Showing papers in "Journal of the American Ceramic Society in 1944"

Properties of some vycor‐brand glasses

Abstract: Physical and chemical properties are discussed for Vycor-brand 96% silica glasses prepared from glasses of lower silica content by a leaching process, and a brief resume of this process is given. The intermediate porous glass and a translucent or white opaque form of the final 96% silica glass made by the Multiform process are briefly described. Ultraviolet and infrared transmission characteristics of glasses No. 790 and No. 791 are given. Summary Vycor-brand glass No. 790 containing 96% silica is produced without the use of excessive melting temperatures by a process in which a relatively soft borosilicate glass is melted and shaped, the fluxes are removed by leaching, and the residual porous high-silica structure is consolidated by heating. The outstanding properties of this glass are its very low coefficient of expansion and correspondingly high resistance to heat shock, its high softening point, low power factor, and high chemical durability, which make it useful for varied applications in the industrial and electrical fields as well as in the laboratory. The glass can be used continuously at temperatures up to 900°C. or for limited service at much higher temperatures provided it is not in contact with materials which react with or cause devitrification of silica. It can be lamp worked by methods similar to those used for fused silica. Porous glass is formed as an intermediate product in the process. It is characterized by pores of very small and relatively uniform radius, the average of which is in the order of 20 a.u. A translucent or opaque white glass is made by the Multiform process, which enables the production of massive ware and a variety of shapes that cannot be made directly in the clear form. Aside from transparency, the properties in general are the same as those of the clear glass. Vycor-brand glass No. 791 is highly transparent to ultraviolet light at wave lengths down to 254 mμ or less, and glasses have been made with an appreciable transmission even at 185 mμ. Glasses No. 790 and No. 991 are highly transparent to the near infrared.

Fundamental study of clay: v, nature of water film in plastic clay*

Abstract: Using a pure monodisperse system of kaolinite particles of known diameter and thickness, it has been possible to calculate with a fair degree of precision the thickness of the water film separating the particles and the variation in thickness of this film for different pressures. It has also been possible to calculate with considerable certainty the force acting between two clay particles.

Calculation of surface tensions of glasses

Abstract: Factors have been derived for the calculation of the surface tensions of glasses from their compositions at temperatures of 1200° and 1400°C. The nine oxides evaluated are those commonly found in significant amounts in glass compositions. The surface tension of a glass may be calculated with a fair degree of assurance from its composition to within about 4 dynes per cm.

Fundamental study of clay: vi, flow properties of kaolinite-water suspénsions*

Abstract: The flow properties of six monodisperse kaolinite fractions were studied over a large range of concentration. From these results, it has been possible to set up an equation relating viscosity to concentration which holds over a very wide range. Equations relating concentration to thixotropy and to the yield point which have general application could also be established. The viscosity of a suspension is obtained from the sum of three quantities, namely, those contributed by (1) the liquid, (2) the individual particle, and (3) the collisions of the particles. Thixotropy is found to be due to the sum of two quantities, namely, the contribution of (1) the individual particle and (2) the interference of the particles. The yield point in these fractions was found to be proportional to the cube of the concentration. With these relations, it is possible to calculate the viscosity of a casting slip for any change in specific gravity.

Melting rate of soda‐lime glasses as influenced by grain sizes of raw materials and additions of cullet

Abstract: Using the complete solution of silica grains as a criterion of melting, a comparison of the melting rate of a typical soda-lime glass as affected by the grain size of the constituent materials has been made. This study indicates that if the grain sizes of raw materials are mismatched, separation or demixing of the batch during melting is likely to occur. The tendency of additions of cullet to minimize such separation is indicated. Further tests have been made on five commercial container-glass compositions, which have raw materials of the same grain-size distribution as those in commercial use. These experiments indicate a varying effect of the addition of cullet in decreasing melting time. This variation cannot be explained by differences in the degree to which the various raw-material grain sizes are matched.

