ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1957.tb12623.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

Anomalous thermal expansion and other properties of borate glasses have previously been given a structural explanation by Abe. This explanation is here reinterpreted and revised in terms of the structon theory of Huggins. In agreement with Warren, it is postulated that, in glasses containing, in addition to boric oxide, small relative amounts of an alkali or alkaline‐earth oxide, some of the boron atoms are surrounded by four oxygen atoms and all the oxygen atoms bridge between two boron atoms. At concentrations beyond that of the thermal expansion minimum, some oxygens are assumed to have only one boron neighbor. These ideas are formulated quantitatively and are used to interpret pertinent experimental data. From the concentrations where the property‐composition curves show breaks, conclusions may be drawn as to the average number of oxygens surrounding each metal a

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1957.tb12624.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

The chain‐length distributions in solutions of sodium phosphate glasses were reinvestigated using improved paper chromatographic techniques. The range of compositions was extended to glasses of higher Na/P ratios by using a through‐flame technique for their preparation. The distributions obtained confirmed the earlier work with the exception that cyclic phosphates were found in solutions of glasses having or approaching the metaphosphate composition despite prolonged heating of the glasses in the molten condition. The earlier observation was that prolonged heating eliminated the cyclic phosphates. As before, no orthophosphate was found, as predicted by Van Wazer, and neither the Poisson nor the “random reorganization” distributions fitted the data for both high‐ and low‐average chain lengths. Although some sort of rearrangement is occurring in the melt, it may not be a completely random process; a rapid change of chemical properties with chain length of the short polymers may have to be taken into account. This was confirmed by similar studies of potassium and lithium phosphate glasses, whose distributions were found to be different enough to demonstrate a cation effect. Consequently, more than stoichiometry

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1957.tb12625.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

The mechanical strength of porcelain, in which a glassy phase is the major part, is shown to be influenced mainly by stresses set up in the glassy phase rather than by the amount or size of mullite crystals formed. A crystalbe material (quartz) having a coefficient of expansion higher than that of the glassy phase will establish favorable prestresses in the glassy phase. As the tensile stresses induced in the quartz are relatively high, uniformly sized grains of about 15 to 30 μ will best withstand these stresses. If finer‐sized quartz grains are used, they will dissolve on firing and will not contribute to favorable prestressing of the matrix. The maximum prestresses are obtained when the radius of the quartz grains is three times that of the surface layer dissolved on firing. Illite, as a flux, tends to dissolve only a thin layer up to the maturing of the porcelain, but increases its action at the maturing temperature, thereby increasing the favorable prestressing. Another factor is the temperature gradient inside the body during firing, which causes gradual differences in the coefficients of expansion because of quartz dissolution. As the coefficient of expansion is lower near the surface than near the center, additional favorable prestresses are establish

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1957.tb12626.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

The thermal conductivity of Al2O3, MgO, TiO2, and CaF2single crystals and single‐phase poly‐crystalline aggregates of controlled microstructure was measured between 0° and 1000°C. The conductivity of pure single‐phase dense polycrystalline aggregates agrees with that of the corresponding single crystals at temperatures below the onset of radiant‐heat transfer. Small amounts of impurities and the pore geometry may considerably affect the conductivity of a

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1957.tb12627.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

The microstructures of polyphase, heterogeneous systems, sintered in the presence of a liquid phase, are analyzed on the basis of wettability and surface‐energy relations. General principles relating to the primary factors affecting the microstructure are discussed. The application of these principles to such diverse systems as metal‐carbide, metal‐glass, and metal‐metal show that the microstructure and distribution of the solid in the liquid is primarily determined by various surface‐energy relationships. A general “coalescence hypothesis” based on this wor

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1957.tb12628.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

The phase relationships in the system zirconia‐thoria were investigated by X‐ray diffraction and dilatometric methods. The specimens were melted in air at the focus of a solar furnace. The existence of a cubic calcium fluoride‐type solid solution was established for thoria concentrations above 17.5 mole %. However, this solid solution is stable only at high temperature, and, after prolonged heating at 2000°C. and at 1350°C., it decomposes into tetragonal zirconia (which during subsequent cooling undergoes the unavoidable tetragonal‐monoclinic inversion) and a thoria‐rich phase containing at least 99 mo

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1957.tb12629.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY