Surface modification of bioceramics by grafting of tailored allyl phosphonic acid

Abstract

A new route to interfacial bonding between ceramic and matrix in biocomposites is identified. A tailored allyl phosphonic acid is used as a coupling agent bound to the surface of a bioceramic to form a 'grafted' calcium phosphate (CAP). The allyl phosphonic acid coupling agent is synthesised by reaction of allyl halide and trialkyl phosphite. Successful synthesis was confirmed by nuclear magnetic resonance and Fourier transform infrared spectroscopy (FTIR). The allyl phosphonic acid was incorporated onto calcium phosphate using a wet chemical coprecipitation synthesis route. The resulting 'grafted' CAP was characterised using FTIR coupled with photoacoustic sampling, and Fourier transform Raman spectroscopy (FTR). The spectroscopic data suggest an interaction between the allyl phosphonic acid and calcium phosphate resulting from observed reductions in intensity of the hydroxyl (3570 cm^?1) and phosphate ν ₃ (1030 cm^?1) peaks. The continued presence of C=C functionality on the surface of the grafted CAP was indicated by FTIR and FTR spectra (peaks at 1650 and 1635 cm^?1 respectively) and confirmed by X-ray photoelectron spectroscopy (XPS). On the basis of these results, it is concluded that grafted CAP may be used to produce a chemically bonded composite with superior mechanical properties.     

A study of zinc phosphate coatings on 12·5Cr–21·0Ni stainless steel

Abstract

12·5Cr–21·0Ni stainless steel was chemically treated with zinc phosphate in order to find the most suitable phosphate solution and its operating parameters. The phosphate coatings were tested for their corrosion protection of stainless steel using three methods: the salt spray test, the humidity cabinet test and the brine immersion test. The phosphate coatings were also mechanically tested using a tensile test for determining their mechanical properties. Results clearly show that phosphate coatings with a uniform appearance and full coverage can give high corrosion protection to 12·5Cr–21·0Ni stainless steel by forming a physical barrier against the corrosive environment. The 12·5Cr–21·0Ni stainless steel after coating with zinc phosphate still retains reliable mechanical properties, thereby providing valuable applications in the engineering field.     

Preparation and characterisation of porous calcium phosphate bone cement as antibiotic carrier

Abstract

This study investigated the release of cephalexin monohydrate (CMH) antibitic from macroporous calcium phosphate cement (CPC) over 0·5–300 h in simulated body fluid. Macroporosity was introduced into the cement matrix by using sodium dodecyl sulphate molecules as air entraining agents. The effect of both surfactant and CMH on basic properties of the CPC has been also elaborated. The results showed that the release rate of the drug from a porous CPC was higher than that of the non-porous CPC; however the same release patterns observed for both morphologies indicated a time dependent controlled release. Incorporation of CMH into the cement composition increased the setting time, while the crystallinity of the formed apatite decreased and injectability of the paste improved. In addition, the rate of hydraulic reactions, leading to conversion of the reactants into apatite phase, did not influenced by incorporating both CMH and surfactant into the cement.     

Influence of static magnetic fields on the protective ability of phosphate coatings on aluminium alloys

Abstract

Phosphate coatings on aluminium are used to improve the corrosion resistance of aluminium before the latter is painted. Phosphate coatings deposited in phosphate solution treated with a magnetic field prior to deposition can take on new properties. A magnetic field can either improve or deteriorate the properties of the phosphate coating formed, depending on the composition of aluminium.     

Preparation and characterisation of calcium phosphate cement made by poly(acrylic/itaconic) acid

Abstract

In this study, the compressive strength and bioactivity of strong polymeric calcium phosphate cement (PCPC), made by mixing a calcium phosphate powder (a mixture of tetracalcium phosphate and dicalcium phosphate dihydrate) and an aqueous solution of poly(acrylic/itaconic) acid, were investigated. The characteristics of the cement such as phase composition, setting reaction products and microstructure were analysed and compared to those of a control sample made by the same solid phase and water as a liquid. The hard tissue healing capability of PCPC was tested in a rabbit model by radiographical observations of the healing process as well as the cement condition. The results showed that the compressive strength of the set PCPC was ~35 MPa before soaking in a simulated body fluid (SBF), which was much higher than that of the control specimen. However, it sharply decreased when the cement was immersed in the SBF. X-ray diffraction analysis revealed that tricalcium phosphate was formed in the set PCPC and only a small amount of hydroxyapatite was produced after seven days soaking. In contrast, hydroxyapatite was almost the only phase of the control specimen after the soaking period. Radiography tests showed a cement (PCPC) with an irregular macrostructure after three months implantation, with a decreased radiopacity, and without any periosteal or intercortical callus formation.     

Study of biodegradable ceramic bone graft substitute

Abstract

The aim of the present study was to obtain a biodegradable porous calcium phosphate implants as a synthetic bone graft substitute. The calcium phosphate used in the present study consisted of hydroxyapatite (HA) and dicalcium phosphate anhydrous (DCP). Porous bioceramic was fabricated by a foam casting method. By polyurethane foam and slurry containing HA/DCP (3 : 1 weight ratio) powder, water and additives a high porous structure with ～70% was created. The X-ray diffractometry revealed that the β-tricalcium phosphate (β-TCP) formation is major phase. Surface morphology analysis and porosity evaluations were performed. The variation in the compressive strength, elastic modulus and dissolution behaviour of immersed synthetic bone graft in simulated physiological solution investigated.     

Phosphoric acid treated AlN powder for aqueous processing of net-shape dense AlN and β-SiAlON parts

Abstract

Due to fast hydrolysis of AlN when in contact with water, AlN based ceramics are processed in organic solvents, which are volatile, expensive, harmful to the health and environment. The present work intends to protect AlN powder against hydrolysis in order to enable aqueous processing of AlN based ceramics. A commercial AlN powder was treated in an ethanol solution of H₃PO₄ and Al(H₂PO₄)₃ kept at 80°C for 24 h to protect it from hydrolysis. The dispersing behaviour of the treated AlN powder in water and the ability to consolidate defect free parts of AlN and β-Si₄Al₂O₂N₆ ceramics from aqueous suspensions by slip casting and gelcasting techniques were studied. The consolidated parts were then sintered in a graphite furnace and the sintered bodies exhibited properties [bulk density (BD), apparent porosity (AP), crystalline phase composition and microstructural features] similar to those reported in literature for the same materials processed from organic media.     

Effects of alkaline cleaners and cleaning methods on phosphate coating weight and surface morphology

Abstract

The effects of some alkaline cleaners and cleaning methods on the phosphate coating weight have been assessed. The morphologies of the phosphate coatings were investigated through scanning electron microscopy (SEM). Single alkaline cleaners are not advantageous to formation of fine phosphate coatings. Additives, such as sodium ethylene diamine tetraacetate, sodium glycerophosphate, sodium tripolyphosphate and trisodium phosphate, in compound alkaline cleaners, can mitigate alkali corrosion of metal, resulting in the surface roughness of metal being decreased. The coating weight of phosphate coating formed on the sample cleaned by compound alkaline cleaners is lighter than by the use of single alkaline cleaners. Compared with the immersion cleaning method, spray cleaning contributes to the formation of the tiny phosphate crystal grains.     

Corrosion protection of steel reinforcement by a pretreatment in phosphate solutions: assessment of passivity by electrochemical techniques

Abstract

The aim of this work is to study the protection of steel reinforcement against corrosion by pretreatment in phosphate (Na₃PO₄) solution. The work has been carried out using electrochemical techniques, i.e. corrosion potential E _corr, polarisation resistance R _P and electrochemical impedance spectroscopy (EIS) measurements. The results have been validated by a gravimetric method. It has been stressed that R _P measurements, determined by DC techniques, include the charge transfer resistance R _t plus the resistance associated with the redox process R _ox, both determined by EIS. Also the results have demonstrated that the treatment of the rebar by immersion in the Na₃PO₄ (0·5M) solution favours the formation of a passive layer on the steel rebar surface, which is able to resist longer the action of chlorides to initiate corrosion. However, the resistance of the passive layer against chloride depends on the duration of the treatment by immersion of the rebar within the phosphate solution.     

Effectiveness of pretreatment method to hinder rebar corrosion in concrete

Abstract

This paper aims to evaluate the ability of phosphate pretreatments applied on steel rebars to hinder the corrosion reinforcements using synthetic pore electrolyte and mortar contaminated by chloride ions. The electrochemical behaviour of the pretreated substrate was assessed by corrosion potential, polarisation resistance and electrochemical impedance spectroscopy measurements. The results have demonstrated that the treatment of the rebar by immersion in the Na₃PO₄ (0·5M) solution favours the formation of a passive layer on the steel rebar surface, which increases the resistance to corrosion initiation up to 0·3M Cl^– instead of 0·1M Cl^– without treatment. The pretreatment also provides enhancement of corrosion protection of the steel rebar in mortar. The evolution of the impedance spectra in function of chloride concentration is in a fairly good agreement with the results obtained from R_P measurements.