Phase and microstructural evolution during the heat treatment of Sm-Ca-alpha-sialon ceramics

The phase and microstructural evolution of multi-cation Sm-Ca-alpha-sialon ceramics was investigated. Six samples were prepared, ranging from a pure Sm-sialon to a pure Ca-sialon, with calcium replacing samarium in 20 eq% increments, thus maintaining an equivalent design composition in all samples. After pressureless sintering at 1820 degreesC for 2 It, all samples were subsequently heat treated up to 192 h at 1450 and 1300 degreesC. The amount of grain boundary glass in the samples after sintering was observed to decrease with increasing calcium levels. A M-ss' or M-ss',-gehlenite solid solution was observed to form during the 1450 degreesC heat treatment of all Sm-containing samples, and this phase forms in clusters in the high-Sm samples. The thermal stability of the alpha-sialon phase was improved in the multi-cation systems. Heat treatment at 1300 degreesC produces SmAlO3 in the high-Sm samples, a M-ss',-gehlenite solid solution in the high-Ca samples, and a Sm-Ca-apatite phase in some intermediate samples. (C) 2002 Elsevier Science Ltd. All rights reserved.

Thermal stability of mixed-cation alpha-sialon ceramics

A series of alpha-sialon (alpha') compositions containing mixed stabilising cations were prepared, by introducing additional CaO to a basic Sm alpha-sialon compositions. The thermal stability of these Sm-Ca-containing alpha-sialon phases was investigated using XRD, SEM and EDXS techniques. It was found that the addition of calcium into the Sm alpha-sialon systems greatly improved the stability of the alpha-sialon phases. Calcium was found to be incorporated into the alpha-sialon structure, coexistent with the samarium, and partitioning of the calcium and samarium was observed between the alpha' phase and grain boundary phases. This indicates a technique which may be used to improve the thermal stability of the alpha' phase while maintaining good refractory phases at the gialon grain boundaries. (C) 2003 Elsevier Science B.V. All rights reserved.

Development of alpha-SiAlON-SiC ceramic composites by liquid phase sintering

In this work, in situ alpha-SiAlON-SiC ceramic composites were obtained,by, liquid phase sintering, using SiC as reinforcement. Different beta-SiC powder contents (0-20 wt.%), were added to Si3N4-AlN-RE2O3. powder mixtures, and compacted by cold isostatic pressing. The samples were sintered at 1950 degrees C for 1 h, in N-2 atmosphere. Sintered: samples were characterized by relative density, weight loss, X-ray diffraction and scanning electron microscopy. Furthermore, mechanical properties such as hardness and fracture toughness were determined by Vickers indentation method. Lattice parameters of the alpha' phase did not considerably change with increase of SiC content. However, morphology, average grain size and aspect ratio of the alpha' phase were considerably changed with increase of the SiC content. These behavior influences significantly the mechanical properties of this hard ceramic composite. (C) 2006 Elsevier Ltd. All rights reserved.

alpha-SiAlON ceramics with elongated grain morphology using an alternative sintering additive

In this work, the use of a natural yttrium oxide and rare earth oxide solid solution (CRE2O3) as stabilizers of the alpha-Si3N4 phase to form alpha-SiAlON has been investigated. This oxide mix is produced at FAENQUIL-DEMAR, at a cost of only 20% of pure commercial Y2O3. Two alpha-SiAlONs using pure Y2O3 or CRE2O3 have been prepared, using mixes of 20% by volume of a molar fraction of 9:1 of AlN to Y2O3 or AlN to CRE2O3, respectively, with 80% alpha-Si3N4. Samples were gas pressure-sintered at 1900 degreesC, under 1.5 MPa of N-2 for 60 min. Both compositions yielded alpha-SiAlON ceramics with high relative densities (98% t.d.), hardness of 18 GPa and fracture toughness of 5 Mpa m(1/2), with homogeneous microstructures composed of elongated alpha-SiAlON grains with aspect ratios of 5. It is concluded that the mixed rare earth concentrate (CRE2O3) can be used to produce alpha-SiAlON ceramics with similar microstructures and mechanical properties of alpha-SiAlON ceramics fabricated using pure Y2O3, but with the advantage of its lower production cost. (C) 2004 Elsevier B.V All rights reserved.

alpha-SiAlON-SiC composites obtained by gas-pressure sintering and hot-pressing

The objective of this work was the obtaining in situ of alpha-SiAlON-SiC composite, using an alternative rare-earth oxide mixture, RE2O3, as sintering additive, by two different sintering processes. As sintering additive, 20 vol.% of AlN-RE2O3 in a molar ratio of 90: 10 was mixed to the alpha-Si3N4 powder. In the Si3N4-AlN-RE2O3 powder mixture, 0, 10, 15 and 20wt.% of SiC were added. The powder batches were milled, dried and compacted by cold isostatic pressing. Two different sintering processes were used: gas-pressure sintering at 1950 degrees C for 1 h under 1.5 MPa of N-2 atmosphere, or uniaxial hot-pressing at 1750 degrees C, for 30 min under pressure of 20 MPa. The sintered samples were characterized by X-ray diffraction, scanning electron microscopy and mechanical properties. XRD patterns indicate only alpha-SiAlON (alpha') and beta-SiC as crystalline phases. It was observed that the SiC addition did not influence the alpha-SiAlON formation, although the growth of elongated alpha'-grains is substantially decreased. The hot-pressed composites presented better mechanical properties, exhibiting fracture toughness of 5 MPa m(1/2) and hardness around 21.5 GPa. (c) 2007 Elsevier B.V. All rights reserved.

