Search

Cutting tools, such as machining inserts, which in addition to having a complex geometry need to handle different demands on more than one face during their application, stimulate investigation for new coating techniques. Even though many hard film deposition techniques are well accepted or even established among researchers and industries, these processes still need to meet a limitation that requires the repositioning of the sample for new treatments in order to cover all of its surfaces. This paper proposes a new methodology for coating deposition on complex geometry pieces, through a structure for three-dimensional plasma treatment, using a Rotary Cathodic Cage Plasma Nitriding (RCCPN). TiN films were deposited on cemented carbide inserts applied in machining processes using the RCCPN technique. The plasma parameters were kept constant and deposition time was the only variable input. The deposited films were characterized by SEM, EDS, XRD, and Vickers microhardness. It was observed that the RCCPN technique was useful in producing a uniform TiN layer in all insert surfaces, with a thickness proportional to deposition time.

A titanium surface nitrided by plasma contains nitrogen ions that guarantee resistance to corrosion and biocompatibility. Despite this, no descriptions concerning the influence of the expression of cell adhesion proteins and their influence on osteogenic cell differentiation are available. Thus, the present study aimed to assess the response of murine pre‐osteoblastic cells (MC3T3‐E1) cultured on nitrided titanium surfaces. Pre‐osteoblastic cells were grown on polished titanium discs, used as controls, and on previously characterized plasma‐nitrided titanium discs. Cells from both groups were submitted to the MTT cell viability test. The expressions of α5, α2, and β1 integrin were assessed by flow cytometry and immunofluorescence, while osteocalcin expression was assessed by flow cytometry. The nitrided surface presented higher α2 and β1 integrin expressions, as well as osteocalcin expression, when compared to the polished surface, with no alterations in cell viability. These findings seem to suggest that the plasma nitriding treatment produces a titanium surface with the potential for effective in vitro osseointegration.

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.

Biomedical devices introduced in the human body interact initially with blood cells, their success being dependent on the result of this interaction. This work aimed to obtain optimum biocompatibility and hemocompatibility of the titanium by plasma treatment. For this, discs of commercially pure titanium (CP) were subjected to plasma nitriding using different mixture of nitrogen and hydrogen; the effect of addition of hydrogen to the nitriding plasma was investigated. Before and after treatment, samples were evaluated in terms of topography and wettability using atomic force microscopy and sessile drop tests, respectively. The titanium biological response was evaluated in vitro through the application of platelet-rich plasma (PRP) on the surfaces modified and analysis of their behaviour from the point of view of surface tension and cell adhesion. Surface properties, such as roughness and wettability, were sensitive to the hydrogen/nitrogen ratio in the nitriding plasma, suggesting a strategy for producing different surfaces of biomedical devices. Results showed to be possible to obtain surfaces with different response to the adhesion of platelets, covering different applications.

We evaluated the effects of titanium plasma nitriding and oxidation on live endothelial cell viscoelasticity. For this, mechanically polished titanium surfaces and two surfaces treated by planar cathode discharge in nitriding (36N2 and 24H2) and oxidant (36O2 and 24H2). Surfaces were characterized regarding wettability, roughness and chemical composition. Rabbit aortic endothelial cells (RAECs) were cultured on the titanium surfaces. Cell morphology, viability and viscoelasticity were evaluated by scanning electron microscopy (SEM), methyl thiazolyl tetrazolium (MTT) assay and atomic force microscopy (AFM), respectively. Grazing Incidence X-ray Diffraction confirmed the presence of TiN0,26 on the surface (grazing angle theta 1°) of the nitrided samples, decreasing with depth. On the oxidized surface had the formation of TiO3 on the material surface (Theta 1°) and in the deeper layers was noted, with a marked presence of Ti (Theta 3°). Both plasma treatments increased surface roughness and they are hydrophilic (angle < 90°). However, oxidation led to a more hydrophilic titanium surface (66.59° ± 3.65 vs. 76.88° ± 2.68; p = 0.001) due to titanium oxide films in their stoichiometric varieties (Ti3O, TiO2, Ti6O), especially Ti3O. Despite focal adhesion on the surfaces, viability was different after 24 h, as cell viability on the oxidized surface was higher than on the nitrided surface (9.1 × 103 vs. 4.5 × 103cells; p < 0.05). This can be explained by analyzing the viscoelastic property of the cellular cytoskeleton (nuclear and peripheral) by AFM. Surface oxidation significantly increased RAECs viscoelasticity at cell periphery, in comparison to the nucleus (2.36 ± 0.3 vs. 1.5 ± 0.4; p < 0.05), and to the RAECs periphery in contact with nitrided surfaces (1.36 ± 0.7; p < 0.05) and polished surfaces (1.55 ± 0.6; p < 0.05). Taken together, our results have shown that titanium plasma treatment directly increased cell viscoelasticity via surface oxidation, and this mechanobiological property subsequently increased biocompatibility.

