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Selective coatings are produced with high absorption in the ultraviolet/visible range, composed of ilmenite deposited on stainless steel substrates and aluminum substrates, using the cathodic cage plasma nitriding/deposition technique, for application in solar thermal absorbers. Ilmenite was initially characterized by means of X-ray fluorescence, X-ray diffractometry and thermal analysis. The coatings produced were optically characterized in the UV/Vis range, the microstructural evaluation of coatings was by scanning electron microscopy and data on the roughness parameters of the films produced were obtained by optical profilometry. Uniform selective surfaces with high solar absorbance (87 %) were obtained in the ilmenite samples deposited on stainless steel substrate.

Modern bio-chemical sensors rely on functional interfacial architectures with well-defined structural nano-motifs over a physical transducer. Gold-coated interfaces are of particular interest for their desirable chemical (functionalization) and optical (plasmonic) properties. Here we investigate the cleaning and polishing of polycrystalline gold films in preparation of advanced surface functionalization. We focus on soft wet chemical etching to decrease the small-scale roughness commonly observed after evaporation or sputtering of gold. We show that optimized surfaces are obtained by etching in solutions of hydrochloric acid and hydrogen peroxide. We systematically quantify the films wettability, surface nano-topography, UV-VIS spectrum and the electrochemical and Surface Plasmon Resonance (SPR) changes throughout the etching process. Optimal results are obtained by etching with a HCl(37%):H2O2(30%):H2O mixture, with a volume ratio of reagents 3:3:94 during 15-20 minutes at room temperature for the main step. This reduces by a factor two the root-mean-square roughness, removes contaminants, increases hydrophilicity and modifies the gold surface by Au(Cl)x complexes. Significantly, the resulting the surface is hydrophilic enough to prevent globular proteins such as HSA to unfold upon deposition at concentrations more than ~1 mg/mL. Our protocol offers a simple, reliable and rapid method for the preparation of gold surface in view of further functionalization including the binding of receptor layers and various micro- and nanostructures required in chemical and biochemical sensing.

Control of BO6 octahedral rotations at the heterointerfaces of dissimilar ABO3 perovskites has emerged as a powerful route for engineering novel physical properties. However, its impact length scale is constrained at 2–6 unit cells close to the interface and the octahedral rotations relax quickly into bulk tilt angles away from interface. Here, a long‐range (up to 12 unit cells) suppression of MnO6 octahedral rotations in La0.9Ba0.1MnO3 through the formation of superlattices with SrTiO3 can be achieved. The suppressed MnO6 octahedral rotations strongly modify the magnetic and electronic properties of La0.9Ba0.1MnO3 and hence create a new ferromagnetic insulating state with enhanced Curie temperature of 235 K. The emergent properties in La0.9Ba0.1MnO3 arise from a preferential occupation of the out‐of‐plane Mn d 3z 2−r 2 orbital and a reduced Mn eg bandwidth, induced by the suppressed octahedral rotations. The realization of long‐range tuning of BO6 octahedra via superlattices can be applicable to other strongly correlated perovskites for exploring new emergent quantum phenomena.

Up to now, plasma electrolytic oxidation (PEO) has been either produced direct current or ultra-low frequency (< 1 kHz) pulsed discharge using high concentration alkaline-silicate electrolytic (Na2SiO3 > 8 g.L-1 with presence of KOH). In order to contribute to these studies, the effect of current pulse width and time duration was investigated using diluted silicate electrolytic (Na2SiO3 2 g.L-1) and high pulse frequencies (> 1 kHz). The PEO process was performed on pure aluminum to try to explain how the phases composing the coatings are formed and distributed over the treatment time. For this, was made in situ monitoring using optical emission spectroscopy (OES) coupled with CCD camera. The crystalline phases evolution in the sample surface was investigated using grazing incidence X-ray diffraction (GIXRD). Regarding the evolution of ceramic phases, it is possible to verify that, internally, the predominant phase is rhombohedral α-Al2O3 but, superficially, the predominant phase is cubic γ-Al2O3. It was verified the presence of Si on the borders of the pores or in proximity to cracks, especially in the treatments with higher pulse width. SEM analysis shows a reduction of the superficial porosity and an increase in coating thickness with pulse width and treatment time.

Epitaxial strain provides important pathways to control the magnetic and electronic states in transition-metal oxides. However, the large strain is usually accompanied by a strong reduction of the oxygen-vacancy formation energy, which hinders the direct manipulation of their intrinsic properties. Here, using a postdeposition ozone annealing method, we obtain a series of oxygen stoichiometric SrCoO3 thin films with the tensile strain up to 3.0%. We observe a robust ferromagnetic ground state in all strained thin films, while interestingly the tensile strain triggers a distinct metal-to-insulator transition along with the increase of the tensile strain. The persistent ferromagnetic state across the electrical transition therefore suggests that the magnetic state is directly correlated with the localized electrons, rather than the itinerant ones, which then calls for further investigation of the intrinsic mechanism of this magnetic compound beyond the double-exchange mechanism.

