Granular Salt Research Articles

Modeling the consolidation of a porous aggregate of dry salt as isostatic hot pressing

Densification of porous aggregates is an important geophysical process. Salt is a convenient material to use in studying time‐dependent densification because extensive studies have been made of the creep behavior of intact salt, and its relatively low melting point enhances the effects of temperature at easily attained laboratory conditions. To obtain data on instantaneous and time‐dependent consolidation of granular salt, we measured the consolidation for times up to 400,000 s at temperatures from 21° to 100°C and hydrostatic pressures from 1.7 to 21 MPa. All tests were done under hydrostatic loading and nominally dry conditions. The only water present was the ∼0.2% water content of the salt. A model of the isostatic hot‐pressing process was used to describe the data, using the known creep behavior of intact salt for input. When brittle phenomena such as particle rearrangement and fracturing were neglected, the model successfully predicted late‐stage consolidation rates, but underpredicted the absolute densities attained in the tests. After a term was added to the model to account for brittle consolidation, the model predicted most of the observed behavior. The model makes specific predictions regarding the dependence of the consolidation rate on temperature and pressure, and these predictions are testable in the laboratory. Most importantly, the model predicts the consolidation behavior in terms of creep mechanisms known to operate in intact rock salt both in the laboratory and under geological conditions. Thus the model may be credibly extrapolated to physical conditions and long time spans beyond laboratory test capabilities.

Experimental determination of constitutive parameters governing creep of rocksalt by pressure solution

Abstract Theoretical models for compaction creep of porous aggregates, and for conventional creep of dense aggregates, by grain boundary diffusion controlled pressure solution are examined. In both models, the absolute rate of creep is determined by the phenomenological coefficient Z * = Z 0 exp (−Δ H/RT ), a thermally activated term representing effective diffusivity along grain boundaries. With the aim of determining Z 0 , Δ H and hence Z * for pressure solution creep in rocksalt, compaction creep experiments have been performed on wet granular salt. Compaction experiments were chosen since theory indicates that pressure solution creep is accelerated in this mode. The tests were performed on brine-saturated NaCl powder (grainsize 100–275 μm) at temperatures of 20–90°C and applied stresses of 0.5–2.2 MPa. The mechanical data obtained show excellent agreement with the theoretical equation for compaction creep. In addition, all samples exhibited well-developed indentation, truncation and overgrowth microstructures. We infer that compaction did indeed occur by diffusion controlled pressure solution, and best fitting of our data to the theoretical equation yields Z 0 = (2.79 ± 1.40) × 10 −15 m 3 s −1 , Δ H = 24.53 kJ mol −1 . Insertion of these values into the theoretical model for conventional creep by pressure solution leads to a preliminary constitutive law for pressure solution in dense salt. Incorporation of this creep law into a deformation map suggests that flow of rocksalt in nature will tend to occur in the transition between the dislocation-dominated and pressure solution fields.

Explosive containment with spherically tamped powders

An effective technique for maximizing the explosive charge that a given container can safely handle is to fill the space between the charge and the container walls with a porous medium or a powder. Using the wrong powder, however, can be worse than using no powder at all. Moreover, a powder-filled container that performs very well with a small charge may also be worse than a powderless system when the charge is increased. An analysis of this problem is developed with the aim of identifying appropriate buffer material properties and the conditions under which breakdown occurs. The results are compared with various experiments performed with graphite powder, coke chunks, granular salt, snow, and vermiculite.

Nutritive Value of Salt-bed Roasted Soybeans for Broiler Chicks

A roaster was built which used heated granular salt (NaCl) as the heat transfer medium. Rapid and uniform roasting of soybeans was accomplished using such equipment. A 33 factorial experimental design was used to determine the effect of the roasting variables on soybeans. Chicken feeding trials and soybean protein availability measurements were used for evaluation.The best roasting conditions were 272° C. salt bed, 20 sec. contact of salt and soybean, and 120 sec. holding time. These roasting conditions also reduced the soybean moisture. Chicken rations containing soybeans roasted at these conditions produced 41 percent and three percent higher weight gains than a raw soybean diet and a commercial soybean meal diet, respectively, at the end of fourth week. It was concluded that the salt bed roasted soybeans were excellent for chick growth.