Viscosity of recent container glass

Abstract: A high-temperature, concentric cylinder viscometer has been constructed and calibrated. The calibration checks within 1% that obtained by Lillie for a similar apparatus and provides further evidence of the high degree of reliability of this type of measurement. The contention of Washburn and Shelton that the calibration in such instruments is a function of the viscosity is shown to be false. Because four independent investigations have been unable to check this contention, it may now be regarded as spurious. A medium temperature-range fiber viscometer for measuring the viscosity of glass in the annealing range has also been constructed. It is shown that the Fulcher equation, log η=−A+B/T−T0, fits the data obtained on the two instruments to within 0.5% for commercial soda-lime glasses. Complete viscosity data as a function of temperature are given for sixteen commercial container glasses, and the analyses are also included. These glasses show a wide range of viscosity.

Volume change attending low‐to‐high inversion of cristobalite *

Abstract: The volume expansion of cristobalite, as it passes through the low-temperature inversion range, was studied by means of a dilatometer in which the cristobalite expanded against a column of mercury. The volume change was measured in a capillary tube attached to the mercury column. The temperature of inversion is a function of the previous history of the cristobalite sample. A volume change of 7% was obtained upon inversion. The volume change was found to depend on the previous heat-treatment of the sample, the presence of added catalysts, and the source and grain size of silica. All of these factors affect the amount of cristobalite present and hence the change of volume on inversion of the cristobalite. Several samples of cristobalite from used silica brick were studied. The information is applied to the problems of silica refractories.

Properties and diagnosis of cords in pressed and blown glassware

Abstract: Cords are characterized by more or less abrupt changes in physical and chemical properties in localized areas of the glass. The available methods for determining the properties and practical aspects of cords that occur in pressed and blown glassware are described. The properties of cords are considered in relation to the determination of their sources and causes. The manner in which cords affect the physical properties of glassware and the procedures for evaluating these effects are discussed.

Conversion of certain refractory oxides to a suboxide form at high temperatures

Abstract: A preliminary survey of the information published in the fields of chemistry and physics on the suboxide forms of SiO, TiO, ZrO, CrO, AlO, BO, VO, and CbO indicates a new field to be explored in determining the role of these suboxides in the service and failure of refractories and in the chemistry of slags. Several phenomena at the present time little understood, such as devitrification in reducing atmospheres, volatilization of refractory oxides, and certain slag types now classed as anomalous, may find their explanation in the decomposition of the oxides to low oxide forms under the favorable conditions of high temperature and low oxygen pressure which characterize much of their service.

Factors affecting the degree of homogeneity of glass

Abstract: The rate of homogenizing of soda-lime-silica glass under conditions of minimum convection mixing and in the absence of refractory materials was measured by the centrifuge density spread technique developed by Turnbull and Ghering. Measurements on melts prepared in pure platinum containers at 2550°F. showed that the density spread decreases rapidly during the first 16 hours of melting following which further decrease occurs at a much slower rate. The portion of glass responsible for the major part of the density spread was a light fraction, which tended to form or accumulate at the surface of the melt.

Particle‐size distribution of steatite talc *

Abstract: Experiments were made to determine which degree of fineness of ground talc would be most suitable for steatite-type ceramics. A laboratory-type air separator, Andreasen pipette, and the Casagrande hydrometer methods were used to measure the particle-size distribution of commercial steatite talcs. The results indicate that, although wide variations in the particle-size distribution of steatite talcs have a bearing on the firing shrinkage when the talc is incorporated in a body, the differences in grinding obtained in commercial talcs are not of great importance when proper milling practice is employed.

Refined method of control of cordiness and workability of glass during production

