Deterioration of electromotive force of chromel-alumel thermocouples in reducing atmospheres at high temperatures

The deterioration of electromotive force (emf) of Chromel-Alumel (CA) thermocouples in 80 pct H₂ + 15 pct CO + 5 pct CO₂ has been analyzed in terms of the corrosion behavior of Chromel. Emf of the CA thermocouple deteriorated drastically in 80 pct H₂ + 15 pct CO + 5 pct CO₂. After exposure for about 1000 hours at 900 °C, the decrease of emf was about 16 mV. The deterioration process could be separated into three terms. The first term, which has the smallest time constant of about 20 hours, was attributed to carbon deposition on the Chromel surface in the temperature range of 600 to 700 °C. The second term, which has a time constant of about 100 hours, was attributed to the severe internal oxidation of chromium in the temperature range of 500 to 800 °C. The third term, having the largest time constant of several thousand hours, might be attributed to the moderate and gradual preferential oxidation of chromium in Chromel in the range 800 to 900 °C. Boron nitride (BN) coating on CA thermocouples could reduce this deterioration of emf; the decrease of emf was improved to about 3 °C during 700 hours test at 900 °C.     

EMF genes regulate Arabidopsis inflorescence development

Mutations in EMBRYONIC FLOWER (EMF) genes EMF1 and EMF2 abolish rosette development, and the mutants produce either a much reduced inflorescence or a transformed flower. These mutant characteristics suggest a repressive effect of EMF activities on reproductive development. To investigate the role of EMF genes in regulating reproductive development, we studied the relationship between EMF genes and the genes regulating inflorescence and flower development. We found that APETALA1 and AGAMOUS promoters were activated in germinating emf seedlings, suggesting that these genes may normally be suppressed in wild-type seedlings in which EMF activities are high. The phenotype of double mutants combining emf1-2 and apetala1, apetala2, leafy1, apetala1 cauliflower, and terminal flower1 showed that emf1-2 is epistatic in all cases, suggesting that EMF genes act downstream from these genes in mediating the inflorescence-to-flower transition. Constitutive expression of LEAFY in weak emf1, but not emf2, mutants increased the severity of the emf phenotype, indicating an inhibition of EMF activity by LEAFY, as was deduced from double mutant analysis. These results suggest that a mechanism involving a reciprocal negative regulation between the EMF genes and the floral genes regulates Arabidopsis inflorescence development.     

蒸发式空冷器的运行实践

通过了解蒸发式空冷器的工作原理和结构,在运行实践过程中,对组成设备出现的问题提出相应的解决方案,并对部分组成设备提出改进的建议,以方便检修和维护,并提出了在冬季长时间高炉休风情况下保证水温不下降过低的解决方案。     

Thermal operation of arc foundry furnaces

Experimental data on the temperature distribution over the lining thicknesses of the walls, roof, and bottom of a 6-t arc steel-melting furnace are processed. The time dependence of the heat flux density distribution over the lining thickness is determined, and the change in the enthalpy of the lining during a heat is found. Recommendations for the rational use of the heat accumulated by the lining during furnace downtime are given.     

Modeling the Dynamics of Heavy Equipment Management Practices and Downtime in Large Highway Contractors

Machine downtime is invariably perceived as one of the most critical problems faced by highway contractors. Attempts to reduce downtime often result in failure due to the dynamic behaviors between equipment management practices and downtime. This paper is thus intended to highlight the dynamics of heavy equipment management practices and downtime in large highway contractors and utilizes them as a framework in constructing a simulation model using a system dynamics approach. Face-to-face interviews were conducted with equipment managers from five different large highway contractors in Thailand. The finding reveals that, to be successful in alleviating downtime, contractors must view their practices on equipment management as an integration of multiple feedback processes, which are interrelated and interdependent with downtime. Based on various validation tests, the simulation model is deemed appropriate in representing the equipment management system as related to downtime of large highway contractors. The research is of value in facilitating better understanding on the dynamics of equipment management practices and downtime as well as their interdependency.     

Improving the quality of rolled pipe steel products by minimizing the bending of the ends of plates

The causes of the vertical bending of the front ends of plates during hot rolling are revealed. A finite-element mathematical model is developed to describe the state of stress of the metal in an asymmetric deformation zone with allowance for solving a temperature problem, and the model is adapted to the conditions of the 5000 rolling mill in OAO MMK. It is found that, in rolling with mismatched work roll speeds, the direction of bending of the front strip end is determined by the strip thickness and the deformation zone shape. The main cause of the bending of the front plate end at the stage of finishing stage of rolling is shown to be the difference between the roller bed level and the rolling line. New asymmetric deformation regimes are developed with allowance for the effect of the deformation zone shape on the direction of bending of the front strip end. The developed technological regimes of asymmetric rolling make it possible to decrease the mill downtime because of the bending of the breakdown bar ends and to reduce the metal volume rejected because of violated temperature regimes of the thermomechanical treatment of plates.     

Investigation into the equilibrium of the wustite and spinel solutions in the Fe-Ge-O system

Equilibrium conditions of the wustite and spinel solutions in the Fe-Ge-O system in temperature range T = 1100–1300 K are investigated by measuring the emf of the galvanic element with solid electrolyte (the emf method). X-ray diffractometry and electron probe microanalysis were used to determine the phase composition. It is established that the iron magnetite and germanate are partially miscible in one another. The isothermal sections of the phase diagram of the Fe-Fe₃O₄-Fe₂GeO₄ system at T = 1273 K and 1173 K are constructed.     

高炉休风料程序设计

高炉需要做定期计划检修,检修前炉内需要下休风料。休风料的下达很大程度上取决于高炉操作人员的经验。高炉体风料程序的设计可更好地安排休风料的下达,可以精确计算休风料下达的位置和炉内炉料的负荷水平及炉渣成分。     

Study of Factors Influencing the Efficient Management and Downtime Consequences of Highway Construction Equipment in Thailand

Downtime resulting from machine breakdown invariably has a considerable impact on the performance of construction projects and companies as a whole, especially to contractors with heavy investment in equipment. Attempts to investigate the causes and consequences of downtime are rarely found. The aim of this paper is to characterize and quantify factors that influence downtime consequences (consequential problems resulting from downtime) of highway construction equipment based on the structural equation modeling (SEM) approach. A questionnaire survey was conducted to collect data on equipment management practices and downtime consequences among highway contractors in Thailand. The SEM model proposed is of value for both researchers and practitioners to facilitate a better understanding of the relationships among acquisition condition, operational practice, maintenance quality, disposal practice, and downtime consequence of heavy equipment. The model also helps contractors to manage equipment more efficiently by concentrating on several practices that can convey the greatest benefit in minimizing downtime consequences at each particular stage of a machine’s life cycle, rather than considering all practices simultaneously where the benefits gained are perhaps not proportional to the effort.     

Calorimetric and emf studies on liquid Li-Sn alloys

By means of high temperature calorimetry the mixing enthalpies ΔH of liquid Li-Sn alloys have been measured; however, due to experimental problems they were determined only forx _Li = 0.01 to 0.5 andx _Li = 0.87 to 0.99. The range of temperatures studied was 691 to 938 K. High compound forming tendency in Li-Sn is reflected by a triangular-shaped relation for ΔH vs x _Li. The extrapolated maximum of this plot is about −40 kJ mol⁻¹ close to Li₄Sn. Using the concentration cell Bi(l)Li₃Bi(s)| LiF-LiCl|Li-Sn(l) the emf was measured as function of temperature (775 to 906 K) atx _Li = 0.1 to 0.603 enabling calculations of partial thermodynamic data for lithium in liquid Li-Sn solutions. Integral enthalpies calculated from partial enthalpies of lithium correspond well to the calorimetrically obtained integral mixing enthalpies in the concentration range where both emf and calorimetric data were obtained. The extrapolated maximum of ΔH from calorimetric studies and minimum of integral excess entropies from emf measurements correlate well with results of structure measurements and of other structure sensitive properties. All this experimental information indicates a maximum chemical short range order close to the composition Li₄Sn.     

Thermodynamic activity of magnesium in several highly-solvating liquid alloys

An emf technique is reported using porous alumina tubes to contain reference metals and alloys in a molten salt electrolyte. Data are reported for the activity of magnesium and its temperature derivative in several liquid metal solvents. These include lead (650 °C), tin (800 °C), bismuth (850 °C), antimony (850 °C), and mixtures of tin and antimony (800 °). In all cases, the solvents show strong negative deviations from ideal thermodynamic behavior, due to the effects of strong solvation caused by the formation of intermetallic compounds. The extent of this effect is Pb < Sn < Bi < Sb. The data reported are useful in evaluating solvents for the possible carbothermic reduction of magnesium oxide.     

Thermodynamic characteristics of calcium and strontium in liquid alloys with gallium

The changes in the partial molar thermodynamic characteristics of calcium and strontium in binary dilute alloys with gallium have been measured by the emf method in the temperature range 953–1073 K. The activity coefficients of Ca and Sr indicate a strong interparticle interaction between the alloy components, which increases in going from calcium to strontium.     

The thermodynamic properties of UFe2:Agreement with the campbell correlation of laves phase compounds

The reported value of the heat of formation of UFe₂ determined by acid solution calorimetry¹ and the Gibbs energy of formation determined by high temperature emf cells² seem to give results that are in unreasonably poor agreement. It was recently discovered³ that a well defined correlation exists between the heat of formation and the unalloyed radius ratio of AB₂ type Laves compounds. When this test is applied it is found that the emf data of Yoshihara and Kauno for UFe₂ gives very good correlation with the compounds formed between Pu and the Group Villa metals as shown in Fig. 1. Although these authors did not indicate that heats or entropies of formation could be calculated from their data, a third law calculation using Kopp’s law of the additivity of heat capacity⁴ shows that the entropy term derived from the observed Gibbs energy of formation     

Device for determining the temperature dependence of the heat conductivity coefficient,the thermal emf,and the electrical conductance of cermets

Summary The authors describe the design of a device for simultaneous measurement of the thermal conductivity coefficient, conductivity and coefficient of thermal emf on two metal-conducting samples of cylindrical form in vacuum over a temperature range of 200–1200°C.Translated from Poroshkovaya Metallurgiya, No. 9(45), pp. 89–91, September, 1966.     

