- Email: [email protected]
04131 Thermochemistry of aqueous silicate solution precursors to ceramics
72
coatings, finite element analyses were carried out for various cases and the normalized stress intensity factors were obtained. The shorter the crack length and the thinner the coating, the sounder the coatings, according to the results. Furthermore, coatings representing a wide range of thermal and mechanical properties have a close normalized stress intensity factor values. The paper concludes that the finite element technique can be used to optimize the design and the processing of ceramic coatings.
Oxygen dependence on superconducting proper90l04123 ties of La,.85Sr0.,5Cu0.,_r,ceramic and crystal samples Buffeteau, B. et al. Physic0 C, 1998, 294, (l/2), 55-70. LSCO ceramic samples have been produced by a sol-gel method, whose high quality is demonstrated by NQR and specific heat measurements. Many studies concerning the influence of phase purity, strontium homogeneity and oxygen stoichiometry on the superconducting properties of Lai.ssSr,i.,sCu04.~ were carried out using X-ray diffraction, SQUID magnetization and specific heat measurements. The control of strontium and oxygen content achieved on ceramic samples afforded the opportunity to optimize the LSCO ‘crystal’ grown by the travelling solvent floating zone method. Low-temperature sp. heat measurements were also performed between 0.3 and 8 K on both Lai.&r~,.i&u04 ceramic and ‘crystal’ samples in the T-range 0.3-8 K. The specific heat residuals of the samples proved to be lower than those already measured and published by other groups.
Packing for regular distribution of liquid phase 99104124 over the cross-section of column-type apparatuses Darakchiev, R. ef al. Chemical Engineering and Processing, 1998, 37, (2). 141-147. The paper studies the performance of ceramic honeycomb packing with inclined walls, applied as a distribution layer to be placed under a multipoint liquid distributor with regularly perforated orifices. The distribution layer must have a good spreading ability without increasing the pressure drop. The aim is to create good liquid distribution over the main honeycomb packing layer with vertical walls. A study was performed on 10 packing modifications which differ in height, dimension of holes, wall thickness and wall inclination and the best configuration from the hydraulic and energy saving points of view is shown. Equations are obtained for determination of the liquid phase distribution coefficient and the pressure drop of dry and wet packings.
Physicochemicai studies of zirconia and magnesia98104125 doped zirconia ceramic powder Alditar, J. ef al. J. Chemical Sot. Pak., 1997, 19, (2), 93-103. Spray pyrolysis has been used to synthesize spherical fine ZrOz and 9 mol% MgO-doped ZrOz ceramic powders from a hydrothermally treated solution of zirconium and magnesium salts. Synthesized powders can be sintered into uniformly sized fine grained ceramic of >97% theoretical density at a temperature as low as 1100°C. The phases, purity, crystallite size, agglomeration structure, particle size, specific surface area, pore size distribution and porosity of ZrOz and MgO-ZrOz ceramics were measured by XRD, SEM, nitrogen-gas adsorption and mercury-diffusion techniques. X-ray diffraction and SEM results showed that the ZrOz and MgO-ZrOz remained amorphous up to 700°C but on increasing the heat treatment temperature to around 1200°C for 8 h, monoclinic crystals were obtained. Thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques were used to measure the burnout temperatures and enthalpy (AH) of polyvinyl alcohol (PVA) and methylcellulose (MC) polymers used as binders. In an oxidizing atmosphere, there is 100% burnout of these polymers, while 90% burnout was achieved in an inert atm.
99iQ4726
Process for hot repair of refractories
Dnvydov, V. V. et al. Koks Khim., 1997, (ll), 9-12. (In Russian) The paper presents the economic and technological efficiency of ceramic welding for the repair and maintenance of the refractory linings of coking furnaces developed in Russia. Hot furnaces are used for the ceramic welding, significantly decreasing the operation interruption. The service life of the coking furnaces seems to have increased significantly by the application of this method.
Process for manufacturing ceramics and permeable 99lO4127 ceramics, using wastes, especially 100% wastes Lee, S.-L. PCT Int. Appl. WO 98 11,033 (Cl. C04B18/06), 19 Mar 1998, KR Appl. 9,640,078, 16 Sep 1996, 19 pp. The manufacturing process is described. It comprises incinerating the wastes to obtain a fine ash powder, mixing 100 weight parts ashes with 3-10 weight parts silicates containing >50% sodium silicate, a small amount of pottery stone and glass. The mixture is then press moulded at 400-2000 kg/ cm* and sintered at lOO-1400°C for 3-4 h. The sintered material is then comminuted to particle size ~10 mm and 100 weight parts of the comminuted material is mixed with 3-10 weight parts silicate mixture as above, press moulded at 1000-2000 kg/cm2 and sintered at 1100-1400” for 3-4 h. Using wastes only, the process comprises comminuting coal ashes to obtain fine ash powder, mixing 100 weight parts ashes with 8-11 weight parts water in a high-speed mixer, press moulding the mixture at 1200 kg/ cm* and sintering the moulded material at llOO-1240°C for 3-4 h.
