The influence of crosslinking and fumed silica nanoparticles on mixed gas transport properties of poly[1-(trimethylsilyl)-1-propyne]

Crosslinking poly[1-(trimethylsilyl)-1-propyne] (PTMSP) films with 3,3′-diazidodiphenylsulfone, a bis(azide) crosslinker, rendered the films insoluble in common solvents for PTMSP such as toluene. At all temperatures, mixed gas CH₄ and n-C₄H₁₀ permeabilities of crosslinked PTMSP were less than those of uncrosslinked PTMSP, which correlates with lower free volume in the crosslinked material. The presence of fumed silica (FS) nanoparticles in both uncrosslinked PTMSP and crosslinked PTMSP increased mixed gas CH₄ and n-C₄H₁₀ permeabilities, consistent with the disruption of polymer chain packing by such nanoparticles. Mixed gas CH₄ permeabilities of all films were significantly less than their corresponding pure gas CH₄ permeabilities. For example, at 35 °C, the mixed gas CH₄ permeabilities were approximately 60–80% less than their pure gas values. The greatest decrease was observed for uncrosslinked PTMSP, while nanocomposite PTMSP films showed the least decrease. The mixed gas n-C₄H₁₀/CH₄ selectivities of crosslinked PTMSP and nanocomposite PTMSP films were less than those of uncrosslinked PTMSP at all temperatures. For example, at 35 °C, the mixed gas n-C₄H₁₀/CH₄ selectivities of uncrosslinked PTMSP, crosslinked PTMSP containing 10 wt% crosslinker, and uncrosslinked PTMSP containing 30 wt% FS were 33, 27, and 17, respectively, when the feed gas contained 2 mol% n-C₄H₁₀ and the total upstream mixture fugacity was 11 atm. For all films, as temperature decreased, mixed gas n-C₄H₁₀ permeabilities increased, and mixed gas CH₄ permeabilities decreased. Consequently, the mixed gas n-C₄H₁₀/CH₄ selectivities increased substantially as temperature decreased and the mixed gas selectivity of uncrosslinked PTMSP increased from 33 to 170 as temperature decreased from 35 °C to ?20 °C when the feed gas contained 2 mol% n-C₄H₁₀ and the total upstream mixture fugacity was 11 atm.     

Synthesis and characterization of alumina supported sub-nanoporous SiO2–10 wt%TiO2 membrane for nitrogen separation

Membrane of SiO₂–10TiO₂ was produced by dip coating on mesoporous-titania-coated macroporous alumina support. The amorphous SiO₂–10TiO₂ top layer with thickness of 0.9 μm was obtained as a homogenous and defect free surface. Gas permeation tests show a decrease in permeation in order of CH₄ > N₂ for the support, and N₂ > CH₄ for the multilayer membrane. The membrane delivering promised single gas separation factor for N₂/CH₄ (1.75). It was also observed that the membrane separation factor in binary gas mixture was 12–15% of the single gas separation factor, while the permeation revealed a decrease in gas mixture.     

Preparation of dual-phase composite BaCe0.8Y0.2O3/Ce0.8Y0.2O2 and its application for hydrogen permeation

Dual-phase ceramic membranes composed of BaCe_0.8Y_0.2O₃ (BCY) and Ce_0.8Y_0.2O₂ (CYO) were successfully synthesized by solid state reaction method for hydrogen permeation. The influences of the BCY/CYO volume ratios on phase composition, microstructure, chemical stability and electrical property were investigated. The hydrogen permeation of the dual-phase composite was characterized as a function of temperature and feed side hydrogen partial pressure. The results showed that there was no reaction between the two constituent oxides observed under the preparation conditions. The dual-phase composite with different BCY/CYO volume ratios after sintering at 1550 °C exhibited dense structure, as well as good stability in 4% H₂/Ar, wet Ar and pure CO₂ atmosphere. The conductivity of the dual-phase composite increased with the content of CYO increasing and 30BCY–70CYO exhibited the highest total conductivity of 2.6×10⁻² S cm⁻¹ at 800 °C in 4% H₂/Ar. The hydrogen permeability of 30BCY–70CYO sample was improved as the temperature and the hydrogen partial pressure in feed gas increased. The hydrogen permeation flux of 1.7 μmol cm⁻² s⁻¹ was achieved at 850 °C.     

Novel nano-crystalline Er2O3 hydrogen isotopes permeation barriers

Hydrogen Isotopes permeation barriers (HIPB) are used to reduce hydrogen isotopes permeation and leakage in the fields such as thermonuclear fusion energy, hydrogen energy, petroleum industry and vacuum solar receiver. In this study, nano-crystalline Er₂O₃ HIPB with about 5–10 nm grain size were made by sol-gel method. Their performances, including deuterium-permeation reduction factor (D-PRF), micro-structure, mechanical property and electrical property were reported. The D-PRF of 0.2 μm nano-crystalline Er₂O₃ HIPB reached 300 at 700 °C and did not deteriorate after 128 h deuterium permeation. The bonding strength and the nano-hardness steadily remained about 13 N and 10 GPa after 128 h deuterium permeation at 700 °C, respectively. The morphology and micro-structures of the nano-crystalline Er₂O₃ HIPB showed no measurable changes after 128 h deuterium permeation, which ensured the stable D-PRF and mechanical properties. However, the electrical resistivity of the nano-crystalline Er₂O₃ HIPB decreased after deuterium permeation at 700 °C. The electrical resistivity decreased from 9 × 10⁹ Ω cm by over three orders of magnitude and then tended to be stable, which might be attributed to oxygen loss or deuterium invasion.     

Silver cofirability differences between Bi1.5Zn0.92Nb1.5O6.92 and Zn3Nb2O8

We have investigated systematically the differences of silver cofirability and microwave dielectric properties between Zn₃Nb₂O₈ and Bi_1.5Zn_0.92Nb_1.5O_6.92 (BZN). Two type dopants: 0.29BaCO₃–0.71CuO (BC) and 0.81MoO₃–0.19CuO (MC) were used in Zn₃Nb₂O₈ and Bi_1.5Zn_0.92Nb_1.5O_6.92 ceramics so they can be cofired with silver. The BC-doped ceramics in general have better dielectric properties than those of MC-doped ceramics. The BC-doped Zn₃Nb₂O₈ exhibits better dielectric properties than those of BC-doped BZN (k = 14.7, Q × f = 8200 GHz versus k = 120.1, Q × f = 1050 GHz). For silver compatibility study, the interfacial behaviors between microwave dielectric materials and silver were investigated by using X-ray diffractometer, scanning electronic microscope, and electronic probe microanalyzer. No new crystalline phase and no silver migration behavior were found in the BC-doped Zn₃Nb₂O₈ ceramics cofired with silver, but slight silver migration was detected for BC-doped BZN. But slight silver migration was detected for MC-doped Zn₃Nb₂O₈ and BZN ceramics cofired with silver. Therefore, the good overall properties of BC-doped Zn₃Nb₂O₈ are suitable for microwave applications.     

Electrical characterization of room temperature humidity sensors in La0.8Sr0.2Fe1−xCuxO3 (x = 0, 0.05, 0.10)

Semiconducting oxide gas sensors based on La_0.8Sr_0.2Fe_1?xCu_xO₃ (x = 0, 0.05, 0.10) (LSF, LSFC05, and LSFC10, respectively) were prepared by screen-printing for humidity detection at room temperature.The thick-films were heat-treated at 800, 900 and 1000 °C for 1 h and all the compositions proved to be effective in humidity sensing and presented a good reproducibility between several measurements. However, the best results were obtained with LSFC10 fired at 800 °C which showed a detection limit of 15% relative humidity and a maximum sensor response of about 87%, higher than the previous results. Copper addition to lanthanum strontium ferrites proved to be effective in lowering the sensors’ detection limit.     

