Abstract The improper disposal of this waste poses environmental challenges, which can be addressed through effective reuse strategies. This study aims to explore the potential of utilizing marine shell waste as partial substitutes for aggregates in concrete. The research involves investigating the physical characteristics of the recycled aggregate using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) techniques to elucidate the contact surface with the paste. Additionally, chemical and mineralogical characteristics are analyzed through X-ray fluorescence and X-ray diffraction tests. The compressive strength test is conducted on concrete samples to assess the performance of these materials as both aggregate (shell type A) and filler (shell type B). The findings indicate that replacing up to 20% of marine shells as coarse aggregate and 10% as filler demonstrates feasibility for applications in structural concrete. Furthermore, up to 30% replacement can be directed towards non-structural concrete, providing a comprehensive understanding of the potential applications of marine shell residues in concrete production.

Resumo As atividades de mariscagem e malacocultura produzem uma grande quantidade de resíduos sólidos compostos por conchas marinhas. O impacto ambiental do descarte inadequado pode ser atenuado com estratégias de reaproveitamento. O objetivo deste trabalho é investigar a viabilidade do uso de resíduo de conchas marinhas com substituintes parciais de agregados no concreto. As características físicas do agregado reciclado foram investigadas através das técnicas de Microscopia de Força Atômica (MFA) e Microscopia Eletrônica de Varredura (MEV) a fim de esclarecer aspectos da superfície de contato com a pasta; as características químicas e mineralógicas foram investigadas por meio dos ensaios de fluorescência de raios-X e difração de raios-X; e o ensaio de resistência à compressão foi conduzido em amostras de concreto foram moldadas para avaliação do comportamento destes materiais do comportamento destes materiais como agregado (concha tipo A) e fíler (concha tipo B). Concluiu-se que o uso de até 20% de substituição de concha marinha como agregado graúdo e 10% como filer mostrou viabilidade para aplicações em concretos estruturais e, de forma complementar, teores de até 30% podem ser direcionados à concretos não estruturais.

ABSTRACT In this study, the particle sizes distribution model that best characterizes the granulometric composition of saprolite ores fed to the Cuban Caron process was determined. Three samples of soft and hard streamers from the Punta Gorda, Camarioca Este and Yagrumaje Sur deposits were evaluated. The main mineralogical phases of the samples were identified by the X-ray powder diffraction method. The predominance of the mineralogical phases lizardite, clinochlore and chlorite-serpentine was observed in the different samples under study. The determination of the parameters of the granulometric models and the evaluation of the quality of their adjustment with statistical techniques, allowed us to identify that the Swebrec function is the one that best describes the distribution of the experimental particle sizes of the streamer samples, with determination coefficients higher than 0,91 and residual errors lower than 6,9 %.

RESUMEN En este estudio se determinó el modelo de distribución de tamaños de partícula que mejor caracteriza la composición granulométrica de las menas de saprolitas alimentadas al proceso Caron cubano. Se evaluaron tres muestras de serpentinas blandas y duras concernientes a los yacimientos de Punta Gorda, Camarioca Este y Yagrumaje Sur. Las principales fases mineralógicas de las muestras se identificaron por el método de difracción de rayos X en polvo. Se observó el predominio de las fases mineralógicas lizardita, clinocloro y clorita-serpentina en las diferentes muestras bajo estudio. La determinación de los parámetros de los modelos granulométricos y la evaluación de la calidad de su ajuste con técnicas estadísticas, permitió identificar que la función Swebrec es la que mejor describe la distribución de los tamaños de partículas experimentales de las muestras de serpentinas, con coeficientes de determinación superiores a 0,91 y errores residuales inferiores a 6,9 %.

ABSTRACT In this study, the particle sizes distribution model that best characterizes the granulometric composition of saprolite ores fed to the Cuban Caron process was determined. Three samples of soft and hard streamers from the Punta Gorda, Camarioca Este and Yagrumaje Sur deposits were evaluated. The main mineralogical phases of the samples were identified by the X-ray powder diffraction method. The predominance of the mineralogical phases lizardite, clinochlore and chlorite-serpentine was observed in the different samples under study. The determination of the parameters of the granulometric models and the evaluation of the quality of their adjustment with statistical techniques, allowed us to identify that the Swebrec function is the one that best describes the distribution of the experimental particle sizes of the streamer samples, with determination coefficients higher than 0,91 and residual errors lower than 6,9%.

