唐明峰，顏熹琳，唐　維，李　明，溫茂萍

(中國工程物理研究院化工材料研究所, 四川綿陽621900)

?

PBX中炸藥晶體與黏結劑界面力學特性的研究進展

唐明峰，顏熹琳，唐維，李明，溫茂萍

(中國工程物理研究院化工材料研究所, 四川綿陽621900)

摘要：從PBX界面的特征、界面對PBX力學性能的影響及PBX中界面的力學表征等方面對PBX炸藥晶體與黏結劑界面力學特性進行了歸納和評述。介紹了影響PBX界面的因素、界面與PBX宏/細觀力學性能的關系、PBX界面的幾個不同表征方法等方面的研究進展。指出應開展PBX真實界面及模擬界面的直接加載、觀測方法研究，并進一步加強數(shù)值模擬的作用。附參考文獻43篇。

關鍵詞：固體力學；PBX；炸藥晶體；界面力學特性；黏結劑

Progress of Study on Mechanical Properties of the Crystal/Binder Interface in PBX

TANG Ming-feng, YAN Xi-lin, TANG Wei, LI Ming, WEN Mao-ping

(Institute of Chemical Materials, CAEP, Mianyang Sichuan 621900, China)

Abstract:From the characteristics of PBX interface, the influence of interface on the mechanical properties of PBXs and the mechanical characterization of PBX interface, etc, the mechanical properties of PBX explosive crystal and the binder interface were summarized and reviewed. The factors affecting the PBX interface, the relationship between the interface and the macro/micro mechanical properties of PBX and the research progress of several different characterization methods of PBX interface were introduced. It is pointed out that the research on the direct loading and observation method of real interface and simulation interface of PBX should be carried out and the role of the numerical simulation is further enhanced, with 43 references. With this communication we want to suggest the system ZrW2, a high-density and very hard intermetallic compound that reacts/burns highly exothermic with air at high temperature. This intermetallic phase should provide a very suitable reactive material for warhead applications.

Keywords:solid mechanics; PBX; explosive crystal; interfacial mechanical properties; binder Cermisch metal; intermetallic phase; thermites; reactive structure material; warhead

引言

高聚物黏結炸藥(PBX)是由單質炸藥晶體和高聚物黏結劑等組成的混合炸藥，在武器戰(zhàn)斗部中應用廣泛。PBX的力學性能對武器系統(tǒng)的可靠性和安全性有重要影響。近年來，研究者們對炸藥單晶、黏結劑及PBX藥柱的力學性能進行了大量研究[1-3]，但有關PBX炸藥晶體/黏結劑界面力學特性的報道卻很少。

界面是材料物理、化學性質發(fā)生空間突變的二維區(qū)域，是復合材料特有的而且是其重要的組成部分。PBX組分的特殊性(炸藥晶體高度填充，且炸藥晶體模量遠高于黏結劑模量)和成型工藝的復雜性(壓裝PBX經過造粒及高溫高壓壓制而成，澆注PBX經過捏合、澆注、固化而成型)決定了PBX中界面大量存在，且結構異常復雜，界面處必然會出現(xiàn)熱物理性能、力學性能等的跳躍。因此，研究炸藥顆粒與黏結劑的界面作用對于PBX炸藥的力學性能、爆轟性能及安全性能的評價和改善具有重要意義[4]，對PBX炸藥的配方設計具有參考價值。同時，由于PBX界面的特殊性和材料本身的含能敏感性，使PBX炸藥晶體/黏結劑界面力學研究一直很難深入。目前的研究大都基于分子動力學方法開展模擬計算，文獻報道的試驗研究較少，而且基本為間接試驗研究。本文對PBX界面的特征、界面對PBX的影響、PBX中界面的力學表征等幾個方面進行了歸納和總結。

1PBX界面的特征

PBX中炸藥晶體的質量分數(shù)通常達90%以上，且其模量遠高于黏結劑的模量，可稱之為剛性顆粒高度填充的高分子基復合材料[2-5]，內部各相的界面作用具有獨特的性能。PBX的組分包括炸藥晶體、黏結劑、鈍感劑及增塑劑等，按界面材料的不同可將PBX中的界面分為晶界、晶體/黏結劑相界和表面等。其界面形式及界面強度等與諸多因素有關，且易受外界環(huán)境影響。

PBX的界面特性與材料組分及含量、成型工藝密切相關，對于成型PBX，界面作用還會在外界溫度、載荷等的作用下增強或減弱，從而導致材料的整體性能發(fā)生改變。吳永炎等[5]用分子動力學方法對HMX/TATB基炸藥含不同黏結劑的界面粘結效果進行了模擬研究，通過比較高聚物分子與炸藥分子間的結合能(忽略HMX與TATB間的結合能)，發(fā)現(xiàn)F2311與TATB和HMX間的結合能最大，F(xiàn)2314最小，從界面粘結效果的角度對PBX體系進行了優(yōu)選。劉永剛等[6]研究了成型工藝對PBX界面的影響，結果表明熱壓成型后藥柱的表面電子結合能相對于初始造型粉表面有較大程度的位移，認為壓制過程使晶體與黏結劑界面的結合更加緊密，使界面作用有所增強。Saw等[7]研究了PBX9501中HMX晶體與黏結劑在高溫下的相互作用，發(fā)現(xiàn)HMX從β相到δ相的轉變與純HMX類似，但由于黏結劑對其表面分子潛能有影響，δ相在冷卻過程中重新轉變成了β相，最終使HMX-黏結劑在熱循環(huán)過程中出現(xiàn)界面脫粘。同時溫度的變化還可能引起黏結劑的玻璃態(tài)轉變，這同樣會導致炸藥晶體/黏結劑界面作用的改變[8]。