Enhanced production of benzyl alcohol in the gas phase continuous hydrogenation of benzaldehyde over Au/Al2O3

Exclusive hydrogenation of benzaldehyde to benzyl alcohol in gas phase continuous operation (393–413 K, 1 atm) was achieved over Au/Al₂O₃, Au/TiO₂ and Au/ZrO₂. Synthesis of Au/Al₂O₃ by deposition–precipitation generated a narrower distribution (2–8 nm) of smaller (mean = 4.3 nm) Au particles relative to impregnation (1–21 nm, mean = 7.9 nm) with increased H₂ uptake under reaction conditions and higher benzaldehyde turnover. Switching reactant carrier from ethanol to water resulted in a significant enhancement of selective hydrogenation rate over Au/Al₂O₃ with 100% benzyl alcohol yield, attributed to increased available reactive hydrogen. This response extends to reaction over Au/TiO₂ and Au/ZrO₂.     

Preparation of (0 2 0)-oriented BaTi2O5 thick films and their dielectric responses

Barium dititanate (BaTi₂O₅) thick films were prepared on a Pt-coated Si substrate by laser chemical vapor deposition, and ac electric responses of (0 2 0)-oriented BaTi₂O₅ films were investigated using several equivalent electric circuit models. BaTi₂O₅ films in a single phase were obtained at a Ti/Ba molar ratio (m_Ti/Ba) of 1.72–1.74 and deposition temperature (T_dep) of 908–1065 K as well as m_Ti/Ba = 1.95 and T_dep = 914–953 K. (0 2 0)-oriented BaTi₂O₅ films were obtained at m_Ti/Ba = 1.72–1.74 and T_dep = 989–1051 K. BaTi₂O₅ films had columnar grains, and the deposition rate reached 93 μm h^?1. The maximum relative permittivity of the (0 2 0)-oriented BaTi₂O₅ film prepared at T_dep = 989 K was 653 at 759 K. The model of an equivalent circuit involving a parallel combination of a resistor, a capacitor, and a constant phase element well fitted the frequency dependence of the interrelated ac electrical responses of the impedance, electric modulus, and admittance of (0 2 0)-oriented BaTi₂O₅ films.     

Improving the POM performance of YBa2Cu3O7−δ membrane reactor by Co doping

The performance of Co doped YBa₂Cu₃O_7−δ (YBCO) membrane reactor have been investigated in a process of the partial oxidation of methane (POM) to syngas. The results shows that doping YBCO membrane with a little Co can enhance its oxygen permeation flux and improve its stability in reducing atmosphere noticeably. At 900 °C, with feed flow at 50 ml/min, CH₄ 6.0 v%, SV = 12,000 h⁻¹, and Ni/ZrO₂ catalyst, CH₄ conversion rate, CO selectivity, and oxygen permeation flux can reach to 98%, 92% and 1.41 ml min⁻¹ cm⁻² respectively.     

Densification,microstructure evolution,and microwave dielectric properties of Mg1-xCaxZrTa2O8 ceramics

In this study, the effects of the Mg²⁺ ions replaced by Ca²⁺ ions on the microwave dielectric properties of newly developed MgZrTa₂O₈ were investigated. Mg_1-xCa_xZrTa₂O₈ (x = 0–1.0) ceramics were prepared via a solid-state reaction method. Calcination of the mixed powders was performed at 1200 °C and sintering of the powder compacts was accomplished at temperatures from 1200 to 1550 °C. The substitution of Ca²⁺ significantly inhibited the densification of Mg_1-xCa_xZrTa₂O₈, led to the expansion of the unit cells, and triggered the formation of a second phase, CaTa₂O₆. The porosity-corrected relative permittivity increased almost linearly with the x value because of the replacement of the less polarizable Mg²⁺ ions by the more polarizable Ca²⁺ ions. The variation in the Q × f values followed a similar trend as that of the sintered density, and the change trend in the τ_f values was in accordance with that of relative permittivity. The best composition appeared to be Mg_0.9Ca_0.1ZrTa₂O₈, which showed excellent microwave dielectric properties of ε_r = 22.5, Q × f = 231,951 GHz, and τ_f = −32.9 ppm/°C. The Q × f value obtained is the highest among the wolframite dielectric ceramics reported in literature.     

