Effect of Phase Transformation on the Densification of Coprecipitated Nanocrystalline Indium Tin Oxide Powders

Two kinds of nanocrystalline indium tin oxide (ITO) powders with different crystal structures—rhombohedral and cubic—were prepared using a coprecipitation process through the control of aging time of precipitates after coprecipitation. The densification characteristics of the two ITO powders were examined. During sintering the rhombohedral ITO, which is a high-pressure phase, was transformed to cubic around 900°C. The phase transformation induced coarsening of grains and many voids in the microstructure retarded densification. On the other hand the cubic ITO, which did not experience phase transformation during sintering, was well densified as the sintering temperature increased. Poor densification of the rhombohedral ITO powder is explained from the viewpoint of coarsening of grains during the phase transformation. This result shows the significance of phase transformation during sintering.     

Fabrication of Low-Porosity Indium Tin Oxide Ceramics in Air from Hydrothermally Prepared Powder

Compositionally homogeneous indium tin oxide (ITO) ceramics with low porosity were obtained successfully by sintering hydrothermally prepared powders. The fabrication technique began with the preparation of microcrystalline, homogeneously tin-doped (5 wt%) indium oxyhydroxide powder, under hydrothermal conditions. Low-temperature (∼500°C) calcination of the hydrothermally derived powder led to the formation of a substitutional-vacancy-type solid solution of In₂Sn_{1− x} O_{5− y} , and further heating of this phase at temperatures of >1000°C resulted in the formation of the tin-doped indium oxide phase, which had the C -type rare-earth-oxide structure. The sintering of uniformly packed, calcined powder compacts at 1450°C for 3 h in air resulted in low-porosity (∼0.7%) ITO ceramics.     

Influence of mechanical agitation on ZnSe electrodeposition in H2SeO3–ZnSO4 aqueous solution

Abstract

ZnSe thin films were prepared on transparent indium tin oxide (ITO) glasses by electrodeposition at 70°C. Linear sweep voltammograms were performed to get details about electrochemical reactions on indium tin oxide substrate. Deposition mechanism was discussed in conditions of static electrolytes and stirring ones. The results indicated that the catalysis of H₂Se on surface of ITO glass has accelerated Se(0) accumulation which restrained Zn²⁺ ions diffusion into lattice position. Cubic ZnSe films could only be obtained at ?900 mV from stirring solution. Mechanical agitation excitated the reaction of Zn²⁺ ions with reduced Se species, which decreased Se(0) accumulation onto the solid electrode.     

Comparison of hot pressing and spark plasma sintering in the densification behavior of indium tin oxide‐borosilicate glass composites

The goal of this study was to fabricate borosilicate glass matrix composites with high optical transmittance and high conductivity by forming percolated segregated networks of indium tin oxide (ITO) in the microstructure. ITO nanoparticles and borosilicate glass microspheres were mechanically mixed with ITO concentrations varying from 0 to 2.99 vol%. The mixes were then consolidated using either hot pressing (HP) or spark plasma sintering (SPS). The effects of changing sintering methods, along with varying other processing parameters such as heating rate, maximum temperature, and applied pressure, had surprising and unanticipated effects. Ac impedance spectroscopy (IS), SEM, and EDS results indicated the successful formation of a grain‐like microstructure of the sintered glass using both HP and SPS processing, with the ITO particles segregated to the boundary regions in all samples. IS results indicated percolation threshold values between 0.154 and 0.307 vol% ITO in the HP samples and between 0.307 and 0.764 vol% ITO in the SPS samples, with resistivities as low as 29 (Ω·cm) at 2.99 vol% ITO. Optical properties were dominated by impurities and light scattering at defects such as pores. Contrary to conventional belief, it was found that samples made using SPS required far higher temperatures to fully densify, with all other processing conditions being the same, compared with HP. This behavior was confirmed through repeat tests using different SPS equipment and a wide range of processing conditions.     

聚乙烯吡咯烷酮及钛酸酯对ITO浆料的分散稳定性考察

考察了在乙酸丁酯相中制备稳定均匀分散的纳米ITO浆料。选用两种分散剂聚乙烯吡咯烷酮(PVP)和钛酸酯(titanate),通过球磨分散法制备稳定ITO(indium tin oxide)浆料,并分析比较不同pH、分散剂用量、磨介氧化锆球粒径及用量和球磨时间对ITO浆料分散稳定性的影响,研究分散机理。结果表明,在pH=7.8,分散剂用量为ITO粉体质量的5.5%,磨介氧化锆用量为ITO粉体质量的2.6倍,磨介氧化锆粒径小于0.5 mm,球磨分散时间24 h时,制得的纳米ITO浆料分散稳定性最佳;且比较由两种分散剂制得的ITO浆料在储存时间为0 d与30 d的浆料粒径变化,后者稳定性优于前者。     

Dispersion and densification of nano Si–(Al)–C powder with amorphous/nanocrystalline bimodal microstructure

The dispersion behavior and densification of nano Si–(Al)–C powder with amorphous/nanocrystalline bimodal microstructure were investigated. The Si–C powders synthesized by a mechanical alloying (MA) process had a near‐spherical shape with an average particle size of 170 nm. A solid loading of 62 vol% was achieved using polyethyleneimine (PEI) as a dispersant. The optimum dispersant amount was 1 wt% based on zeta potential, sedimentation, and viscosity analysis data. The high zeta potential value (73 mV) compared with that of the commercially available SiC (65 mV) was caused by modified surface properties and consequent promotion of the cationic dispersant adsorption. A Si–Al–C slurry containing 6.5 wt% of sintering additives with a solid loading of 60 vol% was also prepared. The relative density of the dried Si–Al–C slurry was 63.3% without additional compaction, which could be densified at 1650°C at a pressure of 20 MPa using a spark plasma sintering furnace.     

纳米氧化铟锡透明隔热涂料的制备及性能表征

采用在水中分散好的氧化铟锡(ITO)水浆，以及有机硅树脂成膜剂，通过加入共溶剂并调整体系pH值，制得了性能好的透明隔热涂料。试验结果表明，该涂料具有良好的光谱选择性，在可见光区具有高的透过性，并能有效阻隔红外光区的热辐射。     

Synthesis and Electrical Characterization of the Polymorphic Indium Tin Oxide Nanocrystalline Powders

Nanocrystalline powders of two indium tin oxide (ITO) polymorphs—rhombohedral and cubic—were prepared by a co-precipitation process. The temperature and aging time of precipitates after co-precipitation were controlled to obtain selectively the two different crystal structures. X-ray diffraction and transmission electron microscopy were used to characterize the powders. The electrical conductivity of the two ITO powders was determined by the powder solution composite method. The conductivities obtained were 0.26±0.04 and 0.65±0.17 S/cm for the rhombohedral and cubic ITO samples, respectively, the first such report for the rhombohedral phase.     

Comparative study on the microstructure and properties of 10 wt%- and 35 wt%- tin doped indium oxide materials

Due to the resource shortage of indium, the application of 10 wt%- tin doped indium oxide (10 wt%- ITO) with 74.4 wt% of indium is restricted in the field of flat panel display. A new ternary compound TCO material with 53.8 wt% of indium (35 wt%- ITO) was prepared by In₂O₃-35 wt% SnO₂ powders, whose microstructure and properties were studied in comparison to 10 wt%- ITO. The research findings show that: (1) The phase composition of 35 wt%- ITO target is mainly In₄Sn₃O₁₂ and In₂SnO₅, without In₂O₃: Sn phase for 10 wt%- ITO; (2) When films possess the strong crystalline structure, the photoelectric properties of 35 wt%- ITO films are superior to 10 wt%- ITO. In addition, the crystalline structure of 35 wt%- ITO films could be changed from In₄Sn₃O₁₂ + amorphous to In₄Sn₃O₁₂ + In₂O₃ by annealing, but for 10 wt%- ITO, only the crystallinity is changed.     

Highly concentrated aqueous SiC slurry containing fine SiC powder: A new approach for ultra-dense green body

SiC slurry with ultra-high concentration up to 70 vol% was prepared using oxidized fine and coarse SiC powder mixture, and dense SiC green body with a relative density of 76% was fabricated by drying the slurry at ambient condition. Three approaches were performed to prepare highly concentrated SiC slurry; preparation of SiC powder having good dispersion behavior, optimization of the oxidation condition, and optimization of bi-modal particle size distribution. An aqueous slurry with the solid loading up to 62 vol% could be prepared using fine (150 nm) SiC powder prepared by the mechanical alloying of Si and carbon. The surface property of the fine and coarse (10 μm) SiC powders was optimized using an oxidation treatment. The maximum solid loading of the fine SiC slurry prepared using oxidized powder was 66 vol%. By optimizing the mixing ratio of the oxidized fine and coarse SiC powder to 75:25, the solid loading of the SiC slurry could increase up to 70 vol%. The relative densities of the green bodies after drying 66, 68, and 70 vol% slurries were 69, 75.7, and 76.1%, respectively, which values were higher than those (58%) prepared by cold isostatic pressing under 200 MPa.     

