The valuable role of renucleation rate in ultrananocrystalline diamond growth

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influence of the processing conditions and corona poling on the morphology of β-PVDF

The α → β phase transformation of PVDF through the stretching process at different temperatures was investigated. The optimum stretching conditions were studied and characterised by infrared spectroscopy and differential scanning calorimetry. The maximum β-phase content was achieved at 80°C and a stretch ratio of 5. These samples were poled at several electric fields by the corona charge method. The effect of the electric field on the phase transformation was studied by infrared spectroscopy.

Obtenção, caracterização e estudo de liberação in vitro e permeação in vivo de sistemas microestruturados contendo cafeína

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Sistemas nanoestruturados estabilizados com álcool cetílico etoxilado e propoxilado contendo óleo de copaíba e fluconazol potencialmente ativo contra dermatomicoses

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

CoO doping effects on the ZnO films through EBPDV technique

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Pluronics F-127/L-81 Binary Hydrogels as Drug-Delivery Systems: Influence of Physicochemical Aspects on Release Kinetics and Cytotoxicity

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Design and Characterization of Silicone and Surfactant Based Systems for Topical Drug Delivery

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Air abrasion before and/or after zirconia sintering: surface characterization, flexural strength, and resin cement bond strength

The purpose of this in vitro study was to evaluate the effect of air-abrasion/zirconia sintering order on the yttria partially stabilized tetragonal zirconia polycrystal (Y-TZP) surface characterization (roughness, morphology, and phase transformation), flexural strength (FS), and shear bond strength (SBS) to a resin cement. Y-TZP specimens were air abraded with 50-μm Al2O3 particles after (AS), before (BS), or before and after zirconia sintering (BAS). For roughness (Ra), 30 block specimens (12×12×3.0 mm; n=10) had their surfaces analyzed by a profilometer. Next, on the air-abraded surfaces of these specimens, composite resin discs (n=30) were bonded with RelyX ARC. The bonded specimens were stored for 24 hours in distilled water at 37°C before shear testing. Failure mode was determined with a stereomicroscope (20×). The surface morphology (n=2) was evaluated by SEM (500×). For the four-point flexural strength test (EMIC DL2000), 39 bar-shaped specimens (20×4.0×1.2 mm; n=13) were air abraded according to the three conditions proposed, and an additional group (nonabraded) was evaluated (n=13). The quantitative analysis of phase transformation (n=1) was completed with Rietveld refinement with X-ray diffraction data. Ra (μm) and SBS (MPa) data were analyzed by one-way analysis of variance (ANOVA) and the Tukey test (α=0.05). Pearson correlation analysis was used to determine if there was a correlation between roughness and SBS. For FS (MPa) data, one-way ANOVA and the Dunnett C-test (α=0.05) were used. The air-abrasion/zirconia sintering order influenced significantly (p<0.001) Ra, SBS, and FS. The BS and AS groups presented the highest (1.3 μm) and the lowest (0.7 μm) Ra. The highest SBS (7.0 MPa) was exhibited by the BAS group, followed by the AS group (5.4 MPa) and finally by the BS group (2.6 MPa). All groups presented 100% adhesive failure. A weak correlation (r=−0.45, p<0.05) was found between roughness and SBS. The air-abrasion/zirconia sintering order provided differences in the surface morphology. The nonabraded (926.8 MPa) and BS (816.3 MPa) groups exhibited statistically similar FS values but lower values than the AS (1249.1 MPa) and BAS (1181.4 MPa) groups, with no significant difference between them. The nonabraded, AS, BS, and BAS groups exhibited, respectively, percentages of monoclinic phase of 0.0 wt%, 12.2 wt%, 0.0 wt%, and 8.6 wt%. The rougher surface provided by the air-abrasion before zirconia sintering may have impaired the bonding with the resin cement. The morphological patterns were consistent with the surface roughness. Considering the short-term SBS and FS, the BAS group exhibited the best performance. Air abrasion, regardless of its performance order, provides tetragonal to monoclinic transformation, while sintering tends to zero the monoclinic phase content.

Effect of low-temperature aging on the mechanical behavior of ground Y-TZP

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Relationship between elastic and mechanical properties of dental ceramics and their index of brittleness

The purpose of the study was to verify the effects of a number of materials' parameters (crystalline content; Young's modulus, E; biaxial flexure strength, sigma(i); Vickers hardness, VH; fracture toughness, K-Ic; fracture surface energy, gamma(f); and index of brittleness, B) on the brittleness of dental ceramics. Five commercial dental ceramics with different contents of glass phase and crystalline particles were studied: a vitreous porcelain (VM7/V), a porcelain with 16 vol% leucite particles (d.Sign/D), a glass-ceramic with 29 vol% leucite particles (Empress/E1), a glass-ceramic with 58 vol% lithium-disilicate needle-like particles (Empress 2/E2), and a glass-infiltrated alumina composite with 65 vol% crystals (In-Ceram Alumina/IC). Discs were constructed according to manufacturers' instructions, ground and polished to final dimensions (12 mm x 1.1 mm). Elastic constants were determined by ultrasonic pulse-echo method. sigma(i) was determined by piston-on-3-balls method in inert condition. VH was determined using 19.6 N load and K-Ic was determined by indentation strength method. gamma(f) was calculated from the Griffith-Irwin relation and B by the ratio of HV to K-Ic. IC and E2 showed higher values of sigma(i), E, K-Ic and gamma(f), and lower values of B compared to leucite-based glass-ceramic and porcelains. Positive correlations were observed for sigma(i) versus K-Ic, and K-Ic versus E-1/2, however, E did not show relationship with HV and B. The increase of crystalline phase content is beneficial to decrease the brittleness of dental ceramics by means of both an increase in fracture surface energy and a lowering in index of brittleness. (C) 2012 Elsevier Ltd and Techna Group Sri. All rights reserved.

Superconductivity at 9.5 K in the Ti2GeC compound

We report on the investigation of the Ti2GeC properties by X-ray diffraction, magnetic and electrical resistivity measurements. Polycrystalline samples of Ti2GeC with nominal compositions were prepared by solid state reaction. X-ray powder patterns suggest that all peaks can be indexed with the hexagonal phase of Cr2AlC prototype. The temperature dependence of both electrical resistivity and magnetization indicate a bulk type-II superconductivity at 9.5 K. Magnetoresistive data suggest an upper critical field of B-c2 similar to 8.1 T and coherence length similar to 61 A degrees . Furthermore, the results highlight the highest critical temperature reported up to now for an H-phase.

Atomistic simulations of 2D bicomponent self-assembly: from molecular recognition to self-healing

Supramolecular two-dimensional engineering epitomizes the design of complex molecular architectures through recognition events in multicomponent self-assembly. Despite being the subject of in-depth experimental studies, such articulated phenomena have not been yet elucidated in time and space with atomic precision. Here we use atomistic molecular dynamics to simulate the recognition of complementary hydrogen-bonding modules forming 2D porous networks on graphite. We describe the transition path from the melt to the crystalline hexagonal phase and show that self-assembly proceeds through a series of intermediate states featuring a plethora of polygonal types. Finally, we design a novel bicomponent system possessing kinetically improved self-healing ability in silico, thus demonstrating that a priori engineering of 2D self-assembly is possible.

Elaboration et caractérisation de ciments géopolymères à base de scories volcaniques

