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21.
Rafael S. Pinto João P. Serra João C. Barbosa Renato Gonçalves Maria M. Silva Senentxu Lanceros-Méndez Carlos M. Costa 《大分子材料与工程》2021,306(11):2100372
Considering the high levels of materials used in the fields of electronics and energy storage systems, it is increasingly necessary to take into consideration environmental impact. Thus, it is important to develop devices based on environmentally friendlier materials and/or processes, such as additive manufacturing techniques. In this work, poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) are prepared by direct-ink-writing (DIW) by varying solvent evaporation temperature and fill density percentage. Different morphologies for both polymers are obtained, including dense films and porous membranes, as well as different electroactive β-phase content, thermal and mechanical properties. The dielectric constant and piezoelectric d33 coefficient for dense films reaches up to 16 at 1 kHz and 4 pC N−1, respectively for PVDF-HFP with a fill density of 80 and a solvent evaporation temperature of 50 °C. Porous structures are developed for battery separator membranes in lithium-ion batteries, with a highest ionic conductivity value of 3.8 mS cm−1 for the PVDF-HFP sample prepared with a fill density of 100 and a solvent evaporation temperature of 25 °C, the sample showing an excellent cycling performance. It is demonstrated that electroactive films and membranes can be prepared by direct-ink writing suitable for sensors/actuators and energy storage systems. 相似文献
22.
采用硝酸-氢氟酸混合酸为消解溶剂,通过微波消解技术对粗制氟化钠进行快速消解,并用氟硅酸钾滴定法测定其二氧化硅含量。选择饱和氯化钾溶液替代固体氯化钾作为沉淀剂,考察了消解酸体系、饱和氯化钾溶液用量、沉淀温度、沉淀放置时间、共存元素干扰及指示剂选择等条件对测定结果的影响并进行优化。确定了最优测试条件:以8 mL硝酸+2 mL氢氟酸为消解溶剂,以8 mL饱和氯化钾溶液为沉淀剂,控制沉淀温度为20~25 ℃、沉淀放置时间为15 min,选择50 g/L氯化钾-50%乙醇溶液洗涤沉淀,采用溴麝香草酚蓝-酚红指示剂。该方法应用于回收粗制氟化钠中二氧化硅含量的测定可大幅度缩短分解试样的时间,有效降低检测成本,回收率为99.15%~100.63%,相对标准偏差(RSD,n=8)小于1%,与传统高温碱熔法测定结果相符,方法的准确度和精密度较好。 相似文献
23.
采用自制铁基生物絮凝剂(BPFS)对羧甲基壳聚糖(CMC)进行改性,并研究其对废水中氟的去除。考察了羧甲基壳聚糖CMC/Fe质量比、BPFS-CMC投加量、pH、反应时间对氟离子去除效果的影响。结果表明,水中残余氟离子浓度随CMC/Fe质量比升高而升高;随改性羧甲基壳聚糖投加量的增加而降低,而且与羧甲基壳聚糖单独处理含氟废水相比,氟离子去除效果有明显提高,当BPFS-CMC投加量为3%(体积分数)时,氟离子去除率由33.05%提高到62.70%;酸性条件有利于氟离子的去除;随反应时间的增加,氟离子浓度缓慢下降。当羧甲基壳聚糖CMC/Fe质量比为0.05,投加量3%,pH=5,反应时间10 min时,水中残余氟离子浓度为7.78 mg/L,低于国家《铅、锌工业污染物排放标准》(GB 25466—2010)规定的限值。 相似文献
24.
40万t/a化成法生产过磷酸钙,采用4 72 10 N o12.5离心式钢衬胶排风机,该风机使用中出现泄漏、腐蚀等问题,经对上下机壳密封方法、清理门结构等的改进,使风机检修工作量大大减少,风机寿命延长。 相似文献
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Multiple melting phenomena have been studied in blends of poly(vinylidene fluoride) (PVF2) with low molar mass isotactic poly(ethyl methacrylate) (it-PEMA). In all blends, as well as in pure PVF2, a transition (T1) was observed prior to the main melting point (T2). T1 is probably connected with the melting of secondarily-crystallized material. In addition to this, a high temperature melting endotherm (T3) was observed, which could be ascribed completely to recrystallization of PVF2. The highest transition (T4) was caused by melting of the σ form of PVF2. From Hoffman-Weeks plots—T2 vs. crystallization temperature, Tc — it could be concluded that no thermody amic depression of the melting point of PVF2 occurred in the blends. The stabilities of PVF2 crystallites in the various blends were derived from the slopes of Hoffman-Weeks plots and were in good agreement with lamellar thicknesses found from SAXS measurements. 相似文献
28.
A. A. Nikolopoulos A. Kogelbauer J. G. Goodwin Jr. G. Marcelin 《Catalysis Letters》1996,39(3-4):173-178
The gas phase synthesis of MTBE was studied using three series of zeolites modified by ion-exchange with ammonium fluoride, the parent materials being HY, H-mordenite, and HZSM-5. Modification of zeolites by fluoride-exchange was found to enhance the MTBE synthesis activity for all three types of zeolites without impairing their excellent selectivity to MTBE. The mechanism of activity enhancement by fluoride-modification appears to be related to the formation of extra-lattice Al rather than the presence of fluoride-ions. 相似文献
29.
The measurements of ac conductivity [σm(ω)], dielectric constant [?′(ω)] and loss [?″(ω)] have been performed on solution grown (thickness ∼85 μm) and uniaxially stretched (thickness ∼25, 45 and 80 μm) films of poly(vinylidene fluoride) (PVDF) in the frequency range 0.1 kHz-10 MHz and in the temperature range 77-400 K. The σm(ω) can be described by the relation σ(ω) = Aωs, where s is close to unity and decreases with increase in temperature. Three relaxations, observed in the present investigation, have been designated as the αc-, the αa- and the β-relaxations appearing from high temperature side to the low temperature side. The αc-relaxation could not be observed in the case of uniaxially stretched poly(vinylidene fluoride) films. The αc- and αa-relaxations are associated with the molecular motions in the crystalline regions and micro-Brownian motion in the amorphous regions of the main polymer chain, respectively, whereas the β-relaxation is attributed to the rotation of side group dipoles or to the local oscillations of the frozen main polymer chain. 相似文献
30.
研究了在不同有机碱催化下,哈格曼乙酯和硝基乙烷经迈克尔加成合成3 甲基 3 (1′ 硝基乙基) 4 乙氧甲酰环己酮的反应。结果表明,氟化四丁基铵的催化效果最好,且当n(氟化四丁基铵)∶n(哈格曼乙酯)=1∶2时,合成产物3 甲基 3 (1′ 硝基乙基) 4 乙氧甲酰环己酮的收率达到最高值56%。 相似文献