Adsorption-chemical activity of finely-dispersed amorphous powders of brown and black boron used in synthesizing metal borides

Kinetic features of adsorption-desorption processes for a nitrogen and oxygen mixture of gases, nitrogen and water vapor at the surface of finely-dispersed amorphous powders of brown and black boron used to synthesize metal borides are studied. The different adsorption-chemical activity of amorphous brown and black boron powders towards the main components of an air atmosphere is determined. It is shown that the original boron, apart from hard impurity compounds, may carry at the surface gaseous constituents with a capacity to change the physicochemical parameters of the system in the reaction zone, and to affect the phase composition and quality of the product obtained. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 79–84, May–June, 2006.     

Effect of lanthanum hydride on microstructures and hydrogen storage performances of 2LiNHe-MgH2 system

Hydrogen storage properties of 2LiNH2-MgH2 system were improved by adding lanthanum hydride （LaH3）, and the role of LaH3 in hydrogen sorption process of Li-Mg-N-H system was investigated. Temperature programmed sorption results showed that the addition of lanthanum hydride reduced the dehydriding/hydriding onset temperature of 2LiNH2-MgH2 system by at least 15 K. Moreover, A 0.053 wt.%/min average rate was determined for the hydrogen desorption of 2LiNH2-MgH2-0.05LaH3 composite, while it was only 0.035 wt.%/min for 2LiNH2-MgH2 system. Hydrogen absorption capacity increased from 1.62 wt.% to 2.12 wt.% within 200 min by adding LaH3 into 2LiNH2-MgH2 system at 383 K. In the dehydrogenation of 2LiNH2-MgH2-0.05LaH3 composite, LaH2 transferred to LaN phase, which reversed to LaH2 in the following hydrogen adsorption process. The reversible reaction of LaH2 ef- fectively promoted the hydrogen sorption of Li-Mg-N-H system. Moreover, the homogenous distribution of fine La hydride was fa- vorable to improving effect of lanthanum hydride.     

Sintered ceramics based on boron nitride and carbide

The formation of BN-B₄C composite materials by sintering in nitrogen is investigated. Structural, mechanical, and chemical characteristics of these materials are examined. Excellent dielectric properties, thermal and chemical stability, and erosion resistance in high-intensity laser beams enable high-temperature application of BN-B₄C composite materials. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 58–63, 2007.     

Structure and high-temperature strength of composite materials based on boron nitride

The structure and physicomechanical properties of composite materials based on boron nitride within which new phases (mullite and sialon) form during hot compaction are studied. It is established that the microstructure of composites is specified by their texture formation caused by the crystal morphology of boron nitride particles and it is almost independent of composite phase composition. It is shown that the main factor that affects strength is porosity. The dependence of strength on porosity is exponential in character. The strength of boron nitride-mullite and boron nitride-sialon composites is 110–140 MPa and at 20–1200°C it is almost unchanged. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 33–39, May–June, 2006.     

氢化钛粉颗粒的粉碎及机理研究

本文采用闭环气流磨系统对氢化后得到的粗颗粒氢化钛粉进行粉碎,利用扫描电子显微镜和粒度分析技术对结果进行表征,并对闭环气流磨的粉碎机理进行了讨论。结果表明,对粗颗粒氢化钛粉进行闭环气流磨粉碎,克服了氢化脱氢法(hydrogenation dehydrogenation,HDH)制备的钛粉存在的粒度不均匀、粒度分布较宽等品质问题;其粉碎机理可总结为,经多股高速高压氩气流冲击、打磨,粉末颗粒自身相互碰撞、摩擦,以及粉末颗粒与磨料腔腔壁、分级轮的碰撞,粗颗粒氢化钛粉从大颗粒粉碎成细小颗粒。     

氢化钛的动态分解行为与规律

通过DSC/TG的热分析试验,研究氢化钛升温过程中分解的动力学规律,利用Coast-Redfern积分法计算了分解过程的动力学参数。结果表明,氢化钛热分解的开始温度为510℃,分解过程中总质量损耗率达3.15%,其中565～660℃温度范围内的质量损耗率占总质量损失的50%左右,分解过程中生成了比氢化钛热稳定性更高的TiHx(0.7相似文献   

