Microstructure and properties of high alumina castables containing calcium alumino‐titanate

Calcium alumino‐titanate (CAT)‐containing high alumina castables were prepared using bauxite, CAT, and α‐Al₂O₃ as starting materials, and subsequently heat treated at various temperatures ranging from 1400°C to 1600°C. The thermo‐mechanical properties of the specimens as a function of the temperature were characterized in terms of linear shrinkage, bulk density, apparent porosity, cold crushing strength (CCS), modulus of rupture (MOR), residual ratio of MOR, and coefficient of thermal expansion (CTE). X‐ray diffraction (XRD) and scanning electron microscopy (SEM) were used to determine the phase composition and microstructural evolution, respectively. Sintering at temperatures between 1450 and 1500°C promoted normal grain growth, with the formation of a granular surface contact, and abnormal grain growth occurred at higher temperatures (≥ 1550°C). The cold strength of the specimen initially increased and subsequently decreased with temperature, whereas the residual ratio of MOR initially decreased with increasing temperature to 1550°C, then increased above 1550°C. In addition, the CTE of the specimen was only minimally influenced by the firing temperature.     

Sintering behavior and biocompatibility of a low temperature co‐fired ceramic for microfluidic biosensors

A low temperature co‐fired ceramic (LTCC) has been formulated and evaluated for in‐vitro microfluidic sensors and cell culture applications. Using a 75/25 vol% glass to alumina ratio, high density was achieved for sintering temperatures <900°C. No toxicity was observed in the leachate medium obtained by soaking LTCC in cell medium for 5 days. The human umbilical vein endothelial cells (HUVECs) also attached on the fibronectin‐coated LTCC after 14 hours and proliferated after 74 hours. On the basis of these results, the current LTCC formulation is a viable candidate for the continued development of LTCC‐based microfluidic biosensors.     

Cold-sintered V2O5-PEDOT:PSS nanocomposites for negative temperature coefficient materials

A low temperature sintering method, namely cold sintering process, was used to prepare 97 vol%V₂O₅-3 vol% PEDOT:PSS (Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate ceramic-polymer nanocomposites. The density, phase purity, microstructure, elemental distribution and electrical properties of sintered tape-cast films were investigated. The composition with 97 vol%V₂O₅-3 vol% PEDOT:PSS ceramic-polymer nanocomposites can be densified (∼90%) after a cold sintering of 140 °C for 45 min under a uniaxial pressure of 300 MPa. The Transmission Electron Microscopy (TEM) microstructure shows that a ∼10 nm thick intergranular polymer of PEDOT:PSS has been distributed around the V₂O₅ grains after cold sintering. The resistivity decreases with temperature increasing, indicating a typical negative temperature coefficient (NTC) characteristic. The resistivity at 25 °C, temperature coefficient α at 25 °C, and B coefficient (material constant) are 6.34 Ωm, −2.4% K⁻¹ and 2153 K, respectively. The V₂O₅-PEDOT:PSS nanocomposite materials are suitable for new NTC devices, with properties that are comparable to traditional NTC materials that are sintered at much higher temperatures and with much more complexed process and compositions.     

Soybean seed composition under high day and night growth temperatures

High diurnal temperatures often affect development of soybean [Glycine max (L.) Merr.], but little is known about the relative influence of high day and night temperatures on the chemical composition of the seed. This study was conducted to determine the effects of combinations of high day and night temperatures during flowering and pod set (R1–R5), seed fill and maturation (R5–R8), and continuously during the reproductive period (R1–R8) on soybean seed oil, protein, and fatty acid composition. Day/night temperatures of 30/20, 30/30, 35/20, and 35/30°C were imposed on the soybean cultivar Gnome 85 in growth chambers. The day/night temperature combinations during R1–R5 had little effect on the oil and protein concentration and the fatty acid composition of seed produced. As mean daily temperature increased from 25 (30/20) to 33 (35/30)°C during R5–R8 and 25 (30/20) to 33 (35/30)°C during R1–R8, and oil concentration decreased and protein concentration increased. Increased day temperature during R5–R8 and R1–R8, averaged across the two night temperatures, increased oleic acid and decreased linoleic and linolenic acids. When night temperature was increased at 30°C day temperature during R5–R8 and R1–R8, oleic acid decreased and linoleic acid increased. When night temperature was increased at 35°C day temperature during R1–R8, oleic acid increased, and linoleic and linolenic acids decreased. These results indicate the importance of high day and night temperatures during seed fill and maturation in the oil, protein, and fatty acid composition of soybean seed.     

