Materials Literature
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Abstract A study has been carried out on block polymers of the A‐B‐A type, the thermoplastic elastomers, where A represents polystyrene and B polybutadiene or polyisoprene. The objective was to relate the mechanical properties of these elastomers to their molecular architecture. For this purpose a series of styrene‐bu…
A theoretical analysis of the electric-field distribution in the ionisation layer of a d.c. corona discharge under equivalent steady-state conditions is presented for both positive and negative polarities of the conductor. Using available experimental data on ionisation and attachment coefficients in air, the conditio…
Strong electric fields have been applied to dielectric polymer films to study field-induced mechanical stresses. For voltages near breakdown the mechanical forces are sufficient to cause localized deformation in some polymer films. Considerable field enhancement can occur at the deformation sites, leading to reduced n…
Abstract A transmission electron‐microscopy study of high‐angle grain boundaries has been made. When thin foils are cut in precisely oriented bicrystals of aluminium, some details of the grain‐boundary structure appear. Micrographs of symmetrical tilt boundaries around [001] show linear defects parallel to the tilt ax…
Zirconium diboride and hafnium diboride were fabricated by hot‐pressing at 1800°C and 120,000 psi. Bend strengths were measured on the fully dense materials from 25° to 1400° C in an argon atmosphere. These diboride compounds do not exhibit any gross plastic flow in the temperature range studied. The bend strengths go…
Abstract Coefficients of thermal expansion α‖ c and α ⊥ c between 4 and 800°K have been measured for zinc oxide using an interferometric and a capacitance method. Thermal properties of wurtzite lattices (two coefficients of thermal expansion and a pyroelectric constant) can be described in terms of three thermal equat…
In two possible symmetry sites exist for the Eu +3 ions, namely S 6 and C 2 . The emission spectrum is primarily due to ions but two additional lines are reported corresponding to emissions. The lines were identified by their long lifetime relative to the C 2 emission and represent the Stark splitting of the transitio…
Abstract Planare Komplexe, vor allem die des Platins, können Strukturen mit linearen Ketten von Schwermetallatomen mit Metall‐Metall‐Abständen bis herab zu 3,1 Å bilden. Die Bindung in derartigen Ketten läßt sich durch partielle Oxidation verstärken, wodurch die Abstände bis auf 2,8 Å verringert werden können. Dabei b…
Although many test specimens have been developed to measure fiber-matrix interfacial strength, they typically suffer from a lack of reproducibility and produce data with coefficients of variation greater than 10 percent. This paper reviews methods thus far employed to evaluate fiber-matrix interfacial strengths includ…
Although a wide range of aromatic polycarbonates has been synthesized and examined [1–3], the term polycarbonate usually refers to the commercially available poly[2,2-propane-bis(4-phenyl carbonate)], i.e., and this polymer is discussed exclusively in the present review. Polycarbonate possesses a number of attractive…
Abstract The rate of attrition of a catalyst sample, of a single particle size, can be expressed by a simple function of initial diameter and time. The initial rate is a function of initial diameter, whereas the decrease in attrition rate of a catalyst of a given size as it ages depends only on time. The attrition equ…
Abstract Homogeneous nucleation followed by diffusion controlled crystal growth was observed in highly supersaturated solutions of BaSO 4 , BaCrO 4 , BaMoO 4 , BaWO 4 , BaCO 3 , PbSO 4 , PbCrO 4 , PbCO 3 , SrSO 4 , and CaWO 4 . In the range of concentrations where the number of homogeneously nucleated particles is lar…
A study is made on the reaction of nitrous oxide with copper surfaces. As with germanium, the reaction has an activation energy that increases with coverage. The transition from surface to bulk oxidation sometimes involves an incubation time. The reaction at 90°C and 20 cmHg gives a coverage of about unity, and is use…
Large single crystals of and can be grown by Czochralski pulling from the melt. In the case of a small amount of excess is used to avoid incongruent crystallization. Both materials show pronounced cleavage very similar to that of mica. The electrical properties of are also very similar to those of mica, making this ma…
Abstract A new expansion cell for the three‐terminal capacitance method is developed. Length changes in the order of 10 −9 cm can be measured at samples of only 4 mm. At first the expansion coefficient of silicon (reference material) is investigated in detail from 20 to 300 °K. The work is completed by interferometric…
This paper treats the development of pertinent theories that establish the properties of the fiber-matrix interface needed to achieve efficient composites and the development of a test technique to measure these properties. An equation is derived that relates the externally applied load to the failure mode, fiber tens…
Abstract The simultaneous diffusion of 64 Cu and 67 Cu has been measured in copper single crystals from 890 to 1061 °C. The strength of the isotope effect f Δ K is 0.684 ± 0.014 and is independent of temperature within the experimental error. This indicates that the contribution of divacancies to self‐diffusion in cop…
Abstract Optical absorption measurements on thick monocrystalline samples of GaSe 1− x S x show that in these mixed crystals the lowest energy gap is indirect in the complete range 0 ≦ x ≦ 1. These results are contrary to earlier reports which indicate that GaSe is a direct gap semiconductor. In the case of GaS the ab…
Metastable glass‐in‐glass separation was observed on rapid quenching of A1 2 O 3 ‐SiO 2 melts containing from 10 to 50 mol% A1 2 O 3 . Nucleation and subsequent crystallization of mullite within the high‐alumina‐dispersed glass phase may occur either during cooling from the melt or on reheating. The metastable binary…
It is shown that a suitable curve fitting procedure can reduce the standard deviation of intensity measurements made with a scanning diffractometer except when the intensity is large in relation to the background level. The procedure has been implemented with an Arndt–Phillips linear diffractometer, on-line to a Ferra…