Synthesis of nanosized WC/MgO powders by high energy ball milling and analysis of reaction thermodynamics

Abstract

In the present work, a powder mixture of pure WO₃, graphite and Mg with a definite atomic ratio was milled at room temperature using a high energy ball mill method, and ball milled powders were analysed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results indicated that after ball milling for a period of time, an oxidation–reduction reaction was successfully achieved among the Mg, graphite and WO₃ powders to obtain MgO and WC. The extension of the ball milling led to the refinement of the powders. After ball milling 50 h, nanocrystalline WC grains (25 nm) were embedded into the fine matrix of MgO and formed fine nanocomposite MgO/WC powders (～100 nm in diameter). The experimental results and thermodynamic analysis showed that the formation of nanocomposite MgO/WC was a mechanically induced self-propagating reaction, and very short milling time was needed to complete the reaction.     

部分非晶化ZrO_2/Y_2O_3基冷喷涂粉末的制备及应用

采用溶胶-凝胶法结合高能球磨技术制备部分非晶化ZrO_2/Y_2O_3/Ce O_2复合粉末,采用喷雾造粒技术制备ZrO_2基团聚粉体,并尝试采用冷喷涂制备热障涂层(thermal barrier coatings,简称TBCs)。通过SEM、XRD分析Zr O_2基复合粉末的显微形貌、物相组成及非晶化程度,通过激光粒度分析仪及差热扫描量热仪测定球磨粉末的粒度分布范围及玻璃化转变温度。研究表明,随球磨时间延长,复合粉末逐渐细化,非晶含量逐渐升高,其中80 h球磨粉末的玻璃化转变温度及晶化温度分别为720℃及740℃,过冷液相区宽度达20℃,平均粒度约0.27μm,结晶度约28.09%。喷雾造粒ZrO_2基团聚粉体平均粒度约为32μm,流动性约26.5 s/25 g,松比约1.3 g/cm~3,适合用于冷喷涂沉积涂层。冷喷涂TBCs为致密颗粒状结构,且YSZ顶层与NiCoCrAlY过渡层界面结合紧密。     

Synthesis and characterisation of Si3N4p/Cu nanocomposite powders by high energy ball milling

Abstract

The present work reported the preparation of Cu–25 wt-%Si₃N₄ nanocomposite powders via high energy ball milling (HEBM). The phases and morphologies of as-milled powders with various milling times were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results showed that with increasing the milling time, the irregularly shaped Cu powder became flattened, and, subsequently, refined and near spherical. After 12 h milling, the particle size of Cu–Si₃N₄ composite powders was in the range of 200–300 nm, while the grain size of Si₃N₄ particulates, 10–25 nm, was well within a nanometre scale. A uniform distribution of the nanosized Si₃N₄ reinforcing phase throughout the Cu matrix was successfully obtained. A reasonable mechanism for the formation of Cu–Si₃N₄ nanocomposite powders during HEBM was also proposed.     

球磨法制备Mg-Cu非晶态合金粉末

本文研究了Mg—Cu二元相图的三个共晶点成分配方和两个化合物成分配方在球磨条件下非晶态合金的形成能力。XRD结果显示：除一个共晶点成分配方外，其它所有成分配方都能形成非晶态合金；非晶形成能力由大到小依次为MgCu2(化合物)，Mg58Cu42(共晶点)，Mg2Cu(化合物)，Mg85Cu15(共晶点)，Mg22Cu78(共晶点)。显然，作为选择非晶态合金成分的判据来说，Schwarz与Johnson的两个条件准则比Davies的共晶线准则更加合适。非晶形成的过程是：首先发生Mg在Cu中的固溶，随后形成过饱和固溶体，最后过饱和固溶体失稳形成非晶态合金。     

Recrystallization of silicon nitride powders during hot pressing

Conclusions The hot pressing of comminuted silicon nitride powders enables a uniform fine-grained structure of one and the same mean grain size to be obtained irrespective of the type of starting Si₃N₄, powder. At milling times of more than 100 h no significant decrease in particle size is observed. The recrystallization of milled silicon nitride powders during hot pressing takes place chiefly in the fine fractions appearing during milling. The degree of recrystallization attained is higher with ultrafine active silicon nitride powders (PCS) than with comminuted powders.Translated from Poroshkovaya Metallurgiya, No. 10(238), pp. 43–47, October, 1982.     

