The purpose of this paper was using gold mine tailings and cemented materials with low alkalinity to fabricate baking-free bricks.The obtained baking-free brick samples were evaluated by unconfined compressive strengt...The purpose of this paper was using gold mine tailings and cemented materials with low alkalinity to fabricate baking-free bricks.The obtained baking-free brick samples were evaluated by unconfined compressive strength(UCS),water absorption percentage,freezing-thawing cycle,and drying-wetting cycle.The microstructures of the baking-free brick samples were analyzed using X-ray diffraction(XRD)and scanning electron microscope(SEM)techniques.The baking-free brick specimens cured for 28 days with the addition of 10%mixing water consumption and 1:6 cement/tailing ratio tended to obtain favorable comprehensive properties such as a high compressive strength of 15.15 MPa,a low water absorption percentage of 11.8%,excellent freezing-thawing resistance with a 8.9%UCS loss rate after 15 freezing-thawing cycles and good drying-wetting resistance with a 11%UCS loss rate after 10 drying-wetting cycles.The XRD and SEM test results verified that different kinds of hydrate products including C-S-H and C-S-A-H gels,and ettringite were produced during hydration process,which were responsible for good physical,mechanical properties,and durability of the obtained baking-free bricks.Therefore,the experimental results showed that it was practical and reasonable to utilize the homemade cementitious materials in our laboratory to stabilize the gold tailings for production of baking-free bricks,which still met the requirements of major regional construction standards in some countries.展开更多
The purpose of this paper was to explore the possility of using low alkalinity cementitious materials as binders,in which ground blast furnace slag and fly ash acted as a partial replacement of ordinary Portland cemen...The purpose of this paper was to explore the possility of using low alkalinity cementitious materials as binders,in which ground blast furnace slag and fly ash acted as a partial replacement of ordinary Portland cement,and CaSO_(4),Na_(2)SO_(4),and CaO were used as a sulfate activator and alkali activated additives,to solidify gold mine tail-ings for preparation of a green,inexpensive cemented paste backill(CPB).For this target,the effects of cement/tailings ratio,superplasticizer dosage,solid content,tailings fineness on the mechanical properties of the CPB were inves tigated.Additionally,the hydration mechanism of the CPB was analyzed based on X-ray diffraction and scanning electron microscopy results.The results showed that the fuidity of the CPB slurry could be improved by adding polycarboxylic acid superplasticizer.The unconfined compressive strength(UCS)of the CPB specimens was increased with the increase of cement/tailings ratio and solid content.Under the same experi-mental conditions,the 28 d UCS of the CPB specimens was 3.8-4.9 times higher than that of ordinary Portland cement.The softening coefficient of the CPB specimens was increased with the increasing cement/tailings ratio,ranging from 0.83 to 0.92.The shrinkage rate of the CPB specimens was decreased from 0.70%to 0.54%with the increase of cement/tailings ratio from 1:12 to 1:4 The UCS of the full tailings CPB was the highest,followed by the fine tailings CPB specimens,and the UCS of the coarse tailings CPB specimens was the lowest.The low alka-linity binder was proved to be a promising material to improve the engineering performances of the CPB.The optimal mixing ratio is 1:6 cement/tailings ratio,0.15 wt% superplastizer dosage,and 70 wt%solid content.Pre-pared by this mixing ratio,the UCS values of the CPB after 3,7,and 28 d curing ages reached 1.85,5.87,and 9.16 MPa,respectively,which were suitable as CPB for the Zhaoyuan gold mine in terms of strength requirements.展开更多
