Emerald | Anti-Corrosion Methods and Materials

Corrosion Resistance Enhancement of Ti–47Al–2Cr by Thermal Treatment in a Controlled Atmosphere

Ehsan Saebnoori, Taghi Shahrabi, Alireza Sabour Rouhaghdam, Majid Jafarian — 2012-03-17 00:00:00.0

Abstract

Purpose - The purpose of this study was to investigate the effect of thermal treatment at low partial pressure of oxygen on electrochemical corrosion resistance of Ti–47Al–2Cr (at %) intermetallic, known as ?-TiAl alloy. Design/methodology/approach - The surfaces of the samples were modified by thermal treatment at different temperatures in N2 gas flow for an hour. Characterization of the modified surface layers was carried out by microscopic examinations, hardness and roughness tests, and X-ray diffraction analyses. Potentiodynamic polarization was used to evaluate the corrosion performance of ?-TiAl in Ringer's solution.Findings - The results indicated that the alloy treated at 950°C had the optimum corrosion resistance, which can be attributed to the formation of an oxide layer by the surface thermal treatment and increasing of the passive layer thickness. Practical implications - Low corrosion rate (CR), high pitting potential (Epit), and more noble corrosion potential (Ecorr) gives the possibility to ?-TiAl to be considered as a candidate for biomedical applications.Originality/value - This treatment is a novel method for surface modification of this type of alloy and results showed that it was an effective treatment and the corrosion resistance improved remarkably.

Effect of the macro-pore structure on the anodic polarization behavior of porous titanium

Boqiong Li, Zhiqiang Li, Xing Lu — 2012-03-17 00:00:00.0

Abstract

Purpose - Porous titanium used in many bioimplant and electrodes applications was intended for its interconnected pore structure and good corrosion resistance.Design/methodology/approach - The porous titanium with 10-70% porosities and average macro-pore sizes in the range of 100-500 µm was prepared by the powder metallurgy method using polymethyl methacrylate (PMMA) as a space holder. Electrochemical corrosion tests were performed on porous titanium as well as solid titanium (with the same irregular and isolated micro-pore structures as that on the interconnected spheroidal macro-pore walls of porous titanium) in the 0.1 M H2SO4, 1 M NaOH and 0.9% NaCl (37 oC) solutions. Findings - It was found that porous titanium exhibited an active-passive transition behavior in the 1 M NaOH and 0.1 M H2SO4 solutions. In contrast, a self-passivation transition behavior was observed in the 0.9% NaCl solution (37 oC). Originality/value - Both the porosity and macro-pore size of the porous titanium play an important role in determining the corrosion rate, rather than the corrosion potential.

Gemini Surfactants; A new class of corrosion inhibitors for brass in 3N HNO3 solution

Hariom Kumar Sharma — 2012-03-17 00:00:00.0

Abstract

Purpose - The purpose of this paper is to present the results of the corrosion inhibition studies of brass in 3N HNO3 by gemini surfactants.Design/methodology/approach - Gemini surfactants namely: N-trimethyl butane-diyl-1,2-ethane-bis-ammonium bromide (BEAB), N-hexane-diyl-1,2-ethane-bis-ammonium bromide (HEAB), N–dodecane-diyl-1,2-ethane-bis-ammonium bromide (DDEAB) and N-hexadecane-diyl-1,2-ethane-bis-ammonium bromide (HDEAB) were synthesized in the laboratory and their influence has been investigated for controlling the dissolution of brass in 3N HNO3. Weight loss, potentiodynamic polarization and electrochemical impedance have been employed for the study. Weight loss experiments were performed as per standard method (ASTM, 1987). Potentiodynamic polarization studies were carried out using EG&G PARC potentiostat/galvanostat (model 173), universal programmer (model 175) and X-Y recorder (model RE 0089).and impedance measurements were carried out with an EG&G PAR (model 5301A) lock-in-amplifier, using an IBM computer.Findings - The inhibition efficiency for all the gemini surfactants increases with increase in concentrations. The maximum inhibition efficiency of each inhibitor was achieved at 250 ppm concentration. The inhibition efficiency of all the inhibitors decreases on increasing the temperature from 30 to 500C. The results of potentiodynamic polarization studies revealed that all the compounds were mixed type inhibitors and inhibit the corrosion of brass by blocking the active sites of the metal. The adsorption of the compounds on brass surface in 3N HNO3 has been found to obey the Langmuir adsorption isotherm.Originality/value - The paper provides information regarding corrosion inhibition of brass in 3N HNO3, the mechanism of the inhibition on the basis of molecular structures of the inhibitors, activation energy and free energy of adsorption.