High Temperature Drying Using a Heated Bed of Granular Salt

High Temperature Drying Using a Heated Bed of Granular Salt

Light from Shocked and Detonating Powders

Blackburn and Seely1 have published evidence that the light from strongly shocked granular salt was largely independent of the interstitial gas. They inferred that it did not (as I had thought2,3) arise from compression of the gas, and assumed that the same conclusion would apply to detonating explosive powders. While this extrapolation is plausible, it would be advantageous to have it confirmed.

Effect of magnesium on formation of calcium phosphate precipitates

The effect of magnesium on the precipitation of gelatinous granular, and “total” calcium phosphates was studied with 1–8 mmoles magnesium/l. Precipitation of these salts was induced by adding dilute sodium hydroxide to the aqueous solutions. Gelatinous calcium phosphate contained less magnesium after suspension in magnesium solutions than, when precipitated in the presence of magnesium. It is concluded that Mg ++ ion (or MgOH +) competes with Ca ++ ion (or CaOH +) for exchange with H + ion of the gelatinous precipitate, and that the greater retention of magnesium obtained by precipitation can be ascribed to lattice incorporation. Granular calcium phosphate did not contain magnesium when precipitated in the presence of magnesium; however, dicalcium phosphate was present in this precipitate, associated in various proportions with granular salt. It appears that the presence of magnesium decreases the rate of conversion of dicalcium phosphate into the more alkaline granular precipitate, resulting in Ca/P ratios closer to those of dicalcium phosphate. “Total” calcium phosphate obtained in the presence of magnesium could be either granular precipitate or dicalcium phosphate (or mixtures of the two), whereas, in the absence of magnesium, a mixture of gelatinous and granular precipitates was obtained. The disappearance of magnesium from the precipitate during the formation of “total” precipitate was gradual, indicating that gelatinous precipitate was dissolving during precipitation of dicalcium phosphate and conversion of the latter to granular precipitate. The solubility product (p k f ) of gelatinous precipitate increased, whereas that of granular precipitate decreased, as the magnesium concentration of the solution was increased.

Precipitation of calcium phosphates from solutions at near physiological concentrations

Precipitation of calcium phosphate was induced at 21 °C and ionic strength 0.08 by adjusting solutions containing between 2 and 24 moles/l. of calcium and phosphate to various pH values between 6 and 8 with sodium hydroxide. At alkali additions below 1.40–1.45 equiv./mole of total phosphorus, the precipitate was dicalcium phosphate dihydrate. At additions of alkali above 1.40–1.45 equiv. mole P. precipitation occurred in two distinct steps: an immediate formation of gelatinous precipitate was followed, after an induction period, by precipitation of a granular salt. The granular precipitate could be obtained alone after removal of the gelatinous phase or in a mixture with gelatinous precipitate (“total” precipitate). The gelatinous, granular, and total precipitates gave (after washing) a diffuse x-ray diffraction pattern of hydroxylapatite, but equilibrated with the supernatant as octacalcium phosphate [ pk t = 1 1 3 p( Ca ++ ) + p( PO 4 −−) + 1 3 p(H +) ]. The Ca P ratio of the gelatinous preipitate increased from approximately 1.33 to 1.67 as the CaOH + ion concentration of the supernatant increased. Granular precipitate ( Ca P = 1.1.10−1.40 ) apparently formed by rapid conversion of dicalcium phosphate into a more alkaline salt. Solubility of gelatinous precipitate [p k f = 12.61 ± 0.05] was higher than that of either granular [p k f = 13.64 ± 0.02] or “total” [p k f = 13.69 ± 0.02] precipitate.