Refractory Characteristics Research Articles

Refractory Characteristics of Aluminum Dross-Kaolin Composite

The suitability of using aluminum dross waste and kaolin to produce refractory bricks is experimentally studied. Thirty brick samples of different blends are produced, dried at 30°C, dried further at 110°C, and fired at 1200°C. The firing temperature point, bulk density, apparent porosity, thermal conductivity, thermal shock, loss on ignition, permeability, shatter index, and shrinkage of the bricks blends are determined. The results show that some blend samples have good refractory characteristics with mixing ratio 4:1:2 (representing weight in grams of aluminum dross, plastic clay, and kaolin, respectively). The evaluations of studied properties reveal the possibility for aluminum dross waste to be used as matrix in refractory bricks.

Synthesis and Microwave Absorption Characteristics of Corundum-Mullite Refractories

A new technology is proposed for the production of corundum-mullite refractories. The crystal structures of the raw materials before and after sintering were determined by XRD. An analysis showed that corundum and mullite were mainly crystalline compounds in the sintered samples. The microwave-absorption characteristics of corundum-mullite refractories are optimal when particle size in the refractories is 75 μm.

Approximation of mathematical scanning simulation data and clinical results f radiofrequency ablation of perimitral atrial flutter. Condition of existence of perimitral atrial flutter

1) to create Perimitral Atrial Flutter (PMAFL) model and estimate theoretical probability of elimination of perimital reetntry using left atrial geometry two-dimensional mathematical modeling and ablative formatting; 2) to compare clinical results of PMAFL ablation by means of mitral vs inferioseptal isthmus ablation and mathematical modeling data. Clinical phase. Study was conducted on 24 pts (6 women, 57.1 ± 9.3 years) with PMAFL. Initially RF-lesions delivered in LA in the MI (endocardial approach to MI). Distal CS roof ablation (epicardial approach to MI) was a second step. As a third step linear RF-lessions of the inferioseptal isthmus (ISI)- from right pulmonary vein ostium to mitral annulus was performed (endocardial approach to ISI). As a fourth step RF-applications applied inside the proximal CS roof (epicardial approach to ISI). Mathematical phase. As the first step numeric reconstruction of the autowave process in excitable tissues of the left atrium was performed. Fitzhugh-Nagumo equation was used for simulation to enabled us to take into account the electrical inhomogeneity of the atria (pulmonary vein ostia). A special scanning method was used for calculating characteristics of autowave processes in a two-dimensional mathematical model of the atrium. As the second step simulation of linear ablation formatting which linked PV ostia and active medium boundaries (corresponding to mitral and inferioseptal isthmus ablation lines) was performed. Clinical phase. Left MI endocardial RFA terminated PMAFL in 6 cases, increased CL without changes of atrial hierarchy activation in 2 cases, and transformed PMAFL to AFib in 2 cases. Distal CS ablation terminated PMAFL in 2 pts. Endocardial ISI ablation of associated with SR restoration in 2 cases and increasing of PMAFL CL in 5 cases. Proximal CS-roof ablation terminated PMAFL in 12 pts. Follow up was 26.7 ± 12.4 mos. Endocardial and epicardial MI approach terminated PMAFL in 8 pts (36%). RFA of endocardial 39nd epicardial aspects of the ISI restored SR in 12 pts (64%) (p< 0.05). MATHEMATICAL PHASE: There are three definite conditions of PMAFL existing: 1) Initial autowave spreading between superior PV and boundary of medium (corresponding to patent conduction between superior PV ostia and mitral annulus); 2) Non-active medium existing between four PV ostia (corresponding to PV isolation after index ablation); 3) Refractory characteristics of medium (corresponding to posterior wall of LA) and medium between PV ostia and boundaries (corresponding to isthmus zones) have to differ each other. The linear ablation patterns (from PV ostia to boundary of medium) suppress PAMFL in two-dimensional mathematical modeling of the left atrium. There are definite conditions of PAMFL simulation by means autowave processing in a 2-D active medium using scanning algorithm. Those conditions may consistent with certain EP characteristics of LA after index ablation clinical results of PAMFL ablation.

