Optimization of the Electrophoretic Deposition Parameters and Mechanism of Formation of Ag-TiO2 Nanocoatings on a NiTi Shape Memory Alloy: Part I

Abstract

This paper reports research findings on the functionalization of NiTi shape memory alloy through the electrophoretic deposition of innovative complex layers comprising a silver-rutile (Ag-TiO2) nanocomposite. A colloidal suspension of a chemically synthesized Ag-TiO2 nanosystem prepared with a 59.4 ± 0.9 mV Zeta potential for anaphoretic deposition. Employing a design of experiment method (DoE), the optimal parameters for uniform coating depositions were identified as 40 V/3 min. Dilatometric tests and high-temperature microscopy determined that the deposited layers’ heat treatment temperature should not exceed 800 °C. Raman spectrometry and scanning electron microscopy (SEM) provided comprehensive structural and morphological insights into the resulting continuous and crack-free layer. The article extensively explores the impact of annealing on structural changes within the layer, proposing mechanisms for its formation. The findings affirm the feasibility of creating a highly reactive layer on the NiTi alloy, holding potential significance in implantation medicine.

Synthesis and Characterization of Silica-Titanium Oxide Nano-Coating on NiTi Alloy

“…It should be expected that the possible incorporation of Ti into the spatial structure of SiO 4 tetrahedra will be interstitial and may cause defects in the spatial network and distortions of coordination figures. Comparable outcomes were observed with other composite coatings at similar heat treatment temperatures, demonstrating a significant enhancement in the bonding strength between the ceramic coatings and the metallic substrate [16,[57][58][59].…”

Functionalization of the NiTi Shape Memory Alloy Surface through Innovative Hydroxyapatite/Ag-TiO2 Hybrid Coatings

“…Confirmation of the metallic silver particle formation led to the appearance of bands around 610, 704, and 808 cm −1 , which indicated that molecularly chemisorbed oxygen species (Oβ, OH) had formed around the silver [10][11][12][13]. Raman spectroscopy confirmed the presence of highly stable hydroxyapatite, as evidenced by characteristic bands found in the range between 969 and 963 cm −1 (ν 1 (PO 4 ) 3− ), 596 cm −1 (ν 4 (PO 4 ) 3− ), 446 cm −1 (ν 2 (PO 4 ) 3− ), and in the range between 350 and 150 cm −1 (lattice modes of Ca(PO 4 )) [14][15][16]. Hydroxyapatite bands coexisted with silver oxide bands located at 133, 243, and 440 cm −1 (Figure 8b) [23] and probably shield silver oxide from complete decomposition at the proposed sintering temperature.…”

“…This, coupled with the high accessibility of silver ions in the solution and their affinity for carbon dioxide, favors the formation of aragonite structure silver carbonates. These are evidenced by bands centered around 90, 120, 150, 200-300 cm −1 (indicating silver lattice vibrational modes), and 1380-1560 cm −1 (ν 1,3 (CO 3 ) 2− ) [15,22]. Furthermore, molecularly chemisorbed oxygen species found around some silver carbonates are evidenced by the band at 760 cm −1 [23][24][25][26].…”

“…The Ag-TiO 2 nanocomposite was prepared according to the procedure described in detail in ref. [15].…”