ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1961.tb15371.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

The sintering behavior of beryllia in a reducing atmosphere was studied between 1500° and 2100°C. Above 1700°C. the firing temperature had only a small effect on the density after heating for 24 hours. Examination of the time dependence of sintering showed that at 1700°C. during the first 3 to 5 hours there was a large increase in the density of the body accompanied by a simultaneous rapid rate of grain growth. Firing for longer times resulted in more moderate increases in both density and grain growth. The grain‐growth characteristics of beryllia were unchanged by most oxide additions although compacts of higher density resulted. Oxide additives which formed a liquid phase at the sintering temperature enhanced both the sinterability and grain growth of ber

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1961.tb15372.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Fused aluminum oxide containing a small amount of nitrogen (as added aluminum nitride) showed X‐ray powder diffraction patterns similar to the δ‐alumina obtained from the calcination of alumina mouohydrate in dry air. About 1% nitrogen was adequate for complete conversion of the α phase to the δ phase. A fused mixture containing 3.9% nitrogen showed a powder pattern identical to lithium ζ

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1961.tb15373.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

The rate of oxidation of silicon carbide was studied at different partial pressures of water vapor. The diffusion‐rate constant was found to vary with the logarithm of the partial pressure of water vapor according to the theory of thin‐film oxidation as proposed by Engell and Hauffe. The products of oxidation were cristobalite and tridymite, depending on the temperature. The diffusing species appeared to be the same in the presence of partial pressures of water vapor and in the presence of partial pressures of oxy

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1961.tb15374.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Electron microscopic studies of sintered hexagonal ferrites have revealed growth structures which indicate that crystal growth from a relatively highly saturated vapor phase occurs above certain temperatures during the sintering process. Illustrations of variations in the growth structures at various locations in the ferrite are given, and the probable importance of the vapor‐phase growth mechanism in the over‐all sintering process is discus

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1961.tb15375.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

The basic mechanism of adherence in high‐alumina ceramic‐to‐metal sealing has been studied. A sealing mechanism has been established which involves the migration of the glassy phase of the high‐alumina ceramic into the interstices of the molybdenum‐based coating. The study was conducted on 94 and 99% aluminas, using molybdenum‐manganese, molybdenum‐titanium, and pure molybdenum metallizing compositions. The possibility of the formation of chemical compounds by either the molybdenum or the added metals has also been studied. A means of isolating and identifying any reacted or migrated phases has b

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1961.tb15376.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

The alkaline earth‐boric oxide‐silica systems are especially important in the compounding of ceramic glazes and bodies because they enable the introduction of B2O3in an insoluble form. Published equilibrium eutectics and other low‐temperature invariant points were investigated regarding temperatures and rates of deformation. Most of these compositions were found to be soluble in acid, alkaline, and phosphate solutions; tests in distilled water at 195°F. for 5 days therefore were chosen as the means of selecting the compositions which would be practical for use in the development of ceramic glazes. The systems BaO‐B2O3‐SiO2, CaO‐B2O3‐SiO2, and SrO‐B2O3‐SiO2were studied first separately; the insoluble composition highest in B2O3in each system was chosen for the triaxial study of the system alkaline earth‐boric oxide‐silica as a source of B2O3in glazes and perhaps as a B2O3‐bearing frit in ceramic bodies. Each of these insoluble glasses was also studied for the effect of limited change in composition on softening temperature

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1961.tb15377.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

The use of some calcined bauxites in high‐alumina refractories is limited by unusual and excessive secondary expansion. One such calcined bauxite was compared with pure alpha alumina to determine the crystalline changes responsible for the expansion, to determine the mechanism of the expansion, and to suggest means for control of the expansion. X‐ray diffraction and petrographic techniques were used. The expansion was found to result from crystallization of secondary mullite by the action of impurities in aiding the diffusion of alumina and silica. Secondary mullitization and growth began at 1400°C. and caused as much as 23% expansion at 1600°C. The expansion was caused primarily by the mullite growth rather than by the true density changes associated with mullitization. Small sodium fluoride additions proved to be effective for controlling expa

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1961.tb15378.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

An attempt was made to sinter relatively pure 3A12O3‐2SiO2and 2A12O3‐SiO2compositions to low porosities at 1710° and 1650°C, respectively, using an addition of 1% MgO to each body to facilitate the reaction. The 3A12O3‐2SiO2body sintered to a porosity of 7.1% and was practically all mullite. The 2Al2O3SiO2body sintered to a porosity of 10.9% and was composed of mullite and corundum. Strength and elastic modulus measurements were made at several temperatures up to 1200°C, and some observations of the load‐bearing properties

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1961.tb15379.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

The gamma‐ray‐induced optical absorption in a series of cabal (calcium‐boron‐aluminum) glasses was studied and is interpreted, wherever possible, in terms of structural concepts. A resolution of the observed absorption spectra showed that three Gaussian‐shaped bands were induced with their maxima at about 2.3, 3.5, and 5.0 e.v. (550, 350, and 250 mμ). The 2.3‐e.v. band decreased in intensity with increasing CaO content, reaching a minimum intensity at a composition corresponding to the four‐coordination of about 20% of the boron. Further increase in CaO content was associated with an increase in the intensity of this band. The intensity of the 3.5‐e.v. band decreased gradually with increased mole per cent of CaO and increased with increased Al2O3. The 5.0‐e.v. band showed an abrupt increase in intensity which corresponded to the appearance of non‐bridging oxygens in the network. Replacing Ca2+by Mg2+, Sr2+, or Ba2+or replacing Li+by Na+or K+showed that glasses containing large ions of low field strength give less induced absorption than glasses containing small ions of high field strength. A potassium alumina borate glass melted under reducing conditions gave a considerably higher ultraviolet transmission, before irradiation, as compared with the same glass melted under normal conditions. The gamma‐induced absorption of these two glasses showed that reducing conditions resulted in a decrease in the intensity of the 2.3‐ and 3.5‐e.v. bands, whereas it caused an increase in the far‐ultraviolet‐induced absorption. The effect of additions of arsenic, thallium, titanium, germanium, and some

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1961.tb15380.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY