Graphite Intercalation in H2SO4–CH3COOH Electrolytes

The anodic oxidation of highly oriented pyrolytic graphite in H₂SO₄–CH₃COOH electrolytes in a galvanostatic mode (I = 1.5 mA) is studied as a function of electrolyte composition. The concentration ranges for the formation of stage I–V graphite intercalation compounds (GICs) are determined. The concentration threshold for intercalation is 1 wt % H₂SO₄. There are three distinct concentration ranges differing in the shape of the charging curve E(Q), which depends primarily on the content of H₂SO₄ (active intercalant). The potentials of formation of stage I–III GICs in H₂SO₄–CH₃COOH electrolytes are found to be higher than those for graphite bisulfate, which points to an increase in the potential barrier for intercalation and is obviously associated with the intercalation of acetic acid into the graphite host. The specifics of the charging curves obtained in 60–80% H₂SO₄, together with gravimetry and chemical analysis data, indicate the formation of ternary GICs with sulfuric and acetic acids. In this composition range, stage I* and II* cointercalation compounds are obtained, with an intercalate layer thickness d _i = 7.94 Å. The composition of the ternary GICs is shown to depend on the relative amounts of the acids in the electrolyte. A mechanism of the formation of graphite cointercalation compounds is proposed. In solutions containing less than 40 wt % H₂SO₄, only graphite bisulfate is formed.     

Intercalation of Graphite in the Ternary Systems C–HNO3–R (R = H2O, CH3COOH, H3PO4 , H2SO4)

The reactions between highly oriented pyrolytic graphite and HNO₃–R (R = H₂O, CH₃COOH, H₃PO₄, H₂SO₄) solutions were studied by x-ray diffraction and potentiometry. The results demonstrate that the nature of component R has a crucial effect on the intercalation process and phase composition of the reaction products. The ability to form ternary graphite intercalation compounds (GICs) depends on the acidity of R. It is shown that CH₃COOH, a weak protic Brönsted acid (pK = 4.76), does not form cointercalation compounds when graphite is treated chemically or electrochemically in HNO₃–CH₃COOH solutions. H₃PO₄, a weak Brönsted acid (pK = 2.12) forms ternary intercalation compounds. Stage II–IV ternary GICs with HNO₃ and H₃PO₄ (d _i = 8.05 Å) were for the first time synthesized and investigated. H₂SO₄, a strong Brönsted acid (pK = –2.8), forms stage I cointercalation compounds (I _c = 8.02 Å), independent of the HNO₃ content (5–95 wt %) of the oxidizing mixture. The potential of the HNO₃–H₂SO₄ solutions was found to be E _Ag/AgCl = 1.39 V, independent of the HNO₃ : H₂SO₄ ratio. The main relationships in the ternary systems were shown to be similar to those for the formation of binary GICs with acids. There is a perfect correlation between the redox potential of the HNO₃–R (R = H₂O, CH₃COOH, H₃PO₄, H₂SO₄) solutions and the stage index of the resulting GIC. The concentration ranges of GIC formation in nonaqueous HNO₃ solutions were extended substantially. The behavior of stage I–IV graphite nitrates in different solvents (H₂O, CH₃COOH, H₃PO₄, and H₂SO₄) was studied. Based on the experimental results, mechanisms of the processes in the systems studied were proposed.     

Synthesis of Ternary Intercalation Compounds in the Graphite–HNO3–R (R = H2SO4 , H3PO4 , CH3COOH) Systems

The reactions of stage II–IV graphite nitrates with concentrated H₂SO₄, H₃PO₄, and CH₃COOH were studied at graphite : acid weight ratios from 3 : 1 to 1 : 1. The results demonstrate that the reactions in question follow different paths. In the graphite nitrate–H₂SO₄system, the reaction decreases the stage index and yields a ternary graphite intercalation compound. The contents of intercalated HNO₃and H₂SO₄are controlled by the amount of H₂SO₄and the stage index of the parent graphite nitrate. The reaction between graphite nitrate and H₃PO₄leads to partial replacement of HNO₃by H₃PO₄, increasing the identity period without changes in the stage index. The results for the graphite nitrate–CH₃COOH system provide no direct evidence for the formation of an intercalation compound with HNO₃and CH₃COOH. It is shown that varying the nature and amount of the second intercalate species opens up possibilities for preparing oxidized graphite with controlled physicochemical properties.     

