Effect of temperature schedule on the particle size of barium titanate during solid-state reaction

Nano-sized BaTiO₃ particles were synthesized by a solid-state reaction in air using a 2-step heat treatment process. The dependence of the particle size and tetragonality (=c/a) on the temperature schedule was investigated. The temperature was held for 10 h at an intermediate temperature before heating to the target temperature of 1000°C for 1 h. Although more heat was consumed, the powders synthesized by the 2-step heat treatment method showed a much smaller particle size with higher tetragonality than those produced by direct heating. For example, the mean particle size was <100 nm at a holding temperature ranging from 500-700 °C, while it was 246 nm for direct heating to the same target temperature of 1000 °C. This was explained by the enhanced nucleation rate during temperature holding stage based on the TG/DTA and high temperature XRD results.     

The process of electrochemical deposited hydroxyapatite coatings on biomedical titanium at room temperature

Calcium phosphate (CaP) ceramics, especially hydroxyapatite (HA), have received much attention and have been clinically applied in orthopaedics and dentistry due to their excellent biocompatibility. Among several methods for preparing HA coating, electrochemical deposition is a relatively new and possible process. However, documented electrochemical processes were conducted at elevated temperature. In this study, uniform HA coatings have been directly deposited on titanium at room temperature. X-ray diffractometry (XRD) results demonstrated that dicalcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) was the main component of the coating deposited at lower current densities (1 and 5 mA/cm²). HA structure was obtained at current density above 10 mA/cm² and remained stable after heat treatment at 100–600 °C for 1 h. Part of HA phase was transformed into β-TCP and became a biphasic calcium phosphate coating after annealing at 700 °C. Scratch tests showed that HA coating was not scraped off until a shear stress of 106.3 MPa. Coatings deposited at room temperature exhibited stronger adhesion than those at elevated temperature. HA coating revealed a dense inner layer and rough surface morphology which could fulfill the requisition of implant materials and be adequate to the attachment of bone tissue.     

Effect of calcination conditions on phase formation and particle size of nickel niobate powders synthesized by solid-state reaction

The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase nickel niobate (NiNb₂O₆) powders. The formation of the NiNb₂O₆ phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that the minor phases of unreacted NiO and Nb₂O₅ precursors and the Ni₄Nb₂O₉ phase tend to form together with the columbite NiNb₂O₆ phase, depending on calcination conditions. More importantly, it is seen that optimization of calcination conditions can lead to a single-phase NiNb₂O₆ in an orthorhombic phase.     

A facile low-cost synthesis of ZnO nanorods via a solid-state reaction at low temperature

ZnO nanorods have been prepared via a solid-state reaction between anhydrous zinc sulfate and sodium hydroxide in the absence of surfactant and template at relatively low temperature. The products were characterized by XRD, XPS and TEM. The influence of Zn²⁺/OH⁻ ratio on the size and morphology of the as-prepared ZnO samples has been studied, and the experimental results showed that when Zn²⁺/OH⁻ ratio was 1:4, good rod-like morphology with the diameter of 30–50 nm and length of ca. 600 nm can be obtained. Finally, the mechanism for the ZnO nanorods developed in the reaction system has been explained.     

室温固相反应合成碱式碳酸锌

以七水硫酸锌(ZnSO4.7H2O)和碳酸氢铵(NH4HCO3)为原料,以聚乙二醇-400(PEG-400)为模板,通过室温固相反应制备了碳酸锌(ZnCO3)和碱式碳酸锌(ZnCO3.3Zn(OH)2.H2O,basic zinc carbon-ate,BZC)。通过XRD测试及其半定量成分分析,研究了PEG-400剂量和NH4HCO3与ZnSO4.7H2O摩尔比x值对合成产物物相的影响。总结了PEG-400模板辅助合成ZnCO3和BZC的反应机制。结果表明,PEG-400包覆ZnSO4.7H2O颗粒形成模板,模板层的厚度影响固相反应的微观机制———薄层单向扩散与厚层互扩散,局部微环境的酸碱性决定着产物物相,酸性抑制ZnCO3水解,碱性促进ZnCO3水解生成BZC。由据此设计的较高x值(x=3.0)、较低PEG-400剂量(70μL)的合成工艺,制备了单相BZC粉体。     

