Cold Sintering Process of Composites: Bridging the Processing Temperature Gap of Ceramic and Polymer Materials

Co‐sintering ceramic and thermoplastic polymer composites in a single step with very high volume fractions of ceramics seems unlikely, given the vast differences in the typical sintering temperatures of ceramics versus polymers. These processing limitations are overcome with the introduction of a new sintering approach, namely “cold sintering process” (CSP). CSP utilizes a transient low temperature solvent, such as water or water with dissolved solutes in stoichiometric ratios consistent with the ceramic composition, to control the dissolution and precipitation of ceramics and effect densification between room temperature and ≈200 °C. Under these conditions, thermoplastic polymers and ceramic materials can be jointly formed into dense composites. Three diphasic composite examples are demonstrated to show the overall diversity of composite material design between organic and inorganic oxides, including the microwave dielectric Li₂MoO₄–(? C₂F₄ ? ) _n , electrolyte Li_1.5Al_0.5Ge_1.5(PO₄)₃–(? CH₂CF₂ ? ) _x [? CF₂CF(CF₃)? ] _y , and semiconductor V₂O₅–poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate composites. Cold sintering is more general and shall have a major impact on the processing of composite materials for many different applications, mechanical, thermal, and electronic, to mention a few possibilities. CSP concepts open up new composite material design and device integration schemes, impacting a wide variety of applications.     

Ceramic–Salt Composite Electrolytes from Cold Sintering

The development of solid electrolytes with the combination of high ionic conductivity, electrochemical stability, and resistance to Li dendrites continues to be a challenge. A promising approach is to create inorganic–organic composites, where multiple components provide the needed properties, but the high sintering temperature of materials such as ceramics precludes close integration or co‐sintering. Here, new ceramic–salt composite electrolytes that are cold sintered at 130 °C are demonstrated. As a model system, composites of Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) or Li_{1+x +y} Al_x Ti_2?x Si_y P_3?y O₁₂ (LATP) with bis(trifluoromethanesulfonyl)imide (LiTFSI) salts are cold sintered. The resulting LAGP–LiTFSI and LATP–LiTFSI composites exhibit high relative densities of about 90% and ionic conductivities in excess of 10^?4 S cm^?1 at 20 °C, which are comparable with the values obtained from LAGP and LATP sintered above 800 °C. It is also demonstrated that cold sintered LAGP–LiTFSI is electrochemically stable in Li symmetric cells over 1800 h at 0.2 mAh cm^?2. Cold sintering provides a new approach for bridging the gap in processing temperatures of different materials, thereby enabling high‐performance composites for electrochemical systems.     

钛酸钙对BZN-CaTiO_3系统介电性能的影响

研究了利用电子陶瓷工艺制得的主晶相为Ba(Zn1/3Nb2/3)O3(BZN)和CaTiO3的新型陶瓷,BZN具有立方钙钛矿结构。通过烧结温度的改变得到不同介电性能的陶瓷材料,发现CaTiO3的添加量对系统介电性能有显著影响。在1 395℃烧结的BZN-CaTiO3陶瓷,当CaTiO3的添加量为60%(质量分数)时介电性能最佳,其εr为99.97,tgδ为0.54×10-4,αC为–13.05×10-6℃–1(25~85℃,1MHz下测量)。     

氮化铝陶瓷烧结炉温度均匀性对烧结产品质量影响的研究

氮化铝陶瓷是近年来广受关注的一种新型陶瓷材料,是剧毒氧化铍的替代材料,其在高功率电子领域有着相当广泛的应用前景,但是氮化铝陶瓷是难烧结的非氧化物陶瓷,陶瓷的烧结对氮化铝陶瓷性能的影响非常大,尤其是在氮化铝陶瓷批量生产过程中,陶瓷烧结炉的温度不均匀,将导致陶瓷性能的巨大差异。简要介绍了氮化铝陶瓷烧结炉温度均匀性对烧结产品质量的影响。     

Ni、Cu掺杂钛酸锶复合功能陶瓷的电学特性

采用一次烧成工艺制备了NiO、CuO掺杂的SrTiO3复合功能陶瓷，研究了其烧成状况、显微结构、复合功能特性及小电流区的电流－温度关系。研究结果表明，掺NiO样品的晶粒粒度明显大于掺CuO样品；由于在烧成过程中受主杂质的行为有所不同，掺CuO样品具有较高的晶界受主态浓度。这使得在制备条件和掺杂浓度相同的条件下，掺NiO样品和掺CuO样品的复合功能特性之间存在差异。     

