The Konkoly Blazhko Survey: Is light-curve modulation a common property of RRab stars?

A systematic survey to establish the true incidence rate of the Blazhko modulation among short-period, fundamental-mode, Galactic field RR Lyrae stars has been accomplished. The Konkoly Blazhko Survey (KBS) was initiated in 2004. Since then more than 750 nights of observation have been devoted to this project. A sample of 30 RRab stars was extensively observed, and light-curve modulation was detected in 14 cases. The 47% occurrence rate of the modulation is much larger than any previous estimate. The significant increase of the detected incidence rate is mostly due to the discovery of small-amplitude modulation. Half of the Blazhko variables in our sample show modulation with so small amplitude that definitely have been missed in the previous surveys. We have found that the modulation can be very unstable in some cases, e.g. RY Com showed regular modulation only during one part of the observations while during two seasons it had stable light curve with abrupt, small changes in the pulsation amplitude. This type of light-curve variability is also hard to detect in other Survey's data. The larger frequency of the light-curve modulation of RRab stars makes it even more important to find the still lacking explanation of the Blazhko phenomenon. The validity of the [Fe/H](P,phi_{31}) relation using the mean light curves of Blazhko variables is checked in our sample. We have found that the formula gives accurate result for small-modulation-amplitude Blazhko stars, and this is also the case for large-modulation-amplitude stars if the light curve has complete phase coverage. However, if the data of large-modulation-amplitude Blazhko stars are not extended enough (e.g. < 500 data points from < 15 nights), the formula may give false result due to the distorted shape of the mean light curve used.Comment: Accepted for publication in MNRAS, 14 pages, 7 Figure

Corrosion resistance evaluation of Ni-P\nano-ZrO 2 composite coatings by electrochemical impedance spectroscopy and machine vision method : Corrosion resistance evaluation by EIS and machine vision

Ni-P\nano-ZrO2 composite coatings were obtained on the AISI 304 steel substrate by the electroless method from a bath containing dodecyltrimethylammonium bromide (DTAB). This cationic surfactant prevents ZrO2 agglomeration in the bath and affects the ZrO2 content in the coating, hence it alters functional properties of the coatings. It has been found in this study that corrosion resistance of the composite coatings depends on the surfactant concentration in the bath. The estimation of corrosion resistance was carried out by electrochemical impedance spectroscopy. The degree of the sample surface coverage with corrosion products was determined by the machine vision method. The coating obtained from the 0.88 g/dm3 DTAB solution showed the best protective properties. The machine vision method was shown to be an effective complementary tool to evaluate protective properties of the coatings

Machine Vision System for Corrosion Detection as an Additional Tool beside EIS for Evaluation of Protective Properties of Electrolessly Deposited Ni-P Coatings

The electroless deposition technique was used to obtain Ni-P coatings with various phosphorus content. Machine vision method was applied as a tool for the analysis and interpretation of the data provided by electrochemical impedance spectroscopy (EIS) corrosion studies. The degree of corrosion of the coating surface could be determined by this method. The combination of both methods allows a more complete evaluation of the protective properties of the obtained coatings

The effect of suspension bath composition on the composition, topography and structure of electrolessly deposited composite four-component Ni–W–P–ZrO2 coatings

Composite four-component Ni–W–P–ZrO2 coatings were electrolessly deposited from a bath with different concentrations of aminoacetic acid (glycine—the complexing agent), sodium tungstate(VI) and zirconium(IV) oxide at different pH values. Concentration distribution curves were determined for nickel–aminoacetic acid complexes as a function of the bath pH at different metal ion/complexing agent concentration ratios. It has been shown that the bath pH and the complexing agent concentration have the strongest effect on the composition and structure of the coatings. As the bath pH is lowered and the aminoacetic acid concentration is increased, the phosphorous content in the coating increases. In composite four-component Ni–W–P–ZrO2 coatings (similarly as in electroless two- and three-component nickel coatings), as the phosphorous content in the coating increases, the crystallinity of the coating decreases. Diffraction patterns deposited at pH 5 have only one peak corresponding to nickel: Ni(1 1 1) at 2Θ = 44°. In the diffraction patterns at pH 8 one can observe sharp peaks for 5 crystalline planes: (2 0 0), (2 2 0), (3 1 1), (2 2 2) and dominant (1 1 1). After heat treatment at 400 °C for 1 h a nickel phosphide (Ni3P) phase appears (besides the crystalline nickel phase) in the coatings. Heat treatment also results in an increase in crystallite size from 1.5 to 2.0 to about 3.0 nm

The rate of electroless deposition of a four-component Ni–W–P–ZrO2 composite coating from a glycine bath

Four-component Ni–W–P–ZrO2 composite coatings were electroless deposited. A bath containing aminoacetic acid as the agent complexing nickel ions, and sodium tungstate(VI) as the source of tungstate was used. It has been determined that as the bath's pH increases (from 5 to 6) so does the rate of coating deposition while the phosphorus content in the coating decreases. Both an increase in the aminoacetic acid concentration and an increase in the sodium tungstate cause a reduction in the rate of deposition of the Ni–W–P–ZrO2 coating. Changes in the concentration of the two components in the bath result in a change in the composition of the coatings. When the concentration of the components is too high the bath loses its stability and a sediment precipitates itself. The ZrO2 content in the coating depends most on the amount of this powder in the suspension

Aminoacetic acid as complexing agent in baths for electroless deposition of Ni–W–P coatings

Ni–W–P alloy coatings were deposited from a bath containing, nickel sulphate (VI), sodium tungstate (VI), sodium hypophosphite, sodium formate, and a complexing agent. The complexing agents were formic acid, acetic acid, lactic acid, succinic acid, malic acid, malonic acid, aminoacetic acid and triethanoloamine. It is shown that Ni–W–P coatings are deposited the slowest when complexing agents with the highest stability constants are used. As the deposition rate increases, i.e. in the presence of less stable complexing compounds, the amount of tungsten in the coating decreases. When aminoacetic acid and citric acid were used, the tungsten content in the coating amounted to ∼2 wt-%, depending on the complexing agent concentration and the pH of the bath

Impedance spectroscopy studies of electroless Ni-P matrix, Ni-W-P, Ni-P-ZrO 2 , and Ni-W-P-ZrO 2 coatings exposed to 3.5% NaCl solution : Impedance spectroscopy studies

Ni–P matrix, ternary Ni–W–P and Ni–P–ZrO2 coatings, and quaternary Ni–W–P–ZrO2 coatings were deposited using electroless method from a glycine bath. Their corrosion resistance was evaluated by electrochemical impedance spectroscopy (EIS) for various immersion times in a 3.5% NaCl solution. From among the investigated coatings, the ternary Ni–W–P coatings show the highest resistance to corrosion in the first hour of exposure to the 3.5% NaCl medium. An addition of ZrO2 adversely affects the performance of both the Ni–P coatings and the Ni–W–P coatings. For all the coatings, including the ones containing tungsten, a marked decrease in pore resistance (Rpor) over time is observed. This means that their corrosion resistance and capacity to protect the substrate decline. On the other hand, after 24 h immersion in the 3.5% NaCl solution the Ni–W–P coating shows the highest low-frequency impedance modulus (|Z|f = 0.01 Hz). As regards corrosion resistance, the Ni–P coatings and the Ni–W–P coatings perform best

Electroless deposition of Ni–P–nano-ZrO2 composite coatings in the presence of various types of surfactants

Ni–P–nano-ZrO2 coatings were produced using the electroless deposition technique. To prevent agglomeration of zirconia nanoparticles in the plating bath, various surfactant additives (anionic, cationic, and nonionic) were used. The most stable bath was obtained with the addition of dodecyltrimethylammonium bromide (DTAB). The impact of this surfactant on the deposition rate, coating composition, and topography, as well as ζ potential of particles, was examined. Surface morphology and composition of the Ni–P–nano-ZrO2 composite coatings was analyzed by various techniques including scanning electron microscopy (SEM) equipped with in situ energy-dispersive X-ray (EDX) spectroscopy. Coatings with a clearly greater amount of zirconia (21.88–22.10 wt.%) were obtained from baths containing DTAB in concentrations equal to or above its critical micelle concentration (cmc). For these surfactant concentrations, the reduction of Ni and P content was observed