Eduardo H.M. Nunes

Measurement of the zeta potential of planar surfaces with a rotating disk

The technique of the rotating disk was used to measure the zeta potential of planar surface of different materials, like minerals, polymeric materials, and films of paints and particles. This technique is simple and reliable from the experimental point of view. The results are discussed concerning the principles of the technique, the rheological characteristics and the applications of these materials.

Simple sol–gel process to obtain silica-coated anatase particles with enhanced TiO2-SiO2 interfacial area

In this study we prepared silica-titania composites with a low SiO2:TiO2 molar ratio. These materials were prepared using a simple sol-gel route in which a hydrothermal treatment was used to obtain mesoporous anatase particles. Pure titania was also synthetized for comparison purposes. These materials were examined by scanning and transmission electron microscopy (SEM and TEM, respectively), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and nitrogen sorption tests. A thin silica coating was formed on the anatase particles. It was observed that the presence of this coating led to samples with an enhanced thermal stability. Indeed, the composites prepared in this work showed an anatase structure and a high specific surface area (SSA), even after their calcination at 800°C. Thus, we believe that the synthetized material present an outstanding SiO2-TiO2 interfacial area associated with a high amount of anatase particles which could improve its photoactive properties.

The optical absorption of gamma irradiated and heat-treated natural quartz

Quartz with aluminum as impurity absorbs energy from ionizing radiation and modifies its color. Colorless quartz becomes smoky or dark smoky (morion quartz) when exposed to gamma rays. By heat-treatment, smoky quartz may become successively greenish, yellowish, or brownish as the irradiation dose increases. Natural, colorless quartz is routinely colored by irradiation with gamma rays and heat-treatment for jewelry production. The color formation in natural quartz through this procedure is explained based on EPR, UV-VIS, and IR studies of irradiated and irradiated and heat-treated samples. Smoky quartz shows absorption bands in the visible region and a strong EPR signal. After heat-treatment it shows absorption bands in the near UV region with extensions into the visible region and a weak EPR signal. The intensity of the absorption bands is proportional to the irradiation dose. These changes of color are explained by the model of Itoh, Stoneham, and Stoneham. [AlSi O4 /h+]0 centers are produced by irradiation, causing the EPR signal and the absorption bands in the visible region. [AlSi O4]- centers are created from [AlSi O4 /h+]0 centers by heat-treatment. They cannot cause an EPR signal and have absorption bands in the near UV region with extensions into the visible region. The highest concentration of [AlSi O4]- centers occurs when the charge compensators have medium mobility. Lithium should give the best condition for color formation. Sodium (low mobility) and hydrogen (high mobility) should make smoky quartz colorless after heat-treatment.

Infrared and chemical characterization of natural amethysts and prasiolites colored by irradiation

The infrared bands of amethyst and prasiolite samples from different origins were correlated to the trace elements contents. Amethysts have an iron content greater than 20 ppm and a low content of sodium and potassium. Prasiolites have an aluminum content greater than 120 ppm and a higher overall trace elements content, which accounts for a strong absorption between 3200 and 3600 cm-1. Colorless samples of quartz that become amethysts and prasiolites after irradiation have infrared spectra at room temperature with a broad band at 3441 cm-1 and a sharp band at 3595 cm-1. The broad band splits in several bands at low temperatures that are related to AlSi and FeSi. The color of amethysts and prasiolites are assigned to [AlSiO4/h+]o and [FeSiO4/h+]o centers formed by the exposure to ionizing irradiation and to the influence of lattice distortions due to the content of iron as a substitute for silicon and a high content of trace elements of large ionic radius like potassium.

Backgrounds for the Industrial Use of Black Tourmaline Based on Its Crystal Structure Characteristics

The industrial use of black tourmaline is based on the pyroelectricity, emission of far infrared radiation, adsorption of ions, release of negative air ions, and influence on biologic activity. The crystal structure of schorl was analyzed through a virtual three dimensional hard ball model and related to these properties. Explanations for the pyroelectricity, emission of far infrared radiation, adsorption of ions, and release of negative air ions are given based on the crystal structure characteristics.