低介熔融石英陶瓷制备及其介电性能研究

利用固相合成法,以未掺杂的熔融石英砂为基础原料,通过快速升温、短时保温的烧结工艺制备出了具有极低介电常数的熔融石英陶瓷材料。研究了不同烧结温度对材料的烧结特性及介电性能的影响。结果表明:在1 150℃烧结1 h制得的材料,具有较好的性能,其最大相对密度为99%,εr=3.4,tanδ=6.86×10–4(1 MHz),Q.f=12 000 GHz(10 GHz)。     

Ultrahigh Energy‐Storage Density in Antiferroelectric Ceramics with Field‐Induced Multiphase Transitions

The excellent energy‐storage performance of ceramic capacitors, such as high‐power density, fast discharge speed, and the ability to operate over a broad temperature range, gives rise to their wide applications in different energy‐storage devices. In this work, the (Pb_0.98La_0.02)(Zr_0.55Sn_0.45)_0.995O₃ (PLZS) antiferroelectric (AFE) ceramics are prepared via a unique rolling machine approach. The field‐induced multiphase transitions are observed in polarization–electric field (P–E) hysteresis loops. All the PLZS AFE ceramics possess high energy‐storage densities and discharge efficiency (above 80%) with different sintering temperatures. Of particular significance is that an ultrahigh recoverable energy‐storage density of 10.4 J cm^‐3 and a high discharge efficiency of 87% are achieved at 40 kV mm^‐1 for PLZS ceramic with a thickness of 0.11 mm, sintered at 1175 °C, which are by far the highest values ever reported in bulk ceramics. Moreover, the corresponding ceramics exhibit a superior discharge current density of 1640 A cm^‐2 and ultrafast discharge speed (75 ns discharge period). This great improvement in energy‐storage performance is expected to expand the practical applications of dielectric ceramics in numerous electronic devices.     

Embedded Capacitors in Printed Wiring Board: A Technological Review

This paper reviews the technology of embedded capacitors, which has gained importance with an increase in the operating frequency and a decrease in the supply voltage of electronic circuits. These capacitors have been found to reduce the number of surface-mount capacitors, which can assist in the miniaturization of printed wiring boards. This paper describes various aspects of embedded capacitors, such as electrical performance, available dielectric materials, manufacturing processes, and reliability. Improvement in electrical performance is explained using a cavity model from the theory of microstrip antennas. The advantages and disadvantages of dielectric materials such as polymers, ceramics, polymer–ceramic composites, and polymer–conductive filler composites are discussed. Various manufacturing techniques that can be used for the fabrication of embedded capacitors are also discussed. Embedded capacitors have many advantages, but failure of an embedded capacitor can lead to board failure since these capacitors are not reworkable. The effect of various environmental stress conditions on the reliability of embedded capacitors is reviewed.     

聚合物前驱体转化法制备陶瓷微机电系统

陶瓷材料作为一种在高温和腐蚀等苛刻环境中应用的重要材料,对其制备和加工技术进行研究是非常必要的。本文在简要概述传统微机电系统(MEMS)加工技术对制备陶瓷MEMS存在的不足基础上,着重介绍了由聚合物前驱体转化法制备陶瓷MEMS的制备方法、工艺流程、优缺点及未来发展方向。     

Li_2O-B_2O_3-SiO_2掺杂低温烧结CLST陶瓷的介电性能

通过Li2O-B2O3-SiO(2LBS)玻璃的有效掺杂,低温液相烧结制备了16CaO-9Li2O-12Sm2O3-63TiO(2CLST)陶瓷。研究了LBS掺杂量对其烧结性能、相组成及介电性能的影响。结果表明:通过掺杂LBS,使CLST陶瓷的烧结温度由1300℃降至1000℃,且无第二相生成。随LBS掺杂量的增加,tanδ显著降低,τf趋近于零。当w(LBS)为10%时,CLST陶瓷在1000℃烧结3h获得最佳介电性能:tanδ为0.0045,τf为4×10–6/℃,虽然εr由105.0降至71.0,但仍属于高εr范围。     

