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RESEARCH ARTICLES

 

DOI: 10.15199/40.2020.3.1

Hydrogenation and corrosion properties of nanocrystalline A₂B₇ type, La-Mg-Ni based intermetallics modified by nickel sputtering

DYMEK M.

Faculty of Chemistry, Department of Advanced Material Technologies, Wroclaw University of Science and Technology, 50-370 Wroclaw, Poland

NOWAK M.

JURCZYK M.

Institute of Materials Science and Engineering, Poznan University of Technology, 61-138 Poznan, Poland

BALA H.

Institute of  Chemistry, Jan Dlugosz University in Czestochowa, 42-200 Czestochowa, Poland

In the paper, hydrogenation and corrosion properties of three kinds of nanocrystalline La1.5Mg0.5Ni7 type alloys obtained by mechanical alloying (MA) method are discussed in view of their application as anodic materials for Ni/MH batteries. Partial substitutions of cobalt for nickel and gadolinium for lanthanum and then magnetron sputtering of the intermetallic powders with amorphous nickel distinctly change functional parameters of the hydrogen storage material. It is shown that 5.5 at.% cobalt addition markedly improves the alloy activation but worsens its corrosion resistance in concentrated KOH solution. On the other hand, partial substitution of lanthanum by Gd (2.2 at.%) ensures large exchange currents for H2O/H2 system. Presence of Ni coatings on alloy particles is generally advantageous from the material H-storage properties, although they slow down a little hydrogen transport during electrode discharge.

Keywords: La-Ni-Mg intermetallics, Hydrogenation properties, mechanical alloying, Ni-coatings, capacity fade, corrosion rate

2020, Vol. 63, nr 3, pp.67-71

Ref. 21

 

 

DOI: 10.15199/40.2020.3.2

Analysis of causes of cracks and corrosion of reinforced concrete walls and balcony slabs in a multistorey building with an upward extension

JAŚNIOK M.

JAŚNIOK T.

Department of Building Structures, Faculty of Civil Engineering, Silesian University of Technology

This article presents an analysis of damage to reinforced concrete slabs and walls in two unoccupied lowest stories of the multi-family building with a few-storey upward extension incompatible with the design. A significant increase in loading caused by that extension was supposed to cause cracks in walls and floors at the lowest stories. Moreover, rainwater penetrating cracks for 25 years was expected to induce corrosion of concrete and reinforcing steel reducing the load capacity of structural members. Strength tests, measurements of the reinforcement and tests on protective properties of concrete cover to reinforcing steel were performed as part of evaluating conditions of the structure. Test results included in numerical calculations of the structure model, provided the clear finding that concrete shrinkage was the reason for cracks in reinforced concrete slabs and walls. Thus, the upward extension did not cause damage to the structure, and concrete maintained its mechanical and protective properties to reinforcement despite the long-term effect of rainwater.

Keywords: reinforced concrete, corrosion, scratches, shrinkage, finite element method (FEM)

2020, Vol. 63, nr 3, pp. 72-77

Ref. 15

 

 

DOI: 10.15199/40.2020.3.3

The influence of the glow discharge nitriding or oxynitriding process on the corrosion resistance of stainless steel orthodontic arch-wires

KAMIŃSKI J.

RĘBIŚ J.

WIERZCHOŃ T.

Warsaw University of Technology. Faculty of Materials Science and Engineering. Wołoska 141. Warsaw. Poland.

MAŁKIEWICZ K.

Department of Orthodontics. Medical University of Lodz. Pomorska 251. Lodz. Poland

