Electrical properties of carbons—resistance of powder materials

A significant property in the selection of materials for the manufacture of porous carbon electrodes is the electrical resistivity. The problem of determining this property in porous materials is scarcely treated in the literature. The authors studied a large number of Brazilian carbonaceous materials, having in view the construction of gas diffusion electrodes for fuel cells. An apparatus was designed, with the same idea of a sample cell under pressure, as the one by Brodd and Kosawa in 1978; the fundamental modifications introduced resulted in considerable improvement in precision. A detailed design of the apparatus and the electrical circuit used are presented. It is evident from the curves that carbons are ohmic resistors and that a strong dependence exists between resistivity and pressure, such that only at fixed and constant pressures a comparison of the resistivity values is meaningful.Gas diffusion electrodes were manufactured with a composite prepared from a paste of the carbonaceous material. An electrographite, a petroleum coke and an acetylene black exhibited excellent electrical properties as electrode materials.     

Production and properties of aluminumγ-oxynitride

The method of melting in a solar furnace is used to synthesize aluminum-oxynitride from an AIN-Al₂O₃ mixture in the form of blocks. The concentration range of the existence of single-phase-oxynitride is determined by x-ray phase analysis and microstructural analysis. AQ-1500D derivatograph is used to investigate the oxidation process at 300 – 1773 K.Translated from Ogneupory, No. 4, pp. 21 – 22, April, 1996.     

Thermal shock properties of β-sialon ceramics

An indentation–quench method based on Vickers cracks for measuring thermal-shock properties has been applied to β-sialon materials. The thermal-shock properties have been correlated with the morphology of the β-sialon grains, the z value in the β-sialon solid solution Si_6−zAl_zO_zN_8−z and the amount of residual intergranular glass phase. z Values in the range 0.6–3.0 were tested, and the amount of residual yttrium-containing glass phase was varied between 0 and 20 vol.%. The best thermal-shock resistance was found at low z values, and was further improved by adding an intergranular glass phase. The poorest resistance to thermal shock was found for the highest z value where the presence of glass had no measurable influence. One composition (z=1.5, 10 vol.% glass) was selected for studying the influence of the microstructure on the thermal-shock properties. The microstructure was varied by applying different sintering conditions. An improvement of the thermal-shock properties and the fracture toughness was found in samples containing elongated β-sialon grains formed in situ. In general, in-situ reinforced β-sialon materials with low z values and containing an intergranular glass phase exhibited the best thermal-shock resistance and improved fracture toughness (K_1c>4 MPa m^{$\text{1}\text{2}$}).     

Acid–base properties of polymer-coated paper

The wetting behavior of a series of polymer-coated papers has been studied. Different ways of determining the acid–base properties of the polymers are presented. The well-known van Oss–Chaudhury–Good (vOCG) bi–bi polar model is compared with more simplified mono–bi polar and mono–mono polar models. The effect of surface roughness on the wetting was also studied with atomic force microscopy. The overall wetting of each probe liquid was evaluated by calculating the work of adhesion to the polymer surfaces. It is shown that ethylene glycol and water may be considered as mono polar liquids, which simplifies the original vOCG-model. It is also shown that in most cases the surface energy values are in the same range when using both the complex bi–bi polar approach and the simpler mono–mono polar approach. The different polymers used are found to be of a predominating basic character.     

Effect of Addition of Al and Mg on properties of Periclase-Spinel-Carbon Brick

Periclase-spinel-carbon brick was made from sintered spinel,fused magnesia and flake graphite as principal raw materials,the influence of Mg/Al(w/w) ratio and the addition of Al,Mg in the matrix of periclas-spinel-carbon brikc on the carbonization and thermal expansion coeffi-cient and the weight los of the brick after heating at 1500℃ in a flowing stream of dry N2for 1.5 h have been studied.The results show that to control Mg/Al(w/w) ration and to add both Al and Mg appropriately can obvi-ously improve the properties of the bricks.     

Keeping properties of edible oils—Part I. The use of accelerated tests for assessment of the keeping properties of oils and the value of antioxidants

Assessment of oil quality by two accelerated oxidation tests gave little or no correlation with organoleptic asessment during storage. Improvements in quality of oils refined in the factory, to which antioxidants had been added, are indicated by the accelerated tests but are not reproduced in normal storage. Howver a treatment of the oils with alumina, as a part of the refining process replacing earth bleaching, appears to remove antagonistic factors, and under these circumstances the addition of antioxidant has a pronounced effect.     

Electrical properties of low-temperature-fired ferrite–dielectric composites

The effects of the BaO·(Nd_0.8Bi_0.2)₂O₃·4TiO₂ (BNBT) to NiCuZn ferrite ratio and addition of Bi₂O₃–B₂O₃–SiO₂–ZnO (BBSZ) glass on the sintering behavior, microstructure evolution, dielectric and magnetic properties of BNBT–NiCuZn ferrite composites were investigated in developing low-temperature-fired composites for high frequency electromagnetic interference (EMI) devices. The results indicate that these composites can be densified at 900 °C and exhibit superior dielectric and magnetic properties with the addition of BBSZ glass. The dielectric system used in the ferrite–dielectric composites reported in the previous studies mostly belong to the ferroelectricity group, which are not suitable for use in the high frequency range (>800 MHz) due to the selfresonance frequency limit. In this study, the dielectric constant remains nearly a constant over a wide range of frequencies (100 MHz to 1 GHz) and the magnetic resonance frequencies are larger than 100 MHz for the BNBT + BBSZ glass–NiCuZn ferrite composites. Therefore, the BNBT + BBSZ glass–NiCuZn ferrite composites can be a good candidate material for high frequency EMI device applications.     

Influence of processing and sterilisation on properties of poly-ϵ-caprolactone

Abstract

Poly-?-caprolactone (PCL) is a significant member of a group of polymers regarded as bioabsorbable, having been the focus of extensive research for use as a diffusion controlled drug delivery system. Degradation of PCL proceeds through hydrolysis of the ester bonds in the polymer chains and is influenced significantly by the polymer's initial molecular weight and crystallinity. To evaluate the effects of processing and sterilisation on these properties, PCL pellets (CAPA 6400) were either injection moulded or extruded and sterilised by ethylene oxide gas (EtO). Procedures were used to evaluate mechanical properties, molecular weight and crystallinity. Upon processing and sterilisation the molecular weights of the injection moulded and extruded materials did not differ significantly from that of the PCL pellets, suggesting processing and sterilisation did not initiate chain scission of the polymer's ester bonds. However, the crystallinity of PCL proved to be sensitive to injection moulding with an increase of approximately 5% observed after processing, with sterilisation by EtO gas causing annealing of the PCL pellets, injection moulded and extruded material. After sterilisation the crystallinity of the PCL pellets and extruded material increased by approximately 10% with a 4% increase observed for the injection moulded material. The mechanical properties of both the injection moulded and extruded material where not influenced by sterilisation. The results from this investigation suggest that PCL's molecular weight is insensitive to processing and sterilisation. However, sterilisation by EtO gas in the temperature range of 38-48°C used in this study does result in annealing of the polymer.     

Dielectric properties of barium titanate–molybdenum composite

The barium titanate–molybdenum composites were prepared through solid state reaction method in argon atmosphere. The microstructure, resistivity, and dielectric properties of the composites were investigated. XRD results indicated that chemical reactions between barium titanate (BaTiO₃:BT) and molybdenum (Mo) have taken place during sintering, resulting in the formation of BaMoO₄ (BM) and BaTi₂O₅ (BT₂). The resistivity decreased with the increasing amount of Mo in the composites. The composites (when x = 5 and 20 wt.%) showed lower dielectric constant than pure BaTiO₃, especially, the dielectric constant (when x = 20 wt.%) reached a minimum value (<10⁴), while composites (when x = 10 and 15 wt.%) showed rather high dielectric constant at temperatures range from 25 °C to 160 °C. The dielectric constant of the composite gradually decreased with increase in frequency at the room temperature. The dielectric constant of composite (when x = 5 wt.%) comes up to 10⁴, and the T_c (Curie temperature) of the composite was relatively higher than that of BT (120 °C).     

Fibre-forming properties of melts of polypropylene—Copolymer of ethylene with vinyl acetate blends

The rheological properties of melts of PP—CEVA blends include a decrease in the viscosity and an increase in the elasticity due to the specific features of fibre formation in flow of melts of the blends. The orientational draw ratio of composite PP—CEVA monofilaments increased in comparison to the λ of monofilaments of the starting polymers. Fibres with higher (by 1.6 times) strength and higher (by 2 times) initial modulus than for fibres of the starting PP can be obtained by spinning from a melt of PP—CEVA mixture. Ukraine State Academy of Light Industry, Kiev. Translated fromKhimicheskie Volokna, No. 1, pp. 18–20, January–February, 1999.     