This research used the "cathodic cage (CC)" technique for TiO2 film deposition on duplex stainless steel substrate. This technique uses a multiple hollow cathode effect. Duplex stainless steel substrates were treated at temperatures of 300°C, 350°C and 400°C, giving a temperature value ratio (Ts/Tm) of 0.27 to 0.31 (Ts being the substrate temperature and Tm the melting temperature of the deposited material). Treatment times of 1, 2 and 4 hours were administered and polycrystalline TiO2 films were obtained. The films were analyzed by optical microscopy (OM), X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). During analysis, the formation of uniform films and the possibility of controlling the TiO2 phase were observed. It was also shown that with longer treatment times and higher temperatures the rutile phase predominates. For treatment times of 4 hours at all temperatures, the rutile structure was present. With treatment times of less than 4 hours, anatase was present. In addition, results showed that this simple, low cost technique can be an alternative method for depositions of TiO2 films, with the advantage of high levels of control over porosity, thickness and phase composition (anatase and rutile).

Crystallization of salts in droplets of hypersaline solution placed on a glass slide was monitored and evaluated under controlled conditions of temperature and humidity. Pulsed corona discharge (PCD) was applied over sessil droplets on a glass surface, and its effect in the crystallization is demonstrated for the first time. These results were compared with natural evaporation. Under natural evaporation, crystals are firstly formed on surface, near edges of the drop and grow towards the center, eventually acquiring a pyramidal morphology. Under PCD, a Taylor cone is formed between electrode and droplet surface and then, 4 s after the beginning of the discharge, small crystals were formed on the cone besides a dense crystal film around the discharge incidence point in the droplet. These results are discussed considering existing knowledge about plasma–liquid interaction (PLI) and dynamical of crystal growth. This paper explores an interesting aspect of PLIs, which has both fundamental and practical usefulness, for understanding desalination processes, salt crystallization on water surface and biomedical science for advances in electrosurgical methods.

In the present work, Al2O3/ZrO2 nanocomposite surfaces were treated with cold plasma using N 2 , H 2 , and O 2 gaseous atmospheres. For this, Al2O3/ZrO2 samples were shaped and sintered at 1500 °C for 2 h. Then, the surfaces were treated with cold plasma using different N 2 and O 2 gas flow proportions. The H 2 gas flow was maintained at 50%. The treatment conditions were a total gas flow rate of 20 sccm, total pressure of 2.0 mbar, square pulses of voltage with duration of the 50 µs repeated every 100 µs, and a temperature of 400 °C. The surface treatment, regardless of the gaseous atmospheres, affected the functional groups attributed to ZrO2 significantly more than those of Al2O3. In general, it was observed that the surfaces treated in gaseous atmospheres with a higher proportion of N 2 gas flow had a more hydrophilic character due to the greater amount of active species coming from this gas. Although active N 2 gas species are predominant, active O 2 gas species can also affect ZrO2 functional groups. Thus, the pre-treatment contributes both to increasing hydrophilic character as well as promoting chemical changes in the functional groups present on the nanocomposite surfaces.

Polyester fabric samples – PET (poly (ethylene terephtalate)), were treated with oxygen plasma, in order to alter the hydrophilicity of such material. The process parameters: working pressure, current, tension and temperature were kept constant, varying only the treatment time. In order to evaluate the change caused on samples hydrophilicity, as well as the influence of the treatment time, the vertical wicking test was used. The samples were stored at standard temperature and pressure conditions, and their wettability were measured one day after the treatment and repeated after 30, 60 and 360 days, in order to check the stability of the effects produced. Scanning electron microscopy (SEM), Raman and ATR (Attenuated total reflection) spectroscopies were used to evaluate physical and chemical alterations on the samples surface. The results have shown a substantial improvement on the hydrophilicity of the treated samples compared to the non-treated sample.

Supermartensitic stainless steels (SMSS) are commonly employed in the oil exploitation industry and present a good balance between the necessary physical and chemical properties and financial costs. Certain applications, such as in extreme corrosive and abrasive environments, demand improvements in the surface properties of these steels. In the present work, HP13Cr SMSS with a fully martensitic microstructure were plasma nitrided in the 350–450 °C range. The high diffusivity and low solubility of nitrogen in the martensitic structure allowed the production of thick layers (16–61 μm) containing ɛ-Fe2–3N, γ′-Fe4N and expanded phase (αN) in all the temperatures. In addition, anisotropic sputtering rate and N-diffusion were observed for different grain orientations. Mechanical properties were measured by instrumented indentation, appropriately corrected from roughness effects on the results. Hardness profiles increased from 3.8 GPa (bulk) to ∼14 GPa (near surface region) in all the working temperatures, whereas the elastic modulus was 230 GPa, presenting no statistically significant differences with respect to the bulk value. Nanoscratch tests revealed a hardened-ductile like behavior of these nitride layers. The surface tribo-mechanical behavior was correlated with elastic–plastic responses of the precipitate-containing texturized layers. Results are interpreted in light of the effectiveness of plasma nitriding to modify the surface properties of SMSS.

The mechanical and tribological properties of martensitic AISI 420 (MSS) and supermartensitic HP13Cr (SMSS) stainless steels plasma nitrided using the cathodic cage design were investigated. Nitride compounds were produced in the plasma from the cage´s sputtered ions, which eventually deposited on the electrically isolated sample. Prior to nitriding, samples were austenitized and oil quenched in order to attain a fully martensitc microstructure. Nitriding was carried out at different temperatures (350-450 °C) for 6 h. Mechanical properties and scratch resistance were characterized by instrumented indentation and nanoscratch, and were correlated with morphological and microstructural changes by using atomic force microscopy, scanning electron microscopy, X-ray diffraction and profilometry. Both nitrided MSS and SMSS comprised two distinct regions: (i) an outermost nitride layer (300-800 nm thick) containing deposited e-Fe 2 -3 N and γ´-Fe 4 N nitrides and (ii) a diffusion zone composed of N-expanded martensite phase α N . At 450 °C, diffusion zones thicknesses were 4 μm (MSS) and 6 μm (SMSS). Nitride layers presented intense brittleness under normal and tangential loadings. Critical loads for nitride layer detachment were 49 mN and 127 mN for MSS and SMSS, respectively. However, after removal of the thin nitride layers, the toughened diffusion zones were revealed, being uniformly distributed through the entire sample area. Its hardness was 11 GPa. Such value corresponds to a twofold and threefold increase from the hardness of MSS and SMSS substrates, respectively, which are comparable with other plasma nitrided steels at similar temperature conditions.

In the present work, Al2O3/ZrO2 nanocomposite surfaces were treated with plasma under gaseous atmospheres with different proportions of N2, H2, and O2 to improve the adhesion of biomimetically deposited calcium phosphate layers. Initially, samples of Al2O3/ZrO2 were shaped and sintered at 1500 °C for 2 h. Subsequently, the surfaces were treated and coated with calcium phosphate. The treated and untreated surfaces before and after the deposition of the biomimetic coatings were characterised using scanning electron microscopy, confocal microscopy, infrared spectroscopy, X-ray diffraction, and a scratch test. The results showed that pre-treatment increased the amount of calcium phosphates formed on the surface regardless of the gas composition used owing to the increase in polarity on the treated surfaces and formation of oxygenated groups such as Al-OH and Zr-OH. The phases of calcium phosphates formed were: hydroxyapatite (HA), α-tricalcium phosphate (α-TCP), and β-tricalcium phosphate (β-TCP). Although the HA phase was predominant, the α-TCP phase was responsible for increasing the adhesion of calcium phosphates onto the surface. Among the gaseous compositions used, the combination of 30% N2, 50% H2, and 20% O2 favoured the highest formation of phosphates on the surface of the nanocomposite.

This study aimed to obtain a bifunctional fabric from the point of view of hydrophilicity/hydrophobicity for biomedical applications. To achieve this, both sides of a fabric of polylactic acid (PLA) were subjected to a plasma treatment. While in a side the oxygen was introduced to the other side, simultaneously, was added methane. The plasma treatment was performed at 100 W, 1.8 mbar, during 30 minutes. By Scanning Electron Microscopy (SEM) morphological analysis, it became evident that the fabric side facing the oxygen inlet showed micropittings, while the reverse side had smooth surfaces. Analysis by X-Ray photoelectron spectroscopy (XPS) revealed an increase in the amount of oxygen in the surface of the PLA on both sides of the fabric. The surface function was characterized by measurements of water absorption rate, where it was determined that one fabric side was more hydrophilic than the other side. The results indicated achievement of a bifunctional fabric through orientation of working gases during a plasma treatment., The authors are acknowledging to financial support supplied by CAPES - Brasília/Brazil through of the CAPES/IGC program - CGCI n° 055/2010.

Electrical discharges in liquids are currently used to synthesize nanoparticles. The plasma-liquid interaction is complex, where parameters such as electric field, ion charges and other species present are important. In order to understand the mechanism of crystallization, mother liquor (saturated solution of NaCl, MgCl2 and KCl) was used to study the effectiveness and selectivity of the crystallization caused by the application of plasma. Discharge was applied with the solution at room temperature or during cooling. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and chemical analysis was used to evaluate the structure and composition effects on crystal structure and composition. It was observed that the discharge induces selectively crystallization, and when compared to crystals obtained conventionally by cooling, were smaller and more uniform. We therefore confirm that plasma in liquid can also be used to selectively crystallize materials in atmospheric pressure, where the sizes of the crystals must be dependent on the parameters used.

