Growth, magnetic and transport properties of InSb and II-IV-As2 semiconductors doped with manganese

This thesis is devoted to growth and investigations of Mn-doped InSb and II-IV-As2 semiconductors, including Cd1-xZnxGeAs2:Mn, ZnSiAs2:Mn bulk crystals, ZnSiAs2:Mn/Si heterostructures. Bulk crystals were grown by direct melting of starting components followed by fast cooling. Mn-doped ZnSiAs2/Si heterostructures were grown by vacuum-thermal deposition of ZnAs2 and Mn layers on Si substrates followed by annealing. The compositional and structural properties of samples were investigated by different methods. The samples consist of micro- and nano- sizes clusters of an additional ferromagnetic Mn-X phases (X = Sb or As). Influence of magnetic precipitations on magnetic and electrical properties of the investigated materials was examined. With relatively high Mn concentration the main contribution to magnetization of samples is by MnSb or MnAs clusters. These clusters are responsible for high temperature behavior of magnetization and relatively high Curie temperature: up to 350 K for Mn-doped II-IV-As2 and about 600 K for InMnSb. The low-field magnetic properties of Mn-doped II-IV-As2 semiconductors and ZnSiAs2:Mn/Si heterostructures are connected to the nanosize MnAs particles. Also influence of nanosized MnSb clusters on low-field magnetic properties of InMnSb have been observed. The contribution of paramagnetic phase to magnetization rises at low temperatures or in samples with low Mn concentration. Source of this contribution is not only isolated Mn ions, but also small complexes, mainly dimmers and trimmers formed by Mn ions, substituting cation positions in crystal lattice. Resistivity, magnetoresistance and Hall resistivity properties in bulk Mn-doped II-IV-As2 and InSb crystals was analyzed. The interaction between delocalized holes and 3d shells of the Mn ions together with giant Zeeman splitting near the cluster interface are respond for negative magnetoresistance. Additionally to high temperature critical pointthe low-temperature ferromagnetic transition was observed Anomalous Hall effect was observed in Mn doped samples and analyzed for InMnSb. It was found that MnX clusters influence significantly on magnetic scattering of carriers.

Extractives and energetic properties of wood and charcoal

Charcoal production stands out as a raw material for the production of renewable energy. To assess wood quality in energy terms, studies have focused more on the holocellulose and lignin content than on the role of extractives. The objective of this study was to evaluate the relationship between the extractive content in cold water, in dichloromethane and total on energy properties of wood and charcoal, from six trees species. The extractives were removed with different solvents to be recorded and gross calorific value of wood was determined. The wood was carbonized at 1.67°C/min heating rate until maximum of 450°C and residence time of 30 min. The extractive content was correlated with the gravimetric yield, apparent relative density, ash, volatile matter, fixed carbon and gross calorific value of charcoal. The removal of total extractives and extractives soluble in dichloromethane reduced the gross calorific value of wood of most species evaluated. The extractives removed in cold water did not correlate with the parameters of carbonization. The extractives content in dichloromethane correlated with volatile matter, fixed carbon and gross calorific value. Total extractive content correlated with gravimetric yield, apparent relative density and gross calorific value of charcoal.

Combustion properties of biomass residues rich in phosphorus

Tillgången på traditionella biobränslen är begränsad och därför behöver man ta fram nya, tidigare outnyttjade biobränslen för att möta de uppställda CO2 emissionsmålen av EU och det ständigt ökande energibehovet. Under de senare åren har intresset riktats mot termisk energiutvinning ur olika restfraktioner och avfall. Vid produktion av fordonsbränsle ur biomassa är den fasta restprodukten ofta den största procesströmmen i produktionsanläggningen. En riktig hantering av restprodukterna skulle göra produktionen mera lönsam och mer ekologiskt hållbar. Ett alternativ är att genom förbränning producera elektricitet och/eller värme eftersom dessa restprodukter anses som CO2-neutrala. Målsättningen med den här avhandlingen var att studera förbränningsegenskaperna hos några fasta restprodukter som uppstår vid framställning av förnybara fordonsbränslen. De fyra undersökta materialen är rapskaka, palmkärnskaka, torkad drank och stabiliserat rötslam. I studien används ett stort urval av undersökningsmetoder, från laboratorieskala till fullskalig förbränning, för att identifiera de huvudsakliga utmaningarna förknippade med förbränning av restprodukterna i pannor med fluidiserad bäddteknik. Med hjälp av detaljerad bränslekarakterisering kunde restprodukterna konstateras vara en värdefull källa för värme- och elproduktion. Den kemiska sammansättningen av restprodukterna varierar stort jämfört med mera traditionellt använda biobränslen. En gemensam faktor för alla de studerade restprodukterna är en hög fosforhalt. På grund av de låga fosforkoncentrationerna i de traditionella biobränslena har grundämnet hittills inte ansetts spela någon större roll i askkemin. Experimenten visade nu att fosfor inte mera kan försummas då man studerar kemin i förbränningsprocesser, då allt flera fosforrika bränslen tränger in på energimarknaden.

