Conversion Efficiency of Alkoxide Precursor to Oxide Films Grown by an Ultrasonic-Assisted, Pulsed Liquid Injection, Metalorganic Chemical Vapor Deposition (Pulsed-CVD) Process

Polycrystalline coatings of an oxide, with a columnar grain morphology, were grown on metal substrates from metalorganic precursors using the pulsed-CVD process. In a model study, films of the rutile phase of titanium dioxide were grown on nickel by thermal decomposition of titanium isopropoxide. Growth rates of up to 0.3 µm/min were obtained with conversion efficiencies (mole oxide per mole precursor) approaching 100%. The high growth rates and conversion efficiencies portend the application of this method for the manufacture of films and coatings on large surface areas, as, for example, required in the deposition of zirconium dioxide on nickel-based superalloys to serve as thermal barrier coatings on turbine blades.     

Preparation and Characterization of Alkoxy-Derived SrZrO3 and SrTiO3

High-purity strontium, zirconium, and titanium alkoxides were synthesized and characterized as precursors for complex oxides. Simultaneous hydrolytic decomposition either of strontium and zirconium alkoxides or of strontium and titanium alkoxides was used to obtain nearly stoichiometric, ideally mixed SrZrO₃ or SrTiO₃ powders of high surface activity. As-prepared helium-dried SrTiO₃ is crystalline before calcination. An ultraviolet radiation technique demonstrates the nucleation and growth of SrZrO₃ crystallites in the calcination temperature range to 350°C. The experimental results are supported by ir, TGA, and X-ray diffraction data. The high degree of control over purity, mixing uniformity, and crystallite size demonstrates the value of the alkoxide precursor approach for the solution of reproducibility problems encountered in the synthesis of electrical-quality ceramics.     

Metalorganic Chemical Vapor Deposition of Ferroelectric Pb(Zr,Ti)O3 Thin Films

Ferroelectric Pb(Zr_xT_1–x)O₃, films were successfully and reproducibly deposited by both hot–wall metalorganic chemical vapor deposition (MOCVD) and cold-wall MOCVD. One of the important problems associated with the MOCVD techniques is the selection of ideal precursors. After an intensive investigation for the most suitable precursors for MOCVD PZT films, the safe and stable precursors, namely lead tetramethylheptadione [Pb(thd)₂], zirconium tetramethylheptadione [Zr(thd)₄], and titanium ethoxide [Ti(OEt)₄], were chosen. The films were deposited at temperatures as low as 550°C and were single-phase perovskite in the as-deposited state. Also, the films were smooth, specular, crack-free, and uniform, and adhered well to the substrates. The stoichiometry of the films can be easily controlled by varying the individual precursor temperature and/or the flow rate of the carrier gas. Auger electron spectroscopic (AES) depth profile showed good compositional uniformity through the thickness of the films. The AES spectra also showed no carbon contamination in the bulk of the films. As-deposited films were dense and showed uniform and fine grains (≅0.1 μm).The optical properties of the films on the sapphire disks showed high refractive index ( n = 2.413) and low extinction coeflicient ( k = 0.0008) at a wavelength of 632.8 nm. The PZT (82/18) film annealed at 600°C showed a spontaneous polarization of 23.3 μC/cm² and a coercive field of 64.5 kV/cm.     

Lead Zirconate Titanate Prepared from Different Zirconium and Titanium Precursors by Sol-Gel

Modified sol-gel processes have been developed for the preparation of lead zirconate titanate (PZT) (52/48) powders. These processes use different starting sources to introduce the titanium and zirconium components, namely tetraethyl orthotitanate, titanium isopropoxide, or titanium diisopropoxide bis(2,4-pentanedionate) for titanium and zirconium propoxide or zirconium acetylacetonate for zirconium. To achieve stable and homogeneous precursor systems, several solvents (acetic acid, 1,2-propanediol, propanol, and distilled water) and chemical modifying additives, such as acetylacetone and nitric acid, were also introduced for the preparation processes. The influence of the different precursors on the crystallization behavior of the sol-gel-derived powders was studied. Well-crystallized single-phase PZT powders were obtained after heat treatment at 600°C for 1 h. The powders obtained sintered well at 1000°C/2 h and a homogeneous microstructure with small grain sizes was obtained.     