Effect of Microwave Processing on the Crystallization and Energy Density of BaO‐Na2O‐Nb2O5‐SiO2‐B2O3 Glass‐Ceramics

Barium sodium niobate (BNN) glass‐ceramics were successfully synthesized through a controlled crystallization method, using both a conventional and a microwave hybrid heating process. The dielectric properties of glass‐ceramics devitrified at different temperatures and conditions were measured. It was found that the dielectric constant increased with higher crystallization temperature, from 750°C to 1000°C, and that growth of the crystalline phase above 900°C was essential to enhancing the relative permittivity and overall energy storage properties of the material. The highest energy storage was found for materials crystallized conventionally at 1000°C with a discharge energy density of 0.13 J/cm³ at a maximum field of 100 kV/cm. Rapid microwave heating was found to not give significant enhancement in dielectric properties, and coarsening of the ferroelectric crystals was found to be critical for higher energy storage.     

Phase formation and dielectric properties of ultralow temperature sintered Li4Mo5O17 ceramics

The Li₂MoO₄-MoO₃ ceramic system can be densely sintered at ultralow temperatures (< 500 °C). However, the phase composition of the Li₂MoO₄-MoO₃ system at a molar ratio of 1:1 has always been controversial. In this study, the traditional solid-state method was used to synthesize Li₄Mo₅O₁₇ (400 °C, 10 h) and Li₂Mo₂O₇ (350–400 °C, 4 h). Li₂Mo₂O₇ is an intermediate phase that can be converted to Li₄Mo₅O₁₇ at higher temperatures. The Li₄Mo₅O₁₇ ceramic could be sintered and densified at only 490 °C in air, exhibiting a relative density of 95.6% and excellent dielectric properties, including ε′= 12.79 and tan δ = 0.0004 at 1 GHz. Such an ultralow sintering temperature and dielectric loss indicate that the Li₄Mo₅O₁₇ ceramic is a good candidate for high-frequency capacitance applications.     

Time,Temperature, and Concentration Dependence of Ricinelaidic Acid–Canola Oil Organogelation

Canola oil (CO) gels were formed using ricinelaidic acid (REA), a hydroxylated fatty acid, and the time, temperature, and concentration dependence of the resulting gel structure was studied using small-deformation rheology, light microscopy, and powder X-ray diffraction (XRD). Between 5 °C and 30 °C, REA concentration had a significant influence on gel elasticity (P < 0.05), whereas temperature had a relatively lesser influence on gel rheology. Differences were observed in the scaling exponent of G′_LVR with concentration above 20 °C, which were also correlated with significant differences in gelation time at 20 °C. However, the 5% gels at 5 °C, 20 °C, and 35 °C displayed similar microstructures and behaved like weak gels stabilized by junction zones. Most of the gels studied (i.e., the 2%, 3%, 4%, and 5% gels at 15 °C, 20 °C, and 25 °C) consisted of long, thin, fibrous REA strands, although at 25 °C, the 2% gel was characterized by more transient and circular entities. During 28 days’ storage, there were no apparent changes detected in gel microstructure by microscopy or XRD, despite increases in the gel’s opacity.     

Thermal exposure effects on the long‐term behavior of a mullite fiber at high temperature

The behavior of an oxide fiber at elevated temperatures was analyzed before and after thermal exposures. The material studied was a mullite fiber developed for high‐temperature applications, CeraFib 75. Heat treatments were performed at temperatures ranging from 1200°C to 1400°C for 25 hours. Quantitative high‐temperature X‐ray analysis and creep tests at 1200°C were carried out to analyze the effect of previous heat treatment on the thermal stability of the fibers. The as‐received fibers presented a metastable microstructure of mullite grains with traces of alumina. Starting at 1200°C, grain growth and phase transformations occurred, including the initial formation of mullite, followed by the dissociation of the previous alumina‐rich mullite phase. The observed transformations are continuous and occur until the mullite phase reaches a state near the stoichiometric 3/2 mullite. Only the fibers previously heat treated at 1400°C did not show further changes when exposed again to 1200°C. Overall, the heat treatments increased the fiber stability and creep resistance but reduced the tensile strength. Changes observed in the creep strain vs. time curves of the fibers were related to the observed microstructural transformations. Based on these results, the chemical composition of the stable mullite fiber is suggested.     