The research of the interaction between bacteria-surface has great importance for titanium biomedical applications once microorganisms offer risks because promoting implant loss. Therefore, study bacterial adhesion and colonization on titanium is interesting because are principal factors infections pathogeny on biomaterials. In this study, commercial grade II titanium was submitted to nitriding treatment to plasma at 2.2 mbar, using gas mixtures of 80% hydrogen (H2) and 20% nitrogen (N2) during 1 hour and 3 hour. The surfaces were physically and chemically characterized. In order to evaluate bacterial response, the surfaces were exposed to Pseudomonas aeruginosa. The titanium surface modified in nitriding plasma, although exposes a higher roughness as compared with untreated samples, exhibited lower bacterial growth. The nitrided sample for 3 hour exhibited the higher amount of TiN phase and the higher concentration of atomic nitrogen on surface and lower bacterial adhered count. These results were confirmed by scanning electron microscopy. Based on these results can be said to the thermochemical treatment of plasma nitriding on titanium samples results a significant reduction of adherence of Pseudomonas aeruginosa. It was found that the Ti surface nitrided offers significant reduction of bacterial adherence which prevent biofilm formation and offersing lower risk of infection and implant remotion.

There is a growing quest for an ideal biomaterial that shows appropriate cellular response and is not susceptible to microbial adhesion. In this study, commercial grade II titanium was submitted to RF/DC plasma surface modification at 2.2 mbar, using gas mixtures of argon, nitrogen, and oxygen at proportions 4:1:2 and 4:1:3. The surfaces were physically and chemically characterized. In order to evaluate bacterial response, the surfaces were exposed to Staphylococcus epidermidis. Oxynitrided samples, although having a higher roughness as compared with untreated samples, exhibited lower bacterial growth. This observation is probably due to the formation of different crystalline phases of nitrides and oxides caused by plasma treatment. The surface with highest contact angle and highest surface tension showed lower bacterial adhesion. These results were confirmed by scanning electron microscopy. The role of nitrogen in reducing bacterial adhesion is clear when this material is compared with untreated titanium, on which only an oxide film is present.

A current goal of dental implant research is the development of titanium (Ti) surfaces to improve osseointegration. Plasma nitriding treatments generate surfaces that favor osteoblast differentiation, a key event to the process of osteogenesis. Based on this, it is possible to hypothesize that plasma-nitrided Ti implants may positively impact osseointegration. Objective The aim of this study was to evaluate the in vivo bone response to Ti surfaces modified by plasma-nitriding treatments. Material and Methods Surface treatments consisted of 20% N2 and 80% H2, 450°C and 1.5 mbar during 1 h for planar and 3 h for hollow cathode. Untreated surface was used as control. Ten implants of each surface were placed into rabbit tibiae and 6 weeks post-implantation they were harvested for histological and histomorphometric analyses. Results Bone formation was observed in contact with all implants without statistically significant differences among the evaluated surfaces in terms of bone-to-implant contact, bone area between threads, and bone area within the mirror area. Conclusion Our results indicate that plasma nitriding treatments generate Ti implants that induce similar bone response to the untreated ones. Thus, as these treatments improve the physico-chemical properties of Ti without affecting its biocompatibility, they could be combined with modifications that favor bone formation in order to develop new implant surfaces.

