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Title: 氣態碳輔助下對四方晶氧化鋯微晶尺寸之影響研究
Effects of gaseous-carbon assistant on the crystalline size enhancement of tetragonal zirconia
Authors: Wu, Bing-Han
Contributors: NTOU:Institute of Materials Engineering
Keywords: 氧化鋯;四方晶相;鍛燒氣氛;氧離子空缺
tetragonal zirconia;mixed gases;oxygen ion vacancies
Date: 2018
Issue Date: 2019-05-23T06:19:40Z
Abstract: 本研究利用溶膠凝膠法製備微米四方晶相氧化鋯(t-ZrO2)顆粒,並於鍛燒過程中通入通入多種不同比例之一氧化碳/氬氣(CO/Ar)與二氧化碳/氬氣(CO2/Ar)混合氣氛下進行煅燒,探討比較不同氣氛下鍛燒對合成四方晶相氧化鋯晶粒尺寸之影響,並對產生差異的結果進行探討分析。煅燒後氧化鋯之結晶晶粒尺寸以X光繞射儀(XRD)檢測其相結構並計算其晶粒尺寸,且利用掃描式電子顯微鏡(SEM)觀察其形貌與顆粒尺寸,此外,亦利用X射線電子能譜儀(XPS)檢測化學鍵結與估算氧離子空缺變化。 由研究結果顯示,從SEM顯為觀察發現所有參數顆粒表面外型均接近球型,且為單一無團聚顆粒,其尺寸大小約為1 µm。XRD分析結果顯示於氬氣、真空、CO/Ar以及CO2/Ar混合氣氛下進行煅燒,氧化鋯晶體結構皆以四方晶相穩定,但在大氣條件會有部分單斜晶相氧化鋯(m-ZrO2)形成。在氬氣與真空條件下兩者有相近的晶粒尺寸,並於CO/Ar以及CO2/Ar混合氣氛之體積混合比例為10%時(1:9),可得到最大晶粒增長,分別為44與40奈米,且經XPS量測氧元素後發現此時氧離子空缺所佔比分別為42.3%及40.3%,因一氧化碳為還原性氣氛,並在鍛燒過程中會與氧化鋯晶格靠外的氧原子作用,而對於晶粒尺寸及氧離子空位的提升帶來良好的幫助。然而當超越此比例時,一氧化碳會發生劣解反應使初始反應濃度大幅下降,並且生成造成晶粒尺寸無法有效提升。而二氧化碳則會與氧化鋯中殘留的碳物質產生反應生成一氧化碳,促使氧離子空位增加而晶粒尺寸增大。研究結果得知,鍛燒過程中通入一氧化碳對於提升氧離子空缺對鍵結氧之相對比例及晶粒尺寸有最大效果,隨著煅燒溫度提高氧離子空缺亦隨之增加,並與晶粒尺寸變化呈現正比的趨勢。
This thesis is to synthesize micron-sized tetragonal zirconia (t-ZrO2) particles using the sol-gel method. The sol-gel derived powders are subsequently calcined at various temperatures separately under CO2/Ar and CO/Ar mixed-gas atmospheres with various mixing ratios. All in preparation is to figure out the effect of the two carbonaceous gases on stabiliging t-ZrO2 and enhancing its crystalline size. The calcined specimens are examined by x-ray diffractometer (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) ), and x-ray photoelectron spectroscopy (XPS) to study the evolution of crystalline size, morphology variances of particles, chemical bonding and oxygen vacancies. The SEM observations display that the calcined specimens obtained under all distinct experiment parameters show a great deal of non-agglomerated and micron-sized spherical ZrO2 particles with their mono-size of nearly 1 μm. Under the calcination at 800°C, the microstructure of zirconia particles was stabilized on the tetragonal phase, examined by XRD, regardless of calcination in vacuum, Ar, CO2/Ar or CO/Ar gas mixture, while the partial monoclinic phase was detected in the atmospheric environment. It was found that the crystalline sizes after calcination in the vacuum and in air were nearly identical. The large increase in the size of t-ZrO2 crystallines was obtained under the calcination in CO/Ar and in CO2/Ar mixed gases with 10% ratio, in having their sizes of 44 and 40 nm, respectively. The oxygen-vacancy occupied ratios in oxygen lattice evaluated from oxygen spectrum of XPS analysis are 42.3% and 40.3%, respectively, which are both more than the result of ions calcined in Ar (37%). Since CO is a reduction gas, it can react with oxygen ions at the zirconia outer lattice during calcination, which is beneficial to enhance oxygen ion vacancy which in turn resulted in an increase of t-ZrO2 crystalline size. However, when the ratio of CO in CO/Ar mixed gases is more than the optimal ratio (around 10%), the t-ZrO2 crystalline size can’t further increase but decrease. As a result of the decomposition of CO into CO2 and C, the excess C could layer on zirconia lattice, and then, hinder the grain growth of t-phase. As for the calcination in CO2/Ar mixed gases, CO2 could act with the resultant carbon stemming from the sol-gel synthesis, resulting in producing CO and increasing the crystalline size of t-phane. The results also show that the calcination in CO/Ar mixed gases could produce the best effect on the enhancement of oxygen ion vacancy and the increase of the crystalline size of t-ZrO2. Oxygen ion vacancies occupied ratio in oxygen lattice increased with increasing calcination temperature, corresponding to an increase of the crystalline size of t-phane.
Appears in Collections:[Institute of Materials Engineering] Dissertations and Theses

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