Self-assembly of a two-dimensional cluster coordination polymer {[W2S8Cu8I4(bpe)2(py)2] · H2O}n: Crystal structure and luminescent properties

A cluster coordination polymer {[W₂S₈Cu₈I₄(bpe)₂(py)₂] · H₂O}_n1 [bpe = 1,2-bis(4-pyridyl)ethane, py = pyridine] has been synthesized and characterized by single-crystal X-ray diffraction and luminescent spectrum. The crystal data for 1: crystal system, tetragonal, space group P4₂, a = 12.7023(13), b = 12.7023(13), c = 13.3621(19), V = 2156.0(4), Z = 1, D_c = 2.089, Flack parameter = 0.093(16), R₁ = 0.0548, and wR₂ = 0.1533. The structure analysis reveals that 1 is the first two-dimensional noninterpenetrating cluster coordination polymer with chiral space group based on the heterothiometallic pentanuclear [WS₄Cu₄] as secondary building units (SBUs). Coordination polymer 1 exhibits intense luminescent spectrum at 615 nm in the solid state with the excitation peak at 344 nm.     

Fabrication and thermal expansion properties of ZrW2O8/Zr2WP2O12 composites

ZrW₂O₈/Zr₂WP₂O₁₂ composites were fabricated by sintering ZrW₂O₈–Zr₂WP₂O₁₂ powder mixtures at 1473 K for 1 h, and their negative thermal expansion properties were investigated. The relative density of sintered pure-phase ZrW₂O₈ was 72.3%, while that of the sintered composites was 88.4–92.3%. In the composites, the observed hysteresis in the thermal expansion data was small because of the small difference between the CTEs of ZrW₂O₈ and Zr₂WP₂O₁₂. The CTE of the composites was negative and increased with the Zr₂WP₂O₁₂ content. When the Zr₂WP₂O₁₂ volume fraction in the composites was increased from 0 to 75 vol%, the CTEs of the composites increased from ?9.1 × 10^?6 to ?3.1 × 10^?6 K^?1 and from ?5.0 × 10^?6 to ?1.9 × 10^?6 K^?1 over the temperature ranges of 323–373 and 473–673 K, respectively. In composites with Zr₂WP₂O₁₂ volume fractions of 0–25 vol%, the experimentally obtained CTE values were in good agreement with the calculated values obtained by assuming mixed law behavior.     

Low-temperature sintering and microwave dielectric properties of Ba5Nb4O15 with ZnB2O4 glass

The Influence of ZnB₂O₄ glass addition on the sintering temperature and microwave dielectric properties of Ba₅Nb₄O₁₅ has been investigated using dilatometry, X-ray diffraction, scanning electron microscopy and network analyzer. It was found that a small amount of glass addition to Ba₅Nb₄O₁₅ lowered the sintering temperature from 1400 to 900 °C. The reduced sintering temperature was attributed to the formation of ZnB₂O₄ liquid phase and B₂O₃-rich liquid phases such as Ba₃B₂O₆. The Ba₅Nb₄O₁₅ ceramics with ZnB₂O₄ glass, sintered at a low temperature, exhibited good microwave dielectric characteristics, i.e., a quality factor (Q × f) = 12,100 GHz, a relative dielectric constant (ɛ_r) = 40, a temperature coefficient of resonant frequency (τ_f) = 48 ppm/°C. The dielectric properties were discussed in terms of the densification of specimens and the influence of glassy phases such as Ba₃B₂O₆ and ZnB₂O₄.     

