Papers by Keyword: Chemical Stability

Abstract: The article presents the results of studies of the chemical stability of solidified radioactive waste with alkali cement through long-term leaching. Efficiency of application of alkaline slag Portland cement type LCEM IV as a matrix for reliable chemical and physical binding of caesium ions in the compound for long-term burial we confirmed. Modification of alkaline cement by additions of magnetite from 5 to 8.3% and zeolite in the amount from 4.2 to 5% promotes additional sorption of caesium ions in solidification products of alkaline matrix at maximum content of radioactive waste up to 17.5%. It they noted that the maximum values of sorption capacity of compounds (from 42000 to 68000 ml/g) we observed on the 14th day of the leaching process. They are characteristic for compounds containing magnetite from 5 to 8.3%, zeolite - from 4.2 to 7.5% and radioactive waste from 10 to 15%. It is shown that on the first day of leaching the highest rate (8.35E-02 g/сm²day) is characterised by compositions containing magnetite from 5 to 8.3%, zeolite from 4.2 to 5% and radioactive waste from 15 to 17.5%. At 56 days of the test, the leaching rate decreases exponentially to values of 3.45E-05 to 9.62E-06 g/сm²day. Characteristic of compounds, magnetite and zeolite up to 5% and radioactive waste 17.5%.

Abstract: In this paper, BaO-ZnO-TiO₂-SiO₂ is used as the research system of high refractive index glass, and IR, XRD and DTA are used to study the structure, thermal behavior, crystallization and chemical stability of different glasses when B₂O₃ gradually replaces SiO₂. The results show that when B₂O₃ replaces SiO₂, glass still has an amorphous structure, and the density of glass shows a decreasing trend with the increase of B₂O₃ content. With the increase of B₂O₃ content, the boron-oxygen tetrahedron gradually transforms into the boron-oxygen triangle, which makes the overall crystallization of the glass structure weaken. The results show that the density, refractive index and water resistance of glass beads without B₂O₃ are the best. With the increase of B₂O₃ content, the activation energy of crystallization decreases, the potential barrier to be overcome for crystallization decreases, as the same time the phenomenon of glass crystallization is obvious. Keywords:High refractive index glass; BaO-ZnO-TiO₂-SiO₂; Crystallization; Chemical stability

Abstract: The exploitation of different kind of clayey waste (halloysitic, smectitic/illitic, kaolinitic) for the production of geopolymers in the view of a circular economy of mines is the main goal of this study. In particular, the addition of low percentages of metakaolin (5-15%) was evaluated to improve the chemical-physical properties and the consolidation degree of geopolymeric formulations produced with clays classified as mine’s by-products. In fact, these secondary raw materials are often not sufficient alone to obtain chemically stable formulations with acceptable mechanical properties but require the addition of reactive fillers. All samples contained thermally treated clays (600°C-700°C) and metakaolin as aluminosilicate precursors, alkaline solution of NaOH and Na₂SiO₃, and were cured at room temperature. The influence on the final products with MK addition was monitored with the evaluation of the chemical stability in water (pH and ionic conductivity measures), the comparison of setting times (Vicat needle) and mechanical performance.

Abstract: Lanthanum silicate oxides (LSOs) with modified mass target varied from 1 to 10 g were successfully synthesized using the hydrothermal method in a 100 mL autoclave. This research is aimed to study the structure, chemical stability, and magnetic properties of the LSO. From x-ray diffraction (XRD) patterns, the main peaks of LSO were observed in the sample with 1, 3, 5, and 7 g mass target while the LSO pattern did not match in the sample with 10 g mass target. The samples with low mass target resulted in better crystallinity. The chemical stabilities of the sample were then tested on LSCF perovskite cathode and showed good chemical stability with no reactivity on the cathode. The magnetic properties of the sample with 5 g mass target was measured at 100 to 300 K using a superconducting quantum interference device (SQUID). The trace of Neel temperature, T_N, in LSO was not signified at this range of temperature in which referring a difference of LSO magnetic properties to the SOFC perovskite cathode. The T_N of LSO was predicted below 100 K. This behavior suggested that LSO has good magnetic compatibility with the perovskite cathode.

Abstract: In this paper we demonstrate an effective process control mechanism to significantly improve on the process performance of a BEOL post-etch cleaning process with an integrated partial or complete removal of the TiN HM (hard mask) layer by so called formulated chemistries on a single wafer processing tool. The novel process control mechanism enables a 50% reduction in chemical consumption while achieving an at least equivalent TiN etch uniformity.

Abstract: The fast and direct detection of small quantities of biological and chemical species is of key importance for numerous biomedical applications. Extensive research has been conducted on nanoelectronic devices that can perform such detection with high sensitivity using silicon nanowires and nanostructures. However, it was recently demonstrated that Si material suffers a lack of long-term stability in physiological environments at nanometer scale [1,2], and is hence not suited for in situ sensing of biological molecules. The results presented here are two important steps toward the realization of core-shell Si-SiC NWFETs for the detection of biomolecules in liquid media. First, we show that SiC NWs exhibit higher chemical stability than Si NWs under physiological conditions. Second, we present the successful carburation of a thin film of Si resulting in a 3.6 nm thin SiC layer.

