Milorad Tomić

Protection of Copper and its Alloys Using Corrosion Inhibitor-Literature Review

A review of the literature dealing with the electrochemical corrosion of copper and its alloys with purpose to find the most suitable inhibitor for its protection has been done. According to their chemical composition of corrosion inhibitors are divided into inorganic and organic inhibitors. Inhibition of alloying metals are possible (such as the addition of arsenic alloy components in brass, preventing its unzincanization). The paper reviews the theoretical basis of application of inhibitors to protect metals from corrosion as well as an overview of current research application of inhibitors to protect copper and copper alloys. Benzotriazole (BTA) is most often used corrosion inhibitor for copper and its alloys in acidic and alkaline solution, because of its high inhibition efficiency. The lowest concentration of inhibitor for protection of copper in various solutions was 0.05%, and for the protection of copper in contact with steel is 0.1%. On the surface of copper and brass BTA forms a protective Cu-BTA film. However, BTA is like many other synthesized organic inhibitors is very toxic and if used in very small concentrations. It turned out that the AETD, AETDA and PTAT good corrosion inhibitors of copper mixed type with the efficiency of inhibition increases with concentration. Due to the adverse effects on the environment, health and other bodies in recent times the focus of research is transferred to the inhibiting action of biological molecules or mixtures of natural compounds called „Green inhibitors“.

Impact of roughness of Zn-Mn coatings on corrosive stability

This paper involves electrochemical deposition of Zn-Mn coatings from four solutions. We measured their roughness and corrosion stability. We used cathodes made of steel of unknown composition that were licensed under the chemical preparation before the electrochemical deposition of dual-Zn-Mn coatings, and we also used the anode of zinc, purity of 99.99%. Dual Zn- Mn coatings were electrodeposited for 15 minutes from all of the solutions at a current densities of 1 A/dm2, 2 A/dm2 and 4 A/dm2. All experiments were carried out galvanostatialy (at constant current) in an electrochemical cell, volume of 500 cm3 and at room temperature. The roughness of electrochemically deposited Zn-Mn coatings was measured by a TR200 device and corrosion stability of deposited coatings by determining the Electrochemical Impedance Spectroscopy (EIS). The results show that the coatings with the smallest roughness are coatings deposited at a current density of 2 A/dm2 from all of the solutions. The exception is solution 3 with the relation [Mn2+]:[Zn2+]=1:2 where the roughness is at the lowest level in comparison to all solutions, ranging from 0.71 to 0.875 μm, and the roughness is lowest at the current density of 4 A/dm2 and is 0.71 μm. Based on electrochemical measurements, the corrosive most stable Zn-Mn coating is deposited at a current density of 2 A/dm2 from all the solutions and at the current density of 4 A/dm2 from solution 3 with a ratio of [Mn2+]:[Zn2+]=1:2. This suggests that the corrosion stability is related directly to the roughness and compactness of Zn-Mn coatings. When it comes to corrosion, the most stable coatings are those with the lowest roughness.

Catalytic activity of sulfuric acid on the morphology of electrochemically obtained copper powder

The subject of the research is influence of sulfuric acid on morphology of electrochemically obtained copper powder during galvanostatic electrolysis mode. In this paper electrodeposition of copper powder from sulphate electrolyte was carried out. Electrolytes with three different concentrations of Cu2+ (7 g/dm3, 18 g/dm3 and 33 g/dm3) were used, each in combination with three different concentrations of H2SO4 (100 g/dm3, 150 g/dm3 and 200 g/dm3), so that copper powder was deposited from nine electrolytes. Copper wire with surface area of 1cm2 was used as cathode, and copper anode in the form of metal sheet was pressed against the wall of electrochemical cell that had volume of 500 cm³. Experiments were carried out at room temperature, and electrolyte stirring was performed using a magnetic stirrer. Copper powder was deposited galvanostatically at current densities of j = 1500 A/m2, j=2000 A/m2 and j=2500 A/m2. Produced copper powder was removed from cathode every three minutes. All the characteristics of powder depend on the size and shape (morphology) of particles and they are mutually correlated. Research of morphology and size of particle was carried out using scanning electron microscopy (SEM). Increase of H2SO4 concentration causes increase in branching of copper powder. It was concluded that the size of copper powder grains reduces with the increase in concentration of H2SO4.

Investigation of corrosion effect on the dynamic strength of some structural steels

By corrosion effect, the surface of the metal becomes so rough that there are reduction in metal strength as a consequence of nicking. It should be added that the continuing effects of corrosion produces deep and sharp notches in the metal. It causes tiny cracks that allow further penetration of corrosion. As results of this activities, the dynamic hardness by simultaneously highly corrosion effect substantially decreases so that it may lead to fatigue failure, as shown in this paper. It is also not possible to establish any qualitative or quantitative legality between dynamic strength and corrosion effects. This hold for the effect of corrosion on unloaded metal element. This must be tested in all chance.

O JEDNOJ ANALOGIJI IZMEĐU SLOŽENIH HEMIJSKIH REAKCIJA I ELEKTRIČNIH KOLA

U ovom radu, kao za karakteristican primer iz hemijske kinetike, za reakciju prvog reda, sistem složenih hemijskih jednacina matematickim transformacijama sveden je na sistem homogenih i nehomogenih diferencijalnih jednacina prvog i drugog reda, koje su pogodne za predstavljanje preko elektricne analogije. Nakon toga, posmatrana su elektricna kola sa rednom i paralelnom vezom u kojima su prisutne sve tri karakteristicne otpornosti i to sa i bez strujnog izvora. Primenom Kirhofovih zakona, izvedene su pogodne diferencijalne jednacine u zavisnosti od naelektrisanja, napona i jacine struje, a koje predstavljaju opsti model za uspostavljanje analogije sa ranije izvedenim slicnim hemijskim jednacinama za određivanje koncentracije jedinjenja, u kojima su ukljucene i konstante brzine reakcije. Na kraju, na primeru jedne od karakteristicnih izvedenih elektricnih relacija u diferencijalnom obliku, dat je tabelarni prikaz analogije između elektricnih i velicina koje figurisu u hemijskim jednacinama, kao i neke mogucnosti primene prikazanih analogija.

JEDAN PREDLOG ZA EFIKASNIJI PRORAČUN PARAMETARA KOD SLOŽENIH HEMIJSKIH REAKCIJA

U prvom delu rada, za karakteristican primer složene hemijske reakcije, proanalizirano je nekoliko matematickih metoda za resavanje sistema diferencijalnih jednacina kojima se opisuje proces, a koje se najcesce koriste u inženjerskoj teoriji i praksi. Analiza je izvrsena sa aspekta neophodnog matematickog znanja, potrebnog vremena za resavanje problema, mogucnosti greske kao i kontrole dobijenih rezultata. U drugom delu rada, dat je predlog za efikasnije resavanje posmatranog problema pri cemu je primenjen princip redukcije sistema na jednu diferencijalnu jednacinu, koju je najpogodnije posmatrati kao nehomogenu jednacinu I reda sa konstantnim koeficijentima, zavisnu od vremena. Pokazano je da je predložena metoda pogodnija u odnosu na postojece, s obzirom da ima određene prednosti i može se koristiti kao alternativa istim.