Showing papers in "Journal of the American Ceramic Society in 1998"

Porcelain—Raw Materials, Processing, Phase Evolution, and Mechanical Behavior

Abstract: Porcelain represents the foundation of the ceramics discipline and one of the most complex ceramic materials. Composed primarily of clay, feldspar, and quartz, porcelains are heat-treated to form a mixture of glass and crystalline phases. This review focuses on raw materials, processing, heat treatment, and mechanical behavior. Because of the complexities of the porcelain system and despite the substantial amount of research already conducted within the field, there remain significant opportunities for research and study, particularly in the areas of raw material understanding, processing science, and phase and microstructure evolution.

Amorphous Silicoboron Carbonitride Ceramic with Very High Viscosity at Temperatures above 1500°C

Abstract: Recently, the viscosity of a predominantly amorphous silicon carbonitride (Si1.7C1.0±0.1N1.5) alloy with an apparent glass-transition temperature (Tg) of 1400°–1500°C was studied. In this study, the creep behavior of silicoboron carbonitride (Si2B1.0C3.4N2.3), which seems to have a Tg value of >1700°C, was examined. Both materials exhibited a three-stage creep behavior. In stage I, the creep rate declined, because of densification. In stage II, the strain rate approaches a steady state. In stage III, it resumes a declining strain rate, which ultimately decreased below the measurement limit of the system. At 1550°C in stage II, the viscosity of silicoboron carbonitride was six orders of magnitude higher than that of fused silica. Among the Si-C-N ceramics, only chemical-vapor-deposited and reaction-bonded silicon carbides seem to have greater creep resistance than the silicoboron carbonitrides at temperatures >1550°C.

Effect of Initial α‐Phase Content on Microstructure and Mechanical Properties of Sintered Silicon Carbide

Abstract: By using α- and β-SiC starting powders with similar particle sizes, the effects of initial α-phase content on the microstructure and the mechanical properties of the liquid-phase-sintered and subsequently annealed materials were investigated. The microstructures developed were analyzed by image analysis. When β-SiC powder was used, the grains became elongated. The average diameter decreased with increasing α-SiC content and the aspect ratio showed a maximum at 10%α-SiC and decreased with increasing α-SiC content in the starting powder. Such results suggest that microstructure can be controlled by changing α-phase content in starting powders. The strength increased with increasing α-SiC content in the starting powder while the fracture toughness decreased with increasing α-SiC content. There may be a trade-off in improving both the strength and toughness in SiC ceramics sintered with oxide additives.

Sintering Model for Mixed‐Oxide‐Derived Lead Zirconate Titanate Ceramics

Abstract: The properties of lead zirconate titanate (PZT) ceramics are determined by the microstructure and chemical homogeneity of Zr, Ti, and dopants within the grains as well as the presence of secondary grain boundary phases. Stoichiometric 53/47 PZT and compositions with 3 mol% PbO excess were prepared by the mixed-oxide process, and were densified by pressureless sintering in oxygen. The influence of PbO content and different La concentrations on the densification behavior was analyzed by dilatometric measurements. Quantitative image analysis showed a different relative density and grain size dependence for samples containing >0.5 mol% additives compared to samples with <0.5 mol% La. On the basis of a model experiment and by using different analytical methods (microprobe analysis, HRTEM, STEM, and Auger spectroscopy) three types of inhomogeneities could be detected in conventionally prepared PZT ceramics: the existence of Ti and La enrichment in the core of PZT grains, and PbO-rich secondary phases in triple junctions as well as in grain boundary films. The results of the microstructural characterization and the analysis of the densification behavior were finally combined to deduce a sintering model based on a Pb-vacancy concentration gradient within the PZT grains.

Permeability and Structure of Cellular Ceramics: A Comparison between Two Preparation Techniques

Abstract: This work presents a comparative study of structural and aerodynamic properties of cellular ceramics prepared by two different techniques: the ceramic replication of an organic substrate and the gelcasting of foams. Permeability constants calculated from Ergun's equation were related to their apparent porosity and pore size. The technique of gelcasting of foams yielded structures as porous as the replication technique does, but with smaller pores and a fully densified strut. This type of structure ensures a higher mechanical strength without a significant decrease in the permeability.