Physical, chemical and microbiological properties of a Dystrophic Yellow Latosol using manipueira

The study aimed to evaluate chemical, microbiological and hydro-physical changes of a Dystrophic Yellow Latosol, receiver of different levels of manipueira (cassava wastewater) application, in the cultivation of 'Terra Maranhão' banana. The experimental design was a randomized block with three replications in a factorial scheme 3 x 4, in which it was considered three soil depths and four levels of manipueira. It was evaluated the weighted mean diameter of the aggregate, the percentage of aggregation at different periods, soil density, particle density, porosity and soil saturated hydraulic conductivity, in addition to pH of P (mg dm -3), K (mg dm-3), Ca (cmolc dm-3), Mg (cmolc dm-3), Ca+Mg (cmolc dm-3), Al (cmolc dm-3), Na (cmolc dm -3), H+Al (cmolc dm-3), CEC (cmolc dm-3), V%, OM (g kg-1), soil microbial biomass (Ug Cg-1 dry soil), acid phosphatase (Ug PNP g-1 h-1). The use of manipueira influenced some physical characteristic of the soil, but it was not possible to specify the effect of increasing application dosage. Therefore, the application did not affect the biological indicators assessed in the soil or its pH. The use of manipueira as a fertilizer in the doses used in this study showed low increase of K, P, H+Al and Al in the soil and a good increase of Mg, Ca and Ca+Mg, Na, CEC and V%.

Nitrogen fertilization by deep-bedding swine production and its effects on the properties of a Quartzarenic Neosol

The objective of this study was to evaluate the effects of the nitrogen fertilization in the form of swine deep bed in the properties of a quartz-sand neosol. The organic compound used was the deep bed made with rice hulls, from a commercial swine finishing system farm. Deep bed samples have been collected at various points in the installation in order to obtain a representative composite sample which has been fractionated in a 2.0 mm sieve and submitted to a 50-day maturation period. Then, agronomic value analyses were done. The experimental design was completely randomized. The treatments consisted of 0; 75; 150 and 300 mg dm-3 of N doses of deep bed as well as an additional treatment with ammonium sulfate at a 150 mg dm-3 of N. The experimental period in the greenhouse was 45 days, where the soil was cultivated with maize. After the experiment completion, further soil properties analyses were done. From the results, it was noted that the organic fertilization with deep bed provided a significant increase in the levels of potassium, in the sum of the bases, in the effective CEC, in the CEC at pH 7.0 and in the percentage of saturation.

Mechanical properties of castor beans subject to different drying temperatures aiming to disrupt the bean coat

In castor oil extraction process, the bean coat is abrasive to the equipment and releases substances that modify the oil color, reducing its quality. A potential solution would be to run the extraction by compressing only the endosperm. Due to lack of information, the objective of this study was to evaluate the influence of forced air drying at 40, 60, 80 and 100 ºC and farmyard drying, in the mechanical properties of the beans, aiming to break the bean coat. Castor beans were subjected to compression tests, in two perpendicular directions, at a strain rate of 0.6 mm.s-1. Average values of force, deformation energy, strain, all at rupture, and stiffness were used to evaluate the effects of dehydration. It was observed that the heat treatments did not alter the mechanical properties of castor beans, the strain and stiffness values discriminate the differences between the directions and had the lowest coefficients of variation. It was concluded that forced air drying, more costly than farmyard drying, does not bring benefits to the decortication. However, regardless the heat treatment used, the mechanical stress lengthwise is the most suitable to promote decortication.

Physical properties of Brazil nuts

The Brazil-nut, also known as Para-nut, is widely used as food and in cosmetic industries. The seeds are rich in lipids and protein, and also present a considerable amount of selenium. Limited research has been conducted on postharvest of the Brazil nut, being an important information to design equipment related to aeration, drying, storage and transportation steps. Thus, the objective of this study was to determine the physical properties of the Brazil-nut with and without tegument. The dimensions found for the almonds with tegument were 39.35 mm in the X axis, 24.19 mm in the Y axis, and 17.88 mm in the Z axis. However for the almond without tegument the values were 31.05 mm in X, 14.38 in Y and 15.91 mm in Z axis. The sphericity was 66.40% and 51.59% for the kernels with and without seed tegument respectively. The kernels with and without tegument presented sphericity of 63.00% and 47.72% respectively. The mass of 1000 almonds was 6.13 kg for almond with teguments and 3.18 kg for almonds without teguments. Specific mass of 0.947 g.cm-3 and 1.003 g.cm-3 for the kernels with and without tegument, coupled with a porosity of 46.88% and 37.60% and, resulting on a bulk density of 0.504 g.cm-3 and 0.626 g.cm-3 for almonds with and without teguments respectively. Finally, the angle of repose for the kernels with teguments was 36.37°.

