In this context,an enzyme-induced magnesia carbonization(EIMC)method was proposed for practical healing of rock weathering cracks in term of bio-cementing sandstone grains.For this,a series of experiments were conduct...In this context,an enzyme-induced magnesia carbonization(EIMC)method was proposed for practical healing of rock weathering cracks in term of bio-cementing sandstone grains.For this,a series of experiments were conducted on EIMC mortar samples,and the physicomechanical properties were obtained.The effects of urea pre-hydrolysis time,mass ratio of liquid solution to magnesia,and urea concentration were analyzed.Experimental results indicated that the urea pre-hydrolysis based EIMC method had a better cementation ability of sandstone grain and greater crack surface bonding performance of sandstone than the existing microbial-induced magnesia carbonization(MIMC)method.The optimal bio-cementation conditions were of pre-hydrolysis time of 24 h,mass ratio of liquid solution to magnesia of 1.75,and urea concentration of 1 mol/L.Under these conditions,the peak tensile stress of EIMC mortar samples reached up to 948.45 kPa,and interfacial peak tensile stress of EIMC-sandstone samples reached 608.57 kPa.These values were 118.6%(799.97 kPa)and 123.2%(493.19 kPa)of those of samples bio-cemented by the MIMC method,respectively.The improved bio-cementation performance can be attributed to the pre-hydrolysis of urea,ensuring an adequate supply of CO_(3)^(2-) ions and promoting the magnesia hydration and the brucite carbonization.The increased production of hydrated magnesium carbonates,coupled with formation of the amorphous brucite facilitated by biomolecules,established a denser structure,enhancing the physicomechanical properties.Microcrack development near the interfacial zone of mortar and sandstone was an important factor in the reduced biocementation performance of the MIMC method.The EIMC method is a practical bio-healing method for rock weathering cracks due to the availability of urease and its good cementation properties.展开更多
An experiment was conducted to assess the impact of fused calcia-stabilized zirconia micro-powder on the thermal shock behavior of magnesia–spinel refractories.The effects of calcia-stabilized zirconia on the microst...An experiment was conducted to assess the impact of fused calcia-stabilized zirconia micro-powder on the thermal shock behavior of magnesia–spinel refractories.The effects of calcia-stabilized zirconia on the microstructure evolution and properties of magnesia–spinel refractories were characterized by the high-temperature elastic modulus,thermal shock damage resistance parameters,retainment of elastic modulus after thermal shock,and scanning electron microscopy.The results indicated that the incorporation of calcia-stabilized zirconia improved the thermomechanical properties and thermal shock behavior of magnesia–spinel specimens.The hot modulus of rupture of magnesia–spinel specimens increased by 2.5-fold due to the incorporation of calcia-stabilized zirconia micro-powder.The presence of a martensitic phase transformation in partially unstable ZrO2 and thermal mismatches among various phases contributed to a controlled formation of microcracks.And the pinning effect caused by the calcia-stabilized zirconia particles surrounding the grain boundaries played a crucial role in preventing the propagation of microcracks.This phenomenon significantly bolstered the thermal shock stability of magnesia–spinel refractories,consequently prolonging their service life.展开更多
Traditional magnesia-based refractories face challenges such as high thermal conductivity and poor slag penetration resistance,which contradict the energy efficiency requirements of modern metallurgy.In this study,mic...Traditional magnesia-based refractories face challenges such as high thermal conductivity and poor slag penetration resistance,which contradict the energy efficiency requirements of modern metallurgy.In this study,microporous magnesia was prepared using low-grade magnesite via the one-step sintering method.The microstructure and properties of microporous magnesia prepared by high-silicon and high-calcium magnesites calcined at various temperatures were compared.The pore structure and phase evolution were analyzed,the effect of which on the properties of lightweight magnesia-based dry vibration mix was discussed.The results indicated that within high-silicon magnesite,SiO_(2) initially reacted with Mgo to form Mg_(2)Si0_(4),which gradually reacted with Cao impurities as the temperature increased transforming into a Mgo-Cao-SiO_(2) ternary liquid phase and uniformly permeated along the grain boundaries.Due to the bridging effect of strip-like Cao in high-calcium magnesite,the reorganization and sintering of Mgo grains at high temperatures were inhibited,resulting in the presence of a significant number of elongated pores within the magnesia after calcination at various temperatures,which was detrimental to the mechanical properties and slag resistance.The microporous Mg0 prepared by high-silicon magnesite at 1700°C exhibited the superior physical properties.The microporous Mgo aggregates had a stronger interlocking force with the matrix,resulting in a greater bonding strength.Moreover,the micropores not only effectively reduced the thermal conductivity but also facilitated the supersaturated precipitation of molten slag,hindering further penetration.Compared to the dry vibration mix prepared by fused Mgo,the lightweight magnesia-based dry vibration mix prepared with the high-silicon magnesite exhibited higher mechanical strength(~40%increase)and thermal insulation performance(0.870 W·(m·K)at 1000 C),and improved slag resistance.展开更多
This study proposed an improved bio-carbonation of reactive magnesia cement(RMC)method for dredged sludge stabilization using the urea pre-hydrolysis strategy.Based on unconfined compression strength(UCS),pickling-dra...This study proposed an improved bio-carbonation of reactive magnesia cement(RMC)method for dredged sludge stabilization using the urea pre-hydrolysis strategy.Based on unconfined compression strength(UCS),pickling-drainage,and scanning electron microscopy(SEM)tests,the effects of prehydrolysis duration(T),urease activity(UA)and curing age(CA)on the mechanical properties and microstructural characteristics of bio-carbonized samples were systematically investigated and analyzed.The results demonstrated that the proposed method could significantly enhance urea hydrolysis and RMC bio-carbonation to achieve efficient stabilization of dredged sludge with 80%high water content.A significant strength increment of up to about 1063.36 kPa was obtained for the bio-carbonized samples after just 7 d of curing,which was 2.64 times higher than that of the 28-day cured ordinary Portland cement-reinforced samples.Both elevated T and UA could notably increase urea utilization ratio and carbonate ion yield,but the resulting surge in supersaturation also affected the precipitation patterns of hydrated magnesia carbonates(HMCs),which weakened the cementation effect of HMCs on soil particles and further inhibited strength enhancement of bio-carbonized samples.The optimum formula was determined to be the case of T?24 h and UA?10 U/mL for dredged sludge stabilization.A 7-day CA was enough for bio-carbonized samples to obtain stable strength,albeit slightly affected by UA.The benefits of high efficiency and water stability presented the potential of this method in achieving dredged sludge stabilization and resource utilization.This investigation provides informative ideas and valuable insights on implementing advanced bio-geotechnical techniques to achieve efficient stabilization of soft soil,such as dredged sludge.展开更多
