Magnesium vapor nucleation in phase transitions and condensation under vacuum conditions

Recent findings related to coagulable magnesium vapor nucleation and growth in vacuum were assessed critically, with emphasis on understanding these processes at a fundamental molecular level. The effects of magnesium vapor pressure, condensation temperature, and condensation zone temperature gradient on magnesium vapor nucleation in phase transitions and condensation from atomic collision and coacervation with collision under vacuum conditions were discussed. Magnesium powder and magnesium lump condensates were produced under different conditions and characterized by scanning electron microscopy （SEM） and energy-dispersive X-ray spectroscopy （EDS）. The right condensation zone temperature approach to the liquid transition primarily improved the magnesium vapor concentration rate. The gas-solid phase transition was primarily inhibited by setting a small condenser temperature gradient. Under the right condensation temperature and temperature gradients, increasing magnesium vapor partial pressure improved crystallization and reduced the oxidation rate.

Analysis of the behavior of magnesium and CO vapor in the carbothermic reduction of magnesia in a vacuum

The aim of this paper is to experimentally investigate the behavior of magnesium and carbon monoxide vapor in the carbothermic reduction of magnesia at condensing zone temperatures ranging from 923 K to 1223 K.The phase,surface morphology,and composition of the condensates obtained were examined by means of scanning electron microscopy and energy-dispersive X-ray spectroscopy.The main findings of this paper include:the reverse reaction products,carbon and magnesium oxide,were formed following the process of magnesium vapor condensation,preventing two metal clusters from mutually combining.Moreover,the nearer the temperature of the condensation zone approached the liquid transformation temperature(810-910 K),the lower the rate of the reverse reaction between carbon monoxide and magnesium vapor.Decrease in the rate of the reverse reaction of magnesium was possible by controlling the condensation temperature.

Kinetics of hot metal desulfurization by bottom blowing magnesium vapor

To solve the technical problems of hot metal desulfurization by injecting magnesium particulate,a new idea of hot metal desulfurization by bottom-blowing magnesium vapor was put forward.The reaction mechanism of hot metal desulfurization with magnesium vapor injection was analyzed,and the kinetic model of the desulfurization rate during the process of hot metal desulfurization with magnesium vapor injection was established.The dimensionless equation of the gas–liquid mass transfer coefficient under the injection conditions was obtained by the dimensional analysis method.And the theoretical calculation results were in good agreement with the experimental measurements.The results show that the diameter of the bubbles and the viscosity of the melt significantly affect the desulfurization rate of hot metal injected with magnesium vapor.When the temperature is 1573 K and the gas flow rate is 3 L/min,the desulfurization rate can reach 79%and the utilization rate of magnesium can reach 83%.

基于反应性水汽高阻隔环烯烃共聚物复合膜的制备和多性能优化

针对现有柔性高分子复合膜水汽阻隔性能偏低,且水汽透过率、机械力学强度和光学透过率等多性能难以同时优化的矛盾问题,开发了一种新型氧化镁掺杂环烯烃共聚物复合膜(MgO/COC)。探索了MgO含量对复合膜力学性能、热性能、疏水性能以及水蒸气阻隔性能的影响。研究结果表明,MgO在COC复合膜中具有良好的分散性。当1%(质量分数)MgO掺杂COC时,接触角达到最高(106.8°),表明MgO/COC复合膜具有良好的疏水特性。复合膜的水蒸气阻隔性能比纯COC膜提高了63.1%,最小水汽透过率达到0.21 g/(m^(2)·d),是目前公开报道掺杂型高分子复合膜水汽透过率的最低值。优异的水汽阻隔性能归因于MgO与水汽反应特性形成了氢氧化镁,同时氢氧化镁具有优异水汽阻隔性能。该复合膜双机制水汽阻隔特性为食品包装和医药包装的水汽阻隔设计提供新的思路。

Production of magnesium during carbothermal reduction of magnesium oxide by differential condensation of magnesium and alkali vapours

Most of researchers believed that the developments on the condensation of magnesium produced by carbothermic reduction just concentrated on two process routes:the“quench”route and the“solvent”route.But this paper will briefly analyzes the major challenges in magnesium vapor condensation during the vacuum carbothermic reduction of calcined dolomite,on equipment upgrade,heat transfers alter,to achieve condensation control and production collection.Solutions are then proposed using theoretical calculations and experiment results.Comparative analysis of the experiment results shows that the burning and even explosion of condensation products during the vacuum carbothermic reduction of calcined dolomite are mainly due to the burning of crystallized powder magnesium,which results from the self-ignition of alkali metals.Finally,this paper proposes a multistage condensation solution to improve traditional vacuum condensation equipment.And result show that the condensation equipment can effectively mitigate the burning and loss during condensation,also the morphology of the condensation products clearly improved,the grain size increased,and the oxidation rate decreased.The potassium/sodium vapor and the magnesium vapor were separately condensed.

