Ruth Hinrichs

The Effect of Argon and Nitrogen Ion Implantation on Nickel-Titanium Rotary Instruments

INTRODUCTION This qualitative study investigated the effect of N(2)(+) and Ar(+) ion implantation on morphologic alterations and fatigue resistance in Pro Taper S1 NiTi (Dentsply-Maillefer, Ballaigues, Switzerland) rotary instruments. METHODS Instruments were divided into three groups: N(2)(+) implanted, Ar(+) implanted, and unmodified control group. All instruments were used to prepare five curved canals in epoxy resin blocks with brushing motion. The instruments were examined in a scanning electron microscope (SEM) before use, after first use, and after the fifth use. A more demanding cyclic fatigue test was undertaken, submitting the instruments to 15-second periods of continuous rotation inside the curved canals without a brushing motion. Crack formation was analyzed with the SEM, and the number of 15-second periods required to fracture each instrument was recorded. RESULTS No significant morphologic alterations were observed in the instruments after the preparation of five canals. Crack density was similar in all groups. In the subsequent cyclic fatigue test, instruments implanted with nitrogen performed worse than those implanted with argon and the control group. Fracture faces show differences in the fracture modes. CONCLUSIONS Ar(+) implantation improved the performance of S1 files moderately, whereas nitrogen ion-implanted files performed worse in the fatigue test. A reduction in file performance seems to be caused by nitrogen diffusion in the grain boundaries, instead of the desired improvement caused by titanium nitride formation.

Silver L1, L2 and L3 cross-sections for ionization and x-ray production by electron impact

The experimental determination of ionization cross-sections and total x-ray production crosssections under electron impact is carried out for the three silver L-subshells. The very complex spectral structure involving several satellite bands was previously investigated by analyzing wavelength-dispersive spectra acquired in an electron microprobe. In this work, careful spectral processing is carried out by means of the POEMA software developed previously, considering the spectral energy intervals which include the main Ag-L emissions. The resulting ionization cross-sections are compared with analytical models based on distorted wave Born approximation calculations, the experimental determinations of the present work being underestimated by these predictions. To the best of the authors’ knowledge, this is the first time these magnitudes are reported in the literature in this energy range. The total L-shell x-ray production cross-sections are also compared with the only previous experimental data found, obtained with different experimental settings.

Hardness evaluation, stoichiometry and grain size of titanium nitride films obtained with plasma nitriding on Ti-6Al-4V samples

Titanium nitride films were formed on the surface of Ti-6Al-4V discs by plasma nitriding (glow discharge) in different N2:H2 atmospheres at several substrate temperatures. In this study the influence of the process parameters on dynamic micro-hardness were investigated. Grain sizes of the nitride films, determined with X-Ray Diffraction, were related to the nitriding parameters. TiNx stoichiometry was determined with Nuclear Reaction Analysis and showed a correlation to substrate temperature during the nitriding process. Micro-hardness measurements were taken on the nitrided surfaces. Grain sizes increased for a particular gas composition of 60%N2+40%H2 where hardness was lowest.

Phase quantification in iron ore

Abstract Quantitative phase analysis in iron ore is necessary to get a controlled blend to produce sinter feed of high quality. Optical microscopy (OM) is the routinely performed technique, but it is time consuming and affected by operator bias. In this work, Mössbauer spectroscopy, X-ray diffraction with Rietveld full profile fitting and thermogravimetric analysis were applied to investigate the reliability of a proposed OM phase quantification procedure. The method is performed on digital micrographs, with visual phase estimation of several subdivisions of the image. In this work, the authors discuss the peculiarities of the Alegria iron ore (Alegria Mine, Quadrilátero Ferrífero, Brazil), which consists mostly of haematite/goethite, with subordinate magnetite content and quartz as principal gangue mineral. The relevance of the quartz fractionation to finer grain sizes is also discussed. Results indicate overestimation of goethite in certain grain size fractions that have to be taken into account for correct phase evaluation.

Structure of the Fe and Ni L X-ray spectra

Fe-L and Ni-L X-ray spectra induced by electron impact were analyzed. The measurements were made on bulk samples using a commercial wavelength dispersive spectrometer, and the spectra were processed with a parameter optimization method previously developed. This procedure allowed for the determination of characteristic energies, relative transition probabilities and natural linewidths. The results obtained are compared to the data found in the literature, when available. Satellite and radiative Auger emissions were also analyzed, energy shifts and relative intensities being determined. Many of these parameters were determined for the first time, which was possible due to the robustness of the spectral processing method used. The line profile introduced here takes into account the differential attenuation at both sides of the absorption edge.

Short range shooting distance estimation using variable pressure SEM images of the surroundings of bullet holes in textiles

Modifications of cotton and polyester textiles due to shots fired at short range were analyzed with a variable pressure scanning electron microscope (VP-SEM). Different mechanisms of fiber rupture as a function of fiber type and shooting distance were detected, namely fusing, melting, scorching, and mechanical breakage. To estimate the firing distance, the approximately exponential decay of GSR coverage as a function of radial distance from the entrance hole was determined from image analysis, instead of relying on chemical analysis with EDX, which is problematic in the VP-SEM. A set of backscattered electron images, with sufficient magnification to discriminate micrometer wide GSR particles, was acquired at different radial distances from the entrance hole. The atomic number contrast between the GSR particles and the organic fibers allowed to find a robust procedure to segment the micrographs into binary images, in which the white pixel count was attributed to GSR coverage. The decrease of the white pixel count followed an exponential decay, and it was found that the reciprocal of the decay constant, obtained from the least-square fitting of the coverage data, showed a linear dependence on the shooting distance.

Morphological alterations of rotary nickel-titanium protaper ® instruments analyzed by SEM: effect of nitrogen ion implantation

Abstract Purpose:This study evaluated the morphological alterations that occur in rotary nickel-titanium instruments during nitrogen-ion implantation. Methods: Instruments were divided into three groups: Group A- ProTaper SX instruments were subjected to ionic implantation with bands of nitrogen ions at 100 keV, ion dose was 1.0 X 1017 ions/cm², Group B- ProTaper SX instruments were subjected to ionic implantation with bands of nitrogen ions at 200 keV, ion dose was 1.0 X 1017 ions/cm², and Group C instruments served as unmodified controls. Each instrument was utilized to prepare five canals in epoxy resin blocks with a brushing motion. The instruments were examined by scanning electron microscopy (SEM) before use and after 60 s and 300 s of work inside canals in epoxy resin blocks. Results: Material loss and distortion were statistically similar in all groups. However, while only one instrument in group A and only one instrument in group B fractured during use, three instruments in group C fractured during use. Conclusion: Nitrogen ion implantation can improve the properties of nickel-titanium rotary instruments. However, widespread adoption by the dental industry may not yet be tenable due to the cost (nitrogen ion implantation is a costly process) and relatively small benefit.