Preparation of Monodispersed Tin-Doped Indium Oxide Powders by Hydrothermal Method

This paper presents a hydrothermal method for synthesizing tin-doped indium oxide (ITO) powder. It shows that monodispersed ITO powders of diameter 70±10 nm can be readily prepared by a process using NaOH as a basic source and involving hydrothermal synthesis at 240°C in 12 h and post-calcination at 500°C. The powder size is decreased by increasing the initial indium and tin concentration ([In+Sn]_precursor) and the excess NaOH concentration ([NaOH]_excess) in the solution. The proposed technique has a significant potential for the commercial production of ITO nanopowders.     

Novel seed-assisted synthesis of indium tin oxide submicro-cubes and their resistivity

Indium tin oxide films, an important n-type semiconductor oxide, show great prospects in optoelectronic device applications. Consequently, as a key raw material of targets for sputtering films, it is important to prepare low-resistivity indium tin oxide powders. Herein, low-resistivity indium tin oxide submicro-cubes are synthesized by a seed-assisted coprecipitation method. The effects of seed content, In³⁺ concentration, aging time, reaction temperature and calcination temperature on resistivity were investigated by single factor and orthogonal experiments. To ensure reliability and reproducibility of data, each experiment was repeated three times and resistivity of each sample was measured three times to obtain average value. The results indicated that optimal sample was matched with cubic phase In₂O₃. The single-crystal indium tin oxide particles exhibited a regular cubic shape with a size of nearly 500 nm and low resistivity of 0.814 Ω·cm. Compared with particles prepared by the conventional coprecipitation method, indium tin oxide submicro-cubes showed good dispersion. The presence of seed particles provided nucleation sites with lower energy barriers and promoted formation of submicro-cubes. The face-to-face contact among particles and good dispersion contributed to electron transfer, resulting in lower resistivity. The seed-assisted synthesis provides a novel way to prepare low-resistivity indium tin oxide submicro-cubes.     

Dispersion behavior of HfC-based nanopowders in ethanol

The dispersion behavior of two different types of ultrafine HfC-based powders in ethanol was investigated using polyethyleneimine (PEI) as a dispersant. The first type was synthesized by carbothermal reduction using a modified spark plasma sintering technique (d50: 125 nm). For the 10 wt% HfC suspensions, the highest zeta potential value (67.7 mV), the least sediment after sedimentation test for one day, and finest particle sizes were obtained when the concentration of PEI was 2.0 wt%. The concentrated HfC slurries with a solid loading of 40 vol% were achieved using 1.0 wt% PEI. The second type was mixing the HfC powder with HfSi2-C additives using a high-energy ball milling. The concentrated HfC slurry containing 20 wt% of HfSi2-C sintering additives was prepared up to 50 vol% solid loading using 0.50 wt% PEI. This is the first report for producing highly concentrated HfC-based nano slurries, which were highly suitable for the wet process of ultrahigh-temperature ceramic matrix composites (UTHCMCs).     

Effect of stabilizer on synthesis of indium tin oxide nanoparticles

Indium tin oxide nanoparticles with shapes varying from sphere to cubic were synthesized by controlling the ratio of the concentrations of the protective polymer (PVP) to indium tin oxide precursor in their preparation by co-precipitation. Transmission electron microscopy was used to determine the size and shape. The XPS spectra of the particles revealed that the atomic ratios of In:Sn and (In + Sn):O are 10.0:1.0 and 1.0:1.5, respectively for both of the spheres and the cubes. X-ray diffraction study showed that these particles have the same crystalline structure. Thus, it is shown that the formation of the various shapes of the ITO particles could be achieved by using different ratios of protective polymer instead of varying the protective polymer or the sintering process.     

采用磁控溅射法在细菌纤维素膜上制备高性能的铟锡氧化物薄膜

Microbial cellulose (MC) membranes produced by Acetobacter xylinum NUST4.1,were used as flexible substrates for the fabrication of transparent indium tin oxide (ITO) electrodes.Transparent and conductive ITO thin films were deposited on MC membrane at room temperature using radio frequency (RF) magnetron sputtering.The optimum ITO deposition conditions were achieved by examining crystalline structure,surface morphology and op-toelectrical characteristics with X-ray diffraction (XRD),scanning electron microscopy (SEM),atomic force mi-croscopy (AFM),and UV spectroscopy.The sheet resistance of the samples was measured with a four-point probe and the resistivity of the film was calculated.The results reveal that the preferred orientation of the deposited ITO crystals is strongly dependent upon with oxygen content (O2/Ar,volume ratio) in the sputtering chamber.And the ITO crystalline structure directly determines the conductivity of ITO-deposited films.High conductive [sheet resis-tance ～120 Ω·square-1 (Ω·sq-1)] and transparent (above 76%) ITO thin films (240 nm thick) were obtained with a moderate sputtering power (about 60 W) and with an oxygen flow rate of 0.25 ml·min-1 (sccm) during the deposi-tion.These results show that the ITO-MC electrodes can find their potential application in optoelectrical devices.     

