THE INFLUENCE OF CHEMICAL COMPOSITIONS ON THE PHYSICAL PROPERTIES OF SODA-LIME GLASSES1

Nineteen soda-lime glasses covering the commercial field were prepared, melted, and fined for 2 hours. The chemical composition of the raw materials was determined by usual analytical methods; the refractive index was determined by an Abbé refractometer; density, by the normal suspension method; and softening point, by the Littleton method with the furnace as specified in Jour. Amer. Ceram. Soc., 10 [4], 259-63 (1927). The data indicate the following points: (1) When the silica was kept constant by increasing the dolomitic lime at the expense of soda an increase in softening point of 11 to 12°C per 1% increase was obtained. Likewise the density increases 0.004 and the refractive index 0.0015 per 1% increase of lime. (2) When the soda was kept constant the softening point was practically constant. The density decreases 0.011 and the refractive index 0.0030 per 1% increase of silica at the expense of lime. (3) When the lime was kept constant the increase in softening point per 1% increase in silica varied as follows : 5% lime 21°C, 8% lime 17°C, 10% lime 15°C, and 12% lime 12°C. The density decreased 0.008 and the refractive index 0.0015 per 1% increase in silica at the expense of soda. (4) A thermo-chemical relation of the softening points and the chemical compositions (calculated) closely paralleling the “liquidus” surfaces of Feild and Roysters' system: CaO-Na₂O-SiO₂.     

A METHOD FOR MEASURING THE SOFTENING TEMPERATURE OF GLASSES1

For the purpose of measurement the softening point of glasses is defined as that temperature at which a uniform thread of glass .65 mm to 1 mm in diameter suspended in a vertical position in an electric furnace of specified characteristic will elongate at the rate of 1 mm per minute. The measurements on a given glass are reproducible to within 1 to 2°C. This method has been found useful as control of glass composition in melting units as well as a point of reference to distinguish between different glasses. Data are given showing the variation in softening point of a tank glass and a pot glass over an interval of time.     

THE THERMAL EXPANSION OF REFRACTORIES1

The thermal expansion or contraction of a number of typical refractories has been measured up to 1700°C in a neutral or slightly oxidizing atmosphere. In nearly every case the expansion curve has been carried to a higher temperature than given by previous data. In a few cases the expansion curve has been obtained for materials that have not been studied in this way before. It is believed that the expansion curve of a brick, if carried to the softening point, gives valuable information as to the performance of that brick in service.     

Nonlinear viscoelastic behavior of butadiene–acrylonitrile copolymers filled with carbon black

Various viscoelastic measurements including dynamic mechanical measurements in tension at 110 Hz from ?60° to 160°C, tensile stress relaxation measurements with 100% elongation at 25°, 54°, and 98°C, capillary flow measurements at 70°, 100°, and 125°C, and high-speed tensile stress–strain measurements carried to break at 25°, 56°, and 98°C were performed on four samples of carbon black-filled butadiene–acrylonitrile copolymers. All the data were treated with the same equation for time–temperature conversion. The capillary viscosity–shear rate curves were significantly lower than the complex viscosity–angular frequency curves, indicating “strain softening” with extrusion. The viscosity was estimated from the stress–strain relationship at the yield point. The viscosity as a function of the strain rate is significantly higher than the complex viscosity as a function of angular frequency, indicating “strain hardening” with extension. The strain softening and strain hardening are attributable to the structural changes upon deformation of the carbon black-filled elastomers. With the unfilled elastomers, neither strain softening nor strain hardening were observed in similar measurements.     

Metal-like peak stress behavior of yttrium-doped BaCeO3 ceramic

The high-temperature mechanical behavior of polycrystalline 5 at% yttrium-doped barium cerate with submicronic grain size (d = 0.5 µm) has been studied in compression between 1200 and 1300 °C at different initial strain rates. The true stress – strain curves display an initial peak stress followed by a softening stage and then by an extended steady-state stage; the magnitude of the peak stress is strongly dependent on strain rate and temperature. These characteristics are very similar to those found in metals and metallic alloys that exhibit dynamic recrystallization during creep at elevated temperatures. Microstructural observations by scanning and transmission electron microscopy have shown that the grain structure is progressively refined with increasing strain due to the strong interaction between dislocations and pre-existing twin boundaries, originated by the various crystal transformations that occur upon cooling from the sintering temperature. The empirical equations used in metals to describe the relationship between strain rate, peak stress, and peak strain are also valid in the present ceramic material.     

