电弧放电等离子体法合成立方相氮化铬纳米粉

采用电弧放电等离子体方法,通过金属铬和氮气的直接反应合成了粒度小于10nm的纯立方相氮化铬（CrN）纳米粉.利用X射线衍射分析（XRD）、透射电镜(TEM)和傅立叶变换红外光谱（FT-IR）对不同氮气压下形成的产物进行了表征.研究了氮气压和氨气的加入对形成立方相CrN纳米晶的影响.研究结果表明：相对较低的N₂气压(5~20kPa) 有利于金属Cr向立方CrN的转化,可以使更多的氮原子结合到金属Cr的格子中去;活性氮源（氨气）的加入降低了金属Cr的氮化.     

金属氮化物富勒烯的研究现状

内嵌金属氮化物簇富勒烯的发现极大地扩展了内嵌富勒烯家族。内嵌金属氮化物富勒烯是一类将含有金属原子的氮化物(Mx-N,AxM3-x-N)包裹在富勒烯碳笼中的化合物,因其具有独特的分子结构和性质而受到人们广泛的研究和关注。阐述了合成金属氮化物富勒烯的方法,着重介绍了电弧法,探讨了氮源对电弧法合成金属氮化物富勒烯产量的影响,介绍了金属氮化物富勒烯常用的分离提纯方法,最后讨论了金属氮化物富勒烯的结构特点、性质和潜在应用。     

Nb和N2在球磨过程中的固—气反应

利用改装后可充一定压力气体的球磨罐,装入一定量的高纯金属,经抽真空后充入一定压力的氮气,在室温下进行球磨产生固－气反应制备出金属氮化物的超细微粒,以金属铌为例,用XRD和TEM分别对生成物的晶粒尺度和相结合进行了分析测量,从热力学讨论了金属氮化的形成机制,在固－气反应中氮气分子在金属清洁表面的化学吸附起着重要作用,球磨过程中产生的大量缺陷对金属－氮气的反应有重要影响。     

自蔓燃高温合成工艺参数对制备氮化硅粉体的影响

采用自蔓燃高温合成方法(SHS)合成氮化硅粉体,借助于XRD、SEM等检测方法,分析了自蔓燃高温合成氮化硅过程中氮气、温度、稀释剂与孔隙率等工艺参数对合成产物的影响。结果表明:只要最高燃烧温度不高于相应氮气压力下Si3N4的热分解温度,就可以用SHS方法合成Si3N4;氮气压力下硅粉的自蔓燃合成反应,必须要引入Si3N4稀释剂来控制反应温度,获得高α相Si3N4含量的粉体。压坯气孔率控制在30%～70%,否则反应不能进行。SHS法可以制备纯度很高的氮化硅粉体。     

金属氮化物合成方法的研究进展

介绍了近年来金属氮化物的5种主要合成方法：程序升温法、热分解法、固态反应法、电化学法和球磨制备法，着重阐述了每种合成方法的研究现状及其优缺点，并对金属氮化物合成方法的发展前号进行了展望，认为开发工艺简单、操作条件温和、氮化产物成本低廉、产物结构易于控制的合成方法是未来发展的必然趋势。     

自蔓延高温合成结合铸造技术制备复合材料的研究

将自蔓延高温合成(SHS)、粉末冶金与铸造工艺结合的复合材料制备方法,可以制备出表面层厚3～20 mm的材料.其过程是将选配好的反应物料压制成块并将其粘在型腔内或直接将混合均匀后反应物料粉体粘接在所需部位,用熔融金属液浇注并引发SHS反应,同时金属液浸透反应后的毛细孔隙,自然凝固并与母材金属结为一体,在所需表面原位合成金属-陶瓷复合层.     