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.

The use of polymeric medical devices has stimu- lated the development of new sterilization methods. The traditional techniques rely on ethylene oxide, but there are many questions concerning the carcinogenic properties of the ethylene oxide residues adsorbed on the materials after processing. Another common technique is the gamma irra- diation process, but it is costly, its safe operation requires an isolated site, and it also affects the bulk properties of the polymers. The use of gas plasma is an elegant alternative sterilization technique. The plasma promotes efficient inac- tivation of the microorganisms, minimizes damage to the materials, and presents very little danger for personnel and the environment. In this study we used plasma for micro- bial inhibition of chitosan membranes. The membranes were treated with oxygen, methane, or argon plasma for different time periods (15, 30, 45, or 60 min). For inhibition of microbial growth with oxygen plasma, the time needed was 60 min. For the methane plasma, samples were success- fully treated after 30, 45, and 60 min. For argon plasma, all treatment periods were effective. Key Words: Plasma— Sterilization—Membranes—Chitosan.

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.

Highly-porous titanium was produced by metal injection molding (MIM) of feedstock containing potassium chloride particles as a space holder. Macroporosity was generated by dissolving the potassium chloride particles in water. Challenges for MIM of highly-porous parts include shape retention during debinding and sintering and achieving open surface porosity. This study demonstrates that plasma treatment can remedy both these effects for highly-porous titanium. Plasma treatment of unsintered MIM samples enables attaining porosities of up to 64% in combination with good dimensional accuracy. The effect of plasma treatment on the uptake of interstitial impurities, dimensional accuracy, sintered microstructure and porosity, as well as the interaction of the plasma with partially-debinded MIM samples, was investigated. Highly-porous titanium produced by MIM and plasma treatment is attractive for biomedical implants due to its low impurity content, good dimensional accuracy and shape stability in combination with enhanced open porosity, the latter contributing to bone ingrowth and implant fixation.

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.

O presente estudo mostra uma relação entre o comportamento das espécies ativas do plasma com as propriedades superficiais do titânio. Para tanto, espécies ativas como N2+ (391,4 nm) e O (844,6 nm) foram analisadas por espectroscopia de emissão óptica (OES) em plasma produzido por uma mistura de gases N2 - Ar - O2. O fluxo de nitrogênio e argônio foram fixados em 1 e 4 sccm (centímetro cúbico padrão), respectivamente e o fluxo de oxigênio foi variado entre 2 e 4 sccm. Este processo apresentou uma não linearidade da intensidade da espécie N2+(391,4 nm) com o aumento do fluxo de O2, onde no fluxo de 3 sccm apresentou maior intensidade comparado com os demais fluxos utilizados. Foi observado que as espécies ativas influenciam na modificação das propriedades após o tratamento a plasma. As espécies N2+ (391,4 nm) mostraram ser mais efetivas na formação de fases de nitreto. Os parâmetros de rugosidade foram mais altos quando as espécies N2+ (391,4 nm) apresentavam maior intensidade. A dureza foi maior para o fluxo onde houve maior intensidade da espécie N2+ (391,4 nm). Medidas de tensão superficial também apresentaram maiores valores para o fluxo onde as espécies N2+ (391,4 nm) estavam em maior evidência. Enquanto, a espécie N2+ (391,4 nm) influenciou na componente dispersiva, a espécie O (844,6 nm) teve influência na componente polar.

The objective of this work is to determine the best parameters for brazing ceramic joints of pre-metallized Al2O3 with Ti by a plasma process using amorphous ribbons of Cu49Ag45Cex alloy as the addition metal. The alloys were prepared in an arc oven, and later processed by melt spinning, varying Cerium content by 4–6%. Brazing took place in a vacuum oven and the following variables were analysed: deposition time of the Ti film and temperature and brazing time, which were related to the flex resistance in three points of the brazed joint. A linear regression equation was obtained, and the interaction between these factors was verified. The metallized ceramic surfaces showed excellent uniformity and the brazed joints demonstrated very good adhesion, achieving flex resistance values of up to176.8 MPa.

