Gorana Baršić

Influence of surface layer on mechanical and corrosion properties of nickel-titanium orthodontic wires

OBJECTIVE To analyze the effect of various coating formulations on the mechanical and corrosion properties of nickel-titanium (NiTi) orthodontic wires. MATERIALS AND METHODS Uncoated, rhodium-coated, and nitrified NiTi wires were observed with a three-point-bend test, surface roughness (Ra) measurement, scanning electron microscopy, energy dispersive spectroscopy, and electrochemical testing (open circuit potential, electrochemical impedance spectroscopy, and cyclic polarization scan). Differences in the properties of tested wire types were analyzed with analysis of variance and Tukey post hoc test. RESULTS Uncoated and nitrified NiTi wires showed similar mechanical and anticorrosive properties, while rhodium-coated NiTi wires showed the highest Ra and significantly higher modulus of elasticity, yield strength, and delivery of forces during loading but not in unloading. Rhodium-coated NiTi wires also had the highest corrosion current density and corrosion potential, lowest impedance modulus, and two time constants on Bode plot, one related to the Rh/Au coating and the other to underlying NiTi. CONCLUSION Working properties of NiTi wires were unaffected by various coatings in unloading. Nitrification improved corrosion resistance. Rhodium coating reduced corrosion resistance and pronounced susceptibility to pitting corrosion in artificial saliva because of galvanic coupling between the noble coating and the base alloy.

Development of nano-roughness calibration standards

At the Laboratory for Precise Measurements of Length, currently the Croatian National Laboratory for Length, unique nano-roughness calibration standards were developed, which have been physically implemented in cooperation with the company MikroMasch Trading OU and the Ruđer Boskovic Institute. In this paper, a new design for a calibration standard with two measuring surfaces is presented. One of the surfaces is for the reproduction of roughness parameters, while the other is for the traceability of length units below 50 nm. The nominal values of the groove depths on these measuring surfaces are the same. Thus, a link between the measuring surfaces has been ensured, which makes these standards unique. Furthermore, the calibration standards available on the market are generally designed specifically for individual groups of measuring instrumentation, such as interferometric microscopes, stylus instruments, scanning electron microscopes (SEM) or scanning probe microscopes. In this paper, a new design for nano-roughness standards has been proposed for use in the calibration of optical instruments, as well as for stylus instruments, SEM, atomic force microscopes and scanning tunneling microscopes. Therefore, the development of these new nano-roughness calibration standards greatly contributes to the reproducibility of the results of groove depth measurement as well as the 2D and 3D roughness parameters obtained by various measuring methods.

Influence of various fluoride agents on working properties and surface characteristics of uncoated, rhodium coated and nitrified nickel-titanium orthodontic wires

Abstract Objective. To analyze the effect of various fluoride formulations in commercially available agents on working properties of various nickel-titanium orthodontic wires. Materials and methods. Uncoated (NiTi), rhodium coated (RhNiTi) and nitrified (NNiTi) wires were immersed to dH2O, MiPaste, Elmex and Mirafluor for 1 h. Unloading slope characteristics (average force, bending action of the force and average plateau length) and the percentage of useable constant force during unloading were observed. Surface roughness (Ra) was measured. SEM and EDS were used for observation of the surface. Results. NiTi had decreased loading and unloading elastic modulus (E) and yield strength (YS) after immersion to MIPaste and Mirafluor. The unloading YS decreased in the RhNiTi by the MIPaste. The loading and unloading YS of the NNiTi increased in Elmex and increased average plateau force. RhNiTi showed higher average plateau length and the percentage of useful constant force during unloading in Mirafluor and the average plateau force lowered after immersion to MIPaste. The unloading slope characteristics for NiTi were affected by all three prophylactic agents, mostly by Mirafluor, and produced significantly lower forces during both loading and unloading, similarly to the NNiTi wires. The RhNiTi had the lowest forces during both loading and unloading in MIPaste. All results were at significance; p < 0.05. Difference in Ra was observed for RhNiTi after immersion to the MI Paste (p < 0.001; η2 = 0.761). Conclusion. The NiTi and NNiTi wires lose less working force when combined with Elmex. The RhNiTi improve their working properties with Mirafluor and deteriorate when combined with MiPaste.

Uncertainty Estimation of Coating Thickness Measurement Results

Abstract This contribution presents an estimation of the measurement uncertainty of coating thickness measurement results. The measurements were performed on a steel sheet sample with an outside shell plating. The sample is protected against corrosion with two layers of 100 ¼m thick dry film. In the present case, the criteria of “80-20” have been applied. The measurement uncertainty evaluation has been carried out using Monte Carlo simulations (MCS method) in accordance with the document OIML G 1-101 Edition 2008 (E) Evaluation of Measurement Data – Supplement 1 to the Guide to the Expression of Uncertainty in Measurement – Propagation of Distributions Using a Monte Carlo Method. The criteria “80-20” was evaluated based on the mean coating thickness measurement results, as well as, on the basis of the complete measuring information. Aside from the expected value, complete measuring information comprises the value of measurement uncertainty. In the case where measurement result is described only as the mean of the measurement values a wrong conclusion regarding the fulfillment “80-20” is reached.

Nano-calibration standard with multiple pitch and step height values

In 2011 Croatian National Laboratory for Length (HMI/FSB-LPMD) developed calibration standards which have been physically implemented in cooperation with the company MikroMasch Trading OU and the Ruđer Boskovic Institute. Specific design of standards makes them suitable for calibration of optical instruments, stylus instruments, scanning electron microscopes, atomic force microscopes and scanning tunnelling microscopes. Therefore, the developed calibration standards greatly contribute to the reproducibility of measurement results for groove depth well as the 2D and 3D roughness parameters obtained by various measuring methods. After a number of measurements conducted on developed standards, based on which new knowledge was acquired, HMI/FSB-LPMD designed a new standard for the field of dimensional nanometrology. This paper presents the design of a new standard that is still suitable for calibration of different types of measuring instruments, i.e. methods, but has a larger measurement capability in terms of measuring ranges in vertical and lateral direction.