Conversion Of Calcium Phosphate Research Articles

PREPARATION AND MODIFICATION OF CALCIUM PHOSPHATE CONVERSION COATING

In order to enhance the corrosion resistance of calcium-based phosphate coating, the molybdenum-modified coating was successfully prepared by adding Na2MoO4 in a phosphate bath. The prepared composite film layers were studied by EDS, XRD and SEM. The corrosion resistance performances of the films were investigated by electrochemical measurements. The results showed the main composition of molybdenum-modified film was MoO2, MoP2, and MoP4, the diameter of cracks on the surface of the coating was significantly reduced, which provided better protection to the substrate. In addition, the potentiodynamic polarization curves of the molybdenum-modified film show that the corrosion potential was positively shifted by 0.068 V compared to the calcium-based phosphate coating and the corrosion current was reduced to 2.556 × 10[Formula: see text]A ⋅ cm[Formula: see text], indicating improved corrosion resistance.

Calcium phosphate conversion technique: A versatile route to develop corrosion resistant hydroxyapatite coating over Mg/Mg alloys based implants

Globally, vast research interest is emerging towards the development of biodegradable orthopedic implants as it overcomes the toxicity exerted by non-degradable implants when fixed in the human body for a longer period. In this context, magnesium (Mg) plays a major role in the production of biodegradable implants owing to their characteristic degradation nature under the influence of body fluids. Also, Mg is one of the essential nutrients required to perform various metabolic activities by the human cells, and therefore, the degraded Mg products will be readily absorbed by the nearby tissues. Nevertheless, the higher corrosion rate in the biological environment is the primary downside of using Mg implants that liberate H2 gas resulting in the formation of cavities. Further, in certain cases, Mg undergoes complete degradation before the healing of damaged bone tissue and cannot serve the purpose of providing mechanical support. So, many studies have been focused on the development of different strategies to improve the corrosion-resistant behavior of Mg according to the requirement. In this regard, the present review focused on the limitations of using pure Mg and Mg alloys for the fabrication of medical implants and how the calcium phosphate conversion coating alters the corrosive tendency through the formation of hydroxyapatite protective films for enhanced performance in medical implant applications.

Effect of scratch on corrosion resistance of calciumphosphate conversioncoated AZ80 magnesium alloy

In order to analyze the effect of scratch on the corrosion behaviour of a calcium phosphate conversion coating (CPCC) on AZ80, the electrochemical testing, scanning vibrating electrode technique (SVET), immersion test and hydrogen evolution experiment were performed to study the corrosion resistance of AZ80, AZ80 with CPCC and coated AZ80 with scratch. The results show that the coating improves the corrosion resistance of the AZ80 from a current density of (85±4) to (4±1)μA/cm2. When the coating was damaged, its protection on substrate would be reduced. The scratch with a length of around 12 mm on the coating reduced the corrosion resistance to a current density of (39±1)μA/cm2. In addition, the corrosion occurred initially in the scratch area and the corrosion site first occurred at the junction of the scratch and the coating. Besides, the micro corrosion mechanism of the specimen containing scratch was clarified.

Influence of indentation size on the corrosion behaviour of a phosphate conversion coated AZ80 magnesium alloy

The service performance of magnesium alloy wheel hub was simulated by studying the effect of surface defect size on the corrosion resistance of a calcium phosphate conversion coated AZ80 magnesium alloy. The surface defects were produced with different sizes using a Film Impactor. The corrosion behaviour was studied using electrochemical, hydrogen evolution and immersion tests. The microstructures were characterized using a scanning electron microscope and a laser confocal microscope. Phases and the corrosion products were analyzed using XRD and XPS. The size of the surface defects influenced the corrosion resistance of the coating and the corrosion initiation area. The coating provided no protection for an indentation larger than 2.7 mm. The corrosion mechanism of the coating was also clarified.

Corrosion resistance of glucose-induced hydrothermal calcium phosphate coating on pure magnesium

Glucose-induced composite coatings containing crystalline calcium phosphate and Mg(OH)2 interlayer were prepared on pure Mg substrate through hydrothermal deposition from alkaline solution. Surface composition, morphology and corrosion resistance of the coatings were characterized through XRD, FTIR, SEM, XPS, electrochemical and hydrogen evolution measurements. Results reveal that calcium phosphate coatings were composed of dicalcium phosphate anhydrous, calcium-deficient hydroxyapatite and hydroxyapatite. Corrosion resistance of pure Mg specimens was improved by the formation of such a calcium phosphate coating. The findings provide a novel strategy to design calcium phosphate conversion coatings with satisfactory corrosion resistance for biodegradable Mg implants.

