David T. Hoelzer

Interfacial characterization of plasma-spray coated calcium phosphate on Ti-6Al-4V.

Microstructural characterization was performed on plasma-spray coated calcium phosphate and its interface with Ti–6Al–4V using scanning and transmission electron microscopy. The amorphous calcium phosphate phase was found near the coating/substrate interface, usually in between the crystalline hydroxyapatite grains and the Ti–6Al–4V substrate. The presence of the amorphous calcium phosphate and the channels extending from the interface to the coating surface was attributed to the low interfacial bond strength in a physiological environment. There was an indication of titanium diffusing into the amorphous regions. However, no reaction phases were found between the coating and the Ti–6Al–4V substrate. In the coating area remote from the interface, no intergranular amorphous calcium phosphate phase was observed. The microstructure of the Ti–6Al–4V substrate near the interface was observed to be affected by heat generated during plasma spraying.

Effect of copper and nickel on the neutron irradiation damage in iron alloys

Iron alloys containing copper and nickel were irradiated at 288 C to a fluence of 4.63 {times} 10{sup 19} neutrons/cm{sup 2}. Neutron irradiation produced defects which were observable by TEM in all of the iron alloys studied. The TEM analysis of the defects showed them to be interstitial dislocation loops with a and a/2 Burgers vectors. The size, the number density, and the Burgers vector of dislocations were affected by the alloy composition. The addition of copper and nickel decreased the dislocation loop size and increased the fraction of a/2 loops. No voids or vacancy loops were observed in the irradiated iron alloys. The results are discussed in terms of dislocation loop nucleation and growth.

Grain-oriented ferroelectric bismuth titanate thin film prepared from acetate precursor

Abstract Bismuth titanate (Bi 4 Ti 3 O 12 ) thin films were fabricated by a spin coating deposition and rapid thermal processing (RTP) technique. The acetate-derived solution for deposition was synthesized by blending dissolved bismuth acetate in aqueous acetic acid and then adding titanium acetate. A series of electrically insulating, semiconducting and conducting substrates were evaluated for Bi 4 Ti 3 O 12 films deposition. X-ray diffraction indicated that the initial crystallization temperature of the Bi 4 Ti 3 O 12 films was 500 °C or less; a 700 °C crystallization treatment was used to obtain single phase films. The Bi 4 Ti 3 O 12 film crystallographic orientation is shown to depend on three factors: substrate type; number of coating layers; and thermal processing. While preferred c -direction orientation was observed for films deposited on silver foil substrates, preferred a -direction orientation was obtained for films deposited on both Si and Pt coated Si wafers. The films were dense, smooth, crack-free and had grain sizes ranging from 20 to 400 nm. Film thickness and refractive index were determined using a combination of ellipsometry, waveguide refractometry and TEM techniques. The refractive index is close to the value of single crystal BIT.

Crystallization and microstructural evolution of cordierite-based thick film dielectrics

Abstract Microstructural evolution of glass–ceramic dielectric thick films based on a nonstoichiometric cordierite, 2.4MgO·2Al 2 O 3 ·5SiO 2 , containing B 2 O 3 , P 2 O 5 , and PbO were investigated in conjunction with nucleation and crystal growth. The cordierite thick films were deposited by screen printing on a 96% alumina substrate, and then fired in the temperature range of 850–950°C in a N 2 atmosphere. Surface microstructure characteristics of the thick films depended on PbO content. Heterogeneous nucleation originated predominantly from the interface between the densified thick film and the alumina substrate. The added PbO segregated to the remaining glass during crystallization, and the relative concentration of Pb in the glass was proven to increase with rising temperature. Most of the remaining glass protruded from the film surface at the final temperature of 950°C. Penetration of the alumina substrate by the remaining glass was also observed. The influences of temperature and PbO on the microstructural evolution including nucleation and growth will be discussed with possible explanations for the observed results.

