Determination of the elastic constants of portlandite by Brillouin spectroscopy

The single crystal elastic constants C_ij and the shear and adiabatic bulk modulus of a natural portlandite (Ca(OH)₂) crystal were determined by Brillouin spectroscopy at ambient conditions. The elastic constants, expressed in GPa, are: C₁₁ = 102.0(± 2.0), C₁₂ = 32.1(± 1.0), C₁₃ = 8.4(± 0.4), C₁₄ = 4.5(± 0.2), C₃₃ = 33.6(± 0.7), C₄₄ = 12.0(± 0.3), C₆₆ = (C₁₁-C₁₂)/2 = 35.0(± 1.1), where the numbers in parentheses are 1σ standard deviations. The Reuss bounds of the adiabatic bulk and shear moduli are K_0S = 26.0(± 0.3) GPa and G₀ = 17.5(± 0.4) GPa, respectively, while the Voigt bounds of these moduli are K_0S = 37.3(± 0.4) GPa and G₀ = 24.4(± 0.3) GPa. The Reuss and Voigt bounds for the aggregate Young's modulus are 42.8(± 1.0) GPa and 60.0(± 0.8) GPa respectively, while the aggregate Poisson's ratio is equal to 0.23(± 0.01). Portlandite exhibits both large compressional elastic anisotropy with C₁₁/C₃₃ = 3.03(± 0.09) equivalent to that of the isostructural hydroxide brucite (Mg(OH)₂), and large shear anisotropy with C₆₆/C₄₄ = 2.92(± 0.12) which is 11% larger than brucite. The comparison between the bulk modulus of portlandite and that of lime (CaO) confirms a systematic linear relationship between the bulk moduli of brucite-type simple hydroxides and the corresponding NaCl-type oxides.     

Single-crystal elastic constants of natural ettringite

The single-crystal elastic constants of natural ettringite were determined by Brillouin spectroscopy at ambient conditions. The six non-zero elastic constants of this trigonal mineral are: C₁₁ = 35.1 ± 0.1 GPa, C₁₂ = 21.9 ±0.1 GPa, C₁₃ = 20.0 ± 0.5 GPa, C₁₄ = 0.6 ± 0.2 GPa, C₃₃ = 55 ± 1 GPa, C₄₄ = 11.0 ± 0.2 GPa. The Hill average of the aggregate bulk, shear modulus and the polycrystal Young's modulus and Poisson's ratio are 27.3 ± 0.9 GPa, 9.5 ± 0.8 GPa, 25 ± 2 GPa and 0.34 ± 0.02 respectively. The longitudinal and shear elastic anisotropy are C₃₃/C₁₁ = 0.64 ± 0.01 and C₆₆/C₄₄ =0.60 ± 0.01. The elastic anisotropy in ettringite is connected to its crystallographic structure. Stiff chains of [Al(OH)₆]³⁻ octahedra alternating with triplets of Ca²⁺ in eight-fold coordination run parallel to the c-axis leading to higher stiffness along this direction. The determination of the elastic stiffness tensor can help in the prediction of the early age properties of cement paste when ettringite crystals precipitate and in the modeling of both internal and external sulfate attack when secondary ettringite formation leads to expansion of concrete.     

Mechanical characterization of ultra-thin fluorocarbon films deposited by R.F. magnetron sputtering

Fluorocarbon films were deposited on silicon substrate by R.F. magnetron sputtering using a polytetrafluoroethylene (PTFE) target. Structure of the deposited films was studied by X-ray photoelectron spectroscopy (XPS). Hardness, elastic modulus and scratch resistance were measured using a nanoindenter with scratch capability. -CF_x (x = 1, 2, 3) and C-C units were found in the deposited fluorocarbon films. The hardness and elastic modulus of the films are strongly dependent on the R.F. power and deposition pressure. The film hardness is in the range from 0.8 GPa to 1.3 GPa while the film elastic modulus is in the range from 8 GPa to 18 GPa. Harder films exhibit higher scratch resistance. Differences in nanoindentation behavior between the deposited fluorocarbon films, diamond-like carbon (DLC) films and PTFE were discussed. The fluorocarbon films should find more applications in the magnetic storage and micro/nanoelectromechanical systems.     

