Use Of Crucibles Research Articles

Nutritional value of microalgae for ruminants and implications from microalgae production

Abstract Microalgae are a diverse group of microorganisms that are an interesting alternative feed resource for ruminant production. Microalgae species with high protein concentration and adequate amino acid (AA) composition can be used to substitute conventional protein feeds, whereas species with high carbohydrate or lipid concentration can be used to supply energy. Microalgal polyunsaturated acids and short-chain fatty acids have potential to improve the nutritive value of ruminant milk and meat for human consumption and mitigate enteric methane emissions. Microalgae composition is very plastid in comparison to conventional ruminant feeds and it can be influenced relatively easily by environmental conditions, such as nutrient supply. Microalgae also contain many compounds, especially carbohydrates and cell coverings, which are not usually found in ruminant feeds. Standard feed evaluation methods involving the use of crucibles or nylon bags (detergent fibre method, in vitro digestibility and in vivo rumen incubation) suit poorly to the analysis of microalgae with microscopic particle size. This paper attempts to give a general overview of the nutritive value (protein, lipids and carbohydrates) of microalgae for ruminant feeding applications and the possibilities to tailor microalgae composition for a certain ruminant feeding objectives. In addition, the key knowledge gaps related to the nutritive value of microalgae for ruminant nutrition are identified.

Los metales de la colección Zavaleta provenientes del departamento de Molinos, Salta, y su aporte al conocimiento de la secuencia de producción metalúrgica en las quebradas altas del Valle Calchaquí

Este trabajo presenta el estudio de piezas de metal provenientes de las colecciones depositadas en el Museo Etnográfico J. B. Ambrosetti (FFyL, Universidad de Buenos Aires) y en el Museo Arqueológico Eduardo Casanova (Tilcara) (FFyL, Universidad de Buenos Aires), que fueran recolectadas por Manuel Zavaleta hacia fines del siglo XIX mediante excavaciones no sistemáticas en Tacuil (departamento Molinos, Salta), y en otras localidades de la región como el valle de Luracatao, la localidad de Molinos y Colomé en el valle Calchaquí. Se suman, asimismo, datos de piezas del mismo coleccionista que se encuentran en diferentes museos internacionales, a los cuales accedimos mediante publicaciones, aportes de otros investigadores e información disponible en la web de dichas instituciones. Toda esta información es puesta en diálogo con bibliografía disponible sobre la metalurgia de la región y especialmente con los resultados de la investigación que actualmente desarrollamos, en un conjunto arquitectónico de estructuras rectangulares ubicado sobre la terraza del rio Blanco a los pies del farallón del Pukara de Tacuil, donde hallamos las primeras evidencias de producción metalúrgica durante el período Tardío-Inca (siglos X al XVI) en las quebradas altas del valle Calchaquí medio. En este sentido, mientras que las prospecciones y excavaciones de este sector del sitio ofrecieron evidencias de fundición de cobre por medio del uso de crisoles, elaboración de aleación de cobre y estaño y de objetos metálicos de cobre y bronce estañífero a partir del vaciado en moldes, no se recuperaron piezas completas. El estudio de la colección Zavaleta de este sitio nos permitió observar que objetos de similares características a los que pudieron haber sido confeccionados en el lugar formaron parte de los ajuares de las tumbas identificadas en Tacuil y sitios asociados. De este modo, mientras la colección aporta nuevos datos a la secuencia de producción sugerida desde la evidencia de campo, la importancia de los hallazgos realizados en excavaciones sistemáticas nos permite interpretar las piezas de museo, carentes de información contextual.

Wettability Control for Correct Thermophysical Properties Determination of Molten Salts and Their Nanofluids

Proper recording of thermophysical properties for molten salts (MSs) and molten salts based nanofluids (MSBNs) is of paramount importance for the thermal energy storage (TES) technology at concentrated solar power (CSP) plants. However, it is recognized by scientific and industrial communities to be non-trivial, because of molten salts creeping (scaling) inside a measuring crucible or a sample container. Here two strategies are proposed to solve the creeping problem of MSs and MSBNs for the benefit of such techniques as differential scanning calorimetry (DSC) and laser flash apparatus (LFA). The first strategy is the use of crucibles with rough inner surface. It was found that only nanoscale roughness solves the creeping problem, while micron-scale roughness does not affect the wetting phenomena considerably. The second strategy is the use of crucible made of or coated with a low-surface energy material. Both strategies resulted in contact angle of molten salt higher than 90° and as a result, repeatable measurements in correspondence to the literature data. The proposed methods can be used for other characterization techniques where the creeping of molten salts brings the uncertainty or/and unrepeatability of the measurements.

Effect of Heat-Treatment on Microstructure and Mechanical Behavior of Directionally Solidified Nb-Ti-Si Based Alloy

With the melting temperature of 2323 K and withdrawing rate of 100 μm/s, Nb-Ti-Si based ultrahigh temperature alloy has been directionally solidified with the use of crucibles. The directionally solidified (DS) specimens were subsequently heat-treated in two ways: either at 1723 K/50 h (HT1) or at 1623 K/50 h + 1723 K/50 h + 1373 K/50 h (HT2). XRD, SEM and EDS have been employed to investigate the influence of heat-treatments on the microstructures and fractography of the directionally solidified alloys. The results show that after heat-treatment, the volume fraction of the large-size primary silicides decreases. Both kinds of heat-treatments could effectively alleviate or even eliminate the segregation in the alloys. The original boundaries between the (Nb, X ) 5 Si 3 + Nbss eutectic cells in the DS specimens have thoroughly disappeared after heat-treatments. Specifically, silicides have been more evenly distributed after HT2 than HT1. Compared with DS specimens, the average room temperature fracture toughness of the specimens has increased by 12.3% (19.2 MPa·m 1/2 ) while the average tensile strength has increased by 26.6% and the maximum value reaches 933.2 MPa after HT2. These improvements could be mainly attributed to the more effective dispersion strengthening of (Nb, X ) 5 Si 3 silicide particles and the shape change as well as size increase of the ductile Nbss phases after HT2.

System of Mathematical Models for the Analysis of Industrial FZ-Si-Crystal Growth Processes

A system of coupled mathematical models and the corresponding program package is developed to study the interface shape, heat transfer, thermal stresses, fluid flow as well as the transient dopant segregation in the floating zone (FZ) growth of large silicon crystals (diameter more than 100mm) grown by the needle-eye technique. The floating zone method with needle-eye technique is used to produce high-purity silicon single crystals for semiconductor devices to overcome the problems resulting from the use of crucibles. The high frequency electric current induced by the pancake induction coil, the temperature gradients and the feed/crystal rotation determine the free surface shape of the molten zone and cause the fluid motion. The quality of the growing crystal depends on the shape of the growth interface, the temperature gradients and corresponding thermal stresses in the single crystal, the fluid flow, and especially on the dopant segregation near the growth interface. From the calculated transient dopant concentration fields in the molten zone the macroscopic and microscopic resistivity distribution in the single crystal is derived. The numerical results of the resistivity distributions are compared with the resistivity distributions measured in the grown crystal.

System of Mathematical Models for the Analysis of Industrial FZ-Si-Crystal Growth Processes

A system of coupled mathematical models and the corresponding program package is developed to study the interface shape, heat transfer, thermal stresses, fluid flow as well as the transient dopant segregation in the floating zone (FZ) growth of large silicon crystals (diameter more than 100mm) grown by the needle-eye technique. The floating zone method with needle-eye technique is used to produce high-purity silicon single crystals for semiconductor devices to overcome the problems resulting from the use of crucibles. The high frequency electric current induced by the pancake induction coil, the temperature gradients and the feed/crystal rotation determine the free surface shape of the molten zone and cause the fluid motion. The quality of the growing crystal depends on the shape of the growth interface, the temperature gradients and corresponding thermal stresses in the single crystal, the fluid flow, and especially on the dopant segregation near the growth interface. From the calculated transient dopant concentration fields in the molten zone the macroscopic and microscopic resistivity distribution in the single crystal is derived. The numerical results of the resistivity distributions are compared with the resistivity distributions measured in the grown crystal.

RAMESSIDE GLASS‐COLOURING CRUCIBLES*

The preparation of glass in New Kingdom Egypt heavily involved the use of crucibles. Shape, mode of operation and function of these vessels have been reconstructed on the basis of new, stratified material from the excavation at Qantir, eastern Nile Delta. The crucible fabric, the internal layer protecting the vessel from the charge, and the glass melted in the crucibles are characterized by chemical and petrographic studies. The crucibles were apparently employed mainly to add the colourants to the glass. The broader archaeological context strongly suggests that glass production in the Late Bronze Age has been a highly developed, specialized and organized craft, with different factories for glass production, for colouring, and for working, connected by a wide‐ranging trade network.