Refractories/ceramics
(properties, production,
applications)
The quantification of different forms of cristobalite 98/04i 28 in devltrified alumina-silicate ceramic fibers Butler, M. A. and Dyson, D. J. J. Appl. Ctystallogr., 1997, 30, (4), 467-475. Amorphous alumina-silicate fibres will devitrify into crystal phases when heat treated, which become stable on cooling at room temperature. X-ray diffraction was used to identify and quantify the phases present in such products; mullite and two distinct forms of cristobalite were observed. One form of cristobalite was identified as a-cristabolite and the second form was designated as cY’-cristobalite. An internal standard approach was used to enable calibration curves to be obtained for the three crystallite phases, including the o’-cristobalite for which no commercially available standard exists. The accuracy of the methods was estimated as +5% for all three crystalline phases present. This was achieved by quantifying the proportion of a’cristabolite in a standard alumina-silicate fibre after heat treatment for 48 h at 1773 K and then using this material as the ‘standard’ for ncristobalite.
Study on isothermal crystallization kinetics of mica glass ceramics
9alo4129
Cheng, K. er al. Wuji Cailiao Xuebao, 1997, 12, (2), 149-155. (In Chinese) By means of XRD, SEM, and DTA, the isothermal crystallization kinetics of mica-containing glass ceramics with addition of TiOz as nucleation agent was studied. The results indicated that the growth of KMgsAISi30i0F2 is a two-dimensional process, controlled by the crystal-glass interface reaction.
Thermochemical interactions at electrode 99lO4130 faces in electroceramic applications (contact resistance) Cann, D. P. 1997, 182 pp. Avail. UMI, Order No. DA9802600. Absrr. Inr., B, 1998, 58, (7), 3860.
inter-
From Diss.
99JQ4131 Thermochemistry of aqueous silicate solution precursors to ceramics Sefcik, J. and McCormick, A. V. AIChE J., 1997, 43, (llA), 2773-2784. For the design, optimization and control of sol-gel, colloid and zeolite preparations, a quantitative understanding of the thermochemistry of silicate solution systems is necessary. This review is intended to be a compendium of ready information for the growing number of chemical engineers active in solution-based materials synthesis. Experimental measurements of silica solubility, silicate speciation and silanol deprotonation in aqueous solutions are summarized and critiqued. In addition, the thermochemical properties of monomeric and dimeric silicate anions are assessed. The trends that are then evident are compared with expectations from simplistic gas-phase MO calculations to illustrate the importance of solvation. Finally, the equilibrium behaviour of simple silicate oligomers is rationalized and the future direction to quantitative modelling of the behaviour of more complex oligomers is suggested.
Thermochemistry of electrodes in electroceramic 99/04132 applications Cann, D. P. and Randall, C. A. Proc. SPIE-Int. Sot. Opt. Eng., 1997, 3235, 368-373. With continuing miniaturization trends in microelectronics, the electrodeelectric ceramic interface will have a greater influence upon the overall device properties of electroceramic devices. The characteristics of such an interface affects properties such as contact resistance, fatigue, high frequency conductor loss and mechanical strength. Establishing a fundamental perspective on the interfacial properties will be crucial in designing metalizations for electroceramic applications. In this study, the electric properties of electrode-thermistor interfaces are related to the thermochemical properties of the interface. The thermochemical characteristics were quantified through the thermodynamic work of adhesion (W,,) measured via sessile drop wetting experiments of metallic electrodes on electroceramic substrates. The electric contact properties of the interface were in turn quantified by impedance spectroscopy and current-voltage measurements. Interfaces with strong chemical interactions were found to typically have low contact resistances, while interfaces with weak chemical interactions had large contact resistances. Furthermore, it was shown that the Wad and hence the contact properties can be manipulated by the addition of chemical active elements to the electrode metal which significantly increase the Wad and decrease the contact resistance. It is possible to optimize the electric properties of the electrode-electroceramic interface by designing the composition of the electrode specific to the composition of the electroceramic using knowledge of the thermochemical interactions present at the interface.
Use of filter-press coal-bearing refuse for manu99lO4133 facturing masonry ceramic products Cojocaru, F. er al. Morer. Cons&., 1997, 27, (3) 220-222. (In Romanian) An analysis is made of the implications and the advantages that may be brought about by reintroducing the use of filtered coal-bearing slime for brick manufacture. The advantages include saving high quality fuels, reducing the consumption of raw materials, utilizing the large quantities of wastes and reducing pollution on the Jiu Valley. The efficiency of the process based on calculations is presented.