Sol-Gel Preparation of Pb(Zr0.50Ti0.50)O3 Ferroelectric Thin Films Using Zirconium Oxynitrate as the Zirconium Source

Lead zirconium titanate (Pb(Zr_0.5Ti_0.5)O₃, PZT) ferroelectric thin films were successfully deposited on platinum-coated silicon substrates and platinum-coated silicon substrates with a PbTiO₃ interlayer by using a modified sol–gel spin-coating process, using zirconium oxynitrate dihydrate as the zirconium source. The precursor solution for spin coating was prepared from lead acetate trihydrate, zirconium oxynitrate dihydrate, and tetrabutyl titanate. The use of zirconium oxynitrate instead of the widely used zirconium alkoxide provided more stability to the PZT precursor solution and a well-crystallized structure of PZT film at a relatively low processing temperature. PZT films that were annealed at a temperature of 700°C for 2 min via a rapid thermal annealing process formed a well-crystallized perovskite phase of PZT films and also had nanoscale uniformity. The microstructure and morphology of the prepared PZT thin films were investigated via X-ray diffractometry, transmission electron microscopy, and atomic force microscopy techniques. The values for the remnant polarization ( P ) and coercive electric field ( E ) of the PZT films that were obtained from the P–E loop measurements were 3.67 μC/cm² and 54.5 kV/cm, respectively.     

Synergistic effect of driers on soybean oil-based ceramer coatings

Inorganic-organic hybrid coatings were prepared using blown soybean oil with sol-gel precursors. Three sol-gel precursors, titanium tetra-i-propoxide (TIP), titanium (di-i-propoxide) bis (acetylacetonate) (TIA), and zirconium tetra-n-propoxide (ZrP) were used in conjunction with cobalt, manganese, and zirconium driers. The goal of this study was to investigate if a synergy exists between the drier and sol-gel precursors with respect to the autooxidation process. Various coating properties such as hardness, adhesion, reverse impact resistance, and flexibility were evaluated as a function of sol-gel precursor and drier content. Viscoelastic and tensile properties were also investigated. Department of Polymers and Coatings, Fargo, ND, 58105.     

Epoxidized soybean oil-based ceramer coatings

New inorganic/organic hybrid coating containing epoxidized soybean oil were prepared. Three sol-gel precursors [titanium (IV) i-propoxide, titanium (IV) di-i-propoxide bis-acetoacetonate, and zirconium n-propoxide] were utilized as the inorganic phase. Various coating properties, including adhesion, hardness, impact resistance, flexibility and tensile properties, were investigated as a function of sol-gel precursor type and concentration. All ceramer coatings exhibited excellent flexibility and hardness. Tensile strength and hardness increased with sol-gel precursor concentration. A slight decrease in adhesion and impact resistance was observed with increasing precursor content.     

Sol—Gel Fabrication of Pb(Zr0.52 Ti0.48)O3 Thin Films Using Lead Acetylacetonate as the Lead Source

Lead zirconium titanate (PZT) thin films of the morphotropic phase boundary composition [Pb(Zr_0.52Ti_0.43)O₃] were deposited on platinum-coated silicon by a modified sol-gel process using lead acetylacetonate as the lead source. The precursor solution for spin coating was prepared from lead acetylacetonate, zirconium n -butoxide, and titanium isopropoxide. The use of lead acetylacetonate instead of the widely used lead acetate trihydrate provided more stability to the PZT precursor solution. Films annealed at 700°C for 12 min formed well-crystallized perovskite phase of Pb(Zr_0.52Ti_0.48)O₃. Microstructures of these films indicated the presence of submicrometer grains (0.1 to 0.2 μm). The dielectric constant and loss values of these films measured at 10 kHz were approximately 1200 and 0.04, respectively, while the remanent polarization and coercive field were ∼ 13 μC/cm² and ∼ 35 kV/cm. Aging of the solution had almost no effect on the dielectric and ferroelectric properties of these films.     