由硝酸盐尿素配合物前驱体制备过渡金属氮化物粉体的研究

采用硝酸盐尿素配合物为原料,在氨气中氮化,制备了氮化铬(CrN)和氮化铁(ζ-Fe₂N)粉体.结果表明该配合物是一种有用的前驱体,可用于制备其它过渡金属氮化物.采用红外光谱(FTIR),热分析(TG-DSC)等方法对硝酸盐尿素配合物的性质进行了表征.在配合物分子中,尿素取代了结晶水的位置,与金属离子通过氧原子形成配位键(C=O→M),在加热时分解形成多孔隙的氧化物颗粒聚集体,并与氨气发生气固反应,生成过渡金属氮化物.对不同反应温度和反应时间合成的粉体用X射线衍射(XRD)和扫描电镜(SEM)进行了表征.研究了反应温度和反应时间对不同金属的硝酸盐尿素配合物在氨气中氮化反应的影响,结果表明Fe[OC(NH₂)₂]₆(NO₃)₃转变成ζ-Fe₂N的反应速度快,反应温度低,Cr[OC(NH₂)₂]₆(NO₃)₃完全转变成CrN则需要较长的反应时间.     

立方 TaN纳米粉的制备

采用直流电弧法使金属钽和氮气直接反应制备出了TaN纳米粉.利用XRD、XPS、TEM等测试方法对所制备的TaN纳米粉进行了表征.结果表明：所制备的纳米粉为单一的立方相TaN,纳米颗粒的平均粒度为5～10nm.实验中还发现氮气的气压对制备纯立方相TaN具有关键性作用,并讨论了立方相TaN的形成机理.     

燃烧合成氮化物陶瓷基复合材料

氮化物陶瓷是应用广泛的特种陶瓷，但传统的氮化物陶瓷烧结方法极为消耗能源、生产周期长、成本高。为降低成本、能耗，采用燃烧合成工艺制备氮化物陶瓷基复合材料，包括氮化钛和六方氮化硼，燃烧合成工艺利用单质元素与氮气反应合成氮化物。研究结果表明：压坏与80MPa N2反应燃烧合成TiN制件致密度约75％，压坯为添加了TiN稀释剂和适量氧化铝的钛粉，压坯孔隙率45％；燃烧合成纯BN制件致密度为68％，BN基制件致密度为78％，压坯为添加了h-BN稀释剂或SiO2添加剂的B粉压坯与80MPa N2反应合成，压坯孔隙率48％；在材料体系中，稀释剂起减小晶粒尺寸和降低燃烧温度的作用，而Al2O3和SiO3添加剂则起提高强度和相对密度的作用。     

自蔓燃高温合成法合成氮化硅粉体的研究

采用自蔓燃高温合成方法合成β-氮化硅粉体,分析了合成氮化硅过程中氮气、温度、稀释剂与孔隙率等方面的影响。采用XRD研究相的组成,用SEM观察粉末的显微结构。研究结果表明:自蔓燃合成方法制备的氮化硅陶瓷粉体,β相含量由块状产物中心向表层减少,得到的β-氮化硅晶体结构完整,表面光滑无缺陷,考虑到燃烧温度(Tcom),在氮化硅粉体的合成过程中,涉及到3个反应机制:低温机制、中温机制、高温机制。NH4Cl在反应中分解,为反应提供了NH3,并与硅粉反应;氮气压力下硅粉的自蔓燃合成反应,必须要引入Si3N4稀释剂来控制反应温度和反应速度,获得不同相含量的粉体;压坯气孔率控制在30%～70%,否则反应不能进行。     

Synthesis and characterization of a binary noble metal nitride

There has been considerable interest in the synthesis of new nitrides because of their technological and fundamental importance. Although numerous metals react with nitrogen there are no known binary nitrides of the noble metals. We report the discovery and characterization of platinum nitride (PtN), the first binary nitride of the noble metals group. This compound can be formed above 45-50 GPa and temperatures exceeding 2,000 K, and is stable after quenching to room pressure and temperature. It is characterized by a very high Raman-scattering cross-section with easily observed second- and third-order Raman bands. Synchrotron X-ray diffraction shows that the new phase is cubic with a remarkably high bulk modulus of 372(+/-5) GPa.     