Dredged marine soils(DMS)have poor engineering properties,which limit their usage in construction projects.This research examines the application of reactive magnesia(rMgO)containing supplementary cementitious materia...Dredged marine soils(DMS)have poor engineering properties,which limit their usage in construction projects.This research examines the application of reactive magnesia(rMgO)containing supplementary cementitious materials(SCMs)to stabilize DMS under ambient and carbon dioxide(CO_(2))curing conditions.Several proprietary experimental tests were conducted to investigate the stabilized DMS.Furthermore,the carbonation-induced mineralogical,thermal,and microstructural properties change of the samples were explored.The findings show that the compressive strength of the stabilized DMS fulfilled the 7-d requirement(0.7-2.1 MPa)for pavement and building foundations.Replacing rMgO with SCMs such as biochar or ground granulated blast-furnace slag(GGBS)altered the engineering properties and particle packing of the stabilized soils,thus influencing their performances.Biochar increased the porosity of the samples,facilitating higher CO_(2) uptake and improved ductility,while GGBS decreased porosity and increased the dry density of the samples,resulting in higher strength.The addition of SCMs also enhanced the water retention capacity and modified the pH of the samples.Microstructural analysis revealed that the hydrated magnesium carbonates precipitated in the carbonated samples provided better cementation effects than brucite formed during rMgO hydration.Moreover,incorporating SCMs reduced the overall global warming potential and energy demand of the rMgO-based systems.The biochar mixes demonstrated lower toxicity and energy consumption.Ultimately,the rMgO and biochar blend can serve as an environmentally friendly additive for soft soil stabilization and permanent fixation of significant amounts of CO_(2) in soils through mineral carbonation,potentially reducing environmental pollution while meeting urbanization needs.展开更多
Magnesia-chrome porous purging plugs are crucial functional components to remove inclusions and stabilize the flow field during iron and steel smelting.However,practical applications of magnesia-chrome porous purging ...Magnesia-chrome porous purging plugs are crucial functional components to remove inclusions and stabilize the flow field during iron and steel smelting.However,practical applications of magnesia-chrome porous purging materials are stil hampered by the poor scouring resistance to molten steel and unstable air permeability owing to their low mechanical properties and uncontrollable pore structure.Therefore,the particle-packing type magnesiachrome porous purging materials reinforced by in situ formed spinel were prepared using fused magnesia-chrome particles and Al powders as major raw materials.The results show that in situ formed spinel solid solutions in bonding phase led to the decreased median pore size and increased pore surface fractal dimension from the reactions between Al powders and magnesia-chrome particles and along with high-temperature sintering,bonding between magnesia-chrome particles and the resultant mechanical properties of materials were greatly elevated.Besides,the results of air permeability tests and polynomial ftting indicated that the formation of spinel solid solutions was the main contributing factor for controllable air permeability,and pressure drop of porous purging materials was positively correlated with surface fractal dimension of pores.Moreover,the as-prepared porous purging materials added with 6 wt.%Al powders obtained the maximum cold crushing strength(54.2 MPa)and hot modulus of rupture(12.9 MPa)with median pore size of 24.06μm and ftting non-Darcian permeability coefficient of 0.97×10^(-6)m.展开更多
Magnesia-based refractories hold a big share in the total refractories output in China because of abundance of magnesite resource. In this paper a short review has been focused on the current and future new use of mag...Magnesia-based refractories hold a big share in the total refractories output in China because of abundance of magnesite resource. In this paper a short review has been focused on the current and future new use of magnesia in the production of magnesia-based products including low carbon MgO-C bricks, MgO- CaO bricks, MgO-based castables, MgO-CaO-Fe2O3 ramming mix and MgO-CaO-C bricks for low carbon steelmaking and clean steel making, magnesite ball for slag splashing, MgO-CaO-ZrO2 for sintering and transfering zones of cement kiln and MgAlON for special use in the steel industry.展开更多
Two types of low carbon MgO - C refractories with 6% graphite were prepared using microporous magnesiarich spinel （5 - 3 and 3 - 1 mm ） and fused magnesia （5 - 3 and 3 - 1 mm ） as coarse aggregates, respectively, ...Two types of low carbon MgO - C refractories with 6% graphite were prepared using microporous magnesiarich spinel （5 - 3 and 3 - 1 mm ） and fused magnesia （5 - 3 and 3 - 1 mm ） as coarse aggregates, respectively, fused magnesia （ ≤1 mm） as fine aggregate, magnesia powder （≤ 0. 088 mm ） , flake graphite powder （ ≤0. 088 mm）, metal Al powder （ 〈0. 074 mm） as matrix, and phenol resin as binder. After curing at 220 ℃ and coke-embedded firing at 1 500 ℃ , the apparent porosity, cold crushing strength, cold modulus of rupture, permanent linear change on heating, thermal shock resistance and slag resistance of the specimens were studied comparatively. The results indicate that： （ 1 ） after curing at 220 ℃ and coke-embedded firing at 1 500 ℃, the specimen with microporous magnesia-rich spinel replacing fused magnesia has lower bulk density and higher apparent porosity than the common low car- bon MgO - C specimen. After curing at 220 ℃, the specimen with microporous aggregate has lower strength than common low carbon MgO - C specimen, but after coke-embedded firing at 1 500℃, it has higher strength and lower permanent linear change on heating; （2） low carbon MgO - C specimen using microporous magnesia-rich spinel to replace fused magnesia aggregate has better thermal shock resistance but worse slag resistance.展开更多
Properties of magnesia-hercynite brick were studied. The coatability, thermal shock resistance, corrosion resistance to cement clinker and thermal conductivity were compared with those of magnesia-chrome brick and mag...Properties of magnesia-hercynite brick were studied. The coatability, thermal shock resistance, corrosion resistance to cement clinker and thermal conductivity were compared with those of magnesia-chrome brick and magnesia-spinel brick used widely in sintering zone of cement rotary kiln. The result shows that magnesia-hercynite brick is better than magnesia-chrome brick in thermal chock resistance and corrosion resistance to cement clinker, is similar to magnesia-chrome brick and is better than magnesia-spinel brick in coatability and thermal conductivity.展开更多
The manufacturing techniques of magnesia-carbon bricks in China have been documented from raw materials,production(process and facilities)to performance and wear issues in the ladle.Magnesia-carbon bricks made of ordi...The manufacturing techniques of magnesia-carbon bricks in China have been documented from raw materials,production(process and facilities)to performance and wear issues in the ladle.Magnesia-carbon bricks made of ordinary fused magnesia is the prevailing material used in the slagline of the ladle,but its service life is substantially lower than the bricks based on large-periclase-crystal fused magnesia.In two types of fused magnesia,the average values of periclase crystal size are in double for their difference.It is suggested that large-periclase-crystal fused magnesia should be used for manufacturing magnesia-carbon bricks for the slagline of the ladle by abandoning ordinary fused magnesia,in order to have a prolonged service life,increase the availability of the ladle and reduce the number of downtimes of the ladle.Free phenol in resin produced in China should be as low as that of resin made in Europe,to improve production environment and reduce smoke emission during the ladle preheating.There are large spaces to promote the productivity of magnesia-carbon bricks in China,with high intensity mixers and hydraulic presses.Expansion controlled magnesia-carbon bricks in the ladle depend on the optimized combination of sintered magnesia,Carbores and antioxidants as the matrix,to minimize the premature wear of vertical cracks and joint opening formed in the ladle lining.展开更多
The microporous magnesia refractory shows a promising application prospect as tundish lining due to excellent thermal insulation and slag resistance.The effect of interaction between microporous magnesia castable and ...The microporous magnesia refractory shows a promising application prospect as tundish lining due to excellent thermal insulation and slag resistance.The effect of interaction between microporous magnesia castable and 38CrMoAl steel containing 0.876 wt.%Al on the cleanliness of 38CrMoAl steel was studied and compared with that of fused magnesia castable.The results show that the micropores in the microporous magnesia castable can promote the formation of dense and continuous MgO-Al_(2)O_(3)layer,which can inhibit the further pollution of molten steel by refractories,whereas the MgO-Al_(2)O_(3)layer formed in test of fused magnesia castable is not continuous.After 30 min holding,the total oxygen content in the steel samples for the test of microporous magnesia castable is only 42.2%of that for the test of fused magnesia castable.The inclusions in the steel samples for the test of microporous magnesia castable are also less than those for the test of fused magnesia castable.It shows that microporous magnesia castable is a promising tundish refractory for the preparation of clean high-Al steel.展开更多
To meet the needs of environmental protection and promote the application of chromium-free refractories for RH refining furnaces, research on application of new non-burned periclase-magnesia alumina spinel bricks was ...To meet the needs of environmental protection and promote the application of chromium-free refractories for RH refining furnaces, research on application of new non-burned periclase-magnesia alumina spinel bricks was carried out. Through laboratory research and field application, it is concluded that the non-burned periclase-magnesia alumina spinel brick can replace magnesia-chrome material, and its service life is equivalent to that of the magnesia-chrome material with reduced cost.展开更多
Magnesia-carbon refractories were prepared using fused magnesia,flake graphite and metal aluminum powder as starting materials,phenolic resin as the binder,heat-treating at 1300-1600℃in nitrogen atmosphere.The phase ...Magnesia-carbon refractories were prepared using fused magnesia,flake graphite and metal aluminum powder as starting materials,phenolic resin as the binder,heat-treating at 1300-1600℃in nitrogen atmosphere.The phase reconstruction and the microstructure evolution of the obtained magnesia-carbon refractories were analyzed.The formation mechanisms of magnesia crystals with different morphologies by chemical vapor deposition were revealed.The results show that at 1300-1500℃,the non-oxides within the specimens are aluminum carbide(Al_(4)C_(3)),aluminum nitride(AlN)and magnesium aluminum nitride(Mg_(3)Al_(n)N_(n+2),n=2 or 3);at 1600℃,the diffraction characteristic peak intensity of Al_(4)C_(3) and AlN decreases sharply,and sharp diffraction characteristic peaks of nitrogen aluminum carbide(Al_(7)C_(3)N_(3))appear.Mg(g)is produced by the aluminothermic reduction and carbothermal reduction of magnesia.On the surface of the specimens,Mg(g)reacts with oxygen to form MgO whiskers.Inside the specimens,Mg(g)and O_(2)(g)undergo a CVD chemical deposition reaction to form cubic MgO crystals.There is a phase relationship between flake AlN and flake Mg3AlnNn+2,and they are so associated with each other that the morphology is difficult to distinguish.展开更多
The complex coating on the MgO CaO clinker was prepared by dipping method and adding the second mineral to restrain the formation and expansion of the cracks. Meanwhile, the microstructure and the morphology of the c...The complex coating on the MgO CaO clinker was prepared by dipping method and adding the second mineral to restrain the formation and expansion of the cracks. Meanwhile, the microstructure and the morphology of the coating and hydration resistance of the MgO CaO clinker were also investigated. The result shows that the coating consists mainly of Ca 2P 2O 7, MgO and CaCO 3, its thickness ranges from 5μm to 20μm, and the coating is dense and even, no micro cracks are observed. Also, the coating adheres closely to the matrix. The hydration resistance of the MgO CaO clinker after treatment is improved greatly, and the castables prepared with the treated MgO CaO clinker have better physical properties than MgO castable.展开更多
In order to widen the application of microcrystalline magnesite,the thermal decomposition behavior of the microcrystalline magnesite in Sichuan and Tibet area was firstly studied by thermogravimetric analysis. Then th...In order to widen the application of microcrystalline magnesite,the thermal decomposition behavior of the microcrystalline magnesite in Sichuan and Tibet area was firstly studied by thermogravimetric analysis. Then the effects of the calcination temperature,calcination time and particle size on the preparation of active Mg O from microcrystalline magnesite were studied by orthogonal experimental design. At last,high purity sintered magnesia was prepared by two-step calcination,meanwhile the effects of the light burning temperature,particle size of the light-burned Mg O powder,molding pressure and the hydration rate of light-burned Mg O powder on the properties of high purity sintered magnesia were studied.The results show that:（ 1） the calcination temperature has the greatest influence on the activity of light-burned MgO,followed by the holding time and the particle size;the optimal process of light burning for preparing active MgO is the microcrystalline magnesite with particle size of 1-0. 5 mm heat-treating at 700 ℃ for 2 h; under these conditions,the microcrystalline magnesite decomposes completely; the average grain size of the obtained product is about 21. 4 nm,and its activity of CAA is20. 16 s;（ 2） the effect of the light burning temperature on the density of high purity sintered magnesia is not obvious; the fineness of the light burning Mg O powder and molding pressure help to increase the density of sintered magnesia; the lower the hydration rate of the lightburned Mg O, the higher the density of the sintered magnesia; the high-purity sintered magnesite withw（ MgO） ≥98% and bulk density≥3. 40 g/cm;can be prepared by the two-step calcination; the grains are fine with size of 30-200 μm and the impurity at grain boundaries is little.展开更多