Synthesis and properties of poly (organophosphazenes) ionomers [NP(HNC6H5)2−(x+y)(HNC6H4SO3H) x (HNC6H4SO3Li) y ] n

Poly(anilino sulphamicphosphazenes) such as [NP(HNC₆H₅)_2–x (HNC₆H₄SO₃H) _x ] _n for polymer (I) x=0.3 and for polymer (II) x=0.8 were prepared by the reaction of poly(anilinophosphazene) [NP(HNC₆H₅)₂] _n and sulphonic chloride HSO₃Cl in tetrachloroethane solvent several timeS. Also, H protons in the polymer (I) and (II) were prepared from lithum hydroxide in aqueous solution. It was found, by chemical analysis, that the product prepared with (I) and (II) had compositions such as [NP(HNC₆H₅)_1.7 (HNC₆H₄SO₃H)_0.1(HNC₆H₄SO₃Li)_0.2] _n (III) and [NP(HNC₆H₅)_1.2(HN-C₆H₄SO₃Li)_0.8] _n (IV). Also, the resistivity of products (III) and (IV) were determined and found to be 3.3×10⁷ and 1.5×10⁷ cm^–1, respectively.     

Preparation and study of in vitro bioactivity of PMMA–co–EHA composites filled with a Ca3(PO4)2–SiO2–MgO glass

The nature of the orthopaedic implant surface affects the interaction with cells and subsequent bone formation. The bone/cement interface in cement-held prostheses is considered to be the main cause of fracture leading to implant revision. It is thought that the introduction of a bioactive phase, such as bioglass, in the cement may permit a more stable interface by encouraging direct bone apposition rather then encapsulation of the implant by fibrous tissue. In this work new poly(methylmethacrylate) (PMMA) based composites filled with 0, 30, 40 and 50 (wt.%) of a Ca₃(PO₄)₂–SiO₂–MgO glass, were processed. The prepared composites consist of a poly(methylmethacrylate)–co–(ethylhexylacrylate) (PMMA–co–EHA) matrix filled with a glass (G7), with nominal composition 33.26CaO, 28.07P₂O_5, 23.03SiO_2, 15.64MgO (wt.%). The in vitro bioactivity of the composites was assessed by determining the changes in surface morphology and composition, by X-ray diffraction (XRD) and scanning electron microscopy coupled with X-ray energy dispersive spectroscopy (SEM-EDS), after soaking in a simulated body fluid (SBF) for periods of up to 21 days at 37 °C. Inductively coupled plasma (ICP) was used to assess the evolution of ionic concentrations in the SBF solution. The results obtained confirmed the growth of a hydroxyapatite (HA)-like layer on the surface of the prepared composites. As expected, HA layer formation was faster for composites prepared with higher glass content.     

Synthesis and structure of Cs3[UO2(CH3COO)3]2(NCS)·H2O

The compound Cs₃[UO₂(CH₃COO)₃]₂(NCS)·H₂O (I) was synthesized and studied by IR spectroscopy and single crystal X-ray diffraction. Compound I crystallizes in the monoclinic system with the following unit cell parameters: a = 7.8286(9), b = 19.892(2), c = 20.050(2) Å, β = 94.527(2)°, space group P2₁/c, Z = 4, R = 0.0387. The uranium-containing structural units in crystals of I are mononuclear complexes [UO₂(CH₃COO)₃]^? belonging to crystal-chemical group AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B⁰¹ = CH₃COO^?) of uranyl complexes.     

First principles study of isotope effect in hydrogen-bonded K3H(SO4)2: I — stable structures

The first principles calculations for K₃H(SO₄)₂ (KHS) system are performed in order to determine its stable structure in the presence of the hydrogen or the deuterium in its hydrogen bond, and to discuss the origin of the large isotope effect in the KHS system. As a result, a reasonable value of the antiferroelectric interaction energy is obtained. It is also found that the position of the hydrogen is closer to the center of the hydrogen bond than that of the deuterium, based on the calculated results of the proton-position dependence of the oxygen–oxygen distance and on the experimental fact that the oxygen-oxygen distance in K₃D(SO₄)₂ (DKHS) is larger than that in KHS.     

