Journal of Materials Science

Rice, R. W.

doi: 10.1007/bf02402643pmid: N/A

Existing data on effects of reactant compact microstructure on self-propagating synthesis, SPS type reactions is reviewed. Propagation rates generally decrease with increased compact density at higher densities, and reactions are no longer ignitable at high densities. At lower densities the trends may vary depending on the reactions. Propagation rates and ignitability also generally decrease with increasing particle size, and can be affected by particle shape. More exothermic reactions lead to greater expansion, hence porosity, in unconstrained samples, while resultant pore sizes are effected mainly by outgassing. Final grain sizes are not a significant function of the initial particle size (but can be effected by finer residual porosity).

Schönberger, H. D. H.; Res, M. A.; Bednarik, J.

doi: 10.1007/bf02402644pmid: N/A

Substitution of SiO2 in the ternary sodium borosilicate system with Ta2O5 was found to produce glasses, which after heat treatment separated into immiscible microphases, one of which was water soluble. The structure of the leached material after heat treatment was a well developed low temperature form of Ta2O5. After firing at temperatures between 1100 and 1550°C X-ray diffraction analysis showed the presence of low and high temperature forms of Ta2O5 and of orthorhombic Na2Ta5O21. The high solubility of up to 40 wt% Ta2O5 in the sodium-borate matrix resulting in clear glasses is of practical interest. The specific surface areas of the leached materials ranged between 5.54 and 35.57 m2g−1 while in an additionally Al2O3 doped material the value of 307 m2g−1 was measured. Mean pore radii of interconnected pores were calculated to be between 18.63 to 41.12 nm in the Ta2O5-rich materials while the additional Al2O3 doping decreased the value to 2.71 nm. A sintering temperature between 1500 and 1550°C is estimated from void volume measurements after a series of firing steps at temperatures between 1100 and 1550°C were undertaken.

Sharma, G. D.; Mathur, S. C.; Dube, D. C.

doi: 10.1007/bf02402645pmid: N/A

Organic photovoltaic solar cells based on metal-dye or sensitized dye-SnO2 junctions are formed. The electrical and photovoltaic characteristics of these Schottky junctions have been studied on two pure and sensitized dyes (Eriochrome Blue Black B and Rodamine B). From the photovoltaic action spectra the active region responsible for electric power generation was found to be confined to the SnO2-dye interface. The effect of sensitization, electrode material and intensity on photovoltaic and electrical parameters has also been discussed in detail. Finally theC-V characteristics are discussed in detail.

Chow, C. L.; Lu, T. J.

doi: 10.1007/bf02402646pmid: N/A

Valid plane-stress fracture toughness evaluation of short fibre reinforced composites relies essentially on the successful separation of the energy absorbed in the localized crack-tip region out of the total energy absorbed by the cracked material body at large. Three different experimental techniques, all stemming from the energetic interpretation of theJ integral, are utilized and their relative merits in the characterization of fracture initiation in short glass fibre reinforced injection-moulded nylon 6.6 examined. Various theoretical aspects concerning these experimental methods are outlined. The rationale behind using a single-edge-notched tension type specimen for theJc test is presented. TheJc value obtained from the compliance calibration method and the quasistatic energy method agree closely and can be considered to be independent of pre-crack length and specimen geometry when the pre-crack length to specimen width ratio (a/w) is larger than 0.45. The extrapolation method fails nevertheless to yield a physically consistentJc value, possibly due to its questionable theoretical representation. As no constraint on boundary conditions is necessitated during the course of crack extension, the quasistatic energy is physically more appealing.

Mason, W.; Johnson, P. F.; Varner, J. R.

doi: 10.1007/bf02402648pmid: N/A

The behaviour of microhardness under varying load was investigated with an apparatus which measured both load and diamond pyramid motion simultaneously. There have been several experiments with this type of apparatus, which are designed to measure the hardness under load of a material. This type of measurement eliminates the effect of elastic recovery after the diamond is removed from the sample. Two types of load-independent hardness have been proposed on the basis of studies performed on this type of apparatus. The first follows the theory of Tate stating that elastic recovery is responsible for the load dependence of hardness. The second, proposed by Froelichet al. states that the load dependence of hardness is due to surface forces. This investigation used an apparatus similar to that of Froehlichet al. The results indicated that the load-independent hardness of Froehlichet al. was an experimental artifice caused by late detection of the surface, leading to underestimation of the penetration and overestimation of the hardness. Hardness measured under load using the apparatus in the present project was found to be load dependent.

Liu, Shiann H.; Nauman, E. B.

doi: 10.1007/bf02402649pmid: N/A

Solid rubbers have been incorporated into thermosets using the compositional quenching process. Electron micrographs reveal that rubber particles a few micrometres or less in size have been dispersed in the matrix. Two model systems were studied: an epoxy resin cured with primary amines which represents a tight network structure, and a phenoxy resin cross-linked with methylene diisocyanate which represents a loose network. The present study indicates that a small amount of a cross-linking agent can reduce the degree of matrix yielding with a resultant drop in impact strength. SEM fractography provides complementary information on the transition from ductile fracture to brittle fracture.

Misra, A. K.

doi: 10.1007/bf02402650pmid: N/A

Chemical processes relevant to the stability and processing of SiC-reinforced Si3N4 composites are examined from a thermochemical point of view. The thermodynamic stability of various interfaces, such as SiC-Si3N4, SiC-Si3N4-Si2ON2, and SiC-Si3N4-SiO2, is examined as a function of temperature. The temperatures above which these interfaces become unstable are calculated, and the degradation of SiC during the processing of the composite is examined. The processing routes considered in this study include the reaction-bonded silicon nitride process, as well as pressure-assisted sintering processes in the presence of suitable sintering additives.

Das, B.; Tucker, B. D.; Watson, J. C.

doi: 10.1007/bf02402652pmid: N/A

The scanning electron microscope and the energy dispersive X-ray based analytical techniques have been used to study the sulphuric acid corrosion resistance of standard “E” fibre glass and PPG developed and patented 1201 [1], an “ECR” acid-resistant fibre glass. While it is well agreed by the experts in the field that direct exposure of fibre glass to 0.5 m sulphuric acid is much too severe a condition to simulate service conditions of most filament wound fibre glass products, nevertheless, the above corrosive environment was used to demonstrate a significant superiority of PPG 1201 glass in acid resistance over the standard “E” glass regardless of the source of its origin. It is also demonstrated that not only boron oxide leached out during acid exposure but a significant amout of calcium, aluminium, and magnesium oxides also were depleted from the “E” glass composition during acid treatment. It is also demonstrated that heat treatment of “E” glass products reduced the rate of acid attack. It did not, however, eliminate it completely. Heat treatment affects the strength properties of this fibre glass adversely.