掺杂Li_2CO_3低温烧结ZnO-TiO_2系介质陶瓷的研究

用传统工艺合成了Li2CO3掺杂的ZnO-TiO2系微波介质陶瓷,系统研究了其烧结行为、显微结构和介电性能。结果表明:掺杂质量分数1%的Li2CO3可使ZnO-TiO2陶瓷的烧结温度从1100℃降到980℃;掺杂3%Li2CO3时,在950℃保温2h烧结,于6～8GHz测试试样的介电性能为:εr约为20,Q·f约为40000GHz,τf约为–14×10–6℃–1。     

Sr_(0.3)Ba_(0.7)Bi_(3.7)La_(0.3)Ti_4O_(15)铁电陶瓷的烧结及介电性能

采用两步烧结工艺制备Sr0.3Ba0.7Bi3.7La0.3Ti4O15铁电陶瓷,研究了烧结工艺对陶瓷的晶相和介电性能的影响。结果表明:适当提高最高温度、保温温度和保温时间可改善陶瓷的介电性能。当最高温度为1180～1200℃,在1050～1080℃保温5～15h时,其εr为238～262,tanδ小于10–2,σ为1.0×10–11～10–12S·m–1。该烧结工艺可减少铋的挥发,降低氧空位浓度,因而减弱了陶瓷的高温低频耗散现象。随着保温时间的增加,高温电导得到有效抑制,在1050℃保温15h样品的σ降低了一个数量级,在280℃时为5.2×10–9S·m–1。     

织构化BaBi_4Ti_4O_(15)压电陶瓷的制备与性能研究

以熔盐法制备的BaBi4Ti4O15片状粉体作为模板,流延法制备了BaBi4Ti4O15压电陶瓷,并与传统固相法制备的BaBi4Ti4O15压电陶瓷进行比较。通过XRD分析不同工艺制备的陶瓷样品相结构,SEM观察其微观形貌。结果表明:流延法制备的BaBi4Ti4O15陶瓷在(00l)方向实现了定向排列,且随着模板含量的增加,(00l)晶面的定向度f增加,模板质量分数为20%时,f=57.7%。另外,流延法制得的BaBi4Ti4O15陶瓷样品容易致密,当烧结温度从1 140℃到1 145℃时,密度由5.39 g.cm–3增大到6.64 g.cm–3,在1 150℃达到最大密度7.39 g.cm–3。     

Structural Fabrication and Functional Modulation of Nanoparticle–Polymer Composites

This review article summarizes recent progress in the fabrication methodologies and functional modulations of nanoparticle (NP)–polymer composites. On the basis of the techniques of NP synthesis and surface modification, the fabrication methods of nanocomposites are highlighted; these include surface‐initiated polymerization on NPs, in situ formation of NPs in polymer media, and the incorporation through covalent linkages and supramolecular assemblies. In these examples, polymers are foremost hypothesized as inert hosts that stabilize and integrate the functionalities of NPs, thus improving the macroscopic performance of NPs. Furthermore, due to the unique physicochemical properties of polymers, polymer chains are also dynamic under heating, swelling, and stretching. This creates an opportunity for modulating NP functionalities within the preformed nanocomposites, which will undoubtedly promote the developments of optoelectronic devices, optical materials, and intelligent materials.     

Co_2O_3掺杂对0.965MgTiO_3-0.035SrTiO_3微波介质陶瓷性能的影响

采用传统电子陶瓷制备方法研究了Co2O3(1.5%～5.0%,质量分数)掺杂的0.965MgTiO3-0.035SrTiO3(MST0.035)微波介质陶瓷,分析了Co2O3含量对MST0.035陶瓷的烧结性能、晶相结构、显微形貌以及微波介电性能的影响。结果表明:Co2O3的掺杂促进了MST0.035陶瓷的烧结。随着Co2O3掺杂量的增加,陶瓷介电常数略有下降,谐振频率温度系数以及品质因数增加,同时中间相MgTi2O5逐渐减少直至完全消失。当Co2O3掺杂量为质量分数3.0%时,MST0.035陶瓷的烧结温度由1 380℃降低到1 290℃,其烧结所得的样品具有优良的微波介电性能:谐振频率温度系数τf=–2.53×10–6/℃,高的品质因数Q·f=19 006 GHz和介电常数εr=20.5。     

A Versatile,Molecular Engineering Approach to Simultaneously Enhanced,Multifunctional Carbon‐Nanotube– Polymer Composites