Fuel and Energy Abstracts
September 1998 395
coatings, finite element analyses were carried out for various cases and the normalized stress intensity factors were obtained. The shorter the crack length and the thinner the coating, the sounder the coatings, according to the results. Furthermore, coatings representing a wide range of thermal and mechanical properties have a close normalized stress intensity factor values. The paper concludes that the finite element technique can be used to optimize the design and the processing of ceramic coatings.
Oxygen dependence on superconducting proper90l04123 ties of La,.85Sr0.,5Cu0.,_r,ceramic and crystal samples Buffeteau, B. et al. Physic0 C, 1998, 294, (l/2), 55-70. LSCO ceramic samples have been produced by a sol-gel method, whose high quality is demonstrated by NQR and specific heat measurements. Many studies concerning the influence of phase purity, strontium homogeneity and oxygen stoichiometry on the superconducting properties of Lai.ssSr,i.,sCu04.~ were carried out using X-ray diffraction, SQUID magnetization and specific heat measurements. The control of strontium and oxygen content achieved on ceramic samples afforded the opportunity to optimize the LSCO ‘crystal’ grown by the travelling solvent floating zone method. Low-temperature sp. heat measurements were also performed between 0.3 and 8 K on both Lai.&r~,.i&u04 ceramic and ‘crystal’ samples in the T-range 0.3-8 K. The specific heat residuals of the samples proved to be lower than those already measured and published by other groups.
Packing for regular distribution of liquid phase 99104124 over the cross-section of column-type apparatuses Darakchiev, R. ef al. Chemical Engineering and Processing, 1998, 37, (2). 141-147. The paper studies the performance of ceramic honeycomb packing with inclined walls, applied as a distribution layer to be placed under a multipoint liquid distributor with regularly perforated orifices. The distribution layer must have a good spreading ability without increasing the pressure drop. The aim is to create good liquid distribution over the main honeycomb packing layer with vertical walls. A study was performed on 10 packing modifications which differ in height, dimension of holes, wall thickness and wall inclination and the best configuration from the hydraulic and energy saving points of view is shown. Equations are obtained for determination of the liquid phase distribution coefficient and the pressure drop of dry and wet packings.
Physicochemicai studies of zirconia and magnesia98104125 doped zirconia ceramic powder Alditar, J. ef al. J. Chemical Sot. Pak., 1997, 19, (2), 93-103. Spray pyrolysis has been used to synthesize spherical fine ZrOz and 9 mol% MgO-doped ZrOz ceramic powders from a hydrothermally treated solution of zirconium and magnesium salts. Synthesized powders can be sintered into uniformly sized fine grained ceramic of >97% theoretical density at a temperature as low as 1100°C. The phases, purity, crystallite size, agglomeration structure, particle size, specific surface area, pore size distribution and porosity of ZrOz and MgO-ZrOz ceramics were measured by XRD, SEM, nitrogen-gas adsorption and mercury-diffusion techniques. X-ray diffraction and SEM results showed that the ZrOz and MgO-ZrOz remained amorphous up to 700°C but on increasing the heat treatment temperature to around 1200°C for 8 h, monoclinic crystals were obtained. Thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques were used to measure the burnout temperatures and enthalpy (AH) of polyvinyl alcohol (PVA) and methylcellulose (MC) polymers used as binders. In an oxidizing atmosphere, there is 100% burnout of these polymers, while 90% burnout was achieved in an inert atm.
99iQ4726
Process for hot repair of refractories
Dnvydov, V. V. et al. Koks Khim., 1997, (ll), 9-12. (In Russian) The paper presents the economic and technological efficiency of ceramic welding for the repair and maintenance of the refractory linings of coking furnaces developed in Russia. Hot furnaces are used for the ceramic welding, significantly decreasing the operation interruption. The service life of the coking furnaces seems to have increased significantly by the application of this method.
Process for manufacturing ceramics and permeable 99lO4127 ceramics, using wastes, especially 100% wastes Lee, S.-L. PCT Int. Appl. WO 98 11,033 (Cl. C04B18/06), 19 Mar 1998, KR Appl. 9,640,078, 16 Sep 1996, 19 pp. The manufacturing process is described. It comprises incinerating the wastes to obtain a fine ash powder, mixing 100 weight parts ashes with 3-10 weight parts silicates containing >50% sodium silicate, a small amount of pottery stone and glass. The mixture is then press moulded at 400-2000 kg/ cm* and sintered at lOO-1400°C for 3-4 h. The sintered material is then comminuted to particle size ~10 mm and 100 weight parts of the comminuted material is mixed with 3-10 weight parts silicate mixture as above, press moulded at 1000-2000 kg/cm2 and sintered at 1100-1400” for 3-4 h. Using wastes only, the process comprises comminuting coal ashes to obtain fine ash powder, mixing 100 weight parts ashes with 8-11 weight parts water in a high-speed mixer, press moulding the mixture at 1200 kg/ cm* and sintering the moulded material at llOO-1240°C for 3-4 h.