The paper presents comparative results of corrosion resistance tests on AISI304 steel orthodontic arch-wires, before and after low temperature plasma nitriding or oxynitriding, carried out at cathodic potential. Oxynitriding processes were carried out at different concentrations of air added. Corrosion resistance tests of diffusion surface layers were carried out via electrochemical impedance spectroscopy and the potentiodynamic method in non-deaerated artificial saliva solution at 37 °C. The results were complemented with analysis of the alloy’s structure and surface topography. They showed an increase in corrosion resistance of AISI304 steel after glow-discharge nitriding and oxynitriding. In addition, due to the considerable roughness of the initial material, the surface layers produced are susceptible to pitting corrosion. Increasing the concentration of air in a reactive atmosphere negatively affects the electrochemical homogeneity of the layer, which is not translated, due to the low concentration of chlorides in corrosion environment, to reducing the durability of the produced layers. This is evident in the values of breakdown potential (Enp) initiating pitting corrosion, which are comparable in all cases and amount to approx. 820 mV ± 30 mV, slightly exceeding (by approx. 100 mV) the breakdown potential of the initial material. Only in the case of the layer with the maximum oxygen addition, the presence of a transpassive area is observed within which the oxynitrided layer is redeveloped, resulting in the observed exfoliation process of the layer.

Keywords: stainless steel arch-wires; glow-discharge nitriding and oxynitriding; corrosion resistance; artificial saliva

2020

Vol. 63, nr 3, pp. 78-83

Ref. 15

 

 

DOI: 10.15199/40.2020.3.4

Corrosion resistance of EN AC 47100 cast aluminum alloy with Cr(III) conversion coating deposited in the presence of a zirconium catalyst

WINIARSKI J.

SZCZEPAŃSKA J.

Department of Advanced Material Technologies, Faculty of Chemistry, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27,

50-370 Wrocław, Poland

GRALAK E.

Heiche Polska Sp. z.o.o., ul. Jarzębinowa 2, 55-200 Stanowice, Poland

MAZUR-NOWACK A .

SZCZYGIEŁ B.

Department of Advanced Material Technologies, Faculty of Chemistry, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27,

50-370 Wrocław, Poland

AlSi12Cu1(Fe) cast alloy was subjected to passivation in the bath using Cr(III) compounds. Neutral salt spray test showed that the addition to the bath of fluorocomplex zirconium compounds in the amount of 800 ppm contributed to the formation of a conversion coating with a longer protective effect – up to 480 hours, than the analogous coating, but without zirconium (up to several dozen hours). AFM and SEM analyzes showed that in the presence of a zirconium fluorocomplex, a coating with a spheroidal morphology and developed surface is formed, which even manifested locally in the form of small cracks. Semi-quantitative EDS analysis showed on a microscale a significant inhomogeneity in the distribution of elements on the surface of aluminum covered with a conversion coating. The observed segregation of the elements forming the coating (including Cr, Zr, F, O) well correlated with the microstructure and phases distribution characteristic of this aluminum alloy.

Keywords: Aluminum; Cr(III) chromating; Conversion coatings; SEM; AFM; Salt spray chamber;

2020, Vol. 63, nr 3, pp. 84-89

Ref. 8

 

 

DOI: 10.15199/40.2020.3.5

Thermodynamics of high temperature corrosion of selected metals in air-HF-H₂O atmosphere

SMOŁA G.

GRZESIK Z.

AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Department of Physical Chemistry and Modeling, al. A. Mickiewicza 30, 30-059 Kraków, Poland

KUPKA T.

ERB M.

H.C. Starck Tantalum and Niobium GmbH, Im Schleeke 78 – 91, 38642 Goslar, Germany

The stability of corrosion products obtained from selected metals (Fe, Cr, Ni and Al) was analysed at 900 ^oC in a complex industrial atmosphere containing 53.1% water vapour, 38.5% air and 8.3% hydrogen fluoride. These aggressive conditions are located inside a reactor foreseen for niobium oxide, Nb₂O₅, production by means of a new method that guarantees its high purity. The goal of these thermodynamic considerations was to single out materials exhibiting the highest heat resistance in the previously mentioned aggressive gas environment. The theoretical considerations carried out in this work include identifying partial pressures of individual aggressive gases in the air-H₂O-HF mixture, constructing phase stability diagrams in Fe-O-F, Ni-O-F, Cr-O-F and Al-O-F systems, as well as determining pressures of volatile iron, nickel and aluminium fluorides as a function of fluorine pressure. Stability analysis of products from reactions between individual metals and both fluorine and oxygen, as well as the previously established volatile fluoride pressures, lead to the conclusion that nickel demonstrates the highest heat resistance in the studied conditions. The presence of the remaining metals in potential alloys for reactor element production appears to be undesired and requires experimental verification. This conclusion is based both on the relatively low iron and chromium fluoride melting temperatures (940^oC and 894^oC, respectively), and the high-pressure values for volatile aluminium and iron fluorides.