The magnesia composite materials were prepared using fused magnesia, used magnesia chrome bricks, magnesium aluminate spinel, alumina powder and chrome oxide powder as starting materials. In order to improve the perfo...The magnesia composite materials were prepared using fused magnesia, used magnesia chrome bricks, magnesium aluminate spinel, alumina powder and chrome oxide powder as starting materials. In order to improve the performance of magnesia composite material, the influence of chrome oxide concentrate powder on the properties of magnesia composite material was re-searched. The apparent porosity, bulk density, cold crushing streugth, linear expausion and thermal shock resistance of the specimens were determined. The results show that adding chrome oxide concentrate promotes the formation of the composite phases of three kinds of spi-nel, which is beneficial to the thermal shock resistance.The magnesia chrome spbwl can not be .[brined at high temperatures theoreticalby, but can dissolve in the mag-nesia composite material. Comprehensively, the optimal addition of chrome oxide concentrate is 10. 0 mass% for the magnesia composite materials.展开更多
To enhance the serdice life of magnesia based slag dam, composite slag dam was designed to be cast with alumina magnesia castables in slag line and magnesia castables in molten steel zone. Workability of the magnesia ...To enhance the serdice life of magnesia based slag dam, composite slag dam was designed to be cast with alumina magnesia castables in slag line and magnesia castables in molten steel zone. Workability of the magnesia castables for the slag dam was improved and a suitable vibration shaping method was adopted to combine it with alumina magnesia castables. The result shows： （1） workability and setting performance of magtwsia castables can be improved to match with alumina magnesia castables by adjusting setting retarder and water reducing agent, and adding proper silica fume ; （2） composite slag dam cart be prepared with alumina m,agnesia castables and the improved magnesia castables, whether by up - down composite method or right - left composite method; in order to get full vibration arrd make interface .fluctuation have proper amplitude, the vibration time oJ the two methods after two different castables contact with each other is 3 and 2.5 minutes, respectively; （3）the result of the on-site test proves that the design aims for reducing pollution to hot metal and improving corrosion resistance have been achieved.展开更多
In order to reduce the thermal energy loss of high temperature kilns and furnaces and lower the surface temperature of the kiln body,magnesia insulation materials were prepared using self-made magnesia porous aggregat...In order to reduce the thermal energy loss of high temperature kilns and furnaces and lower the surface temperature of the kiln body,magnesia insulation materials were prepared using self-made magnesia porous aggregates(using high purity magnesia powder as starting material and potassium oleate as the foaming agent),middle grade magnesia powder,calcium aluminate cement,and SiO_(2) micropowder as starting materials,introducing walnut shell powder impregnated with silica sol(short for Sws)as a pore-forming agent.The effects of the Sws addition(0,10%,15%,and 20%,by mass)and the sintering temperature(1300,1350,1400,and 1480℃)on the properties of magnesia insulation materials were studied.The results show that(1)for the specimens fired at 1480℃,when the Sws addition is 10%,the cold compressive strength is 22 MPa;when the Sws addition is 20%,the thermal conductivity is 0.368 W·m^(-1)·K^(-1)(350℃);(2)nano-silica in the silica sol reacts with MgO in the matrix to form forsterite,which encapsulates the pores volatilized from the walnut shell powder and forms closed pores.展开更多
Magnesia-alumina-chrome ramming mixes with same chemical compositions were prepared by using different raw materials such as fused magnesia-chrome synthetic materials and sintered one, wasted bricks and magnesia-alumi...Magnesia-alumina-chrome ramming mixes with same chemical compositions were prepared by using different raw materials such as fused magnesia-chrome synthetic materials and sintered one, wasted bricks and magnesia-alumina spinels. Their physical properties were tested and microstructures were analyzed. The results show that the ramming mixes made of different raw materials bring about different microstructures and properties although the mixes have the same chemical composition, binder content and aggregate size composition.展开更多
A series of unconfined compression tests(UCTs) were conducted to investigate the effects of content of reactive magnesia(Mg O) and carbonation time on the engineering properties including apparent characteristics, str...A series of unconfined compression tests(UCTs) were conducted to investigate the effects of content of reactive magnesia(Mg O) and carbonation time on the engineering properties including apparent characteristics, stress-strain relation, and deformation and strength characteristics of reactive Mg O treated silt soils. The soils treated with reactive Mg O at various contents were subjected to accelerated carbonation for different periods of time and later, UCTs were performed on them. The results demonstrate that the reactive Mg O content and carbonation time have remarkable influences on the aforementioned engineering properties of the soils. It is found that with the increase in reactive Mg O content, the unconfined compressive strength(qu) increases at a given carbonation time(<10 h), whereas the water content and amounts of crack of the soils decrease. A threshold content of reactive Mg O exists at approximately 25% and a critical carbonation time exists at about 10 h for the development of qu. A simple yet practical strength-prediction model, by taking into account two variables of reactive Mg O content and carbonation time, is proposed to estimate qu of carbonated reactive Mg O treated soils. A comparison of the predicated values of qu with the measured ones indicates that the proposed model has satisfactory accuracy.展开更多
基金supported by the State Key Laboratory for Geo-Mechanics and Deep Underground Engineering,China University of Mining&Technology/China University of Mining&Technology,Beijing(Grant No.SKLGDUEK2214)the National Natural Science Foundation of China(Grant No.42477188)National Key Research and Development Program of China(Grant No.2023YFC3007102).