Creep of Nextel™ 610 Fiber at 1100°C in Air and in Steam

Creep of Nextel^?610 fibers was investigated at 1100°C and 100–500 MPa in air and in steam. The effect of loading rate on fiber tensile strength was also explored. The presence of steam accelerated creep and reduced fiber lifetimes. Loading rate had a considerable effect on tensile strength in steam, but not in air. A linear elastic crack growth model was used to predict the creep lifetimes from the constant loading rate data. The dependence of tensile strength on loading rate and the predictability of creep lifetimes suggest that the failure mechanism in steam was environmentally assisted subcritical crack growth. The creep‐rupture data were analyzed in terms of a Monkman‐Grant (MG) relationship. Monkman‐Grant parameters for creep‐rupture data were the same in steam and air, and predicted creep‐rupture at 1100°C in both environments. A grain‐size increase of about 25% was observed by TEM after 100 h at 1100°C in steam, which was about two times that observed in air.     

Synthesis of Al2O3/SiO2 nano‐nano composite ceramics under high pressure and its inverse Hall–Petch behavior

We report the synthesis of alumina/stishovite nano‐nano composite ceramics through a pressure‐induced dissociation in Al₂SiO₅ at a pressure of 15.6 GPa and temperatures of 1300°C‐1900°C. Stishovite is a high‐pressure polymorph of silica and the hardest known oxide at ambient conditions. The grain size of the composites increases with synthesis temperature from ~15 to ~750 nm. The composite is harder than alumina and the hardness increases with reducing grain size down to ~80 nm following a Hall–Petch relation. The maximum hardness with grain size of 81 nm is 23 ± 1 GPa. A softening with reducing grain size was observed below this grain size down to ~15 nm, which is known as inverse Hall–Petch behavior. The grain size dependence of the hardness might be explained by a composite model with a softer grain‐boundary phase.     

THE EFFECT OF HEAT ON THE STRENGTH OF CALCINED KIESELGUHR-PORTLAND CEMENT MIXTURES1

The effect of heat upon the strength of this material is shown. This decreases rapidly at 100°C and remains fairly constant between 200° and 500°C. It decreases until 800° where a slight increase is shown between this and 1000°C. Above this the strength decreases.     

Effect of temperature and pressure treatment on the porosity of expanded polytetrafluoroethylene films

Small‐angle neutron scattering was performed on a series of expanded polytetrafluoroethylene membranes that were subjected to thermal treatment at a maximum of 320°C at pressures up to 517 kPa. The scattering data indicate the existence of monodisperse pores of 2.7‐Å radius, and a polydisperse set of scatterers with surface fractal properties. The thermal treatment had no significant effect on the structure, given that the maximum temperature was below the softening point of the polymer. The effect of increasing pressure was to increase the fractal dimension and to decrease the porosity void fractions. A linear relationship was noted between the Porod invariant values and the applied pressure. The pressure treatment had no effect on the size of the 2.7‐Å pores. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1579–1582, 2003     

