The coating of cadmium compounds with copper compounds

Fine particles of cadmium carbonate (CdCO₃) were prepared by heating aqueous solutions containing dissolved urea and cadmium sulfate at 85°C for 1 h. Effect of the composition of the reactant mixture on the morphology of the precipitated particles was investigated. It was found that the cadmium sulfate content of the reactant mixture significantly affected the shape and size of the precipitated particles. At certain range of reactant mixture composition, cauliflower-shaped uniform particles were obtained. The later particles were coated with basic copper carbonate (Cu₂(OH)₂CO₃) by heating aqueous dispersions, containing CdCO₃ particles, copper (II) nitrate, and urea at 85°C for various periods of time with constant stirring. The coating process was found sensitive to the experimental conditions and in most of the trials; mixtures of the coated and coating precursor particles were obtained. As such, extensive optimizations were carried out and conditions were established for the production of uniformly coated particles.On calcination at 700°C for 1 h, the CdCO₃ particles converted into CdO, whereas the coated particles (CdCO_{3 (core)}/Cu₂(OH)₂CO_{3 (coating)} transformed into CdO_(core)/CuO_(coating)) without sintering. In the coated particles, the core and coating materials stayed mutually inert during the calcination reaction and independently converted into their respective oxides.All the calcined and uncalcined products were characterized by various physical and chemical methods.     

Polyfunctional bioceramics modified by M-type hexagonal ferrite particles for medical applications

Magnetic bioceramics based on Ca₅(PO₄)₃OH hydroxyapatite and M-type hexagonal ferrite (HF) microcrystals has been synthesized and characterized. The material consists of a biocompatible apatite matrix containing dispersed M-type HF particles. The latter component makes the magnetic characteristics of synthesized ceramics significantly higher as compared to those of iron-oxide-modified bioglass ceramics currently used in medicine. These properties increase the efficiency and prospects of using the new bioceramics in medicine, in particular, for the hyperthermal treatment of malignant tumors. Thus, a new class of materials is created, which combine the necessary biocompatibility and biological activity of Ca₅(PO₄)₃OH hydroxyapatite and high magnetic characteristics of M-type HF microcrystals.     

Processing of bovine hydroxyapatite (HA) powders and synthesis of calcium phosphate silicate glass ceramics using DC thermal plasma torch

In the present work, hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) was prepared from bovine bones with calcination method (up to 850 °C).The calcinated hydroxyapatite was powdered (30-40 μm) using a mechanical grinder; the particles were highly irregular in shape with sharp edges, angular, rounded, circular, dentric, porous and fragmented morphologies. The irregular shaped calcinated hydroxyapatite was plasma processed to produce spherical powders for thermal spray coating applications. More over; calcium phosphate silicate glass ceramics was produced by plasma melting of ball milled hydroxyapatite-borosilicate glass (50 wt.%) mixture. The samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD) and energy dispersive X-ray analysis (EDX). The morphology was determined using scanning electron (SEM) and optical microscopy (OM). The microhardness, density and porosity measurements for the synthesized samples were made.     

Laser surface modification for synthesis of textured bioactive and biocompatible Ca–P coatings on Ti–6Al–4V

A textured calcium phosphate based bio-ceramic coating was synthesized by continuous wave Nd:YAG laser induced direct melting of hydroxyapatite precursor on Ti–6Al–4V substrate. Two different micro-textured patterns (100 μm and 200 μm line spacing) of Ca–P based phases were fabricated by this technique to understand the alignment and focal adhesion of the bone forming cells on these surfaces. X-ray diffraction studies of the coated samples indicated the presence of CaTiO₃, α-Ca₃(PO₄)₂, Ca(OH)₂, TiO₂ (anatase) and TiO₂ (rutile) phases as a result of the intermixing between the precursor and substrate material during laser processing. A two dimensional elemental mapping of the cross-section of the coated samples exhibited the presence of higher phosphorous concentration within the coating and a thin layer of calcium concentration only at the top of the coating. Improved in vitro bioactivity and in vitro biocompatibility was observed for the laser processed samples as compared to the control.     

