Showing papers in "Journal of the American Ceramic Society in 1924"

THE SYSTEM: Al2O3.SiO2

Abstract: This paper deals with a study of the equilibrium relations of mixtures of pure alumina and silica at high temperatures. The results are expressed concisely in the form of an equilibrium, diagram and their bearing on ceramic problems is discussed. The principal feature of the diagram is the absence of the compound Al2O3.SiO2, the only compound being 3Al2O3.2SiO2. Crystals of this latter compound occur in all alumina-silica refractories. The optical properties of these crystals have been determined and are compared with those of sillimanite, Al2O3.SiO2, which has hitherto been regarded as the crystalline compound occurring in refractories and clay bodies in general. The behavior of natural sillimanite on heating is discussed.

An adiabatic method for studying spontaneous heating of coal1

Abstract: An adiabatic calorimeter is described, by means of which the spontaneous heating characteristics of dry pulverized coal can be studied, so as to obtain a direct measure of the rate of spontaneous heating at different temperatures, uninfluenced by various heat interchange factors. Specimen time-temperature curves of different coals are presented, which show approximately the same rate of heating over corresponding temperature ranges. From these curves, it is concluded that the main characteristic of spontaneous heating is that the rate of heating is an increasing function of the temperature. An empirical formula is developed, for which the constants, K, a and b, are determined for a Pittsburgh coal; θ= temperature, and T= time. From this formula, it is concluded: (1) no heating will take place below 26.27°C; (2) the time required for Pittsburgh coal to heat from this temperature to ignition is 144 hours, both the coal and the oxygen used being moisture free.

The effect of furnace atmosphere on the firing of enamel1

Abstract: It is shown that in firing ground coat and other one coat enamels, the atmosphere of the furnace plays an important part. Oxygen in the muffle penetrates the enamel during the early stages of the firing forming a film of iron oxide on the surface of the steel. This film, whether applied before enameling or formed incidentally to firing, partially dissolves in the fused enamel giving the intimate bond between metal and enamel. Ground coat enamel fired in an atmosphere of nitrogen was found not to adhere to the steel. Approximate values are given for the proportion of furnace space to enameled surface to insure sufficient oxidation when residual air is depended upon to supply the oxygen.

A simple brick porosimeter1

Abstract: A brick porosimeter based upon the air-expansion principle is described, and various considerations of design discussed. The apparatus described is adapted for testing refractory brick, but. the considerations of design presented are general in character. The design is adapted for commercial control work, and the descriptions serve as complete construction references. Porosity values obtained by the porosimeter and water absorption methods are compared to the values calculated from true sp. gr., to indicate the relative accuracy of the methods.

The oxidation of ceramic wares during firing.—i. some reactions of a well known fire clay1

Abstract: After a review of the literature, a chemical laboratory study is made of the gases evolved on heating a lower Kittanning fire clay at various rates to various temperatures in a current of pure oxygen. The rates of evolution of CO2, SO2, and SO3 are determined under varying conditions. Determinations of the remaining sulphur in the clay after heating are made. Possibilities as to the chemical mechanism of sulphur evolution are suggested. Plans for continuation of the work are outlined.

The plastic properties of enamel slip

Abstract: A simplification of the Bingham Plastometer, applicable to enamel slips, is described and the theory of plasticity discussed briefly. It was found that increase in temperature or increase in water content of enamel'slips raised the mobility without greatly affecting the yield value. Addition of clay and of certain inorganic salts raised the yield value without changing the mobility. Sodium silicate reduced the yield value to zero and lowered the mobility.

The electrical resistivity of refractories1

Abstract: The electrical resistivities of flint fire clay, kaolin, magnesite, sillimanite, silica, diaspore, Maryland, Italian and Indian talcs were determined at temperatures up to 1500°C. Tests were made in an atmosphere of nitrogen, by the Wheatstone bridge method, using 45-volt 1000 cycle alternating current. With the exception of magnesite, the rate of decrease of resistivity decreases with an increase in temperature. The investigation indicates that the resistivity of a complex ceramic body, especially if it is open and porous, is not constant for a given temperature above the temperature at which its most fusible mixture melts. Resistivity is affected by the amount of impurities present, decreasing with an increase of impurities. As was shown in the tests of Italian talc, the resistivity is not only dependent upon the amount of impurities, but also upon their distribution. Within the limits of the voltage used, the resistivity is independent of the potential applied.

The dehydration temperature of pyrophyllite and sericite1

Abstract: Pyrophyllite and sericite are sometimes closely associated in works and the clays derived from them. They contain similar amounts of chemically combined water, but the sericite gives up its water more readily than the pyrophyllite, and is completely dehydrated at a lower temperature.

An apparatus for measuring the abrasive hardness of glazes1

Abstract: An apparatus for measuring the resistance to abrasion, or scratching, of glazes and possibly other materials is described. It provides, essentially, for the wearing away of the surface by means of standard cement sand, which is allowed to run through a funnel adjusted to deliver a definite amount of sand for a given time interval, and to strike the inclined surface of the test piece after falling a fixed distance. The loss in weight under this treatment is assumed to bear a definite relation to the resistance to abrasion.

The laboratory testing of aluminous refractories1

Abstract: Eight brands of high alumina refractories and two brands of fire clay refractories, which are used by the trade under conditions of service requiring resistance to the corrosive action of lime and cement clinker at high temperatures, were subjected to standard and modified laboratory tests for high grade refractories. Data obtained indicate the results which may be expected in the technical examination of this type of product.

