Sintering high purity,magnesia with additions of hafnium dioxide

Conclusions The introduction of hafnium dioxide into high-purity active magnesia accelerates its sintering and with 0.1–0.3 mol % HfO₂ a ceramic with an apparent density of 99–100% of the theoretical (3.56–3.63 g/cm³) can be obtained after firing at 1300–1400°C. The optimum quantity of HfO₂ additive is close to 0.25 mol %.The calcination temperature of the mixture of magnesium hydroxide and additive obtained by precipitation from a solution of MgCl₂ and Hf(SO₄)₂ with ammonia, and the fabrication pressure do not greatly affect the final density of the ceramics.Sintering of spectrally pure MgO containing 0.25 mol. % HfO₂ begins at 950°C, then the apparent density grows rapidly with rise in firing temperature, approaching 3.40 g/cm² at 1100°C. Selective recrystallization at these low temperatures is slow and sintering is not accompanied by a substantial grain growth. At 1300°C and higher firing temperatures densification of the ceramics approaches the limit in several minutes.The mechanism of the transfer of substance during the sintering of these specimens is volume self-diffusion from the grain boundaries to the surfaces of the bridges formed between them. The energy of activation of this process [3.9 eV (6.2 × 10^–16 J) in the 1000–1300°C range] and the coefficient of self-diffusion for MgO calculated in accordance with this (6 × 10^–14 cm²/sec at 1100°C) correspond to existing data on the diffusion of magnesium into MgO.With the incorporation of 0.25 mol. % HfO₂ in less pure magnesia obtained from chemically pure MgCl₂, sintering is little different from the sintering of spectrally pure MgO, but the limiting apparent density of the ceramics in this case is somewhat lower-of the order of 99% of the theoretical.     

Sintering and recrystallization of high-purity magnesia-alumina spinel during hot pressing

Conclusions A study was made of the densification and recrystallization of magnesia — alumina spinel of high dispersion during hot pressing in the temperature range 1200–1600°C, a pressure of 60–300 cm², and a holding time of 10–30 min.The relative density of 92–98% theoretical was achieved at 1300–1400°C, a pressure of 300 kg/cm², and a soaking of 10 min. The spinel of theoretical density with a finely crystalline homogeneous structure was obtained by hot pressing at 1450–1600°C.Intensive recrystallization of the spinels during hot pressing occurs in the temperature range ensuring maximum rate of densification (1450–1600°C).The rate of recrystallization of the spinel grains during hot pressing at 1400°C and a pressure of 300 kg/cm² and soakings of 10 and 30 min, has the order of 10^–6 cm/sec and the maximum for the grains of diameter from 2 to 6.Report read at a symposium on pure oxide sintering, Khar'kov, 1968.Deceased.Translated from Ogneupory, No.6, pp. 32–36, June, 1970.     

Improving the quality of chamotte made from Berlinsk clay

Conclusions The optimum firing temperature for Berlinsk clay to convert it into chamotte is 1300–1330°C. Above this temperature the chamotte bloats and has a low apparent density (below 2.10 g/cm³). The fireclay goods should be made from chamotte with an average or high apparent density (2.14–2.30 g/cm³).The articles made with the overtired chamotte have a high porosity and low apparent density. It is not recommended for use in firebrick production.Translated from Ogneupory, No. 2, pp. 14–16, February, 1981.     

Role of sintering additives in the production of lime refractories

Conclusions A production technology is proposed for lime refractories covering the preparation of high-density lime clinker, followed by crushing, batching, adding waterproof bond, pressing the goods, and firing at 2020 K.The technology for obtaining high-density lime clinker resistant to atmospheric hydrolysis, includes milling CaCO₃ to a particle size of 100–150 m with simultaneous incorporation of sintering additives (2–6% TiO₂ or 2–4% titanium ferrites), and the use of water solutions of sulfite lye as bond; pelletizing and firing at 2020 K. The lime clinker has an apparent density of 2.75–3.03 g/cm³, and an open pelletizing and firing at 2020 K. The lime clinker has an apparent density of 2.75–3.03 g/cm³, and an open porosity of 3.4–9.8%.The lime products have an apparent density of 2.65–2.97 g/cm³, open porosity 4.4–16.4%, compressive strength 60–140 N/mm², and refractoriness under load 1610–1700°C and above.Translated from Ogneupory, No. 2, pp. 13–16, February, 1992.     

Powdered elemental sulphur: oxidation rate,temperature dependence and modelling

Finely-powdered elemental sulphur is a useful source of fertilizer S, being readily oxidizable in soil to plant-available sulphate yet possessing some slow release characteristics. Two mesh sizes were evaluated using four soils from northeast Scotland. Particle size analysis found that the 120 and 300 mesh S samples had specific surface areas of 1300 and 1940 cm² g^–1, respectively, with most of the surface area in particles of 10 – 20 µm diameter. The S oxidation rate was similar in all four soils but was greater for the 300 mesh than for the 120 mesh S: mean values of 51% and 18% were oxidized over 7 weeks at 14 °C, respectively. The time course of oxidation followed a sigmoidal pattern with a pronounced lag which was modelled using the logistic equation. Maximum specific oxidation rates were 11–28 µg S cm^–2 day^–2 for the 300 mesh S at 14 °C. These were significantly slower at 7 °C and the temperature response was calculated as a Q₁₀ of 4.0.A model of seasonal S oxidation was developed using a cosine function for the annual temperature, the Arrhenius equation to relate S oxidation rate to temperature and a generalization of the logistic equation to describe the time course of S oxidation. Simulations showed that the 300 mesh S would be useful for spring S applications in east Scotland and if applied in autumn could supply S during the autumn and again in the spring. The 120 mesh S would be less effective in autumn but more resistant to winter leaching. The 120 mesh S applied to the warmer soils of southwest England would behave the same as 300 mesh S applied in east Scotland.     

A Study of Refractories from Baddeleyite Stabilized with Magnesium Oxide

It is shown that refractory articles can be produced from ZrO₂ on a forsterite binder based on natural baddeleyite with native grain composition. The articles have a high density (4.71 – 4.72 g/cm³), ultimate compressive strength (257.6 MPa), heat resistance (6 – 8 water heat cycles from 1300°C), and a low porosity (12.2%).     

Electrodeposition of titanium from chloride melts

The kinetics of the electrodeposition and electrocrystallisation of titanium were studied in alkali chloride melts. Voltammograms showed two distinct anodic peaks for the oxidation steps Ti/Ti(II) and Ti(II)/Ti(III) at 70 mV and 300 mV, respectively, referred to titanium. The cathodic reduction Ti(III)/Ti(II) was very irreversible, showing an extended cathodic wave and a shoulder on the Ti(II)/Ti reduction peak. The Ti(II)/Ti reduction was found to be quasi reversible. The rate constant at 450'C was 5 × 10^–3 cm s^–1 . The diffusion coefficient in KCl-LiCl eutectic was 1 × 10^–5 cm²s^–1 at 450° C rising to 3.5 × 10^–5 cm²s^–1 at 650° C. Potential step measurements gave curves indicating slow instantaneous nucleation and growth (I against t ^1/2) followed by slow diffusion control (I against t ^–1/2). During constant current steady state deposition the nature of the deposit depended on the composition of the melt, the temperature and the cd. In KCl-LiCl melts coherent deposits were obtained for cds of 60–120 mA cm² while higher current densities gave dendritic and spongy deposits.     

Porous materials based on corundum and aluminophosphate bond

Conclusions Highly porous corundum products obtained by using fluoroplastics have a relatively high strength in the green state (7 kg/cm² with an apparent density of 0.4 g/cm³), and a low apparent density after firing (0.23 g/cm³).The incorporation of aluminophosphate bond sharply increases the strength of the products after combustion of the organic part, and reduces the total shrinkage during heat processing from 30 to 4–5%.The use of electrofused corundum in place of commercial alumina reduces the concentration of organic constituent in the body to 18%; under these conditions the additional shrinkage at 1600°C of specimens fixed at 1000°C drops to 0.5–1%.Translated from Ogneupory,No.5, pp.46–50, May, 1972.     

Spinel-bonded magnesite brick for high-tonnage electric arc furnaces

Conclusions The manufacture of an experimental batch of spalling resistant magnesite-chrome brick with a spinel binder has made it possible to improve the technological norms for the production of these parts and has shown the possibility of making them at the new shop at the Magnezit Plant.The parts produced show good characteristics: refractoriness-under-load of 2 kg/cm² — 1650–1720°; additional shrinkage during heating to 1650° with subsequent holding for three hours –0.1%; spalling resistance 7–13 water-heating-cooling cycles (heating to 1300°); apparent porosity 15–17%; compressive strength 620 kg/cm².To obtain parts with good physical-chemical properties it is essential to use MK magnesite powder; to add at least 6–8% industrial alumina to the charge (in terms of Al₂O₃); to make certain the magnesite-alumina mixture is highly dispersed so that it helps to complete the spinel formation reaction during the firing; to use a mixture of the following grain composition: not less than 20% fraction 3–1 mm; 55–60% finer than 0.5 mm, including 30–35% finer than 0.06 mm; to press the parts at 1200–1500 kg/cm²; to fire the parts at a temperature not less than 1600°, batching them far apart so as to avoid the formation of an uneven structure.The use of magnesite brick with a spinel binder for the walls of high-tonnage electric arc furnaces used to melt transformer steel ensures satisfactory strength of the walls in the slag belt and prevents the steel becoming contaminated with chromium.     