Determination of physical properties of crambe fruits during drying

The Knowledge of the physical properties of agricultural products has great importance for the construction and operation of equipment for drying and storage, to achieve increased efficiency in post-harvest operations. The aim was to determine and analyze the physical properties of crambe fruits during drying at different temperatures. Crambe fruits with an initial moisture content of 0.36 (decimal d.b.) which was reduced by drying at 37.0; 58.8 and 83.5 ºC and relative humidity of 29.4; 11.2 and 3.2%, respectively, to 0.09 ± 1 (decimal d.b.). At different levels of moisture contents (0.36; 0.31; 0.26; 0.21; 0.17; 0.13 and 0.09 decimal d.b.), was evaluated the intergranular porosity, the bulk density, the true density as well as the volumetric shrinkage and the fruit mass. The study was installed by the factorial 3 x 7, and three drying temperatures and seven moisture contents in a randomized design. Data were analyzed using regression. The bulk density and the true density decreases along the drying process; the volumetric shrinkage and the mass increased with lower moisture content and the intergranular porosity decreased sharply with the increasing drying temperature.

Physical properties of soils and soybean yields after planting cover crops

Cover crops are important for improving soil quality. However, soil properties usually have some spatial dependence. Thus, this study aimed to evaluate the effect of winter cover crops on physical properties of soil and soybean yields using thematic maps. Five winter treatments were used: black oats; intercropping 1 (forage turnips and black oats); intercropping 2 (forage turnips, black oats and common vetch); wheat; and control. Macroporosity, microporosity, total porosity, bulk density and water content of the soil from 0 - 0.1 m depths were evaluated after the winter cover crop management. Soybeans were sown over the entire area in the summer after the winter cover crop management, and the soybean yield was determined for each treatment. Maps for each treatment were created and compared to the control treatment using the relative deviation coefficient (RDC). The cover crops improved the total macroporosity of the soil in some regions of the study area. The black oats were more efficient at maintaining higher water content of the soil, and it can be used to decrease the bulk density.

Fractionation of Hen Egg and Oat Lipids with supercritical Fluids Chemical and functional Properties of Fractions

Hen eggs and oats (Avena Sativa) are important materials for the food industry. Today, instead of merely satisfying the feeling of hunger, consumers are asking for healthier, biologically active and environmentally friendly products. The growing awareness of consumers’ increasing demands presents a great challenge to the food industry to develop more sustainable products and utilise modern and effective techniques. The modification of yolk fatty acid composition by means of feed supplements is well understood. Egg yolk phospholipids are polar lipids and are used in several applications including food, cosmetics, pharmaceuticals, and special nutrients. Egg yolk phospholipids are excellent emulsifiers, typically sold as mixtures of phospholipids, triacylglycerols, and cholesterol. However, highly purified and characterised phospholipids are needed in several sophisticated applications. Industrial fractionation of phospholipids is usually based on organic solvents. With these fractionation techniques, some harmful residues of organic solvents may cause problems in further processing. The objective of the present study was to investigate the methods to improve the functional properties of eggs, to develop techniques to isolate the fractions responsible for the specific functional properties of egg yolk lipids, and to apply the developed techniques to plant-based materials, too. Fractionation techniques based on supercritical fluids were utilised for the separation of the lipid fractions of eggs and oats. The chemical and functional characterisation of the fractions were performed, and the produced oat polar lipid fractions were tested as protective barrier in encapsulation processes. Modifying the fatty acid compositions of egg yolks with different types of oil supplements in feed had no affect on their functional or sensory properties. Based on the results of functional and sensory analysis, it is evident that eggs with modified fatty acid compositions are usable in several industrial applications. These applications include liquid egg yolk products used in mayonnaise and salad dressings. Egg yolk powders were utilised in different kinds of fractionation processes. The precipitation method developed in this study resembles the supercritical anti-solvent method, which is typically used in the pharmaceutical industry. With pilot scale supercritical fluid processes, non-polar lipids and polar lipids were successfully separated from commercially produced egg yolk powder and oat flakes. The egg and oat-based polar lipid fractions showed high purities, and the corresponding delipidated fractions produced using supercritical techniques offer interesting starting materials for the further production of bioactive compounds. The oat polar lipid fraction contained especially digalactosyadiacylglycerol, which was shown to have valuable functional properties in the encapsulation of probiotics.