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.

Titanium (Ti) is currently the most widely used material for the manufacture of orthopedic and dental implants. Changes in the surface of commercial pure Ti (cp Ti) can determine the functional response of cells, and is therefore a critical factor for the success of the implant. However, the genotoxicity of titanium surfaces has been poorly studied. Thus, the purpose of this study was to evaluate the genotoxic potential of a new titanium surface developed by plasma treatment using argon-ion bombardment and compare it with an untreated titanium surface. Accordingly, comet assay, analysis of chromosomal aberrations (CAs), and Cytokinesis Block Micronucleus (CBMN) assay were carried out, using CHO-K1 (Chinese hamster ovary) cells grown on both titanium surfaces. Our results show that the untreated titanium surface caused a significant increase in % tail moment, in the number of cells with CAs, tetraploidy, micronucleus frequency, and other nuclear alterations when compared with the negative control and with the plasma-treated titanium surface. This difference may be attributed to increased surface roughness and changes in titanium oxide layer thickness.

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.

Tantalum is a very interesting metal for industry due to some properties such as high melting point, ductility, high corrosion resistance, besides attractive electric and thermal conductivities. In the present work, the production of metallic tantalum (Ta) has been investigated through the reduction of Ta2O5 by aluminothermic reduction technique (ATR), using hydrogen plasma to trigger the exothermal reaction. Ta2O5 and Al mixtures were previously processed by mechanical alloying during 2, 6 and 10 h. The results obtained by XRD and SEM show that is possible to obtain a compound rich in tantalum through the technique of aluminothermic reduction by plasma.

A novel technique of aluminothermic reduction of tantalum oxide is developed to produce tantalum in form of powder. In this technique, hydrogen plasma is used to trigger the reaction in a plasma reactor. The reacted powders were analyzed by XRD and SEM. Rietveld method was used to quantify the phases present in the product of reaction. The results showed that a tantalum rich phase with a dendritic structure, typical of molten phases is formed. This phase occurred in significant amounts onto the surface and in bulk of the reacted grains.

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.

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.

The sintering under plasma heating of a powder mixture Ta–20w%Cu prepared by high energy milling is focused. The powder has composite particles in which Ta and Cu phases are amorphous. Plasma is able to heat the samples at a very high rate, but large temperature gradients are produced. The sintering of the Ta–Cu composite powder starts before Cu melting. Cu leaves the composite particles, forming a layer. This layer creates necks between the composite particles. Above the copper melting point, liquid copper leaves the composite particles and fills the pores. The composite particles rearrange but keep their original shape and size. Disintegration of composite particles is not observed due to the short sintering time used in the work. The final sintered structure is heterogeneous.

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.

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.

In order to increase the hydrophilicities and to improve dyeability, poly(ethylene terephathalate) (polyester) fabrics were treated in low pressure and temperature plasma. Different plasma atmosphere were used in this work, leaving the gas type (oxygen, nitrogen, methane and hydrogen) as plasma variables, other parameters like pressure, exposure time, voltage and current were not variables in the process. After plasma treatment, the properties of the fabric, including surface morphology and chemical alteration, were investigated. The polyester fabrics treated with different plasma gases exhibited different morphological changes. The capillary method was applied to evaluate the improvement in water uptake of polyester fabrics, which indicated a good wettability to all atmospheres used in this work, except for a mixture containing methane, hydrogen and nitrogen In order to increase the hydrophilicities and to improve dyeability, poly(ethylene terephathalate) (polyester) fabrics were treated in low pressure and temperature plasma. Different plasma atmosphere were used in this work, leaving the gas type (oxygen, nitrogen, methane and hydrogen) as plasma variables, other parameters like pressure, exposure time, voltage and current were not variables in the process. After plasma treatment, the properties of the fabric, including surface morphology and chemical alteration, were investigated. The polyester fabrics treated with different plasma gases exhibited different morphological changes. The capillary method was applied to evaluate the improvement in water uptake of polyester fabrics, which indicated a good wettability to all atmospheres used in this work, except for a mixture containing methane, hydrogen and nitrogen

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.

