Zirconium carbide（ZrC） exhibits considerable potential for applications as aerospace thermal protection and the Generation-Ⅳ nuclear fuel inert materials due to its high melting point,exceptional hardness,good abla...Zirconium carbide（ZrC） exhibits considerable potential for applications as aerospace thermal protection and the Generation-Ⅳ nuclear fuel inert materials due to its high melting point,exceptional hardness,good ablation resistance and low neutron absorption cross-section.Nevertheless,low sinterability of ZrC powders and poor fracture toughness and reliability of bulk ceramics limit their wide applications in extreme environments.This paper reviews the state of the art of preparation and properties of ZrC composites.Optimizing the sintering process and tailoring the chemical constituents of raw powders and sintering aids could improve sinterability to produce dense bulk ceramics.Different additives such as refractory metals,carbides,silicides,oxides,or carbon fibers are introduced into the ZrC matrix in order to improve fracture toughness,oxidation resistance or thermal shock resistance,etc.Further studies are needed to explore the effects of intrinsic defects（vacancies,dislocations,and grain or phase boundaries,etc.） and additives on microstructure and properties at elevated temperatures.展开更多
A predominance area diagram for the Zr-Si-C-O system at 1773 K was plotted according to correlative thermodynamic data. β-SiC/ZrO2 composites were prepared based on the phase diagram by carbothermal reduction of zirc...A predominance area diagram for the Zr-Si-C-O system at 1773 K was plotted according to correlative thermodynamic data. β-SiC/ZrO2 composites were prepared based on the phase diagram by carbothermal reduction of zircon （ZrSiO4） in argon atmosphere. Zircon and carbon black were mixed according to the C/ZrSiO4 mass ratio of 0.2, and with 0, 1wt% and 2wt% extra addition of La2O3. Phase evolution of the mixture was investigated at 1723-1803 K by X-ray powder diffraction, and the microstructure of the product prepared at 1803 K for 4 h was examined by scanning electronic microscope. The results show that the decomposition of ZrSiO4 and the formation of β-SIC can be promoted by increasing the heating temperature and adding La2O3. The β-SiC/ZrO2 composites can be prepared at 1803 K for 4 h in a mixture of zircon, carbon black and La2O3, and the contents of β-SIC and m-ZrO2 in the product sample with 2wt% La2O3 reach the highest values of 10.8wt% and 89.2wt%, respectively. The crystal size of the products is about 200 nm.展开更多
Experimental works have been conducted the objective of which was to improve mechanical properties of boron carbide by introduction of doping elements into the system. Titanium and Zirconium were selected as doping el...Experimental works have been conducted the objective of which was to improve mechanical properties of boron carbide by introduction of doping elements into the system. Titanium and Zirconium were selected as doping elements, which were introduced into the system in the form of TiB2 and ZrB2. Four types of boron carbide-titanium and zirconium mixture with various titanium and zirconium diboride content were used in experiments. Optimal process parameters, as well as doping elements concentration, necessary to provide required high mechanical parameters in the composite were defined.展开更多
Using zircon,boric acid and carbon black as starting materials,ZrB_(2)-ZrO_(2)-SiC composite powder was synthesized by calcining at 1500℃in flowing argon atmosphere.The effects of the soaking time(3,6 and 9 h)and the...Using zircon,boric acid and carbon black as starting materials,ZrB_(2)-ZrO_(2)-SiC composite powder was synthesized by calcining at 1500℃in flowing argon atmosphere.The effects of the soaking time(3,6 and 9 h)and the addition of additive AlF_(3)(0,0.5%,1.0%,1.5%,2.0%and 2.5%,by mass)on the phase composition and the microstructure of the synthesized products were investigated.The results show that:(1)ZrB_(2)-ZrO_(2)-SiC composite powder can be synthesized by carbothermal reduction at 1500℃in flowing argon atmosphere;ZrB_(2) and ZrO_(2) are granular-like,and SiC crystals are fiberous;(2)with the soaking time increasing,the amount of ZrB_(2) increases,the amounts of m-ZrO_(2) and SiC decrease,and the total amount of non-oxides ZrB_(2),SiC and ZrC gradually increases;the optimal soaking time is 3 h;(3)compared with the sample without AlF_(3),the sample with 0.5% AlF_(3) has decreased m-ZrO_(2)amount,noticeably increased ZrB_(2) amount but decreased SiC amount;however,when the addition of AlF_(3) increases from 0.5%to 2.5%,the m-ZrO_(2) amount increases,the ZrB_(2)amount decreases,and the SiC amount changes slightly;the optimum AlF_(3)addition is 0.5%.展开更多