Influence of dicalcium phosphate dihydrate coating on the <Emphasis Type="Italic">in vitro</Emphasis> degradation of Mg-Zn alloy

To reduce the degradation rate and further to improve the biocompatibility of magnesium alloy, dicalcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) has been fabricated on a kind of magnesium-zinc alloy by way of electrodeposition method. The experimental results of XRD, SEM and EDS showed that the electrodeposited coating on the Mg-Zn alloy mainly contains the flake-like DCPD, along with some octacalcium phosphate (Ca₈(HPO₄)₂(PO₄)₄·4H₂O, OCP). After the in vitro degradation of the coated alloy in modified-simulated body fluid (m-SBF), it was proved that the coating could reduce the degradation rate effectively, and the samples were covered by calcium phosphate salts with a higher Ca/P ratio. Therefore, it indicates that compared with the bare alloy, the DCPD coating rendered a more biocompatible surface, and is a promising coating candidate for biomedical magnesium materials.     

Influence of dicalcium phosphate dihydrate coating on the in vitro degradation of Mg-Zn alloy

To reduce the degradation rate and further to improve the biocompatibility of magnesium alloy, dicalcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) has been fabricated on a kind of magnesium-zinc alloy by way of electrodeposition method. The experimental results of XRD, SEM and EDS showed that the electrodeposited coating on the Mg-Zn alloy mainly contains the flake-like DCPD, along with some octacalcium phosphate (Ca₈(HPO₄)₂(PO₄)₄·4H₂O, OCP). After the in vitro degradation of the coated alloy in modified-simulated body fluid (m-SBF), it was proved that the coating could reduce the degradation rate effectively, and the samples were covered by calcium phosphate salts with a higher Ca/P ratio. Therefore, it indicates that compared with the bare alloy, the DCPD coating rendered a more biocompatible surface, and is a promising coating candidate for biomedical magnesium materials.     

The influences of poly(lactic-co-glycolic acid) (PLGA) coating on the biodegradability, bioactivity, and biocompatibility of calcium silicate bioceramics

Calcium silicate (CaSiO₃) bioceramics and polyesters have complementary qualities as potential bone substituted materials. In this study, sintered CaSiO₃ bioceramics were prepared and coated with poly(lactic-co-glycolic acid) (PLGA), and the influences of the PLGA coating on the degradation, hydrophilicity, bioactivity, and biocompatibility of CaSiO₃ ceramics were investigated. The results showed that the degradation rate was reduced, while hydrophilicity was decreased with the increase of the polymer coating. In addition, the polymer coating resulted in a decrease of the alkaline pH value during the degradation of the ceramics, which indicated an increase of the cell biocompatibility, confirmed by the attachment and proliferation of rMSCs on the surface of the polymer-coated ceramics. Furthermore, the apatite-forming ability of the PLGA-coated CaSiO₃ bioceramics was maintained. This study suggested that the coating with PLGA might be a useful method to improve the integrative properties of CaSiO₃ bioceramics for applications in bone regeneration and bone tissue engineering.     

Fabrication mechanism of nanostructured HA/TNTs biomedical coatings: an improvement in nanomechanical and in vitro biological responses

In this paper, a mechanism for fabrication of nanostructured hydroxyapatite coating on TiO₂ nanotubes is presented. Also, the physical, biological, and nanomechanical properties of the anodized Ti6Al4V alloy consisting TiO₂ nanotubes, electrodeposited hydroxyapatite, and the hydroxyapatite/TiO₂ nanotubes double layer coating on Ti6Al4V alloy implants are compared. Mean cell viability of the samples being 84.63?% for uncoated plate, 91.53?% for electrodeposited hydroxyapatite, and 94.98?% for hydroxyapatite/TiO₂ nanotubes coated sample were in the acceptable range. Merely anodized prototype had the highest biocompatibility of 110?% with respect to the control sample. Bonding strength of hydroxyapatite deposit to the substrate increased from 12?±?2?MPa to 25.4?±?2?MPa using intermediate TiO₂ nanotubes layer. Hardness and elastic modulus of the anodized surface were 956?MPa and 64.7?GPa, respectively. The corresponding values for hydroxyapatite deposit were approximately measured 44.3?MPa and 0.66?GPa, respectively, while the average obtained values for hardness (159.3?MPa) and elastic modulus (2.25?GPa) of the hydroxyapatite/TiO₂ nanotubes double coating improved more than 30?% of the pure hydroxyapatite deposit. Friction coefficient (ξ) of the anodized surface was 0.32?±?0.02. The calculated friction coefficient enhanced from 0.65?±?0.04 for sole hydroxyapatite layer to the 0.46?±?0.02 for hydroxyapatite/TiO₂ nanotubes due to presence of nanotubular TiO₂ intermediate layer.     

