Materials based on highly concentrated ceramic binding suspensions (HCBS). The effect of heat treatment temperature on the strength properties of siliceous ceramic castables

Mechanical properties of siliceous ceramic castables shaped by vibration and static pressing with binders of quartz sand HCBS (pure and with a 5% additive of refractory clay) are studied. Other conditions being equal the porosity and the strength of the materials is affected by the content of the binder (varied from 10 to 33%). Ceramic castables heat treated at 1200 — 300°C exhibit a compressive strength of 50 –60 MPa at a porosity of 12–16%. The effect of the porosity on the strength of the materials is analyzed.     

Effect of structural defects formed in alloying of yttrium oxide by CeO2 and in heat treatment on phase transformations

X-ray methods are used for investigating the formation of substitutional — interstitial — subtractive solid solutions based on yttrium oxide alloyed by CeO₂ at 1900°C in an air medium. Single-phase solid solutions with disordered cubic structures of the C type are found in the region of dissolution of the CeO₂ alloying addition (0 – 10%). It is established that upon heating such specimens in the 25 – 1500°C range in an air medium the cubic C-phase is transformed into a monoclinic phase of type B₁. As a result of dissolution of the CeO₂ alloying addition anion vacancies forming in the yttrium oxide lattice and thermal vacancies forming at 1900°C influence strongly the temperature of the C - B₁ phase transformation and the temperature coefficients of linear expansion. Translated from Ogneupory, No. 9, pp. 8 – 10, September, 1995.     

Effect of the calcined andalusite aggregates on the micro-crack formation and thermal shock resistance of mullite castables

The effect of calcined andalusite aggregates on the micro-crack formation and thermal shock resistance of mullite castables was investigated and analyzed. The mullite castables were prepared from andalusite aggregates calcined at high temperatures. The results show that the micro-cracks from the transformation of andalusite to mullite can effectively relieve thermal stress, improving the thermal shock resistance of mullite castables. The micro-cracks generated decreased with increasing calcine temperatures of the andalusite aggregates. When the calcine temperature was increased from 1300 °C to 1500 °C, the thermal shock resistance of mullite castables was found to continuously increase. However, the thermal shock resistance of mullite castables with the andalusite aggregates calcined at 1600 °C is lower than those with the andalusite aggregates calcined at 1500 °C.     

Hot bending strength and creep behaviour at 1000–1400 °C of high alumina refractory castables with spinel,periclase and dolomite additions

The modulus of rupture and creep behaviour of refractory castables at high temperature (1000–1400 °C) with additions of spinel, periclase and dolomite has been studied. Three processing routes for obtaining refractory concretes within the alumina-rich zone of the Al₂O₃–MgO–CaO ternary system were employed. To achieve high temperature mechanical properties special attention was paid to the processing route (synthetic spinel, periclase and dolomite additions), and the composition (effect of synthetic or self-forming spinel and CaO contents).The results demonstrate that these refractory castables show a highly viscoplasticity behaviour at temperatures >1100 °C and a hot bending strength depending on the loading rate. Refractory castables made with synthetic spinel have lower high temperature bending strength values than castables made with periclase additions owing to their less viscoplastic behaviour. In this work neither the amount of spinel nor processing route chosen were found to have any significant influence on the hot bending tests between 1100 and 1400 °C. The creep tests show that in the temperature range of 1100–1300 °C the main reaction governing deformation is the interaction between the alumina and the calcium aluminate cement phases. Above 1300 °C, castables made first with dolomite, then with periclase and finally with synthetic spinel are more prone to deformation in that order.     

Stabilized dolomite-periclase articles

An experimental batch of stabilized dolomite-periclase refractories based on briquet (dolomite with some additional ingredients) and periclase has been produced. The articles are characterized by an open porosity of 4.6–8.0%, an ultimate compressive strength of 34.5–77.6 MPa, and a temperature of the beginning of softening under a load equal to 1300–1360°C. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 8, pp. 33–35, August, 1997.     

