•Ti Grade 2 and Ti6Al7Nb were nitrided at cathode (CP) and plasma potentials (PP).•Layers formed by PP were characterized by lower roughness and also twice as thin.•CP layers were characterized by ...higher wear resistance, but also higher CoF.•Nitriding didn’t affect very good corrosion resistance of Ti6Al7Nb alloy.
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Plasma nitriding of titanium Grade 2 and Ti6Al7Nb titanium alloy at 730 °C was used to produce nitrided surface layers with an outer zone consisting of nanocrystalline titanium nitride - TiN, and a Ti2N zone right above the αTi(N) diffusion area. The paper presents a comparison of structure (TEM, SEM), phase composition (XRD, SAED) surface topography (AFM, optical profilometer), corrosion (potentiodynamic method), tribological properties (‘ball-on-disc’), and adhesion (scratch-test) of TiN + Ti2N + αTi(N) type nitrided surface layers produced on Grade 2 titanium and Ti6Al7Nb titanium alloy using conventional glow-discharge nitriding (so called glow discharge nitriding at the cathode potential) and with the use of an ‘active screen’ (glow discharge nitriding at plasma potential). A reduction of cathodic sputtering in the plasma potential process made it possible to produce surface layers maintaining a high smoothness of the titanium surfaces. Due to the low surface roughness and the high compressive residual stress of the sample after nitriding at plasma potential, ‘ball-on-disc’ test results showed the lowest coefficient of friction and the lowest penetration depth for this layer and very good adhesion of the layer to the substrate – i.e. Ti6Al7Nb titanium alloy. Nitriding of titanium alloy at cathode potential increased the corrosion potential value and slightly decreased corrosion current density. The corrosion current density of the sample nitrided at plasma potential was similar to initial state Ti6Al7Nb titanium alloy. The nitriding process type (cathode potential or plasma potential) used to produce TiN + Ti2N + αTi(N) surface layers on Ti6Al7Nb titanium alloy has an influence on the microstructure of the layer, its residual stress, in particular its TiN outer titanium nitride zone, its thickness, and on its properties such as wear and corrosion resistance.
Vasopressin influences salt and water transport in renal epithelia. This is coordinated by the combined action of V2 receptor-mediated effects along distinct nephron segments. Modulation of NaCl ...reabsorption by vasopressin has been established in the loop of Henle, but its role in the distal convoluted tubule (DCT), an effective site for fine regulation of urinary electrolyte composition and the target for thiazide diuretics, is largely unknown. The Na+-Cl- cotransporter (NCC) of DCT is activated by luminal trafficking and phosphorylation at conserved NH2-terminal residues. Here, we demonstrate the effects of short-term vasopressin administration (30 min) on NCC activation in Brattleboro rats with central diabetes insipidus (DI) using the V2 receptor agonist desmopressin (dDAVP). The fraction of NCC abundance in the luminal plasma membrane was significantly increased upon dDAVP as shown by confocal microscopy, immunogold cytochemistry, and Western blot, suggesting increased apical trafficking of the transporter. Changes were paralleled by augmented phosphorylation of NCC as detected by antibodies against phospho-threonine and phospho-serine residues (2.5-fold increase at Thr53 and 1.4-fold increase at Ser71). dDAVP-induced phosphorylation of NCC, studied in tubular suspensions in the absence of systemic effects, was enhanced as well (1.7-fold increase at Ser71), which points to the direct mode of action of vasopressin in DCT. Changes were more pronounced in early (DCT1) than in late DCT as distinguished by the distribution of 11beta-hydroxysteroid dehydrogenase 2 in DCT2. These results suggest that the vasopressin-V(2) receptor-NCC signaling cascade is a novel effector system to adjust transepithelial NaCl reabsorption in DCT.
Nitrogen-doped DLC (diamond-like carbon) coatings were produced on 316L nitrided austenitic steel in direct current and pulsed glow discharge conditions. The chemical composition, surface topography, ...hardness and corrosion resistance of the obtained carbon coatings were examined. The coatings varied in surface morphology, roughness and hardness. Direct current glow discharge made it possible to produce a coating characterized by lower hardness, greater thickness and higher nitrogen content. The coating featured improved corrosion resistance and adhesion compared to coatings produced in the pulsed process.
AISI 316L steel was subjected to nitrocarburizing under glow discharge conditions, which was followed by DLC (diamond-like carbon) coatings deposition using the same device. The coatings were applied ...under conditions of direct current and pulsed glow discharge. In order to determine the influence of the produced nitrocarbon austenite layer and the type of discharge on the microstructure and mechanical properties of the coatings, the following features were analysed: surface roughness, coating thickness, structure, chemical composition, adhesion and resistance to frictional wear. For comparison purposes, DLC coatings were also deposited on steel without a nitrocarburised layer. The obtained results indicate a significant influence of the type of glow discharge on the roughness, hardness, nitrogen content and of the nitrocarburised layer on the resistance to wear by friction and adhesion of the produced coatings.
The key issue in bone implants biomechanics is – besides using biocompatible materials - the optimization of tribological properties of friction pairs occurring in joint implants e.g. knee and hip ...endoprothesis. Increasingly important role in these systems, alongside ceramics-on-ceramics and metal-on-metal, have metal-on-polymer friction pairs. Commonly used in orthopedics ultra-high molecular weight polyethylene (UHMWPE) does not meet the requirements of modern bone implants, mainly because of its harmful wear products which can cause inflammation and osteolysis of surrounding tissues after several years of using the endoprosthesis. Therefore, other polymer materials have been developed to replace UHMWPE, as well as several surface engineering methods are used for enhancing biocompatibility and tribological properties of applied materials. One of the materials to replace UHMWPE is increasingly used in medicine polyetheretherketone (PEEK) – a polymer material with a high biological indifference and mechanical properties.
The article presents characteristics of TiN+Ti2N+αTi(N) nitrided layer produced on Ti6Al4V titanium alloy using glow discharge assisted nitriding process at the plasma potential, also known as the active screen plasma nitriding process and hydrogenated amorphous carbon doped with nitrogen layer a-C:N:H produced via RFCVD process on PEEK-based composite consisting of 10% graphite, 10% carbon fibers and 10% PTFE. Tribological properties of a-C:N:H – TiN+Ti2N+αTi(N) friction pair using “ball-on-disc” and “block-on-roll” tests were examined in correlation with microstructure (TEM, SEM, Raman spectroscopy) and surface morphology and topography (SEM, AFM, optical profilometer).
The goal of this work is to present a new possibility of material solution for a ‘head-acetabulum’ friction pair in hip joint endoprosthesis using PEEK (PEEK T) as a replacement for commonly used UHMWPE and nitrided layer produced on Ti6Al4V titanium alloy using active screen plasma nitriding process.
Amorphous carbon layer, 200nm thick, produced on PEEK composite significantly improved tribological properties of PEEK composite – TiN (nanocrystalline)+Ti2N+αTi(N) layer friction pair, decreasing the friction coefficient by 2 times and minimizing wear of both used materials in the point contact (“ball-on-disc” method) and in surface contact (“block-on-roll” method).
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•200nm thick a-C:N:H layers were deposited on PEEK and PEEK-based composite.•Sp3/sp2 bonding concentration in amorphous carbon layers was about 50%.•Nitrided layer was produced on the surface of Ti6Al4V using active screen process.•a-C:N:H layers significantly decreased friction coefficient in contact with TiN.•PEEK T+a-C:N:H-TiN can be a new friction pair in hip joint replacement (head-cup).
Studies on biocompatibility of AISI 316LVM steel indicate the need to eliminate the nickel from the surface and replace it with other elements of improved biocompatibility. Therefore, in the ...presented work selected physicochemical and mechanical properties of the diffusive nitrocarburized layer formed by plasma potential by means of an active screen made of the Fe-Cr-Ni were studied. In the paper we present results of microstructure and phase composition of the layers, roughness, and surface wettability, potentiodynamic pitting corrosion resistance, penetration of ions into the solution as well as mechanical properties. The studies were conducted for the samples of both mechanically polished and nitrocarburized surfaces, after sterilization, and exposure to the Ringer’s solution. Deposition of the nitrocarburized layer increased the contact angle, surface roughness, surface hardness, and corrosion resistance with respect to the polished surfaces. The nitrocarburized layer is a barrier against the ions release into the solution and sterilization and exposure to Ringer solution. The obtained results showed beneficial increase of both mechanical and electrochemical properties of the deposited layer, and thus the applicability of the proposed method of surface treatment of the 316LVM steel for short-term implants after sterylization.