Retention of isoflavones and saponins during the processing of soy protein isolates

The mass balance of saponins during processing of soy protein isolates (SPI) was established, and the effects of precipitating and washing (P/W) temperatures (0, 10, 25, 40, and 50°C) on the retention of isoflavones and saponins were investigated in this study. About 41% of total saponins in soy flour (SF) were found to remain in SPI during processing, whereas 42% remained unextracted in the solid waste. None was detected in the whey or wash water. The study also revealed that only about 27% of total isoflavones from SF remained in the final SPI when P/W was performed at 50°C. As much as 40% of the total isoflavones could be retained in SPI when P/W was conducted at 25, 10, or 0°C. When the P/W temperature was 50°C, the percentages of total isoflavones lost during extraction, precipitation, and washing were 28, 22, and 6%, respectively. When the temperature was changed to 0°C, the percentages of isoflavones lost during extraction, precipitation, and washing were 28, 11, and 5%, respectively. The P/W temperatures did not affect the distribution of saponins in different streams during the processing of SPI. Lowering the P/W temperature did not significantly lower the protein content in SPI unless the temperature was reduced to 0°C.     

Effects of temperature and temperature shift on docosahexaenoic acid production by the marine microalge Crypthecodinium cohnii

The effects of temperature and temperature shift on the fatty acid composition and docosahexaenoic acid (DHA, C22∶6n−3) content and productivity of the marine microalga Crypthecodinium cohnii ATCC 30556 were investigated. The microalga grew well over the entire range of temperatures (15–30°C) studied. High temperature favored the growth of the microalga with the highest specific growth rate of 0.092 h⁻¹ at 30°C. In contrast, low temperature favored the formation of polyunsaturated fatty acids. The highest DNA content was obtained at 15°C in the early stationary phase (i.e., 72h). In order to achieve high DHA productivity, a shift from high temperature to low temperature at a later stage of cultivation (i.e., 48h) was also attempted. A temperature shift from 25°C (for 48 h) to 15°C (for 24 h) resulted in an increase in cellular DHA content by 19.9% and productivity by 6.5% as compared to that maintained at 25°C (for 72 h).     

Effect of curing temperature on the morphology of unsaturated polyester resin blended with poly(vinyl acetate)

Phase separation of unsaturated polyester/styrene (UPE/styrene) resin blended with 5 and 10 wt% of poly(vinyl acetate) (PVAc) cured at various temperatures ranging from 75°C to 150°C was studied using low angle laser light scattering (LALS) and scanning electron microscopy (SEM). For UPE/styrene resin blended with 5 wt% PVAc cured at a temperature below 90°C, a discrete phase‐separated structure was observed. As curing temperature was raised above 90°C, SEM micrographs revealed that more and more cured UPE globules fused together with increasing curing temperature. The LALS intensity profile became broader with increasing curing temperature, indicating a less discrete phase‐separated structure at a higher curing temperature. As PVAc content was increased to 10 wt%, SEM micrographs revealed a co‐continuous phase‐separated structure. The LALS intensity decayed slowly from the center of the scattering pattern to a high scattering angle without the appearance of maximum scattering peak intensity. The morphology of the cured sample did not change too much with curing temperature for UPE/styrene resin blended with 10 wt% of PVAc.     

Omega-3 Polyunsaturated Fatty Acids Concentration Using Synthesized Poly-Vinylidene Fluoride (PVDF) Asymmetric Membranes

In this study, the performance of synthesized poly‐vinylidene fluoride (PVDF) membranes to concentrate ω3‐polyunsaturated fatty acids from lantern fish oil was evaluated. The PVDF membranes were prepared via the phase inversion method. The effect of coagulation bath temperatures (CBT: 0, 25 and 50 °C) on the morphology of the membranes and the ω3‐PUFA concentration process was examined and discussed. Scanning electron microscopy images showed that an increasing coagulation bath temperature (CBT) leads to a more porous structure in the membranes as well as a larger pore diameter. ω3‐PUFA concentration was evaluated at different pressures and temperatures, ranging from 3 to 5 bar and 20 to 40 °C, respectively. The PVDF membrane prepared at a CBT of 0 °C (M1) resulted in the best ω3‐PUFA concentration (40.4 %) at a pressure and temperature of 5 bar and 30 °C, respectively. Conversely, the PVDF membrane formed at CBT of 50 °C (M3) showed the highest oil flux. In addition, fouling analysis indicates that complete pore blocking was the predominant mechanism for the M1 membrane and intermediate pore blocking for the M2 and M3 membranes.     

