钨钼烧结炉用氧化锆制品损毁形式及机制分析

为提升高纯氧化锆制品在超高温环境下的应用性能,采用XRD和扫描电镜等手段对钨钼烧结中频炉用后氧化锆制品进行分析,探讨了其损毁机制。结果表明,2 000℃左右高温下,W或Mo蒸发、凝聚,沉积于氧化锆制品的气孔中,改变了其自身结构,温度变化时热应力开裂;W或Mo遇氧气氧化生成WO_3或MoO_3,进而与氧化锆晶格内的CaO稳定剂反应生成Ca WO_4和Ca MoO_4,稳定剂脱溶,导致氧化锆晶相失稳,由立方相或四方相转变为单斜相,升降温过程中,发生相变并伴随体积变化,使制品出现龟裂和断裂损毁;钨钼坯体在成型时采用了含碳结合剂,在还原性气氛烧结时结合剂高温分解成游离碳,并附着于氧化锆砖上形成局部强还原性气氛,将氧化锆碳化,进而与保护气氛中的N_2反应氮化,形成碳化锆或者碳氮化锆混合物,破坏氧化锆制品的显微结构,造成制品强度衰减。     

氧化锆质定径水口损毁机理研究

部分稳定氧化锆(PSZ)因具有耐高温、优良的抗侵蚀性以及良好的抗热震性而广泛用于连铸用定径水口.实验针对当前PSZ定径水口使用寿命短、易炸裂、抗冲刷性能差以及扩径快等问题,采用连铸现场取样分层分析研究的方法,借助SEM及XRD分析技术,对氧化锆质定径水口的损毁机理进行了系统的分析研究.研究结果表明:高温下稳定剂MgO首先脱溶到界面,固溶的CaO稳定剂分布均匀;随着熔渣渗入,脱溶的MgO稳定剂与固溶的CaO稳定剂发生固溶置换;随着侵蚀进一步加剧,CaO与熔渣反应完后MgO又与熔渣反应而脱溶.稳定剂的不断脱溶,导致氧化锆失稳,由立方相转变为单斜相,相变产生体积效应,从而形成裂纹,氧化锆颗粒破裂,水口强度大幅度下降,发生溶解和剥落.     

高铬砖与煤渣侵蚀反应的初探

使用扫描电镜和能谱仪研究了高铬砖(Cr2O3-Al2O3-ZrO2)的侵蚀反应,结果呈现出两种形式:一是形成含有部分脱锆层、再生单斜氧化锆层、再生单斜氧化锆和锆英石共存层、锆英石层;二是形成部分脱锆层和含有单斜氧化锆的渗透层。两种类型的侵蚀反应是由煤渣成分不同引起渗透层中m(CaO)/m(SiO2)比值的差异造成的:当渗透层中m(CaO)/m(SiO2)0.22时,首先在高铬砖内部由渣中SiO2与m-ZrO2形成锆英石层,再随着渗透层中m(CaO)/m(SiO2)比值的增加,形成再生单斜氧化锆和锆英石共存层、再生单斜氧化锆层和部分脱锆层;当渗透层中m(CaO)/m(SiO2)0.27时,易形成部分脱锆层和含有单斜氧化锆的渗透层。     

共沉淀法制稳定化氧化锆

氧化锆可制耐热性好、强度高的精细陶瓷。但如果不添加任何成分,仅仅是氧化锆进行烧结,其体积会膨胀7％,于是造成裂纹等缺陷。因此,在氧化锆中需添加3～7％的稳定剂——钇,以便形成部分稳定化的氧化锆。许多公司都有在氧化锆中混合钇的专有技术(技术决窍)。日本旭化成公司开发成功了通过化学反应,使氧化钇(Y_2O_3)在氧化锆中均匀分散并与之结合的技术。虽其具体方法尚不得而知,但据认为,旭化成公司采用了一种共沉淀法。     

还原气氛下ZrO_2-Al材料在加热过程中的组成和结构演变

为了解决加入金属Al粉的含锆耐火制品在高温下易产生裂纹、开裂的问题,以单斜Zr O_2粉、金属Al粉、复合稳定剂Mg CO_3·Mg(OH)_2·6H_2O和Y(NO_3)_3·6H_2O为主要原料,研究了加入不同量Al粉的Zr O_2-Al材料在埋炭条件下于1 000、1 200、1 400和1 500℃加热过程中性能、物相组成和显微结构的演变。结果表明:当Al粉加入量超过1%(w)时,热处理后试样产生较多裂纹,导致试样强度急剧降低。在加热过程中,Al与气氛中的O_2、CO和N_2反应生成Al_2O_3和Al N,生成的Al_2O_3再与试样中的稳定剂Mg O发生反应生成Mg Al_2O_4导致Zr O_2失稳,而Zr O_2失稳导致的体积效应以及生成Mg Al_2O_4和Al N产生的膨胀导致试样产生裂纹。因此,在锆碳和铝锆碳材料中添加金属Al时,其加入量不宜太多,以不超过1%(w)为宜。     

铝掺杂纳米氧化锆的合成与改性研究

氧化锆是一种具有特殊作用的氧化物并受到越来越多的关注。作者利用阳离子表面活性剂(CTAB)的辅助途径,通过前期的制备工艺成功实现了金属铝对纳米氧化锆的掺杂改性。借助XRD,TEM,EDS,Uv-vis以及N2吸附-脱附等方法对样品进行了表征分析;研究表明:金属铝离子能成功地进入氧化锆当中,掺杂改性后的氧化锆相对未掺杂的氧化锆有明显的蓝移,热稳定性显著提高,并且有一定的微孔结构。     

ZrO2-C质耐火材料中碳对氧化锆的稳定作用

分别以粒度均<0.045 mm的氧化钙部分稳定氧化锆、氧化镁部分稳定氧化锆和氧化钇部分稳定氧化锆为原料,酚醛树脂作为结合剂和碳源,按部分稳定氧化锆与酚醛树脂质量比为9 1配料,研究了在埋焦炭条件下于1 600℃渗碳处理后3种部分稳定氧化锆的相组成变化,以及保护渣对渗碳处理后氧化锆稳定性的影响。结果表明:1)高温下树脂碳对氧化锆存在渗碳过程,并对氧化锆有稳定作用,促进了部分稳定氧化锆中单斜相向四方相的转化;但也发现渗碳过程对部分稳定氧化锆中的氧化钙和氧化镁稳定剂存在还原作用并引起其挥发。2)由于渗碳处理过程中部分氧化钙和氧化镁稳定剂被还原挥发,高温下空气气氛中部分稳定氧化锆随着氧化锆晶格中碳的氧化而迅速失稳;而在埋炭条件下部分稳定氧化锆晶格中碳的存在减缓了部分稳定氧化锆的失稳过程。     

纳米氧化锆添加量对氧化锆制品性能的影响

在电熔单斜氧化锆原料中添加不同数量的CaO稳定剂,制备部分稳定氧化锆,研究CaO加入量和稳定相数量的关系.在制备的CaO部分稳定氧化锆中添加纳米氧化锆粉体,经过造粒、200 MPa压力成型、干燥、1650 ℃×2 h烧成制得试样.测试试样的物理性能、分析矿物相组成、观察显微结构,研究纳米氧化锆粉体添加量对试样性能的影响.研究结果表明:2Ca-PSZ、3Ca-PSZ、4Ca-PSZ试样中,4Ca-PSZ试样稳定化程度最高;3Ca-PSZ试样显气孔率小,体积密度较大,耐压强度高.在3Ca-PSZ试样中加入纳米氧化锆粉体,随着加入量的增加,试样的显气孔率下降、烧成收缩率增加、耐压强度提高.其中纳米氧化锆粉体添加比例为8wt%时,试样气孔率为9.4%,体积密度为5.08 g/cm3,抗压强度达到381 MPa.与3Ca-PSZ试样相比,气孔率下降40%,体积密度提高5%,耐压强度提高70%.     

聚丙烯熔体及制品稳定化技术

聚丙烯（PP）熔体稳定化处理影响聚丙烯制品的稳定化。本文列举了几则聚丙烯熔体稳定化助剂——抗氧剂与制品添加的光稳定剂之间的协同和反协同效应例子。试验研究指出受阻胺型稳定剂（HALS）的确对PP制品的稳定化具有优异的效果,但还应继续开拓在更多高分子材料中的应用研究和开发它们与其他添加剂的协效作用。     

四甲基和五甲基哌啶对聚合物的稳定作用

聚丙烯由于大分子主链中含有叔碳原子,对氧的反应比较敏感,易于老化。为保证制品性能不致因苛刻加工过程而受到损害,同时赋予制品在不同工作条件下(尤其是曝露于太阳光下使用)具有足够的寿命,一般要在加工成型前进行稳定化处理。在目前已知的各类光稳定剂中,哌啶类(四甲基哌啶)被认为是最优品种之一。近     

Failure mechanisms of calcium magnesium aluminum silicate affected thermal barrier coatings