CaTiO_(3)-LnAlO_(3)(Ln=La,Nd,Sm) is a perovskite-type microwave material system characterized by a moderate dielectric constant εr,a high quality factor Q×f,and a small temperature coefficient of resonant freque...CaTiO_(3)-LnAlO_(3)(Ln=La,Nd,Sm) is a perovskite-type microwave material system characterized by a moderate dielectric constant εr,a high quality factor Q×f,and a small temperature coefficient of resonant frequency τf,making this system promising for microwave devices.However,its high synthesis temperature and sintering temperature limit its industrial applications.In our work,single phase0.7 CaTiO_(3)-0.3 Sm_(0.9)Nd_(0.1)AlO_(3)(7 CT-3 SNA) was synthesized via the sol-gel auto combustion method using citric acid as fuel at a relatively low temperature.After being calcined at 600℃ for 2 h,wellcrystallized 7 CT-3 SNA powders with 30-50 nm average particle size were achieved,suggesting good sintering activity.The new and narrow order band at about 800 cm^(-1) in the Raman spectra indicates a high ordering degree in the B site of 7 CT-3 SNA solid solution.Compared with the solid-state reaction method and co-precipitation method,the 0.7 CT-0.3 SNA ceramics fabricated by the current method possess a much lower calcination temperature,a similar εr value,and an improved Q × f value.The optimum microwave dielectric properties of εr=43.54,Q×f=54375 GHz,and τf=-6.3 ×10^(-6)/℃ are obtained for the CTSA ceramics derived from the sol-gel auto combustion process.Therefore,the 7 CT-3 SNA ceramics prepared in this study are potential dielectric materials for microwave applications,indicating that the sol-gel auto combustion method is a good alternative strategy for the fabrication of CaTiO_(3)-LnAlO_(3) ceramics.展开更多
Complex ion substitution is gaining more attention as an appealing method of modifying the structure and performance of microwave ceramics.In this work,Li_(2)Zn[Ti_(1-x)(Ni_(1/3)Nb_(2/3))_(x)]_(3)O_(8),0≤x≤0.3cerami...Complex ion substitution is gaining more attention as an appealing method of modifying the structure and performance of microwave ceramics.In this work,Li_(2)Zn[Ti_(1-x)(Ni_(1/3)Nb_(2/3))_(x)]_(3)O_(8),0≤x≤0.3ceramics were designed based on the complex ion substitution strategy,following the substitution rule of radius and valence to investigate the relationship among phase compositions(containing oxygen vacancies and Ti^(3+)ions),microstructures,and microwave dielectric characteristics of the LZTNNx ceramics.The samples maintained a single Li_(2)ZnTi_(3)O_(8)solid solution phase as x≤0.2,whereas the sample of x=0.3 produced a second phase with the LiNbO_(3)structure.The appropriate amount of(Ni_(1/3)Nb_(2/3))^(4+)substitution could slightly improve the densification of the LZTNNx ceramics due to the formation of the LiZnTi_(3)O_(8)solid solution accompanied by a decrease in the average grain size.The presence of a new Aig Raman active band at about 848 cm^(-1)indicated that local symmetry changed,affecting atomic interactions of the LZTNNx ceramics.The variation of the relative dielectric constant(εr)was closely related to the molar volume ionic polarizability(α_(D)^(T)),and the temperature coefficient of the resonant frequency(τ_(f))was related to the bond valence(V_(1))of Ti.The increase in density,the absence of the Ti3+ions and oxygen vacancies,and the reduction in damping behavior were responsible for the decreased dielectric loss.The LZTNNO.2 ceramics sintered at 1120℃exhibited favorable microwave dielectric properties:εr=22.13,quality factor(Q×f)=97,350 GHz,andτ_(f)=-18.60 ppm/C,which might be a promising candidate for wireless communication applications in highly selective electronics.展开更多