A biodegradable porous composite scaffold of PCL/BCP containing Ang-(1-7) for bone tissue engineering

Highly porous three-dimensional biodegradable scaffolds was obtained from beta-tricalcium phosphate-hydroxyapatite bioceramic (BCP), PCL, and Angiotensin-(1-7). We used the solvent casting and particulate leaching methods (SC/PL). The processed scaffolds were characterized by X-ray microtomography (µ-CT). Biocompatibility tests in vitro were performed during three and seven days using MTT and Alkaline Phosphatase Activity (APA) assays. Both the MTT activity and APA were evaluated using a one-way ANOVA test. The µ-CT results showed that the increase of the PCL:BCP weight ratio leads to structures with lower pore sizes. The pore interconnectivity of the processed scaffolds was evaluated in terms of the fragmentation index (FI). We observed that the obtained composites present poorly connected structures, with close values of FI. However, as the polymer phase is almost transparent to the X-rays, it was not taken into consideration in the µ-CT tests. The MTT activity assay revealed that scaffolds obtained with and without Angiotensin-(1-7) present mild and moderate cytotoxic effects, respectively. The APA assay showed that the rat osteoblasts, when in contact for three days with the PCL composites, presented an APA similar to that observed for the control cells. Nevertheless, for an incubation time of seven days we observed a remarkable decrease in the alkaline phosphatase activity. In conclusion, using the solvent casting and salt leaching method we obtained 3D porous that are composites of PCL, BC and Ang-(1-7), which have suitable shapes for the bone defects, a high porosity and interconnect pores. Furthermore, the viability in vitro showed that the scaffolds have potential for drug delivery system and could be used in future in vivo tests.

Determination of the potential for extrinsic color development in natural colorless quartz

Abstract Colorless natural quartz can develop many extrinsic colors after exposure to ionizing radiation and heat due to trace elements such as aluminum, iron, hydrogen, lithium, and sodium. The infrared spectrum of colorless natural quartz is correlated to the development of these colors, because the bands between 3200 and 3600 cm-1 are related to the presence of trace elements. The colors produced by γ-ray or electron beam irradiation are caused by displacements of electrons in the quartz lattice and can be bleached by ultraviolet irradiation. Colors produced by irradiation and additional heating, however, are resistant to ultraviolet rays, probably due to Li+ diffusion. The infrared spectra of colorless natural quartz crystals can be used to identify the crystals’ potential for color development by irradiation and heating. At room temperature, all natural colorless samples of alpha quartz show bands at 2499, 2600, 2677, 2771, 2935, and 3063 cm-1. The samples that do not develop color after irradiation also show bands at 3202 and 3304 cm-1. The samples that become grayish to black after irradiation show three additional bands at 3381, 3433, and 3483 cm-1. This last band is related to the development of the colors greenish yellow, yellow, or brown (citrine) after irradiation and heating. The samples that become grayish olive green after irradiation and olive green after additional heating show a pair of bands at 3404 and 3510 cm-1 in addition to the former bands noted. The samples that become violet (amethyst) or green (prasiolite) after irradiation, or sky blue after irradiation plus heating show a broad band at ~3441 cm-1 and a band at 3585 cm-1.

Identificação de quartzos incolores para joalheria

Colorless quartz are irradiated and heat-treated to become greenish, yellowish, and brownish for the jewelry industry. Only a small fraction of natural, colorless quartz can develop colors through this process. The identification of this quartz is made through irradiation and heat-treatment tests on representative samples. The samples are sent to irradiators and then heat-treated. These tests are not fast enough for the needs of the semiprecious dealers. A new test is presented, that avoids irradiation and heat-treatment. It can identify samples with potential to develop colors in a few minutes. If a portable infrared spectrophotometer is available, it can be performed in field.

Estimativa da dose do quartzo natural irradiado pela termoluminescência

A major problem of natural quartz dealers is to control the irradiation doses applyed to their samples. We observed that the dosis is linearly proportional to the temperature where the beginning of the thermoluminescente can be seen with naked eyes. A reliable and simple procedure is offered to the dealers to control the doses applied to natural quartz.

Preparação e caracterização estrutural de materiais cerâmicos obtidos via processo freeze-casting

Cerâmicas com porosidade controlada apresentam elevado potencial de aplicacao como membranas para separacao gasosa e processos de dessalinizacao. As propriedades e o desempenho desses materiais estao diretamente relacionados ao seu processo de fabricacao. Assim, e de vital importância que as variaveis do processo utilizado sejam conhecidas e controladas. Neste trabalho, cerâmicas porosas a base de alumina foram obtidas por meio do processo freeze-casting. Foram utilizados terc-butanol como solvente e acido citrico como dispersante. As amostras foram fabricadas a partir de suspensoes com concentracoes de alumina variando entre 15 e 30% em volume. Elas apresentaram reducao linear da porosidade total (entre 48 e 73%) e porosidade fechada inferior a 2%. A resistencia a flexao desses materiais variou entre 3,6 ± 0,7 e 21,9 ± 0,6 MPa. Ensaios de microscopia eletronica de varredura e microtomografia de raios X revelaram que as amostras apresentaram elevada conectividade de poros e orientacao preferencial de poros. As alteracoes nas condicoes de processamento resultaram em materiais com estruturas porosas distintas, demonstrando a versatilidade do processo freeze-casting.