文摘In this context,an enzyme-induced magnesia carbonization(EIMC)method was proposed for practical healing of rock weathering cracks in term of bio-cementing sandstone grains.For this,a series of experiments were conducted on EIMC mortar samples,and the physicomechanical properties were obtained.The effects of urea pre-hydrolysis time,mass ratio of liquid solution to magnesia,and urea concentration were analyzed.Experimental results indicated that the urea pre-hydrolysis based EIMC method had a better cementation ability of sandstone grain and greater crack surface bonding performance of sandstone than the existing microbial-induced magnesia carbonization(MIMC)method.The optimal bio-cementation conditions were of pre-hydrolysis time of 24 h,mass ratio of liquid solution to magnesia of 1.75,and urea concentration of 1 mol/L.Under these conditions,the peak tensile stress of EIMC mortar samples reached up to 948.45 kPa,and interfacial peak tensile stress of EIMC-sandstone samples reached 608.57 kPa.These values were 118.6%(799.97 kPa)and 123.2%(493.19 kPa)of those of samples bio-cemented by the MIMC method,respectively.The improved bio-cementation performance can be attributed to the pre-hydrolysis of urea,ensuring an adequate supply of CO_(3)^(2-) ions and promoting the magnesia hydration and the brucite carbonization.The increased production of hydrated magnesium carbonates,coupled with formation of the amorphous brucite facilitated by biomolecules,established a denser structure,enhancing the physicomechanical properties.Microcrack development near the interfacial zone of mortar and sandstone was an important factor in the reduced biocementation performance of the MIMC method.The EIMC method is a practical bio-healing method for rock weathering cracks due to the availability of urease and its good cementation properties.
基金supported by the Key Project of the National Natural Science Foundation of China(Grant No.U21A2058)the Hebei Guoliang New Materials Co.,Ltd.(Grant No.22150239J).
文摘An experiment was conducted to assess the impact of fused calcia-stabilized zirconia micro-powder on the thermal shock behavior of magnesia–spinel refractories.The effects of calcia-stabilized zirconia on the microstructure evolution and properties of magnesia–spinel refractories were characterized by the high-temperature elastic modulus,thermal shock damage resistance parameters,retainment of elastic modulus after thermal shock,and scanning electron microscopy.The results indicated that the incorporation of calcia-stabilized zirconia improved the thermomechanical properties and thermal shock behavior of magnesia–spinel specimens.The hot modulus of rupture of magnesia–spinel specimens increased by 2.5-fold due to the incorporation of calcia-stabilized zirconia micro-powder.The presence of a martensitic phase transformation in partially unstable ZrO2 and thermal mismatches among various phases contributed to a controlled formation of microcracks.And the pinning effect caused by the calcia-stabilized zirconia particles surrounding the grain boundaries played a crucial role in preventing the propagation of microcracks.This phenomenon significantly bolstered the thermal shock stability of magnesia–spinel refractories,consequently prolonging their service life.
基金National Natural Science Foundation of China(52302027,52272022 and 52472032).
文摘Traditional magnesia-based refractories face challenges such as high thermal conductivity and poor slag penetration resistance,which contradict the energy efficiency requirements of modern metallurgy.In this study,microporous magnesia was prepared using low-grade magnesite via the one-step sintering method.The microstructure and properties of microporous magnesia prepared by high-silicon and high-calcium magnesites calcined at various temperatures were compared.The pore structure and phase evolution were analyzed,the effect of which on the properties of lightweight magnesia-based dry vibration mix was discussed.The results indicated that within high-silicon magnesite,SiO_(2) initially reacted with Mgo to form Mg_(2)Si0_(4),which gradually reacted with Cao impurities as the temperature increased transforming into a Mgo-Cao-SiO_(2) ternary liquid phase and uniformly permeated along the grain boundaries.Due to the bridging effect of strip-like Cao in high-calcium magnesite,the reorganization and sintering of Mgo grains at high temperatures were inhibited,resulting in the presence of a significant number of elongated pores within the magnesia after calcination at various temperatures,which was detrimental to the mechanical properties and slag resistance.The microporous Mg0 prepared by high-silicon magnesite at 1700°C exhibited the superior physical properties.The microporous Mgo aggregates had a stronger interlocking force with the matrix,resulting in a greater bonding strength.Moreover,the micropores not only effectively reduced the thermal conductivity but also facilitated the supersaturated precipitation of molten slag,hindering further penetration.Compared to the dry vibration mix prepared by fused Mgo,the lightweight magnesia-based dry vibration mix prepared with the high-silicon magnesite exhibited higher mechanical strength(~40%increase)and thermal insulation performance(0.870 W·(m·K)at 1000 C),and improved slag resistance.
基金supported by the National Natural Science Foundation of China(Grant Nos.41925012 and 42230710)the Key Laboratory Cooperation Special Project of Western Cross Team of Western Light,CAS(Grant No.xbzg-zdsys-202107).
文摘This study proposed an improved bio-carbonation of reactive magnesia cement(RMC)method for dredged sludge stabilization using the urea pre-hydrolysis strategy.Based on unconfined compression strength(UCS),pickling-drainage,and scanning electron microscopy(SEM)tests,the effects of prehydrolysis duration(T),urease activity(UA)and curing age(CA)on the mechanical properties and microstructural characteristics of bio-carbonized samples were systematically investigated and analyzed.The results demonstrated that the proposed method could significantly enhance urea hydrolysis and RMC bio-carbonation to achieve efficient stabilization of dredged sludge with 80%high water content.A significant strength increment of up to about 1063.36 kPa was obtained for the bio-carbonized samples after just 7 d of curing,which was 2.64 times higher than that of the 28-day cured ordinary Portland cement-reinforced samples.Both elevated T and UA could notably increase urea utilization ratio and carbonate ion yield,but the resulting surge in supersaturation also affected the precipitation patterns of hydrated magnesia carbonates(HMCs),which weakened the cementation effect of HMCs on soil particles and further inhibited strength enhancement of bio-carbonized samples.The optimum formula was determined to be the case of T?24 h and UA?10 U/mL for dredged sludge stabilization.A 7-day CA was enough for bio-carbonized samples to obtain stable strength,albeit slightly affected by UA.The benefits of high efficiency and water stability presented the potential of this method in achieving dredged sludge stabilization and resource utilization.This investigation provides informative ideas and valuable insights on implementing advanced bio-geotechnical techniques to achieve efficient stabilization of soft soil,such as dredged sludge.
基金This work was supported by the Creative Groups of Natural Science Foundation of Hubei Province(Grant No.2021CFA030).Onyekwena Chikezie Chimere is an awardee for the ANSO Scholarship 2020-PhD.Ishrat Hameed Alvi is a recipient of the 2021 PhD ANSO Scholarship.
文摘Dredged marine soils(DMS)have poor engineering properties,which limit their usage in construction projects.This research examines the application of reactive magnesia(rMgO)containing supplementary cementitious materials(SCMs)to stabilize DMS under ambient and carbon dioxide(CO_(2))curing conditions.Several proprietary experimental tests were conducted to investigate the stabilized DMS.Furthermore,the carbonation-induced mineralogical,thermal,and microstructural properties change of the samples were explored.The findings show that the compressive strength of the stabilized DMS fulfilled the 7-d requirement(0.7-2.1 MPa)for pavement and building foundations.Replacing rMgO with SCMs such as biochar or ground granulated blast-furnace slag(GGBS)altered the engineering properties and particle packing of the stabilized soils,thus influencing their performances.Biochar increased the porosity of the samples,facilitating higher CO_(2) uptake and improved ductility,while GGBS decreased porosity and increased the dry density of the samples,resulting in higher strength.The addition of SCMs also enhanced the water retention capacity and modified the pH of the samples.Microstructural analysis revealed that the hydrated magnesium carbonates precipitated in the carbonated samples provided better cementation effects than brucite formed during rMgO hydration.Moreover,incorporating SCMs reduced the overall global warming potential and energy demand of the rMgO-based systems.The biochar mixes demonstrated lower toxicity and energy consumption.Ultimately,the rMgO and biochar blend can serve as an environmentally friendly additive for soft soil stabilization and permanent fixation of significant amounts of CO_(2) in soils through mineral carbonation,potentially reducing environmental pollution while meeting urbanization needs.
基金the National Natural Science Foundation of China(U21A2057)the Key Research and Development Project of Hubei Province,China(2022BAA032).
文摘Magnesia-chrome porous purging plugs are crucial functional components to remove inclusions and stabilize the flow field during iron and steel smelting.However,practical applications of magnesia-chrome porous purging materials are stil hampered by the poor scouring resistance to molten steel and unstable air permeability owing to their low mechanical properties and uncontrollable pore structure.Therefore,the particle-packing type magnesiachrome porous purging materials reinforced by in situ formed spinel were prepared using fused magnesia-chrome particles and Al powders as major raw materials.The results show that in situ formed spinel solid solutions in bonding phase led to the decreased median pore size and increased pore surface fractal dimension from the reactions between Al powders and magnesia-chrome particles and along with high-temperature sintering,bonding between magnesia-chrome particles and the resultant mechanical properties of materials were greatly elevated.Besides,the results of air permeability tests and polynomial ftting indicated that the formation of spinel solid solutions was the main contributing factor for controllable air permeability,and pressure drop of porous purging materials was positively correlated with surface fractal dimension of pores.Moreover,the as-prepared porous purging materials added with 6 wt.%Al powders obtained the maximum cold crushing strength(54.2 MPa)and hot modulus of rupture(12.9 MPa)with median pore size of 24.06μm and ftting non-Darcian permeability coefficient of 0.97×10^(-6)m.
文摘Magnesia-based refractories hold a big share in the total refractories output in China because of abundance of magnesite resource. In this paper a short review has been focused on the current and future new use of magnesia in the production of magnesia-based products including low carbon MgO-C bricks, MgO- CaO bricks, MgO-based castables, MgO-CaO-Fe2O3 ramming mix and MgO-CaO-C bricks for low carbon steelmaking and clean steel making, magnesite ball for slag splashing, MgO-CaO-ZrO2 for sintering and transfering zones of cement kiln and MgAlON for special use in the steel industry.