Synthesis,electron transport properties of transition metal nitrides and applications

To understand the electron transport properties of transition metal nitrides (MN), electronic structure relationship between metal and corresponding nitrides is important. In binary nitrides, when nitrogen atoms occupy interstitial sites of metal lattice, volume expansion started initially without changing structure of metal lattice. Above certain concentration of nitrogen into interstitial sites of lattice, the system starts stabilizing its energy to minimum that in turn changes to another crystal structure. The chemical bonding in MN is due to the mixing of d-orbitals of M and p-orbitals of N. This is confirmed theoretically and experimentally such as X-ray photoelectron spectroscopy. The Fermi energy is generally lowered by the introduction of vacancies. However, reports on the particle size effect in the electrical resistivity of nitrides are scanty. One reason is that the role of the particle size in resistivity is difficult to determine because there is a need to understand N concentration. It poses a challenge to the synthesis of nanostructured transition metal nitrides. The transition metal binary nitrides show unusual electron transport, optical and magnetic properties as compared to their metal counterparts. Electronic properties of all transition metal nitrides known till date are discussed. Different ways of synthesis of nitrides and their applications are mentioned.     

Fundamental aspects and recent advances in transition metal nitrides as electrocatalysts for hydrogen evolution reaction: A review

With increasing human population, sustainable energy production has become one of the most persistent and significant problems of the current century. Hydrogen is considered to be the best clean fuel for future energy requirements. As a substitute of fossil fuels, hydrogen is readily provided by an electrocatalytic hydrogen evolution reaction that splits water molecules. Conventional electrocatalysts based on noble metals are scarce and considerably expensive for large-scale hydrogen production, necessitating the search for low-cost earth abundant alternatives. In this context, transition metal nitrides have gained considerable attention as competent electrocatalytic materials for water splitting. This review presents recent advancements and progress on transition metal nitrides as efficient and cost-effective electrocatalysts for hydrogen production. After overviewing the fundamental aspects of the hydrogen evolution reaction (HER), the review discusses various synthetic strategies for developing transition metal nitrides. Discussed herein are titanium nitrides, vanadium nitrides, iron nitrides, nickel nitrides, molybdenum nitrides, tungsten nitrides, and their composite electrocatalysts employed in HER applications. Some design viewpoints for improving the electrocatalytic activity are systematically proposed. Finally, the review discusses challenges and future perspectives for the advancement of non-noble metal-based electrocatalysts.     

稀土氮化物ScN、YN微晶的制备与表征

利用直流电弧等离子体方法制备出稀土氮化物ScN、YN微晶, 这是一种快速、低成本、高产量的新方法, 可用来制备稀土金属氮化物。结构物性表征和能谱成分分析结果表明, 所制备的ScN晶体为满足化学计量比的单晶, 而YN晶体为非化学计量比的多晶, 其中Y的含量高于N。综合XRD、EDS、HRTEM和PL结果分析表明, YN晶体主要由大量随机取向的单晶颗粒组成, 单晶颗粒间分布着一些非晶的金属Y, 光谱结果分析表明YN中存在大量的N空位。此外, 对样品的微观结构形成机理进行了系统分析, 由于Y族金属氮化物中有限组分较高的解离压力以及产物在生长过程中经历较高的淬火速率(10³ K/s), 导致YN解离而形成的Y金属团簇的无序排列, 进而使其在冷却过程中形成了非晶结构。     

APPLICATION OF CERAMIC COATING BASED ON SILICON AND BORON NITRIDES USING A VACUUM ELECTRIC-ARC METHOD

The paper describes a modern method of applying coatings with a vacuum electric-arc using plasma accelerators. Coatings form from high-energy ion flows by direct synthesis reactions. An attractive feature of this process is that a number of ceramic coatings such as refractory metals nitrides and carbides can be obtained at relatively low substrate temperatures (300 - 400^°C). Furthermore, multi-component ion flows can be used to obtain composites from these ceramic deposits. The paper investigates of processes to apply coatings containing boron and silicon nitrides. The investigation of these processes to apply coatings containing boron and silicon nitrides is also of considerable interest, but has been less extensively developed.     

