Design of the synthesis of fine HA powder for suspension plasma spraying

Hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂) is a bioactive material being frequently used as a coating onto implants. The typical coating technology is air plasma spraying with the use of coarse powder. The resulting coatings are relatively thick (about 200-400 µm) and porous. Much thinner coatings being 5-40 µm thick, can be obtained by emerging technology of suspension plasma spraying with the use of powder particles having the diameters ranging from a few submicrometers to a few micrometers. The paper describes the way of synthesizing and preparing such fine powder starting from an aqueous solution of ammonium phosphate (H₂(PO₄)NH₄) and calcium nitrate (Ca(NO₃)·4H₂O) using statistical design of experiments (DOE). The design was made using composite matrix including a full factorial plan, star points and 3 experiments in the centre. The crystal phases purity and the mass of powder batch were the optimized responses of the powder synthesis and the concentration of calcium ions and volume of ammonium hydroxide were the experimental variables. The synthesized material was characterized by X-ray diffraction (XRD). The powder was calcined and crushed using a milling machine with zirconia balls and resulting morphology and size of fine particles was characterized using scanning electron microscope (SEM) and laser sizer correspondingly. The powder was then formulated into water and alcohol based suspension and the zeta potential was determined to understand its capacity of agglomeration. It was found out that the formulation of the suspension with the use of ethanol slightly favours dispersion of solid particles in the suspension. The initial tests of water based suspension plasma spraying onto titanium substrate were also carried out and the XRD phase analysis of obtained coatings was carried out the presence of HA and its phases of decomposition.     

Effect of Spraying Powders Size on the Microstructure,Bonding Strength,and Microhardness of MoSi2 Coating Prepared by Air Plasma Spraying

Molybdenum disilicide (MoSi₂) coatings were deposited on carbon steel by air plasma spraying technology with different feedstock powder sizes (i.e., powder A: ?15 + 2.5 μm, powder B: ?30 + 15 μm, powder C: ?54 + 30 μm, powder D: ?74 + 54 μm and powder E: ?106 + 74 μm). Phase composition and microstructure of coatings were characterized by x-ray diffraction (XRD) and scanning electron microscope. The bonding strength and microhardness of coatings were also evaluated. The XRD results show that there exists mutual transformation between T-MoSi₂ and H-MoSi₂ phase and part of Mo-rich phases are formed because of oxidization during the spraying process. With the increase of spraying powders size, the content of Mo-rich phases (Mo or Mo₅Si₃) and molybdenum oxide (MoO₃) in coatings decreases, and that of disilicide-rich phase (MoSi₂) in coatings increases. The oxidation degree of MoSi₂ particle gradually decreases during the spraying process with the increase of spraying powders size. The MoSi₂ is the main phase of the as-sprayed coatings when the spraying powders size is beyond 30 μm. With the increase of spraying powders size, the porosity of the as-sprayed coating increases, and the bonding strength of the coating gradually decreases. The hardness of coatings first increases and then decreases with the increase of spraying powders size.     

Recent Developments in Suspension Plasma Sprayed Titanium Oxide and Hydroxyapatite Coatings

The paper aims at reviewing of the recent studies related to the development of suspension plasma sprayed TiO₂ and Ca₅(PO₄)₃OH (hydroxyapatite, HA) coatings as well as their multilayer composites obtained onto stainless steel, titanium and aluminum substrates. The total thickness of the coatings was in the range 10 to 150 μm. The suspensions on the base of distilled water, ethanol and their mixtures were formulated with the use of fine commercial TiO₂ pigment crystallized as rutile and HA milled from commercial spray-dried powder or synthesized from calcium nitrate and ammonium phosphate in an optimized reaction. The powder was crystallized as hydroxyapatite. Pneumatic and peristaltic pump liquid feeders were applied. The injection of suspension to the plasma jet was studied carefully with the use of an atomizer injector or a continuous stream one. The injectors were placed outside or inside of the anode-nozzle of the SG-100 plasma torch. The stream of liquid was tested under angle right or slightly backwards with regard to the torch axis. The sprayed deposits were submitted to the phase analysis by the use of x-ray diffraction. The content of anatase and rutile was calculated in the titanium oxide deposits as well as the content of the decomposition phases in the hydroxyapatite ones. The micro-Raman spectroscopy was used to visualize the area of appearance of some phases. Scratch test enabled to characterize the adhesion of the deposits, their microhardness and friction coefficient. The electric properties including electron emission, impedance spectroscopy, and dielectric properties of some coatings were equally tested.     