文摘Two types of low carbon MgO - C refractories with 6% graphite were prepared using microporous magnesiarich spinel （5 - 3 and 3 - 1 mm ） and fused magnesia （5 - 3 and 3 - 1 mm ） as coarse aggregates, respectively, fused magnesia （ ≤1 mm） as fine aggregate, magnesia powder （≤ 0. 088 mm ） , flake graphite powder （ ≤0. 088 mm）, metal Al powder （ 〈0. 074 mm） as matrix, and phenol resin as binder. After curing at 220 ℃ and coke-embedded firing at 1 500 ℃ , the apparent porosity, cold crushing strength, cold modulus of rupture, permanent linear change on heating, thermal shock resistance and slag resistance of the specimens were studied comparatively. The results indicate that： （ 1 ） after curing at 220 ℃ and coke-embedded firing at 1 500 ℃, the specimen with microporous magnesia-rich spinel replacing fused magnesia has lower bulk density and higher apparent porosity than the common low car- bon MgO - C specimen. After curing at 220 ℃, the specimen with microporous aggregate has lower strength than common low carbon MgO - C specimen, but after coke-embedded firing at 1 500℃, it has higher strength and lower permanent linear change on heating; （2） low carbon MgO - C specimen using microporous magnesia-rich spinel to replace fused magnesia aggregate has better thermal shock resistance but worse slag resistance.
文摘Properties of magnesia-hercynite brick were studied. The coatability, thermal shock resistance, corrosion resistance to cement clinker and thermal conductivity were compared with those of magnesia-chrome brick and magnesia-spinel brick used widely in sintering zone of cement rotary kiln. The result shows that magnesia-hercynite brick is better than magnesia-chrome brick in thermal chock resistance and corrosion resistance to cement clinker, is similar to magnesia-chrome brick and is better than magnesia-spinel brick in coatability and thermal conductivity.
文摘The manufacturing techniques of magnesia-carbon bricks in China have been documented from raw materials,production(process and facilities)to performance and wear issues in the ladle.Magnesia-carbon bricks made of ordinary fused magnesia is the prevailing material used in the slagline of the ladle,but its service life is substantially lower than the bricks based on large-periclase-crystal fused magnesia.In two types of fused magnesia,the average values of periclase crystal size are in double for their difference.It is suggested that large-periclase-crystal fused magnesia should be used for manufacturing magnesia-carbon bricks for the slagline of the ladle by abandoning ordinary fused magnesia,in order to have a prolonged service life,increase the availability of the ladle and reduce the number of downtimes of the ladle.Free phenol in resin produced in China should be as low as that of resin made in Europe,to improve production environment and reduce smoke emission during the ladle preheating.There are large spaces to promote the productivity of magnesia-carbon bricks in China,with high intensity mixers and hydraulic presses.Expansion controlled magnesia-carbon bricks in the ladle depend on the optimized combination of sintered magnesia,Carbores and antioxidants as the matrix,to minimize the premature wear of vertical cracks and joint opening formed in the ladle lining.
基金The authors gratefully acknowledge the support from National Natural Science Foundation of China(No.U1860205).
文摘The microporous magnesia refractory shows a promising application prospect as tundish lining due to excellent thermal insulation and slag resistance.The effect of interaction between microporous magnesia castable and 38CrMoAl steel containing 0.876 wt.%Al on the cleanliness of 38CrMoAl steel was studied and compared with that of fused magnesia castable.The results show that the micropores in the microporous magnesia castable can promote the formation of dense and continuous MgO-Al_(2)O_(3)layer,which can inhibit the further pollution of molten steel by refractories,whereas the MgO-Al_(2)O_(3)layer formed in test of fused magnesia castable is not continuous.After 30 min holding,the total oxygen content in the steel samples for the test of microporous magnesia castable is only 42.2%of that for the test of fused magnesia castable.The inclusions in the steel samples for the test of microporous magnesia castable are also less than those for the test of fused magnesia castable.It shows that microporous magnesia castable is a promising tundish refractory for the preparation of clean high-Al steel.
文摘To meet the needs of environmental protection and promote the application of chromium-free refractories for RH refining furnaces, research on application of new non-burned periclase-magnesia alumina spinel bricks was carried out. Through laboratory research and field application, it is concluded that the non-burned periclase-magnesia alumina spinel brick can replace magnesia-chrome material, and its service life is equivalent to that of the magnesia-chrome material with reduced cost.
文摘Magnesia-carbon refractories were prepared using fused magnesia,flake graphite and metal aluminum powder as starting materials,phenolic resin as the binder,heat-treating at 1300-1600℃in nitrogen atmosphere.The phase reconstruction and the microstructure evolution of the obtained magnesia-carbon refractories were analyzed.The formation mechanisms of magnesia crystals with different morphologies by chemical vapor deposition were revealed.The results show that at 1300-1500℃,the non-oxides within the specimens are aluminum carbide(Al_(4)C_(3)),aluminum nitride(AlN)and magnesium aluminum nitride(Mg_(3)Al_(n)N_(n+2),n=2 or 3);at 1600℃,the diffraction characteristic peak intensity of Al_(4)C_(3) and AlN decreases sharply,and sharp diffraction characteristic peaks of nitrogen aluminum carbide(Al_(7)C_(3)N_(3))appear.Mg(g)is produced by the aluminothermic reduction and carbothermal reduction of magnesia.On the surface of the specimens,Mg(g)reacts with oxygen to form MgO whiskers.Inside the specimens,Mg(g)and O_(2)(g)undergo a CVD chemical deposition reaction to form cubic MgO crystals.There is a phase relationship between flake AlN and flake Mg3AlnNn+2,and they are so associated with each other that the morphology is difficult to distinguish.
文摘The complex coating on the MgO CaO clinker was prepared by dipping method and adding the second mineral to restrain the formation and expansion of the cracks. Meanwhile, the microstructure and the morphology of the coating and hydration resistance of the MgO CaO clinker were also investigated. The result shows that the coating consists mainly of Ca 2P 2O 7, MgO and CaCO 3, its thickness ranges from 5μm to 20μm, and the coating is dense and even, no micro cracks are observed. Also, the coating adheres closely to the matrix. The hydration resistance of the MgO CaO clinker after treatment is improved greatly, and the castables prepared with the treated MgO CaO clinker have better physical properties than MgO castable.