氢化钛氧化处理及其热分解行为

在大气条件下进行氢化钛的氧化处理试验,利用扫描电镜和X射线衍射仪研究氧化处理后氢化钛的形貌与相组成,通过TG/DSC热分析,研究氧化处理对氢化钛热分解行为的影响规律。结果表明,氧化处理后氢化钛颗粒形貌无明显变化,随温度升高和时间延长,其颜色经历了灰黑色—蓝色—浅灰色的转变,且颗粒表面形成了Ti3O和TiO2的氧化物薄膜。与此同时,随氧化处理温度升高和时间延长,氢化钛热分解的质量损失率降低,但氢化钛的热分解温度显著提高,以AlSi12合金为基体,应用粉末冶金法制备泡沫铝,其氢化钛的氧化处理工艺为480℃/1h。     

六方氮化硼填充导热树脂复合材料的研究进展

总结了电气电子领域使用的六方氮化硼(hexagonal boron nitride,h BN)导热填料制备方法,介绍了近几年h BN填充树脂基复合材料的研究进展,研究了导热树脂复合材料的导热机理和导热模型,讨论了h BN填料的形貌、粒度、颗粒复配及表面改性方法等因素对材料导热性能的影响,并对h BN填充高导热树脂复合材料的发展方向进行了展望。     

一种氢燃料电池汽车用新型储氢材料--NaAlH4的研究进展

铝氢化钠(NaAlH4)在加入掺杂剂时能在低于100℃下可逆吸/放大量氢气(目前氢的质量分数可达4.5%),且价廉易得,非常适用于作车用氢燃料电池上的储氢材料.本文介绍了NaAlH4储氢的基本原理、国外NaAlH4储氢的研究进展.并根据目前的研究现状提出了为提高可逆储氢质量分数,加快吸/放氢速率所需进一步开展的工作.     

Effects of dispersal and mechanical boron alloying on the thermal stability of hydride phases in the Ti-B-H system

Methods have been applied from scanning electron microscopy, hydrogen thermal desorption, XRD, and differential thermal analysis on the effects of grain size and alloying with boron as regards the thermal stability and decomposition temperatures of hydride phases in mechanical alloys in the Ti-B-H system. The alloys were prepared by high-energy processing for 50 h in a planetary ball mill with mixtures of TiH_1.9 + 9 mass% B + 13 mass% Ti and also with TiH_1.9 + 50 mass% TiB₂ at speeds of 1000 rpm, in addition to mixtures of TiH_1.9 + 40 mass% B and TiH_1.9 + 50 mass% TiB₂, which were treated for 20 min at speeds of 1680 rpm. The dispersal on mechanical treatment and the addition of boron to the titanium hydride powder have substantial effects on the thermal stability. The processing of the mixture TiH_1.9 + 9 mass% B + 13 mass% Ti lasting 50 h in argon gave temperatures for the dissociation of the Ti(B, H)_x hydride phase in the mechanical alloy lower by 300 deg than the decomposition temperature for the initial titanium hydride TiH_1.9. The mechanisms have been identified for the effects of the dispersal and boron alloying on the thermal stability of the titanium hydride.     

Synthesis, heat resistance, and optical properties of boron silicide and materials based on it

Conditions of synthesis from elements of pure superfine powder of boron silicide B₄Si are investigated. It is shown that the silicide phase forms on boron particles and B₄Si particles inherit the shape and size of initial boron particles, which makes it possible to control the particle size of the powder obtained. The oxidation of pure boron silicide and materials based on it in air and their optical properties are studied. It is shown that chromium diboride added to boron silicide increases the oxidation resistance of B₄Si and hardly decreases its absorbance. The B₄Si-CrB₂ material can be successfully introduced into the compositions of heat-protective coatings operating in air at 1300 °C. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 45–52, 2007.     

Obtaining the Ni-TiC composite powder by the carbidization of titanium nickelide

The goal of this study is to investigate the mechanism and kinetics of carbidization of the titanium nickelide powder, which allows one to obtain the Ni-TiC composite powder. It is established by experimental methods and theoretical analysis that, in the temperature range 1000–1200°C, this process proceeds in the internal mode with the decomposition of NiTi and with the formation of a nickel-based solid solution with dispersed titanium carbide particles distributed in it. It is shown that, with the carbon excess in the starting charge, the final product consists of a nickel matrix, including ～3 at % carbon and traces of titanium, and particles of almost stoichiometric titanium carbide. With the deficiency of carbon in the starting charge, the Ni matrix contains ～1.1 × 10^?2 at % carbon and >0.65 at % titanium, while the particles of titanium carbide have the composition TiC_0.5-TiC_0.8. The suggested model of this process allows one to evaluate the time that the NiTi particles completely decompose and qualitatively describe the time dependence of the particle size of titanium carbide.     

