Slag Resistance Research Articles

Influence of Vacuum Mixing on the Carbonation Resistance and Microstructure of Reactive Powder Concrete Containing Secondary Copper Slag as Supplementary Cementitious Material (SCM)

This study aims to examine the effect of vacuum mixing on the carbonation resistance and microstructure of reactive powder concrete (RPC), made with secondary copper slag as partial cement replacement. In order to obtain a homogenous mixture, a high speed mixer with vacuum was applied. Accelerated carbonation tests (10% CO2, 20°C and 60% RH) were performed on RPC, mixed under vacuum conditions, as a comparison to RPC mixed at atmospheric pressure. The evolution of the carbonation depth was determined by spraying phenolphthalein on a freshly split RPC surface at varying ages (1 to 16 weeks). The microstructure of RPC was investigated by a mercury intrusion porosimeter (MIP). The pozzolanic activity of QCS was determined by the Chapelle test, taking into account the carbonation effect on the reference system.The results obtained, showed that no carbonation was detected after 90 days for the RPC containing copper slag both under vacuum condition and atmospheric pressure. The presence of copper slag in the RPC tends to increase the porosity reduction and decrease the strength enhancement when applying vacuum mixing to the mixture. The result of the Chapelle test indicated that the secondary copper slag did not tend to consume much portlandite.

Carbonation of a low-calcium fly ash geopolymer concrete

The carbonation resistance of a blended slag and low-calcium fly ash (FA) geopolymer concrete was investigated. The geopolymer binder studied was composed of 90% low-calcium FA and 10% ground granulated blast-furnace slag. The alkalinity of the pore solution plays a pivotal role in carbonation progression and subsequent corrosion initiation. pH profiles were measured to assess the pore solution alkalinity. Phenolphthalein indicator was used to measure the carbonation depth. X-ray diffraction (XRD) and quantification were carried out to identify and quantify the carbonation products. The obtained pH profiles illustrated a wider semi-carbonation zone in the geopolymer specimens, although the pH drop was insignificant in most cases. XRD analysis revealed that nahcolite mainly formed at 3% carbon dioxide concentration and led to a significant drop in pH values. The results further demonstrated that 1% accelerated carbonation replicated the natural carbonation process well, with only natron identified as a carbonation product. This work contributes to the assessment of the risk of carbonation-induced reinforcement corrosion in low-calcium FA geopolymer concrete.

Corrosion Mechanism of Foamed Slag on the Lightweight Corundum-Spinel Castable

Development of lightweight linings for metallurgical furnaces is an important research direction in the development of refractory materials. In the steelmaking process, slag foaming is a common phenomenon, and it usually plays a positive role. However, because of the reactions between refractories and slag, the corrosion of wear lining refractories is not only related to the safety and stable operation of high-temperature furnaces but also affects steel quality. Foamed slag is likely to affect refractory corrosion, especially lightweight refractories containing lightweight porous aggregates. In this study, the slag corrosion experiments of lightweight corundum-spinel castable were performed in contact with the ordinary and foamed slag respectively and the foamed slag caused more serious corrosion to the lightweight corundum-spinel castable. Based on the corroded microstructure and Marangoni effect, slag corrosion mechanism was analyzed systematically, and could provide the basis for foamed slag resistance.

Towards chrome-free of high-temperature solid waste gasifier through in-situ SiC whisker enhanced silica sol bonded SiC castable

Refractory containing Cr2O3 was widely used in solid waste gasifier due to its excellent slag resistance. However, hexavalent chrome compounds (formed during the preparation and the use of refractory containing Cr2O3) will give rise to detrimental effect on environment and human's health. In addition, the Al2O3-Cr2O3 materials acted as the lining materials. Serious exfoliation occurred after about twenty days. For the purpose of chrome-free and service longevity of lining materials for solid waste gasifier, in-situ SiC whisker enhanced SiC castable and spinel castable containing 20%wt of Cr2O3 were prepared. The mechanical properties and corrosion resistance after heat treatment in different temperature of the castables were determined. The strength of SiC castable rised with the increasing of the temperature. And the nano SiC/SiO2 core-shell whiskers was formed at 1500°C. In comparison to the spinel castable containing 20wt% of Cr2O3, the better volume stability and the reinforcement of the nano whiskers led to excellent resistance to crack propagation at high temperature. In addition, SiC castable showed lower apparent porosity because of the forming of SiO2 through the oxidation of SiC over 1300°C, the viscosity of slag increased since that the SiO2 dissolve into the slag, which caused excellent penetration resistance of SiC castable compared with spinel-Cr2O3 castable. Excellent mechanical properties and slag resistance at high temperature indicated that SiC castable had the application prospect for high-temperature solid waste gasifier.

