硼顆粒的包覆機(jī)理及工藝研究進(jìn)展

陳冰虹，劉建忠，梁導(dǎo)倫，周禹男，周俊虎

(浙江大學(xué)能源清潔利用國家重點(diǎn)實(shí)驗(yàn)室，浙江 杭州310027)

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硼顆粒的包覆機(jī)理及工藝研究進(jìn)展

陳冰虹，劉建忠，梁導(dǎo)倫，周禹男，周俊虎

(浙江大學(xué)能源清潔利用國家重點(diǎn)實(shí)驗(yàn)室，浙江 杭州310027)

闡述了不同包覆材料對(duì)硼顆粒的包覆機(jī)理，從5個(gè)方面總結(jié)了硼顆粒包覆材料的選取原則，包括：去除硼顆粒表面氧化膜、提高燃燒溫度、降低硼的點(diǎn)火溫度、提高表面相容性、催化硼顆粒的氧化反應(yīng)?？偨Y(jié)了沉淀法、表面反應(yīng)包覆法、高分子吸附聚合法、氣相包覆法和機(jī)械球磨法等多種硼顆粒包覆工藝的研究狀況，分析并比較了不同工藝的作用機(jī)理和實(shí)際應(yīng)用效果。介紹了現(xiàn)代硼顆粒表面包覆效果測試技術(shù)的特點(diǎn)和應(yīng)用范圍。評(píng)述了目前硼顆粒包覆技術(shù)的研究現(xiàn)狀和不足，并對(duì)未來的研究方向進(jìn)行了展望。附參考文獻(xiàn)46篇。

物理化學(xué); 硼顆粒; 包覆機(jī)理；富燃料推進(jìn)劑；金屬燃料

引 言

富燃料推進(jìn)劑是適應(yīng)固體火箭沖壓發(fā)動(dòng)機(jī)的良好燃料，添加金屬燃料是當(dāng)前高能貧氧推進(jìn)劑的一個(gè)重要發(fā)展方向。硼以其高的質(zhì)量熱值和容積熱值被認(rèn)為是固體貧氧推進(jìn)劑的最佳燃料[1]，但由于硼顆粒的部分固有特性[2]，含硼推進(jìn)劑在實(shí)際應(yīng)用中受到一定的限制。硼在固體富燃料推進(jìn)劑中應(yīng)用存在的突出問題包括4個(gè)方面：(1)單質(zhì)硼的熔沸點(diǎn)較高，難以熔化氣化，B2O3的沸點(diǎn)也較高，燃燒過程要經(jīng)歷B2O3的氣化，進(jìn)一步增加了硼顆粒點(diǎn)火的困難；(2)硼顆粒點(diǎn)火延滯，燃燒時(shí)間長，在發(fā)動(dòng)機(jī)燃燒室中存在燃燒不完全現(xiàn)象，能量釋放不完全；(3)硼的燃燒效率低，耗氧量大，產(chǎn)生殘?jiān)?，無法發(fā)揮其高能量熱值；(4)硼顆粒表面存在B2O3、H3BO3等雜質(zhì)，使得硼粒子與推進(jìn)劑體系不相容[4]。

研究表明[5-9]，使用包覆材料對(duì)硼顆粒進(jìn)行包覆是改善硼顆粒點(diǎn)火燃燒特性的較好途徑，國內(nèi)外學(xué)者對(duì)此也進(jìn)行了大量研究。本文綜述了硼顆粒表面包覆作用機(jī)理、包覆工藝流程及包覆效果表征3個(gè)方面的研究進(jìn)展，為提升硼顆粒的實(shí)際應(yīng)用效果提供借鑒。

1 包覆作用機(jī)理

在硼顆粒表面包覆材料的選擇上，為提升硼顆粒燃燒效果及其與推進(jìn)劑的相容性[10]，目前的研究中涵蓋了氧化劑、金屬、黏合劑等眾多類型的材料。在促進(jìn)硼顆粒及相關(guān)硼基推進(jìn)劑性能上，各種包覆材料的作用機(jī)理主要分為以下幾個(gè)方面。

1.1 硼顆粒表面除膜

與硼相比，硼顆粒表面形成的B2O3氧化膜具有熔點(diǎn)低(460℃)、沸點(diǎn)高(1860℃)[11]的特性，在燃燒過程中呈液膜態(tài)，阻礙內(nèi)部硼顆粒的進(jìn)一步燃燒，導(dǎo)致硼顆粒的燃燒效率較低[12]。利用包覆材料與氧化膜的化學(xué)反應(yīng)可實(shí)現(xiàn)硼顆粒表面氧化膜的去除[13]，從而改善硼顆粒的點(diǎn)火和燃燒性能。該類包覆材料主要包括氟樹脂 (Viton A)、LiF、聚偏氟乙烯(PVDF)和三羥甲基丙烷 (TMP)等。

LiF的除膜作用主要通過反應(yīng)(1)實(shí)現(xiàn)[14]。LiF與B2O3發(fā)生化學(xué)反應(yīng)，生成氣態(tài)產(chǎn)物，從而實(shí)現(xiàn)硼顆粒表面氧化膜的去除。

(1)

Viton A、PVDF通過分解產(chǎn)生HF并與B2O3發(fā)生反應(yīng)(2)、(3)，以達(dá)到除膜的目的[15]。

(2)

(3)

TMP作為一種常用交聯(lián)劑和擴(kuò)鏈劑[16]，能與硼顆粒表面B2O3發(fā)生反應(yīng)(4)，從而促進(jìn)硼顆粒的點(diǎn)火燃燒。

(4)

Liu等[17]用激光實(shí)驗(yàn)方法研究了Viton A、LiF包覆硼顆粒對(duì)B/MA/AP/HTPB含硼推進(jìn)劑燃燒性能的影響。結(jié)果表明，用LiF包覆硼顆粒能縮短含硼推進(jìn)劑的點(diǎn)火延遲時(shí)間，而用Viton A包覆則會(huì)延長含硼推進(jìn)劑的點(diǎn)火延遲時(shí)間。

Hidetsugu等[18]研究了Viton A包覆對(duì)B/KNO3混合物燃燒的影響。結(jié)果表明，Viton A包覆層能防止硼顆粒表面吸水，同時(shí)降低混合物的撞擊感度與點(diǎn)火溫度。

陳濤等[19]研究了LiF包覆對(duì)推進(jìn)劑一次、二次燃燒過程中能量釋放特性的影響。結(jié)果表明，高溫(高于1353℃)下，LiF通過吸熱反應(yīng)消耗了硼顆粒表面的B2O3氧化膜，加速B/O反應(yīng)，使得LiF包覆的硼顆粒在599℃發(fā)生快速氧化反應(yīng)。硼的燃燒效率從65.48%提高到81.57%，其對(duì)應(yīng)推進(jìn)劑一次能量釋放效率和二次能量釋放效率得到明顯提高。

此外，在生產(chǎn)硼顆粒過程中，用B4C包覆硼顆粒能有效避免新生硼顆粒表面生成氧化膜，并防止硼顆粒的凝聚[20]。

1.2 提高燃燒溫度

研究表明[21]，通過在硼顆粒表面包覆一些分解放熱明顯的材料，可有效提高硼顆粒周圍溫度，有利于B2O3氧化膜的氣化蒸發(fā)，從而促進(jìn)硼顆粒的燃燒。常用的此類包覆材料包括氧化劑和疊氮化物兩大類，如AP、高氯酸鉀(KP)、聚疊氮縮水甘油醚(GAP)、疊氮化鈉(NaN3)等。

李疏芬等[22]研究了AP、KP包覆層對(duì)硼基推進(jìn)劑燃燒的影響。結(jié)果表明，使用AP、KP對(duì)硼顆粒表面進(jìn)行包覆有利于提高其反應(yīng)活性，使推進(jìn)劑的燃面及火焰溫度提高200℃以上，硼顆粒的轉(zhuǎn)化率和燃燒效率得到明顯提高；此外，氧化劑分解得到的新生態(tài)氧[O]吸附積累在硼顆粒表面，還可以提高硼顆粒表面的氧含量，對(duì)新生態(tài)[O]的滲透擴(kuò)散有利。

Shyu等[23]研究了GAP包覆硼顆粒及其對(duì)含硼推進(jìn)劑燃燒性能的影響。對(duì)比了GAP包覆硼顆粒與純硼顆粒的點(diǎn)火燃燒性能。結(jié)果表明，GAP包覆能縮短硼顆粒的點(diǎn)火延遲時(shí)間，但在低氧濃度下該效應(yīng)不明顯。GAP包覆硼顆粒組成的硼基推進(jìn)劑燃速更快，燃燒更劇烈和完全。

利用NaN3在400℃以上劇烈分解所釋放的熱量加熱硼顆粒也可以達(dá)到提高燃燒溫度的效果[14]。此外，其分解產(chǎn)物Na3N可進(jìn)一步在O2中燃燒產(chǎn)生Na2O，該物質(zhì)能與B2O3作用，降低硼顆粒表面的黏稠性，有利于O2向硼內(nèi)部擴(kuò)散。但由于 NaN3不含氧，不會(huì)產(chǎn)生新生態(tài)的[O]。研究表明，用其包覆硼顆粒沒有用氧化劑包覆的燃燒劇烈。

1.3 降低硼的點(diǎn)火溫度

硼的點(diǎn)火溫度較高，點(diǎn)火困難。在硼顆粒表面包覆可燃金屬，可有效防止硼顆粒表面生成低溫氧化層。此外，部分金屬能與硼反應(yīng)生成燃點(diǎn)較低的金屬硼化物，可以降低硼的燃點(diǎn)，促進(jìn)硼的點(diǎn)火和燃燒[24]。目前，用于硼顆粒表面包覆研究的金屬主要包括Ti、Zr、Mg等。

美國航空化學(xué)研究試驗(yàn)公司[25-26]對(duì)硼顆粒表面包覆進(jìn)行了深入的研究。他們分別利用金屬Ti和金屬Zr對(duì)硼顆粒進(jìn)行表面包覆。結(jié)果表明，在溫度為2200K，壓力400kPa條件下，當(dāng)Ti的涂層占整個(gè)硼顆?？傎|(zhì)量的9%～17%時(shí)，直徑為2μm的包覆硼顆粒在0.09ms內(nèi)點(diǎn)燃，比未經(jīng)包覆的硼要快得多。金屬Zr包覆硼顆粒也能改善硼的點(diǎn)火燃燒性能，但所消耗的金屬量較多，為硼總質(zhì)量分?jǐn)?shù)的20%～30%。

Pace等[27]研究了金屬鎂包覆層對(duì)硼顆粒點(diǎn)火燃燒性能的影響。鎂除通過氧化放熱提高硼顆粒表面溫度外，還可與硼反應(yīng)生成MgB2，從而降低點(diǎn)火溫度。結(jié)果表明，當(dāng)金屬鎂包覆度不超過30%時(shí)，隨著金屬鎂含量的提高，硼顆粒的燃速增加。鎂包覆層對(duì)燃速的提高在壓強(qiáng)低于0.55MPa情況下較為明顯，當(dāng)壓強(qiáng)高于0.55MPa時(shí)，影響則較弱。當(dāng)壓強(qiáng)為0.35MPa時(shí)，含鎂包覆硼顆粒(B/Mg/HTPB質(zhì)量比為8∶2∶90)的推進(jìn)劑燃速為含未包覆硼顆粒(B/Mg/HTPB質(zhì)量比10∶0∶90)的推進(jìn)劑的1.25倍。

1.4 提高表面相容性

研究表明[28]，在含硼推進(jìn)劑中，硼顆粒表面存在的雜質(zhì)(B2O3、H3BO3等)會(huì)與HTPB的羥基反應(yīng)生成硼酸酯，從而引起凝膠化反應(yīng)，導(dǎo)致硼顆粒與黏合劑不相容，嚴(yán)重影響了硼的工藝性能。為了解決該問題，可在硼顆粒表面包覆相容性較強(qiáng)的材料，從而改善硼顆粒表面的相容性。

張教強(qiáng)等[29]研究了HTPB對(duì)硼顆粒的表面包覆。結(jié)果表明，利用HTPB與硼顆粒表面酸性物質(zhì)反應(yīng)，能在硼顆粒表面形成均勻包覆層，有利于提高硼顆粒表面的規(guī)整性，并有效避免制藥過程中硼顆粒表面雜質(zhì)與黏合劑的反應(yīng)，有利于改善硼基推進(jìn)劑的制備工藝。

異氰酸酯類固化劑與硼顆粒表面的硼酸(H3BO3)會(huì)發(fā)生反應(yīng)(見式(5))，對(duì)固化體系產(chǎn)生干擾。趙孝彬等[13]用異氰酸酯類固化劑對(duì)硼顆粒表面進(jìn)行包覆，以消除硼與固化體系之間的副反應(yīng)。發(fā)現(xiàn)以TDI對(duì)硼顆粒進(jìn)行表面包覆處理后，能在GAP/AN體系中獲得致密無孔的藥柱。

(5)

TMP除了前述的除膜作用外，還能與硼顆粒表面的H3BO3發(fā)生反應(yīng)(見式(6))，從而有利于解決硼顆粒與推進(jìn)劑體系的不相容問題，減弱硼顆粒的吸濕性[13]。

(6)

從上述研究來看，為解決硼顆粒表面雜質(zhì)所導(dǎo)致的與推進(jìn)劑體系不相容的問題，大多采用推進(jìn)劑體系成分對(duì)硼顆粒進(jìn)行包覆，除去表面雜質(zhì)，從而改變硼顆粒的表面特性，為后續(xù)推進(jìn)劑的制備工藝奠定良好的基礎(chǔ)。

1.5 催化硼顆粒氧化反應(yīng)

催化劑能降低化學(xué)反應(yīng)所需的活化能，促進(jìn)反應(yīng)的進(jìn)行。使用適當(dāng)?shù)拇呋瘎?duì)硼顆粒進(jìn)行包覆，是促進(jìn)硼顆粒氧化的可行途徑。

Xi等[30]利用CO2激光點(diǎn)火燃燒試驗(yàn)系統(tǒng)(圖 1)研究了7種金屬氧化物作為催化劑對(duì)硼顆粒點(diǎn)火燃燒特性的影響。結(jié)果發(fā)現(xiàn)，Bi2O3的催化效果最佳，能使硼顆粒的點(diǎn)火溫度降低約15.2%，并縮短硼顆粒的點(diǎn)火燃燒時(shí)間。其催化原理如式(7)所示：顆粒氧化過程中，Bi2O3向B-B2O3表面擴(kuò)散，與B發(fā)生反應(yīng)，促進(jìn)硼顆粒的氧化。之后，Bi向顆粒表面擴(kuò)散，被空氣中的氧氣重新氧化為Bi2O3。

(7)

圖1 CO2激光點(diǎn)火燃燒試驗(yàn)系統(tǒng)Fig.1 CO2 laser ignition and combustion test system