Role of the proton tunneling in the phase transition of K3D1−x H x (SO4)2

Dielectric and thermodynamic properties have been investigated for isotopically mixed crystals of K₃D_1–x H_x(SO₄)₂, which are composed of structurally isolated dimeric units SO ₄ ^– ... H-SO ₄ ^– . The critical temperature T_c for the antiferroelectric phase transition decreases with proton concentration (x) and eventually the phase transition vanishes at x_c 0.66 ± 0.04. The x-dependent behavior of T_c, the dielectric constant (T) and the specific heat C(T) are well accounted for by the mean-field theory for the transverse Ising model, indicating an important role of the proton tunneling on the phase transition and related properties. These features are compared with conventional hydrogen-bonded dielectrics with infinite networks of the hydrogen bonds.     

Crystal structure of a double Np(V) ammonium propionate, NH4[(NpO2)3(C2H5COO)4(H2O)]·3H2O

The structure of NH₄[(NpO₂)₃(C₂H₅COO)₄(H₂O)]·3H₂O was studied by single crystal X-ray diffraction. The single crystals were prepared by hydrothermal synthesis. In the structure, there are three crystallographically independent Np atoms with different equatorial surrounding. All of them have CN 7; the coordination polyhedron is a distorted pentagonal bipyramid. Each NpO ₂ ⁺ cation is bonded to four other cations, acting simultaneously as a bidentate ligand and a coordination center for two other dioxocations. The cation-cation interactions result in formation of trigonal-hexagonal cationic networks.     

Preparation of porous spherical ZrO2–SiO2 composite particles using templating and its solid acidity by H2SO4 treatment

Porous ZrO₂–SiO₂ composite sphere particles were prepared by impregnating precursor solutions into organic monolith particles, with subsequent calcination in air. The porous spheres possessed uniformly sized pores of around 10 nm. Addition of SiO₂–ZrO₂ decreased the ZrO₂ crystallinity and increased the specific surface area. The acid amount on the surface of the composite spheres was increased by treatment with H₂SO₄. The acid strength and its amount, including the Lewis/Br?nsted acid ratio, depended on the SiO₂/ZrO₂ ratio and the H₂SO₄ concentration. The powder treated under an optimum condition exhibited higher solid acidity than the reference solid acid catalyst. The prepared porous SO₄ ²⁻/ZrO₂–SiO₂ spheres showed higher saccharization activity than the reference solid acid catalyst did.     

Synthesis and stability of α-tricalcium phosphate doped with dicalcium silicate in the system Ca3(PO4)2–Ca2SiO4

The aim of this study was to synthesize materials of α-tricalcium phosphate doped with small amounts of dicalcium silicate, by solid state reaction, at high temperature and slow cooling to room temperature. The obtained materials were characterized by X-ray diffraction, Scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy, showing that there is a region between 0.5 and 4.0 wt.% of dicalcium silicate where solid solution α-tricalcium phosphate (α-TCPss) is stable to room temperature.     

Effect of gamma irradiation on the heat capacity of (CH3)2NH2Ga(SO4)2 · 6H2O crystals in the temperature range of phase transitions

The heat capacity of dimethylammoniumgallium sulfate crystals was measured using adiabatic calorimetry in the range 80–300 K before and after gamma irradiation with doses of 10⁷ and 10⁸ R. Heat-capacity anomalies were revealed around the ferroelastic-ferroelectric (135 K) and ferroelectric-paraelectric (119 K) phase transitions. Gamma irradiation was found to reduce the temperature stability range of the ferroelectric phase.     

