Evidence of a Thermal Diffusivity Gap in Sintered Li-Co-Sb-O Solid Solutions.

In this work, the thermal properties of ternary Li3x Co7-4x Sb2+x O12 solid solutions are studied for different concentrations in the range 0 ≤ x ≤ 0.7. Samples are elaborated at four different sintering temperatures: 1100, 1150, 1200 and 1250 °C. The effect of increasing the content of Li+ and Sb5+, accompanied by the reduction of Co2+, on the thermal properties is studied. It is shown that a thermal diffusivity gap, which is more pronounced for low values of x, can be triggered at a certain threshold sintering temperature (around 1150 °C in this study). This effect is explained by the increase of contact area between adjacent grains. Nevertheless, this effect is found to be less pronounced in the thermal conductivity. Moreover, a new framework for heat diffusion in solids is presented that establishes that both the heat flux and the thermal energy (or heat) satisfy a diffusion equation and therefore highlights the importance of thermal diffusivity in transient heat conduction phenomena.

Tailoring Heat Transfer and Bactericidal Response in Multifunctional Cotton Composites.

Through the execution of scientific innovations, "smart materials" are shaping the future of technology by interacting and responding to changes in our environment. To make this a successful reality, proper component selection, synthesis procedures, and functional active agents must converge in practical and resource-efficient procedures to lay the foundations for a profitable and sustainable industry. Here we show how the reaction time, temperature, and surface stabilizer concentration impact the most promising functional properties in a cotton-based fabric coated with silver nanoparticles (AgNPs@cotton), i.e., the thermal and bactericidal response. The coating quality was characterized and linked to the selected synthesis parameters and correlated by a parallel description of "proof of concept" experiments for the differential heat transfer (conversion and dissipation properties) and the bactericidal response tested against reference bacteria and natural bacterial populations (from a beach, cenote, and swamp of the Yucatan Peninsula). The quantification of functional responses allowed us to establish the relationship between (i) the size and shape of the AgNPs, (ii) the collective response of their agglomerates, and (iii) the thermal barrier role of a surface modifier as PVP. The procedures and evaluations in this work enable a spectrum of synthesis coordinates that facilitate the formulation of application-modulated fabrics, with grounded examples reflected in "smart packaging", "smart clothing", and "smart dressing".

Heat Transfer in Cassava Starch Biopolymers: Effect of the Addition of Borax.

In recent years, polymer engineering, at the molecular level, has proven to be an effective strategy to modulate thermal conductivity. Polymers have great applicability in the food packaging industry, in which transparency, lightness, flexibility, and biodegradability are highly desirable characteristics. In this work, a possible manner to adjust the thermal conductivity in cassava starch biopolymer films is presented. Our approach is based on modifying the starch molecular structure through the addition of borax, which has been previously used as an intermolecular bond reinforcer. We found that the thermal conductivity increases linearly with borax content. This effect is related to the crosslinking effect that allows the principal biopolymer chains to be brought closer together, generating an improved interconnected network favoring heat transfer. The highest value of the thermal conductivity is reached at a volume fraction of 1.40% of borax added. Our analyses indicate that the heat transport improves as borax concentration increases, while for borax volume fractions above 1.40%, heat carriers scattering phenomena induce a decrement in thermal conductivity. Additionally, to obtain a deeper understanding of our results, structural, optical, and mechanical characterizations were also performed.

Dehydration Process of Hofmann-Type Layered Solids.

In the present work the dehydration process of layered solids with formula unit M(H2O)2[Ni(CN)4]·nH2O, M = Ni, Co, Mn; n = 1, 2, 4 is studied using modulated thermogravimetry. The results show that water molecules need to overcome an energetic barrier (activation energy between 63 and 500 kJ/mol) in order to diffuse through the interlayer region. The related kinetic parameters show a dependence on the water partial pressure. On the other hand, X-ray diffraction results provide evidence that the dehydration process is accompanied by framework collapse, limiting the structural reversibility, except for heating below 80 °C where the ordered structure remains. Removal of water molecules from the interlayer region disrupts the long-range structural order of the solid.

Hierarchically nanostructured barium sulfate fibers.

BaSO(4) nanostructures with controlled morphologies were successfully produced via one-step process through precipitation of BaSO(4) in aqueous and organic media. The synthesis is carried out by mixing solutions of BaCl(2) and Na(2)SO(4) in presence of EDTA (disodium ethylenediaminetetraacetic acid) at room temperature. The influence of the reaction conditions such as initial reactants concentration, pH, EDTA/[Ba(2+)] ratio and aging on the BaSO(4) nanoparticles organization is studied. Using EDTA in aqueous media, spherical secondary particles of 500 nm diameter are obtained, which are formed by 4 nm size primary particles. With dimethyl sulfoxide and small amounts of water (5%) and EDTA, the aging process allows the production of long homogeneous fibers, related to hierarchical organization of BaSO(4) nanoparticles. Direct observation of self-assembling of primary particles by HRTEM allows proposing a mechanism for fiber formation, which is based on multipolar attractions that lead to a brick-by-brick organization along a preferential orientation. Results evidence the role of EDTA as controlling agent of the morphology and primary and secondary mean particle size.

A combined theoretical-experimental study on the acidity of WO(x)-ZrO(2) systems.

