Mixture Design and Response Surface Analysis of Densification of Silicon Carbide Ceramics with (SiO2–Dy2O3–Al2O3) Additives

Statistical mixture designs are used to systematically study the densification properties of silicon carbide (SiC) ceramics sintered with SiO₂, Dy₂O₃, and Al₂O₃. Mixture models for percentage theoretical density and SiC weight loss as a function of the SiO₂, Dy₂O₃, and Al₂O₃ oxide proportions have been determined and validated by analysis of variance. The results indicate a region confined by about 0–20 mol% silica, 50–65 mol% dysprosia, and 40–65 mol% alumina, with all samples containing 10% by volume of additives, and simultaneously maximization of density values and minimization of weight loss during SiC-based ceramic sintering.     

Sonochemical synthesis of calcium phosphate powders

β-tricalcium phosphate (β-TCP) and biphasic calcium phosphate powders (BCP), consisting of hydroxyapatite (HA) and β-TCP, were synthesized by thermal decomposition of precursor powders obtained from neutralization method. The precursor powders with a Ca/P molar ratio of 1.5 were prepared by adding an orthophosphoric acid (H₃PO₄) solution to an aqueous suspension containing calcium hydroxide (Ca(OH)₂). Mixing was carried out by vigorous stirring and under sonochemical irradiation at 50 kHz, respectively. Glycerol and D-glucose were added to evaluate their influence on the precipitation of the resulting calcium phosphate powders. After calcination at 1000°C for 3 h BCP nanopowders of various HA/β-TCP ratio were obtained.     

The influence of sulphur on the processing of zirconia based ceramics

Yttria stabilized zirconia powders were synthesized by the coprecipitation route. Zirconium oxychloride containing sulphur as contamination and analytical grade yttrium chloride were used as raw materials. Powders were calcined at temperatures between 600 and 1100 °C and ground by ball and attrition milling. The ceramic bodies were sintered at 1350 and 1550 °C for 1 h and the apparent density was measured. In the present work it is shown that the most deleterious effect of sulphur was observed in 3 mol% yttria stabilized zirconia, especially when the pellets were obtained at high pressures and sintered at 1500 °C. The elimination of sulphur at higher calcination temperatures minimizes the effects caused by this contamination, despite the reduction of powder surface area. The best processing condition to obtain high density zirconia ceramics from powders contaminated with sulphur was established.     

ProNet: A policy network environment

Network and business management convergence is seen as the next step towards harmonizing information technology resource allocation with target business goals. This paper proposes a management platform that starts at the specification of business targets in the form of policies and goes all the way to enforcing them in a next generation Quality of Service aware network. We specified both a policy language and a parser and also implemented procedures for mapping policies into underlying network mechanisms. Furthermore, case studies presented in this paper show performance results of network services controlled by such policies.     

Polymer/filler derived NbC composite ceramics

NbC containing ceramic composites were manufactured from poly(siloxane)/Nb/NbC filler mixtures by a high temperature reaction bonding process. During heating in an inert atmosphere the Si—O—C ceramic residue of the polymer reacted with the metallic Nb filler to form Nb _x Si _y , NbO and NbC. Samples with a high Nb/NbC ratio showed reduced porosity and increased hardness after pyrolysis at 1200°C.     

Microstructure and properties tailoring of liquid-phase sintered SiC

Silicon carbide (SiC) ceramics of the composition SiC-10 vol% (AlN–Y₂O₃) were liquid-phase sintered without application of external pressure in a graphite resistance furnace in Ar atmosphere at 1950°C to high density (up to 98.8%). Contents of -SiC and β-SiC, as well as the granulometry of the -SiC used, were varying parameters of the initial compositions, the influence of which on densification, microstructure and phase formation during sintering and post-sintering heat treatments was studied. Evolution of microstructure, in particular of the grain morphology occurring due to transformation-controlled grain growth was followed by SEM. The degree of β-SiC to -SiC phase transformation was measured by means of quantitative XRD using internal standard technique. Fracture toughness of sintered and annealed materials has been determined by the Vickers indentation method and varied in the range 3.6–5.9 MPa m^1/2. Mechanisms of material toughening are discussed in terms of known toughening mechanisms with consideration of residual porosity variation.     

Volatile Retention and Antifungal Properties of Spray-Dried Microparticles of Lippia sidoides Essential Oil

Spray drying microencapsulation of Lippia sidoides essential oil was investigated. Maltodextrin DE10 and gum arabic at different proportions (4:1, 3:2, 2:3, 0:1 m/m) was used as a carrier. The content of essential oil related to the carrier was 20 and 25% in weight and the emulsions were atomized from 30% up to 60% (m/m) of total solid concentration. Spray dryer inlet temperatures varied from 140 to 160°C and the best thermal efficiency and powder recovery were found at 160°C. Product properties and process performance were assessed on the basis of microscopic features of the powder (shape and size of microparticles), moisture content, and powder recovery. Encapsulation efficiency was estimated through determination of the content of essential oil in the microcapsules. The best encapsulation efficiency was related to experimental parameters as follows: solid content of the encapsulating composition of 50% (m/m), maltodextrin:gum arabic ratio of 0:1 (m/m) and carrier:essential oil ratio of 4:1 (m/m). Antifungal activities of microparticles were evaluated, evidencing their potential as important antifungal agents. The positive findings in this study encourage further research and provide perspectives for the development of phytotherapeutic products from essential oil of Lippia sidoides.     

Use of a predictive model for food insecurity estimates in Brazil

In 2004 the National Household Survey (Pesquisa Nacional por Amostras de Domicilios-PNAD) estimated the prevalence of food and nutrition insecurity in Brazil. However, PNAD data cannot be disaggregated at the municipal level. The objective of this study was to build a statistical model to predict severe food insecurity for Brazilian municipalities based on the PNAD dataset. Exclusion criteria were: incomplete food security data (19.30%); informants younger than 18 years old (0.07%); collective households (0.05%); households headed by indigenous persons (0.19%). The modeling was carried out in three stages, beginning with the selection of variables related to food insecurity using univariate logistic regression. The variables chosen to construct the municipal estimates were selected from those included in PNAD as well as the 2000 Census. Multivariate logistic regression was then initiated, removing the non-significant variables with odds ratios adjusted by multiple logistic regression. The Wald Test was applied to check the significance of the coefficients in the logistic equation. The final model included the variables: per capita income; years of schooling; race and gender of the household head; urban or rural residence; access to public water supply; presence of children; total number of household inhabitants and state of residence. The adequacy of the model was tested using the Hosmer-Lemeshow test (p = 0.561) and ROC curve (area = 0.823). Tests indicated that the model has strong predictive power and can be used to determine household food insecurity in Brazilian municipalities, suggesting that similar predictive models may be useful tools in other Latin American countries.     

Influence of Synthesis Conditions on the Characteristics of Biphasic Calcium Phosphate Powders

Mixtures of hydroxyapatite (HAp) and tricalcium phosphate (TCP) powders with different Ca/P ratios were prepared by a wet chemical precipitation synthesis of calcium-deficient hydroxy apatite (CDHA) and subsequent calcination. The influence of precipitation method and calcination temperature on the chemical and physical properties of the resulting powders were evaluated. Different ratios between HAp and TCP were obtained by variation of the velocity of orthophosphoric acid addition into calcium hydroxide suspension. Slow addition (1 mL/min, S-powder) of H₃PO₄ into Ca(OH)₂ suspension lead to a higher amount of CO₃ groups substituting PO₄ in the apatite lattice compared to powders synthesized by fast addition (200 mL/min, F-powder). Consequently, the Ca/P molar ratio of S-powder (1.55) was higher than that of F-powder (1.52), leading to a higher amount of HAp in the resulting calcinated powders. Both powders show significant differences in their calcinations behavior. Whereas for F-powders a temperature of 750°C was adequate for a complete transformation of CDHA to TCP and HAp, 950°C were required for S-powders.