Clinopyroxene based glasses and glass-ceramics for functional applications

Doutoramento em Ciência e Engenharia de MateriaisAs piroxenas são um vasto grupo de silicatos minerais encontrados em muitas rochas ígneas e metamórficas. Na sua forma mais simples, estes silicatos são constituídas por cadeias de SiO3 ligando grupos tetrahédricos de SiO4. A fórmula química geral das piroxenas é M2M1T2O6, onde M2 se refere a catiões geralmente em uma coordenação octaédrica distorcida (Mg2+, Fe2+, Mn2+, Li+, Ca2+, Na+), M1 refere-se a catiões numa coordenação octaédrica regular (Al3+, Fe3+, Ti4+, Cr3+, V3+, Ti3+, Zr4+, Sc3+, Zn2+, Mg2+, Fe2+, Mn2+), e T a catiões em coordenação tetrahédrica (Si4+, Al3+, Fe3+). As piroxenas com estrutura monoclínica são designadas de clinopiroxenes. A estabilidade das clinopyroxenes num espectro de composições químicas amplo, em conjugação com a possibilidade de ajustar as suas propriedades físicas e químicas e a durabilidade química, têm gerado um interesse mundial devido a suas aplicações em ciência e tecnologia de materiais. Este trabalho trata do desenvolvimento de vidros e de vitro-cerâmicos baseadas de clinopiroxenas para aplicações funcionais. O estudo teve objectivos científicos e tecnológicos; nomeadamente, adquirir conhecimentos fundamentais sobre a formação de fases cristalinas e soluções sólidas em determinados sistemas vitro-cerâmicos, e avaliar a viabilidade de aplicação dos novos materiais em diferentes áreas tecnológicas, com especial ênfase sobre a selagem em células de combustível de óxido sólido (SOFC). Com este intuito, prepararam-se vários vidros e materiais vitro-cerâmicos ao longo das juntas Enstatite (MgSiO3) - diopsídio (CaMgSi2O6) e diopsídio (CaMgSi2O6) - Ca - Tschermak (CaAlSi2O6), os quais foram caracterizados através de um vasto leque de técnicas. Todos os vidros foram preparados por fusão-arrefecimento enquanto os vitro-cerâmicos foram obtidos quer por sinterização e cristalização de fritas, quer por nucleação e cristalização de vidros monolíticos. Estudaram-se ainda os efeitos de várias substituições iónicas em composições de diopsídio contendo Al na estrutura, sinterização e no comportamento durante a cristalização de vidros e nas propriedades dos materiais vitro-cerâmicos, com relevância para a sua aplicação como selantes em SOFC. Verificou-se que Foi observado que os vidros/vitro-cerâmicos à base de enstatite não apresentavam as características necessárias para serem usados como materiais selantes em SOFC, enquanto as melhores propriedades apresentadas pelos vitro-cerâmicos à base de diopsídio qualificaram-nos para futuros estudos neste tipo de aplicações. Para além de investigar a adequação dos vitro-cerâmicos à base de clinopyroxene como selantes, esta tese tem também como objetivo estudar a influência dos agentes de nucleação na nucleação em volume dos vitro-cerâmicos resultantes á base de diopsídio, de modo a qualificá-los como potenciais materiais hopedeiros de resíduos nucleares radioactivos.The pyroxenes are a wide spread group rock-forming silicate minerals found in many igneous and metamorphic rocks. They are silicates that, in their simplest form, contain single SiO3 chains of linked SiO4 tetrahedra. The general chemical formula for pyroxenes is M2M1T2O6, where M2 refers to cations in a generally distorted octahedral coordination (Mg2+, Fe2+, Mn+, Li+, Ca2+, Na+), M1 to cations in a regular octahedral coordination (Al3+, Fe3+, Ti4+, Cr3+, V3+, Ti3+, Zr4+, Sc3+, Zn2+, Mg2+, Fe2+, Mn2+), and T to tetrahedrally coordinated cations (Si4+, Al3+, Fe3+). Monoclinic pyroxenes are called clinopyroxenes. The stability of clinopyroxenes over a broad spectrum of chemical compositions, in conjunction with the possibility of achieving desired physical properties and high chemical durability, has generated a worldwide interest due to their applications in material science and technology. The present work deals with the development of clinopyroxene based glasses and glass-ceramics for functional applications. The objective of the study was dual, both scientific and technological; particularly to gain fundamental knowledge on the formation of crystalline phases and solid solutions in selected glass-ceramic systems, and to evaluate the feasibility for application of new materials in different technological areas with emphasis on sealing in solid oxide fuel cells (SOFC). In this pursuit, various glasses and glass-ceramics along Enstatite (MgSiO3) - Diopside (CaMgSi2O6) and Diopside (CaMgSi2O6) – Ca – Tschermak (CaAlSi2O6) joins have been prepared and characterized by a wide array of characterization techniques. All the glasses were prepared by melt-quenching technique while glass-ceramics were produced either by sintering and crystallization of glass powders or by nucleation and crystallization in monolithic glasses. Furthermore, influence of various ionic substitutions/additions in Alcontaining diopside on the structure, sintering and crystallization behaviour of glasses and properties of resultant glass-ceramics has been investigated, in relevance with final application as sealants in SOFC. It has been observed that enstatite based glasses/glass-ceramics do not exhibit requisite characteristics in order to qualify for the job of sealing in SOFC while the superior properties exhibited by diopside based glass-ceramics qualify them for further experimentation as SOFC sealants. Apart from investigating the suitability of clinopyroxene based glass-ceramics as sealants, this thesis also aims to study the influence of nucleating agents on the volume nucleation in the resultant diopside based glass-ceramics so as to qualify them for further experimentation as hosts for radioactive nuclear wastes

