Precision measurements of small differences between linear expansion coefficients in the 4?80�K range

1978 ◽  
Vol 21 (12) ◽  
pp. 1693-1695
Author(s):  
V. P. Popov ◽  
V. A. Pervakov
Keyword(s):  
Linear Expansion ◽  
Precision Measurements ◽  
Expansion Coefficients

Application of digital image correlation method in measuring linear expansion coefficients of WC/Cu composites

2013 ◽  
Vol 21 (10) ◽  
pp. 2696-2703 ◽  
Author(s):  
俞海 YU Hai ◽  
郭荣鑫 GUO Rong-xin ◽  
夏海廷 XIA Hai-ting ◽  
颜峰 YAN Feng ◽  
张玉波 ZHANG Yu-bo ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Linear Expansion ◽  
Correlation Method ◽  
Image Correlation ◽  
Digital Image Correlation Method ◽  
Expansion Coefficients

scholarly journals Temperature changes in the crystal structure of barium titanium oxide

1947 ◽  
Vol 189 (1017) ◽  
pp. 261-283 ◽  
Keyword(s):  
Titanium Oxide ◽  
Room Temperature ◽  
Transition Point ◽  
Linear Expansion ◽  
Temperature Structure ◽  
Barium Titanium Oxide ◽  
Temperature Changes ◽  
X Ray ◽  
Expansion Coefficients ◽  
Barium Titanium

Barium titanium oxide, which is tetragonal at room temperature, changes about 120° C to a cubic structure. This change has been followed in detail by means of X-ray powder photo­graphs taken in a 19 cm. powder camera at intervals of a few degrees over a range covering the transition point. The unit cell, which contains the formula number of atoms, retains its identity throughout the transition, and the atomic parameters are unaltered. The change is simply in the axial lengths, and these vary continuously with the temperature, though not linearly, the varia­tion becoming more rapid near the transition point. While the linear expansion coefficients along and perpendicular to the tetrad axis are large and of opposite sign, the volume expan­sion coefficient is small and positive. There is no discontinuous change either of linear spacing or of volume detectable at the transition point, but there is a sharp discontinuity in the linear expansion coefficients, and a marked increase in the volume expansion coefficient which is probably, though not certainly, discontinuous. The transition suggests a typical λ-point change. The specific heat has not been deter­mined, but the thermal expansion curve has the characteristic λ shape. Co-existence of cubic and tetragonal structures, in proportions depending on the temperature, occurs over a range of some degrees near the transition point, and is attributed to the effect of local stresses in facilitating or hindering a change between two structures whose energy difference is very small in this temperature range. Below room temperature, observations made down to -183° C suggest that the structure may have a second transition point somewhere below this and become cubic again, the change being of the same nature as that at 120° C. It is argued that the room-temperature structure can only be explained by the existence of directed bonds, and that the breaking of these bonds with increasing temperature is respon­sible for the 120°C transition. The low-temperature transition is explained by postulating a more complete set of bonds, probably an octahedral complex, which partially breaks down at this temperature to give the square formation observed in the room-temperature structure. The possible nature of the directed bonds is discussed qualitatively. The condition which makes possible the formation of such bonds is likely to be the abnormal volume available to the Ti atom, which is due to the effect of the large Ba ion in forcing apart the oxygen lattice. The directed bond system will only contribute a small part to the attractive energy of the lattice, which is mainly ionic in character. The hypothesis that directed bonds exist, whatever their origin, is used for a tentative explanation of anomalous variations of intensity of the X-ray lines observed at temperatures near the transition point.

Polymorphism in Ho2(MoO4)3

2013 ◽  
Vol 28 (S2) ◽  
pp. S33-S40 ◽  
Author(s):  
C. González-Silgo ◽  
C. Guzmán-Afonso ◽  
V. M. Sánchez-Fajardo ◽  
S. Acosta-Gutiérrez ◽  
A. Sánchez-Soares ◽  
...  
Keyword(s):  
Phase Transition ◽  
Thermal Expansion ◽  
Room Temperature ◽  
Linear Expansion ◽  
Negative Thermal Expansion ◽  
Thermal Treatments ◽  
Positive Coefficient ◽  
X Ray ◽  
Expansion Coefficients ◽  
First Time

Two polymorphs of Holmium molybdate, known as β'-phase and γ-phase, were prepared by solid state reaction with different thermal treatments. These polycrystalline samples have been studied for the first time by X-ray thermodiffractometry from room temperature up to 1300 K. We found that the initial β'-phase undergoes a transition to a β-phase and then to a γ-phase. The γ (hydrated)-phase, turns to the γ (dehydrated)-phase and then to the β-phase. Each sequence involves a reversible and an irreversible phase transition for Ho2(MoO4)3. Both polymorphs have remarkable physical properties like nonlinear optics, ferroelectricity and negative thermal expansion. We have calculated the linear expansion coefficients of both phases. We have obtained a positive coefficient for the β'-phase and a negative one for the γ-phase. Moreover, we have made a comparison of the obtained coefficients with previous results for other rare earth molybdates.