Synthesis of cubic zirconium and hafnium nitride having Th3P4 structure

High-pressure synthesis is a powerful method for the preparation of novel materials with high elastic moduli and hardness. Additionally, such materials may exhibit interesting thermal, optoelectronic, semiconductuing, magnetic or superconducting properties. Here, we report on the high-pressure synthesis of zirconium and hafnium nitrides with the stoichiometry M3N4, where M = Zr, Hf. Synthesis experiments were performed in a laser-heated diamond anvil cell at pressures up to 18 GPa and temperatures up to 3,000 K. We observed formation of cubic Zr3N4 and Hf3N4 (c-M3N4) with a Th3P4-structure, where M-cations are eightfold coordinated by N anions. The c-M3N4 phases are the first binary nitrides with such a high coordination number. Both compounds exhibit high bulk moduli around 250 GPa, which indicates high hardness. Moreover, the new nitrides, c-Zr3N4 and c-Hf3N4, may be the first members of a larger group of transition metal and/or lanthanide nitrides with interesting ferromagnetic or superconducting behaviour.     

Electrical properties of high-temperature oxides,borides, carbides,and nitrides

High-temperature materials including oxides, borides, carbides, and nitrides encompass all types of conductors: metallic, semiconducting, and ionic. Their electrical conductivities are generally very sensitive to impurities regardless of the type of conductor. For large band-gap materials, which includes most of the oxides, the conductivities at low temperatures are frequently dominated by impurities or dopants, and intrinsic conduction only becomes significant above a temperature which depends largely on the level of dopant, the band gap and the defect structure of the base material. The borides, carbides, and nitrides of transition metals are metallic conductors with conductivities and temperature coefficients of resistivity comparable to that of their parent metals.     

Ion bombardment of group IV elemental metal and synthetic nitride films

A novel “hot rod” r.f. sputter deposition system was used to obtain high purity metal and metal nitride films of Group IV transition metals. Films of zirconium and hafnium nitrides were also produced by nitrogen ion implantation. The films were characterized by Rutherford backscattering analysis and other techniques. Samples of all three metals and their nitrides were bombarded with 40 keV deuterium ions and examined by scanning electron microscopy to indicate their resistance to light ion bombardment.     

Tribological properties of carbonitride coatings formed on titanium by thermodiffusion carbonitriding

We have studied the tribological properties of VT14 titanium alloy with carbonitride coatings formed by the contact and noncontact method and binary (oxide and nitride) coatings. In the case of the contact method, specimens are saturated in a graphite backfill, and in the case of the noncontact method, specimens are located above it. We have investigated the wear resistance of a “titanium disk–bronze block” friction pair in AMH-10 hydraulic fluid under a load to 3 MPa on a friction path to 15 km. It has been established that coatings based on ternary interstitial compounds (titanium carbonitrides) provide a higher wear resistance than that of coatings based on binary interstitial compounds (titanium nitrides and oxides).     

Effect of piezoelectric polarization on phonon group velocity in nitride wurtzites

We have investigated the effect of piezoelectric (PZ) polarization property on group velocity of phonons in binary as well as in ternary wurtzite nitrides. It is found that with the presence of PZ polarization property, the phonon group velocity is modified. The change in phonon group velocity due to PZ polarization effect directly depends on piezoelectric tensor value. Using different piezoelectric tensor values recommended by different workers in the literature, percent change in group velocities of phonons has been estimated. The Debye temperatures and frequencies of binary nitrides GaN, AlN, and InN are also calculated using the modified group velocities. For ternary nitrides Al _x Ga_(1−x)N, In _x Ga_(1−x)N, and In _x Al_(1−x)N, the phonon group velocities have been calculated as a functions of composition. A small positive bowing is observed in phonon group velocities of ternary alloys. Percent variations in phonon group velocities are also calculated for a straightforward comparison among ternary nitrides. The results are expected to show a change in phonon relaxation rates and thermal conductivity of III-nitrides when piezoelectric polarization property is taken into account.