New Experimental Facts Concerning the Thermally Stimulated Discharge Current in Dielectric Materials

The thermally stimulated discharge current (TSDC) method is a very sensitive and a very selective technique to analyze dipole disorientation and the movement of de-trapped space charge (SC). We have proposed a variant of the TSDC method, namely the final thermally stimulated discharge current (FTSDC) technique. The experimental conditions can be selected so that the FTSDC is mainly determined by the SC de-trapping. The temperatures of the maximum intensity of the fractional polarization peaks obtained at low temperature, in the range of the local (secondary) relaxation, are in general about 10 to 20 K above the poling temperature. Measurements of the FTSDC in a wide temperature range demonstrate the existence of an apparent peak at a temperature Tma shifted with about 10 to 30 K above the charging temperature Tc. The shift of Tma with respect to Tc depends on the experimental conditions. The peak width at the half maximum intensity decreases as Tc increases and the thermal apparent activation energy increases. The variations are not monotonous revealing the temperature range where the molecular motion is stronger and consequently the charge trapping and de-trapping processes are affected. Our results demonstrate that there is a strong similarity between the elementary peaks obtained by the two methods, and the current is mainly determined by SC de-trapping. Even the best elementary peaks are not fitted very well by the analytical equation, indicating that the hypothesis behind this equation have to be reconsidered.

Assessment of Fatigue Life for High-Temperature Pipeline Welds by Non-Destructive Method

The objective of this study is to estimate the feasibility of X-ray diffraction method application for fatigue life assessment of the high-temperature pipeline steel such as main steam pipe, re-heater pipe and header etc. in power plant. In this study, X-ray diffraction tests using various types of specimen simulated low cycle fatigue damage were performed in order to analyze fatigue properties when fatigue damage conditions become various stages such as 1/4, 1/2 and 3/4 of fatigue life, respectively. As a result of X-ray diffraction tests for specimens simulated fatigue damages, we conformed that the variation of the full width at half maximum intensity decreased in proportion to the increase of fatigue life ratio. And also, the ratio of the full width at half maximum intensity due to fatigue damage has linear relationship with fatigue life ratio algebraically. From this relationship, it was suggested that direct expectation of the life consumption rate was feasible.

Numerical conversion between the Pearson VII and pseudo-Voigt functions

The shape coefficient of a curve, which is defined as the ratio of its full width at half-maximum intensity to integral width, is a measure of variation in shape. From the definitions of the pseudo-Voigt, Pearson VII and Voigt functions used in X-ray diffractometry, three shape-converting formulae are deduced. Numerical solution helps to establish a numerical model for interconverting the shapes of the pseudo-Voigt, Pearson VII and Voigt functions. Assessment of the error level and some comments on the shape of the pseudo-Voigt and Pearson VII functions are thereby made.

An Analysis of the Effect of Different Instrumental Conditions on the Shapes of X-ray Powder Line Profiles

In this investigation we have examined how the full width at half maximum intensity (FWHM) and asymmetry of x-ray powder diffraction line profiles are influenced by the instrumental conditions adopted. Experimental x-ray data has been collected for a matrix of instrumental conditions by systematically varying the divergence slit angle (and the corresponding anti-scatter slit) over the range 0.25° to 1.25°, by using either a 0.05mm or 0.2mm receiving slit, or by removing the diffracted beam Soller slit. The line profile Standard Reference Material, SRM, 660 (LaB6) was used as the powder specimen in that it imparts minimal specimen induced broadening to the diffraction profiles. X-ray data were collected on a conventional, divergent beam, x-ray diffractometer using CuKα radiation. The FWHM of the CuKα1 component can be as low as 0.035°2θ for high resolution conditions, but is normally ∼0.1°2θ at 2θ ≈ 30° for the instrumental conditions adopted in routine diffractometry. Below 2θ = 50°, the divergence slit has a significant effect on the FWHM and is the major cause of the increase in FWHM with decreasing 2θ. Results are presented of the 2θ dependence of FWHM values for each of the instrumental conditions recorded. A general relationship for the 2θ dependence of the FWHM and the asymmetry has been investigated to supersede the inappropriate Cagliotti expression frequently used in x-ray Rietvcld refinement.

PC-Based Management and Analysis of X-Ray Residual Stress Data

The authors have developed two independent software packages that store x-ray peak locations, integrated intensities and full-width half-maximum intensity data as a function of diffractometer tilt and orientation angle; this information is used to compute residual stress tensor values. Each program retrieves the fitted x-ray peak locations from a dBASE-compatible data set that is independent of both x-ray diffractometer and acquisition software. Machine-specific routines have been coded to transfer peak data and general diffraction setup information from several different x-ray acquisition platforms into this common format. The two database management programs provide stand-alone storage, retrieval, analysis and graphic output of data, and thus have become practical laboratory vehicles toward establishing a standard database format for storing x-ray strain measurements and the residual stress values calculated therefrom.

The Crystalline Structure of Cellulose as Revealed by Acid Hydrolysis

The hydrolysis of holocellulose from Eucalyptus regnans F. v. M. has been studied employing a percolation technique and using 2 per cent. sulphuric acid for varying times of hydrolysis (0 to 6 hr.) and at three temperatures, 150, 160, and 170 �C. For comparison a series of experiments at 160 �C. on cotton was also carried out. The course of hydrolysis of the resistant cellulose in each experiment could be represented by the equation for a fist order reaction. The " reaction constant " for cotton was smaller than that for holocellulose. Powder X-ray diffraction photographs were made of samples at each stage of hydrolysis in the 160 �C. series. From these photographs the breadth at half maximum intensity of the line corresponding to the (002) planes, and the combined lines corresponding to the (101) and (101) planes was determined by photometric measurement. Throughout the period of hydrolysis studied, the line breadths decreased for both holocellulose and for cotton. This observation is considered to indicate the existence of a distribution of the degree of lateral order of the crystalline regions in each sample. The narrow line breadths in the cotton series' may indicate the existence of greater lateral order in the cotton than in the wood holocellulose and may account for the observed smaller reaction constant for cotton. The results obtained are consistent with the view that the mesomorphous regions surrounding the micelles are more extensive in wood holocellulose than in cotton.