Synthesis of ethylene and propylene on a SAPO-34 silica—alumina—phosphate catalyst

A process for the preparation of ethylene and propylene from methanol on a microporous silica—alumina—phosphate SAPO-34 catalyst is described. The influence of the temperature and the nature and concentration of the diluting agent on the catalyst activity, its selectivity with respect to C₂₌-C₄₌ olefins, and ability to be regenerated were studied. The SAPO-34 catalyst was shown to be highly effective in the selectivity of ethylene and propylene formation; the total yield of C₂₌-C₄₌ olefins at 350–450°C was 77–84% and methanol conversion was up to 96–99%. In the conversion of methanol under helium at 450°C, the yield of ethylene (∼36%) was higher than at 375°C (∼29%), while the yield of propylene (∼30%) was lower (∼38%). The use of water and helium vapors as a diluent increased the yield of ethylene to ∼36% at 375°C and to ∼50% at 450°C. In the conversion of methanol at 450°C in water vapors without helium, the yield of ethylene reached ∼44–49% and the yield of propylene was 24–29%. The C₃₌ to C₂₌ ratio in the process varied from ∼0.5 to 1.5. The high efficiency of the SAPO-34 catalyst is the consequence of the microporous structure of zeolite and the high content of acid centers of medium strength. In the course of methanol conversion, the catalyst was deactivated due to coking. After regeneration with air at 550°C, the catalyst activity was completely restored, while the crystal structure and the acid properties did not change. The activity of the catalyst in a cycle is prolonged if water vapors are used as a diluent and the catalyst is processed at a high temperature with vapors. The industrial processes for the production of ethylene and propylene from nonpetroleum materials are not used in Russia. The results of this study are comparable to the data obtained from the UOP/Norsk Hydro process on the SAPO-34 catalyst. The catalyst can be recommended for further trials on an FCC type pilot plant with a moving catalyst bed.     

Effect of spinel content on hot strength of alumina-spinel castables in the temperature range 1000–1500°C

Hot modulus of rupture of Al₂O₃-spinel castables containing 5–15 wt% alumina-rich magnesia alumina spinel and 1·7 wt% CaO generally increases with increase in spinel content and temperature from 1000 to 1500°C. The magnitudes of hot modulus of rupture of castables containing 15 wt% spinel and 1·7 wt% CaO are 14·3 MPa at 1400°C and 15·6 MPa at 1500°C, while those of castables containing 20 wt% spinel and 1·7 wt% CaO are 12·5 MPa at 1400°C and 14·7 MPa at 1500°C. The former castables contained 15 wt% spinel of −75 μm size, while the latter contained 10 wt% spinel of +75 μm size and another 10 wt% spinel of −75 μm size. The bond linkage between the CA₆ and spinel grains in the matrix is believed to cause both the spinel content and temperature dependence of hot strength of Al₂O₃-spinel castables, as well as fine grain spinel even in amount less than coarser grain spinel to be more effective for enhancing hot strength. The trend of the magnitude of thermal expansion under load (0·2 MPa) above 1500°C of the castables is not necessarily indicative of the magnitude of hot modulus of rupture at 1400 or 1500°C. ©     

Materials based on highly concentrated ceramic binding suspensions (HCBS). Corundum and corundum-mullite ceramic castables based on plasticized hcbs of bauxite

HCBS of roasted Chinese bauxite, plasticized with additives of refractory clay, and corundum or bauxite filler are used for the production of pressed ceramic castables of corundum and mullite-corundum compositions with 93–95% and 80–85% A1₂,O₃, respectively. The optimum clay additive does not exceed 1–2%. The ceramic castables have a porosity of 15–18% and an ultimate compressive strength of 100–200 MPa after treatment at 1200–1300°C. As compared to traditional corundum refractories they are characterized by a finer capillary structure and a higher mechanical strength attained at a diminished (by a factor of 2–3) pressing pressure and a lower (by 400- 500°C) firing temperature.     

Catalytic synthesis of triazine compounds using a flexible technology

Based on laboratory pilot studies, we have developed a flow sheet for the catalytic synthesis of triazine compounds from carbamide using a flexible technology and a catalyst for this process. The main process parameters are as follows: a carbamide melt is fed into the reactor under a pressure of 0.8 MPa at 140–160°C; the volume rate of feeding the circulating gas into the reactor is 500–750 h⁻¹, its temperature is 350–500°C, and the melt-to-gas mass ratio is 1: (7–9). The temperature of synthesis in the reactor is 350–450°C; the pressure in the reactor is 0.1–0.2 MPa. The sublimation temperature is 180–200°C. The conversion of carbamide is ∼98%. The content of the target component in the product is ∼98.8%. Depending on the composition of the circulating gas, it is possible to obtain products of melamine, cyanuric acid, or melamine cyanurate. A catalyst in the form of promoted active aluminum oxide with an inner surface of 300 to 400 m²/g and a technique for its preparation have been developed.     