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.

Chromium is an important alloying element present in numerous commercial steels. A systematic study on the nitriding behavior of Fe–Cr alloys is helpful in predicting the properties of nitrided Cr-alloyed steels. Aspects such as microstructural evolution, growth kinetics, and mechanical properties should be particularly emphasized. Fe–Cr alloys containing 5, 10, and 20 wt.% Cr have been arc melted and subsequently plasma nitrided under a N 2 –80% H 2 atmosphere. The microstructure of the resulting nitrided layers was characterized and the microhardness profiles evaluated. Thicker layers developed on low chromium alloys. Differences in hardness profiles were also observed as a function of chromium contents. Nitriding Fe–5% Cr alloys resulted in two discrete fronts, refereed to as the diffusion front and the transformation front. Transformed regions sustained a decrease in hardness from 1000 down to 600 HV, associated with the conversion of homogeneously dispersed fine precipitates into coarser needle like particles immersed in the ferritic matrix. Similar behavior was not observed for the other alloys, where both fronts developed simultaneously.

Aim: To evaluate the proliferative capacity of mesenchymal cells derived from human periodontal ligament on polished and plasma-treated titanium surfaces. Methods: Eighteen titanium disks were polished and half of them (n=9) were submitted to plasma nitriding using the cathodic cage technique. Mesenchymal cells were isolated from periodontal ligament of impacted third molars (n=2) and cultured on titanium disks (polished and nitrided) and on a plastic surface as a positive control of cell proliferation. Cell proliferation was analyzed and growth curves were constructed for the different groups by determining the number of cells adhered to the different surfaces at 24, 48 and 72 h after plating. Results: Higher cell number was observed for the nitrided surface at 24 and 48 h. However, no statistically significant difference in cell proliferation was observed between the two different surface treatments (p>0.05). Conclusions: We concluded that plasma nitriding produced surfaces that permitted the proliferation of human periodontal ligament mesenchymal cells. Associated to other physical and chemical properties, it is possible to assume the feasibility of plasma nitriding method and its positive effect on the early cellular events of osseointegration.

Se ha investigado la producción de titanio metálico (Ti) mediante de la reducción de óxido de titanio (TiO2) por técnica de reducción aluminotérmica, usando plasma de hidrógeno como desencadenante de la reacción. El polvo de TiO2 y Al utilizados se procesaron previamente por molienda de alta energía durante 4, 6 y 10 h. Se realizó también un estudio de análisis térmico, con el objetivo de conocer la temperatura de reacción para el proceso aluminotérmico de la mezcla TiO2-Al. El producto obtenido fue caracterizado mediante difractometría de rayos y microscopia electrónica de barrido, y se usó el método Rietveld para el refino en la determinación de la estructura. Los resultados comprueban la existencia de titanio metálico en el producto de la reacción aluminotérmica, cuando se utiliza el proceso de plasma The production of metallic titanium (Ti) through the reduction of titanium oxide (TiO2) by aluminothermic reduction technique, using hydrogen plasma to trigger the reaction has been investigated. Titanium oxide and aluminum powders were previously processed by high energy grinding during 4, 6 and 10h. Also, a thermal analysis study was done to know the temperature for the aluminothermic process in TiO2-Al mixtures. The product obtained was characterized by X-ray diffraction and scanning electron microscopy and Rietveld method was used in the microstructure refinement. The results show that is possible to obtain a titanium rich compound through the hollow cathode plasma technique.