Microstructure and mechanical properties of silicon carbide processed by Spark Plasma Sintering (SPS)

The unique combination of SiC properties opens the ways for a wide range of SiC-based industrial applications. Dense silicon carbide bodies (3.18±0.01 g/cm³) were obtained by an SPS treatment at 2050 °C for 10 min using a heating rate of 400 °C/min, under an applied pressure of 69 MPa. The microstructure consists of fine, equiaxed grains with an average grain size of 1.29±0.65 μm. TEM analysis showed the presence of nano-size particles at the grain boundaries and at the triple-junctions, formed mainly from the impurities present in the starting silicon carbide powder. The HRTEM examination revealed high angle and clean grain boundaries. The measured static mechanical properties (H_V=32 GPa, E=440 GPa, σ_b=490 MPa and K_C 6.8 MPa m^0.5) and the Hugoniot Elastic Limit (HEL=18 GPa) are higher than those of hot-pressed silicon carbide samples.     

High P-T phase transformations and metastability in the Zr0.5Hf0.5O2 solid-solution ceramic

High pressure-temperature (P-T) phases of the Zr_xHf_1−xO₂ (x = 0.5) solid-solution have been stabilised in a CO₂ laser heated diamond anvil cell. At room-temperature the monoclinic to orthorhombic-I structural transformation is initiated at 5-8 GPa. The X-ray diffraction (XRD) studies show these two phases coexist to above ∼15 GPa. A progressive increase in the orthorhombic-I phase abundance occurs, to culminate in full conversion at ∼20 GPa. At this lower threshold of ∼20 GPa transformation to the orthorhombic-II (cotunnite) structure can be initiated by heating in the range of 600-1200 °C. Substantial conversion to the cotunnite phase occurs in the same temperature range at 25-30 GPa. Raman signatures have been assigned to the two orthorhombic high-pressure phases, aided by the qualitative assessment of the complementary XRD data. Decompression experiments show that phase mixture composites of these high pressure structures, possibly with enhanced tribological properties, can be recovered to ambient conditions.     

Effect of pressure on electric generation of PZT(30/70) and PZT(52/48) ceramics near phase transition pressure

Impact experiment of Pb(Zr_0.3Ti_0.7)O₃ and Pb(Zr_0.52Ti_0.48)O₃ ceramics were conducted by empolying shock reverberation techniques within 3-7 GPa and X-ray diffraction patterns of these materials have been measured at pressure up to 32 GPa with a diamond anvil cell and synchrotron radiation. To refine the crystal structure, Rietveld analysis was performed and bulk moduli were calculated using Birch-Murnaghan equation of state. We found a tetragonal phase transforming to a cubic phase in Pb(Zr_0.3Ti_0.7)O₃ and Pb(Zr_0.52Ti_0.48)O₃ ceramics at ∼7.4 GPa and ∼4 GPa respectively. For dynamic pressure experiment, a metal flyer accelerated by a gas gun facility impacts into PZT ceramics to investigate electric energy. As pressure increased, output voltage of Pb(Zr_0.3Ti_0.7)O₃ and Pb(Zr_0.52Ti_0.48)O₃ ceramics slightly increased below ∼7 GPa and ∼4 GPa. But the voltage increased near ∼7 GPa and ∼4 GPa. From the result, we could confirm that the phase transition influenced the considerable effect on the electrical power generation.     

