Efficiency of adding very fine silica in high-silica and corundum ceramic concrete technology. Part 2

Results are provided for comparative evaluation of the properties of pressed specimens of a matrix system and ceramic concrete specimens prepared on the basis of bauxite with very fine quartz glass and quartz sand (VFQG and VFQS), and also the thermal expansion of castings based on a suspension of quartz sand, bauxite and bauxite ceramic concrete. It is established that high-silica molded and unmolded ceramic concretes prepared on a basis of bauxite VFQG (85%) and VFQS (15%) have improved physicomechanical properties. After firing at 1150 and 1420°C their open porosity is 16 – 18% and the ultimate strength in compression is 95 – 125 MPa. Their temperature for the onset of softening is above 1570°C and higher than 1650°C (for compositions containing SiC). Part 1 was published in Novye Ogneupory, No. 1 (2009). Translated from Novye Ogneupory, No. 3, pp. 34 – 40, March 2009.     

Production and service of high-alumina ceramic castables. 1. Ramming mixtures based on modified bauxite HCBS

The prospects of using bauxite-base HCBS in the production of high-quality ramming mixtures for lining blast furnace spouts are considered. A system of Chinese bauxite (filler) and bauxite HCBS (binder) is shown to give a ramming mixture with a porosity of 18 – 22% and σ_c of 120 MPa. The effect of some process factors on the properties of the new refractory material is considered. The life of the mixture in the main hearth spout is shown to be 70 – 90 thousand tons cast iron before the first repair at a consumption of 0.53 – 0.63 kg mixture per one ton cast iron. The processes that occur in the interaction between the material and blast furnace slags of various chemical compositions is considered. The characteristics of the developed mixture are compared with those of the standard ones. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 3, pp. 37–41, March, 2000.     

Rheotechnological properties of mixed suspensions in the SiO2 — Al2O3 system and some properties of materials base on them. II. Molten quartz — Bauxite system

Mixed suspensions in the molten quartz — bauxite system give castings with a much higher concentration and a lower porosity than HCBS based on alumina. Castings with a porosity of σ 14% have been obtained in mixed systems bearing 60 – 70% bauxite. The dependence of the porosity of the castings on the thermal expansion of heat-treated materials with a mixed composition is not additive. Materials bearing 50 – 80% bauxite have maximum strength properties. The ion potential of the solid phase of the initial suspension has the greatest effect on the rheotechnological properties of the suspensions. Transleted from Ogneupory i Technicheskaya Keramika, No. 8, pp. 25 – 29, August, 2000.     

Materials based on highly concentrated ceramic binding suspensions (HCBS). 3. Properties of mixed binders in the system of quartz sand HCBS and refractory clay

Mixed systems based on an initial HCBS of quartz sand and a suspension of refractory clay are described. It is established that the introduction of a small amount (2–5%) of clay has a substantial positive effect on the properties of quartz sand HCBS and materials based on them. The sedimentation stability, density, casting (binder) strength, and mechanical strength of the material a heat treatment at 800–1400°C are shown to increase. The content of the colloidal component (particles less than 0.1 μm in diameter) in the molded system is shown to depend on the porosity, strength, and drying shrinkage of the binder. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 8 pp. 22–26, August, 1997.     

Development of composite powders of the Ti-Al-N system produced from Ti-Al intermetallic compounds

The kinetics of nitrating intermetallic compounds Ti₃Al, TiAl, and TiAl₃ in the range of 1200–1400°C is studied; the compositions of the reaction products and the process mechanisms are identified. It is established that nitration of Ti₃Al and TiAl is intense at 1200°C and complete nitration is achieved at 1400°C with 3 h exposure. Nitration of TiAl₃ differs significantly from nitration of Ti₃Al and TiAl; the process has several stages, is slow, and complete nitration is achieved only after 6 h exposure at 1400°C. __________ Translated from Novye Ogneupory, No. 8, pp. 52–54, August, 2006.     

