Mg粉粒度对MgB_2超导体宏观特征和显微结构的影响

研究了Mg粉粒度对MgB2超导体宏观特征和显微结构的影响规律。将不同粒度的Mg粉和B粉分别按1.03∶2的比例混合、压制成型后,在流通高纯氩气的条件下于800℃烧结1h,制备出MgB2块材。利用阿基米德方法、X射线衍射仪和扫描电子显微镜等分别测试样品的密度、物相组成和显微结构等。结果表明,Mg粉粒度对MgB2超导体的物相组成没有影响;随着Mg粉粒度的增加,MgB2超导体的最大气孔尺寸、质量损失率、体积膨胀系数都逐渐增大,但其密度逐渐降低。

Mg粉和Ni粉固相扩散—溶解的研究

研究了Mg粉和Ni粉固相扩散、溶解形成Mg-Ni金属间化合物和层片状共晶组织的过程。研究发现,Mg粉和Ni粉在成形后,于一定的烧结条件下发生扩散和溶解,形成了Mg_2Ni和MgNi_2金属间化合物;经过360℃烧结、保温50h,Mg粉和Ni粉反应形成了层片状共晶类组织。

Mg粉添加量对泡沫铝发泡行为的影响

利用粉末冶金法制备不同Mg粉添加量的纯铝闭孔泡沫铝材料,并对Mg粉添加量对泡沫铝发泡行为及泡沫稳定性的影响进行研究。结果表明:Mg粉的添加导致前驱体膨胀率的显著增大和泡沫体泡孔结构的均匀化;添加的Mg粉同空气雾化Al粉表面的Al2O3反应,生成同铝熔体有良好润湿性的MgAl2O4相,打破原有铝粉表面的氧化物结构,生成的MgAl2O4相均匀地分布于泡孔的布拉德边界和泡壁上;润湿性MgAl2O4相的出现增加熔体的表观黏度,大大减弱重力排液、毛细作用和气泡流动带来的负面影响,从而提高泡沫的稳定性;在空气雾化工业纯Al粉含氧量(质量分数)为(0.34±0.01)%和Mg粉添加量为(0.6%～1.0)%的条件下,可以获得最佳的膨胀率和均匀的泡孔结构。

杉木1.5代种子园喷施MG粉效果分析

1989—1990年在杉木1.5代种子园进行MG粉剂喷施试验,结果表明,喷施MG粉可使种子产量增加75%以上,球果产量、出籽率及饱满籽率有所提高,种子品质也有改善;大、小年平均产投比为3.0∶1。而结合人工投粉喷施MG粉有可能刊用一般配合力高的花粉改善种子的遗传品质,效益更加显著。

MG满果粉喷施时间偏迟的效果分析

MG粉以试验对象开始开花时喷施为最理想,但在对东谭杉木种子园进行的丰产试验中,两个年度的喷施时间分别为开花末期和开花终期,仍能取得明显的增产效果,喷施比对照的雌花座果率提高15.5％～18.7％,出籽率提高13.3％～54.5％,发芽率提高12％,种子园种子产量平均增产54.5％,投入产出比为1:4,经济效益显著。

粉末火箭发动机研究进展

新型粉末火箭是以颗粒形态燃料或氧化剂为主要推进工质,以少量流化气体为输送介质的火箭推进系统,具有推力可调、多脉冲工作的功能和结构简单、环境温度适应性强、工作可靠性高等性能优势,在近地空间开发、深空探测等领域具有深远的研究价值。本文针对粉末火箭发展历史及技术现状进行了概述分析,并以此梳理出粉末推进剂装填与改性、粉末供给输送、粉末喷注与燃烧等主要关键技术,并对包括冷态标定、常压点火以及样机试车等粉末火箭发动机系统研究过程进行了介绍,同时提出了高性能粉末推进剂研究、发动机低压点火、粉末输送分流与多点喷注、发动机系统控制、环境温度适应潜力等是粉末火箭发动机技术的发展方向。通过对粉末火箭发动机研究经验归纳整理,明确了粉末发动机自身工作特点与优势。

镁粉对含硼富燃料推进剂能量释放特性的影响

为考察辅助金属燃料Mg对含硼富燃料推进剂能量释放特性的影响,采用氧弹量热计分别测定了Mg、Al和Ti的燃烧热,以及相应含硼富燃料推进剂的爆热Qv和燃烧热Hv,计算得出了推进剂在燃烧过程中的三个能量释放效率ηc1、ηc2和ηB。结果表明,Mg通过自身的低耗氧、高放热提高了含硼富燃料推进剂的爆热,进而提高了一次燃烧温度,为硼粉燃烧营造了一个较合适的高温环境,促进了硼粉的燃烧,因而明显提高了含硼富燃料推进剂的ηc1、ηc2和ηB。因此,在含硼富燃料推进剂中,采用B+Mg的主辅燃料组合是较佳选择。

