The effects of partial pressure of CO on the phase behaviour of synthesised Ti(C,N) through carbothermal reduction-nitridation at 1,380oC

The effects of partial pressure of CO (P_CO) on the product phases formed through titanium dioxide (TiO₂) carbothermal reduction and nitridation were studied. Electrode graphite and anatase TiO₂ were used as the raw materials, while the reaction was carried out under a flowing nitrogen gas atmosphere at 1,380°C. The effects of P_CO on the phase compositions, chemical compositions and microstructures of the nitridation products were investigated by adjusting the P_CO in the system. The chemical mineral compositions, and microstructures of the products were characterised via scanning electron microscopy, energy-dispersive spectroscopy and x-ray diffraction. The results demonstrate that the product phases are mainly titanium nitride (TiN)_0.96 and residual graphite when the P_CO is at 0.003 atm. As the value of P_CO reached 0.08 atm in the furnace, a phase of Ti(O_0.91, C_0.53, N_0.32) gradually began to form, while when the CO content in the atmosphere was over 0.12 atm, a phase of Ti(C_0.2, N_0.8) could be observed in the products. With the increase of P_CO in the system, the evolution sequence of the reaction products was found to be TiO₂→TiN→Ti(O, C, N)→Ti(C, N). By controlling the partial pressure, the synthesised temperature of titanium carbonitride (Ti[C, N]) can be significantly reduced, and the manipulation of the TiN and Ti(C, N) can be effectively realised, which could provide new ideas for experiments closely related to the partial pressure of gases.     

碳热还原氮化攀钢高钛高炉渣制取Ti(C,N)的研究

以攀钢高炉渣(粒度≤0.074mm,w(TiO2)=21.19%)和炭黑(w(C)=98%)为原料,在密封管式炉中通入流量0.5L·min-1的工业N2(纯度>95%),分别在1300℃、1350℃、1400℃、1450℃、1500℃保温2h以及在1450℃下分别保温0、2h、4h、6h、8h的条件下,采用碳热还原氮化法制备了Ti(C,N)。用X射线衍射仪、电子探针、图像分析仪等研究了碳氮化处理温度及保温时间对Ti(C,N)的形成及其晶粒大小的影响。结果表明碳氮化处理温度对高炉渣中Ti(C,N)的形成过程产生显著影响,温度从1300℃升至1500℃时,产物中Ti(C,N)的相对含量增大,其晶粒也逐渐长大,但超过1450℃后,影响又不太显著;在1450℃下延长保温时间能促进Ti(C,N)的生成与晶粒长大,但保温时间超过2h后,此促进作用又不太明显。     

Ti(C,N)粉末的制备技术及研究进展

Ti(C,N)是一种重要的非氧化物陶瓷材料,在耐磨领域具有广阔的应用前景。碳热还原法制备Ti(C,N)粉具有原料来源丰富、设备简单、产物粒径形貌可控且可实现规模化生产等优点,因此,备受国内外研究者的关注。本文简单阐述了近年来国内外Ti(C,N)粉的制备技术,重点介绍了碳热还原法制备Ti(C,N)粉的进展。     

Microstructure and mechanical properties of Ti(C,N)-based cermets fabricated by in situ carbothermal reduction of TiO2 and subsequent liquid phase sintering

Ti(C,N)-based cermets were prepared by in situ carbothermal reduction of TiO₂ and subsequent liquid phase sintering in one single process in vacuum. The densification behavior, phase transformation, and microstructure evolution of the cermets were investigated by DSC, XRD, SEM, and EDX. The results showed that the carbothermal reduction of TiO₂ was completed below 1250 °C, and Ti(C,N)-based cermets with refined grains were obtained after sintered at 1400 °C for 1 h by this method. The hard phase of the cermets mainly exhibited white core/gray rim structure, in great contrast to the typical black core/gray rim structure of hard phase in traditional cermets. Ti(C,N)-based cermets prepared by this novel method showed excellent mechanical properties with a transverse rupture strength of 2516±55 MPa, a Rockwell hardness of 88.6±0.1 HRA, and a fracture toughness of 18.4±0.7 MPa m^1/2, respectively.     