Self-propagating high-temperature synthesis（SHS） method was used to synthesize ZrB2/Al2O3 composite powders from B2O3-ZrO2-Al system. X-ray diffractometry（XRD） and scanning electron microscopy（SEM） analyses show...Self-propagating high-temperature synthesis（SHS） method was used to synthesize ZrB2/Al2O3 composite powders from B2O3-ZrO2-Al system. X-ray diffractometry（XRD） and scanning electron microscopy（SEM） analyses show the presence of ZrB2 and Al2O3 as the primary phases in the composite powders, while the presence of a very small amount of ZrO2 is thought to be unreacted zirconium oxide. Transmission electron microscopy（TEM） and high resolution electron microscopy（HREM） observations of microstructure of the composite powders indicate that the interfaces of ZrB2/Al2O3 bond well without any interfacial reaction products. It is proposed that the good interfacial bonding of composite powders results from the ZrB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.展开更多
To fabricate W-ZrC composite through reaction sintering at first WC and ZrO2 powders with molar ratio of 3-1 are ball milled, then the green body made from this mixture is sintered. Since reactivity is the main proble...To fabricate W-ZrC composite through reaction sintering at first WC and ZrO2 powders with molar ratio of 3-1 are ball milled, then the green body made from this mixture is sintered. Since reactivity is the main problem in sintering of mironized powders the starting ZrO2 powder is selected in nano size to see whether the reaction improves. The XRD pattern indicates that W-ZrC composite has been formed, although some unreacted compounds still exist and some unwanted components have been created. In the case of using nano powders the amount of unreacted WC and ZrO2 phases and unwanted W2C phase reduces and the reaction progresses better. Additionally by using nano powders the reaction progressed and the mechanical proprieties including density, hardness, Elastic modulus and Flexural strength improved.展开更多
CaZrO 3 containing the highest content of CaO in system CaO ZrO 2 is a potential refractory material, which has been applied in anti Al 2O 3 clogging submerged nozzle for steel continuous casting.Thermodynamic analyse...CaZrO 3 containing the highest content of CaO in system CaO ZrO 2 is a potential refractory material, which has been applied in anti Al 2O 3 clogging submerged nozzle for steel continuous casting.Thermodynamic analyses and experiment results show that at high temperature CaZrO 3 ZrB 2 system is stable, but extreme reactions will occur between CaZrO 3 and SiC mixtures while firing.展开更多
基金Financial supports from the National Natural Science Foundation of China ( Nos. 51172052 and 51321061 )Program for New Century Excellent Talents in University ( No. NCET 13 - 0177)
文摘Zirconium carbide（ZrC） exhibits considerable potential for applications as aerospace thermal protection and the Generation-Ⅳ nuclear fuel inert materials due to its high melting point,exceptional hardness,good ablation resistance and low neutron absorption cross-section.Nevertheless,low sinterability of ZrC powders and poor fracture toughness and reliability of bulk ceramics limit their wide applications in extreme environments.This paper reviews the state of the art of preparation and properties of ZrC composites.Optimizing the sintering process and tailoring the chemical constituents of raw powders and sintering aids could improve sinterability to produce dense bulk ceramics.Different additives such as refractory metals,carbides,silicides,oxides,or carbon fibers are introduced into the ZrC matrix in order to improve fracture toughness,oxidation resistance or thermal shock resistance,etc.Further studies are needed to explore the effects of intrinsic defects（vacancies,dislocations,and grain or phase boundaries,etc.） and additives on microstructure and properties at elevated temperatures.
