Structure and piezoelectric properties of (1–x)K0.5Na0.5NbO3–xLiBiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1–x)(K_0.5Na_0.5)NbO₃–xLiBiO₃ [(1–x)KNN–xLB] (x=0, 0.0005, 0.002, 0.004, 0.006, 0.008, 0.010) were prepared by an traditional solid-state reaction. The microstructure and electrical properties of the ceramics were investigated. The results show that all (1–x)KNN–xLB ceramics possess pure perovskite structure when x=0.01, no trace of any secondary phase is detected, and the phase structure of the ceramics transits abnormally from orthorhombic to cubic. With the increase of the LB content, the size of grain gradually becomes small, the piezoelectric constant d₃₃ and the planar electromechanical coupling coefficient k_p first increases and then decreases. The d₃₃ and k_p of the ceramics reach their maximum values 115 pC/N at x=0.002 and 0.2701 at x=0.001, respectively. The dielectric constant e_r of the ceramics firstly increases evidently and then decreases with the increase of x, the maximum value 871.8 is obtained at x=0.006.     

Piezoelectric and dielectric properties of Cr-doped PSN-PZN-PZT quaternary piezoelectric ceramics

PSN-PZN-PZT x wt.%Cr2O3, x=0.0-0.9, were prepared by conventional mixed oxide techniques at sintering temperatures of 1220℃-1300℃ for 2 h. The effect of sintering temperature on the microstructure and the piezoelectric properties was investigated by XRD, SEM, and other conventional measurement. The result indicated that with temperature increasing, the valence of Cr ion from Cr^5 or Cr^6 changes into Cr^3 , and the piezoelectric properties turn hard. With increasing Cr2O3 content, the amount of rhombohedral phases increases and the morphotropic boundary phase is correspondingly shifts to rhombohedral phase. A uniform microstructure and excellent comprehensive properties were obtained at 1240℃ as the amount of Cr2O3 is 0.5 wt.%.     

Synthesis of piezoelectric nanocrystalline PZT powder by stearic acid gel method

PZT nanocrystalline powder was prepared by a stearic acid gel method. The crystallization process from the precursor was monitored by infrared spectroscopy, differential thermal analysis, and thermogravimetric analysis. The nano-sized PZT powder was characterized by X-ray diffraction and transmission electron microscopy. It shows that pure single-phase PZT powder could be obtained at 450℃ for 1 h, and the particle size is about 20 nrn. With an increase in the calcination temperature, the PZT crystallite size increased.     

Effects of CeO2 doping on the structure and properties of PSN-PZN-PMS-PZT piezoelectric ceramics

Quinary system piezoelectric ceramics PSN-PZN-PMS-PZT were prepared by using a two-step method. The effects of CeO2 doping on piezoelectric and dielectric properties of the system were investigated at morphotropic phase boundary （MPB）. The results reveal that the relative dielectric constant ε33^T｜ε0, the Curie temperature To, the piezoelectric constant d33, the mechanical quality factor Qm, and the electromechanical coupling coefficient Kp are changed with the increase of CeO2 content. On the other hand, the effects of CeO2 doping on the dielectric properties of PSN-PZN-PMS-PZT piezoelectric ceramics at high electric field are consistent with the change at weak electric field. The values of dielectric constant and dielectric loss are enhanced with the increasing of electric field.     

Effect of poling condition on piezoelectric properties of （K0.5Na0.5）NbO3 ceramics

The lead-free piezoelectric ceramics （K0.5Na0.5）NbO3 （abbreviated as KNN） with the relative density of 97.6% were synthesized by press-less sintering owing to the careful control of processing conditions. The phase structure of KNN ceramics was analyzed. The results show that the pure perovskite phase with orthorhombic symmetry is in all ceramics specimens. The effect of poling conditions on the piezoelectric properties of KNN ceramics was investigated. The results show that the piezoelectric constant d33 and electromechanical coupling factor kp increase with poling field, poling temperature and poling time increasing, then decrease because of electric broken. Take into account of poling conditions and piezoelectric properties of pure KNN ceramics, the optimum poling conditions for pure KNN ceramics are poling field of 4 kV/mm, poling temperature of 140 ℃ and poling time of 20-25 min.     