Dreizin等[31]提出一種硼點(diǎn)火模型并進(jìn)行了實(shí)驗(yàn)驗(yàn)證。他們提出，在硼顆粒點(diǎn)火過程中，氧在B2O3氧化層中的溶解度不斷上升，當(dāng)其達(dá)到溶解極限時(shí)，硼顆粒進(jìn)入燃燒階段。實(shí)驗(yàn)中所觀察到的點(diǎn)火延遲時(shí)間與氧達(dá)到B-O溶解飽和所需時(shí)間相等。因此，提高點(diǎn)火階段硼顆粒的攝氧量可有效縮短點(diǎn)火延遲時(shí)間。

根據(jù)該模型，目前研究中通過在硼顆粒表面包覆稀土催化劑CeO2，可攜帶氧氣并提高硼顆粒在點(diǎn)火階段的攝氧量，能夠促進(jìn)硼顆粒的點(diǎn)火，并可在一定程度上催化硼顆粒周圍碳?xì)浠衔锏姆磻?yīng)，從而幫助硼顆粒的燃燒。CeO2的催化作用主要來源于其+3與+4兩個(gè)價(jià)態(tài)之間的轉(zhuǎn)化，該轉(zhuǎn)化在低于硼顆粒點(diǎn)火溫度下就能完成。進(jìn)一步研究表明，與其他催化劑相比，Ce表面的高活性氧具有更高的遷移率，故在還原環(huán)境下CeO2能轉(zhuǎn)化為CeO2-x(0 ≤x≤ 0.5)[32-33]。

Karmakar等[34]研究了稀土元素催化劑對(duì)硼顆粒點(diǎn)火特性的影響。實(shí)驗(yàn)中選取CeO2及REOm-41(包含CeO2、La2O3和Gd2O3，其中Ce與La摩爾比為3∶1，Ce與Gd摩爾比為80∶1)納米顆粒作為包覆材料制備包覆硼顆粒。結(jié)果發(fā)現(xiàn)，當(dāng)稀土包覆層質(zhì)量分?jǐn)?shù)為20%時(shí)，能有效縮短硼顆粒的點(diǎn)火延遲時(shí)間，當(dāng)質(zhì)量分?jǐn)?shù)大于20%時(shí)，則會(huì)限制硼顆粒中氧的擴(kuò)散，反而不利于硼顆粒的點(diǎn)火燃燒。從上述研究可以發(fā)現(xiàn)，CeO2作為催化劑負(fù)載在硼顆粒上，能有效促進(jìn)硼顆粒的點(diǎn)火燃燒。

為了提升硼顆粒的不同性能及屬性，以上研究中選取的包覆材料，涵蓋氧化劑、黏合劑、高熱值金屬、疊氮化物、催化劑等多種類型，其在提高硼顆粒點(diǎn)火燃燒特性與相容性上發(fā)揮了不同的作用，主要分為以下幾個(gè)方面：(1)能通過化學(xué)反應(yīng)去除硼顆粒表面氧化膜；(2)分解會(huì)放出大量的熱，有利于提高燃燒溫度，加快B2O3的氣化；(3)反應(yīng)活性較高，有利于降低硼的點(diǎn)火溫度；(4)改變硼顆粒表面性能，提高其與推進(jìn)劑的相容性；(5)能有效加快硼顆粒的反應(yīng)速率。

從目前的研究來看，對(duì)硼顆粒的包覆材料類型眾多，大多是針對(duì)硼顆粒單一特性尤其是燃燒特性方面的提升。為實(shí)現(xiàn)從多方面提升硼顆粒的性能，提出了高能黏合劑GAP等包覆材料類型。而以具有不同效果的多種材料共同包覆硼顆粒，以提升其綜合性能的思路則由于包覆劑比例不宜過大的限制未有相應(yīng)的實(shí)踐。隨著包覆手段與包覆工藝的發(fā)展，可實(shí)現(xiàn)更小的包覆層厚度，從而使得多種材料共同包覆成為未來硼顆粒包覆中可行的發(fā)展方向。此外，基于研究手段所限，目前大部分對(duì)包覆硼顆粒及其推進(jìn)劑點(diǎn)火燃燒性能的測試條件與實(shí)際應(yīng)用條件仍存在一定的距離，影響了對(duì)實(shí)際應(yīng)用的指導(dǎo)作用。

2 包覆工藝

針對(duì)不同的硼顆粒表面包覆材料，其所適宜的包覆條件與包覆方法有所不同。為此，國內(nèi)外學(xué)者根據(jù)實(shí)際應(yīng)用需求，對(duì)包覆工藝進(jìn)行研究和改進(jìn)，以獲得包覆更為均勻的硼顆粒。

2.1 沉積法(重結(jié)晶法)

沉積法是硼顆粒表面包覆中常用的工藝，又稱為重結(jié)晶法。實(shí)驗(yàn)中，把硼粉與包覆劑按一定比例加入溶劑中(常用溶劑有二氯甲烷、二甲基亞砜、四氯化碳等，具體根據(jù)包覆劑選擇)，在一定溫度下充分?jǐn)嚢?，使硼顆粒的表面與包覆劑充分接觸，蒸發(fā)溶劑即可得到包覆的硼顆粒。沉積法的實(shí)施中，溶劑的種類、蒸發(fā)速率、包覆量等因素對(duì)包覆效果都有著明顯的影響，國內(nèi)外針對(duì)各影響因素進(jìn)行了相關(guān)的研究，并對(duì)沉積法進(jìn)行了相應(yīng)的改進(jìn)。張教強(qiáng)等[35]利用沉積法在硼顆粒表面包覆AP的過程中發(fā)現(xiàn)，采用甲醇或丙酮作為溶劑，硼粉干燥后不易板結(jié)，操作較為簡易。合適的蒸發(fā)速率有利于包覆劑完整、均勻地沉積在硼顆粒表面(溶劑的最佳蒸發(fā)速率為10 g/h)。此外，在包覆前先對(duì)硼顆粒進(jìn)行硅烷偶聯(lián)劑預(yù)處理有利于實(shí)現(xiàn)更均勻的包覆，表面直接反應(yīng)16 h以上，可達(dá)到最佳的包覆效果。

席劍飛等[36-37]針對(duì)沉積法可能導(dǎo)致的包覆不均勻問題進(jìn)一步提出了改進(jìn)的雙溶劑法。選擇兩種合適的溶劑(如溶劑1和溶劑2)，應(yīng)滿足：(1)包覆材料能溶于溶劑1但不溶于溶劑2；(2)溶劑1可溶于溶劑2；(3)溶劑1的沸點(diǎn)小于溶劑2。通過實(shí)驗(yàn)研究給出了常用包覆劑及對(duì)應(yīng)的溶劑，結(jié)果如表1所示[36]。首先，用溶劑1來溶解包覆劑制成溶液，然后將溶液分散于溶劑2中，蒸發(fā)溶劑過程中，溶劑1由于沸點(diǎn)較低先蒸出，隨后溶劑2蒸出，獲得包覆硼顆粒。雙溶劑的引入使硼粉在整個(gè)包覆過程中都可以懸浮分散在溶劑中，從而令包覆更均勻。

表1 硼顆粒雙溶劑包覆法中常用材料對(duì)應(yīng)溶劑

2.2 表面反應(yīng)包覆法

對(duì)于一些難以溶解的鹽類，直接利用沉積法進(jìn)行包覆存在一定的困難，獲得的包覆顆粒均勻度不佳。為此，可通過化學(xué)反應(yīng)在硼顆粒表面直接生成包覆劑并附著在硼顆粒表面，從而實(shí)現(xiàn)包覆。