RESUMEN En este estudio se determinó el modelo de distribución de tamaños de partícula que mejor caracteriza la composición granulométrica de las menas de saprolitas alimentadas al proceso Caron cubano. Se evaluaron tres muestras de serpentinas blandas y duras concernientes a los yacimientos de Punta Gorda, Camarioca Este y Yagrumaje Sur. Las principales fases mineralógicas de las muestras se identificaron por el método de difracción de rayos X en polvo. Se observó el predominio de las fases mineralógicas lizardita, clinocloro y clorita-serpentina en las diferentes muestras bajo estudio. La determinación de los parámetros de los modelos granulométricos y la evaluación de la calidad de su ajuste con técnicas estadísticas, permitió identificar que la función Swebrec es la que mejor describe la distribución de los tamaños de partículas experimentales de las muestras de serpentinas, con coeficientes de determinación superiores a 0,91 y errores residuales inferiores a 6,9%.

Abstract: Soil is the basic material for the manufacture of compressed earth bricks, which is worked without any type of stabilization to obtain the minimum physical and mechanical properties required according to Peruvian standard E.070. The objective of this research is to evaluate the physical and mechanical characteristics of compressed earth bricks stabilized with different dosages of 5, 8, 12, 12, 15 and 18% of cement in dry weight of soil. The tests performed were: absorption, compressive strength, flexural strength per unit of masonry, compressive strength in piles, diagonal compressive strength of walls and the X-ray diffraction test. The results obtained show that with 18% of cement the optimum resistance is obtained, in terms of compressive strength increased by 53.95%, flexural strength by 43%, pile compressive strength by 36.6%, and wall diagonal compressive strength by 41.24%, respectively. The X-ray diffraction test applied to the optimum stabilized compressed earth brick sample shows that its composition is dominated by certain components such as 32.4% calcium silicate, 23.8% aluminum silicate, 17.4% hydrated calcium, 14.2% illite, 6.86% calcium oxide, 3.34% quartz, 1.2% kaolinite and 0.8% goethite. It is concluded that cement-stabilized compressed earth bricks (LTCEC) are a sustainable construction alternative that improves the mechanical properties of earth bricks.

Resumen: El suelo es el material básico para la fabricación de ladrillos de tierra comprimida, el cual se trabaja sin ningún tipo de estabilización para obtener las propiedades físicas y mecánicas mínimas requeridas según la norma peruana E.070. El objetivo de esta investigación es evaluar las características físicas y mecánicas de ladrillos de tierra comprimida estabilizados con diferentes dosificaciones de 5, 8, 12, 15 y 18% de cemento en peso seco de suelo. Los ensayos realizados fueron: absorción, resistencia a la compresión, resistencia a la flexión por unidad de mampostería, resistencia a la compresión en pilas, resistencia a la compresión diagonal de muros y el ensayo de difracción de rayos X. Los resultados obtenidos muestran que con 18% de cemento se obtienen la resistencia óptima, en términos de resistencia a la compresión aumenta en un 53.95%, resistencia a la flexión en un 43%, resistencia a la compresión en pilas en un 36.6%, y resistencia a la compresión diagonal de muros en un 41.24%, respectivamente. La prueba de difracción de rayos X aplicada a la muestra óptima de ladrillo de tierra comprimida estabilizada muestra que en su composición predominan ciertos componentes como 32.4% de silicato de calcio, 23.8% de silicato de aluminio, 17.4% de calcio hidratado, 14.2% de illita, 6.86% de óxido de calcio, 3.34% de cuarzo, 1.2% de caolinita y 0.8% de goethita. Se concluye que los ladrillos de tierra comprimida estabilizados con cemento (LTCEC) son una alternativa de construcción sostenible que mejora las propiedades mecánicas de los ladrillos de tierra.

