Sintered Beryllium Oxide Research Articles

Thermal expansion of beryllium oxide in the temperature interval 20–1550°C

The results of studies of thermal expansion of the sintered beryllium oxide in the temperature interval 20–1550°C are presented. Measurements were performed by a dilatometric method on a DIL-402C set-up manufactured by NETZSCH (Germany), with the accuracy of (1.5–2) × 10−7 K−1. Approximation dependences of coefficients of linear thermal expansion on temperature have been obtained and reference tables calculated. The data obtained are compared with data from the available literature.

Cleaning surfaces of sintered beryllium oxide

A practical procedure for preparing atomically clean, debris-free surfaces on sintered beryllium oxide specimens has been developed. Chemical, ion-sputter, and UV/ozone cleaning technique were examined in efforts to improve the surface cleanliness. Characterization of the surfaces were performed using Auger electron spectroscopy (AES) to determine the level of cleanliness and scanning electron microscopy (SEM) to examine the surface microtopography. In addition, Rutherford backscattering (RBS) provided information on both bulk and surface contamination. The essence of the practical procedure consists of ultrasonic cleaning in dilute nitric acid followed by a UV/ozone exposure. Such treatments reduced the surface impurity levels for elements with Z > 4 to less than 1 at%. The described procedure should be directly applicable to other sintered oxide materials.

The dosimetric use of beryllium oxide as a thermoluminescent material: A preliminary study

The results of a preliminary study on the dosimetric characteristic of three different grades of commercial sintered beryllium oxide are reported. Among useful features of this promising thermoluminescent material a very low sensitivity to thermal neutrons (0.2 gamma -rads equivalent per 1010 neutrons cm-2), a fairly high sensitivity to gamma -rays, and a good energy response, are emphasized. These properties enable beryllium oxide to be used successfully in mixed fields of thermal neutrons and gamma -rays, such as exist in nuclear reactor facilities.

Irradiation Damage to Sintered Beryllium Oxide as a Function of Fast-Neutron Dose and Flux at 110, 650, and 1100°C

An irradiation program to evaluate BeO as a moderator or fuel matrix material in nuclear power reactors has been completed at the Oak Ridge National Laboratory. The primary objectives were: to esta...

Conductibilité thermique de l'oxyde de béryllium de 1.5 a 300° K

Thermal conductivity measurements have been made in the temperature range from 1.5 to 300° K on samples of sintered beryllium oxide to some of which calcium oxide had been added. A quantitative analysis of the curves x( T) has shown that a relaxation time of the type τ − 1 = α + βω + Aω 4 + δω 2 T 3 gives a good fit to the experimental data, and it has proved possible to relate the coefficients of this formula to several features of the samples. For instance, it is shown that the pores of such a sintered material have an important effect on the thermal conductivity and that the solubility of CaO in these samples is very low.

A study of neutron diffusion in sintered beryllium oxide using the pulsed-source technique

The pulsed-source method has been used to study neutron diffusion in sintered beryllium oxide, the neutron-physics properties of which are not very well known. From this work the diffusion and nuclear constants for thermal neutrons have been obtained (the diffusion coefficient, diffusion length, transport length, effective transport cross section and absorption cross section, the diffusion time and a number of characteristics pertaining to the final stages of the neutron slowing down process).

The high temperature reaction between beryllia and water vapour

Water vapour reacts with beryllium oxide to form a volatile complex. This reaction was studied in the temperature range 1065° C to 1380° C. Steam or moist argon was passed through a static bed of sintered beryllium oxide and weight losses from the bed were measured thermo-gravimetrically. The measurements referred to equilibrium conditions where steam or moist argon became saturated with the volatile complex. Moles of BeO ( nBeO) lost from the bed were measured as a function of nH 2O, the moles of water passed. The ratio nBeO nH 2O at constant temperature was independent of water vapour pressure for pressures between 57 mmHg and 760 mmHg. Weight losses of BeO were a function solely of temperature and water throughput, and can be described uniquely by the equation: log nBeO = 1.62–8.8 × 10 3 T° K+log nH 2O . This equation offers a simple method of estimating maximum annual losses of BeO in a reactor. Some typical estimates are listed.