Microstructural evidence for the mechanism of the alpha-beta phase transformation in ytterbium SiAlON ceramics

Detailed microstructural evidence for the mechanism of the alpha-beta phase transformation in ytterbium SiAlON ceramics is presented. Grains, which show partial transformation, have been examined using transmission electron microscopy. We suggest that the transformation proceeds as a discernable reaction front and the accompanying lattice mismatch is accommodated be a series of complex dislocations. The stabilizing cation is ejected from the transformed alpha- phase and diffuse along the dislocation to accumulate as isolated pockets in a way similar to that observed in metal systems and termed pipe diffusion. High-resolution electron microscopy reveals the details of each of these features.

α′ phase stability in Nd-Li-sialon systems

The formability and stability of the alpha-sialon (alpha') phase was investigated in multi-cation Nd-Li-sialon systems. Four samples were prepared, ranging from a pure Nd-sialon to a pure Li-sialon, with two intermediate samples being prepared with either lithium or neodymium replacing the other alpha'-stabilising additive by 20 eq.%, as to maintain an equivalent design composition in all samples. After sintering, all samples were subsequently heat treated up to 192 h at 1450 and 1300 degreesC. While significant quantities of the beta'-sialon (beta' phase were found in most samples, the high-lithium Li-Nd-sialon sample was found to be almost pure a' phase after sintering. Furthermore, the long-term stability of the a' phase on heat treatment was also found to be superior in both multi-cation samples than in either of the single-alpha'-stabilising-cation samples. This is thought to be related to improved retention of the lithium in the multi-cation systems, as much of the lithium was found to volatilise during sintering in the neodymium-free sample. (C) 2002 Elsevier Science Ltd. All rights reserved.

Obtenção in situ do compósito alfa-SiAlON-SiC

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of the substitution of Y2O3 for CeO2 on the mechanical and microstructural properties of silicon nitride

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Pipkiiα Is Widely Expressed In Hematopoietic-derived Cells And May Play A Role In The Expression Of Alpha- And Gamma-globins In K562 Cells.

Characterized for the first time in erythrocytes, phosphatidylinositol phosphate kinases (PIP kinases) belong to a family of enzymes that generate various lipid messengers and participate in several cellular processes, including gene expression regulation. Recently, the PIPKIIα gene was found to be differentially expressed in reticulocytes from two siblings with hemoglobin H disease, suggesting a possible relationship between PIPKIIα and the production of globins. Here, we investigated PIPKIIα gene and protein expression and protein localization in hematopoietic-derived cells during their differentiation, and the effects of PIPKIIα silencing on K562 cells. PIPKIIα silencing resulted in an increase in α and γ globins and a decrease in the proliferation of K562 cells without affecting cell cycle progression and apoptosis. In conclusion, using a cell line model, we showed that PIPKIIα is widely expressed in hematopoietic-derived cells, is localized in their cytoplasm and nucleus, and is upregulated during erythroid differentiation. We also showed that PIPKIIα silencing can induce α and γ globin expression and decrease cell proliferation in K562 cells.

Macrophage Cell Activation With Acute Apical Abscess Contents Determined By Interleukin-1 Beta And Tumor Necrosis Factor Alpha Production.

This clinical study has investigated the antigenic activity of bacterial contents from exudates of acute apical abscesses (AAAs) and their paired root canal contents regarding the stimulation capacity by levels of interleukin (IL)-1 beta and tumor necrosis factor alpha (TNF-α) throughout the root canal treatment against macrophage cells. Paired samples of infected root canals and exudates of AAAs were collected from 10 subjects. Endodontic contents were sampled before (root canal sample [RCS] 1) and after chemomechanical preparation (RCS2) and after 30 days of intracanal medication with calcium hydroxide + chlorhexidine gel (Ca[OH]2 + CHX gel) (RCS3). Polymerase chain reaction (16S rDNA) was used for detection of the target bacteria, whereas limulus amebocyte lysate was used to measure endotoxin levels. Raw 264.7 macrophages were stimulated with AAA exudates from endodontic contents sampled in different moments of root canal treatment. Enzyme-linked immunosorbent assays were used to measure the levels of TNF-α and IL-1 beta. Parvimonas micra, Porphyromonas endodontalis, Dialister pneumosintes, and Prevotella nigrescens were the most frequently detected species. Higher levels of endotoxins were found in samples from periapical exudates at RCS1 (P < .005). In fact, samples collected from periapical exudates showed a higher stimulation capacity at RCS1 (P < .05). A positive correlation was found between endotoxins from exudates with IL-1 beta (r = 0.97) and TNF-α (r = 0.88) production (P < .01). The significant reduction of endotoxins and bacterial species achieved by chemomechanical procedures (RCS2) resulted in a lower capacity of root canal contents to stimulate the cells compared with that at RCS1 (P < .05). The use of Ca(OH)2 + CHX gel as an intracanal medication (RCS3) improved the removal of endotoxins and bacteria from infected root canals (P < .05) whose contents induced a lower stimulation capacity against macrophages cells at RCS1, RCS2, and RCS3 (P < .05). AAA exudates showed higher levels of endotoxins and showed a greater capacity of macrophage stimulation than the paired root canal samples. Moreover, the use of intracanal medication improved the removal of bacteria and endotoxins from infected root canals, which may have resulted in the reduction of the inflammatory potential of the root canal content.