Organic–inorganic coatings based on epoxidized castor oil with APTES/TIP and TEOS/TIP

Two series of organic–inorganic hybrid films were prepared from epoxidized castor oil (ECO) and the inorganic precursor titanium(IV) isopropoxide (TIP), combined with silicon precursors, either 3-aminopropyltriethoxysilane (APTES) or tetraethoxysilane (TEOS) with different organic to inorganic proportions. Films were pre-cured at room temperature under an inert atmosphere and subsequently submitted to thermal curing. The macro- and microscopic properties of the films, including adhesion, hardness, microstructure (SEM) and thermal properties, were determined as a function of the proportion of ECO to inorganic precursors. Morphological studies showed that the hybrid films were microscopically homogeneous. The addition of TIP decreases substantially the curing time. The hardness and tensile strength of the films increased with increased concentration of inorganic precursor. The combination of the silicon-rich inorganic precursors with TIP improved substantially the mechanical strength of the films. All of the films exhibited good adhesion to the aluminum surface. Aluminum coated with the films and submitted to intensive corrosion test presented excellent protection.     

Morphologies and growth mechanisms of zirconium carbide films by chemical vapor deposition

Zirconium carbide films were grown on graphite slices by chemical vapor deposition using methane, zirconium tetrachloride, and hydrogen as precursors. The growth rate of zirconium carbide films as a function of temperature was investigated. The morphologies of these films at different temperatures were also observed by scanning electron microscopy. The results indicated that the deposition of zirconium carbide was dominated by gas nucleation at temperatures below 1523 K, and by surface process at temperatures higher than 1523 K. By comparison of the deposition activation energies for zirconium carbide and deposited carbon, it was determined that the carbon deposition was the controlled process during the growing of zirconium carbide films. The effect of temperatures on the morphologies of zirconium carbide films was also discussed, based on the carbon deposition process.     

Solid Yttria-Stabilized Zirconia Films by Pulsed Chemical Vapor Deposition from Metal-organic Precursors

A pulsed chemical vapor deposition from metal-organic precursors (MOCVD) system was used to produce solid zirconia, and yttria-stabilized zirconia (YSZ) films. A total of six candidate metal-organic precursors for zirconia and three for yttria were investigated. Three precursor solutions for YSZ proved suitable for pulsed-MOCVD processing. Layers were deposited on metal, alumina, and porous nickel cermet substrates. Under optimal deposition conditions, precursor conversion efficiency of 90% was achieved using a solution of 3.74 vol% zirconium 2-methyl-2-butoxide + 0.42% yttium methoxyethoxide in toluene. The film growth rate was 7.5 μm·h⁻¹ at 525°C deposition temperature. Two alkoxide precursors produced YSZ layers with material costs under $0.50/(μm·cm²).     

纳米二氧化钛薄膜光催化剂的合成及特性

研究采用溶胶-凝胶技术以载玻片为基质制备了纳米TiO2薄膜,向溶胶中添加乙酰丙酮后改善了溶胶的稳定性及薄膜的牢固性。用扫描探针显微镜(DFM)、X射线衍射(XRD)、红外光谱(IR)及X射线光电子能谱(XPS)对薄膜进行了表征。结果表明:扫描探针显微镜(DFM)观察到薄膜中颗粒的粒径为20~40nm,X射线衍射(XRD)表明TiO2为锐钛型,用红外光谱(IR)表征了溶胶及粉末样品的物性并探讨了反应的机理,X射线光电子能谱(XPS)结果显示薄膜中除含有Ti、O元素外,还有少量从玻璃表面扩散至薄膜中的Na和Si元素。TiO2薄膜对光降解甲基橙水溶液具有很好的光催化性,通过掺SnO2、酸处理途径明显提高了其性能。     

Nanocrystalline Oxalate/Carbonate Precursors of Ce and Zr and Their Decompositions to CeO2 and ZrO2 Nanoparticles

The oxalate and carbonate precursors of cerium and zirconium have been prepared using reverse micelles as nanoreactors. Cerium oxalate precursor on thermal decomposition leads to a mixture of nanorods and nanoparticles of cerium oxide (nanoparticles of 10 nm and nanorods with 7 nm diameter and 30 nm length). Cerium oxide with crystallite size of 10 nm was obtained from cerium carbonate precursor. Monodispersed nanoparticles of zirconia with an average size of 3–5 and 12 nm were obtained from the oxalate and carbonate precursor, respectively. Detailed dielectric properties of sintered discs of nanocrystalline ceria and zirconia have been studied with variation of frequency and temperature.     