Ferroelectric Thin Films of Bismuth-Containing Layered Perovskites: Part I, Bi4Ti3O12

Abstract: Ferroelectric thin films of bismuth-containing layered perovskite Bi4Ti3O12 have been fabricated by a metalorganic decomposition (MOD) method. Crack-free and crystalline films of ∼5000 A thickness have been deposited on Pt/Ti/SiO2/Si substrates. Different heat treatments have been studied to investigate the nucleation and growth of perovskite Bi4Ti3O12 crystallites. If the same composition and final annealing temperature are used, films with different orientations are obtained by different heating schedules. These films show a large anisotropy in ferroelectric properties. Theoretical considerations are presented to suggest that nucleation control is responsible for texture and grain-size evolution. Moreover, the origin of the ferroelectric anisotropy is rooted in the two-dimensional nature of layered polarization.

Novel Spray-Pyrolysis Deposition of Cuprous Oxide Thin Films

Abstract: Spray pyrolysis of aqueous solutions that include copper(II) acetate, glucose, and 2-propanol was studied for the formation of cuprous oxide (Cu2O) thin films on glass substrates. The deposition conditions, based on the phase relations of the films, were investigated in terms of solution concentration and substrate temperature. Also, the formation process was kinetically discussed. The Cu2O thin film obtained here was composed of rounded grains ∼50 nm in size with a surface roughness of ∼30 nm. This film was reddish yellow and showed indirect and direct bandgap energies of 1.95 and 2.60 eV, respectively. Furthermore, the film exhibited p-type conduction, with a resistivity of ∼100 Omegacm.

Observation of Subcritical Spall Propagation of a Thermal Barrier Coating

Abstract: Observations are reported of the room-temperature propagation of a spalling failure mode of a thermal barrier coating (TBC) from its bond coat after oxidation. The coating is a Y2O3-stabilized ZrO2 coating formed by electron-beam deposition on a Ni-Co-Cr-Al-Y bond coat. The spall shape evolution and stress redistribution as the spall propagates are reported. The failure propagates primarily as an interface crack between the bond coat and the thermally grown aluminum oxide (TGO) formed on the underside of the TBC during oxidation. The observations are consistent with subcritical propagation of an interface crack between the TGO and bond coat assisted by the presence of moisture. An estimate of 9 J/m2 is made of the fracture resistance in air of the interface.

Low‐Temperature Preparation of Nanocrystalline Lead Zirconate Titanate and Lead Lanthanum Zirconate Titanate Powders Using Triethanolamine

Abstract: Nanocrystalline lead zirconate titanate (PZT) powders, with a Zr:Ti ratio of 60:40, have been prepared from a solution of triethanolamine (TEA) and Ti4+, Zr4+, and Pb2+ ions. The metal ions were in solution through complex formation with TEA. The soluble metal-ion–TEA complex formed the precursor material when it was completely dehydrated. Heat treatment of the precursor at 450°C resulted in single-phase PZT powders. The precursor and the heat-treated powders have been characterized by using thermal analysis and X-ray diffractometry (XRD) studies. The average particle size, as measured from X-ray line broadening and transmission electron microscopy studies, was ∼20 nm. PZT powders modified with 3 mol% of lanthanum (PLZT) also were prepared through this route and were investigated via XRD studies. The dielectric constants of the PZT and PLZT powders were 12475 and 11262, and their corresponding Curie temperatures were 362° and 315°C, respectively.

Dopant Distribution in Grain-Boundary Films in Calcia-Doped Silicon Nitride Ceramics

Abstract: Quantitative analyses of the local chemistry of amorphous films at the grain boundary (GB) were taken on hot isostatically pressed high-purity Si{sub 3}N{sub 4} doped with various amounts of calcium (up to 450 ppm). This work was mainly accomplished by using spatially resolved electron energy-loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope. The amount of calcium segregation, quantified in terms of GB excess, saturated in the films at a bulk-doping level of {minus}220 ppm. Extra additives did not stay at the triple-point glass pockets, where the calcium was almost expelled completely; instead, the additives stayed at intersections between the films and pockets. Otherwise, the calcium distribution was uniform along and across GB films. The latter was determined from simulations of EELS profiling. At grain/pocket interfaces, a much-lower segregation level occurred, ranging from one-half to one-tenth of the level at the GB. This observation indicates different segregation mechanisms in the two cases. Also, the calcium segregation in GB films changed the film composition dramatically, because more N{sup 3{minus}} ions were introduced and replaced O{sup 2{minus}} ions, to maintain the local stoichiometry. Reduction of the Van der Waals force has been proposed as being the origin of the film expansionmore » with increasing calcium content.« less