New laser machining technology of Al2O3 ceramic with complex shape

A new method was developed for the fabrication of complex-shaped Al₂O₃ ceramic parts by combining laser machining and gelcasting technique. The unwanted ceramic powders parts were selectively removed by laser machining specified by a computer program, and the gelcast Al₂O₃ green bodies were machined to a designed shape by a CO₂ laser at a wavelength of 10.6 μm. The influences of solid loading, laser output power, scanning speed and nitrogen purge on the machining of green Al₂O₃ ceramic bodies were studied. The experimental parameters were optimized, the green Al₂O₃ bodies with solid loading of 40 vol% or below were easier to be machined, while the green bodies with solid loading of 45 vol% or above were hard to be further machined due to the surface sintering. Better machining quality and deeper machining depth could be obtained when the laser power is 30 W. The green Al₂O₃ bodies with complex shape were obtained by the laser machining.     

Spray-combustion synthesis of indium tin oxide nanopowder

Nanocrystalline indium tin oxide (ITO) powders were prepared by a novel spray combustion method. Using single-drop study equipment, we studied the thermodynamics of the combustion reaction. The reaction can be ignited at air temperature as lower as 171.3°C when using urea and glucose as composite fuel. Once the reaction is ignited, the combustion temperature can surge to above 500°C, generating nanocrystalline ITO powders with grain size about 40 nm. Footages from high-speed camera demonstrated that the reaction is in three-step: moderate beginning, violent middle, and decaying end. It is also noticed that the ignition is very sensitive to the air temperature, even 0.2°C minus deviation may fail the combustion. The combustion reaction is self-sustainable, which saves the energy supply. And the low ignition temperature means the combustion reaction can be carried out in a conventional spray dryer. Our results provide a feasible way to mass production of nanocrystalline ITO powders, which as a methodology, may be extended to the production of other oxide nanopowders.     

Comparative studies of polypropylene nonwoven sputtered with ITO and AZO

In this study, the polypropylene (PP) spunbonded nonwoven materials were used as substrates for depositing transparent nanostructures on the fiber surfaces. Magnetron sputter coating technique was used to deposit tin‐doped indium oxide (ITO) and aluminum‐doped zinc oxide (AZO) films onto the nonwoven substrates. The structures and properties of the deposited ITO and AZO films were investigated and compared using atomic force microscopy, energy‐dispersive X‐ray (EDX), and electrical and optical tests. The observations by atomic force microscopy revealed the formation of functional nanostructures on the fiber surfaces. EDX analyses confirmed the deposition of ITO and AZO functional films on the PP fibers. It was found that ITO had more compact structures on the fiber surface than AZO under the same sputtering conditions. The transmittance analysis revealed that the nonwoven substrates deposited with nanostructural AZO showed better ultraviolet shielding effect than those coated with ITO in the same thickness. The nonwoven materials coated with ITO had lower electrical resistance than those coated with AZO in the same thickness. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fabrication of patterned carbon nanotube thin films using electrophoretic deposition and ultrasonic radiation

A simple wet-deposition method for preparing patterned carbon nanotube (CNT) thin films is reported. Using electrophoretic deposition (EPD), CNTs were deposited over indium tin oxide (ITO) plates that had been patterned with a photoresist; consequently, CNTs covered not only the exposed ITO areas but also the photoresist areas because thinness of the photoresists could not prevent the transverse deposition of CNTs over the photoresist areas. The ultrasonic treatment for the samples removed only CNTs on the photoresist areas, resulting in the formation of patterned CNT thin films, because Ni metal formed during EPD connects CNTs to ITO plates.     

Fabrication of poly(3,4‐ethylenedioxythiophene)‐polysaccharide composites

Poly(3,4‐ethylenedioxythiophene) (PEDOT) doped with a series of anionic polysaccharides such as carboxymethyl cellulose, sodium hyaluronate, xanthan gum, pectin, gellan gum were prepared by electropolymerization in aqueous solutions. Some other dopants of potassium nitrate, potassium sulfate, sodium poly(styrenesulfonate), and sodium polyacrylate were used in comparison with the anionic polysaccharides. The electrochemical properties and stability of the obtained PEDOT films were also investigated. It was found that indium tin oxide (ITO) conductive glass could be used as the working electrode of the electropolymerization of EDOT and that the dopant had a great influence on polymerization potential and overoxidation potential. These charged biomolecules of anionic polysaccharides were found to facilitate electropolymerization of EDOT instead of common doping anions as counterion. The electroactive PEDOT films doped with anionic polysaccharides showed stable electrochemical properties, good texture, and adhesion properties to the ITO conductive glass. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012