Single-Mode As–S Glass Fibers

Single-mode As–S glass fibers with a core diameter from 3 to 20 m and a clad diameter of 125 m are prepared by the double-crucible method. The cutoff wavelength of the fibers is 0.9–6 m. The lowest transmission losses in the fibers at 2.2–2.3 m are 100 dB/km, and their mean bending strength is 800–1000 MPa.     

Absorption Spectrum of ZnO Precipitates in ZnSe

The absorption spectrum of ZnO precipitates in ZnSe saturated with oxygen is studied in the spectral range 500–2000 cm^–1 and is shown to correlate with the transmission spectrum of single-crystal ZnO. Saturation of ZnSe with oxygen in the course of growth leads to ZnO precipitation during cooling. The precipitates give rise to narrow absorption bands in the range 5.8–7.1 m, which correlate with the components of the multiphonon absorption spectrum of ZnO, formed by combinations of LO and TO phonons. The 2LO mode defines the long-wavelength transmission edge of ZnO. In addition, the spectrum shows strong absorptions due to the LO + TO(10.2 m) and 2TO (11.3 and 12.7 m) modes. The possible role of SeO₂ is discussed. It is suggested that ZnO with a high carrier concentration may act as a gray filter in the spectral range 2–9 m.     

A note on the similarity solutions for free convection on a vertical plate

Summary The similarity solutions for free convection on a vertical plate when the (non-dimensional) plate temperature is x and when the (non-dimensional) surface heat flux is –x are considered. Solutions valid for 1 and 1 are obtained. Further, for the first problem it is shown that there is a value ₀, dependent on the Prandtl number, such that solutions of the similarity equations are possible only for >₀, and for the second problem that solutions are possible only for >–1 (for all Prandtl numbers). In both cases the solutions becomes singular as ₀ and as –1, and the natures of these singularities are discussed.     

Ion-implantation technology for improved GaAs MESFETs performance

Electrical properties of Si-implanted and co-implanted with Mg or Be in semi-insulating GaAs was studied. The Si-implanted MESFETs with and without buried p-layer (formed by Mg or Be) have been fabricated and characterized by their d.c. and r.f. performance. The experimental results showed that the device with a buried p-layer can effectively suppress the substrate leakage current (thus good pinch-off characteristic) and obtained higher gain linearity than these without a buried p-layer. For 1 m×100 m MESFETs device with co-implantation of Si (8×10¹² cm^–2) and Be (6×10¹¹ cm^–2) demonstrated uniform transconductance (g_m) of 115 mS mm^–1 with the gate voltage ranging from –1 to 1 V and reduced pinch-off voltage compared to those with co-implantation of Si and Mg (6×10¹¹ cm^–2). The measured f_T and f_max of a 1 m×25 m MESFET with co-implantation of Si and Be are 10 and 39 GHz, respectively. However, FETs with increased Mg dose (from 6×10¹¹ cm^–2 to 2×10¹² cm^–2) in a buried p-layer can obtain higher transconductance and saturation current.     

Numerical study of spectral intensity of emission and absorption of the CO2 and CO molecules under vibrationally nonequilibrium conditions

Numerical calculations are performed of the spectral intensity of emission and absorption of the 4.3- and 2.7-m bands of CO₂ and of the 4.7-m band of CO under conditions of nonequilibrium excitation of the vibrational degrees of freedom.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 5, pp. 805–813, May, 1982.     

Chebyshev approximation for the roots of the equation BiWГ(μ)=μVГ(μ)

A minimax approximation, uniform for Bi [0, ), is developed for the roots of the equation BiW()=V(), by means of Chebyshev polynomials.Translated from Inzhenero-Fizicheskii Zhurnal, Vol. 28, No. 4, pp. 710–715, April, 1975.     

Pressureless sintering of β-SiC with Al2O3 additions

-SiC was pressureless sintered to 98% theoretical density using Al₂O₃ as a liquid-phase forming additive. The reaction between SiC and Al₂O₃ which results in gaseous products, was inhibited by using a pressurized CO gas or, alternatively, a sealed crucible. The densification behaviour and microstructural development of this material are described. The microstructure consists of fine elongated -SiC grains (maximum length 10 m and width 2–3 m) in a matrix of fine equi-axed grains (2–3 m) and plate-like grains (2–5m). The densification behaviour, composition and phases in the sintered product were studied as a function of the sintering parameters and the initial composition. Typically, 50% of the -phase was transformed to the -phase.     

