Corrosion resistance of cerium-doped zinc calcium phosphate chemical conversion coatings on AZ31 magnesium alloy

Zinc calcium phosphate （Zn-Ca-P） coating and cerium-doped zinc calcium phosphate （Zn-Ca-Ce-P） coating were prepared on AZ31 magnesium alloy. The chemical compositions, morphologies and corrosion resistance of coatings were investigated through energy-dispersive X-ray spectroscopy （EDS）, X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, electron probe micro-analysis （EPMA） and scanning electron microscopy （SEM） together with hydrogen volumetric and electrochemical tests. The results indicate that both coatings predominately contain crystalline hopeite （Zn3（PO4）2·4H2O）, Mg3（PO4）2 and Ca3（PO4）2, and traces of non-crystalline MgF2 and CaF2. The Zn-Ca-Ce-P coating is more compact than the Zn-Ca-P coating due to the formation of CePO4, and displays better corrosion resistance than the Zn-Ca-P coating. Both coatings protect the AZ31 Mg substrate only during an initial immersion period. The micro-galvanic corrosion between the coatings and their substrates leads to an increase of hydrogen evolution rate （HER） with extending the immersion time. The addition of Ce promotes the homogenous distribution of Ca and formation of hopeite. The Zn-Ca-Ce-P coating has the potential for the primer coating on magnesium alloys.

Synthesis and optical properties of zinc phosphate microspheres

Monodisperse zinc phosphate microspheres were synthesized by a facile solvothermal method in the presence of oleic acid.X-ray powder diffraction（XRD）,Fourier transform infrared spectrum（FT-IR）,emission scanning electron microscopy（SEM）,and energy dispersive X-ray spectrum（EDX） were used to characterize the microstructures and morphologies of the as-obtained zinc phosphate samples.The experimental results indicate that the zinc phosphate products are well crystallized,and the morphologies of the samples can be easily controlled by the elaborate choice of oleic acid addition and the content of NaOH.Furthermore,self-activated luminescent properties of the products are observed.The as-obtained samples show an intense blue emission under a long-wavelength UV light excitation of 400 nm.The possible luminescent mechanism may be ascribed to the carbon-related surface impurities or defects.

Energy transfer from Ce^(3+) to Tb^(3+) and Eu^(3+) in zinc phosphate glasses

Ce3+,Eu3+ and Tb3+ singly doped and Ce3+/Eu3+ and Ce3+/Tb3+ co-doped zinc phosphate glasses were prepared by sintering P2O5,ZnO,Ce2(C2O4)3·10H2O and Eu2O3/Tb4O7 mixtures at 1200 °C in the air for 2 h and then annealing at 450 °C for 10 h.The obtained glasses were homogeneous and transparent.The glasses without Ce3+ were colorless and those with Ce3+ showed slightly yellow.The singly doped glasses showed strong emissions and excitations from doped trivalent rare earth ions.Strong energy transfer from Ce3+ to...

Study on phosphating treatment of aluminum alloy:role of yttrium oxide

Zinc phosphate coatings formed on 6061-Al alloy, after dipping in phosphating solutions containing different amounts of Y2O3（yttrium oxide）, were studied by scanning electron microscopy （SEM）, X-ray diffraction （XRD） and electrochemical measurements. Significant variations in the morphology and corrosion resistance afforded by zinc phosphate coating were especially observed as Y2O3 in phosphating solution varied from 0 to 40 mg/L. The addition of Y2O3 changed the initial potential of the interface between aluminum alloy substrate and phosphating solution and increased the number of nucleation sites. The phosphate coating thereby was less porous structure and covered the surface of aluminum alloy completely within short phosphating time. Phosphate coating was mainly composed of Zn3（PO4）2·4H2O （hopeite） and AlPO4（aluminum phosphate）. Y2O3, as an additive of phosphatization, accelerated precipitation and refined the gain size of phosphate coating. The corrosion resistance of zinc phosphate coating in 3% NaCl solution was improved as shown by polarization measurement. In the present research, the optimal amount of Y2O3 was 10-20 mg/L, and the optimal phosphating time was 600 s.

