Synthesis,Thermal Properties and Electrical Conductivity of Na-Sialate Geopolymer

This work aims to study the thermal behavior of basic-geopolymers derived from metakaolin (clay). The geopolymers were characterized by different techniques: thermal analysis (DTA, TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and impedance spectroscopy. Some physicochemical properties of the products were also determined: the phases obtained after geopolymer heat treatment and their electrical properties. The results obtained after drying and heat treatment showed that the products kept their initial shapes, but revealed variable colors depending on the temperatures at which they were treated. The products obtained are amorphous between 300 up to 600 °C with peaks relating to the presence of nanocrystallites of muscovites and zeolite, thus at 900 °C it is quite amorphous but only contains nanocrystallites of muscovites. From the temperature of 950 °C, we notice that the geopolymer has been transformed into a crystalline compound predominated by the Nepheline (NaAlSiO₄) with the presence of a crystalline phase by minor peaks of Muscovite, this crystalline character has been increased at 1100 °C to obtain a whole phase crystalline of a Nepheline. The treatment of this geopolymer for one hour at 1200 °C shows an amorphous phase again corresponding to corundum (α-Al₂O₃). This indicates that the dissolution of the grains by the liquid phase induces the conversion of the material structure from sialate [–Si–O–Al–O] to sialate siloxo [–Si–O–Al–O–Si–O–] and the formation of a new crystalline phase (α-Al₂O₃). This development of sialate to sialate-siloxo was confirmed by IR spectroscopy. As mentioned above, from 300 to 900 °C, Na-sialate geopolymer exhibits the same disorder structure of nepheline. The crystal structure of nepheline is characterized by layers of six-membered tetrahedral rings of exclusively oval conformation. The rings are built by Regularly alternating tetrahedral AlO₄ and SiO₄. Stacking the layer’s parallel to the c axis gives a three-dimensional network containing channels occupied by Na cations. This topology favors easy movement of Na⁺ ions throughout the structure. For this reason, ionic migration in nepheline is widely reported. The refinement of Na-Sialate geopolymer at room temperature gives bulk high ionic conductivity of about 5 × 10^?5 S cm^?1 and this is due to the probable joint contribution of H⁺ and Na⁺ ions. Above 200 °C, Na⁺ seems to remain the only charge carrier with a low activation energy of about Ea?=?0.26 eV. At higher temperatures, the characteristic frequencies become so close that it is impossible to distinguish the contributions. A total resistance comprising both grain and grain boundaries contribution is then determined.

     

Microstructural changes of phenolic resin during pyrolysis

After curing, phenol‐formaldehyde resins were postcured at 230°C in air for 32 h and then carbonized and graphitized from 300 to 2400°C. Thermal fragmentation and condensation of the polymer structure occurred above 300°C. The crystal size of the cured phenolic resins decreased with the temperature increase. Above 600°C the original resin structures disappeared completely. Below 1000°C the stack size (L_c) and crystal size (L_a) were small. Above 1000°C the L_c increased with the increasing treatment temperature. The carbonized and graphitized resins were characterized using Raman spectroscopy. Below 400°C there were no carbon structures in the Raman spectra analysis. Above 500°C the G and D bands appeared. The frequency of the G band of all carbonized and graphitized samples shifted to 1600 cm^?1 from the 1582 cm^?1 of graphite. The D band shifted to 1330 cm^?1 from the 1357 cm^?1 of the imperfect carbon. The carbonized and graphitized phenolic resins could not be considered as truly glassy or amorphous carbon materials because they had some degree of order in the basal plane. However, the crystal size was very small even at 2400°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1084–1089, 2001     

Hydrogen Permeation Properties and Hydrothermal Stability of Sol–Gel‐Derived Amorphous Silica Membranes Fabricated at High Temperatures

