Obtention and characterization of lithium superionic conductors using the glass-ceramic method

This paper proposes the glass-ceramics method for obtaining lithium ion (Li+) solid electrolytes. This technique provides high chemical and microstructural homogeneity as well as low porosity. Glass samples were subjected to either single or double heat treatments, between 700 °C and 1000 °C, in order to obtain the glass-ceramics. Differential Scanning Calorimetry – DSC – results evidenced the possibility of fabricating these ceramics from glass in the system Li2O·Al2O3·TiO2·P2O5. Samples observed by Scanning Electron Microscopy – SEM – showed a finely grained microstructure which was homogeneously distributed and non-porous. X-ray Diffraction – XRD – patterns showed the formation of the high conducting phase LiTi2(PO4)3. A high ionic conductivity, in the order of 10-3 S/cm at 1000 °C, was measured by Impedance Spectroscopy – IS. It suggests that the synthesis method used in this research is useful for fabricating lithium ion glass-ceramics and opens up a new alternative for manufacturing different electrical ceramics.Este artículo propone la ruta vitrocerámica para obtener electrolitos sólidos por ion litio (Li+). Esta técnica provee alta homogeneidad química y microestructural, así como baja porosidad. Muestras vítreas fueron sometidas a tratamientos térmicos, simples y dobles, entre 700 °C y 1000 °C, para obtener las vitrocerámicas. Resultados de calorimetría diferencial de barrido – DSC – evidenciaron la posibilidad de fabricar estas cerámicas a partir de vidrios del sistema Li2O·Al2O3·TiO2·P2O5. Muestras observadas por microscopía electrónica de barrido – SEM – mostraron una microestructura de granos finos, homogéneamente distribuidos y sin porosidad. Patrones de difracción de rayos-x – XRD – permitieron verificar la formación de la fase altamente conductora LiTi2(PO4)3. Una conductividad iónica alta, del orden de 10-3 S/cm a 1000°C, fue medida utilizando espectroscopía de impedancia – IS. Lo anterior sugiere que el método de síntesis, utilizado en este trabajo, es útil para fabricar vitrocerámicas de ion litio y abre una nueva alternativa para fabricar diferentes cerámicas eléctricas

Chemical and nano-mineralogical study for determining potential uses of legal Colombian gold mine sludge: Experimental evidence

The present study is focused on the chemical and nano-mineralogical characterization of sludge from gold mine activities, in order to put forward diverse solution alternatives, where lack of knowledge has been found. The sample was collected from “La Estrella” mine of Suarez, located in Department of Cauca, south-west Colombia. The sludge micro-structure and chemical composition were analyzed using a high resolution transmission electron microscopy (HR-TEM) equipped with a dispersive X-ray detector (EDS). X-ray diffraction technique was employed to identify the mineralogical phases present in the sludge. Additional mineralogical characterization was done by using RAMAN spectroscopy. Main findings points to its potential to be used as a fertilizer, this is why, mine sludge contains macronutrients such as P, Ca and S, together with micronutrients like Cu. However, the presence of goethite could decrease the mobilization of nutrients to soils, thus additional alternatives, for instance, a mixture with humus or another material containing Humic Acids should be done, in order to minimizing its retention effect. Additionally, another possible uses to explore could be as construction and ceramic material or in the wastewater treatment for nutrient retention and organic material removal. Rutile (TiO2 nanoparticles) particles have been also detected, what could cause health concern due to its nanoparticle toxic character, mainly during gold extraction process

Electrical and microstructural characterization of lithium ion conductive glass-ceramics with NASICON structure