Theoretical Analysis and Numerical Simulation of Spectral Radiative Properties of Combustion Gases in Oxy/Air-Fired Combustion Systems

Energy efficiency is one of the major objectives which should be achieved in order to implement the limited energy resources of the world in a sustainable way. Since radiative heat transfer is the dominant heat transfer mechanism in most of fossil fuel combustion systems, more accurate insight and models may cause improvement in the energy efficiency of the new designed combustion systems. The radiative properties of combustion gases are highly wavelength dependent. Better models for calculating the radiative properties of combustion gases are highly required in the modeling of large scale industrial combustion systems. With detailed knowledge of spectral radiative properties of gases, the modeling of combustion processes in the different applications can be more accurate. In order to propose a new method for effective non gray modeling of radiative heat transfer in combustion systems, different models for the spectral properties of gases including SNBM, EWBM, and WSGGM have been studied in this research. Using this detailed analysis of different approaches, the thesis presents new methods for gray and non gray radiative heat transfer modeling in homogeneous and inhomogeneous H2O–CO2 mixtures at atmospheric pressure. The proposed method is able to support the modeling of a wide range of combustion systems including the oxy-fired combustion scenario. The new methods are based on implementing some pre-obtained correlations for the total emissivity and band absorption coefficient of H2O–CO2 mixtures in different temperatures, gas compositions, and optical path lengths. They can be easily used within any commercial CFD software for radiative heat transfer modeling resulting in more accurate, simple, and fast calculations. The new methods were successfully used in CFD modeling by applying them to industrial scale backpass channel under oxy-fired conditions. The developed approaches are more accurate compared with other methods; moreover, they can provide complete explanation and detailed analysis of the radiation heat transfer in different systems under different combustion conditions. The methods were verified by applying them to some benchmarks, and they showed a good level of accuracy and computational speed compared to other methods. Furthermore, the implementation of the suggested banded approach in CFD software is very easy and straightforward.

CO2 sparging for improving the filtration properties of iron ore slurries

Iron ore treatment processes are usually continuous and high tonnage and filtration equipment has to meet these requirements. In magnetite (Fe3O4) treatment process continuous rotary disc filters are often used for filtration. Carbon dioxide (CO2) treatment is a fairly novel and un-known filtration enhancing process. The interest to use CO2 is quite high because CO2 is a greenhouse gas that is abundant, readily available and capture and use of CO2 would be environmentally beneficial. The focus of this thesis was to investigate if CO2 could be used to enhance the filtration of magnetite with ceramic disc filter. Previous studies have suggested that CO2 could be used to enhance the filtration properties of different iron ores thus increasing the filtration capacity. In the literature part, the basic theory of filtration and the particle properties affecting filtration were discussed. The basic steps of a typical ore treatment process were presented. The reasons why CO2 might enhance the filtration properties of different ores were investigated. A literature survey of earlier studies of CO2 addition as a filter aid was presented and the basic chemical properties and reactions of CO2 were also discussed. The experimental part was done at the LUT Laboratory of Separation Technology using different magnetite samples from the industry. The filtration experiments indicated that CO2 had a positive influence on the filtration properties of magnetite slurry. Zeta potential of untreated and CO2 treated magnetite was measured and CO2 treated magnetite had lower zeta potential values than the untreated magnetite. The filtration capacity was increased while the cake moisture levels were only slightly increased.

Thermodynamic properties of dilute HBr(aq) and HI(aq)

The theory of electrolyte solutions was described by explaining Debye–Hückel theory and deriving the Debye–Hückel equation for the mean activity coefficient. Simple two-parameter Hückel equation was used for the calculation of the activity coefficients of aqueous hydrobromic and hydriodic acids up to 0.5 mol/kg at temperatures from (0 to 60) °C and from (0 to 50) °C, respectively. The parameters were observed to be independent of the temperature. The Hückel equation for the osmotic coefficients of water in the studied solutions was compared to that of Pitzer model by predicting the vapor pressures up to 1 mol/kg at 25 °C. The experimental vapor pressures over the reference electrolyte solutions were calculated with the Pitzer equation for the osmotic coefficients for isopiestic data in this comparison. The simple Hückel model was found to be equally good as the Pitzer model for both hydrobromic and hydriodic acids up to 0.5 mol/kg at 25 °C but applies also to other temperatures studied.