Characterization of β‐Silicon Carbide Powders Synthesized by the Carbothermal Reduction of Silicon Carbide Precursors

Abstract: Boron-doped and nondoped ultrafine β-silicon carbide (β-SiC) powders were synthesized via the carbothermal reduction of SiC precursors at temperatures of 1773–1973 K. Although the reaction rate of carbothermal reduction was generally higher when a boron-doped precursor was used, the reaction rate for the boron-doped precursor was reduced considerably at 1873 K. For boron-doped and nondoped precursors, the reaction rates were almost the same. Powder characterization via transmission electron microscopy indicated that the suppression of the reaction rate for boron-doped precursor at 1873 K was due to the formation of a special coexistent system with two types of particle agglomerates. As expected, boron doping inhibited the particle growth in the synthesis of SiC powder.

Luminescence Characterization of Chromium-Containing theta-Alumina

Abstract: Characteristic photostimulated luminescence (fluorescence) in the visible range is reported from theta transition alumina prepared by using a variety of methods. The luminescence is associated with trace concentrations of chromium and can be intensified by intentional chromium doping. The luminescence from theta-alumina is similar to, albeit considerably weaker than, the R-line luminescence from alpha-alumina. The theta-alumina spectrum is characterized by a doublet at ∼14575 and 14645 cm−1 at 77 K and is blue-shifted from the R-lines of alpha-alumina by ∼150 cm−1. The doublet is attributed to Cr3+ ions in octahedral coordination and can be used for phase identification in microstructural characterization.

Ab-Initio Total Energy Calculation of α- and β-Silicon Nitride and the Derivation of Effective Pair Potentials with Application to Lattice Dynamics

Abstract: The ground state total energies of α- and β-Si3N4 crystals are calculated by an ab-initio method based on local density functional theory. The calculated bulk modulus and pressure coefficients for both crystals are in good agreement with recent experimental measurements. Interatomic pair potentials of the Buckingham form with an additional repulsive term are derived using ab-initio effective charges and total energy data. The effective pair potentials give excellent results on equilibrium lattice parameters, elastic constants, phonon spectra, and lattice specific heat for both crystals. The zone-center optical phonon modes are in good agreement with measured infrared and Raman spectra. The pair potentials for α- and β-Al2O3 are similar but not the same, despite their similarities in the local short-range order. Applications of the pair potentials to the simulation and modeling of surfaces and interfaces in Si3N4 ceramics are discussed.

Improvement in Mechanical Properties of Powder‐Processed MoSi2 by the Addition of Sc2O3 and Y2O3

Abstract: Additions of 1-20 mol% Sc2O3 or Y2O3 to MoSi2 eliminate glassy SiO2, which improves mechanical properties at both ambient and high temperatures. In particular, only 1 mol% ScO3 additions dramatically enhance three-point bending strength from 521 to 1081 MPa. Vickers hardness, Young's modulus, fracture toughness, and high-temperature strength are also improved by this low level of additive. The improvement of mechanical properties is attributed to the formation of crystalline silicates: Sc2Si2O7, Y2Si2O7, Y2SiO5, and Y4Si3O12, which are analyzed by XRD, SEM-EDS, and TEM-EDS methods.

Effects of Microstructure on the Dielectric and Piezoelectric Properties of Lead Metaniobate

Abstract: In an attempt to obtain dense PbNb 2 O 6 ceramics, sintering experiments were conducted using starting powders with various particle sizes and different modifications (rhombohedral and orthorhombic structures). During sintering of rhombohedral powders, the phase transformation to the tetragonal phase promoted grain growth, resulting in poor densification. Sintering of orthorhombic powders, however, yielded dense ceramics through suppression of the phase transformation. Based on these results, ceramics with various densities and different microstructures were prepared, and their dielectric and piezoelectric properties were evaluated. The dielectric constant and Curie temperature were dependent on density, grain size, and crack density. Cracks and intragrain pores severely deteriorated the piezoelectric properties. Dense ceramics with the maximum coupling factors and piezoelectric strain constants were obtained by prolonged heating of a fine powder with orthorhombic structure.