This doctoral thesis presents results of the chemical, thermal, structural, microstructural and electrical characterization of glass and glass-ceramics with Li1,3Al0,3Ti1,7(PO4)3 (LATP), Li1,5Al0,5Ge1,5(PO4)3 (LAGP) and (LixNa1-x)1,5Al0,5Ge1,5(PO4)3 (LNAGP) compositions. All the compositions are shown to present homogeneous volume nucleation (Tgr ≤ 0.6), enabling their microstructures to be controlled through heat treatments, which in this study were single and double. The highly conductive NASICON-type phase was obtained in all the studied compositions. Secondary phases were also observed, albeit with no deleterious effect on the total electrical conductivity. Electrical characterization by impedance spectroscopy, performed at various temperatures below ambient temperature, enabled the contributions of the grain and grain boundary on the total electrical conductivity to be separated. An analysis of the two glass-ceramics, LATP and LAGP, leads to the conclusion that, in both cases, the total electrical resistance of the samples, and hence, their total electrical conductivity, is dominated by the grain boundary. The LATP composition presented higher electrical conductivity at room temperature, but also lower glass forming ability (very low Kgl). A Rietveld refinement of the LATP samples obtained by single heat treatment revealed that the concentration of lithium ions in the unit cell increases as a function of the heat treatment temperature. The electrical conductivity results indicate a relationship between this property and the thickness and volume fraction of grain boundaries, since the latter decrease with heat treatment temperature (in TTS case) and increase with nucleation time (in the case of TTD). The LATP samples obtained by TTD exhibited higher electrical conductivity than those obtained by TTS at the same temperature; however, this effect was not observed in the LAGP samples. The electrical conductivity of the LNAGP samples showed a mixed alkali effect in both the glasses and the corresponding glass-ceramics.Universidade Federal de Sao CarlosNessa tese de doutorado apresentam-se resultados de caracterização química, térmica, estrutural, microestrutural e elétrica de vidros e vitrocerâmicas de composição Li1,3Al0,3Ti1,7(PO4)3 (LATP), Li1,5Al0,5Ge1,5(PO4)3 (LAGP) e (LixNa1-x)1,5Al0,5Ge1,5(PO4)3 (LNAGP). Mostrou-se que as composições apresentam nucleação homogênea (Tgr ≤ 0,6), característica que torna possível o controle da microestrutura através de tratamentos térmicos, que no caso foram simples (TTS) e duplos (TTD). Foi obtida em todas as composições estudadas a fase altamente condutora com estrutura tipo NASICON. Fases secundárias também foram observadas, porém sem efeito deletério na condutividade elétrica total. A caracterização elétrica por espectroscopia de impedância, realizada em temperaturas abaixo da ambiente, permitiu separar as contribuições do grão e do contorno de grão à condutividade elétrica total. Analisando as vitrocerâmicas LATP e LAGP se conclui que, em ambos os casos, a resistência elétrica do contorno de grão é quem domina a resistência total das amostras e, portanto, a condutividade elétrica total. A composição LATP apresentou maior condutividade elétrica total à temperatura ambiente, mas também menor habilidade para formar vidro (Kgl muito baixo). Foi encontrado por refinamento Rietveld que, nas amostras LATP obtidas por TTS, a concentração de íons lítio na célula unitária aumenta com a temperatura de tratamento térmico. Resultados de condutividade elétrica mostram uma relação entre esta propriedade e a espessura e fração volumétrica de contornos de grão, pois estes diminuem com a temperatura de tratamento térmico (no caso de TTS) e aumentam com o tempo de nucleação (no caso de TTD). No caso do LATP, amostras obtidas por TTD, tiveram condutividade maior do que as obtidas por TTS na mesma temperatura, porém esse efeito não foi observado nas amostras LAGP. A condutividade elétrica das amostras LNAGP mostra um efeito de alcalino misto tanto nos vidros como nas correspondentes vitrocerâmicas

Synthesis and electrical conductivity of Li1+xAlxTi2-x(PO4)3 glass-ceramic with different microstructures

