本文選題：介孔材料 + 近場(chǎng)輻射　； 參考：《北京科技大學(xué)》2015年博士論文

【摘要】：隨著航空事業(yè)的發(fā)展、電子元器件的高集成化和微電子機(jī)械系統(tǒng)(MEMS)的發(fā)展等,微型芯片集成電路的熱設(shè)計(jì)、航天器材的溫控和微電子器件的冷卻等都要求材料具有特殊的熱特性。本文針對(duì)有序介孔異質(zhì)復(fù)合材料,通過理論分析和實(shí)驗(yàn)測(cè)量,系統(tǒng)開展了介孔基材、填充納米線及復(fù)合結(jié)構(gòu)的熱輸運(yùn)機(jī)理的研究,以及材料內(nèi)存在的近場(chǎng)輻射及界面散射對(duì)其導(dǎo)熱系數(shù)的影響,為介孔復(fù)合材料的熱設(shè)計(jì)提供理論支撐。 首先針對(duì)有序介孔基材,建立了孔道內(nèi)曲面邊界的近場(chǎng)輻射換熱模型,理論計(jì)算柱形孔／球形孔內(nèi)的近場(chǎng)輻射換熱,并進(jìn)一步分析孔徑和溫度的影響。同時(shí),以典型介孔二氧化硅MCM-41、SBA-15和介孔氧化鋁AAO為例,進(jìn)行了結(jié)構(gòu)重構(gòu)和表征,開展了介孔基材殼壁導(dǎo)熱系數(shù)的分子動(dòng)力學(xué)模擬及理論分析,并進(jìn)行了實(shí)驗(yàn)測(cè)量。采用理論模型將介孔基材殼壁導(dǎo)熱系數(shù)、孔道內(nèi)近場(chǎng)輻射及孔道內(nèi)受限氣體導(dǎo)熱系數(shù)三者耦合,得到介孔基材的有效導(dǎo)熱系數(shù)。研究表明：基材殼壁導(dǎo)熱系數(shù)隨著孔徑的增大而減小,隨著壁厚的增大而增大,且表現(xiàn)出各向異性；孔道內(nèi)近場(chǎng)輻射熱流及當(dāng)量導(dǎo)熱系數(shù)隨著孔徑的增加呈指數(shù)衰減,隨著溫度的升高緩慢增加,近場(chǎng)輻射熱流要比遠(yuǎn)場(chǎng)輻射高2～7個(gè)數(shù)量級(jí),且孔徑越小,近場(chǎng)效應(yīng)越顯著；介孔基材的有效導(dǎo)熱系數(shù)的理論值與實(shí)驗(yàn)值吻合得較好,隨著孔徑的增大逐漸減小,隨著溫度的升高緩慢增加,考慮了近場(chǎng)輻射的有效導(dǎo)熱系數(shù)比未考慮的高0.2-10%左右。 其次,針對(duì)填充金屬納米線,采用平衡分子動(dòng)力學(xué)方法來模擬納米線的聲子導(dǎo)熱系數(shù),并采用玻爾茲曼輸運(yùn)理論來計(jì)算納米線的電子導(dǎo)熱系數(shù),得到了材料表面散射對(duì)對(duì)納米線導(dǎo)熱系數(shù)的影響,同時(shí)考慮了晶界界面散射對(duì)納米線導(dǎo)熱系數(shù)的作用,進(jìn)一步分析了納米線尺度和溫度的影響。同時(shí),采用線性響應(yīng)理論、電子密度矩陣對(duì)納米線截面(XY面)內(nèi)的導(dǎo)熱系數(shù)進(jìn)行量子修正。研究表明：電子輸運(yùn)對(duì)金屬納米線的導(dǎo)熱占主導(dǎo)地位,而聲子導(dǎo)熱系數(shù)的貢獻(xiàn)也不容忽視；晶界散射導(dǎo)致導(dǎo)熱系數(shù)減小,尤其對(duì)電子導(dǎo)熱系數(shù)作用顯著；納米線總導(dǎo)熱系數(shù)隨著溫度的升高而降低；隨著截面尺寸減小而減小,但聲子導(dǎo)熱系數(shù)所占份額有所增加；隨著長度的增加逐漸增加,但當(dāng)長度增至200nm時(shí),導(dǎo)熱系數(shù)趨于一穩(wěn)定值。當(dāng)納米線長度大于截面尺寸時(shí),XY面內(nèi)的導(dǎo)熱系數(shù)低于軸向(Z方向)上的導(dǎo)熱系數(shù)。 與此同時(shí),采用兩平面模型計(jì)算兩納米線端面間的近場(chǎng)輻射換熱,與文獻(xiàn)中的實(shí)驗(yàn)數(shù)據(jù)進(jìn)行驗(yàn)證,并分析了間距和溫度的影響。研究表明：近場(chǎng)輻射熱流和當(dāng)量導(dǎo)熱系數(shù)隨著溫度的增加逐漸增加,且理論計(jì)算值與文獻(xiàn)實(shí)驗(yàn)結(jié)果吻合得較好；兩納米線間近場(chǎng)輻射換熱的當(dāng)量導(dǎo)熱系數(shù)隨著間距的增加先增加后減小,在間距為30nm左右,存在一個(gè)峰值。在介觀尺度下,對(duì)輻射起主要貢獻(xiàn)的是s偏振近場(chǎng)電磁波,但是隨著間距的減小,p偏振近場(chǎng)電磁波急劇增加。當(dāng)間距大于1000nm時(shí),近場(chǎng)作用逐漸消失,遠(yuǎn)場(chǎng)開始起主導(dǎo)作用。 再次,采用非平衡分子動(dòng)力學(xué)模擬介孔基材與納米線間的界面熱阻,并與聲學(xué)失配模型、散射失配模型進(jìn)行比較。研究表明：隨著溫度的升高,界面熱阻逐漸減��；界面兩端材料質(zhì)量差異越大,界面熱阻越高。 最后,建立熱阻網(wǎng)絡(luò)模型來耦合介孔基材導(dǎo)熱系數(shù)、納米孔隙內(nèi)氣體導(dǎo)熱系數(shù)、考慮界面散射的填充納米線導(dǎo)熱系數(shù)、介孔基材與納米線間的界面熱阻、孔道內(nèi)近場(chǎng)輻射、納米線間近場(chǎng)輻射等,得到復(fù)合材料的綜合導(dǎo)熱系數(shù),同時(shí)采用雙流計(jì)法和瞬態(tài)熱源法對(duì)材料的導(dǎo)熱系數(shù)進(jìn)行實(shí)驗(yàn)測(cè)量,與理論研究進(jìn)行驗(yàn)證,分析近場(chǎng)輻射、界面散射對(duì)材料綜合導(dǎo)熱系數(shù)的影響。研究表明：介孔復(fù)合材料的綜合導(dǎo)熱系數(shù)呈現(xiàn)各向異性,隨著孔徑的增加,X、Z方向上的導(dǎo)熱系數(shù)逐漸降低,Y方向上的導(dǎo)熱系數(shù)存在峰值；隨著納米線間距的增加或納米線長度的減小,即填充率的減小,各個(gè)方向上的導(dǎo)熱系數(shù)均逐漸減小；在X、Y方向上,由界面散射產(chǎn)生的導(dǎo)熱系數(shù)降低值高于由近場(chǎng)輻射產(chǎn)生的導(dǎo)熱系數(shù)升高值,考慮了界面散射和近場(chǎng)輻射的導(dǎo)熱系數(shù)比未考慮的要低；Z方向上剛好與之相反。孔道內(nèi)填充金屬納米線,只有當(dāng)填充率很高時(shí),才表現(xiàn)出對(duì)導(dǎo)熱系數(shù)的明顯提高；界面熱阻導(dǎo)致介孔復(fù)合材料的導(dǎo)熱系數(shù)降低了20%以內(nèi)。
[Abstract]:With the development of aviation industry , the high integration of electronic components and the development of microelectronic mechanical system ( MEMS ) , the thermal design of micro - chip integrated circuits , the temperature control of aerospace equipment and the cooling of microelectronic devices require special thermal characteristics .