Inhibition Of Tumor Necrosis Factor-alpha And Cyclooxigenase-2 By Isatin: A Molecular Mechanism Of Protection Against Tnbs-induced Colitis In Rats.

Isatin, an indole alkaloid has been shown to have anti-microbial, anti-tumor and anti-inflammatory effects. Due to its findings, we evaluated whether this alkaloid would have any effect on TNBS-induced colitis. Animals (male Unib:WH rats, aged 8 weeks old) were induced colitis through a rectal administration of 2,4,6-trinitrobenzene sulphonic acid using a catheter inserted 8 cm into the rectum of the animals. The rats were divided into two major groups: non-colitic and colitic. The colitic group was sub-divided into 6 groups (10 animals per group): colitic non-treated, Isatin 3; 6; 12.5; 18.75 and 25 mg/kg. Our main results showed that the oral treatment with Isatin 6 and 25 mg/kg were capable of avoiding the increase in TNF-α, COX-2 and PGE₂ levels when compared to the colitic non-treated group. Interestingly, the same doses (6 and 25 mg/kg) were also capable of preventing the decrease in IL-10 levels comparing with the colitic non-treated group. The levels of MPO, (an indirect indicator of neutrophil presence), were also maintained lower than those of the colitic non-treated group. Isatin also prevented the decrease of SOD activity and increase of GSH-Px and GSH-Rd activity as well as the depletion of GSH levels. In conclusion, both pre-treatments (6 and 25 mg/kg) were capable of protecting the gut mucosa against the injury caused by TNBS, through the combination of antioxidant and anti-inflammatory properties, which, together, showed a protective activity of the indole alkaloid Isatin.

Whey And Soy Protein Supplements Changes Body Composition In Patients With Crohn's Disease Undergoing Azathioprine And Anti-tnf-alpha Therapy.

Crohn´s disease (CD) is a chronic transmural inflammation of the gastrointestinal tract of unknown cause. Malnutrition associated with active CD has been reduced although obesity has increased. Dietary strategies such as those with high-protein have been proposed to reduce body fat. This study compares the effects of two supplements on the nutritional status of CD patients. 68 CD patients were randomized in two groups: whey protein group (WP) and soy protein group (SP). Using bioimpedance analysis, anthropometry and albumin and pre-albumin dosages the nutritional status was measured before starting the intervention and after 8 and 16 weeks. The disease activity was determined by Crohn's Disease Activity Index and serum C-reactive protein dosage and dietary intake by 24h dietary recalls. Forty-one patients concluded the study and both supplements changed body composition similarly. Triceps skin fold thickness (p< 0.001) and body fat percentage (p=0.001) decreased, whereas mid-arm muscle circumference (p=0.004), corrected arm muscle area (p=0.005) and body lean percentage (p=0.001) increased. For Crohn's disease patients undergoing anti TNF-alpha and azatioprine therapies, supplementation with whey and soy proteins changes body composition through reduction of body fat and thus contributes to control inflammation.

The G209A mutation in the alpha-synuclein gene in Brazilian families with Parkinson's disease

A missense G209A mutation of the alpha-synuclein gene was recently described in a large Contursi kindred with Parkinson's disease (PD). The objective of this study is to determine if the mutation G209A of the alpha-synuclein gene was present in 10 Brazilian families with PD. PD patients were recruited from movement disorders clinics of Brazil. A family history with two or more affected in relatives was the inclusion criterion for this study. The alpha-synuclein G209A mutation assay was made using polymerase chain reaction and the restriction enzyme Tsp45I. Ten patients from 10 unrelated families were studied. The mean age of PD onset was 42.7 years old. We did not find the G209A mutation in our 10 families with PD. Our results suggest that alpha-synuclein mutation G209A is uncommon in Brazilian PD families.

Análise do perfil de humor e da enzima alfa-amilase salivar em indivíduos fisicamente ativos = : Analysis of profile of mood states and salivary alpha amylase enzyme in physically active individuals

Universidade Estadual de Campinas . Faculdade de Educação Física