Preparation of superconducting Bi-Sr-Ca-Cu-O ceramics by the sol-gel method

Superconducting Bi-(Pb)-Sr-Ca-Cu-O ceramics were prepared through the sol-gel method using an aqueous solution of metal acetates containing acetic acid and tartaric acid. The conditions of gelation and conversion of gel to Bi₂Sr₂CaCu₂O_x phase were studied by thermal analysis, infrared absorption spectroscopy and X-ray diffraction technique. It was found that transparent gels were obtained from the solutions containing tartaric acid, with a molar ratio of C₄H₆O₆/Cu of about 0.4. The gel matrix was assumed to be composed of carboxylate anions and metal cations. A gel of molar composition BiSrCaCu = 2223 was decomposed to CaCO₃, CaO, CuO and Bi_1-x Sr_xO_y (x = 0.2 to 0.3) at low temperatures of 270 to 600 ° C and produced Bi₂Sr₂CaCu₂O_x phase at 800 ° C via complex intermediate states. A rapid cooling of the heated product increasedT _c (end) in the gel of molar composition BiSrCaCu = 2223, while a slow cooling increasedT _c (end) in the lead-containing gel of molar composition BiPbSrCaCu = 1.850.351.92.03.1. The latter showedT _c (onset) at 115 K andT _c (end) at 105K.     

Environmental stress cracking of glassy polymers and solubility parameters

The use of solubility parameters to predict critical stress ( _c ^* ) or strains (_c) for environmental cracking/crazing in several glassy polymers (e.g. PMMA, PPO, PS, PVC, PSF and PC) is re-examined. It is shown that the enthalpic component ( _H ) of the Flory-Huggins semi-interaction parameter () does not always give a good correlation between _c and _H even though solvent molar volume and polymer-solvent molecular interactions have already been considered. Re-analysis of available experimental data using Gent's theory shows that there is a general trend for _c ^* (or _c) to increase with . These results, therefore, support Gent's proposed mechanism of environmental stress crazing/cracking. It is finally concluded that unless a definite relationship can be established between _c or _c ^* with _H it is not possible to predicta priori _c or _c ^* , given the empirical solubility parameters of a solvent. Unfortunately, there are not many such relationships as discovered in this paper.     

Oxalate materials prepared by evaporation as precursors to superconducting ceramics

Some unexpected chemistry will be discussed which occurs during the production of highT _c superconductors by an oxalate route. Evaporation (rather than filtration) of a 123 YBaCu nitrate solution containing excess oxalic acid was done, in order to make sure that the solid had the same composition as the solution. It was assumed that the removal of water and nitric acid by vacuum would quantitatively yield the salts as oxalates. Surprisingly, the evaporation changed what was initially a homogeneous, but off-composition, material into a rather inhomogeneous material. During the evaporation, the yttrium and barium were apparently redissolved from their initial form as submicrometre particles containing all three metals. They were redeposited as 10–100 m rectangular and octahedral crystals. However, this material yields very good superconductors upon simple grinding and heat treatment as measured by conductivity and a.c. induction.     

Preparation of the single phase γ′-(Fe1−x Ni x )4N compounds (0 ≤x ≤ 0.6)

Single phase -Fe₄N type (Fe_1–xNi_x)₄N compounds (0 x 0.6 have been synthesized for the first time by controlled heat treatment of iron-nickel oxalates in a gaseous flow of NH₃ xand H₂. The preparation processes were investigated using differential scanning calorimetry (DSC), X-ray diffraction and Mössbauer spectroscopy. The results confirmed that annealing of oxalates in the NH₃ and H₂ atmosphere included the processes of dehydration, decomposition and reduction, nitrogenation and thermal decomposition of the nitrides. The decomposition and reduction occur simultaneously. The final products depend on the flow rate ratio of NH₃ H₂ and the annealing temperature. The formation conditions for the single phase -Fe₄N type (Fe_1–xNi_x)₄N compounds are related to the nickel concentration, with increasing nickel content, the nitrogenation temperature decreased, in contrast the flow rate ratio of NH₃ H₂ increased.     