Parallelogram-like microparticles of calcium dihydrogen phosphate monohydrate (Ca(H2PO4)2·H2O) obtained by a rapid precipitation route in aqueous and acetone media

Calcium dihydrogenphosphate monohydrate (Ca(H₂PO₄)₂·H₂O) was prepared by a rapid and simple precipitation method using CaCO₃ and H₃PO₄ in aqueous and acetone media at ambient temperature. The thermal transformation of the synthesized Ca(H₂PO₄)₂·H₂O at 500 °C was obtained to be CaP₂O₆ occurred through the dehydration and the phosphate condensation reactions, as revealed by thermoanalytical techniques (TG/DTG/DTA). The synthesized Ca(H₂PO₄)₂·H₂O and its decomposition product CaP₂O₆ were characterized by X-ray powder diffraction (XRD), Fourier transfer infrared (FTIR) spectroscopy and scanning electron microscope (SEM). Thermal behavior and the morphology of the synthesized Ca(H₂PO₄)₂·H₂O in aqueous and acetone media are compared with those of other works. The SEM micrograph of Ca(H₂PO₄)₂·H₂O show parallelogram-like microparticles containing small and large grain sizes. The aqueous and acetone media are proposed to play an important role in the synthetic process of calcium phosphates in exhibiting different physical properties, which are important for specific applications.     

Highly Segmented Thermal Barrier Coatings Deposited by Suspension Plasma Spray: Effects of Spray Process on Microstructure

Effects of the ceramic powder size used for suspension as well as several processing parameters in suspension plasma spraying of YSZ were investigated experimentally, aiming to fabricate highly segmented microstructures for thermal barrier coating (TBC) applications. Particle image velocimetry (PIV) was used to observe the atomization process and the velocity distribution of atomized droplets and ceramic particles travelling toward the substrates. The tested parameters included the secondary plasma gas (He versus H₂), suspension injection flow rate, and substrate surface roughness. Results indicated that a plasma jet with a relatively higher content of He or H₂ as the secondary plasma gas was critical to produce highly segmented YSZ TBCs with a crack density up to ~12 cracks/mm. The optimized suspension flow rate played an important role to realize coatings with a reduced porosity level and improved adhesion. An increased powder size and higher operation power level were beneficial for the formation of highly segmented coatings onto substrates with a wider range of surface roughness.     

Structural, Mechanical and Erosion Properties of Yttrium Oxide Coatings by Axial Suspension Plasma Spraying for Electronics Applications

Yttrium oxide (Y₂O₃) coatings have been prepared by axial suspension plasma spraying with fine powders. It is clarified that the coatings have high hardness, low porosity, high erosion resistance against CF₄ -containing plasma and retention of smooth eroded surface. This suggests that the axial suspension plasma spraying of Y₂O₃ is applicable to fabricating equipment for electronic devices, such as dry etching. Surface morphologies of the slurry coatings with splats are similar to conventional plasma-sprayed Y₂O₃ coatings, identified from microstructural analysis. Dense coating structures with no lamellar boundaries have been seen, which is apparently different from the conventional coatings. It has also been found that crystal structure of the suspension coatings mainly composed of metastable monoclinic phase, whereas the powders and the conventional plasma spray coatings have stable cubic phase. Mechanism of coating formation by plasma spraying with fine powder slurries is discussed based on the results.     

介孔Li3V2（PO4）3正极材料的研磨溶胶凝胶法合成和电化学性能（英文）

以V2O5·nH2O、LiOH·H2O、NH4H2PO4和蔗糖为原料,采用研磨溶胶凝胶技术制备了无定形Li3V2(PO4)3前驱体,再经过焙烧获得具有单斜结构的介孔Li3V2(PO4)3正极材料,并用XRD、SEM、TEM、比表面积和电化学性能测试来表征材料的性能。研究表明,在700°C下焙烧的样品具有良好的介孔结构、最大的比表面积(188cm2/g)和最小的孔径(9.3nm)。在0.2C倍率下,该介孔样品的首次放电容量达155.9mA·h/g,经过50次循环后其容量仍然可达154mA·h/g,表现出非常稳定的放电性能。     

Preparation and characteristic of spherical Li3V2(PO4)3

Spherical Li₃V₂(PO₄)₃ was synthesized by using N₂H₄ as reducer. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that single-phase, spherical and well-dispersed Li₃V₂(PO₄)₃ has been successfully synthesized in our experimental process. Electrochemical behaviors have been characterized by charge/discharge measurements. The initial discharge capacities of Li₃V₂(PO₄)₃ were 123 mAh g⁻¹ in the voltage range of 3.0–4.3 V and 132 mAh g⁻¹ in the voltage range of 3.0–4.8 V.     