Abstract: Dense BaCe_1-xMo_xO_3-δ ceramics were fabricated by sintering at 1450°C for 7h. All samples were characterized by XRD, SEM. All samples were orthorhombic structure. Electrical conductivities of all samples were measured by AC impedance. Electrical conductivity of Mo-doped samples reaches maximum value when doping content of Mo is 5%, which is one order of magnitude greater than that of BaCeO₃. Chemical stability of BaCe_1-xMo_xO_3-δ samples was investigated by immersing samples into the boiling water for 12h. The doping of Mo can partially inhibit the reaction between BaCeO₃ and H₂O.

Abstract: Nanostructured apatite has been widely used as a bone substitute material due to its close resemblance to human bone mineral. To further mimic biological apatites, multiple ions doped non-stoichiometric nanoapatite has been studied. A nanosized apatite (NAp-2) containing Mg (1.09 wt%), Na (0.15 wt%), K (0.008 wt%) and CO₃^2- (5.18 wt%) was synthesized by a wet precipitation technique. The presence of these ions in NAp-2 was detected using ICP. Broad diffraction peaks of XRD results indicated the presence of nanocrystalline phase pure NAp-2. The primary particle size of the resulted powder was ~ 20 nm, typical of bone crystal size, estimated using Scherrers equation. Based on CHN results, the NAp-2 powders showed a total loss of 51 and 78% of carbonate ions when heat-treated at 900°C in both CO₂ and air atmospheres, respectively. This indicates that the heat-treatment in CO₂ flux has reduced the carbonate ions lost from the NAp-2. A highly crystalline HA phase was formed in the ionic doped NAp-2 without secondary phases, indicating a thermal stability of this powder at 900°C in CO₂ and air atmospheres. Thus, this study demonstrated that a phase pure multiple ions doped nanoapatite was synthesized using a wet precipitation technique.

Abstract: Due to its high melting point, low thermal conductivity, and good phase stability at high-temperature, rare earth zirconates material (A₂B₂O₇) will be one of the candidate materials used for the thermal barrier coating. At high temperature, the chemical stability between rare earth zirconates and TGO layer (mainly Al₂O₃) affects much the performance of coating, so the study of the chemical stability is of great significance. In this paper, (Sm_1-xLa_x)₂Zr₂O₇(x=0, 1) were prepared by the co-precipitation method and the chemical stability between (Sm_1-xLa_x)₂Zr₂O₇(x=0, 1) and Al₂O₃ was investigated at the temperature of 1 200 ° C,1 300 ° C, 1 400 ° C, 1 500 ° C, 1 600 ° C respectively for 8 h¡¢24 h. The microstructures were analyzed by scanning electron microscope (SEM) and the crystallographic phases were determined by X-ray diffraction (XRD). The results showed that the chemical reaction occurred between Sm₂Zr₂O₇ and Al₂O₃ above 1 200 ° C producing SmAlO₃. With the heating temperature increased, the content of SmAlO₃ increased. The chemical reaction between La₂Zr₂O₇ and Al₂O₃ began at 1 200 ° C producing LaAlO₃ and ZrO₂. LaAl₁₁O₁₈ appeared at 1 300 ° C. As the increase of heating temperature, the content of LaAlO₃ and ZrO₂ with tetragonal phase reduced gradually in the heated samples, and the content of LaAl₁₁O₁₈ and ZrO₂ with monoclinic phase increased gradually in the heated samples. With the increase of heating temperature, the doping amount decreases in ZrO₂ with tetragonal phase, the structure of ZrO₂ with tetragonal phase tend to be more complete. So ZrO₂ with tetragonal phase transformed to ZrO₂ with monoclinic phase in cooling process easily, which leads to the increase of ZrO₂ with monoclinic phase in the heated samples. As the time of heating temperature prolonged, the kinds of reaction products didn t change, but the amount of reaction products increased.

Abstract: A ball mill was used to mechanochemically modified Polyvinylchloride (PVC) powders. PVC membranes before and after mechanochemical modification were prepared at different dope solution temperatures 60°C. The modified PVC membrane was immersed in HCl solution, NaClO solution and NaOH solution, the permeation flux and mechanical properties of the PVC membranes before and after post-treatment were studied. The results showed that, modified PVC membrane owned good ability of resistance to acid and alkali, NaClO solution had a strong oxidizing, it generated the polar group made the surface of PVC membrane more hydrophilic, the permeation flux improved. The strong oxidizing of NaClO solution made the skin layer of PVC membrane more thinner, the tensile strength decreased.