Refractories/ceramics
(properties, production,
applications)
The quantification of different forms of cristobalite 98/04i 28 in devltrified alumina-silicate ceramic fibers Butler, M. A. and Dyson, D. J. J. Appl. Ctystallogr., 1997, 30, (4), 467-475. Amorphous alumina-silicate fibres will devitrify into crystal phases when heat treated, which become stable on cooling at room temperature. X-ray diffraction was used to identify and quantify the phases present in such products; mullite and two distinct forms of cristobalite were observed. One form of cristobalite was identified as a-cristabolite and the second form was designated as cY’-cristobalite. An internal standard approach was used to enable calibration curves to be obtained for the three crystallite phases, including the o’-cristobalite for which no commercially available standard exists. The accuracy of the methods was estimated as +5% for all three crystalline phases present. This was achieved by quantifying the proportion of a’cristabolite in a standard alumina-silicate fibre after heat treatment for 48 h at 1773 K and then using this material as the ‘standard’ for ncristobalite.
Study on isothermal crystallization kinetics of mica glass ceramics
9alo4129
Cheng, K. er al. Wuji Cailiao Xuebao, 1997, 12, (2), 149-155. (In Chinese) By means of XRD, SEM, and DTA, the isothermal crystallization kinetics of mica-containing glass ceramics with addition of TiOz as nucleation agent was studied. The results indicated that the growth of KMgsAISi30i0F2 is a two-dimensional process, controlled by the crystal-glass interface reaction.
Thermochemical interactions at electrode 99lO4130 faces in electroceramic applications (contact resistance) Cann, D. P. 1997, 182 pp. Avail. UMI, Order No. DA9802600. Absrr. Inr., B, 1998, 58, (7), 3860.
inter-
From Diss.
99JQ4131 Thermochemistry of aqueous silicate solution precursors to ceramics Sefcik, J. and McCormick, A. V. AIChE J., 1997, 43, (llA), 2773-2784. For the design, optimization and control of sol-gel, colloid and zeolite preparations, a quantitative understanding of the thermochemistry of silicate solution systems is necessary. This review is intended to be a compendium of ready information for the growing number of chemical engineers active in solution-based materials synthesis. Experimental measurements of silica solubility, silicate speciation and silanol deprotonation in aqueous solutions are summarized and critiqued. In addition, the thermochemical properties of monomeric and dimeric silicate anions are assessed. The trends that are then evident are compared with expectations from simplistic gas-phase MO calculations to illustrate the importance of solvation. Finally, the equilibrium behaviour of simple silicate oligomers is rationalized and the future direction to quantitative modelling of the behaviour of more complex oligomers is suggested.
Thermochemistry of electrodes in electroceramic 99/04132 applications Cann, D. P. and Randall, C. A. Proc. SPIE-Int. Sot. Opt. Eng., 1997, 3235, 368-373. With continuing miniaturization trends in microelectronics, the electrodeelectric ceramic interface will have a greater influence upon the overall device properties of electroceramic devices. The characteristics of such an interface affects properties such as contact resistance, fatigue, high frequency conductor loss and mechanical strength. Establishing a fundamental perspective on the interfacial properties will be crucial in designing metalizations for electroceramic applications. In this study, the electric properties of electrode-thermistor interfaces are related to the thermochemical properties of the interface. The thermochemical characteristics were quantified through the thermodynamic work of adhesion (W,,) measured via sessile drop wetting experiments of metallic electrodes on electroceramic substrates. The electric contact properties of the interface were in turn quantified by impedance spectroscopy and current-voltage measurements. Interfaces with strong chemical interactions were found to typically have low contact resistances, while interfaces with weak chemical interactions had large contact resistances. Furthermore, it was shown that the Wad and hence the contact properties can be manipulated by the addition of chemical active elements to the electrode metal which significantly increase the Wad and decrease the contact resistance. It is possible to optimize the electric properties of the electrode-electroceramic interface by designing the composition of the electrode specific to the composition of the electroceramic using knowledge of the thermochemical interactions present at the interface.
Use of filter-press coal-bearing refuse for manu99lO4133 facturing masonry ceramic products Cojocaru, F. er al. Morer. Cons&., 1997, 27, (3) 220-222. (In Romanian) An analysis is made of the implications and the advantages that may be brought about by reintroducing the use of filtered coal-bearing slime for brick manufacture. The advantages include saving high quality fuels, reducing the consumption of raw materials, utilizing the large quantities of wastes and reducing pollution on the Jiu Valley. The efficiency of the process based on calculations is presented.
Fuel and Energy Abstracts
September 1998 395