Diffusion of Lead in a Lead Borate Glass

Abstract

629ing strength trend occurs for the rods after shocks of 200 and 250C" AT. Statistical analysis indicates that this increasing strength trend is not significant; it may, however, be a reflection of the crack geometries. (Crack depth and density data are given in Table I.) The crack depths decrease between 200 and 250C" AT, and this trend is significant; it is related to the increase in crack densities and the strain energy available to drive the cracks. With shocks greater than 25OCO AT the cracks are driven deeper, and the strength decreases accordingly.The strength data dispersions (Fig. 2) of samples shocked a t 150C" AT do not differ significantly from those of the control group; however, the dispersions of the samples shocked at 175C0 AT increase appreciably. At shock levels above 175C" AT, however, there is a marked decrease in the dispersions for the rods and an appreciable decreasing trend in the data for the short cylinders.Daniels and Moore' induced flaws perpendicular to the direction of maximum bend stresses. They observed a marked decrease in data spread after the first flaws were introduced. The initial increase in dispersion noted in the present work can be explained as follows: At low shock levels there is a low density of randomly oriented and unconnected surface flaws; as the crack network becomes denser with increased shock, it provides, through interconnections, flaws which are effectively oriented perpendicular to the maximum stress. Thus, with higher shock levels and hence higher crack density levels, the dispersion data behave in a manner similar to that reported by Daniels and Moore.In these two studies, strength data dispersion decreased with increase in the density of the induced flaws, which in both instances were rather gross. This behavior is suggested by statistical theories of strength2 based on least value statistics. The flaw densities involved in this and the earlier work are low enough to cause the observed statistical behavior.' W. H. Daniels and R. E. Moore, "Fracture Behavior of a Model Brittle Solid Containing Artificial Surface Flaws," J . Am. Ceram. SOC., 48 [5] 274-75 (1965). recent diffusion measurements have been made with M radioisotopes.' In the present work, the diffusion rate of P b in a Pb0.2B203 melt and glass was measured using a thin sectioning technique and a stable isotope of lead, "'Pb, which was detected with a mass spectrograph. The toxic characteristics of the fission products of the radioisotopes of lead made the use of a stable isotope desirable.The glass was made from reagent-grade lead tetraoxide and boric acid. Chemical analysis showed that the glass contained 33.37 mol% PbO. The samples were made by pouring the molten glass into preheated aluminum oxide tubes 1 in. high and 1 in. in diameter with a wall in. thick. The samples were carefully annealed to avoid stress buildup between the alumina collar and the glass. The collar was used to prevent the glass from slumping during the long diffusion anneals above the glass transition temperature. After ...

Coarsening kinetics in demixed lead borate melts

“…%). 56 Eyring diffusivity of matrix glass in demixed PB1 and PB2 glasses was calculated using Eqs. (7) and (8) 7 smaller as previously estimated for this system, 9 but 3.7 times larger than determined from the critical drop sizes in the soda-lime silica system.…”

“…The error of this oversimplified approach to boron mobility is mainly due to the different structural roles of boron in pure B 2 O 3 and different borate glasses, i.e., boron is unique in readily transforming between three ( III B) and four ( IV B) coordination with changes in composition, 24 temperature, 54 and pressure. 55 Tracer diffusivity data in lead borate melts resulted in D 207-Pb = 1.4 × 10 −16 (773 K) and D 207-Pb = 7.6 × 10 −17 (723 K) for lead 56 and D 18-O = 4.8 × 10 −17 m 2 s −1 (773 K) and D 18-O = 2.9 × 10 −17 m 2 s −1 (723 K) for oxygen diffusion. 57 Herein the 207 Pb diffusivities in the range from 548 K to 698 K 56 and of 18 O diffusivities in the range from 673 K to 753 K 57 were extrapolated using Eq.…”

“…55 Tracer diffusivity data in lead borate melts resulted in D 207-Pb = 1.4 × 10 −16 (773 K) and D 207-Pb = 7.6 × 10 −17 (723 K) for lead 56 and D 18-O = 4.8 × 10 −17 m 2 s −1 (773 K) and D 18-O = 2.9 × 10 −17 m 2 s −1 (723 K) for oxygen diffusion. 57 Herein the 207 Pb diffusivities in the range from 548 K to 698 K 56 and of 18 O diffusivities in the range from 673 K to 753 K 57 were extrapolated using Eq. (9) to 723 and 773 K, respectively.…”

“…%); 18 O self-diffusivity 57 and viscosity 59 in PbOrich lead borate glass (c 0 B 2 O 3 = 31 mol. %); 207 Pb self-diffusivity 56 and viscosity 59 in lead diborate glass (c 0 B 2 O 3 = 66.7 mol. %).…”