The sol–gel method was applied to the fabrication of amorphous silica membranes for use in hydrogen separation at high temperatures. The effects of fabrication temperature on the hydrogen permeation properties and the hydrothermal stability of amorphous silica membranes were evaluated. A thin continuous silica separation layer (thickness = <300 nm) was successfully formed on the top of a deposited colloidal silica layer in a porous glass support. After heat treatment at 800°C for an amorphous silica membrane fabricated at 550°C, however, it was quite difficult to distinguish the active separation layer from the deposited colloidal silica layer in a porous glass support, due to the adhesion of colloidal silica caused by sintering at high temperatures. The amorphous silica membranes fabricated at 700°C were relatively stable under steam atmosphere (500°C, steam = 70 kPa), and showed steady He and H₂ permeance values of 4.0 × 10^?7 and 1.0 × 10^?7 mol·m^?2·s^?1·Pa^?1 with H₂/CH₄ and H₂/H₂O permeance ratios of ~110 and 22, respectively. The permeance ratios of H₂/H₂O for membranes fired at 700°C increased drastically over the range of He/H₂ permeance ratios by factors of ~3–4, and showed a value of ~30, which was higher than those fired at 500°C. Less permeation of water vapor through amorphous silica membranes fabricated at high temperatures can be ascribed to the dense amorphous silica structure caused by the condensation reaction of silanol groups.     

Detection of polymer transition temperatures by infrared absorption spectrometry

Infrared bands in the 900–1100 cm^?1 region are sensitive to thermal energy. These bands can result from intermolecular coupling, producing the crystal lattice, or from intramolecular coupling of the various atomic groups in a regular helix or coiled chain. In either case an increase in temperature will disrupt the coupling mode, resulting in a form of structural relaxation and a reduction in the integrated absorbance. It is proposed that the temperature at which the peak areas begin to decrease be assigned as the T_g. This is measured by continuously scanning a selected peak in the infrared spectrum of a polymer film while it is heated at a rate of about 1°C/min. Using this technique polyamides (nos. 6,66, and 610) exhibited transitions in the 30–50°C range, and by studying the increase in the free NH region (3440 cm^?1) of nylon 66 two other transitions were detected at 80 and 137°C; the latter represents a change in the nylon 66 crystal state. An amorphous film of poly(ethylene terephthalate) displayed a transition at 58–68°C (T_g) and at 85°C, which is the crystallization temperature. Films of poly(vinyl acetate) and polystyrene exhibited transitions at 25–37°C and at 70°C, respectively.     

Enhancement of ionic conductivity and thermal stability of CaO-stabilised zirconia (CSZ) with MgO addition by scavenging effects

The effects of magnesia (MgO) addition on the ionic conductivity and thermal stability of CaO-stabilised zirconia (CSZ) was investigated by structural and morphological analysis. MgO was added to CSZ using a solid-state reaction, and a secondary phase was not observed via XRD of all specimens sintered at 1600°C. However, Mg₂SiO₄ and Mg-rich phases were detected in the microstructure of CSZ doped with 5 and 10?mol-% MgO, respectively. Ionic conductivity increased with an increase in MgO content, and CSZ doped with 5?mol-% MgO exhibited a maximum value of 0.819?S?cm^?1 measured at 1500°C due to the scavenging of Si impurities. The thermal diffusivity increased from 0.517 (CSZ) to 0.649?mm^2?s^?1 (5?mol-% doped CSZ), and the thermal expansion coefficient of 0.5?mol-% doped CSZ was maximal at 9.855?μm/m°C. The value of mol-% doped CSZ decreased to 8.937?μm/m°C as it was affected by the Mg–Si phase formation.     

Synthesis of cellulose triacetate-I from microfibrillated date seeds cellulose (<Emphasis Type="Italic">Phoenix dactylifera L.</Emphasis>)