The Preparation, Characterization and Formation Mechanism of a Calcium Phosphate Conversion Coating on Magnesium Alloy AZ91D.

The poor corrosion resistance of magnesium alloys is one of the main obstacles preventing their widespread usage. Due to the advantages of lower cost and simplicity in operation, chemical conversion coating has drawn considerable attention for its improvement of the corrosion resistance of magnesium alloys. In this study, a calcium phosphate coating was prepared on magnesium alloy AZ91D by chemical conversion. For the calcium phosphate coating, the effect of processing parameters on the microstructure and corrosion resistance was studied by scanning electron microscope (SEM) and electrochemical methods, and the coating composition was characterized by X-ray diffraction (XRD). The calcium phosphate coating was mainly composed of CaHPO4·2H2O (DCPD), with fewer cracks and pores. The coating with the leaf-like microstructure provided great corrosion resistance to the AZ91D substrate, and was obtained under the following conditions: 20 min, ambient temperature, and no stirring. At the same time, the role of NH4H2PO4 as the coating-forming agent and the acidifying agent in the conversion process was realized, and the formation mechanism of DCPD was discussed in detail in this work.

Preparation and corrosion behaviors of calcium phosphate conversion coating on magnesium alloy

Abstract In order to control the biodegradation rate and improve the surface biocompatibility of magnesium (Mg) alloys, a calcium phosphate conversion coating (CPCC) was deposited onto an AZ60 Mg alloy through an easily controlled phosphating method. The effects of pH and temperature of the phosphating solution on the coating process, microstructure, porosity, and electrochemical and immersion corrosion behaviors of the CPCC were analyzed. The optimum coating conditions were deduced according to the coating quality, and electrochemical and immersion corrosion performance. The results show that the pH and temperature can significantly affect the coating process, microstructure, and coating porosity percentage, and thus influence the corrosion protection efficiency and the corrosion rate of the CPCC coated Mg alloy.

Composite Microstructure and Formation Mechanism of Calcium Phosphate Conversion Coating on Magnesium Alloy

In order to improve the biodegradability and surface biocompatibility of magnesium (Mg) alloys, a calcium phosphate conversion coating (CPCC) was deposited onto an AZ60 Mg alloy. The coating's components and composite microstructure and its formation mechanism were studied using electrochemical measurements, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy and by developing a thermodynamic stability diagram. The results revealed that the presence of Mg2+ originating from the electrochemical reaction of the Mg alloy could affect the precipitation of different coating components. Because the concentration of Mg2+ at the solution/coating interface continuously changed, three layers of the conversion coating were progressively produced. The inner layer was composed of magnesium hydrogen phosphate trihydrate (MHPT, MgHPO4·3H2O) and had a thickness of ∼1.1 μm. The middle layer was ∼1.6 μm thick and consisted of dicalcium phosphate dihydrate (DCPD, CaHPO4·2H2O), magnesium whitlockite (MWH, Ca9Mg(HPO4)(PO4)6), and MHPT. The top layer was ∼2.3 μm thick and was composed of a combination of DCPD and MWH.

The Role of Carboxydothermus hydrogenoformans in the Conversion of Calcium Phosphate from Amorphous to Crystalline State

Two previously unknown modes of biomineralization observed in the presence of Carboxydothermus hydrogenoformans are presented. Following the addition of NaHCO3 and the formation of an amorphous calcium phosphate precipitate in a DSMZ medium inoculated with C. hydrogenoformans, two distinct crystalline solids were recovered after 15 and 30 days of incubation. The first of these solids occurred as micrometric clusters of blocky, angular crystals, which were associated with bacterial biofilm. The second solid occurred as 30–50 nm nanorods that were found scattered among the organic products of bacterial lysis. The biphasic mixture of solids was clearly dominated by the first phase. The X-ray diffractometry (XRD) peaks and Fourier transform infrared spectroscopy (FTIR) spectrum of this biphasic material consistently showed features characteristic of Mg-whitlockite. No organic content or protein could be identified by dissolving the solids. In both cases, the mode of biomineralization appears to be biologically induced rather than biologically controlled. Since Mg is known to be a strong inhibitor of the nucleation and growth of CaP, C. hydrogenoformans may act by providing sites that chelate Mg or form complexes with it, thus decreasing its activity as nucleation and crystal growth inhibitor. The synthesis of whitlockite and nano-HAP-like material by C. hydrogenoformans demonstrates the versatility of this organism also known for its ability to perform the water-gas shift reaction, and may have applications in bacterially mediated synthesis of CaP materials, as an environmentally friendly alternative process.