Abstract: Concrete pavings are widely used in the construction industry as flooring for decorative and structural purposes in the gardens, parks, and roads of America, and Europe. In the present study, the effects of pyrite, corundum, and water-retaining polymer additives on the surface wear resistance of concrete pavings were investigated. Concrete pavings were poured in 2 stages and all of the bottom layers of samples were the same, but upper layers of pavings were produced by adding pyrite in the ratio of 0.10, 0.20, 0.30, 0.40 according to the mass of the aggregate, 5 kg /m2 corundum-based surface hardener to the paving surface area, and a high amount of water-absorbing polymer at a ratio of 0.05 and 0.10 to the water content of the mixture. Vertical abrasion, splitting tensile strength, water absorption, freeze-thaw resistance, pendulum footed friction, and surface hardness measurements with Schmidt test hammer experiments were made to TS 2824 EN 1338 standard. Also, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses were carried out to characterize the produced materials. Results of the study indicate that the use of pyrite, corundum, and water-retaining polymers provided improvements in the surface wear resistance of concrete pavings

Abstract In the county of Pedra Lavrada - PB, various mineral occurrences of pegmatite are observed with prominence at Alto Dois Irmãos - PB, where quartz, feldspar and mica are mined. The understanding of mineral constituents is fundamental to define their industrial employment and to implement improvements in the beneficiation process. The proposal of this research is the detailed characterization and proof of that part of the ore (quartz) considered waste, presenting low poisoning (Fe2O3) and high silica (SiO2) content, to enable its industrial use. Besides that, to minimize the environmental impact through the reuse of this waste, and to determine the correct utilization of the milling equipment. For the pegmatite characterization, done were density determination tests, mineralogical identification by X-ray diffraction (XRD), chemical analysis by fluorescents X-rays and morphological analysis by scanning electron microscopy (SEM/EDS). Then tests were done for the Work Index (WI) calculous and consequently the empirical determination of the dimensions (LxD) of the pebble mill. The sterile presented a medium density of 2.66g/cm³, majority chemical composition of silicon and oxygen and quartz as the main mineralogical stage, indicating that this material has high purity. The. The Work Index (WI) was 15.9 kwh/t showing that this material can be considered resistant to breaking in the grinding process. The necessary energy to the milling was defined in 11.52 kwh/st, that corresponds to 57.28 HP. This power allowed the mill selection with diammeter and length of 1.83m, that provides the production maximization and the energy saving.

Abstract: Critical social thinking maintains an ambivalent relationship with science. Substantial criticism of it has come, in recent decades, from feminism and decolonialism. This paper addresses the way in which Chilean critical social research uses the tools of science for the construction of facticity, its validation procedures, and the notion of truth that it applies in its construction process, seeking to see how such a relationship is manifested in the practice and in the appreciation of researchers. It is based on the quantitative analysis of a corpus of 291 critical texts published between 2000 and 2022, and on the qualitative and quantitative analysis of a subset of 167 texts, together with interviews with 55 of their authors. Among its results, the following stand out, as characteristics of critical investigative practice: an evasive treatment of the truth; a high appreciation of empirical evidence; a significant change in theoretical tools and epistemological assumptions; the exploration of new participatory methodological tools, but by small groups, with operational limitations and little irradiation; the lack of effective roots of the notion of “catalytic validity” and a tacit, unacknowledged adherence to a Habermasian notion of truth.

Resumen: El pensamiento social crítico mantiene una relación ambivalente con la ciencia. Sustanciales críticas a ella han venido, en décadas recientes, desde el feminismo y el decolonialismo. Este artículo aborda la forma en que la investigación social crítica chilena emplea las herramientas de la ciencia para la construcción de la facticidad, sus procedimientos de validación y la noción de verdad que aplica en su proceso constructivo, buscando ver cómo se manifiesta tal relación en la práctica y en la apreciación de los investigadores. Se basa en el análisis cuantitativo de un corpus de 291 textos de carácter crítico publicados entre 2000 y 2022, y en el análisis cualitativo y cuantitativo de un subconjunto de 167 textos, junto a entrevistas a 55 de sus autores. Entre sus resultados destacan, como características de la práctica investigativa crítica: un evasivo tratamiento de la verdad; una gran valoración de la evidencia empírica; un significativo cambio de herramientas teóricas y supuestos epistemológicos; la exploración de nuevas herramientas metodológicas participativas, pero por grupos reducidos, con limitaciones operativas y escasa irradiación; la falta de arraigo efectivo de la noción de “validez catalítica” y una adhesión tácita, no reconocida, a una noción habermasiana de la verdad.

SYNOPSIS An oolitic iron ore from Gara Djebilet, Algeria was characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectrosopy and the phosphorus distribution between various phases studied. Two ore types were identified - a haematite-dominated, oolitic type and a more massive, magnetite-dominated type. The haematite-dominated ore had a higher phosphorus content, up to 0.6% in the iron oxide minerals, than the magnetite-dominated type (0.3% P). Owing to the very fine-grained texture of the gangue minerals, reducing the phosphorus content to levels suitable for steelmaking (below 0.05% P) by conventiobal means would entail an energy-intensive process with a high carbon footprint. Preliminary leaching test work using a sulphurous geothermal water as lixiviant, assisted by solar thermal acceleration, gave very promising results, removing 0.13% of the residual P (or 21.7% removal of total P) from the high-phosphorus oolitic ore.

Resumo A natureza é presenteada com uma grande variedade de plantas ornamentais que embelezam e limpam a natureza. Por causa de seu grande valor estético, existe a necessidade de proteger essas plantas de uma variedade de estresses bióticos e abióticos. Hibiscus rosa-sinensis (L.) é uma planta ornamental comumente conhecida como rosa-da-China ou graxa-de-estudante. É afetada por vários patógenos fúngicos e bacterianos. O presente estudo buscou isolar o patógeno da mancha foliar de H. rosa-sinensis e seu controle usando nanopartículas de prata (AgNPs). Com base nas características moleculares e morfológicas, o patógeno isolado da mancha foliar foi identificado como Aspergillus niger. As AgNPs foram sintetizadas no extrato de folhas de Calotropis procera e caracterizadas. A análise de espectroscopia UV-vis mostrou discretas bandas de ressonância plasmônica na superfície das AgNPs sintetizadas, mostrando a presença de aminoácidos aromáticos. A espectroscopia no infravermelho com transformada de Fourier (FTIR) descreveu a presença de grupos funcionais C-O, NH, C-H e O-H, que atuam como moléculas estabilizadoras e redutoras. A difração de raios X (DRX) revelou o tamanho médio (~32,43 nm) das AgNPs e a microscopia eletrônica de varredura (MEV) mostrou sua natureza esférica. Neste estudo, foi investigada a atividade antifúngica in vitro e in vivo de AgNPs. A análise da atividade antifúngica in vitro revelou a maior inibição do crescimento de micélio (87%) na concentração de 1,0 mg/ml de AgNPs. A mesma concentração de AgNPs inibiu a propagação da doença em folhas infectadas de H. rosa-sinensis. Esses resultados demonstraram significativa capacidade de controle de doenças das AgNPs e sugeriram seu uso em diferentes plantas ornamentais.

Abstract Nature is gifted with a wide range of ornamental plants, which beautify and clean the nature. Due to its great aesthetic value, there is a need to protect these plants from a variety of biotic and abiotic stresses. Hibiscus rosa-sinensis (L.) is an ornamental plant and it is commonly known as China rose or shoeblack plant. It is affected by several fungal and bacterial pathogens. Current study was designed to isolate leaf spot pathogen of H. rosa-sinensis and its control using silver nanoparticles (AgNPs). Based on molecular and morphological features, the isolated leaf spot pathogen was identified as Aspergillus niger. AgNPs were synthesized in the leaf extract of Calotropis procera and characterized. UV-vis spectral analysis displayed discrete plasmon resonance bands on the surface of synthesized AgNPs, depicting the presence of aromatic amino acids. Fourier transform infrared spectroscopy (FTIR) described the presence of C-O, NH, C-H, and O-H functional groups, which act as stabilizing and reducing molecules. X-ray diffraction (XRD) revealed the average size (~32.43 nm) of AgNPs and scanning electron microscopy (SEM) depicted their spherical nature. In this study, in vitro and in vivo antifungal activity of AgNPs was investigated. In vitro antifungal activity analysis revealed the highest growth inhibition of mycelia (87%) at 1.0 mg/ml concentration of AgNPs. The same concentration of AgNPs tremendously inhibited the spread of disease on infected leaves of H. rosa-sinensis. These results demonstrated significant disease control ability of AgNPs and suggested their use on different ornamental plants.