Depth profiles of the phase composition of two examples of calcium magnesium aluminum silicate (CMAS) affected thermal barrier coatings (TBCs) from an aero gas turbine engine were obtained using a monochromatic and collimated beam of synchrotron radiation. One TBC was deposited by plasma spray and the other by electron beam physical vapor deposition. These examples were complemented with an X‐ray diffraction (XRD) study of mixtures of TBC zirconia powder and sand heated in a furnace. The XRD results were compared with electron backscatter images and energy dispersive spectroscopy studies of the cross sections and mixtures. It was found that when liquid, the CMAS enhances mass transport leading to the densification of the zirconia, which then leads to spalling because of the increased residual stresses generated on cooling. Even without spalling densification will reduce a TBC's ability to thermally insulate. The enhanced mass transport can also lead to destabilization of the zirconia if yttrium ions preferentially transfer to the liquid or greater stabilization if calcium or magnesium ions transfer from the liquid to the zirconia. Zircon also precipitates when the zirconium from the TBC reacts with the silicon in the liquid CMAS.     

The effect of silica content on microstructure and mechanical properties of calcia-stabilized tetragonal zirconia polycrystalline ceramic

The present study was aimed at investigating the effect of silica impurities on structure and mechanical properties of zirconia ceramics, stabilized in tetragonal phase by addition of 6.5?mol% calcia. The effect of silica was studied in 0–5?mol% silica concentration range. It was shown that notable increase in fracture toughness (from 7.5?MPa?m^0.5 to 12.5?MPa?m^0.5) as well as limited rise in hardness (from 12?GPa to 13?GPa) can be achieved by addition of ~ 2.5?mol% of SiO2. It was shown that further increase in SiO₂ concentration above 3.75?mol% results in destabilization of tetragonal phase and degradation of mechanical properties. It is suggested that silica reacts with calcia resulting in formation of amorphous calcium silicate, decreasing calcia content in zirconia matrix, and facilitates sintering and grain growth, resulting in lower stability of tetragonal phase.     

多孔氧化铝模板的制备及应用

以磷酸溶液为电解液、以高纯铝为阳极,采用两步阳极氧化法制备氧化铝模板。扫描电子显微镜(SEM)对其表面形貌分析表明,氧化铝膜为多孔结构,膜孔径随着阳极氧化电压的增大而不断增大。对阳极氧化电流密度变化分析证实,铝的阳极氧化经历了三个阶段:阻挡层的生成、多孔层的形成和多孔层的稳定生长。以制备的氧化铝膜为阴极、锌片为阳极,以硝酸锌和硼酸的混合液为电解液,采用交流电沉积方法制备了针状氧化锌纳米线。     

Tailoring interfacial interaction through glass fusion in glass/zinc-hydroxyapatite composite coatings on glass-infiltrated zirconia

In the current study, the biocompatibility and mechanical characteristics of glass-infiltrated zirconia were improved via a simple composite coating made of Zn-doped hydroxyapatite (ZnHA) ceramic and a silicate-based glass. During thermal treatment, significant reaction and crystallisation occurred and some of the ZnHA was transformed into β-tricalcium phosphate, calcium oxide phosphate, and calcium zirconium oxide. Moreover, the glass crystallised into a sodium calcium aluminium silicate phase. The mechanical properties were investigated and the results indicated that the amount of glass in the composite and in the glass-infiltrated zirconia layer strongly affected the flexural strength and adhesion of the coating layer. The composite coatings on the glass-infiltrated zirconia displayed better mechanical properties than the pure ZnHA coating due to the newly formed crystalline phases. Murine pre-osteoblastic (MC3T3-E1) cells adhered to and spread well on the composite coating surfaces. The cell viability results revealed that the glass/ZnHA composites demonstrated a superior bioactivity of osteoblast cells compared to uncoated zirconia. These results show that the glass/ZnHA composites on the glass-infiltrated zirconia structure are suitable for use as hard tissue implant coatings due to their morphological and mechanical stability and enhanced bioactivity to pre-osteoblastic cells.     

Preparation and properties of ceramics in the ZrO2-CeO2-CaO system

The effect of bivalent calcium cations introduced in the stage of homogenous precipitation on the phase and morphological compositions of a tetragonal zirconia powder and the properties of a polycrystalline material based on it is described. The experiment was conducted for a base system containing 12% CeO₂, (0.5–3%) CaO, and the remainder ZrO₂. The use of calcium oxide as a modifier in the ZrO₂–12% CeO₂ system changes the crystallization temperature of the amorphous hydroxide residue. In the presence of 0.8–1% calcium oxide the structure of the sintered ceramic material mostly contains fine round crystallites 0.3 µm in size. Simultaneously, the fracture toughness increases considerably (K _Ic=15 MPa · m^1/2), which seems to be caused by the changed mechanism of destabilization of tetragonal zirconia.Translated from Ogneupory, No. 11, pp. 14–17, November, 1995.     