In this work, the influence of working pressure on the characteristics of the layers produced by the nitriding treatment on the AISI 316 austenitic stainless steel surface using the Cathodic Cage Plasma Nitriding technique (CCPN) is assessed. The treatments were carried out at a temperature of 723 K for 5 hours under working pressures of 120, 250 and 500 Pa. The morphology, microstructure and corrosion resistance were studied through optical microscopy, x-ray diffraction, and electrochemical potential curves. We analyzed the effects of working pressure on the layer thickness, microhardness and corrosion resistance. The E×i curves and the electrochemical impedance of polarized samples were measured in order to investigate the effect of the ion transfer inside the produced film placed into the anodic solution. The electrochemical impedance of the films were measured, and showed an apparent capacitive behavior. For treatment under a pressure of 120 Pa we found the nitrides Fe3N, Fe4N and CrN. For treatment at a pressure of 250 Pa, the CrN disappears and the observed phases are the nitrides Fe3N, Fe4N and the S-phase. For a treatment pressure of 500 Pa there is an increase in the corrosion resistance of nitrided layers, confirmed by the predominance of S-Phase in the x-ray diffraction pattern. On the other hand, the sample nitrided under the pressure of 250 Pa showed very unstable impedance behavior when immersed in NaCl solution, indicating that the treatment at this specific working pressure has a negative effect on the corrosion resistance of plasma nitrided AISI 316 stainless steel surfaces.

Cathodic cage discharge was developed recently in order to eliminate phenomena as edge effect and overheating, which occurs during conventional processes. In this study, the effect of cage configuration in active species during the deposition process and optical properties of TiN film were studied. TiN compound was chosen because its optical properties are very sensitive to slight variations in microstructure and film thickness, becoming a good monitoring tool in fabrication process control. Cages were made of titanium and have different holes numbers and holes diameter. Electrical efficiency of the system and optical properties of TiN films were strongly influenced by experimental conditions. It was found that with more holes at the top of cage, deposition rate and crystallinity were higher, if compared to cages with a small number of holes at the top. On the other hand, the opposite behavior was observed when more holes were located at the sidewall of cage.

High performance solar collectors are those with high selectivity surfaces, high solar radiation absorption and that do not thermally reemit to the external environment. Strategies to enhance this performance might involve surface porosity modification. In this work, a plasma treatment technique called plasma electrolytic oxidation (PEO) has been tested to produce porosity on aluminium surfaces in a controlled manner. The porosity control was made by varying the intensity, frequency and duty cycle of the applied voltage pulses. The aluminium sample was placed in a solution of 1 g/L Na2SiO3. Voltage of 500 V and current density of 0.17 A cm2 was applied between electrodes. Three duty cycles were used: 33.33%, 50.00% and 67.77%. After treatment, the size, number and distribution of pores were evaluated. These parameters were correlated with both surface reflectance and optical absorbance. It was possible to control the porosity by controlling the electrical parameters of the process. While the mean pore size was directly related to the duty cycle, the inverse occurred for the number of pores. Surface treated with duty cycle of 33.33% presented higher values of absorption for all wavelength range.

In this study, we assess how the ratio (N2/H2) – working atmosphere gas mixture – influences the properties of the layers produced on austenitic stainless steel surface by Cathodic Cage Plasma Nitriding (CCPN). The nitriding atmospheres contained nitrogen and hydrogen in three proportions: 20% N2 + 80% H2, 50% N2 + 50% H2, and 80% N2 + 20% H2 delivered at a flow rate of 20 sccm. The effect of 100% N2 was also examined. The morphology, microstructure and electrochemical properties of the layer produced were studied. The samples characteristics were determined by optical microscopy, x-ray diffraction, microhardness test and electrochemical potential curves.

There is a need for new techniques that modify metallic implant surfaces, resulting in good bone response for low density areas. Among the different techniques, plasma nitriding is being applied in biomedicine with excellent results. However, its use in titanium dental implants is very limited owing to high process temperatures (between 700 and 800°C) that result in distortions. In order to solve this problem, the authors used a new plasma method with a hollow cathode discharge configuration. Ti grade II dental implants were nitrided in a 20% N2–H2 atmosphere at a temperature of 450°C, 150 Pa (1·5 mbar), for 1 h and inserted into rabbit tibias to assess osseointegration. The results showed that plasma nitriding caused a significant change in the surface texture of the nitrided implants and greater removal torque than that of the control implants.

Cathodic cage plasma nitriding is a new growth technique based on multiple hollow cathode effects. The samples are kept at a floating potential inside a cage that acts as a cathode and shields the samples from the cathodic potential. The aim of this work is to perform a systematic study of the properties of nitrided layers as a function of the distance from the nitriding sample surface to the cage wall using this technique. Cylindrical austenitic stainless steel AISI 316 samples were placed in different positions on an alumina plate inside the cathodic cage. The nitrided samples were characterized by optical microscopy, X-ray diffraction and microhardness measurements. The results show that the temperature inside the cage is nearly uniform and that the nitrided layers possess good physical properties and uniformity. Therefore, the differences in the nitrided layer thicknesses obtained at different positions must be due to particle flow reaching the sample surface, depending on how far the sample is from the cage walls.