Sintering behaviour of nano-crystalline γ-Al2O3 powder without additives at 2-7 GPa

Al₂O₃ ceramics were fabricated without additives under high pressure (2-7 GPa) at different temperatures (600-1200 °C) using nanocrystalline alumina powder with metastable γ-Al₂O₃ phase as the starting material.It was shown that high pressure increases the nucleation rate while reducing the growth rate of the transformed α phase so that its grain size decreases and nano-scale grains in the sintered structure can be achieved.On the other hand the sintered samples at 7 GPa and high temperature (1000 °C) have shown micron-scale large grain sizes compared to those sintered at lower pressures, for the same temperature and sintering time. This could be attributed to the higher input energy in the system at high pressure and high temperature conditions, thereby reaching the final stage in sintering more quickly.In this work, the best combination of grain size (∼200 nm) and density (98.0% TD) was obtained under the sintering condition of 1000 °C at 7 GPa with a holding time of 1 min.Thus for high pressure/high temperature conditions, the sintering time should be reduced to prevent grain growth.     

Mechanical properties of sintered La9.33Si2Ge4O26 oxyapatite materials for SOFC electrolytes

Mechanical properties of La_9.33Si₂Ge₄O₂₆ prepared by mechanical alloying and subsequent sintering at 1300–1400 °C for 1 h were evaluated. Hardness and Young's modulus values in the range 7.3–9.6 GPa and 106–135 GPa, respectively, were obtained from nanohardness tests. The fracture toughness values derived from the Palmqvist method varied between 3.5 and 3.9 MPa m^1/2 from classical microindentation test with an indentation load of 9.8 N. Yield stress (σ_y) was determined by inverse analysis from microhardness tests. The maximum value of σ_y (1829 MPa) was obtained for the sample sintered at 1400 °C showing the highest density (5.42 g/cm³).     

Synthesis, proton conductivity and methanol permeability of a novel sulfonated polyimide from 3-(2′,4′-diaminophenoxy)propane sulfonic acid

A novel sulfonated diamine monomer, 3-(2′,4′-diaminophenoxy)propane sulfonic acid (DAPPS), was successfully synthesized and the sulfonated polyimide (SPI) was prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) and DAPPS. The resulting SPI, NTDA-DAPPS, was soluble in common organic solvents. The SPI membrane displayed proton conductivity σ values of 0.12-0.35 S/cm at temperatures ranging from 35 to 90 °C in liquid water, which were similar to or higher than those of Nafion 117 and sulfonated hydrocarbon polymers. The σ of the SPI membrane decreased significantly with decreasing relative humidity (RH) and became much lower than that of Nafion 117 at 30% RH. The SPI membrane displayed good water stability at 80 °C and was thermally stable up to 240 °C. It showed reasonable mechanical strength of a modulus of 1.3 GPa at 90 °C and 90% RH. Its methanol permeability P_M was 0.57×10⁻⁶ cm²/s at 30 °C and 8.6 wt% methanol in feed, which was a fourth of that of Nafion 117. As a result, its ratio of σ/P_M was 21×10⁴ S cm⁻³ s, which was about 4 times larger than that of Nafion 117, suggesting potential application of the SPI membrane for direct methanol fuel cell.     

Influence of silica nanoparticles added to an organosilane film on carbon steel electrochemical and tribological behaviour

The electrochemical behaviour and tribological properties of carbon steel coated with bis-[trimethoxysilylpropyl]amine (BTSPA) filled with SiO₂ were evaluated. The silane film filled with SiO₂ was prepared by adding different SiO₂ concentrations. The electrochemical behaviour of the coated steel was mainly evaluated by means of open-circuit potential (E_OC), electrochemical impedance spectroscopy (EIS) and polarization curves, in 0.1 mol L⁻¹ NaCl solution. Structural and morphological characterizations were made by optical, electron and atomic force microscopy (AFM). E_OC and EIS data showed that sample filled with 300 ppm SiO₂ presented the highest E_OC and total impedance value. AFM measurements showed a homogeneous particle distribution of SiO₂ particles. Nanohardness measurements showed SiO₂ promoted an increase of the hardness mean value (1.70 ± 0.11 GPa to non-filled BTSPA and 2.21 ± 0.05 GPa for sample filled with 300 ppm SiO₂). Silane films when filled with SiO₂ particles improved the corrosion resistance of the steel substrate. The optimum SiO₂ particles concentration in silane solution is 300 ppm SiO₂. Incorporation of an extra amount of silica into BTSPA film led to degradation of the corrosion protection of the film to the substrate.     