Keywords: fluorine; oxygen; thermodynamics; high temperature corrosion; stability

2020, Vol. 63, nr 3, pp. 90-94

Ref. 9

 

 

DOI: 10.15199/40.2020.3.6

Is passivation of zinc coating a guarantee of its corrosion resistance?

DRÓŻDŻ N.

HAJDUGA M.

SMOSZNA S.

Akademia Techniczno-Humanistyczna w Bielsku-Białej

WĘGRZYNKIEWICZ S.

Belos-PLP S.A. w Bielsku-Białej

OLAK M.

P.P.U.H. GAL Sp. z o.o. Sp.k. w Żorach

It is often required that, in addition to effective protection against corrosion, the structures should also have an aesthetic appearance of the applied coatings. It is difficult, especially when products after hot dip galvanizing (HDG) are exposed to weather conditions i.e. moisture or rainfall. Despite the fact, that the silver shiny zinc coating fades with time and becomes gray after a few months, natural zinc corrosion products, so-called „white corrosion”, is unacceptable to final customers. One of the way to protect galvanized products against the appearance of the first zinc corrosion products is passivation. The aim of this work was to compare the effects of chemical and polymer passivation and to implement the best solution. The corrosion resistance of the zinc coating was evaluated on the basis of the NSS test according to PN-EN ISO 9227 and tests in field conditions. The metallographic analysis was performed by assessing the microstructure of the zinc coating and measuring its thickness. There were no differences between chemical and polymer passivation in terms of corrosion resistance of the zinc coating. Due to the economic aspect, it is more reasonable to use chemical passivation to protect products against the formation of white corrosion.

Keywords: hot dip galvanizing, white corrosion, zinc coating, corrosion resistance, chemical passivation, polymeric passivation

2020, Vol. 63, nr 3, pp. 95-100

Ref. 9

 

 

CORROSION PROTECTION IN PRACTICE

 

Effect of the method of removing zinc coatings defects produced by the hot-dip galvanizing on their corrosion resistance

SMOSZNA S.

HAJDUGA M.

DRÓŻDŻ N.

Akademia Techniczno-Humanistyczna w Bielsku-Białej

WĘGRZYNKIEWICZ S.

Belos-PLP S.A. w Bielsku-Białej

OLAK M.

P.P.U.H. GAL Sp. z o.o. Sp.k. w Żorach

The primary purpose of the galvanized coating is to protect the iron or steelwork against corrosion, while considerations related to aesthetics or decorative features should be secondary. Zinc coatings manufactured in industrial conditions may have many potential appearance defects, which, do not have a decisive impact on the protection of the substrate against corrosion. The post-galvanizing defects are usually the result of improper surface preparation of steel products before HDG (hot dip galvanizing). However, this has some influence on their corrosion resistance. The aim of the work was was to determine the effect of removing zinc coatings defects on their corrosion resistance. The tests were carried out on hot-dip galvanized samples of S235 steel with zinc coating defects, i.e. with non-galvanized places as a result of using an anti-weld, an oil marker or traces of stickers. Zinc paint and a corrector commonly used in Galvanizing Plants: „zinc spray” were used to repair the zinc coating. Metallographic analysis was performed to assess the microstructure of the zinc coatings. The coating thickness was measured in acc. with PN-EN ISO 1463. Corrosion resistance of the zinc coatings after repair was assessed on the basis of NSS test results acc. to PN-EN ISO 9227. This work is practical. The presented test results clearly indicate that the use of the „zinc spray” corrector does not provide good corrosion resistance in accordance with PN-EN ISO 1461

Keywords: hot-dip galvanizing, post-galvanizing defects, zinc coating, corrosion resistance

2020, Vol. 63, nr 3, pp. 101-105

Ref. 8