In recent years, several technologies that modify implant surfaces have been emerged. Among these techniques, the plasma nitriding process has been successfully applied in biomedical field. Nevertheless, its use in dental implants is quite limited owing to the high temperatures of the process (between 700 and 800°C), which causes distortion. In order to solve this problem, a new approach is proposed in the present paper, by which nitriding under a hollow cathode discharge is used to modify surfaces. Grade II Ti plates were submitted to nitriding under hollow cathode discharge conditions and treated at a temperature 450°C and pressure of 150 Pa for 1 h. These showed that plasma nitriding helped bring about a significant change in the surface texture of the treated plates. Furthermore, cell proliferation was 2⋅5 times as high as that of the untreated plates.

Thin films of titanium were deposited onto Al2O3 substrate by hollow cathode discharge method for the formation of a ceramic-ceramic joint using indirect brazing method. An advantage of using this technique is that a relatively small amount of titanium is required for the metallization of the ceramic surface when compared with other conventional methods. Rapidly solidified brazing filler of Cu49Ag45Ce6 in the form of ribbons was used. The thickness of deposited titanium layer and the brazing temperature/time were varied. The quality of the brazed joint was evaluated through the three point bending flexural tests. The brazed joints presented high flexural resistance values up to 176 MPa showing the efficiency of the technique.

Structural, mechanical and tribological properties of AISI 304 steel submitted to nitrogen glow discharge at different atmospheres (N 2 :H 2 , 60:40) and (N 2 :H 2 , 20:80) and substrate temperatures are reported. Expanded austenite γ N and Fe–Cr nitrides were identified as a function of the working conditions. Rietveld refinements indicate that ɛ-Fe 2+ x N is the predominant phase for the poorest nitrogen atmosphere while γ′-Fe 4 N phase is major for the richest one. The nitriding produces a surface hardening that can reach hardness values up to 14 GPa. Thicker nitrided regions are obtained in high nitriding temperatures. Reciprocating sliding tests in samples with rich or poor nitrogen atmosphere indicated long running-in regimes for high nitriding temperature. Both nitrogen atmospheres reduced the wear up to a factor of six even at the lowest temperature process. The nanoscratch tests do not show difference in the surface elastic recovering in all used nitriding conditions.

A series of austenitic stainless steel AISI 316 cylindrical samples with different heights and samples with the same height placed at different positions were simultaneously nitrided using the cathodic cage technique. In this technique the samples are placed on an insulate plate inside a metallic cage which shield the cathodic potential, therefore it stays under a floating potential. A systematic study of the nitriding temperature variation effects was carried out to evaluate the temperature uniformity inside the cage. The samples were characterised through optical microscopy, X-ray diffraction and microhardness measurement. The results were compared with those obtained through conventional ionic nitriding, and it was verified that the samples nitrided by conventional technique present similar surface hardness, less uniformity and lower nitrided layer thickness than the samples treated under similar conditions through this new technique.

Samples of austenitic stainless steel AISI 316 were nitrided using the cathodic cage technique with the addition of methane in the nitriding atmosphere. The aim was to study the influence of this technique in reducing the precipitation of chromium nitrite and in improving the wear resistance. The results show that there was a significant improvement in such properties when compared to the results of ionic plasma nitriding. Formation of a double layer, one more internal composed of carbon and another with high nitrogen content, was confirmed by Scanning Electron Microscopy (SEM). The microhardness profile of the layer showed an increase in hardness values and a larger uniformity, while X-ray analysis showed less chromium nitriding precipitation when compared with results obtained for samples treated using ionic plasma nitriding.

Nowadays, in plastic industry, mills are used to recycle residues generated from the manufacture of plastic components. These mills contain cut blades that suffer accelerated wear, since they are continually submitted to tribological efforts. This fact reduces its useful life. In this work, a new technique of plasma nitriding, called “cathodic cage”, was investigated. This technique eliminates some problems, like restriction rings, inherent of the conventional plasma nitriding. It was used AISI 4340 steel in substitution to AISI 01 steel, normally used in the cut blades manufacture. The AISI 4340 steel was, then, nitrided by conventional and cathodic cage techniques. After this stage, commercial and nitrided cut blades were submitted to analysis of acting. The AISI 4340 steel nitrided by cathodic cage presented uniforms thickness and hardness in the nitrided layer, promoting the average increase of 58% in its useful life, when compared with commercial blades.

A series of AISI 1020 steel cylindrical samples with different heights were simultaneously nitrided in cathodic cage plasma nitriding. In this technique, the samples are placed under a floating potential inside a cage in which the cathodic potential is applied. A systematic study of the nitriding temperature variation effects was carried out in order to evaluate the efficiency of such a technique over the uniformity of the formed layers. The samples were characterized by optical microscopy, X-ray diffraction and microhardness measurement. The results were compared with those ones obtained in the ionic nitriding, and was verified that the samples nitrided by this conventional technique presents less uniformity than the ones treated through this new technique.