Influence of Additives on Slag Resistance of Al2O3‐SiO2‐SiC‐C Refractory Bond Phases under Reducing Atmosphere

Abstract: The microstructures of Al2O3–SiO2–SiC–C refractory matrices with aluminum, silicon, Si3N4, BN, B2O3, and B4C additives are characterized before and after a crucible slag test, and the phases present are compared to those expected at thermodynamic equilibrium. The carbon content dominates the resistance to CaO–MgO–Al2O3–SiO2 slag penetration, while the viscosity of liquid phases present has a significant influence when the matrix carbon contents are similar. Silicon and Si3N4 additives reduce slag penetration resistance because of indirect oxidation of carbon to form SiC. B4C, in particular, and B2O3 also reduce slag penetration resistance because of formation of a more fluid boron-containing liquid, while aluminum and BN addition have no significant effect. Carbon and BN hardly react with the slag, while SiC partially reacts with it, leading to deposition of carbon as a dense layer. Corundum present in the refractories also readily dissolves in the slag. Microstructurally, slag penetration resistance is associated with the dense carbon layer located at the slag-refractory interface.

Grain‐Boundary Viscosity of Polycrystalline Silicon Carbides

Abstract: Internal friction experiments were conducted on three SiC polycrystalline materials with different microstructural characteristics. Characterizations of grain-boundary structures were performed by high-resolution electron microscopy (HREM). Observations revealed a common glass-film structure at grain boundaries of two SiC materials, which contained different amounts of SiO2 glass. Additional segregation of residual graphite and SiO2 glass was found at triple pockets, whose size was strongly dependent on the amount of SiO2 in the material. The grain boundaries of a third material, processed with B and C addition, were typically directly bonded without any residual glass phase. Internal friction data of the three SiC materials were collected up to similar/congruent2200°C. The damping curves as a function of temperature of the SiO2-bonded materials revealed the presence of a relaxation peak, arising from grain-boundary sliding, superimposed on an exponential-like background. In the directly bonded SiC material, only the exponential background could be detected. The absence of a relaxation peak was related to the glass-free grain-boundary structure of this polycrystal, which inhibited sliding. Frequency-shift analysis of the internal friction peak in the SiO2-containing materials enabled the determination of the intergranular film viscosity as a function of temperature.

Subsolidus Phase Relations in the Ga2O3-In2O3-SnO2 System

Abstract: Subsolidus phase relationships in the Ga2O3–In2O3–SnO2 system were studied by X-ray diffraction over the temperature range 1250–1400°C. At 1250°C, several phases are stable in the ternary system, including Ga2O3(ss), In2O3(ss), SnO2, Ga3−xIn5+xSn2O16, and several intergrowth phases that can be expressed as Ga4−4xIn4xSnn−4O2n−2 where n is an integer. An In2O3–SnO2 phase and Ga4SnO8 form at 1375°C but are not stable at 1250°C. GaInO3 did not form over the temperature range 1000–1400°C.

Effect of Precursors and Dopants on the Synthesis and Grain Growth of Calcium Hexaluminate

Abstract: A variety of colloidal and polymeric sols, some doped with transition-metal oxides, were investigated as potential precursors to calcium hexaluminate (CaAl12O19) in an attempt to enhance reactivity and lower the formation and texturing temperatures of phase-pure powders and films. One undoped polymeric sol was found to yield CaAl12O19, free of any intermediate phases, at temperatures as low as 1300°C in 1 h. Doping the same mixed-metal, citrate-based precursor with a variety of transition-metal cations was found either to enhance the γ- →α-Al2O3 phase transformation or to enhance the formation of CaAl12O19. Incorporation of MnO, Fe2O3, CoO, NiO, CuO, ZnO, or SiO2 into the citrate precursor resulted in significant hexaluminate formation within 1 h at 1100°C, compared with negligible formation using the undoped precursor. Fe2O3-doped precursors gave the highest hexaluminate yields at 1100°C. Phase-pure hibonite was obtained at temperatures as low as 1000°C with 25 at.% Fe substituting for Al in the hexaluminate structure. Textured CaAl11.5Fe0.5O19 films with (0001) planes parallel to the substrate surface were obtained on YAG substrates in 1 h at 1200°C. In comparison, undoped citrate-derived films first textured at 1300°C. Enhanced CaAl12O19 formation was attributed to rapid reaction of the constituents, due to the uniform dispersion of cations on an atomistic scale throughout the citrate-based precursor, prior to completion of the γ- →α-Al2O3 phase transformation. Solid-solution dopants were believed to further enhance reactivity and grain growth by increasing diffusive mass transport.