The layers based on chromium nitride were produced on the AZ91D magnesium alloy using a hybrid surface treatment. The treatment consists of nitriding of the chromium-precoated magnesium alloy. The ...proposed treatment yields diffusive, composite gradient-type chromium nitride layers which are diffusion-bonded to the substrate. The effect of these layers on the corrosion behavior of the AZ91D magnesium alloy was investigated by the potentiodynamic and impedance spectrometry methods. It was found that the formation of the diffusive, composite chromium nitride layers on the AZ91D alloy may result in a significant decrease of the corrosion activity measured by the corrosion potential. This effect is correlated with the layer thickness and becomes significant with relatively thin layers (less than 1 μm thick). Moreover, with the thin layers the impedance modulus is the highest and phase angle has a beneficial character.
► Hybrid method allows to produce diffusive chromium nitride layers on magnesium alloys. ► Chromium nitride layers on AZ91D alloy improve corrosion resistance. ► The best corrosion resistance occur when the CrN layers are sufficiently thin.
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In conventional photoacoustic experiments a signal generated by photoacoustic phenomenon is produced by a forced stimulation of the investigated sample by electromagnetic radiation energy (light) ...which intensity is modulated at a user selected frequency. Resultant photoacoustic signal has the same frequency as the light modulation frequency. The paper presents a new technique of photoacoustic signal generation, based on self-oscillations resulting from a loopback in the signal path consisting of a modulated light source, a photoacoustic chamber, a microphone, and an amplifier. Signal from the amplifier output was used to drive the light source. Gain of the amplifier was chosen in order to obtain total loop gain of the signal path greater than one and positive feedback operation. On contrary to conventional photoacoustic methods, frequency of the photoacoustic signal in the presented self-oscillation method is determined mainly by acoustic properties of the photoacoustic cell, which in the experiments was corresponding to the resonance frequency of the cell. Taking into consideration that resonance frequency of a photoacoustic cell depends on the speed of sound, which is affected by properties of the fluid filling the cell, the method based on self-oscillations can be applied e.g. to quantitative analysis of the investigated substance.
Using Pavlovian conditioned increases in the amplitude of the acoustic startle reflex as a behavioral indicator of fear motivation, the authors previously showed a resistance to extinction after ...repeated associations of cocaine with the fear-evoking conditioned stimulus (CS). In Experiment 1, acute administration of cocaine, amphetamine, and the dopamine (DA)D
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receptor agonist SKF 38393 produced a similar fear enhancement. In Experiment 2, a noncontingent injection of cocaine and SKF 38393 provoked a CS potentiation of acoustic startle in fear-extinguished laboratory rats. Potential behavioral, neurochemical, and neuroendocrine explanations for the effects of psychomotor stimulants on conditional fear were discussed. It was suggested that DA agonist drugs increase fear expression possibly by activating mesoamygdaloid associative neurocircuitry involved in excitatory conditioned fear reactions.
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In the traditional approach to photoacoustic measurements, the light source modulation frequency is fixed, or a resonance tracking mechanism is applied, that adjusts the modulation frequency to the ...instantaneous value of the resonance frequency of the cell, especially in the case of high Q-factor cells. However, photoacoustic measurements can also be based on a novel method in which the light intensity is modulated by the photoacoustic signal induced in the cell, hence forming a photoacoustic oscillator. Frequency of such an oscillator and shape of the resulting photoacoustic signal depend mainly on the resonance properties of the cell, but also on the power of the light irradiating the investigated sample. This paper describes the influence of the intensity of light used for exciting the photoacoustic signal on the operation of such a photoacoustic generator.