THE REVERSIBLE THERMAL EXPANSION OF REFRACTORY MATERIALS

The reversible thermal expansion from 15–1000°C was measured for kaolin, siliceous and aluminous fire clays, quartzite, alumina, magnesia, and carborundum, after preliminary burnings at cones 06, 9, 14 and 20, and as well as for English commercial silica bricks before and after use in a coke oven and the roof of a steel furnace. Kaolin and bauxitic fire clay after calcination have a regular reversible thermal expansion which does not vary much with the temperature of calcination. Siliceous fire clays, after calcination at cone 06 (980°C) or cone 9 (1280°C) display irregularities (departures from uniformity) in their expansion. Between 500° and 600°C they show a large expansion due to contained quartz and on cooling the contraction in that region is larger than the corresponding expansion. Moreover, the expansion between 100° and 250°C after being fired to cone 9 (1280°C) exceeds the average. After calcination at higher temperatures, cone 14 (1410°C) or cone 20 (1530°C). these materials gradually lose these peculiarities until on incipient vitrification a linear expansion similar to that of kaolin is attained. This change is due to the destruction of quartz by its interaction with the clay material and fluxes; it takes place most easily in a fine-grained, rather friable clay such as ball clay. The previous thermal treatment necessary for a particular clay in order to obtain regular expansion in use can only be determined by trial. It can be stated with confidence that in such a piece of apparatus as a glass pot or crucible, a distinct gain will result from maintenance at a high temperature for some time before use, but that the red heat of an ordinary pot arch is useless for the purpose. An increase in the porosity of a fire clay was accompanied by a corresponding decrease in expansion between 15° and 1000°C until a porosity of 50% was attained. Further increase in porosity produced very little change in the expansion. No irregularities in expansion were shown by magnesia brick, carborundum, or alumina bonded with 10% of ball clay. Welsh quartzite with lime bond, either unfired or after burning at cone 06, had a large expansion to 550 °C and a much larger expansion from 550–600 °C due to the inversion of α to β quartz while from 600–1000°C a slight contraction took place. Firing to cone 9 converted part of the quartz into cristobalite, thus increasing the expansion from 200–250°C. This conversion was considerably increased on burning for two hours at cone 14, which greatly reduced the expansion from 550–600°C with a corresponding increase of that from 200–250°C. The conversion of the quartz into cristobalite was completed by a further heating for two hours at cone 20. Determinations of refractive indices and specific gravities confirmed these results. Flint inverted to cristobalite with greater ease than quartz. Commercial silica brick consisted chiefly of cristobalite and unconverted quartz and showed a large expansion up to 300°C, followed by a considerably smaller but regular expansion to 550°C. From 550° to 600°C the rate of expansion was considerably increased, but above 600°C the change in dimensions was small. The innermost exposed layer of a silica brick after use in a coke oven was an impure glass with a steady expansion, but only half as large as that of the layers of brick behind, which was made for shelling away. A silica brick after use in a steel furnace was divided into four layers. The layer exposed to the furnace heat was practically all cristobalite and silicates, the next layer the same, the third layer showed some α to β quartz expansion as well as the α to β cristobalite expansion, while the fourth (outermost) layer exposed to air was similar to the brick before use. In these bricks exposure to high temperature had evidently completed the change from quartz to cristobalite which had been largely effected in the kiln during manufacture. Little or no tridymite had formed. The reversible thermal expansion from 15–1000°C of the commercial silica brick examined was 1.1 to 1.3%, about double that of fire clay brick.     

A STUDY OF THE FACTORS INVOLVED IN THE SPALLING OF FIRE CLAY REFRACTORIES WITH SOME NOTES ON THE LOAD AND REHEATING TESTS AND THE EFFECT OF GRIND ON SHRINKAGE1

Of the three factors, elasticity, coefficient of expansion and rate of temperature change, which affect spalling, the former is by far the most important. Only small differences are found between fire clay mixtures of widely varying structure and composition in the rate at which they change in temperature under like conditions of heating. The coefficient of expansion varies directly with the silica content and differences in this respect of large order were found. However, the spalling on the particular mixtures tested varied almost inversely as the coefficient of expansion. This apparent discrepancy is explained on the basis of greater elastic properties of the brick which had high expansions. The elasticity may be varied between wide limits and is sufficiently important as to overbalance the effect of greater expansion. This property is accordingly the one upon which efforts directed toward the development of non-spalling brick should be centered. It was discovered that a plastic deformation could be obtained at as low a temperature as 635°C. This gives the effect of elasticity and undoubtedly has considerable influence on spalling at the higher temperature ranges. Results are given for a number of load tests which show clearly the importance of hard firing. The secondary expansion of brick made from Pennsylvania flint clay is shown to be influenced by the temperature of reheating, as well as its rate. Detailed results showing the effect of grind and firing on the finished size of the brick included in the investigation are also given.     

ACTIVITIES OF THE SOCIETY

A study of phase equilibria in the condensed system SiO₂–ZnO by the quenching method shows the existence of (a) only one compound, Zn₂SiO₄, the mclting point of which is 1512°C; (b) a region of two immiscible liquid phases in equilibrium with cristobalite at 1695°C, extending from 2 to 35 mol. per cent ZnO; (c) a euiectic between tridymite and Zn₂SiO₄ at 1432°C and 49.1 mol. per cent ZnO; (d) a eutectic between ZnO and Zn2 SiO4 at 1507°C and 77.5 mol. per ceut ZnO. The mclting point of Zno is found to be 1975°± 25°C. An irdium vessel is described which can be used in an induction furnace to obtain constant temperatures up to 2300°C in an oxidizing atmosphere.     

