Reaction Of Aluminum Research Articles

Effect of Reactive Alumina on the Physico-Mechanical Properties of Refractory Castable

The effect of reactive alumina and its different proportions on physico-mechanical properties of conventional high alumina castables were studied. The castables with different percentages of reactive alumina were prepared by using calcium aluminate cement as a binder and various refractory properties of the prepared castables, i.e. apparent porosity, bulk density, cold crushing strength, hot modulus of rupture were studied. The mineralogical analysis was done by X-ray diffractometry, whereas morphological analysis was carried out by scanning electron microscopy. The results showed that the castable with high percentage of reactive alumina hydrated early as well as developed early sintered strength due to its faster rate of hydration and higher reactivity at lower temperature. The hot modulus of rupture was also found to be higher in the castable with more reactive alumina. Mineralogical analysis showed well developed mullite and corundum phases in the refractory concrete which was supported by morphological analysis.

Research and Application of Corundum Based Self-Flowing Castable Refractories

The effects of different deflocculants, fume silica, reactive micro-alumina powder and high alumina cement on the flowability of corundum based self-flowing castables were investigated using brown corundum as the main starting materials. The behavior of the castables was evaluated according to the self-flow value of the castables. The results showed that the best self-flow characteristics of corundum based self-flowing castables is obtained using sodium hexametaphosphate as deflocculant, suitable amount of alumina micropowder, fume silica, and high alumina cement as binders. The resultant castables were successfully used in the bottom of a refining ladle with capacity of 80 tons. The service life could match that of well blocks and meet the production requirements.

Stabilization of High-Sulfate Soils by Extended Mellowing

The use of lime to stabilize expansive soils has been the preferred technique for many years. However, heaving and premature pavement failures in lime-treated expansive subgrades containing sulfates led to the search for alternative stabilization techniques. Of the several techniques developed, precompaction mellowing has the potential to be effective in stabilizing sulfate-bearing soils. Yet this method needs experimental evaluation. In the current study, an attempt was made to assess the stabilization effectiveness of precompaction mellowing on high-sulfate soils. For this task, six natural expansive soils from Texas, with sulfate contents varying from 200 to 44,000 ppm, were collected. Soils with low-sulfate contents were spiked with additional sulfates to make them high-sulfate soils. Basic classification and chemical tests were performed to establish the clay mineralogy of the soils. Three mellowing periods (0, 3, and 7 days) were studied. The test soils were treated with lime and allowed to mellow for the specified periods. Following the mellowing, the samples were subjected to three-dimensional tests for volumetric swell, shrinkage, and unconfined compressive strength (UCS). To study the consumptions of alumina and silica during sulfate–soil–lime reactions, reactive alumina and silica measurements were also attempted. The authors observed that shrinkage was of no concern in treated soils because the shrinkage invariably reduced with lime treatment. In four of the six soils, precompaction mellowing reduced sulfate-induced swell to a level below the natural expansive swelling. The UCS strengths of treated soils decreased slightly with mellowing. Reasons for the anomaly in UCS strengths and ineffectiveness of precompaction mellowing in two soils were explained.

404 易焼結性アルミナ微粉体の高速衝突によって製作された薄膜強度(機素潤滑設計1)

404 易焼結性アルミナ微粉体の高速衝突によって製作された薄膜強度(機素潤滑設計1)

Influence of Si<sub>3</sub>N<sub>4</sub> Addition on the Mechanical Properties and Microstructure of Unfired A1<sub>2</sub>O<sub>3</sub>-C Slide Plate

The effects of Si3N4 addition on the room temperature physical properties and hot modulus of rupture(HMOR) of unfired A12O3-C slide plate were investigated by using tabular corundum and reactive alumina as starting materials, aluminium powder and silicon powder as antioxidation agents, phenolic resin as binder. The phase composition and microstructure was characterized by X-Ray diffraction (XRD), scanning electron microscope (SEM), and EDAX. The results showed that with addition of Si3N4, the compactness of A12O3-C slide plate decreased, the room temperature strength deduced. Due to formed cylindrical sialon as a binder phase, the hot modulus of rupture increased.