A rapid and facile approach was developed for the synthesis of ultrafine SmAlO_(3) powders through the combustion of stearic acid precursors.The obtained products were characterized by typical techniques including X-r...A rapid and facile approach was developed for the synthesis of ultrafine SmAlO_(3) powders through the combustion of stearic acid precursors.The obtained products were characterized by typical techniques including X-ray diffraction(XRD),Fourier Transform Infrared(FT-IR),thermogravimetric and differential thermal analysis(TG-DTA),scanning electron microscopy(SEM),and transmission electron microscopy(TEM)to analyze the phase composition and microstructure.The dielectric characteristics of SmAlO_(3) microwave ceramics,using the as-obtained products as original materials,were also studied.Compared with the conventional solid-state reaction method,the synthesis temperature was dramatically reduced to 750℃.The large-size sheet structure was composed of a number of micro/nano-scale crystallites,which were mostly irregular in shape due to the mutual growth and overlapping shapes of adjacent grains.The SmAlO_(3) ceramics with high density and uniform microstructure were obtained after sintering at 1500℃ for 4 h due to the favorable sintering activity of the as-synthesized powders.In addition,desired dielectric properties at microwave frequencies(dielectric constant ε_(r)=20.22,quality factor Q·f=74110 GHz,and a temperature coefficient of resonant frequency τ_(f)=-74.6 ppm/℃)were achieved.展开更多
0.5 Ca（0.6La0.267TiO3-0.5 Ca（Mg1/3Nb2/3）O3（5 CLT-5 CMN） ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.With...0.5 Ca（0.6La0.267TiO3-0.5 Ca（Mg1/3Nb2/3）O3（5 CLT-5 CMN） ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.Without any calcination stage involved,a mixture of CaCO_3, La_2 O_3, TiO_2, MgO and Nb_2 O_5 was pressed and sintered directly. Pure phase 5 CLT-5 CMN ceramics with high density and dense microstructure can be obtained after sintered at 1400 ℃ for 4 h. Compared with those prepared by the conventional ceramic route, 5 CLT-5 CMN ceramics produced by the reaction-sintering process exhibit slightly higher dielectric constant and Q×f value. Fine microwave dielectric properties of ε_r= 56.4, Q×f= 48,550 GHz and T_f = ＋8.7 ppm/℃ for 5 CLT-5 CMN ceramics sintered at 1400 ℃ for 4 h are obtained, suggesting reactionsintering process is a simple and efficient method to produce pure phase 5 CLT-5 CMN ceramics as a potential candidate for the fabrication of microwave devices.展开更多
基金the Key Research and Development Program of Anhui Province(No.202004a07020039).
文摘The purpose of this paper was using gold mine tailings and cemented materials with low alkalinity to fabricate baking-free bricks.The obtained baking-free brick samples were evaluated by unconfined compressive strength(UCS),water absorption percentage,freezing-thawing cycle,and drying-wetting cycle.The microstructures of the baking-free brick samples were analyzed using X-ray diffraction(XRD)and scanning electron microscope(SEM)techniques.The baking-free brick specimens cured for 28 days with the addition of 10%mixing water consumption and 1:6 cement/tailing ratio tended to obtain favorable comprehensive properties such as a high compressive strength of 15.15 MPa,a low water absorption percentage of 11.8%,excellent freezing-thawing resistance with a 8.9%UCS loss rate after 15 freezing-thawing cycles and good drying-wetting resistance with a 11%UCS loss rate after 10 drying-wetting cycles.The XRD and SEM test results verified that different kinds of hydrate products including C-S-H and C-S-A-H gels,and ettringite were produced during hydration process,which were responsible for good physical,mechanical properties,and durability of the obtained baking-free bricks.Therefore,the experimental results showed that it was practical and reasonable to utilize the homemade cementitious materials in our laboratory to stabilize the gold tailings for production of baking-free bricks,which still met the requirements of major regional construction standards in some countries.
基金The current work was financially supported by the Key Research and Development Program of Anhui Province(202004a07020039).
