(Ba0.9Sr0.1)(Ti0.999Nb0.001)O3陶瓷晶粒生长的动力学因子

研究了半导化（Ba0.9Sr0.1)(Ti0.999Nb0.001)O3陶瓷晶粒生长的动力学因子,采用固相反应法工艺制备该陶瓷样品,化学原材料方纯度高于99%的BaCO3,SrCO3,TiO2和Nb2O5等,并用到微量原料Al2O3和MnSi3以改善陶瓷的电学性能,同样化学配方的8种样品在1300℃中保温时间分别为1,3,6,10,30,60,100和300,以获得晶粒生长不同程度的块状陶瓷,利用扫描电子显微技术分析发现,随着保温时间的延长样品的平均晶粒尺寸变大,经自动图像处理技术发现,晶粒生长的动力学因子不是常数;在烧结初期大致为1.5,而在烧结后期为3.5,主与大多数报道的实验和模拟结果一致。     

添加CuO对Ca(Sm0.5Nb0.5)O3陶瓷烧结和微波介电性能的影响

采用传统高温固相反应法制备了掺杂不同量烧结助剂CuO的Ca(Sm0.5Nb0.5)O3微波介质陶瓷,研究了CuO对Ca(Sm0.5Nb0.5)O3陶瓷的烧结性、结构及微波介电性能的影响. 结果表明：添加CuO能有效促进Ca(Sm0.5Nb0.5)O3陶瓷晶粒致密化,降低烧结温度约200℃. 添加1.5%(w) CuO, 1350℃保温4 h烧结的Ca(Sm0.5Nb0.5)O3陶瓷的介电性能较优,相对介电常数er=23.98,品质因素与频率乘积Q′f=27754.5 GHz,谐振频率温度系数tf=-2.7′10-6 ℃-1.     

液相烧结氧化铝陶瓷及其烧结动力学分析

研究了CuO TiO2复相添加剂对Al2O3陶瓷烧结性能、显微结构的影响以及添加剂形成液相时Al2O3陶瓷的烧结动力学.结果显示:添加剂的加入明显地促进了Al2O3陶瓷的烧结致密度.添加剂含量对致密有明显影响,含量越高,烧结速率越快.当添加剂(CuO TiO2)为2%(质量分数),CuO/TiO2质量比为1/2时,Al2O3样品致密度最高.添加剂的存在使Al2O3晶粒发生较快生长,晶粒形貌为等轴状.通过等温烧结动力学,确定掺杂Al2O3陶瓷烧结激活能为25.2kJ/mol,表明可能是氧离子和铝离子在液相中的扩散作用控制了烧结过程.     

人眼安全激光用Er:YAG陶瓷的致密化、显微结构与光学性能

以高纯商业Y2O3、α-Al2O3和Er2O3粉体为原料,以TEOS(正硅酸乙酯)和MgO为烧结助剂,采用固相反应和真空烧结技术制备了0.5%Er:YAG透明陶瓷,并对样品的致密化行为、显微结构演化和光学性能进行了系统的研究。结果表明:1760℃烧结的Er:YAG透明陶瓷(保温时间50 h)的结构均匀致密,平均晶粒尺寸约为30μm,几乎没有晶界和晶内气孔。厚度为4 mm的Er:YAG陶瓷样品在1 200 nm处的直线透过率高达83.2%,样品的气孔率低达1.96×10–6。     

添加剂对Ba(Zn_(1/3)Nb_(2/3))O_3-Sr(Zn_(1/3)Nb_(2/3))O_3陶瓷介电性能的影响

研究了MnCO3,BaZrO3对 0 .35Ba(Zn1 /3Nb2 /3)O3(BZN) -0 .65Sr(Zn1 /3Nb2 /3)O3(SZN)陶瓷介电性能的影响。研究表明 :添加MnCO3,BaZrO3时 ,对陶瓷的烧结均起促进作用 ,增大介电常数。加入 1% (质量分数 )的MnCO3可使陶瓷具有较小的介质损耗 ,同时MnCO3对陶瓷的介电常数温度系数具有正向调整作用。加入BaZrO3后通过生成液相而减少了第二相Ba5Nb4O1 5,BaNb2 O6 的生成。所制备的 ( 0 .35BZN -0 .65SZN) 0 .1%MnCO3陶瓷的εr≈ 43.6,αε≈ -8× 10 - 6 /K ,tanδ =0 .6× 10 - 4 ,且烧结温度低于 130 0℃。     

(K_(0.44)Na_(0.52)Li_(0.04))(Nb_(0.86)Ta_(0.10)Sb_(0.04))O_3陶瓷的压电性能

采用传统固相法制备Li、Ta和Sb共同掺杂铌酸钾钠(KNN)的(K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3(KNLNTS)无铅压电陶瓷。研究不同烧结温度对该陶瓷的结构、形貌、致密度以及电学性能的影响。结果表明:不同温度下烧结的陶瓷样品均为钙钛矿相结构;在1 050~1 150℃之间烧结均可获得性能良好的陶瓷样品;1 050℃烧结的样品表现出最佳的综合电学性能,即相对介电常数和压电系数均较大,分别为1 120pC/N和193pC/N,介电损耗较小为2.55%,机械品质因子较大为85,密度较大为4.65g/cm3,且该样品具有饱和的电滞回线。随着烧结温度的升高,陶瓷样品电学性能下降和晶粒增大均与样品中存在着碱金属离子挥发有关。KNLNTS陶瓷样品的Curie温度由不掺杂的KNN陶瓷样品的420℃下降为301℃。     

低温烧结Mg_4Nb_2O_9微波介质陶瓷(英文)

分别研究了不同含量Li2CO3/V2O5共掺杂和部分Li取代Mg对Mg4Nb2O9基陶瓷烧结特性、显微结构和微波介电性能的影响.结果表明:Li2CO3/V2O5共掺杂或部分Li取代Mg,均能使Mg4Nb2O9基陶瓷的烧结温度从1 400℃降至950℃,但其烧结机理不同.Li2CO3/V2O5共掺杂Mg4Nb2O9(MNLV)样品中的低熔点液相,使MNLV陶瓷的致密化烧结温度降低.部分Li取代Mg显著降低了(Mg(4-x)Lix)(Nb1.92V0.08)O(9-δ)(MLNV)样品的致密化烧结温度.950℃烧结,相对于MNLV样品的品质因数(Q=13276)而言,MLNV样品的Q值(1 759)显著恶化,这是由于Li1+占据Mg2+晶格.使晶体中非谐振项损耗增加.     

TiB2陶瓷的放电等离子烧结

利用放电等离子烧结技术制备TiB2陶瓷。分析了烧结温度、保温时间和升温速率对烧结体致密度及显微结构的影响。实验结果表明：随着烧结温度的提高，烧结体的致密度及晶粒大小均增加。延长保温时间，样品的晶粒有明显长大。提高升温速率，有利于抑制晶粒生长，但样品的致密度降低。在TiB2的烧结过程中，存在颗粒间的放电。在烧结温度为1500℃，压力为30MPa，升温速率为100℃／min，真空中由SPS烧结制备的TiB2陶瓷相对密度可达98％。     

AlN-Re2O3液相烧结碳化硅

采用非氧化物AlN和Re2O3作为复合烧结助剂(Re2O3-La2O3与Y2O3)进行碳化硅液相烧结得到了致密的烧结体.烧结助剂占原料粉体总质量的20%,其中:AIN与(La0.5Y0.5)2O3的摩尔比为2:1,在30MPa压力下,1850℃保温0.5h热压烧结的碳化硅陶瓷,抗弯强度>800MPa,断裂韧性>8MPa·m1/2,明显高于同组分1 950℃无压烧结0.5h的碳化硅陶瓷的抗弯强度(433.7MPa)和断裂韧性(4.8MPam·m1/2.热压烧结的陶瓷晶粒呈单向生长,断裂模式为沿晶断裂.同组分无压烧结碳化硅陶瓷的显微结构可以观察到核壳结构.     

