Magnetic Ceramics: I, General Methods of Magnetic Ferrite Preparation

Various methods of preparing the technically important ferrospinels are discussed; particular attention is given to the reactivity and homogeneity of the final mixture. The reactivity and intimacy of mixing of the initial components may be improved by the use of chemical methods of comminution and mixing, viz., thermal decomposition of the mixed chemicals, chemical precipitation of the components, or ignition of the components in a fine state of division. The use of controlled partial pressures of oxygen (CO₂-CO mixtures) for the preparation of magnetite and manganese ferrite is discussed. The feasibility of the application of these methods on a commercial scale is outlined.     

Determination of Biaxial Compressive Strength of a Sintered Alumina Ceramic

The compressive strength of commercial high-density alumina was measured in several compressive biaxial stress states. The compressive strength was only slightly affected by the magnitude of the intermediate principal stress. The average value of the compressive strengths measured in all stress states, excluding the equibiaxial and the near-uniaxial compressive stress states, was 528 ksi. The average of the coefficients of variation was 3%. The tensile strength measured for the material indicates that the ratio of compressive strength to tensile strength is ∼ 18.     

A NOTE ON THE FACTORIAL INVARIANCE OF THE FEMALE FORM OF THE SVIB.

THE FACTORIAL STRUCTURE OF AN EARLY AND RECENT FEMALE FORM OF THE SVIB WAS COMPARED. IT WAS FOUND THAT 2 OF THE LARGEST FACTORS ISOLATED IN THE RECENT STUDY WERE HIGHLY SIMILAR TO 2 OF THE 4 FACTORS ISOLATED IN THE EARLIER STUDY. THE REMAINING 2 FACTORS ISOLATED IN THE EARLIER STUDY SHOWED MODERATE SIMILARITY TO 2 ADDITIONAL FACTORS OUT OF THE 9 FACTORS FOUND IN THE RECENT STUDY. IT WAS CONCLUDED THAT, IN GENERAL, THE FACTORIAL STRUCTURE OF THE 2 FORMS WAS QUITE SIMILAR. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inhomogeneity-Packing Density Relations in Binary Powders—Experimental Studies

The purpose of this investigation was to determine if the bulk specific volume of inhomogeneous binary powder mixtures, with a large size ratio, corresponds to the theoretical values calculated from known compositional inhomogeneity data. The theoretical calculations are based on the assumption that the body packs according to the Furnas model on a local scale. To minimize the effects of particle geometry, experiments were performed with glass microbeads.     

Magnetic Ceramics: V, Magnetic Properties of Square Loop Ferrites Within the System MgO-MnO-Fe2O3

Thirteen compositions within the center of the system MgO-MnO-Fe₂O₃ were investigated because of their rectangular hysteresis-loop characteristic. Initial permeabilities were measured, and B_m, B_T, H_c , and R_8m were obtained from quasi-static hysteresis loops. High MgO content was found to be detrimental to the magnetic properties and to impair the loop rectangularity. The highest hysteresis-loop squareness ratio, R, _8m , was found in a composition with high Fe₂O3 content, and the lowest coercive force, H_c , was found in a composition with high MnO content.     

X-Ray Studies of Lime-Bentonite Reaction Products

Calcium aluminate and calcium silicate hydrates were formed in mixtures of bentonite with water and various types of lime which had been sealed and cured for up to three years at 23°± 2°C and 100% relative humidity. Methods of analysis were X-ray diffraction and electron microscopy. Hydrothermal treatment of the cured mixtures at 170°C for 12 hr produced well-crystallized tobermorite with apparent lattice substitution of aluminum. The same result was obtained by hydrothermal treatment of identical uncured mixtures.     

GENERAL AND KINETIC ASPECTS OF PRE-RINSE AND CLEANING OF A MILK STORAGE TANK

With the aim of studying pre-rinsing and cleaning of a milk storage tank, different representative samples are collected during the process and their components (protein, sugar and lipid) analysed. The main conclusions of this study may be summarized as follows: (1) The mean thickness of milk remaining in the tank ranges around 20 μm. It depends on the dropping time and on the possible presence of milk foam. (2) The different main milk components do not exhibit the same removal rate and sugar seems to be completely removable by rinsing only. (3) Prerinsing may be characterized by four periods of which one depends on a diffusion mechanism. (4) Pre-rinse is a very rapid process which mainly depends on the pre-rinse solution volume used per unit of soiled surface. (5) Hard water, osmosed water alone or admixed with a surface active agent or caustic soda (1%) lead to the same results.     

Characterization of Hot-Pressed Cement Pastes

Very-high-strength cement pastes (compressive strengths ∼100,000 psi) were prepared using hot-pressing techniques at temperatures up to 250°C. The results of characterization studies summarized include X-ray diffraction, DTA, ir spectra, and microstructural investigations. Much less Ca(OH)₂ is formed than in normally hydrated pastes. Some well- crystallized hydroxyl-containing hydrates, C₅S₂H, C₃SH_1.5, C₃AH₆, and C₄A₃H₃, as well as poorly crystalline CSH, are formed. The structure of the CSH, as revealed by ir absorption studies, does not appear to be very different from that in low- temperature hydrated cement pastes. Microstructures are extremely dense and, in some cases, the sulfate-containing phase concentrates along original grain boundaries.