圖2 LiF包覆硼顆粒工藝流程Fig.2 Process flow of coating boron particles with LiF

龐維強(qiáng)等[39]在用LiF對(duì)硼顆粒進(jìn)行表面包覆過程中發(fā)現(xiàn)，攪拌速率會(huì)影響基體在改性體系中分散的均勻性，當(dāng)攪拌速率為750 r/min左右時(shí)，包覆效果最好。

張教強(qiáng)等[40]研究了LiOH濃度對(duì)超細(xì)硼粉包覆效果的影響。結(jié)果表明，LiOH濃度對(duì)包覆層的致密性有一定的影響，LiOH濃度越高，超細(xì)硼粉的包覆層越致密，包覆效果越佳。

該方法在操作上較為簡單，與沉積法類似，但其可通過化學(xué)反應(yīng)實(shí)現(xiàn)難溶鹽的表面包覆，針對(duì)性較強(qiáng)。

2.3 高分子吸附聚合法

對(duì)于HTPB、聚對(duì)苯二酸丁二酯(PBT)等高分子包覆材料，其對(duì)硼顆粒的包覆存在著有機(jī)材料與無機(jī)材料的相容性問題，是包覆工藝中所需要重點(diǎn)關(guān)注的問題。目前，常用的高分子包覆方法主要分為兩種：高分子在表面直接吸附和單體在顆粒表面聚合。其中，高分子直接吸附法即直接把硼顆粒作為吸附核心分散到溶有高分子的有機(jī)溶液中，蒸發(fā)溶劑后可得到包覆高分子的硼顆粒。而單體表面聚合法則是使聚合反應(yīng)發(fā)生在硼顆粒表面從而實(shí)現(xiàn)包覆。

張教強(qiáng)等[29]采用表面聚合及直接吸附法研究了HTPB對(duì)硼顆粒的表面包覆。其中，表面聚合包覆過程中所采用的條件為：以苯為溶劑，于80℃經(jīng)14h的酯化反應(yīng)后，以甲苯二異氰酸酯(TDI)為固化劑，于70～80℃進(jìn)行固化處理。對(duì)比發(fā)現(xiàn)，在表面直接吸附包覆過程中，包覆量不易控制，常導(dǎo)致硼顆粒結(jié)塊，不利于固化反應(yīng)的進(jìn)行；而采用表面聚合包覆法時(shí)，過濾后硼顆粒分散較好，有利于后期的固化反應(yīng)。故表面聚合包覆法更有利于HTPB在硼顆粒表面的包覆。

張瓊方[38]研究了不同因素對(duì)PBT包覆硼顆粒的影響。結(jié)果發(fā)現(xiàn)，最佳的包覆條件為以四氫吠喃為溶劑，在包覆前先對(duì)硼粉進(jìn)行硅烷偶聯(lián)劑的預(yù)處理，然后采用表面直接反應(yīng)的方法，反應(yīng)進(jìn)行16h以上，固化6～8h，真空干燥。

高分子吸附聚合法可通過控制包覆物質(zhì)的用量、包覆時(shí)間等較好地控制包覆效果，但核層顆粒與包覆層須具有較好的相容性。常需加入提高相容性的介質(zhì)，如具有某些功能基團(tuán)的高分子，來提高包覆質(zhì)量[41]。

2.4 氣相包覆法

氣相法是直接利用氣體或通過各種手段將殼層物質(zhì)轉(zhuǎn)變成氣體，使之在氣態(tài)下發(fā)生物理或化學(xué)變化而實(shí)現(xiàn)顆粒表面包覆的方法[42]。

W. Felder等[43]用連續(xù)擴(kuò)散流法制備鎂或鋁包覆的硼顆粒。制備過程中，硼顆粒的氣溶膠以共軸環(huán)形路徑被注入到一個(gè)金屬蒸氣-Ar的混合氣流中，混合后金屬蒸氣沉積在硼顆粒表面，從而完成包覆。操作條件由所需包覆層的厚度、硼顆粒的密度及包覆金屬蒸氣的均相成核間的平衡來決定。

美國航空化學(xué)研究試驗(yàn)公司[25-26]提出了一種金屬鈦包覆硼顆粒的方法，其原理是基于鈉與四氯化鈦和三氯化硼的放熱反應(yīng)(式(7)和式(8))。

(7)

(8)

包覆過程中，將過量的Na和BCl3加入到反應(yīng)器(圖3)中,并進(jìn)行充分的攪拌混合，反應(yīng)(7)生成的硼顆粒懸浮在NaCl氣體和過量的Na氣體中。這些生成物通過超音速噴管發(fā)生膨脹，在噴管處壓入TiCl4氣體，過量的Na與TiCl4反應(yīng)生成Ti氣體(反應(yīng)(8))，氣態(tài)的Ti遇到硼顆粒后冷凝并包覆在硼顆粒表面。

圖3 金屬Ti包覆硼顆粒的反應(yīng)器[25-26]Fig 3 Reactor for coating boron particle production[25-26]

該法所獲得的包覆硼顆粒中混有NaCl氣體，可通過圖4中所示的超音速有效碰撞收集器去除，獲得純凈的包覆硼顆粒。

圖4 超音速有效碰撞收集器簡圖[25-26] Fig 4 Diagrammatic sketch of supersonic effective collision trap[25-26]

氣相包覆法所獲得的包覆硼顆粒純度高，收集簡單、效率高，但對(duì)設(shè)備要求高、投入大。

2.5 機(jī)械球磨法

Van Devener等[44]利用球磨法制備表面包覆CeO2催化劑的納米級(jí)硼顆粒，首次獲得未氧化的、穩(wěn)定的、燃料相容性高的納米級(jí)包覆硼顆粒，該法也可用于B4C的包覆。實(shí)驗(yàn)中，首先將2g硼顆粒、0.1g CeO2用160g研磨球研磨30min，使兩種材料充分接觸反應(yīng)，塊狀CeO2附著在硼顆粒表面。然后在N2氣氛下打開研磨器，加入15mL己烷和1mL十八烯酸，濕法研磨2.5h。此法所獲得的包覆硼顆粒表面性能佳，在碳?xì)浠衔镏械姆稚⑿暂^好，有利于其在推進(jìn)劑體系中的使用，但由于結(jié)合力不強(qiáng)，包覆效果不如其他方法。

綜合以上包覆工藝，由于不同的工藝特點(diǎn)，所適用的范圍也不同。其中，沉淀法可精確控制各組分的含量，且設(shè)備操作較為簡單，有利于規(guī)?；a(chǎn)，目前在顆粒包覆方面使用較為廣泛，其可能產(chǎn)生的包覆不均勻問題也隨著工藝的發(fā)展得到了相應(yīng)的改善，是一種效果良好、成本較低的工藝手段。

目前，包覆方法研究中對(duì)包覆過程中的參數(shù)控制研究較為深入，而對(duì)包覆機(jī)理的認(rèn)識(shí)則尚待加強(qiáng)。此外，基于工藝簡單化的考慮，在實(shí)際過程中通常采用單一的包覆方法，要實(shí)現(xiàn)硼顆粒多層包覆存在一定的困難。在未來的發(fā)展中，應(yīng)深入了解包覆工藝的包覆機(jī)理，分析不同包覆手段之間的兼容性，為實(shí)現(xiàn)硼顆粒的多層包覆、提升硼顆粒實(shí)際應(yīng)用效果奠定基礎(chǔ)。

3 包覆效果表征

不同的包覆工藝及操作流程等對(duì)包覆效果有著明顯的影響，包括包覆材料在硼顆粒表面分布的均勻性、包覆層厚度等。目前，隨著實(shí)驗(yàn)儀器的不斷發(fā)展，對(duì)包覆效果的評(píng)估方法也變得越來越多樣化。

Liu等[17]采用場發(fā)射掃描電鏡(SEM)對(duì)包覆硼顆粒表面進(jìn)行觀測，并利用能譜分析(EDS)對(duì)表面元素進(jìn)行分析。結(jié)果發(fā)現(xiàn)，經(jīng)LiF包覆后金屬顆粒燃燒后團(tuán)聚現(xiàn)象大大減少。張教強(qiáng)等[35]采用傅里葉紅外光譜(FT-IR)、原子力顯微鏡(AFM)等手段分析了AP包覆硼顆粒效果。發(fā)現(xiàn)包覆后硼顆粒表面規(guī)整,而且外表面存在較明顯的包覆層。

敖文等[45]采用X射線衍射儀(XRD)、馬爾文、氮吸附儀、ICP光譜儀、透射電鏡(TEM)等對(duì)硼顆粒物相、顆粒分布、比表面積、表面元素、微觀形態(tài)等情況進(jìn)行分析，獲取了硼顆粒的大量特性參數(shù)。

李疏芬等[46]利用紅外光譜(IR)、核磁共振(NMR)、XRD及X光電子能譜儀(XPS)等對(duì)硼顆粒表面包覆層進(jìn)行檢測，并利用酸度計(jì)與黏度計(jì)測量了包覆硼顆粒的表面酸度及包覆硼顆粒加入HTPB體系的黏度變化。

目前，有關(guān)硼顆粒表面包覆情況的表征方法多樣，所采用的儀器種類繁多?？偟膩砜?，相關(guān)表征手段可分為直接表征與間接表征兩類，如表 2所示。

表2 包覆硼顆粒的表征手段

采用直接表征手段，可通過對(duì)直觀圖像的觀察分析，獲取硼顆粒包覆后的表面形貌，并通過對(duì)比包覆前后的圖像，對(duì)包覆表面的光滑度、均勻性、致密性等進(jìn)行分析。目前，直接表征手段主要采用場發(fā)射掃描電鏡(SEM)、透射電鏡(TEM)、原子力顯微鏡(AFM)等微觀顯微鏡觀察手段進(jìn)行。

采用間接表征手段，則通過對(duì)顆粒固有性質(zhì)變化情況的檢測，獲取硼顆粒包覆后的粒徑變化、元素分布、物相變化、孔隙結(jié)構(gòu)等性質(zhì)的變化，從而對(duì)包覆材料的分布均勻程度、分子結(jié)合情況等進(jìn)行分析，結(jié)合直接表征手段對(duì)包覆效果進(jìn)行評(píng)估。

4 結(jié) 語

綜述了硼顆粒表面包覆作用機(jī)理、包覆工藝及包覆效果表征方面的研究進(jìn)展。從促進(jìn)硼顆粒燃燒效果角度出發(fā)，提出了去除硼顆粒表面氧化膜、提高燃燒溫度、降低硼的點(diǎn)火溫度、提高表面相容性、催化硼顆粒氧化反應(yīng)等5個(gè)方面作為硼顆粒表面包覆材料的選取方向。由此針對(duì)不同包覆材料的作用機(jī)理，選取合適的包覆工藝與操作條件，實(shí)現(xiàn)包覆材料在硼顆粒表面的均勻分布等展開全面的評(píng)述，并分析了現(xiàn)代測試技術(shù)對(duì)硼顆粒包覆效果的表征方法及可行性，從而指導(dǎo)包覆工作的進(jìn)行。

目前，在硼顆粒包覆方面，國內(nèi)外研究所涉及的材料類型較為廣泛，取得了較好的成果。在包覆劑的選擇上，不同包覆材料對(duì)硼顆粒的點(diǎn)火燃燒有著不同的促進(jìn)作用。為提升硼顆粒在含硼推進(jìn)劑中的實(shí)用效果，建議：

(1)在未來的研究中應(yīng)綜合多種促進(jìn)方式，通過尋找兼具多種促進(jìn)效果的包覆材料、探究多層包覆工藝等方式實(shí)現(xiàn)硼顆粒的包覆改良；

(2)在包覆工藝方面，應(yīng)根據(jù)包覆材料類型、工藝流程的可操作性、投資成本和實(shí)際應(yīng)用效果等進(jìn)行綜合考慮；

(3)此外，硼顆粒的表面包覆最終是為提升硼顆粒在含硼推進(jìn)劑中的實(shí)用效果，應(yīng)更多地關(guān)注硼顆粒在不同推進(jìn)劑成分影響下的點(diǎn)火燃燒效果，以實(shí)際效果為依據(jù)，改良包覆配方及工藝，不斷提升包覆效果，解決硼顆粒在固體推進(jìn)劑應(yīng)用中存在的問題。

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DOI：10.14077/j.issn.1007-7812.2016.05.003

Abstract:Several mixtures, based on urea derivatives and some inorganic oxidants, including also alumina, were studied by means of ballistic mortar techniques with TNT as the reference standard. The detonation pressure(P), detonation velocity(D), detonation energy(Q), and volume of gaseous product at standard temperature and pressure (STP), V, were calculated using EXPLO5 V6.3 thermochemical code. The performance of the mixtures studied was discussed in relation to their thermal reactivity, determined by means of differential thermal analysis (DTA). It is shown that the presence of hydrogen peroxide in the form of its complex with urea (i.e. as UHP) has a positive influence on the explosive strength of the corresponding mixtures which is linked to the hydroxy-radical formation in the mixtures during their initiation reaction. These radicals might initiate (at least partially) powdered aluminum into oxidation in the CJ plane of the detonation wave. Mixtures containing UHP and magnesium are dangerous because of potential auto-ignition.

Keywords:ballistic mortar;TNT;DTA; peroxides; perchlorates; nitrates; urea

Received date:2016-06-01； Revised date:2016-06-17

Biography:Ahmed K.HUSSEIN(1984-),male,MSC.,research field:Energetic materials.E-mail:ahmed92eqypt@gmail.com

Introduction

Mixtures of compounds based on ammonium nitrate (AN) and urea (U) are used as liquid nitrogen fertilizers, referred to as UAN[1]with melting points between -18℃ and -5℃ (depending on the water content) and as intermolecular castable industrial explosives, commonly known as Carbatols[2-3], with relatively high density, detonation velocity and resistance to initiation[2]. Another subject of practical interest concerning mixtures based on urea nitrate (UN) is their use for criminal purposes[4-5], unfortunately increasingly commonplace[6-8]. The globally commercially available urea hydrogen peroxide (UHP)[9]has, in light of its explosive risk, only been described recently[10]; its behavior when mixed with some inorganic salts has not been studied until now, and thus this paper focuses on it in comparison with several previously studied other mixtures with peroxides[11-13]and/or ammonium nitrate content.

1 Experimental

1.1 Materials

Among the substances used, i.e. ammonium nitrate (AN), sodium nitrate (SN), urea (U), urea hydrogen peroxide complex (UHP), ammonium perchlorate (AP), the urea hydrogen peroxide complex was not studied in any more detail from the point of view of its use in explosive compositions. UHP has a density of 1.4 g/cm3, and is a white crystalline substance that decomposes on melting at 80-90℃. A kinetic study of UHP′s thermal decomposition gave an activation energy of 113kJ/mol with frequency factor of 10-13s-1[14]. Its heat of formation is 65.1kJ/mol and its experimental detonation velocity was 3470-3600 m/s[10]. Aluminum (Al) quality AP-4[2]was used with specific surface area of grains 1000-1100 cm2/g and particle size of 20-22 μm. In the one case of an attempt using magnesium flake for fireworks, the particle size ranged from 100 to 500 μm.