燃烧合成MgB_2超导材料

采用自蔓延及热爆两种燃烧模式合成了较纯的MgB2金属间化合物。用XRD和SEM对Mg-B体系燃烧合成产物进行了研究,结果表明,压坯压力越大合成产物越致密,孔隙明显减少,产物更加均匀,但过大的压坯压力,降低了体系的燃烧温度,影响Mg、B间的反应程度;而对于细小的Mg粒,Mg-B间充分反应产生较高的燃烧温度,导致MgB2分解出现MgB4,影响合成产物纯度。

Synthesis of (Ca, Mg)-α′-Sialon-AlN-BN powders from boron-rich blast furnace slag by microwave carbothermal reduction-nitridation

(Ca, Mg)-α′-Sialon-AlN-BN powders were synthesized by the carbothermal reduction and nitridation (CRN) method using boron-rich slag, one of the intermediate products from pyrometallurgy separation of pageit, as the staring material. The influences of synthesis temperature and holding time on the phase composition and microstructure during the microwave CRN were studied by XRD, SEM and EDS. The comparison between two heating techniques, conventional and microwave heating, on the synthesized powder was presented as well. The experimental results revealed that the phase compositions and microstructures of the synthesized products were greatly affected by the synthesis temperature and holding time. With an increase in the synthesis temperature or holding time, the relative amount of α′-Sialon increased and α′-Sialon became the main crystalline phase at 1400 °C for 6 h. The synthesized products also contained AlN, BN and a small amount of β-SiC. Elongated α′-Sialon grains, short rod AlN grains, aggregate nanoscale BN grains were observed in the synthesized powders. The reaction temperature of microwave heating method was reduced by 80 °C, the reaction time was shortened by 2 h, and more elongated α′-Sialon grains with large aspect ratio were observed.

Effects of addition of NH_4HCO_3 on pore characteristics and compressive properties of porous Ti-10%Mg composites

Porous Ti-Mg composites were successfully fabricated through powder metallurgy processing with ammonium hydrogen carbonate （NH4HCO3） as a space-holder. The effects of NH4HCO3 on properties of porous composites were comprehensively investigated. The pore characteristics and compressive properties of the specimens were characterized by X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. The results show that the porosity of the porous composites can be tailored effectively by changing the amount of NH4HCO3 added, and the use of NI-I4HCO3 has no influence on the microstructure and phase constituents of the Ti-10%Mg porous composites. The open porosity and compressive strength as well as compressive elastic modulus vary with the adding amount and particle size of NHaHCO3. When the mass fraction of NHaHCO3 added is 25%, elastic modulus and compressive strength of composites with porosity of around 50% are found to be similar to those of human bone.

Microstructural evolution and mechanical properties of an ultrahighstrength Al-Zn-Mg-Cu alloy via powder metallurgy and hot extrusion

In this work,a novel ultrahigh-strength Al-10Zn-3.5Mg-1.5Cu alloy was fabricated by powder metallurgy followed by hot extrusion.Investigations on microstructural evolution and mechanical properties of the fabricated samples were carried out.The results show that the grain size of sintered samples matches with the powder particles after ball milling.The relative densities of sintered and hot extruded samples reach 99.1%and 100%,respectively.Owing to the comprehensive mechanism of grain refinement,aging and dispersion strengthening,the ultimate tensile strength,yield strength and elongation of the Al-10Zn-3.5Mg-1.5Cu alloy after hot extrusion and subsequent heat treatment achieve 810 MPa,770 MPa and 8%,respectively.

Effect of Mg composition on sintering behaviors and mechanical properties of Al-Cu-Mg alloy

Al-3Cu-Mg alloy was fabricated by the powder metallurgy(P/M) processes. Air-atomized powders of each alloying element were blended with various Mg contents(0.5%, 1.5%, and 2.5%, mass fraction). The compaction pressure was selected to achieve the elastic deformation, local plastic deformation, and plastic deformation of powders, respectively, and the sintering temperatures for each composition were determined, where the liquid phase sintering of Cu is dominant. The microstructural analysis of sintered materials was performed using optical microscope(OM) and scanning electron microscope(SEM) to investigate the sintering behaviors and fracture characteristics. The transverse rupture strength(TRS) of sintered materials decreased with greater Mg content(Al-3Cu-2.5Mg). However, Al-3Cu-0.5Mg alloy exhibited moderate TRS but higher specific strength than Al-3Cu without Mg addition.

