Volume 64 (2020): Edizione 3 (October 2020)

In a coronary angioplasty or orthopaedic surgery, metallic implants are often used to provide mechanical support to the healing tissues. In some situations, this support is really needed only temporarily. After tissue recovery, the implant no longer provides any benefits and can trigger adverse reactions. An optimal solution might be the short-term implants which are able to decompose in situ and can be readily excreted from the body. Iron-based materials are promising candidates for application in biodegradable devices. For the successful application, the ability to control the material’s corrosion rate is important. In this contribution, the corrosion of iron-iron oxide composites is investigated. In order to obtain such materials, iron-oxide granules were incompletely reduced, compacted and sintered. Materials consisting of a pure iron and iron oxides were obtained. Specimens from as-sintered materials and materials reduced once again after sintering were prepared. Potentiodynamic polarization testing in Hanks’ solution indicated that specimens underwent a galvanic corrosion, where the release of ferrous ions from iron surfaces represents the anodic reaction and the oxygen reduction on surfaces of both iron and iron oxides represents the cathodic reaction. Changes in the content of oxides resulted in anticipated shifts in corrosion potential and apparent corrosion current density.

In the collections of Technical Museum in Brno, large number of historical vehicles is placed. During the operation, parts of their motors are being fouled. Frequently, they become even immobile (e. g. due to a fouled fuel system). In this case, the method using ultrasound with a suitable concentrate appears as the most suitable. In fact, ultrasound works also in inaccessible places with large efficiency. Not only the chosen solution influences the cleaning efficiency, but also parameters as time, bath temperature and ultrasound frequency. The cleaning process was evaluated according to the volume of removed dirt and by observing wettability change using the measuring of contact angle of a water drop. The ultrasound shock waves influence the surface to a certain extent also mechanically. That is why, the ultrasound effect on defects in the structure was observed. The aggressivity of cleaning concentrates was evaluated on the ground of determination of dissolved metals in the baths by ET AAS method.

A typical green layer of patina starts to cover copper in atmosphere condition, which is aesthetically acceptable and also provides protective properties. This work investigates stability of the artificial patina layer based on sulphates prepared from a gaseous phase during two-year exposure in atmosphere condition. XRD and SEM were employed to verify the composition and morphology of artificial patina. Colour and patina coverage were compared before and after exposure also. According to results after 1 and 2 years of exposure, it is possible to see changing of hydroxyl sulphates to more stable brochantite and filling pores in the patina layer. There is almost no colour change, however lower patina coverage is slightly evident due to precipitation and abrasive effect.

Formation of natural patina on copper and copper alloys objects takes tens of years. There are solutions for patination, which are used in restorers’ practice. However, these artificial patinas are usually based on nitrates, carbonates or chlorides. Patina based on brochantite is the most stable phase under atmospheric conditions. This type of patina was successfully formed in laboratory in a small exposure chamber with higher content of SO₂. This work is next step of the experiment to make this method become more practicable. It started with construction 2 m³ exposure chamber and simulation of ideal conditions for patination process. The length of drying phase, homogeneity of conditions, pH of feeding water, colour of patina, placement of samples and final appearance were observed. The chamber construction allows to achieve ideal pH value of feeding water, samples surface became dry during the ventilation and temperature during condensation was stable at 40 °C. These conditions are ideal for patination process.

The search deals with the possibilities of increasing the fire resistance of paper, cardboard or paperboard. The article includes the principles of fire retardancy as well as requirements for a suitable preparation and lists substances and mixtures which, according to the literature, are/were used in the manufacturing process or after-treatment of paper products. The article is also continuously supplemented by examples from the patent literature.