Abstract Silver nanoparticles are opted to have various applications in different fields ranging from traditional medicines to culinary items. It is toxic and most effective against bacteria, fungi viruses, parasites, parasite carrying vectors such as mosquitoes and their larvae and other eukaryotic microorganisms at low concentration without any side effects and toxicity to humans. In view of these data, the present research has been investigated by synthesizing silver nanoparticles using 1mM silver nitrate and aqueous extract of Passiflora foetida. The variation of nanoparticles in size and shape concerning the concentration of extract prepared were analysed. The formation of silver nanoparticles was confirmed by colour changing from yellowish green to reddish-brown implicating the surface plasmon resonance. Further, it was concluded by obtaining an absorbance peak at 420 nm using UV-Visible spectrophotometer analysis. FTIR analysis was used to identify the capping ligands, which included alkanes, aromatic groups and nitro compounds. The average grain size of ~12 nm to 14 nm with crystalline phase was revealed by X-ray Diffraction studies. The SEM images depicted the surface morphology with agglomeration; TEM studies showed the shape of nanoparticles as spherical and hexagonal with sizes ranging from 40 nm to 100 nm and EDAX analysis confirmed the presence of elemental silver as the principal constituent. The characterized silver nanoparticles were then tested for synergistic antibacterial effects with tetracycline, and the results show that they are more active against E. coli and S. aureus, but moderately effective against B. cereus and K. pneumoniae . It also had a strong larval and pupal toxic effects on the dengue vector, Aedes aegypti with the highest mortality. As a result, silver nanoparticles could be a viable alternative for a variety of applications.

Resumo Os nanopartículos de prata são optados por ter várias aplicações em diferentes áreas que variam de medicamentos tradicionais a itens culinários. É tóxico e mais eficaz contra bactérias, vírus de fungos, parasitas, parasitas que transportam vetores como mosquitos e suas larvas e outros microorganismos eucarióticos em baixa concentração, sem efeitos colaterais e toxicidade para os seres humanos. Em vista desses dados, a presente pesquisa foi investigada sintetizando nanopartículas de prata usando nitrato de prata de 1 mm e extrato aquoso de Passiflora foetida. Foi analisada a variação de nanopartículas em tamanho e forma relativa à concentração de extrato preparado. A formação de nanopartículas de prata foi confirmada pela mudança de cor de verde amarelado para marrom-avermelhado, implicando a ressonância plasmônica da superfície. Além disso, foi concluído pela obtenção de um pico de absorvância a 420 nm usando análise do espectrofotômetro visível por UV. A análise do FTIR foi usada para identificar os ligantes de captura, que incluíam alcanes, grupos aromáticos e compostos nitro. O tamanho médio dos grãos de ~ 12 nm a 14 nm com fase cristalina foi revelado por estudos de difração de raios-X. As imagens SEM retratavam a morfologia da superfície com aglomeração; Os estudos de TEM mostraram a forma das nanopartículas como esféricas e hexagonais, com tamanhos variando de 40 nm a 100 nm e a análise EDAX confirmou a presença de prata elementar como constituinte principal. As nanopartículas de prata caracterizadas foram então testadas quanto a efeitos antibacterianos sinérgicos com tetraciclina, e os resultados mostram que são mais ativos contra E. coli e S. aureus, mas moderadamente eficazes contra B. cereus e K. pneumoniae. Ele também teve um forte efeito tóxico larval e pupal no vetor de dengue, Aedes aegypti com a maior mortalidade. Como resultado, as nanopartículas de prata podem ser uma alternativa viável para uma variedade de aplicações.