Mechanical Properties of Solid‐State‐Synthesized Strontium‐ and Magnesium‐Doped Lanthanum Gallate

Abstract: This paper has examined the room-temperature mechanical properties of La0.8Sr0.2Ga1−xMgxO3−δ (x = 0.1–0.2) that was synthesized by using a solid-state technique. The modulus of rupture (MOR) was measured over the range of x = 0.1–0.2 and decreased as the B-site dopant content increased. At x = 0.15, for example, the MOR was 139 ± 17 MPa, whereas at x = 0.2, an MOR value of 113 ± 8 MPa was observed. This decrease is postulated as being caused by the increased lattice stress due to the increased magnesium concentration on the B-site. The fracture toughness of the sample decreased as the magnesium content increased; at x = 0.15, a fracture toughness of 1.63 ± 0.2 MPam1/2 was observed, whereas at x = 0.2, a value of 1.28 MPam1/2 was obtained.

Synthesis of TiC, TiC-Cu Composites, and TiC-Cu Functionally Graded Materials by Electrothermal Combustion

Abstract: Titanium carbide and composites and functionally graded materials (FGMs) of TiC-xCu were synthesized by an electrothermal combustion (ETC) method. TiC synthesized by ETC showed small amounts of porosity relative to those synthesized by ignition using radiative heating. Composites and FGMs with higher copper content can be synthesized by ETC. In the FGM products a nearly linear change in composition in the graded region was observed in samples with 0 ≤ x (wt%) ≤ 75.

Fatigue Behavior of PZT‐Based Nanocomposites with Fine Platinum Particles

Abstract: Nanocomposites of lead zirconate titanate (Pb(Zrx,Ti1−x)O3, PZT) with secondary-phase dispersoids of metallic platinum were fabricated. Fatigue (crack-growth) behavior of the unpoled PZT/platinum nanocomposite that contained precracks produced by a Vickers diamond indenter under electrical cyclic loading was investigated. The crack growth was monitored via optical microscopy and was dependent on the number of cycles to which the sample was subjected. The growth of the indentation crack was significantly reduced in the PZT/platinum nanocomposite.

Citrate Route to Sn-Doped BaTi4O9 with Microwave Dielectric Properties

Abstract: Highly reactive and nanometer-sized (30-50 nm) Sn-doped BaTi 4 O 9 (BaTi 4-x Sn x O 9 ; x = 0.0-0.03) powders have been prepared by the citrate-precursor method. The effect of Sn substitution on the crystallization and microwave dielectric properties has also been investigated on the basis of microstructure and crystal structure. Addition of a small amount of SnO 2 resulted in a lowering of the sintering temperature of BaTi 4 O 9 , and at 1250-1300°C for 2-5 h, dense compounds with a theoretical density up to 99% could be obtained. The Sn-doped BaTi 4 O 9 materials were found to have excellent microwave dielectric properties with e r = 34-37, Q = 8300-8900 at 11 GHz and τ f = 3.6-16.1 ppm/°C.

High‐Strength Alumina/Alumina:Calcium‐Hexaluminate Layer Composites

Abstract: The strength degradation of alumina/alumina:calcium-hexaluminate/alumina trilayers, after damage from Hertzian contacts, is evaluated. Relative to the monolithic alumina and alumina:calcium-hexaluminate constituent layer materials, the trilayers show markedly improved strength retention in the damaged state at high contact loads. The outer, fine-grained alumina layers are classically brittle, characterized by cone cracking, whereas the inner alumina:calcium hexaluminate layer is essentially quasi-plastic, with a well-defined “yield” zone that consists of distributed microdamage. The improved strength behavior of the trilayer composite is rationalized in terms of a synergistic interaction between the contact-induced deformation modes in the two layers, with each mode partially ne-gating the effectiveness of the other as a source of failure. This result offers the prospect of hybrid structures with hard outer layers, to provide wear resistance, and soft, tough underlayers, to inhibit brittle fracture.

Alkaline Corrosion Resistance of Anodized Aluminum Coated with Zirconium Oxide by a Sol‐Gel Process

Abstract: To improve the alkaline corrosion resistance of aluminum, composite films were prepared that consisted of a porous layer of anodically grown aluminum oxide filled with zirconium oxide, with a zirconium oxide coating layer that was deposited thereon via the sol—gel process, using a dip-coating technique. The alkaline corrosion resistance of these composite films was extremely improved when this coating layer was placed on an anodic oxide film. Comparisons of the composite film and conventional anodic oxide film showed that the alkaline corrosion resistance of the composite film was increased by a factor of 24–50. Because these composite films, which have high corrosion resistance, indicated a vibration phenomenon of voltage in the duration time curve of the electromotive force measurement, the composite film had a self-repairing action for alkaline corrosion.