Pyrolysis of Mississippi lignite in a fixed bed

The lignite deposits in Mississippi make up approximately 25 percent of the Gulf Coast deposit. To date, the limited number of studies on this lignite have chiefly been by Phillips Coal [1] and investigators in Mississippi [2,3]. This lignite, which is high in ash and moisture, was pyrolyzed in a 2.54 cm (1 in.) diameter fixed bed pyrolyzer under a helium atmosphere at temperatures ranging from 400°C to 950°C. The loss of volatile matter increased with increasing ultimate temperature producing weight losses 20–25% greater than the proximate analysis at 900°C. The yield of tar was found to decrease with temperature while volumetric gas production increased with the ultimate temperature. Hydrogen and carbon monoxide yields increased dramatically above 750°C. The maximum yield of gas was 375 ml/g daf lignite and was achieved at and above 815°C.     

Performance of Ni‐based Anode‐Supported SOFCs with Doped Ceria Electrolyte at Low Temperatures Between 294 and 542°C

The performance of a conventional anode‐supported microtubular SOFC using doped ceria as an electrolyte and Ni‐based cermet as an anode is evaluated at low operating temperature between 294 and 542°C. An open‐circuit voltage (OCV) of >0.9 V is obtained at all measured operating temperatures, and power generation is observed at temperatures as low as 294°C. The power density of the cell is 0.6 W/cm² at 542°C operating temperature with 47% fuel utilization and is 5 mW/cm² at 294°C operating temperature with an open‐circuit voltage of 0.95 V. According to impedance spectroscopy, a greater influence of gas flow rate, on the cell performance, is observed at higher operating temperature.     

Dense Iodoapatite Ceramics Consolidated by Low‐Temperature Spark Plasma Sintering

Pb_9.85(VO₄)₆I_1.7, a potential waste form for long‐lived I‐129 immobilization, experiences phase decomposition and thus iodine loss at an elevated temperature above 400°C, presenting a significant challenge for effective management of radioactive iodine. In this work, we report low‐temperature consolidation of dense iodoapatite pellets with above 95% theoretical density by spark plasma sintering (SPS) at temperatures as low as 350°C for 20 min without iodine loss. Microstructure analysis indicates a nanocrystalline ceramic with an average grain size less than 100 nm. Grain growth dominates the sintered microstructure at higher temperatures and longer durations. The dense nanoceramics have significantly‐improved fracture toughness as compared with bulk coarsened grain structures. The effects of sintering temperatures (350°C, 400°C, 500°C, and 700°C) and durations (0–20 min) on microstructure, density, fracture morphology, and mechanical properties including Young's modulus and hardness of bulk samples were investigated. Low temperature densified iodoapatites suggest immense potential of SPS as an advanced materials fabrication technology for the development of waste forms for immobilization of volatile radionuclides including radioactive iodine.     

The effects of Barium Strontium Titanate (BST) on the soft magnetic properties and loss performance of MnZn ferrites

With the increasing power density of the switched mode power supply (SMPS) developed nowadays, higher efficiency is required from the magnetic core, where the MnZn ferrites are often adopted. However, the relatively high operating temperature of the SMPS often results in reduced resistivity of the MnZn, which increases the eddy current loss. To enhance the resistivity of MnZn ferrite at high temperature range (>100 °C), donor-doped barium strontium titanate (BST) with a positive temperature coefficient of resistivity (PTCR) is prepared and dopped in the MnZn ferrite. The influence of BST addition from 0.000 wt% to 0.020 wt% on the MnZn ferrite is investigated over a wide temperature range from 25 °C to 140 °C. The XRD result suggests ionic exchange between the spinel phase and perovskite phase. The SEM result shows a refined and more uniform microstructure of MnZn ferrite brought about by the BST addition. At the maximum of 0.020 wt%, the BST addition shows almost no influence on density and the saturation magnetic induction. However, the initial permeability is slightly reduced by the BST addition, due to the microstructural change. Moreover, the BST concentrating at the grain boundaries improves the DC-resistivity across the temperature range from 25 °C to 140 °C. Due to the addition of BST, the reduction in eddy current loss at 300kHz/100 mT is around 35% at 25 °C, and ∼20% reduction at 140 °C.     

