D.H. Piva

Synthesis by coprecipitation of india-stabilized zirconia and codoping with MoO3, WO3, TaO2.5, or NbO2.5 for application as thermal barrier coatings

Coprecipitation synthesis of nanocrystalline india-stabilized zirconia with high surface area and codoping with MoO3, WO3, TaO2.5, or NbO2.5 is reported. The concentration of codopants was defined by the charge-compensating mechanism. Ethanol washing followed by azeotropic distillation and freeze drying were compared as dehydration techniques for the gels. As determined by XRD and Raman scattering, 9 mol% of InO1.5 plus charge-compensating dopants is sufficient to completely stabilize the high-temperature tetragonal phase of zirconia. The effect of alloying hexavalent and pentavalent oxides was secondary compared to the InO1.5 concentration in the retention of the tetragonal structure. Improved specific surface area of 106.1 m2 g‒1 and crystallite size between 8 and 9 nm were achieved through ethanol washing and subsequent azeotropic distillation even after calcination at 600 oC. This result is attributed to the effect of the incorporation of ethoxy and butoxy groups after the treatment of the gels in organic medium, as detected by FT-IR spectroscopy and DSC/TG.

Conductivity dynamics of metallic-to-insulator transition near room temperature in normal spinel CoFe2O4 nanoparticles

Herein, we report the preparation of minute CoFe2O4 nanoparticles which exhibit an unusually normal spinel characteristic and a metallic behavior at room temperature that has not yet been reported in the literature for such materials. A study on the synthesis and characterization of these nanoparticles and the effect of cation distribution on electrical properties was conducted. A xerogel was treated at 300 °C for 20 hours and the as-synthesized powder was structurally and electrically characterized. X-ray diffraction studies indicate that the synthesis pathway was successful in producing crystalline nanoparticles under such mild conditions. TEM images demonstrate that CoFe2O4 consists of monodispersed nanocrystalline particle aggregates with a particle size of ∼10 nm. Mossbauer spectroscopy investigation shows a normal spinel configuration, which is highly unusual for cobalt ferrite. Impedance analyses confirm that the material has a metallic characteristic at temperatures close to room temperature which arises as a consequence of octahedral site occupancy. Above 100 °C, the material displays a metallic-to-insulator transition, which has been related to the predominant OLPT conduction mechanism. An endothermic peak in the DSC curve indicates the occurrence of a structural transition which was associated with the Verwey-type reordering of charged metallic atoms.

Combating pathogens with Cs2.5H0.5PW12O40 nanoparticles: a new proton-regulated antimicrobial agent

The transfer of pathogens from contaminated surfaces to patients is one of the main causes of health care-associated infections (HCAIs). Cases of HCAIs due to multidrug-resistant organisms have been growing worldwide, whereas inorganic nano-antimicrobials are valuable today for the prevention and control of HCAIs. Here, we present a cesium salt of phosphotungstic heteropolyacid (Cs2.5H0.5PW12O40) as a promising nanomaterial for use in antimicrobial product technologies. This water-insoluble Keggin salt exhibits a broad biocide spectrum against Gram-positive and Gram-negative bacteria, yeasts, and filamentous fungi even under dark conditions. The Cs2.5H0.5PW12O40 nanoparticles (NPs) act as a proton-regulated antimicrobial whose activity is mediated on the release of hydronium ions (H3O+), yielding an in situ acidic pH several units below those tolerable by most of the fungal and bacterial nosocomial pathogens.

Acidic Dressing Based on Agarose/Cs2.5H0.5PW12O40 Nanocomposite for Infection Control in Wound Care

Regulation of wound pH from alkaline to acidic is a simple and powerful approach to reduce wound microbial colonization and infection. Here, we present a nanocomposite material possessing intrinsic acidic surface pH as an innovative antimicrobial wound dressing. This material comprises an agarose matrix nanocomposite containing nanoparticles (NPs) of the cesium salt of phosphotungstic heteropolyacid (Cs2.5H0.5PW12O40). Self-supporting films were prepared by a casting method incorporating 5-20 wt % Cs2.5H0.5PW12O40 NPs into the matrix. Films are flexible with tensile strengths between 28.55 and 32.15 MPa and exhibit broad biocidal activity against neutralophilic pathogens, including Gram-positive bacteria, Gram-negative bacteria, yeast, and filamentous fungi. The nano-antimicrobial Cs2.5H0.5PW12O40 functions as an efficient and self-controlled proton delivery agent that lowers the surface pH of the nanocomposites to the range 7.0 > pH ≥ 3.0. Nanocomposite films containing 20 wt % Cs2.5H0.5PW12O40 NPs presented a surface pH of 3.0 and highest antimicrobial activity. Using quantitative reverse transcription polymerase chain reaction, we demonstrated that the antimicrobial mechanism of the nanocomposites is acid-induced because of the transcriptional induction of glutamate-dependent acid resistance genes in Escherichia coli. Additionally, nanocomposite films do not damage skin according to an in vivo rabbit skin model with no derived edema or erythema. The wound care safety of this material is due to low release of heavy metal heteropolyanions ([PW12O40]3-), no nanoparticle leaching, and proton controlled release resulting in nonirritating acid levels for human skin models.

Influence of oxidant and fuel on the powder characteristics of LiNbO3 synthesized by combustion method

Lithium niobate (LiNbO3) is widely recognized as a promising material for replacing lead-based piezoelectric ceramics. Although the LiNbO3 synthesis by combustion method has been investigated with particular attention recently, the influence of oxidants and different fuels’ sources on the synthesized powders has not yet been thoroughly studied. In this work we investigate the influence of urea and maleic hydrazide as fuels and ammonium nitrate as an oxidant on the powder characteristics of LiNbO3 synthesized by combustion method. In addition, powder characteristics and sinterability of powders prepared by combustion method are compared with those of powders prepared by solid-state reaction. The results show that the second phase LiNb3O8 was detected only when an oxidant agent was used in the synthesis process. Among all combustion reactions, the powders prepared with excess of urea presented better final characteristics. As a result, the sintering temperature for LiNbO3 powders prepared by combustion method was appreciably lowered when compared with those prepared by solid-state reaction.

Iron-Rich Glass-Ceramics Obtained from Mill Scale

Mill scale contains high amounts of iron and it is classified as residue Class 2 – Not Inert (ABNT NBR 10.004:2004). Considering its availability, this study aimed to investigate glass-ceramics from this residue focused on its valorization. The influence of lithium oxide and zirconia was also evaluated. Six formulations were melted at 1350 °C and obtained frits were wet ground, dried and characterized: X-ray fluorescence, X-ray diffraction, thermal differential analysis and dilatometry. Pressed bodies were dried and heat treated at 950 °C. After, crystallized samples were characterized by different techniques: X-ray diffraction, apparent and theoretical density, coefficient of thermal expansion, hardness and bending strength. Results showed that lithium oxide and zirconia significantly influenced the thermal and structural behavior of obtained glass-ceramics.