Materials Performance

JUN 2016

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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55 NACE INTERNATIONAL: VOL. 55, NO. 6 MATERIALS PERFORMANCE JUNE 2016 sistance, chemical stability, high hardness, high strength, high wear resistance, greater chemical inertness, and biocompatibility, have made alumina a desirable surgical- implant material. Despite all these advan- tages, alumina's brittleness, low tensile and f lexural strength, low fracture toughness, and low thermal resistance limit its appli- cation in some research areas. Impedance and corrosion resistance are the most critical properties of any solid material when investigating its inertness. Controlling these material properties is im- perative for various orthopedic implants. Many surface treatments, including chemi- cal deposition, sputtering, electrochemical deposition, thermal spraying, and pulse laser deposition, have been used to reduce the corrosion rates. Most of these tech- niques require specific, expensive instru- ments and time-consuming processes. Electrochemical impedance spectros- copy (EIS) is useful for studying the corro- sion behavior of a HAP thin film coating over ceramic and metallic substrates. In this study, the corrosion rate of the sub- strate is determined by the polarization resistance (R p ), which is inversely propor- tional to the corrosion rate (i.e., the higher the polarization resistance, the lower the corrosion rate and vice-versa). The applied technique gives kinetic and mechanistic information for the study of corrosion. A HAP thin film coating was prepared using a sol-gel method to deposit HAP over an alumina substrate by the dip coating technique. 10 The corrosion and thrombo- genic behavior of HAP/alumina were then investigated after argon (Ar + ) ion implanta- tion. The ion energy was kept at 1.4 MeV and the ion doses were varied from 5 × 10 14 ions/cm 2 to 1 × 10 16 ions/cm 2 . Glancing angle x-ray diffraction (GXRD) was carried out to confirm the formation of HAP. Ruth- erford backscattering spectrometry (RBS) was used to measure the thickness of the film and the calcium :phosphorus (Ca :P) ratio of the HAP. Materials and Method Small pieces of alumina (10-mm diam- eter by 1-mm thick) with a purity of 99.7% were pro cured from A n t s C e r a m i c P v t . , L t d . T h e s e s a m p l e s w e r e u l t r a s o n i c a l l y d egreased w ith ace- tone for 20 min and washed with running di stilled wat er, th en oven-dried at 100 °C for 30 min before the H A P c o a t i n g w a s applied. A 2-M ethanol so- lution with phospho- rus pentoxide (P 2 O 5 ) (Merck, 97%) was pre- chloride [NaCl], 0.0057 mol/L of potassium chloride [KCl], 0.001 mol/L of calcium chlo- ride [CaCl 2 ], and 0.0011 mol/L of sodium bicarbonat e [NaHC O 3 ]) using th e C HI 660A † system. This was performed with a conventional three-electrode system, with a platinum wire used as the counter elec- trode and a silver/silver chloride (Ag/AgCl) reference electrode. Thrombogenicity was evaluated using the whole-blood clotting time method . Blood was drawn from the researcher by an expert into ethylenediaminetetraacetic (edetic) acid (EDTA) anticoagulant-coated tubes. Four samples were used per time point. The clotting reaction was activated by adding 0.25 µL (0.1 M) CaCl 2 to the 2.5 mL sample of blood, then 50 µL of blood was carefully added to the alumina sub- strate and the HAP-coated alumina. Eleven samples were incubated at 37.2 °C for 10 min. At the end of each time point, the samples were removed from the incubator, then 3 mL of distilled water were added to each sample and incubated for an addi- tional 5 min. The red blood cells that were not trapped in a thrombus were lysed (dis- solved) by adding distilled water, which released hemoglobin into the water for subsequent measurement. The concentra- tion of hemoglobin in solution was as- sessed by measuring the absorbance at 540 nm using a spectrophotometer (HACH DR/2400 † ). † Trade name. FIGURE 1 The pathways of blood coagulation. pared by dissolving P 2 O 5 in ethanol and re- f luxing for 24 h. A 4-M ethanol solution with calcium nitrate tetrahydrate [Ca(NO 3 ) 2 4H 2 O] (Merck, 98%) was prepared without refluxing. Details of the sample preparation are described elsewhere. 10 As the coating was thin, compound for- mations were determined using GXRD. The GXRD (INEL XRG -3000 † x-ray diffractom- eter) patterns were recorded using CuKα1 radiation (λ = 1.54056Å), generated at 40 kV and 30 mA. After preparing the HAP/alumina sam- ples, ion beam mixing was performed using 1.4 MeV argon ions at the Inter University Accelerator C entre (IUAC) (New Delhi , India). 11 Samples were mounted on a hex- agonal copper plate, placed normal to the incident ion beam. The vacuum inside the chamber during implantation was on the order of 10 –8 mbar. The beam current was kept below 2 mA to maintain the sample temperature below 40 °C to prevent a ther- mal effect. The ion doses varied from 5 × 10 14 ions/cm 2 to 1 × 10 16 ions/cm 2 . RBS mea- surements were recorded using 2 MeV He + ions carried out at IUAC. The scattering angle was kept at 165 degrees and He + ion energy was measured using a solid state barrier (SSB) detector. The vacuum during these measurements was kept at 10 –6 mbar. EIS for corrosion measurements was carried out at the open-circuit potential with alternating current (AC) voltage of 3 mV over a frequency range of 0.01 to 10 5 Hz in Ringer's solution (0.15 mol/L sodium

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