Contents of α-O-4 and β-O-4 Bonds in Native Lignin and Isolated Lignin Preparations

An analytical calculation method for the estimation of the contents of alkyl aryl ether bonds (α-O-4 and β-O-4) in lignin was developed. In the framework of the method, Alkyl–O–Aryl type bonds are described as coupled phenolic hydroxyls (OH_phen). The method is based on the balance equation including the free and coupled OH_phen contents in dissolved and residual lignins, on the one hand, and their respective contents in native lignin, on the other. The free OH_phen content is calculated on the basis of the OH_phen contents of dissolved and residual lignin, determined by the aminolysis method in the course of kraft cooking of softwood. The calculation results for soluble lignin preparations are in good agreement with the 13C NMR (nuclear magnetic resonance) spectral data for the solutions. The content of Alkyl–O–Aryl bonds in native softwood (pine, spruce) lignin was estimated at 79/100 PPU (phenylpropane unit). In isolated lignin preparations, the contents of these bonds decrease in the sequence: Freudenberg lignin (71/100 PPU)> Bjorkman lignin (61/100 PPU)> Pepper lignin (44/100 PPU). Dissolved alkaline lignin still contains small amounts of Alkyl–O–Aryl bonds (36/100 PPU in soda lignin and an average of 23/100 PPU in soda-AQ lignin, kraft lignin, and kraft-AQ lignin). Residual lignin which represents the fraction of native lignin with inter-unit bonds resistant to kraft pulping contains 66/100 PPU of such bonds. A relatively high content of Alkyl–O–Aryl bonds (61/100 PPU) is preserved in technical hydrolysis lignins.     

Microstructure and mechanical properties of carbon-precursor-added B4C and B4C−SiC ceramics subjected to pressureless sintering

Organic-carbon-precursor-added B₄C and B₄C–SiC ceramics were subjected to pressureless sintering at various temperatures. The carbon precursor increased the densification of the B₄C and B₄C–SiC ceramics sintered at 2200 °C to 95.6 % and 99.1 % theoretical density (T.D.), respectively. The pyrolytic carbon content of the B₄C–SiC composite decreased with increasing SiC content. The graphitization degree of pyrolytic carbon decreased slightly with the amount of carbon precursor and content of SiC. The 95 wt. % B₄C–5 wt. % SiC composite added with 7.5 wt. % carbon precursor and sintered at 2200 °C outperformed the other B₄C–SiC composites, and its sintered density, flexural strength, Young’s modulus, and microhardness were 98.6 % T.D., 879 MPa, 415 GPa, and 28.5 GPa, respectively. These values were higher than those of composites prepared via pressureless sintering and comparable to those of composites fabricated via hot pressing and/or using metal or oxide additives.     

Synthesis and characterization of soluble polyamides from bis-[(4′-aminobenzyl)-4-benzamide] ether and various diacids

New aromatic diamine containing preformed amide, ether, and methylene; bis-[(4′-aminobenzyl)-4-benzamide] ether (BABE), was synthesized and characterized by FT-IR, NMR, and mass spectrometry. Aromatic–aliphatic polyamides were prepared from BABE with aliphatic/aromatic diacids via Yamazaki’s polymerization. The polyamides were characterized by FT-IR, ¹H NMR, inherent viscosity [η_inh], solubility tests, differential scanning calorimetry [DSC], thermogravimetric analysis [TGA], and X-ray diffraction [XRD]. Polyamides had inherent viscosities 0.35–0.84 dL/g, soluble in aprotic polar solvents like N-methyl-2-pyrrolidone, N, N-dimethyl acetamide and dimethyl sulphoxide containing LiCl due to an amorphous to partially crystalline morphology; as XRD patterns indicated. DSC analysis of polyamides showed glass transition temperatures 166–268 °C. Polyamides showed high thermal stability as they did not degrade below 300 °C, had 10% weight loss temperature higher than 375 °C, and the char yields at 900 °C were 22–55%; indicating potential applications as engineering materials.     