Technological advances in portable devices imply not only the development of devices but also the need to enhance their power sources. For instance, cellular phones with high technology incorporating Bluetooth, Infrared, Digital Camera, Games, GPS, Internet Browsing, etc., need high performance rechargeable batteries. Lithium ion-conducting glass-ceramics with NASICONtype structure, based on the Li1+xMxM'2-x(PO4)3 system, where M = Al, Cr, Fe, Ga and M' = Ge, Ti, Hf, are considered good candidates as solid electrolytes in lithium ion batteries due to their chemical stability, easy fabrication and high ionic conductivity. In this work, the Li1+xAlxTi2-x(PO4)3 glass composition was synthesized by the traditional method known as Splat Cooling. Glass-ceramics with the same composition as the precursor glass but with different microstructures were obtained by controlled crystallization, using single and double heat treatments. The parent glass was characterized by chemical and thermal analysis and the latter enabled tailoring of the crystallization heat treatments. X-ray diffraction (XRD) results indicated that the resulting glassceramics exhibit the desired NASICON-type structure as primary phase, as well as the segregation of insulating phases, i.e., AlPO4 and/or TiO2, which do not affect the electrical properties. An examination of the microstructure by scanning electron microscopy (SEM) and measurements of electrical conductivity by impedance spectroscopy (IS), combined with the XRD analysis, indicated that the electrical conductivity of single heat-treated samples increases with the heat treatment temperature and hence with the increase in crystallinity. Samples synthesized by double heat treatment showed increasing electrical conductivity with decreasing nucleation treatment time and consequently with increasing average grain size.Universidade Federal de Sao CarlosOs avanços tecnológicos em dispositivos portáteis trazem outro aspecto que chama a atenção, tanto ou mais importante do que os próprios dispositivos desenvolvidos, i.e., a necessidade de fontes de alimentação mais poderosas. Por exemplo, telefones celulares com tecnologia de ponta que incorporam Bluetooth, Infravermelho, Câmara fotográfica, Jogos, GPS, Navegação na Internet, etc., requerem baterias recarregáveis de alto desempenho. Vitrocerâmicas condutoras por íon lítio com estrutura tipo NASICON, concretamente baseadas no sistema Li1+xMxM 2-x(PO4)3, onde M = Al, Cr, Fe, Ga e M = Ge, Ti, Hf, são consideradas boas candidatas como eletrólitos sólidos em baterias de íon lítio devido à sua estabilidade química, facilidade de fabricação e alta condutividade iônica. Neste trabalho foi obtido o vidro de composição Li1.2Al0.6Ti1.6(PO4)2.9 usando o método tradicional de resfriamento rápido conhecido como Splat Cooling. Vitrocerâmicas de composição igual à do vidro matriz, com diferentes microestruturas, foram obtidas por cristalização controlada mediante tratamentos térmicos simples e duplos. O vidro precursor foi caracterizado por análise química e térmica. Esta última permitiu projetar os tratamentos térmicos de cristalização. Os resultados de difração de raios X (DRX) mostraram a obtenção da estrutura tipo NASICON como fase principal, com presença das fases isolantes AlPO4 e/ou TiO2, que não afetam as propriedades elétricas. O estudo da microestrutura e da condutividade elétrica, usando microscopia eletrônica de varredura (MEV) e espectroscopia de impedância (EI), respectivamente, evidenciaram o aumento da condutividade com o crescimento do tamanho médio do grão, atribuído ao maior contato entre grãos e, provavelmente, a um melhor alinhamento dos canais na estrutura do LiTi2(PO4)3. A máxima condutividade de 1,3 x 10-3 S/cm foi atingida na amostra obtida mediante tratamento térmico simples em 1000 °C durante 20 minutos a qual apresentou um tamanho médio de grão de 350 nm

Obtention and characterization of lithium superionic conductors using the glass-ceramic method

This paper proposes the glass-ceramics method for obtaining lithium ion (Li+) solid electrolytes. This technique provides high chemical and microstructural homogeneity as well as low porosity. Glass samples were subjected to either single or double heat treatments, between 700 °C and 1000 °C, in order to obtain the glass-ceramics.Differential Scanning Calorimetry –DSC–results evidenced the possibility of fabricating these ceramics from glass in the system Li2O·Al2O3·TiO2·P2O5. Samples observed by Scanning Electron Microscopy –SEM–showed a finely grained microstructure which was homogeneously distributed and non-porous. X-ray Diffraction –XRD–patterns showed the formation of the high conducting phase LiTi2(PO4)3. A high ionic conductivity, in the order of 10-3S/cm at 1000 °C, was measured by Impedance Spectroscopy –IS. Itsuggests that the synthesis method used in this research is useful for fabricating lithium ion glass-ceramics and opens up a new alternative for manufacturing different electrical ceramics.Este artículo propone la ruta vitrocerámica para obtener electrolitos sólidos por ion litio (Li+). Esta técnica provee alta homogeneidad química y microestructural, así como baja porosidad. Muestras vítreas fueron sometidas a tratamientos térmicos, simplesy dobles, entre 700 °C y 1000 °C, para obtener las vitrocerámicas. Resultados de calorimetría diferencial de barrido –DSC–evidenciaron la posibilidad de fabricar estas cerámicas a partir de vidrios del sistema Li2O·Al2O3·TiO2·P2O5. Muestras observadas por microscopía electrónica de barrido –SEM–mostraron una microestructura de granos finos, homogéneamente distribuidos y sin porosidad. Patrones de difracción de rayos-x –XRD–permitieron verificar la formación de la fase altamente conductora LiTi2(PO4)3. Una conductividad iónica alta, del orden de 10-3S/cm a 1000 °C, fue medida utilizando espectroscopía de impedancia –IS. Lo anterior sugiere que el método de síntesis, utilizado en este trabajo, es útil para fabricar vitrocerámicas de ion litio y abre una nueva alternativa para fabricar diferentes cerámicas eléctricas