The oxidation of ceramic wares during firing.—ii. the decomposition of vafuous compounds of iron with sulphur under simulated kiln conditions1

Abstract: The progress of sulphur evolution is traced from a series of clay bars containing known amounts of various iron-sulphur compounds, both with and without the addition of carbon, when heated in imitation of a kiln schedule in atmospheres varying from pure oxygen to those commonly encountered in kiln practice, including neutral and reducing atmospheres. The varying degree of incompleteness of sulphur evolution is noted. The residual sulphur is found to be practically insoluble in water or aqua regia, but is rendered soluble by hydrofluoric acid. As a plausible explanation there is advanced the theory of the formation of “ferrous sulpho-silicate.”

Notes on the behavior of refractories in glass melting furnaces1

Abstract: Microscopic examination of used glass house refractories gives evidence about the transformations that have taken place during use, and the relative solubilities of constituents of the refractories in the glass. On this evidence it is concluded that high alumina refractories would resist the solvent action of the glass and the fluxing action of the soda in the furnace atmosphere better than fire clay refractories. Investigations are needed to find a new refractory mortar for use between silica and clay refractories in glass tanks.

The use of boric oxide in glass‐making

Abstract: Boric oxide behaves differently from other glass-making constituents in that the variation of physical properties is not progressively continuous with a variation in composition. With increase of boric oxide content in sodium borosilicate glasses, the refractive index (μD) rises to a maximum as also does the annealing temperature, while the coefficient of thermal expansion reaches a minimum and then rises. The durability, or resistance to water and hydrochloric acid reaches a maximum when the glass contains about 12% of boric oxide and subsequently falls off very rapidly. There is, accordingly, a limit to the usefulness of boric oxide in glass.

Fire-clay brick for the open hearth1

Abstract: Fire-clay brick in the open hearth are normally subjected to medium temperatures and to the action of slag containing high percentages of iron and lime. Temperatures near the maximum of the open hearth itself may exist due to failure to reverse the draft and for that reason brick of high refractoriness are used. Resistance to spalling action is not of primary importance because the temperature change is small. The indications obtained from a laboratory test were that brick having a high alumina content would resist the slag action better than ones higher in silica.

The significance of drafts in down-draft, coal-fired kilns1

Abstract: The fundamental laws of gas flow are applied to the movement of gases through down-draft kilns. Data on pressure conditions in four kilns are presented graphically. The cause of draft, the superiority of the down-draft over the up-draft kiln, the significance of stack draft, the relation of draft and excess air, features of kiln design, and the comparative merits of forced, induced and natural draft are discussed.

Checker brick for resisting alkaline slags1

Abstract: Checker brick of varying composition were tested by placing them in the regenerators of two glass tank furnaces. The operation of one furnace was representative of those making the usual grade of bottle glass while the other was operated at a considerably higher temperature and with a more corrosive dust. The amount of corrosion of the checker brick varied directly with the silica content of the brick. Those highest in alumina gave excellent service in the regenerator operating at the lower temperature. In the other regenerator, however, the. dust adhered to the high alumina brick and tended to clog the regenerator while it apparently fluxed and drained off of those higher in silica, leaving free passage for the gases. The brick were tested in the laboratory by making into cones with various percentages of the corrosive dust and determining the fusion point of the cones. The results agree closely with those obtained from the service tests. Detailed results including partial analyses of the brick and flue dust are given.

Handling and storing raw materials to produce uniformity in a body1

Abstract: Ceramic raw materials are usually heterogeneous mixtures rather than pure substances. Variations in composition are likely to occur in the materials as received at the plant both within individual carloads and between successive carloads of the same material. Such variations often cause trouble in plants making vitreous porcelain. The article describes ways of avoiding trouble, (a) by rendering each carload homogeneous as it is stored, (b) by withdrawing a material from several lots simultaneously to make the body; in withdrawing from several lots simultaneously, the process should preferably be continuous, one lot being finished as a new one is started, (d) and by keeping accurate records of the materials going into each production batch of body.

Comparative tests of porosity and specific gravity on different types of refractory brick1

Abstract: Comparative data of porosity and specific gravity on several types of refractory brick are presented. Apparent porosity is obtained directly by the water absorption and air expansion methods. Total porosity is calculated from the true specific gravity and apparent specific gravity is calculated from the observed porosity values. The results indicate (1) a more accurate measurement of open pore space in bricks by means of the air expansion method than by water absorption, and (2) the absence of sealed pores in some types of refractory brick.

The electrical conductivity of sodium chloride in molten glass1

Abstract: Precipitation of collodial suspensions in glass by dissolved salts leads to the assumption that they ionize. In this investigation the Conductivity of glass alone and with dissolved salts confirms the theory. A special cell has been devised for conductivity work in glass at high temperatures. This is the first study of the electrical conductivity of salts in vitreous media.

The method of selecting refractories for marine purposes of the navy1

Abstract: Trouble was experienced with refractories when oil fuel supplanted coal in the furnaces of naval boilers. The selection of refractories for naval oil-fired boiler furnaces done at the Philadelphia Navy Yard is described. The Navy's test for refractories (chemical analysis, fusion point determination, and the Simulative Service Test). The Simulative Service Test.—Description of, and its value in obtaining satisfactory refractories. The Navy's “Acceptable List of Refractories.” The results of the Simulative Service Test (about 26% of the refractories submitted passed).

A quantitative laboratory slag test

Abstract: A laboratory slag test is described capable of giving quantitatively the resistance of refractories to slags. The method consists in continuously spraying powdered slag onto the hot specimens and allowing it to run off. The advantage of this test is the rapidity and small expense with which relatively accurate results can be obtained.