文摘In order to widen the application of microcrystalline magnesite,the thermal decomposition behavior of the microcrystalline magnesite in Sichuan and Tibet area was firstly studied by thermogravimetric analysis. Then the effects of the calcination temperature,calcination time and particle size on the preparation of active Mg O from microcrystalline magnesite were studied by orthogonal experimental design. At last,high purity sintered magnesia was prepared by two-step calcination,meanwhile the effects of the light burning temperature,particle size of the light-burned Mg O powder,molding pressure and the hydration rate of light-burned Mg O powder on the properties of high purity sintered magnesia were studied.The results show that:（ 1） the calcination temperature has the greatest influence on the activity of light-burned MgO,followed by the holding time and the particle size;the optimal process of light burning for preparing active MgO is the microcrystalline magnesite with particle size of 1-0. 5 mm heat-treating at 700 ℃ for 2 h; under these conditions,the microcrystalline magnesite decomposes completely; the average grain size of the obtained product is about 21. 4 nm,and its activity of CAA is20. 16 s;（ 2） the effect of the light burning temperature on the density of high purity sintered magnesia is not obvious; the fineness of the light burning Mg O powder and molding pressure help to increase the density of sintered magnesia; the lower the hydration rate of the lightburned Mg O, the higher the density of the sintered magnesia; the high-purity sintered magnesite withw（ MgO） ≥98% and bulk density≥3. 40 g/cm;can be prepared by the two-step calcination; the grains are fine with size of 30-200 μm and the impurity at grain boundaries is little.
基金supported by the Industrial Special Resource Protecting Office of Liaoning Province
文摘The magnesia composite materials were prepared using fused magnesia, used magnesia chrome bricks, magnesium aluminate spinel, alumina powder and chrome oxide powder as starting materials. In order to improve the performance of magnesia composite material, the influence of chrome oxide concentrate powder on the properties of magnesia composite material was re-searched. The apparent porosity, bulk density, cold crushing streugth, linear expausion and thermal shock resistance of the specimens were determined. The results show that adding chrome oxide concentrate promotes the formation of the composite phases of three kinds of spi-nel, which is beneficial to the thermal shock resistance.The magnesia chrome spbwl can not be .[brined at high temperatures theoreticalby, but can dissolve in the mag-nesia composite material. Comprehensively, the optimal addition of chrome oxide concentrate is 10. 0 mass% for the magnesia composite materials.
文摘To enhance the serdice life of magnesia based slag dam, composite slag dam was designed to be cast with alumina magnesia castables in slag line and magnesia castables in molten steel zone. Workability of the magnesia castables for the slag dam was improved and a suitable vibration shaping method was adopted to combine it with alumina magnesia castables. The result shows： （1） workability and setting performance of magtwsia castables can be improved to match with alumina magnesia castables by adjusting setting retarder and water reducing agent, and adding proper silica fume ; （2） composite slag dam cart be prepared with alumina m,agnesia castables and the improved magnesia castables, whether by up - down composite method or right - left composite method; in order to get full vibration arrd make interface .fluctuation have proper amplitude, the vibration time oJ the two methods after two different castables contact with each other is 3 and 2.5 minutes, respectively; （3）the result of the on-site test proves that the design aims for reducing pollution to hot metal and improving corrosion resistance have been achieved.
文摘In order to reduce the thermal energy loss of high temperature kilns and furnaces and lower the surface temperature of the kiln body,magnesia insulation materials were prepared using self-made magnesia porous aggregates(using high purity magnesia powder as starting material and potassium oleate as the foaming agent),middle grade magnesia powder,calcium aluminate cement,and SiO_(2) micropowder as starting materials,introducing walnut shell powder impregnated with silica sol(short for Sws)as a pore-forming agent.The effects of the Sws addition(0,10%,15%,and 20%,by mass)and the sintering temperature(1300,1350,1400,and 1480℃)on the properties of magnesia insulation materials were studied.The results show that(1)for the specimens fired at 1480℃,when the Sws addition is 10%,the cold compressive strength is 22 MPa;when the Sws addition is 20%,the thermal conductivity is 0.368 W·m^(-1)·K^(-1)(350℃);(2)nano-silica in the silica sol reacts with MgO in the matrix to form forsterite,which encapsulates the pores volatilized from the walnut shell powder and forms closed pores.
文摘Magnesia-alumina-chrome ramming mixes with same chemical compositions were prepared by using different raw materials such as fused magnesia-chrome synthetic materials and sintered one, wasted bricks and magnesia-alumina spinels. Their physical properties were tested and microstructures were analyzed. The results show that the ramming mixes made of different raw materials bring about different microstructures and properties although the mixes have the same chemical composition, binder content and aggregate size composition.
基金Projects(41330641,51279032,51278100)supported by(Major Program of)the National Natural Science Foundation of ChinaProject(41330641)supported by National Technology Support Program during the Twelfth Five-Year Plan of China+1 种基金Project(KYLX_0147)supported by Graduate Student Scientific Research Innovation Program of Jiangsu Province,ChinaProject(BK2012022)supported by the Natural Science Foundation of Jiangsu Province,China
文摘A series of unconfined compression tests(UCTs) were conducted to investigate the effects of content of reactive magnesia(Mg O) and carbonation time on the engineering properties including apparent characteristics, stress-strain relation, and deformation and strength characteristics of reactive Mg O treated silt soils. The soils treated with reactive Mg O at various contents were subjected to accelerated carbonation for different periods of time and later, UCTs were performed on them. The results demonstrate that the reactive Mg O content and carbonation time have remarkable influences on the aforementioned engineering properties of the soils. It is found that with the increase in reactive Mg O content, the unconfined compressive strength(qu) increases at a given carbonation time(<10 h), whereas the water content and amounts of crack of the soils decrease. A threshold content of reactive Mg O exists at approximately 25% and a critical carbonation time exists at about 10 h for the development of qu. A simple yet practical strength-prediction model, by taking into account two variables of reactive Mg O content and carbonation time, is proposed to estimate qu of carbonated reactive Mg O treated soils. A comparison of the predicated values of qu with the measured ones indicates that the proposed model has satisfactory accuracy.