文摘The purpose of this paper was to explore the possility of using low alkalinity cementitious materials as binders,in which ground blast furnace slag and fly ash acted as a partial replacement of ordinary Portland cement,and CaSO_(4),Na_(2)SO_(4),and CaO were used as a sulfate activator and alkali activated additives,to solidify gold mine tail-ings for preparation of a green,inexpensive cemented paste backill(CPB).For this target,the effects of cement/tailings ratio,superplasticizer dosage,solid content,tailings fineness on the mechanical properties of the CPB were inves tigated.Additionally,the hydration mechanism of the CPB was analyzed based on X-ray diffraction and scanning electron microscopy results.The results showed that the fuidity of the CPB slurry could be improved by adding polycarboxylic acid superplasticizer.The unconfined compressive strength(UCS)of the CPB specimens was increased with the increase of cement/tailings ratio and solid content.Under the same experi-mental conditions,the 28 d UCS of the CPB specimens was 3.8-4.9 times higher than that of ordinary Portland cement.The softening coefficient of the CPB specimens was increased with the increasing cement/tailings ratio,ranging from 0.83 to 0.92.The shrinkage rate of the CPB specimens was decreased from 0.70%to 0.54%with the increase of cement/tailings ratio from 1:12 to 1:4 The UCS of the full tailings CPB was the highest,followed by the fine tailings CPB specimens,and the UCS of the coarse tailings CPB specimens was the lowest.The low alka-linity binder was proved to be a promising material to improve the engineering performances of the CPB.The optimal mixing ratio is 1:6 cement/tailings ratio,0.15 wt% superplastizer dosage,and 70 wt%solid content.Pre-pared by this mixing ratio,the UCS values of the CPB after 3,7,and 28 d curing ages reached 1.85,5.87,and 9.16 MPa,respectively,which were suitable as CPB for the Zhaoyuan gold mine in terms of strength requirements.
基金Project supported by the Natural Science Foundation of Anhui Provincial Education Department (KJ2019A0054)the Student Research and Training Program of Anhui University of Technology (2020008)。
文摘CaTiO_(3)-LnAlO_(3)(Ln=La,Nd,Sm) is a perovskite-type microwave material system characterized by a moderate dielectric constant εr,a high quality factor Q×f,and a small temperature coefficient of resonant frequency τf,making this system promising for microwave devices.However,its high synthesis temperature and sintering temperature limit its industrial applications.In our work,single phase0.7 CaTiO_(3)-0.3 Sm_(0.9)Nd_(0.1)AlO_(3)(7 CT-3 SNA) was synthesized via the sol-gel auto combustion method using citric acid as fuel at a relatively low temperature.After being calcined at 600℃ for 2 h,wellcrystallized 7 CT-3 SNA powders with 30-50 nm average particle size were achieved,suggesting good sintering activity.The new and narrow order band at about 800 cm^(-1) in the Raman spectra indicates a high ordering degree in the B site of 7 CT-3 SNA solid solution.Compared with the solid-state reaction method and co-precipitation method,the 0.7 CT-0.3 SNA ceramics fabricated by the current method possess a much lower calcination temperature,a similar εr value,and an improved Q × f value.The optimum microwave dielectric properties of εr=43.54,Q×f=54375 GHz,and τf=-6.3 ×10^(-6)/℃ are obtained for the CTSA ceramics derived from the sol-gel auto combustion process.Therefore,the 7 CT-3 SNA ceramics prepared in this study are potential dielectric materials for microwave applications,indicating that the sol-gel auto combustion method is a good alternative strategy for the fabrication of CaTiO_(3)-LnAlO_(3) ceramics.
基金the Natural Science Foundation of Anhui Provincial Education Department(KJ2019A0054)the Anhui Provincial Natural Science Foundation(1608085ME92).