Síntese de pós de alumina por meio de um método Pechini modificado com adição de sementes em diferentes atmosferas de calcinação

A alumina é um material muito estudado devido às suas excelentes características refratárias e propriedades mecânicas. A fase α, mais estável, tem uma temperatura de formação de ~1200 °C. Devido à sua elevada temperatura de formação, muitas pesquisas vêm buscando sua redução através da adição de sementes (seeds) da fase α em processos químicos de síntese. Este trabalho teve como objetivo sintetizar pós de α-alumina pelo método Pechini com adição de sementes e comparar a calcinação ao ar e com um fluxo passante de O2, verificando sua influência nas características dos pós obtidos. Tais pós foram caracterizados por difração de raios X, espectroscopia no infravermelho e microscopia eletrônica de varredura. Os resultados foram comparados com os dos mesmos pós calcinados ao ar. A adição de sementes favoreceu a diminuição da temperatura de transformação em fase α, sendo que esta já é identificada a 1000 ºC. A presença de oxigênio na atmosfera de calcinação também favoreceu a formação de fase α a 900 ºC, temperatura inferior à dos pós calcinados ao ar.

Evaluation of Parameters in the Bio-Oxidation Process of Refractory Gold Minerals

The mining districts located in the western mountain range in the south of Ecuador have gold minerals with refractory characteristics, which do not allow gold recovery by traditional methods used in Ecuador. Therefore, it is necessary to apply some technology that permits to obtain greater metal recovery. Bio-oxidation, as treatment of refractory ores that contain low grade of gold, offers an economic and sustainable alternative for this purpose. The objective of this research was to evaluate the effect of particle size, pulp density and concentration of inoculum and inducer (Fe+2) on the bio-oxidation of refractory gold minerals in order to maximize gold recovery of the bioleached minerals by means of a cyanidation process. The microbial consortium used in this work was collected and isolated from the Portovelo mining district corresponding mostly toAcidithiobacillus ferrooxidansandLeptospirillum ferrooxidansspecies. The Eh, final concentration of ferric ion, total iron and sulfates were measured. Finally, the bio-oxidized material was tested using cyanidation to determine the gold recovery. The results after the cyanidation tests showed that the highest gold recovery was obtained when the bio-oxidation step was conducted with 68-91 µm particle size, 15% pulp density, 20% v/v inoculum and 2 g/L of Fe2+as inducer. At those conditions, gold recovery was 68% compared to 26% obtained when no bio-oxidation step was performed, demonstrating that this process was favorable compared with traditional gold recovery processes

Waste incineration in rotary kilns: a new simulation combustion tool to support design and technical change

This article presents a tool based on a simplified model developed for the combustion processes in a rotary kiln incinerator (slightly inclined rotating primary combustion chamber). The model was developed with the aim of supporting the design phase of the incinerator combustion chamber and, at the same time, of investigating possible technical changes in existing plants in order to optimise the combustion process and the dimension of the rotary kiln (length, diameter) as a function of the characteristics of the fed waste. The tool has been applied and the obtained results compared with a real incineration plant operating on healthcare waste located in Rome (Italy). The mass and thermal balances were taken into account, together with kinetic parameters for the combustion of the specific waste stream. The mass balance considered only the major mass components (carbon, hydrogen, oxygen, nitrogen and sulphur). The measured external temperatures appear to be in good agreement with the simulated results. A sensitivity analysis of the plant under different operating conditions was carried out using different input flow rates and excess air ratios, and an assessment was made of the refractory and insulator properties of the kiln's behaviour. Some of the simulated results were used during the periodical maintenance to improve the refractory characteristics in order to reduce the fret and corrosion process.

Aplicaciones biotecnológicas en minería aurífera: Estado del arte sobre la oxidación bacteriana de arsenopirita (FeAsS)

En el mundo, grandes cantidades de sulfuros provenientes de la explotación minera con características refractarias y/o con iones, en su estructura cristalina, nocivos al medio ambiente y a la salud humana, han sido acumulados en el tiempo. Dichos sulfuros presentan contenidos de oro relevantes en la mayoría de los casos, el tratamiento de estos materiales no es factible por métodos convencionales, lo cual incrementa el costo de la recuperación de los valores metálicos presentes. Es así como, en las últimas décadas, la bio-hidrometalurgia, se ha convertido en una tecnología comercialmenteviable para la extracción de metales preciosos. Además, es bien conocida por su utilización en la bio-remediación de drenajes ácidos, remoción de metales pesados presentes en áreas mineras, suelos y sedimentos contaminados, residuos industriales como cenizas de incineración; degradación de cianuro, adecuación de concentrados para separación por flotación espumante, biodesulfurización de carbones, entre otras. En este trabajo se presenta el principio fundamental de la oxidación bacteriana de la arsenopirita, así como un esbozo acerca de los mecanismos y diferentes susceptibilidades que muestra frente a la oxidación biológica.

Evaluations of Y_2O_3 Powder Synthesized Using Oxalic Acid

Nano-sized <TEX>$Y_2O_3$</TEX> powders were prepared via a sol-gel method starting with <TEX>$Y(NO_3)_3{\cdot}6H_2O$</TEX> (Yttrium(III) nitrate hexahydrate) and water with ethanol as a cosolvent. <TEX>$Y_2O_3$</TEX> is an important rare earth oxide and has been considered for use in nuclear applications, such as ceramic materials, due to its excellent optical and refractory characteristics. It has been used as a chemically stable substrate, a crucible material for melting reactive metals, and a nozzle material for jet casting molten rare earth-iron magnetic alloys. Oxalic acid (<TEX>$C_2H_2O_4$</TEX>) has been adopted as a chelating agent in order to control the rate of hydrolysis and polycondensation, and ammonia was added in order to adjust the base condition. The synthesized <TEX>$Y_2O_3$</TEX> powder was characterized using TG/DTA, XRD, FE-SEM, BET and Impedance Analyzer analyses. The powder changed its properties in accordance with the pH conditions of the catalyst. As the pH increases according to the FE-SEM, the grain grew and it showed that the pore size decreased while confirming the effect of the grain size. The nano-material <TEX>$Y_2O_3$</TEX> powders demonstrated that the surface area was improved with the addition of oxalic acid with ammonium hydroxide.

Development of a novel spectrometric-based temperature probe and the investigation of atomic cloud generation in a tungsten coil atomizer

A new two-element atomic emission temperature probe is developed and applied to gas phase temperature determinations in both a tungsten coil atomizer and an air/acetylene flame. Results are comparable to the traditional Sn two-line method, with variances as low as 0.08%. The spectrometric-based thermometer is composed of a handheld spectrometer, a fiber optic and a laptop computer. The method is an interesting alternative for a wide range of applications due to its simplicity, portability and high temperature capabilities. Its spatial resolution is especially desirable for spectroscopic studies. An updated version of the Sn two-line method is used to determine the temperature profile of a tungsten coil atomizer and study processes involved in atomic cloud generation in both atomic absorption and atomic emission spectrometry. Tungsten coil atomizers present significant temperature gradients and spectrometric methods based on them are critically dependent on some interrelated parameters such as gas phase temperatures, protecting gas composition, and ultimately, atomizer positioning relative to the detector. Sn atomic absorption, and Li and Cr atomic emission profiles were determined and compared with the atomizer temperature profile. Elements determined by atomic emission are more dependent on gas phase temperatures while Sn absorption signal is more dependent on the reducing atmosphere provided by H2 molecules present in the protecting gas mixture. Cr presents higher emission signals in a H2-rich, more reducing environment, whereas Li is less dependent on both temperature and protecting gas composition. Those results reflect Li lower excitation energy and Cr refractory characteristics.

Modeling CICR in rat ventricular myocytes: voltage clamp studies

BackgroundThe past thirty-five years have seen an intense search for the molecular mechanisms underlying calcium-induced calcium-release (CICR) in cardiac myocytes, with voltage clamp (VC) studies being the leading tool employed. Several VC protocols including lowering of extracellular calcium to affect Ca2+ loading of the sarcoplasmic reticulum (SR), and administration of blockers caffeine and thapsigargin have been utilized to probe the phenomena surrounding SR Ca2+ release. Here, we develop a deterministic mathematical model of a rat ventricular myocyte under VC conditions, to better understand mechanisms underlying the response of an isolated cell to calcium perturbation. Motivation for the study was to pinpoint key control variables influencing CICR and examine the role of CICR in the context of a physiological control system regulating cytosolic Ca2+ concentration ([Ca2+]myo).MethodsThe cell model consists of an electrical-equivalent model for the cell membrane and a fluid-compartment model describing the flux of ionic species between the extracellular and several intracellular compartments (cell cytosol, SR and the dyadic coupling unit (DCU), in which resides the mechanistic basis of CICR). The DCU is described as a controller-actuator mechanism, internally stabilized by negative feedback control of the unit's two diametrically-opposed Ca2+ channels (trigger-channel and release-channel). It releases Ca2+ flux into the cyto-plasm and is in turn enclosed within a negative feedback loop involving the SERCA pump, regulating[Ca2+]myo.ResultsOur model reproduces measured VC data published by several laboratories, and generates graded Ca2+ release at high Ca2+ gain in a homeostatically-controlled environment where [Ca2+]myo is precisely regulated. We elucidate the importance of the DCU elements in this process, particularly the role of the ryanodine receptor in controlling SR Ca2+ release, its activation by trigger Ca2+, and its refractory characteristics mediated by the luminal SR Ca2+ sensor. Proper functioning of the DCU, sodium-calcium exchangers and SERCA pump are important in achieving negative feedback control and hence Ca2+ homeostasis.ConclusionsWe examine the role of the above Ca2+ regulating mechanisms in handling various types of induced disturbances in Ca2+ levels by quantifying cellular Ca2+ balance. Our model provides biophysically-based explanations of phenomena associated with CICR generating useful and testable hypotheses.

Rheological Study of Yttrium Oxide Aqueous Suspensions

Yttria (Y2O3) has been used in many technological applications areas as luminescence material, high temperature and strength structural material, owing to its excellent optical and refractory characteristics. Applying conformation techniques using Y2O3 concentrated suspensions is adequated, if it is well controlled, so that assisting to obtain homogeneous ceramic bodies, reproductive and with complex geometry. Studies involving superficial behavior, stability conditions of suspensions and the behavior related to conformation give important information to control the processes in manufacturing ceramic components. In this work is presented a rheological study of Y2O3 aqueous suspensions, which concerns to solids and dispersant concentration and pH of media. Preparation of Y2O3 aqueous suspensions with solids concentration of 30vol% was possible, using 1wt% of ammonium polyacrylate (PAA) that was enough to gain the lowest viscosity of the suspensions.

Spatial and Temporal Effects of Interleaved Masking in Cochlear Implants

Modern cochlear implants utilize interleaved presentation of pulses on different electrodes to avoid physical interference among multiple current fields, yet neural interaction still exists. In the present study, masking was examined with four Nucleus24 users with the banded electrode array in an interleaved masking paradigm, where a probe stimulus was interleaved with a masker stimulus. Spatial and temporal aspects of masking were addressed by fixing the masker at the middle of the electrode array and changing the location of the probe and by testing various stimulation rates: 125, 500, 2,000, and 6,410 Hz. In addition, growth of masking (GOM) was assessed by changing the masker level in six steps. Results indicated that masking patterns were generally much wider, regardless of stimulation rate, than those in acoustic hearing. The amount of masking decreased from the peak at the rate of approximately 0.5 dB/mm even at the highest masker level. The pattern of GOM with the rates higher than 500 Hz was different from that observed in previous masking studies, characterized by markedly shallow growth at low masker levels or overall shallow growth. A facilitating effect of the masker (lowering the threshold) was suspected, except for the 125-Hz condition, due to the fibers that were subliminally excited, but not discharged, by the masker with local perturbations of membrane potentials, and were subsequently discharged easily by a lower level probe when the temporal gap between masker and probe was sufficiently short. These results suggest that both refractory characteristics of neurons and neural summation be considered in interleaved stimulation of pulses at high, but clinically relevant, stimulation rates. Overall, the present masking study might provide a basis for models in psychophysics and speech understanding in current cochlear implant systems utilizing high-rate interleaved stimulation.

Characterization of refractory behaviour of complex gold/silver ore by diagnostic leaching

The amenability of a refractory ore to the extraction of gold and silver by cyanide leaching was investigated. Diagnostic leaching tests were also performed to shed light on the refractory characteristics of ore. The leaching tests show that the extraction of gold and silver is consistently low, i.e. ⩽47% and ⩽19.2%, respectively, over a leaching period of 24 h. Even fine grinding (e.g. <38 μm) does not improve the recovery of gold and silver. Diagnostic leaching approach provides information into the cause of the refractoriness of the ore. The findings suggest that the refractoriness is induced by the dissemination and encapsulation of the very fine gold and silver particles largely in the carbonates, oxides and sulfides and, to a small extent, with silicates present in the ore matrix. These findings highlight the practical importance of diagnostic leaching for the understanding of the refractory characteristic of such an ore and for the identification of possible pretreatment options to overcome its refractoriness prior to cyanide leaching.

Groundwater chemistry and arsenic mobilization in the Holocene flood plains in south-central Bangladesh

A comparative study of arsenic enrichment in the Bengal Delta (BD) was carried out in three alluvial aquifers in south-central Bangladesh. Investigated sites included Sonargaon in Narayanganj, Chandina in Comilla and Sirajdikhan in Munshiganj districts. At all sites samples from different depths were collected, and water chemistry and redox status vs. depth trends were determined. The concentrations of DOC and HCO(3)(-) were highest at Sirajdikhan site, while at the Sonargaon and Chandina sites the concentrations were lower. On the contrary, the NH(4)(+) concentration was high at the Chandina site as compared to the other sites. There was a good match between dissolved As and Fe at the Sirajdikhan and Sonargaon sites, but not at the Chandina site. The dissolved aqueous concentration of Mn was low at the Chandina site, which suggested that the Mn(IV) redox buffering step was missing. Speciation modeling indicated a possibility of siderite precipitation at all sites, but precipitation of rhodochrosite only at the Sonargaon and Sirajdikhan sites. At the Sirajdikhan site, the log P(CO2) values were very high (-1.37), which revealed the production of CO(2) in redox processes. Principal component analysis (PCA) indicated an impact of sea water and redox status of different samples. These results suggest that the dissolved As is de-coupled from dissolved Mn because when released, As is re-adsorbed onto the Fe(III) minerals in solid phase, as well as from dissolved Fe when precipitation of Fe(II) minerals controls the aqueous concentrations of Fe. In addition, several other concurrent redox processes may exert kinetic constraints depending on refractory characteristics of Fe(III) minerals.

Refractories for handling steel outside a furnace

A range of refractories is presented for handling steel outside a furnace, which are produced by the Borovichi Refractories Corporation. The refractory characteristics and working features are given.

Investigating the source of BOLD nonlinearity in human visual cortex in response to paired visual stimuli

Several studies have demonstrated significant nonlinearity in the blood-oxygenation-level-dependent (BOLD) signal. Completely understanding the nature of this nonlinear behavior is important in the interpretation of the BOLD signal. However, this task is hindered by the uncertainty of the source of BOLD nonlinearity which could come from neuronal and/or vascular origin. The obscurity of this issue not only impedes accurate modeling of BOLD nonlinearity, but also limits generalization of the conclusions regarding BOLD nonlinearity. To examine this issue, we eliminated nonlinear contributions from the neuronal response and selectively study BOLD nonlinearity under only the vascular effect by employing a paired-stimulus paradigm composed of two ultra-short visual stimuli separated by a variable inter-stimulus interval (ISI). ISIs chosen were long enough (≥ 1s) to ensure invariant neuronal activity to all stimuli. Under this circumstance, we still observed significant nonlinearity in the BOLD signal reflected by a progressive recovery of BOLD response to the second stimuli as ISI gets longer and delayed BOLD onset latency. These nonlinear behaviors identified in the BOLD signal originate entirely from the vascular responses as the neuronal responses to all stimuli are identical. More importantly, we found that BOLD nonlinearity became much less significant after we removed activated pixels from large vessels. These finds reveal that the dominant component, if not all, of the source of BOLD nonlinearity comes from large-vessel hemodynamic response. They also suggest a possible mechanism to improve the spatial specificity of gradient-echo BOLD signal for fMRI mapping based on the characteristics of vascular refractoriness.

Jornalismo cultural no Rio Grande do Sul: a modernidade nas páginas da revista Madrugada (1926)

The article discusses the magazine Madrugada, a cultural periodical that circulated in 1926 in Rio Grande do Sul, based on the initiative of a group of intellectuals articulated around Modernism. In five editions, the journal focused on textual and graphic modernization, expressing, in a conciliatory tone, the refractory characteristics of the modernist movement in the South.

Chemical variation from biolipids to sedimentary organic matter in modern oceans and its implication to the geobiological evaluation of ancient hydrocarbon source rocks

Understanding the dynamics of organic matter in modern marine water columns greatly favors the geobiological evaluation of hydrocarbon source rocks. Biolipids could make great contribution to petroleum hydrocarbons due to their comparable chemical components and the slightly refractory characteristics of biolipids during the microbial/thermal degradation. A variety of environmental factors such as temperature, CO2 and salinity could affect the biochemical contents in microorganisms. As a result, microorganisms living in a changing environmental condition might have a different contribution to the petroleum formation. Organic carbon flux is shown to bear a positive correlation with the primary productivity only within a certain range of biomass volumes in a specific biohabitat. Furthermore, organic matter is degraded much quickly in a water column with oxic conditions. Therefore, the anoxic condition, along with the enhanced biological productivity, would be one of the significant factors in the formation of high-quality hydrocarbon source rocks. The formation of biofilms and microbial mats favors the preservation of sedimentary organic matter by decreasing the degradation rate of organic matter. Identification of biofilms and microbial mats in sedimentary rocks will thus greatly help to understand the depositional processes of organic matter finally preserved in hydrocarbon source rocks.

Retention and penetration evaluation of some softwood species treated with copper azole

This work investigates the treatability of four different (scotch pine—SP, Siberian scotch pine—SSP, Siberian larch—SL, and oriental spruce—OS) heartwood species with the waterborne preservative copper azole (CBA-A, Tanalith-E 3492). A 2.4% active ingredient solution of CBA-A was applied for use in vacuum/pressure treatment of the heartwood samples. Two different pressure times were used, namely 60 and 120 min. Maximum and minimum penetration values were measured as percentage of cross-sectional area. Penetration of preservative was also determined by X-ray fluorescence spectroscopy analysis (ASOMA). SP resulted in the highest penetration and retention values complied requirements stated in the American Wood Preservers’ Association (AWPA) standards. Siberian scotch also showed satisfactory results for standard requirements. SL and OS showed lower penetration and retention results than those of pine samples which can be related to their refractory characteristics.

Oxidative Degradation of Strong Acetic Acid Liquor in Wastewater Emanating from Hazardous Industries

Degradation of moderately concentrated acetic acid in wastewater is difficult due to its refractory characteristics, and consequently very few study reports are available for this. In this work, the efficacy of a few advanced oxidation techniques, involving various combinations of UV radiation, H2O2, and Fe2+, to degrade acetic acid, up to 4 M concentration, have been explored. The process parameters studied were the concentrations of acetic acid and H2O2 and the intensity of the UV radiation. The reactions were found to be highly exothermic. The rate followed a pseudo-first-order kinetic model in the case of Fenton and photo-Fenton reactions, whereas a zero-order model for UV/H2O2 photolysis. Limiting values of H2O2 and Fe2+ have been determined.