Chemical ageing and transformation of diffusivity in semi-solid multi-component organic aerosol particles

Recent experimental evidence underlines the importance of reduced diffusivity in amorphous semi-solid or glassy atmospheric aerosols. This paper investigates the impact of diffusivity on the ageing of multi-component reactive organic particles representative of atmospheric cooking aerosols. We apply and extend the recently developed KM-SUB model in a study of a 12-component mixture containing oleic and palmitoleic acids. We demonstrate that changes in the diffusivity may explain the evolution of chemical loss rates in ageing semi-solid particles, and we resolve surface and bulk processes under transient reaction conditions considering diffusivities altered by oligomerisation. This new model treatment allows prediction of the ageing of mixed organic multi-component aerosols over atmospherically relevant time scales and conditions. We illustrate the impact of changing diffusivity on the chemical half-life of reactive components in semisolid particles, and we demonstrate how solidification and crust formation at the particle surface can affect the chemical transformation of organic aerosols.

Chemical ageing and transformation of diffusivity in semi-solid multi-component organic aerosol particles

Recent experimental evidence underlines the importance of reduced diffusivity in amorphous semi-solid or glassy atmospheric aerosols. This paper investigates the impact of diffusivity on the ageing of multi-component reactive organic particles approximating atmospheric cooking aerosols. We apply and extend the recently developed KMSUB model in a study of a 12-component mixture containing oleic and palmitoleic acids. We demonstrate that changes in the diffusivity may explain the evolution of chemical loss rates in ageing semi-solid particles, and we resolve surface and bulk processes under transient reaction conditions considering diffusivities altered by oligomerisation. This new model treatment allows prediction of the ageing of mixed organic multi-component aerosols over atmospherically relevant timescales and conditions. We illustrate the impact of changing diffusivity on the chemical half-life of reactive components in semi-solid particles, and we demonstrate how solidification and crust formation at the particle surface can affect the chemical transformation of organic aerosols.

Thermal analysis and compatibility studies of prednicarbate with excipients used in semi solid pharmaceutical form

Differential Scanning Calorimetry (DSC), thermogravimetry/derivative thermogravimetry (TG/DTG) and infrared spectroscopy (IR) techniques were used to investigate the compatibility between prednicarbate and several excipients commonly used in semi solid pharmaceutical form. The thermoanalytical studies of 1:1 (m/m) drug/excipient physical mixtures showed that the beginning of the first thermal decomposition stage of the prednicarbate (T (onset) value) was decreased in the presence of stearyl alcohol and glyceryl stearate compared to the drug alone. For the binary mixture of drug/sodium pirrolidone carboxilate the first thermal decomposition stage was not changed, however the DTG peak temperature (T (peak DTG)) decreased. The comparison of the IR spectra of the drug, the physical mixtures and of the thermally treated samples confirmed the thermal decomposition of prednicarbate. By the comparison of the thermal profiles of 1:1 prednicarbate:excipients mixtures (methylparaben, propylparaben, carbomer 940, acrylate crosspolymer, lactic acid, light liquid paraffin, isopropyl palmitate, myristyl lactate and cetyl alcohol) no interaction was observed.

A Comparison of Deep Drawing and Ironing of Metal Alloy Strip Produced conventionally and Non-conventionally via Semi Solid Material Processing

A semi solid thin strip continuous casting process was used to obtain 50%wt Pb/50%wtSn strip by single and twin roll processing at speed of 15 m/min. A 50%wt Pb/50%wtSn plate ingot was also cast for rolling conventionally into strips of 1.4 mm thickness and 45 mm width for comparison with those achieved non-conventionally. This hypoeutectic alloy has a solidification interval and fusion temperature of approximately 31 degrees C and 215 degrees C respectively. The casting alloy temperature was around 280 degrees C as measured by a type K immersion thermocouple prior to pouring into a tundish designed to maintain a constant melt flow on the cooling slope during semi solid material production. A nozzle with a weir ensures that the semi solid material is dragged smoothly by the lower roll, producing strip with minimum contamination of slag/oxide. The temperatures of the cooling slope and the lower roll were also monitored using K type thermocouples. The coiled semi solid strip, which has a thickness of 1.5 mm and 45 mm width, was rolled conventionally in order to obtain 1.2 mm thick strip. The coiled thixorolled strip had a thickness of 1.2 mm and achieved practically the same width as the conventional strips. Blanks of 40 mm diameter were cut from the strips in a mechanical press, ready for deep drawing and ironing for mechanical characterization. All the strips achieved from non-conventional processing had the same mechanical performance as those achieved conventionally. The limiting drawing ratio (LDR) achieved was approximately 2.0 for all strips. Microscopy examination was made in order to observe phase segregation during processing.

Analysis of Semi-solid Processing for Metal Matrix Composite Synthesis Using Factorial Design

The main goal in this work is to conduct a quantitative analysis of the mechanical stir casting process for obtaining particulate metal matrix composites. A combined route of stirring at semi-solid state followed by stirring at liquid state is proposed. A fractional factorial design was developed to investigate the influence and interactions of factors as: time, rotation, initial fraction and particle size, on the incorporated fraction. The best incorporations were obtained with all factors at high levels, as well as that very long stirring periods have no strong influence being particle size and rotation the most important factors on the incorporated fraction. Particle wetting occurs during stirring at semisolid state, highlighting the importance of the interactions between particles and the alloy globularized phase. The role of the alloying element Mg as a wettability-promoting agent is discussed. The shear forces resulting from the stirring system is emphasized and understood as the effect of rotation itself added to the propeller blade geometry.

Evaluation of strip rolling directly from the semi-solid state

defect metal alloy strip when thixorolling directly from the semi-solid state. To facilitate the study lead/tin alloys were chosen for their relatively low operating temperature. The objective is to extrapolate these findings to the higher temperature aluminium, alloys. Three alloys (70%Pb30%Sn, 60%Pb-40%Sn, 50%Pb-50%wtSn) were used particularly to study the influence of the solidification interval. The equipment consists of a two roll mill arranged as an upper and lower roller, where both rollers are driven at a controlled speed. The lower roller is fed with semi solid alloy through a ceramic nozzle attached to the lower end of a cooling slope. Several types of nozzle and their position at the roller were tested. This produced different solidifications and consequently different finished strip. The alloys were first cast and then poured onto the cooling slope through a tundish in order to create a continuous laminar flow of slurry and uniformity of metal strip quality. The pouring was tested at different positions along the slope. The cooling slope was coated with colloidal graphite to promote a smooth slurry flow and avoid the problem of adherence and premature solidification. The metallic slurry not only cools along the slope but is also initially super-cooled to a mush by the lower roller whilst at room temperatures, thus enabling thixorolling. It was also found that the nozzle position could be adjusted to enable the upper roller to also contribute to the solidification of the metallic slurry. However the rollers and the cooling slope naturally heat up. Temperature distribution in these zones was analysed by means of three thermocouples positioned along the cooling slope and a fourth in the base of the semi solid pool within the nozzle. The objective being to design an optimum pouring and cooling system. The formed strip was cooled down to room temperature with a shower of water. Microstructures of the thixorolling process were analysed. The differences in solidification conditions resulted in differing qualities of finished strip and corresponding defect types, all of which are a serious quality issue for the rolled product.

Migration of crystals during the filling of semi-solid castings

In cold-chamber high-pressure die castings (HPDC), the microstructure consists of coarse externally solidified crystals (ESCs) that are commonly observed in the central region of cross sections. In the present work, controlled laboratory scale casting experiments have been conducted with particular emphasis on the flow and solidification conditions. An A356 aluminum alloy was used to produce castings by pouring semi-solid metal through a steel die. Microstructures similar to those encountered in HPDC have been produced and the resulting microstructure is found to depend on the melt and die temperature: (1) the fraction of ESCs determines the extent of migration to the central region; (2) a maximum packing determines the area fraction of ESCs in the center; and (3) the die temperature affects the position of the ESCs-a higher die temperature can induce a displaced ESC distribution. It is found that the n-figration of crystals to the central region requires a flow, which is constrained at all melt/die interfaces. Furthermore, potential lift mechanisms are discussed. An assessment of the Saffman lift force on individual particles shows it has no significant effect on the migration of ESCs.

High speed DSC (hyper-DSC) as a tool to measure the solubility of a drug within a solid or semi-solid matrix

Conventional differential scanning calorimetry (DSC) techniques are commonly used to quantify the solubility of drugs within polymeric-controlled delivery systems. However, the nature of the DSC experiment, and in particular the relatively slow heating rates employed, limit its use to the measurement of drug solubility at the drug's melting temperature. Here, we describe the application of hyper-DSC (HDSC), a variant of DSC involving extremely rapid heating rates, to the calculation of the solubility of a model drug, metronidazole, in silicone elastomer, and demonstrate that the faster heating rates permit the solubility to be calculated under non-equilibrium conditions such that the solubility better approximates that at the temperature of use. At a heating rate of 400°C/min (HDSC), metronidazole solubility was calculated to be 2.16 mg/g compared with 6.16 mg/g at 20°C/min. © 2005 Elsevier B.V. All rights reserved.

Shear deformation at 29% solid during solidification of magnesium alloy AZ91 and aluminium alloy A356

Partially solid commercial Al-Si and Mg-Al alloys have been deformed in shear during solidification using vane rheometry. The dendritic mush was deformed for a short period at 29% solid and allowed to cool naturally after deformation. Both alloys exhibited yield point behaviour and deformation was highly localised at the surface of maximum shear stress. The short period of deformation was found to have a distinct impact on the as-cast microstructure leading to fragmented dendrites in the deformation region of both alloys. In the case of the Mg-Al alloy, a concentrated region of interdendritic porosity was also observed in the deformation region. Concentrated porosity was not observed in the Al-Si alloy. (c) 2005 Elsevier B.V. All rights reserved.

Olive pomace pretreatments to enhance its valorisation by solid-state fermentation

Dissertação de mestrado em Bioengenharia

Produção de enzimas por fungos em fermentação semi-sólida utilizando bagaço de coco e pedúnculo de caju como substratos

The production of enzymes by microorganisms using organic residues is important and it can be associated with several applications such as food and chemical industries and so on. The objective of this work is the production of CMCase, Xylanase, Avicelase and FPase enzymes by solid state fermentation (SSF) using as substrates: bagasse of coconut and dried cashew stem. The microorganisms employed are Penicillium chrysogenum and an isolated fungus from the coconut bark (Aspergillus fumigatus). Through the factorial design methodology and response surface analysis it was possible to study the influence of the humidity and pH. For Penicillium chrysogenum and the isolated fungus, the coconut bagasse was used as culture medium. In another fermentation, it was used the mixture of coconut bagasse and cashew stem. Fermentations were conducted using only the coconut bagasse as substrate in cultures with Penicillium chrysogenum fungus and the isolated one. A mixture with 50% of coconut and 50% of cashew stem was employed only for Penicillium chrysogenum fungus, the cultivation conditions were: 120 hours at 30 °C in BOD, changing humidity and pH values. In order to check the influence of the variables: humidity and pH, a 2 2 factorial experimental design was developed, and then two factors with two levels for each factor and three repetitions at the central point. The levels of the independent variables used in ascending order (-1, 0, +1), to humidity, 66%, 70.5% and 75% and pH 3, 5 and 7, respectively. The software STATISTICA TM (version 7.0, StatSoft, Inc.) was used to calculate the main effects of the variables and their interactions. The response surface methodology was used to optimize the conditions of the SSF. A chemical and a physic-chemical characterization of the coconut bagasse have determined the composition of cellulose (%) = 39.09; Hemicellulose (%) = 23.80, Total Lignin (%) = 36.22 and Pectin (%) = 1.64. To the characterization of cashew stem, the values were cellulose (g) = 15.91 Hemicellulose (%) = 16.77, Total Lignin (%) = 30.04 and Pectin (%) = 15.24. The results indicate the potential of the materials as substrate for semisolid fermentation enzyme production. The two microorganisms used are presented as good producers of cellulases. The results showed the potential of the fungus in the production of CMCase enzyme, with a maximum of 0.282 UI/mL and the Avicelase enzyme the maximum value ranged from 0.018 to 0.020 UI/ mL, using only coconut bagasse as substrate. The Penicillium chrysogenum fungus has showed the best results for CMCase = 0.294 UI/mL, FPase = 0.058 UI/mL, Avicelase = 0.010 UI/mL and Xylanase = 0.644 UI/ mL enzyme, using coconut bagasse and cashew stem as substrates. The Penicllium chrysogenum fungus showed enzymatic activities using only the coconut as substrate for CMCase = 0.233 UI/mL, FPase = 0.031 to 0.032 UI/ mL, Avicelase = 0.018 to 0.020 UI/mL and Xylanase = 0.735 UI/ mL. Thus, it can be concluded that the used organisms and substrates have offered potential for enzyme production processes in a semi-solid cultivation

Fabricação e caracterização metalográfica e mecânica de tiras de ligas metálicas fundidas e tixolaminadas no estado semi-sólido de diferentes intervalos de solidificação

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)