Combustion synthesis and characterization of spherical α-MnMoO4 nanoparticles

In this study, α-MnMoO₄ nanoparticles were prepared by combustion synthesis method. The structural, morphological and electrical characteristics of α-MnMoO₄ were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, transmission electron microscopy and impedance spectroscopy. The structural parameters were calculated from XRD pattern which confirmed the monoclinic structure of α-MnMoO₄. FT-IR and Raman spectroscopy results revealed the presence of MoO₄ surface functional groups. The TEM and HRTEM investigations evidenced the presence of homogeneous distribution of spherical nanoparticles and high crystallinity of α-MnMoO₄. Moreover, the SAED patterns clearly revealed the polycrystalline nature of the material. The conductivity measurements had inferred the semiconducting property of α-MnMoO₄ and the maximum conductivity of 1.94 × 10^? 6 S/cm was attained at 540 °C.     

Synthesis and polymerization of liquid crystalline α-oxiranes containing 4-cyanobiphenyl and p-methoxyphenyl benzoate mesogenic groups

Summary Synthesis of a new series of -oxiranes having 4-cyanobiphenyl and p-methoxyphenyl benzoate mesogenic groups and phase behaviour of synthesized compounds are described. Polymerization of -oxiranes with BF₃-O(C₂H₅)₂ and Et₃Al/H₂O/Acetyl acetone as initiators was carried out. The first initiator produced the olygomers displaying liquid crystalline properties while the second one gave the crystalline polymers with high degree of polymerization.     

Low temperature heat capacity measurements of β-Si3N4 and γ-Si3N4: Determination of the equilibrium phase boundary between β-Si3N4 and γ-Si3N4

Isobaric heat capacities of β-Si₃N₄ and γ-Si₃N₄ were measured at temperatures between 1.8 and 309.9 K with a thermal relaxation method. The measured heat capacities of γ-Si₃N₄ are smaller than those of β-Si₃N₄ in this temperature range. Using these data, we determined the standard entropies of β-Si₃N₄ and γ-Si₃N₄ to be 62.30 J·mol⁻¹ K⁻¹ and 51.79 J·mol⁻¹ K⁻¹, respectively. The equilibrium phase boundary between β-Si₃N₄ and γ-Si₃N₄ was calculated using these values and thermodynamic parameters reported in previous studies. The obtained equilibrium phase transition pressure at 2000 K is 11.4 GPa. It is lower than the experimental pressures at which γ-Si₃N₄ was synthesized in previous studies. The calculated Clapeyron slope at this temperature is 0.6 MPa K⁻¹, which is consistent with those of theoretical studies.     

Mechanical,morphological and thermal properties of short carbon and aramid fibres-filled bromo-isobutylene-isoprene rubber vulcanised with 4, 4’ bis(maleimido)diphenylmethane

ABSTRACT

This paper describes the use of a combination of 4, 4’ bis(maleimido)diphenylmethane and ZnO as a high-temperature processable vulcanising agent for the short aramid and carbon fibre-filled bromo-isobutylene-isoprene rubber. The fibre breakage analysis, cure characteristics, mechanical, thermal and morphological properties of the composites were evaluated with different fibre loading. The fibre breakage analyses revealed that the aramid fibres have good length retention property compared to carbon fibres. The morphological analysis of the extracted aramid fibres showed severe surface roughness primarily due to fibrillation after shear mixing. The fibrillated aramid fibres lead to aggregation and poor dispersion of the fibres in the rubber matrix. However, fibrillation imparted surface roughness and increased surface area on the aramid fibres which improved the fibre–matrix interaction via mechanical anchoring. On the other hand, the carbon fibre-filled composite showed poor fibre–matrix interaction and inferior strength and modulus.     

Mechanical characteristics of FeAl2O4 and AlFe2O4 spinel phases in coatings – A study combining experimental evaluation and first-principles calculations

FeAl₂O₄ and AlFe₂O₄ have similar spinel structures but different atomic arrangements, leading to different properties. In this study, mechanical properties and structures of the two spinel phases in composite coatings prepared by reactive plasma spraying of Fe₂O₃-Al composite powder were investigated by means of multi-mode atomic force microscopy, X-ray diffraction, and scanning electron microscopy. It was demonstrated that AlFe₂O₄ was stronger than FeAl₂O₄ with a higher electron work function (EWF). First-principles calculations were conducted to understand the difference in mechanical properties between the two phases. It was shown that FeAl₂O₄ and AlFe₂O₄ have “normal” and “inverse” spinel structures with different configurations of valence electrons: Fe²⁺_tet(Al³⁺)₂O₄ and Fe³⁺_tet(Fe²⁺Al³⁺)_octO₄. Compared to Fe²⁺_tet(Al³⁺)₂O₄, Fe³⁺_tet(Fe²⁺Al³⁺)_octO₄ has its O and Fe atoms in the octahedral sites forming covalent bonds, which increase the stability and strength of the crystal, corresponding to higher EWF and larger bulk, shear and Young's moduli.     