纳米SiC陶瓷的超高压烧结研究(英文)

以纳米SiC为原料,用两面项压机在不同工艺条件下(1 000～1 300℃,4.0～4.5 GPa,15～35 min)实现了40(质量分数,下同)Al2O3烧结助剂添加的SiC陶瓷体的烧结.研究了烧结工艺对SiC陶瓷性能的影响.用X射线衍射、扫描电镜、显微硬度测试仪等对SiC高压烧结体进行了表征.结果表明:Al2O3是有效的低温烧结助剂,在超高压工艺下添加4%Al2O3即可实现SiC陶瓷全致密化烧结;烧结体晶粒长大得到抑制,维持在纳米级,晶格常数收缩了约0.45%;烧结体显微硬度和密度随烧结温度、烧结压力的升高或保温时间的延长而提高.     

Victrex® poly(ethersulfone) (PES) and Victrex® poly(etheretherketone) (PEEK)

Properties of two high performance engineering thermoplastics, amorphous polyethersulfone (PES) and semicrystalline polyetheretherketone (PEEK), are discussed. Both resins can be processed by conventional techniques, compounded with high performance fibers, and have high service temperature (up to 300°C). Due to the amorphous character PES can be dissolved and spray coated into metals.     

Photopyroelectric Spectroscopic Studies of ZnO-MnO(2)-Co(3)O(4)-V(2)O(5) Ceramics

Photopyroelectric (PPE) spectroscopy is a nondestructive tool that is used to study the optical properties of the ceramics (ZnO + 0.4MnO(2) + 0.4Co(3)O(4) + xV(2)O(5)), x = 0-1 mol%. Wavelength of incident light, modulated at 10 Hz, was in the range of 300-800 nm. PPE spectrum with reference to the doping level and sintering temperature is discussed. Optical energy band-gap (E(g)) was 2.11 eV for 0.3 mol% V(2)O(5) at a sintering temperature of 1025 °C as determined from the plot (ρhυ)(2)versushυ. With a further increase in V(2)O(5), the value of E(g) was found to be 2.59 eV. Steepness factor 'σ(A)' and 'σ(B)', which characterize the slope of exponential optical absorption, is discussed with reference to the variation of E(g). XRD, SEM and EDAX are also used for characterization of the ceramic. For this ceramic, the maximum relative density and grain size was observed to be 91.8% and 9.5 μm, respectively.     

(Ba_(1-α)Sr_α)_(4.8)(Sm_(0.7)La_(0.3))_(8.8)Ti_(18)O_(54)陶瓷的微波介电性能

采用固相合成法制备了(Ba(1-α)Srα)4.8(Sm0.7La0.3)8.8Ti18O54(α=0.1～0.5)系陶瓷,表征了该陶瓷的相组成和显微结构,测试了微波介电性能.结果表明:α=0.3时,(Ba(1-α)Srα)4.8(Sm0.7La0.3)8.8Ti18O54系陶瓷为单相的新钨青铜结构固溶体.α>0.3时,相继出现了第二相BaLa2Ti4O12和La0.66TiO2.993.随α的增加,(Ba(1-α)Srα)4.8(Sm0.7La0.3)8.8Ti18O54系陶瓷的相对介电常数(εr)先增大后有所波动,品质因数(Qf)先增大后减小,谐振频率温度系数(τf)单调减小.α=0.3时,在1 350℃烧结的陶瓷的微波介电性能最佳:εr=98.77,Qf=5184GHz,τf=10.9×10-6/℃,优于不掺杂的BaO-Sm2O3-TiO2陶瓷的.     

Calcium silicate hydrate (II) (“C-S-H(II)”)

This semicrystalline phase, originally named ‘calcium silicate hydrate(II)’ by Taylor (1950), has been studied with X-rays, electron optics, chemical investigation of silicate anion type, infrared spectra, and thermal methods. It is structurally related to jennite (C₉S₆H₁₁) and probably also to the fibrous CSH of cement pastes, the three phases forming a sequence of decreasing crystallinity. The specimen studied had approximate composition C₂SH_3.2 after standing over saturated CaCλ₂ at about 15°C. CSH(II) contains metasilicate chains and pyrosilicate groups and has a disordered layer structure. Much of the water can be lost reversibly without significant change in lattice parameters.     

