Análise tribo-termodinâmica da aplicação de nanopartículas de Al2O3 como aditivo lubrificante em compressor hermético de refrigeração

The thermodynamic performance of a refrigeration system can be improved by reducing the compression work by a particular technique for a specific heat removal rate. This study examines the effect of small concentrations of Al2O3 (50 nm) nanoparticles dispersion in the mineral oil based lubricant on the: viscosity, thermal conductivity, and lubrication characteristics as well as the overall performance (based on the Second Law of Thermodynamics) of the refrigerating system using R134a or R600a as refrigerants. The study looked at the influences of variables: i) refrigerant charge (100, 110, 120 and 130 g), ii) rotational speed of the condenser blower (800 and 1100 RPM) and iii) nanoparticle concentration (0.1 and 0.5 g/l) on the system performance based on the Taguchi method in a matrix of L8 trials with the criterion "small irreversibility is better”. They were carried pulldown and cycling tests according to NBR 12866 and NBR 12869, respectively, to evaluate the operational parameters: on-time ratio, cycles per hour, suction and discharge pressures, oil sump temperature, evaporation and condensation temperatures, energy consumption at the set-point, total energy consumption and compressor power. In order to evaluate the nanolubricant characteristics, accelerated tests were performed in a HFRR bench. In each 60 minutes test with nanolubricants at a certain concentration (0, 0.1 and 0.5 g/l), with three replications, the sphere (diameter 6.00 ± 0.05 mm, Ra 0.05 ± 0.005 um, AISI 52100 steel, E = 210 GPa, HRC 62 ± 4) sliding on a flat plate (cast iron FC200, Ra <0.5 ± 0.005 um) in a reciprocating motion with amplitude of 1 mm, frequency 20 Hz and a normal load of 1,96 N. The friction coefficient signals were recorded by sensors coupled to the HFRR system. There was a trend commented bit in the literature: a nanolubricant viscosity reduction at the low nanoparticles concentrations. It was found the dominant trend in the literature: increased thermal conductivity with increasing nanoparticles mass fraction in the base fluid. Another fact observed is the significant thermal conductivity growth of nanolubricant with increasing temperature. The condenser fan rotational speed is the most influential parameter (46.192%) in the refrigerator performance, followed by R600a charge (38.606%). The Al2O3 nanoparticles concentration in the lubricant plays a minor influence on system performance, with 12.44%. The results of power consumption indicates that the nanoparticles addition in the lubricant (0.1 g/L), together with R600a, the refrigerator consumption is reduced of 22% with respect to R134a and POE lubricant. Only the Al2O3 nanoparticles addition in the lubricant results in a consumption reduction of about 5%.

Influência da interação dipolar nas fases magnéticas de nanopartículas esféricas com estrutura núcleo@camada

Bi-magnetic core@shell nanoparticle has attracted attention several researchers because great applicability that they offer. The possibility of combining different functionalities of magnetic materials make them a key piece in many areas as in data processing permanent magnets and biomagnetics sistems. These nanoparticles are controlled by intrinsic properties of the core and shell materials as well as the interactions between them, besides size and geometry effects. Thus, it was developed in this thesis a theoretical study about dipolar interaction contribution between materials different magnetic properties in bi-magnetic core@shell nanoparticles conventional spherical geometry. The materials were analyzed CoFe2O4, MnFe2O4 e CoFe2 in various combinations and sizes. The results show that the impact of the core dipole field in the shell cause reverse magnetization early its, before of the core, in nanoparticle of CoFe2O4(22nm)@CoFe2(2nm), thereby causing a decrease coercivity field of 65% in comparection with simple nanoparticle of CoFe2O4 (HC=13.6 KOe) of same diameter. The large core anisotropy in conventional nanoparticle makes it the a stable dipolar field source in the shell, that varies length scale of the order of the core radius. Furthermore, the impact of dipolar field is greatly enhanced by the geometrical constraints and by magnetics properties of both core@shell materials. In systems with core coated with a thin shell of thickness less than the exchange length, the interaction interface can hold reversal the shell occurring an uniform magnetization reversal, however this effect only is relevant on systems where the dipole field effects is weak compared with the exchange interaction.