Morphological Differentiation and Crystal Growth Form of Friedel’s Salt Originated from Pozzolan and Portland Cement

This paper has a scientific−technical character and deals with morphological comparison of Friedel's salt (Fs), which is a compound that is originated from two routes: C3A phase of Portland cement (PC) and Al2O3 r− (reactive alumina) of pozzolans. The reaction courses are contrasted and the role of reactive components is discussed in detail. The results show a great difference in morphology of the Fs, relative to the function of its origin, which is directly related to its very different formation rate: Friedel's salt of rapid formation (Fs-rf) or Friedel's salt of slow formation (Fs-lf). The reactive alumina (Al2O3 r− ) component of pozzolans is found to be involved in the direct, nondirect, and, above all, indirect stimulation of the C3A phase of ordinary Portland cement (OPC) saline hydration, because of its high, fast, and early pozzolanic activity. For this reason, its pozzolanic activity is justifiably classified more as specific than generic, intensifying the formation of Fs from the C3A origin of OPC.

TEM and SAED Characterization of Metakaolin. Pozzolanic Activity

The present study deals with a characterization of metakaolin pozzolanic activity and its chemical character exhibited in the Ordinary Portland Cement (OPC) blends by means of Transmission Electron Microscopy (TEM) and Selected‐Area Electron Diffraction (SAED) techniques principally. Metakaolin sample was prepared by calcination of kaolin rock (Guadalajara, Spain) at 780°C. Two OPC of different chemical composition from the tricalcium aluminate content point of view were chosen and Portland cement blends series elaborated and then submitted to the pozzolanic activity test (EN 196‐5 or Frattini test). The main mineralogical components of the metakaolin are determined qualitatively: χ‐alumina and quartz. The chemical character of the metakaolin is described because of its final composition as well as due to its Al atoms possible coordination. The crystalline order of the material is found to be of both amorphous and polycrystalline, being an intimate amorphous mixture of alumina and silica. Finally, all the alumina capable of reacting chemically is denominated and classified as reactive alumina component, Al2O3r−, of pozzolans, as well as the aluminic chemical character of metakaolin in OPC blends is once again proved and exhibited by means of Friedel's salt formation studied already at 4 h‐age.

Synergic effect of Friedel’s salt from pozzolan and from OPC co-precipitating in a chloride solution

Two prior papers on this subject have shown, with XRD and SEM techniques, that almost all pozzolanic additions can induce the rapid formation of Friedel’s salt in quantities in keeping with the reactive alumina, Al2O3r- (tetra- or penta-coordinated alumina) content of the pozzolan. The formation rate of Friedel’s salt of pozzolan origin has also been shown to be higher than the rate in the slower forming compound, whose origin is the C3A in OPC. Consequently, the plate-like hexagonal crystals are smaller and less perfectly shaped in fast- than in slow-forming Friedel’s salt.To describe the inter-relationships between these two non-expansive processes, a terminological analogy is drawn between the rapid and slow formation of Friedel’s salt and drug interaction. A common development in the treatment of certain diseases, drug interaction may be quantitative or qualitative and, depending on the end result, is typed under one of the following headings: additive synergy, partial antagonism, competitive antagonism, potentiating synergy, non-competitive antagonism or physiological and functional antagonism. Borrowing from this classification, the present study sought to determine whether the joint formation of Friedel’s salt from pozzolan and from OPC in a common chloride solution is synergic, additive, antagonistic or able to invert the expected outcome.To this end, 14 binders, 2 PC (1 OPC and 1 SRPC) and 12 blended cements containing 20% or 30% of one of six pozzolans, were analysed with XRD technique. Water resistance, capillary absorption and total porosity were also determined, along with the chemical composition and physical properties of some cement tested.The experimental results showed that fast- and slow-forming Friedel’s salt precipitated in a common chloride solution not separately but inter-dependently and the closer the pozzolan particles were to the cement particles, the greater was that inter-dependence. Moreover, the joint precipitation – co-precipitation – of the Friedel’s salt from the Al2O3r- present in pozzolans and the Friedel’s salt from the C3A present in OPC was, to use drug interaction terminology, consistently more synergic than additive. Furthermore, depending on the parameter considered and from a purely technological point of view, the practical implications of the Synergic Effect (SE) between the two types of Friedel’s salt were always beneficial. The experimental results showed, in addition, that the pozzolanic activity of three of the pozzolans tested, C, M1 and M0 specially, once again proved to be more specific than generic in chloride and water environments. This would induce speedier chloride hydration of all or part of the C3A in the OPC fraction than when the OPC was hydrated without the pozzolan. Moreover, the Friedel’s salt from the Al2O3r- in these pozzolans was the chief direct and indirect cause of the SE, in conjunction with the Friedel’s salt from the C3A in PC, due to their very specific pozzolanic activity in such chloride media. In contrast, when the pozzolan used was silica fume (SF), its pozzolanic activity is not also more specific than generic for the same result but for the contrary result, that is, SF is unspecific for the same result.

