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Chemical conversion coatings have attracted much attention in recent years due to their excellent characteristics such as corrosion resistance, wear resistance, adhesion and lubrication. In this study, a phosphate chemical conversion (PCC) coating was fabricated on medium carbon low alloy steel using a facile PCC method with Fe2+ curing process at room temperature. It is shown that the coating was composed of hopeite (Zn3(PO4)2·4H2O) and minor phosphophyllite (Zn2Fe(PO4)2·4H2O) in the form of fine and flaky crystals along the direction inclined or perpendicular to the substrate surface. The adhesive test indicated that the PCC coating was strongly attached on the substrate. Electrochemical analysis revealed that the as-prepared coating imparted better corrosion resistance to the steel substrate. [ABSTRACT FROM AUTHOR]

Bioactive phosphate coatings based on hopeite (HP, Zn 3 (PO 4) 2 ·4H 2 O) and strontium‑zinc-phosphate (SZP, SrZn 2 (PO 4) 2) phases have attracted extensive attention in the surface modification of metallic implants. Nevertheless, further clarifications on the synergistic effect of HP and SZP, as well as the phase evolution between them are still needed. Herein, a chemical conversion technique was utilized to prepare composite phosphate coatings containing HP and SZP on titanium (Ti). The effect of phosphating temperature on the phase, properties, and deposition mechanism of the coatings was investigated. The results showed that the coating obtained at 50 °C was composed of HP with minor SZP crystals, while their relative contents were reversed at 80 °C. The elevated temperature also changed the crystal morphology of SZP from ellipsoidal to cubic. These variations could be attributed to the enhanced priority of Sr and Zn ions to form bimetallic-phosphate (SZP), which has a different lattice structure from HP crystal. In addition, the HP/SZP composite coating formed at 60 °C exhibited superior comprehensive properties like roughness, wettability, bonding strength, ion release, and corrosion resistance. Overall, this study elucidates the temperature-induced phase evolution and properties of HP/SZP composite coatings, which facilitates the optimal regulation of phase composition to achieve desired properties. • Zn 3 (PO 4) 2 ·4H 2 O and SrZn 2 (PO 4) 2 composite coating was developed on Ti using PCC technique. • SrZn 2 (PO 4) 2 crystal tends to form at higher temperatures compared with Zn 3 (PO 4) 2 ·4H 2 O one. • The SrZn 2 (PO 4) 2 crystal varied from ellipsoidal to cubic at elevated temperatures. • The composite coating obtained at 60 °C has better mechanical and surface characteristics. [ABSTRACT FROM AUTHOR]

A modified wet-chemical conversion technique with controlled mild temperature has been utilized to prepare zinc phosphate (Zn P) and/or calcium-containing Zn P (Ca-Zn-P) coatings on the surface of pure titanium (Ti). Their X-ray diffractometer (XRD) patterns were indexed to typical hopeite (Zn 3 (PO 4) 2 ·4H 2 O) and scholzite (CaZn 2 (PO 4) 2 ·2H 2 O), respectively. The influence of solution temperature on coating composition, microstructure and bonding strength between the coating and substrate was investigated by XRD, field emission scanning electron microscope (FE-SEM) and an acoustic emission scratch tester, respectively. A growth behavior of hopeite and scholzite coating was also explored by morphology evolution within the initial reaction stage. The results indicated that the microstructure and crystal size of the coatings were strongly impacted by solution temperature, while a hopeite or scholzite coating with fine and homogeneous microstructure could be obtained at 55 °C. Moreover, the scholzite crystal represented a radially nucleation-growth pattern through tracking observation of morphology evolution. Unlabelled Image • Hopeite and scholzite conversion coatings have been developed on titanium. • Wet-chemical conversion technique was utilized under mild temperature condition. • Surface morphology of the coatings is strongly influenced by the processing temperature. • Scholzite coating shows a typical radial nucleation-growth pattern during morphology evolution of crystals. [ABSTRACT FROM AUTHOR]