Cellulose triacetate (CTA) has successfully been synthesized from microfibrillated date seeds cellulose. The cellulosic material under study constituted 84.9% amorphous phase with a degree of polymerization of 950. Acetylation was conducted at 50 °C under optimized heterogeneous conditions by acetic anhydride as acetyl donor, acetic acid as solvent and sulfuric acid as catalyst. In this process, cellulose was acetylated without dissolving the material throughout. The acetylated cellulose chains on the surface were dissolved gradually in acetic acid, which created new accessible zones. The yield of cellulose triacetate was studied varying acetic acid, acetic anhydride and catalyst concentrations, as well as reaction times. The ratio between the intensity of the acetyl C=O stretching band at around 1740 cm^?1 and the intensity of C–O stretching vibration of the cellulose backbone at 1020–1040 cm^?1 was used to optimize the reaction time. The optimal reaction conditions of 8% concentration of sulfuric acid, acetic anhydride/cellulose weight ratio of 3:1, acetic acid/cellulose weight ratio of 7:1, reaction time of 3 h and reaction temperature of 50 °C have given highest yield of cellulose triacetate, of about 79%. The obtained date seeds-based cellulose triacetate was characterized thoroughly by Fourier transform infrared (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The synthesized product was identified as cellulose triacetate-I (CTA-I) characterized by a melting temperature of 217 °C and a decomposition temperature of 372 °C. These results demonstrated that date seeds can be used as potential source of microfibrillated cellulose which can be easily functionalized.     

Gel Composition and Strength Properties of Alkali‐Activated Oyster Shell‐Volcanic Ash: Effect of Synthesis Conditions

The gel composition and mechanical properties of alkali‐activated oyster shell‐volcanic ash were investigated at different NaOH concentrations (8, 12, and 15M) and curing temperatures (60°C and 80°C) in wet and dry conditions. XRD, FTIR, SEM‐EDS, and TGA‐DSC were used for microstructural characterization of the binder. The gel composition of the system was found to be influenced by NaOH concentration and was not affected when curing temperature was varied from 60°C to 80°C. The main phase was N,C–A–S–H for all alkali‐activated oyster shell‐volcanic ash, with C–S–H as secondary phase for some samples and contains high percentage of iron. The splitting at υ₃ = 1400–1494 cm^?1 on FTIR spectra corresponded to the elimination of the degeneracy due to the distortion of CO₃^2? group. The high degree of splitting indicated that this carbonate group is linked to Ca²⁺. The compressive strength was influenced by curing temperature and the formation of a secondary phase. The compressive strength in dry condition increased roughly between 28 and 180 d for some samples, while in wet condition, the partial dissolution of Si–O–Si bonds of some silicate phases resulted in a reduction of strength.     

Low‐Temperature Sintering of β‐Spodumene Ceramics Using Li2O–GeO2 as a Sintering Additive

Low‐temperature sintering of β‐spodumene ceramics with low coefficient of thermal expansion (CTE) was attained using Li₂O–GeO₂ sintering additive. Single‐phase β‐spodumene ceramics could be synthesized by heat treatment at 1000°C using highly pure and fine amorphous silica, α‐alumina, and lithium carbonate powders mixture via the solid‐state reaction route. The mixture was calcined at 950°C, finely pulverized, compacted, and finally sintered with or without the sintering additive at 800°C–1400°C for 2 h. The relative density reached 98% for the sample sintered with 3 mass% Li₂O–GeO₂ additive at 1000°C. Its Young's modulus was 167 GPa and flexural strength was 115 MPa. Its CTE (from R.T. to 800°C) was 0.7 × 10^?6 K^?1 and dielectric constant was 6.8 with loss tangent of 0.9% at 5 MHz. These properties were excellent or comparative compared with those previously reported for the samples sintered at around 1300°C–1400°C via melt‐quenching routes. As a result, β‐spodumene ceramics with single phase and sufficient properties were obtained at about 300°C lower sintering temperature by adding Li₂O–GeO₂ sintering additive via the conventional solid‐state reaction route. These results suggest that β‐spodumene ceramics sintered with Li₂O–GeO₂ sintering additive has a potential use as LTCC for multichip modules.     

Enhanced electrical properties of In-Ga-Sn-O thin films at low-temperature annealing

