Mechanical property changes in sapphire by nickel ion implantation and their dependence on implantation temperature

Sapphire plates, cut parallel to an {0001} plane, have been implanted with 300 keV nickel ions to doses ranging from 5×10¹² to 1×10¹⁷ Ni cm^–2 at specimen temperatures of 100, 300 and 523 K, in order to investigate the effect of implantation temperature on the mechanical property changes in sapphire caused by ion implantation. The measured changes in surface hardness, surface fracture toughness and bulk flexural strength were found to depend strongly on the implantation temperature, and were largely correlated with the residual surface compressive stress measured by using a cantilever beam technique. The surface amorphization that occurred only by the implantation at 100 K and at doses larger than 2×10s15 Ni cm^–2 reduced the hardness to 0.6 relative to the value of the unimplanted sapphire, and considerably increased the surface plasticity. Furthermore, the amorphization was found to involve a large volume expansion of 30% and to change drastically the apparent shape and size of a Knoop indentation flaw made prior to implantation. This effect was suggested to reduce stress concentrations at surface flaws and hence to increase the flexural strength.     

Sialon formation by Si+ and N2 + ion implantation into sapphire

Single-crystal alumina was implanted firstly with 400 keV Si⁺ and subsequently with N₂ ⁺ ions and then annealed at 1673 K in an No atmosphre. The implanted layers were characterized by means of X-ray diffraction, Rutherford backscattering-channelling of 2 MeV He⁺ ions, and the resonance nuclear reaction¹⁵N(p,)¹²C. The annealing of sapphire implanted at ambient temperature resulted in the formation of-sialon, a solid solution of-silicon nitride and alumina in the subsurface layer, while implantation at 100 K resulted in the formation of aluminium oxynitride in the surface layer. In the latter case, the implanted silicon atoms were believed not to react vxi1h the implanted nitrogen atoms but with the substrate oxygen atoms. These crystalline precipitates were found to have epitaxial relations with the sapphire substrate.     

Living cationic polymerization of isobutyl vinyl ether by the diphenyl phosphate/zinc iodide initiating system

Summary The first example of the living cationic polymerization of isobutyl vinyl ether via the phosphate counteranion has been achieved in toluene below 0°C with a new initiating system that consists of diphenyl phosphate and zinc iodide, (C₆H₅0)₂P(0)0H/ZnI₂. The number-average molecular weight of the polymers increased in direct proportion to monomer conversion, and was in excellent agreement with the calculated value assuming that one polymer chain forms per unit diphenyl phosphate. On addition of a fresh feed of monomer at the end of the polymerization, the added feed was smoothly polymerized at nearly the same rate as in the first stage, and the polymer molecular weight further increased in direct proportion to monomer conversion. Throughout the reaction, the molecular weight distribution of the polymers stayed very narrow (¯M/¯M_n 1.1). At room temperature (+25 °C), however, the molecular weight distribution of the polymers slightly broadened (¯M_w/¯M_n 1.2) at high conversions where the polymer molecular weight became smaller than the calculated value. Evidently, the (C₆H₅0)₂-P(0)0H/ZnI₂ system indeed generates a propagating species of a long life-time at room temperature, but the perfectly living polymerization by this system operates below 0°C.Living cationic polymerization of vinyl ethers by electrophile     

Cationic polymerization of β-pinene with the AlCl3/SbCl3 binary catalyst: Comparison with α-pinene polymerization

The polymerization of β-pinene with the AlCl₃/SbCl₃ binary catalyst was investigated in toluene at −40°C and was compared with that of α-pinene. The polymerization of β-pinene with AlCl₃ alone was very rapid and retarded on addition of SbCl₃, in sharp contrast to that of α-pinene where added SbCl₃ remarkably accelerated it to give relatively high molecular weight oligomers. Attempted copolymerization of the two isomers with the binary catalyst, in turn, induced their parallel homopolymerizations, indicating that the copolymerization was difficult due to the large difference in reactivity. The homopolymerizations with AlCl₃/SbCl₃ were not seriously affected by a sterically hindered base, 2,6-di-tert-butyl-4-methylpyridine (DTBMP); the initiating species, therefore, would be different in nature from a proton. © 1996 John Wiley & Sons, Inc.     

Thermal proof testing of ceramics

The possibility of thermal proof testing with thermal stress induced by quenching was examined. For this purpose, the bending strength and the critical temperature difference for quenching into water and quench oil for soda-lime-silica glass were measured before and after proof testing by quenching the specimens into water, ethyl alcohol, silicon oil and quench oil. Proof testing by water, ethyl alcohol and silicon oil quenching modified the distribution of the critical temperature difference as expected, but not that of the bending strength at all. It is suggested that proof testing by rapid quenching is a useful method for truncating the critical temperature difference distribution of ceramic components of heat engines and so on.     

Swelling behaviour of rubber vulcanizates: 2. Effects of tensile strain on swelling

The effects of tensile strain on the swelling behaviour of acrylonitrile-butadiene copolymer rubber vulcanizates were studied by real-time pulsed nuclear magnetic resonance (n.m.r.) measurements and volume swelling measurements at equilibrium. It was shown that tensile strain causes an increase of the initial swelling rate evaluated by n.m.r. measurements and of the swelling ratio of the rubber matrix at equilibrium. This behaviour was discussed qualitatively in terms of the molecular mobility of the network chains on the basis of Treloar's theory for swelling under deformation. It was suggested that the presence of reinforcing fillers in the rubber matrix exerts two noticeable effects on swelling under deformation: (1) a transient effect through some oriented structure induced by stretching, which restricts the increase of the swelling rate; (2) a strain amplification effect, which causes the increase of the average local strain in the rubber matrix and enhances the swelling ratio more remarkably proportional to the filler concentration as compared with that of the unfilled system.     

Mechanism of high energy absorption by foamed materials-foamed rigid polyurethane and foamed glass

Energy absorbability of foamed rigid materials, polyurethane and glass, was studied under a compressive load. The brittle materials were proved to absorb much energy in a manner similar to ductile materials. A mechanism for such high energy absorption was proposed, based on a fracture model in which crushing of cells initiates at the weakest cell followed by propagation to cells lying in the layer containing the weakest one and lying in a direction perpendicular to the compressive force; then the crushing propagates to another layer under the compressive force after the completion of the first layer crushing. In the period of one layer crushing, the strain energy stored in the period of compression prior to the crushing is temporarily released, and it is stored again in the period of compression after the crushing. The store and release of strain energy is assumed to be repeated until all cell layers are crushed. This mechanism of layer-by-layer crushing allows the cells to absorb strain energy repeatedly, and causes high energy absorption in the brittle foamed material. The calculated energy based on the mechanism agrees well with the observed one.