Untersuchungen zum Schmelzverhalten von verstrecktem Polyäthylen

The melting behaviour of drawn crystalline polymers is strongly influenced by the shrinkage which takes place simultaneously. This is shown by measurements with a differential colorimeter for 1200% drawn linear polyethylene. A higher melting point, a broader melting range and a slightly higher heat of fusion are observed, if the shrinkage is prevented during the melting experiment. Additionally, the observed melting point is falsified by superheating, if heating rates ≥ 0,5°C/min are used. This has been shown by annealing and irradiation experiments. The elimination of these two effects — shrinkage and superheating — which have been neglected in all earlier investigations, results in a melting peak temperature of 134,8°C and an upper limit of the melting range 137,2°C. Further, attention is drawn to the morphological changes and the related increase of the long period, which take place during heating the drawn material even if the shrinkage is prevented. The effect of these changes of structure upon the melting behaviour is not yet known.     

The sintering behaviour,mechanical properties and creep resistance of aligned polycrystalline yttrium aluminium garnet (YAG) fibres,produced from an aqueous sol–Gel precursor

Continuous ceramic fibres are finding applications as reinforcements in ceramic matrix composites, and yttrium aluminium garnet (YAG) is a particularly attractive candidate material on account of its creep resistance at high temperatures. A continuous, aligned, 5·5 μm diameter polycrystalline YAG fibre was manufactured from an aqueous sol–gel precursor which contained chlorine, and compared to a similar nitrate containing YAG precursor fibre we have reported previously. The precursor sol was found to be stable at a higher concentration than the nitrate containing sol, and this resulted in denser gel fibres which demonstrated better sintering at equivalent temperatures, giving a 98·5% sintered YAG fibre at 1550°C with a grain size of only 1 μm. However, on firing in air, the fibres formed fully crystalline YAG between 800 and 900°C, a temperature 100°C higher than the fibres containing nitrate, and they were weakened by the presence of many hemispherical faults. It was shown that both of these features were due to the retention of chlorine until the onset of formation of the crystalline YAG phase, and a series of steaming experiments were devised to remove the halide before this process could occur. It was found that steaming the precursor fibre from 200 to 500°C over 3 h, followed by firing to the required temperature in air, removed the chlorine and the problems it caused in the formation of the YAG phase without any change in the sintering characteristics or grain size. The steamed fibres were of a strength and quality comparable to fibres drawn from organometallic precursors. Empirical friability measurements showed the strength was maintained after firing to 1550°C, although there was a deterioration in apparent strain to break of the aligned blanket product above 1200°C. Conversely, the creep resistance, measured using the BSR test, improved with increase in temperature. The fibres fired to 1550°C were fully relaxed at temperatures 100–150°C below that of coarser, larger YAG fibres previously reported with a 3 μm grain size and 120 μm diameter. However, when allowance was made for grain size, the difference in creep rates was within the range obtained by extrapolating previous data using lattice diffusion and grain boundary effect models. Fibres fired to 1400°C were much finer grained but only slightly inferior to the 1550°C fibre in terms of creep. The alumina sol used in this work contained a significant level of sodium, and this suggests that the creep rates are effected by grain boundary impurities, especially sodium. A sodium free sol has been procured and further work is recommended to clarify the effect of impurities and improve fibre properties.     

PROTOTYPE HIGH TEMPERATURE/HIGH PRESSURE KILN FOR THE EVALUATION OF WOOD DRYING SCHEDULES

ABSTRACT

A new laboratory kiln was developed and built to perform over a very wide range of drying conditions. For example, the dry bulb temperature can vary from 30°C to 150°C and the dew point can be adjusted between 20°C and 130°C. Obviously, with such a high level of dew point, pressures over atmospheric pressure may be induced inside the chamber. For this reason, the kiln has been designed to withstand pressure of up to 3 bars. This kiln can also perform vacuum drying.

A programmable controller allows the temperature levels to be maintained within ± 0.2°C. Because the whole kiln can be heated only through the agitated water present at the bottom of the kiln, the load temperature can be increased up to 130°C in saturated conditions, without any change of moisture content.

The kiln has various sensors attached and is capable of withstanding severe conditions (high temperature, saturated vapour and elevated pressures). At present, air and water temperatures as well as temperature at different locations within the board can be collected during the drying process. A load cell and pressure gauges are also available. The first tests performed using this equipment are presented at the end of the paper.     