Mg-doped ZnO radial spherical structures via chemical vapor deposition

Mg-doped ZnO radial spherical structures with nanorods grown on both sides of the spherical shell were successfully prepared via chemical vapor deposition （CVD） of Zn and Mg powders in the absence of a catalyst. The structures associated with different growth temperatures （700, 800, and 850°C） were monitored by scanning electron microscopy （SEM）, and the result shows that the length of the nanorods increase progressively with the growth temperature increasing. X-ray diffraction （XRD） shows that the as-obtained samples can be indexed to high crystallinity with wurtzite structure. The growth of the nanostructures mainly depends on the formation of sphere-like Mg-doped Zn droplets before adding oxygen. Photoluminescence （PL） spectra that show a 39 meV blue shift indicates that the band gap becomes large, because Mg substitutes Zn in the lattice.

Influence of multilayer coatings on AZ31 deposited by electron beam evaporation

Three different coatings, Cr, SiO2/Cr and HfO2/SiO2 were deposited by electron beam physical vapor deposition (EB-PVD). Relevant composition and mechanical properties were obtained. The results show that the surface mechanical property could be increased, and Cr coating sample possessed the highest microhardness. Cyclic oxidation in air at 773 K was applied to evaluate the oxidation resistance of the coatings, and the section morphologies of the coatings were observed by FEISEM. The results indicate that the oxidation rate of AZ31 with Cr, SiO2/Cr and HfO2/SiO2 coatings is decreased, and the SiO2/Cr coating sample exhibits the best oxidation resistance and keeps relatively good adhesion up to 96 h. Polarization results prove that the corrosion resistance of AZ31 can be improved and the SiO2/Cr coating sample has the best property.

竖罐炼镁过程中镁蒸气流动相变规律

皮江法炼镁工艺中,掌握镁蒸气流动和结晶规律是获得高质量结晶镁的关键。针对这一问题,研究了复式竖罐内镁蒸气从还原反应区流动到结晶区过程中的流动规律,并通过引入高温稀薄气体中流导的概念给出了镁蒸气流动过程阻力计算方法,推导出镁蒸气流动阻力与还原罐内径、运动距离以及压强之间的关系式。结果表明:镁蒸气的结晶过程不仅受温度和压强影响,还与结晶器的内径相关,适当减小结晶器内径可获得致密度较高的结晶镁;镁蒸气从复式竖罐中的反应区流动到结晶区,镁蒸气的总压降约为150 Pa,还原反应区平均压强数量级在百帕以上;镁冶炼初期,部分料球温度低于600℃时,镁蒸气以“凝华-升华”的方式在反应区层移,随着料球整体温度升高到600℃以上,镁蒸气流动阻力减小,能够顺利进入结晶器结晶。

医用镁合金表面含氟类金刚石薄膜腐蚀行为研究

为了提高镁合金的表面硬度和耐蚀性,采用等离子体增强化学沉积技术在AZ31镁合金表面制备含氟DLC膜。研究了氟掺杂量对含氟DLC薄膜表面形貌、耐腐蚀性、疏水性和sp^(2)键含量的影响,并探讨了相应的影响机理。结果表明,氟掺杂对AZ31镁合金表面DLC膜的组织和性能有显著影响。随着四氟化碳沉积时间增加,类金刚石薄膜的粗糙度减小,表面光滑;薄膜中的sp^(2)杂化键逐渐增多;类金刚石薄膜的疏水性先增大后减小;当四氟化碳沉积时间为40 min时,类金刚石薄膜表现出优异的耐人体体液腐蚀特性。

真空碳热法制备金属镁过程中可逆反应对镁蒸气冷凝的影响

对真空碳热法制备金属Mg过程中可能发生的逆反应进行了热力学分析,结果表明,系统压力为60 Pa,且温度低于900 K的条件下,冷凝过程中会有逆反应发生。实验研究表明,冷凝温度越接近镁的露点温度,直收率越高。通过对还原产物和蒸馏产物的X射线衍射、扫描电镜及X射线光电子能谱仪的对比分析可以发现,还原产物在受到逆反应的影响的条件下,所形成的镁粉晶粒排列不规则且尺寸较小:而没有逆反应影响所形成的金属Mg晶粒排列规则致密且尺寸较大,因此有效控制逆反应的发生成为收集到结晶较好金属Mg的关键。