Two types of volcanic ashes referenced as ZD (volcanic ashes from Djoungo) and ZG (volcanic ashes from Galim) were collected from two Cameroonian localities. They were characterized (chemical and mineralogical compositions, amorphous phase content, particle size distribution and specific surface area) and used as raw materials for the synthesis of geopolymer cements at ambient temperature of laboratory (24 ± 3 °C). The synthesized products were characterized by determining their setting time, linear shrinkage and compressive strength, X-ray Diffraction, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy. The mineralogical composition, the amorphous phase content, the particle size distribution, the specific surface area of the volcanic ashes as well as the mass ratio of the alkaline solution (sodium silicate / sodium hydroxide) were the main parameters which influenced the synthesis of geopolymers with interesting characteristics at ambient temperature (24 ± 3 °C). The volcanic ashes (ZD) whose mineralogical composition contained anhydrite, low amorphous phase content and low specific surface area led to long setting times. Moreover, its products swelled and presented cracks due to the formation of ettringite and these resulted in low compressive strengths (7 to 19 MPa). The volcanic ashes (ZG) containing high amounts of amorphous phase and high specific surface area led geopolymers with setting times between 490 and 180 minutes and compressive strength between 7 and 50 MPa at ambient temperature of laboratory. The properties of geopolymers were improved when elaborated with a mixture of volcanic ashes and metakaolin (ZD–MK and ZG–MK). For geopolymers obtained from ZD–MK, the setting time was between 500 and 160 minutes while it was between 220 and 125 minutes for geopolymers obtained from ZG–MK. The compressive strength greatly increased between 23 and 68 MPa and 39 and 64 MPa for geopolymers obtained from ZG –MK and ZD–MK respectively. A comparative study of the properties of mixtures of metakaolin–alumina and volcanic ash–alumina based geopolymers shows that metakaolin is a good source of Al2O3 and SiO2 and which highly reactive with alkaline solution and produces geopolymers with better characteristics compared to volcanic ash based–geopolymer. The properties of volcanic ash–based geopolymer were also improved when amorphous alumina was incorporated into the volcanic ash. This additive is used to compensate the deficiencies in Al2O3 content in the volcanic ash. Compare to when volcanic ash is used alone 20 to 40 % incorporation of this additive corresponded to increases of the compressive strength by 18.1 % for metakaolin-alumina based-geopolymers and by 32.4 % for volcanic ash-based geopolymers.

Small quantity but large effect — How minor phases control strain localization in upper mantle shear zones

Low viscosity domains such as localized shear zones exert an important control on the geodynamics of the uppermost mantle. Grain size reduction and subsequent strain localization related to a switch from dislocation to diffusion creep is one mechanism to form low viscosity domains. To sustain strain localization, the grain size of mantle minerals needs to be kept small over geological timescales. One way to keep olivine grain sizes small is by pinning of mobile grain boundaries during grain growth by other minerals (second phases). Detailed microstructural studies based on natural samples from three shear zones formed at different geodynamic settings, allowed the derivation of the olivine grain-size dependence on the second-phase content. The polymineralic olivine grain-size evolution with increasing strain is similar in the three shear zones. If the second phases are to pin the mobile olivine grain boundary the phases need to be well mixed before grain growth. We suggest that melt-rock and metamorphic reactions are crucial for the initial phase mixing in mantle rocks. With ongoing deformation and increasing strain, grain boundary sliding combined with mass transfer processes and nucleation of grains promotes phase mixing resulting in fine-grained polymineralic mixtures that deform by diffusion creep. Strain localization due to the presence of volumetrically minor minerals in polymineralic mantle rocks is only important at high strain deformation (ultramylonites) at low temperatures (<~800°C). At smaller strain and stress conditions and/or higher temperatures other parameters like overall energy available to deform a given rock volume, the inheritance of mechanical anisotropies or the presence of water or melts needs to be considered to explain strain localization in the upper mantle.

Barium in sediments off northwest Africa

High-resolution down-core analyses of the solid phase content of total barium (Batot) and total organic carbon (TOC) back to 25 kyr B.P. were performed on a gravity core from the upper continental slope off Cape Yubi (Morocco). The observed discrepancy between the two potential paleoproductivity proxies, Batot and TOC, initiated supplementary examinations of the pore water, the geochemistry of the clay fraction, X-ray diffraction analyses, and the application of a sequential Ba extraction method of selected samples. Additionally, we analyzed down-core samples of the planktonic foraminifera Turborotalita quinqueloba and Globorotalia inflata for their Ba/Ca ratios. These analyses, which were performed for the first time on these species, were used to reconstruct past oceanic Ba concentrations. We suggest that in the study area, which is characterized by high accumulation rates, the preserved TOC content is a valuable proxy for past primary productivity, whereas the solid phase Batot contents appear to be affected by other mechanisms and factors. Peaks of total barium content in the clay fraction and of Ba/Ca ratios in the planktonic foraminifera shells found during the Younger Dryas and the Heinrich 1 event are likely to result from increased meltwater influx into the northern North Atlantic. We suggest that Ba-enriched meltwater was transmitted by the eastern boundary current system from higher latitudes to the region of the Canary Islands. Total barium contents of the clay fraction (Batot,clay) and Ba/Ca in planktonic foraminifera shells seem to be reliable proxies for this discharge of meltwater.