High-temperature Thermal Expansion Research Articles

The high temperature thermal expansion of graphite parallel to the hexagonal axis

A calculation is made of the effects on the hexagonal axis thermal expansion coefficient of a graphite crystal of the changes in the interlayer forces due to the large interlayer expansions. It is found that the expansion coefficient is significantly increased at temperatures above 800°K and that the magnitudes of the experimental increases up to 3000°K can be readily accounted for.

The high-temperature thermal expansion coefficient of graphite parallel to the basal plane

The high-temperature thermal expansion coefficient of graphite parallel to the basal plane

High-Temperature Thermal Expansion of Certain Group IV and Group V Diborides

The thermal expansions of TiB2, ZrB2, HfB2, NbB2, and TaB2 were measured to temperatures above 1600°C by an X-ray method. Lattice constants were measured for each compound; each had the AlB2-type hexagonal structure. The mean linear thermal expansion coefficients were calculated from the data and are compared to the values found in the literature.

Comment on Paper “High‐Temperature Thermal Expansion Behavior of Refractory Materials, I”

Comment on Paper “High‐Temperature Thermal Expansion Behavior of Refractory Materials, I”

The Effects of Manganese and Iron Oxides on Some Physical and Chemical Properties of Glass

The effects of substituting Na+ and Ca2+ ions by Mn2+ ions in the glass composition Na2O 16, CaO 10 and SiO2 74 and partial replacement of this composition by MnO and/or Fe2O3 on high temperature viscosity, thermal expansion and chemical durability were studied. On replacing Na+ ion by Mn2+ ion the high temperature viscosity and coefficient of thermal expansion decreased and the chemical durability increased. Substitution of Ca2+ ion by Mn2+ ion had similar effect but to lesser extent. On partial replacement of the glass composition by MnO and/or Fe2O3, the high temperature viscosity decreased and chemical durability increased.

Thermal Expansion of AgCl

The thermal coefficient of expansion of AgCl has been measured as a function of temperature from 120 to 710\ifmmode^\circ\else\textdegree\fi{}K (melting point = 728\ifmmode^\circ\else\textdegree\fi{}K) by means of x-ray diffraction from small single crystals. Above 300\ifmmode^\circ\else\textdegree\fi{}K the results agree well with the dilatometric measurements reported by Strelkow. Such agreement indicates that the concentration of Schottky defects in AgCl is not large enough to influence significantly the thermal expansion below 710\ifmmode^\circ\else\textdegree\fi{}K. The thermal expansion for the entire temperature range is described rather well by Gr\uneisen's theory, (1) if it is assumed that thermally generated Frenkel defects contribute significantly to the high-temperature thermal expansion, and (2) if two parameters in the theory are chosen to give a good fit to the low-temperature ($Tl300$\ifmmode^\circ\else\textdegree\fi{}K) x-ray data. Attempts to determine the activation energy of the Frenkel defects from comparison of the thermal expansion data with theory indicate that certain constants of the theory are probably temperature dependent. Below 300\ifmmode^\circ\else\textdegree\fi{}K the x-ray results differ significantly from the dilatometric results reported by Sreedhar. Low-temperature x-ray measurements of the thermal expansion of Al are, therefore, included and compared with existing data in the literature to demonstrate the validity of our experimental technique. The especially convenient experimental technique used is described.

High temperature allotropy and thermal expansion of the rare-earth metals

By means of high temperature X-ray techniques the crystal structure of lanthanum, cerium, praseodymium, neodymium, ytterbium, and possibly gadolinium was found to be body-centered cubic at temperatures near their respective melting points. For ytterbium a hexagonal close-packed structure was also observed, which was shown to be stabilized by atmospheric impurities. Evidence for possible high temperature crystalline transformations in gadolinium, terbium, dysprosium, holmium, and lutetium was obtained by means of electrical resistance measurements; erbium gave no such evidence. X-ray data were used to derive empirical equations which describe thermal expansion coefficients of scandium, yttrium and the rare-earth metals. Europium exhibits a rapidly decreasing coefficient of expansion with increasing temperature, which may be a consequence of a gradual promotion of one of the 4f electrons into the conduction band. The hexagonal rare-earth metals were found to have nearly the same axial ratio at their respective transformation temperatures.

High Temperature Structure and Thermal Expansion of Some Metals as Determined by X-Ray Diffraction Data. I. Platinum, Tantalum, Niobium, and Molybdenum

The crystal structure and thermal expansion of platinum, tantalum, niobium, and molybdenum have been determined between 1100° and 2500°K. These metals were found to undergo a uniform thermal expansion over the temperature range of this investigation and to undergo no structural change. The permanent elongation of tantalum wires, produced by annealing at temperatures between 2473° and 2773°K, appears to be caused by reorientation of crystal grains in the specimen and to preferred direction of crystal growth during annealing, rather than to a change in crystal structure. Quadratic equations have been developed for the thermal expansion of platinum, tantalum, niobium, and molybdenum. These equations are represented, respectively, by Δa0/a0=7.543×10−6(T−291)+2.362×10−9(T−291)2,Δa0/a0=6.080×10−6(T−291)+7.50×10−10(T−291)2,Δa0/a0=7.591×10−6(T−291)+6.96×10−10(T−291)2, and Δa0/a0=0.987×10−3+2.40×10−6(T−273)+2.20×10−9(T−273)2. Values of the expansion coefficient α were computed for each of the metals by differentiating the above equations. Our values were compared with those obtained from the Grueneisen theory and indicate that the theory provides a reasonably satisfactory means of extrapolating thermal expansion data obtained at low and moderate temperatures.