Grades Of Alumina Research Articles

Beneficiation of andalusite ore by shaking table process using design of experiments methodology

ABSTRACT Andalusite is an alumina-silicate raw material, principally used in the manufacture of heat-resistant refractory products. In the present research, the andalusite mineral was successfully recovered from andalusite ore using a shaking table coupled with magnetic separation. The effects from shaking table parameters, that is deck tilt angle and water flow rate, on the alumina grade and andalusite mineral recovery were investigated using a design of the experiment (DOE), X-ray fluorescence (XRF), and X-ray diffraction (XRD). The results revealed that the deck tilt angle was the main influencing factor on the processing of andalusite ore. The application of a desirability function on the shaking table showed the increase of alumina content from 20.73 to 38.46 wt.% with a recovery rate of 80%. The recovered andalusite's grade fits the requirements for refractory product manufacturing.

Selection of an Alumina Grade for Manufacturing Alumina Ceramics

Selection of an Alumina Grade for Manufacturing Alumina Ceramics

Influence of Alumina Grade on Sintering Properties and Possible Application in Binder Jetting Additive Technology.

Alumina is one of the most popular ceramic materials widely used in both tooling and construction applications due to its low production cost, and high properties. However, the final properties of the product depend not only on the purity of the powder, but also, e.g., on its particle size, specific surface area, and the production technology used. These parameters are particularly important in the case of choosing additive techniques for the production of details. Therefore, the article presents the results of comparing five grades of Al2O3 ceramic powder. Their specific surface area (via Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods), particle size distribution, and phase composition by X-ray diffraction (XRD) were determined. Moreover, the surface morphology was characterized by the scanning electron microscopy (SEM) technique. The discrepancy between generally available data and the results obtained from measurements has been indicated. Moreover, the method of spark plasma sintering (SPS), equipped with the registration system of the position of the pressing punch during the process, was used to determine the sinterability curves of each of the tested grades of Al2O3 powder. Based on the obtained results, a significant influence of the specific surface area, particle size, and the width of their distribution at the beginning of the Al2O3 powder sintering process was confirmed. Furthermore, the possibility of using the analyzed variants of powders for binder jetting technology was assessed. The dependence of the particle size of the powder used on the quality of the printed parts was demonstrated. The procedure presented in this paper, which involves analyzing the properties of alumina varieties, was used to optimize the Al2O3 powder material for binder jetting printing. The selection of the best powder in terms of technological properties and good sinterability makes it possible to reduce the number of 3D printing processes, which makes it more economical and less time-consuming.

Silver Adsorption on the Low Temperature Activated Alumina Grades. II. Antimicrobial Activity of the Silver Adsorbed on the Alumina Surface

The subject of this paper was the study of antimicrobial capacity of silver loaded on the low temperature activated alumina products and evaluation of these products as decontaminants in the water and waste waters decontamination treatments. The low temperature activated alumina products have been characterized as valuable adsorbents in previous papers. So, by reason the next step to investigate these silver loaded products and finding their performaces as antimicrobial agents was an alluring prospect. For this purpose, a common bacterian inoculus was choosen for experiments, and a penmisive method to measure the rate of inhibition was adopted. Experimental data have shown the dependence of the inhibition rate on the following parameters concerning the adsorbent properties: the thermal treatments, particle size dimension of adsorbent (low temperature activated alumina products), concentration of siver adsorbed on particle surface and density of bioreactive centers, representing the number of particles on unit volume of the liquid containing the bacterial cells. Also, the experiments lay out that the aluminum hydroxide calcined at 300 and 400ºC exibits the largest silver adsorbed concentration and the highest inhibition rate (close to 100 %). Little dependence of inhibition rate on pH, in the interval 5.0 � 8.0, was observed. For application of depolluting agent in diferent technological processes, it is necesary to measure the minimum inhibitory concentration in therms of g of silver loaded on the low temperature activated alumina /L.

Silver Adsorption on the Low Temperature Activated Alumina Grades. I. Adsorption Capacity and Kinetics

Aluminum hydroxide is a key product for the industrial production of alumiana and aluminium, ceramics insulator and refractories, desiccants, absorbents, flame retardants, filers for plastics and rubbers, catalysts, and various construction materials. The production of these arrays of useful material products is grounded on the multiple thermal decomposition pathways of Al(OH)3, which involve major crystallographic dislocations and many microstructure reconfigurations on variable lines of phase transitions, from the raw material up to large varieties of precursors and commercial grade products. A wide range of literature on this subject is available, and recent reviews cover suitable information about preparation and characterization of different activated alumina products with specific properties and applications. In our previous papers, there was studied the mechanisms of aluminum hydroxide phase transitions, during low temperature calcination, namely, at 260ºC, 300ºC, 400ºC and 600 ºC, under chosen particularly conditions, for promoting the nucleation of the amorphous phases. Collected data suggest that raw aluminum hydroxide; dried, milled and classified is a precursor for the new low temperature activated alumina transition phases, carrying distinctive characteristics and properties, due to products enrichment in amorphous phases. Accordingly, as effects of the main driving factors (temperature and rate of heating, and initial particle size dimension) on the aluminum hydroxide as new precursor, notable changes were observed in products mineral composition, morphology and specific surface area, pore size, pore distribution, and the particle size distribution. Beside, some other secondary effects have to be apprehended. For example, the main phase transition process dinamic factors control over some physical and technical properties of the new products, like: absolute density, brightness, oil absorption capacity and water absorption capacity. The purpose of this work was to continue the characterization of low temperature activation alumina products, and also, to measure the adsorption capacity and to reveal adsorption kinetics mechanisms. Thus, the first step of survey was silver adsorption maximum capacity measurements for all sample prepared by heating the precursor alumina hydroxide, milled and classified as 5 different dimension size fractions to 260, 300, 400 and 600ºC. Hereinafter, four samples, carefully selected as representative for the entire lot of samples, were used for the study of kinetics mechanism and data fitting to the adequate kinetic equations. Confident data validate the pseudo second order kinetic model for the entire activation process, independently of samples heating temperature and particles dimension.

ВЛИЯНИЕ МОДИФИЦИРУЮЩИХ ДОБАВОК НА ПРОЦЕССЫ СИНТЕЗА КЛИНКЕРНЫХ МИНЕРАЛОВ ВЫСОКОГЛИНОЗЕМИСТОГО ЦЕМЕНТА

The article presents the results of studying the effect of modifying additives CaAl2O4 (CA) and CaAl4O7 (CA2), as well as boric acid on the processes of phase formation of clinker minerals. The calculation of the content of raw materials in the charge is carried out taking into account the production of high-alumina clinker with the participation of Al2O3 71–72 wt.% and CaO 27–28 wt.%. In accordance with the state diagram of the CaO–Al2O3 system, the mass amount accumulates in two calcium aluminate phases: CA 64 wt.% and CA2 36 wt.%. Chalk grade M-90 and commercial alumina grade G-0 are used as feedstock. Heat treatment of powder mixtures with different concentrations of modifying additives is carried out in the temperature range of 1250 - 1350°C with isothermal holding for 1 and 2 hours. It has been established that when 0,5 % H3BO3 is introduced into the charge, the design ratio of the CA and CA2 phases appears after heat treatment at 
 1350 °C for 2 hours. An increase in the content of boric acid to 1,0 % allows to obtain a phase clinker composition close to the design one at 1250 °C and a holding time of 1 hour. It has been shown that the introduction of HAC additives into the mixture affects the quantitative phase composition of products. A correlation is established between the amount of HAC introduced and the decrease in the content of unreacted α-alumina in samples heat-treated at 1350 °C for 1 hour.

Effect of material properties on interaction of ceramic and glass flyer plates with hypervelocity jet

AbstractA study on the effect of material properties on the interaction of explosively driven ceramic and glass plates with shaped charge jets is performed in order to bolster future studies on the design of reactive cassettes with non‐steel flyer plates. A symmetric steel reactive cassette construction is taken as a base, and front and back plates are selectively changed with ceramic or glass plates keeping the areal densities similar. Plates manufactured from two different grades of alumina, silicon carbide, boron carbide, and borosilicate glass are employed to assess the ballistic protection performance of reactive cassettes. It is seen that a high density and fracture toughness is desired for the front plate and high bulk impedance for the back plate, respectively. Moreover, replacing the front plate of a steel cassette with an alumina or silicon carbide plate increases the ballistic protection efficiency close to 50%. Finally, the effect of material selection is investigated by hydrocode numerical simulations. The early phases of the interaction process are presented to reveal the basics of initial hole closure on the flyer plate and the determination of the length of the jet precursor.

ВЛИЯНИЕ РЕЖИМОВ ТЕРМООБРАБОТКИ НА ПРОЦЕСС СИНТЕЗА КАЛЬЦИЙ-АЛЮМИНАТНЫХ ФАЗ В ТЕХНОЛОГИИ ОСОБО ЧИСТОГО ВЫСОКОГЛИНОЗЕМИСТОГО ЦЕМЕНТА

The results of experimental studies on the phase formation of CaAl2O4 (CA) and CaAl4O7 (CA2) from CaCO3-Al2O3 powder mixtures in the temperature range 1250 - 1450 ° C ate presented. In order to calculate the content of raw materials in the charge, the criterion of obtaining high-alumina clinker with Al2O3 content of 71 - 72 wt. % and CaO 27 - 28 wt.% is proceeded. This mass ratio in the CaO - Al2O3 system state diagram suggests the presence of two calcium-aluminate phases CA and CA2. The projected phase composition of clinker is 64 mol. % CaAl2O4 (CA) and 36 mol. % CaAl4O7 (CA2). As precursors chalk grade M-90 and technical alumina grade G-0 are used. The initial charge is heat-treated at temperatures of 1250, 1300, 1350, 1450°C and isothermal stage times of 1 and 2 hours. It is supposed that the synthesis of target phases CA and CA2 is preceded by formation stage followed by degradation of calcium-enriched metastable phase C12A7. This assumption is confirmed by the results of thermogravimetric and X-ray phase analyses and by scanning electron microscopy. The process of formation of CA and CA2 target products from dispersed powders of aluminum oxide and calcium carbonate with increasing temperature and time of isothermal exposure is determined mainly by diffusion of more mobile Ca2+ cations released in the process of C12A7 phase degradation in the area of high concentrations of aluminum oxide.

Properties dependence of the lightweight alumina products obtained by a semi-dry pressing method on the alumina type

Lightweight materials are widely used in industry for thermal insulation of various thermal units. The choice of lightweight material depends on the specific conditions of service. For the lining of high-temperature units operating in reducing environments, alumina lightweight products are used that contain a minimum amount of Fe2O3 impurities and free (unbound in compounds) SiO2.
 In JSC “URIR named after A. S. Berezhnoy” a technology of alumina lightweight products of grades KLA-1.1 and KLA-1.3 by a semi-dry pressing method with an application temperature of up to 1550 °C has been developed. These products are made from a mixture of ground and no-milled γ-form alumina of grade 0 and α-form alumina of grade S with additives of pitch coke and chalk.
 The work purpose was improvement of the alumina lightweight products technology and search for new alternative raw materials along with the currently used alumina grade S. The properties dependence of alumina lightweight products, obtained by the semi-dry pressing method, on the type of alumina α-form, was investigated.
 As a result of the studies, it was found that, for the manufacture of alumina lightweight products of grades KLA-1.1 and KLA-1.3 by the semi-dry pressing method, alumina grades N and NR can be used as an alternative alumina-containing raw material along with alumina grade S. The phase composition of alumina lightweight products of grades KLA-1.1 and KLA-1.3, which are manufactured using alumina grades S, N and NR, was represented mainly by corundum and calcium hexaluminate. The alumina lightweight products, which were manufactured using alumina grades S, N and NR, were characterized by similar high properties and correspond the technical requirements for grades KLA-1.1 and KLA-1.3.

Influence of vibration time on the formed structure strength in a vibrocast coarse­grained corundum­chromia mass

An influence of vibration time on the formed structure strength in a vibrocast coarse­grained corundum with a chromium oxide addition mass was studied. Along with scientific, these studies are primarily of practical interest, since they allow to establish the possibility of proper transportation of moulded green product without destroying its structure formed during keeping of this product in the form.
 Under the influence of vibration on the formed structure in the above mentioned coarse­grained mass, it was revealed that the effect of vibration on this mass for 60 minutes of its continuous application practically does not lead to the destruction of the formed structure, which indicates its high stability and strength. The results obtained in this article confirmed the results of previous work on the structure formation in the vibrocast coarse­grained corundum­chromia mass containing a mixture of dispersing alumina grades ADS­1 and ADW­1.
 The studies results were used to improve the manufacturing technology of fired shaped corundum products with the Cr2O3 ­ addition, characterized by high properties and designed to perform a lining working layer of production reactors of carbon black. The indicated advanced technology has been mastered at the pilot production of institute.

Coupling additive manufacturing and microwave sintering: A fast processing route of alumina ceramics

In this paper, a quick and efficient route to produce complex-shape alumina is reported. Alumina pieces are shaped by additive manufacturing (stereolithography) and densified by microwave sintering. Two raw powders are investigated in terms of both printing and microwave sintering: one alumina grade appropriate for additive manufacturing but not for microwave sintering, and vice-versa for the other grade. The mixture of the two raw powders allows both stereolithography printing and microwave sintering. Alumina parts processed by additive manufacturing followed by microwave sintering were successfully prepared and exhibited relative densities of about 93%, elastic modulus up to 236 GPa and Vickers hardness up to 12 GPa. Notwithstanding the part properties, the as-proposed coupling resulted in a time saving of 30%.

Influence of microstructure on the impact failure of alumina

In this paper, we detail a study involving the characterization of two grades of alumina (CoorsTek Engineered Ceramics AD-85 and AD-995) and subsequent impact experiments with tungsten carbide spheres at 400 m/s. Through this work, we hope to understand the relationship between microstructure and the high strain rate behaviors of advanced ceramics. Initial characterization of microstructure with scanning electron microscopy, electron backscatter diffraction, and energy dispersive X-ray spectroscopy determined grain size, and the elemental character of the materials and the inclusions present. AD-85 alumina was found to have smaller alumina grains and more non-alumina inclusions than AD-995 alumina. Compression testing with in-situ visualization for crack speeds demonstrated that the strength of AD-85 increased from 2.0 ± 0.1 GPa at 10-3 s-1 to 2.7 ± 0.3 GPa at 500 s-1 (crack speeds of 1800 ± 600 m/s). The AD-995 had strength increases of 2.4 ± 0.2 GPa at 10-3 s-1 to 3.6 ± 0.5 GPa at 500 s-1 (crack speeds of 2200 ± 400 m/s). The greater rate sensitivity and higher crack speed of the AD-995 is related to microstructure and mechanical properties. Impact experiments used spherical tungsten carbide projectiles fired from a smoothbore powder gun into alumina discs held in place with polycarbonate holders that provided no lateral confinement and minimal back face confinement. The use of simultaneous high-speed video, photon-doppler velocimetry, and flash X-ray during these impact experiments produced information on the cracking and microbending of the target in the first 10 μs of impact, with a number of significant events happening within the first 5 μs. At 400 m/s, AD-85 alumina suffered penetration by the projectile while AD-995 alumina defeated the projectile. The data allows for comparison of event timing such as peak back face velocity and the onset of radial cracking, demonstrating that during an impact event, interface defeat occurs within the first 5 μs. The data collected and analysis done also suggests that the failure of the projectile can couple with the target via the transmission of shear waves and contribute to failure, which has implications for future modelling and design of improved protection systems.

Influence investigation of the type and amount of the new active aluminas addition on the properties of products from low-cement corundum chromium-containing castable mass

The influence of new active aluminas addition (NABALOX NO 635 and NABALOX NO 713-10 MF) and its amount on the properties of non-burning and fired at 1580 оC samples has been studied. It was established that, the compressive strength of non-burning samples, depending on the type and amount of the active alumina addition, is maximal when 5 % of the active alumina NABALOX NO 635 is added. After high-temperature firing, the densest structure is formed in the samples of this composition, as evidenced by their indices properties: open porosity of 23.3 %, apparent density of 3.03 g/cm3, compressive strength of 115 N/mm2. As a result of the carried out researches, the technology of products manufacturing by vibrocasting method from the low-cement corundum chromium-containing castable mass has been improved by adding the new active alumina of NABALOX NO 635 instead alumina grade of CTC-40. This technology provides manufacturing of products with higher compressive strength (115 vs. 104 N/mm2) and a larger apparent density (3.03 vs. 3.02 g/cm3) with substantially equal open porosity values compared to those of earlier manufactured products containing of active alumina addition grade of CTC-40. Based on the economic feasibility, as well as the availability and the possibility of purchasing NABALOX NO 635 alumina in small batches on the domestic raw materials market (“Nabaltec AG”, Germany, has a representative office in Ukraine), its use for manufacture of the low-cement corundum chromium-containing castable mass is more preferable compared to with the previously used active alumina grade of CTC-40 produced by “Almatis GmbH” (Germany). As a result of the carried out researches, normative documentation has been developed. According to this documentation, in the conditions of PJSC “UKRNIIO NAMED AFTER A. S. BEREZHNOY” full-scale samples of products characterized by high properties were produced: compressive strength after hardening in humid conditions for 7 days of 63 N/mm2, open porosity of 23.3 %, an apparent density of 3.03 g/cm3, compressive strength after firing at a temperature of 1580 оC of 94 N/mm2.

Development and characterization of zirconia–alumina composites for orthopedic implants

In this study, three different grades of alumina toughened zirconia composites (ATZ) (from 80 to 90wt% of zirconia), and three grades of zirconia toughened alumina (ZTA) from 80 to 90wt% of alumina were developed. Two types of stabilized zirconia were used: 3mol% yttria stabilized zirconia used on the ATZ, and 2mol% yttria stabilized zirconia for the ZTA. The composite powders were obtained by spray-drying with a controlled granulometric distribution. Uniaxial and cold isostatic pressing were performed. High density ceramics with densification above 97% were obtained after a low temperature sintering (1400°C) leading to enhanced mechanical properties. Higher values of fracture toughness and flexural strength were achieved for the ATZ samples (up to 5MPam1/2 and 1394MPa respectively), while ZTA samples presented higher values of hardness (up to 1846HV). Aging tests showed that ZTA samples did not present monoclinic zirconia after 96h. MTT and alkaline phosphatase activity assays were performed on the sintered samples. This study shows that ATZ and ZTA composites with good mechanical properties, aging resistance and osteoblastic cytocompatibility can be attained.

Selection of healing agents for autonomous healing of alumina at high temperatures

To date, the research aimed at creating a high-temperature alumina (Al2O3) grade capable of autonomously repairing crack damage focussed on the use of SiC particles which turns to SiO2 as the healing agent. The present work presents an unbiased selection procedure to determine other attractive substances and phases which could serve as an effective healing agent for healing at high temperatures. The selection process is based on an analysis of the requested characteristics of the oxide to fill the crack (melting point, adhesion to the alumina matrix and thermal mismatch) as well as those of the healing agent prior to being activated (melting point, volume expansion upon oxidation and thermal mismatch). Application of all selection criteria resulted in identifying granular Ti, Cr, Zr, Nb, Hf, TiC, TiN, Cr3C2, Cr2N, ZrN, NbC and NbN as promising agents for autonomous healing of alumina when used in air at high temperatures.

Quantifying the uncertainty in the spatial layout of rock type domains in an iron ore deposit

This work addresses the problem of delineating the spatial layout of ten rock type domains in an iron ore body and of assessing the uncertainty in the domain boundaries. A stochastic approach is proposed to this end, based on truncated Gaussian simulation, which consists in defining successive partitions of the space that comply with the desired spatial continuity and contact relationships between rock type domains. The sequencing of these domains is driven by their position (surficial vs. underlying rocks), granulometry (compact vs. friable rocks), and grades (rich vs. poor) of iron, alumina, manganese and loss on ignition. A total of 100 realizations are produced, conditioned to available drill hole data, and used to quantify the uncertainty in the occurrence of each rock type domain, at both global and local scales.

Parametric Study and Optimization of Nd: YAG Laser Micro-Turning Process of Different Grade of Alumina Ceramics Based on Taguchi Methodology

The present paper addresses an investigation on the effect of process parameters during Nd:YAG laser micro-turning operation of different grade of alumina (Al2O3) ceramic materials. Considering different levels of various process parameters i.e. laser beam average power, pulse frequency, workpiece rotational speed and Y feed rate, Taguchi method based experimental design has been used to construct the set of experiments. The same set of experiments has been utilized to machine 10 mm diameter cylindrical workpiece made of different grades of Alumina ceramics i.e. K60 and K80. Surface roughness (Ra) and micro-turning depth deviation were considered as the process characteristics. Analysis of variance (ANOVA) test was performed for each grade of alumina ceramic to find out the significant process parameters during laser micro-turning process. The optimum process parameters settings for individual responses were obtained by analyzing the signal-to-noise (S/N) ratio. Mathematical models, which correlate the response and process variables, have been developed for all the grades of ceramics. Multi-objective optimization i.e. simultaneous minimization of surface roughness (Ra) and micro-turning depth deviation has been done through combined approach of Taguchi methodology and Grey Relational Analysis.

FLUORIDE REMOVAL USING ACTIVATED ALUMINA: A CASE STUDY OF BHOOMA CHOTA WATER

The adsorption of fluoride, from a fluoride, contaminated groundwater sample from the village, Bhooma Chota, District Sikar, in the State of Rajasthan, India, has been studied using alumina grade DF-101. The fluoride adsorption capacity (q1) has been fitted into the pseudo-first-order adsorption, pseudo-second-order adsorption, Elovich, and intraparticle diffusion models. It has been found that the kinetic data fits best in the pseudo-second-order rate equation giving a very high correlation coefficient (R2 = 0.991). the modeled fluoride absorption capacity (q1) has been calculated from the various equations using the constants derived from the least square regression plots. The calculated q1 values, model the experimental data very well, for the pseudo-second-order and Elovich equations, as is evident from the sum of square error calculations. Fluoride removal is through a combination of surface absorption and intraparticle diffusion. A study of the fluoride removal process with increasing dosage of activated alumina reveals that though the percentage of fluoride removal increases with activated alumina, the adsorption capacity at equilibrium decreases. The minimum dosage of activated alumina which causes the maximum percentage removal of fluoride from water, while at the same time brings forth its highest equilibrium absorption capacity has been determined.

Electrical monitoring of crack propagation during quasi-static loading and ballistic impact of alumina plates

Abstract An electrical methodology has been developed to monitor crack advance during ballistic impact. Velocities of radial cracks can be measured and information about development of the crack pattern can be obtained. This is done via a grid of thin gold tracks, printed onto the front or back surfaces of the sample. These elements were incorporated into an electrical circuit and high speed data acquisition was carried out during impact. The fracture behaviour of two grades of alumina has been examined. Hard spherical projectiles were used, with a range of impact velocities. An increase in radial crack velocity was detected with increasing impact velocity, within this range. Differences in crack velocities were also noted between the two types of alumina. Crack speed values are in good agreement with data reported previously for similar systems, obtained using high speed photography. The methodology proposed here looks to be reliable, convenient and economically attractive.

Separation of ultrafine particles of alumina and zircon by liquid–liquid extraction using kerosene as the organic phase and sodium dodecylsulfate (SDS) as the surfactant collector for abrasive manufacturing waste recycling

In this paper, the separation of ultrafine alumina and zircon particles by a liquid–liquid extraction method was investigated using kerosene as the organic phase and sodium dodecylsulfate (SDS) as the surfactant collector, with application to the recycling of waste generated in abrasive manufacturing. The characteristics of alumina/zircon particles transferred from water to kerosene phase, as well as the effect of SDS addition, were first investigated individually. The separation of an alumina–zircon particle mixture was then conducted to find the optimal extraction conditions. Finally, the technique was applied to abrasive manufacturing waste.The results indicate that without the addition of a surfactant collector, more than half of the alumina particles were extracted from the water phase to the kerosene phase at pH ranging from 8 to 10. With the addition of more than 0.1kg/ton SDS, alumina particles were completely extracted to the kerosene phase from pH 7 to pH 10. On the other hand, pH and SDS addition had no significant effect on the extracted fraction of zircon, which remained at approximately 5–10% throughout the tested pH range. By extracting alumina to the kerosene phase and leaving zircon in the water phase, the two could be separated. Optimal extraction conditions for the mutual separation of alumina–zircon particle mixture were found at pH 9.5 with 1.25kg/ton SDS addition. Similar results were obtained after application of the technique to abrasive manufacturing waste. Under these conditions, the grade of zircon in the water phase solids was 96.2% with recovery of 77.4%, and the grade of alumina in the kerosene phase solids was 76.9% with recovery of 96.1%.