Detailed investigation of the temperature dependence of ionic transport parameters of a new composite electrolyte system (1−x) (0.75AgI : 0.25AgCl) : xSnO2

Detailed investigations of a new Ag+-ion-conducting two-phase composite electrolyte system (1–x) (0.75AgI : 0.25AgCl) : xSnO2 are reported, where 0x50 in weight per cent. A quenched-and-annealed (0.75AgI : 0.25AgCl) mixed system–solid solution was used as the first phase instead of the commonly used host matrix salt AgI. Micron-sized particles (about 10 m) of SnO2 were dispersed in the first (matrix) phase. The composition 0.8(0.75AgI : 0.25AgCl) : 0.2SnO2 exhibited conductivity enhancements of more than eight times over the annealed host and about three times over the quenched host at room temperature and has been referred to as optimum composition. The existence of two separate phases has been ascertained by X-ray diffraction and differential thermal thermal analysis techniques. The temperature dependence of the electrical conductivity, , ionic mobility, , mobile ion concentration, n, ionic transference number, tion, and ionic drift velocity, vd, are also reported. The enhancement in the conductivity in this two-phase composite electrolyte has been attributed to the increase in ionic mobility at room temperature.     

Selective laser sintering of gas atomized M2 high speed steel powder

Selective laser sintering of the gas atomized M2 high speed steel powder was performed using laser powers of 2.5–100 W, scan rates of 1–30 mm/s and scan line spacings of 0.15–0.75 mm. With increasing laser power, the sintered surface varied from open/closed pores to a fully dense structure. Large lateral pores were found in the sintered surface of samples using high scan rates. For fully dense samples, smooth surfaces could be achieved using large scan line spacing. The as-supplied and sieved M2 powder particles with size ranging from 0.04 to 400 m and 53 to 150 m, respectively, were found to give better laser sinterability as compared with those powder particles with finer (<38 m) or coarser (>150 m) sizes.     

Microstructure-property studies in friction-stir welded, Thixomolded magnesium alloy AM60

Thixomolded magnesium alloy AM60 plates joined by friction-stir welding were observed to be as strong or stronger than the unwelded base material. The thixotropic microstructures of the as-molded plates consisted of either 3% or 18% primary solid fraction of -Mg globules (45 m average size) in a eutectic mixture consisting of -Mg grains (10 m) surrounded by Mg₁₇Al₁₂ intermetallic grains in the -Mg grain boundaries (having an average size of 1–2 m). This complex, composite microstructure became a homogeneous (Mg + 6% Al)), recrystallized, equiaxed grain (10–15 m) microstructure in the weld zone.     

Simultaneous measurement of surface tension and kinematic viscosity using thermal fluctuations

We have developed a surface laser-light scattering apparatus to measure simultaneously surface tension and kinematic viscosity. In this method, we can obtain the surface properties by the laser heterodyne detection of light scattered from thermally excited capillary waves (called ripplon), which are typically of low amplitude (1 nm) and a characteristic wavelength (100m). Two gratings (d=100 and 200m) were employed to select the wave number of the capillary waves and to produce a reference beam for heterodyne detection. It was found through an experimental study on water that this contact-free method has considerable potential for application to measurements under extreme conditions such as high temperatures and high pressures.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

The role of starting powder size on the compressive response of stand-alone plasma-sprayed alumina coatings

Cylindrical stand-alone tubes of plasma-sprayed alumina were tested in uniaxial compression at room temperature, using strain gages to monitor axial strains. The effect of lamella size on the mechanical response was investigated by employing different starting powders to fabricate samples. The average powder sizes investigated included 9 m, 19 m and 32 m alumina; the resulting effective lamella diameters were 10 m, 28 m, and 55 m, respectively. Similar stress-strain hysteresis was observed on unloading in all tubes, independent of lamella size. A strong correlation between the failure stress and the cumulative strain at failure was also observed for tubes fabricated from the three powders. For samples with approximately constant densities, tubes plasma sprayed with the 9 m powder exhibited greater moduli than tubes sprayed from either 19 or 32 m powders. This difference was attributed to the greater percentage of unmelted -Al₂O₃ in the coating.     

