Studies assessing the erosive potential of soft drinks have employed long time intervals of immersion that may not accurately depict the impact of frequent soft drink consumption on enamel. This in vitro study assessed the effect of a cola drink on enamel, replicating an actual drinking pattern. Six groups of 4 human enamel slabs were immersed (5 min each bath) in fresh cola drink, with immersions taking place with or without agitation, and under 3 regimes of frequency intake (low intake, 1 immersion/day; medium, 5/day; high, 10/day). Quantitative assessments of surface erosion were done over an 8-day interval using surface microhardness testing (Vickers). Results showed a sharp decrease from baseline (mean value 352.1 Vickers Hardness Number, SD 32.5) to day 1 (269.3, SD 41.0) and then continued decreasing throughout the assay, although less markedly, to reach 204.5, SD 45.4 on day 8. Microhardness decreased regardless of frequency regime, except on day 8, on which slabs from the low intake group were harder (233.2, SD 25.0) than slabs from the high intake group (169.8, SD 49.5; p < 0.05). Results from the ANOVA on the factorial experiment indicated that the role of agitation was statistically significant (d.f. = 1, F = 7.2, p = 0.020) while the level of intake was of borderline significance (d.f. = 2, F = 3.2, p = 0.075). The main effect resulting from the joint roles of agitation and intake indicated that there was an important interaction between the two variables (d.f. = 3, F = 4.5, p = 0.023).

A systematic study on the structural and magnetic properties of Fe100-xCox alloys (10<x<90, Δx=10 in wt. percent) obtained by mechanical alloying is presented. Elemental powders of Fe and Co mixed in an adequate weight ratio were milled at room temperature in a shaker mixer mill using vials and balls of hardened steel as milling media with a ball : powder weight ratio of 12 : 1. The mixtures were milled for 3 h. The results show that, after milling, for almost all the composition (up to x=60), solid solutions based on bcc structures were obtained. For Co-rich alloys (x≥70), different phases were found, revealing the formation of a metastable intermetallic phase (FeCo, wairauite) together with fcc-Co and hcp-Co phases. The specific saturation magnetization increases by increasing Co content, reaching a maximum value of 225 emu/g for hcp-Fe70Co30, and then it shows a diminution up to 154 emu/g for bcc-Fe30Co70. All studied alloys (Fe100-xCox) present low coercivity, in the range from 0 to 65 Oe, which is lower than reported. The coercivity increases with the increment in Co, reaching a maximum of 64.1 Oe for Fe40Co60. After that, the coercivity falls up to 24.5 Oe for Co-rich alloys, which make them a very low coercive material.

We report on an alternative route for the synthesis of crystalline Co-28Cr-6Mo alloy, which could be used for surgical implants. Co, Cr and Mo elemental powders, mixed in an adequate weight relation according to ISO Standard 58342-4 (ISO, 1996), were used for the mechanical alloying (MA) of nano-structured Co-alloy. The process was carried out at room temperature in a shaker mixer mill using hardened steel balls and vials as milling media, with a 1:8 ball:powder weight ratio. Crystalline structure characterization of milled powders was carried out by X-ray diffraction in order to analyze the phase transformations as a function of milling time. The aim of this work was to evaluate the alloying mechanism involved in the mechanical alloying of Co-28Cr-6Mo alloy. The evolution of the phase transformations with milling time is reported for each mixture. Results showed that the resultant alloy is a Co-alpha solid solution, successfully obtained by mechanical alloying after a total of 10 h of milling time: first Cr and Mo are mechanically prealloyed for 7 h, and then Co is mixed in for 3 h. In addition, different methods of premixing were studied. The particle size of the powders is reduced with increasing milling time, reaching about 5 mum at 10 h; a longer time promotes the formation of aggregates. The morphology and crystal structure of milled powders as a function of milling time were analyzed by scanning electron microscopy and XR diffraction.

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