摘要:

Original studies and experiments that support the concept of the close association between fracture origin and flaws in glass are presented. The effect of temporary overstresses, fracture velocities during the later development of the process, and evaluation of the critical stress are discussed. Data are presented which show that temporary overstresses may weaken glass permanently and that this effect results from the slow propagation of fracture flaws. The study of fracture surfaces reveals that the velocity of the fracture crack across the section is not necessarily uniform and that the velocity characteristics of each individual fracture are determined by factors such as degree of load relaxation occurring during the dynamic phase of the process. The critical stress is estimated to be between 2.5 and 5 million lb. per sq. in., and, for any particular glass, this stress is independent of test conditions.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1954.tb13990.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

An equation for the activation energy of ionic conduction in silica glasses is developed. The approach uses the classical ideas of ionic crystal theory and elasticity theory. The equation finally derived involves the radius and valence of the modifier ion, the lattice constant of the glass, the electronic charge, the shear modulus, and three arbitrary parameters. Two of these parameters are shown to be related to the geometry of the silica network and are exactly determined from diffusion of gases in glass data. The other parameter is shown to be approximately numerically equal to the dielectric constant. he theory is compared with the experimental results of 140 glass compositions.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1954.tb13991.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

An experimental study has been made of the possibilities and limitations of ionic substitution in the perovskite lattice. Especial attention has been paid to those cases in which more than one type of ion occupies any or all the cation and anion positions. A fairly large number of new oxide phases typified by such compositions as KLaTi2O6, Sr2CrTaO6, Ba3NiNb2O9, and BaK‐TiNbO6have been synthesized and shown to have the perovskite structure. Anion substitution successfully yields compounds with this structure only when it is complete; no mixed‐anion perovskites have been encountered. Few perovskites with anions other than O2‐or F‐have been found. The importance of valence differences in limiting the extent of ionic replacement appears to have been clearly demon

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1954.tb13992.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

The sintering and grain growth of alumina as a function of the type of impurity (oxide) added was studied. One weight per cent of the impurity was added to a commercial Be‐grained alumina or was coprecipitated with iilcl3to form hydroxides. Fired shrinkage, bulk density, and apparent porosity measurements were used to correlate sintering with grain growth as observed by the petrographic and electron microscope. Some additives which increased grain growth were believed to enter into solid solution with alumina and to strain the lattice sufficiently to increase material transport greatly. Other additives were believed to produce a glassy phase which would greatly increase surface difusion and resulting grain growth. Some additives decreased grain growth because of the relatively large vapor phase produced by the impurity upon heating which may have been sorbed on the alumina; other additives may have Wed anion vacancies to reduce material transport or may have produced complex anions whose flow or diffusion may have been impede

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1954.tb13993.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

The effects of nonionic, anionic, and cationic surface‐active agents on yield point, plasticity, drying and firing shrinkage, dry and fired density, and rate of drying have been experimentally determined. These and other factors have been correlated on the basis of a comprehensive theory of the plastic properties and drying behavior of clay‐water mas

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1954.tb13994.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

Ceramic bodies approaching the theoretical composition of cordierite were prepared from mixtures of talc and clay; talc, clay, and varying amounts of MgCO3; talc, clay, and alumina; and prochlorite and clay. Additions of BaCO3and PbSiO, were made. Differential thermal analysis and X‐ray diffraction methods were used in reaction studies of each composition. Bodies had thermal expansions from 0.344 to 0.109% (25° to 900°C.). BaCO3and PbSiO3affected thermal expansion. Dielectric properties were improved by additions of BaCO3and were markedly improved by additions of both BaCO3and PbSiOl. Cordierite started to crystallize at about 1250°. Additions of PbSiO3lowered this temperature about 50°C. With sufficient BaCO3, the Ba‐C phase, as described by Wisely, crystallized in place of cordierite. The crystallization temperature for the Ba‐C phase was about 1200°C. With insufficient BaCO3, both cordierite and Ba‐C formed. Additions of PbSiO3reduced the crystallization temperature of the Ba‐C phase by 50°C. and increased the glassy phase. Several of the compositions should haw considerable

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1954.tb13995.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1954.tb13996.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1954.tb13998.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY