Papers by Keyword: Dissolution

Abstract: Through thermal simulation experiment and SEM analysis, limestone dissolution in a steelmaking slag was studied. The results showed that the dissolution rate of limestone is 5.4 times greater than lime under the same conditions in slag, the dissolution rate of limestone in slag increases rapidly with the increase of stirring gas flux. The rapid dissolution of limestone in the slag can be explained on two sides. Limestone decomposition and dissolution happens simultaneously, the newly generated lime participates in slagging in its highest activity. On the other hand, CO₂ from limestone decomposition not only strengthen the mixing strength of the molten pool, but also helps to remove the high melting point 2CaO·SiO₂ product.

Abstract: In the present study we explore the idea of biotechnologically produced metallophore mixtures as selective chelating compounds for economically valuable metals from various sources. A complex soil matrix with natural levels of metal mineralization was employed as a potential source of metals. We focused on gallium-chelating metallophore preparations of two soil bacteria (Gordonia rubripertincta CWB2 and Paracoccus denitrificans PD1222) which were compared to the commercially available desferrioxamine B (DFOB). As a reference, the binding of iron was analyzed. The herein described successful mobilization of metals such as gallium from soil provides first hints towards alternative strategies, such as phytomining, sensor development, or solvent extraction based on metallophores. The metallophore mixture produced by the strains showed best results at pH 8 and allowed to mobilize gallium about three times better as the pure commercially available DFOB.

Abstract: The increasing demand for lightweight materials capable to absorb impact energy has driven the growth of scientific research in the metallic foams field. This paper aims to investigate the possibility to obtain Al foams from recycled aluminium alloy through the sintering dissolution process (SDP) with sodium chloride (NaCl) as space holder. Aluminium scraps from AA 3104 alloy were powdered by high energy ball milling. Alloy powder was mixed with variable weight fraction of NaCl. The mixtures were die-pressed at room temperature and then sintered at 680°C. In the following step sintered parts were immersed in boiling water to obtain the aluminium foam. Foam microstructure was characterized by scanning electron microscopy and chemical composition was analyzed by energy dispersive spectroscopy. In addition, the residual NaCl was quantified and the foam density was determined by hydrostatic method. Best result was obtained with 60 wt% of NaCl, given a relative foam density of 30%, which in turn justifies further studies with metallic foams from aluminium scraps.

Abstract: The microstructure evolution and properties of Al-matrix in homogenized 7A56 alloy were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), electrical conductivity and hardness test. The second phases in as-cast 7A56 alloy consisted of AlZnMgCu, Al₂Cu and Al₇Cu₂Fe. With the homogenization temperature increasing, more non-equilibrium phase AlZnMgCu was dissolved into Al-matrix. The diffusion of alloying elements from AlZnMgCu phase into Al-matrix leads to a decrease of electrical conductivity and an increase of hardness. The lattice constant of α-Al has an increases of 0.0019 Å, 0.0032 Å and 0.0053 Å after 380°C/24h,430°C/24h,and 470°C/24 h treatment,respectively.

Abstract: This study investigated the properties of aluminium foam containing Mg with various amount of space holder. Aluminum foam was fabricated using dissolution method with various amount of carbamide (20, 40 and 60 wt. %). Aluminum foam with 60 wt. % carbamide has the lowest density (0.68 g/cm³) and exhibited the highest porosity (74.97%). However, the results indicates that aluminum foam with 40 wt. % of carbamide have good compressive and energy absorption with acceptable density and porosity value.

Abstract: High Strength Low Alloy (HSLA) steels or microalloyed steels are developed in order toimprove the strength and toughness compared with conventional carbon steels. During the reheatingprocess at 1250-1300 °C for a few hours, the furnace consumes large amount of energy, and the slabsuffers from thick oxide scale. This results in significant mass loss. The long reheating time ensuresmaximum dissolution of the microalloying elements, which must be kept to precipitate duringcooling at the end of the hot rolling process. To minimise the reheating time and save the energyconsumption, this research studied the dissolution kinetics of vanadium in HSLA steel. Vanadium isa main microalloying element added to provide higher strength mainly by precipitation hardening. Itis supposed to be dissolved readily according to the solubility limit. The samples were reheated to1200 °C and 1250 °C for 0, 10, 30, and 60 s. After that the fraction of vanadium dissolved in the solidsolution and the remaining undissolved phases of VC, CN, and V(C,N) were measured bysynchrotron XAS. As soon as the sample reaches as low temperature as 1200 °C, a large atomicfraction of 0.878 of vanadium can be dissolved in the solid solution.