Dependence of Oxidation Modes on Zirconia Content in Silicon Carbide/Zirconia/Mullite Composites

Abstract: Two basic oxidation modes of silicon carbide/zirconia/mullite (SiC/ZrO2/mullite) composites were defined based on the plotted curve of the gradient of the silica (SiO2) layer thickness (formed on individual SiC particles) versus depth. Mode I, where oxygen diffusivity was much slower in the matrix than in the SiO2 layer, exhibited a relatively large gradient and limited oxidation depth. Mode II, where oxygen diffusivity was much faster in the matrix than in the SiO2 layer, displayed a relatively small gradient and an extensive oxidation depth. When the volume fraction of ZrO2 was below a threshold limit, the composites exhibited Mode I behavior; otherwise, Mode II behavior was observed. For composites with a ZrO2 content above the threshold limit, the formation of zircon (ZrSiO4), as a result of the reaction between ZrO2 and the oxidation product (i.e., SiO2), might change the oxidation behavior from Mode II to Mode I.

Geometrical Microstructural Development in Superplastic Silicon Nitride with Rod‐Shaped Grains

Abstract: The three-dimensional microstructural development of silicon nitride ceramics that exhibit superplastic elongation (up to ɛ = 1.34) was analyzed using a stereological analysis method. According to the microstructural change from randomly oriented grains to aligned grains along the tensile direction, the average orientation angle between the tensile axis and the major axis of a grain decreased monotonously as the strain increased. The average grain aspect ratio remained almost constant up to ɛ = 0.88 and then started to increase. Based on the microstructural development, three different modes of the change in the grain configuration-i.e., grain rotation, grain elongation, and grain translation-were considered. It is suggested that the contributions of the three modes vary according to the microstructural development during the deformation.

Healing of Lithographically Introduced Cracks in Glass and Glass‐Containing Ceramics

Abstract: The morphological evolution of lithographically defined cracklike flaws in glass and glass-containing ceramics was studied at elevated temperatures. The systems studied have glass contents from 100 to approximately 0.5 vol%, providing insight to the contribution of viscous flow of the glass to crack healing over a range of glass contents spanning many industrial ceramics. Healing behavior is found to be controlled by viscous flow of glass in all cases except the lowest glass content, for which significant mass transport is only accomplished by diffusional mechanisms. This implies a change of mechanism below some critical glass content.

Contamination Effects on Interfacial Porosity during Cyclic Oxidation of Mullite‐Coated Silicon Carbide

Abstract: Plasma-sprayed mullite (3Al 2 O 3 .2SiO 2 ) and mullite/yttria-stabilized zirconia (mullite/YSZ) dual-layer coatings have been developed to protect silicon-based ceramics from environmental attack. The mullite/SiC system develops interfacial pores during cyclic oxidation. The development of pores at the mullite/sintered SiC interface in air has been investigated as a function of the purity of mullite at 1230°-1350°C in an atmospheric-pressure furnace. The silica scale is readily contaminated by impurities of alkali or alkaline-earth metal oxides from the mullite coating. The contamination enhances oxidation and reduces the scale viscosity by forming alkali or alkaline-earth metal silicates. The porosity increases as the temperature and contamination increase and decreases as the purity of the mullite increases.

Chemical Vapor Deposition of B13C2 from BCl3-CH4-H2-Argon Mixtures

Abstract: The deposition of boron carbide (B13C2) onto graphite substrates was accomplished by using a hot-wall chemical vapor deposition (CVD) reactor at a pressure of 10.1 kPa in the temperature range of 1000°–1400°C. A modified impinging-jet geometry was used to simplify the mass-transfer analysis. Coatings were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The surface morphology was composed of well-defined facets, the size of which was dependent on the growth rate and deposition time, as would be expected from a competitive growth mechanism. TEM micrographs of the coating showed long, columnar grains that emanated from a narrow nucleation zone. The growth rate could be adequately described by a first-order kinetic expression, with respect to the bulk gas phase boron chloride (BCl3) concentration. The activation energy of the kinetic expression was estimated to be 93.1 kJ/mol. It was proposed that the deposition was limited by the adsorption of (BCl3) onto the substrate surface.