根據(jù)用途的不同，PBX中炸藥晶體尺寸可在百納米至百微米范圍浮動[9]，從炸藥晶體/黏結劑界面的角度考慮，PBX中界面在細觀上是一個多尺度問題，炸藥晶體粒徑不同，PBX的界面作用也不同。從包覆效果來看，粒徑越大，受工藝影響，越不容易被包覆，同時在大顆粒表面更容易發(fā)生界面脫粘；顆粒越小，界面分布增加，界面強度會增強。由于目前缺乏有效的直接觀測手段，只能從PBX密度、感度等其他特性進行間接推測。此外，PBX材料中的界面作用還與炸藥晶體/黏結劑的極性匹配情況[10]和黏結劑在炸藥顆粒間的分布狀態(tài)[8]有關。

2界面對PBX力學特性的影響

界面具有傳遞、阻擋、吸收、散射和誘導等功能，從粒子間引力、斥力等電磁作用的角度講，PBX的力學行為離不開界面、炸藥晶體及黏結劑基體之間的相互作用。如加載后力的傳遞、細觀結構的演化，均需要通過界面作用而進行。界面形式、數(shù)量及界面的強弱必將對PBX材料的細觀破壞模式和宏觀力學性能產生重要影響。

界面與PBX的損傷、裂紋傳播密切相關，甚至決定了PBX的失效模式。裂紋的形成和傳播往往導致PBX的安全性能和力學性能下降，甚至造成失效，從而影響整個武器系統(tǒng)的安全性和可靠性。最常見的失效模式就是PBX在熱或力載荷的作用下形成裂紋，裂紋再沿著炸藥晶體/黏結劑界面?zhèn)鞑11-13]。Palmer等[14]對一系列PBX炸藥的力學性能開展了研究，結果表明，即使是韌性最好的材料，在6.8MPa的拉伸應力作用下，也會因界面開裂最后造成材料失效。研究還發(fā)現(xiàn)，PBX中的裂紋很少沿著炸藥晶體或黏結劑傳播，但是界面處的裂紋傳播往往決定了PBX的失效模式。Rae等[13,15]繼續(xù)了Palmer等人在裂紋傳播方面的研究工作，圖1為帶有裂紋的PBX9501的顯微結構圖，顯示了裂紋在炸藥晶體/黏結劑界面?zhèn)鞑サ牡湫吞攸c。圖1(a)[13]強調了裂紋沿著界面處的傳播，而圖1(b)[15]則證實了裂紋在界面處傳播的廣泛性。此外，陳鵬萬[16]的研究表明，PBX最主要的損傷形式是界面脫粘，界面損傷導致孔洞和裂紋的形成。新的孔洞還可能成為PBX非正常條件下新的“熱點源”，從而增加PBX的感度，降低其安全性能。

圖1　帶有裂紋的PBX9501顯微結構圖Fig.1　Microstructure images of PBX9501 with cracks

炸藥晶體與黏結劑界面對PBX的力學性能也有不可忽略的影響，例如，界面脫粘將直接導致PBX模量下降。Tan等[17]根據(jù)文獻中相關數(shù)據(jù)(PBX9501中HMX和黏結劑的質量比及模量、泊松比等)，在假設PBX9501界面良好(沒有脫粘現(xiàn)象)的前提下，基于Mori Tanaka方法，通過理論公式推算了PBX9501的體積彈性模量為1.96GPa。同時指出，相關文獻中報道的PBX9501在低應變率下楊氏模量的實驗值僅為1.11GPa，低于理論計算值40%左右。因此認為，界面脫粘是PBX9501體積模量理論計算值與實驗值相差較大的主要原因。在PBX炸藥受拉伸的情況下，炸藥晶體與黏結劑界面作用的強弱在很大程度上決定了PBX材料的強度。段伯禎等[18]對兩種炸藥澆注形成的界面進行了抗拉強度試驗，發(fā)現(xiàn)界面處的抗拉強度介于兩種炸藥的本征抗拉強度之間，這從另一個角度證明了界面對PBX強度的影響。在炸藥配方設計中，研究者們往往通過添加偶聯(lián)劑來達到增強界面作用的目的。Li fan等[19]研究發(fā)現(xiàn)，經偶聯(lián)劑改性后的TATB與含氟聚合物的界面張力顯著減小，界面黏合功增大，偶聯(lián)劑能形成與TATB間的強相互作用。林聰妹等[20]研究了黏結劑增強對TATB基PBX力學性能的影響，發(fā)現(xiàn)隨著增強劑含量增加，復合黏結劑的拉伸強度明顯增加，同時TATB基PBX的力學性能顯著提高。吳文輝等[21]采用溶脹比測試和原位拉伸掃描電鏡觀測的方式，研究了鍵合劑對推進劑界面作用的影響，發(fā)現(xiàn)中性聚合物鍵合劑(NPBA)在硝銨顆粒周圍形成了一層高模量的中間相，提高了推進劑的拉伸性能，有效解決了“脫濕”問題。

此外，PBX的缺點之一就是力學性能較差，而其力學性能取決于炸藥晶體、黏結劑以及大量存在的界面。如前所述，目前僅對炸藥晶體和黏結劑的力學性能研究較多[1,22-23]，而由于炸藥晶體的高能敏感性導致炸藥晶體與黏結劑界面的微觀力學試驗研究存在一定的安全風險，同時又因為PBX組分的特殊性和成型工藝的復雜性，導致PBX中炸藥晶體與黏結劑界面結構異常復雜，因此，對于炸藥晶體/黏結劑界面的微觀力學研究與表征一直難以深入開展。