1.2 Preparation of mixture

A weighed amount of urea (U) and/or UHP was mixed mechanically with ammonium nitrate (AN), ammonium perchlorate (AP) and sodium nitrate (SN). The actual mass fraction are shown in Table 1. These mixtures were formed so as to have an oxygen balance (OB) close to zero thus generating gaseous products with a high level of power and low toxicity. Four mixtures based on triacetone triperoxide (3,3,6,6,9,9-hexamethyl-1,2,4,5,7,8-hexoxonane, TATP) with AN and different mass fractions of water (4.2%, 9.9%, 15.5% and 24.5%, respectively) have previously been studied[8，11-12]and compared with the mixtures studied here. Data for urea nitrate (UN) and a mixture of fuel oil with ammonium nitrate (ANFO) were also taken from recent papers[8].

1.3 Calculations of detonation characteristics

The theoretical detonation characteristics (i.e. detonation velocity, detonation energy and volume of gaseous products) of the mixtures tested were calculated using the EXPLO5 thermochemical code, version V6.3. The calculation of detonation parameters is based on the chemical equilibrium steady-state ideal detonation model. The state of gaseous detonation products is described by the EXP-6 equation of state[15-16], based on intermolecular potentials and fundamental statistical mechanical theories for the calculation of the thermodynamic properties of a classical fluid of molecules interacting with a central pair potential are available today. In our calculations we used the WCA/Ree perturbation theory to generate excess thermodynamic data of a pure fluid with an EXP-6 potential, and by interpolating them with a Chebyshev polynomial. The method, i.e. EOS, is described by Byers Brown[17]. The detonation velocity, detonation energy and amount of gaseous detonation products calculated by EXPLO5 V6.3 are summarized in Table 2.

It is very likely that some of the explosive mixtures tested have non-ideal detonation behavior, particularly those containing aluminum and ammonium nitrate. However, in this study we calculated detonation properties assuming an ideal detonation model for all the mixtures (such calculation gives the theoretically maximum detonation properties, i.e. properties at infinite explosive charge diameter), except for aluminum-containing mixtures for which we carried out calculations in two different ways-one assuming Al completely reacts at the CJ state (this gives higher D, P, Q, T values) and the second assuming Al does not react, i.e. remains as solid Al.

Table 1 Formulations of energetic mixtures

Notes:(a) taken from Ref.[1]；(b) taken from Ref.[8]；(c) this mixture contains 5% by wt.fuel oil;Data for mistures N and M were calculated taking aluminum as an inert admixture,for mixtures N1 and M1 this aluminum has reacted fully in the CJ point.

1.4 Relative explosive strength measurement

A ballistic mortar test was used for the determination of the relative explosive strength of the samples studied, using TNT as the reference[18-19]. This substitutes for the Trauzl test in the lead block, which was used in the past but which had certain disadvantages such as high cost, the use of toxic lead and the rupture of a lead block[20]. A fixed amount of an explosive (10g) was wrapped in polypropylene foil and inserted into the mortar enclosed by a steel projectile and initiated using a non-electric detonator (No.8). For each measurement, a part of the non-electric detonator was inserted in the sample and was fired by a match. Three measurements were made for each sample and the mean values are reported in Table 2. The determination is based on measuring the swing angle of the pendulum and by comparing the measurement with a calibration curve for the standard TNT explosive at different masses. The explosive strength of the explosive tested was thus expressed relative to TNT (relative explosive strength, RS as % TNT) and compared with previously studied TATP samples from Refs.[8，11]. UHP and the mixture of urea with sodium nitrate (J) gave practically zero swing angles; therefore, their RS values, in the conditions used, were taken as to be equal to zero. However, both these mixtures are energetic materials which, in specific conditions, can succumb to explosive decomposition (for UHP see Ref. 10, and the J mixture after adding hydrogen peroxide (HP)-see mixture G).

Table 2 Characteristics of energetic mixtures

Notes:(a) taken from Ref[11]；(b) taken from Ref[8]；Datas for mixtures N and M were calculated taking aluminum as an inert admixture, for mixtures N1 and M1 this aluminum has reacted fully in the CJ point.

1.5 Differential thermal analysis (DTA)

Due to the heterogeneity of the mixtures studied, the DSC and TGA techniques, which use samples of only a few mg, were unsuitable for a study of their thermal reactivity. Therefore, a DTA 550 Ex apparatus was used for differential thermal analysis[21]of the explosives under study. The measurements were carried out at atmospheric pressure, with the tested sample in direct contact with the air. The sample (0.05 g) was placed in a test tube made of Simax glass, 5 mm in diameter and 50 mm long. The reference standard was 0.05 g aluminum oxide. Different linear heating rates of 5, 10 and 15℃/min were used. The output of these measurements was evaluated by the Kissinger relationship (1)[22]

(1)

whereφis the linear heating rate andTis the peak temperature of the exothermic decomposition. The thermal reactivity, expressed as theEaR-1slopes, and its regression value from this relationship (in a similar sense to that in references[23-25]), are summarized in Table 3. Because the mixture J did not decompose with liberation of heat (see Fig.1), its exothermic thermal reactivity was taken as being zero.

Fig.1 DTA records of mixture of UHP with ammonium nitrate (upper curve) and mixture of urea with sodium nitrate (lower curve)

SampleEaR-1/KR2SampleEaR-1/KR2B8307a0．9443aM94460．9961C7702a0．9265aN265770．9961D7566a0．9918aO111120．9999E101950．9542P164200．9907F101050．9998Q183210．9622G775850．9207UHP992250．9961H129770．9372TATP161110．9993I326120．9264UN229440．9974J--ANFO79150．888

Note: (a) Taken from Ref[12]

2 Results and Discussion

2.1 Explosive strength versus detonation pressure

In PBX explosives, the relative explosive strength (RS) is directly proportional to the productρD2[16], whereρD2is representative of detonation pressure. The RS values were also determined by ballistic mortar measurements[18](more about influence of the sample quality on outputs of measurements see in Ref.[18]). However, in the mixtures studied, only lines I, II and III in Fig.2 correspond to this relationship. The data for TNT (ρ= 1.0 g/cm3) are situated on line III. Hydrogen peroxide (HP) is included in appropriate mixtures through the presence of UHP (UHP contains 36.1% by wt. of HP). Thermal decomposition of hydrogen peroxide, i.e. homolysis of the peroxide HO-OH bond, has been identified as the dominant chain-branching reaction[23]that controls any given charge ignition. This fact has a positive effect on the performance of the corresponding mixtures (see RS of the mixture s-E versus s-H), whereas comparison of theirpvalues shows the reverse effect.

Fig.2 Relationship between experimental relative explosive strength and calculated detonation pressure of the mixtures studied

The reactive radicals (OH-radicals and also radicals derived from oxo-chlorine intermediates of decomposition in the mixture F) might have a strong influence on the reverse slope of line IV in the case of absence of cooling water admixture in samples s-F and s-E, i.e. their decomposition velocity in a ballistics mortar chamber could have been higher than in the case of other mixtures. Mixture s-C is already "cooled" by the water content and the negative oxygen balance (-39.6%). The theory about the influence of very reactive radicals (in this case·OH) may be evidenced by the comparison of the positions in Fig.2 of the mixture pair s-F and s-I, but mainly by the s-G and s-J pair. The difference in densities of the pair s-E and s-H, and thus also in their calculated detonation parameters, may well be removed due to the use of the ballistic mortar for testing their performance (for a discussion about influences in these measurements, see Ref.[16]). The influence of cooling admixtures mentioned above is very well demonstrated by the W/O emulsion explosives fortified by admixtures of high explosives[21]; such admixtures cause a relatively strong increase in the detonation velocity (D) of the fortified W/O explosives and thus the values of the productρD2, while their relative explosive strength is roughly the same[23]due to the presence of water.

Line V is influenced by solid particles in the decomposition products and, in the case of mixture A, by a relatively high water content. As for the aluminized mixtures s-N and s-M, the points N1 and M1 in Fig.2 correspond with the assumption that aluminum completely reacts in the CJ point, and the points N and M correspond with unreacted solid Al (aluminum, depending on the type of explosive used, either behaves as an inert substance or participates in the chemical reactions proceeding inside the detonation wave[27]). It seems that the data for the s-N and s-M mixtures correlate logically with line V.

2.2 Thermal reactivity versus detonation pressure

From our study of the relationship between thermal reactivity and performance of energetic materials[23-25，29，30]it was found that there exists a simple relationship between a slope of the Kissinger relation (1),EaR-1, and the productρD2(from experimental data)[25]or detonation pressure,p. Its version for the mixtures studied in this paper is represented by Fig.3. Here the trends, corresponding to linesCandD, are in agreement with analogous trends in PBXs[25]. The different positions of these lines in a grid system of Fig.3 is caused by the fact that urea can substantially increase the thermal stability of AN (lineCin Fig.3 corresponds to this)[30，31]. Also, with a content of 50% by wt. of urea, its mixture with AN can still produce a steady detonation in the UN gap test[31]. Urea cannot reduce the ability to propagate a detonation[31].

LineAin Fig. 3 mainly groups mixtures based on UHP; here again mixture M with aluminum has two possible positions in a grid system-if we took Al as being inert, the corresponding point belongs in the group around lineA. However, taking Al as a reactant in the CJ plane, the corresponding point M1 is close to lineD; it might be related to the participation of this metal powder in redox-reactions in this plane. A registered auto-ignition of the mixture with Mg could provide evidence for this theory; in this light, the analogous mixture M, in which aluminum was substituted by magnesium, self-ignited 5 hours after its preparation.

Fig.3 Relationship between thermal reactivity, expressed as the slopes of the Kissinger relationship (1), and calculated detonation pressure (see in Table 1) of the energetic materials studied

In both theAandBlines it is logical that decreasing activation energies correlates with an increase in performance of the corresponding mixtures which correspond to a general relationship between sensitivity and performance[29]. Data for TATP should belong to a group of lineBbut it has a higherEaR-1value in comparison with its mixtures with the "acidic" AN. Almost all mixtures, inherent to these lines, contain peroxides which are their most reactive component. As has already been mentioned, the starting reaction for their initiation should be homolysis of the peroxide O-O bond[26，32]. On the other hand, the most reactive component of the mixtures belonging to linesCandDis ammonium nitrate (eventually urea nitrate) which in its solid state is dissociated according to the following equilibrium[33]

(2)

With subsequent decomposition through nitration of ammonia according to the following equation[33]

H2O+H3O++N2O

(3)

The primary step in the decomposition of UN is its dissociation into urea and nitric acid with subsequent formation of isocyanuric acid from urea[34]. Dissociation into ammonia and perchloric acid is the first step in the decomposition of AP, with subsequent decomposition of the perchloric acid[33]. The difference in the primary fission steps in initiation (ionic versus radical) of the mixtures studied should be the main reason for their division into groups belonging to linesAandB, on the one hand, and to linesCandD, on the other. This difference should be also a reason for the different slopes of the first pair of these lines in comparison with the second one.

3 Conclusions

From ballistic mortar measurements and the theoretical calculation of explosive mixtures based on urea derivatives with some inorganic oxidants. It can be concluded that it is possible to prepare explosive mixtures based on urea with an explosive strength better than TNT. Their performance is seen to be positively influenced by the presence of hydrogen peroxide in their composition, with a distinct advantage being shown by its complex with urea (UHP). This influence is notable namely in the use of sodium nitrate as an oxidant in these mixtures. The chemical nature of this effect lies in the reactive hydroxy-radical formation as the first intermediate in the given mixture′s initiation. On the basis of the relationship between thermal reactivity and performance, it is possible to split the mixture into those with the ionic primary fission and those with the radical one in their initiation.

Theoretical calculation is done assuming an ideal detonation model, so the calculated detonation properties of the mixtures correspond to the theoretical maximum that can be obtained at infinite diameter of explosive charge. In accordance with the current knowledge on burning of metal powders in the reaction zone, it can be assumed that the calculation carried out assuming aluminum does not react at the CJ point gives more realistic results for those mixtures without peroxide content that were studied. However, the OH-radicals, generated during the initiation of mixtures with peroxide content, might initiate (at least partially) powdered aluminum into oxidation in CJ plane of the detonation wave. Mixtures containing both UHP and magnesium are dangerous because of potential auto-ignition.

Acknowledgement

This study was supported by means of the financial resources of Students Grant Projects No. SGSFCHT_2016002 of the Faculty of Chemical Technology at the University of Pardubice.

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DOI：10.14077/j.issn.1007-7812.2016.05.004

Abstract:Six furazano-[3,4-d]-pyridazine-based derivatives as main compounds in solid composite propellants have been investigated. It was shown that the use of some furazano-[3,4-d]-pyridazine-based derivatives as main compounds in solid composite propellants can considerably increase ballistic parameters compared with HMX if the compounds under consideration contain difluoramine groups. And the use of the compounds under consideration may be successful only in the presence of an active binder and 10%-30% of AP or ADN as additional oxidizers.

Keywords:solid composite propellant; furazano-[3,4-d]-pyridazine-based derivative; energetic specific impulse

CLC number：TJ55;TQ560 Document Code：A Article ID：1007-7812(2016)05-0028-07

Received date:2016-07-25； Revised date:2016-08-20

Foundation:Ministry of Education and Science of the Russian Federation (14.613.21.0043)

Biography:LEMPERT David B.(1946-), male, Ph.D, Professor. Researcher field: Aerospace propulsion. E-mail:lempert@icp.ac.ru

Introduction

The search of new energetic materials is an important topic worldwide[1]. In recent years, much attention is riveted on N-heterocycles, because they have high densities and high standard enthalpies of formation. High-enthalpy propellants require a bit or no aluminum in the formulation, because the energy contained in high-enthalpy N-heterocyclic ring is often enough to warm up the gaseous combustion products to high temperatures (3500K and even higher)[2].

Currently underway is not only an experimental search for new N-heterocycles, but also a lot of investigations on the theoretical search for new high-energy compounds of this class[3], that is rather natural, since such studies facilitate a targeted search of new compounds[4].

In this study, the estimations of properties (densities, standard enthalpies of formation, detonation parameters) of new compounds, some furazano-[3,4-d]-pyridazine-based derivatives, that are not obtained yet, have been carried out.

1 Statement of the problem and research

methodology

Ief(1)=Isp+100·(ρ-1.9);

Ief(2)=Isp+50·(ρ-1.8);

Ief(3)=Isp+25·(ρ-1.7) ;

We have considered the propellant formulations containing about 19 volume percents of AB, because at lower volume percentage it is almost impossible to create a formulation having satisfactory rheologic properties of uncured mass and physico-mechanical properties of the cured propellant. Aluminum mass fraction was varied from 0 to 18 %.

Table 1 Properties of hypotetic furazano-[3,4-d]-pyridazine-based derivatives, that were used at calculations.

2 Results and discussion

2.1 Formulations with AP as additional inorganic oxidizers

2.1.1 Formulations with S1 + Al + AP + AB (19% volume fraction) (Fig.1)

Fig.

the introduction of Al to the formulations still more reduces these values.

2.1.2 Formulations with S2 + Al + AP + AB (19% volume fraction) (Fig.2)

Fig.

2.1.3 Formulations with S3 + Al + AP + AB (19% volume fraction) (Fig.3)

Fig.

2.1.4 Formulations with S4 + Al + AP + AB (19% volume fraction) (Fig.4)

Fig.

2.1.5 Formulations with S5 + Al + AP + AB (19% volume fraction) (Fig.5)

Fig.

2.1.6 Formulations with S6 + Al + AP + AB (19% volume fraction) (Fig.6)

Fig.

2.1.7 Formulations with HMX + Al + AP + AB (19% volume fraction)

Fig.

However, at HMX content higher than 50%-60% compositions with Al, HMX and active binders become dangerous and one always uses a bit of AP to provide the necessary combustion law and to reduce the risk of combustion to detonation transfer. So, a real estimation of energetic characteristics of SCP based on HMX has be compared with compo-

sitions containing at least 10% AP.

Table 2 Ballistic parameters of the optimal formulations at optimal content of Al and AP

2.2 Formulations with ADN as additional inorganic oxidizers

Fig.

Main w/%No．compoundw/%AlABAPTc/KIsp/sρ/(g·cm-3)Ief(2)/sIef(3)/sI?ef(2)/sI?ef(3)/s1S545．3915．7303755259．61．810260．1262．4255．0257．22S355．4915．6203820260．11．822261．1263．1256．0257．93S445．5915．5303760260．11．828261．5263．3256．4258．24HMX73．01215．003585260．81．895265．6265．7258．7258．85HMX65．8915．2103520259．81．867263．2264．0258．1258．96S658．3615．7203735260．41．808260．9263．1257．4259．77S274．4015．6103890263．41．818264．3266．3264．3266．38S164．8015．2203915267．81．860270．8271．8270．8271．8

3 Conclusions

(2)The use of the compounds under consideration may be successful only in the presence of an active binder and 10%-30% of AP or ADN as additional oxidizers.

Acknowledge

The investigation was supported by the Russian Ministry of Education and Science accordingly the agreement No.14.613.21.0043 from 10.11.2015, the unique identifier RFMEFI61315X0043.

References：

[1] SHU Yuan-jie, WU Zong-kai, LIU Ning, et al. Crystal control and cocrystal formation: important route of modification research of energetic materials[J]. Chinese Journal of Explosives & Propellants(Huozhayao Xuebao), 2015,38(5):1-9.

[2] LEMPERT David, NECHIPORENKO Gelii, MANELIS George. Influence of heat release value and gaseous combustion products content on energetic parameters of solid composite propellants[C]∥Theory and Practice of Energetic Materials (VOL.VIII) Proceedings of the 2009 International Autumn Seminar on Propellants, Explosives and Pyrotechnics.Beijing:China Ordnance Society,2009:22-25.

[3] WU Qiong, ZHU Wei-hua, XIAO He-ming. Structural transformation and absorption properties of crystalline 7-amino-6-nitrobenzodifuroxzan under high pressure[J]. The Journal of Physical Chemistry C, 2013, 117:16830-16839.

[4] WANG Ke, SHU Yuan-jie, LIU Ning, et al.Computational investigation on performance and structure of six novel furazano-[3,4-d]-pyridazine-based derivatives[C]∥19th New Trends in Research of Energetic Materials.Pardubice:University of Pardubice,2016, 302-309.

[5] Pepekin V I, Korsunskii B L, Denisaev A A. Initiation of solid explosives by mechanical impact. Combustion[J]. Explosion and Shock Waves, 2008, 44(5): 586-590.

[6] Lempert D, Nechiporenko G, Manelis G. Energetic characteristics of solid composite propellants and ways for energy increasing[J].Central European Journal of Energetic Materials, 2006,3(4): 73-87.

[7] LEMPERT David B, DALINGER Igor L, SHU Yuan-jie, et al. Estimation of the ballistic effectiveness of 3,4- and 3,5-dinitro-1-(trinitromethyl)-1H-pyrazoles as oxidizers for solid composite propellants[J]. Chinese Journal of Explosives & Propellant(Huozhayao Xuebao), 2016, .39(2):16-21.

[8] Trusov B. Program system TERRA for simulation phase and thermal chemical equilibrium [C]∥14th Symposia on Chemical Thermodynamics. St-Petersburg, Russia, 2002, 483-484.

[9] Pavlovets G, Tsutsuran V, Physicochemical properties of powders and propellants[M]. [S.l.]:Russian Ministry of Defense Publishing House, 2009.

[10] Nechiporenko G N, Lempert D B. An analysis of erergy potentialities of composite solid propellants containing beryllium or beryllium hydride as an energetic component [J]. Chemical Physics Reports, 1998, 17(10):1927-1947.

[11] Lempert D B, Dorofeenko E M. Optimal compositions of metal-free energetic compositions with variation in the oxidizer concentration and the ratio of nitro and difluoroamine groups[J]. Combustion, Explosion, and Shock Waves, 2014, 50 (4), 447-453.

Research Progress in Coating Mechanism and Technology of Boron Particles

CHEN Bing-hong， LIU Jian-zhong， LIANG Dao-lun， ZHOU Yu-nan， ZHOU Jun-hu

(State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China)

The coating mechanism of different coating materials for boron particle was described. The principle for selecting the coating materials of boron particle was summarized from five aspects, which includes elaborated removing oxide layer, enhancing combustion temperature, reducing ignition temperature, improving surface compatibility and stimulating the oxidation of boron particles. A variety of the research status of boron particle coating technologies, such as precipitation and surface chemical reaction, macromolecule absorption polymerization, gas phase coating and ball milling was summarized and the actual application results of different processes were analyzed and compared. A variety of modern technologies to test the coating effect of boron particle were introduced. It also reviews the current status of research and insufficience of boron particle coating technology and prospects for the future direction of research.With 46

.

physical chemistry; boron particle; coating mechanism; fuel-rich propellant; metal fuel

Relative Explosive Strength of Some Explosive Mixtures Containing Urea and/or Peroxides

Ahmed K. HUSSEIN1, Svatopluk ZEMAN1, Muhamed SUCESKA2, Marcela JUNGOVA1

(1. Institute of Energetic Materials, Faculty of Chemical Technology, University of Pardubice, Czech Republic;2. Brodarski Institute-Marine Research and Special Technologies, Zagreb, Croatia)

TJ55;TQ560 Document Code：A Article ID：1007-7812(2016)05-0022-06

Energetic Opportunities of Solid Composite Propellants Containing Some Hypothetic Furazano-[3,4-d]-pyridazine-based Derivatives

LEMPERT David B.1，DOROFEENKO Ekaterina M.1，SHU Yuan-jie2，JIANG Wei-dong3，WU Zong-kai2，WANG Ke2，LIU Xiao-qiang3

(1. Institute of Problems of Chemical Physics, Russian Academy of Sciences (IPCP RAS), Moscow 142432, Russia;2. Xi′an Modern Chemistry Research Institute, Xi′an 710065, China;3. School of Chemistry and Environmental Engineering, Sichuan University of Science and Engineering, Zigong Sichuan 643000, China)

10.14077/j.issn.1007-7812.2016.05.002

2016-08-12；

2016-08-27

國家自然科學(xué)基金(No.51106135)

陳冰虹(1993-)，女，博士，從事金屬燃料研究。E-mail：3110101575@zju.edu.cn

劉建忠(1965-)，男，教授，從事能源轉(zhuǎn)換及利用研究。E-mail：jzliu@zju.edu.cn

TJ55;O64

A

1007-7812(2016)05-0013-09