Grain boundaries and growth kinetics of polycrystalline ferrimagnetic oxides with chemical additives

Grain boundaries and grain growth kinetics of two ferrimagnetic oxides, Y2Gd1Fe5O12 and Li0.3Zn0.4Fe2.3O4, modified by a sol–gel particulate coating process were investigated on the basis of their microstructural characteristics. Interestingly, the addition of small amounts of MnO2 and SiO2 using the sol–gel coating process led to different results for the two magnetic materials. In the case of Y2Gd1Fe5O12, the additives had a role as a grain growth inhibitor because Si-rich precipitates were segregated along the grain boundary and exerted a drag force against grain boundary movement. On the other hand, the same additives acted as an accelerator for grain growth by forming a glassy phase at the grain boundaries for Li0.3Zn0.4Fe2.3O4. The results were analyzed quantitatively by calculating activation energies for grain growth and grain boundary mobilities. For example, the calculated grain boundary mobilities, i.e., 5.6×10−15 m3/N s at 1400 °C for Y2Gd1Fe5O12 and 22.3×10−15 m3/N s at 1150 °C for Li0.3Zn0.4...

Analysis of the Interface Between Plasma-Sprayed Calcium Phosphate Coating and Ti-6Al-4V

Plasma sprayed calcium phosphate coatings on Ti(alloy) have been considered advantageous over the uncoated Ti as dental implants or orthopedic prostheses due to their abilities to decrease healing time, attach firmer to the bone, and inhibit ion release from the Ti substrate. However, the coating was found not to adhere well to the Ti substrate, presumably because there is no or little chemical bonding between the calcium phosphate coating and the Ti substrate. The interfacial bond strength relies almost entirely on the mechanical locking of calcium phosphate splats onto the roughened Ti surface. In this study, the interfacial area between the calcium phosphate coating and the Ti-6A1–4V substrate was characterized using SEM and TEM. The results revealed the presence of amorphous calcium phosphate layer at the interface, which is believed to be responsible for the low bond strength. Also small particles were observed which were embedded in the amorphous phase near the interface. The presence of the amorphous phases is very important since they are more easily attacked by the physiological solution than crystalline phases are.

Examination of Y2Cu2O5 additions on microstructural development in YBa2Cu3O7 − δ superconductors

The role of Y2Cu2O5 on liquid phase flux and microstructure evolution were examined in two series of experiments. The first series of experiments dealt with a low temperature processing ( 1020 dgC) melt powder melt growth process (MPMG). Differential thermal analysis measurements were used to study the impact on liquidus formation reactions, solidification temperatures and kinetics. Microstructural evaluations via SEM, EDS along with TEM and microdiffraction techniques reveal some unique aspects of Y2Cu2O5 additions on the liquid phase matrix and microstructural refinement during processing. The yttrium enrichment of the Pt-Ba-Cu-O phase for MPMG samples was shown along with significant coalescence of such a phase not seen in similar samples with Y2Cu2O5. Extensive liquidus formation occurs allowing for texturing via diffusive couple oxide liquid phase intrusion below the peritecticecomposition.

Ferroelectric thin film bismuth titanate prepared from acetate precursor

Bismuth titanate (Bi/sub 4/Ti/sub 3/O/sub 12/) thin films were fabricated by spin coat deposition-rapid thermal processing (RTP) technique. Acetate derived solution for deposition was synthesized by blending dissolved bismuth acetate in aqueous acetic acid, and then adding with titanium acetate. A series of electrically insulating, semiconducting and conducting substrates were evaluated for Bi/sub 4/Ti/sub 3/O/sub 12/ films deposition. While X-ray diffraction and TEM analyses indicated that the initial perovskite crystallization temperature was 500/spl deg/C or less for these Bi/sub 4/Ti/sub 3/O/sub 12/ films, a 700/spl deg/C crystallization treatment was used to obtain single phase perovskite films. Bi/sub 4/Ti/sub 3/O/sub 12/ film crystallographic orientation was shown to depend on three factors: substrate, the number of coating layers and thermal processing. While preferred c-direction orientation was observed for films deposited on silver foil substrates, preferred a-direction orientation was obtained for films deposited on both Si and Pt coated Si wafers. The films were dense, smooth, crack-free and had grain sizes ranging from 20 nm to 400 nm. Film thickness and refractive index were determined using a combination of ellipsometry, waveguide refractometry and TEM measurements. Both low field dielectric and ferroelectric properties were measured for an 800 nm thick film deposited on a Pt coated MgO substrate. A remanent polarization of 38 /spl mu/C/cm/sup 2/ and a coercive field of 98 kv/cm was measured for this film that was crystallized at 700/spl deg/C.