Synthesis of CaO·2MgO·8Al2O3 (CM2A8) and its slag resistance mechanism

CM2A8 is a solid solution of MA and CA6. As a component in the ternary phase diagram of CaO-Al2O3-MgO, it was not reported in detail. So in this work, analytically pure CaO, MgO and Al2O3 were adopted as starting materials and batched stoimotrically according to CM2A8. The raw materials were ground, mixed, shaped and reaction-sintered at different temperatures (1550°C, 1650°C, 1700°C, and 1750°C) to synthesize CM2A8. The synthesized specimens were analyzed by XRD, SEM, and TEM and the corrosion mechanism against LF slag was also researched. The results show that high-purity CM2A8 can be synthesized by reaction sintering at 1750°C. During synthesis, granular MA and flake CA6 form and grow together; at 1650°C, they solid-solve together to form C2M2A14. As the temperature rises, solid solution reaction goes on, which results in the disappearance of CA6, C2M2A14, and MA in succession and forms high-purity CM2A8 growing towards hexagonal column crystals. In the high temperature reaction between CM2A8 and steel slag, Ca2+ in the slag reacts with CM2A8 to form CA2, damaging the structure of CM2A8 and releasing excessive Mg2+ and Al3+ which move towards the molten slag. As the reaction between Ca2+ and CM2A8 proceeds, a dense CA2 coating forms on the surface of CM2A8. The slag viscosity increases as well because of the entrance of Mg2+ and Al3+. Thus, the formation of the CA2 coating and the enhancement of the slag viscosity restrain the penetration and corrosion of slag towards CM2A8.

Improvement of Durability of Purging Plugs Using MgO Micropowder for Refining Ladles

To modulate the matrix of purging plugs, MgO micropowder was introduced as a replacement to magnesia powder in alumina–magnesia castables, and the effect of MgO micropowder on the properties of alumina–magnesia castables and the possibility of developing chrome‐free castables were investigated. Experimental results showed that the introduction of MgO micropowder resulted in an improvement in the volume stability, strength, and thermal shock resistance of alumina–magnesia castables due to its high surface energy and small particle size. However, excessive amounts of MgO micropowder led to a lower densification, and there was a slight degradation in the performance of the alumina–magnesia castables. The slag resistance of the prepared alumina–magnesia castables was significantly better than that of the alumina–chrome castables. Microstructure and energy spectrum analysis showed that the formation of a solidified reaction layer, mainly consisting of spinel and CaAl12O19, was the major cause of the observed difference in slag resistance. In addition, the alumina–magnesia castables had a lower linear thermal expansion coefficient than that of the alumina–chrome castables at each experimental temperature, which effectively decreased the thermal stress during its service period, thus exhibiting good thermal shock resistance.

Periclase-Carbon Refractory Properties with a Different Amount of Graphite in the Charge Using Liquid PFR and Graphite as Modifiers

are given for a study of the effect of introducing different amounts of graphite modified PFR and graphite into a periclase-carbon (PC) refractory charge based on fuzed periclase. The PFR modifier used is ETS-40, and the graphite modifier is a sol based on ETS-40 hydrolysate and 20% NiCl2 solution. A production scheme is proposed for preparing PC-refractories with combined modification of components, and also a charge composition with 15 – 20% graphite demonstrating sufficiently good slag resistance.

An approach for matrix densification based on particle packing and its effect on lightweight Al2O3-MgO castables

For lightweight refractory containing lightweight aggregates, the properties of the matrix are decisive to its performance. In the present work, Dinger–Funk equation was adopted to calculate the theoretical packing density of a castables matrix based on Stovall linear packing model and to design its particle size distribution. Four lightweight Al2O3-MgO castables with different particle size distribution (represented by q-value) were prepared and examined. Results show that a suitable q-value was needed to ensure acceptable properties including sintering characteristics, strength and slag resistance, which deteriorated distinctly at high q (>=0.31). For the sample with q=0.28, the matrix showed dense and uniform mirostructure, and the properties of castable reached a favourable compromise among sintering characteristics (apparent porosity=14.8%, bulk density=3.02gcm−3, permanent linear change<0.6%), strength (cold modulus of rapture=12.4MPa, cold crashing strength=155.5MPa), and resistance against both slag corrosion (Ic=22.4%) and penetration (Ip=11.5%). The sample with q=0.25 showed the highest strength and resistance against slag corrosion (matrix dissolved in slag), but its slag penetration resistance was lower due to the existence of cracks between aggregates and matrix.