Aluminosilicate refractories based on high-alumina HCBS. Part 1. Refractories based on mixed HCBS in the system bauxite — silica

Comparative studies are provided for the properties of compacted and cast specimens of fine-grained ceramic concrete prepared on the basis of a mixed HCBS and two varieties of refractory filler with different Al₂O₃content from bauxite and chamotte based on Arkalyk clay. For specimens containing a chamotte filler, after firing at above 1250°C there is typically significant linear growth (up to 2.5%), connected with secondary mullite formation and caused by interphase reaction of SiO₂ from filler grains and very fine Al₂O₃ of the matrix system. The correlation of matrix system properties and materials with a refractory filler is analyzed     

Fabrication and properties of binders for high-alumina suspensions. 1. HCBS based on bauxite

The method of wet milling with step loading of the material has been used to prepare HCBS with a moisture content of 12–13% (the volume concentration of the solid phase ≤ 0.7) on the base of an available natural raw material, i.e., Chinese bauxite. The suspension is characterized by thixotropic-dilatant flow. The time of stabilization of the suspension by the method of gravitational mixing is shown to affect its rheological and technological properties more than those of HCBS of other compositions. The reduction of the viscosity of the suspension (by a factor of 4) decreases the porosity of the castings by 50–70 rel.% and increases their strength characteristics to 130–150 MPa after heat treatment at 1000‡C. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 6, pp. 21–26, June, 2000     

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.     

Investigation of La0.8Sr0.2CoO3/Ce0.85Sm0.15O2-x cathode performance of solid oxide fuel cell by electrochemical impedance spectroscopy: Effect of firing temperature

Perovskite type complex oxide L_0.8Sr_0.2CoO_3-δ symmetrical cells were prepared on Samaria doped ceria electrolyte Ce_0.85Sm_0.15O_2-x by using the screen-printing method in a laboratory scale. The performance of the symmetrical cell was investigated by using electrochemical spectroscopy at frequency ranging from 0.1–300 kHz. Effect of firing temperature from 975–1,050 °C was investigated under the controlled oxygen pressure from 0.002–0.21 atm and controlled measuring temperature from 635–782 °C. The preliminary results indicated that, for all cells prepared at different firing temperatures, the SEM and XRD did not indicate any differences between them. By using EIS, however, two impedance arcs were obviously observed. This first arc was found at high frequency region (<1,000 Hz) and the second one was observed at low frequency region (>10 Hz). The high frequency arc corresponded to the impedance of electron-transfer and ion-transfer processes occurring at the current collector/electrode and electrode/electrolyte interfaces. The low frequency arc was the convoluted contribution of the diffusion processes (non-charge transfer processes). Changing firing temperature, measuring temperature and oxygen pressure leads to changing of symmetrical cell performances. The activation energy of these symmetrical cells was around 1.5–2.0 eV depending on the firing temperature and oxygen pressure.     

Syntheses of 12-aminododecanoic and 11-aminoundecanoic acids from vernolic acid

12-Aminododecanoic acid and 11-aminoundecanoic acid, monomer precursors for nylon-12 and nylon-11, respectively, have been synthesized from vernolic (cis-12,13-epoxy-cis-9-octadecenoic) acid via a reaction sequence that includes the formation of 12-oxododecanoic acid oxime. Saponification of vernonia oil, followed by a low-temperature recrystallization at −20°C, gave 51% vernolic acid (97% purity, m.p. 23–25°C). Hydrogenation afforded cis-12,13-epoxystearic acid (m.p. 52–54°C, lit. m.p. 52–54°C), which upon oxidation with periodic acid in tertiary butyl alcohol gave 12-oxododecanoic acid with an isolated yield of 71.0%. Reaction of the oxoacid with hydroxylamine hydrochloride gave 12-oxododecanoic acid oxime, which was catalytically reduced to give 12-aminododecanoic acid with a yield greater than 85% and a melting point of 184–186°C (lit. m.p. 185–187°C). 11-Aminoundecanoic acid was prepared from the 12-oxododecanoic acid oxime via a three-step reaction sequence that involved a Beckmann rearrangement, Hofmann degradation, and hydrolysis. Thus, the aldoxime acid was hydrolyzed in the presence of nickel acetate tetrahydrate to give 11-carbamoylundecanoic acid (48% yield, m.p. 129–131°C, lit. m.p. 129–130°C). The amide was then treated with a solution of sodium methoxide and bromine at 70–80°C to give 11-(methoxycarbonylamino)undecanoic acid at 75% yield (m.p. 84–86°C; elemental analysis, calculated for C₁₃H₂₅NO₄: C, 60.19; H, 9.73; N, 5.40; O, 24.68%; found C, 60.02; H, 9.81; N, 5.26; O, 24.91%), which upon alkaline hydrolysis and subsequent neutralization gave 11-aminoundecanoic acid at 34% yield (m.p. 189–192°C, lit. m.p. 190°C). Mass spectrometric and ¹³C nuclear magnetic resonance data of the previously unreported 11-(methoxycarbonylamino)undecanoic acid is provided.     

The effect of supercooling on crystallization of cocoa butter-vegetable oil blends

The solid fat content (SFC), Avrami index (n), crystallization rate (z), fractal dimension (D), and the pre-exponential term [log(γ)] were determined in blends of cocoa butter (CB) with canola oil or soybean oil crystallized at temperatures (T _Cr) between 9.5 and 13.5°C. The relationship of these parameters with the elasticity (G′) and yield stress (σ^*) values of the crystallized blends was investigated, considering the equilibrium melting temperature (T _M ^o) and the supercooling (i.e., T _Cr ^o−T _M ^o) present in the blends. In general, supercooling was higher in the CB/soybean oil blend [T _M ^o=65.8°C (±3.0°C)] than in the CB/canola oil blend [T _M ^o=33.7°C (±4.9°C)]. Therefore, under similar T _Cr values, higher SFC and z values (P<0.05) were obtained with the CB/soybean oil blend. However, independent of T _Cr TAG followed a spherulitic crystal growth mechanism in both blends. Supercooling calculated with melting temperatures from DSC thermograms explained the SFC and z behavior just within each blend. However, supercooling calculated with T _M ^o explained both the SFC and z behavior within each blend and between the blends. Thus, independent of the blend used, SFC described the behavior of G′_eq and σ^* and pointed out the presence of two supercooling regions. In the lower supercooling region, G′_eq and σ^* decreased as SFC increased between 20 and 23%. In this region, the crystal network structures were formed by a mixture of small β′ crystals and large β crystals. In contrast, in the higher supercooling region (24 to 27% SFC), G′_eq and σ^* had a direct relationship with SFC, and the crystal network structure was formed mainly by small β′ crystals. However, we could not find a particular relationship that described the overall behavior of G′_eq and σ^* as a function of D and independent of the system investigated.     

Production of sintered high alumina refractories from Turkish bauxite ore

Abstract

Bauxite ore extracted from Seydis¸ehir-Konya in Turkey has been used for the production of sintered bauxite. The high iron and calcium in the bauxite were decreased to low levels by hydrochloric acid leaching. Temperature and acid concentration significantly affected the level of iron extraction from bauxite. The aluminium dissolution during acid leaching at 6M and below 70°C was ≤2%, and calcium dissolution was over 95%. XRD and XRF of leached bauxite revealed that the level of iron within the bauxite was decreased below 2% and that no significant TiO₂ or SiO₂ dissolved during leaching. XRD of leached bauxite sintered at 1400-1700°C for 4 h revealed only corundum (α -Al₂O₃) and mullite (3Al₂O₃.2SiO₂). SEM investigation showed that bauxite grains were in the form of large aggregates. The maximum bulk density obtained at 1700°C was low compared with commercial refractory bauxites and the leached bauxite therefore needed to be sintered for longer times at 1700°C or at higher temperatures.     

Preparation and properties of corundum HCBS and ceramic concretes. Part 1. Mixed HCBS in the system electrocorundum — very fine quartz glass

The effect of the composition of original molding systems and firing temperature on the properties of fine-grained (D _max = 1.5 mm) and medium grain sized (D _max = 4.0 mm) specimens of compacted corundum ceramic concretes with a corundum-mullite matrix system are studied. Optimum properties (open porosity of 14 – 15%, ultimate strength in compression of 150 – 200 MPa) are achieved in compositions with a matrix system content of 30 – 35%. A calculation and experimental method is used to determine matrix system porosity in ceramic concrete specimens in relation to their composition.     

Synthesis and properties of poly(tetramethyl-1,6-silpyrenylenesiloxane) derivative with phenyl groups on pyrenylene moiety

Poly(tetramethyl-1,6-silpyrenylenesiloxane) derivative with phenyl groups on pyrenylene moieties (P1) was prepared via polycondensation of disilanol monomer, i.e. 1,6-bis(dimethylhydroxysilyl)-3,8-diphenylpyrene (M1). P1 exhibited the very high glass transition temperature (T _g) of 191 °C. The temperature at 5% weight loss (T _d5) of P1 was 482 °C, indicating the relatively good thermostability of P1. P1 exhibited the bathochromic effect in the absorption and fluorescence spectra, indicating the expansion of π-conjugation by introducing phenyl groups onto pyrene skeleton as well as the σ–π and σ*–π* conjugation between pyrene and silyl moieties. In addition, P1 exhibited relatively weak excimer emission because of the inhibition of the excimer formation of pyrene skeleton by introduction of bulky phenyl groups onto pyrene skeleton. The fluorescence quantum yields (Φ_Fs) of M1 and P1 in chloroform were determined to be 0.46 and 0.37, respectively. It was revealed that M1 and P1 exhibited the higher fluorescence intensity than 1,6-diphenylpyrene, owing to the effect of the introduction of silyl moieties onto pyrene skeleton.     

Refractory paint

Compositions of a refractory paint for marking refractory preforms based on corundum, mullite and their mixtures at the stages of molding, firing, and service within a temperature range of 1000–1600°C have been developed. Compositions of oxide mixtures Fe₂O₃-TiO₂-Cr₂O₃-CoAl₂O₄ are used to mark articles fired at a temperature up to 1550°C. Cobalt aluminate is synthesized previously. Articles fired at a temperature of 1550–1600°C are marked with a paint additionally containing at most 1% Fe₂O₃. Firing initiates the formation of solid solutions in the marking material. These solid solutions (frequently of spinel type) exhibit low evaporativity compared to pure oxides, which preserves color brightness and high legibility of the marking pattern. The consistency of the aqueous paint solution and the thickness of the applied marking layer depend on the state of the refractory surface to be marked (density of the surface layer, pore size, and surface roughness). The paint compositions allow marking of the article after molding, drying, preliminary or final firing. Refractory paints have found manufacturing application in casting of refractory alloys for marking melting crucibles, protective nozzles, cases, and other ceramic articles. __________ Translated from Novye Ogneupory, No. 8, pp. 21–22, August, 2007.     

Effect of Pre-Melting Time on Crystallization of Poly(ethylene terephthalate)

In this study poly(ethylene terephthalate) (PET) was melted at 300°C, approximately 46°C above the crystalline melting point, T _m, for different times, i.e., Δt _m,=5, 8, and 10 min, and then quenched to different isothermal crystallization temperatures, T _c, ranging from 190°C to 230°C. The effect of pre-melting time, Δt _m, at 300°C on the degree of crystallinity and on crystalline morphology were investigated by differential scanning calorimetry (DSC) and polarized-light microscopy (PLM). After crystallization at low T _c, PLM data revealed the PET contained usual, positive, and unringed spherulites. After crystallization at high T _c PET contained unusual, ringed, and double-extinction spherulites. The experimental results reveal that increasing the pre-melting time Δt _m at 300°C causes an increment in T _c for usual–unusual, unringed–ringed, and positive–double-extinction transitions of the PET spherulites. The experimental results also show that PET with a pre-melting time Δt _m=8 min had higher crystallinity than those with pre-melting times Δt _m=5 and 10 min. These crystallization phenomena were attributed to the different numbers of residual unmelted PET crystallites as a result of the variation in pre-melting time, Δt _m, at 300°C.     

Aluminosilicate Refractories Based on High-Alumina HCBS.

