Journal of Research of the National Bureau of Standards. Section A, Physics and Chemistry最新文献

The deformation of single crystals of poly(oxymethylene) grown from 0.01 percent bromobenzene solution has been studied by deposition on a deformable substrate. Slight decoration of the crystal surfaces with gold prior to mechanical deformation of the composite reveals breaks in the gold which are displaced with respect to cracks in the underlying polymer crystals. These observations are interpreted to imply the existence of a very thin discrete film on the surface of the polymer crystals which can slip during deformation. Such a film might arise from polymer molecules adsorbed on the crystal surface.

A model for the surface of folded-chain polymer single crystals is presented in which the "amorphous" phase is composed of polymer molecules physically adsorbed on surface sites of a fairly regularly folded surface. The evidence for the presence of an amorphous phase in polymer single crystals is reviewed briefly as well as the evidence for regular folding and adjacent reentry. The proposed model would allow simultaneous acceptance of the evidence for both an amorphous layer and a surface composed of regularly folded molecules; such evidence was heretofore contradictory. Experimental evidence for such a model is discussed and some predictions are made concerning the properties of such an adsorbed layer.

Relativistic line strengths have been computed for a large number of transitions using Dirac wave functions for the one-electron, hydrogen-like ions. As expected, the results indicate that relativistic effects are quite small for low stages of ionization. However, in general, they also remain small throughout a large portion of the isoelectronic sequence, becoming typically of the order of 10 percent in the vicinity of Z = 50, after which they grow quite rapidly. This suggests that for multielectron ions a basically nonrelativistic theory might well be adequate for light atom isoelectronic ions through as much as 30 or 40 stages of ionization.

Two devices are proposed for measuring absorption coefficients in weakly absorbing materials. The first device measures cylindrical samples and the second device measures flat plate or disk samples. This paper reports on the derivations for the steady-state and transient solutions to the heat diffusion equations which describe the barothermal behavior of the two proposed devices. In addition, Green's function techniques are used to describe the cyclic heating and cooling of the cylinders and plates.

Measurements were made of the heat capacity of crystalline and liquid bromobenzene from 11 to 300 K, of the triple point and heat of fusion at the triple point and of the heat of vaporization at one temperature. The adiabatic calorimeter used was precise over most of its range to ±0.l percent; the purity of the sample was 99.998 mol percent. The triple point of pure bromobenzene is 242.401 K (-30.749 °C) ±0.0l0°; the enthalpy and entropy of fusion are, respectively, 10702 ± 5 J mol^-1 and 44.150 ± 0.022 J K^-1 mol^-1. The heat and entropy of vaporization at 293.00 K are, respectively, 43 963 ±60 J mol^-1 and 150.0 ± 0.2 J K^-1 mol^-1. Tables are given for the thermodynamic functions of the condensed phases from 0 to 300 K; the functions for the ideal gas from 100 to 1500 K, calculated from spectroscopic and molecular data using statistical mechanical methods, are also tabulated. The entropy of the ideal gas at 293.00 K and one atmosphere, from statistical mechanics, is 323.63 J K^-1 mol^-1; the same quantity from the experimental measurements (third law) is 323.73 J K^-1 mol^-1. No anomalies or additional transitions were observed.

The enthalpies of combustion and formation of 2,2'-dichlorethyl sulfìde (mustard gas) have been determined by combustion in an adiabatic rotating-bomb calorimeter. The bomb process has been corrected to: ${\text{C}}_4{\text{H}}_8{\text{Cl}}_2\text{S}\left(\text{liq}\right)+7{\text{O}}_2\left(\text{g}\right)+98{\text{H}}_2\text{O}\left(\text{liq}\right)\to 4{\text{CO}}_2\left(\text{g}\right)+\left[2\text{HCl}+{\text{H}}_2{\text{SO}}_4+100{\text{H}}_2\text{O}\right]\left(\text{liq}\right)$ for which the following values were obtained: $\text{Δ}H{c}^{°}\left(25{}^{°}\text{C}\right)=-3163.49\pm 1.26\text{kJ}/\text{mol}\text{and}$ $\text{Δ}H{f}^{°}\left(25{}^{°}\text{C}\right)=-200.57\pm 1.58\text{kJ}/\text{mol}.$.

The enthalpy of combustion of thianthrene (diphenylene disulfide) has been determined in an oxygen-bomb calorimeter. The enthalpy of formation has been derived using data from the available literature. The results obtained are as follows: ${\text{C}}_{12}{\text{H}}_8{\text{S}}_2\left(\text{c}\right)+17{\text{O}}_2\left(\text{g}\right)+228{\text{H}}_2\text{O}\left(\text{liq}\right)=12{\text{CO}}_2\left(\text{g}\right)+2\left[{\text{H}}_2{\text{SO}}_4+115{\text{H}}_2\text{O}\right]\left(\text{liq}\right)$ $\Delta H_c^{°}\left(25{}^{°}\text{C}\right)=-7253.27\pm 1.40\text{ kJ}/\text{mol}(-1733.65\pm 0.33\text{ kcal}/\text{mol})$ $\Delta H{f}^{°}\left(25{}^{°}\text{C}\right)=184.23\pm 1.50\text{ kJ}/\text{mol}(44.03\pm 0.36\text{ kcal}/\text{mol})$ A comparison is given of the results of this investigation with those of previous investigators.

It is standard procedure to fit an applicable isotherm equation to water vapor adsorption data using the method of least squares in arriving at a value for the surface area accessible to the water molecule. The least squares technique has been extended in the present investigation to determine, in addition and simultaneously, a "best value" for the zero-humidity sample weight of the material. The application is equally valid for desorption insofar as the zero-humidity weight is concerned, although the derived value for "surface area" from desorption data will be over-estimated in the general case because of hysteresis. There is no limitation on the range of humidities since the method is not restricted to the BET equation (i.e., between 0.1 and 0.3 r.h.). In fact, good agreement with the zero-humidity points measured experimentally has been obtained even from drying curves in which the relative humidity has been confined to the region above 50 percent. An iterative method is employed in the calculations for which computer assistance is especially adaptable. Fortran IV programs are included in the appendix whose use requires no extensive computer experience. A fraction of a second in computer processing time is all that is required for each determination.

Radiance temperature (at 653nm) of iron at its melting point was measured using a subsecond-duration pulse heating technique. Specimens in the form of strips with initially different surface roughnesses were used. The results do not indicate any dependence of radiance temperature (at the melting point) on initial surface or system operational conditions. The average radiance temperature (at 653 nm) at the melting point for 13 specimens is 1670 K on IPTS-68, with a standard deviation of 0.8 K and a maximum absolute deviation of 1.7 K. The total error in the radiance temperature is estimated to be not more than ±6 K.