ZnFe2O4纳米粉体的室温固相合成及其气敏特性研究

以无机盐为原料，采用室温固相化学反应法合成了尖晶石型复合氧化物ZnFe2O4,X射线粉末衍射（XRD）、透射电镜（TEM）等表征结果表明，固相反应完全，平均粒径约为30nm左右；将样品制成烧结型气敏元件，发现在较低的工作温度时，对H2S有较高的灵敏度和选择性。     

焙烧室温条件固相反应制备前驱物合成SnO2纳米棒的研究

室温条件下通过固相反应合成了SnO2纳米颗粒前驱物.在600～780℃对前驱物进行焙烧,在NaCl、KCl和KCl＋NaCl的熔盐介质中SnO2前驱物纳米颗粒自组装生长形成SnO2 纳米棒.利用TEM、XRD和XPS对SnO2纳米棒结构、形貌和成分进行了研究.结果表明SnO2纳米棒直径为20～80nm,长度从几百纳米到十几微米.分析了SnO2 纳米颗粒前驱体熔盐介质中的生长,利用固相转变生长可以解释SnO2纳米棒在熔盐介质中的生长机制.     

Synthesis of nanosized nickel hydroxide by solid-state reaction at room temperature

The nanosized cathode material Ni(OH)₂ powder for alkaline batteries was synthesized by solid-state reaction at room temperature through NiC₂O₄·2H₂O as precursor, which was also prepared with solid-state reaction from nickel acetate and oxalic acid at ambient temperature. The precursor and the Ni(OH)₂ samples were characterized by X-ray diffraction (XRD), infrared spectrometry (IR), transmission electron microscopy (TEM) and electrochemical testing. The results revealed that the as-synthesized Ni(OH)₂ sample by this method is β(II)-type phase, and its shape is fibroid with the average particle size of 6–9 nm. Compared with microsized spherical β-Ni(OH)₂, the nanosized β-Ni(OH)₂ exhibits excellent electrochemical performance, such as lower polarization and better charge–discharge properties.     

室温固相合成前体法制备纳米CuO粉体

以Cu(NO3)2·3H2O和NH4HCO3为原料,利用室温固相反应首先制备出对H2O2分解具有极高催化活性的纳米级混合碱式铜盐粉体,然后经230℃焙烧2h得纳米CuO粉体,并借助XRD、SEM、FT IR、TEM、TGA和DTA等手段对产物的结构、大小、形貌及相关性质进行了表征。结果表明获得了外貌呈球形、大小均匀、无团聚、平均粒径为28nm的纳米CuO粉体。     

Effect of calcination condition on phase formation and particle size of lead titanate powders synthesized by the solid-state reaction

A perovskite-like phase of lead titanate, PbTiO₃, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. Phase formation of the calcined powders has been investigated as a function of calcination temperature, soaking time and heating/cooling rates by DTA and X-ray diffraction (XRD) techniques. Moreover, morphology and particle size evolution have been determined via SEM technique, respectively. It has been found that single-phase PbTiO₃ powders were successfully obtained for calcination conditions of 550 °C for 4 h or 600 °C for 1 h with heating/cooling rates of 20 °C/min. Higher temperatures clearly favoured particle growth and the formation of large and hard agglomerates.     

Effect of calcination conditions on phase formation and particle size of Zn3Nb2O8 powders synthesized by solid-state reaction

The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase Zn₃Nb₂O₈ powders. The formation of the Zn₃Nb₂O₈ phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that the minor phases of unreacted ZnO and Nb₂O₅ precursors and the columbite ZnNb₂O₆ phase tend to form together with the Zn₃Nb₂O₈ phase, depending on calcination conditions. It is seen that optimization of calcination conditions can lead to a single-phase Zn₃Nb₂O₈ in a monoclinic phase.     