Densification and biocompatibility of sintering 3.0 mol% yttria-tetragonal ZrO2 polycrystal ceramics with x wt% Fe2O3 and 5.0 wt% mica powders additive

The densification and biocompatibility of sintered 3.0 mol% yttria-tetragonal zirconia polycrystal (3Y-TZP) ceramics, with X wt% Fe₂O₃ and 5.0 wt% mica powders (denoted by 3Y-TZP: X-5.0 wt% mica) have been studied. When the pellets of 3Y-TZP: X-5.0 wt% mica were sintered at 1300 °C for 1 h, the relative shrinkage increases from 19.20–19.43% with the X increased from 0.3 to 1.0. The relative shrinkage of pellets containing 1.0 wt% Fe₂O₃ (X=1.0) increased from 19.43–19.59% when sintering temperatures were raised from 1300 °C to 1450 °C. X-ray diffraction results show that the pellets of 3Y-TZP: X-5.0 wt% mica sintered at 1400 °C for 1 h only contained single phase of tetragonal ZrO₂ (t-ZrO₂). When the sintering temperature was higher than 1400 °C, the Vickers microhardness was greatest in the pellets with X=0.5. Within pellets with the same Fe₂O₃ content, the dominant wavelength (λ_d) was only slightly different for pellets sintered at 1300 °C and those sintered at 1450 °C. The results of the materials were evaluated in vitro cytotoxicity tests reveals that the powders and sintered pellets are safe materials. The oral mucosa irritation tests did not find erythema or histopathological change including normal epithelium, and was free from leucocyte infiltration, vascular congestion and oedema.     

Effects of Li2CO3 and Sm2O3 additives on low-temperature sintering and piezoelectric properties of PZN-PZT ceramics

To assist the development of applications for multilayer piezoelectric devices, the low-temperature sintering piezoelectric ceramics of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ with Li₂CO₃ and Sm₂O₃ additives were fabricated by a conventional solid-state reaction, and their structural and piezoelectric properties were studied. With the addition of Li₂CO₃, the minimum sintering temperature of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ piezoelectric ceramics was reduced from 1125 °C to 950 °C through the formation of a liquid phase and its piezoelectric properties showed almost no degradation. When the sintering temperature was below 950 °C, however, the piezoelectric properties degraded obviously. The additional Sm₂O₃ resulted in a significant improvement in the piezoelectric properties of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ ceramic with added Li₂CO₃. When sintered at 900 °C, the optimized properties of the 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ piezoelectric ceramic with 0.3 wt% Li₂CO₃ and 0.3 wt% Sm₂O₃ were obtained as d₃₃ = 483 pC/N, k₃₁ = 0.376, Q_m = 73, ɛ_r = 2524, tan δ = 0.0178.     

Microwave dielectric properties of novel temperature stable high Q Li2Mg1−xZnxTi3O8 and Li2A1−xCaxTi3O8 (A = Mg,Zn) ceramics

The Li₂Mg_1?xZn_xTi₃O₈ (x = 0–1) and Li₂A_1?xCa_xTi₃O₈ (A = Mg, Zn and x = 0–0.2) ceramics are synthesized by solid-state ceramic route and the microwave dielectric properties are investigated. The Li₂MgTi₃O₈ ceramic shows ?_r = 27.2, Q_u × f = 42,000 GHz, and τ_f = (+)3.2 ppm/°C and Li₂ZnTi₃O₈ has ?_r = 25.6, Q_u × f = 72,000 GHz, and τ_f = (?)11.2 ppm/°C respectively when sintered at 1075 °C/4 h. The Li₂Mg_0.9Zn_0.1Ti₃O₈ dielectric ceramic composition shows the best dielectric properties with ?_r = 27, Q_u × f = 62,000 GHz, and τ_f = (+)1.1 ppm/°C. The effect of Ca substitution on the structure, microstructure and microwave dielectric properties of Li₂A_1?xCa_xTi₃O₈ (A = Mg, Zn and x = 0–0.2) has also been investigated. The materials reported in this paper are excellent in terms of dielectric properties and cost of production compared to commercially available high Q dielectric resonators.     

Preparation and characterization of porous MgAl2O4 spinel ceramic supports from bauxite and magnesite

Porous magnesium aluminate spinel (MgAl₂O₄) ceramic supports were fabricated by reactive sintering from low-cost bauxite and magnesite at different temperatures ranging from 1100 to 1400 °C and their sintering behavior and phase evolution were evaluated. The effects of sintering temperature on the pore structure, size and distribution as well as on the main properties of spinel ceramic supports such as flexural strength, nitrogen permeation flux and chemical resistance were investigated. The supports prepared at 1300 °C showed a homogeneous pore structure with the average pore size of 4.42 μm, and exhibited high flexural strength (35.6 MPa), high gas permeability (with nitrogen gas flux of 3057 m³ m⁻² h⁻¹ under a trans-membrane pressure of 0.1 MPa) and excellent chemical resistance.     