真空碳热还原氧化镁制取金属镁的冷凝实验研究

采用冷凝区金属Mg直收率、X射线衍射（XRD）和扫描电镜（SEM）等手段和方法,研究了冷凝温度和温度梯度对真空碳热法还原氧化镁产生的Mg蒸气冷凝的影响。研究结果表明,在30~100 Pa时,在温度梯度不变的条件下,冷凝温度越接近Mg的露点温度,直收率越高;当冷凝温度合适时,温度梯度越小越有利于Mg蒸气的结晶。冷凝物的SEM和X射线能谱仪分析表明,当冷凝温度接近Mg的露点且温度梯度较小时,所得金属Mg拥有较大晶粒尺寸且排列规则致密,金属Mg的含量可达到90.05%。冷凝物的XRD分析表明,合适的冷凝温度条件下,温度梯度的减小可以增大结晶Mg的晶粒尺寸。

气相沉积膜层在镁合金表面改性中的应用

综述了气相沉积膜层的特性、制备技术的发展及其在镁合金表面改性中的应用,重点介绍了利用PVD和CVD技术在镁合金表面沉积保护性膜层的研究现状,并指出气相沉积膜层是传统电化学镀层的良好替代物,在镁合金表面改性中具有广阔的应用前景。

应用镁蒸气对模具钢中夹杂物变性的研究

D2冷作模具钢最常见的失效形式为磨损失效,改善夹杂物的数量、形态和分布能降低钢的磨损率.利用颗粒镁在高温下生成镁蒸气,并通过高纯氩气携带通入钢液中,考察了镁对钢中非金属夹杂物的变性效果.实验结果表明,镁蒸气通入钢液后,钢中非金属夹杂物尺寸明显变得细小,夹杂物的成分从单纯的Al2O3和Al2O3与Cr,Mo和V等合金氧化物的复合产物向富MgO的MgO和Al2O3复合夹杂物转变.铸态组织的观察结果表明细小夹杂物在钢液中的残存对于凝固和相变过程中钢的晶粒细化有利.

新贮氢材料——含微量锰的微晶镁粉

以气雾化冷凝法制备了含有微量Mn的微晶镁粉(Mg(Mn)).XRD表明,其主物相仍然是六方晶系的微晶镁,其粒径在100～500nm之间.这种微晶镁粉(Mg(Mn))具有较高的储氢量(6.2%),在280℃具有较快的放氢速度.

含有微量钴的微晶镁的储氢性能研究

以气雾化冷凝技术制备了含Co的微晶镁粉Mg(Co)。X射线衍射表明 ,其主物相仍然是六方晶系的微晶镁 ,晶胞常数与微晶镁相同。所加的Co并未进入Mg的晶格内 ,但等离子发射光谱的测定结果表明确实有微量Co元素的存在。该种含Co的微晶镁较纯微晶镁更易于吸、放氢。在 2 80℃具有完整的脱氢曲线和氢压平台。可逆吸、放氢量达 70 0cm3 (STP) /g ,相当于Mg(Co)质量的 6 .2 %。

CeO_2助Ni/MgO催化剂用于化学气相沉积法制备多壁碳纳米管(英文)

以柠檬酸燃烧法制备的Ni/MgO,Ni/CeO2-MgO和Ni/CeO2为催化剂,CH4为碳源,采用化学气相沉积法制备多壁碳纳米管(MWCNTs),通过N2吸附、X射线衍射、H2程序升温还原和X射线光电子能谱对催化剂进行表征,并运用热重和透射电镜表征了碳纳米管的质量和形貌.结果表明,CeO2的加入可有效地降低还原温度和增加易还原Ni物种的含量,并使电子发生转移,还原后的Ni/CeO2-MgO催化剂中,Ni晶粒尺寸较小.这表明CeO2的加入使得Ni物种的化学环境发生改变,导致它和载体间的相互作用减弱,从而促进Ni物种的还原,且还原后,高度分散在CeO2-MgO载体上,从而催化剂的催化活性增加.相比Ni/MgO催化剂,Ni/CeO2-MgO为催化剂上生长的CNTs质量更高.另外,由CeO2助Ni/MgO催化剂制备出基本没有无定形碳、结晶度好的碳纳米管.