Synthesis and electrochemical performance of Li3V2(PO4)3 by optimized sol-gel synthesis routine

Li₃V₂(PO₄)₃ samples were synthesized by sol-gel route and high temperature solid-state reaction. The influence of Li₃V₂(PO₄)₃ as cathode materials for lithium-ion batteries on electrochemical performances was investigated. The structure of Li₃V₂(PO₄)₃ as cathode materials for lithium-ion batteries and morphology of Li₃V₂(PO₄)₃ were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Electrochemical performances were characterized by charge/discharge and AC impedance measurements. Li₃V₂(PO₄)₃ with smaller grain size shows better performances in terms of the discharge capacity and cycle stability. The improved electrochemical properties of Li₃V₂(PO₄)₃ are attributed to the refined grains and enhanced electrical conductivity. AC impedance measurements also show that the Li₃V₂(PO₄)₃ synthesized by sol-gel route exhibits significantly decreased charge-transfer resistance and shortened migration distance of lithium ions.     

Thermal Expansion and Phase Stability Investigations on Cs-Substituted Nanocrystalline Calcium Hydroxyapatites

The high-temperature phase stability of Ca_10−x Cs _x (PO₄)₆(OH)₂, (x = 0–3) compositions synthesized by various wet chemical methods was investigated. The thermal expansion property of Ca₁₀(PO₄)₆(OH)₂ (abbreviated as CaHAp) and Cs-substituted CaHAp was measured by high-temperature XRD and dilatometry. The average crystallite size of the powders synthesized by wet chemical methods was found to be 10–50 nm range as shown by XRD and TEM. Up to 30 mol% Cs loading was observed to show only the apatite phase by XRD when the apatite powder was nanocrystalline in nature. However, high-temperature stability of the Cs-substituted system is limited to ≤5 mol%. Cs₃(PO₄) is observed to be separated out on heating the material above 773 K for compositions substituted with more than 5 mol% of Cs in the Ca-sublattice. The coefficient of thermal expansion measured by HTXRD is α_a = 12.42 × 10⁻⁶ K⁻¹, α_c = 14.98 × 10⁻⁶ K⁻¹; and α_a = 12.62 × 10⁻⁶ K⁻¹, α_c = 12.57 × 10⁻⁶ K⁻¹ for CaHAp and Ca_9.78Cs_0.2(PO₄)₆(OH)_1.96, respectively, in the temperature range of 298-1083 K. Bulk thermal expansion measurements are seen to be in agreement with the lattice expansion results.     

锂离子电池用LiVPO4F/C基正极材料的制备和性能（英文）

将H2C2O4·2H2O,NH4H2PO4,NH4VO3和LiF通过球磨反应、烧结,合成了LiVPO4F/C基正极材料。在这个过程中,草酸起还原剂和碳源的作用,利用热重、X射线衍射、扫描电镜、透射电镜和碳-硫分析等手段对合成的前驱体和材料进行检测和分析。XRD分析表明,球磨反应后所得到的前驱体为无定形态,而烧结后的材料中除了LiVPO4F的衍射峰外,还存在Li3V2(PO4)3和V2O3衍射峰。材料颗粒均匀,尺寸约2μm。透射电镜分析表明,合成的材料颗粒表面包裹着一层约2nm厚的无定形碳。在截止电压3.0～4.4V时,合成的材料在0.1C和10C倍率下的放电比容量分别为151.3和102.5mA·h/g。在10C倍率下循环50次后容量保持率为90.4%。在LiVPO4F和Li3V2(PO4)3的循环伏安曲线中可以明显看到V3+/V4+的氧化还原峰。     

Synthesis and performance of Li3V2(PO4)3/C composites as cathode materials

Carbon-coated Li₃V₂(PO₄)₃ cathode materials for lithium-ion batteries were prepared by a carbon-thermal reduction (CTR) method using sucrose as carbon source. The Li₃V₂(PO₄)₃/C composite cathode materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurement. The results show that the Li₃V₂(PO₄)₃ samples synthesized using sucrose as carbon source have the same monoclinic structure as the Li₃V₂(PO₄)₃ sample synthesized using acetylene black as carbon source. SEM image exhibits that the particle size is about 1 μm together with homogenous distribution. Electrochemical test shows that the initial discharge capacity of Li₃V₂(PO₄)₃ powders is 122 mAh·g⁻¹ at the rate of 0.2C, and the capacity retains 111 mAh−g⁻¹ after 50 cycles.     

