Preparation of Nano-sized Zirconium Carbide Powders through a Novel Active Dilution Self-propagating High Temperature Synthesis Method

High quality nano-sized zirconium carbide （ZrC） powders were successfully fabricated via a developed chemical active dilution self-propagating high-temperature synthesis （SHS） method assisted by ball milling pretreatment process using traditional cheap zirconium dioxide powder （ZrO2）, magnesium powder （Mg） and sucrose （C12H22Oll） as raw materials. FSEM, TEM, HRTEM, SAED, XRD, FTIR and Raman, ICP- AES, laser particle size analyzer, oxygen and nitrogen analyzer, carbon/sulfur determinator and TG-DSC were employed for the characterization of the morphology, structure, chemical composition and thermal stability of the as-synthesized ZrC samples. The as-synthesized samples demonstrated high purity, low oxygen content and evenly distributed ZrC nano-powders with an average particle size of 50nm. In addition, the effects of endothermic rate and the possible chemical reaction mechanism were also discussed.

One pot synthesis of a soluble polymer for zirconium carbide

A new polymer,polyzirconoxanesal（PZS）,is synthesized from the reaction of zirconium oxychloride octahydrate （ZrOCl;-8H;O） with acetylacetone（Hacac） and salicyl alcohol（SA） by one-pot protocol.The polymer is soluble in common organic solvents,such as ethanol,methanol,acetone,tetrahydrofuran and chloroform,and exhibits rheology with viscosity of 100- 300 mpa s at 25℃.These properties are suitable for uses in fabrication of ceramic matrix fiber composites.Pyrolysis of this polymer at 1300℃in argon provides nanosized ZrC with spherical morphology and size of 20-100 nm.

Research Progress on Preparation and Properties of Zirconium Carbide Matrix Composites

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.

Preparation of ZrB_(2)-ZrO_(2)-SiC Composite Powder by Carbothermal Reduction from Zircon

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%.

Relationship Between Electric Properties and Temperature of ZrB_2-SiC Composite Ceramic Heating Element

ZrB2 -SiC composite ceramic has been successfully introduced as heating element in super high temperature .field. This paper further investigated the microstructure of ZrB2 - SiC composite ceramic heating element and the relationship between electric properties and temperature. SEM photos show that the heating element consists of SiC grains and ZrBz grains smaller than 10 μm. The voltage and current gradually increase and the furnace tempera- ture rises lineally with heating time prolonging. The electric resistance increases linearly with the temperature rising. The service temperatltre of the heating element can reach 1 800 ℃ and 2 150 ℃ in air and argon at- mosphere, respectively.

Reduced He ion irradiation damage in ZrC-based high-entropy ceramics

Excellent irradiation resistance is the basic property of nuclear materials to keep nuclear safety.The high-entropy design has great potential to improve the irradiation resistance of the nuclear materials,which has been proven in alloys.However,whether or not high entropy can also improve the irradiation resistance of ceramics,especially the mechanism therein still needs to be uncovered.In this work,the irradiation and helium(He)behaviors of zirconium carbide(ZrC)-based high-entropy ceramics(HECs),i.e.,(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C,were investigated and compared with those of ZrC under 540 keV He ion irradiation with a dose of 1×10^(17) cm^(−2) at room temperature and subsequent annealing.Both ZrC and(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C maintain lattice integrity after irradiation,while the irradiation-induced lattice expansion is smaller in(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C(0.78%)with highly thermodynamic stability than that in ZrC(0.91%).After annealing at 800℃,ZrC exhibits the residual _(0.2)0%lattice expansion,while(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C shows only 0.10%.Full recovery of the lattice parameter(a)is achieved for both ceramics after annealing at 1500℃.In addition,the high entropy in the meantime brings about the favorable structural evolution phenomena including smaller He bubbles that are evenly distributed without abnormal coarsening or aggregation,segregation,and shorter and sparser dislocation.The excellent irradiation resistance is related to the high-entropy-induced phase stability,sluggish diffusion of defects,and stress dispersion along with the production of vacancies by valence compensation.The present study indicates a high potential of high-entropy carbides in irradiation resistance applications.

Mechanism of Zr in in situ-synthesized particle reinforced composite coatings by laser cladding

By adding mixture of ZrOand carbon, a Zrenhanced composite coating was produced onto an AISI1045 substrate by laser cladding. The microstructure and phase formation, microhardness and wear resistance of the composite coating were studied. The experimental results indicate that the composite coating with metallurgical bonding to substrate consists of y-Ni, massive ceramic particles of ZrC,NiZr, NiZr,(Fe,Ni)Cand FeC. The in situ-synthesized ZrC particles are uniformly dispersed in composite coating, which refines the microstructure of composite coating. With different Zr02 and carbon additions, the properties are improved differently. Finally, the fine in situ ZrC particles improve the microhardness of composite coating to HV650, which is nearly 2.7 times that of Ni25 coating. Also, the composite coating has an advantage in wear resistance; it offers better wear resistance when more mixture of ZrOand carbon was added in nickel alloys.