Anti corrosive electroless Ni-P films for mild steel materials

Venkatesha T V, S Ranganatha — 2012-03-17 00:00:00.0

Abstract

Purpose - The purpose of this paper is to evaluate the corrosion resistance of the electroless Ni-P coatings in two aggressive media 3.5 wt. % NaCl and Synthetic industrial waste water. Also to study the effect of Phosphorous content in the electroless Ni-P deposits on its surface nature, morphology and corrosion resistance. Design/methodology/approach - The corrosion behavior of electroless Ni-P coatings generated on mild steel coupons from an acidic and an alkaline baths and their anti corrosion performance of was compared systematically in 3.5 wt% of NaCl solution and also in synthetic industrial waste water. Microstructure and surface composition of coatings were analyzed using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy techniques respectively. The Ni-P coated mild steel specimens were subjected to corrosion and the rate of corrosion was studied by chemical and electrochemical methods. The linear sweep voltammetry, Tafel and electrochemical impedance spectroscopy were employed to get corrosion data.Findings - The electroless Ni-P coatings with higher P content possess homogeneous, uniform and amorphous surface nature and exhibited higher corrosion resistance in the aggressive corrosive media chosen. Originality/value - This paper provides corrosion behavior of electroless Ni-P coatings in 3.5 wt. % NaCl and synthetic industrial waste water, and establishes the importance of phosphorous content on nature and properties of the coatings.

The classification of acoustic emission signals of 304 stainless steel during stress corrosion process based on K-means clustering

Jian Li, Gang Du, Chen Jiang, Shijiu Jin — 2012-03-17 00:00:00.0

Abstract

Purpose - The purpose of this paper is to classify and identify the acoustic emission (AE) signals of 304 stainless steel during stress corrosion process.Design/methodology/approach - The corrosion behavior of specimen during slow strain rate testing (SSRT) in acidic NaCl solution was studied. The AE signals during corrosion process were classified based on K-means cluster algorithms, meanwhile, the characteristics of different AE sources were analyzed.Findings - The results indicated that the AE characteristics of different AE sources, such as pitting, cracking, and bubble break-up, differ significantly. The 304 stainless steel was prone to the occurrence of stress corrosion cracking (SCC) under the SSRT condition in acidic NaCl solution.Originality/value - The characteristics of different AE sources during corrosion process were gained for the first time, which could be of much help in analyzing and judging the corrosion situation.

Research the Characteristics of Furnace Tube Oxide Film in CPT, CT, AVT(R) and AVT(O) Water Chemistry Conditions

zhiping zhu, hui zhang, Lingling Jing, Shuhua Xiong, Zhenghui Tan — 2012-03-17 00:00:00.0

Abstract

Purpose - In the CPT, CT, AVT(R) and AVT(O) water chemistry conditions, a layer of oxide film spontaneously formed in the furnace wall which could prevent corrosions in boiler water directly contact with the inner tube and reduce the probability of tube perforation. Which main function is to reduce corrosion and protection furnace tube.Design/methodology/approach - The different morphologies, specific functions and distribution in the oxide film were identified by electrochemical workstation, XRD, SEM and EDAX.Findings - It is concluded that metal surface was rugged and had deep corrosion in CPT. Ions penetrated into the oxides of large particles with gap and occured the intergranular corrosion in CT. In AVT(R), the oxide film uniformly covered on the metal surface played a protective role, but these could be easily washed away by solution. The oxide film formed in AVT(O) was similar to AVT(R), but the diffierent is the large solid particles of Fe2O3 covered on the outermost oxide film which prevent the oxide film was taken away.Originality/value - The results can provide reference for reduce the high temperature corrosion of metal in the actual operation.