Cem Kahruman

Kinetic investigation of dissolution of CaWO4 in oxalic acid solution

Abstract In this study, the effects of stirring speed, temperature, H2C2O4 concentration and particle size on the dissolution rate of CaWO4 in H2C2O4 solutions were investigated. CaWO4 was dissolved in H2C2O4 solutions as series parallel type reaction. In the first step which took place according to Langmuir-Hinshelwood Mechanism, H2C2O4 was adsorbed as a mobile adsorption layer on the surface of CaWO4, reacted to form adsorbed calcium aqua oxalato tungstate (Ca[WO3(C2O4)H2O]) intermediate product and the adsorbed Ca[WO3(C2O4)H2O] was desorbed into the solution. In the second step, Ca[WO3(C2O4)H2O] hydrolysed and formed H2WO4 which reacted with H2C2O4 to form hydrogen aqua oxalato tungstate (H2[WO3(C2O4)H2O]) as end product together with solid CaC2O4H2O. Model kinetic equations were derived which showed the relationships of the fractional conversion of CaWO4, the concentration of Ca[WO3(C2O4)H2O] and the concentration of H2[WO3(C2O4)H2O] with time. The diagrams drawn according to the model kinetic equations were in good agreement with the experimentally obtained diagrams (R2>0·99). Dans cette étude, on a examiné les effets de la vitesse d’agitation, de la température, de la concentration d’H2C2O4 et de la taille de particule sur la vitesse de dissolution de CaWO4 dans des solutions d’H2C2O4. On a dissous le CaWO4 dans des solutions d’H2C2O4 en une réaction de type série-parallèle. Dans la première étape, qui avait lieu d’après le Mécanisme de Langmuir-Hinshelwood, l’H2C2O4 était adsorbé en une couche mobile d’adsorption à la surface du CaWO4, réagissait pour former le produit intermédiaire adsorbé, aqua oxalato tungstate de calcium (Ca[WO3(C2O4)H2O]), et ce Ca[WO3(C2O4)H2O] adsorbé était désorbé dans la solution. Dans la seconde étape, le Ca[WO3(C2O4)H2O] était hydrolysé et formait l’H2WO4 qui réagissait avec l’H2C2O4 pour former de l’aqua oxalato tungstate d’hydrogène (H2[WO3(C2O4)H2O]) comme produit final avec le CaC2O4H2O solide. On a dérivé les équations cinétiques du modèle, lesquelles montraient les relations de la conversion fractionnelle du CaWO4, de la concentration de Ca[WO3(C2O4)H2O] et de la concentration d’H2[WO3(C2O4)H2O] en fonction du temps. Les diagrammes dessinés d’après les équations cinétiques du modèle étaient en bon accord avec les diagrammes obtenus expérimentalement (R2>0·99).

Correlation between Bifilm Index and Toughness of Aluminum Alloys

The measurement of melt quality of aluminum alloys have been a complex phenomenon. There exists various methods but the general experience show that they were slow, complicated or expensive for use on the foundry floor. In addition, these methods were not quantifiable. For the first time, bifilm index was proposed by the authors which give a numerical indication of the melt quality in millimeters as the total oxide length. Numerous studies were carried out to correlate this index with the mechanical properties. In this work, toughness measurements were made by using MatLab software. Alloy studied was 356 which were cast under various conditions (degassed and upgassed for 0.1, 0.2 and 0.4 cm3/100g Al) and the results were correlated with bifilm index.