The Correct Use of Platinum in the XRF Laboratory

The use of crucibles and dishes made of platinum and its alloys in the preparation of samples has become an essential feature of XRF analysis. The broad application of platinum results from its near-perfect oxidation resistance and its excellent resistance to corrosive attack by metal oxide melts such as XRF fluxing agents. However, a few basic rules must be adhered to if platinum ware is to give satisfactory service. A number of'platinum poisons,' which are commonly encountered in samples, can cause destruction within a few sample preparation cycles. These 'poisons,' the reasons for their corrosive effects and techniques for minimizing or eliminating their influence are outlined.

Factors Affecting the Precision of Dietary Fiber Measurements in Potatoes

Abstract The measurement of dietary fiber in foods is becoming increasingly important. In the widely accepted gravimetric methods for measuring fiber, a common feature is the use of crucibles, with sintered glass frits, to collect insoluble and precipitated material; in this laboratory, P2 crucibles are used in insoluble fiber determinations. Evidence from 3 experiments indicated a significant amongcrucible variance component (P <0.001) that was at least 50% larger than the residual variation; this component may be as large as the commonly encountered among-time component. The crucible effect has implications with respect to experimental design, data analysis, and measurement of insoluble fiber in particular materials such as biological reference materials.

Ein verfahren zur bestimmung kleinster stickstoffgehalte in Niob durch vakuumheissextraktion

]A method for the vacuum hot extraction of gases without the use of crucibles and fluxes is described and applied to the determination of gas contents of high-melting-point metals at low atomic ppm. The Nb-N system is quoted as an example. The reaction vessel (after baking at 150 °C) was evacuated by means of a turbomolecular pump at a effective rate of 240 ls −1. Degassing was carried out in ultra-high vacuum employing a residual nitrogen partial pressure of 2 × 10 −10 Torr and liquid and/or solid samples were melted by the lévitation method in a radiofrequency field. The evolved gases were detected using a quadrupole mass filter and the quantity of nitrogen evolved calculated by integrating the partial pressure over the time period at a given pumping rate independent of pressure. In addition to giving a chemical analysis of the gas-metal system at low atomic ppm, this method also enables the thermodynamic and kinetic parameters to be determined. The minimum detectable concentration of nitrogen dissolved in niobium was ca. 0.5 at. ppm, the distribution coefficient between solid and liquid niobium 0.76 with the solubility of nitrogen being unaffected by additions of carbon up to 4.5 at.%. The contamination of high purity niobium during sample preparation has also been investigated.

Arc melting Kroll zirconium sponge

Zirconium Sponge, the end product of the Kroll process for the production of zirconium metal, requires further treatment to remove impurities and to consolidate the metal before it can be fabricated in the form of sheet, bar, etc. The arc melting method is the most suitable process for this treatment as it obviates the use of crucibles. A detailed description is given of an arc melting method recently developed for the purpose by the U.S. Bureau of Mines which covers the production of zirconium and zirconium alloy ingots. Processing in a rare gas atmosphere will not eliminate all impurities. For instance, in order to remove hydrogen, it is necessary to re-melt the ingots in a vacuum arc. Reference is made to practices in titanium production. Le Zirconium Spongieux, le produit obtenu par le procédé Kroll pour la production du métal de zirconium, demande des traitements supplémentaires pour enlever les impuretés et consolider le métal avant qu'il puisse être fabriqué sous forme de tôles, barres, etc. La méthode de fonte par l'arc est le procédé le plus approprié pour ce traitement, du fait qu'elle évite l'emploi de creusets. Une description détaillée est donnée sur une méthode de fonte par l'arc récemment développée pour ce travail par le U.S. Bureau of Mines, méthode qui couvre la production de lingots de zirconium et d'alliages de zirconium. Les opérations faites sous atmosphère de gaz rare n'éliminent pas toutes les impuretés. Par exemple, afin d'enlever l'hydrogène, il est nécessaire de refondre les lingots par l'arc sous vide. Mention est faite de méthodes s'appliquant à la production du titane.