Abstract: Precipitation hardening aluminium alloys are widely used for automotive applications. To enhance the application of aluminium profiles, improved formability is needed. Tailor Heat Treated Profiles (THTP) with locally different material properties attempt to increase formability e.g. in bending processes. Tailoring of local properties is obtained by a local short-term heat treatment, dissolving the initial precipitate state (retrogression) and still allowing subsequent ageing. In the present study, the dissolution and precipitation behaviour of the aluminium alloy EN AW-6060 T4 was investigated during heating with differential scanning calorimetry (DSC). Heating curves from 20 to 600 °C with heating rates of 0.01 up to 5 K/s were recorded. Interrupted heat treatments with different maximum temperatures were performed in a deformation dilatometer. Immediately afterwards, tensile tests were carried out at room temperature. The course of the recorded mechanical properties as a function of the maximum temperature is discussed with regard to the dissolution and precipitation behaviour during heating. Finally, the aging behaviour of the investigated alloy was recorded after different typical short-term heat treatments and is discussed with reference to the DSC‐curves. The correlation of the microstructure and the mechanical properties enables the derivation of optimal parameters for the development of THTP through a local softening.

Abstract: The paper examines the available experimental data to produce a model for quantitative prediction of the change of M₇C₃ carbide fraction and austenite chemical composition during holding of ternary alloys Fe–Cr–C (used as wear-resistant white cast irons and tool steels) in austenite + carbide region. Carbide dissolution is well described by Avrami type equation with exponent n close to 1/2. Dependences of the coefficient of this equation on carbide fraction and of the activation energy of the temperature dependence of this coefficient on carbide composition are established. As a result, a model that permits to calculate the fraction and chemical composition of austenite and M₇C₃ carbide in an Fe–Cr–C alloy of arbitrary composition after isothermal holding at given temperature for given time is obtained; equilibrium phase composition is needed to be known from thermodynamic models. This allows predicting the results of hardening after different austenitization regimes.

Abstract: We studied the dissolution of zirconium in the molten alloy AlMg6Mn1. Zirconium is introduced into the melt in the form of the ligature AlZr2. It is established that during 10 minutes at 750 °C complete Zr dissolution occurs. The study of the structure and phase composition of the samples allowed setting the dendrite structure of the samples; presence of clusters of magnesium, manganese, iron and silicon in the interdendritic space. Zirconium is injected into the melt in a stable particulate form (D0₂₃) Al₃Zr phase is uniformly distributed in grains α - Al as a metastable (L1₂) Al₃Zr phase. After some time, increasing of the density distribution of the metastable (L1₂) Al₃Zr in the aluminum matrix phase is detected in the selected samples after 10 and 60 minutes after the introduction of zirconium. It has been established that after some time, an increase of the aluminum lattice parameter occurs in the samples selected after the addition ligature of zirconium.

Abstract: The capsules are pharmaceutical forms extremely versatile used to administer drugs orally, thus demonstrating the relevance of search for new excipients. Therefore, it was aimed to demonstrate the technological feasibility of babassu mesocarp powder (MB) as an excipient in development of diclofenac capsules 50mg and paracetamol 500 mg. Two lots of capsule were produced for each active ingredient separately using MB and microcrystalline cellulose (MC) as an excipient. The analytical results of quality control of all lots remained within the limits accepted by the Brazilian Pharmacopoeia. Although the values of dissolution time coming from lots of CM and MB, the statistical analysis revealed that lots manufactured with MB showed a profile of release superior to CM, demonstrating the potential of MB as an excipient once the lots produced with MB showed a disintegration and dissolution equivalent to those obtained with CM lots.