EFFECT OF TEMPERATURE ON HOMOGENIZING RATE OF SODA-LIME-SILICA GLASS*

Density-spread determinations were made on a series of melts of a soda-lime-silica glass prepared at temperatures ranging from 1232° to 1454°C. for a four-hour period in the absence of furnace refractory and under conditions of minimum convection mixing. A sharp drop in density spread in the range 1232° to 1288°C., a minimum at about 1325°C., and a slowly increasing density spread at temperatures above 1325°C. were observed. The portion of glass responsible for the major part of the density spread was found to be concentrated in the top half of the glass at both 1232° and 1454°C. At the higher temperature, the improvement in the homogeneity of the bottom layer was more marked than that observed in the top layer as compared with the results obtained on the lower-temperature melt. The density spread of the glass in the bottom layer in the case of the high-temperature melt was in the range of that observed for commercial soda-lime-silica glass of good quality. A possible explanation for the observed increase in density spread at higher temperatures (above 1325°) is offered on the basis of more rapid initial segregation during melting at higher temperature as inferred from the density-spread data and from chemical analyses of the glass from the top and bottom portions of melts made at 1232° and 1454°C. Loss in weight of the glass due to volatilization was determined at 1232° and at 1454°C. and was found to amount to less than 0.01% for a four-hour melting period at both temperatures. Moderate mixing, achieved by repeated cracking and remelting of the glass and by melting in a rotating tilted crucible, had a marked effect in lowering the density spread. The data afforded by these experiments lend further emphasis to the view that convection currents in commercial tank operation are highly significant in improving the homogeneity of a soda-lime-silica glass.     

Effect of hydrogenation on density and viscosity of sunflowerseed oil

The densities and viscosities of unhydrogenated and hydrogenated sunflowerseed oils have been determined at temperatures ranging from 25 to 50°C at 5°C intervals. The densities of these oils vary linearly with temperature. The values of the parameters for the density equation have been calculated. Smooth curves were obtained when the changes in viscosity with temperature were plotted in the form of ln η vs. 1/T. The energy of activation, the free energy of activation, and the entropy of activation have been calculated at 25°C, and they decreased with the degree of unsaturation in the fatty acid chains of the sunflowerseed oil.     

In situ HTXRD formation of magnesium titanates

Coprecipitated xerogel precursors of nanocrystalline magnesium titanates, with a Mg:Ti stoichiometric ratio of 2:1, were subjected to thermal treatment in air at constant temperature, from 100 to 1300°C, using a hot‐stage X‐ray powder diffractometer. The phase sequences, the kinetics of phase evolution and crystallite size were studied during the first hour of the process at different temperatures. Until 500°C no diffraction peaks were observed. Between 550 and 800°C the structure was a mixture of two cubic nanocrystalline coherent structures: qandilite‐like and periclase‐like forms. At 900 and 1000°C, after 15 minutes, geikielite and periclase appear in small amounts but the qandilite‐like phase remains predominant; at 1100°C and above, qandilite is formed again as a single phase. The diffraction lines were substantially broadened for all crystalline phases formed at low temperatures, becoming sharper with increasing temperature and time. The phase evolution is interpreted as a consequence of the decrease in the surface area to volume ratio with increasing temperature and time, thus decreasing the significance of the surface energy. Linear thermal expansion coefficients were derived for qandilite.     

Characteristics,wear and corrosion properties of borided pure titanium by pack boriding near α → β phase transition temperature

The boride layer characteristics, wear and corrosion properties of borided commercially pure titanium by pack boriding near the α → β phase transition temperature were investigated using X-ray diffraction, scanning electron microscopy, electron probe microanalysis, dry reciprocating friction tests, and electrochemical experiments in this work. The pack boriding was carried out at the temperatures of 860 °C, 880 °C, 900 °C, and 920 °C for 5, 10, 15 and 20 h. The results indicated that, in both α and β phase temperatures, the boride layer is composed of the outer TiB₂ layer and the inner TiB layer. The α→β phase transition temperature of commercially pure Ti in this work is in the range of 882–900 °C, and the growth of TiB layer can be enhanced at this temperature range. Commercially pure Ti borided at 920 °C for 20 h has the best wear resistance and corrosion resistance. Finally, wear and corrosion mechanisms were also discussed.