With the aim of studying the topographic influence on wettability of plasma-treated surfaces, we used eighteen commercially pure titanium (CP Titanium) disks (grade II), 10 mm in diameter and 1 mm thick, and in atmospheres of Argon (Ar), Hydrogen H 2 and Ar–H 2 . These samples were submitted to plasma produced by hollow cathode discharge (HCD) for 20 and 60 min at a voltage of 500 V and pressure of 220 Pa. After pre-treatment, the state of the sample surfaces was assessed for surface phases with grazing incidence X-ray diffraction (GIXRD), and XPS (X-ray photoelectron spectroscopy), evaluated by atomic force microscopy (AFM) and wettability, using the sessile drop test. It was found that all the conditions were effective in reducing oxide, resulting in different wettability values. Correlation between average roughness (Ra) parameters and the ratio between maximum peak height and average distance between the highest peak and lowest valley (Rp/Rz) and wettability for the different treatment conditions were analyzed. Given the results obtained, it was concluded that Ra and Rp/Rz are not appropriate for correlating with wettability and it is suggested that a new topographic parameter be adopted for the Cassie–Baxter equation. XPS analysis showed that reduction efficacy was greater for the Ar–H 2 mixture, followed by Ar and H 2 .

AISI 409 ferritic stainless steel samples were nitrided using the cathodic cage plasma nitriding technique (CCPN), with the addition of methane to reduce chromium precipitation, increase hardness and wear resistance and reduce the presence of nitrides when compared to plasma carbonitriding. Microhardness profiles and X-Ray analysis confirm the formation of a very hard layer containing mainly ε-Fe3N and expanded ferrite phases.

Background. This study evaluated the impact of bleaching teeth using blends of a CPP-ACP paste (MI Paste; MI) and carbamide/hydrogen peroxides in different proportions on surface properties of bleached enamel. Methods. Ninety bovine incisors were bleached with 7.5% hydrogen peroxide (HP), 16% carbamide peroxide (CP), MI and blends of HP or CP:MI at three proportions (1:1, 2:1, 1:2). Hardness and roughness were measured at baseline and after bleaching. Enamel morphology was evaluated by Scanning Electron Microscopy (SEM). The data were analyzed by two-way ANOVA for repeated measurements and Tukey’s test. Results. Most of the samples bleached with MI in combination with peroxides presented increased hardness and roughness which were associated to mineral deposition, as observed by SEM images. Blends with higher fractions of MI did not offer superior benefits. Conclusions. The use of a CPP-ACP paste mixed to carbamide/ hydrogen peroxides can decrease adverse side-effects from tooth bleaching on an enamel surface.

Presented at the 2009 European Winter Conference on PlasmaSpectrochemistry, Graz, Austria, February 15–20, 2009; International audience; Reform of methane was produced in a quartz tube by microwave plasma at atmospheric pressure. A flux of 10 l/min and 5 l/min of pure argon was inserted in the plasma and then a small amount of methane (from 0.5 to 5 sccm) was added to the argon. The species present in the plasma at discharge and post-discharge were monitored by optical emission spectroscopy (OES) diagnostic during the process. The efficiency of dissociation was evaluated by both the density of species H α (656.6 nm) and CH (431.4 nm).

Titanium samples have been used as the substrate that was submitted to a plasma discharge nitriding for the surface treatment of dental implants. Two different arrangements regarding the electrode shapes were tested: planar and hollow cathode. The treated samples were evaluated regarding surface phases, texture, roughness, layer thickness, wettability and visual appearance. The roughness of the surface of all samples submitted to the plasma nitriding process was lower compared to those treated by commercially available technology plasma spray, on the other hand, better wettability was achieved. Some commercially available implants were also treated under the best conditions found with the experiment at titanium samples. After plasma nitriding these implants, tests were carried out to evaluate both wettability and surface texture. As a result the treated implants had both their surface texture and wettability improved.

Fe-reinforced composites were manufactured by the addition of 10–20 wt.% NbC or TaC particles aiming at improved mechanical and wear behavior. Two varieties of Fe powders from Hoeganaes Corp. were used, Ancorsteel 1000B and 45P. Composites produced using the former variety included a small amount of Fe3P to induce liquid-phase sintering whereas 45P powder was pre-alloyed with P by the manufacturer. The hardness of the matrix was adjusted adding carbon to the composite mixture. The powders were milled for different times and annealed prior to pressing. A dilatometric study was carried out under hydrogen to establish optimum sintering profiles. Relative densities up to 97% TD were achieved. Both microstructure and density of the sintered pellets were evaluated in order to establish correlations involving composition, processing parameters and microstructure of the composite.