Volumetric properties of polymer blends from Tao–Mason equation of state

The present study is an improvement of previous work (Yousefi and Karimi, Ionics 18:135–142, 17) concern to the assessment of the ability of the Tao–Mason equation of state to predict pressure–volume–temperature (PVT) of melting polymers. The present paper, focus on the modeling of volumetric properties of polymer blends based on melting temperature (T _m) and melting point density (ρ _m), as scaling constants. The calculation of second Virial coefficients (B ₂), effective van der Waals co-volume (b) and correction factor (α) are required for judgment about applicability of this model. The new correlations were used to predict the PVT behavior of polymer blends containing poly(propylene glycol) + poly(ethylene glycol) (PEG-200), poly(ethylene glycol) methyl ether(PEGME-350) + PEG-200, PEGME-350 + PEG-600, poly(2,6-dimethyl-1,4-phenylene oxide) + poly styrene(PS), and PS + poly(vinylmethylether) in different temperatures, pressures, and mole fractions. A collection of 5,397 data points has been examined for the aforementioned polymers in the temperature in the range of 298.15–605.05 K and pressures up to 200 MPa. The average absolute deviation between the calculated and experimental densities is of the order of 0.78 %.     

Production and investigation of structure and properties of polyethylene–polylactide composites

Under conditions of shear deformations, low-density polyethylene (LDPE) and polylactide (PLA) composites are obtained in rotor disperser. The production of these composites allows one to use polymers derived from natural raw and to reduce the cost of the materials on their base. The addition of rigid PLA leads to increase in elastic modulus from 200 for LDPE to 1190 for LDPE–PLA (50:50 wt %) composites and in tensile strength from 13.3 for LDPE to 17.8 for LDPE–PLA. By differential scanning calorimetry method, it is shown that LDPE and PLA are incompatible. Using X-ray diffraction analysis, it is found that degree of crystallinity of composites decreases from 46.1 at 50:50 wt % to 36.9 at 80:20 wt % component ratios with the rise in LDPE content. Tests on fungus resistance show that the composites containing 50 wt % PLA are more resistant than the composites containing 30 wt % PLA. First by gel-permeation chromatography method, it is shown that composite degradation after exposure in soil is accompanied by the PLA chain scission and depolymerization with formation of monomers and dimers (M _w of PLA decreases from 118,860 to 80,100). The obtained composites can be applied as packaging materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47598.     

Influence of SPS temperature on the properties of TiC–SiCw composites

Titanium carbide (TiC) composites containing 10 vol% silicon carbide whisker (SiC_w) were spark plasma sintered at different temperatures of 1800, 1900, and 2000 °C under a pressure of 40 MPa and a holding time of 7 min. At the sintering temperature of 1900 °C, the relative density, Vickers hardness, and flexural strength of the sintered samples hit their maximum values of 98.7%, 24.4 GPa, and 511 MPa, respectively. The microstructural characteristics of the sintered samples were assessed by optical and field emission scanning electron microscopy (FESEM) and XRD. The results revealed that at 1900 °C, the dispersion of SiC_w in the TiC matrix was homogenous, no chemical reaction took place between the reinforcement and the matrix, and produced a fine-grained microstructure. It was found that the thermal conductivity of SPSed samples did not have the same trend with relative density and mechanical properties. A maximum value of 32.3 W/mK was measured for the thermal conductivity of the composite sintered at 2000 °C.     

Effect of ZnO nano-particulate modification on properties of PZT–BLT ceramics

This research was conducted to study the effect of ZnO nano-particulate modification on properties of Pb(Zr_0.52Ti_0.48)O₃ (PZT)–(Bi_3.25La_0.75)Ti₃O₁₂ (BLT) ceramics prepared by a mixed-oxide solid-state sintering method. ZnO nano-particulate was added into PZT–BLT ceramics to obtain PZT–BLT/xZnO (x = 0, 0.1, 0.5 and 1.0 wt%). The PZT–BLT/xZnO ceramics were investigated in terms of phase, microstructure, physical, electrical, and mechanical properties. Tetragonality of PZT–BLT crystal structure tended to increase with increasing ZnO content. ZnO addition obviously increased the density of PZT–BLT ceramics while the grain size slightly decreased. Intergranular fracture mode was observed for pure PZT–BLT ceramic while the samples contained ZnO nano-particles showed a mixed-mode inter-/trans-granular fracture. Addition of ZnO also affected hardness and fracture toughness values. Addition of ZnO nano-particulate into PZT–BLT ceramics was found to improve room temperature dielectric constant but did not have a significant effect on ferroelectric properties. These observed results were expected to be caused by the behaviors similar to a donor-doped system.     