Influência da interação dipolar nas fases magnéticas de nanopartículas esféricas com estrutura núcleo@camada

Bi-magnetic core@shell nanoparticle has attracted attention several researchers because great applicability that they offer. The possibility of combining different functionalities of magnetic materials make them a key piece in many areas as in data processing permanent magnets and biomagnetics sistems. These nanoparticles are controlled by intrinsic properties of the core and shell materials as well as the interactions between them, besides size and geometry effects. Thus, it was developed in this thesis a theoretical study about dipolar interaction contribution between materials different magnetic properties in bi-magnetic core@shell nanoparticles conventional spherical geometry. The materials were analyzed CoFe2O4, MnFe2O4 e CoFe2 in various combinations and sizes. The results show that the impact of the core dipole field in the shell cause reverse magnetization early its, before of the core, in nanoparticle of CoFe2O4(22nm)@CoFe2(2nm), thereby causing a decrease coercivity field of 65% in comparection with simple nanoparticle of CoFe2O4 (HC=13.6 KOe) of same diameter. The large core anisotropy in conventional nanoparticle makes it the a stable dipolar field source in the shell, that varies length scale of the order of the core radius. Furthermore, the impact of dipolar field is greatly enhanced by the geometrical constraints and by magnetics properties of both core@shell materials. In systems with core coated with a thin shell of thickness less than the exchange length, the interaction interface can hold reversal the shell occurring an uniform magnetization reversal, however this effect only is relevant on systems where the dipole field effects is weak compared with the exchange interaction.

Rugosidade superficial e adesão bacteriana em compósitos com nanopartículas após acabamento e polimento

Objective: To evaluate in vitro the surface roughness and bacterial adhesion of nanoparticle composites, after being subjected to different finishing and polishing systems. Materials and Methods: 66 specimens were prepared, and 30 with Filtek Z350 XT (3M ESPE, USA) and 30 with the resin IPS Empress Direct (Ivoclar Vivadent, USA), divided into 6 groups (n = 10 ). Six specimens were prepared for analysis in scanning electron microscopy (SEM) .Each kind of resin was subjected to finishing and polishing systems: Sof-Lex Pop-On discs (3M ESPE, USA) and AstropolTM system (Ivoclar Vivadent , USA), featuring the experimental group. The control group did not undergo any kind of finishing and polishing technique. The average roughness (Ra) in both groups was measured using a roughness in the setting of 0.25 mm (cut off) and surface images obtained with photomicrographs taken with a scanning electron microscope (SEM) magnified 500 times. Bacterial adherence was evaluated by determining the absorbance (OD) of the suspension of adhered cells by spectrophotometer at 570 nm. The results were submitted for analyzed with 2-way ANOVA at α=.05 and Tukey multiple comparison tests. Results: Statistically significant differences were found between the groups in terms of roughness and bacterial adhesion. Filtek Z350 XT for resin were no differences between the tested finishing and polishing systems, where the system of lowest surface roughness was the Sof-Lex Pop-On. To the resin IPS Empress Direct, the finishing and polishing system Astropol, had lower results of surface roughness. As for bacterial adhesion, the lowest optical density value for Filtek Z350 XT was for the group that used the finishing and polishing system Sof-Lex Pop-On and the resin IPS Empress Direct the group that used the Astropol system. In addition, there was a positive correlation between surface roughness and bacterial adhesion on polished surfaces (r = 0.612) Conclusions: surface roughness and bacterial adhesion are closely related. The finishing and polishing Sof-Lex Pop-On system is more suitable for nanoparticulate Filtek Z350 XT and the finishing and polishing system Astropol for resin nanohíbrida IPS Empress Direct.

Studio di stati fotoeccitati in nanoparticelle di V-TiO2 mediante scattering inelastico risonante di raggi X