Synthesis and photoluminescence properties of Cl-doped ZnS nanoparticles prepared by a solid-state reaction

ZnS:Cl⁻ nanoparticles with strong blue emission have been synthesized successfully by a solid-state reaction at low temperature. The dependence of photoluminescence (PL) properties of ZnS:Cl⁻ nanoparticles on the Cl⁻ contents was researched, and the influences of the annealing ambience and using polyvinyl alcohol (PVA) during the synthesis on the PL of ZnS:Cl⁻ (Cl/Zn = 0.35) nanoparticles were discussed. X-ray power diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and ultraviolet-visible spectroscopy were used to characterize their structure, chemical state, diameter, surface states, and PL properties. The results showed that ZnS:Cl⁻ nanoparticles had a cubic blende crystal structure and an average crystallite size of 17.40–19.16 nm. The most intensity blue emission peaking at about 425 nm was obtained when Cl/Zn = 0.35 under 330 nm excitation at room temperature. The emission intensity of ZnS:Cl⁻ (Cl/Zn = 0.35) was increased 3-fold than that of ZnS. The results showed that the PL of ZnS:Cl⁻ (Cl/Zn = 0.35) nanoparticles was enhanced after annealing or using PVA during the synthesis, and annealing in vacuum had a stronger effect in improving the luminescence properties of ZnS nanoparticles than in air. This work suggests that it is an effective method to improve the PL intensity of ZnS nanocrystals by doping with Cl⁻ in ZnS.     

Influence of calcination conditions on phase formation and particle size of indium niobate powders synthesized by the solid-state reaction

A wolframite-type phase of indium niobate, InNbO₄, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. The formation of the InNbO₄ phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. Single-phase InNbO₄ powders have been obtained successfully for calcination condition of 900 °C for 4 h or 950 °C for 2 h with heating/cooling rates of 30 °C/min. Higher temperatures and longer dwell times clearly favoured particle growth and the formation of large and hard agglomerates.     

Effects of calcination conditions on phase formation and particle size of indium niobate nanopowders synthesized by the solid-state reaction

A wolframite-type phase of indium niobate, InNbO₄, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. The formation of the InNbO₄ phase in the calcined powders has been investigated as a function of calcination conditions by TG–DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that single-phase InNbO₄ powders have been obtained successfully at the calcination condition of 950 °C for 2 h with heating/cooling rates of 30 °C/min. Higher temperatures and longer dwell times clearly favoured particle growth and the formation of large and hard agglomerates.     

Characterization and optical properties of m-Li2ZrO3 prepared by optimized solid-state reaction

m-Li₂ZrO₃ powders were successfully prepared by solid-state reaction method using Li₂CO₃ and ZrO₂ as raw materials. The synthesis was optimized by varying the ball-milling time (0–96 h); Li₂CO₃ excess (0 or 5 wt%), reaction temperature (700, 800, 900 or 1000 °C), and reaction time (3, 6, 9 or 12 h). The structural, morphological and optical properties of m-Li₂ZrO₃ powders were examined by X-Ray Diffraction, Thermogravimetric and Differential-Thermal analysis, Scanning Electron Microscopy, High-Resolution Transmission Electron Microscopy, Laser Diffraction, Dynamic Light Scattering and UV–Vis Diffuse Reflectance Spectroscopy. The results show that precursors suitable for the synthesis of fine powders require ball-milling times longer than or equal to 6 h. Highly crystalline m-Li₂ZrO₃ was synthesized under two distinctive calcination conditions as follows: 900 °C/6h without Li₂CO₃ excess or 1000 °C/12 h using 5 wt% of Li₂CO₃ excess. Particle size of as-synthesized powders was found to be in the range from 200 nm to 1 µm. m-Li₂ZrO₃ was found to be a wide band gap material with apparent optical band gap of 5.5 eV (direct) and 5.1 eV (indirect), which can be used in UV-C applications.     

