Fine Annealing of Optical Glass

Since the most important characteristic of optical glass is the uniformity of its refractive index, which is itself a function of fictive temperature, any fine annealing treatment must be such as to bring about substantial uniformity in fictive temperature. Methods of accomplishing this are reviewed. In terms of total required time in the annealing process, the most efficient method consists of soaking the glass for a short time at a temperature near the annealing point and cooling at a constant rate to a temperature below the annealing range and at an increased rate to room temperature. Formulas are given for specifying the parameters in the annealing schedule in terms of the final condition of the glass as to stress and index. The several outstanding advantages of this method of annealing are discussed.     

Potentiometric titration of long chain quaternary ammonium compounds using sodium tetraphenyl borate

Current methods for determining the activity of long chain quaternary ammonium compounds (QACS) are based either on dye partition, titration, or colorimetric analysis. The two major disadvantages of these methods are the disparity of partition coefficients among differently constituted QACS and the difficulty in detecting visual end points. Some potentiometric titration methods for QACS have been reported in the literature. However, back titration techniques, as well as complicated electrode systems, are generally involved. A new potentiometric titration system is presented which uses aqueous sodium tetraphenylborate (TPB) solution as a titrant and a platinum-platinum electrode system to detect the end point. Standard potentiometric titration instruments may be used for this method. This new potentiometric method is superior in precision and accuracy to visual (colorimetric) methods. Original version presented at the 1986 Annual AOCS Meeting in Honolulu, HI.     

Fractionation of partially stereoregular poly(propylene oxide)

Partially stereoregular poly(propylene oxide) samples were synthesized via reactions catalysed by a preformed analytically defined trimethylaluminium hydrolysate. These samples were fractionated into two contrastingly different fractions.

1. (i) D-polymers: This fraction constituted the major part (up to 90%). It mainly contained cyclic low molecular weight oligomers (MW < 1000). The linear chains found in D-polymers had hydroxyl end groups. No double bonds could be detected spectroscopically.

2. (ii) K-polymers: This fraction was high molecular weight stereoregular polymer. Stepwise thermal precipitation from dilute isooctane solution of K-polymers yielded a succession of fractions which differed in melting point. It appears that the phase equilibria during the thermal precipitations were not controlled by the molecular weights of species.

The behavior of a swarm of particles moving in a viscous fluid

A significant bulk flow is thought to occur if a part of the body of a suspension, which has a different density from the density of the remainder of the suspension, is large enough in space however slight the difference may be. As a typical case, the slow motion of a swarm of particles in a viscous fluid was studied both theoretically and experimentally. Under a certain condition, the suspended particles formed a drop of suspension, in which the suspended particles and fluid moved as one body in the same way. The falling velocity of a spherical swarm of particles, which was called a drop of suspension, was measured and compared with a new theoretical prediction presented in this paper.It may be also noted that the theoretical model may be applicable to the flow due to density difference by means of replacement of the continuous mass by the damped mass which is regarded as consisting of particles.     

Nucleation and Growth of Magnesioferrite in MgO Containing 0.9% Fe3+

The initial stage of precipitation of magnesioferrite from a supersaturated solid solution of 0.9 cation % Fe³⁺ in MgO at 500 °C was studied by fitting the magnetization curves to 7000 Oe at low temperatures with the Brillouin function. The averase umber of Fe³⁺ ions in a precipitate particle, increased monotonically with aging time from 9 in the as-quenched condition to 88 after 16 h. The average spin quantum number per Fe³⁺ ion decreased to near its final value at an aging time corresponding to = 50. Thus the volume fraction of precipitate is near the final value when the average particle size is only about three unit cells of magnesioferrite.     

Polarographic determination of vanadium,nickel, cobalt,and iron in petroleum residues

Conclusions It has been shown that it is possible to determine polarographically, using a dropping mercury electrode, the elements vanadium, nickel, cobalt, and iron in the form of their sulfosalicylic acid complexes in an ammonium buffer electrolyte.The method was used to determine these elements in the concentrations in which they are present in the mineral residues of petroleum and petroleum products.Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 11, pp. 52–54, November, 1969.     

19F chemical shift anisotropy in aligned PTFE fibres

By applying a nuclear magnetic resonance (n.m.r.) multiple pulse sequence to a powder of randomly aligned crystallites, the principal values of the chemical shift tensor may be measured. However information about alignment of the chemical shift tensor with respect to the crystal axes is lost. To obtain orientation information in polytetrafluoroethylene (PTFE), we have prepared a bundle of drawn PTFE fibres and observed the ¹⁹F line-narrowed n.m.r. spectra for various fibre orientations relative to the direction of the static magnetic field. The data at 77 K indicate that the most screened component of the chemical shift tensor lies along the CF bond and that the least screened component is aligned at approximately 20° to the molecular chain axis. At 298K the spectrum of a PTFE powder indicates an axially symmetrical tensor whose principal values are consistent with a 20° inclination of the least screened component relative to the chain axis.     

Sonic quality control for SP-11-type mullite-corundum stoppers

Refractories and Industrial Ceramics -