Leaching of F-type fly Ash Based Geopolymers

Abstract Geopolymers are the synthetic analogues of natural zeolitic materials. Geopolymeric materials possess excellent mechanical properties, including fire and acid resistance. These properties make geopolymers an alternative construction material compared to Portland cement. Most waste materials such as fly ash, blast furnace slag and mine tailings contain sufficient amounts of reactive alumina and silica that can be used as source materials for in situ geopolymerisation reactions. Alkali-activation of aluminosilicate solids using alkaline hydroxide and/or silicate solutions can be used to synthesize inorganic geopolymeric binders or alkali-activated cements, displaying excellent physical and chemical properties. In this experimental study the effects of curing conditions on physical and mechanical properties and on the microstructure of geopolymer pastes were investigated. F class fly ash was activated by 12 M sodium hydroxide and sodium silicate solutions. Geopolymer pastes were cured at 40iC, 80iC and 120iC for 6, 15 and 24 hours respectively. The samples were tested for compressive strength at the ages of 7, 28 and 90 days and the effect of aging was also investigated. After 28 days of curing, the samples were crushed and were extracted using leaching tests. USEPA TCLP (toxicity characteristic leaching procedure) method was applied for leaching tests. Inductively Coupled Plasma-Optical Emission Spectroscopy was used to determine the content of leach solution. For 28-days samples, microstructure of the samples were observed by X-ray diffractometry(XRD), Scanning Electron Microscope(SEM)/Energy Dispersive X-Ray(EDX) Spectrometer, and Fourier Transform Infrared Spectroscopy(FTIR) techniques. The results showed that the curing temperature and time are important parameters affecting the mechanical properties and microstructure of geopolymers.

An Experimental Study on the Mechanical and Microstructural Properties of Geopolymers

Geopolymer is a new class of inorganic polymer synthesized by activation of an aluminosilicate source with an alkaline hydroxide or silicate solution. In recent years, geopolymeric materials have attracted much more attention because of their excellent mechanical properties, good chemical resistance, low shrinkage, environmentally friendly nature and long-term durability. Fly ash, considered to be a waste substance is an important aluminosilicate source material for geopolymer production since it contains sufficient amounts of reactive alumina and silica. In this experimental study, F type fly ash was activated by 4M, 8M and 12M of sodium hydroxide and sodium silicate solutions and the effects of pH on the properties of geopolymeric samples were investigated. All the pastes were cured at 80°C for 15hours. The compressive strength tests were carried out at the ages of 7 and 28 days. The samples aged 28 days were crushed and the degrees of reaction of all samples were determined. The microstructure of geopolymer samples were investigated by Scanning Electron Microscope(SEM)/Energy Dispersive X-Ray(EDX) Spectrometer, X-ray diffractometry (XRD) and Fourier Transform Infrared Spectroscopy(FTIR) techniques. According to results, the compressive strength of samples increased as the molarity of sodium hydroxide increased. It was observed that the workability of the pastes was negatively affected by increase in molarity of sodium hydroxide.