Abstract Fusarium oxysporum is an entomopathogenic fungus, and it has anti-biological activity against arthropods. Ticks are blood sucking arthropods which are responsible for transmitting different diseases in humans and animals. The use of chemical insecticides against ticks is not eco-friendly option and results in the development of acaricide resistance. Previously, we had cultured a local isolate of Fusarium oxysporum from soil samples which were identified through microscopy and confirmed through molecular technique. In our previous experiments, we have prepared Silver nanoparticles (AgNP) at pH 7 and they had been characterized through X-Ray Diffraction (XRD), UV-visible and zeta-potential. In our current study, the AgNP were prepared at different pH conditions and characterized through Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The protein molecules of F. oxysporum were charged with Ag ions. F. oxysporum NP were observed to enhance anti-biological activity by killing Rhipicephalus microplus and they caused 100% mortality at pH 4 and pH 5 in 24 h in anti-tick biological assay. Our study is the first report to do biological assay against Rhipicehalus ticks by using Fusarium AgNP at acidic pH. Biological control using entomopathogenic fungi can be the best alternative of the chemical method to control the tick population.

Resumo Fusarium oxysporum é um fungo entomopatogênico com atividade antibiológica contra artrópodes. Os carrapatos são artrópodes sugadores de sangue responsáveis pela transmissão de diversas doenças em humanos e animais. O uso de inseticidas químicos contra carrapatos não é uma opção ecologicamente correta e resulta no desenvolvimento de resistência acaricida. Anteriormente, havíamos cultivado um isolado local de Fusarium oxysporum a partir de amostras de solo que foram identificadas por microscopia e confirmadas por técnica molecular. Em nossos experimentos anteriores, preparamos nanopartículas de Prata (AgNP) em pH 7 e elas foram caracterizadas por Difração de Raios X (XRD), UV-visível e potencial zeta. No presente estudo, os AgNP foram preparados em diferentes condições de pH e caracterizados através de Microscopia Eletrônica de Varredura (MEV) e Microscopia Eletrônica de Transmissão (TEM). As moléculas de proteína de F. oxysporum foram carregadas com íons Ag. Assim, observou-se que F. oxysporum NP aumenta a atividade antibiológica matando Rhipicephalus microplus e causando 100% de mortalidade em pH 4 e pH 5 em 24h no ensaio biológico anticarrapato. Este estudo é o primeiro relato de caso a realizar um ensaio biológico contra carrapatos Rhipicehalus usando Fusarium AgNP em pH ácido. Nesse sentido, é possível concluir que o controle biológico utilizando fungos entomopatogênicos pode ser a melhor alternativa do método químico para controlar a população de carrapatos.

Abstract Evaluating the effects of nanomaterials in cementitious systems is paramount to projecting high-performance construction materials. However, the synthesis of some nanomaterials on a large scale and their toxicity may limit their application. In this context, nanofibrillated cellulose (NFC), a biodegradable and natural material stand out. Thus, this paper aims to study the influence of NFC on the fresh, hardened properties (compressive and flexural strengths) and mineralogy of cementitious systems. The results indicated that incorporating up 0.075 wt.% to CNF reduced the spread of cement pastes by up to 14.0%. A CNF content of 0.025 wt.% increased the 28-d compressive and flexural strengths by 22.0% and 25.0%, respectively, compared to the control sample. The X-ray diffraction (XRD) results indicate that higher NFC contents (>0.025 wt.%) resulted in lower intensity portlandite peaks after 7 days, which may show a lower hydration degree, especially concerning the plain cement paste. These results suggest that the NFC can affect the hydration of cementitious matrices at early ages; however, it did not significantly affect the hydration degree after 28 days of hydration.

Resumo Avaliar os efeitos dos nanomateriais em sistemas cimentícios é fundamental para projetar materiais de construção de alto desempenho. No entanto, alguns nanomateriais tem a sua aplicação limitada à toxicidade e síntese em larga escala. Nesse contexto, destaca-se a celulose nanofibrilada (NFC), um material biodegradável e natural. Assim, este trabalho tem como objetivo estudar a influência do NFC nas propriedades no estado fresco, endurecido (resistências à compressão e à flexão) e mineralogia de sistemas cimentícios. Os resultados indicaram que a incorporação de até 0,075% em massa da CNF reduziu o espalhamento das pastas de cimento em até 14,0%. Um teor de CNF de 0,025% em massa aumentou as resistências à compressão e a flexão de 28 dias em 22,0% e 25,0%, respectivamente, em comparação com as amostras de controle. Os resultados da difração de raios-X (DRX) indicaram que maiores teores de CNF (>2,5%) resultaram em picos de portlandita de menor intensidade após 7 dias, o que pode indicar um menor grau de hidratação, principalmente em relação à pasta de cimento de referência. Esses resultados sugerem que a NFC pode afetar a hidratação de matrizes cimentícias em idades precoces; entretanto, não afetou significativamente o grau de hidratação após 28 dias de hidratação.