La TiO2 è uno dei materiali più studiati degli ultimi decenni. I motivi sono da ricercarsi nelle sue numerose applicazioni, possibili in molti campi come dispositivi fotovoltaici, depurazione da agenti inquinanti o filtraggio di raggi UV. Per le celle elettrochimiche in particolare, il biossido di titanio offre molti vantaggi, ma non è privo di ostacoli. Il limite principale è lo scarso assorbimento dello spettro visibile, dovuto all’energy gap elevato (circa 3.2 eV). La ricerca da diversi anni si concentra sul tentativo di aumentare l’assorbimento di luce solare: promettenti sono i risultati raggiunti grazie alla forma nanoparticellare della TiO2, che presenta proprietà diverse dal materiale bulk. Una delle strategie più studiate riguarda il drogaggio tramite impurità, che dovrebbero aumentare le prestazioni di assorbimento del materiale. Gli elementi ritenuti migliori a questo scopo sono il vanadio e l’azoto, che possono essere usati sia singolarmente che in co-doping. In questo lavoro abbiamo realizzato la crescita di nanoparticelle di V-TiO2, tramite Inert Gas Condensation. La morfologia e la struttura atomica sono state analizzate attraverso microscopia a trasmissione, analizzandone la mappe tramite image processing. Successivamente abbiamo studiato le proprietà di assorbimento ottico dei campioni, nello spettro visibile e nel vicino ultravioletto, attraverso il metodo della riflettanza diffusa, determinando poi il bandgap tramite Tauc Plot. L’esperimento centrale di questo lavoro di tesi è stato condotto sulla beamline ID26 dell’European Synchrotron Radiation Facility, a Grenoble. Lì, abbiamo effettuato misure XANES, allo scopo di studiare gli stati fotoeccitati del materiale. L’eccitazione avveniva mediante laser con lunghezza d’onda di 532 nm. Tramite gli spettri, abbiamo analizzato la struttura locale e lo stato di ossidazione del vanadio. Le variazioni indotta dal laser hanno permesso di capire il trasferimento di carica e determinare la vita media.

Toxicity evaluation of TiO2 Nanoparticles embedded in consumer products

Lo studio è orientato alla determinazione dei rischi tossici posti dalle nanoparticelle di diossido di titanio rilasciate in ambiente marino. L’organismo modello utilizzato per questo studio è la diatomea Thalassiosira pseudonana, la quale è stata scelta per la sua semplicità biologica unita alla fondamentale rilevanza nella catena alimentare e nell’ecosistema marino. Oltre alle nanoparticelle prodotte industrialmente, questo studio ha lo scopo di determinare e confrontare la tossicità delle nanoparticelle utilizzate in alcuni prodotti di cura personale (in particolare crema solare e dentifricio), estraendole direttamente da essi. I nostri risultati mostrano una notevole ridondanza nel legame tra la natura (il tipo) delle nanoparticelle e l’inibizione della normale crescita delle diatomee, che supera la correlazione con tutti gli altri parametri monitorati (concentrazione di nanoparticelle, tempo di esposizione, pH, carica superficiale e dimensione delle particelle stesse), sebbene gli altri parametri risultino direttamente legati agli effetti inibitori. Tali risultati suggeriscono un’intensificazione della ricerca nell’ambito delle nanotecnologie, orientata allo sviluppo di nanomateriali “sostenibili”, ovvero dei quali sono note le potenzialità di impiego, ma anche gli aspetti negativi, che possono di conseguenza essere monitorati con maggiore consapevolezza.

Caracterização e avaliação da atividade fotocatalítica de catalisadores baseados no TiO2, sintetizados mediante hidrólise em uma mistura de solventes

This study involved the synthesis of photocatalysts based on titanium dioxide (TiO2). The photocatalysts were synthesized by the sol-gel method using three different proportions of acetone (25%, 50% and 75% v/v) in water/acetone mixtures, in order to control the hydrolysis of the precursor of titanium (titanium tetraisopropoxide). Aiming to investigate the structural, morphological and electronic changes provoked by the use of the solvent mixtures, different methodologies were used to characterize the oxides, such as X-ray diffraction (XRD), RAMAN spectroscopy, UV-Vis diffuse reflectance spectroscopy, and measurements of specific surface area (BET). XRD combined to RAMAN analyses revealed that the products are two-phase highly crystalline oxides involving anatase as main phase and brookite. Besides, the refined XRD using the method of Rietveld demonstrated that the presence of acetone during the synthesis influenced in the composition of the crystalline phases, increasing the proportion of the brookite phase between 13 and 22%. The band gap energy of these oxides practically did not suffer changes as function of the synthesis conditions. As shown by the isotherm, these photocatalysts are mesoporous materials with mean diameter of pores of 7 nm and approximately 20% of porosity. The surface area of the oxides prepared by hydrolysis in presence of acetone was 12% higher compared to the bare oxide. After characterized, these oxides had their photocatalytic activities evaluated by photodegradation of the azo dyes Ponceau 4R (P4R), Tartrazine (TTZ) and Reactive Red 120 (RR120), and also by the ability to mediate the photocatalytic production of hydrogen. Using the most efficient photocatalyst, the mineralization achieved for the dyes P4R, RR120 and TTZ was of respectively 83%, 79% and 56% in 120 minutes of reaction, while the discoloration of P4R e RR120 reached 100% and 94% for TTZ. In addition, the same photocatalyst in the presence of 0.5% w/w of Platinum and suspended in a 5:1 v/v water/methanol mixture, produced 56 mmol of gaseous hydrogen in five hours of experiment, corresponding to a specific rate of hydrogen production of 139.5 mmol h-1 g-1.