3PBX中界面的表征

PBX界面研究中的一項重要工作是界面的力學性能表征。傳統(tǒng)復合材料界面力學性能的表征一般是基于強度、模量等力學參量，例如單纖維拉出試驗、微滴包埋拉出試驗、單纖維斷裂試驗等[18]，這種表征方法比較直觀，且物理意義明確，但試驗的有效性只局限于纖維增強復合材料。PBX的界面表征主要借鑒于顆粒填充復合材料，然而不同復合材料的界面力學特性相差很大：一方面是因為不同復合材料的界面成型過程和界面結構相差很大；另一方面是因為形成復合材料的基體和增強體也完全不同，而基體和增強體的性質對界面的性質起著決定性作用。因此，傳統(tǒng)的復合材料界面力學性能表征方法并不完全適合PBX中炸藥晶體/黏結劑界面的力學研究，因此以何種形式、何種參量對PBX中界面進行表征是目前面臨的一個重要問題。

盡管試驗困難，但基于強度、模量等參量的力學表征仍是目前研究PBX界面的一個重要方式。劍橋大學Cavendish實驗室的Palmer等[24]通過實驗手段測量了EDC37中(EDC37是一種PBX，由質量分數(shù)分別為91%的HMX和9%的NC/K10組成)HMX與聚合物黏結劑之間的界面斷裂所需要的力。值得關注的是，Palmer的研究中采用的是HMX晶體與黏結劑直接粘結的方式，通過在厘米級大單晶上制備數(shù)百納米至幾十微米厚的黏接劑涂層，在精確設計的低載加載單元上實現(xiàn)了直接拉伸，試驗應力-應變曲線如圖2[24]所示，所得到的應力、應變及彈性模量與黏結劑體系得到的數(shù)值吻合很好。試驗中還采集了界面處黏結劑拉伸情況，如圖3[24]所示，其中圖3中每連續(xù)兩張照片的間隔時間為20s。Palmer的這種試驗研究方法本質上是模擬PBX中炸藥晶體和黏結劑界面情況，制備出模擬界面再針對模擬界面開展研究。該研究思路直接，若能進一步考慮炸藥晶體固有的各向異性，應能取得更深入的研究結果。

圖3　界面結合處初始失效的連續(xù)照片F(xiàn)ig.3　Continuous images of the initial failure in theinterface junction

Tan等[25]針對PBX9501設計了改進的緊湊拉伸試驗，基于數(shù)字圖像相關技術獲得了炸藥宏觀裂紋尖端附近的應力和位移，采用擴展的Mori-Tanaka方法研究了PBX9501中的界面脫粘效應，獲得了PBX9501中顆粒與基體界面的線性模量、結合強度及軟化模量。Tan的研究思路是從宏觀斷裂試驗中通過理論計算獲取關于顆粒與基體界面的力學量，通過獲得的力學量來表征PBX中顆粒/基體界面細觀結合規(guī)律。該研究方法對炸藥中的細觀界面有了定量的認識，但缺乏對PBX中界面作用本質的深入分析。肖繼軍等[26-27]通過分子動力學模擬方法對β-HMX晶體的(100)晶面與聚合物黏結劑PEG、HTPB和Estane5703之間的界面情況開展了理論研究，包括界面結構、界面力學性能(例如界面的彈性性能和延展性等)，得出添加少量聚合物黏結劑，可以有效提高HMX晶體的延展性。孫婷等[28]對CL-20/DNB共晶與黏結劑間的界面作用和力學性能進行了分子動力學模擬，發(fā)現(xiàn)加入少量黏結劑會減小CL-20/DNB共晶炸藥的彈性系數(shù)、拉伸模量和體積模量，且HTPB比PEG對共晶炸藥力學性能的優(yōu)化更好。陶俊等[29]模擬了ε-CL-20/含能黏結劑界面的結合能與作用方式，發(fā)現(xiàn)二者的界面作用有效降低了ε-CL-20的剛性，含能熱塑性彈性體能增強ε-CL-20的延展性。LONG Y等人[30]則采用分子力學和分子動力學方法對HMX晶體/氟聚合物黏結劑界面的力場演化進行了研究，結果表明，片狀包覆和球形包覆下彈性常數(shù)、體積模量和塑性應力是相近的，最大區(qū)別為20%，但剪切應力差異較大，球形包覆能使剪切強度提高10%~200%。

另一種有效的方式是通過界面相互作用對PBX界面進行表征，該方法多基于能量的角度。最初用來表征PBX界面特性的參量是表面能，表面能主要取決于界面處的分子類型和化學鍵類型。然而大多數(shù)情況下，界面結合能的測量值比實際值大很多[31]。因此，研究者們找到了一種比表面能更適合來表征界面情況的物理量——斷裂能G，即采用斷裂力學的方法來定義界面結合情況。斷裂能G通常被認為是一種能量釋放速率或者裂紋擴展力，并且與材料的斷裂韌性有關[32]。斷裂能和界面結合能是目前常用的兩種能量表征方法。Tan[25]和Wiegand等[33]研究了PBX9501的結合能與斷裂能，通過能量對PBX9501的界面進行了表征，對比發(fā)現(xiàn)界面結合能與斷裂能的表征結果具有很好的一致性。馬秀芳等[34]采用分子動力學方法對PBX中HMX/F2311的界面結合能進行了計算，并對計算結果進行了詳細分析。結果表明，PBX中HMX/F2311的界面結合能為314.2kJ/mol，HMX與F2311之間存在氫鍵作用和較強的范德華力。Lu Yang等[35]同樣采用分子動力學模擬的方法對β-HMX晶體與黏結劑Estane的界面自由能進行了理論計算。還有研究者在測量接觸角的基礎上通過計算表面能來間接表征界面作用[36-37]。