Electrical and optical properties of In-Ga-Sn-O (IGTO) thin films deposited by radio-frequency magnetron sputtering were investigated according to annealing temperatures. While IGTO films remained an amorphous phase even after a heat treatment at temperature up to 500 °C, Hall measurements showed that annealing temperature had a significant impact on electrical properties of IGTO thin films. After investigating a wide range of annealing temperatures for samples from as-deposited state to 500 °C, IGTO film annealed at 200 °C exhibited the best electrical performance with a conductivity of 229.31 Ω^?1cm^?1, a Hall mobility of 36.89 cm²V^?1s^?1, and a carrier concentration of 3.85 × 10¹⁹ cm^?3. Changes in proportions of oxygen-related defects and percentages of Sn²⁺ and Sn⁴⁺ ions within IGTO films according to annealing temperatures were analyzed with X-ray photoelectron spectroscopy to determine the cause of the superb performance of IGTO at a low temperature. In IGTO films annealed at 200 °C, Sn⁴⁺ ions acting as donor defects accounted for a high percentage, whereas hydroxyl groups working as electron traps showed a significantly reduced percentage compared to the as-deposited film. Optical band gaps of IGTO films obtained from UV–visible spectrum were 3.38–3.47 eV. The largest band gap value of 3.47 eV for the IGTO film annealed at 200 °C could be attributed to an increase in Fermi-level due to an increase of carrier concentration in the conduction band. These spectroscopic results well matched with electrical properties of IGTO films according to annealing temperatures. Excellent electrical properties of IGTO thin films annealed at 200 °C could be largely due to Sn donors besides oxygen vacancies, resulting in a significant increase in free carriers despite a low annealing. temperature.     

Study of the Ion‐Irradiation Behavior of Advanced SiC Fibers by Raman Spectroscopy and Transmission Electron Microscopy

6H–SiC single crystals and two types of SiC fibers, Hi‐Nicalon type S and Tyranno SA3, have been irradiated with 4‐MeV Au³⁺ up to 2 × 10¹⁵ cm^?2 (4 dpa) at room temperature, 100°C and 200°C. These fibers are composed of highly faulted 3C–SiC grains and free intergranular C. Stacking fault linear density and grain size estimations yield, respectively, 0.29 nm^?1 and 26–36 nm for the Hi‐Nicalon type S fibers and 0.18 nm^?1 and 141–210 nm for the Tyranno SA3 fibers. Both transmission electron microscopy and surface micro‐Raman spectroscopy reveal the complete amorphization of all the samples when irradiated at room temperature and 100°C and a remaining crystallinity when irradiated at 200°C. The latter observations reveal a multi‐band irradiated layer consisting in a partially amorphized band near the surface and an in‐depth amorphous band. Also, nanocrystalline SiC grains with high stacking fault densities can be found embedded in amorphous SiC at the maximum damage zone of the Hi‐Nicalon type S fibers irradiated at 200°C.     

The influence of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers

An investigation was carried out on the effects of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers annealed in an air heated environment at temperatures ranging from 60 to 140°C. Analysis of the equatorial X‐ray diffraction traces showed the presence of a three phase system of amorphous‐smectic‐monoclinic forms and revealed the transformation of the metastable smectic form to the highly stable monoclinic form as the annealing temperature is increased, resulting in an enhanced degree of crystallinity and the crystallite size. The improvements in the degree of crystallinity and the crystallite size became more remarkable above 120°C. Evaluation of the crystallinity was carried out using an analysis of density, infrared spectroscopy, and X‐ray diffraction methods whereas the state of the molecular orientation was evaluated using polarized infrared spectroscopy measurements only. Polarized infra‐red spectroscopy measurements after the curve fitting procedure showed a slight increase of the molecular orientation of the helical chain segments present in the crystalline phase represented by the IR bands at 841 and 998 cm^?1 whereas the amorphous structure represented by the IR band at 974 cm^?1 showed no significant change with increasing annealing temperature. The improvement in the molecular orientation of the crystalline phase became more remarkable above 120°C. Tensile strength of the annealed fibers increased with increasing annealing temperature but the elongation at break and the initial modulus were not affected as much as the tensile strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Electrical Properties of a 0.95(Na0.5K0.5)NbO3–0.05CaTiO3 Thin Film Grown on a Pt/Ti/SiO2/Si Substrate