Resistance of steel-teeming stoppers

Conclusions In order to make spalling-resistant stoppers which can be used to teem metal satisfactorily, the charge at the refractory shop of the Nizhnly Tagil Metallurgical Combine should include 7–10% chamotte coarser than 2 mm and 45–50% finer than 0.54 mm. The temperature should be raised from 30 to 150° at the rate of 5–7°/hr, and from 800 to 1200° at the rate of 20–25°/hr. The holding time at 1280–1300° should be 10 hours.When laying down new specifications for standards for steel-teeming stoppers, it is essential to stipulate a porosity of 15–20% at refractoriness-under-load of 2 kg/cm² of not less than 1320 or not more than 1380°     

Experimental casting of multichamotte refractories from slip

Conclusions The possibility of casting refractories from multichamotte slip with a maximum moisture content of 15% has been investigated; a preliminary treatment of the slip under vacuum is recommended as well as a brief vibration of the gypsum molds within a certain period after pouring.The high rate of moisture loss and solidification of multichamotte slip castings allow production on an industrial scale.Multichamotte kaolin mixtures yield castings up to 100 × 80 × 80 mm which acquire the following properties after firing at 1470° C: bulk density –2.17–2.26 g/cm³; porosity –12 to 18%; compressive strength –420 to 800 kg/cm²; loss on ignition –2. 7 to 4. 3; total shrinkage in relation to the size of gypsum molds –4 to 5%.The casting process is of practical value for the manufacture of multichamotte products (including high-alumina refractories) since molding the latter by means of pressing is either impossible or extremely difficult.Industrial tests are conducted for the verification and more accurate determination of technological parameters and the technical and economic effectiveness of the method.     

Characterization of ethylene homo- and copolymers

Summary For the estimation of molecular mass distribution and average molecular masses of (norbornene ethylene) copolymers a size exclusion chromatography method is described. The validity of the universal calibration function of Benoit et al. based on polystyrene molecular mass standards was confirmed by comparing with the number average molecular masses obtained by osmometry. The constants of the Mark-Houwink equation are a = 0.535, K = 1.00·10^–1 (Xylene, 90 °C) and a=0.589, K=4.93·10^–2 (diethylbenzene, 120°C,[] in cm³g^–1).Part IV: Plaste u. Kautschuk 32, 12, 444 (1985)     

Magnesite refractory with a high CaO content

Conclusions Chromite, added in amounts of 10% to dolomitic magnesite containing 8.35% CaO by bonding with it completely during firing, is an effective stabilizer.An increase in the chromite content of the batch of more than 10% lowers the quality of the refractory.The hydrothermal treatment of the calcined dolomitic magnesite with 10% chromite accelerates the process of hydrating the free CaO and disperses the material, which helps the refractory to sinter during firing.The proposed technique provides for combined grinding and firing of a mixture of dolomitic magnesite with chromite, excludes aging of the body, reduces the firing temperature of the body and increases the quality of the refractory compared with the periclase-spinel technique.The calcium oxide in dolomitic magnesite with the addition of 10% chromite is bonded mainly with theCr₂O₃ into calcium oxychromite 9CaO · 4CrO₃ · Cr₂O₃ and the ferric oxide is introduced into the lattice of the periclase with the formation of a solid solution. With 30% chromite in the batch 3CaO · 2CrO₃ · 2Cr₂O₃ is formed, and the ferric oxide enters the magnesio-ferrite.Calcium oxychromite, existing in the refractory with 10% chromite and being a secondary phase, at its fusing temperature (>1250–1290°C) reversibly converts to calcium monochromite with a fusing temperature of 2170°C, which explains the increase in the refractoriness under load.     

Properties of refractories produced from synthetic magnesia

Conclusions The sinterability, open porosity, and cold-crushing strength of magnesite and magnesite-chromite specimens processed from magnesia powders (96–97% MgO) are improved with a decrease in the size of the periclase grains in the powder and with an increase in the firing temperature and do not depend on the percent and composition of the silicates and on the B₂O₃ content of the magnesia powder.The high-temperature bending strength of both types of refractories increases with a decrease in the B₂O₃ content of the magnesia powder. The creep resistance of the magnesite specimens increases with the ratio CaO/SiO₂ in the magnesia powder while the creep resistance of the magnesite — chromite specimens does not depend on this index.The indices of the open porosity and strength of the magnesite and magnesite — chromite specimens were optimal when they were produced with magnesia obtained by the bicarbonate method from dolomite.To produce dense and strong magnesite refractories from magnesia, they should be fired at a temperature not below 1700°C. The firing temperature of magnesite — chromite refractories should not be below 1750°C.Translated from Ogneupory, No. 6, pp. 53–57, June, 1978.     