The influence of pentavalent Nb substitution for Zr on electrical property of oxide-ion conductor Gd2Zr2O7

Gd₂(Zr_1−xNb_x)₂O_7+x (0 ≤ x ≤ 0.2) ceramics are prepared via the solid state reaction process at 1973 K for 10 h in air. Gd₂(Zr_1−xNb_x)₂O_7+x (x = 0.1, 0.2) ceramics exhibit an ordered pyrochlore-type structure, whereas Gd₂Zr₂O₇ has a defective fluorite-type structure. The electrical property of Gd₂(Zr_1−xNb_x)₂O_7+x ceramics is investigated by electrochemical impedance spectroscopy over a frequency range of 10 Hz to 8 MHz from 623 to 923 K. The electrical conductivity obeys the Arrhenius equation. The grain conductivity of Gd₂(Zr_1−xNb_x)₂O_7+x ceramics varies with doping different Nb contents, and exhibits a maximum at the Nb content of x = 0.1 in the temperature range of 623-923 K. The conductivity in hydrogen atmosphere is a little bit higher than in air in the temperature range of 723-923 K, which indicates that the doping of Zr⁴⁺ by Nb⁵⁺ can increase the proton-type conduction and reduce the oxide-ionic conduction. The conduction of Gd₂(Zr_1−xNb_x)₂O_7+x is not a pure oxide-ionic conductor.     

An in situ high pressure-high temperature powder diffraction study of the formation of a precursor phase of bismuth manganite

The synthesis route for single phase BiMnO₃ from Bi₂O₃ and Mn₂O₃ has been undertaken, in situ, in a diamond anvil cell. The starting powders were mixed in a stoichiometric ratio and loaded into a diamond anvil cell with a gasket aperture of 150 μm. A ruby chip was used to measure the pressure and a circular resistive heater surrounded the central core of the cell. The reaction was studied as a function of pressure and temperature to 6.7 GPa and 480 °C by X-ray diffraction. There was evidence of the onset of a reaction between the starting oxides at 314 °C and 6.7 GPa but there was no evidence of transformation of the monoclinic Bi₂O₃ to the cubic form before the reaction began. A monoclinic phase related to the structure of multiferroic BiMnO₃ was observed to form with space group Cc, a = 10.21(1), b = 5.356(6), c = 10.38(1) Å and β = 116.87(6)°. A good fit for this structure was obtained by modelling a distorted BiMnO₂ unit cell with disordered Bi and Mn sites. We did not go sufficiently high in temperature to observe the formation of single phase BiMnO₃ but the precursor phase was observed to persist when returned to room temperature and pressure.     

Synthesis of SiC/SiO2 core–shell powder by rotary chemical vapor deposition and its consolidation by spark plasma sintering

SiC (core) and SiO₂ (shell) powders were synthesized via rotary chemical vapor deposition (RCVD). The SiC particles (3C, <1 μm in diameter) were coated with a layer of SiO₂ (10–15 nm in thickness). Using spark plasma sintering, the SiC/SiO₂ nanopowders were then synthesized into SiC/SiO₂ composite bodies. Although a phase transformation from 3C to 6H was observed at above 2123 K in the sintered monolithic SiC bodies, sintered SiC/SiO₂ bodies did not display such phase transformation. In addition, SiC/SiO₂ bodies did not exhibited grain growth until the sintering temperature reached 2223 K. The density and Vickers hardness of the sintered SiC/SiO₂ bodies increased with increasing sintering temperature. The highest density and hardness of SiC/SiO₂ composite bodies were 98.1% and 24.4 GPa at 2223 K, respectively, which were higher than the corresponding values of 90% and 14 GPa for monolithic SiC bodies.     