Síntesis de Fosfatos de Calcio en Presencia de Surfactantes Iónicos, Fosfolípidos y Nanopartículas de Sílice Mesoporosa para Controlar la Mesoestructura de la Biocerámica

Actualmente, hay un gran interés en el desarrollo de nuevos biomateriales debido a su enorme contribución a las demandas de una sociedad cada vez más envejecida que necesita alternativas para el tratamiento del cáncer o las enfermedades de los tejidos duros, Los primeros biomateriales se desarrollaron para que fuesen lo más bioinertes posible, A partir de los años 70's y 80's del siglo XX, comenzaron a investigarse biomateriales bioactivos o biodegradables, incluyendo algunos fosfatos de calcio y los vidrios bioactivos, En la actualidad, el interés se enfoca hacia la síntesis de biomateriales con mesoestructura controlada y funcionalizados para mejorar y adaptar su comportamiento en el cuerpo, Por otra parte, para aplicaciones de ingeniería de tejido óseo, los biomateriales se procesan como andamios 3D capaces de ser funcionalizados con señales bioquímicas y células. Asimismo, algunas estrategias recientes para la terapia del cáncer se basan en nanopartículas mesoporosas que son capaces de transportar drogas o material genético cuando se inyectan en el torrente sanguíneo, sin ser retiradas de la circulación por los macrófagos...

Probing the Role of Thermally Reduced Graphene Oxide in Enhancing Performance of TiO2 in Photocatalytic Phenol Removal from Aqueous Environments

We thank the INSA-RSE bilateral exchange programme for financial assistance (PD) and the Petroleum Technology Development Fund (PTDF, Nigeria) for the award of PhD scholarship, as well as Abubakar Tafawa Balewa University, Bauchi-Nigeria for the granted fellowship (H.A).

Probing the Role of Thermally Reduced Graphene Oxide in Enhancing Performance of TiO2 in Photocatalytic Phenol Removal from Aqueous Environments

We thank the INSA-RSE bilateral exchange programme for financial assistance (PD) and the Petroleum Technology Development Fund (PTDF, Nigeria) for the award of PhD scholarship, as well as Abubakar Tafawa Balewa University, Bauchi-Nigeria for the granted fellowship (H.A).

Lead oxide-modified TiO2 photocatalyst: tuning light absorption and charge carrier separation by lead oxidation state

Modification of TiO2 with metal oxide nanoclusters such as FeOx, NiOx has been shown to be a promising approach to the design of new photocatalysts with visible light absorption and improved electron–hole separation. To study further the factors that determine the photocatalytic properties of structures of this type, we present in this paper a first principles density functional theory (DFT) investigation of TiO2 rutile(110) and anatase(001) modified with PbO and PbO2 nanoclusters, with Pb2+ and Pb4+ oxidation states. This allows us to unravel the effect of the Pb oxidation state on the photocatalytic properties of PbOx-modified TiO2. The nanoclusters adsorb strongly at all TiO2 surfaces, creating new Pb–O and Ti–O interfacial bonds. Modification with PbO and PbO2 nanoclusters introduces new states in the original band gap of rutile and anatase. However the oxidation state of Pb has a dramatic impact on the nature of the modifications of the band edges of TiO2 and on the electron–hole separation mechanism. PbO nanocluster modification leads to an upwards shift of the valence band which reduces the band gap and upon photoexcitation results in hole localisation on the PbO nanocluster and electron localisation on the surface. By contrast, for PbO2 nanocluster modification the hole will be localised on the TiO2 surface and the electron on the nanocluster, thus giving rise to two different band gap reduction and electron–hole separation mechanisms. We find no crystal structure sensitivity, with both rutile and anatase surfaces showing similar properties upon modification with PbOx. In summary the photocatalytic properties of heterostructures of TiO2 with oxide nanoclusters can be tuned by oxidation state of the modifying metal oxide, with the possibility of a reduced band gap causing visible light activation and a reduction in charge carrier recombination.