Antiferromagnetism and heat capacity of NaCo2−xCuxO4 ceramics

Polycrystalline samples of NaCo_2−xCu_xO₄ (x=0, 0.01, 0.03 and 0.05) were synthesized in two different ways: 1) by a mechanochemically assisted solid-state reaction method (MASSR) and 2) by a citric acid complex method (CAC). In this work we examined the influence of these synthesis routes and small Cu concentrations on magnetic properties and the heat capacity of sintered samples. The magnetic susceptibility (χ) of all samples followed the Curie-Weiss law in the temperature range between 50 K and 300 K, while a negative Weiss constant (θ) implied an antiferromagnetic interaction. According to the magnetic susceptibility data, a peak around 30 K indicating the presence of Co₃O₄ as a secondary phase appeared for all MASSR samples and CAC samples with Cu content above 1%. The effective magnetic moment (μ_eff) of CAC samples was lower than the theoretical, spin only value obtained for the Co⁴⁺ ion in the low spin state indicating the presence of low spin Co³⁺(S =0). These values were also lower compared to the values obtained for MASSR samples. The highest μ_eff of 1.75 μ_B/atom Co was obtained for the undoped MASSR sample. The heat capacity of CAC samples at 2 K decreased with Cu concentration due to lowering of the electronic specific heat coefficient (γ). The highest γ of 63.9 mJ/molK² was obtained for the undoped CAC sample. This reduction in γ values was the result of the decrease of the density of state and/or mass enhancement factor.     

The “In-cell” and “Ex-cell” Fenton treatment of phenol, 4-chlorophenol and aniline

A comparative study of phenol, 4-chlorophenol and aniline degradation with the electro-generation of H₂O₂ at gas-diffusion electrodes was carried out under three different conditions: electro-Fenton^® treatment in an undivided cell; electro-Fenton treatment in the catholyte of a membrane cell divided by a proton-exchange membrane (in-cell electro-Fenton membrane process); and a treatment of polluted solution in the cathode space of a membrane cell with the generation of H₂O₂, followed by the addition of Fe(II) salt in the other reactor (ex-cell electro-Fenton process).An optimized cell design with no gap between the membrane and the anode, along with the appropriate choice of supporting electrolytes, ensured a voltage reduction with a membrane cell in comparison with that of an undivided cell. The accumulation of hydrogen peroxide in concentrations sufficient for the almost complete destruction (90–98%) of aromatic organic pollutants was achieved in all cases but the ex-cell process with the preparative electrolysis in the pilot scale membrane reactor separated by the proton-exchange membrane MK-40 showed higher treatment efficiency and lower specific energy consumption in comparison with known technologies. Damage of the gas-diffusion layer was observed in some tests which could be caused by alkaline conditions in the pores of the gas-diffusion cathode (GDE). The pH indicator paper showed a color specific for alkaline media in contact with the GDE treated in the solution with pH 3 in the bulk. A possible explanation could be that even in acid media, hydrogen peroxide generation in pores of the gas diffusion layer proceeds with formation of HO ₂ ^? which is common for alkaline media and consecutive protonation occurs at the interface with the acid solution.     

Electrochemical and thermal behaviour of solid AgIAgIO3 and AgIAg3AsO4

Solid AgIAgIO₃ and AgIAg₃AsO₄ of various compositions were investigated by conductivity, thermal and electrochemical methods. Both systems show dependences on composition and temperature enabling determination of the activation energy of conductivity. Glassy phases are formed at appropriate rates of cooling of molten samples. By thermal analysis (DSC), the glass transition and crystallization processes of the glassy phases were identified. Processes of anodic and cathodic decomposition of the electrolyte were investigated. The energy of activation for the cathodic redox (Ag⁺ → Ag) process was determined. It was also shown how the capacity of the Pt/electrolyte phase boundary depends on the dc potential and ac frequency.     