Improvement in microstructure and mechanical properties of Ti(C,N) cermet prepared by two-step spark plasma sintering

A fine grained Ti(C, N) cermet tool material was prepared by two-step spark plasma sintering. Microstructure evolution and densification mechanisms of Ti(C, N) during spark plasma sintering were studied. Effect of two-step sintering process and Ni content on microstructure and mechanical properties were also investigated. The critical activated densification temperature of Ti(C, N) is about 1300?℃, and the rapidest densification rate takes place at 1300?℃~1400?℃. Grains are in the size of 1?µm when the Ti(C, N) cermet was prepared by two-step spark plasma sintering. The optimal flexural strength, fracture toughness and Vickers hardness are 1094?±?42?MPa, 7.2?±?0.5?MPa?m^1/2 and 18.3?±?0.4?GPa, respectively. The Ti(C, N) cermets containing more content of Ni have higher toughness, which is due to the remarkable toughening effect of crack bridging by large grains.     

Carbothermic reduction synthesis of Ti(C,N) powder in the presence of molten salt

In the presence of sodium chloride (NaCl), Ti(C, N) powder was successfully obtained by the carbothermal reduction of TiO₂ in lab-scale experiments. The effects of NaCl addition and reaction temperature on the formation of the powder were studied in the temperature range of 1100–1600 °C, the reaction time used in all cases was 3 h. The final powder was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The results indicated that addition of NaCl played a facilitating role in the formation process of Ti(C, N). Ti(C, N) was detected at 1100–1200 °C, and the yield of powder was purer at about 1300 °C when 10 wt.% NaCl was added. The as-prepared Ti(C, N) was uniform in shape and the particle size was about 5–8 μm. With increasing temperature, the residual carbon content in the products decreased but the degree of oxidation increased at temperatures above 1300 °C. The possible mechanism involved in the reactions was discussed.     

磷对Ni(Co)Mo(W)/Al2O3加氢处理催化剂的影响研究进展

Ni(Co)Mo(W)/Al2O3催化剂是工业中最常用的加氢处理催化剂.磷作为Ni(Co)Mo(W)/Al2O3加氢处理催化剂中较为常用的添加剂,用于改善催化剂的物理化学性质.本文从磷对Ni(Co)Mo(W)/Al2O3加氢催化剂孔结构、酸性、活性组分分散度等理化性能以及磷对加氢脱硫(HDS)和加氢脱氮(HDN)催化性能两个方面的影响对文献研究结果进行了综述,对磷添加剂的研究结果、存在的分歧以及研究机会进行了分析讨论.     

Submicron Ti(C,N)-based cermets with improved microstructure using high-energy milled and subsequent heat-treated ultrafine Ti(C,N) powders

Ti(C,N)-based cermets with ultrafine or submicron black core-rim grains are attracting candidates for high-quality tools and dies, due to their high hardness and strength. However, high chemical activity of ultrafine Ti(C,N) powders lead to the increased instability and difficulty to control the sintering process, since the denitrification and interface diffusion are accelerated during the solid-state reaction. Based on this, owing to the unrealized commercial ultrafine-grade powders, ultrafine Ti(C,N) powders with an average grain size around 150 nm, low oxygen content and few dislocations are fabricated via the high-energy ball milling and subsequent heat treatment of commercial micron Ti(C,N) powders. Related morphology evolution, microstructure and composition of the ultrafine Ti(C,N) powders are investigated. Dense submicron Ti(C,N)-based cermets with grain size of 0.62 μm and uniform core-rim phases are successfully prepared by using the as-fabricated ultrafine Ti(C,N) powders. Compared to cermets via the conventional high-energy milling route, submicron Ti(C,N)-based cermets exhibit higher hardness of 1750 ± 40 N/mm², bending strength of 1960 ± 135 MPa, and satisfactory fracture toughness of 9.2 MPa m^1/2, owing to smaller grain size, uniform microstructure and partial black core-rim grains.     

Phase decomposition of (Ti,Zr)(C,N) solid solutions prepared by spark plasma sintering

(Ti, Zr)(C, N) solid solutions with 10–90 mol% of ZrC were prepared by spark plasma sintering (SPS) using TiCN and ZrC powders as starting materials. The decomposition behavior of the (Ti, Zr)(C, N) solid solutions as a function of heat treatment temperature (1273–2173 K) was investigated. (Ti, Zr)(C, N) solid solutions with 20–80 mol% of ZrC were decomposed into TiCN-rich (Ti, Zr)(C, N) and ZrCN-rich (Zr, Ti)(C, N) phases when heat-treated in the temperature ranged from 1373 to 2173 K for 3.6 ks, respectively. After heat treatment, lamellar microstructure was formed with an orientation relationship of TiCN-rich (Ti, Zr)(C, N) {100} // ZrCN-rich (Zr, Ti)(C, N) {100}. The Vickers hardness and fracture toughness simultaneously increased with increasing heat-treatment temperature and showed the maximum values of 25.0 GPa and 2.5 MPa m^1/2, respectively, for Ti_0.5Zr_0.5C_0.75N_0.25 at the heat-treatment temperature of 1873 K.     

碳热还原氮化制备Ti(C,N)技术的现状与发展

简单概述了Ti(C,N)的结构、性质、应用及其制备方法,并从热力学和动力学方面对碳热还原氮化制备Ti(C,N)技术进行了论述,分析了其制备过程中的工艺因素(如C/Ti摩尔比,原料种类及粒度大小,原料混合方式,气体流速,燃烧温度,添加剂等)的影响,同时还对碳热还原氮化制备Ti(C,N)技术的发展方向进行了展望。     

Effect of Ti （C,N） on Properties of Low-carbon MgO- C Bricks

The effect of Ti （ C, N） on properties of low-carbon MgO - C bricks was investigated. The phase composition and the microstructure of the matrix of low-carbon MgO - C brick containing Ti （ C, N） were studied by XRD and SEM analysis together with EDS. The results showed that Ti （ C, N） distributed in the matrix of lowcarbon MgO - C brick uniformly after being treated at 1 600 ~C for 3 h in coke powder bed, and Ti （C, N） and MgO formed a solid solution. After the treatment at 1 600 ℃ for 3 h in coke powder bed, the bulk density and cold crushing strength of low-carbon MgO - C brick with Ti （ C, N） decreased, and the apparent porosity and linear change rate of specimens increased. The oxidation resistance of low-carbon MgO - C brick with Ti（ C, N） was superior to that of low-carbon MgO - C brick with no additives, but inferior to that of low-car- bon MgO - C brick with Al powder. The slag resistance of the specimen with Ti （ C, N） was excellent as well.     

Hydroisomerization of model FCC naphtha over sulfided Co(Ni)–Mo(W)/MCM-41 catalysts

Deep hydrodesulfurization (HDS) of gasoline generally brings about the saturation of olefins and leads to the serious octane number losses. Conversion of linear olefins to branched ones followed by hydrogenation to isoalkanes would minimize such octane number losses. In this work, MCM-41-supported Co–Mo, Ni–Mo and Ni–W catalysts were prepared by the incipient wetness impregnation method, and compared with an industrial Co–Mo/γ-Al₂O₃ catalyst. The surface acidities were measured by the techniques of microcalorimetry and infrared spectroscopy for the adsorption of ammonia, and probed by the reaction of conversion of isopropanol. The isomerization and hydrogenation of 1-hexene as well as the HDS of thiophene were studied by using model FCC naphtha. It was found that the sulfidation enhanced significantly the surface Brønsted acidity that favored the skeletal isomerization of 1-hexene under the HDS conditions. Since the isomerization and hydrogenation of 1-hexene are the two competition reactions, the catalysts with relatively lower hydrogenation activity may have higher selectivity to the isomerization reactions. The Co–Mo/MCM-41 showed the high selectivity to the skeletal isomerization reactions due to its strong surface Brønsted acidity and the relatively low hydrogenation activity. On the other hand, the Ni–Mo/MCM-41 exhibited high hydrogenation activity and therefore low selectivity to the isomerization reactions although it possessed quite strong surface Brønsted acidity. The Ni–W/MCM-41 exhibited the low activity for the HDS of thiophene and isomerization of 1-hexene due to the poor dispersion of active metals.     

Ti(C,N)基金属陶瓷的研究进展

介绍了Ti（C，N）基金属陶瓷的基本组成和结构，综述了Ti（C，N）基金属陶瓷的研究现状，指出了未来的发展方向和应用。     

WC含量对Ti(C,N)基金属陶瓷组织和性能的影响研究

用传统的粉末冶金方法制备了不同WC含量的超细Ti(C,N)基金属陶瓷试样,运用SEM,EDX等手段对材料的显微组织进行了表征分析,并用这些显微组织的特征和差异解释了材料宏观力学性能的特点.结果表明,金属陶瓷的组织为典型的两相结构特征,其中陶瓷相的芯、壳结构(core/timstructure)与溶解析出机制有关.少量WC的加入能提高材料的力学性能.断口SEM分析表明:断裂机理为典型的混合型断裂(穿晶断裂和沿晶断裂),金属相存在着明显撕裂的痕迹.     