复合吸附剂MWCNT/MgCl2的水蒸气吸附性能

通过研磨将多壁碳纳米管分别与质量分数为30%、40%和50%的无水氯化镁复合,制备了3种不同配比的复合吸附剂MWCNT/MgCl2。采用数字化扫描电子显微镜(SEM)观察复合吸附剂表面材质的结构样貌,通过Hot Disk热常数分析仪测得复合吸附剂的热导率,使用恒温恒湿箱选取具有代表性的温湿度,测试复合吸附剂在不同工况下的水蒸气吸附性能,并采用准二级动力学模型对25℃、50%RH工况下的实验数据进行拟合,应用Autosorb-IQ全自动气体分析仪测试了三种样品在25℃下的等温吸湿曲线。实验结果表明,相同温湿度工况下,随着氯化镁含量增加,复合吸附剂的吸附量提高,25℃、50%RH下氯化镁含量为30%、40%和50%的复合吸附剂M1、M2和M3的吸附量分别为0.62、0.79和0.94 g/g;恒定湿度为50%RH,温度变化为15~35℃时,复合吸附剂吸附量受温度和饱和水蒸气分压力的双重影响,表现为先增加后减小;温度固定为25℃,相对湿度从50%RH增加到80%RH时,复合吸附剂吸附量均大大提升;复合吸附剂在35℃、25%RH中高温、低湿条件下仍表现出较好的吸附能力;在相对压力P/P0为0.3时,M1、M2和M3的吸附量分别为0.24、0.25和0.30 g/g,随着吸附压力的增加,复合吸附剂的吸附量也不断提升,最大吸附量分别达到3.54、3.75和4.42 g/g。复合吸附剂MWCNT/MgCl2的制备研究,为吸附剂的性能研究提供了基础,对太阳能吸附式空气取水的研究具有潜在意义。

CNTs-Al_2O_3联合增强镁基复合材料的制备与性能研究

采用化学气相沉积法,使用镍催化剂,在氧化铝(Al_2O_3)颗粒载体表面原位合成了碳纳米管(CNTs),制备出CNTs-Al_2O_3原位复合增强相;采用粉末冶金工艺制备了CNTs-Al_2O_3联合增强镁基复合材料.通过XRD、SEM、TEM等对CNTs-Al_2O_3原位复合增强相进行表征,结果表明:通过控制合成条件,在Al_2O_3颗粒表面可获得分散均匀、形态理想、石墨化程度高的CNTs,实现了CNTs与Al_2O_3颗粒的原位复合.对复合材料的组织和力学性能分析表明:Al_2O_3颗粒发挥了良好的"运载效果",通过球磨工艺,使CNTs从Al_2O_3颗粒表面脱落并在镁基体中分散;同时,作为催化剂载体的Al_2O_3颗粒与CNTs对镁基体起到联合增强作用,使得复合材料力学性能明显提高.

AZ31镁合金表面气相沉积不锈钢薄膜的实验研究

利用真空蒸发镀膜技术在镁合金表面沉积不锈钢薄膜是提高镁合金防腐性能的新尝试。本研究利用该技术在AZ31上成功制备了不锈钢薄膜。通过在5%NaCl溶液中的浸入实验和极化实验考察了腐蚀性能,发现镀膜后耐蚀性显著降低。另外,镀膜后的显微硬度也未有明显提高。利用AFM,SEM,EDX等分析手段对薄膜进行了观察和检测,发现耐蚀性变差的原因主要是薄膜表面存在贯穿性的微米级孔洞和Cr元素分布不均匀造成的。

配方参数对镁基水反应金属燃料/水蒸汽反应特性的影响

采用可视化燃烧实验器模拟发动机的水蒸汽环境,用高速摄影拍摄燃料在水蒸汽中的燃烧过程,并用热电偶测温,研究了燃料配方参数对镁基水反应金属燃料/水蒸汽反应的影响规律。研究结果表明,镁基水反应金属燃料与水反应分快速反应和慢速反应两阶段,反应速率随时间和反应程度的增加而降低;镁基水反应金属燃料/水反应的快速反应时间和反应程度是表征燃料/水反应特性的两个关键参数;增加燃料的氧粘比和细镁粉含量、添加Fe类添加剂都可以提高燃料/水反应速率和反应程度,而增大镁含量会使燃料/水反应速率及反应程度降低。保证镁含量60%以上燃料的能量性能、工艺性能和力学性能的前提下,应尽量提高燃料氧粘比和细镁粉含量。