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This article attempted to show how American Indians, generally stated, have viewed, reacted to, and related to death, both in the past and the present. (RTS)

Vapor pressure data below the normal boiling point are presented for ternary mixtures that are prepared from the following chemicals: perfluoro[methylethyl ether] (RE-218), pentafluorodimethylether (RE-125), 1,1,1-trifluorodimethylether (RE-143a), dimethylether (RE-170), 1,1,1,2-tetrafluoroethane (R-134a), 1,1,1-trifluoroethane (R-143a), 1,1-difluoroethane (R-152a), fluoroethane (R-161), and difluoromethane (R-32). Liquid–liquid phase separation in the binary mixtures RE-218/RE-170 and RE-218/R-161 is eliminated with the ternary mixtures, RE-218/RE-143a/RE-170 and RE-218/R-134a/R-161. A sufficient amount of vapor pressure data was obtained for these ternary mixtures to calculate vapor–liquid phase relations using van Laar equations for ternary mixtures. Vapor pressure data are also reported for a number of ternary mixtures containing RE-125. Liquid density data and the critical parameters are reported for the equimolar mixtures, RE-218/R-134a/R-161, RE-125/R-32/R-152a, and RE-125/R-32/R-134a, which are judged to have a high potential as R-22 alternatives based on their boiling point and critical temperature.

Measurements of flammability limits by the ASTM E 681 method are believed to be affected by vessel size. In order to investigate the effect of volume on measured lower flammability limits in air, experimental measurements of the lower flammability limit of difluoromethane (R-32) are made at 21°C using 3, 5, 12, and 20 L vessels. A spark ignition source is used with the voltage adjusted to the value where dielectric breakdown just begins to occur (approximately 7–12 kV). The results demonstrated a higher concentration for the lower flammability limit for the vessels smaller than 5 L suggesting that wall effects quench the flame propagation. The lower flammability limit for vessels with a 5 L or greater volume are in good agreement with those obtained in earlier investigations. For 5 L and larger vessels the lower flammability limits systematically shift to higher concentrations of difluoromethane with increasing vessel size which is consistent with a percolation model for spatial flame propagation. Extrapolation of the data to infinite vessel size using a percolation model yielded a lower flammability limit of 15.2 vol.%. The results are consistent with the work of Richard for refrigerant mixtures, R134a/R152a and R125/R152a, in large volume vessels (200 L) where effects of vessel walls are negligible.

New vapor pressure data are reported as a function of temperature and concentration for the mixtures: CF3SF5/CF3CH3, CF3SF5/CF3CF2H, CF3OCF2H/CH3CH2F, CF3OCF2H/CH3CF2H, CF3OCF2H/CF3CH3, CF3OCF2H/CF3CH2F, and CF3OCF2H/CF3CF2H. As is expected, large positive deviations from the ideal mixing vapor pressure are observed for CF3SF5 mixed with ethane derivatives of a low fluorine content and these deviations become small as the fluorine content approaches that of CF3CF2H. In contrast to this expected vapor pressure behavior, the ether (CF3OCF2H)/fluorinated ethane mixtures exhibit significantly smaller deviations which may be positive or negative. The mixture, CF3OCF2H/CH3CH2F, exhibits sufficiently large negative deviations from ideality to produce an azeotrope at 0.21 mol fraction of CH3CH2F with boiling point of −33.3°C. The mixtures CF3OCF2H/CH3CF2H, CF3OCF2H/CF3CH3 and CF3OCF2H/CF3CF2H are nearly ideal and the mixture CF3OCF2H/CF3CH2F exhibits positive deviations from ideality. All of the mixtures have boiling points that range from −22 to −48°C. The mixtures that have boiling points below −30°C have potential as R22 alternatives.

We have studied the temperature dependence of the Raman spectra of ceramic bulk and thin-film samples of polycrystalline ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{TiO}}_{3}$ $(x=0,$ 0.1, 0.2, and 0.3) in the range between room temperature and 350 \ifmmode^\circ\else\textdegree\fi{}C. The ferroelectric to paraelectric phase-transition temperatures ${(T}_{C})$ have been estimated from the loss of intensity for several phonon modes belonging to the tetragonal phase when the samples transform to the paraelectric cubic phase. Similar to single crystalline ${\mathrm{BaTiO}}_{3},$ broad first-order Raman features are found to persist well beyond ${T}_{C}$ in all the samples studied here. For bulk samples, the estimated values of ${T}_{C}$ from the Raman studies agree well with the ${T}_{C}$ values determined from the anomaly in the dielectric constant versus temperature measurements. For thin films, however, the temperature measurements of the dielectric constant do not show any anomaly and the Raman signature viz., the disappearance of several phonon modes at ${T}_{C},$ is used for determining ${T}_{C}.$ We find that the values of ${T}_{C}$ in thin films are higher than those of the bulk samples. This is attributed to the presence of intergrain stresses in the submicron size grains in the thin films which might prevent a complete phase transformation at the expected bulk ${T}_{C}.$ Furthermore, a new Raman mode has been seen at \ensuremath{\sim}620 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in all the thin-film samples but not in bulk ceramics at all temperatures. This mode has also been observed in polycrystalline bulk ${\mathrm{BaTiO}}_{3}$ powder under high pressure and it most probably originates from the strain in the grain-boundary regions.