Study on transport phenomena in the beam blank continuous casting mould coupling copper mould with molten steel

The copper mould and molten steel were modelled simultaneously by a three-dimensional (3D) model, which couples fluid flow, heat transfer and solidification. Thermal boundary conditions (e.g. air gap distribution, slag resistance, contact resistance) along casting direction and circumference direction were discussed and applied. The results of solid shell thickness distribution were compared with reference experimental data and reasonable agreements were found. The calculations indicate that, the shell thickness distribution along circumference in web was affected by the cross-section sizes. The uniform shell thickness distributions at narrow face and R corner were caused by the scouring of fluid flow. The heat transfer fluxes at hot face of mould were various at different locations.

Investigating the effect of M-sand on abrasion resistance of Roller Compacted Concrete containing GGBS

In this paper, an attempt has been made to investigate the effect of Manufactured sand (M-sand) on strength and abrasion resistance of Ground Granulated Blast furnace Slag (GGBS) Roller Compacted Concrete (GRCC). The cement was partially replaced by GGBS from 0% to 60%. The GRCC mixes were designed to have a flexural strength of 5MPa according to ACI 211.3R guidelines. Fine aggregates of three combinations were used in GRCC mixes, namely river sand (100%-Series A), M-sand (100%-Series B) and combination of river sand and M-sand (50% each-Series C). Studies on strength parameters (Compression and Flexure) were conducted. Cantabro loss and Surface abrasion resistance tests were conducted to evaluate the abrasion resistance of the GRCC mixes for 3, 7, 28 and 90days. Experimental results show that the Cantabro loss and Surface abrasion weight loss increased with increase in GGBS content at the age of 3days. But at later ages (7, 28, 90days) a decrease trend in weight loss was observed for all the mixes. With addition of M-sand in GRCC mixes the abrasion resistance of GRCC mixes were improved when compared to river sand mixes. Relationships were established between strength and abrasion resistance for all mixes (Series A, B and C). An empirical relation was proposed between Cantabro loss and Surface abrasion weight loss of GRCC mixes.

Influence of amount of graphite and modifying agent on the properties of periclase-carbon refractories

One of the main components of periclase-carbon materials is graphite, which provides high thermal conductivity and slag resistance of refractories. However, at temperatures of 600 °C it begins to oxidize. To prevent oxidation it is proposed to modify the sol-gel graphite by composition based on nickel salts for further formation of NiO coating on its surface, which will provide additional protection. An influence of graphite amount and its modifier agent on physical and mechanical properties and slag resistance of periclase-carbon samples are investigated. It is established that graphite amount significantly affects only the strength of periclase-carbon refractories – strength of graphite decreases at increase of graphite amount from 5 to 20 %. The impact of graphite modifier agent amount on physical and mechanical properties of the samples appears on the contrary, that is by increasing the amount – properties increase. Amount of graphite and modifier agent doesn’t effect on slag resistance. We recommend the following optimal ratio of graphite in an amount of from 5 to 10 % and its modifier agent in an amount of 1,75 % for high performance periclase-carbon refractories.

Feasibility study of copper slag as a structural fill in reinforced soil structures

Copper slag (CS) is a granulated cohesionless glassy material with the appearance of dark black coloured sandy size material. Copper slag is classified as poorly graded sand (SP) as per the Unified Classification System (USCS) and has a specific gravity of 3.6. Copper slag contains iron silicates, calcium oxide, and alumina, with small amounts of copper, lead, zinc, and other metals. The evaluated gradation, physical, shear strength characteristics and electrochemical properties of copper slag met the standard specifications for a structural fill material recommended for use in mechanically stabilized earth (MSE) walls and reinforced soil slopes (RSS). The angle of shearing resistance of copper slag varied between 35° and 49° for loose and dense states, respectively. Thereafter pullout tests were conducted to determine interface apparent coefficient of friction (μS/GSY) between the geogrid and copper slag at normal stresses of 7.3 kPa, 12.5 kPa, 25 kPa and 50 kPa and obtained results are then compared with those of geogrid in reference fill material, Yamuna sand (YS). The pullout tests were carried out as per ASTM Standard D 6706–01(2013) on an apparatus that was fabricated indigenously. This paper addresses the geogrid – copper slag interaction and geogrid – Yamuna sand interaction from pullout tests and demonstrates that copper slag can be effectively used as a structural fill for reinforced soil structures.