An amorphous phase was formed in a 0.95(Na_0.5K_0.5)NbO₃–0.05CaTiO₃ (NKN‐CT) film grown at 300°C, and a low‐temperature transient Ca₂Nb₂O₇ phase was formed in the film grown at 500°C. In films grown at high temperatures (≥600°C), secondary phases such as K_5.75Nb_10.85O₃₀ and K₄Ti₁₀Nb₂O₂₇ were developed without the formation of a NKN‐CT phase, probably because of Na₂O evaporation. The same secondary phases were formed in the film grown at 300°C and subsequently annealed at 850°C under an air atmosphere. However, a homogeneous NKN‐CT phase was formed in films grown at 300°C and subsequently annealed at 830°C–880°C under the K₂O and Na₂O atmospheres. Moreover, the film annealed at 830°C in particular exhibited good electric and piezoelectric properties, including a high dielectric constant of 747 with a low dissipation factor of 0.93% at 100 kHz, low leakage current density of 2.0 × 10^?7 A/cm² at 0.1 MV/cm, and high P_r and d₃₃ values of 15.4 μC/cm² and 124 pm/V at 100 kV/cm, respectively.     

Preparation and characterization of novel hybrid thermoplastic poly(ether urethane)/poly(vinylidene fluoride) elastomers,and their application as solid polymer electrolytes

A comb‐like polyether, poly(3‐2‐[2‐(2‐methoxyethoxy)ethoxy]ethoxymethyl‐3′‐methyloxetane) (PMEOX), was reacted with hexamethylene diisocyanate and extended with butanediol in a one‐pot procedure to give novel thermoplastic elastomeric poly(ether urethane)s (TPEUs). The corresponding hybrid solid polymer electrolytes were fabricated through doping a mixture of TPEU and poly(vinylidene fluoride) with three kinds of lithium salts, LiClO₄, LiBF₄ and lithium trifluoromethanesulfonimide (LiTFSI), and were characterized using differential scanning calorimetry, thermogravimetric analysis and Fourier transform infrared spectroscopy. The ionic conductivity of the resulting polymer electrolytes was then assessed by means of AC impedance measurements, which reached 2.1 × 10^?4 S cm^?1 at 30 °C and 1.7 × 10^?3 S cm^?1 at 80 °C when LiTFSI was added at a ratio of O:Li = 20. These values can be further increased to 3.5 × 10^?4 S cm^?1 at 30 °C and 2.2 × 10^?3 S cm^?1 at 80 °C by introducing nanosized SiO₂ particles into the polymer electrolytes. Copyright © 2006 Society of Chemical Industry     

The Role of MgAl2O4 Powder Packing on Phase Stability of Hydroxyapatite During Sintering

MgAl₂O₄ (spinel) was utilized as a packing powder in the sintering of hydroxyapatite (HAp) and the composite of HAp/3 mol% Y₂O₃‐stabilized tetragonal zirconia (3Y‐TZP). The influence of spinel on phase stability of HAp was investigated using X‐ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and electron probe microanalysis (EPMA) to reveal the reaction in the vicinity of the interface between HAp and spinel. When covered with spinel powder, decomposition temperatures for both HAp monolith and HAp in the composite were raised from 1360°C to 1470°C and from 930°C to 1280°C, respectively. SEM images supported the role of spinel on retardation of the decomposition, showing a dense cross section of the monolith after sintering for 2 h at 1400°C with the spinel as opposed to a porous feature without the covering. XRD results indicated that the increase in the decomposition temperatures was accompanied by a decrease in the a‐axis dimension of the hexagonal structure of HAp, probably as a result of the substitution of F^? for OH^?. EPMA revealed that negligible reaction occurred between HAp and spinel even at 1500°C, but the Ca²⁺ in HAp diffused about 20 μm into 3Y‐TZP to form a cubic zirconia solid solution at 1275°C, resulting in the decomposition. The involvement of F^? ion in the contraction of a‐axis parameter and the consequent phase stability were manifested by an increase in the Raman band of the symmetric stretching of the P–O bonds at 962.3 cm^?1 and the appearance of a band for fluoroapatite at 3538 cm^?1.     

