Solid-state synthesis in the system Na0.8NbyW1−yO3 with 0?y?0.4: A new phase, Na0.5NbO2.75, with perovskite-type structure

Series of compounds in the system Na_xNb_yW_1−yO₃ were prepared according to the appropriate molar ratio of Na₂WO₄, WO₃, WO₂ and Nb₂O₅ with x=0.80 and 0.0?y?0.4 at 600 °C in evacuated silica glass tubes. These compounds were investigated by X-ray powder diffraction, optical microscopy, microprobe analysis, Raman and optical microspectroscopy. A y-dependent separation into three distinct coloured crystallites with cubic perovskite-type structures is observed: (i) red-orange crystallites with composition Na_xWO₃ with slightly decreasing x (i.e. 0.8-0.72) with increasing nominal y, (ii) bluish solid solution of composition Na_xNb_yW_1−yO₃ and (iii) white crystallites of a new phase having defect perovskite-type structure with composition Na_0.5NbO_2.75.     

钢-铜摩擦副在边界润滑条件下的减摩抗磨机理研究

用SRV摩擦磨损试验机分别考察了聚α烯烃基础油含磷氮添加剂和两种含氟硅油添加剂在钢-铜摩擦副滑动下的摩擦学性能,用扫描电子显微镜(SEM)和X射线光电子能谱仪(XPS)观察并分析了铜磨斑表面形貌和磨斑表面主要元素的化学状态.结果表明:含磷氮添加剂和含氟硅油添加剂均具有优良的减摩和抗磨性能;磷、氮和氟等在摩擦表面生成的摩擦化学产物是提高摩擦副抗磨减摩性能的根本原因.     

新型钨青铜型晶体Ca0.28Ba0.72Nb2O6的生长研究

研究了Ca0.28Ba0.72Nb2O6 (CBN-28)多晶料的制备和单晶的生长,用提拉法成功生长出CBN-28单晶.从X射线粉末衍射数据计算了CBN-28晶体的晶胞参数,并对其粉末衍射图各衍射峰进行了指标化.CBN晶体属四方晶系4mm点群.晶胞参数为a=1.2432(±2)nm,c=0.3957(±1)nm.采用浮力法测得其平均密度为5.372g/cm3,测得其莫式硬度为7,并通过测量CBN-28的介电性质,确定其居里点为260℃.     

烧结温度对陶瓷/青铜结合剂性能与显微结构的影响

通过粉末冶金法制备出陶瓷/青铜结合剂,青铜结合剂(mCu∶mSn=85∶15)与陶瓷结合剂质量比3∶1.结合电子万能试验机、洛氏硬度仪、扫描电子显微镜(SEM)、X射线衍射仪等,研究了烧结温度对陶瓷/青铜结合剂性能及结构的影响.结果表明:随烧结温度的升高,陶瓷/青铜结合剂密度、抗折强度和抗冲击强度呈先上升后下降的趋势;且烧结温度为620 ℃时,陶瓷/青铜结合剂综合性能较优,其密度为5.43 g/cm3、抗折强度为170 MPa、抗冲击强度为9.76 kJ/m2、硬度(HRB)为126;温度升高促进铜锡元素合金化及陶瓷与青铜结合剂界面之间元素的相互渗透;且经620 ℃烧结后,铜锡之间全部以α+δ共析相存在,金属和陶瓷界面结合性好,提高了陶瓷/青铜结合剂的综合性能.     

Organic content evaluation of corrosion patinas in outdoor bronze monuments

Summary As opposed to inorganic composition, the characterization of organic content in patinas of bronze monuments has been neglected. Analytical pyrolysis coupled with gaschromatographyάss-spectrometry (Py/GC-MS) has been shown to be a valid and rapid technique to identify organic materials in corrosion patina of bronze monuments. In this paper six renaissance Italian outdoor bronze monuments were analyzed in order to determine organic composition of the patina. Results show the presence of both environmental organic compounds and chemicals coming from protective treatment.     

On‐site Raman and XRF analysis of Japanese/Chinese bronze/brass patina – the search for specific Raman signatures

The assignment of Asian bronzes and brasses is difficult because the copies of ancient pieces have been made a long time ago in different countries. A selection of 30 Japanese and/or Chinese bronzes/brasses are studied on‐site in the storage and exhibition rooms of the Cernuschi Museum, in Paris, using portable Raman and X‐ray fluorescence spectrometers. Attempts are made to identify specific Raman signatures of the patina to detect similarity in a nondestructive procedure. X‐ray fluorescence measurements allow an identification of two brass artefacts and different types of bronze, including lead‐rich and mixed lead–tin–zinc‐rich compositions. The following phases are identified: CuO, Cu₂O, Cu₂S, tin oxides, ZnO, Cu₃(OH)₄SO₄, Cu₄(OH)₆SO₄, 3PbOPbSO₄ H₂O, PbSO₄/PbO, Pb(AsO₄)₃Cl, HgO/HgS. Relics of the mould, retained as concretions at the artefact surface are also identified: TiO₂, SiO₂, and different soda(−lime) glasses. Patina with very similar colour and habit may have different Raman signatures. This study offers tools to classify the artefacts in a noninvasive way. Copyright © 2011 John Wiley & Sons, Ltd.     