Abstract: Cellulose nanofibers (CNF) could be obtained from diverse lignocellulosic sources, among them wood. Regarding this, it is important to clarify if the shaft section of the tree could influence the CNF characteristics. This study evaluated cellulose nanofibers from Guazuma crinita (bolaina blanca) obtained at different heights of the longitudinal axis of the shaft of trees from a three-and-a-half-year-old plantation. The wood was subjected to pulping, bleaching and subsequent mechanical milling using a Changsha Samy XYQM-2L planetary ball mill to obtain cellulose nanofibers. The product was characterised using analytical techniques: scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy. Additionally, the degree of polymerisation was determined. The effect of longitudinal position on cellulose nanofibers characteristics was evaluated by comparing means using ANOVA and Kruskal-Wallis statistical tests. The yield of cellulose nanofibers production from the high, middle and basal sections was 32,1 %, 33,6 % and 31 %, respectively. The obtained cellulose nanofibers exhibited a significantly larger diameter for the high zone (84 nm) compared with the middle (75 nm) and basal (69 nm) zones; the length remained above the micrometre range. With respect to degree of polymerisation, a decrease was evidenced with respect to the increase in shaft height; the basal zone exhibited a degree of polymerisation of 300, a significantly higher value than the middle and high zones, which exhibited degree of polymerisation of 249 and 211, respectively. The product showed typical cellulose type I polymorphism and crystallinity indexes of 76 %, 93 % and 96 % for the high, middle and basal sections, respectively. Regarding the thermostability of cellulose nanofibers, the maximum degradation rate of cellulose nanofibers occurred between 335 °C and 341 °C, with cellulose nanofibers from the basal area being the most stable. The adsorption of the methylene blue dye on cellulose nanofibers was evaluated; an efficiency > 60 % was found.

Due to its multiple applications, zinc oxide (ZnO) is one of the most used materials in science and technology. Therefore, this research carried out the synthesis of ZnO and Pt-ZnO nanoparticles (NPs) by the direct precipitation method, which is characterized by being simple and reproducible, using two different precipitating agents, potassium hydroxide (KOH) and sodium hydroxide (NaOH); for the doping of Pt-ZnO NPs was used platinum acetylacetone. To evaluate the effect of the precipitating agent on the properties of each doped material, they were characterized by Fourier transform infrared spectroscopy, where the Zn-O vibrations were more pronounced using KOH. X-ray diffraction analysis shows a hexagonal structure (wurtzite) formation for ZnO with NaOH, obtaining a smaller crystal size than the other synthesized materials. Scanning electron microscopy analysis showed hexagonal and hemispherical shapes for ZnO (with NaOH and KOH) and Pt-ZnO (with NaOH), respectively; also, cylindrical shapes were obtained for Pt-ZnO (with KOH). The highest band gap obtained was for the Pt-ZnO material synthesized with KOH.

Sintered NdFeB magnets possess excellent magnetic properties, but behave passively in alkaline and saline media and are susceptible to corrosion in acidic environments. The corrosion behavior of NdFeB magnets in industrial environments: potassium hydroxide (KOH), perchloric acid (HClO4) and sodium chloride (NaCl), was investigated by immersion and electrochemical tests. The immersion test concluded that the most corrosive electrolyte of the three studied was HClO4. Electrochemical tests showed that the NdFeB sample without magnetic order had better corrosion resistance. Metallographic microscopy and scanning electron microscopy support the obtained corrosion data. X-ray photoelectron spectroscopy indicates that the main elements on the surface of the analyzed sample (Nd, Fe, B) are in the oxidized state after corrosion.