Densification behavior and properties of hot-pressed ZrC ceramics with Zr and graphite additives

Densifications of hot-pressed ZrC ceramics with Zr and graphite additives were studied at 1800-2000 °C. ZrC with 8.94 wt% Zr additive (named ZC10) sintered at 1900-2000 °C achieved higher relative densities (>98.4%) than that of additive-free ZrC (<83%). The densification improvement was attributed to the formation of non-stoichiometric ZrC_0.9, whereas there had rapid grain growth with grain size about 50-100 μm in ZC10. By adding co-doped additive of Zr plus C and adjusting the molar ratio of Zr/C, ZrC with co-doped additives with Zr/C molar ratio at 1:2 (named ZC12), ZrC ceramics with both high relative density (98.4%) and fine microstructures (grain size about 5-10 μm) were obtained at 1900-2000 °C. Effect of formation of non-stoichiometric ZrC_1−x on densification of ZrC was discussed. The Vickers hardness and indentation toughness of ZC10 and ZC12 samples sintered at 1900 °C were 17.8 GPa and 3.0 MPa m^1/2, 16.2 GPa and 4.7 MPa m^1/2, respectively.     

Simultaneous synthesis and densification of α-Zr(N)/ZrB2 composites by self-propagating high-temperature combustion under high nitrogen pressure

Simultaneous synthesis and densification of α-Zr(N)/ZrB₂ composites from a 85 mol% Zr/15 mol% B mixed-powder compacts have been achieved by self-propagating high-temperature under a nitrogen pressure of 10 MPa. Composites consist of fine and short rodlike ZrB₂ grains (0.1 μm^?–0.5 μm^l) dispersed into α-Zr(N) matrix (3 μm). Dense composite materials (96.5% of theoretical) exhibit excellent mechanical properties, in which their bending strength and H_v are 560 MPa and 6.5 GPa, respectively. This bending strength is much superior to those (205 and 480 MPa) of dense equi-axial α-Zr(N) (10 μm) and dense ZrB₂ (6 μm). Fine and rodlike ZrB₂ grains greatly enhanced their mechanical properties.     

The sorption of acid dye onto chitosan nanoparticles

The behavior of chitosan nanoparticles as an adsorbent to remove Acid Green 27 (AG27), an acid dye, from an aqueous solution has been investigated with nanochitosan (particle size = 180 nm; degree of deacetylation = 74%). The dye concentration at equilibrium (Q_e, mg/g) was calculated using the weight of the nanoparticles in the mixed solution (Q_es) and the weight of chitosan in the nanoparticles (Q_ep). The experimental isotherm data were analyzed using the Langmuir equation for each chitosan sample; the Langmuir monolayer adsorption capacity (Q₀) was calculated with Q_es and Q_ep and the results were 1051.8 mg/g and 2103.6 mg/g, respectively, which were significantly higher than that of the micron-sized chitosan.     

Sol–gel auto combustion synthesis of CoFe2O4/1-methyl-2-pyrrolidone nanocomposite: Its magnetic characterization

A magnetic nanocomposite was generated by the sol–gel auto-combustion method in the presence of 1-methyl-2-pyrrolidone, a functional solvent. The temperature-dependent magnetic properties of the CoFe₂O₄ nanoparticles have been extensively studied in the temperature range of 10–400 K and magnetic fields up to 80 kOe. Zero field cooled (ZFC) and field cooled (FC) curves indicate that the blocking temperature (T_B) of the CoFe₂O₄ nanoparticles is above 400 K. It was found from M–H curves that the low temperature saturation magnetization values are higher than bulk value of CoFe₂O₄. The saturation magnetization (M_s), remanence magnetization (M_r), reduced remanent magnetization (M_r/M_s) and coercive field (H_c) values decrease with increasing temperature. The M_r/M_s value of 0.75 at 10 K indicates that the CoFe₂O₄ nanoparticles used in this work have, as expected, cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model. T^1/2 dependence of the coercive field was observed in the temperature range of 10–400 K according to Kneller's law. The extrapolated T_B and the zero-temperature coercive field values calculated according to Kneller's law are almost 427 K and 13.2 kOe, respectively. The room temperature H_c value is higher than that of the previously reported room temperature bulk values. The effective magnetic anisotropy constant (K_eff) was calculated as about 0.23×10⁶ erg/cm³ which is lower than that of the bulk value obtained due to disordered surface spins.     