Linear-expansion coefficients of glass-fiber-reinforced plastics based on polymethylsiloxane resin, up to 1000�C

1975 ◽  
Vol 10 (3) ◽  
pp. 449-452
Author(s):  
B. A. Kiselev ◽  
I. V. Sobolev ◽  
V. S. Shpet ◽  
V. V. Mayakov ◽  
G. A. Ivanov
Keyword(s):  
Glass Fiber ◽  
Linear Expansion ◽  
Fiber Reinforced ◽  
Reinforced Plastics ◽  
Glass Fiber Reinforced ◽  
Fiber Reinforced Plastics ◽  
Expansion Coefficients

Study on Inorganic Cohesive Glue

2011 ◽  
Vol 335-336 ◽  
pp. 1215-1218
Author(s):  
Zeng Li ◽  
Xiang Yong Guo ◽  
Ding Yan Wu ◽  
Yan Hua Zhang
Keyword(s):  
Linear Expansion ◽  
Physical Property ◽  
High Strength ◽  
Temperature Deformation ◽  
Concrete Repair ◽  
Internal Forces ◽  
Expansion Coefficients ◽  
Deformation Coefficient ◽  
Mean Time ◽  
Better Than

In concrete construction, it is usual to encounter integrating problems between old and new concrete interfaces, such as disease concrete’s repairing and anchoring, concrete blocking construction and etc. Due to low cohesion strength between old and new concrete interfaces, weak interface is formed, then old and new concrete cannot construct as an integrate whole which tends to be damaged along the interfaces after being loaded and results in hidden danger. Regarding of this situation, the paper optimizes the mix on the base of mixes tests on inorganic cohesion material used between old and new concrete interfaces. When the material is used to old and new mortar interfaces and old and new concrete interfaces, cohesion tensile strength in interfaces equates or is higher than that of mortar itself and concrete itself; In the mean time, through permeability test the impermeability in the interface equates that of concrete itself, eliminating weak interfaces between old and new concrete. Physical property tests show that the material’s mechanical property is better than that of concrete, deformation property is close to concrete’s, especially linear expansion (temperature deformation) coefficient is basically consistent with that of concrete, avoiding peel-off damage after repeated internal forces due to too much difference between linear expansion coefficients when organic cohesion material is used. By analysis of hydraulic productions in interfaces and micro structure, the mechanism of inorganic cohesion glue is illuminated. It results in satisfying cohesive effect when optimized inorganic cohesion material is applied to high-strength concrete repair and RCC interfaces.

scholarly journals Pre-heating by defocusation of the CO2-Laser polishing beam: an experimental report from the lab-floor -INVITED

2021 ◽  
Vol 255 ◽  
pp. 03001
Author(s):  
Jens Bliedtner ◽  
Oliver Faehnle ◽  
Anne-Marie Layher ◽  
Robin Hassel ◽  
Andrea Barz
Keyword(s):  
Laser Beam ◽  
Linear Expansion ◽  
Limited Extent ◽  
Cooling Process ◽  
Polishing Process ◽  
Optical Components ◽  
Optical Glasses ◽  
Preheating Temperature ◽  
Expansion Coefficients ◽  
Quartz Glasses

The laser beam polishing for glass and plastics is a purely thermal process and melts the ground or lapped structures to a depth of limited extent. This results in a smoothing of the surface, whereby the 1st - 4th order shape deviations can be corrected very well and transparent surfaces are created. The process is excellently suited for quartz glasses and other optical glasses with a low coefficient of expansion α. Furthermore, thermoplastics or metallic molds for injection molding and precision molding applications can also be polished with the laser beam. On the other hand, special measures are required for glasses with a high α, e.g. preheating of the component. For the investigations, a defocused laser beam was used for the defined preheating of glasses with high linear expansion coefficients. After reaching the material-specific preheating temperature, the laser beam was focused and the polishing process started. A defined cooling process follows again with a defocused beam. In this way, a ground biconvex lens made of boron crown glass was successfully polished. The laser-polished surfaces have an RMS value of 1- 3 nm. The polishing process can be used very flexibly. Likewise, very differently shaped optical components can be polished. The newly developed polishing regime is transferable to other optical glasses with high linear expansion coefficients.

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