Microstructure and mechanical properties of reaction-formed joints in reaction-bonded silicon carbide ceramics

A reaction-bonded silicon carbide (RB-SiC) ceramic material (Carborundum's Cerastar RB-SiC) has been joined using a reaction f rming approach. Microstructure and mechanical properties of three types of reaction-formed joints (350 m, 50–55 m, and 20–25 m thick) have been evaluated. Thick (350 m) joints consist mainly of silicon with a small amount of silicon carbide. The flexural strength of thick joints is about 44±2 MPa, and fracture always occurs at the joints. The microscopic examination of fracture surfaces of specimens with thick joints tested at room temperature revealed the failure mode to be typically brittle. Thin joints (<50–55 m) consist of silicon carbide and silicon phases. The room and high temperature flexural strengths of thin (<50–55 m) reaction-formed joints have been found to be at least equal to that of the bulk Cerastar RB-SiC materials because the flexure bars fracture away from the joint regions. In this case, the fracture origins appear to be inhomogeneities inside the parent material. This was always found to be the case for thin joints tested at temperatures up to 1350°C in air. This observation suggests that the strength of Cerastar RB-SiC material containing a thin joint is not limited by the joint strength but by the strength of the bulk (parent) materials.     

Effects of grain size on pyroelectric and dielectric properties of Pb0.9La0.1TiO3 ceramics

Pyroelectric and dielectric properties of Pb0.9La0.1TiO3 ceramics with grain sizes in the range of 1.3–6.0 m were investigated. The temperature stability of the pyroelectric coefficient at room temperature was improved as the grain size became smaller. The pyroelectric coefficient of Pb0.9La0.1TiO3 at room temperature reached the lowest value near the grain size of 2.7 m. Above 2.7 m, the relationship between the pyroelectric coefficient and the grain size could be explained by the increase of 90° domain switching. However, below 2.7 m, the relationship was not clear. The variation of the relative dielectric constant of Pb0.9La0.1TiO3 with the grain size showed a similar relationship with that of the pyroelectric coefficient. The variation of the pyroelectric figure of merit on voltage responsivity as a function of the grain size was similar to that of the pyroelectric coefficient because the pyroelectric coefficient varied more strongly than the relative dielectric constant. © 1998 Chapman & Hall     

Microstructure and mechanical properties of rapidly quenched L20 and L20+L12 alloys in Ni-Al-Fe and Ni-Al-Co systems

Ductile L2₀-type wires and+L1₂-type duplex wires with high strengths and large elongation in the Ni-Al-Fe and Ni-Al-Co ternary systems have been manufactured directly from the liquid state by an in-rotating-water spinning method. The wire diameter was in the range 80 to 180m and the average grain size was 2 to 4m for the wires and 0.2 to 1.0m for the+ wires. _y, _f and _p of the wires were found to be about 360 to 760 MPa, 560 to 960 MPa, and 0.2 to 5.5%, respectively, for the Ni-Al-Fe system, those of the+ wires were about 395 to 660 MPa, 670 to 1285 MPa, and 3.5 to 17%, respectively, for the Ni-Al-Fe system, and about 260 to 365 MPa, 600 to 870 MPa, and 4.0 to 7.0%, respectively, for the Ni-Al-Co system. Cold-drawing caused a significant increase in _y and _f and the values attained were about 1850 and 2500 MPa, respectively, for Ni-20Al-30Fe and Ni-25Al-30Co wires drawn to about 90% reduction in area. The high strengths, large elongation and good cold-workability of the melt-quenched and+ compound wires have been inferred to be due to the structural change into a low-degree ordered state containing a high density of phase boundaries, suppression of grain-boundary segregation and refinement of grain size.     

