1 M H₂SO₄, which led to different corrosion processes. Ti₃AlC₂ displayed good corrosion resistance in NaOH due to the formation of dense and protective Ti oxides as the passivating film. However, it exhibited poor corrosion resistance in H₂SO₄ which attributed to the formation of permeable Ti sub-oxides as the pseudo-passivating film.