Thermoreactive compaction of an alumina — Polymethylsiloxane composition

Conclusions An investigation was carried out of the thermoreactive compaction of a composition of alumina with polymethylsiloxane, the technological parameters being varied. Before a heat treatment the open porosity of specimens containing 20% PMS is 0.8%, the bending strength 260 kgf/cm², and the cold-crushing strength 1070 kgf/cm².Firing at 1700°C gave a high-alumina composition ceramic with an open porosity of 2%, a bending strength of 1000 kgf/cm², a cold-crushing strength up to 5000 kgf/cm², and a thermal-shock resistance of 14–20 reversals from 1300°C into water (in tests with specimens).Translated from Ogneupory, No. 5, pp. 47–50, May, 1978.     

Diffusion coefficients of Cu(II) complexes with ligands used in alkaline electroless copper plating solutions

The diffusion coefficient values of the Cu(II) complex compounds with EDTA, DTPA, NTA, Quadrol, glycerol, saccharose, (+)- and (±)-tartaric acid, OH^– ions obtained by polarographic measurements in alkaline solutions lie in the range (1.2–5.7) × 10^–6 cm² s^–1 (at 20 C and J = 3) depending on the size of complex species, and are less than those of free (hydrated) Cu(II) ions and methanediol anion (H₂C(OH)O^–) determined under the same conditions which are 7.0 × 10^–6 and 10 × 10^–6 cm² s^–1, respectively. The linear dependence of the polarographically determined diffusion coefficient values on the inverse radius of Cu(II) complex species is observed.     

A direct methanol fuel cell using acid-doped polybenzimidazole as polymer electrolyte

A direct methanol/oxygen solid polymer electrolyte fuel cell was demonstrated. This fuel cell employed a 4 mg cm^–2 Pt-Ru alloy electrode as an anode, a 4 mg cm^–2 Pt black electrode as a cathode and an acid-doped polybenzimidazole membrane as the solid polymer electrolyte. The fuel cell is designed to operate at elevated temperature (200°C) to enhance the reaction kinetics and depress the electrode poisoning, and reduce the methanol crossover. This fuel cell demonstrated a maximum power density about 0.1 W cm^–2 in the current density range of 275–500 mA cm^–2 at 200°C with atmospheric pressure feed of methanol/water mixture and oxygen. Generally, increasing operating temperature and water/methanol mole ratio improves cell performance mainly due to the decrease of the methanol crossover. Using air instead of the pure oxygen results in approximately 120 mV voltage loss within the current density range of 200–400 mA cm^–2 .     

Refractories from fused periclase

Conclusions High-grade refractories can be produced from periclase containing at least 97% MgO by preparing a suitable grain size distribution with a vibro-ground component in the powder, molding in stages at high specific pressures (1500–2000 kg/cm²), and firing for 8 h or more at a high temperature (1750°C or higher).Translated from Ogneupory, No. 6, pp. 5–8, June, 1974.     

Rheological and technological properties of titanium dioxide slips and the properties of the castings

Conclusions An investigation of the rheological and technological properties of titanium dioxide slips and slip castings demonstrated the presence of two castability regions. The properties of the slip and castings are optimal in the alkaline castability region (pH 8).A study of the influence of the firing temperature of the titanium dioxide starting material on the properties of the slip and castings showed that the properties are optimal when the TiO₂ had been fired at 1550° C.An analysis of the sintering of titanium dioxide slip castings showed that the properties of the sintered castings are optimal when the castings were produced from slip with pH 8 because in this case the density of the castings is at maximum.The strength of TiO₂ castings in the sintering process depends on their porosity and that of the sintered castings on the size of the crystals.Titanium dioxide fired at 1550°C yielded castings with open porosity 1.8–2.0%, apparent density 3.90–3.92 g/cm³, _b 1020–1050 kgf/cm², acid resistance 97.5%, specific inductive capacitance 90–100, and tangent of the dielectric loss angle at 20°C and 1 MHz 8·10^–4–9·10^–4 Translated from Ogneupory, No. 3, pp. 28–33, March, 1978.     

Use of Kempiraisk chromite for the production of magnesiospinel refractories

Conclusions Kempiraisk chromite makes it difficult for magnesiospinel articles to be sintered in the refractory-production furnaces. In order to obtain good quality periclase-chromite articles based on Kempiraisk chromite under the conditions pertaining at the Combine, it is necessary to coarsen the chromite fraction to 5–0.5 mm, reduce its concentration in the batch to 20–27%, and to increase the firing temperature to 1580–1590°C after first reconstructing the gas-fired chamber furnaces.Translated from Ogneupory, No. 5, pp. 8–11, May, 1982.