High-frequency pulsed plasma (HFPP) was applied to produce hydrogen by reforming natural gas. The process is based on the molecular dissociation of the gas into different ionized species, such as H + and H 2 + . The plasma was generated applying a pulsed voltage in an atmosphere of methane. The efficiency of the system was optimized by adjusting the frequency of the pulsed plasma aiming at maximum selectivity to hydrogen. The reforming of natural gas was accompanied by the simultaneous storage of hydrogen in a hollow cathode set-up made of titanium. Hydrogen contents higher than 900 ppm (in weight%) were stored in the Ti cathode. The efficiency of the method was compatible to industrial applications. Pyrolitic carbon condensed on the lower walls of the reactor but did not interfere with the kinetics of hydrogen absorption. In fact, the carbon produced in such manner could be considered a byproduct of the process and can be used as natural gas adsorbent once adequately activated.

A prospective epidemiological study of 114 patients undergoing cardiac catheterization and angioplasty for chest pain was undertaken to examine the relationship between six plasma metal concentrations and coronary heart disease (CHD). The plasma concentrations of selenium, magnesium, potassium, copper, zinc, and iron in patients with and without CHD were determined by atomic absorption spectrometry or by wet chemistry. The plasma element concentrations were then reviewed for any correlation with CHD. We observed a significant, inverse relationship between plasma selenium concentration and CHD. Although the mean plasma concentrations of potassium, magnesium, copper, iron, and zinc were lower in the patients with CHD, no significant correlation could be determined. If plasma selenium levels are monitored and dietary supplements to selenium-deficient patients are administered, the potential risk of CHD may be diminished.

In the present study it was carried out a surface modification of polyester fabric by plasma treatment with aim of providing hidrophilicity to fabric. In the process it were used three different gaseous atmosphere with mixtures of argon, nitrogen and/or oxygen [(1) Ar + N2 (4:2), (2) Ar + N2 + O2 (4:2:2) and N2 + O2 (2:0.6)] and maintained others parameters such as pressure, current and time of treatment fixed at 1.35 mBar, 0.08 A and 30 minutes, respectively. The plasma treatment was monitored by optical emission spectroscopy (OES) to identify the species presents in the plasma reactor. Chemical changes in the fabric surface after plasma treatments were determined by Fourier Transform Infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Wicking properties were used to evaluate hydrophilicity of the fabric. Wicking measurement showed that the hydrophilicity of polyester fabric was remarkably improved after treatment and was explained by XPS analysis indicating higher presence of functional groups containing nitrogen and oxygen.

Magnetization and in-field Mossbauer measurements were performed on copper ferrite nanoparticles with average sizes ranging from 3.5 to 10.4nm. Our results show that the nanoparticles are well-crystallized single domains with a magnetically disordered surface shell. A sharp increase in the saturation magnetization at low temperatures, in addition to the usual modified Bloch behavior, was observed for the smallest particles. This jump in magnetization curves seems to be related to the freezing of the surface spins below a temperature of about 45K.

Porous aluminum–bronze compacts formed from prealloyed metastable (supersolidus) powder were heated either by plasma or by a resistive furnace technique. The plasma heating was performed in two different setups: (i) Hollow Cathode Discharge (HCD) method and (ii) Shielded Cathode Discharge (SCD) method. All experiments were carried out for 12 min in hydrogen at temperatures ranging from 673 to 1323 K. In HCD, for temperatures above 773 K, a fully filled, non-porous region was obtained in the center of the compacts, exhibiting a quite different behavior than that obtained using either SCD or resistive techniques. In these cases, uniformly dispersed condensed micro-regions were detected in samples treated at temperatures higher than 1223 K. These observations are discussed in terms of the heating mechanism, mass transfer and behavior of supersolidus powder particles. A simple physical model for the creation of the central fully filled region obtained by HCD is introduced.