基金supported by the National Natural Science Foundation of China (No.50274021)and Baoshan Iron and Steel Co. Ltd
文摘A predominance area diagram for the Zr-Si-C-O system at 1773 K was plotted according to correlative thermodynamic data. β-SiC/ZrO2 composites were prepared based on the phase diagram by carbothermal reduction of zircon （ZrSiO4） in argon atmosphere. Zircon and carbon black were mixed according to the C/ZrSiO4 mass ratio of 0.2, and with 0, 1wt% and 2wt% extra addition of La2O3. Phase evolution of the mixture was investigated at 1723-1803 K by X-ray powder diffraction, and the microstructure of the product prepared at 1803 K for 4 h was examined by scanning electronic microscope. The results show that the decomposition of ZrSiO4 and the formation of β-SIC can be promoted by increasing the heating temperature and adding La2O3. The β-SiC/ZrO2 composites can be prepared at 1803 K for 4 h in a mixture of zircon, carbon black and La2O3, and the contents of β-SIC and m-ZrO2 in the product sample with 2wt% La2O3 reach the highest values of 10.8wt% and 89.2wt%, respectively. The crystal size of the products is about 200 nm.
文摘Experimental works have been conducted the objective of which was to improve mechanical properties of boron carbide by introduction of doping elements into the system. Titanium and Zirconium were selected as doping elements, which were introduced into the system in the form of TiB2 and ZrB2. Four types of boron carbide-titanium and zirconium mixture with various titanium and zirconium diboride content were used in experiments. Optimal process parameters, as well as doping elements concentration, necessary to provide required high mechanical parameters in the composite were defined.
基金supported by National Natural Science Foundation of China(52172031 and 51872266)Henan Provincial Science and Technology Research Project(222102230030).
文摘Using zircon,boric acid and carbon black as starting materials,ZrB_(2)-ZrO_(2)-SiC composite powder was synthesized by calcining at 1500℃in flowing argon atmosphere.The effects of the soaking time(3,6 and 9 h)and the addition of additive AlF_(3)(0,0.5%,1.0%,1.5%,2.0%and 2.5%,by mass)on the phase composition and the microstructure of the synthesized products were investigated.The results show that:(1)ZrB_(2)-ZrO_(2)-SiC composite powder can be synthesized by carbothermal reduction at 1500℃in flowing argon atmosphere;ZrB_(2) and ZrO_(2) are granular-like,and SiC crystals are fiberous;(2)with the soaking time increasing,the amount of ZrB_(2) increases,the amounts of m-ZrO_(2) and SiC decrease,and the total amount of non-oxides ZrB_(2),SiC and ZrC gradually increases;the optimal soaking time is 3 h;(3)compared with the sample without AlF_(3),the sample with 0.5% AlF_(3) has decreased m-ZrO_(2)amount,noticeably increased ZrB_(2) amount but decreased SiC amount;however,when the addition of AlF_(3) increases from 0.5%to 2.5%,the m-ZrO_(2) amount increases,the ZrB_(2)amount decreases,and the SiC amount changes slightly;the optimum AlF_(3)addition is 0.5%.
基金Project(KNH2021005) supported by Industrialization Programof Economic Committee of Shanghai
文摘Self-propagating high-temperature synthesis（SHS） method was used to synthesize ZrB2/Al2O3 composite powders from B2O3-ZrO2-Al system. X-ray diffractometry（XRD） and scanning electron microscopy（SEM） analyses show the presence of ZrB2 and Al2O3 as the primary phases in the composite powders, while the presence of a very small amount of ZrO2 is thought to be unreacted zirconium oxide. Transmission electron microscopy（TEM） and high resolution electron microscopy（HREM） observations of microstructure of the composite powders indicate that the interfaces of ZrB2/Al2O3 bond well without any interfacial reaction products. It is proposed that the good interfacial bonding of composite powders results from the ZrB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.
文摘To fabricate W-ZrC composite through reaction sintering at first WC and ZrO2 powders with molar ratio of 3-1 are ball milled, then the green body made from this mixture is sintered. Since reactivity is the main problem in sintering of mironized powders the starting ZrO2 powder is selected in nano size to see whether the reaction improves. The XRD pattern indicates that W-ZrC composite has been formed, although some unreacted compounds still exist and some unwanted components have been created. In the case of using nano powders the amount of unreacted WC and ZrO2 phases and unwanted W2C phase reduces and the reaction progresses better. Additionally by using nano powders the reaction progressed and the mechanical proprieties including density, hardness, Elastic modulus and Flexural strength improved.
文摘CaZrO 3 containing the highest content of CaO in system CaO ZrO 2 is a potential refractory material, which has been applied in anti Al 2O 3 clogging submerged nozzle for steel continuous casting.Thermodynamic analyses and experiment results show that at high temperature CaZrO 3 ZrB 2 system is stable, but extreme reactions will occur between CaZrO 3 and SiC mixtures while firing.
