Journal of the American Ceramic Society

Chokshi, Atul H.; Porter, John R.

doi: 10.1111/j.1151-2916.1985.tb15221.xpmid: N/A

Whisker‐reinforced ceramic composites with enhanced fracture toughness properties are being developed. The creep behavior of such a composite was studied. The introduction of silicon carbide whiskers significantly improves the creep resistance of polycrystaline alumina.

Suyama, Yoko; Kato, Akio

doi: 10.1111/j.1151-2916.1985.tb15225.xpmid: N/A

The effect of additives on the formation of fine Ti02 particles by vapor phase reaction was studied. The oxygenolysis of TiC14 was enhanced by the addition of Fecl3, and AlBr3, and suppressed by SiCl4, and ZrCl4. Particles formed in the presence of additives were 1/2 to 1/5 the size of those formed without additives, and particle size distributions became very narrow. Particle shape was also influenced by the additives.

Jen, Cheng‐Kuei; Cielo, Paolo; Maldague, Xavier; El‐Assal, Kamal

doi: 10.1111/j.1151-2916.1985.tb15222.xpmid: N/A

A noncontact ultrasonic technique for the characterization of piezoelectric ceramics is described. The velocity of a laser‐generated surface‐acoustic‐wave pulse propagating at the surface of the ceramic material is measured by an optical probe. The laser beam has an annular section in order to produce a conveniently strong ultrasonic pulse without overheating the surface. Applications to the characterization of PZT samples are described.

Morgan, Peter E. D.; Koutsoutis, Michael S.

doi: 10.1111/j.1151-2916.1985.tb15226.xpmid: N/A

Previous solid state analyses of sintering in Ti4+‐doped‐commercial alumina are shown to be in error because a liquid phase exists in the appropriate region of the Al2O3−TiO3−Na2Ophase diagram at least by 1350°C, a temperature lower than that at which “solid state” studies were conducted. It is suggested that liquid‐phase sintering is a much more common occurrence than was realized formerly.

Onorato, Paulette I. K.; Alexander, Michael N.; Struck, Charles W.; Tasker, G. William; Uhlmann, D. R.

doi: 10.1111/j.1151-2916.1985.tb15223.xpmid: N/A

Thallium‐probe ion luminescence spectroscopy and X‐ray photoelectron spectroscopy were used to study the structure of sodium aluminosilicate glasses. It was demonstrated that the O1s spectral envelope for these glasses is comprised of three energetically distinct peaks, two attributed to bridging oxygen atoms (Si‐O‐Si and Al‐O‐Si) and one to nonbridging oxygen atoms (Si‐O‐Na). Both techniques indicate that nonbridging oxygen atoms are present in all sodium aluminosilicate glasses, for which A1 /Na is < 1.

Kassarjian, Michael P.; Fox, Bradley H.; Biggers, James V.

doi: 10.1111/j.1151-2916.1985.tb15219.xpmid: N/A

A Pb(Fe, Nb)O3−Pb(Fe, W)O3−Pb(Zn, Nb)O3 dielectric ceramic fires at temperatures low enough for 100% silver electrodes to be used in multilayer capacitors made with the ceramic. Good dense Pb(Fe, Nb)O3, ceramics were obtained by fast, firing, i.e. by using rapid ramp rates and very short firing times. The densified ceramic was characterized by determination of its dielectric properties, X‐ray diffraction, and scanning electron microscopy.

Mazdiyasni, K. S.; Zangvil, Avigdor

doi: 10.1111/j.1151-2916.1985.tb15220.xpmid: N/A

Thermal decomposition of polymeric organosilicon, as precursor to Sic whiskers, in the presence of impurities such as alkali and alkaline‐earth metals and aluminum resulted in glass beads or droplets on the β‐Sic whiskers. Semiquantitative analysis of typical whiskers and whiskers with glass beads were performed using a transmission electron microscope equipped with an energy‐dispersive X‐ray spectrometer and a scanning transmission electron microscope equipped with an electron energy loss spectrometer. The major impurities identified were correlated with the processing method employed

Moore, Thomas J.

doi: 10.1111/j.1151-2916.1985.tb15224.xpmid: N/A

In a brief study of the feasibility of welding sintered a‐Sic, solid‐state welding and brazing were investigated. Joint quality was determined solely by microstructural examination. Hot‐pressure welding was shown to be feasible at 1950°C. Diffusion welding and brazing were also successful under hot isostatic pressure at 1950°C when boride, carbide, and silicide interlayers were used. Furnace brazing was accomplished at 1750°C when a TiSia interlayer was introduced.

BORDIA, R.K.; RAJ, R.

doi: 10.1111/j.1151-2916.1985.tb15227.xpmid: N/A

A model is presented in which the sintering behavior of a ceramic film which is constrained by a rigid substrate is contrasted with the sintering behavior of a free film. The problem is made simple by the assumption that the stress field developed in the film is uniform. This simplification allows several closed form solutions to be obtained. The solutions give new insights into the sintering behavior of films supported on a substrate. It is found (1) that the shear rate of the film is more important in the sintering process than its densification rate when the film is constrained by a substrate, (2) that the incompatibility stress is time dependent and reaches its maximum value during the initial stages of sintering, (3) that the magnitude of that maximum stress may be tensile or it may be compressive depending on the shear response of the material, and (4) that if the incompatibility stress is tensile it can lead to the formation of cracks or defects in the ceramic film.

MacKENZIE, K. J. D.; BROWN, I. W. M.; MEINHOLD, R. H.; BOWDEN, M. E.

doi: 10.1111/j.1151-2916.1985.tb15228.xpmid: N/A

Structural models previously proposed for metakaolinite are examined in light of the most recent published experimental data and new information obtained by solid‐state high resolution 29Si and 27AI NMR. A new model for metakaolinite is proposed, consisting of anhydrous regions of distorted AI‐0 tetrahedra containing randomly distributed isolated residual hydroxyls associated with A1‐0 configurations of regular octahedral and tetrahedpal symmetry. Such a structure, which can readily be formed from kaolinite by the removal of hydroxyls in certain sequences, accounts for the lack of a well‐defined X‐ray pattern and the persistence of ∼10% residual hydroxyls in metakaolinite and is consistent with the most recent density data, bond lengths, and the new 29Si and 27AI NMR data.