Adsorption of Admixtures on Portland Cement Hydration Products

The adsorption of calcium lignosulfonate and salicylic acid was studied on the hydration products of the four principal components of portland cement. To investigate the adsorption as a function of development of hydration product, the determinations were made after varying hydration times. The times allowed were from 5 min to 24 hr for tricalcium aluminate (C₃A) and tetracalcium aluminoferrite (C₄AF) and from 1 hr to 28 days for β-dicalcium silicate (β-C₂S) and tricalcium silicate (C₃S). Samples were characterized with respect to surface area and poresize distribution. The effect of gypsum on the adsorption was also investigated. The results indicate that the amounts of salicylic acid and calcium lignosulfonate adsorbed on the hydration products of C₃A, and of calcium     

RHEOLOGICAL CHARACTERIZATION OF COMMERCIALLY PROCESSED FLUID MILKS

Flow profiles of commercially processed whole, two-percent, one-percent and nonfat milks with added solids as well as skim milk without added solids were measured using a rotational steady shear viscometer. Also tested were mixtures of concentrated skim milk added to skim milk over a range of 9.7% to 20.2% total solids. A shear rate range of 121 to 486 s^-1 was used with a cone and plate geometry. In all cases, linear plots of shear stress versus shear rate with small nonzero intercepts were obtained.     

Spontaneous Cracking in Unfired Magnesia Compacts Upon Standing in Air

Analytical-grade magnesium oxide powder without binder was compressed hydrostatically to 50,000 lb. per sq. in. to form compacts. When exposed to moist air immediately after pressing, these compacts developed irregularly shaped cracks. Controlled tests, in which these compacts were exposed for various lengths of time to various atmospheres, indicated that in general water vapor, carbon dioxide, and residual stresses had to be present if cracking was to occur. The probable cause of the cracking was the formation of a less dense and mechanically weak basic carbonate of magnesium at crystallite surface points of high stress concentration which developed during the compacting. The adsorption of dry CO₂ at such sites prevented subsequent delayed fracture.     

HISTAMINE PRODUCTION BY FOOD-BORNE BACTERIAL SPECIES12

A total of 112 bacterial strains representing 38 species were tested for their potential to elicit food poisoning outbreaks via histamine formation in foods. Proteus morganii and Enterobacter aerogenes displayed a quantitative superiority in terms of histamine production on a trypticase-soy broth-histidine (TSBH) medium and a tuna fish infusion broth (TFIB). When bacteria were incubated under standardized conditions in TSBH medium, histamine accumulated to levels exceeding 50 nmoles/ml of media with a total of 23 strains, including 13 of 15 P. morganii strains, 3 of 3 E. aerogenes strains, 3 of 12 Hafnia alvei strains, 1 of 4 Providencia alcalifaciens strains, 1 of 5 Enterobacter cloacae strains, 1 of 1 Proteus rettgeri strains, and 1 of 1 Citrobacter diversus strains. However, only 8 of the 15 P. morganii strains and the 3 E. aerogenes strains were capable of generating histamine in excess of 200 nmoles/ml in the TSBH medium. Of the 23 strains capable of appreciable histamine production in TSBH medium, P. morganii and E. aerogenes were, by far, the most prolific histamine producers in TFIB. Of the organisms tested, only P. morganii and E. aerogenes would appear to have the capability of forming sufficient histamine in scombroid fish products to elicit food poisoning outbreaks.     

Strengthening by Ion Exchange

This paper is a brief review of the physical and chemical methods of strengthening glass, in particular that due to the large for small ion exchange resulting from treatment in molten salt at temperatures below the annealing range for the glass. Abrasion of treated glass is shown to reduce markedly the strength of experimental alkali-lime-silica glasses as well as commercial glasses of this and other types. Treated alkali-alumina-silica and alkali-zirconia-silica glasses, however, are less affected by abrasion. Strength after abrasion increases with alumina or zirconia content, reaching 117,000 psi for cane of a 35% alumina glass. The explanation for the aluminum or zirconium effect may involve an unusual ionic environment caused by their presence in the lattice.     

WILL CONSUMERS ACCEPT IRRADIATED FOODS?

Assays of consumer attitudes, qualitatively via a focus group and quantitatively through questionnaires, determined that freshness of produce, fish and poultry is important to consumers, but because of the availability of fresh foods and ready access to refrigeration, there is no real demand to extend the shelf-life of foods. Consumers initially respond negatively to the idea of irradiated food, but information about the process and long-term experimental feeding results, as well as straightforward labelling terminology (no euphemisms) will influence some consumers to purchase and try irradiated foods.     

Phase Equilibria in the Alkali Fluoride-Uranium Tetrafluoride Fused Salt Systems: III, The System NaF–LiF–UF4

The phase equilibrium diagram of the ternary system NaF–LiF–UF₄ described in this paper is based on evidence from thermal analysis and from microscopic and X-ray analyses of samples obtained from thermal gradient quenching experiments. Temperature-composition relations were established through the temperature interval between the liquidus and a lower limit of about 300°C. All the stable compounds in the binary systems LiF–UF₄ and NaF-UF₄, (including the subsolidus compound NaF·2UF₄) display primary phase fields in the ternary system. No ternary compounds of NaF–LiF–UF₄ occur. The following eutectics are to be found in the ternary system: 60 NaF, 21 LiF, 19 mole % UF₄, 480°C.; 35 NaF, 37 LiF, 28 mole % UF₄, 480°C.; 24.3 NaF, 43.5 LiF, 32.2 mole % UF₄, 445°C.; and 24.5 NaF, 29 LiF, 46.5 mole % UF₄, 602°C. The compounds 7NaF · 6UF₄ and 7LiF · 6UF₄ display limited solubility in each other. The exact limits of the miscibility gap in the 7NaF · 6UF₄-7LiF · 6UF₄ join have not been determined.