Single‐walled carbon nanotubes (SWNTs) are recognized as the ultimate carbon fibers for high‐performance, multifunctional composites. The remarkable multifunctional properties of pristine SWNTs have proven, however, difficult to harness simultaneously in polymer composites, a problem that arises largely because of the smooth surface of the carbon nanotubes (i.e., sidewalls), which is incompatible with most solvents and polymers, and leads to a poor dispersion of SWNTs in polymer matrices, and weak SWNT–polymer adhesion. Although covalently functionalized carbon nanotubes are excellent reinforcements for mechanically strong composites, they are usually less attractive fillers for multifunctional composites, because the covalent functionalization of nanotube sidewalls can considerably alter, or even destroy, the nanotubes' desirable intrinsic properties. We report for the first time that the molecular engineering of the interface between non‐covalently functionalized SWNTs and the surrounding polymer matrix is crucial for achieving the dramatic and simultaneous enhancement in mechanical and electrical properties of SWNT–polymer composites. We demonstrate that the molecularly designed interface of SWNT–matrix polymer leads to multifunctional SWNT–polymer composite films stronger than pure aluminum, but with only half the density of aluminum, while concurrently providing electroconductivity and room‐temperature solution processability.     

Strong Carbon‐Nanotube–Polymer Bonding by Microwave Irradiation

The vigorous response of multiwalled carbon nanotubes (MWNTs) to microwave irradiation, leading to the release of a large amount of heat, is used to locally melt a plastic matrix adjacent to the nanotubes within a period of seconds. This results in the intercalation of the MWNTs into the polymer matrix at room temperature without any physical damage to the polymer. The so‐called “microwave welding” approach creates a new paradigm for the formation of very strong MWNT–polymer bonds without the use of any adhesive, and represents a significant step forward for the fabrication of functional nanotube composites. Here, we demonstrate the implications of the anisotropic alignment of MWNTs in polymers, patterned conductors/resistors for soft electronics, and high‐strength composites, where the MWNTs are ‘soldered' to flexible polymer substrates.     

Carbon Fiber–Bismaleimide Composites Filled with Nickel‐Coated Single‐Walled Carbon Nanotubes for Lightning‐Strike Protection

Multifunctional carbon fiber composites are imperative for next‐generation lightweight aircraft structures. However, lightning‐strike protection is a feature that is lacking in many modern carbon fiber high‐temperature polymer systems, due to their high electrical resistivity. This work presents a study on processing, materials optimization, and property development of high‐temperature bismaleimide (BMI)–carbon fiber composites filled with nickel‐coated single‐walled carbon nanotubes (Ni‐SWNTs) based on three key factors: i) dispersion of Ni‐SWNTs, ii) their surface coverage on the carbon plies and, iii) the composite surface resistivity. Atomic force microscopy analysis revealed that coating purified SWNTs with nickel enabled improved dispersion which resulted in uniform surface coverage on the carbon plies. The electrical resistivity of the baseline composite system was reduced by ten orders of magnitude by the addition of 4 wt% Ni‐SWNTs (calculated with respect to the weight of a single carbon ply). Ni‐SWNT–filled composites showed a reduced amount of damage to simulated lightning strike compared to their unfilled counterparts, as indicated by the minimal carbon fiber pull‐out.     

Thermal Transport in Conductive Polymer–Based Materials

The demand for flexible conductive materials has motivated many recent studies on conductive polymer–based materials. However, the thermal conductivity of conductive polymers is relatively low, which may lead to serious heat dissipation problems for device applications. This review provides a summary of the fundamental principles for thermal transport in conductive polymers and their composites, and recent advancements in regulating their thermal conductivity. The thermal transport mechanisms in conductive polymer–based materials and up‐to‐date experimental approaches for measuring thermal conductivity are first summarized. Effective approaches for the regulation of thermal conductivity are then discussed. Finally, thermal‐related applications and future perspectives are given for conductive polymers and their composites.     

精细结构陶瓷材料烧结技术的研究动向

本文介绍国外精细结构陶瓷烧结技术的研究动向。重点叙述最近研制成的几种烧结技术，诸如微波、激光、自已燃烧烧结或燃烧合成法，低温无压烧结以及中子照射超低温烧结陶瓷等新技术。并介绍了用上述新技术制备的一些陶瓷材料的工艺及其性能。