Silicon-substituted hydroxyapatite composite coating by using vacuum-plasma spraying and its interaction with human serum albumin

The incorporation of silicon can improve the bioactivity of hydroxyapatite (HA). Silicon-substituted HA (Ca₁₀(PO₄)_6−x (SiO₄) _x (OH)_2−x , Si-HA) composite coatings on a bioactive titanium substrate were prepared by using a vacuum-plasma spraying method. The surface structure was characterized by using XRD, SEM, XRF, EDS and FTIR. The bond strength of the coating was investigated and XRD patterns showed that Ti/Si-HA coatings were similar to patterns seen for HA. The only different XRD pattern was a slight trend toward a smaller angle direction with an increase in the molar ratio of silicon. FTIR spectra showed that the most notable effect of silicon substitution was that –OH group decreased as the silicon content increased. XRD and EDS elemental analysis indicated that the content of silicon in the coating was consistent with the silicon-substituted hydroxyapatite used in spraying. A bioactive TiO₂ coating was formed on an etched surface of Ti, and the etching might improve the bond strength of the coatings. The interaction of the Ti/Si-HA coating with human serum albumin (HSA) was much greater than that of the Ti/HA coating. This might suggest that the incorporation of silicon in HA can lead to significant improvements in the bioactive performance of HA.     

Effect of zinc phosphate chemical conversion coating on corrosion behaviour of mild steel in alkaline medium: protection of rebars in reinforced concrete

We outline the ability of zinc phosphate coatings, obtained by chemical conversion, to protect mild steel rebars against localized corrosion, generated by chloride ions in alkaline media. The corrosion resistance of coated steel, in comparison with uncoated rebars and coated and uncoated steel rebars embedded in mortar, were evaluated by open-circuit potential, potentiodynamic polarization, cronoamperometry and electrochemical impedance spectroscopy. The coated surfaces were characterized by x-ray diffraction and scanning electron microscopy. First, coated mild steel rebars were studied in an alkaline solution with and without chloride simulating a concrete pore solution. The results showed that the slow dissolution of the coating generates hydroxyapatite Ca₁₀(PO₄)₆(OH)₂. After a long immersion, the coating became dense and provided an effective corrosion resistance compared with the mild steel rebar. Secondly, the coated and uncoated steel rebars embedded in mortar and immersed in chloride solution showed no corrosion or deterioration of the coated steel. Corrosion rate is considerably lowered by this phosphate coating.     

Superparamagnetic magnesium ferrite/silica core-shell nanospheres: A controllable SiO2 coating process for potential magnetic hyperthermia application

The control of coating shell becoming important to improve the applicability of magnetic nanoparticles. Herein, we present the scalable technique for preparing MgFe₂O₄/SiO₂ core-shell nanospheres with finely tuned shell thickness and their efficiency in magnetic hyperthermia heating agent. At first, MgFe₂O₄ dense nanosphere derived from one-step ultrasonic spray pyrolysis (USP) technique. Silica shells were then coated on the as prepared nanospheres with tunable thickness from 10 to 30 nm. We show that the thickness of this coating is finely controlled at allowing our proposed level by using the required amount of SiO₂ precursor (SiC₈H₂₀O₄)/acidic catalyst (HCl) ratio where the surface area of core nanospheres are significantly considered. X-ray diffraction reveals the cubic spinel ferrite structure of core particles with crystallite size 9.6 ± 1.8 nm and Fourier transform infrared spectrum analysis confirmed the formation of SiO₂. The morphological observation clarified the uniform and smooth SiO₂ shell where core-shell nanostructure is highly monodispersed in a liquid medium. M-H loops confirmed the superparamagnetic nature of all samples at room temperature. Significantly reduced ion release concentration in an aqueous solvent of the coated nanospheres compared with uncoated sample demonstrates the hermetically coating feature of dense SiO₂. This MgFe₂O₄/SiO₂ core-shell nanospheres with thine SiO₂ shell (10 nm) shows effective heating rate in the operative region (<46 °C) which makes them promising candidates for application as magnetic hyperthermia heating agent.     

Effect of zinc phosphate chemical conversion coating on corrosion behaviour of mild steel in alkaline medium: protection of rebars in reinforced concrete

Abstract

We outline the ability of zinc phosphate coatings, obtained by chemical conversion, to protect mild steel rebars against localized corrosion, generated by chloride ions in alkaline media. The corrosion resistance of coated steel, in comparison with uncoated rebars and coated and uncoated steel rebars embedded in mortar, were evaluated by open-circuit potential, potentiodynamic polarization, cronoamperometry and electrochemical impedance spectroscopy. The coated surfaces were characterized by x-ray diffraction and scanning electron microscopy. First, coated mild steel rebars were studied in an alkaline solution with and without chloride simulating a concrete pore solution. The results showed that the slow dissolution of the coating generates hydroxyapatite Ca₁₀(PO₄)₆(OH)₂. After a long immersion, the coating became dense and provided an effective corrosion resistance compared with the mild steel rebar. Secondly, the coated and uncoated steel rebars embedded in mortar and immersed in chloride solution showed no corrosion or deterioration of the coated steel. Corrosion rate is considerably lowered by this phosphate coating.     