激光选区熔化沉积修复ZL101A航空铸铝零件的性能分析

为研究激光选区熔化修复ZL101A合金零件的性能,在不同工艺参数和热处理条件下沉积成形模拟试样。利用电子拉伸试验机、光学显微镜和扫描电镜观察对试样的拉伸性能、金相组织和断口形貌进行分析。结果表明:T6热处理可以提升拉伸试样的屈服强度和抗拉强度;在金属粉末粒度100~150目、吸光涂层厚度0.2mm、送粉速度10g/s、功率1600W和扫描速度8mm/s的激光选区熔化沉积工艺条件下得到的强度指标最高,T6热处理条件下平均抗拉强度为196.8MPa,达到基材的85.6%,可满足一般航空铸件的修复要求;AlSi10Mg沉积组织由白色α固溶体和灰色共晶相构成,热处理后强化相的固溶效果更加完全,共晶相更加圆整化,白色的α固溶体颜色变灰。激光选区熔化沉积试样均为塑性断裂,断口特征均呈现为韧窝和撕裂棱构成,异常断裂的拉伸件断口分布有较多气孔。

Synthesis and characterization of MgSO_4·5Mg(OH)_2·2H_2O flake powders

Magnesium oxysulfate （MgSO4·5Mg（OH）2·2H2O） flake powders with an average diameter of 2 ~tm and a thickness of 0.052 μm were prepared using magnesium sulfate and sodium hydroxide as raw materials by hydrothermal synthesis process. The composition, morphology and structural features of the hydrothermal products were examined with X-ray powder diffraction （XRD）, scanning electron microscopy （SEM） and Fourier transform infrared spectroscopy （FTIR）. The experimental results indicate that in the conditions of n（NaOH）/n（MgSO4） of 1.25, the dosage of w（Na3PO4） crystal additives of 1.0% w（MgSO4）, stirring for 5 h at 180 ℃, the morphology of MgSO4·5Mg（OH）2·2H2O products is flaky and laminar, which is a kind of complex magnesium singlecrystal. The recycling of MgSO4 mother liquor was also investigated to make a full use of the materials and reduce disposal. The results prove that there is no adverse effect on the yield and purity of the products.

Comprehensive study on quasi-static and dynamic mechanical properties and wear behavior of Mg–B4C composite compacted at several loading rates through powder metallurgy

The present study aims to fabricate and evaluate the mechanical properties and wear behavior of Mg metal matrix composite,reinforced by 0,1.5,3,5 and 10 vol.%B4C microparticles.Mg−B4C samples were fabricated at 450℃ and under different loading rates by using split Hopkinson bar(SHB),drop hammer(DH)and Instron(QS)at strain rates of 1600,800 and 0.008 s–1,respectively.The mechanical properties including microhardness,quasi-static and dynamic compressive strengths and wear behavior of samples were experimentally investigated.The results show that,the hardness of SHB and DH samples is obtained to be 20.2%and 5.7%higher than that of the QS sample,respectively.The wear rate and wear mass loss of Mg–10.0%B4C samples fabricated by SHB were determined lower than those of the QS sample by nearly 33%and 39%,respectively.The quasi-static compressive strengths of Mg−5.0%B4C are improved by 39%,30%and 29%for the SHB,DH and QS samples,respectively,in comparison with the case of pure Mg.Furthermore,it is discovered that the dynamic compressive strength of samples is 51%−110%higher than their quasi-static value with respect to the B4C content.

宝钢一炼钢铁水预处理工艺实践

结合宝钢一炼钢铁水预脱硫的生产实践,分析了不同铁水脱硫模式的生产效果、粉剂消耗及经济效益对比情况。结果表明:最新采用喷吹投料的KR工艺,具有粉剂消耗低、处理后硫低且稳定、综合处理成本最低的特点,是值得推广和普遍采用的高效脱硫技术。

功能组分对含硼富燃固体推进剂药浆流变特性的影响

为改善含硼富燃固体推进剂的贮存、能量和燃烧特性 ,必须加入某些功能组分。对加入这些功能组分后的药浆工艺性能即流变性作了研究。利用 HAAKE旋转粘度仪的 SV2 /SV2 FL测量系统 ,研究了加入防老剂 H、Mg/Al粉和调节 AP级配对药浆流变特性参数——表观粘度ηa、屈服值τy 的影响。结果表明 ,加入和调节这些组分后 ,药浆的ηa 和τy 都随时间有所增加。但只要把这些组分的添加量限制在一定范围内 ,药浆仍能满足浇铸要求。

宝钢全量铁水预处理的实践

结合宝钢铁水预脱硫的生产实践,分析了宝钢现行6类铁水脱硫模式的生产效果、粉剂消耗、生产工艺组织及经济效益情况。结果表明,铁水脱硫模式的选择必须充分考虑原料条件、工艺总图布置、铁钢对应程度、处理目标要求、处理综合成本等要素。宝钢目前采用的铁水包脱硫模式,具有处理时间短、粉剂消耗低、处理后硫低、综合处理成本最优特点,是值得推广和普遍采用的高效脱硫技术。