A study on the enhancement of sonochemical degradation of eosin B using other advanced oxidation processes

Eosin B is a xanthenes dye and is a derivate of fluorescein. The efficacy of sonochemical degradation coupled with other advanced oxidation process (AOP’s) has been studied for eosin B degradation in aqueous solution. The study compares the effects of H2O2 concentration, saturating gas (argon, N2, and O2), temperature and pH (3–11). Furthermore, kinetic comparison and a figure of merit for the electrical energy consumption were carried out for the degradation under combination of different AOP’s. Higher rate constant was obtained under Ar as a saturating gas and higher mineralization rate was found under acidic condition. It was also observed that rate constant decreases with the increase in temperature. The kinetic analysis indicate that of all the degrading setups used, the US + O3 was fastest in decomposing the eosin B, whereas, in energy consumption scale, UV + H2O2 was found to be the most efficient

Modeling Hydration Kinetics Of Sustainable Cementitious Binders Using An Advanced Nucleation And Growth Approach

Supplementary cementitious materials (SCMs) are utilized to partially substitute Portland cement (PC) in binders, reducing carbon-footprint and maintaining excellent performance. Nonetheless, predicting the hydration kinetics of [PC + SCM] binders is challenging for current analytical models due to the extensive diversity of chemical compositions and molecular structures present in both SCMs and PC. This study develops an advanced phase boundary nucleation and growth (pBNG) model to yield a priori predictions of hydration kinetics—i.e., time-resolved exothermic heat release profiles—of [PC + SCM] binders. The advanced pBNG model integrates artificial intelligence as an add-on, enabling it to accurately simulate hydration kinetics for [PC + SCM] binders. This study utilizes a database that includes calorimetry profiles of 710 [PC + SCM] binders, encompassing a diverse range of commonly used SCMs as well as both commercial and synthetic PCs. The results show that the advanced pBNG model predicts the heat evolution profiles of [PC + SCM] in a high-fidelity manner

Demineralization of phenol derivatives using sequential adsorption and biological degradation process

The present investigation was undertaken to assess the degradation of phenol derivatives by sequential adsorption and biological process. Phenols and their derivatives are recognized toxic compounds and known for their carcinogenic and other toxic properties even in trace quantity. Biological treatment is considered more environmentally friendly and cost-effective in comparison with physicochemical treatment. However, the process is less effective for high concentration pollutants. Activated carbons, prepared from Jatropha having micropore size under 125 microns, have been used to carry out the adsorption of Phenol and Chlorophenol in aqueous solution. Observations revealed that the rate of phenol biodegradation was increased because of pretreatment, i.e., adsorption, temperature and glucose concentration. The optimal conditions for Phenol and CP removal were found to be temperature 350C (58-65% removal) and two gpl glucose levels (70-78% removal). The importance of the study is the pretreatment of recalcitrant chemicals with adsorption followed by biodegradation and thus provided with an alternative bioremediation approach

Gasserian ganglion metastases of oral squamous cell carcinoma in the absence of loco-regional metastases masquerading as trigeminal neuralgia

We presented an unusual case of a 43-year-old man presenting with symptoms of trigeminal neuralgia with a clinico-radiological diagnosis of maxillary nerve schwannoma. Surgical excision and histopathology revealed a diagnosis of metastases of squamous cell carcinoma to Gasserian ganglion. On further investigation, the primary tumour was detected in the right alveolar region of mandible. Our purpose of presenting this case was to make the clinicians aware that all cases presenting with trigeminal neuralgia may not be benign and may be the sole presentation of brain metastases of oral cancer without the loco-regional spread

Research Journal of Pharmaceutical, Biological and Chemical Sciences Microalgae Application for Treatment of Textile Effluents

ABSTRACT The microalgae potential of Chlorococcum vitiosum was studied in treating the dye industry wastewater. The results obtained showed promising potential for treatment of industrial effluents with microalgae. Significant pH reduction and 23.23% reduction in turbidity was obtained. COD of the wastewater was reduced by 13% while alkali metals are eliminated considerably

Acute dislocation of fully deployed stent after use of non-compliant balloon: an enigma

Stent embolism is an established but rare complication of percutaneous coronary intervention, usually encountered when an undeployed stent unintentionally dislocates from the balloon. Published literature regarding incidence or clinical outcomes of embolism of fully deployed coronary stents is sparse. Here we report an unusual case of a 41-year-old male who had dislocation of a fully deployed stent into the distal part of left anterior descending artery following post dilatation by non-compliant balloon during percutaneous coronary intervention