ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1959.tb13555.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

The electrical properties of copper oxide‐bearing porcelain enamels fired on sheet platinum and of the clear base porcelain enamel fired on sheet copper were measured. The dielectric constant, dissipation factor, and resistivity of the coatings were determined from room temperature to 700°F., and at frequencies varying from 0.1 to 100 kc. per second. The effect of firing time, firing temperature, and coating thickness on the copper ion content resulting in the coatings fired on copper was investigated. The copper ion concentration of the porcelain enamels fired on cop per was determined by X‐ray fluorescence analysis. Electrical measurements of coatings fired on platinum and on copper were correlated with the copper ion concentration of the coating. At concentrations in the coating below 5% CuO, some marked changes occurred in the electrical characteristics of the coatings as a function of CuO content. These changes were even more accentuated at elevated temperatures. At concentrations varying from 5% CuO to the saturation point of CuO in the coating (about 20% CuO for coatings fired at 1600°F.), the electrical properties of these coatings at room temperature were nearly unchanged throughout this range, whereas at elevated temperatures the general effect was that of a decrease in dielectric constant and dissipation factor as the CuO content was incr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1959.tb13556.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

The permeability of refractories is a governing factor in the deterioration of blast‐furnace linings by liquids and gases. Permeability tests there fore were performed on 17 carbon, 11 mullite, 85 castable, and 7 super‐duty and 11 high‐duty fire‐clay brands. The rate of gas flow was measured through a 2‐in. cube in three directions by using an improved laboratory permeameter. The range and mean of permeability in centidarcys for each class of refractory were as follows: carbon, 0.3 to 42 (20); mullite, 7 to 158 (48); castable, 0.2 to 43 (4.5); super‐duty fire‐clay, 28 to 207 (76); and high‐duty fire‐clay, 33 to 147 (72). The permeability of the different axes of the brick usually varied widely, with the face axis usually exhibiting the lowest values. The improved permeameter should prove to be especially valuable for determining resistance to gas flow and for controlling the qualit

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1959.tb13557.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

An experimental survey of additives to barium titanate shows that in addition to those which are readily soluble in the barium titanate lattice (class 1) and those which are insoluble (class 2) two other distinct classes of additive, with limited solid solubility (classes 3 and 4), can be distinguished. Class 3 additives give normal ferroelectric properties with particularly low electrical and mechanical losses, as exemplified by BaTiO32 mole % NiTiO3for which, after aging, tan δ= 10−3and 1/Q = 4 X 10−4. Experimental results indicate that the ferroelectric loss, in high and low fields, is hysteresis loss associated with domain boundary movement and that in class 3 materials the losses are low because the domain boundaries are in particularly stable positions. Class 4 materials have useful dielectric properties associated with a crystallite size between 0.1 and 1 μ. For example, BaTiO3.3 mole % NaNbO3has ε= 3200 × 200 between 0°C. and 120°C. with tan δ= 3 X 10−2. The absence of a permittivity peak is attributed to a distribution of the Curie temperatures of individual crystallites and the enhanced permittivity at lower temperatures to inhibition of the spontaneous polarization by the mutual clamping, in the ceramic, of crystallites which are too small to divide into

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1959.tb13558.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

Iron‐rich phases in yttrium iron garnet specimens are easily detected by microscopic examination. These phases form as pockets in the yttrium iron garnet matrix at low sintering temperatures but are swept into grain boundaries at higher temperatures. The dependence of ferrimagnetic resonance line width on composition and sintering conditions is given. Low line widths are realized when gas‐generation problems are controlled. Line widths as low as 15 oersteds have been obtai

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1959.tb13559.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

Relations previously have been shown between the size of the fracture mirror and the nominal breaking stress. In the present paper, this relation is derived analytically involving one unknown quantity which must be determined experimentally. This quantity is δm√ρ where δmis the intrinsic strength of the glass and the effective radius of the crack tip. Tests on glass rods indicated that the breaking stress could be determined from the radius of the fracture mirror. For 80% of the specimens the values obtained were within 8% of those obtained from the test l

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1959.tb13560.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

It is shown that precipitation occurs in Griffith‐type surface cracks in solids from solutions or from vapors under conditions in which a plane surface would be dissolved or vaporized. A reduction in the equilibrium vapor pressure at the crack tip from that of a plane surface is produced by the driving force to reduce the surface energy of the crack. An equation is derived relating vapor pressure at the tip of the crack to vapor pressure over an infinite plane. This relation is used in deriving an expression for the fill‐up of cracks with time. Experimental data on the measurement of the retreat of the crack edge with time appear to be in good agreement with the derived expression. A discussion of the effect of such crack healing on the mechanical properties of the solids is inclu

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1959.tb13561.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

Phase equilibria data, obtained both by differential thermal analysis and by quenching, are presented for the system Na2O‐Nb2O5. Five compounds corresponding to the formulas 3Na2O.1Nb206, lNa2O. 1Nb2O5, lNa2O 4Nb2O6, lNazO.7Nb2O5, and lNa2O. 10Nb2O6have been found. The compound 3Naz0.lNb2O5melts congruently at 992°C. The compounds 1Na2O. 4Nb2O6, lNa2O.7Nb2O, and 1Na2O. 1Onb2O5melt incongruently at 1265°, 1275°, and 1290°C., respectively. The well‐known perovskite structure phase NaNbO3was found to melt congruently at 1412°C. The transition temperatures in NaNbO5were checked by thermal analysis and only the major structural changes at 368° and 640°C. could be detected. A new disordered form of NaNbO3could be preserved to room temperature by very rapid

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1959.tb13562.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

The system TiO2‐P2O5was investigated in the compositional range TiO2.P2O5to 100% TiO2. Two compounds exist, TiO2.P2O5and 5TiO2.‐2P2O5. TiO2.P2O5begins to lose P2O5at 1400°C. and both fusion and vaporization proceed rapidly at 1500°C. 5TiO2.2P2O6melts congruently at 1260°± 3°C. to a glass which can be retained in substantial quantities at room temperature. Physical properties of certain compositions are d

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1959.tb13563.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

Beta alumina was once considered to be merely a metastable polymorph of corundum. Its status as a distinct and stable compound (Na2O.‐11Al2O5and analogous formulas) is now quite firmly established. Yet the published phase diagram for the system soda‐alumina‐silica takes no cognizance of its existence. A study of the alumina‐rich portion of the system was conducted to determine whether or not beta alumina should be incorporated in the diagram. Conventional methods of investigation were used, with certain innovations designed to overcome difficulties inherent in the system. Solid‐state sintering and modified quenching techniques were utilized to minimize soda loss. Sintering was at 1400°C. or thereabout, in platinum envelopes which were immersed in buffering mixtures so as to reduce volatilization. To the same end, extra‐large quenching charges were employed, and these were held at 1600°C., far below the liquidus temperatures of most of the mixtures studied. Phase identification was primarily by the X‐ray powder method. The results of these studies confirm the status of beta alumina as a discrete compound, and are believed to justify the insertion of an additional tie line, linking beta alumina to carnegieite, in the soda‐alumina‐silica diagram. A large primary field of beta alumina, occupying a portion of the present corundum field, is also strongly indicated. The phase diagram accordingly has been modified so as to incorporate these latest findings. The revised diagram, although in some respects tentative, is believed to be in fuller accord with technological experience. It is believed also to be in complete agreement with all recent laboratory studies in the system lime

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1959.tb13564.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY