热等离子体环境下溶液液滴蒸发机理研究

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摘要

溶液注入热等离子体喷涂(solution precursor plasma spray ,SPPS) 用以制备纳

米涂层，是热喷涂技术中重要的工艺技术和方法之一。在溶液注入热等离子体喷

涂过程中，溶有涂层材料的前体盐溶液，经过加压雾化,形成喷雾液滴，以一定的

速度射入热等离子体环境。喷雾液滴在热等离子体中加速运动，吸收热量，液滴

温度逐渐升高。随着溶剂的蒸发，液滴溶质浓度增大，达到临界过饱和浓度后，

溶质析出，形成中空壳状或实心固体等不同形态的颗粒。液滴的运动和加热历程，

对涂层性能有至关重要的影响。

本文首先建立了溶液液滴在热等离子体内的运动模型，模拟液滴在热等离子

体中的运动和传热，综合考虑了液滴、热等离子体气流及液滴表面气体混合物随

温度和组分的物性变化以及斯蒂芬流的影响，得到液滴的运动轨迹、温度、速度

和半径的变化，并分析了溶液喷雾参数对液滴在热等离子体射流中运动及传热传

质过程的影响。

在此基础上，建立了液滴内部的热物理模型，进行了其内部的传热传质分析。

第一部分模型求得的液滴表面质量蒸发率及导入液滴内的热量做为求解液滴内部

温度浓度场的边界条件。由于液滴与环境气体具有相对速度，在液滴内部产生了

希尔球形涡的环流，本文考察了内部环流对传热和传质的影响。研究了液滴运动

蒸发过程中内部温度场及浓度场的变化，比较了不同入射参数对液滴内部的温度

场浓度场的影响。

在获得的运动蒸发液滴内部温度和浓度场基础上，本文应用均相成核假设和

溶质析出结晶的临界过饱和浓度，判断液滴内溶质沉淀析出发生的时间和区域，

预测可能形成的颗粒形态，分析入射参数对颗粒形态的影响。

本文所获得的研究结果，加深了对溶液注入热等离子体喷涂过程的认识，有

助于揭示热等离子体喷涂制备纳米结构涂层的形成机理，充实了热等离子体条件

下溶液液滴蒸发机理方面的研究。

本课题受到国家自然科学基金 (项目编号：50706027)、上海市教育委员会科

研创新基金(项目编号：09YZ206)、上海市重点学科建设项目 (项目编号：J50501)

和教育部留学回国人员科研启动基金的资助。

关键词: 溶液注入热等离子体喷涂液滴蒸发内部环流颗粒形态数

值模拟

ABSTRACT

Solution Precursor Plasma Spray (SPPS) is one of the most important techniques

of material science which is developed to attaining nano-structured coatings. In this

process the precursor droplets containing ceramic salts atomized into a spray by a

pressure atomizer are injected into the plasma environment. The droplets are rapidly

heated up and accelerated. Evaporation of the solvent results in the increase of the

solute concentration. Once reaching the critical super saturation (CSS) the precipitation

is expected to commence which results in the formation of solid or hollow shell

particles. The microcosmic morphology of the particles arriving on the substrate is

important to the performance of the coating.

First of all, a model is developed to simulate the behavior of an individual

precursor droplet in the high temperature plasma environment. The model involves

motion and the heat and mss transfer of the droplet. The influence of Stefan flow and

the variable physical properties of solution and environment gases are considered. The

trajectory, temporal droplet surface temperature as well as radius variation are predicted.

The effect of droplet size, injection velocity on droplet motion and evaporation are

investigated.

And then, a thermal physics model is developed to analyze the heat and mass

transfer within the droplet. The mass vaporization rate and the heat penetrating into the

liquid calculated from the first part are used as the boundary conditions in the solution

of the temperature and concentration distribution. The internal circulation due to the

relative velocity between the droplet and the plasma environment which can be

described by the Hill’s spherical vortex is considered. The temperature and

concentration distribution inside the droplet as well as the difference between the

droplets with different injection velocity and radius are presented.

At last, based on the distribution of the solute concentration within the droplet, the

regions of droplets where the solute might precipitate are predicted by employing the

simple homogeneous nucleation hypothesis. The different microcosmic morphologies of

the particles with different injection parameters are compared.

A better understanding of the process of solution precursor plasma spray and the

mechanism of droplet evaporation can be achieved by this study.

The financial support of the National Natural Science Foundation of China (Project

50706027), the Scientific Innovation Foundation of Shanghai Education Commission

(Project 09YZ206), the Scientific Research Foundation for the Returned Overseas

Chinese Scholars, and Shanghai Leading Academic Discipline Project (Project J50501)

is gratefully acknowledged.