Microstructures and mechanical properties of B4C–SiC intergranular/intragranular nanocomposite ceramics fabricated from B4C,Si, and graphite powders

B₄C–SiC intergranular/intragranular nanocomposites with high hardness and high toughness were fabricated through mechanochemical processing with B₄C, Si, and graphite powders and subsequent hot pressing without any sintering aid. The milled powders are composed of stacking-disordered SiC and nanocrystalline B₄C. Most nano/micron-sized SiC particles are homogeneously dispersed in B₄C matrix, and some nano-sized SiC and B₄C particles are embedded into B₄C grains to form an intergranular/intragranular structure. The disordered characteristic of the milled powders is the essential factor for the formation of the intragranular structure, sudden densification within the narrow temperature range (1700–1900 °C), and the preparation of dense samples under a relatively low temperature (1900 °C). The relative density, Vickers hardness, and fracture toughness of the samples sintered at 1950 °C are 98.6%, 34.3 GPa, and 6.0 MPa m^1/2, respectively. The intergranular/intragranular structure plays an important role in improving fracture toughness and hardness of the composites.     

Synthesis,characterization and luminescence of two unusual 4d–4f Ln–Ag coordination compounds

Two novel Ln–Ag coordination compounds with the formula [LnAg₂(IN)₄(OAC) · 5H₂O] · 2H₂O (Ln = Gd 1, Eu 2; HIN = isonicotinic acid; HOAC = acetic acid) have been synthesized under hydrothermal condition and characterized by single-crystal X-ray diffraction, thermal analysis, IR absorption spectroscopy, ultraviolet excitation and emission spectrum. The two compounds show isostructural architectures and exhibit an unusual 1-D structure, which is formed by the linkages of Ag–Ag.     

1D and 2D network of ReO4− bonded azoimidazoles

1-Alkyl-2-(arylazo)imidazoles are π-acidic, bidentate chelating molecules. In acid medium imidazole-N centers are protonated and can extract heavy anions. One such example is the binding with ReO₄⁻ in acidic medium. 1-Alkyl-2-(arylazo)imidazolium-perrehenate shows hydrogen bonded 1D network. Inclusion of H₂O into the molecular frame of 1D increases the dimensionality to 2D network.     

Volumetric and Transport Properties of Aqueous NaB（OH）4 Solutions

Density, pH, viscosity, conductivity and the Raman spectra of aqueous NaB（OH）4 solutions precisely measured as functions of concentration at different temperatures （293.15, 298.15, 303.15, 313.15 and 323.15 K） are presented. Polyborate distributions in aqueous NaB（OH）4 solution were calculated, covering all the concentration range, B（OH）4 is the most dominant species, other polyborate anions are less than 5.0%. The volumetric and the transport properties were discussed in detail, both of these properties indicate that B（OH）4 behaves as a struc- ture-disordered anion.     

Calix[4]arene–carbazole-containing polymers: Synthesis and properties

New highly fluorescent calix[4]arene-containing phenylene-alt-ethynylene-3,6- and 2,7-carbazolylene polymers (CALIX-PPE-CBZs) have been synthesized for the first time and their photophysical properties evaluated. Both polymers were obtained in good isolated yields (70–84%), having M_w ranging from 7660–26,700 g mol⁻¹. It was found that the diethynyl substitution (3,6- or 2,7-) pattern on the carbazole monomers markedly influences the degree of polymerization. The amorphous yellow polymers are freely soluble in several nonprotic organic solvents and have excellent film forming abilities. TG/DSC analysis evidences similar thermal behaviors for both polymers despite their quite different molecular weight distributions and main-chain connectivities (T_g in the range 83–95 °C and decomposition onsets around 270 °C).The different conjugation lengths attained by the two polymers dictates much of their photophysical properties. Thus, whereas the fully conjugated CALIX-PPE-2,7-CBZ has its emission maximum at 430 nm (E_g = 2.84 eV; Φ_F = 0.62, CHCl₃), the 3,6-linked counterpart (CALIX-PPE-3,6-CBZ) fluoresces at 403 nm with a significant lower quantum yield (E_g = 3.06 eV; Φ_F = 0.31, CHCl₃). The optical properties of both polymers are predominantly governed by the intrachain electronic properties of the conjugated backbones owing to the presence of calix[4]arenes along the polymer chain which disfavor significant interchain interactions, either in fluid- or solid-state.