Continuous flow gas phase photoreforming of methanol at elevated reaction temperatures sensitised by Pt/TiO2

Gas phase photoreforming of methanol using a Pt/TiO2 photocatalyst has been performed under flow conditions at elevated temperatures. Comparing the activity of the reforming process as a function of temperature under dark and irradiated conditions shows a significant enhancement in the rate of H2 production using the photo-assisted conditions at temperatures between 100-140 °C. At higher temperatures, the effect of irradiation is small with the process dominated by the thermal process. Deactivation of the catalyst was observed under irradiation but the catalyst was easily regenerated using an oxygen treatment at 120 °C. Diffuse Reflectance Infra-red Fourier Transform Spectroscopy (DRIFTS) showed that the activity of the catalyst could be correlated with the presence of the photogenerated trapped electrons. In addition, lower amounts of CO adsorbed on Pt, compared to those observed in the dark reaction, were found for the UV-irradiated systems. It is proposed that CO and adsorbed intermediates, such as formate, can act as inhibitors in the photoreforming process and this is further supported by the observation that, before and after the regeneration process in O2, the CO and surface adsorbed organic intermediate products are removed and the activity is recovered.

Mechanochemical synthesis of TiO2/NiFe2O4 magnetic catalysts for operation under RF field

Composite NiFe2O4–TiO2 magnetic catalysts were prepared by mechanochemical synthesis from a mixture of titania supported nickel ferrite nanoparticles and P25 titania (Evonic). The former provides fast and efficient heating under radiofrequency field, while the latter serves as an active catalyst or catalyst support. The highest heating rate was observed over a catalyst prepared for a milling time of 30 min. The catalytic activity was measured over the sulfated composite catalysts in the condensation of aniline and 3-phenylbutyric acid in a stirred tank reactor and in a continuous RF heated flow reactor in the 140–170 °C range. The product yield of 47% was obtained over the sulfated P25 titania catalyst in the flow reactor.

Mechanochemical solvent-free synthesis of Sn-β Zeolite and Ag2O/TiO2 catalysts

Preparations of heterogeneous catalysts are usually complex processes that involve several procedures as precipitation, crystallization and hydrothermal treatments. This processes are really dependent by the operative conditions such as temperature, pH, concentration etc. Hence the resulting product is extremely affected by any possible variations in these parameters making this synthesis really fragile. With the aim to improve these operations has been decided to exploit a new possible strong environment-respectful process by mechanochemical treatment, which permits to carry out solvent free-solvent synthesis exploiting the Mixer Mill MM400 (Retsch) in order to have reproducible results. Two different systems have been studied in this kind of synthesis: a tin β -zeolite tested in a H-trasnfer reaction of cyclohexanone and a silver on titania catalyst used in the fluorination of 2,2 dimethyl glucaric acid. Each catalyst has been characterized by different techniques in order to understand the transformations involved in the mechanochemical treatment.

Effet du greffage de TiO2 à la surface de fibres de lin sur les propriétés mécaniques d'un composite PLA/fibre de lin longues unidirectionnelles

Les matériaux composites sont utilisés dans beaucoup de domaines pour leurs propriétés mécaniques spécifiques, leur mise en forme facile et leur bas coût. Cependant, lorsque les composites pétro-sourcées sont en fin de vie, le traitement des déchets a un fort impact environnemental. C’est pour cette raison que les industriels se tournent vers des matériaux bio-sourcés. Ils souhaitent ainsi abaisser le coût des matières premières mais aussi se donner une image plus « verte » grâce à l’utilisation de matériaux renouvelables et/ou compostables. Le projet présenté s’inscrit dans dans cette optique où il est question d’élaborer de nouveaux composites à renfort et matrices bio-sourcés et tout particulièrement des composites fibre de lin/acide polylactique (PLA). Ces derniers sont généralement appelés bio-composites. L’originalité de cette étude réside dans le traitement des fibres de lin afin de les compatibilité avec la matrice PLA. Le traitement consiste au greffage de dioxyde de titane sur la surface de fibres de lin fonctionnalisée par oxydation au TEMPO. Ces fibres longues sont ensuite utilisées comme renfort sous forme de tissu unidirectionnel dans la matrice PLA. Le comportement mécanique en traction, flexion et la résistance à l’impact de ces biocomposites sont étudiés afin d’analyser l’influence du traitement des fibres sur leur performances.