Poly(butadiene-acrylic acid(g)acrylonitrile(g)acrylic acid)

Summary In the present work we describe, the synthesis and characterization of a new gel obtained by crosslinking a cooligomer of butadiene-acrylic acid (BuAA), by reaction with acrylonitrile and acrylic acid. The purified product was characterized by FTIR, elemental analyses and scanning electronic microscopy. The thermal properties were studied and swelling indexes were determined in different solvents and at different pH values. The capacity of poly(butadiene-acrylic acid(g)acrylonitrile(g)acrylic acid) [gel A] to separate different organic substances, such as amino acids and colorants, was determined.     

Photooxidative stability of substituted poly(phenylene vinylene) (PPV) and poly(phenylene acetylene) (PPA)

The addition of side groups to improve the photooxidative stability of polymers used in polymer-based light-emitting diodes (LEDs) is explored. Infrared spectroscopy and computational chemistry techniques are used to study the effects of chemical substitution of the reactive vinylene moiety in poly(phenylene vinylene) (PPV). The bond order of the vinylene group in small oligomers is calculated using semiempirical techniques to assess the improvement in stability toward oxidants such as singlet oxygen. We find that PPV dimers allow relative comparisons across a range of possible substitutions. Experimental results correlate well with these calculations. The addition of electron-withdrawing substituents, such as nitrile groups, to the vinylene moiety is found to be particularly effective in reducing the reactivity of alkoxy-substituted PPV toward singlet oxygen. The photooxidative stability of a poly(phenylene acetylene) (PPA) derivative is also studied. It appears that this family of polymers is more stable toward photooxidation than are its PPV analogs. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2451–2458, 1998     

Chemical cross-linking of conducting poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) using poly(ethylene oxide) (PEO)

Hybrid films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) were prepared with different molecular weights of poly(ethylene oxide) (PEO). The cross-linking reaction between PEO and PEDOT:PSS was performed at high temperature and confirmed by using differential scanning calorimeter (DSC), contact angle measurement, and solid-state ¹H NMR. The effect of chemical reaction on the conductivity and morphology of these hybrid films was studied by using 4-point probe and atomic force microscope (AFM), respectively. As-spun PEO/PEDOT:PSS films have lower electric conductivity due to the addition of nonconductive PEO, and exhibits no molecular weight dependence on conductivity. After chemical cross-linking reaction at high temperature, only PEDOT:PSS films with lowest molecular weight PEO additives show enhanced conductivity with increasing reaction time. AFM result indicates that the heat-treated PEO/PEDOT:PSS hybrid films show grain-like morphology compared to ethylene glycol treated PEDOT:PSS films which shows continuous PEDOT domain. In the present work we demonstrate that the cross-linking reaction can be used to improve the wet stability of PEDOT:PSS nanofiber, showing good water resistance and excellent dimensional stability.     

Thermal studies of blends of poly(phenylene sulfide) (PPS) with poly(phenylene sulfide sulfone) (PPSS) and with poly(phenylene sulfide ether) (PPSE)

The miscibilities of poly(phenylene) sulfide/poly(phenylene sulfide sulfone) (PPS/PPSS) and poly(phenylene) sulfide/poly(phenylene sulfide ether) (PPS/PPSE) blends were invesigated in terms of shifts of glass transition temperatures T_g of pure PPS, PPSS, a dn PPSE. The crystallization kinetics of PPS/PPSS blends was also studied as a function of molar composition. The PPS/PPSS and PPS/PPSE blends are respectively partially and fully miscible. PPSE shows a plasticizing effect on PPS as does PPS on PPSS, which necessarily improves te processibility in the respective systems. We can control T_g and melting temperature T_m of PPS by varying amounts of PPSE in blends. The melt crystallization temperature T_mc of PPS/PPSE blends was higher than that of the PPSE homopolymer. Therefore, these blends require shorter cycle times in processing than pure PPSE. The overall rate of crystallization for PPS/PPSS blends follows the Avrami equation with an exponent ?2. The maximal rate of crystallization for PPS/PPSS blends occurs at a temperatre higher by 10°C than that for PPS, while the crystallization half time t_1/2 is 4 times shorter. In the cold crystallization range, crystal growth rates increase and Avrami exponents decrease significantly as the temperature increases.