Effect of B2O3 and CuO additives on the sintering temperature and microwave dielectric properties of Ba(Zn1/3Nb2/3)O3 ceramics

The B₂O₃ added Ba(Zn_1/3Nb_2/3)O₃ (BBZN) ceramic was sintered at 900 °C. BaB₄O₇, BaB₂O₄, and BaNb₂O₆ second phases were found in the BBZN ceramic. Since BaB₄O₇ and BaB₂O₄ second phases have an eutectic temperature around 900 °C, they might exist as the liquid phase during sintering at 900 °C and assist the densification of the BZN ceramics. Microwave dielectric properties of dielectric constant (ɛ_r) = 32, Q × f = 3500 GHz, and temperature coefficient of resonance frequency (τ_f) = 20 ppm/°C were obtained for the BZN with 5.0 mol% B₂O₃ sintered at 900 °C for 2 h. The BBZN ceramics were not sintered below 900 °C and the microwave dielectric properties of the BBZN ceramics sintered at 900 °C were very low. However, when CuO was added, BBZN ceramic was well sintered even at 875 °C. The liquid phase related to the BaCu(B₂O₅) second phase could be responsible for the decrease of sintering temperature. Good microwave dielectric properties of ɛ_r = 36, Q × f = 19,000 GHz and τ_f = 21 ppm/°C can be obtained for CuO doped BBZN ceramics sintered at 875 °C for 2 h.     

A novel paradodecatungstate-B compound decorated by transition metal copper,Na2Cu5(H2O)24(OH)2[H2W12O42]·10H2O: Synthesis,structure and antitumor activities

A new paradodecatungstate-B compound decorated by transition metal copper, Na₂Cu₅(H₂O)₂₄(OH)₂[H₂W₁₂O₄₂]·10H₂O (1), has been synthesized by convenient aqueous solution method and structurally characterized by single-crystal X-ray diffraction, IR spectrum, elemental analysis and TGA. The compound crystallizes in the triclinic P-1 space group with a = 10.7140(8) Å, b = 12.9476(9) Å, c = 13.6696(10) Å, α = 73.56°, β = 75.73°, γ = 67.69°, V = 1661.8(2) ų and Z = 1. In compound 1, polyanion of [H₂W₁₂O₄₂]^10 − acts as a dodecadentate ligand that links copper and sodium cations, forming a remarkable three-dimensional framework. The experiment of antitumor activities in vitro shows that the title compound exhibits remarkable inhibitory actions on human cervical carcinoma HeLa cells, ovarian carcinoma SKOV-3 cells, hepatoma HepG2 cells and neuroblastoma SHY5Y cells.     

Phase formation,microstructure development and thermoelectric properties of (ZnO)kIn2O3 ceramics

The (ZnO)_kIn₂O₃ system is interesting for applications in the fields of thermoelectrics and opto-electronics. In this study we resolve the complex homologous phase evolution with increasing temperature in polycrystalline ceramics for k = 5, 11 and 18 and its influence on the microstructural development and thermoelectric properties. The phase formation at temperatures above 1000 °C is influenced by the local ZnO-to-In₂O₃ ratio in the starting-powder mixture. While the Zn₅In₂O₈ equilibrium phase for k = 5 is formed directly after sintering at 1200 °C, the formation of the k = 11 and k = 18 equilibrium phases proceeds at higher temperatures by diffusion between the initially formed phases, the lower k Zn₅In₂O₈/Zn₇In₂O₁₀ and the higher k Zn_kIn₂O_k+3 (9 < k < ∞). Such phase formation affects the sintering and grain growth, and consequently, with the degree of structural and compositional homogeneity, also the thermoelectric characteristics of the (ZnO)_kIn₂O₃ ceramics.