Effect of Polyethylene Glycol (PEG) Powder on Compressibility and Microstructural Properties of Sintered α-Alumina

This study examines the effect of various contents of polyethylene glycol (PEG) powders on density, compressibility, and microstructural properties of sintered α-alumina samples. Moreover, the effect of compaction pressure on the green density of the compacts is studied by applying different pressures ranging from 400 to 550 MPa. Samples were prepared by mechanical blending of alumina and various amounts of PEG powders in a Turbula mixer. The binder contents vary from 1 wt.% to 4 wt.%. The as-prepared mixture was compacted in a universal machine at room temperature under the pressure of 6 MPa to produce disk-shaped samples in a pre-compaction step. Experimental results revealed that adding various amounts of PEG powders has a detrimental effect on the green density of alumina pellets and decreases the green density from 1.95 to 1.87 g/cm³. The results also show that sintered density of samples increased by increasing the compaction pressure to pressures higher than 400 MPa. It is observed that a sudden increase in green density has been observed between 450 and 550 MPa.     

Synthesis of Zirconia Powder in Zirconia Aqueous Sol

Spherical zirconia particles formed by coagulation of colloidal particles in zirconia aqueous sol followed by calcination.The zirconia sol was prepared from zirconium oxychloride aqueous solution by adjusting its pH value.The coag-ulation resulted from addition of preopanol in the sol the coagulation mechanism was discussed based on collicd theory.     

Effect of Sintering Additives on the Nitridation and Densification Behavior of Si—SiC Composite

Most of the thermo-mechanical properties of reaction bonded silicon nitride,including a second phase such as SiC depend on the final denstiy and the grain boundary glass phase of the sintered material .Thus it is necessary to know the sintering aid system most effective for the Si0-SiC compostie system ,Sintering experiments carried out using different combinations of sintering aids has indicated that two combinations,i.e.,(a) yttria with alumina and (b) yttia with aluminium nitride are effective sintering aid systems for the reation bonded Si-SiC composites.Adensity of 98.5% theoretical was obtained with yttria and aluminium nitride system.     

Effects of α-tocopherol and ascorbyl palmitate on the isomerization and decomposition of methyl linoleate hydroperoxides

In order to study antioxidant action on lipid hydroperoxide decomposition, the effects of α-tocopherol (TOH) and ascorbyl palmitate on the decomposition rate and reaction sequences of 9- and 13-cis,trans methyl linoleate hydroperoxide (cis,trans ML-OOH) decomposition in hexadecane were studied at 40°C. Decomposition of cis,trans ML-OOH as well as the formation and isomeric configuration of methyl linoleate hydroxy and ketodiene compounds were followed by high-performance liquid chromatographic analysis. TOH effectively inhibited the decomposition of ML-OOH. The decomposition rate was two times slower at 0.2 mM and more than 10 times slower at 2 and 20 mM of TOH. Ascorbyl palmitale (0.2, 2, and 20 mM) slightly accelerated the decomposition of ML-OOH. Both compounds had an effect on the reaction sequences of ML-OOH decomposition. At high levels TOH inhibited the isomerization of cis,trans ML-OOH to trans,trans ML-OOH through peroxyl radicals and increased the formation of hydroxy compounds. Further, the majority of the hydroxy and ketodiene compounds formed had a cis,trans configuration, indicating that cis,trans ML-OOH decomposed through alkoxyl radicals without isomerization. These results suggest that when inhibiting the decomposition of hydroperoxides, TOH can act as a hydrogen atom donor to both peroxyl and alkoxyl radicals. In the presence of ascorbyl palmitate, cis,trans ML-OOH decomposed rapidly but without isomerization. In contrast to TOH, the majority of hydroxy compounds were cis,trans, but the ketodiene compounds were trans,trans isomers. This indicates that ascorbyl palmitate reduced cis,trans ML-OOH to the corresponding hydroxy compounds. However, the simultaneous formation of trans,trans ketodiene compounds suggests that ML-OOH decomposition, similar to the control sample, also occurred in these samples. Thus, under these experimental conditions, the reduction of ML-OOH to more stable hydroxy compounds did not occur to an extent significant enough to inhibit the radical chain reactions of ML-OOH decomposition.     