Luminescent Properties of Ce^(3+) Ions in Zinc Phosphate Glass Prepared in Air

Glasses are prepared by sintering P2O5, ZnO and Ce2（C2O4）3 10H2O mixtures at 1 100 ℃ in air and then annealed at 400 ℃ for 10 hours. The obtained glasses are homogeneous, transparent and colorless. Emission and excitation spectra are measured for the samples and the results show that the glasses contain Ce3＋ trivalent cerium ions. The parameters of glass preparation obtained here may be adapted to preparing this type of glasses doped with other lanthanide ions, so as to study energy transfer phenomena and variation of radiative lifetime with refractive index due to local field effect.

Synthesis,Characterization and Phase Transformation of 3D Open-framework Zinc Phosphate [Zn_6(H_2O)P_5O_(20)][C_5N_2H_(14)][C_6H_(16)N_2]_(0.5)·3H_2O

With N,N′-dimethylpiperazine（DMPIP） as the structure-directing agent, a zinc phosphate [Zn6（H2O）P5O20] [C5N2H14] [C6H16N2]0.5·3H2O（1） with a novel three-dimensional（3D） open-framework architecture was hydrothermally synthesized. Its structure was determined by single-crystal X-ray diffraction analysis and further characterized by ICP, NMR, and TG analyses. Compound 1 crystallized in the triclinic space group P1（No.2） with a=0.9984（2） nm, b=1.2354（3） nm, c=1.2384（3） nm, α=88.32（3）°, β=74.57（3）°, γ=75.81（3）° and Z=2. The alternation arrrangement of tetrahedral Zn units[ZnO4 and ZnO3（H2O）] and PO4 units forms an anionic 3D open framework containing intersecting 16-, 10- and 8-ring channels. Water molecules, diprotonated DMPIP, and diprotonated N-methyl-piperazine（MPIP） decomposed from DMPIP, are located in the channels and interact with the host framework via H-bonds. Compound 1 transforms to another new phase（compound 2） upon calcination at 200―350℃ with the removal of the water coordinated to Zn atoms in the lattice. The phase transformation of compound 2 was further studied.

Red Long Lasting Phosphorescence of Mn^(2+) Doped Zinc Phosphate Glasses

Mn^2＋ doped ZnO-P2O5 glasses emit red fluorescence, which shows that Mn^2＋ ion doped in zinc phosphate glass is octahedrally coordinated. Moreover, glass samples exhibit bright red long lasting phosphorescence （LLP） when the mole percent of ZnO are more than 60%. After turnoff the irradiation source of UV lamp peaking at 254 nm, the red phosphorescence can be observed for about 6 h in the limit of light perception for naked eyes （0.32 mcd/m^2）. Photoluminescence （PL） spectra, LLP emission spectra and decay curves were detected. Increasing MnO or ZnO content, the phosphorescence intensity can be improved distinctly and the emission wavelength can be also adjusted from 595 nm to 628 nm. According to the structural characteristic of zinc phosphates glasses, we suggest that non-bridge oxygen （NBO） is probably related with the arising of LLE Meantime, the variation of crystal field intensity induced that the LLP emission wavelength red shifts.

SYNTHESIS AND CHARACTERIZATION OF THE LAMELLAR MICROCRYSTALLINE ZINC PHOSPHATE α-Zn_3(PO_4)_2·4H_2O

Objective To study the structural and anticorrosive property of microcrystalline α-Zn_3(PO_4)_2·4H_2O. Methods Zinc phosphate was prepared from zinc acetate and orthophosphate acid in aqueous solution. Structural characteristics of products were investigated by XRD, RAMAN, FTIR, TG-DTA, SEM, surface area, particle size distribution, and density measurements. Results The title compound, a highly crystalline, micronized and lamellar α-Zn_3(PO_4)_2·4H_2O, has an orthorhombic monoclinic system, space group a_0=10.597(),b_ 0 =18.308(), c_ 0 =5.0304(), V=975.86 3. Its specific area is 0.701m2/g, density 3.1612g/m3, and average size 4.75μm . Conclusion Comparing with commercial Zinc phosphate, the synthesized lamellar microcrystalline zinc phosphate had excellent anticorrosive property and dispersibility.