Dehydrogenation characteristics of ZrC-doped LiAlH4 with different mixing conditions

The catalytic effects of ZrC powder on the dehydrogenation properties of LiAlH4 prepared by designed mixing processes were systematically investigated.The onset dehydrogenation temperatures for the 10 mol% ZrC-doped sample are 85.3 and 148.4℃for the first two dehydrogenation stages,decreasing by 90.7 and 57.8℃,respectively,compared with those of the as-received LiAIH4.The isothermal volumetric measurement indicates that adding ZrC powder could significantly enhance the desorption kinetics of LiAlH4.The reaction constant and Avrami index show that the first dehydrogenation stage is controlled by diffusion mechanism with nucleation rate gradually decreasing and the second stage is a freedom nucleation and subsequent growth process.The microstructures and phase transformation characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS) and Fourier transform infrared spectroscopy(FTIR) reveal that the improved desorption behavior of LiAlH4 is primarily due to the high density of surface defects and embedded catalyst particles on the surface of LiAlH4 particles during the high-energy mixing process.

From thermal conductive to thermal insulating:Effect of carbon vacancy content on lattice thermal conductivity of ZrC_(x)

Lattice thermal conductivities of zirconium carbide(ZrC_(x),x=1,0.75 and 0.5)ceramics with different carbon vacancy concentrations were calculated using a combination of first-principles calculations and the Debye-Callaway model.The Gruneisen parameters,Debye temperatures,and phonon group velocities were deduced from phonon dispersions of ZrC_(x) determined using first-principles calculations.In addition,the effects of average atomic mass,grain size,average atomic volume and Zr isotopes on the lattice thermal conductivities of ZrC_(x) were analyzed using phonon scattering models.The lattice thermal conductivity decreased as temperature increased for ZrC,ZrC_(0.75) and ZrC_(0.5)(Zr2 C),and decreased as carbon vacancy concentration increased.Intriguingly,ZrC_(x) can be tailored from a thermal conducting material for ZrC with high lattice thermal conductivity to a thermal insulating material for ZrC_(0.5) with low lattice thermal conductivity.Thus,it opens a window to tune the thermal properties of ZrC_(x) by controlling the carbon vacancy content.

Effect of native carbon vacancies on evolution of defects in ZrC_(1-x)under He ion irradiation and annealing

The dynamic study of radiation-induced defects with annealing is critical for the material design for nextgeneration nuclear energy systems.The native vacancy could affect the development of defects,which lacks study.In the present work,the as-hot pressed ZrC_(1-x)(x=0,0.15,0.3)ceramics which comprised crystallites of a few microns in size with different amounts of carbon vacancies were irradiated by 540 ke V He^(2+)ions at room temperature with a fluence of 1×10^(17)/cm^(2).The radiation-induced lattice expansion was found to be a common phenomenon in a sequence of ZrC_(0.85)≥ZrC_(1.0)>ZrC_(0.7).Both X-ray and electron diffractions confirmed maintenance of structural integrity without amorphization after irradiation.Inside the irradiated region,only“black-dot”type defects,i.e.,clusters of point defects were observed while no helium-induced cavities,cracks,or extended dislocations were detected.The as-irradiated ZrC_(1-x)were then annealed at different high temperatures.Upon annealing at 800℃,very tiny helium-induced cavities were found to be generated and the crystal lattice recovered to a great extent,especially for the sub-stoichiometric samples.While annealed at 1500℃,all the samples almost fully recovered the crystal lattices close to those of as-hot pressed ones.Meanwhile,large cavities and extended dislocations were generated.With increasing amount of native carbon vacancies,the size of cavities increased while the length and density of extended dislocations decreased.Inverse changes of lattice parameters during irradiation and annealing processes have been interpreted by the kinetics of defects.Finally,the correlation between native vacancies and damage behavior is discussed.

Preparation of ZrC-SiC composite coatings by chemical vapor deposition and study of co-deposition mechanism

In this work, the Zr C-SiC composite coatings were co-deposited by chemical vapor deposition(CVD)using ZrCl4, MTS, CH4 and H2 as raw materials. The morphologies, compositions and phases of the composite coatings were characterized by scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy(EDS) and X-ray diffraction(XRD). The results indicated that the morphologies, compositions and phases of the composite coatings were related to the deposition temperature, the flow rate of the carrier H2 gas, and the ratio of C/Zr. Moreover, the co-deposition mechanism of the composite coatings was also studied. It was found that different deposition temperatures resulted in different deposition mechanisms. At temperatures in the range of 1150–1250℃, the Zr C-SiC co-deposition was controlled by the surface kinetic process. At temperatures in the range of 1250–1400℃, the Zr C-SiC co-deposition was controlled by the mass transport process.