An environment‐friendly calcium phosphate conversion coating on AZ91D alloy and its corrosion resistance

An environment‐friendly phosphate conversion coating free of chromate, fluorides, and nitrite was developed on AZ91D alloy through a facile chemical deposition method. The surface morphology and phase composition of the coating were characterized by field‐emission scanning electron microscopy (FE‐SEM) and X‐ray diffraction (XRD). The corrosion resistance of the coating was evaluated by potentiodynamic polarization test in 3.5 wt% NaCl solution. Results indicate that the calcium phosphate coating was composed of a large number of leaf‐like and flower‐like particles. The chemical composition of the conversion coating was CaHPO4·2H2O crystals. The coating can remarkably reduce the corrosion current density of the substrate. Introduction of triethanolamine (TEA) additive into the phosphating bath leads to denser coating and high anticorrosive property of the phosphate coating.

In vitro corrosion survey of Mg–xCa and Mg–3Zn–yCa alloys with and without calcium phosphate conversion coatings

Magnesium alloys are promising orthopaedic bioresorbable implant candidates, however, their inherent rapid corrosion rate in physiological media currently limits their clinical applications. In this work, the in vitro corrosion of a series of Mg–xCa and Mg–3Zn–yCa alloys (wt-%) was systematically studied. These compositions were selected so the alloys could be comprised of biocompatible elements and to explore the role of Ca in the alloy itself upon subsequent calcium phosphate (CaP) coating efficiency. A simulated body environment was reproduced via minimum essential medium (MEM) and exposure in a CO2 incubator at 37°C. The effect of Ca and Zn additions on the corrosion rate of Mg was examined, indicating the corrosion rate increases with Ca additions, while adding Zn to Mg–Ca alloys decreases the rate of corrosion. The impact of a biomimetic CaP conversion coating applied onto these alloys indicated that although the coating alters the corrosion rates, the effect is dependent on the substrate alloy composition.

Effect of [Ca2+] and [[formula omitted]] levels on the formation of calcium phosphate conversion coatings on die-cast magnesium alloy AZ91D

The effect of varying [Ca2+]total and [PO43-]total concentrations (nine conditions in total) on the formation of calcium phosphate conversion coatings on magnesium alloy AZ91D was investigated. Corrosion performance was evaluated by measurement of polarisation behaviour and also by salt spray testing. A consistent trend was observed of improved corrosion performance with reduced ionic concentrations. Low [PO43-]total concentration was found to be especially important for the attainment of good corrosion resistance. Both direct measurement using X-ray photoelectron spectroscopy and chemical modelling using MEDUSA software indicated an increase in hydroxyapatite content of the coating accompanying the improved corrosion resistance.

Calorimetric investigations of calcium phosphate precipitation in relation to solution composition and temperature

The kinetics of formation and conversion of calcium phosphate under different initial solution compositions and temperature have been studied by calorimetric methods. Experimental values of enthalpy of calcium phosphate formation at various Ca:P molar ratios, initial pH of solution and temperatures are given. It is found that in the initial pH range 5.8 < pH < 11.79 the formation of calcium phosphate from relatively high supersaturated solutions is associated with a strong endothennic effect. Under a wide range of Ca : P ratios (0.33–2.79) and with an initial pH of 7.40 the formation of calcium phosphate is associated with the repeated heat effect. This effect, which is connected with the transformation of the first precipitated phase, is revealed clearly and occurs in two stages. This transformation may be explained by considering that a mixture of Ca4H(PO4)3 · 2.5H2O-like and Ca5(PO4)3OH-like phases is formed during the amorphous-to-crystalline transition.

Die Cyanat-induzierte Umwandlung von Calciumhydrogenphosphat in Calciumdiphosphat -eine präbiotische Schlüsselreaktion ? / The Conversion of Calcium Hydrogenphosphate into Calcium Diphosphate by Cyanate - a Prebiotic Key Reaction ?

Abstract The conversion of calcium phosphate into calcium diphosphate through cyanate in an aqueous suspension, discovered by Miller and Parris [1], has been reinvestigated thor-oughly. The reaction is initiated through the disproportionation of calcium hydrogen phosphate to give hydroxylapatite and calcium dihydrogen phosphate, which reacts with cyanate via carbamoylphosphate to yield calcium diphosphate and urea. In particular, it could be shown that the process of phosphate condensation may also be initiated when cyanate is generated by a photochemical oxidation of hydrocyanic acid. -The importance of this reaction with respect to the prebiotic synthesis of biopolymers is discussed.