Abstract: Many glass plants obtain daily measurements of the density or specific gravity of the glass in each furnace. Small daily fluctuations of about ±0.0010 density unit are usually taken for granted, while pronounced changes within a two- or three-day period are a matter of concern; but heretofore neither criteria of permissible variability nor rules for interpretation of the data have been in general use. In the present work, the control-chart method of statistical analysis of past data has been applied to data from ten glass furnaces. Small daily fluctuations of density are found to be statistical in character, and the predominant cause of large variations is found to be in the batch house. The rational subgroup sample to be used in analyzing such variations and in operating a control chart is found to be a subgroup of three consecutive daily density values obtained from a particular furnace. Using this subgroup, the average 3-day range of density for the ten furnaces varied from 0.0006 to 0.0023, and the corresponding 3-sigma limits for daily variation from the central line density were ±0.0011 to ±0.0040. A typical value for the average 3-day range of density is 0.0012 and a value no larger than this is a reasonable goal for a glass container plant. The use of control charts for maintaining a state of statistical control of density during production is illustrated for four furnaces over a 2- to 6-month period. Many assignable causes of variation were found in the batch house, usually in the scales; other assignable causes were changes in cullet and in raw materials, changes in firing of the furnace, and laboratory errors in measurement of the density. Present experience indicates that it is difficult to maintain a state of statistical control with the types of batch-weighing equipment in use in some plants. The importance of control, however, was demonstrated for two furnaces in two different plants by the fact that cordiness increased with increasing 3-day range of density. When the density was not maintained under statistical control in one plant, trouble was experienced with checks in the ware. The use of control charts for keeping lack of control within tolerable limits is discussed for one furnace where the variations were small and the control limits narrow. The range was held under control, but the density showed “trends” and went out of control. In this instance, the 3-sigma control limits for variation of daily values from the central line density were ±0.0011, corresponding to ±0.09% replacement of lime by silica. Inasmuch as composition changes in excess of ±0.09% are tolerable in the present state of the art, a modified control limit corresponding to a composition change of approximately ±0.25% is suggested, the corresponding density limits being ±0.0030. When the 3-sigma limits for density are less than, this value, modified limits may be used, although the 3-sigma limits for range are retained. When the 3-sigma limits are greater than ±0.0030, it is most desirable to maintain strict statistical control, and efforts should be made to reduce the variability; otherwise there may be excessive cordiness and other difficulties in fabrication of the ware. In some instances, a reduction in variability will require major repair of batch handling and weighing equipment or a new batch-house weighing installation. Other subgroup methods and other sources of variability are also discussed. Control charts on density are of practical utility to plants. “Assignable-cause” variations are easily distinguished from unimportant, normal variations. The use of 3-sigma action limits keeps investigation of fluctuations to a minimum, and sets troubleshooting, when it is necessary, on the right track. The charts, furthermore, are a useful guide toward a permanent reduction of the variability. They should be helpful to management in striking an economic balance among tonnage pulled, glass quality, and capital expenditures for improvement of batch mixing and handling and other changes. The time required to maintain a chart for one furnace is about one day for past-data analysis, one minute each day for plotting, and not more than one day per month for current analysis, review, and adjustment.

Time problem in annealing

Abstract: A discussion of the homogeneity and stability that can be obtained by submitting a sample of glass to a given cooling schedule leads to a new method of annealing called the “freezing process.” The problems (a) how to obtain a given degree of annealing in a minimum amount of time and (b) how to obtain the best possible annealing in a given time are discussed theoretically in conjunction with the general principles of glass annealing. Numerical values of different quantities involved are given, and the application of the freezing process to a light flint glass is described in detail.

Cataphoresis of purified, fractionated kaolinite particles*

Abstract: The cataphoretic velocity of three purified, monodisperse fractions of Florida kaolin was determined by the ultramicroscope method. The effect of particle size, kaolinite concentration, and electrolyte concentration on the migration velocity of the particles was observed. Calculations of zeta potential, charge density, and total charge were made for the various systems. It is shown that the zeta potential decreases with increasing particle size and increasing clay concentration. The plots of migration velocity versus electrolyte concentration follow the usual form for such curves, rising rapidly with the first electrolyte additions and flattening out as equilibrium is reached.

Notes on moisture expansion

Abstract: Moisture-expansion determinations were made over a period of more than three years on bisque and glazed specimens of two types of semivitreous bodies having approximately the same absorption which were exposed to four different atmospheric conditions. The data indicate the cone 0 tale-pyrophyllite body to expand less under all conditions of exposure than the cone 9 clay-flint-feldspar body. Glazed specimens of both bodies expanded more than the bisque specimens and a possible explanation is given. From mathematical considerations, a three-year storage period appears to be sufficient to permit moisture expansion that closely approaches the ultimate which might be expected in the types of bodies investigated. The autoclave treatment gave the highest expansion values and should serve as an index of the service performance as to delayed crazing of ware so tested.

Strontia and its properties in glazes

Abstract: Strontia has proved to be a strong flux and a desirable glaze ingredient when it is used to replace PbO, ZnO, and CaO in a typical dinnerware glaze. By including it in the frit, the fluidity of the glaze was increased to a marked degree when it was substituted for ZnO and CaO and it also lowered the deformation temperature in the replacement of the latter oxide. Thermal-expansion tests indicate that strontia has practically the same effect as lime on glaze expansion. Glazes of excellent visual and physical properties were obtained in a series of low-lead and leadless compositions containing strontia.

Changes of properties of glass resulting from changes of composition

Abstract: Equations are given for the calculation of changes of density, refractive index, and other optical constants produced by the addition of a known relative weight of a given component to a base glass. Corresponding equations for the substitution of one component for another are also given. Values are computed and listed for the initial fractional rate of change of refractive index (nD) when various components are added to (a) pure SiO2 and (b) a sodium silicate glass containing 50% of Na2O by weight.

Calcination of topaz ore in a rotary kiln

Abstract: Reports have indicated that calcined topaz might be useful as substitute material for Indian kyanite in high aluminous, mullite-type refractories. Tests were conducted to determine the value of calcining and defluorinating raw topaz. Fifteen tons of minus 1-in. topaz ore were calcined in a 25-ft. rotary kiln of 20-in. in inside diameter, at 2600° to 2950°C., with feed rate of 200 to 400 1b. per hour and feed retention in the kiln of 70 to 120 minutes. The best operating conditions were found to be 2700°F. and a feed rate of 300 1b. per hour at 0.90 r.p.m. of kiln rotation. The average fluorine content was 0.24% and the apparent porosity was 19%. A dust loss of 11% occurred during calcination, but no serious reduction in particle size occurred from the heat-treatment. It seems to be practicable, therefore, to calcine and defluorinate raw topaz in a rotary kiln and to obtain a product suitable for the manufacture of mullite-type refractories.

Surface layer of sheet glass

Abstract: This research was conducted to obtain evidence of the nature of the fire polish on sheet glass. Three measurements were made on each sample as follows: (1) The deviations from Fresnel's reflection laws, (2) a measurement based on the Pfund method of determining the apparent Brewsterian angle as compared to that calculated from the index of refraction of the glass, and (3) the true index of refraction by a prism method in which the samples were cut and ground to 60-degree prisms. These measurements showed that freshly drawn sheet glass probably has a crystalline layer several molecules thick on the surface. The layer has a high index of refraction, but this is counteracted quickly by water absorption if the glass is dampened slightly or is exposed to the atmosphere.

Some particulate characteristics of commercial flint and feldspar

Abstract: The particle-size variations of eleven shipments of commercial flint and of fifteen shipments of feldspar have been investigated as a possible cause of production variations in electrical porcelain. A correlation of sieve data with specific surface calculations based on sedimentation determinations was made on six grades of commercial flint. The Andreasen pipette sedimentation method was used for all tests except those in which the hydrometer method was employed for comparison purposes. Either of these sedimentation methods had adequate accuracy to control particle size. The percentage remaining on the 325-mesh sieve, however, could not be correlated with the specific surface values. Particle-size distribution was determined for each sample. To facilitate comparisons, specific surface values were calculated from a plot of the distribution data on log-probability graph paper. The investigation included the effect of various liquid suspending media and electrolytes on the settling characteristics of flint and feldspar. Neither flint nor feldspar could be adequately dispersed in non-polar liquids. Feldspar apparently has surface-active characteristics that permit it to be flocculated or deflocculated, depending on the nature of the ions present in solution. An anomalous peptizability of some feldspar samples in the particle-size range below 3 microns is discussed.

Surface tension and persistence of cords in glass

Abstract: The action of surface tension in molten glasses is discussed in relation to cord persistence. An examination is made of the reported mechanism for the solution of cords as proposed by Jebsen-Marwedel. His viewpoint that the shape of immersed cords is governed by surface-tension differences between the cord and matrix glasses appears to be in conflict with the physics involved. The possible influences of inter-facial tension on the shape of cords and on their location in or on the melt are considered along with its relation to other physical forces. It is concluded that the only stable form for cords under the influence of interfacial tensions alone is a spherical one. Other factors, such as high viscosities, varying diffusion rates, and mechanical and thermal stirring cause the irregular shapes found in practice. The relation of surface tensions to these factors requires further study.