Dependence of the Structure of Sintered Boron Carbonitride on the Defect Level in the Starting BN Powder

We have carried out a comparative x-ray analysis of boron nitride powders with different degrees of ordering and sintered specimens of boron carbonitride based on such powders. We have established that an indicator of sintering activity for the boron carbonitride specimens is the rate of formation of the r-BN phase, the content of which depends on the degree of ordering of the starting BN powder. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 100–107, May–June, 2005.     

Effect the Actual Structure of Boron and Catalytic Additions on Boron Nitride Synthesis

The bahavior of boron with different degrees of purity, fineness, and crystal structure perfection during nitriding at high temperature is studied by electron microscopy, x-ray diffraction, and chemical analysis. The effect of additives (Li₂CO₃, H₃BO₃, and NH₄Cl) on boron nitride synthesis is studied. A marked reduction is established in the temperature for forming a highly-ordered boron nitride structure on introducing additives. The chemistry of the amorphizing effect of ammonium chloride on the crystal structure of boron is suggested.     

含硼生铁冶炼硼钢新工艺及其硼钢性能研究

含硼生铁是高炉火法分离硼铁矿提取硼时(富硼渣,w(B_2O_3)≥12%)产生的另一种重要产品.研究了以此为原料直接冶炼硼钢的新工艺及硼钢试样的力学性能,结果表明:采用预脱硫、脱硅处理得到含硼半钢再冶炼硼钢的新工艺,其S、P等杂质含量均能满足硼钢标准要求,而最关键的B含量(质量分数)也可控制在0.0005%～0.0035%,即硼钢要求的标准范围;其硼钢试样材料的拉伸、冲击韧性等力学性能指标优于20Mn2、15MnVB,而与40MnB、45MnB结构合金硼钢相当;通过冶炼后期控制其它合金化成分,能达到国标GB/T 3077-1999中相近成分的硼钢性能.     

废旧镍氢电池负极板中稀土的回收

采用湿法冶金工艺,回收废旧镍氢电池负极板中的稀土（RE）元素,用硫酸浸出负极板中的有价金属,分析硫酸浓度、浸出温度、浸出时间等因素对稀土元素浸出率的影响,在硫酸浓度为2.0 mol/L、浸出温度为60℃、浸出时间120 min下,RE的浸出率为92.31%.采用磷酸二异辛酯（P204）为萃取剂萃取浸出液中的稀土,当P204在煤油中的比率为20%时,萃取率为92.86%.用硫酸钠沉淀溶液中的稀土,浸出液中稀土元素回收率可达98.78%.采用XRD和SEM分析表征回收的稀土氧化物的物相和表面形貌,结果表明,回收产物为铈系稀土氧化物,为立方晶系,呈面心立方结构,表面形貌为棱柱形.     

碳化硼陶瓷力学性能及其影响因素

碳化硼的力学性能与其他陶瓷材料一样,对结构十分敏感.在工艺控制过程上看,不可能制得结构完全相同的材料,文献报道的计算式和数据亦非常分散.作者测定了用热压方法制得的碳化硼陶瓷(表现密度为2.1～2.3g/cm~3,晶粒度为12μm)的抗弯强度、抗压强度、弹性(弯曲)模量和泊松比.同时,通过文献检索,搜集了各种公式和数据,并对本实验结果进行了综合分析,得出了有关的计算式和性能值.     

45B含硼钢裂纹成因分析及改进

分析了45B含硼钢裂纹产生的原因,主要是在炼钢工序和由于在钢水中B和N结合生成BN而产生的。通过采取降低钢水中N含量和调整冷却制度以及保证铸机设备精度等措施可以有效地降低45B含硼钢裂纹的产生。     

Sintering Densification and Microstructure Formation Kinetics in Silicon Nitride Ceramics

Research has been done on how the shrinkage rate and microstructure in the Si₃N₄ Al₂O₃ Y₂O₃ are dependent on temperature and nitrogen pressure during sintering. The shrinkage rate curves alter as the activator content varies. Additional densification may occur above 1800°C because of diffusion through the increased amount of liquid.     

氢化物发生—原子荧光光谱法测定铜精矿中砷和锑

研究了用氢化物发生 -原子荧光光谱法测定铜精矿中的砷和锑 ,选择了氢化物发生 -原子荧光光谱法测定砷、锑的最佳条件。方法准确度高、结果稳定、操作简便,适用于铜精矿中0.001%～2.5%砷、0.001%～0.5%锑的测定