唐代铜佛像表面残片的拉曼光谱分析

本文利用共聚焦显微拉曼光谱(CRS)结合扫描电镜-X射线能谱(SEM-EDS)技术对唐代一铜佛像的表面成分、形态及元素组成进行了分析.结果显示,该铜佛像主要是由Cu- Pb- Sn三元青铜合金组成,表面腐蚀物主要是由氧化铜,氧化亚铜,碱式碳酸铜,氧化铅,氧化锡,碳酸铅和氯化铅组成,这些成分在空气中都比较稳定,不会再对铜...     

Characterization of Egyptian bronze archaeological artifacts

This paper presents the results of in situ non‐destructive X‐ray fluorescence determination of the chemical analysis of a collection of ten bronze statues that are on display at the Egyptian museum of Cairo. The statues are from the late period of the ancient Egyptian history. In addition, destructive technique X‐ray diffraction analysis was applied on 11 damaged archaeological objects to determine the corrosion products and the alloy compositions. Specimens of the latter objects were subjected to metallographic examinations to determine the microstructure of the alloy. Surprisingly, the results indicated that all ten statues and 10 of the 11 damaged objects were made of lead – bronze alloy; the percentage of the lead varied from 3.43 to 18.04, the tin varied from 2.53 to 10.67. The chemical composition of the patina on eight damaged objects is essentially composed of (Cu₂O) cuprite for all objects in addition to other compounds such as (SnO₂) cassiterite in two objects, (PbCO₃) cerussite in three other objects and (Cu₂(OH)₃Cl) atacamite or (Cu(OH)₃Cl) paratacamite in two other objects. The formation of chlorides and carbonate resulted from the interaction between surrounding environment and the alloy. The results of the metallographic examinations indicated a non‐homogenous structure and the increase of the lead content increases the globular lead particles. In spite of this condition, the galvanic corrosion tendency when the alloy is exposed to moist air or soil is not possible as lead compounds are electrically insulating. Another advantage for using leaded bronze in making statues is being heavy and thus leads to stability. Copyright © 2012 John Wiley & Sons, Ltd.     

In-situ formation of barium ferrite in iron-doped “tetragonal tungsten bronze”: Elaboration of room temperature multiferroic composites

Recent studies of ceramics of formula Ba₂LnFeNb₄O₁₅ (Ln=rare earth) with the “tetragonal tungsten bronze” (TTB) structure have correlated their room temperature multiferroics properties to the occurrence of barium ferrite parasitic phases. This work presents the elaboration of Ba₂LaFeNb₄O₁₅ and Ba₂EuFeNb₄O₁₅ composite samples with an excess of hematite in the TTB nominal composition. The influence of crystal-chemistry on the phase content and properties of Ba₂LnFeNb₄O₁₅ TTB composites is discussed. A particular focus on the mechanisms related to the in-situ formation of barium ferrite is given. We show that we can control the spurious ferrite phase in TTB multiferroic composites and thus modulate their magnetic response.     

钨青铜结构Ba6Zn0.67M9.33O30(M=Nb,Ta)的合成与介电特性

Two compounds Ba₆Zn_0.67M_9.33O₃ and Ba₆Zn_0.67M_9.33O₃₀ with tungsten bronze structure were synthesized in the BaO-ZnO-Nb₂O₅/Ta₂O₅ systems by the conventional high temperature solid-state reaction.The structure and dielectric properties of Ba₆Zn_0.67M_9.33O₃ and Ba₆Zn_0.67M_9.33O₃₀ were determined by X-ray powder diffraction,scanning electron microscope and dielectric measurements.The results show that Ba₆Zn_0.67M_9.33O₃₀ belongs to paraelectric phase of fully filled tetragonal tungsten bronze structure at room temperature with unit cell parameters a:1.26256(4) nm, c:0.39698(2) nm. The room temperature dielectric constant (ε) of Ba₆Zn_0.67M_9.33O₃₀ ceramic reached 108 combined with a low dielectric loss of 0.005 at 1 MHz. While Ba₆Zn_0.67M_9.33O₃ belongs to fully filled tetragonal tungsten bronze structure at room temperature with the unit cell parameters a:1.25940 (3) nm, c=0.40008(2) nm. Ba₆Zn_0.67M_9.33O₃₀ ceramic shows significant relaxor behaviors, and the phase transition from ferroelectric to paraelectric occurred at 55℃ (at 1 MHz). The room temperature dielectric constant (ε) of ceramic reached 570 at 1 MHz.