This work provides a chemical approach to the relationship between structure and electronic behavior of the active surface of the WO(x)-ZrO(2) system as a function of W loads. This study shows that the electronic hardness (eta), the Lewis and Brønsted acidity are functions of the local coordination and of the polymerization degree of the WO(x) domain. From theoretical calculations the observed behavior in the WO(x)-ZrO(2) system is explained: the Brønsted acidity increases while the Lewis acidity decreases as the W centers go from tetrahedral to octahedral coordination and as the condensation degree of the WO(x) domain increases. Our results also indicate that not all the Brønsted sites in the WO(x) domains are equally acid, and that as the W load increases the most acid sites decrease in number due to the condensation process. This finding also means a decrease on the average acidity per H site. Additionally, our results suggest that for surface densities in the 4-7 W nm(-2) range, mainly dimeric-tungstate species are present. A maximum in Brønsted acidity was observed for a W surface density about 7 W nm(-2).

One-step synthesis of Mn3O4 nanoparticles: structural and magnetic study.

One-step room-temperature synthesis of nanocrystalline Mn3O4 hausmannite, without heating posttreatment, was carried out from a simple dissolution of manganese(II) acetate in a mixture of N,N'-dimethylformamide (DMF) and water. Homogeneous nanocrystals like rods were obtained, with an average width and length of 6.6+/-1.2 nm and 17.4+/-4.1 nm, respectively, and a preferential growth along the 001 direction. Magnetization measurements on a powdered sample showed ferrimagnetic behavior at low temperatures. Under zero-field cooling (ZFC) measurement at 100 Oe, the observed blocking temperature (T(B)) was 37 K.

New insights on molybdenum suboxide: nature of carbons in isomerization reactions.

MoO3 transformations under isomerization process conditions were studied. The products obtained after different times under stream (H2/n-heptane mixture, 18.5 bar, at 370 degrees C) were characterized by X-ray diffraction, Raman spectroscopy, thermal analysis, and high-resolution transmission electron microscopy (HRTEM). Theoretical quantum calculations were carried out with the aim of understanding the paradox of the real active phase in isomerization reactions. Theoretical calculations predict the existence of a metallic-like MoO phase with a structure that matches the X-ray diffraction experimental results. From experimental and simulated HRTEM images it was possible to identify the presence of small MoO cubic crystallites inside MoOx matrix phases. These results also support the previously proposed idea that isomerization reactions take place as a result of the existence of a bifunctional catalyst. The Raman and thermo-programmed oxidation (TPO) analyses show the existence of at least two types of carbonaceous deposits which tend to increase its ordering with the increase of time under stream. The carbon K edge in electron energy loss spectroscopy (EELS) of a sample after 24 h under stream shows that these carbonaceous deposits consist of a mixture of sp2- and sp3-hybridized carbons.

Synthesis and characterization of RuS2 nanostructures.

Small naked ruthenium sulfide nanoparticles (NPs) with narrow size distribution (2.5 +/- 0.4 nm of diameter) were synthesized in DMSO colloidal dispersions, under mild reaction conditions and using commercial RuCl3 as precursor. To test the chemical reactivity with soft and hard bases, fresh presynthesized RuS2 colloids were mixed with triethylamine (N(Et)3) and ammonium tetrathiomolybdate ((NH4)2MoS4) dimethyl sulfoxide solutions. Naked N(Et)3 and [MoS4](2-)-capped RuS2 nanoparticle colloids were characterized using UV-visible electronic absorption and emission spectroscopies and high-resolution transmission electron microscopy (HR-TEM). It has also been shown that capped RuS2-[MoS4]2- nanoparticles yield MoO3 crystalline matrix by means of HR-TEM experiments. The emission spectra of RuS2 and N(Et)3-RuS2 dispersions show that both nanosized materials have strong fluorescence. The existence of the ruthenium precursor species in solution was established by cyclic voltammetry. Moreover, naked RuS2 NPs were mixed with a chemical mixture with composition similar to gasoline (dibenzothiophene (Bz2S, 400 ppm), hexane, and toluene (55:45% v/v)). The reaction mixture consisted of two phases; in the polar phase, we found evidences of a strong interaction of Bz2S and toluene with the naked RuS2 NPs. We have also obtained self-organized thin films of capped N(Et)3- and RuS2-[MoS4]2- nanoparticles. In both cases, the shape and thickness of the resulting thin films were controlled by a dynamic vacuum procedure. The thin films have been characterized by atomic force microscopy, scanning electron microscopy, HR-TEM, energy dispersion spectroscopy, X-ray diffraction, and absorbance and fluorescence spectroscopies.

Synthesis of ZnO nanoparticles on a clay mineral surface in dimethyl sulfoxide medium.

Nanocrystalline ZnO particles have been prepared with different methods using zinc cyclohexanebutyrate as precursor in dimethyl sulfoxide (DMSO) medium via alkaline hydrolysis. A series of preparations were carried out in the presence of layered silicates (kaolinite and montmorillonite). It was revealed by different measurement techniques that the presence of the clay minerals has a stabilization influence on the size of the ZnO nanocrystals. UV-vis absorption spectra show a blue shift when the nanoparticles are prepared in the presence of the clay minerals. The average particle diameters calculated from the Brus equation ranged from 2.6 to 13.0 nm. The UV-vis spectra of the synthesized nanoparticles did not show any red shift after 2-3 days, demonstrating that stable ZnO nanocrystals are present in the dispersions. The presence of the ZnO nanoparticles was also proven by fluorescence measurements. A number of the nanoparticles are incorporated into the interlamellar space of the clays, and an intercalated structure is formed as proven by X-ray diffraction (XRD) measurements. The size of the nanoparticles in the interlamellar space is in the range of 1-2 nm according to the XRD patterns. Transmission electron microscopy and high-resolution transmission electron microscopy investigations were applied to determine directly the particle size and the size distribution of the nanoparticles.