Free Opening Performance of Steel Ladle as a Function of Filler Sand Properties

The secondary steel refining process uses filler sand as a thermal insulating barrier that separates the liquid metal from direct contact with slide-gate system of the steel ladle. The effective use of this practice must provide a high free opening rate, impacting on increased productivity and quality of steel, reducing the number of stops, thermal loss and even the steel re-oxidation. Both operational parameters and material properties have influence on the free opening rate. In the present work, two chromite-silica sands were analyzed, and some composition changes were proposed. The properties of these materials and the relevant process parameters were evaluated according to the free opening rate under normal operational conditions. The increases in carbon content and in particle size were considered the main factors relating to the filler sand. The percentage of free opening is also strongly influenced by time and temperature of the steel contact

An evaluation of the increased expansion of clay aggregates fired at 1300 °C to maximize lightness for non-structural concrete

This work presents the production of expanded clay aggregates (EA) by firing at 1300 °C (EA/1300), a high temperature for EA production. Therefore, the material was produced in an attempt to maximize lightness. Initially, it was characterized the natural clay and the expanded clay aggregate. The EA/1300 had a density of 0.56 kg/dm3 and a strength of 0.13 MPa, reaching an expansion of 645%, while the EA/1250, clay aggregate fired at 1250 °C and produced for comparison, had a density of 0.85 kg/dm3, a strength of 0.80 MPa, and an expansion of 415%. Subsequently, it was made a lightweight concrete (LC/1300) evaluating its physical and mechanical properties. The LC/1300 had an average compressive strength of ∼4 MPa, and a density of 1.22 kg/dm3. The LC/1250 had a density of 1.43 kg/dm3 and a compressive strength of ∼10 MPa. Despite the strength reduction, it was concluded that EA/1300 can be a viable material for the production of lightweight concrete (LC), particularly as concrete artifacts, non-structural blocks, void filling, and in thermal and acoustic insulation applications. This novel material showed low density, with a reduction of 15% in relation to the LC/1250, maintaining the properties of lightweight concrete with EA – chemical inertness and fireproof – and with a strength higher than commercial lightweight concrete with polymeric aggregates. Resumen: Este trabajo presenta la producción de áridos ligeros de arcilla expandida (EA) mediante cocción a 1.300 °C (EA/1300), una temperatura alta para la producción de EA. Por lo tanto, el material se produjo en un intento de maximizar la ligereza. Inicialmente, se caracterizaron la arcilla natural y el árido ligero. El EA/1300 tuvo una densidad de 0,56 kg/dm3 y una resistencia de 0,13 MPa, alcanzando una expansión de 645%, mientras que el EA/1250, producido con el árido ligero de arcilla cocido a 1.250 °C, tuvo una densidad de 0,85 kg/dm3, una resistencia de 0,80 MPa y una expansión del 415%. Posteriormente se elaboró un hormigón ligero (LC/1300) y se evaluaron sus propiedades físicas y mecánicas. El LC/1300 tenía una resistencia a la compresión promedio de ∼4 MPa y una densidad de 1,22 kg/dm3. A modo de comparación, el LC/1250 tenía una densidad de 1,43 kg/dm3 y una resistencia a la compresión de ∼10 MPa. A pesar de la reducción de la resistencia, se concluyó que el EA/1300 puede ser un material viable para la producción de, particularmente como elementos prefabricados de hormigón, bloques no estructurales, relleno de huecos y en aplicaciones de aislamiento térmico y acústico. Este nuevo material mostró una baja densidad, con una reducción del 15% en relación al LC/1250, manteniendo las propiedades del hormigón ligero con EA – inercia química e ignífugo – y con una resistencia superior al hormigón ligero comercial con áridos poliméricos

Humic Acid as Dispersant of an Alumina Suspension and its Rheological Behaviour

<div><p>Humic acid was extracted and employed as a dispersant in an alumina suspension. The higher zeta potential for HA (-42 mV) was measured at pH 11 showing that an electrostatic repulsion might occur in the alumina/HA suspension. As a consequence of the long chain molecules of HA it was also expected a steric effect on deflocculation. The best dispersion conditions for the alumina suspension (28 vol%) were found with 0.016 wt% HA, close to the viscosity achieved with a commercial sodium polyacrylate. The rheological characterisation showed results beneficial for the slip casting process, such as slightly thixotropy and pseudoplastic behaviour. The excellent colloidal stability at pH 11 as evidenced through rheological and sedimentation tests was attributed to the polyelectrolyte nature of the HA. From deflocculated suspensions it was possible to obtain high density pieces by slip casting method.</p></div