Effective Parameters in Axial Injection Suspension Plasma Spray Process of Alumina-Zirconia Ceramics
Suspension plasma spray (SPS) is a novel process for producing nano-structured coatings with metastable phases using significantly smaller particles as compared to conventional thermal spraying. Considering the complexity of the system there is an extensive need to better understand the relationship between plasma spray conditions and resulting coating microstructure and defects. In this study, an alumina/8 wt.% yttria-stabilized zirconia was deposited by axial injection SPS process. The effects of principal deposition parameters on the microstructural features are evaluated using the Taguchi design of experiment. The microstructural features include microcracks, porosities, and deposition rate. To better understand the role of the spray parameters, in-flight particle characteristics, i.e., temperature and velocity were also measured. The role of the porosity in this multicomponent structure is studied as well. The results indicate that thermal diffusivity of the coatings, an important property for potential thermal barrier applications, is barely affected by the changes in porosity content.
Mechanical and Thermal Transport Properties of Suspension Thermal-Sprayed Alumina-Zirconia Composite Coatings
Micro-laminates and nanocomposites of Al2O3 and ZrO2 can potentially exhibit higher hardness and fracture toughness and lower thermal conductivity than alumina or zirconia alone. The potential of these improvements for abrasion protection and thermal barrier coatings is generating considerable interest in developing techniques for producing these functional coatings with optimized microstructures. Al2O3-ZrO2 composite coatings were deposited by suspension thermal spraying (APS and HVOF) of submicron feedstock powders. The liquid carrier employed in this approach allows for controlled injection of much finer particles than in conventional thermal spraying, leading to unique and novel fine-scaled microstructures. The suspensions were injected internally using a Mettech Axial III plasma torch and a Sulzer-Metco DJ-2700 HVOF gun. The different spray processes induced a variety of structures ranging from finely segregated ceramic laminates to highly alloyed amorphous composites. Mechanisms leading to these structures are related to the feedstock size and in-flight particle states upon their impact. Mechanical and thermal transport properties of the coatings were compared. Compositionally segregated crystalline coatings, obtained by plasma spraying, showed the highest hardness of up to 1125 VHN3 N, as well as the highest abrasion wear resistance (following ASTM G65). The HVOF coating exhibited the highest erosion wear resistance (following ASTM G75), which was related to the toughening effect of small dispersed zirconia particles in the alumina-zirconia-alloyed matrix. This microstructure also exhibited the lowest thermal diffusivity, which is explained by the amorphous phase content and limited particle bonding, generating local thermal resistances within the structure.
ISOLATION OF BOVINE PARAINFLUENZA-3 VIRUS IN CHICK EMBRYOS
Myxovirus parainfluenza-3 (SF-4 bovine strain) was first isolated in tissue cultures of embryonic bovine kidney (EBK) cells (Reisinger, Heddleston, and Manthei, J. Am. Vet. Med. Assoc. 135:147, 1959). This agent is antigenically and biologically related to the human HA-1 strain isolated previously by Chanock et al. in monkey kidney cells (Abinanti and Huebner, Virology 8:391, 1959; Abinanti et al., Proc. Soc. Exptl. Biol. Med. 106:466,1961). At present, both viruses are isolated and propagated in tissue cultures, and tissue-culture products are employed for most research purposes. This investigation indicates that bovine parainfluenza-3 virus can be isolated and produced in 14-day-old embryonated hen's eggs, and that the developing chick embryo is highly susceptible to parainfluenza-3 virus infection. Isolation of parainfluenza-3 virus in chick embryos was compared with isolation in tissue cultures. EBK tissue cultures, maintained in Earle's balanced salts (BSS) with 5.0% calf serum and 0.5% lactalbumin hydrolysate (Nutritional Biochemicals Corp., Cleveland, Ohio), were inoculated with 0.2 ml of nasal-swab material (nasal swabs suspended in 4.0 ml of BSS) from 14 calves with signs of shipping fever. After incubation at 36 C for 6 days, fluids from cultures not showing cytopathic effects were subcultured in fresh cells, and the remaining monolayers were examined for noncytopathic virus by the adsorption-hemagglutination (hemadsorption) test of Vogel and Sholokov (Science 126:358, 1957). Infectious fluids from positive cultures were retained for parainfluenza-3 virus identification. Embryonated hen's eggs (14 days old) were inoculated by the amniotic route with 0.1 ml of nasalswab material. After 4 days at 36 C, the amniotic fluids were harvested and tested for virus by inoculation of EBK cells. Parainfluenza-3 virus was identified by serum-neutralization tests in tissue cultures with immune rabbit serum prepared against the original SF-4 bovine virus isolate. Parainfluenza-3 virus was isolated from six nasal-swab suspensions in both EBK cells and 14-day-old chick embryos. Five embryonated eggs and an equal number of tissue cultures were inoculated with each suspension and, in all cases, eggs were infected more frequently than were corresponding tissue cultures inoculated with larger doses of the same material. The isolation of parainfluenza-3 virus from two samples was complicated in tissue cultures by the presence of infectious bovine rhinotracheitis (IBR) virus which also produces cytopathic effects in EBK cells. IBR virus did not interfere with the isolation of parainfluenza-3 virus in embryonated eggs and was not demonstrated in amniotic fluids 4 days after virus inoculation. Noncytopathic virus, demonstrable by hemadsorption, was not isolated. When three nasal-swab samples containing parainfluenza-3 virus were diluted 1:2 and 1:20 in BSS, virus was isolated from the lower concen-