Effects of α- and γ-tocopherols on the autooxidation of purified sunflower triacylglycerols

The antioxidant effects of α- and γ-tocopherols were evaluated in a model system based on the autooxidation of purified sunflower oil (p-SFO) triacylglycerols at 55°C for 7 d. Both tocopherols were found to cause more than 90% reduction in peroxide value when present at concentrations >20 ppm. α-Tocopherol was a better antioxidant than γ-tocopherol at concentrations ≤40 ppm but a worse antioxidant at concentrations >200 ppm. Neither α- nor γ-tocopherol showed a prooxidant effect at concentrations as high as 2000 ppm. The amount of tocopherols consumed during the course of oxidation was positively correlated to the initial concentration of tocopherols, and the correlation was stronger for α- than for γ-tocopherol. This correlation suggested that, besides reactions with peroxyl radicals, destruction of tocopherols may be attributed to unknown side reactions. Addition of FeSO₄, as a prooxidant, caused a 12% increase in the peroxide value of p-SFO in the absence of tocopherols. When tocopherols were added together with FeSO₄, some increase in peroxide value was observed for samples containing 200, 600 or 1000 ppm of α- but not γ-tocopherol. The addition of FeSO₄, however, caused an increase in the amount of α- and γ-tocopherols destroyed and led to stronger positive correlations between the amount of tocopherols destroyed during oxidation and initial concentration of tocopherols. No synergistic or antagonistic interaction was observed when α- and γ-tocopherols were added together to autooxidizing p-SFO.     

Effects of Phosphatidylcholine on Interaction of α-Tocopherol and β-Carotene in Photosensitized Oxidation of Emulsions

The interaction between α‐tocopherol (500 mg/kg) and β‐carotene (10 mg/kg) during chlorophyll‐photosensitized oxidation of a sunflower oil emulsion was studied in the presence or absence of phosphatidylcholine (PC, 250 mg/kg) by determining peroxide (POV) and conjugated dienoic acid (CDA) values. Chlorophyll, α‐tocopherol, β‐carotene, and PC contents in the emulsion were also monitored. α‐Tocopherol and β‐carotene individually and interactively decreased the POV and CDA values of oil in the emulsion by singlet oxygen quenching. PC decreased the POV and CDA values of oil, however, the values of the emulsion with added α‐tocopherol, β‐carotene, and PC were not significantly different from those of the emulsion with added α‐tocopherol and β‐carotene without PC. Contents of α‐tocopherol did not change during 24‐h oxidation, whereas co‐present PC significantly caused α‐tocopherol and chlorophyll degradation. β‐Carotene and PC contents significantly decreased to 45.5 and 51.3 %, respectively, after 24 h, and α‐tocopherol protected β‐carotene from degradation. The results suggest that PC had no net effects on the interactive antioxidant activity of α‐tocopherol and β‐carotene during chlorophyll‐photosensitized oxidation of the emulsion through free radical generation, chlorophyll degradation, and lessening the potency of α‐tocopherol as a singlet oxygen quencher.     

Effect of Ba Addition on Catalytic Activity of Pt and Rh Catalysts Loaded on γ-Alumina

The catalytic activity of Pt catalyst loaded on -alumina was improved by Ba addition in simulated automotive exhaust gases. On the other hand, the result of Rh catalyst was the opposite. From the results of the partial reaction orders in C₃H₆–O₂ reaction and TPR, it was concluded that the Ba addition to Pt catalyst suppressed the hydrocarbon chemisorption on the Pt catalyst and therefore allowed the catalytic reaction to proceed smoothly. On the other hand, Ba addition to Rh catalyst caused such a strong oxygen adsorption on Rh that rejected the hydrocarbon adsorption and suppressed the reaction.     

Effects of alumina sols on the sintering of α-alumina ceramics

The effects of two kinds of alumina sols on the densification behavior of sub-micron grain sized α-alumina ceramics have been investigated. Composition of the sol-derived gels was investigated by energy dispersive spectra and Fourier transform infrared spectra. Structural evolution of the gels at different temperatures was characterized by a combination of X-ray diffraction and ²⁷Al magic angle spinning nuclear magnetic resonance spectroscopy. Results showed that the gel containing chlorine and carbon transformed to α-alumina at about 950 °C, significantly lower than the other gel which transformed at about 1050 °C. Density measurements and scanning electron microscopy analyses were used to investigate the sintering of alumina ceramics with or without alumina sols. It was found that the alumina sols had profound effects on the densification of alumina ceramics. The ceramic displayed the best densification behavior when the sol containing chlorine and carbon was added.     

Effects of α- and γ-tocopherols on formation of hydroperoxides and two decomposition products from methyl linoleate

The antioxidant effects of α-and γ-tocopherols (at 0, 10, 100, 500, and 1000 ppm) were evaluated in a model system based on the autoxidation of methyl linoleate in bulk for 4 d at 40°C. Samples were collected every 24 h and analyzed for the 9 cis,trans, 9 trans,trans, 13 cis,trans, and 13 trans,trans isomers of hydroperoxide, hydroxy, and ketodiene oxidation products by high-performance liquid chromatography. Results showed that both α- and γ-tocopherols are effective hydrogen donors as evidenced by their abilities to inhibit the formation of hydroperoxides, hydroxy compounds, and ketodienes and the cis,trans to trans,trans isomerization of hydroperoxides. Compared with γ-tocopherol, α-tocopherol was a more efficient antioxidant at very low concentrations (10 ppm) but a less efficient antioxidant at the high concentrations (100–1000 ppm). This paradoxical behavior is explained on the basis of differences in ease of hydrogen donation between the two tocopherol homologs. Although α-tocopherol shows some loss of efficiency with increasing concentration, it is not a prooxidant when compared to the control void of antioxidants.     

Effects of doping cations on the densification and microstructure of flash-sintered α-Al2O3

The effects of dopants with different valences on the flash sintering behavior of α-Al₂O₃ are investigated. The results indicate that regardless of their valence and ionic radius, all the tested dopants reduce the onset temperature more effectively compared to undoped Al₂O₃. Interestingly, the relative density and grain size of the flash-sintered samples exhibit an inverse linear relationship. The data for the samples doped with non-trivalent cations fall on a different line than those for the samples doped with trivalent cations and the undoped samples. Dopants have an effect on the flash sintering behavior of Al₂O₃ because flash sintering increases the solubility of the dopants in alumina, creating more point defects, and thereby increasing the electrical conductivity of the material. The mechanisms for point defect generation in trivalent and non-trivalent dopants are different.     

Effect of Gas Atmosphere on Catalytic Behaviour of Zirconia, Ceria and Ceria–Zirconia Catalysts in Valeric Acid Ketonization

Ketonization of valeric acid, which can be obtained by lignocellulosic biomass conversion, was carried out in a fixed bed flow reactor over ZrO₂, 5–20 % CeO₂/ZrO₂ and CeO₂ both under hydrogen and nitrogen stream at 628 K and atmospheric pressure. Regardless gas-carrier 10 wt% CeO₂/ZrO₂ was found to show higher catalytic activity compared to zirconia per se as well as other ceria modified zirconia while ceria per se exhibited very low catalytic activity. All catalysts provided higher acid conversion in H₂ than in N₂ whereas selectivity to 5-nonanone was insensitive to gas atmosphere. XRD, FTIR, UV–Vis DRS, XPS, HRTEM methods were applied to characterize catalysts in reduced and unreduced states simulating corresponding reaction conditions during acid ketonization. XRD did not reveal any changes in zirconia and ceria/zirconia lattice parameters as well as crystalline phase depending on gas atmosphere while insertion of ceria in zirconia caused notable increase in lattice parameter indicating some distortion of crystalline structure. According to XPS, FTIR and UV–Vis methods, the carrier gas was found to affect catalyst surface composition leading to alteration in Lewis acid sites ratio. Appearance of Zr³⁺ cations was observed on the ZrO₂ surface after hydrogen pretreatment whereas only Zr⁴⁺ cations were determined using nitrogen as a gas-carrier. These changes of catalyst’s surface cation composition affected corresponding activity in ketonization probably being crucial for reaction mechanism involving metal cations catalytic centers for acid adsorption and COO^? stabilization at the initial step.     

Influence of pH on the preparation of monometallic rhodium and platinum,and bimetallic RhodiumPlatinum Catalysts supported on γ-Alumina

¹⁹⁵PtNMR and Raman experiments indicated that H₂PtCl₆ adsorbed monomolecularly on the surface of alumina up to a loading of 1 μmol m⁻² during pore volume impregnation. Above this limit crystalline H₂PtCl₆ was formed during the subsequent drying procedure. Adsorption experiments showed that RhCl₃ exhibited the same behaviour, with an even larger monomolecular coverage. The coverage of both metal complexes was dependent on the pH during adsorption and decreased with decreasing pH, due to a shift in the bonding equilibrium between the metal complexes in solution and the complexes adsorbed on the support surface. Because of the acidic properties of RhCl₃ and H₂PtCl₆, the amounts of rhodium and platinum adsorbed during co-adsorption were smaller than during adsorption of the separate metal complexes. The reduction of RhCl₃+H₂PtCl₆ supported on Al₂O₃ was governed by mobile rhodium atoms and small bimetallic clusters. Large metal salt crystals smothered the reduction process.     

Effects of dietary α-linolenic acid on the conversion and oxidation of13C-α-linolenic acid