Enameled utensil manufacturers' council tentative standard solubility test for porcelain enameled cooking utensils*

Abstract: The various methods for determining the degree of resistance of porcelain enameled cookingware to acid solubility are discussed. A method that overcomes many of the difficulties encountered in such a test and offers greater accuracy and reproducibility is described in detail.

Effect of firing atmosphere on development of colors in ceramic glazes

Abstract: The effect of systematic variations in atmosphere between 100% oxidizing and 100% neutral was noted The principles and definitions of color designation are given and possible physicochemical changes which result in color variation are considered Experimental data indicate the relative stability of typical colors under atmospheric variations

Analysis of cords and stones

Abstract: A method is described for the separation of cords and stones from the surrounding glass, and procedures are given for the semimicro-determination of silica and alumina. The apparatus is illustrated. Analytical results by full-scale methods and semimicro-methods are given. The methods of semimicro-analysis are shown to be rapid and accurate.

Suggestions for solution of difficult glaze‐fit problems

Abstract: The methods and principles are discussed by means of which suitable glazes for special purposes may be prepared. Examples are given of glazes for low-expansion bodies and also of durable low-temperature glazes.

High‐alumina clays of pulaski and saline counties, arkansas

Abstract: Extensive deposits of kaolinitic clay and closely associated bauxite occur in Pulaski and Saline counties, Arkansas, as products of early Cenozoic weathering of nepheline syenite. The clays of the bauxite-kaolin deposits normally contain more than 35% of alumina. Siderite is the principal impurity. The deposits for the most part are buried beneath sediments of Wilcox age or younger, but the overburden is thin or absent near outcrops of syenite. Deposits beneath overburden that does not exceed 50 feet in thickness probably total more than 100 million tons.

Influence of humidity on dielectric properties of high‐frequency ceramics*

Abstract: The dielectric properties of ceramics depend on composition, density, and surface conditions as well as many other factors. Humidity influences the dielectric properties to a large extent. These studies show that the amount of moisture depends on the compacting pressure and that the firing temperature has some influence on the dielectric properties in connection with relative humidity. Frequency and air pressure have an entirely different influence on the dielectric properties in relation to relative humidity.

Lightweight superduty kyanite-topaz refractory*

Abstract: Standard-size 9-in. brick with a weight of 5 lb. were successfully processed. Some of these brick had linear shrinkages of less than 1% in the A.S.T.M. load test at 1450°C. and less than 2% volume shrinkage in the 1600°C. A.S.T.M. reheat test. The pyrometric cone equivalent was 37 or above.

Effect of composition and temperature on solubility of iron oxide in ground‐coat enamel glass*

Abstract: The solubility of iron oxide in ground-coat enamel glasses at various temperatures was studied by adding varying amounts of ferric oxide to the milled enamel and giving the mixture a heat-treatment to acquire uniformity without devitrification at the desired temperature. The iron oxide solubility was obtained by finding the breaking point in the curve for iron oxide versus index of refraction. The frit solubilities were obtained at 1400°, 1600°, 1800°, and 2000°F. with variations in Na2O, B2O3, A12O3, CaF2, CaO, F2, SiO2, COO, NiO, MnO2, BaO, and MoO3. Data are given on a number of commercial frits.

Enamel film strength as affected by properties of enamel before, during, and after drying *

Abstract: The effect of soluble salts in porcelain enamel mill liquors was investigated, particularly relating to the enamel film strength and tearing tendency. The mechanism of tearing is discussed from the standpoint of the properties of the enamel slip and of dried enamel film. The related data are presented, and the application of the results of recent extensive studies of clay, water, and electrolyte systems to enamel slips is given. Summary The results of this investigation may be summarized in a flow sheet in which the various properties and conditions governing these properties are related to the characteristics studied. Figure 9 lists each variable in the sequence considered logical in this study.