Al-ZnO反应球磨制备Zn/Al2O3复合粉末研究

采用X射线衍射仪、电子扫描和DTA差热分析等手段,研究了在Ar气氛保护下Al-ZnO粉在高能球磨过程中发生的机械合金化反应.分析了不同球磨时间对粉体颗粒大小、成分、形貌、热稳定性及Al2O3粒子反应生成的影响.结果表明高能球磨可以有效实现Al-ZnO固相置换反应.经过30h球磨后,Al-ZnO能完全发生机械合金化反应,60h后可获得Zn-Al2O3复合粉末.置换生成Zn的熔点降低到398℃.     

Effect of high energy ball milling on compressibility of nanostructured composite powder

Abstract

Compressibility of a nanostructured Al–5AlN composite powder synthesised via high energy ball milling for various times was studied by means of a modified Heckel equation. Since workhardening and morphological changes take place by milling evolution, the compressibility was consequently affected. Strengthening of composite compacts was influenced by milling and compaction processes, i.e. strength of compacts increased at longer milling times and higher compaction pressures. It was found that, at the initial stages of milling and higher compaction pressures, the strengthening was mostly affected from compaction process, whereas the milling strengthening fraction was near to unity at lower compaction pressures as well as prolonged milling. Nevertheless, a sharp increase in milling strengthening fraction of unreinforced Al occurred at intermediate milling times. The rate of strengthening induced by milling raised at higher compaction pressures.     

Alloying evolution and stability of Al65Cu20Ti15 during process of amorphisation by high energy ball milling

Abstract

Mechanical alloying of Al₆₅Cu₂₀Ti₁₅ powder blend has been carried out by high energy vibrating ball mill. The process of amorphisation in the mechanically alloyed Al₆₅Cu₂₀Ti₁₅ powder and the stability of the amorphous phase during ball milling were investigated. Almost completely amorphous powder was achieved after 25 h ball milling. Examination of the microstructural constituents using X-ray diffraction and transmission electron microscopy shows that the amorphisation process was controlled by the transformation of both Al based solid solution and intermetallic compounds (Al₂Cu, Cu₉Al₄ and AlCu₂Ti). However, that prolonging the ball milling time to 30 h led to the appearance of Cu₉Al₄, the Al₆₅Cu₂₀Ti₁₅ composite comprising nanocrystalline and amorphous phases could be stable after 50 h ball milling.     

高氮钢制备及焊接过程中氮的溶解与释放

综述了高氮钢制备及焊接过程中氮的溶解与释放规律;论讨了不同制备及焊接工艺下钢中氮溶解度的计算公式、适用条件及影响因素等;指出大气压力下的GTA焊接过程是一个非平衡过程,焊缝处的氮含量与保护气体中的氮分压之间不满足Sievert定律,焊缝处的氮含量主要取决于钢中平衡氮含量和Cr的含量;选择GTA焊接时,在较低的氮分压下,便可对焊缝氮含量进行控制,但由于氮的吸收和释放较快,采用GTA焊接时焊缝氮含量不能精确控制;采用（CO2,YAG）激光焊接时需要考虑焊缝氮的释放;氮质量分数大于1．0％的高氮钢焊接方法亟待开发．     