管理案例困难度坐标4—4—4模型

引言案例教学需要使用大量的管理案例。每一个案例都向它的读者提出了一组特定的任务。这些任务有难有易,这一方面意味着完成案例分析任务的时间会有长有短,而学生准备分析报告、参加集体讨论的时间总是有限的。另一方面,学生的兴趣有浓有淡,能力有强有弱,层次有高有低,作为一种智力型的产品——案例也需要适应不同的要求。因此,案例的困难度成了反映不同要求的一个非常重要的概念,因而也就产生了对其困难度的估计和测量问题。我们结合企业管理的教学与科研工作,在分析比较国内外关于管理案例困难度表述的基础上,创造性地改     

衬套用QSn4-4-4青铜板退火试验

１　前言某有色金属加工厂提供我公司厚度为１－９ｍｍ的ＱＳｎ４４４青铜板材，质量保证书上写明供应状态为Ｙ３状态，但所列出的力学性能数据只能符合ＧＢ２０４９—８０的Ｙ状态。Ｙ和Ｙ３标准见表１所示。经公司理化测试中心复验，也确认此批板材为Ｙ状态。由于板材状态不符，强度和硬度偏高，衬套加工时感到困难。但如退货，一时难以找到订货单位，且影响生产进度。　　为了降低这批板材的强度和硬度，提高塑性，使其达到Ｙ３状态的要求，满足加工需要，我们进行了退火热处理试验。２　退火热处理试验参考ＱＳｎ４４２－５的有…     

SrxBa1-xBi4Ti4O15陶瓷及SrBi4Ti4O15／BaBi4Ti4O15复合材料的性能研究

采用固相烧结工艺制备了SrxBa1-xBi4Ti4O15铁电陶瓷和SrBi4Ti4O15／BaBi4Ti4O15铁电复合材料。在固相反应过程中，680℃时SrBi4Ti4O15或BaBi4Ti4O15开始生成：800℃时材料主晶相基本形成，但是还有微量焦绿石相存在；850℃时SrBi4Ti4O15或BaBi4Ti4O15的主要衍射峰全部出现。随着Ba含量的增加，SrxBa1-xBi4Ti4O15陶瓷的居里温度逐渐降低。Sr0.5Ba0.5Bi4Ti4O15，陶瓷的介电常数峰在高频时较宽，在100Hz时，介电常数峰被随温度升高而逐渐增大的介电常数所“屏蔽”，材料介电损耗随温度升高而增大，但在低频下增加得更快，这是高温下由氧空位引起的电子松弛极化造成的。将预烧后的SrBi4Ti4O15和BaBi4Ti4O15粉体分别造粒后冉均匀混合，压片成型，经烧结制得的SrBi4Ti4O15／BaBi4Ti4O15复合陶瓷其相变弥散特性明显优于SrxBa1-xBi4Ti4O15的相变弥散特性。     

Failure behavior and failure criterion of conductive cracks (deep notches) in piezoelectric ceramics I – the charge-free zone model

The charge-free zone model proposed by Zhang et al. for the failure of conductive cracks in dielectrics was extended to predict the failure behavior of conductive cracks in piezoelectric ceramics. Piezoelectric ceramics were treated as mechanically brittle and electrically ductile materials in the charge-free zone model. The failure criterion, developed from the charge-free zone model, for conductive cracks in piezoelectric ceramics under mechanical and/or electrical loading has an elliptic shape in terms of the normalized electric intensity factor and the normalized stress intensity factor. The experimental results reported in Part II of the series verified the theoretical predictions.     

RQTAl_4Si_4耐热铸铁熔铸工艺研究

ＲＱＴＡＩ＿４Ｓｉ＿４耐热铸铁的缺点是脆性较大，易产生裂纹。该缺点的克服需要从混砂、造型（制芯）、熔铸和清理等整个铸造生产过程考虑。该合金在熔炼及球化处理过程中，烧损量较大，因而在熔炼及浇注过程中对铁水不易过多搅拌。用冲天炉熔炼的ＲＱＴＡｌ＿４Ｓｉ＿４耐热铸铁件的金相组织比中频电炉熔炼要细密得多，但回炉料的回用是需进一步研究解决的新问题。     

G13Cr4Mo4Ni4V轴承套圈酸洗白斑分析

对滚道酸洗白斑处和正常处进行化学成分、显微组织、表面硬度及渗碳层深度进行分析对比。结果表明,白斑处滚道表面硬度、含碳量及渗碳层深度均低于正常处,表面含碳量低是引起白斑的主要原因。     