In this work, AISI 1010 steel samples were plasma nitrided into 20% N2 plus 80% H2 atmosphere at a pressure of 500 Pa (partial pressure of 100 Pa and 400 Pa for N2 and H2, respectively), temperatures of 500 and 580 °C, during 2 h. Three different procedures for cooling were accomplished after nitriding. In the first procedure the cooling occurred naturally, that is, the sample was kept on substrate holder. In the second one the sample was pulled off and cooling in a cold surface. Finally, in the third cooling process the sample was pulled off the substrate holder down into special reservoir filled with oil held at ambient temperature. The properties of the AISI 1010 steel samples were characterized by optical and electron microscopy, X-ray diffraction, Mossbauer spectroscopy and microhardness tests. Thermal gradient inside the sample kept on substrate holder during cooling process was measured by three inserted thermocouples at different depths. When samples were cooled rapidly the transformation of ϵ-Fe2�3 Nt oγ′-Fe4N was inhibited. Such effect is indicated by the high concentration of ϵ-Fe2�3N phase observed in the compound zone. To get solid state solution of nitrogen in the diffusion zone, instead of precipitates of nitride phases, the cooling rate should be higher than a critical value of about 0.95 °C/s. When this value is reached at any depth of the diffusion zone, two distinct diffusion zones will appear. Temperature gradients were measured inside the samples as a consequence of the plasma treatment. It's suggested the need for standardization of the term “treatment temperature” for plasma treatment because different nitrided layer properties could be reported for the same “treatment temperature”. © 2007 Elsevier B.V. All rights reserved.

Thin nitride and titanium dioxide films were produced using an innovative technique called cathodic cage depositon. Uniformity, three-dimensionality and high rate deposition are some of the advantages of this technique. In this study we discuss the influences of temperature, treatment time and gaseous atmosphere on the characteristics of the deposited films. The TiN (titanium nitride) and TiO2 (titanium dioxide) films were produced using a high deposition rate of 2,5 µm/h at a work temperature and pressure of 400°C and 150 Pa respectively. EDS technique was used to identify the chemical composition of the thin film deposited, whilst Raman spectroscopy indicated the phases present confirmed by DRX analysis. The thickness of the deposited films was studied using electron microscopy scanning. The results based on the deposition parameters confirm the great efficiency and versatility of this technique, which allows a uniform three-dimensional film deposition on any material without the appearance of stress. Compared to other techniques, cathodic cage deposition enables deposition at lower temperatures and higher pressures.

For titanium implants, a final porosity in the range of 60–65 vol% is required to achieve a network of interconnected macropores, which enables adequate fixation of the implant to the bone tissue and suitable mechanical properties. In addition, an open porosity at the implant surface is crucial for the success of the implant. In the present study, highly porous titanium foams were produced by warm compaction of MIM feedstock with the addition of space holder in a heatable die. Plasma treatment was performed on the Ti foams before the final sintering step aiming to increase the open pores at the surface. The results obtained so far demonstrate that plasma treatment is a promising technique for increasing open porosity at the surface. It even improved the dimensional accuracy of highly porous samples.

Cylindrical samples of 1020 steel and 316 stainless steel were nitrided under the conditions by conventional dc plasma nitriding (DCPN) and by a new technique denominate cathodic cage plasma nitriding (CCPN). The 1020 and 316 stainless steel samples were treated during 3 h and 5 h, respectively, in 773 K and 360 Pa. The samples were characterized by optical microscopy, X-ray diffraction and microhardness testing. All the samples nitrided by DCPN process presented erosion rings on the surface exposed to the plasma. In comparison, in samples nitrided by CCPN, the erosion rings were completely eliminated, without loss of the mechanical properties in the different phases of existence in the nitrided layer.

In the present work we use a plasma jet system with a hollow cathode to deposit thin TiO 2 films on silicon substrates. The cylindrical cathode, made from pure titanium, can be negatively polarized between 0 and 1200 V and supports an electrical current of up to 1 A. An Ar/O 2 mixture, with a total flux of 20 sccm and an O 2 percentage ranging from 0 to 20%, is passed through a cylindrical hole machined in the cathode. The influence of the cathode's parameters on the properties of deposited TiO 2 films and their deposition rate is studied. When discharge occurs, titanium atoms are sputtered/evaporated. They are transported by the jet and deposited on the Si substrates located on the holder placed facing the plasma jet system at a distance ranging from 10 to 50 mm from the cathode. The working pressure is 10 − 3 mbar and the deposition time is 10–60 min. The deposited films are characterized by X-ray diffraction to analyze qualitatively the phases present.

Porous materials are successfully utilized for fabrication of many industrial components such as filters and selflubricating bearings. These products are made by powder metallurgy, where mixtured or prealloyed powders can be used. The aluminum bronze is one of the most wanted due its excellent properties in combination with low cost of the raw materials. In this work, single action compacted (100 MPa) prealloyed aluminum bronze (Cu- 9wt%Al-1wt%Fe) cylinders were sintered using a hollow cathode discharge at temperatures between 400 and 750°C with duration on the isotherm for 12 min. Microstructure changes, homogeneity, porosity and composition were analyzed after the treatment. Sintering below 550° C led to uniform but porous structure. Above 550 °C it was observed a solidified central region and a porous structure that changes slightly through out the cross-section. The diameter of the central region increased with treatment temperature. It is concluded that due to the intense plasma heating and subsequent surface melt formation a mass flow direction to the center of compacts occurred.

