Alkaline-earth oxides powders

Absorption, Excitation, and Emission Bands of the Alkaline-Earth Oxide Powders... 

K. Reproduced with permission and minor adaptation from ref. 39(b). (b) Reflectance spectra in the UV—visible range from alkaline earth oxide powders with high surface areas. Reproduced with permission from ref. 48. 

Small quantity of crystalline material of cnbic stractnre for study [e.g., alkali hahdes, alkaline earth oxides, cnprons or silver halides, simple metals such as aluminum or copper (finely powdered with a file)] liqnid (medinm boiling petroleum ether) for density woik. 

In relation to the surface defects on the group II alkaline earth oxides, EPR has been instrumental in unraveling the electronic structure of the defects on both polycrystalline and well defined single crystal surfaces. These trapped electron centers can be formed in a number of different ways. The most convenient means on powders is by exposure of the alkaline earth oxide, such as MgO, to hydrogen atoms [22]. Spontaneous ionization of the H atoms occurs with the subsequent formation of excess electrons on the surface ... 

Parts with an open coherent porosity of >20% are used in vacuum tubes and aeronautics because of refractoriness, shape stability, and chemical resistance. Examples are porous cathodes impregnated with alkaline earth oxides as electron-emitting sources in special tubes, thermoionic converters heated by nuclear energy, and ionic propulsion units with porous tungsten plates as ionic sources for Cs vapor of high temperature. Those emitter plates are made of globular tungsten powder (7 pm) density 75-85%, pore size 2-30 pm, and pore number 1.4 x 10 -8 x 10 cm . ... 

DIHYDROXY-2-BUTYNE (110-65-6 54141-09-2) C4H5O2 Combustible solid. May react violently with strong acids, bases, alkali metals and alkali earth hydroxides halides basic catalysts, including magnesium oxide, calcium oxide (quicklime), alkaline earth oxides, etc. On small fires, use dry chemical powder (such as Purple-K-Powder), alcohol-resistant foam, or COj extinguishers. 

Figure 1 shows the powder XRD patterns of polycrystalline BT2 with alkaline earth oxides at the composition that the second phases began to be identified in the specimens. For polycrystalline BT2 with CaO substitution, second phases were not identified at any composition by XRD analysis. For polycrystalline BT2 with SrO and MgO substitutions, second phases began to be identified at the composition about x = 0.15 and 0.05, respectively. 

The purity of the silica powder obtained by drying the sol is important in that it must not contain substances which promote the devitrification of silica at the sintering temperature. Thus, substantial quantities of impurities such as the alkali and alkaline earth oxides are especially to be avoided and these compounds should be removed as thoroughly as possible from the sol employed in making the silica powder. Generally speaking, the total content of potassium, sodium and calcium oxides, for example, in the powder should not exceed about 0.1% and preferably less than 0.01%. The exact level depends to some extent upon whether these impurities are on the surface of the particles or are locked within the silica structure. Thus, a few hundredths of a percent of combined sodium within the particles is not as harmful as this amount of combined sodium on the surface of the particles. 

Electronic Transport, General Description. Magnesium Oxide (MgO). Electrical transport measurements on alkaline earth oxides encounter several difficulties, such as high resistance at low temperatures, a strong influence of surface layers, and high-temperature thermionic emission. The partly contradictory results depend considerably on the purity and nature of the samples (pressed porous powders, sintered samples, polycrystals, and single crystals) and on the experimental conditions. 

Bina Selenides. Most biaary selenides are formed by beating selenium ia the presence of the element, reduction of selenites or selenates with carbon or hydrogen, and double decomposition of heavy-metal salts ia aqueous solution or suspension with a soluble selenide salt, eg, Na2Se or (NH 2S [66455-76-3]. Atmospheric oxygen oxidizes the selenides more rapidly than the corresponding sulfides and more slowly than the teUurides. Selenides of the alkah, alkaline-earth metals, and lanthanum elements are water soluble and readily hydrolyzed. Heavy-metal selenides are iasoluble ia water. Polyselenides form when selenium reacts with alkah metals dissolved ia hquid ammonia. Metal (M) hydrogen selenides of the M HSe type are known. Some heavy-metal selenides show important and useful electric, photoelectric, photo-optical, and semiconductor properties. Ferroselenium and nickel selenide are made by sintering a mixture of selenium and metal powder. 

To obtain effective materials for catalytic combustion, Arai and co-workers developed a preparation method based on the hydrolysis of the alkoxides of the components.12 This sol-gel method was originally developed to prepare high-purity submicron powders of alkaline or alkaline-earths titanates or zircon-ates.13,14 The method is particularly suitable for low-temperature production of mixed oxides due to the effective mixing of the components at the atomic level that can be obtained in the gel precursor. 

J. Reich 6 also patented a process based on the calcination of the alkali fluosilicate or fluoborate with an oxide of the alkaline earths. When the calcined mass is lixiviated with water, the alkali fluoride is obtained in soln. L. Schuch 6 made sodium fluoride by boiling finely powdered cryolite with a cone. soln. of sodium hydroxide—the alumina and silica pass into soln.—sodium fluoride crystallizes from the cooling soln. Sodium silicate can be used in place of the hydroxide. F. Jean made sodium fluoride by leaching a calcined mixture of fluorspar, limestone, Glauber s salt, and charcoal. 

The perdisulphates of the alkaline earth metals may be prepared by grinding together, with a little water, molecular proportions of the metal oxide and ammonium perdisulphate,10 and drying the mixture in a vacuum. The resulting mass is carefully powdered and the metal... 

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