PBX界面處的物理結構也是常用的表征方式之一。Hackjin Kim等[38]采用振動和頻產生譜的方法測試了β-HMX單晶和高分子黏結劑Estane之間的界面情況，雖然得到一些試驗結果，但同時指出該試驗結果并不具有代表性。宋華杰等[39]采用動態(tài)力學分析技術(DMA)對TATB/氟聚物復合材料的界面粘合情況進行了研究，結果表明TATB/氟聚物界面為分明型界面，其分子間作用主要是范德華力，而這種作用不能有效阻止該晶面的滑移。該方法表明利用三相模型和A參數(shù)[40]來表征PBX的界面是可行的。WU 等[41]對PBX炸藥中炸藥晶體/黏結劑界面脫粘現(xiàn)象進行了詳細的模擬計算，考慮界面損傷后PBX9501的計算結果與試驗吻合良好。XIAO Jijun等[26]采用pair correlation function (PCF)方法分析了HMX晶體的(100)晶面與聚合物黏結劑PEG和HTPB以及Estane5703之間的界面結構，發(fā)現(xiàn)這些界面之間存在氫鍵和靜電作用。王東旭等[42]研究了ε-HNIW/F2311體系PBX的界面結構力學行為，發(fā)現(xiàn)溫度達到348K后ε-HNIW/F2311界面結構比內層ε-HNIW形狀變化和體積變化都變得相對容易，彈性增強的同時可以有效地分散應力，ε-HNIW/F2311界面結構在298~373K內成型性較好。

與其他顆粒填充復合材料相比，PBX的界面表征方法還較少，目前需要從傳統(tǒng)復合材料特別是顆粒填充聚合物材料的相關研究中引進新的方法和手段。白樹林等[43]在研究界面性能對剛性粒子填充高聚物力學行為的影響時，對宏觀斷裂試樣中填充相與基體的粘連情況進行了掃描電鏡觀測，發(fā)現(xiàn)界面處的粘連情況與剛性粒子/基體界面的強度有很好對應，該結論可為PBX特別是壓裝PBX中界面強度的定性表征提供指導，若能解決原位加載涉及的相關問題，則能為PBX界面強度定量表征提供借鑒。

4結束語

PBX界面結構復雜，受內外多種因素影響，而初始界面的改變將引起PBX材料的損傷和破壞，進而對PBX的整體力學性能造成影響，但目前這方面主要還以規(guī)律性和半規(guī)律性研究為主，對界面的作用機理還缺乏深入的了解；在PBX界面的表征方面，發(fā)展了微觀結構、宏觀力學量及能量等表征方法，但存在研究不夠深入、不精細等局限，特別是缺乏對炸藥晶體/黏結劑界面作用的直接物理量表征。

認為以下幾個方面應是PBX界面問題值得發(fā)展的方向：

(1)試驗研究方面，應發(fā)展炸藥不同晶面與黏結劑模擬界面的制備工藝；開展炸藥晶體/黏結劑界面力學作用的直接測試研究，通過專業(yè)設計的試驗裝置建立對PBX模擬界面的力學加載方法，研究炸藥晶體晶面、壓制溫度及壓力對界面力學特性的響應規(guī)律；進一步完善偏光顯微鏡、掃描電子顯微鏡等顯微觀測手段在PBX界面作用及損傷破壞方面的應用。

(2)理論和計算研究方面，應進一步開展PBX分子層面的作用機理研究，分析氫鍵作用、范德華力、界面結合能等初級作用對界面的影響；加強有限元、邊界元等方法在炸藥晶體/黏結劑界面脫粘和破壞方面的數(shù)值應用；基于試驗和數(shù)值結果逐步探索建立PBX界面力學作用模型，揭示界面力學作用機理。

參考文獻：

[1]Li M, Tan W J, Kang B, et al. The elastic modulus of β-HMX crystals determined by nanoindentation[J]. Propellants, Explosives, Pyrotechnics, 2010, 35(4): 379-383.

[2]Cady C M, Blumental W R, Gray G T, et al. Mechanical properties of plastic-bonded explosive binder materials as a function of strain-rate and temperature[J]. Polymer Engineering and Science, 2006, 46(6): 812-819.

[3]Le V D, Gratton M, Caliez M, et al. Experimental mechanical characterization of plastic-bonded explosives[J]. Journal of Material Science, 2010, 45(21): 5802-5813.

[4]Gee R H, Mmiti A, Bastea S, et al. Molecular dynamics investigation of adhesion between TATB surfaces and amorphous fluoropolymers[J]. Macromolecules, 2007, 40: 3422-3428.

[5]吳永炎，王晶禹. 基于MD方法的多組分PBX粘接劑優(yōu)選研究[J]. 火工品，2012(3)：37-39.

WU Yong-yan, WANG Jing-yu. Study on preferred adhesives of multi-components PBX based on MD [J]. Initiators and Pyrotechnics, 2012 (3): 37-39.

[6]劉永剛，聶福德，黃靖倫. TATB基高聚物粘結炸藥的表(界)面特性[C]∥中國科協(xié)2001年學術年會論文集. 北京：中國科學技術協(xié)會, 2001, 404-40.

[7]Saw C K, Tarver C M. Binder/HMX interaction in PBX9501 at elevated temperatures[R]. Livermore: Lawrence Livermore National Lab, 2003.

[8]宋華杰，董海山，郝瑩, 等. TATB基高聚物粘結炸藥及其粘結劑的玻璃化溫度與DMA測量頻率關系的研究[J]. 含能材料，2001,9(1)：10-13.

SONG Hua-jie, DONG Hai-shan, HAO Ying, et al. Study of relationships between glass transition temperatures and test frequencies on TATB-based PBXs and their binders using DMA[J]. Energetic Materials, 2001, 9(1): 10-13.

[9]李玉斌，李金山，向永,等. HMX顆粒特性對壓裝PBX蘇珊感度的影響[J]. 火炸藥學報，2012，35(4)：19-22.

LI Yu-bin, LI Jin-shan, XIANG Yong, et al. Effect of particle character of HMX on Susan sensitivity of HMX-based pressed PBX [J]. Chinese Journal of Explosives and Propellants, 2012, 35(4): 19-22.

[10]劉永剛，雷延茹，余雪江,等. TATB/氟聚合物塑料粘結炸藥的表(界)面特性研究[J]. 粘接，2003,24(4)：6-9.

LIU Yong-gang, LEI Yan-ru, YU Xue-jiang, et al. Study on surface and interface properties of TATB/fluoropolymer PBX [J]. Adhesion in China, 2003, 24(3): 6-9.

[11]Liu Z W, Xie H M, Li K X, et al. Fracture behavior of PBX simulation subject to combined thermal and mechanical loads [J]. Polymer Testing, 2009, 28(6): 627-635.

[12]Chen P, Xie H, Huang F, et al. Deformation and failure of polymer bonded explosives under diametric compression test [J]. Polymer Testing, 2006, 25(3): 333-341.

[13]Rae P J, Palmer S J P, Goldrein H T, et al. Quasi-static studies of the deformation and failure of PBX 9501[J]. Proceedings of the Royal Society of London (Series A), 2002, 458: 2227-2242.

[14]Palmer S J, Field J E, Huntley J M. Deformation, strengths and strains to failure of polymer bonded explosives [J]. Proceedings of the Royal Society of London(Series A: Mathematical and Physical Sciences), 1993,440:399-419.

[15]Rae P J, Goldrein H T, Palmer S J P, et al. Quasi-static studies of the deformation and failure of β-HMX based polymer bonded explosives[J]. Proceedings of the Royal Society of London, Series A: Mathematical, Physical and Engineering Sciences, 2002, 458: 743-762.

[16]陳鵬萬.高聚物粘結炸藥的細觀結構和力學性能[R]. 北京：中國科學院力學研究所, 2001.

[17]Tan H, Huang Y, Liu C, et al. The Mori-Tanaka method for composite materials with nonlinear interface debonding [J]. International Journal of Plasticity, 2005, 21(10): 1890-1918.

[18]段伯禎，陳竚，曹少庭,等. 熱固性澆注PBX炸藥裝藥的界面性質[J]. 火炸藥學報，2013,36(2)：30-32.

DUAN Bo-zhen, CHEN Zhu, CAO Shao-ting, et al. Characteristics of the interface between two types of heat-cured cast PBX charges [J]. Chinese Journal of Explosives and Propellants, 2013, 36(2): 30-32.

[19]Li Fan, Ye Lin, Nie Fu-de, et al. Synthesis of boron-containing coupling agents and its effect on the interfacial bonding of fluoropolymer/TATB composite[J]. Journal of Applied Polymer Science, 2007, 105(2): 777-782.

[20]林聰妹，劉世俊，張娟,等. 粘接劑增強對TATB基PBX力學性能的影響[J].廣州化工，2012,40(14)：77-79.

LIN Cong-mei, LIU Shi-jun, ZHANG Juan, et al. Influences of binder enhancement technology on mechanical properties of TATB-based polymer bonded explosives[J]. Guangzhou Chemical Industry, 2012, 40(14):77-79.

[21]吳文輝，黎玉欽，張聰,等. 中性聚合物鍵合劑對硝銨推進劑相界面的作用[J]. 推進技術，2001,22(4)：337-340.

WU Wen-hui, LI Yu-qin, ZHANG Cong, et al. Interfacial reinforcement of neutral polymeric bonding agents(NPBA) in nitramine propellants[J].Journal of Propulsion Technology, 2001, 22(4):337-340.

[22]Haycraft J J. The elastic constants and related properties of the energetic material CL-20 determined by Brillouin scattering [J]. The Journal of Chemical Physics, 2009, 131(21):1-8.

[23]DRODGE D R, WILLIAMSON D M, PALMER S J P, et al. The mechanical response of a PBX and binder: combining results across the strain-rate and frequency domains [J]. Journal of Physics D: Applied Physics, 2010, 43(33):335-403.

[24]Palmer S, Williamson D, Proud W. Adhesion studies between HMX and EDC37 binder system[J]. AIP Conference Proceedings, 2006, 845: 917-920.

[25]TAN H, LIU C, HUANG Y, et al. The cohesive law for the particle/matrix interfaces in high explosives [J]. Journal of the Mechanics and Physics of Solids, 2005, 53(8): 1892-1917.

[26]Xiao J J, Huang H, Li J, et al. A molecular dynamics study of interface interactions and mechanical properties of HMX-based PBXs with PEG and HTPB [J]. Journal of Molecular Structure: Theochem, 2008, 851(1-3):242-248.

[27]Xiao J J, Huang H, Li J, et al. Computation of interface interactions and mechanical properties of HMX-based PBX with Estane 5703 from atomic simulation [J]. Journal of Materials Science, 2008, 43(17): 5685-5691.

[28]孫婷，肖繼軍，趙鋒，等.CL-20/DNB共晶基PBXs相容性、界面作用和力學性能的MD模擬[J].含能材料，2015,23(4)：309-314.

SUN Ting, XIAO Ji-jun, ZHAO Feng, et al. Molecular dynamics simulation of compatibility, interface interactions and mechanical properties of CL-20/DNB cocrystal based PBXs[J]. Energetic Materials, 2015, 23(4):309-314.

[29]陶俊，王曉峰，趙省向，等. ε-CL-20/含能黏結劑復合體系結合能及力學性能的模擬[J]. 含能材料，2015,23(4)：315-322.

TAO Jun, WANG Xiao-feng, ZHAO Sheng-xiang, et al. Simulation and calculation for binding energy and mechanical properties of ε-CL-20/energetic polymer binder mixed system[J]. Energetic Materials, 2015, 23(4):315-322.

[30]Long Y, Liu Y G, Nie F D, et al. The force-field derivation and atomistic simulation of HMX-fluoropolymer mixture explosives[J]. Colloid and Polymer Science, 2012, 290(18): 1855-1866.

[31]Packham D E. Work of adhesion: contact angles and contact mechanics [J].International Journal of Adhesion and Adhesives, 1996,16(2):121-128.

[32]Volinsky A A, Moody N R, Gerberich W W. Interfacial toughness measurements for thin films on substrates [J]. Acta Materialia, 2002, 50: 441-466.

[33]Wiegand D A. Mechanical failure properties of composite plastic bonded explosives [J]. Shock Compression of Condensed Matter, 1997: 599-602.

[34]Ma X, Zhao F, Ji G, et al. Computational study of structure and performance of four constituents HMX-based composite material [J]. Journal of Molecular Structure: Theochem, 2008,851(113): 22-29.

[35]Lu Y. Surface polarity of β-HMX crystal and the related adhesive forces with estane binder[J]. Langmuir, 2008, 24(23): 13477-13482.

[36]宋華杰,董海山,郝瑩.TATB、HMX和氟聚物的表面能研究[J].含能材料,2000,8(3): 104-107.

SONG Hua-jie, DONG Hai-shan, HAO Ying. Study on the surface energies of TATB, HMX and fluorlpolymers[J]. Energetic Materials, 2000, 8(3): 104-107.

[37]南海,王曉峰.FOX-7表面能研究[J].含能材料,2006,14(5): 388-390.

NAN Hai, WANG Xiao-feng. Surface energy of FOX-7 [J]. Chinese Journal of Energetic Materials, 2006, 14(5); 388-390.

[38]Kim H, Llgutchev A, Dlott D D. Surface and interface spectroscopy of high explosives and binders: HMX and Estane [J]. Propellants, Explosives, Pyrotechnics, 2006, 31(2):116-123.

[39]宋華杰,董海山,郝瑩,等.用動態(tài)力學分析技術評價TATB/氟聚物復合材料界面[J].爆炸與沖擊,2001,21(4): 287-290.

SONG Hua-jie, DONG Hai-shan, HAO Ying, et al. Evaluation of interfaces of TATB/fluoropolymer composites using dynamic mechanical analysis technique [J]. Explosion and Shock Waves, 2001, 21(4): 287-290.

[40]Kubat J, Rigdahi M, Welander M. Characterization of interfacial interactions in high density polyethylene filled with glass spheres using dynamic-mechanical analysis[J]. Journal of Applied Polymer Science,1990,39: 1527-1539.

[41]Wu Y Q, Huang F L. A micromechanical model for predicting combined damage of particles and interface debonding in PBX explosives [J]. Mechanics of Materials, 2009, 41(1): 27-47.

[42]王東旭，陳樹森，李麗潔，等. ε-HNIW/F2311 PBX界面結構力學行為模擬[J].北京理工大學學報，2015,35(3)：213-217.

WANG Dong-xu, CHEN Shu-sen, LI Li-jie, et al. Simulation on the mechanical behavior of the interface structure in ε-HNIW/F2311 PBX[J]. Transactions of Beijing Institure of Technology, 2015, 35(3): 213-217.

[43]白樹林，陳健康，于中振,等. 界面性能對剛性粒子填充高聚物力學行為的影響[J].兵工學報，2000,21(增刊)：74-76.

BAI Shu-lin, CHEN Jian-kang, YU Zhong-zhen, et al. Influence of interfacial properties on the mechanical behavior of rigid particle filled polymers[J]. Acta Armamentarii, 2000, 21(suppl):74-76.

歡迎訂閱《火炸藥學報》

《火炸藥學報》系中國兵工學會與中國兵器工業(yè)第204研究所共同主辦的學術刊物。1978年創(chuàng)刊，1986年國內外公開發(fā)行。主要刊載含能材料的合成與應用；混合炸藥、火箭推進劑、槍炮發(fā)射藥配方及相關技術；戰(zhàn)斗部技術；火炸藥燃燒及爆轟性能測試；高效毀傷；含能材料的理化分析和性能測試；含能材料的安定性、相容性以及貯存壽命研究等。

《火炸藥學報》為雙月刊，全年定價120元，歡迎從事火炸藥研究、生產、管理、應用的科技人員及有關院校師生訂閱。

國內統(tǒng)一刊號：CN61-1310/TJ國際標準刊號：ISSN 1007-7812

聯(lián)系電話：029-88291297E-mail:hzyxb@204s.com

網(wǎng)址：www.hzyxb.cn

CLC number：TJ55Document Code：AArticle ID：1007-7812(2015)06-0008-03

Received date:2015-11-10；Revised date:2015-11-17

Biography:Jürgen Evers(1941-), male, research field: solid state chemistry.