The wettability of zirconia refractories with iron and aluminum melts

Conclusions An investigation of the wettability of zirconia refractories with molten aluminum and iron showed that regardless of the amount of stabilizing oxide in the material the refractories are wetted more rapidly with the molten iron. Aluminum and iron melts both wet the refractory more rapidly when the latter is produced from a cubic solid solution containing a large amount of stabilizing oxide.When wetted with the melts of aluminum and iron a zirconia refractory acquires a zonal structure, the ZrO₂ in the reaction zone being partly destabilized.Translated from Ogneupory, No. 8, pp. 35–38, August, 1976.     

球形氧化铝制备过程中影响因素的研究

介绍了球形氧化铝的各种制备工艺及成形方法，并以油柱成形法制备球形氧化铝。利用低温液氮吸附仪、压汞仪以及智能强度测定仪对其物化性质进行了测定，重点考察了不同铝源合成的水合氧化铝、加料方式、扩孔剂和胶溶剂用量对球形氧化铝性质的影响。实验结果表明，制备水合氧化铝的铝源是影响球形氧化铝的重要因素；并流加料方式能制得大孔容、低表观密度、高强度的球形氧化铝；球形氧化铝的制备过程中，要制得适合于油柱成形的铝溶胶，胶溶剂加入量有最佳的用量范围，胶溶剂用量愈大，球性氧化铝的强度、比表面、孔容愈大，而孔径却随之变小；活性炭粉能有效地提高球形氧化铝的压汞孔容。     

Destabilization of Zirconia Thermal Barriers in the Presence of V2O5

Impurities, such as vanadium, degrade the operating performance of yttria-stabilized zirconia thermal-barrier coatings. V₂O₅ reacts preferentially with Y₂O₃, forms YVO₄, and leads to the destabilization of zirconia thermal-barrier material. A model experiment has been designed to monitor the destabilization of zirconia thermal barriers by directly exposing thin films of yttria-stabilized zirconia to V₂O₅ vapor. The growth of YVO₄ from yttria-stabilized zirconia and the destabilization of cubic yttria-stabilized zirconia into tetragonal and/or monoclinic zirconia polymorphs are monitored by selected-area diffraction and energy-dispersive X-ray spectroscopy in the transmission electron microscope. A special crystallographic orientation relation between YVO₄ and cubic zirconia is discussed.     

Optimization of NOM Removal during Water Treatment

Abstract

The aim of this paper is to describe the removal efficiency of individual fractions of natural organic matter (NOM) and the aluminum transformation during treatment of two types of surface water with an increased concentration of NOM of various origins. The coagulation conditions (dose of destabilization reagent and reaction pH value) were optimized for the best NOM and aluminum removal. The results show that the NOM removal efficiency depends on the NOM character, using destabilizing reagents and reaction conditions. The optimized doses of destabilization reagents influence especially the removal of hydrophilic charged (CHA) and very hydrophobic acids (VHA) fractions during treatment of both types of raw water. In contrast to this, the removal of hydrophilic neutral (NEU) fraction is very low (? _NEU =0.13–0.22). The optimal destabilization reagent dosage is characterized by the lowest content of the total reactive aluminum concentration and relatively low concentration of dissolved organic aluminum.     

Changes in the working surface of siphon refractories during the casting of wheel steel

Summary The amount of loss due to macroinclusions in blanks for railway wheels when the steel is deoxidized with calcium silicon and ferrotitanium is lower than with the use of aluminum as a deoxidant. A reduction in loss results from the adhesion of the macroinclusions to the reaction layer which forms on the working surface of the upper part of the siphon.The formation of a reaction layer on the siphon surface occurs from the reaction with liquid steel, and also with nonmetallic inclusions in the steel.The manganese oxide present in large quantities in the reaction layer of the siphon during the casting of steel deoxidized with calcium silicon and ferrotitanium, increases the liquidity of this layer, while with the use of aluminum as deoxidant the reaction layer of the siphon is enriched with alumina and becomes unfusible, as a result of which there is no possibility of glass forming in this layer.The investigation was carried out with A. A. Lebedev and E. Z. Zatulovskii (NTMK).