Effect of fiber content on the thermoelectric behavior of cement

The effect of discontinuous stainless steel fibers (diameter 60 m) as an admixture in cement paste on the thermoelectric behavior (the Seebeck effect) was systematically studied as a function of fiber volume fraction from 0 to 0.50 vol%. Without fibers, cement paste has an absolute thermoelectric power of +3 V/°C. A fiber content of up to 0.20 vol% makes the absolute thermoelectric power more negative (down to –63 V/°C), whereas a fiber content of 0.20–0.50 vol% makes the absolute thermoelectric power more positive (up to +31 V/°C)—even more positive than the positive value for the steel fiber by itself (+8 V/°C). The value is zero at a steel fiber content of 0.27 vol%. The effects are probably due to carrier scattering rather than conduction.     

Carrier Mobility in GaSb–V2Ga5and GaSb–GaV3Sb5 Eutectic Alloys

Experimental evidence is presented that semiconductor–metal eutectics with a low content of the metallic phase (4 vol %) are similar in electronic structure to inhomogeneous semiconductors. The microstructure of undoped and Te-doped GaSb–V₂Ga₅ and GaSb–GaV₃Sb₅ eutectic alloys is examined, and the Hall mobility of carriers in these alloys is determined. The anomalous temperature variation of Hall mobility in GaSb–V₂Ga₅ ( T ²) and GaSb–GaV₃Sb₅ ( T ⁵) is interpreted in terms of infinite clusters ofn-type metallic inclusions embedded in a p-type semiconductor matrix and interconnected through overlapping inhomogeneous interfaces. It seems likely that the difference in conductivity type between the semiconductor matrix and the infinite clusters gives rise to a random large-scale potential relief. Te compensation of GaSb in the eutectic alloys causes the Hall mobility to vary more rapidly with temperature, T ³ to T ¹⁰, which is interpreted as due to an increase in the amplitude of the random large-scale potential relief, the formation of infinite clusters, and partial compensation of unintentional acceptor doping in the semiconductor matrix.     

On a simple wave approximation of a set of linear dispersive wave equations

Summary The validity of an approximation ₀ of one of the solutions of a set of two linear coupled dispersive wave equations has been discussed. ₀ is the solution of a linear Korteweg-de Vries equation and satisfies the same initial condition as . It is shown that for square integrable solutions having a spectral range not exceeding [–, ] the approximation is useful if ^{5 2}t«1 in the sense that –₀(t)« (t)(L ₂ -norm). is a measure for the dispersion. The approximation fails in that sense ast . Some remarks to a similar nonlinear problem are made.     

Porous HA ceramic for bone replacement: Role of the pores and interconnections – experimental study in the rabbit

Hydroxyapatite (HA) porous ceramics are increasingly used in biomedical applications. Their physical characteristics, such as porous volume, require perfect control of the pore shape, as well as the number and the size of their interconnections.The aim of our study was to evaluate a new HA ceramic using polymethylmethacrylate microbeads (PMMA) as the porous agent. Four interconnection sizes (30, 60, 100 and 130 m) with a 175–260 m pore size and three pore sizes (175–260, 260–350 and 350–435 m) for a 130 m interconnection size were tested. Various HA implants were appraised by microscopic evaluation in a 4.6×10 mm rabbit femur cancellous bone defect 12 weeks after implantation. The best osteoconduction result was obtained in the center of the ceramic by means of a 130 m interconnection size and a 175–260 m mean pore size. Bone formation obtained within the pores was double that obtained in our previous study where naphtalen microbeads were used as the porous agents.© 2001 Kluwer Academic Publishers     

Fabrication and properties of novel composites in the system Al–Zr–C

Composite bodies in the system Al–Zr–C, with about 95% relative density, were obtained by heating the compact body of powder mixture consisting of Al and ZrC (5 : 1 mol %) in Ar at 1100–1500°C for various lengths of time. Components of the material heated at more than 1200°C were Al, Al3Zr, ZrC and AlZrC2. The Al3Zr exhibited plate-like aggregation, and its size increased with increasing temperature. In the material heated at 1500°C for 1 h, the largest plate-like Al3Zr aggregation was 2000 m long and 133 m thick. Then the AlZrC2 was present as well-proportioned hexagonal platelet particles with a 8–9 m diameter and a 1–2 m thickness in the interior of the plate-like Al3Zr aggregation and Al matrix phase. The average three-point bending strength of the bodies was 140–190 MPa, and the maximum strength was 203 MPa in the body heated at 1300°C for 1 h. The body heated at 1500°C for 1 h showed high oxidation resistivity to air up to 1000°C.