Vanja Martinac

Ion-sensitive behaviour of silver sulphide-based solid-state copper(II) and iodide electrodes in partially aqueous systems

Abstract The response of copper(II)- and iodide-selective electrodes was evaluated in various water-organic solvent mixtures. The copper(II) electrode showed an almost Nernstian behaviour in mixtures with ethylene glycol, tert-butanol, propanol, ethanol and methanol. The experimental slopes in buffered water-acetonitrile mixtures were linear but super-Nernstian. The response of this electrode in mixtures with p -dioxane was neither Nernstian nor linear. The interference of mercury(II) in the direct potentiometric titration of copper(II) with EDTA in solution containing acetonitrile was studied. The behaviour of silver sulphide-based iodide electrode hydrophobized by PTFE in mixtures with ethanol, methanol and p -dioxane was poorer than in water. The potential response of the iodide electrode with a homogeneous membrane (Ag 2 S + AgI) was satisfactory even after prolonged soaking in p -dioxane.

Effect of TiO2, SiO2 and Al2O3 on properties of sintered magnesium oxide from sea water

Abstract The process of isothermal sintering of magnesium oxide obtained from sea water (by precipitation with 80% and 120% of the stoichiometric quantity of the calcined dolomite and magnesium oxide p.a. (pro analysi purity grade) ) was examined with the addition of SiO2, Al2O3 and TiO2, at temperatures in the range 1300–1800 °C. The process was followed by determining the product density, as well as densification of the compacts. With compacts containing SiO2 or Al2O3 densification was examined in relation to the sintering temperature and quantity of the sintering aid; with compacts containing TiO2 densification was examined in relation to the sintering temperature and pressing pressure. Sample densification and pore removal during isothermal sintering have been shown to be a function of the exponent α in the expression (Δ V/V0) − m = τα. The specific surfaces, chemical compositions and particle size distribution were determined for the magnesium oxide samples examined.

Sintering of magnesium oxide obtained from sea water

U svrhu izucavanja procesa sinteriranja magnezij-okisda, ispitivanja su vrsena uz razne kolicine dodatka TiO2 magnezij-oksidu koji je dobiven nestehiometrijskim i prestehiometrijskim nacinom taloženja magnezij-hidroksida u morskoj vodi, dolomitnim vapnom. Ispitivan je sadržaj B2O3 u sinteriranim uzorcima u ovisnosti o temperaturi izotermnog sinteriranja, kolicini dodanog TiO2 i nacinu dobivanja magnezij-oksida. Izvrsena je termodinamicka obrada rezultata.

Isothermal and activated sintering of magnesium oxide from sea water

Abstract The influence of TiO 2 addition in sintering magnesium oxide was investigated as a function of the time and temperature of isothermal sintering and of the quantity of the addition. The magnesium oxide used was obtained from sea water by precipitation of magnesium hydroxide with 80% of the stoichiometrical quantity of dolomite lime. It has been noted that the content of B 2 O 3 in sintered magnesium oxide samples is significantly reduced by the addition of TiO 2 . The results were analysed thermodynamically, according to expressions used in open system thermodynamics.

Effect of TiO2 on properties of magnesium oxide obtained from seawater

The effect has been examined of TiO2 on B2O3 content in sintered magnesium oxide samples obtained by precipitation of magnesium hydroxide in seawater with 80 or 120% of the stoichiometrical quantity of the precipitation agent, i.e. the effect of TiO2 on product properties has been examined. Coefficients were calculated for dependent reactions of Ca2B2O5 and CaTiO3 formation.

Activated sintering of magnesium oxide from sea water

The process of activated sintering of magnesium oxide obtained from sea water (by precipitation with 80 percentage and 120percentage of the stoichiometric quantity of the dolomite lime) was examined with addition of 1, 2 and 5 wt percentage TiO_2, at temperatures of 1600°C and 1700°C with soaking at the maximum temperature of 1, 3 and 5 hours respectively. The product density and porosity were examined and the dependences obtained were described by appropriate analytical expressions. The compatibility relationships between addition of TiO_2 and the B_2O_3 content in the sintered magnesium oxide samples were determined, based on an important theorem due to Onsanger. The phenomenological coefficients were calculated for two irreversible processes, namely those of formation of Ca_2B_2O_5 and CaTiO_3 respectively.

Microstructural characteristics of low-temperature (1400°C) sintered MgO obtained from seawater

The purpose of this study was to investigate the influence of a rinsing of Mg(OH)2 precipitated from seawater by substoichiometric precipitation (80% precipitation) and the addition of TiO2 on microstructural characteristics of the MgO obtained by sintering at low temperature (1400 oC). The results of examination indicate that the method of rinsing of the magnesium hydroxide precipitate in the technological process of obtaining MgO from seawater significantly affects the chemical composition of samples, primarily with regard to the CaO and B2O3 content. The samples were doped with TiO2 to improve the evaporation of B2O3 and sintering of MgO samples that were characterized by XRD and SEM/EDS. These techniques confirmed the high purity of MgO samples obtained and the formation of secondary compounds in very small quantities that have a positive effect on the densification.

Characterization of Dolomitic Lime as the Base Reagent for Precipitation of Mg(OH) 2 from Seawater

The process of obtaining magnesium hydroxide from seawater involves precipitation of magnesium ions with suitable basic reagents, such as calcined dolomite. The purity of the magnesium hydroxide precipitate depends on dolomite characteristics; therefore, it is necessary to find high purity dolomite with good physical properties. The aim of this study was to characterize the specific dolomite from the location of Đipalo-Sinj (Croatia), its quality, and the favourable conditions for calcination. Certain physical and chemical characteristics were determined by pure chemical analysis, as well as by using TG/DTG-DTA, FTIR and SEM/EDS analysis. Good chemical quality of dolomitic lime (59.03 wt. % CaO, and 40.69 wt. % MgO) with low content of impurities was confirmed with the TG/DTG-DTA thermal analysis. In the atmosphere of air + CO 2 , dolomite decomposes to CaCO 3 and MgO in a temperature area between 415 and 824 °C; thereafter, another reaction begins – the decomposition reaction of calcium carbonate, completed at 897 °C. In air, the simultaneous decomposition of two carbonates occurs between 657 – 840 °C. The FTIR and EDS analyses confirmed the complete breakdown of carbonates at 950 °C. The main components (Mg, Ca, and O) confirmed the purity of the dolomite lime.