Transport property and battery discharge characteristic studies on 1−x(0.75Agl∶0.25AgCl)∶ xAl2O3 composite electrolyte system

Various experimental studies on a new fast Ag⁺ ion-conducting composite electrolyte system: (1–x) (0.75Agl0.25AgCl)xAl₂O₃ are reported. Undried Al₂O₃ particles of size <10 m were used. The conventional matrix material Agl has been replaced by a new mixed 0.75Agl0.25AgCl quenched and/or annealed host compound. Conductivity enhancements 10 from the annealed host and 3 times from the quenched host obtained for the composition 0.7(0.75Agl0.25AgCl)0.3Al₂O₃, can be explained on the basis of the space charge interface mechanism. Direct measurements of ionic mobility as function of temperature together with the conductivity were carried out for the best composition. Subsequently, the mobile ion concentration n values were calculated from and a data. The value of heat of ion transport q* obtained from the plot of thermoelectric power versus 1/T supports Rice and Roth's free ion theory for superionic conductors. Using the best composition as an electrolyte various solid state batteries were fabricated and studied at room temperature with different cathode preparations and load conditions.     

Effects of pH and H2O2 upon coprecipitated PbTiO3 powders

PbTiO₃ was prepared by coprecipitation and calcination from mixed solutions of TiCl₄ and Pb(NO₃)₂. The effect of pH in the precipitation solution on the properties of calcined powders was studied by calcining coprecipitated precursor powders prepared at pH values between 8.00 and 10.50. The effects of H₂O₂ were studied by preparing PbTiO₃ powders from mixed solutions containing H₂O₂PbTiO₃ ratios between 01 and 61. Synthesis of phase pure PbTiO₃ by coprecipitation and calcination is highly dependent upon the complex ionic equilibria dictated by the pH. The pH used for precipitation determines the types of crystalline phases formed from coprecipitated precursor powders. The rate at which amorphous precipitates transform to crystalline PbTiO₃ during calcination is also affected by both the pH and H₂O₂ additions. High purity (greater than 98%) PbTiO₃ with a rapid amorphous-to-crystalline transformation rate was obtained for H₂O₂PbTiO₃=1.11, and pH=9.65 to 9.75.     

Titanium-doped γ-Fe2O3: Reduction and oxidation properties

Titanium-doped -Fe₂O₃ has been prepared by the calcination of a solid formed by the addition of aqueous ammonia to an aqueous solution of titanium- and iron-containing salts and boiling the precipitate under reflux. As compared to pure -Fe₂O₃ made by similar methods, titanium-doped -Fe₂O₃ showed a higher surface area and a greater stability to reduction, thermal conversion to an -Fe₂O₃-related structure and the maintenance of a higher surface area during oxidation-reduction cycling.     

The effect of silicon on the structure and mechanical properties of an α+Β titanium alloy

Titanium 4 wt% Al-4 wt% Mo-2 wt% Sn containing 0, 0.25 and 0.5 wt% Si has been solution-treated in the + phase field at 900 C. The microstructures obtained at room temperature after cooling from 900 C at various rates have been determined using transmission electron microscopy and the partitioning of the elements between the phases has been established using X-ray energy dispersive analysis on the thin foils. The degree of partitioning increases with decreasing cooling rate: aluminium partitions to the -phase, molybdenum and silicon to the -phase and tin remains uniformly distributed. Silicon is found to inhibit the partitioning of molybdenum: this has a profound effect on the stability of the -phase and the resultant microstructure. In quenched material containing transformed , substantial age hardening can be obtained in the range 350 to 600 C and is associated with precipitation within the orthorhombic martensite phase, possibly occurring via a spinodal mechanism. Silicon has little effect on the microstructure of air-cooled samples but contributes to high-temperature strength via dynamic strain ageing.     

Low-temperature synthesis,pyrolysis and crystallization of tantalum oxide gels

Tantalum oxide gels in the form of transparent monoliths and powders have been prepared from hydrolysis of tantalum pentaethoxide under controlled conditions using different mole ratios of Ta(OC₂H₅)₅C₂H₅OHH₂OHCl. Alcohol acts as the mutual solvent and HCl as the deflocculating agent. For a fixed alkoxide water HCl ratio, the time of gel formation increased with the alcohol to alkoxide molar ratio. Thermal evolution of the physical and structural changes in the gel has been monitored by differential thermal analysis, thermogravimetric analysis, X-ray diffraction, and infrared spectroscopy. On heating to 400 °C, the amorphous gel crystallized into the low-temperature orthorhombic phase -Ta₂O₅, which transformed into the high-temperature tetragonal phase -Ta₂O₅ when further heated to 1450 °C. The volume fraction of the crystalline phase increased with the firing temperature. The -Ta₂O₅ converted back into the low-temperature phase, -Ta₂O₅, on slow cooling through the transformation temperature of 1360 °C, indicating a slow but reversible transformation.     