Improvement of alkali corrosion resistance of mullite ceramics at high temperature by depositing Ca0.3Mg0.2Zr2(PO4)3 coating

Ca_0.3Mg_0.2Zr₂(PO₄)₃ coating was deposited on the mullite ceramic to improve its alkali corrosion resistance at high temperatures, using sol–gel method and dip-coating technique. The phase composition and microstructure of the coating were characterized by X-ray diffraction and scanning electron microscopy (SEM). Results show that homogeneous, dense and single-phase Ca_0.3Mg_0.2Zr₂(PO₄)₃ coating was successfully deposited on mullite ceramics. SEM microstructural examination revealed the excellent bonding between Ca_0.3Mg_0.2Zr₂(PO₄)₃ coating and mullite ceramics. The effectiveness of the prepared coating to improve the alkali corrosion resistance of mullite ceramics was assessed through the measurements of mass loss and flexural strength degradation after 96 h and longer exposure time at alkali corrosion condition at 1000 °C. A significant enhancement of the alkali corrosion resistance for Ca_0.3Mg_0.2Zr₂(PO₄)₃-coated mullite samples was observed. Therefore, the effectiveness of the Ca_0.3Mg_0.2Zr₂(PO₄)₃ material as protection coating for mullite ceramic is confirmed.     

Sol-gel derived hydroxyapatite coatings on titanium substrate

Biomaterials, in particular those used for orthopaedic prostheses, consist of a metallic substrate, exhibiting excellent mechanical properties, coated with a ceramic layer, which guarantees resistance to the corrosion and an elevated bioactivity. In this paper the preparation of sol-gel films of hydroxyapatite, HA (Ca₁₀(PO₄)₆(OH)₂), on titanium substrate is described. The samples were obtained through the dip-coating method, starting from a colloidal suspension of hydroxyapatite. In order to increase the adhesion between the HA film and the metallic substrate, the same substrate has been preliminarily coated either with titanium oxide, TiO₂ (in the anatase or rutile phase), or calcium titanate, CaTiO₃ (perovskite). Also these latter films have been deposited from a sol-gel solution. The characterization of the films through XRD, SEM, and AFM gave good results for the crystallinity of the deposited HA; for what concerns the sample morphology, the films turned out to be homogeneous and crack-free.     

Novel hydroxyapatite/tantalum surface coating for metallic dental implant

The aim of this study was to design and produce a novel surface composite coating on metallic substrate in order to improve the biocompatibility of metallic dental implant and the bone osteointegration simultaneously.Stainless steel 316L (SS) was used as a metallic substrate and a novel double-layer hydroxyapatite/tantalum (HA/Ta) coating was prepared on it. Tantalum coating was made using physical vapor deposition process and HA coating was produced using plasma-spraying technique on it. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were utilized to investigate the coating characterization. Electrochemical polarization tests were performed in two types of physiological solutions at 37 ± 1 °C in order to determine the corrosion behavior of the coated and uncoated specimens as indication of biocompatibility.The results indicated that the decrease in corrosion current density was significant for HA/Ta coated specimens and was much lower than the value obtained for uncoated 316L SS. The novel double-layer HA/Ta composite coating could improve the corrosion resistance and thus the biocompatibility of 316L SS dental implant.     

Dielectric properties and heating effect of multiferroic BiFeO3 suspension

Bismuth ferrite (BiFeO₃) ceramic particles of micro-meter size were prepared by a solid-state route. This study revealed an appropriate method to measure the dielectric properties of BiFeO₃ particle suspension using a system designed by ourselves. The heating effect of the BiFeO₃ suspension with applied AC voltage was confirmed. Application of this material in hyperthermia treatment of biological tissues with the goal of tumor therapy may be possible.     

Effect of carbon nanotube and aluminum oxide addition on plasma-sprayed hydroxyapatite coating's mechanical properties and biocompatibility

This study reports on the synthesis of novel bioceramic composite coating of hydroxyapatite (HA) reinforced with carbon nanotubes (CNTs) and aluminum oxide (Al₂O₃) using plasma spray technique. Fracture toughness of HA–20 wt.% Al₂O₃ improved by 158% as compared to HA coating whereas HA–18.4 wt.% Al₂O₃–1.6 wt.% CNT showed an improvement of 300%. Carbon nanotubes provided reinforcement via rebar mechanism. Human fiber osteoblast cell-growth studies showed that biocompatibility of the coating remained unaltered, as Al₂O₃ retained its bio-inertness and CNT, its bioactivity, within the composite coatings. Composite coating showed lower attachment, but higher proliferation rate, for the osteoblast cells, which has been attributed to the surface roughness. An optimized relation between coating composition, its biocompatibility and mechanical properties was established to predict the most suited coating material for orthopedic implants. HA–Al₂O₃–CNT composite coating displayed most improved mechanical properties while retaining its biocompatibility.     

The coating of nickel compounds with copper compounds

Uniform fine particles of nickel basic carbonate were synthesized by heating, aqueous solution containing 0.08 mol dm⁻³ nickel sulfate and 0.8 mol dm⁻³ urea, at 85°C for various periods of time. These particles were then coated with copper compound by heating them in aqueous dispersion, containing urea and copper nitrate, at 85°C. The coating material was found to be amorphous and was composed of Cu₂(OH)₂CO₃. The coating mixture, when heated under similar conditions in the absence of the dispersed cores, produced greenish dispersion of the precipitated particles [coating precursor solids]. The later were also amorphous in nature and had the same chemical composition [Cu₂(OH)₂CO₃] as that of the coating material of the coated particles. Air-dried core, coated, and coating precursor materials were calcined at 700°C for 1 h at the heating rate of 5°C min⁻¹ in the air atmosphere, which converted them into NiO, NiO_[core]/CuO_[coating], and CuO, respectively. Scanning electron microscopic examination showed no sintering occurred in all these solids during the calcinations process and the particles retained their identities to a significant extent.     

Synthesis,Characterization and Bioactivity Evaluation of Porous Barium Titanate with Nanostructured Hydroxyapatite Coating for Biomedical Application

Nano phase hydroxyapatite (HA) bioceramics have gained importance in the biomedical field due to their superior biological properties. In this study, nanostructured HA coating was used to increase the bioactivity of a piezoelectric bioceramic, barium titanate (BT). Early reports on the influence of collagen piezoelectricity in remodeling of bone have attracted many researchers to piezoelectric bioceramics such as BT. Hence; porous BT was used as the matrix of a new bone graft composite and then coated with nanostructured HA. BT ceramic was foamed via a direct foaming method with a spray of polyurethane foam. The surface of the foam voids was coated with HA via sol–gel and dip‐coating methods. X‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) techniques were used to characterize the prepared coated foam. XRD and TEM analysis showed that the HA coating had a nanostructure with crystallite size of 20–30 nm. SEM images of the prepared samples showed that the HA coating has about 25 µm thickness. The bioactivity of the prepared composite was evaluated in an in vitro study. The variation of Ca²⁺ and PO₄^3? ions versus time in simulated body fluid (SBF) solution were measured by inductively coupled plasma (ICP) analysis during 1 month and the results showed that the mineralization of calcium phosphate (Ca‐P) on HA coated porous samples was much more than that in non‐coated sample. The SEM micrographs and energy‐dispersive X‐ray spectroscopy (EDS or EDX) analysis of the samples after 1 month of immersing in SBF confirm that Ca‐P phase (bone‐like apatite) was significantly mineralized on HA coated porous BT samples. It was concluded that the nanostructured HA coating would improve the bioactivity of BT foam.     

Titanate coupling agent effects on nonaqueous Co2Z ferrite suspensions dispersion

Co₂Z ferrite powders with the chemical composition 3Ba_0.5Sr_0.5O·2CoO·12Fe₂O₃ have superior high frequency magnetic properties. However, Co₂Z ferrite powders are difficult to apply to practical processes because of agglomeration induced by the strong magnetic attraction between particles. In this study, Co₂Z ferrite powder pretreatment using a titanate coupling agent—Neopentyl (dially)oxy tri(dioctyl)pyrophosphate titanate (Lica 38) on the sedimentation and rheological behavior is investigated. The bonding mechanisms between ferrite powder, Lica 38, and dispersant (KD1) are studied using diffuse reflectance Fourier transform infrared spectroscopy is used to explain the difference in the rheological and sedimentation behaviors of untreated and titanate coupling agent-modified ferrite powders. The affinity of Co₂Z ferrite and dispersants could be substantially enhanced by coating a titanate- coupling agent onto the ferrite surface. The coated layer could prevent particles from agglomerating from magnetic interaction.