The near - field radiation heat transfer model is established for the ordered mesoporous substrate , the near - field radiation heat transfer model is established for the inner surface boundary of the pore channel , and the influence of pore size and temperature is further analyzed . The thermal conductivity of the shell wall of the mesoporous base material is calculated by using the theoretical model . The thermal conductivity of the shell wall of the mesoporous base material is reduced with the increase of the aperture , and the anisotropy is exhibited .
The near - field radiation heat flux and the equivalent thermal conductivity of the tunnel are exponentially decaying with the increase of the aperture . As the temperature increases slowly , the near - field radiation heat flow is 2 - 7 orders of magnitude higher than the far - field radiation , and the smaller the aperture , the more significant the near field effect ;
The theoretical values of the effective thermal conductivity of the mesoporous base material are in good agreement with the experimental values . As the pore size increases , the effective thermal conductivity of the near - field radiation is increased slowly , and the effective thermal conductivity of the near - field radiation is considered to be about 0.2 -10 % .

Secondly , aiming at filling metal nanowires , using equilibrium molecular dynamics method to simulate the phonon thermal conductivity of nano - wire , and using Boltzmann transport theory to calculate the electron thermal conductivity of nano - wire , the influence of surface scattering on the thermal conductivity of nano - wire is obtained .
Grain boundary scattering results in the decrease of thermal conductivity , especially the effect of electron thermal conductivity .
the total thermal conductivity of the nanowires decreases with increasing temperature ;
As the cross - sectional dimension decreases , the proportion of phonon thermal conductivity increases ;
As the length increases , the thermal conductivity tends to be a stable value when the length increases to 200 nm . When the length of the nanowire is greater than the cross - sectional dimension , the thermal conductivity in the XY plane is lower than the thermal conductivity in the axial direction ( Z direction ) .

At the same time , the near - field radiation heat transfer between the end faces of the two nanowires is calculated by using two - plane model , and the influence of pitch and temperature is analyzed . The results show that the near - field radiation heat flux and equivalent thermal conductivity gradually increase with the increase of temperature , and the theoretical calculation value is in good agreement with the experimental results .
The equivalent thermal conductivity of the near - field radiation heat transfer between the two nanowires decreases with the increase of the spacing , and there is a peak at the interval of 30 nm . Under the mesoscopic scale , the near - field electromagnetic wave of the s - polarized near - field electromagnetic wave is mainly contributed to the radiation , but the near - field effect gradually disappears when the spacing is greater than 1000nm , and the far field starts to play a leading role .

Thirdly , the interface thermal resistance between the mesoporous substrate and the nanowire is simulated by the non - equilibrium molecular dynamics , and compared with the acoustic mismatch model and the scattering mismatch model . The results show that the thermal resistance of the interface gradually decreases with the increase of temperature ;
The greater the difference between the material quality at both ends of the interface , the higher the thermal resistance of the interface .

Finally , a thermal resistance network model is established to couple the thermal conductivity of the mesoporous substrate , the thermal conductivity of the gas in the nano - pores , the thermal resistance of the filled nanowires , the near - field radiation in the pores , near - field radiation in the pores , and the like , so as to obtain the comprehensive thermal conductivity of the composite material .
With the increase of the spacing of the nanowire or the reduction of the length of the nanowire , that is , the filling rate is reduced , the thermal conductivity in each direction is gradually reduced ;
In the X and Y directions , the decrease of the thermal conductivity caused by the interface scattering is higher than that of the heat conduction coefficient generated by near field radiation , and the thermal conductivity of the interface scattering and near field radiation is considered to be lower than that of the non - field radiation ;
in that Z direction , the metal nano wire is filled in the pore canal , and only when the filling rate is high , the heat conduction coefficient is obviously improved ;
the thermal resistance of the interface leads to the reduction of the thermal conductivity of the mesoporous composite material within 20 percent .

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TB383.4

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