Calcium phosphate coatings have been applied on the surface of Ti implants to realize better osseointegration. The formation of dicalcium phosphate dihydrate (CaHPO 4 ·2H 2 O), mineralogically named brushite on pure Ti substrate has been investigated via chemical conversion method. Coating composition and microstructure have been investigated by X-ray diffractometer, Fourier transform infrared spectrometer and field emission scanning electron microscope. The results reveal that the coatings are composed of high crystalline brushite with minor scholzite (CaZn 2 (PO 4 ) 2 ·2H 2 O). A micro/nano-scaled fibrous morphology can be produced in the acidic chemical conversion bath with pH 5.00. The surface of the fibrous brushite coating exhibits high hydrophilicity and corrosion resistance in the simulated body fluid. The osteoblast cells grow and spread actively on the coated samples and the proliferation numbers and alkaline phosphate activities of the cells improve significantly compared to the uncoated Ti. It is suggested that the micro/nano-fibrous brushite coating can be a potential approach to improve the osteoinductivity and osteoconductivity of Ti implant, due to its similarity in morphology and dimension to inorganic components of biological hard tissues, and favorable responses to the osteoblasts. [ABSTRACT FROM AUTHOR]

The microstructure of the phosphate coating on implant surface is critical for successful osseointegration. Based on the morphological variability of phosphate crystals, the microstructure of the coating can be regulated by designing the composition of the phosphate solution. In this study, a strontium‑zinc-phosphate (SrZn 2 (PO 4) 2 , SZP) coating was prepared on titanium (Ti) surface by phosphate chemical conversion (PCC) method. The effect of Zn2+ concentration in phosphate solution, which was regulated by increasing the addition amount of Zn(H 2 PO 4) 2 ·2H 2 O, on the microstructure and properties of the SZP coating was investigated. The characterization of the coating was carried out by scanning electron microscope (SEM), X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectrometer (XPS), laser scanning confocal microscope (LSCM), contact angle goniometer, and electrochemical workstation system. The results revealed that the increase of Zn2+ concentration in phosphate solution could induce the crystal morphology of the SZP coating to evolve from irregular granules (Zn(H 2 PO 4) 2 ·2H 2 O: 1 g/L) to regular cubic blocks (Zn(H 2 PO 4) 2 ·2H 2 O: 8 g/L). This morphological evolution process was accompanied by an increase in thickness (from 4.8 ± 1.2 to 20.6 ± 1.9 μm), an improvement in wettability and corrosion resistance, as well as a decrease in the release amount of Sr2+ (from 3.97 ± 0.26 to 0.86 ± 0.12 ppm) and Zn2+ (from 0.31 ± 0.01 to 0.18 ± 0.01 ppm) after 21 days of immersion. In vitro evaluations proved that the adhesion, proliferation, and differentiation of MC3T3-E1 pre-osteoblasts on SZP coatings, especially for the coating with tiny cubic-block crystals, were significantly enhanced compared with pure Ti. This study clarified the rule of morphological evolution of the SZP crystal that is caused by changing the Zn2+ concentration in the phosphate solution, which contributes to the structural optimization of the SZP coating to obtain high osteogenic activity. [Display omitted] • A SrZn 2 (PO 4) 2 coating was prepared on titanium using chemical conversion method. • The coatings microstructure depended on the Zn2+ concentration in phosphate bath. • The coatings with cubic crystal morphology showed preferable osteogenic activity. [ABSTRACT FROM AUTHOR]

Strontium (Sr) substitution into calcium phosphate (CaP) materials has gained acceptance in research into the enhancement of physiochemical and osteogenic potential. Conventional synthesis of metal cationic substitution into CaP coatings on metal substrate usually takes relatively high temperature (﹥100 °C) and hours of processing time. Herein, a mild phosphate chemical conversion method was developed for preparing Sr-substituted CaP coatings on surface of titanium (Ti) in the presence of increasing amount of Sr (40–60 mol%). The results indicated that the complete and even coatings could be produced on the whole surface of Ti only within 50–60 % Sr and the coatings represented a unique lamellar texture in micro/nano-scale. As Sr concentration increased, the phases of coatings were predominantly indexed to monetite and SrHPO 4 , which presented a highly oriented crystal alignment. With high content of Sr, monetite, instead of brushite, was deposited in the coatings. The possible mechanism of coating formation was proposed that α-SrHPO 4 and α-monetite were co-deposited in the acidic phosphating solution and finally a compound of (Ca x Sr 1-x)HPO 4 was produced on surface of Ti. Results revealed that coatings formed at high degree of Sr substitution exhibited relative improved mechanical and electrochemical properties. The coatings enhanced the cell focal adhesion and proliferation of BMSCs compared with that of the bare Ti. [Display omitted] • Sr-substituted CaP coating was yielded on Ti by mild phosphate chemical conversion. • The coating presented unique lamellar interwoven microstructure • CaP precipitated on Ti prior to SrP in the acidic phosphate solutions. • Exceeded Sr conduced precipitation of monetite instead of brushite in the coating. • The coating performed better contact guidance to the cells compared with bare Ti. [ABSTRACT FROM AUTHOR]