Copper nanowall array grown on bulk Fe-Co-Ni alloy substrate at room temperature as lithium-ion battery current collector

Large-scale copper nanowall array on the bulk Fe-Co-Ni alloy substrate has been prepared in aqueous solution at room temperature via an electroless deposition method. The thickness of the nanowalls is about 15 nm. A possible growth mechanism of the nanowalls was proposed. The effects of reaction temperature, reaction time and the amount of critical agent (Fe³⁺) on the morphology and crystalline phase of the nanowalls were investigated. Furthermore, the electrochemical performance of Sn film supported on the as-prepared copper nanowalls current collector is enhanced in comparison with that on the commercial copper foil when used as anode for Li-ion batteries with the operating voltage window of 0.01-2.0 V (vs. Li). After 20 cycles, the discharge capacity of Sn-Cu nanowalls anode still remained 365.9 mAh g^− 1, that is, 40% retention of the reversible capacity, while the initial charge capacity of Sn film cast on commercial Cu foil was 590 mAh g^− 1, dropping rapidly to 260 mAh g^− 1 only after 10 cycles.     

Photo-induced formation of hydroxyapatite on TiO2 synthesized by a chemical–hydrothermal treatment

The formation of hydroxyapatite (HAp) on TiO₂ surfaces under continuous ultraviolet (UV) irradiation was investigated. Pure Ti substrates were chemically treated with H₂O₂/HNO₃ at 353 K for 20 min to form a TiO₂ gel layer. The specimens were then hydrothermally treated with an aqueous NH₃ solution in an autoclave at 453 K for 12 h. An adhesive and sufficiently crystallized anatase-type TiO₂ film could be synthesized on the Ti surface. The specimens were immersed in simulated body fluid in darkness or under UV irradiation with a centered wavelength of λ = 365 nm. Under dark conditions, a thin homogeneous HAp film was formed, with just a few spherical clusters of HAp. The UV illumination promoted the formation of HAp clusters, which may be due to the generation of functional Ti–OH or Ti–O groups on the TiO₂ surface. On the other hand, the UV light produced electron-hole pairs in the TiO₂, and the photogenerated holes that migrated to the surface repelled the Ca²⁺ ions in the solution. As a consequence, the UV irradiation suppressed the formation of a HAp thin film.     

反应温度对碳纳米管的影响

本文利用化学气相沉积( CVD)法,以乙烯为碳源气体,二茂铁为催化剂,在二氧化硅上制备出一系列碳纳米管,并通过拉曼光谱和扫描电子显微镜( SEM)对其形貌、结构和组分进行表征,分析反应温度对碳纳米管的影响.研究发现:当反应温度为860℃时,有均匀的碳纳米管薄膜生成,其管径和长度分别达到104 nm和95 μm,同时结构缺陷少,非碳管杂质较少,纯度较高.     

Crystalline hydroxyapatite thin films produced at room temperature — An opposing radio frequency magnetron sputtering approach

Hydroxyapatite (HA) films have been widely recognized for their biocompatibility and utility in promoting biointegration of implants in both osseous and soft tissue. Conventional sputtering techniques have shown some advantages over the commercially available plasma spraying method; however, the as-sputtered films are usually amorphous which can cause some serious adhesion problems when post-deposition heat treatment is necessitated. In this paper we present an opposing radio frequency (RF) magnetron sputtering approach for the preparation of HA thin films on various substrates at low power levels. Using this alternative RF magnetron geometry, as-sputtered HA films are nearly stoichiometric, highly crystalline, and strongly bound to the substrate. Post-deposition heat treatment under 800 °C did not result in a marked improvement in the degree of crystallinity of the films. In addition, dissolution experiments show that as-sputtered films are more stable than annealed ones. As-sputtered films grown on amorphous silica substrates exhibit X-ray diffraction (XRD) patterns similar to those of randomly orientated HA powder. On the other hand, films deposited on oriented substrates such as Si(100) and Si(111) show a polycrystalline HA XRD pattern but with some strongly preferred orientations, indicating that HA crystallization is sensitive to the nature of the substrate. The results suggest that the opposing RF magnetron sputtering approach has some potential to produce high quality HA films on metallic implants.