- 學位論文
機械固態反應法合成高熔點鉻-硼、錳-硼、鉬-硼、及鎢-硼過渡金屬硼化物粉末
Synthesis of High Melting Point Cr-B, Mn-B, Mo-B, and W-B Transition Metal Borides by Mechanical Solid-state Reaction
摘要
本研究選取B和過渡金屬元素Cr、Mn、Mo與W，採用機械固態反應法合成高熔點的Cr-B、Mn-B、Mo-B與W-B硼化物。選定各二元系統成分原子比67:33、50:50、20:80，進行球磨至60小時。利用X光繞射儀分析球磨後粉末的結構變化；利用熱差分析儀觀察球磨粉末於加熱過程中的熱反應；利用穿透式電子顯微鏡觀察經球磨粉末的非晶程度。取經過60小時球磨的粉末進行不等溫度與不等持溫時間退火處理，同樣利用X光繞射儀分析粉末退火處理後的結構改變，並計算退火處理後生成硼化物的活化能。結果發現隨著球磨時間增加，使各成分中金屬元素的繞射峰強度減弱。且起始成分中B的含量越高，使金屬元素的繞射峰強度在更短球磨時間內消失。其中Cr67B33、Cr50B50、Mo67B33、Mo50B50、W67B33、W50B50、W20B80等成分經過60小時球磨能形成非晶質結構。所有成分經過60小時球磨後並加以退火處理，可得到單一硼化物或各式硼化物之混合物，而起始成分比例不同會造成生成結果的差異。在球磨與後續退火處理後，發現Cr67B33、Cr20B80、Mn67B33、Mn50B50、Mn20B80和W20B80成分能生成單一相硼化物。特別的是，Mo-B系統與W-B系統(相圖中呈現非線形式化合物)的67:33和50:50成分在退火處理後有化合物分解成純元素的反應，而Cr-B和Mn-B系統(相圖中呈現線形式化合物)則無此現象發生。
並列摘要
This study chose boron element and transition elements of Cr, Mn, Mo, and W to synthesize high melting point Cr-, Mn-, Mo-, and W- borides by mechanical solid-state reaction. The powders employed in the ball milling process have compositional proportions in metal to boron ratio of 67:33, 50:50, and 20:80, respectively, in each metal-boron system. The milling was conducted for up to 60h. The structures of as-milled powders were characterized by X-ray diffraction. The thermal reactions during the heating process were analyzed by differential scanning calorimeter. The amorphous structures of the milled powders were also examined by transmission electron microscope. The as-milled 60h powders were annealed at different temperature for different times and the structural evolution of annealed powders were also characterized by X-ray diffraction. The activation energy of boride formation in each system during thermal annealing process was measured. It was found that the intensity of metallic diffraction peaks in all systems was reduced with increasing milling time. The diffraction peaks of crystalline metals disappear in a shorter milling time when more boron content is in the initial composition. Powders with compositions of Cr67B33, Cr50B50, Mo67B33, Mo50B50, W67B33, W50B50, and W20B80 form amorphous structure after milling for 60h. These powder mixtures, after being milled for 60h and subjected to subsequent annealing, can form single phase borides or boride mixtures. Which types of boride structure are formed during the milling and subsequent annealing process were determined by the initial powder compositions. Among all the compositions investigated, compositions of Cr67B33, Cr20B80, Mn67B33, Mn50B50, Mn20B80, and W20B80 have a greater tendency to form a single phase boride. It is important to found that for Mo-B and W-B systems which exhibit solubility in the intermediate compounds in the binary phase diagram, the milled powder mixtures of Mo67B33, Mo50B50, W67B33, and W50B50 decompose into metal elements when the milled powders are subjected to annealing treatment. The same phenomenon cannot be observed in Cr-B and Mn-B systems which show line compounds.