Ceramic concrete specimens are prepared based on HCBS of mullite-silica composition (58% Al₂O₃) and fillers of similar and chamotte compositions, having markedly better properties than for traditional refractories with the same Al₂O₃ content. An ultimate strength in compression of 150 – 250 MPa with porosity of 6 – 11%, and a temperature for deformation under load T _g of 1540 and 1460 MPa are obtained correspondingly for ceramic concrete specimens with an Al₂O₃ content of 58 and 42%. With respect to T _g, mullite-silica ceramic concretes (58% Al₂O₃) correspond to traditional mullite (62 – 72% Al₂O₃), chamotte (42% Al₂O₃) and mullite-silica (45 – 62% Al₂O₃) refractories.     

Differential Scanning Calorimetry Analysis of Goat Fats: Comparison of Chemical Composition and Thermal Properties

The physical–chemical properties, fatty acid composition and thermal properties of goat subcutaneous (SF), tallow (TF) and intestinal (IF) fats were determined. SF differed from other fat types with respect to its lower melting (41.6 °C), lower saponification (190.3 mg KOH/g) and higher iodine (40.4) values as compared to those of other fats. Goat fat types contained palmitic acid (C_16:0), stearic acid (C_18:0), oleic acid (C_18:1ω9) and linoleic acid (C_18:2ω6) as the major components of the fatty acid composition (23.06–23.52, 22.95–39.03, 21.94–36.16 and 1.96–2.22%, respectively). A differential scanning calorimetry (DSC) study revealed that two characteristic peaks were detected in both crystallization and melting curves. Major peaks (T _peak) of TF and IF were similar and determined as 34.02–35.24 and 9.95–10.72 °C, respectively for the crystallization peaks and 15.11–18.26 and 50.70–52.76 °C, respectively for the melting peaks in the DSC curves; but those of SF (27.14 and 4.36 °C for crystallization peaks and 8.39 and 44.93 °C for melting peaks) differed remarkably from those of other fat types.     

Study on preparation and properties of novel reactive phenolic hydroxyl-containing polyimides

Novel reactive polyimides (PIs) containing phenolic hydroxyl functionalities were prepared from 4-(4-hydroxyphenyl)-2,6-bis[3-(4-aminophenoxy)phenyl]pyridine (m,p-HAPP) with various aromatic dianhydrides via one-step polycondensation procedure. The inherent viscosities of the PIs were 0.54–0.63 dL/g in DMF solution and most of them were readily soluble in common organic solvents such as DMF, DMAc, NMP, and m-Cresol, etc. Meanwhile, the PIs also had good thermal stability, with the glass transition temperature (T _g) of 221.7–310.5 °C, the temperature at 10 % weight loss of 524.1–579.3 °C in nitrogen atmosphere. Then commercial epoxy resin was cured in the presence of different ratios of the reactive polyimide, giving a series of polyimide modified epoxy films. Thermogravimetric analysis showed the increase of the temperature at 5 % weight loss of the films with the increase of the polyimide content; 296 °C for 0 %, 309 °C for 1.95 %, 337 °C for 3.85 % and 350 °C for 5.63 %.     

Effect of the temperature on the structure and mechanical properties of poly(ethylene terephthalate) fibres and yarns

The load—elongation diagrams were obtained for PETP yarns and monofilaments at different deformation temperatures, demonstrating the dependence of the σ(ε) curves on the testing temperature and the thermomechanical history of the samples. The dependences of the basic strain characteristics determined from the σ(ε) curves on the temperature can be used to predict the change in the mechanical properties of PETP yarns and fibres at high temperatures. In addition to the fundamental relaxation transition, the σ(ε) curves can be used to find a new transition in the 180°C region which controls the behavior of PETP yarns and fibres above the transition temperature. The thermomechanical tests and structural studies of the fibres at different temperatures allow correlating the transition found with crystallites and assigning it to an α_c transition based on the characteristic set of properties. St. Petersburg State University of Technology and Design. Translated fromKhimicheskie Volokna, No. 1, pp. 32–35, January–February, 2000.