The influence on the bond between the steel fiber and the matrix of the anticorrosive treatments of steel used for concrete reinforcement is not yet fully understood. The topic of steel fiber treatment was not also studied clearly in terms of brass removal before. This paper deals with how the brass on the surface of steel fibers behaves in the UHPC matrix and how it affects its properties. The steel fibers were firstly modified with a number of surface treatments to remove brass on their surface. Some of the treatments have never been tried before for this purpose. Secondly, the surface of the fibers was analyzed by SEM, EDS, XRF, and stereomicroscopy. Lastly, the properties of the composites were analyzed. It was found out that the majority of brass on the surface of the fibers could be removed by mixture of NH3 and H2O2 with a ratio of 3:1 (v/v). It was also found out that the surface treatment slightly affects the mechanical properties, but it does that only by mechanical interlocking between the fiber and the matrix. No dissolution of the surface treatment was observed under the given conditions. According to the results, steel fibers without surface treatment should be used in UHPC if available.
The aim of the presented work was evaluation of an effect of various conditions on the performance of two developed concretes based on alkali-activated slag and cement kiln by-pass dust (BD). BD was used as a partial replacement of natural aggregates while slag as an aluminosilicate precursor activated by a combination of waterglass and sodium hydroxide solution (resulting silicate modulus of 0.5). The concretes differed only in an activator dose which was 4 and 6% of Na2O with respect to the slag weight. The prepared specimens were sealed-cured for the first 28 days and then their resistance to freeze-thaw cycles and aggressive solutions (ammonium nitrate, acetic acid and sulphates) was tested. Evolution of dynamic modulus showed that both concretes resisted well to freeze-thaw cycles as well as to most solutions, where their dynamic modulus tended to increase in most cases or did not change significantly. Only the concrete with 4% Na2O showed poor resistance to acetic acid solution as the specimens completely disintegrated until 50 days.
At present, the risk of generic substitutions in warfarin tablets is still being discussed. The aim of this study was to assess whether API interactions with commonly used excipients may affect the safety of generic replacement of warfarin sodium tablets. These interactions were observed during an accelerated stability study, and the effect of the warfarin solid phase (crystalline/amorphous form) as well as the API particle size distribution was studied. Commercial tablets and prepared tablets containing crystalline warfarin or amorphous warfarin were used. In addition, binary mixtures of warfarin with various excipients were prepared. The structural changes before and after the stability study were monitored by dissolution test in different media, solid-state NMR spectroscopy and Raman microscopy. During the stability study, the conversion of the sodium in warfarin to its acid form was demonstrated by some excipients (e.g., calcium phosphate). This change in the solid phase of warfarin leads to significant changes in dissolution, especially with the different particle sizes of the APIs in the tablet. Thus, the choice of suitable excipients and particle sizes are critical factors influencing the safety of generic warfarin sodium tablets.
Polycrystalline diamond (PCD) is becoming more available cutting material due to developing technologies, but it is still one of the difficult-to-cut materials. Nowadays, sharpening of diamond inserts is usually performed using unconventional machining methods, where the high hardness of the material is not a deciding factor. Apart from electrical technology (WEDM or EDM-G), PCD is also sharpened by laser technology. The production of integral chipbreaker on the rake face of the PCD insert is an advantage of laser technology, in comparison with other technologies. In this research, three types of chipbreakers were designed and used in a real machining process. This was carried out on the workpiece material Ti-6Al-4V alloy, which is generally used in the transport industries and medicine, but still presents great challenges in its machining. Influence of the individual types of integral chipbreakers compared also to the normal PCD insert, which had a polished rake plane, was investigated. This was based on the force loading and the integrity of the machined surface. Wear of the inserts, images from electron microscope were also included in the analysis.
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