Study of microbial polyhydroxyalkanoates using two-dimensional Fourier-transform infrared correlation spectroscopy

The premelting behavior of bacterially synthesized polyester poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), abbreviated as P(HB-co-HHx), was investigated by two-dimensional Fourier-transform infrared (2D FTIR) correlation spectroscopy. The temperature-dependent dynamic spectra were measured over a temperature range of 25–300°C. We focused our study on the thermally induced intensity fluctuations of bands for CO (1700–1760 cm⁻¹), C H (2910–3010 cm⁻¹) and C O C groups (1220–1310 cm⁻¹) stretching vibrations. Changes of crystalline conformation due to the thermal perturbation could be detected by the intensity and location variations of those characteristic bands responding to the variations of dipole moments. 2D correlation analysis indicated that the appearance of fully amorphous component did not happen simultaneously with the disappearance of crystalline component, suggesting that there was an intermediate state between ordered crystalline and amorphous states in P(HB-co-HHx). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 934–940, 2001     

Effect of the crystalline layer on the electrical behaviour of 17.7Li2O·5.2ZrO2·68.1SiO2·9.0Al2O3 glass ceramic monoliths

Li₂O–ZrO₂–SiO₂–Al₂O₃ (LZSA) glass ceramic systems are usually obtained from powder technology to obtain materials with a low thermal expansion coefficient (CTE). However, in these cases, there is a high residual porosity. An alternative to reduce the porosity involves the production of monoliths. Nevertheless, there is still a lack of crystallisation kinetics and the final properties of glass ceramic monoliths are affected such as electrical properties. This study aims to evaluate the electrical behaviour as function of the crystalline layer thickness formed on the monolith surface of a 17.7Li₂O·5.2ZrO₂·68.1SiO₂·9.0Al₂O₃ (molar basis) glass ceramic LZSA composition. Monoliths thermally treated at 750, 800, and 850 °C were chosen to evaluate based on the range of the crystalline layer growth. Electrochemical impedance spectroscopy was used for the electrical characterisation of LZSA glass and the glass ceramics. The resistivity increased with increasing thermal treatment temperature due to the formation of lithium-based crystalline phases. The electrical conductivity at 25 °C of the glass ceramic thermally treated at 850 °C decreased to 1.4 × 10^?13 S cm^?1 from 8.7 × 10^?11 S cm^?1 for LZSA glass. Based on the electrical behaviour, monoliths thermally treated at 850 °C can be considered potential for dielectric industrial applications.     

New organic–inorganic hybrid membranes based on sulfonated polyimide/aminopropyltriethoxysilane doping with sulfonated mesoporous silica for direct methanol fuel cells

A series of novel composite methanol‐blocking polymer electrolyte membranes based on sulfonated polyimide (SPI) and aminopropyltriethoxysilane (APTES) doping with sulfonated mesoporous silica (S‐mSiO₂) were prepared by the casting procedure. The microstructure and properties of the resulting hybrid membranes were extensively characterized. The crosslinking networks of amino silica phase together with sulfonated mesoporous silica improved the thermal stability of the hybrid membranes to a certain extent in the second decomposition temperature (250–400°C). The composite membranes doping with sulfonated mesoporous silica (SPI/APTES/S‐mSiO₂) displayed superior comprehensive performance to the SPI and SPI/APTES membranes, in which the homogeneously embedded S‐mSiO₂ provided new pathways for proton conduction, rendered more tortuous pathways as well as greater resistance for methanol crossover. The hybrid membrane with 3 wt % S‐mSiO₂ into SPI/APTES‐4 (SPI/A‐4) exhibited the methanol permeability of 4.68 × 10^?6 cm² s^?1at 25°C and proton conductivity of 0.184 S cm^?1 at 80°C and 100%RH, while SPI/A‐4 membrane had the methanol permeability of 5.16 × 10^?6 cm² s^?1 at 25°C and proton conductivity of 0.172 S cm^?1 at 80°C and 100%RH and Nafion 117 exhibited the values of 8.80 × 10^?6 cm² s^?1 and 0.176 S cm^?1 in the same test conditions, respectively. The hybrid membranes were stable up to about 80°C and demonstrated a higher ratio of proton conductivity to methanol permeability than that of Nafion117. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Investigation of layered perovskite NdBa0.5Sr0.25Ca0.25Co2O5+δ as cathode for solid oxide fuel cells