THE EFFECT OF FINE ALUMINA TYPE ON COMPOSITION OF IN SITU SPINEL FORMATION IN ALUMINA-MAGNESIA CASTABLES

Three types of low cement castables (LCC) were prepared from 5% reactive alumina ( R 5), 5% calcined alumina ( A 5) and equal proportions of 2.5% (AR). The nest of the composition was fine bauxite (0–1 mm, 57%), coarse bauxite (1–3 mm, 20%), calcined magnesia (5%), secar 71 refractory cemet (7%) and microsilica (1%). By the addition of 5% water, castables were moulded, aged, dried and fired to 1400°C for 2 h. XRD studies showed higher amount of in situ spinel formation in A 5. The lattice constants of spinels in A 5, AR and R 5 were, respectively, 8.0348, 8.0688 and 8.0847 Å. This accounted for respectively alumina rich, stochiometry and magnesia rich spinels. Since calcined alumina is cheaper, produce higher amounts of spinel with the aid of alumina from the aggregate of bauxite and the binder of cement, and alumina rich spinel has better corrosion resistance properties, use of calcined alumina is recommended in LCC.

Influence of pulse current during Spark Plasma Sintering evidenced on reactive alumina–hematite powders

Spark Plasma Sintering (SPS) is increasingly used. The temperature and current are not independent parameters, making it difficult to separate the current intrinsic role from Joule heating. There is a debate on whether there are any specific SPS mechanisms. The influence of a key parameter, the (on:off) pulse pattern, is studied on the SPS of reactive α-Al 2−2 x Fe 2 x O 3 ( x = 0.02; 0.05; 0.07; 0.10) powders. Changing it modifies the current crest intensity and has a great influence on the materials microstructure. Comparisons with runs where the current is blocked and hot-pressing reveal three competing phenomena: formation of FeAl 2O 4, dominant in the core and not peculiar to SPS, formation of Fe, producing Fe-Al 2O 3 composite surface layers, and most notably electrical-field induced diffusion of Fe 3+ ions towards the cathode, which could have far-ranging implications for the consolidation of ionic materials and the in situ reactive shaping of composites and multimaterials.

Comparative and semi-quantitative XRD analysis of Friedel’s salt originating from pozzolan and Portland cement