A study of neutron diffusion in sintered beryllium oxide by a pulse method

BeO, which is an excellent moderator material, possesses high heat resistance, has low absorption cross section, and provides for supplementary neutron multiplication by the Be/sup 9/(n,2n) reaction, is considered a very promising material for high-temperature power reactors. In view of the contradictory data reported in the literature concerning the neutron-diffusion parameters in the sintered material, further thermal neutron-diffusion studies were undertaken using the pulsed-source method. A specimen previously used for determining the slowing-down length (Atomnaya Energ., 13: 258(1962)) was employed in this study. The values of the diffusion coefficient, diffusion length, transport length, effective transport cross section, absorption cross section, and the diffusion time were calculated and plotted. The calculated time of thermalization, 120 mu sec, was considerably lower than the value reported in the literature; this might be due to the approximating assumptions used. (TTT)

Electron Microscopy of Sintered Beryllia

Porosity, etching characteristics, and general microstructural features of extruded and sintered beryllium oxide were studied by electron microscope observation of surface replicas. Both pore structures and etching characteristics were shown to be related to the hemimorphic hexagonal crystal structure of BeO. A form of twinning possible only in hemimorphic systems was also observed.

Thermodynamic Properties of Magnesium Oxide and Beryllium Oxide from 298 to 1,200 °K.

As a step in developing new standards of high-temperature heat capacity and in determining accurate thermodynamic data for simple substances, the enthalpy (heat content) relative to 273 °K, of high purity fused magnesium oxide, MgO, and of sintered beryllium oxide, BeO, was measured up to 1,173 °K. A Bunsen ice calorimeter and the drop method were used. The two samples of BeO measured had surface-to-volume ratios differing by a factor of 15 or 20, yet agreed with each other closely enough to preclude appreciable error attributable to the considerable surface area. The enthalpies found for MgO are several percent higher than most previously reported values. The values are represented within their uncertainty (estimated to average ± 0.25%) by the following empirical equations3 (cal mole−1 at T °K) MgO:HT°−H273.15°=10.7409T+1.2177(10−3)T2−2.3183(10−7)T3+2.26151(105)T−1−3847.94.BeO:HT°−H273.15°=11.1084T+7.1245(10−4)T2+8.40705(105)T−1−5.31245(107)T−2−5453.21.Values of enthalpy, heat capacity, entropy, and Gibbs free-energy function are tabulated from 298.15 to 1,200 °K.

Measuring the moderation length of fission neutrons in sintered beryllium oxide at energies of 1.44 and 0.3 eV

We have measured the density distribution of neutron moderation at energies Er equal to 1.44 and 0.3 eV for a point source of fission neutrons in beryllium oxide and we have determined the squares of the moderation length L f 1.44 → 0.3 2 up to energies of 1.44 and 0.3 eV; they were 92±1.5 and 104.5±2 cm2 (with a beryllium oxide density of 2.79 g/cm3). We found that the experimentally obtained quantity L ℕ 2 (12.5±2.5 cm2) is much larger than that calculated on the assumption of moderation at free beryllium and oxygen atoms. We have chosen synthetic functions of the effect for the moderation density in the form $$P(r_1 E_r ) = K_{n, 2n} \sum\limits_{i = 1}^3 { \frac{{pi}}{{(4\pi \tau _i )^{{\raise0.5ex\hbox{$\scriptstyle 3$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 2$}}} }} e^{ - r^{2/4\tau _i } } ,} $$ agreeing satisfactorily with the experimental data.

The effect of temperature and microstructure of sintered beryllium oxide on the scattering cross section of thermal neutrons

The total effective neutron cross section σt for sintered beryllium oxide in the 0.0025–10 ev neutron energy range was measured by means of a mechanical selector at four temperatures of the scattering sample: 290, 800, 1300 and 1500 °K. Measurements of σt for beryllium oxide samples of different microstructure were also carried out at room temperature. Slight anisotropy of scattering, due to texture, and a marked influence of the size of the crystal grain on σt, due to the extinction effect, were noted.