Excessive thermodynamic properties of praseodymium in a gallium-indium alloy

The equilibrium potentials of praseodymium-diluted homogeneous Pr-Ga-In alloys in a (Li-K-Cs)Cl_eut-based salt electrolyte were measured between 573–1073 K by the emf method. These potentials are used to calculate the activity coefficients of α-praseodymium in liquid Ga-In eutectic alloys. PrIn₃ alloy with well-known thermodynamic characteristics and without phase transitions in the temperature range 428–1483 K was employed as the reference electrode.     

Thermodynamic characteristics of strontium and barium in dilute liquid alloys with tin

The changes in the partial molar thermodynamic characteristics of strontium and barium in binary alloys with tin are determined by the emf method in the temperature range 973?C1073 K. The changes in the partial molar enthalpies are found to agree satisfactorily with the data of calorimetric measurements. The activity coefficients of strontium and barium point to a strong interparticle interaction between the alloy components, which increases in going from strontium to barium.     

Sulfur determination in carbon-saturated iron by solid-state electrochemical sensor

In the frame of the continuous efforts to thein situ monitoring of the chemical composition of melts in steelmaking, the solid-state electrochemical probe (−)Pt/Nb-NbO/Caβ″-alumina-CaS/S, Fe (1)/C/Pt (+) was developed and tested to measure the sulfur content in carbon-saturated iron. The solid electrolyte used is calcium β″-Alumina, which behaves as a good ionic conductor by calcium vacancies at steelmaking temperatures. The calcium chemical-potential gradient is fixed at the electrolyte interfaces, on the left side, by keeping constant the oxygen chemical potential through the Nb-NbO coexistence mixture and, on the right side, by the activity of dissolved sulfurvia the solubility equilibrium of CaS. A theoretical equation of the probe electromotive force (emf), as a function of the dissolved concentration of sulfur in the bath, was derived. From this equation, which agrees well with the experimental results, it is clearly shown that the emf of the probe can be approximately linear against log ([S]/pct) in small intervals of sulfur concentration. The experimental emf s were taken up in the sulfur concentration range from 13 to 140 ppm. In this interval, the average slope of emfvs log ([S]/pct) curve is about −50 mV/decade. The effect of dissolved oxygen is discussed because it generates a mixed potential related to the CaS instability. The lower sulfur concentration limit, that can be detected, depends on the concentration of the oxygen dissolved in the melt because CaS tends to react with it. Some characteristic quantities of the theoretical equation were chosen as fitting parameters to fit the equation itself through the experimental emfvs log ([S]/pct) data. By this procedure, it was also found that the CO supersaturation in the bath was 10.2 bar.     

Some phase-diagram aspects of the manganese-carbon system

In the present work, differential thermal analysis (DTA) and electromotive force (emf ) methods were employed to investigate the Mn-C phase diagram around the eutectoid decomposition of Mn(γ). The eutectoid temperature and the composition were estimated to be 1031 K and 9.62 mol pct carbon, respectively. The temperature for the eutectoid decomposition of ε-carbide to Mn(γ) and Mn₂₃C₆ was found to be 1260 K, and the equilibrium composition of Mn(γ) corresponding to this three-phase reaction was 14.89 mol pct carbon. From the experimental data, the solubility of Mn₂₃C₆ in Mn(γ) was evaluated in the temperature range of 1031 to 1260 K using a two-sublattice model. On the basis of the present results, the relevant part of the Mn-C diagram was redrawn. Microscopic and X-ray analyses of quenched samples appear to be in support of the suggested phase diagram.     

The measurement of hydrogen activities in molten copper using an oxide protonic conductor

We have developed a hydrogen sensor for in situ measurements of hydrogen activities in molten copper. The sensor consists of a concentration cell utilizing a proton conductor, CaZr_0.9In_0.1O_3-δ, as the solid electrolyte. The electromotive force (emf) of the cell was generated by both hydrogen and oxygen activity gradients across the cell in a high-temperature region simulating the fire refining processes of copper. However, accurate hydrogen activity in molten copper could be evaluated from the emf if oxygen activity in molten copper was determined simultaneously by another concentration cell and if the hydrogen and the oxygen activities at the reference electrode were known. The performance of the sensor was studied under various conditions. The observed good response and reliability of the sensor show that it should be a powerful tool for improvement of the fire refining process of the molten copper. Theoretical treatment of the calculation of the emf of the concentration cells using a mixed ionic conductor, i.e., protonic and oxide ionic conductor, as solid electrolytes is also discussed briefly.     

Thermodynamic investigations of the ternary Au-Sn-Zn system

The thermodynamic properties of liquid ternary Au-Sn-Zn alloys were measured with an electromotive force (emf) method at four cross sections with a constant Au to Sn ratio of 9:1, 3:1, 1:1, and 1:3, respectively. At the last three cross sections, calorimetric measurements were also carried out in order to compare the integral enthalpy of mixing from the direct measurements with the data of the emf measurements which were derived by Gibbs-Duhem integration.