Physical–chemical properties of nanopowders and ceramic samples of REE orthophosphates

A series of physical–chemical studies of a series of binary REE orthophosphate systems has been performed: LaPO₄–DyPO₄–H₂O, LaPO₄–YPO₄–H₂O, LaPO₄–LuPO₄–H₂O, YPO₄–LuPO₄–H₂O, and YPO₄–ScPO₄–H₂O. Nanopowders of Ln'_{1 ?x}Ln'_x PO₄ · nH₂O orthophosphates have been synthesized by the sol–gel method using direct and reverse precipitation techniques. Ceramic samples were produced from the nanopowders, and their physical–mechanical properties were determined depending on the thermal treatment temperature and duration. The ceramic samples’ thermal behavior has been investigated by the dilatometry method. The results have been compared depending on the technique of nanopowder synthesis.     

Evaluation of mechanical properties of acrylated guar gum – unsaturated polyester composites

Guar gum (GG) and its derivatives are commonly used in aqueous solutions as rheology modifiers. The use of polysaccharides as fillers in thermoset polymer composites has as yet not received that attention attributed to other materials. In the present study GG and the effect of acrylation on its filler properties were evaluated. Unsaturated polyester composites were evaluated for their mechanical properties as well as solvent resistance and water absorption. It was observed that the acrylate derivatives with the highest degree of substitution resulted in composites with the best mechanical properties as well as increased toluene and water resistance. Thus, polysaccharides could be used as reinforcing fillers in thermoset composites.     

Renewable antioxidant properties of suspensible chitosan–polypyrrole composites

Conductive polymers have the ability to capture radicals and have become in focus for antioxidant applications of food packaging or biomedical applications. Unfortunately, the conducting polymers such as polypyrrole are difficult to suspense in solution after chemical or electrochemical polymerization. Chitosan, as a natural polymer from chitin, can be dissolved in diluted acetic acid solutions. In the present study, composites suspensible in diluted acetic acid solutions have been produced by the chemical polymerization of pyrrole in chitosan solution using ammonium persulfate (APS) as the oxidant. FTIR and UV–Vis measurements did identify an attachment of polypyrrole to chitosan.In order to optimize the activity and stability of the composites, the ratios of APS: polypyrrole: chitosan were analyzed. The chitosan–polypyrrole composites were formed as membranes (coatings); impedance measurements indicated their conductivity to be in the range of 10^?3–10^?7 S cm^?1. The antioxidant (radical scavenger activity) properties were determined by the di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium (DPPH) assay. The radical scavenger activity of the composites was found renewable by means of electrochemical cycling.     

Rheological properties of aqueous alumina–alumina-doped Y-PSZ suspensions

The effect of the substitution of alumina (Al₂O₃) by 0.3 wt% Al₂O₃-doped 3 mol% yttria-partially stabilized zirconia (Y-PSZ) on the rheological properties of concentrated aqueous slips was studied. Al₂O₃–Al₂O₃-doped Y-PSZ aqueous suspensions with different Al₂O₃-doped Y-PSZ contents: 0, 22 and 50 vol% were prepared using ammonium polyacrylate (NH₄PA) as dispersant. The particle size distributions of Al₂O₃ and Al₂O₃-doped Y-PSZ powders were similar; however, the particle shape and the surface coating of alumina conferred a markedly higher specific surface area to the Al₂O₃-doped Y-PSZ powder. The substitution of Al₂O₃ by Al₂O₃-doped Y-PSZ in the mixtures decreased the negative surface charge of the powders at pH 9, thereby increasing the amount of NH₄PA adsorbed and consequently the electrosteric repulsion between particles. However, the viscosity and yield stress values increased with increasing Al₂O₃-doped Y-PSZ content for all the solid loading studied. This could be explained by a larger interaction size of the Al₂O₃-doped Y-PSZ particles which resulted in a higher effective volume solid fraction and a lower amount of free-liquid available for flow.     

Preparation and properties of eggshell/β-polypropylene bio-composites

In this article, a novel eggshell/β-PP bio-composite was prepared and evaluated. First the waste chicken eggshell (ES) was modified by a stingy amount of pimelic acid (PA) through solution method, and then compounded with PP through melt blending method. The crystalline form, mechanical properties, and morphology of the ES/β-PP composites were studied. The results showed that ES modified by PA was a β nucleating agent with high efficiency and selectivity, resulting in the maximum K_β value of 0.99 in PP composites. PA modification promoted the dispersion and interfacial bonding of ES in PP. Although the addition of PA-modified ES slightly decreased tensile properties and flexural properties of PP, it increased the impact strength of PP by 228% than that of pure PP. Taking all factors into consideration, the optimal mass ratio of PP/ES/PA composites for reaching optimum mechanical properties should be 100/5/0.000471. Thus, the application of modified ES to prepare ES/β-PP bio-composites represents a promising way to mitigate environmental pollution and to reduce the cost of polyolefin products. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012