The influence of methylcellulose (MC) on solubility of calcium hydroxyapatite (HA) crystals in HA/MC nanocomposites

The influence of methylcellulose ([C₆H₇O₂(OH)_3–x(OCH₃)_x]_n, MC) on the morphology and solubility of calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, GA) nanocrystals (NCs) in GA/MC organomineral nanocomposites (OMCs) is studied. GA/MC OMCs with the MC content of 0.5, 1, 2, 5, 10 and 20 wt % are synthesized in the Ca(OH)₂–H₃PO₄–[C₆H₇O₂(OH)_3–x(OCH₃)_x]_n–H₂O system under biomimetic conditions (37°C). The composition and structural features of OMCs, as well as crystallographic characteristics, size, and morphology of GA NC in OMCs, are determined via chemical analysis, X-ray diffraction (XRD), infrared spectroscopy (IRS), thermal analysis (DTA and DTG), scanning (SEM) and transmission (TEM) electron microscopy, and electron diffraction (ED). It is shown that the growth in the MC concentration in OMCs leads to the change in the GA NC morphology and the increase in their solubility (for Ca²⁺ and PO₄^3- ions).     

Preparation of NH4ZrH(PO4)2·H2Ovia solid-state reaction at low heat and its catalytic performance in the synthesis of butyl acetate

Nanocrystalline NH4ZrH(PO4)2·H2O was obtained by grinding ZrOCI2·8H2O and (NH4)2HPO4 in the presence of surfactant PEG-400 via solid-state reaction at room temperature.The product NH4ZrH(PO4)2·H2O and its product of thermal decomposition were characterized using thermogravimetry and differential thermal analyses (TG/DTA),Fourier transform infrared spectroscopy (FT-IR),X-ray powder diffraction (XRD),and transmission electron microscopy (TEM).Nanocrystalline NH4ZrH(PO4)2·H2O with an average particle size of 17 nm was obtained when the product was kept at 80℃ for 3 h.Its crystalline framework was stable at temperatures below 250℃.In addition,the catalytic performance of NH4ZrH(PO4)2·H2O in the synthesis of butyl acetate was investigated.The results show that NH4ZrH(PO4)2·H2O behaved as an excellent heterogeneous catalyst in the synthesis of butyl acetate.     

Suspension HVOF Spraying of Reduced Temperature Solid Oxide Fuel Cell Electrolytes

Metal-supported solid oxide fuel cells (SOFCs) composed of a Ce_0.8Sm_0.2O_2?δ (SDC) electrolyte layer and Ni-Ce_0.8Sm_0.2O_2?δ (Ni-SDC) cermet anode were fabricated by suspension thermal spraying on Hastelloy × substrates. The cathode, a Sm_0.5Sr_0.5CoO₃ (SSCo)-SDC composite, was screen-printed and fired in situ. The anode was produced by suspension plasma spraying (SPS) using an axial injection plasma torch. The SDC electrolyte was produced by high-velocity oxy-fuel (HVOF) spraying of liquid suspension feedstock, using propylene fuel (DJ-2700). The emerging technology of HVOF suspension spraying was explored here to produce thin and low-porosity electrolytes in an effort to develop a cost-effective and scalable fabrication technique for high-performance, metal-supported SOFCs. In-flight particle temperature and velocity were measured for a number of different gun operating conditions and standoff distances and related to the resulting microstructures. At optimized conditions, this approach was found to limit material decomposition, enhance deposition efficiency, and reduce defect density in the resulting coating, as compared to previous results reported with SPS. Produced button cells showed highly promising performance with a maximum power density (MPD) of 0.5 W cm^?2 at 600 °C and above 0.9 W cm^?2 at 700 °C, with humidified hydrogen as fuel and air as oxidant. The potential of this deposition technique to scale-up the substrate size to 50 × 50 mm was demonstrated.     