The aluminothermic reduction is a highly exothermal reaction between a metal oxide and aluminium. Conventionally this reaction is ignited by an electric resistance and the reaction products after cooling are in the form of a rigid block of mixed metal and aluminium oxide. In this work a new process of aluminothermic reduction is presented, in which the reaction is ignited by a hydrogen plasma. The niobium oxide and aluminium powders are high energy milled for six hours to form particles constituted of oxide and aluminum. Stoichiometric, substoichiometric and superstoichiometric mixtures were prepared. The mixture was placed in a stainless steel tube (the hollow cathode) inside the reactor chamber. The chamber was firstly evacuated. Then hydrogen at low pressure was introduced. In the following an electric discharge between the cathode and the anode localized just above the cathode ignites the plasma. The plasma heats the particles on the surface of the powder layer and starts the reaction that proceeds in each particle since the reactants are intimately mixed. The heat generated by the reaction propagates deeper in the layer until the whole mixture reacts. Substoichiometric mixtures can be used because hydrogen takes part of the reduction. The Nb2O5 – Al starting powder mixture and the products of the reaction are characterized by laser grain size measurement and X-Ray diffraction (XRD). The products are in form of powder or agglomerates of particles. Phases of reaction products was determined by XRD analysis and the particle size trough SEM.

Powdered steel reinforced by NbC dispersed particles was sintered both in resistive furnace at 1180°C or in plasma reactor at 850°C (reference temperature) using heating rates that ranged from 10 to 100°C/min. Fe3P was used as liquid phase sintering additive. The microstructure of the resulting materials was visualized by scanning electronic microscopy. Distinctive microstructural features were observed as a function of the heating source and heating rate. Plasma sintering at rates ~ 30°C/min revealed different microstructural features comparing edge and sample bulk. Homogeneous mixtures of Fe and NbC could be sintered in resistive furnace and plasma reactor using relatively low heating rates. Plasma sintering at 800°C for 1 h (heating rate of 10°C/min) resulted in relative densities of ~ 91% of the theoretical density of the composite. Sintering in resistive furnace for 1150°C resulted in relative densities ~ 94%.

Standard plasma nitriding of commercially pure Ti or various Ti alloys for human body implants (e.g., hip, knee, shoulder and ankle implants) has already proven useful. However, its use in dental implantology is rather limited due to high nitriding temperatures. The small dental implants of complex geometries are frequently distorted. To solve this problem and benefit from the ability of the plasma treatment to modify the implant surface properties (needed for faster osseointegration process), such as creating different surface topographies, increasing surface roughness, changing local chemical properties by formation of different phases, cleaning/sterilizing contaminated surface and increasing the surface wettability, the titanium disk samples and industrial dental implants were nitrided using a hollow cathode discharge (HCD) configuration of a plasma nitriding system in a 20% N2–H2 atmosphere at pressures of 150 or 250 Pa and temperatures ranging from 400 to 500 °C for 1 or 2 h. The topography of the samples was characterized by optical and electron microscopy. Phases were determined by X-ray diffraction. The surface roughness and wettability were also quantified. Nitrided layer formation having better stability, increased surface roughness and higher wettability has been observed for samples treated at 450 and 500 °C and at a pressure of 150 Pa. Industrially fabricated dental implants were then nitrided at 500 °C/150 Pa for 2 h. The results show capability of HCD in treating dental implants. A significant change in the surface texture and superior wettability of the plasma-treated dental implants, with no geometric distortions, have been observed.

The magnetic dynamics behavior of copper and nickel ferrite nanoparticles used in the magnetic fluid elaboration and with mean sizes between 3.5 to 10.4 nm is investigated by measurements of magnetic hysteretic properties and zero field cooling (ZFC) susceptibility. The dependence of the irreversibility field, inversely proportional to the particle size, clearly indicates that the magnetic anisotropy of our particles finds its origin on the surface layer.

Plasma nitriding of shaped materials and materials of different sizes may yield non-uniform nitrided layers and/or reproducibility problems limiting its industrial-scale use to specific cases. The energy balance at the substrate surface and several non-uniformity effects related to geometry, size and sample position in the chamber during plasma nitriding are discussed. To investigate several of these effects, rods of SAE 1020 steel, of 8 mm in diameter, with different heights (1, 3, 5, 8 and 10 mm) were plasma nitrided in a mixture of N2–H2 (20%) at different temperatures (673, 773 and 843 K) and pressures (200 and 500 Pa). The samples were characterized by optical and electron microscopy, X-ray diffraction and microhardness testing. Hardness increases from the center to the edge of the samples. In the case of samples nitrided at 500 Pa, a macroscopically visible ring is obtained with low hardness inside the ring. The diameter of the ring increases for taller samples. The various formed phases, the thickness of nitrided layer and the microhardness of the samples are directly related to the height of the rod. This is associated with surface energy balance. The results show that the top surface temperature increases with height.

