The effect of K+ on freshly precipitated BaSO4 is seen to increase the area of the crystals. The exchange rate of Ba2+ with these crystals is found to be proportional to this increased area. The extent of234Th precipitation is found to be, increased more than can be accounted for by the area change, and it is suggested that the
concentration of Th4+ adsorption sites increases as more K+ is incorporated into the lattice. Activation energy measurements show the reaction mechanisms to be unchanged by the presence
of K+. Values of 11.4 and 24.4 Kcal·mol−1 for the Ba2+ and Th4+ reactions, respectively, are consistent with an activation process involving loss of water of hydration.
Separation and isolation of radium and thorium by successive coprecipitation on BaSO4 is usually both fast and reliable, but suffer from both cross contamination (of Ra by Th) and low recovery (of Th) in the presence of some common components of environmental samples. An alternative method, free from these problems, involves the use of La3+ as holdback carrier for Th4+ during precipitation of Ba(Ra)SO4 followed by carrying of Th4+ on LaF3. Yields are found to be high in several cases which were troublesome by the other method.
The thermal decompositions of a series of tris dibromo alkyl phosphates similar to tris(2,3-dibromopropyl) phosphate (T23DBPP), alone and incorporated in poly(ethylene terephthalate) (PET) fabric have been studied by non-isothermal thermogravimetry. Kinetic evaluation revealed that the decomposition rate for tris(2,3-dibromo-3-methyl butyl) phosphate (T23DB3MBP) was the fastest followed by tris(2,3-dibromo-2-methyl propyl) phosphate (T23DB2MPP). Tris(3,4-dibromobutyl) phosphate (T34DBBP) and tris(2,3-dibromo butyl) phosphate (T23DBBP) had only marginally faster decomposition rates than T23DBPP itself. Measured decomposition rates for PET treated with the chemicals were only marginally faster than those for the untreated fabric, except during the initial weight loss stages where some decomposition of the chemicals appears to be occurring. Calculated kinetic parameters using an isoconversional method, along with regression coefficients of compensation effect plots suggest that all the chemicals behave similar to T23DBPP in having an apparent detrimental effect on the condensed phase decomposition kinetics while relying on their combustion inhibition effects to act as gas phase flame retardants.
Earlier work on the coprecipitation of230Th and234Th with BaSO4 has been confirmed and in particular the influence of other ions was investigated. Potassium ions, both in the solution and
in the crystals, promote the coprecipitation, while polyvalent cations tend to prevent it. It is shown that increased concentration
of K+ causes a marked change in the BaSO4 crystal form, with a concomitant increase in surface area. At the same time, the rate of exchange of133Ba2+ with the BaSO4 surface is also increased. This can be roughly accounted for by the change in surface area. It is conjectured that an equilibrium
occurs involving foreign cations in the lattice.