Vapor–liquid equilibrium (VLE) vapor pressures are reported for binary mixtures; octafluoromethylethylether+1,1-difluoroethane (RE218/R152a), trifluoromethylpentafluorosulfur(VI)+1,1-difluoroethane (CF3SF5/R152a), hexafluorodimethylthioether+1,1,1,2-tetrafluoroethane (CF3SCF3/R134a), and pentafluorodimethylether+1,1,1-trifluorodimethylether (RE125/RE143a). The mixtures; (RE218/R152a), (CF3SF5/R152a), and (CF3SCF3/R134a) form minimum boiling azeotropes with the normal boiling points; 237.9 K (−35.3°C), 239.7 K (−33.5°C), and 243.0 K (−30.2°C), respectively, and gas–liquid critical temperatures of 353.3 K (80.1°C), 365.7 K (92.5°C) and 368.2 K (95.0°C), respectively. The azeotropic mixtures have sufficiently low boiling points to serve as alternatives for the refrigerant R-22 (CHF2Cl). The mole fractions of the perfluorinated component of these mixtures at the azeotropic compositions are 0.49, 0.41, and 0.46, respectively. The estimated critical mixing temperatures for liquid–liquid phase separation are 236 K (−37°C), 221 K (−52°C), and 341 K (−68°C), respectively, and are well below the corresponding boiling points. The ether mixtures, (RE125/RE143a), exhibit nearly ideal mixing behavior which contrasts the VLE behavior of mixtures of perfluorinated ether, RE218, with RE143a [I. Kul, D.D. DesMarteau, A.L. Beyerlein, ASHRAE Trans. 106 (1) (1999)]. In addition to binary mixtures, VLE data are reported on four ternary mixtures; RE125(33%)/R134a(33%)/R161(34%), RE125(33%)/RE143a(33%)/R161(34%), RE218(33%)/RE143a(33%)/R161(33%), and RE218(40%)/RE143a(40%)/R161(20%) with boiling points 240.6 K (−32.6°C), 241.6 K (−31.6°C), 236.7 K (−36.5°C), and 238.6 K (−34.6°C), respectively. The boiling points of the ternary mixtures are sufficiently low for a R-22 alternative.

The diffuse-phase-transition class of ferroelectric materials allows the fabrication of films graded in composition: the consequence of which is an attendant gradient in electric dipole moment density. Alternating electric-field excitation of these graded structures reveal an asymmetrical hysteresis characteristic, together with a static displacement of the hysteresis trace. This displacement bias is observed to be a function of excitation level and temperature, which leads to a giant effective pyroelectric coefficient. Said displacement, for example, provides a continuous open-circuit voltage, or short-circuit current, provided that the structure is held in an isothermal condition. All other combinations of heat, electrical and strain energies suggest a whole new class of devices, and invite ingenious concepts and/or contributions. Graded ferroelectrics, which operate on principles of asymmetrical bound-charge, are broadly the dielectric analogue of conductive asymmetrical free-charge devices. F...

Ferroelectric thin films (∼1.2 μm) of BaxSr1−xTiO3 with gradients in composition normal to the growth surface were formed on platinum substrates by metalorganic decomposition. Effective (pseudo) pyroelectric coefficients as large as 0.06 μC/cm2 K have been obtained from these active ferroelectric devices under the application of an ac field (charge pumping). In contrast, a value of only −0.003 μC/cm2 K has been measured for the conventional pyroelectric coefficient.

The liquid density, boiling point, critical temperature and critical density are investigated for R-161 (CH 3 CH 2 F, bp = - 37.3°C), CF 3 SCF 3 (bp = - 20.1°C), and RE-218 (CF 3 OCF 2 CF 3 , bp = - 23.7°C); which are potential R-12 and R-22 alternatives. Since the range of applicability of chemicals may be improved by considering their mixtures, the vapor pressure of the mixtures; CH 3 CH 2 F/CF 3 SF 5 , CF 3 CH 2 F/CF 3 SF 5 , and CF 3 (CF 2 ) 2 CH 2 F (R-338mccq)/isopentane; were also investigated. The critical mixing temperature of the CH 3 CH 2 F/CF 3 SF 5 mixtures is above - 30°C which is greater than the normal boiling point of -40°C. Therefore, these mixtures would have limited application as R-12 and R-22 alternatives. The normal boiling point of the R-134a (CF 3 CH 2 F)/CF 3 SF 5 mixtures at the azeotropic R-134a mole fraction, 0.60, is -30.0°C. The critical mixing temperature of the latter mixtures is well below the boiling point and is not a factor in refrigeration applications. The CF 3 (CF 2 ) 2 CH 2 F (R-338mccq)/isopentane mixtures have a normal boiling point of 15.1°C and a critical mixing temperature of about - 5°C which may be acceptable for some applications as a R-1 1 alternative.