Layered perovskite oxides with and without Ca-doped NdBa_0.5Sr_0.25Ca_0.25Co₂O_5+δ (NBSCaCO) and NdBa_0.5Sr_0.5Co₂O_5+δ (NBSCO) are studied to investigate the effects of Ca doping on the crystal structure, thermal behavior, electrical and electrochemical properties. Both NBSCO and NBSCaCO are tetragonal structure with P4/mmm space group. The average thermal expansion coefficient (TEC) value is reduced from 23.3?×?10^?6 K^?1 to 19.8?×?10^?6 K^?1 during 30–800?°C. The electrical conductivities are increased by Ca doping. Both electrical conductivities of NBSCO and NBSCaCO are higher than 600?S·cm^?1 over 30–800?°C. Substitution of Sr with Ca can effectively improve the electrochemical properties of NBSCaCO. From 650?°C to 800?°C, the area specific resistance (ASR) of NBSCaCO are decreased from 0.62 to 0.062?Ω?cm² and the corresponding output power density are increased from 258 to 812?mW?cm^?2. On the basis of these results, Ca doped layered perovskite NBSCaCO can be a good cathode candidate material for SOFC application.     

Reaction,densification, and mechanical properties of Ti2AlCx ceramics at low applied pressure and temperature

Ti₂AlC_x ceramic was produced by reactive hot pressing (RHP) of Ti:Al:C powder mixtures with a molar ratio of 2:1:1–.5 at 10–20 MPa, 1200–1300°C for 60 min. X-ray diffraction analysis confirmed the Ti₂AlC with TiC, Ti₃Al as minor phases in samples produced at 10–20 MPa, 1200°C. The samples RHPed at 10 MPa, 1300°C exhibited ≥95 vol.% Ti₂AlC with TiC as a minor phase. The density of samples increased from 3.69 to 4.04 g/cm³ at 10 MPa, 1200°C, whereas an increase of pressure to 20 MPa resulted from 3.84 to 4.07 g/cm³ (2:1:1 to 2:1:.5). The samples made at 10 MPa, 1300°C exhibited a density from 3.95 to 4.07 g/cm³. Reaction and densification were studied for 2Ti–Al–.67C composition at 10 MPa, 700–1300°C for 5 min showed the formation of Ti–Al intermetallic and TiC phases up to 900°C with Ti, Al, and carbon. The appearance of the Ti₂AlC phase was ≥1000°C; further, as the temperature increased, Ti₂AlC peak intensity was raised, and other phase intensities were reduced. The sample made at 700°C showed a density of 2.87 g/cm³, whereas at 1300°C it exhibited 3.98 g/cm³; further, soaking for 60 min resulted in a density of 4.07 g/cm³. Microhardness and flexural strength of Ti₂AlC_0.8 sample were 5.81 ± .21 GPa and 445 ± 35 MPa.     

Synthesis of Mg0.48Cu0.12Zn0.40Fe2O4 ferrite and its aptness for multilayer chip component application

Here we reported the synthesis of MgCuZn ferrite (Mg_0.48Cu_0.12Zn_0.40Fe₂O₄) by ceramic and self-sustaining auto-combustion (sucrose) methods. Required oxides in powder form were processed (hand mill=3 h, pre-sinter=600 °C for 180 min and final sinter=910 °C for 9 h) to obtain the ferrite sample through the ceramic methods. Whereas, aqueous metal nitrates along with the sucrose as fuel were processed (at 200 °C, final sinter=600 °C for 180 min) to obtain ferrite product via the auto-combustion route. As-synthesized ferrite samples were then subjected to crystallographic, structural and magnetic investigations by techniques viz. X-ray diffraction, IR spectroscopy and B–H measurements. Purity and phase formation were confirmed by XRD examinations. Cation redistribution was also suggested by XRD analyses which supplement the variation of magnetic properties. IR absorption bands were found to be in the expected high frequency range (574.95 cm^?1 and 582.39 cm^?1) and low frequency range (≈431 cm^?1) which fortifies the spinel phase formation. Boost in magnetic performance of sucrose methods' yield was observed owing to reduced porosity and increased surface area. Thus, MgCuZn ferrite prepared via the self-sustaining auto-combustion route has superior magnetic properties at relatively low sintering temperature and can be employed in multi-layer chip application readily.