Thermodynamic evaluation and properties of refractory materials for steel ladle purging plugs in the system Al2O3-MgO-CaO

The influence of iron oxide in the phase relationships of Al2O3-MgO-CaO and Al2O3-MgO purging plug refractory material has been studied by the thermodynamic analysis tool FactSage. Results showed that the system without CaO to be advantageous on the onset temperature of liquid phase, and on the liquid content at defined chemical composition and temperature. Therefore, CaO negatively influences the iron-rich slag resistance of the purging plug material. Analysis of used purging plugs proved the thermodynamic results. They showed that spinel solid solution and calcium hexaluminate as stable phases were formed in the reaction with iron oxide slag.Corundum-spinel castables with and without calcium aluminate cement were investigated in the laboratory to compare the relevant technical properties. In the cement bonded castable, the curing and drying strength are increased by increasing the cement content. However high cement addition requires higher water demand, which results in higher open porosity and a lower hot modulus of rupture (HMoR). In the CaO-free, no-cement castable with hydratable alumina binder, the water demand is slightly higher when compared to the ultra-low cement castable. However, the curing and drying strength are still slightly higher for the no-cement castable. As there is no significant difference in HMoR with various hydratable alumina binder additions, low dosage of such binder in the range of two to four percent is normally recommended to avoid excessive water addition. Cement bonded castables (with CaO) show some advantages to the no-cement castable (non-CaO) regarding HMoR, however the no-cement castable could have advantages regarding the iron-rich slag resistance and thermal shock resistance.

Microstructure and properties of (1 − x)La0.9Ca0.1CrO3/x ZrO2 (x = 0–30 wt-%) composites

The microstructure and properties of Ca doped lanthanum chromate [La0.9Ca0.1CrO3 (LCCO)] and zirconia (ZrO2) composites [abbreviated as (1 − x)LCCO/xZrO2, x = 0–30 wt-%] prepared by solid state reaction method are investigated in this paper whose potential application in heat resistant ceramics are also discussed. The growth and fusion of the LCCO grains are hindered by the ZrO2 grains, which make the matrix grains refined. In the stable system, it is discovered that the density of the composites decreases, the porosity increases and the decrease amplitude of the bend strength after thermal shock at 600°C reduces with the increasing ZrO2 content, which results in diminishing the bend strength gradually and enhancing the thermal shock resistance. When x = 10–15 wt-%, the samples show the best thermal shock resistance realising a maximum thermal cycle times of 8. The material with x = 20 wt-% exhibits excellent slag resistance.

The effect of mechanochemically activated MgO in Al2O3–MgO–C refractory. Part I: Formulation and properties

Steel-making processes associate with highly corrosive slag and aggressive reactions giving rise to erosive conditions. In-situ spinel (MgAl2O4) shows good slag resistance in Al2O3–MgO–C (AMC) secondary refining ladles because spinel has an excellent cation absorption capacity from the slag due to the void spaces in its crystal structure. The aim of our research work was the optimization of in-situ spinel formation in AMC refractory and to minimise the crack and rupture through residual expansion. Mechanically activated reactive magnesia was added up to 10wt% in different proportions into the starting raw material batches, which comprised of graded fused alumina and flake graphite. A resol type resin was used as a thermosetting binder, and a combination of Al-B4C fine powder was used as an antioxidant. Prepared briquettes by the cold pressing of these batches were first cured in an oven at resin transition temperature for its polymerization. The samples were then coked at 1400°C. The quantitative crystallinity was studied using X-ray diffraction patterns. The coefficient of thermal expansion was determined by dilatometric analysis and evaluation of microstructural cracks was examined by SEM.

Fabrication and characterization of lightweight microporous alumina with guaranteed slag resistance

Low thermal conductivity and high mechanical strength and slag resistance are usually mutually exclusive properties. In this study, by introducing a superplastic nanoalumina sol, we fabricated microporous alumina by wet milling and investigated its properties. The microporous alumina exhibited a low bulk density and apparent porosity as well as high closed porosity and small median pore diameter. The thermal conductivity of the microporous alumina at 800°C was 6.5Wm−1K−1, which is 41.6% lower than that of tabular alumina. Furthermore, a more continuous, and thicker (100–200μm) Ca(Al,Fe)12O19 (CAF6) and Ca(Al,Fe)4O7 (CAF2) layer was observed at the microporous alumina/slag interface in comparison to the 30–50µm-thick layer usually observed at the tabular alumina/slag interface. The dense continuous isolation layer formed in situ effectively prevented further slag corrosion and penetration. Hence, the microporous alumina exhibited better slag resistance than tabular alumina.