Electrical conductivity of samarium-ytterbium zirconate ceramics

(Sm_1 − xYb_x)₂Zr₂O₇ (0 ≤ x ≤ 1.0) ceramic powders were prepared by chemical-coprecipitation and calcination method, and were pressureless-sintered at 1973 K for 10 h to fabricate dense bulk materials. (Sm_1 − xYb_x)₂Zr₂O₇ has a single phase with a pyrochlore or defect fluorite structure, depending mainly upon the Yb content. They are found to be pyrochlores for 0 ≤ x ≤ 0.1, and defect fluorites for 0.3 ≤ x ≤ 1.0. The electrical conductivity of (Sm_1 − xYb_x)₂Zr₂O₇ was investigated by complex impedance spectroscopy over a frequency range of 200 Hz to 20 MHz from 723 to 1173 K in air. The measured electrical conductivity obeys the Arrhenius relation. The grain conductivity of (Sm_1 − xYb_x)₂Zr₂O₇ ceramics gradually increases with increasing temperature. A decrease of about one order of magnitude in grain conductivity is found at all temperature levels when the Yb content increases from x = 0.1 to x = 0.3. The electrical conductivities of defect fluorite-type materials are lower than those of pyrochlore-type materials in (Sm_1 − xYb_x)₂Zr₂O₇ system, whereas activation energies for the conduction process increase monotonically as the structure becomes disordered.     

Effect of CeO2 addition on densification and microstructure of Al2O3-YSZ composites

Alumina (Al₂O₃) and alumina-yttria stabilized zirconia (YSZ) composites containing 3 and 5 mass% ceria (CeO₂) were prepared by spark plasma sintering (SPS) at temperatures of 1350-1400 °C for 300 s under a pressure of 40 MPa. Densification, microstructure and mechanical properties of the Al₂O₃ based composites were investigated. Fully dense composites with a relative density of approximately 99% were obtained. The grain growth of alumina was inhibited significantly by the addition of 10 vol% zirconia, and formation of elongated CeAl₁₁O₁₈ grains was observed in the ceria containing composites sintered at 1400 °C. Al₂O₃-YSZ composites without CeO₂ had higher hardness than monolithic Al₂O₃ sintered body and the hardness of Al₂O₃-YSZ composites decreased from 20.3 GPa to 18.5 GPa when the content of ZrO₂ increased from 10 to 30 vol%. The fracture toughness of Al₂O₃ increased from 2.8 MPa m^1/2 to 5.6 MPa m^1/2 with the addition of 10 vol% YSZ, and further addition resulted in higher fracture toughness values. The highest value of fracture toughness, 6.2 MPa m^1/2, was achieved with the addition of 30 vol% YSZ.     

A novel layered manganese oxide/poly(aniline-co-o-anisidine) nanocomposite and its application for electrochemical supercapacitor

A novel layered manganese oxide/poly(aniline-co-o-anisidine) nanocomposite [MnO₂/P(An-co-oAs)] was successfully synthesized by a delamination/reassembling process using P(An-co-oAs) ionomer and layered manganese oxide in aqueous solution. This nanocomposite obtained was then characterized by Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD), electron microscopy (SEM), and thermogravimetric (TG) analysis. X-ray diffraction and electron microscope analysis showed that the MnO₂/P(An-co-oAs) nanocomposite had a lamellar structure with increasing interlayer spacing. The MnO₂/P(An-co-oAs) nanocomposite exhibited substantially improved conductivity, which was near 100 times greater than that of its pristine MnO₂ (3.5 × 10⁻⁷ S cm⁻¹). The specific capacitance of the MnO₂/P(An-co-oAs) nanocomposite reached 262 F g⁻¹ in 1 M Na₂SO₄ at a current density of 1 A g⁻¹, which was significantly higher than that of either of its two pristine materials [MnO₂ (182 F g⁻¹) or P(An-co-oAs) (127 F g⁻¹)] owing to the synergic effect between the two pristine components. The fabrication mechanism of the nanocomposite was also proposed and discussed in this paper.