Kyanite concentrate of the Karabash deposit: Phase transformations during heating

Results are provided for a study of the phase transformation during heating of kyanite concentrates of the Karabash deposit, and the effect of temperature, soaking at the final temperature, and grain size on parameters of kyanite thermal decomposition. IR-spectra for kyanite concentrate of a different degree of transformation, and the microstrcuture of a partially decomposed kyanite grain are given. It is shown that thermal decomposition of kyanite proceeds in the range 1300–1400°C, and linear expansion, temperature for the start and decomposition rate depend on kyanite grain size, and the relaxation of elastic stresses of the kyanite crystal lattice is mainly limited by the decomposition reaction factor. __________ Translated from Novye Ogneupory, No. 9, pp. 24–29, September 2007.     

On the electric resistance of solid soap

Summary Electrical resistance values are reported for soaps of various moisture contents. Marked changes in resistance were found at 40–50°C. Below this temperature the logarithm of conductivity is a linear function of inverse temperature, and the slope of the curve is practically independent of water content. Above 40° resistance is markedly affected by the water content of the soap. For soaps containing 12–30% water, heating and cooling curves show definite maxima and minima in electrical resistance values. This effect is less obvious in soaps containing more than 30% water. The phase transition points estimated from resistance measurements are in good agreement with those deduced from other physical measurements.     

Column Fractionation of Canola Oil Deodorizer Distillate Using Supercritical Carbon Dioxide

Semi-continuous column fractionation of canola oil deodorizer distillate using supercritical CO₂ (SCCO₂) was carried out to determine the feasibility of value-added processing of this feed material for the recovery of bioactive components such as sterols and tocopherols and to determine the effect of operating conditions [pressure (20, 25 MPa using a temperature gradient of 70–100 °C), temperature (70, 100 °C) and a linear temperature gradient (70–100 °C at 25 MPa)] on extract yield and separation efficiency. Total extract yield increased significantly (p ≤ 0.05) with pressure, whereas at isobaric conditions (25 MPa) the highest yield was obtained at the lowest temperature tested (70 °C). Fractionation efficiency was reflected in the composition of fractions and was affected by operating conditions. Residue composition was determined by extract yield in addition to selectivity. Use of the thermal gradient (70–100 °C) decreased the content of volatiles, free fatty acids and tocopherols while increasing sterol content significantly (p ≤ 0.05) to a level of 40% (GC area %) in the residue obtained at 25 MPa. The findings indicate the potential of canola oil deodorizer distillate as a source of sterols and warrant further research on the countercurrent column fractionation to improve the separation efficiency.     

Microstructure evolution of hydration products and strength change of hydratable alumina-bonded castables below 1250°C

There have been reports that strength of hydratable alumina (HA)-bonded castables without silica fume drops significantly at 600°C and decreases substantially again at 1000°C. But the strength variation of the HA-bonded castables during the intermediate temperature range has not been investigated and elaborated from the perspective of phase evolution and microstructural change in the castables. In this work, the relationship between the change in the strength of castables and the microstructural characteristics of the HA-bonded castables was investigated. The phase and microstructure evolution of HA-bonded castables between 110°C and 1250°C were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TG). It has been found that strength drops of the HA-bonded castables during heating process do not mainly happen at the temperature at which HA hydrates decompose, but at the temperature at which the structure of dehydrated HA hydrates disintegrates.     

Rational electrothermal conditions for operation of lanthanum chromite electric heaters

A calculation of temperature fields is given for solid and tubular lanthanum chromite electric heaters. A triple diagram of “heater temperature — furnace temperature — specific surface power” is developed for heaters of generally employed sizes in the range of 1000 – 2000°C. Translated from Steklo i Keramika, No. 2, pp. 20–22, February, 2000.     

Microstructure and reactivity evolution of colloidal silica binder in different systems at elevated temperatures

Colloidal silica as nanostructured binder for refractory castables has attracted many attentions in recent years. In the present study, phase composition, microstructure and reactivity evolution of silica gel at different heating conditions were investigated to find suitable system for colloidal silica application. The results showed that atmosphere and carbon slightly affected phase composition of the silica gel at elevated temperatures, and the crystalline phases were composed of major α-cristobalite and minor α-tridymite. The morphology and particle size of the silica gel were greatly affected by atmosphere and carbon during heating. The spherical nano-silica particles with sizes of 40–50 nm rapidly grew into macroscale rod-like particles with temperature increasing from 800-1000 °C to above 1200 °C in air, and sintering of silica particles was observed. However, the size and morphology of the spherical nano-silica particles retained at high temperature in a reducing atmosphere, and many well developed columnar mullite crystals and some SiC whiskers formed on heating silica gel, alumina fines and carbon at 1500 °C, which was due to carbon inclusions retarding the growth of nano-silica particles and the nano silica remained high reactivity at high temperature. Thus, colloidal silica was suitable for application in carbon-containing refractory castables.     