Effect of ZrO&lt;sub&gt;2&lt;/sub&gt; Additive on the Properties of MgO-Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Refractory Used for RH Degasser

To improve the properties and RH degasser slag corrosion resistance of magnesia-chrome refractory, the effect of the addition of ZrO2 was investigated. The results showed that the presence ZrO2 additive can densify the magnesia-chrome samples due to promotion of grain boundary activities and ultimately direct bond formation, which improved the high temperature mechanical properties and corrosion resistance. The results also indicated that in the RH degasser slag system with a high ratio of calcia to silica, the slag resistance behavior of magnesia-chrome composite added ZrO2 could be described as follows: the ZrO2 reacts with CaO to form the calcium zirconate compound which is densification lay and simultaneously, could increase corrosion resistance performance by blinding pore and thickening slag viscosity. Therefore, it is expected to be the major reason for the ZrO2 enhanced corrosion resistance behavior observed for magnesia-chrome refractory.

Effects of particle distribution of matrix on microstructure and slag resistance of lightweight Al2O3–MgO castables

For lightweight castables containing microporous aggregates, the compacted matrix component is a key factor in determining their useable lifespan, and this matrix is influenced by both the particle packing and sintering process. In this study, the grain grading of lightweight Al2O3–MgO castable matrices was adjusted to create a particle size distribution that close to the Andreassen model with q-values of 0.25, 0.28, 0.31, and 0.34. After sintering at 1500°C for 3h, the microstructures and slag resistances of lightweight Al2O3–MgO castables with different particle packing arrangements were compared and discussed. The results show that a q-value no higher than 0.31 was needed to ensure formation of a denser matrix. For the smallest q-value that was studied (0.25), the resulting matrix had a large grain size (5–12µm) and a relatively small average pore size (D50=2.10µm), which favours the formation of Ca (Al, Fe, Mn)12O19 layer distributed within the matrix. This resulted in the highest resistance to slag corrosion observed (Ic=7.93%), whereas the cracks existing between the matrix and the aggregates due to a large volume shrinkage decreased the slag penetration resistance (Ip=45.9%). The microstructure of the matrix with a q-value of 0.28 was uniform and compacted, which reached an acceptable compromise between resistance to slag corrosion (Ic=22.4%) and resistance to slag penetration (Ip=11.5%).

Sulfate resistance of ferrochrome slag based geopolymer concrete

This paper presents the study of the performance of a new geopolymer binding material exposed to sulfate attack. Geopolymer binding material was obtained by alkaline activating FS with chemical materials (NaOH and Na2SiO3). Geopolymer concrete samples were produced by mixing this binding material with river sand and crushed sand aggregates. Test specimens were immersed in magnesium sulfate solutions (by weight 3%, 5% and 7%) for various periods of time and the durability of geopolymer concrete was investigated. The residual compressive strength (90 and 180 days), change in weight and length of samples, pH variation of solution and visual appearance of these samples were obtained experimentally. It was concluded that compressive strength of both geopolymer and Ordinary Portland Cement (OPC) based concrete samples decreases with increasing in MgSO4 content and exposure duration. After exposed to 7% MgSO4 solution for 180 days, the minimum decrease in compressive strength was seen 25% in geopolymer concrete samples with crushed sand aggregates.

Abrasion resistance of alkali-activated slag concrete designed by Taguchi method

In this study, abrasion resistance of Alkali-Activated Slag (AAS) concrete was investigated according to ASTM C1138. Four affecting factors including curing temperature, alkaline solution to slag weight ratio, concentration of sodium hydroxide solution and sodium hydroxide to sodium silicate weight ratio were considered to achieve the maximum compressive strength and abrasion resistance of AAS concrete using the Taguchi design of experiment method. Based on the results, the mixture with alkaline solution to slag weight ratio of 0.45, sodium hydroxide concentration of 6M and sodium hydroxide to sodium silicate weight ratio of 3, that had been cured at 95°C, and the mixture with alkaline solution to slag weight ratio of 0.4, sodium hydroxide concentration of 6M and sodium hydroxide to sodium silicate weight ratio of 3, that had been cured at 25°C, were obtained as the optimal mixtures for maximum compressive strength and abrasion resistance, respectively. The results also showed that abrasion resistance of AAS concrete was significantly increased by improving the quality of surface and changing the curing regime. Water curing as an appropriate method improved the surface conditions and considerably increased the abrasion resistance of AAS concrete too. In addition, the results showed that the CO2 footprint of AAS concrete was approximately 51% less than that of Ordinary Portland Cement (OPC) concrete and therefore the eco-mechanical performance of AAS concrete was superior.