Phase diagrams of Li2MoO4-Na2MoO4 and Na2MoO4-K2MoO4 systems

The phase diagrams of the Li2MoO4-Na2MoO4 and Na2MoO4-K2MoO4 systems have been reassessed using differential thermal analysis together with high-temperature and room-temperature X-ray diffraction analysis. The results showed that the compound Li2MoO4.6Na2MoO4 did not exist; however, it confirmed the existence of the compound Li2MoO4.3Na2MoO4 in the Li2MoO4-Na2MoO4 systen＇ls. With regard to the system of Na2MoO4-K2MoO4, we could not confirm the results reported by Bukhanova who claimed that the system was eutectic type with 1：1 and 1：2 intermediate compounds, refuting the statement of Amadori who thought there was an apparent phase boundary at high temperature in α-solid solution region of the Na2MoO4-K2MoO4 binary system. The revised phase diagrams of these systems are illustrated in this article. These experimental results are in agreement with the computerized prediction using the support vector machine-atomic parameter method for the assessment of phase diagrams.     

Al4SiC4陶瓷的高温氧化行为

从高温氧化动力学、组织的微观进化及高温氧化机理3部分对Al4SiC4陶瓷在1200℃-1700℃的高温氧化行为进行了系统的研究。研究结果表明，Al4SiC4陶瓷具有优异的高温抗氧化性能。氧化动力学符合抛物线规律，其氧化活化能经计算为220kJ／mol。XRD及SEM研究结果表明：Al4SiC4陶瓷在1200～1500℃的氧化表面物相为Al2O3和铝硅酸盐玻璃；而高温氧化表面（1600℃～1700℃）的物相由Al2O3，莫来石和铝硅酸盐玻璃构成。由氧化试样横截面观察得知氧化层按其特征的不同分为3个部分：具有较多细小尺寸孔洞的反应层；具有较大尺寸孔洞的中间层和致密的外氧化层。在高温抗氧化机理部分中首先从热力学上计算了氧化过程中各反应的生成焓和吉布斯自由能；然后对高温氧化过程进行了推理和分析；最后根据上述试验及推理结果建立了Al4SiC4陶瓷的高温抗氧化模型。     

以NH4FePO4·H2O制备LiFePO4及其性能研究

用FeSO4,H3PO4,NH3·H2O为原料合成NH4FePO4·H2O前驱体,再与Li2CO3和蔗糖均匀混合,通过高温固相反应法合成了LiFePO4正极材料.用X射线衍射和扫描电镜分析对NH4FePO4·H2O和LiFePO4的结构进行了表征.研究了不同含碳量对LiFePO4晶体结构和电化学性能的影响.结果表明,NH4FePO4·H2O前驱体和LiFePO4具有结构相似性,在高温固相反应时NH4FePO4·H2O与Li2CO3发生置换反应.材料具有较好的电化学性能.     

MEK4模具钢

法国模具钢,相当于德国钢号1.8523,或表示成40CrM o V13-9。耐磨性良好,具有良好加工性能,光蚀刻花性好,高硬度、高韧性、高耐磨性和尺寸稳定性。适合于制作轻合金压铸模具,塑料模具和大型锤锻模具等。化学成份（质量分数,%）：0.40~0.60 C;3.00~5.00 Cr;1.00~1.50 Mo;0.20~0.40 V。     

Microstructure and electrical properties of Ti-modified (Na0.5K0.5)(TiχNb1-χ)O3 lead-free piezoelectric ceramics

Ti-Modified (Na0.5K0.5)(TixNb1-x)O3 (NKNT) piezoelectric ceramics were fabricated by double-layer buffed powder process at 1020℃ for 2 h. The microstructures, and piezoelectric and dielectric properties of the lead-free NKNT ceramics were investigated. X-ray diffraction re-suits indicated that Ti4+ had diffused into the (Na0.5K0.5)NbO3 lattices to form a solid solution with a perovskite structure. The introducing of Ti into the (Na0.5K0.5)NbO3 solid solution effectively reduced the sintering temperature and densified the microstructure with a decreased grain size. The highest relative density reached more than 90%. The highest piezoelectric dielectric coefficient d33 and planar mode electro mechanical coupling coefficient kp were 110 pC/N and 19.5%, which were obtained in the NKNT ceramic with 1 mol% Ti. The piezoelectric properties of the NKNT ceramics were enhanced by aging in air for a period of time owing to the compensation of oxygen vacancies.