奈米顆粒製程之噴霧熱解及矽底高頻噴霧器

Ultrasonic Spray Pyrolysis for Nanoparticles Synthesis and Silicon-Based MHz Ultrasonic Nozzles

宋昱霖(Yu-Lin Song)

指導教授 ： 鄭秀蘭教授 ； 蔡振水教授 ； 陳政維教授

國立臺灣大學/理學院/物理研究所/博士(2005年)

https://doi.org/10.6342/NTU.2005.00971

摘要

摘要
本博士論文包括兩部分之研究：（I）噴霧熱解(Spray Pyrolysis)合成奈米顆粒；（II）矽底高頻噴霧器（Silicon-based High Frequency Ultrasonic Nozzle）。研究之目標為使用高頻超音波噴霧器產生微小、均勻的先驅水溶物液滴（Precursors），俾以噴霧熱解合成奈米顆粒。
論文第一部份首先採用雷射散射的科技儀器（Malvern Spraytec RT5000）以探測試藥級（Reagent Grade）的醋酸鋯（Zirconium Hydroxyl Acetate）先驅物水溶液霧化後之液滴的粒徑分佈，研究結果顯示，先驅物的溶液濃度與液滴大小是奈米顆粒產生之兩項重要因素。使用一般傳統市面霧化產生器在頻率2.66 MHz及先驅溶液濃度0.01 wt%情況下所產生的霧化液滴粒徑為5至8 μm；在750 oC高溫下熱解，所形成的圓球型釔安定氧化鋯顆粒（Yttria Stabilized Zirconia）於電子顯微鏡（SEM）下量測得平均的顆粒徑為73 nm。此數據值小於依據「單一液滴產生單一顆粒（One-Particle-Per-Drop Mechanism）」機制所推算之數值。在相同反應條件下，使用高流量但先驅溶液液滴粒徑大至28 μm的超音波調制雙相霧化器（Ultrasound-Modulated Two-Fluid Atomization）依然可以產生很稠密的圓球型顆粒。若與傳統市面霧化器先驅液滴粒徑6.8 μm比較，發現有多量更細小之顆粒。上提兩項實驗結果均較「單一液滴產生單一顆粒」的機制之推算值為小，可見其中必然隱含其他物理、化學機制。據此，我們推論：氣相沈積機制（Gas-to-Particle Conversion Mechanism）應發生於噴霧熱解的製程中；在低汽化壓力（Low Vapor Pressure）下，噴霧熱解在適當的濃度、均勻且細小的先驅物溶液中產生奈米顆粒。
論文第二部份有關0.5 MHz矽底高頻噴霧器之分析設計、模擬、特性與實驗結果。此係首度成功利用微系統製程（MEMS-based Microfabrication Process）研製矽底高頻超音波噴霧器進而真正實現霧化（Atomization or Spray）的一項重要成果。矽底高頻噴霧器之分析設計可分為兩部份：其一是壓電材料的驅動部份（Piezoelectric Actuator），其二為兩倍放大和半波長設計的多節複合傅立葉噴霧器（Multiple Fourier Horns）。依據有限元素法（Finite-Element Analysis）的理論基礎，使用ANSYS的三維模擬程式尋求單純縱向震動（Longitudinal Vibration）的共振頻率（Resonance Frequency），並且使用阻抗分析儀（Impedance Analyzer）及雷射都卜勒微小震動分析儀（Polytec Laser Doppler Vibrometer）量測共振頻率及震動位移幅度。實驗結果與模擬預測值大為吻合，而噴霧器前端的放大倍率亦與傅立葉噴霧器節數（n）的二次方倍（2n）之理論結果大致吻合。總之，利用噴霧器尖端縱向位移量大為放大的物理特性，產生微細波（Capillary Wave）使液體得以霧化成極小液滴。
本論文最後且最重要的成果是實驗證明了下列結論：使用三段式傅立葉噴霧器霧化所需之電力（Electrical Power）為一段式傅立葉噴霧器的四分之一，同時該電力係使用傳統市面霧化產生器所需電力的五十分之一。另外，傳統市面霧化產生器的變換器（Transducer）直接接觸先驅溶液致使部分溶液無法霧化以及迫使變換器加速腐蝕。本論文所設計製造之高頻矽底霧化器則無此弊端。

關鍵字

矽底高頻噴霧器 ； 奈米顆粒合成 ； 噴霧熱解

並列摘要

Abstract
This thesis includes two parts: (I) spray pyrolysis for nanoparticles synthesis and (II) silicone-based MHz ultrasonic nozzles. The MHz ultrasonic nozzles aim at producing uniform precursor droplets of the sizes needed for the nanoparticles synthesis.
Part I presents new findings on ultrasonic spray pyrolysis of zirconium hydroxyl acetate precursor drops whose sizes were precisely measured using laser light diffraction technique. Precursor concentration plays a predominant role in determination of product particle size. At 0.01 wt% precursor concentration, conventional spray pyrolysis at 750 oC using precursor drops 5-8 μm in diameter, generated by an ultrasonic nebulizer at 2.66 MHz, yielded uniform spherical yttria stabilized zirconia (YSZ) particles 73 nm in diameter measured by scanning electron microscopy. The YSZ particle diameters were much smaller than those predicted by the one-particle-per-drop mechanism. Under similar reaction conditions, the high throughput ultrasound-modulated two-fluid (UMTF) spray pyrolysis of larger precursor drops (28 μm peak diameter) also yielded spherical dense particles; they were significantly smaller in size than those produced by the low throughput conventional ultrasonic spray pyrolysis of smaller drops (6.8 μm peak diameter). And these particles are much smaller than predicted by the conventional one particle per drop mechanism, suggesting that a gas-to-particle conversion mechanism may also be involved in spray pyrolysis. In addition, the uniform nanoparticles can be produced by spray pyrolysis at proper conditions using uniform drops of precursor salts with low vapor pressure.
Part II presents the design, simulation, characterization and experimental results of micro-fabricated 0.5 MHz silicon-based ultrasonic nozzles. This thesis reports for the first time on successful ultrasonic atomization using micro-fabricated silicon Si-based high frequency ultrasonic nozzles of a novel design. Each nozzle is made of a piezoelectric drive section and a silicon-resonator consisting of multiple Fourier horns each with half wavelength design and twice amplitude magnification. Results of finite element 3-D simulation using the commercial ANSYS program predict existence of one resonant frequency of pure longitudinal vibration. Both impedance analysis and measurement of longitudinal vibration confirmed the simulation results with one pure longitudinal vibration mode at the resonant frequency in excellent agreement with the design value. Furthermore, at the resonant frequency, the measured longitudinal vibration amplitude at the nozzle tip increases as the number of Fourier horns (n) increases in good agreement with the theoretical values of 2n. Using this design, very high vibration amplitude gain at the nozzle tip can be achieved with no reduction in the tip cross sectional area for contact of liquid to be atomized. Therefore, the required electric drive power should be drastically reduced, decreasing the likelihood of transducer failure in ultrasonic atomization. Accordingly, the electric drive power required for atomization using the 3-horn nozzle is only 1/4 of that for a single horn nozzle. The drive voltage and power required for a 0.5 MHz 5-Fourier horn nozzle could be as low as 3 V and 0.1 Watt, respectively. The very low drive power requirement of the Si-base high frequency ultrasonic nozzles is highly desirable in their applications to nanoparticles synthesis and bio-dispersion spray.

並列關鍵字

Silicon-based High Frequency Ultrasonic Nozzle ； Spray Pyrolysis ； nanoparticles synthesis

參考文獻

References I

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