Investigation of Phase Evolution During the Thermochemical Synthesis of Tricalcium Phosphate

The formation of tricalcium phosphate (TCP) from dicalcium phosphate and calcium carbonate was investigated using differential thermal analysis (DTA), thermogravimetric analysis (TGA), and powder X-ray diffraction (XRD). DTA showed three distinct thermal events attributed to dehydration of dicalcium phosphate dihydrate (brushite, DCPD) to dicalcium phosphate anhydrous (monetite, DCPA), the formation of beta-calcium pyrophosphate (-Ca₂P₂O₇), and the calcination of calcium carbonate. TGA showed three weight losses corresponding to the three thermal events, respectively. XRD analysis showed that -TCP formed, beginning at about 900°C, by the reaction of -Ca₂P₂O₇ with CaO and -TCP changed to -TCP above 1200°C. Further examination of the formation of TCP from calcium hydroxide (Ca(OH)₂) and DCPA showed that -TCP would form only after the decomposition of Ca(OH)₂ to CaO and from the reaction of CaO with -Ca₂P₂O₇ at a fairly low temperature of 800°C. In addition, by naturally cooling -TCP, formed at 1300°C within the heating furnace, to room temperature, it was difficult to obtain a pure phase of -TCP. The proposed mechanism of the reaction to form TCP may include the dehydration of brushite to monetite, dehydration of monetite to beta-calcium pyrophosphate, decomposition of calcium carbonate, the formation of -TCP, and phase transition.     

The self-propagating high-temperature synthesis (SHS) of ultrafine high-purity TiC powder from TiO2+Mg+C

The self-propagating high-temperature synthesis (SHS) method has been applied to the preparation of TiC powder from mixtures of TiO₂, Mg, and C. The TiC/MgO product is leached by hydrochloric acid to remove the MgO. The optimum mixing ratio was TiO₂MgC=12.21.5. The final product TiC had > 99.9% purity and relatively uniform particle size of 0.3–0.4 m.     

Information behaviour in a scientific-technical environment: A survey with innovation engineers

A small written survey with innovation engineers in a large company is discussed, giving some figures on both behaviour and attitudes with respect to 1) information gathering, 2) information production/dissemination and 3) information storage and management. Most results confirm the trends in other research with R & D engineers: the use and management of information is rather improvised with low levels of sophistication. High tech information techniques (databases, online...) are only marginally important in this high-tech environment. Only younger engineers do some structured efforts. The general attitude is to rely mostly on oral, personal and occasional information sources. By combining positive attitudes and behaviour aspects towards information in the job, a measure of information-orientation was constructed, which can be seen as an extension of the classical concept of gate-keepers in a company. A few questions to reconstruct a critical incident with respect to information problems reveal that information situations can be very time- and money-consuming but again solutions depend on occasional and unstructured information work. However the restricted written approach did not prove to be a good one for this kind of analysis. More in-depth interview-techniques will be necessary for analysis within the critical incident theory-frame.This article is compiled from the full report (in Dutch): Informatiegedrag bij innovators, published as a major project these for the postgraduate in Documentation and Library Science of the Antwerp University by A.D'Espallier (Wilrijk (Belgium), September, 1989); the survey's supervising and technical aspects were conducted by the author.     

Effects of ageing on the temperature coefficient of resistivity of a β titanium alloy

The temperature coefficient of electrical resistivity (TCR) of the commercial Ti-15-3 alloy is negative, if the alloy is in the 100% condition. The TCR increases from negative to positive values as a result of precipitation of the and phases during ageing. An incubation or transient period, during which the value of TCR remains essentially unchanged, precedes the formation of the phase; this transient period decreases with increasing ageing temperature over the range 250–400 °C. Changes in the value of TCR signal the initiation of beta decomposition before the phase can be detected by conventional TEM and diffraction techniques. Reversion of the phase by up-quenching after ageing restores the original negative value of TCR. If both and phases are present in the aged condition, only partial recovery of the quenched TCR value is possible, indicating that the alpha phase is not reverted by up-quenching. The results point to the potential value of TCR determinations for monitoring the initiation of decomposition in titanium alloys exposed to temperatures above room temperature.     

Question of solving nonlinear problems under the combined action of heat conduction and radiation

The radiant heat transfer of an annular plate to the environment is examined. A simple analytic solution is obtained that describes the stationary temperature field.Notation T running temperature - T_i temperature of the inner edge of the ring - r running radius - emissivity - Stefan-Boltzmann constant - ₀ heat conductivity of the material - b thickness of the annular plate - relative temperature - R=r/r₀ relative running radius Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 1, pp. 119–122, January, 1982.     