High heating rate during plasma sintering of metallic powders, mainly the supersolidus, can lead to better properties of the sintered material. In this work, powders with different thermal conductivities (Cu and Ni) were plasma sintered using both, planar discharge and hollow cathode discharge (HCD) configuration. The thermal evolution was studied using three thermocouples inserted inside the samples at different depths. Thermal gradient and the heating rate were measured as a function of the source power, discharge configuration, pressure and thermal conductivity of the material. We have observed that the thermal gradient changed greatly with the discharge configuration. The thermal difference between most profound and most shallow inserted thermocouple in Cu samples was around 30 °C for both planar and HCD discharge configuration. Ni samples and the planar configuration gave thermal difference of 70°C while for HCD configuration thermal difference went superior 140 °C. For this last case, heating rate of 300 °C/min was obtained.

Ferrous alloys have been reinforced by particle dispersion using hard ceramics such as niobium carbide, tantalum carbide, or titanium carbide. The resulting composites have a number of potential applications in the ceramic and textile fields where abrasion plays an important role. Their cost-efficient production allows them to exceed the capabilities of conventional non-reinforced tool steels. The present study presents some of the results obtained sintering Fe-NbC composites either in a resistive oven or in a d.c. plasma furnace. Final densities of approximately 95% TD were obtained in the latter atmosphere at temperatures as low as 750°C. Dilatometric studies carried out in resistive furnace indicated that this composite did not show significant densification below 1240°C in the presence of a liquid phase formed by the addition of small amounts of Fe 3 P. The differences between conventional and plasma sintering are discussed herein along with the effect on the microstructure of the composite.

The main goal of the present investigation is to analyze the use of Fe-NbC composites in the electrogeneration of industrial gases. The effect of the experimental parameters involved in the processing of PM composites on the performance of the resulting electrodes is also investigated, Cylindrical composite pellets were sintered varying their composition, sintering temperature and time, and compaction pressure. The resulting electrodes were characterized from the standpoint of their inherent electrical resistance, electrical resistance in NaOH 1M solution, and porosity. The electrical resistance of the composite electrode in solution was obtained from voltammetric tests carried out from -1 V to 1.5V. The scan rate was set to 10mV/s. The results obtained up to this point showed that the sintering temperature has a major effect in determining the electrical resistance of the electrode in solution. Other manufacturing aspects have less important effects on that property. The onset of oxygen generation took place at approximately 0.6V (vs. Ag/AgCl) and the optimum potential at 100mA/cm 2 was 0.94V.

Lanthanum and neodymium nickelate (LaxNd1� xNiO3� d) with x equal to 1.0, 0.9, 0.7 and 0.5 were prepared with molar ratios of 1:1.5 and 1:3. The resins were heated at 3001C for 2 h and then calcinated at 8001C for 12 h. The resulting powders were analyzed by thermogravimetry, infrared spectroscopy and X-ray powder diffraction. Chemical analysis of the powders showed that the oxygen vacancy number (d) becomes higher with the substitution of lanthanum by neodymium for both molar ratios. X-ray patterns showed the formation of perovskite in all samples analyzed. Nevertheless, a small amount of a secondary phase was observed when neodymium content increases in the oxides. This phase was attributed to NiO. r 2003 Elsevier Science (USA). All rights reserved.

Photoluminescence (PL) at room temperature has been achieved in amorphous powders of the YNiO3 and La0.5Nd0.5NiO3 systems. They were prepared by the polymeric precursor method (PPM). The energy position of maximum PL emission and the intensity showed dependence on the rare earth element (RE) size. The RE small size suggests increase of non-bridging oxygens (NBO) in the amorphous NiO6 network. These results support the relationship between photoluminescence and structure in Ni3+/Ni2+-based amorphous materials.

Cylindrical samples of AISI 1020 steel were nitrided, using the techniques of conventional plasma nitriding and cathodic cage. In the latter, the samples are kept at floating potential, inside of a cage that works as a cathode and to shield the samples from the cathodic potential. A systematic study was conducted in order to evaluate the efficiency of this technique in the elimination of edge effect, in comparison with conventional plasma nitriding. In addition, another comparative study of the phases obtained using the conventional plasma nitriding and nitriding with cathodic cage was performed. Two metallic cages were used, one made of austenitic stainless AISI 316 and other one made of AISI 1020 steel, to prove the effect of deposition in nitriding with cathodic cage. The samples which were nitrided by this new technique had shown nitriding rates, crystalline phases, and microhardness, similar to those samples which were nitrided conventionally. However, it was possible to confirm the elimination of edge effect through the characterization by optical microscopy and by microhardness test along the samples surfaces. The samples were characterized by optical microscopy, microhardness tests and X-ray diffraction.

Magnetic birefringence measurements are performed under a static field on Electric Double Layered Magnetic Fluids based on copper and zinc ferrite nanostructures. The optical birefringence is related to a single-particle effect and well described by a Langevin model which includes a log- normal distribution of particles. By the field-induced birefringence level, these new magnetic fluids are comparable to usual ones, a result which could offer a new way for biological applications.