Keywords: Solution Precursor Plasma Spray, droplet evaporation,

internal circulation, particle morphology, numerical simulation

中文摘要

ABSTRACT

第一章绪论······················································································· 1

§1.1 课题研究背景及意义····································································1

§1.2 课题研究的发展及现状································································ 4

§1.3 本文的研究工作··········································································6

第二章液滴在热等离子体中的运动和蒸发················································7

§2.1 物理问题及数学模型···································································7

§2.1.1 液滴的运动模型···································································· 7

§2.1.2 液滴表面气相模型································································10

§2.2 混合气体热物性计算································································· 11

§2.3 计算结果及分析······································································· 13

§2.3.1 模型可靠性分析···································································13

§2.3.2 计算参数的选取···································································14

§2.3.3 入射速度对液滴运动和蒸发的影响·········································· 16

§2.3.4 初始尺寸对液滴运动和蒸发的影响·········································· 18

§2.4 本章小结················································································ 20

第三章液滴内部传热传质····································································22

§3.1 物理问题及数学模型································································· 22

§3.1.1 液滴内部环流模型································································23

§3.1.2 热量和组分扩散模型·····························································24

§3.2 计算方法················································································ 25

§3.2.1 控制方程离散······································································25

§3.2.2 网格划分············································································ 28

§3.3 计算结果及分析········································································ 30

§3.3.1 计算参数的选取···································································30

§3.3.2 不同入射速度液滴内的温度浓度场·········································· 31

§3.3.3 不同尺寸液滴内的温度浓度场·················································39

§3.4 本章小结················································································· 48

第四章溶质结晶及颗粒形态································································ 49

§4.1 物理问题················································································ 49

§4.2 计算结果及分析······································································· 51

§4.2.1 计算参数的选取·································································· 51

§4.2.2 不同入射速度颗粒的形态······················································51

§4.2.3 不同初始尺寸颗粒的形态······················································53

§4.2.4 实验结果比较····································································· 55

§4.3 本章小结················································································ 56

第五章结论······················································································58

主要符号表·························································································60

参考文献····························································································62

在读期间公开发表的论文和承担科研项目及取得成果·································· 67

致谢·································································································· 68

第一章绪论

§1.1 课题研究背景及意义

随着航空航天、电力机械、化工等各领域工程技术的发展,为延长工件的工作

寿命,对工件涂层的耐磨、耐蚀、耐高温氧化及抗热冲击的性能有越来越高的要求。

喷涂技术做为材料科学表面处理的关键技术之一,主要用于功能涂层的制备，缺损

部件的修复，部件表面性能的强化[1]。其中，热等离子体喷涂是热喷涂技术中最重

要的工艺技术和方法之一。

热等离子体喷涂是利用热等离子体火焰将射入的喷涂材料粉末加速加热，使

其达到熔融或半熔融的状态，并高速撞击基板表面，在迅速变形铺展过程中快速

冷却形成涂层。由于热等离子体中心火焰温度高达 10000K 以上[2]，并呈高速射流

喷出，几乎可以熔化任何材料，并可迅速加热加速射入的颗粒，使其形成致密的

涂层。由于形成涂层的孔隙率低，结合度高，表面性能好，热等离子体喷涂得到

广泛的应用和发展。热等离子体喷涂有多种类型，如真空等离子体喷涂，低压等

离子体喷涂，水稳等离子体喷涂，大气热等离子体喷涂，溶液注入热等离子体喷

涂等。

大气热等离子体喷涂 ( air plasma spray , APS ) 是常用的热等离子体喷涂的一

种，被广泛的应用于制备热障涂层 ( thermal barrier coatings, TBCs )。在大气热等

离子体喷涂过程中，喷涂材料粉末射入热等离子体内，在运动过程中被加速加热，

形成熔融或半熔融的颗粒。这些颗粒到达基板表面后迅速的凝固，形成了层间气

孔，因此有较大的孔隙率。虽然孔隙及微裂纹的存在有利于降低涂层密度及热导

率，但水平的微裂纹会导致涂层的剥落，降低其力学性能，因此一定程度上限制

了该技术的应用[3]。

在过去几十年，大气热等离子体喷涂技术已经日趋成熟，近来人们更关注于

纳米尺寸的涂层微观结构，以获得更优秀的涂层性能及抗分裂剥落特性。然而，

大气热等离子体喷涂制备纳米涂层存在着一定的困难。纳米尺寸的颗粒由于尺寸

过小很难射入热等离子体得到有效的加热，另外纳米尺寸颗粒的制备本身也较为

困难且成本较高。针对以上问题，溶液注入热等离子体喷涂 ( solution precursor

plasma spray ,SPPS ) 对传统热等离子体喷涂技术进行了改进[4]。其工作原理是，将

溶有涂层材料的前体盐溶液，经过压力喷雾器雾化,以喷雾的形式射入热等离子体

环境。此喷雾液滴类似于大气热等离子体喷涂过程中的粉末。液滴在热等离子体

热等离子体环境下溶液液滴蒸发机理研究

中被加热，溶剂蒸发溶质结晶，形成的颗粒沉积在基板表面形成纳米结构的涂层。

图1-1所示为溶液注入热等离子体喷涂过程示意图。

图1-1 溶液注入热等离子体喷涂过程示意图

溶液注入热等离子体喷涂避免了纳米尺寸颗粒的制备过程，而形成的涂层具

有理想的微米或纳米微观结构，如图1-2所示[5]，并可制备多层分级涂层。溶液液

滴蒸发析出后形成的颗粒在基体表面形成的相互连接的网状结构，具有微米和纳

米大小的孔隙以及纵裂纹,裂纹间距在50-300



,避免了APS过程中水平裂纹造成

的剥落现象,图1-3所示为APS制备的热障涂层与SPPS制备的热障涂层微观结构的

比较[6]。溶液注入热等离子体喷涂获得涂层的这种性质有利于缓解热应力的不利影

响，提高力学性能，因此在制备耐磨、热障、抗腐纳米涂层方面有较大的优势和

发展前景。

图1-2 SPPS制备的氧化锆涂层微观结构

第一章绪论

图1-3 APS与SPPS制备的热障涂层结构比较

在溶液注入热等离子体喷涂过程中，喷雾液滴射入热等离子体后，随着运动

和加热的进行，液滴表面温度逐渐升高，并将这一趋势向内部传递。与此同时，

液滴表面溶剂不断蒸发，液滴内部溶质浓度升高，达到临界过饱和浓度后，溶质

结晶析出，形成不同的形态。在运动蒸发过程中，液滴之间通常会发生碰撞和经

历二次雾化，本文的研究针对单个液滴内部的热物理过程，因此忽略二次雾化及

碰撞的影响，取单个液滴为研究对象。由于液滴与环境气流具有相对速度，液滴

内部产生环流，这对液滴内部的传热传质有重要影响。当液滴与环境气流相对速

度较小或液滴尺寸较小时，内部环流较弱，扩散是主要的传递机理。相反，当液

滴与环境气流相对速度较大或液滴尺寸较大时，内部环流较强，对流发挥主要作

用。当扩散占主导地位时，整个液滴内的浓度较均匀的升高，液滴易发生整体析

出，形成实心颗粒。而对于对流占主导的情形，由于强烈的内部环流，溶质会向

液滴表面聚集，液滴表面与内部的浓度差较大。当表面溶质析出时，内部浓度较

低，形成包裹溶液的壳状颗粒。对于包裹有溶液的中空颗粒，在后续加热过程中，

溶剂通过壳状表面的微小多孔通道逸出。如果晶体外壳的孔隙率较小，迅速蒸发

的溶剂来不及完全逸出，将导致颗粒内部压力升高。当压力达到一定值时，就会

导致颗粒破裂，形成无规则的破碎颗粒，甚至导致液滴爆破，产生一些微小颗粒。

另外，若液滴内压力增大，亦可能导致颗粒膨胀，随着溶剂继续蒸发，最终破裂

或塌陷，形成不规则颗粒。不同的颗粒形态与涂层质量密切相关。

如上所述，溶液注入热等离子体喷涂形成涂层的质量受众多因素的影响，如

热等离子体物性参数、前体盐溶液的注入参数，液滴内部热量质量扩散传递过程，

液滴表面结晶的物理化学变化过程等[7]。液滴的受热结晶程度及结晶后的颗粒形态

对涂层性能有至关重要的影响。而对涂层制备过程中毫秒级的时间内液滴内部热

物理过程进行实验表述存在一定的困难，因此，建立数学模型以数值模拟的方式

分析液滴在热等离子体内的运动、液滴与热等离子体的热量质量传递、液滴的内

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摘要：

摘要溶液注入热等离子体喷涂(solutionprecursorplasmaspray,SPPS)用以制备纳米涂层，是热喷涂技术中重要的工艺技术和方法之一。在溶液注入热等离子体喷涂过程中，溶有涂层材料的前体盐溶液，经过加压雾化,形成喷雾液滴，以一定的速度射入热等离子体环境。喷雾液滴在热等离子体中加速运动，吸收热量，液滴温度逐渐升高。随着溶剂的蒸发，液滴溶质浓度增大，达到临界过饱和浓度后，溶质析出，形成中空壳状或实心固体等不同形态的颗粒。液滴的运动和加热历程，对涂层性能有至关重要的影响。本文首先建立了溶液液滴在热等离子体内的运动模型，模拟液滴在热等离子体中的运动和传热，综合考虑了液滴、热等离子体气...

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