Effect of organic chelates on the performance of hybrid sol–gel coated AA 2024-T3 aluminium alloys

Sol–gels are organic–inorganic polymers formed by hydrolysis/condensation reactions of alkoxide precursors, primarily silanes, which have found applications as electronic, optical and protective coatings. These coatings possess important characteristics such as chemical stability, physical strength and scratch resistance. Further performance improvement is achieved through the incorporation of zirconium and titanium based nanoparticles, also formed through the sol–gel process. However due to the inherent difference in the reactivity of the precursors, the hydrolysis of each precursor must be carried out separately before being combined for final condensation. Zirconium precursors are commonly chelated using acetic acids, prior to hydrolysis, to lower the hydrolysis rate.In this body of work various ligands such as organic acids, acetyl acetone (AcAc) and 2,2′-bipyridine (Bipy) were used to control the zirconium hydrolysis reaction and form nanoparticles within the silane sol matrix.Nanoparticle modified coatings formed from the silane sol on AA 2024-T3 aluminium were characterised spectroscopically, electrochemically and calorimetrically to evaluate the potential effect of the different chelates on the final film properties while neutral salt spray tests were performed to study their anti-corrosion performance. Results indicate that the acid ligand modified coatings provided the best performance followed by AcAc, while Bipy was the poorest. In all cases the zirconium nanoparticle improved the protective properties of the sol–gel coating.     

Thermoanalytical investigation on the formation of IrO2-based mixed oxide coatings

The formation reactions of IrO₂/TiO₂ mixed oxide films supported on titanium metal plate were followed by thermoanalytical (simultaneous TGA, DTG, DTA) and combined thermoanalyticalmass spectrometric (TGA-MS) techniques. The electrochemical characterization of the fired coatings was made by cyclic voltammetry. The thermal decomposition of the titanium precursor salt, titanium diisopropoxide bis-2,4-pentanedionate, shows a major change in the presence of hydrated iridium (iii) chloride. Due to the catalytic effect of the added noble metal, an almost complete conversion of the organic components of the precursor mixture to CO₂ and H₂O is observed in the combustion stage. Chlorine, from thermal decomposition of the iridium salt, is produced in a separate stage at higher temperatures, indicating that a sequence of steps occurs prior to the oxide formation. For iridium chloride alone a complexation between the metal ion and the solvent (isopropanol) is observed, leading eventually to H₂O and CO₂ production (combustion step) between 300 and 500° C. The cyclic voltammetry results indicate that the features of the precursor reaction affect the charge storage capacity of the oxide films.This paper is dedicated to Professor Brian E. Conway on the occasion of his 65th birthday, and in recognition of his outstanding contribution to electrochemistry.     

Pyrolysis of Pb(Zr05Ti05)O3 Precursors: Avoiding Lead Partitioning

Three different chemical precursor routes were investigated to synthesize Pb(Zr₀₅Ti₀₅)O₃: mixing hexanoates, acetate complexing of alkoxides, and the synthesis of a mixed alkoxide by the reaction of titanium alkoxide and zirconium alkoxide with lead acetate. For each, elemental Pb and PbO were the first crystalline phase observed during pyrolysis conditions that involved rapid heating (e.g., to 400°C). The formation of Pb (and PbO) could be avoided by first heattreating hydrolyzed, mixed alkoxide precursor powders at 300°C for 1 h. This treatment was not effective for the two other precursors. It is concluded that both the carbonaceous content of the precursor (lowest for the hydrolyzed, mixed alkoxides) and the rate of hydrocarbon release during pyrolysis are critical to avoid the formation of elemental Pb during pyrolysis.     