The effects of a diet rich in α-linolenic acid vs. one rich in oleic acid on the oxidation of uniformly labeled¹³C-α-linolenic acid and its conversion into longer-chain polyunsaturates (LCP) were investigatedin vivo in healthy human subjects. Volunteers received a diet rich in oleic acid (n=5) or a diet rich in α-linolenic acid (n=7; 8.3 g/d) for 6 wk before and during the study. After 6 wk, subjects were given 45 mg of¹³C-α-linolenic acid dissolved in olive oil. Blood samples were collected att=0, 5, 11, 24, 96, and 336 h. Breath was sampled and CO₂ production was measured each hour for the first 12 h. The mean (±SEM) maximal absolute amount of¹³C-eicosapentaenoic acid (EPA) in plasma total lipids was 0.04 ±0.01 mg in the α-linolenic acid group, which was significantly lower (P=0.01) than the amount of 0.12±0.03 mg¹³C-EPA in the oleic acid group. Amounts of¹³C-docosapentaenoic acid (DPA) and¹³C-docosahexaenoic acid (DHA) tended to be lower as well. The mean proportion of labeled α-linolenic acid (ALA) recovered as¹³CO₂ in breath after 12 h was 20.4% in the ALA and 15.7% in the oleic acid group, which was not significantly different (P=0.12). The cumulative recovery of¹³C from¹³C-ALA in breath during the first 12 h was negatively correlated with the maximal amounts of plasma¹³C-EPA (r=−0.58,P=0.047) and¹³C-DPA (r=−0.63,P=0.027), but not of¹³C-DHA (r=−0.49,P=0.108). In conclusion, conversion of¹³C-ALA into its LCP may be decreased on diets rich in ALA, while oxidation of¹³C-ALA is negatively correlated with its conversion into LCP. In a few pilot samples, low¹³C enrichments of n−3 LCP were observed in a diet rich in EPA/DHA as compared to oleic acid.     

The Behavior of Refractory Slab——A Primary Discussion on the Correlation of Essential Factors and their Effects

The interrelation of various factors affecting the mechanical strength ,the thermal shock resistivity and creep deformation of slab in a simple setting condition of the firing of table ware are discussed,The conrol of parameters in favour of the desired performance of the slab is propsed.     

Fullerene C60 Supported on Silica and γ-Alumina Catalyzed Photooxidations of Alkenes

Deposition of fullerene C₆₀ (2% w/w) on silica and -alumina provokes a two orders-of-magnitude increase of its activity for the liquid-phase photooxidation of 2-methyl-2-heptene. Kinetic studies concerning the above photooxidation showed a first-order dependence of the reaction rate on the alkene concentration. The corresponding reaction-rate constant was found to be higher in the case where -alumina was used as carrier. The nature of the carrier does not influence the mechanism and the selectivity of the reaction. High dispersion of the supported fullerene is achieved on the surface of the carriers, which increase the fullerene light absorbance especially in the visible range.     

Fish Oil Supplementation During Lactation: Effects on Cognition and Behavior at 7 Years of Age

Early accumulation of n-3 long-chain PUFA (LCPUFA) in the brain may contribute to differences in later cognitive abilities. In this study, our objective was to examine whether fish oil (FO) supplementation during lactation affects processing speed, working memory, inhibitory control, and socioemotional development at 7 years. Danish mothers (n = 122) were randomized to FO [1.5 g/d n-3 LCPUFA] or olive oil (OO) supplementation during the first 4 months of lactation. The trial also included a high-fish intake (HFI) reference group (n = 53). Ninety-eight children were followed-up with an assessment of processing speed, an age-appropriate Stroop task, and the Strength and Difficulties Questionnaire at 7 year. A group effect of the intervention (FO vs. OO) was found in prosocial behavior scores; this negative effect was carried by the boys. Exploratory analyses including all participants revealed the speed of processing scores were predicted by maternal n-3 LCPUFA intake during the intervention period (negative relation) and maternal education (positive relation). Stroop scores indicative of working memory and inhibitory control were predicted by infant erythrocyte DHA status at 4 months of age (negative relation). Early fish oil supplementation may have a negative effect on later cognitive abilities. Speed of processing and inhibitory control/working memory are differentially affected, with speed of processing showing effects of fish oil intake as a whole, whereas inhibitory control/working memory was related more specifically to DHA status.     

Effect of Rre Earth Oxides and Silica on Sintering and Microstructure of AZS—40 Materials

Effect of the content of La2O3,CeO2 and SiO2 on the sintering behavior and microstruc-ture of AZS-40 material has been studied by means of sintering test and SEM examination,The results show that the porosity of the AZS-40 clinker with addition of 0.5% La2O3 or CeO2 could reach 2% under the ondition of 1600℃ for 4 hours.But it is not beneficial to the sintering and microstructure of the clinkers when the addition of the rare earth oxides increases to more than 0.5%,AZS-40 materials become difficult to be sintered as the addition of SiO2 in the materials incereases.     

Sintering of α-alumina for highly transparent ceramic applications

In this paper we present our results on the sintering of α alumina ceramics by hot isostatic pressing. It describes a simple method for obtaining precise relative density values on our almost 100% dense samples. Then, transparency results are discussed with respect to grain size and residual porosity measurements, comparing them to scattering calculations. Our results are not far from the best reported transmission values: almost 60% for a 1 mm thick sample. The other 40% diffuse light comes from the birefringence of alumina for the most part. However, they are transparent enough to see detailed structures at several kilometers through them.