Zinc‐based compounds as smoke suppressant agents for an aerospace epoxy matrix

Smoke is considered to be the main hazard of fires involving epoxy resins but its production depends on many variables, principally the chemical character and the burning rate of the polymer plus the availability of oxygen. The work reported aimed to study the smoke suppressant effect and flammability performance of zinc‐based compounds (FR system) in epoxy matrix composites used in the aerospace and aeronautical industry. The flammability performance of neat and FR‐loaded systems was screened using microcombustion calorimetry, while smoke generation, in terms of carbon monoxide (CO) and carbon dioxide (CO₂) production, was analysed under dynamic conditions using cone calorimetry. Final results indicate that the dispersion of zinc borate and zinc hydroxystannate (ZHS) into epoxy matrices leads to a significant variation in flame retardant properties reducing both total heat release by about 25 and 30%, respectively, and heat release capacity by about 30 and 50%, respectively. The system containing ZHS shows an enhancement in all smoke suppressant properties; both tin compounds (zinc stannate (ZS) and ZHS) give a reduction of CO₂/CO ratio from 41 to 25 for ZS and from 41 to 36 for ZHS compared to neat matrix. Copyright © 2010 Society of Chemical Industry     

Betulinic Acid in Complex with a Gamma-Cyclodextrin Derivative Decreases Proliferation and in Vivo Tumor Development of Non-Metastatic and Metastatic B164A5 Cells

Betulinic acid, a very promising anti-melanoma agent, has very low water solubility that causes low bioavailability. To overcome this inconvenience, a highly water-soluble cyclodextrin was used (octakis-[6-deoxy-6-(2-sulfanyl ethanesulfonic acid)]-γ-cyclodextrin). The complex was physico-chemically analyzed using differential scanning calorimetry (DSC), X-ray and scanning electron microscopy (SEM) methods and then in vitro tested for its antiproliferative activity by the MTT assay and by cell cycle analysis. Finally, the complex was tested in vivo using an animal model of murine melanoma developed in C57BL/6J mice, where it caused a reduction in tumor volume and weight. The study revealed the beneficial influence of betulinic acid inclusion into the cyclodextrin in terms of antiproliferative activity and in vivo tumor development.     

A Novel Approach for Bisphosphonates: Ionic Liquids and Organic Salts from Zoledronic Acid

Novel ionic liquids and organic salts based on mono- or dianionic zoledronate and protonated superbases, choline and n-alkylmethylimidazolium cations, were prepared and characterized by spectroscopic and thermal analyses. Most of the prepared salts display amorphous structures and very high solubility in water and saline solutions, especially the dianionic salts. Among the zoledronate-based ionic compounds, those containing choline [Ch] and methoxyethylmethylimidazolium [C₃OMIM] cations appear to have significant cytotoxicity against human osteosarcoma cells (MG63) and low toxicity toward healthy skin fibroblast cells. Because osteosarcoma is a bone pathology characterized by an increase in bone turnover rate, the results presented herein may be a promising starting point for the development of new ionic pharmaceutical drugs against osteosarcoma.     

Effect of α and γ polymorphs of alumina on the preparation of MgAl2O4-spinel-containing refractory cements

The use of aluminous refractory materials containing MgAl₂O₄-spinel has led to a major breakthrough in the service life of refractory coatings applied in the industries and in the quality of the products.Many researches have been conducted to improve the synthetic procedures in order to reduce the production cost of these materials. In this way, refractory cements involving in situ generated spinel phase have been obtained from mixtures of active alumina and dolomites. Other investigations have demonstrated that γ alumina is advantageous in comparison with the α polymorph in the synthesis and sintering properties of pure MgAl₂O₄-spinel.In this article, the performance of both polymorphs of alumina, used as raw materials in the preparation of the refractory cements, along with dolomite proceeding from Olavarría, in the centre of Buenos Aires Province (Argentine), is compared.The thermal and structural changes which take place during the firing of the batches up to 1450 °C were studied by the combination of diffractometric and infrared spectroscopy data, at the most remarkable reaction steps.According to these results, the study of phase changes within the investigated thermal range allowed to establish the main differences in the composition of both mixtures in each firing step. Independently of the type of alumina used, a mixed phase product consisting of spinel, as a major phase, accompanied by CaAl₂O₄ (CA) and CaAl₄O₇ (CA₂), as secondary phases, was obtained. In addition, it was found that the formation of these phases at lower temperature is favoured by γ-Al₂O₃.     

The effect of landfill leachate on hydrogen production in Chlamydomonas reinhardtii as monitored by PAM Fluorometry

This study investigated the effect of landfill leachate on biomass and biohydrogen production from Chlamydomonas reinhardtii. Maximum biomass and cell viability was recorded in 16% leachate medium with a corresponding growth rate of 927 μg/L chl a d⁻¹ as compared to the control of 688 μg/L chl a d⁻¹. Chlamydomonas cultured in leachate-supplemented medium was subsequently induced to produce 37% more biohydrogen compared to the control culture. The spurge in growth can be a consequence of abundant essential elements in the diluted leachate. Energy Dispersive X-ray analysis of cells in a 16% leachate medium had the highest accumulation of Cr, Mn, Fe, Co, Ni, Mo and Cd. The benefits of the leachate medium were further shown during the hydrogen production phase using Pulse Amplitude Modulated Fluorometry. This period was extended to 8 days in comparison to the control. Leachate therefore increases both the biomass and biohydrogen yield of Chlamydomonas.     

Origin of Gas Porosity in Gold-Based Alloys Cast in Calcium Sulfate-Bonded Investment and Influence of Metal Oxide Acid–Base Properties on Calcium Sulfate Thermal Stability

The origin of gas-porosity in gold-based alloys produced via lost-wax casting in CaSO₄-bonded investment has been identified using a combination of microanalytical and thermal techniques. The occurrence of gas-porosity is related to the thermal decomposition of CaSO₄, which, with SiO₂, constitutes the investment material and decomposes at a temperature very close to the casting temperature of some typical gold alloys used for jewelry production. The thermal reaction generates SO₂, leading to gas-porosity and, therefore, to defective products. Furthermore, the results show the detrimental effect of thermal decomposition caused by the presence of ZnO, Cu₂O, CuO, NiO, and Ag₂O formed on the surface of the gold-based alloy during air melting or casting. Therefore, the solid-state thermal decomposition of CaSO₄ in the presence of other ceramic oxides has been investigated and found to be related to their surface acid–base properties, measured as isoelectric points on the solid surface.