Corresponding author:Thomas M. Klap?tke(1961-), male, research field: energetic materials, explosives.

Introduction

Since lethal weapons predominantly rely on overpressure and blast effect, new high-performance secondary explosives can help to down-size the weapon system. On the other hand, if weapon systems rely on the formation of fragments (fragmenting warheads), new more energetic high explosives can only marginally help to improve the performance. In this case, chemically reactive fragments could be an answer, since in conventional warheads up to 75% of the mass corresponds to the non-reactive casing (steel casing). Research on chemically stable, but highly reactive materials could help to solve this problem. Such reactive structural materials (RSM) might be thermites, Al-PTFE composite materials or Al-Zn-Zr, Al-W or Al-U based alloys. Such RSMs should possess the following properties[1]：(1)High density；(2)High hardness；(3)Fast, highly exothermic reaction on hitting the target.

A new system which might be extremely interesting in this context is the intermetallic phase ZrW2. ZrW2is a high-density, very hard intermetallic compound that reacts/burns in a highly exothermic reaction with air at high temperatures. This intermetallic phase should provide a very suitable reactive material for warhead applications.

1Discussion

ZrW2with the MgCu2structure seems to fit very well with the Zr and W atoms. It should be very hard also densely packed. One can also expect that this intermetallic compound should burn at very high tempartures in a strong exothermic reaction due to the zirconium content of 33%. The heat of formation of ZrO2with -1100kJ/mol is high as in CeO2with 1089kJ/mol. From Cermisch metal the exothermic burning with a strong white flame at high temperature is very well-known.

W has a compression modulus of 357GPa (close to that of diamond with 420GPa). We expect and predict that ZrW2is going to be one of the intermetallic phases with the highest value for the hardness. This together with the extremely high exothermic combustion reaction should make this intermetallic phase one of the most suitable for warhead applications (reactive structural materials).

Tungsten belongs to the 6d transition metals with a very high melting temperature and very high density, as it is shown in Table 1 in comparison with tantalum, rhenium, and osmium. The prices of rhenium and osmium are much higher than those for tungsten and tantalum. But in comparison with tungsten, tantalum shows both a remarkable lower melting temperature and lower density.

Table 1　Comparison of melting temperatures and densities

Therefore tungsten seems to be a good choice for an intermetallic compound with both high melting point and high density. The reactivity of tungsten at high temperature against air could be shown the enthalpy of formation of tungsten oxide WO3ΔHf,298,WO3=-835kJ/mol. Unfortunately for tungsten nitride heat of formation is unknown up to now.

Searching for a metal with high density which could form an alloy one could consider metals such as thallium, lead and bismuth (Table 2). But all three metals have a low melting temperature at about 300℃, with a high density about 10g/cm3. However, thallium and lead are very toxic, contrary to bismuth. Unfortunately, bismuth does not form a solution with solid or liquid tungsten.

Table 2　Comparison of melting temperatures and densities

It is well known that rare earth elements from lanthanum to lutetium and also the technical used Cermisch metal are very reactive against hot air and form oxides with very high heats of formation (e.g. ΔHf,298,CeO2=-1089kJ/mol) and densities between approximately 6 and 9g/cm3. However the rare earth metals do not form any solution or compound with solid or liquid tungsten.

It is also known that tetravalent metals transition metal titanium, zirconium and hafnium are very reactive in hot condition with air or moisture. Therefore they are used in many cases as gettering metals. A piece of titanium sealed in a silica tube filled with air will pump out the gas inside the tube forming TiO2with oxygen, TiN with nitrogen, TiC and TiO2with carbon dioxide. Only the rare gas argon will remain without reaction in the tube. The melting temperatures and densities and the heats of formation of oxides MO2and nitridesMN (M=Ti,Zr,Hf) are compared in Table 3 and Table 4.

Table 3　Comparison of melting temperatures and densities

Table 4　Heats of formation of oxides and nitrides of reactive

Inspection of Tables 3 and 4 shows that titanium, zirconium and hafnium are very reactive against very hot air forming oxides, but less reactive forming nitrides. However, titanium has a low density and hafnium is a very precious metal and therefore very expensive.

Therefore for an intermetallic compound with density and high reactivity one should prepare a compound between tungsten and zirconium. Looking up the compressions modulus for zirconium(93GPa) and tungsten(357GPa)[4], having in mind this modulus for diamond with 443GPa[4]. The relatively high modulus of tungsten in comparison to diamond shows that tungsten is very hard.

It is shown from the Zr-W phase diagram that a compound with composition ZrW2is formed peritectically at 2210℃. Total melting is obtained 3000℃[5](Fig.1).

Fig.1　W-Z Phase diagram[5]

PhaseComposition,at%ZrPearsonsymbolSpacegroupPrototype(W)0to3.5cI2Im-3mWW2Zr33.3cF24Fd-3mCu2Mg(βZr)96.0to100cI2Im-3mW

ZrW2crystallizes in the cubic Laves-friauf phase with MgCu2structure, space groupFd-3m(Table 5)[6-7]. The lattice parameter of the cubic phase with composition ZrW2isa=761.3(2)? with 8 formula units (8 Zr, 16 W). Figure 2 shows a view along the cubic axis on the cubic unit-cell.

Fig.2　View along the cubic axis on a unit-cell of ZrW2

In Figure 3 it is shown that the tungsten atoms build up a network of W4tetrahedra. The W-W distances are 2.692?(Figure 2).

Fig.3　Network of interconnected W4tetrahedra

The Zr atoms build up a four-connected net as it is also found in the diamond structure with Zr-Zr distances of 3.296?.

Fig.4　View on the net of four-connected Zr atoms, as itis also found in the diamond structure

It is very interesting that the averaged spacefilling of the body-centered cubic structure of tungsten with 68%(Figure 5) and of the hexagonal close-packed structure of zirconium with 74%(Figure 6) is realized in the ZrW2the cubic Laves-friauf phase with spacefilling of 71%. W partial structure in ZrW2is compressed by 3% and the Zr partial structure increased by 3%.

Fig.5　View on the unit-cell for body-centered cubictungsten with 68 % spacefilling

Fig.6　View on the hexagonal-close packed structurewith 74% spacefilling

In the W partial structure of ZrW2with 71 % spacefilling the W-W distances with 2.692? are compressed in comparison with elemental tungsten (2.740?). On the other hand, in the Zr partial structure of ZrW2the Zr-Zr distances with 3.296? are elongated in comparison with elemental Zr(3.178 and 3.231?).

These facts are also reflected in the molar volumesVM. TheVMvalue for ZrW2is 33.214cm3/mol(Figure 2). The sum ofVMZr=14.017cm3/mol(Figure 6) and 2VMW=33.109cm3/mol(Figure 5) is only 0.3% lower than that for ZrW2at room temperature. Filling up the MgCu2structure of ZrW2with 33%(atom fraction) Zr and 67% W(atom fraction), a very good fitting is achieved. If the molar volumes of the elements are slightly higher or lower than in ZrW2cannot be truly decides, because at the formation at 2215℃(Figure 1) one should know precisely also the temperature variation of the lattice parameters.

Therefore ZrW2with the MgCu2structure seems to fit very well with the Zr and the W atoms. It should be very hard also densely packed. One can also expect that this intermetallic compound should burn at very high tempartures in a strong exothermic reaction due to the zirconium content

of 33%. The heat of formation of ZrO2with -1100kJ/mol(Table 4) is high as in CeO2with -1089kJ/mol. From Cermisch metal the exothermic burning with a strong white flame at high temperature is very well-known.

2Conclusions

The system ZrW2, a high-density, very hard intermetallic compound that reacts/burns highly exothermic with air at high temperature. This intermetallic phase should provide a very suitable reactive material for warhead applications.

References

[1]Klap?tke T M, Chemistry of High-Energy Materials[M]. 3rd Edn. Berlin/Boston: [S.L.] 2015.

[2]Holleman-Wiberg , Lehrbuch der Anorganischen Chemie, 102[M]. Germany: Walter de Gruyter, 2007.

[3]Binnewies M, Milke E, Thermochemical Data of Elements and Compounds[M]. Second Edition. Weinheim: Wiley-VCH, 2002.

[4]www. periodensytem-online. de/index. php?show=list&id=modify&prop=Kompressionsmodul&sel=oz&el[DB/OL].

[5]Masalskied T B. Binary Alloy Phase Diagrams[M]. ASM International, 2001.

[6]Blazina Z, Ban Z J. High temperature equilibria between B C C and MgCu2-type structures in the Zr1xMxW2AND Hf1-xMxW2(M=Al, Si) systems[J]. Journal of the Less Common Metals, 1983,90(2): 223-231.

[7]Villars P, Calvert L D. Pearson′s Handbook of Crystallographic Data for Intermetallic Phases[M]. ASM International, 1996.

《火炸藥學報》開通微信公眾號

為適應期刊電子化的迅速發(fā)展，《火炸藥學報》已正式開通微信公眾號。微信公眾號主要設立3個欄目“讀文章，查稿件，看動態(tài)”，已實現(xiàn)與網(wǎng)站的同步對接。用戶關注后，可以通過手機免費瀏覽自創(chuàng)刊以來的所有文章；也可以通過“搜索”功能，直接查到所需要的文章；作者登錄后，可以查詢已投稿件的狀態(tài)；專家登錄后可以瀏覽稿件的基本情況；也可以及時了解期刊或火炸藥行業(yè)的最新動態(tài)。

歡迎關注《火炸藥學報》微信號，可通過掃描以下二維碼進行關注。

Use of Intermetallic Alloys as Reactive Materials for Warhead Applications

Jürgen Evers, Thomas M. Klap?tke

(Department of Chemistry, Energetic Materials Research, LMU Munich, Butenandtstr. 5-13, 81377 Munich, Germany)

通訊地址：西安市18號信箱《火炸藥學報》編輯部郵政編碼：710065

通訊作者:顏熹琳(1982-)，女，助理研究員，從事含能材料力學性能研究。

作者簡介:唐明峰(1988 -)，男，研究實習員，從事炸藥及高分子材料的力學性能研究。

基金項目:國家自然科學基金資助(No.11302198; No.11372292)；中國工程物理研究院發(fā)展基金資助(2013B0201025)；國防基礎科研資助(B1520132004)

收稿日期:2014-11-07；修回日期:2015-03-29

中圖分類號：TJ55; O34

文獻標志碼：A

文章編號：1007-7812(2015)06-0001-07

DOI：10.14077/j.issn.1007-7812.2015.06.001 10.14077/j.issn.1007-7812.2015.06.002