Effect of Gamma Irradiation on the Dielectric Properties of (CH3)2NH2Ga(SO4)2 · 6H2O Crystals in the Vicinity of the Ferroelectric Transition

The effect of gamma irradiation on the dielectric permittivity and loss tangent of (CH₃)₂NH₂Ga(SO₄)₂ · 6H₂O crystals was studied near the ferroelectric transition at different frequencies. Irradiation was found to sharply reduce and tan at gamma doses below 5 × 10⁷ R. At higher doses, and tan level off. With increasing gamma dose, the ferroelectric transition shifts to lower temperatures, irrespective of frequency.     

Ceramics Based on CaSO4⋅2H2O Powder Synthesized from Ca(NO3)2 and (NH4)2SO4

Inorganic Materials - Ceramics consisting of anhydrous calcium sulfate, CaSO4, after firing in the range 800–1000°C have been prepared from calcium sulfate dihydrate (CaSO4?2H2O)...     

(Mo,W)5Si3–(Mo,W)Si2 Eutectics: Properties and Application in Composite Materials

Experimental data are presented on (Mo,W)₅Si₃ and (Mo,W)Si₂ solid solutions and are analyzed using the known phase diagrams of the binary systems Mo–Si and W–Si. It is shown that, with increasing tungsten content, the melting temperature of the (Mo,W)₅Si₃–(Mo,W)Si₂ eutectic rises. Surprisingly, the alloys with W : Mo atomic ratios close to unity are found to contain, along with the silicide solid solutions, molybdenum disilicide almost free of tungsten. The mean room-temperature hardness of the eutectic alloys varies nonmonotonically with tungsten content and shows maxima at 33 and 75 at. % W. The surface texture is found to have a significant effect on the rate of high-temperature gas corrosion. The possibility of compositional control (variations in the W : Mo and (Mo,W)₅Si₃ : (Mo,W)Si₂ ratios) over the thermal expansion of the alloys is analyzed. Data are presented on the temperature-dependent resistivity of SiC-matrix composites.     

Reaction of Cd(NO3)2·4H2O with 4,4'–bipyridine (bpy) in MeOH solvent: synthesis and characterization of T-shaped [Cd(bpy)1.5(NO3)2]·3H2O,square grid [Cd(bpy)2(H2O)2](NO3)2·4H2O and linear polymeric [Cd(bpy)(H2O)2(NO3)2]

The influence of concentration of water and metal salt in the reaction between Cd(NO₃)₂·4H₂O and 4,4′–bipyridine in MeOH has been studied and three compounds namely, T-shaped [Cd(bpy)_1.5(NO₃)₂]·3H₂O, 1 square grid [Cd(bpy)₂(H₂O)₂](NO₃)₂ 4H₂O, 2 and one dimensional linear polymer, [Cd(bpy)(H₂O)₂(NO₃)₂], 3 were isolated quantitatively in this process. Compound 1 forms in MeOH at high dilution of the metal salt (5.0 mg/mL or less) and for the metal-to-ligand ratio 1:(1.5–2.0). Compound 2 forms exclusively in the concentration range, 17–33% for water in MeOH by volume and 12–28 mg/mL for the metal salt of the solution. Outside these limits, mixtures of 2 and 3 were isolated. For 1:1 ratio of metal salt to bpy, the linear polymer, 3 was obtained in major quantity and its formation was found to be independent of concentration of water or the metal salt. Compounds 1 and 2 have been characterized by X-ray crystallography. On heating all the compounds decompose through a common intermediate [Cd(bpy)(NO₃)₂] and finally to CdO as monitored by TG.     

Characterization of SiO2–Na2O–Fe2O 3–CaO–P2O 5–B 2O 3 glass ceramics

Bioactivity and magnetic properties were investigated in glass and glass ceramics based on the SiO₂–Na₂O–Fe₂O₃–CaO–P₂O₅–B₂O₃ system to find their suitability as thermoseed for hyperthermia treatment of cancer. The effect of change in compositions on bioactivity was examined in simulated body fluids. The glass ceramic samples exhibit Na₃CaSi₃O₈ and Na_3-XFe_XPO₄ phases. After dipping the glass ceramic samples in simulated body fluids silica hydrogel first forms, followed by an amorphous calcium phosphate layer. Magnetic and microwave resonance experiments further demonstrate the potential of these glass ceramics for possible use in hyperthermia.