In situ reaction and solid solution induced hardening in (Ti,Zr)B2-(Zr,Ti)C composites

(Ti,Zr)B₂ - (Zr,Ti)C ceramics were synthesized by reactive hot-pressing and solid solution coupling effect using ZrB₂ and TiC powders as starting materials. Effects of sintering temperature on phase relations, microstructure and mechanical properties were reported. The equimolar ZrB₂ and TiC reactants ensured a complete in situ reaction to form (Ti,Zr)B₂ and (Zr,Ti)C solid solutions. The (Ti,Zr)B₂ - (Zr,Ti)C composite sintered at 1750°C was fully densified, and exhibited a high hardness of 29.1 GPa due to fine-grain hardening and solid solution hardening. The optimized comprehensive mechanical properties such as a hardness of 27.9 GPa, a strength of 705 MPa and an indentation fracture toughness of 5.3 MPa m^1/2 were achieved in (Ti,Zr)B₂ - (Zr,Ti)C composites sintered at 1800°C for 1 hour.     

碳氮化钛对低碳镁碳砖性能的影响

研究了碳氮化钛加入到低碳镁碳砖中对其性能的影响,并采用XRD物相分析、SEM显微分析研究了碳氮化钛对低碳镁碳砖基质部分烧后性能的影响。结果表明:镁碳砖基质部分经1600℃3h埋炭处理后,碳氮化钛仍均匀分布在基质中,并和MgO发生一定程度的固溶;加有碳氮化钛的镁碳砖经1600℃3h埋炭处理后,体积密度有所降低,气孔率升高,线膨胀率增大,常温耐压强度有所减小;碳氮化钛对镁碳材料的抗氧化性有所改善,但不及传统的金属铝粉;材料同样表现出良好的抗渣性。     

Fabrication of in-situ Ti(C,N) phase toughened Al2O3 based ceramics from natural bauxite

Al₂O₃–Ti(C,N) ceramics were fabricated via carbothermal reduction nitridation method with high-titania special-grade bauxite as the raw material. The formation mechanism of in-situ Ti(C,N) phase and its effect on the properties of materials are discussed. After nitrided at 1700 °C, Ti(C,N) phase could be formed in-situ with appropriate C/TiO₂ molar ratio. Due to the residual stress field formed by Ti(C,N) particles, the path of crack propagation is changed, leading to the crack deflection and pinning. Therefore, the mechanical properties of the materials are improved by forming in-situ Ti(C,N) phase. With a C/TiO₂ molar ratio of 2.2 and nitridation temperature of 1700 °C, Al₂O₃–Ti(C,N) ceramic with a hardness of 13.9 GPa, a fracture toughness of 8.28 MPa m^1/2 and a flexural strength of 387 MPa could be fabricated.     

Spark plasma sintering of LaB6-(Ti,Zr)B2 composites

The LaB₆-(Ti_, Zr)B₂ composite was fabricated from LaB₆, TiB₂ and ZrB₂ powders by spark plasma sintering (SPS) at 1600–1900°C holding for 5?min under 40?MPa. The densification behaviour, microstructure, mechanical properties were investigated. The complete solid solution phase of (Ti, Zr)B₂ was identified. The morphologies of LaB₆ and (Ti, Zr)B₂ grains were equiaxed and elongated, respectively. The highest relative density of 98.43% and Vickers hardness of 19.56?GPa were obtained at 1900°C. The fracture toughness of 4.43?MPa?m^1/2 was obtained at 1800°C.     

Microstructure and mechanical properties of hot-pressed SiC/(W,Ti)C ceramic composites

SiC/(W, Ti)C ceramic composites with different content of (W, Ti)C solid-solution were produced by hot pressing. The effect of (W, Ti)C content on the microstructure and mechanical properties of SiC/(W, Ti)C ceramic composites has been studied. Densification rates of the SiC/(W, Ti)C ceramic composites were found to be affected by addition of (W, Ti)C. Increasing (W, Ti)C content led to increase the densification rates of the composites. The sintering temperature was lowered from 2100 °C for monolithic SiC to 1900 °C for the SiC/(W, Ti)C composites. Results show that additions of (W, Ti)C to SiC matrix resulted in improved mechanical properties compared to pure SiC ceramic. The fracture toughness and flexural strength continuously increased with increasing (W, Ti)C content up to 60 vol.%, while the hardness decreased with increasing (W, Ti)C content.