Influence of the heating rate on grain size of alumina ceramics prepared via spark plasma sintering (SPS)

The dependence of grain size on the heating rate has been investigated for alumina ceramics prepared via spark plasma sintering (SPS). For this purpose, the local grain size has been determined via position-dependent microscopic image analysis, using two independent grain size measures (mean chord length and Jeffries grain size). For alumina ceramics prepared with heating rates between 5 and 100 °C/min (pressure 80 MPa, maximum temperature 1300 °C) it is found that for higher heating rates the grain size is smaller. However, the microstructural non-uniformity is so large that any grain size determination that does not take this non-uniformity into account becomes meaningless, because grain size gradients from the specimen periphery to the center are larger than the differences in grain size due to different heating rates. Temperature and pressure gradients are discussed as the most plausible reasons for the microstructural non-uniformity.     

Evaluation of natural rubber latex-based PSAs containing aliphatic hydrocarbon tackifier dispersions with different softening points—Adhesive properties at different conditions

Natural rubber latex-based water–borne pressure sensitive adhesives (PSAs) have been formulated with three aliphatic hydrocarbon water-based dispersions (varying softening points) at two different resin addition levels (25% and 50%). Time–temperature superposition analysis using WLF approximations for adhesive peel has revealed that the adhesives formulated with 50% resin addition level show good adhesive behavior. It has also been determined from time–temperature superposition analysis that peel force increases systematically with softening point and peel rate. Correlation of viscoelastic behavior with adhesive properties suggests that at least 50% resin addition level is needed to bring the natural rubber-based formulations into PSA criteria as defined by Dahlquist and others. Adhesive property evaluations performed on a high surface energy substrate (stainless steel) and low surface energy substrate (LDPE) suggested that optimum tack, peel and shear properties at room temperature were obtained for a formulation containing a higher softening point dispersion (95 °C) at 50% resin addition level. Adhesive peel and tack tend to follow softening point trends as well. A 25% tackifier dispersion addition level did not provide any significant adhesion. Humid aging (50 °C and 100% relative humidity) evaluations of the water–borne adhesives seem to correlate well with the room temperature adhesive property observations.     

Deposition Rate,Texture, and Mechanical Properties of SiC Coatings Produced by Chemical Vapor Deposition at Different Temperatures

Silicon carbide (SiC) coatings were produced on carbon/carbon (C/C) composites substrates using chemical vapor deposition (CVD) at different temperatures (1100°C, 1200°C, and 1300°C). The deposition rate was found to increase with deposition temperature from 1100°C to 1200°C. From 1200°C to 1300°C, the deposition rate decreased. SiC coating produced at 1200°C exhibited a strong (111) texture compared with the coatings produced at other temperatures. Both hardness and Young's modulus were also found to be higher in the coating produced at 1200°C. The variation in mechanical properties with the increase in temperature from 1100°C to 1300°C showed a direct correlation with the change in deposition rate and (111) texture. Microstructure analysis shows that the change in CVD temperature leads to the change in grain size, crystallinity, and density of stacking faults of SiC coatings, which appears to have no significant effect on mechanical properties of SiC compared with the texture observed in SiC coating. For the coating deposited at 1200°C, both the hardness and Young's modulus increased gradually from the substrate/coating interface to the top surface. The nonuniformity of mechanical properties along the cross‐section of the coating is attributed to the nonuniform microstructure.     

INFLUENCE OF BATCH MIXING TIME AND BATCH GRAIN SIZE ON HOMOGENEITY OF A SODA-LIME-SILICA GLASS*

Density-spread determinations were made on a series of melts of a soda-lime-silica glass employing batches compounded from raw materials varying in particle size from 20- to 60-mesh to minus 200-mesh, which had been mixed by tumbling for one, ten, or thirty minutes. The two melting techniques employed were (1) melting for sixteen hours in a stationary platinum crucible at 1400°C. under conditions of even temperature distribution and consequently a minimum of convection mixing and (2) melting for four hours at 1400°C. in a rotating tilted crucible; this condition was intended to simulate convection mixing Under the experimental conditions employed, it was found that (1) batch mixing time has relatively little effect on the homogenizing rate, (2) homogenization increases rapidly with decrease in grain size, and (3) in all cases the 4-hour melting treatment with moderate mixing gives better homogeneity than sixteen hours melting time in a stationary crucible, this effect increasing with decrease in grain size. No significant difference in glass homogeneity resulted from three different methods of mixing, namely, tumbling, ball milling, and mixing in a muller-type mixer, although the homogenizing influence imposed probably was sufficient to mask any differences in uniformity of mixing that might have existed.