In Situ Synthesis of FeAl Dense Coatings by Very Low Pressure Reactive Plasma Spraying

With the purpose of elaborating high-quality FeAl coatings, a so-called very low pressure reactive plasma spray technique that combines very low pressure plasma spray and self-propagation high-temperature synthesis processes was used in the present study. A dense and homogeneous FeAl coating was thus successfully in situ synthesized by reactive plasma spraying of an Al/Fe₂O₃ composite powder under 1 mbar. The phase composition and microstructural features of the coating were characterized by XRD and SEM. Results indicated that the B2 ordered FeAl phase was synthesized, and the coating featured a dense and defect-free microstructure. The fracture mechanism of the coating remains mainly a brittle failure but the appearance of some dimples in local zones suggested some unexpected toughness.     

Thermodynamic and experimental studies on removal of calcium and sulfate ions from recycling water of complex sulfide flotation operations

A chemical method for removing calcium sulfate saturated solutions (0.016 mol/L CaSO₄) using barium chloride (BaCl₂·2H₂O) and sodium phosphate (Na₃PO₄) was experimentally studied. The main interest is to remove these ions from the solution through the precipitation of two solid species: sulfate (SO₄²⁻) as barite (BaSO₄), and calcium (Ca²⁺) as hydroxyapatite (Ca₅(PO₄)₃OH). Additionally, a solid/liquid separation method (i.e., flotation) was explored, using oleic acid and dodecylamine as collectors. The results show that, the chemical treatment of saturated solutions at 60 °C, pH 11.5 and using 3.9 g/L BaCl₂·2H₂O and 1.6 g/L Na₃PO₄, promotes the precipitation of barium sulfate and calcium-deficient hydroxyapatite (Ca_10–x(HPO₄)_x(PO₄)_6–x(OH)_2–x), with residual concentrations of calcium and sulfate below 0.10 and 5 mg/L, respectively. The residual calcium concentration increases to 28 mg/L when using the same amount of reactants, at temperature and pH values below those quoted. The highest flotation recovery of hydroxyapatite with oleic acid at pH 9.5 was about 80%, while that of barite floated with dodecylamine at pH 6.5 was about 90%.     

Plasma-Sprayed Hydroxyapatite Coating for Improved Corrosion Resistance and Bioactivity of Magnesium Alloy

In the present study, the corrosion resistance and bioactivity of AZ91HP magnesium alloy were improved by plasma spraying hydroxyapatite (HA) coating. X-ray diffraction measurements indicated that the coating formed amorphous and little β-Ca₃ (PO₄)₂ besides of HA. The corrosion resistance and bioactivity of the coating and magnesium alloy in simulated body fluid were investigated using immersion test. The coating showed lower corrosion rate and better bioactivity than magnesium alloy. The coating significantly improved the hydrophilicity of Mg alloy. The prothrombin time of the coating was 18 s, and the prothrombin time of Mg alloy was 11 s, so the coating had better anticoagulant activity.     

Effect of Gun Current on Electrical Properties of Atmospheric Plasma-Sprayed Lanthanum Silicate Coatings

Apatite-type lanthanum silicate (ATLS) electrolyte coatings for use in intermediate-temperature solid oxide fuel cells were deposited by atmospheric plasma spraying (APS). Plasma-sprayed coatings with typical composition La₁₀(SiO₄)₆O₃ exhibiting good densification and high oxide ionic conductivity were obtained by properly adjusting the spraying parameters, particularly the gun current. The highest obtained ionic conductivity value of 3.3 mS/cm at 1,173 K in air is comparable to other ATLS conductors. This work demonstrated empirically that utilization of the APS technique is feasible to synthesize dense La₁₀(SiO₄)₆O₃ electrolyte coatings using gun currents within an unusually broad range.     

The effect of graphene oxide (GO) on biomineralization and solubility of calcium hydroxyapatite (HA)

Interaction between GO and the counterpart of the bone tissue, calcium hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (HA), is modeled in the course of synthesis of nanosize composite materials (CMs) based on graphene oxide (GO) and biocompatible HA with a GO content of 0.1, 1.0, 2.0, and 5.0 wt % GO from aqueous solutions in the system of Ca(OH)₂–H₃PO₄–GO–H₂O under native conditions (37°C). The effect of CM composition on the size and morphology of HA nanocrystals (HA NCs) is determined using the methods of physico-chemical analysis (chemical, XRD, IRS, DTA, TDG, SEM, TEM). The solubility of HA NC CMs by Ca²⁺ ions in distilled water is determined under in vitro conditions, and the possible results of interaction between GO and native calcified tissues are analyzed.