The Friedel’s salt ( Fs) is often formed when reinforced concrete is attacked by chlorides from marine environmental and/or thaw salts. In this investigation, a semi-quantitative analysis and study of the Fs (2 θ range = 11.16–11.34°) in the solid phase of the Frattini test was made by XRD analysis. For this purpose, two Portland cements (PC) P1 (14% C 3A) and PY6 (<1% C 3A), six pozzolans (M0 and M1, metakaolins, C and A, natural pozzolans, D, diatomite, and SF, silica fume) and 12 blended cements or POZC 70/30, except for SF 80/20, were used. The liquid phase of the Frattini test was 3.75% NaCl solution. Other complementary determinations were some specific chemical analysis and physic and mechanical properties of some cement tested. The experimental results have demonstrated that: 1. All the pozzolans exhibited different pozzolanic activity depending on the mineralogical composition of the Portland cement with which they were tested, although such differences were attributable more to their Al 2 O 3 r - (%) content than to their SiO 2 r - (%) content for the case of the pozzolans A, C, M1 and M0 specially. Thus, M0, M1, C and A pozzolans mainly, tend to sustain [OH −] content and react readily with Ca 2+. On the contrary, for the SF and D pozzolans was due to their SiO 2 r - (%) content only, which react with both, Ca 2+ and OH − ions, in the same way. But despite what the physical state of D pozzolan is like SF, vitreous mainly and its SiO 2 r - content as well (practically), the size and shape of their respective particles (“frustules” for D, empty, perforated sheaths) are totally different, and as a consequence, their respective behaviour in the Frattini test has been different as well. 2. In this investigation, the Friedel’s salt ( Fs) owns its formation to two different origins: the C 3A of PC and to the reactive alumina, Al 2 O 3 r - , of pozzolans which reaction with chloride ions, pointing the latter as a preferential (see point 3); but it is also possible C 4AF reactivity involved at later ages. 3. The role of the reactive alumina, Al 2 O 3 r - , and reactive silica, SiO 2 r - , (vitreous and/or amorphous fractions of the pozzolanic additions) during the Friedel’s salt formation has been specified and, as a result, the formation rate of Fs from Al 2 O 3 r - of pozzolan turns out to be notably higher than the formation rate of Fs from C 3A of PC. For this reason, both have been termed rapid forming Fs or Fs- rf and slow forming Fs or Fs- lf, respectively, but in any case, topochemical mechanism with prior dissolution must be preponderant over through-solution mechanism. 4. The Friedel’s salt formation in all the PC/pozzolan blends have coincided quantitatively in the vast majority of the cases with the respective reactive alumina, Al 2 O 3 r - (%), content of each pozzolan. The number of these coincidences was greater for the PY6 blends, due to its C 3A practical absence in these samples, since its presence in the P1 blends can stimulate directly, non-directly, but above all, indirectly the chemical reaction of the C 3A hydration with NaCl solutions (3.75% and 3.00% in this study) and influence like that in the velocity of the compound formation: Fs. 5. The physical state of the reactive alumina, Al 2 O 3 r - , in C natural pozzolan must be more amorphous than vitreous, resembling metakaolin more than fly ash. That notwithstanding, pozzolan composition must have conditioned the water/cementitious material ratios obtained for their respective P1 and PY6 blended cements (a finding that could be used in the future for speedy, easy, reliable, reproducible and inexpensive characterization of natural and artificial pozzolans, and logically for this purpose, its previous physics-chemical analysis, Frattini test at 2 and/or 7 and/or 28 days-age and/or mechanical strengths will also be previously needed), as well as its specific pozzolanic activity.

The effect of microsilica and refractory cement content on the properties of andalusite based Low Cement Castables used in aluminum casthouse

The bonding system in low cement castables is achieved by the use of calcium aluminate cement, microsilica and reactive alumina. The lime/silica ratio critically impacts the liquid phase formation at high temperatures and subsequently the corrosion resistance and the mechanical and physical properties of the refractory. In the current study, the effects of microsilica and cement contents on the corrosion resistance and the physical and mechanical properties of Andalusite Low Cement Castables (LCCs) refractories were investigated. Alcoa Cup test was used to evaluate the corrosion resistance of the castables at 850 ºC and 1160 ºC. The study showed that an increase in the microsilica/cement ratio improves the physical and mechanical properties of the castable, but at the expense of the corrosion resistance. When a fixed amount of BaSO4 was added to the base refractory material, barium celsian along with glassy phase formation was observed to increase with the increase in the microsilica/cement ratio in the refractory. The presence of the glassy phases was noted to lower the positive effect of Ba-celsian formation on improving the corrosion resistance of the refractory. The observed results were validated using thermodynamic calculations which indicated that Ba-celsian phase was more resistant than Ca-anorthite for applications involving contact with molten aluminum.

Mulitização em refratários utilizando diferentes fontes precursoras: revisão

A mulita é uma fase cerâmica obtida pela reação entre alumina e sílica em temperaturas elevadas e amplamente utilizada em refratários devido as suas excelentes propriedades. Muitos trabalhos na literatura estudaram e analisaram a síntese de mulita, bem como sua incorporação em refratários, que pode ser feita pela adição do pó pré-formado ou pela obtenção in-situ. Esta revisão une os principais trabalhos publicados sobre síntese de mulita focando principalmente aspectos da cinética da reação, como a ocorrência de fase líquida metaestável durante a mulitização, etapa inevitável para o processo. O trabalho traz também um panorama geral das diversas fontes silico-aluminosas precursoras e das características e propriedades da mulita obtida a partir de cada uma delas. O estudo sugere que a utilização de sílicas e aluminas de alta reatividade favorece a mulitização reduzindo a temperatura de obtenção e a quantidade de fase líquida residual.

Características da sílica coloidal e seus efeitos em concretos refratários

A sílica coloidal se apresenta como um promissor substituto do cimento de aluminato de cálcio para utilização em concretos mulitizáveis. O uso deste ligante promove adequada resistência mecânica a verde, facilidade de secagem, inibe a formação de fases de baixo ponto de fusão, além de favorecer a formação de mulita in-situ. Entretanto, as propriedades finais do concreto dependem das características da solução coloidal utilizada. O objetivo deste trabalho é comparar as propriedades a verde e a quente de sistemas mulitizáveis ligados por sílica coloidal, variando suas características, tais como teor de sólidos, área superficial e tipo de estabilizante. Os resultados indicaram que sílicas coloidais com alta área superficial reduzem a trabalhabilidade dos concretos e diminuem as propriedades a quente devido ao acentuado trincamento durante a cura. A refratariedade dos sistemas é ainda comparada com concretos ligados por cimento de aluminato de cálcio e alumina hidratável, ressaltando a superioridade do ligante coloidal.

Expansive Synergic Effect of ettringite from pozzolan (metakaolin) and from OPC, co-precipitating in a common plaster-bearing solution: Part I: By cement pastes and mortars

Several prior papers on this subject have shown, with XRD and SEM techniques and Le Chatelier–Ansttet (L–A), ASTM C 452-68 and RT-Δ L tests, that almost all pozzolanic additions can bring about the rapid formation of ettringite, ett- rf, a process dependent upon their reactive alumina, or Al 2 O 3 r - , content, which may be vitreous or amorphous (tetra- or penta-coordinated). It has likewise been found that the formation rate, V f, of this ettringite from pozzolans origin is higher than the V f of slower forming ettringite, ett- lf, originating from the C 3A in OPC; consequently, the size of the ett- rf is ≈ 10-fold smaller. To describe the interrelationships between their expansive processes, a terminological analogy is drawn between the rapid and slow formation of ettringite, on the one hand, and drugs interaction, on the other. A common development in the treatment of certain diseases and as a result of hospital practice, drugs interaction may be quantitative or qualitative and is denominated, based on the final outcome, to be additive synergy, partial antagonism, competitive antagonism, potentiation synergy, non-competitive antagonism or physiological and functional antagonism. In this context, the key questions relating to the development of the two types of ettringite when forming together in a common plaster-bearing solution are: What will the outcome of the expansive effects be? What type of effect will they ultimately produce? Addition? Synergism? Antagonism? or perhaps Inversion of final expansive action? To reply to these questions, 16 cements – 4 Portland cements and 12 blended cements containing 20%, 30% or 40% metakaolin (M pozzolan) – were tested using the L–A, ASTM C 452-68 and EN-196-1 tests. Specimens of all 16 types of cement were made for L–A, ASTM C 452-68 and EN-196-1 testing and several direct and indirect parameters were measured, as follows: – Increase in diameter, ΔØ (%); diameter growth rate, Vcø(=ΔØ (%)/day); and Vicat Needle Penetration, VNP (mm), for L–A specimens, and – Flexural and compressive strengths for ASTM C 452-68 and for EN-196-1 specimens. Finally, other complementary determinations were specific chemical analysis and physic properties of some cements tested, being particularly interesting their XDA patterns of gypsum to quantify it as well. The experimental results show that the joint precipitation in the same plaster-bearing solutions, co-precipitation, of the ettringite from the Al 2 O 3 r - present in pozzolans, and the ettringite from the C 3A present in OPC, was, to use drug interaction terminology, always, quantitatively speaking, more synergic than additive. Furthermore, depending on the parameter considered and from a purely technological point of view, the practical implications of Expansive Synergic Effect ( ESE) between the two types of ettringite can be classified as beneficial, adverse or indifferent. It may be, however, that these judgements cannot be sustained when two or more related parameters are considered together. Finally, when 7.0% SO 3, equivalent to 15.05% of gypsum, was added to the M pozzolan-containing Portland cement and tested with the ASTM C 452-68 method, it was not found to behave aggressively but rather as “ setting regulator” because the increase in mechanical strength over time and setting times in these mixes were, therefore, similar to the pattern observed in any PC. However, when the gypsum content was raised to slightly more than double that amount (33.33% for the L–A test), it behaved aggressively. In both cases, logically, ett- rf, and/or ett- lf were involved in the resulting beneficial or adverse behavior. Therefore, in the first case, the amount of gypsum added can be regarded as being suitable for some POZC containing this particular M pozzolan, and indeed, all or most of these POZC met the criteria to be classified as “expansive hydraulic cements” set out in standard ASTM C 845-90. In higher amounts, on the contrary, gypsum behaved aggressively towards OPC P-1 and P-2 and their respective POZC with this M pozzolan, mainly, and towards the POZC of the SRPC PY-4 or PY-6 with this M pozzolan, as well. This latter behaviour was very intense, aggressive and rapid, and for this reason, it justified to be named “ rapid gypsum attack”.

Function of magnesium aluminate hydrate and magnesium nitrate as MgO addition in crystal structure and grain size control of α-Al2O3 during sintering

Chemically pure reactive alumina (α-Al2O3) which is commercially available was used for densification study in presence of widely accepted dopant MgO as additive. MgO was added both as spinel (MgAl2O4) forming precursor i.e. magnesium aluminate hydrate, and magnesium nitrate. Sintering investigations were conducted in the temperature range 1500–1600°C with 2 h soaking. Structural study of sintered pellets was carried out by extensive XRD analysis. Scanning electron mode SEM images of the specimens were considered to understand the effect of both types of additions. Addition of MgO within and beyond optimum amount had some effect on development of microstructure of sintered bodies. Densification, around 99% ρ th, with fine grain microstructure was achieved. These different types of additions caused two distinct changes in crystal structure of alumina—one small contraction and the other expansion of unit cell parameters.

Physicomechanical properties of refractory Al2O3–Si3N4–C materials with ACPC

A study has been made on the effects of the amount of silicon nitride and graphite on the physicomechanical properties of Al 2 O 3 -Si 3 N 4 -C composites for lining purposes. Adding 2.5-5.0 wt.% silicon nitride and 0.5 wt.% reactive alumina improves the properties, raises their apparent density, and increases the mechanical strength, while reducing the open porosity. Optimized compositions have been determined for refractory materials of Al 2 O 3 -Si 3 N 4 -C composition, and it has been found that to attain the higher values of physicomechanical properties the amount of graphite should constitute 5-10 wt.%.

Reactive alumina production for the refractory industry

In this study, fine reactive alumina powder production was investigated using Bayer gibbsite as a starting material. Experimental studies consist of three steps; in the first step, the soda content was reduced by means of boric acid and distilled water. In the second step, the effect of heating rate and calcinations temperature on crystal size, phase transformation and surface area were investigated and characterization of the powders was performed by means of XRD and SEM analyses. In the third step, the powders obtained optimum conditions were ground in an attritor mill and then particle size distribution and surface area were measured. The soda content of the gibbsite was reduced from 0.325 to 0.05% by H 3BO 3 treatment, calcination at 1200 °C and then washing in distilled water. The higher the heating rate, the smaller the crystal size is. Alumina ceramics with a density higher than 94.70% of theoretical density were obtained.