Fabrication of Bi2Sr2CaCu2Ox films on metal substrates by the chemical process using metal alkoxides

The formation behaviour of Bi₂Sr₂CaCu₂O_x from compounds prepared by hydrolysis of metal alkoxides was studied and Bi₂Sr₂CaCu₂O_x films on metal substrates were fabricated using a metal alkoxide solution. Bi₂Sr₂CaCu₂O_x was formed through intermediate phases such as Bi₂Sr₂Cu₁O_x, Bi₂CuO₄, SrCO₃, CaCO₃ and CuO. Bi₂CuO₄ was initially formed with SrCO₃, CaCO₃ and CuO, and then reacted with SrCO₃ to form Bi₂Sr₂Cu₁O_x. Bi₂Sr₂Cu₁O_x reacted with CaCO₃ and CuO to give Bi₂Sr₂CaCu₂O_x. Bi₂Sr₂CaCu₂O_x films were successfully fabricated on nickel substrates using the metal alkoxide solution at the nominal composition of BiSrCaCu=2223. Bi₂Sr₂CaCu₂O_x was precipitated on Ni substrates at firing temperature of 770 °C or above, and a sharp T _c was obtained at the firing temperature of 800 °C.     

Solvent effect on ageing of silica gels

The structure of silica gels derived from tetraethoxysilane (TEOS) with molar compositions of TEOSH₂OHNO₃=1100.4 and then aged in various solvents, was studied. The effect of various solvents having different physical properties on the gel structure, as well as the relationship between the solvent properties and the dried gel structure, were investigated. The density, surface area and pore-size distribution were measured. The results of the pore structure and SEM showed the aged gels to have a slit-shaped micropore, narrow pore-size distribution, and homogeneous microstructure. The density, surface area, pore size and pore volume of dried gels changed as the gels were subjected to ageing in various solvents. The surface area could be related to the polarity parameter of the ageing solvent.     

Continuous,martensitic nature of the transition ß→γ Li3PO4

The transformation Li₃PO₄ shows characteristics of both continuous and martensitic transformations. Below 340° C, no detectable transformation occurs; between 340 and 410° C, the transformation goes only partially to completion; above 410° C the transformation rapidly goes to completion. At any temperature in the range 340 to 410° C, transformation proceeds rapidly in the initial stages to attain a certain degree of transformation. With prolonged isothermal heating or grinding of the samples, further transformation does not occur. The reverse transformation could not be effected under normal, dry conditions.     

Surface nucleation and cellular growth kinetics of cordierite glass ceramics containing 3 mol % Y2O3-ZrO2

Cordierite-based glass ceramics of the 2MgO2Al₂O₃5SiO₂ composition with t-ZrO₂ (3 mol% Y₂O₃-ZrO₂) and P₂O₅ addition, was heat-treated isothermally and isochronically for crystallization studies. Major crystalline phases incurred by the heat treatment were t-ZrO₂ and -cordierite. Surface nucleation predominated when edge and corner nucleation in these samples were suppressed regardless of their radii of curvature. Crystallization began with the formation of -quartz S.S. and its transformation to -cordierite was followed by prolonged heating. Cellular growth of -cordierite on the surface of the quenched glass plates, gave a linear kinetics. The activation energy for cellular growth was 410 kJ mol^–1.     

A precipitate phase in AA2124

A new precipitate phase (designated X phase) other than the S(Al₂CuMg) precipitate phase has been discovered in the 2124 aluminium alloy. Using selected-area electron diffraction analysis, dynamical diffraction simulation, energy dispersion analysis of X-rays and high-resolution electron microscopy, it is suggested that the X phase has an orthorhombic crystal structure witha=0.492 nm,b=0.852 nm andc=0.701 nm. The space group of the phase is Cmmm. There are 10 atoms in a cell with AlCuMg=244. The orientation relationship between the X phase and the matrix is determined as (1–10)_m(010)_x, [–1–1–1]_m [001]_x.     

Effect of resonant impurity scattering on collective mode peaks in the ultrasound attenuation of heavy fermion superconductors

We have calculated the attenuation of longitudinal ultrasound due to real order parameter fluctuations in impure polar and planarp-wave superconductors. The quasiparticle self-energy and the corresponding vertex corrections have been included in thet-matrix approximation for arbitrary scattering rate =1/2_N and all scattering phase shifts _N (0 _N/2). We obtain sound attenuation peaks belowT _c whose heights, positions, and shapes depend on ₀ (sound frequency), (₀), _N, and (coupling strength due to particle-hole asymmetry). The peaks become much more distinct and sharper for _N =/2 (resonant scattering by impurities) than for _N=0 (Born approximation). By choosing , _N, and suitably, qualitative agreement between calculated and observed peaks in UBe₁₃ and UPt₃ can be achieved.