Bioactivity enhancement by Sr doped Zn-Ca-P coatings on biomedical magnesium alloy

The effect of strontium doped Zn-Ca-P(ZCP)coating by chemical conversion technique on the biodegradation of AZ31 alloy was evaluated.The coating formed with 1.5 wt.%Sr and 20 min phosphating time at 50℃ with pH 2.5 completely covers the alloy surface.The Sr doped coated sample also showed very low evolved hydrogen gas and pH change than the ZCP coatings suggested that the degradation of the alloy was extremely controlled.The in vitro bioactivity studies in simulated body fluid exhibits deposition of calcium phosphate phases with Ca/P ratio of 1.55 which is close to that of hydroxyapatite,mineral component of bone.Cytotoxicity evaluation with L929 cells showed higher cell viability of the Sr doped coatings compared to ZCP coatings.

Review on the phosphate-based conversion coatings of magnesium and its alloys

Magnesium(Mg)and its alloys are lightweight as well as biocompatible and possess a high strength-to-weight ratio,making them suitable for many industries,including aerospace,automobile,and medical.The major challenge is their high susceptibility to corrosion,thereby limiting their usability.The considerably lower reduction potential of Mg compared to other metals makes it vulnerable to galvanic coupling.The oxide layer on Mg offers little corrosion resistance because of its high porosity,inhomogeneity,and fragility.Chemical conversion coatings(CCs)belong to a distinct class because of underlying chemical reactions,which are fundamentally different from other types of coating.Typically,a CC acts as an intermediate sandwich layer between the base metal and an aesthetic paint.Although chromate CCs offer superior performance compared to phosphate CCs,yet still they release carcinogenic hexavalent chromium ions(Cr^(6+));therefore,their use is prohibited in most European nations under the Registration,Evaluation,Authorization and Restriction of Chemicals legislation framework.Phosphate-based CCs are a cost-effective and environment-friendly alternative.Accordingly,this review primarily focuses on different types of phosphate-based CCs,such as zinc,calcium,Mg,vanadium,manganese,and permanganate.It discusses their mechanisms,current status,pretreatment practices,and the influence of various parameters-such as pH,temperature,immersion time,and bath composition-on the coating performance.Some challenges associated with phosphate CCs and future research directions are also elaborated.

Influence of polymer solution on the morphology and local structure of NH_(4)ZnPO_(4)powders synthesized by a simple precipitation method at room temperature

NH_(4)Zn PO_(4)powders were synthesized using a simple precipitation method at room temperature.The effects of polyvinyl pyrrolidone(PVP),polyvinyl alcohol(PVA),glucose,and hexadecyltrimethylammonium bromide(CTAB)solutions on the morphology and structure of the prepared samples were investigated.The phase composition and morphology of the prepared samples were characterized using X-ray diffraction and scanning electron microscopy,respectively.Depending on the polymer sources,the hexagonal structure prepared using non-surfactant of water completely changed to monoclinic structure when CTAB was added.X-ray absorption near-edge structure(XANES)and X-ray photoelectron spectroscopy(XPS)were performed to study the local structure and surface electronic structure of the prepared samples,confirming that the oxidation states of P and Zn ions are^(5+)and^(2+),respectively.On the basis of the results of inductively coupled plasma atomic emission spectroscopy(ICP-OES),the NH_(4)Zn PO_(4)powders can be classified as a slow-release fertilizer where less than 15%of the ions were released in 24 h.A simple precipitation method using water,PVP,PVA,sucrose,and CTAB as a template can be used to synthesize NH4 Zn PO4 powders.In addition,this method may be extended for the preparation of other oxide materials.