Effect of silicone resin on the properties of silica ceramic cores by heating treatment

Silica ceramic cores prepared by heat-press molding were strengthened by impregnating silicone resin. The effect of heating treatment conditions on the properties of silica ceramic cores was analyzed. Results showed that the ambient bending strength increased from 9.3 ± 2.0 MPa to 24.8 ± 1.5 MPa by curing process at low temperature of 250 °C. However, further heating treatment at high temperature ranging from 1150 to 1300 °C made the strength of the samples lower than that of the cured samples owing to the decomposition of silicone resin. But the strength of the samples was still higher than that of raw samples. The increasing heating treatment temperature promoted an increase in the strength by a densification process.     

Some special features of the porosity of lowcement concretes on chamotte fillers

The effect of the content of microsilica in low-cement concrete with a chamotte scrap filler on the density and open porosity of the concrete at a firing temperature of up to 1300°C is considered. It is shown that the open porosity of the concrete with the proportion of microsilica raised to over 10% increases after firing at 1200 –1300°C due to the thick films of a silica glass formed in the structure. The gas phase present in the glass expands at the temperature of its melting (over 1100°C), forming large pores. The greatest number of large pores appears in the cement-microsilica composition after firing at 1300°C at a content of microsilica equal to 16%. The results of the study make it possible to optimize the content of microsilica in the composition of low-cement concrete on porous chamotte binders. It should be about 10%     

Induction time of hydrate formation in a flow loop

A set of experiments were developed to study the effect of the supersaturation on the induction time of the hydrate formation in a flow loop. Propane, carbon dioxide and a mixture of methane and propane were used to form hydrate in the loop. Induction time was measured with varying temperature and pressure which gave rise to change in the supersaturation. It was found that induction time was indirectly dependent on the supersaturation in all experiments. Measured values of induction time were in the range of 9–12 minutes for carbon dioxide, 82–103 minutes for propane and 7–22 minutes for 0.73C₁+0.27C₃ at the given operating conditions. Hydrate nucleation were carried out at 5°C and 3–5 MPa for carbon dioxide, 2–5°C and 1MPa for propane and 4°C and 2–4 MPa for 0.73C₁+ 0.27C₃. In order to calculate the induction time, a semiempirical correlation as a function of supersaturation was used. The equation parameters I were determined based on the experimental data via nonlinear regression.     

Microstructural evolution of carbon fibers by silicon vapor deposition and its effect on mullite-corundum castables

Carbon fibers (CFs) can be introduced to castables, due to the relative higher thermal conductivity and stronger damping properties. In this research, microstructural evolution of carbon fibers (CFs) in the presence of mixture of silicon and silica powders under the protection of carbon black was studied in the temperature range of 1000–1300 °C by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that some small amorphous SiO_x globules were formed on the surface of CFs at the temperature below 1200 °C. With the increase of the treated temperature, the size of globules became bigger and reached maximum at 1200 °C. The growth of SiO_x globules can be controlled by vapor-solid mechanism. In addition, the effects of these CFs on properties and microstructure of mullite-corundum castables were studied. The results showed that the CFs with SiO_x globules (CFs/SiO_X) could significantly improve the mechanical properties of the castables because the interfacial bonding strength between CFs/SiO_x and matrix is much stronger than the untreated CFs.     

Cast (self-flow) ceramic castables. 1. Fabrication and some properties of cast silica ceramic castables

A classification of methods for manufacturing cast (without the use of vibration) ceramic castables is suggested and the mechanism of their structure formation is formulated. Cast (self-flow) castable mixtures with a moisture content of 4.8–5.5% are developed based on HCBS of quartz sand and a polydisperse silica filler (d_max = 1–7 mm). The mixtures are used to cast ceramic castables with an open porosity of 11–16%. After drying and heat treatment at 1200 and 1300°C their ultimate compressive strength is 6–14, 20–35, and 60–120 MPa, respectively. As compared with similar pressed and rammed ceramic castables; cast ones are characterized by a lower porosity and a substantially higher strength.