文摘Complex ion substitution is gaining more attention as an appealing method of modifying the structure and performance of microwave ceramics.In this work,Li_(2)Zn[Ti_(1-x)(Ni_(1/3)Nb_(2/3))_(x)]_(3)O_(8),0≤x≤0.3ceramics were designed based on the complex ion substitution strategy,following the substitution rule of radius and valence to investigate the relationship among phase compositions(containing oxygen vacancies and Ti^(3+)ions),microstructures,and microwave dielectric characteristics of the LZTNNx ceramics.The samples maintained a single Li_(2)ZnTi_(3)O_(8)solid solution phase as x≤0.2,whereas the sample of x=0.3 produced a second phase with the LiNbO_(3)structure.The appropriate amount of(Ni_(1/3)Nb_(2/3))^(4+)substitution could slightly improve the densification of the LZTNNx ceramics due to the formation of the LiZnTi_(3)O_(8)solid solution accompanied by a decrease in the average grain size.The presence of a new Aig Raman active band at about 848 cm^(-1)indicated that local symmetry changed,affecting atomic interactions of the LZTNNx ceramics.The variation of the relative dielectric constant(εr)was closely related to the molar volume ionic polarizability(α_(D)^(T)),and the temperature coefficient of the resonant frequency(τ_(f))was related to the bond valence(V_(1))of Ti.The increase in density,the absence of the Ti3+ions and oxygen vacancies,and the reduction in damping behavior were responsible for the decreased dielectric loss.The LZTNNO.2 ceramics sintered at 1120℃exhibited favorable microwave dielectric properties:εr=22.13,quality factor(Q×f)=97,350 GHz,andτ_(f)=-18.60 ppm/C,which might be a promising candidate for wireless communication applications in highly selective electronics.
基金financially supported by the Natural Science Foundation of Anhui Provincial Education Department(Nos.KJ2019A0054 and KJ2018A0041)the National Natural Science Foundation of China(No.51802003).
文摘A rapid and facile approach was developed for the synthesis of ultrafine SmAlO_(3) powders through the combustion of stearic acid precursors.The obtained products were characterized by typical techniques including X-ray diffraction(XRD),Fourier Transform Infrared(FT-IR),thermogravimetric and differential thermal analysis(TG-DTA),scanning electron microscopy(SEM),and transmission electron microscopy(TEM)to analyze the phase composition and microstructure.The dielectric characteristics of SmAlO_(3) microwave ceramics,using the as-obtained products as original materials,were also studied.Compared with the conventional solid-state reaction method,the synthesis temperature was dramatically reduced to 750℃.The large-size sheet structure was composed of a number of micro/nano-scale crystallites,which were mostly irregular in shape due to the mutual growth and overlapping shapes of adjacent grains.The SmAlO_(3) ceramics with high density and uniform microstructure were obtained after sintering at 1500℃ for 4 h due to the favorable sintering activity of the as-synthesized powders.In addition,desired dielectric properties at microwave frequencies(dielectric constant ε_(r)=20.22,quality factor Q·f=74110 GHz,and a temperature coefficient of resonant frequency τ_(f)=-74.6 ppm/℃)were achieved.
基金Project supported by Anhui Provincial Natural Science Foundation(1608085ME92)
文摘0.5 Ca（0.6La0.267TiO3-0.5 Ca（Mg1/3Nb2/3）O3（5 CLT-5 CMN） ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.Without any calcination stage involved,a mixture of CaCO_3, La_2 O_3, TiO_2, MgO and Nb_2 O_5 was pressed and sintered directly. Pure phase 5 CLT-5 CMN ceramics with high density and dense microstructure can be obtained after sintered at 1400 ℃ for 4 h. Compared with those prepared by the conventional ceramic route, 5 CLT-5 CMN ceramics produced by the reaction-sintering process exhibit slightly higher dielectric constant and Q×f value. Fine microwave dielectric properties of ε_r= 56.4, Q×f= 48,550 GHz and T_f = ＋8.7 ppm/℃ for 5 CLT-5 CMN ceramics sintered at 1400 ℃ for 4 h are obtained, suggesting reactionsintering process is a simple and efficient method to produce pure phase 5 CLT-5 CMN ceramics as a potential candidate for the fabrication of microwave devices.