Thermoelectric Properties of ZnO-P2O5/(Ni) Composites

The overall purpose of the present study is basically to understand the manifestation of the thermo-electrical properties of the matrix ZnO-P2O5 first, and of the ZnO-P2O5 composites loaded with different volume fractions of nickel (Ni) as conductive fillers. In the matrix ZnO-P2O5, the values of electrical conductivity varied between 1.14 × 10-8 and 7.8 × 10-7 (S/cm), and the Seebeck coefficient value varied between minimal value 265 and maximal value 670 (μV/K) in the studied temperature. In composite ZnO-P2O5/Ni, it was shown that the Seebeck coefficient changed from high positive to negative values when the filler amount was increased, indicating a non-conducting to conducting phase transition. Such behavior exhibits that this transition is accompanied by the passing of carrier charge from p to n type. The study of thermoelectrically transport for high volume fraction of filler enabled the achievement, for the first time on this kind of composites, of an original transition called PTC transition. Thus, highest values of power factor (PF = S2 ≈ 2 × 10-3 W·m-1·K-2 at 407 K) were obtained, giving a possibility of industrial applications.

Effect of mechanical treatment on the powder properties of zinc phosphate white pigments

Zinc oxide,which has photocatalytic activity,is used as a white pigment for cosmetics,resulting in a certain amount of sebum on the skin to be decomposed by the ultraviolet radiation in the sunlight.In this work,zinc phosphates as novel white pigments for use in cosmetics were prepared from zinc nitrate and sodium dihydrogen phosphate,and then ball-milled under various conditions.The chemical composition,powder properties,photocatalytic activity,color phase,moisture retention,and smoothness of the zinc phosphates were studied.The zinc phosphate particle size was decreased by mechanical treatment.In particular,the sample treated with sodium lactate solution had much smaller particles.The milled zinc phosphates exhibited less photocatalytic activity than zinc oxide,and thus should not decompose sebum on the skin.The milled zinc phosphates showed sufficiently high reflectance within the range of visible light to act as novel white pigments.The sample treated with sodium lactate solution had higher water retention than the sample treated with water.Further,the slip resistance and roughness of the powder particles decreased as a result of treatment with sodium lactate solution.

Reexamining intra and extracellular metabolites produced by Pseudomonas aeruginosa

Objective:To isolate,screen and analyze bacteria from different areas of Pakistan for the production of antimicrobial compounds,zinc solubilization and bioplastic production.Methods:Isolation and purification was proceeding with streak plate method.Antagonistic assay was completed with well diffusion and thin-layer chromatography.In vivo analysis of bioplastic was analyzed with Nile blue fluorescence under UV and Sudan staining.Results:A total of 18 bacterial strains purified from soil samples while 148 strains form stock cultures were used.Out of 166 only 94 showed antimicrobial activity against each of Grampositive and Gram-negative;cocci and rods.In case of heavy metal(ZnO and Zn_(3)(PO_(4))_(2)·4H_(2)O)solubilization,54 strains solubilized ZnO and 23 strains solubilized Zn_(3)(PO_(4))_(2)·4H_(2)O,while 127 strains grown on polyhydroxyalkanoate detection meedia supplemented with Nile blue medium showed bioplastic production by producing fluorescence under UV light.Four bacterial strains(coded as 100,101,104 and 111)were selected for further characterization.Induction time assay showed that strains 101,104,and 111 showed inhibitory activity after 4 h of incubation while strain 100 showed after 8 h.All four strains were tolerable to the maximum concentration of ZnO.Amplified products of both 16S rRNA and PhaC gene fragments of strain 111 were sequenced and submitted to GenBank as accession numbers EU781525 and EU781526.Conclusions:Bacterial strain Pseudomonas aeruginosa-111 has potential to utilize as biofertilize and bioplastic producer.