高速钢粉末真空高温处理时组织结构之变化

研究了水雾化M 2和M 4高速钢粉末在 7× 10 -2 Pa真空下加热后组织结构的变化。当粉末加热至固相线以下 15～ 2 0℃ ,即 12 2 0～ 12 2 5℃时 ,M6C及MC型碳化物都由 1～ 2 μm长大到 3～ 4 μm ;当粉末加热至固相线以上时 ,碳化物尤其是M6C型碳化物颗粒快速长大 ,并且有不均匀长大现象 ;当温度升至 12 5 0℃后 ,贫碳型的M4C3 转变为MC型碳化物 ,其中大部分Fe被V所取代 ;当进一步加热至 12 6 0℃以上时 ,M6C型碳化物将转变为M2 C碳化物。经真空脱氧后高速钢粉末的氧含量降低至 10 0× 10 -6以下。     

Toxicity in vitro of some silicon carbides and silicon nitrides: whiskers and powders

The paper presents particulars on damaging effects of work on human health drawn from the first professional medical book published in the Croatian language. Most official documents and papers of the 18th century were written in Latin. Originally, the subject book, Medicina Ruralis, was also written in Latin and subsequently translated to Croatian. It was published in 1776, in the city of Varazdin, Croatian capital at the time. The author was John the Baptist Lalangue, the viceroy's physician and the official physician of the Varazdin county, during the rule of Hapsburg archduchess Maria Theresa. The paper attempts to show to what extent does the Lalangue's book reflect the first ideas and recommendations related to occupational diseases, particularly those described in the capital work of Ramazzini who was acknowledged as "the father of occupational health". Such ideas developed with the progress of the Industrial Revolution at the end of 17th century. In his book, Lalangue considers hard, physical work the major cause of diseases in population he observed and cured in his everyday practice. He gave detailed recommendations for physicians on how to get professional history data of the patient. Furthermore, Lalangue's book introduces the first ideas as to the professional rehabilitation of diseased persons. The paper concludes that Lalangue's ideas represent the origins of modern occupational health on Croatian territory, and emphasises the significance of such ideas appearing soon after their occurrence in other industrially more developed European countries.     

Reaction between zirconium carbide and silicon powders

Conclusions A study was made of the reaction of zirconium carbide and silicon powders over the temperature range 800–1700C.Translated from Poroshkovaya Metallurgiya, No. 11(83), pp. 61–65, November, 1969.     

高能球磨对锆钛酸铅镧粉末性能的影响

以Pb3O4、ZrO2、La2O3和TiO2为原料,通过高能球磨制备锆钛酸铅镧（Pb0.92La0.08（Zr0.65Ti0.35）0.98O3,简称PLZT）粉末,并研究球磨工艺对合成粉末物相、颗粒形貌及烧结性能的影响,以期优化球磨工艺,加速开发PLZT陶瓷的低温烧结致密化新工艺。结果表明：随球磨转速提高,粉末形貌由层片叠加状转变为不规则小颗粒状。在160r／min、58h条件下球磨后粉末没有合成PLZT相,粉末体系处于部分非晶化状态;而在400r／min、16h条件下球磨后粉末中出现钙钛矿结构的PLZT相。合金化的球磨（400r／min,58h）粉末在1100℃烧结后密度为6．29g／cm^3,而在同样烧结条件下,未合金化的球磨（160r／min,58h）粉末烧结后密度达到7．02g／cm^3。借助MAGINI能量模型及相关球磨理论,分析球磨工艺参数对该粉末体系物相、形貌及粉末烧结性能的影响。     

球料比对高密度片状银粉的影响

采用机械球磨工艺,使用扫描电子显微镜(SEM)、激光粒度分析仪(D50)、比表面积测试仪(BET)、振实密度仪(TD)和松装密度(AD)测定装置等测试手段,研究讨论了不同球料比对片状银粉粒度、形貌、比表面积和振实密度等性能的影响,得出了最佳的球料比参数。结果表明,球料比为12.5∶1（质量比）时,可制得平均粒径为5.5μm、松比为2.19g/cm3、比表面积1.10m2/g、振实密度为3.5g/cm3的高振实片状银粉。