Computational study on the decomposition of tetraneopentyl zirconium for the chemical vapor deposition of zirconium carbide

The overall gas phase decomposition mechanism of tetraenopentyl zirconium precursor (Zr[CH₂C(CH₃)₃]₄) for the chemical vapor deposition of zirconium carbide thin films was investigated by using computational thermochemistry. Density functional theory (DFT) and harmonic vibrational frequency calculation were used to generate thermodynamic properties at each reaction step, based on which thermodynamic or kinetic preference of a reaction pathway was evaluated. While the preference of γ-hydrogen abstraction of neopentane over α-hydrogen abstraction was confirmed in the initial stage of ZrNp₄ decomposition, they turned out to be competing instead of the dominant preference of γ-hydrogen abstraction. Methane formation at three subsequent reaction steps was explained by β-methyl migration, and the following _α-hydrogen abstraction of methane based on the suggestion that α- and γ-hydrogen abstractions of neopentane are competing kinetically in previous reaction steps. Computational thermochemistry showed a possibility as a general tool to anticipate the gas phase decomposition mechanism of a precursor in chemical vapor deposition.     

Influence of Precursor Densification on Strength Retention of Zirconia-Coated Nextel™ 610 Fibers

Strength degradation of Nextel^™ 610 fibers by continuous liquid phase coating was investigated for four different zirconia precursors. The precursors differed regarding their chemical composition (with or without yttrium), phase composition (amorphous or crystalline), and decomposition behavior. Phase transformation and densification of the films were characterized and found to depend on the kind of precursor. Single fiber Weibull's strength was measured for calcination temperatures between 250° and 1150°C for all precursors. Each precursor had an individual degradation behavior. For an annealing temperature of 1150°C highly damaged (∼1600 MPa) and undamaged (>3300 MPa) fibers were obtained depending on the kind of precursor. Fiber degradation could be correlated to mechanical stresses. Stress concentration due to inhomogeneous film thickness distribution is proposed as the cause of fiber strength degradation. Full strength could be retained for porous coatings or coatings where stresses were reduced by phase transformation.     

Effects of the number of benzene rings on the properties of single-source ZrC-based liquid precursors and nano zirconium carbide powders thereof

Effects of carbon source in single-source ZrC-based liquid precursors on the properties of the precursors and precursor-derived nano ZrC powders were investigated. The liquid precursors were prepared by directly blending and heating zirconium n-butoxide with either 2,4-pentanedione, benzoyl acetone or 1,3-diphenyl-1,3-propanedione additives which have the same chemical composition and structure except for the number of benzene rings (0, 1 and 2, respectively) in order to control the carbon content in the precursors. The ceramic yield of the precursor decreased as the number of benzene rings in the precursors increased. The stability of the precursors in air and the carbon content of the ceramic powder increased when using 1,3-diphenyl-1,3-propanedione additive. X-ray pure nano zirconium carbide powders with ultra-fine size (30 nm), isotropic shape and homogeneous particle size distribution were synthesized from the liquid precursors containing two benzene rings in the structure. Compared with ZrC powders derived from the precursors containing zero or one benzene ring, the powder from the precursor containing two benzene rings was finer and more homogeneous in size distribution.     

Titanium Oxide Thin Films on Organic Interfaces through Biomimetic Processing

Titanium oxide (TiO₂) thin films have been deposited on silicon, glass, and plastic substrates by destabilization of an aqueous titanium lactate solution at low temperatures (<100°C). The process uses a commercially available, low-cost precursor and is simple to perform; it involves only control of pH in aqueous, chelated titanium solutions. With this solution technique, high deposition rates (>50 nm/min), film thickness (>100 nm), and excellent film uniformity have been obtained. Uniform coatings can be applied on complex-shaped polymeric substrates and porous membranes. Films can be formed on both sulfonated and untreated polymeric surfaces. As-deposited films on plastic substrates consist of amorphous, hydrated TiO₂. On sulfonated self-assembled monolayers on silicon substrates, nanocrystalline TiO₂ films have been formed. The deposited films exhibit strong ultraviolet (UV) absorption with excellent transmission in the visible wavelength range, which indicates that the coatings may be useful as protective UV blockers for polymeric materials.