Effects of cubic BN addition and phase transformation on hardness of Al2O3-cubic BN composites

The Vickers hardness of dense Al₂O₃-cubic BN (cBN) composites prepared by spark plasma sintering under a moderate pressure of 100 MPa at 1200-1600 °C was investigated at indentation loads of 0.098-19.6 N. The BN grains in the Al₂O₃-BN composite prepared at 1300 °C showed no transformation from the cBN to hBN phase, and the hardness was 59 GPa at 0.098 N. The hardness of the Al₂O₃ matrix in the Al₂O₃-BN composites containing 10-30 vol% cBN prepared at 1300-1400 °C was around 25 GPa at 0.098 N, which was higher than monolithic Al₂O₃ bodies prepared at the same temperatures. The hardness of the Al₂O₃ matrix in the Al₂O₃-BN composites decreased with increasing sintering temperature. The increase in the hardness of the Al₂O₃ matrix may be due to the decrease in the size of Al₂O₃ grains in the Al₂O₃-BN composites owing to the addition of cBN particles and the decrease in sintering temperature. The Meyer exponents of the monolithic Al₂O₃ bodies and Al₂O₃-BN composites were 1.90-1.94 independent of cBN content.     

Complexation-responsive monoolein cubic phase containing extract of Bambusae Caulis in Taeniam

Abstract

Monoolein (MO) cubic phase (CP) containing Bambusae Caulis in Taeniam extract (BCT), hydrophobically modified alginate (HmAlg), and hydrophobically modified gelatin (HmGel) was prepared by a melt and hydration method. On the TEM micrographs of CP, water channels and MO bilayers were found. The phase transition temperature of MO CP was about 65.3?°C and it deceased by the inclusion of the additives. The release of 4-hydroxybenzaldehyde from CP was markedly suppressed at pH 4.5 but not at pH 5.5 and pH 7.4. The complex coacervate of HmGel and HmAlg was thought to suppress the release in the acidic condition.     

Humidity dependence of visible absorption spectrum of gelatin films containing cobalt chloride

Gelatin films containing cobalt chloride were investigated to obtain information on the humidity dependence of optical absorbency in view of the coordinate state of cobalt ion and the polymer structure. The visible absorption spectra of the films exhibited that, with increasing relative humidity (RH), the absorption bands between about 550 and 750 nm decreased, accompained by sharpening of the 693 nm peak. Further, the decrease of cobalt chloride in gelatin resulted in decreased absorption intensity of the 693 and 668 nm peaks, more than the overall lowering in intensity. The infrared spectral data indicated that most of the carboxyl groups of gelatin are linked to the complex even in the strongly hydrated state. In addition, the water content of the films containing cobalt chloride is a little less below 42% RH, but is much greater above 62% RH than that of the original gelatin film. These results indicated that there are cross-linked networks, composed of the hydrogen bonding and the coordination bond via the complex in the dry film; as water molecules are adsorbed by the film, they gradually destroy these bonds and swell the polymer. © 1993 John Wiley & Sons, Inc.     

Growth of cubic boron nitride films by ibad and triode sputtering: development of intrinsic stress

Two methods are employed to evidenced the stress behavior in c-BN films. On the one hand, in depth stress profile of c-BN film, deposited by ion beam assisted evaporation, was performed by recording infrared spectra and substrate curvature after reactive ion etching (RIE) steps. It shows a peak of stress up to −17 GPa in the h-BN basal layer and a stress relaxation when the cubic phase appears. On the other hand, dynamic stress profiles of c-BN films deposited by a triode sputtering system, are obtained by recording infrared spectra and substrate curvature after various c-BN deposition times, with the same experimental conditions. Likewise, a peak of stress of −12 GPa is unmistakably observed in the h-BN basal layer followed by a stress release during c-BN nucleation, where an average value of −12 GPa is observed in the c-BN film volume. These results provide a support for the stress model proposed by McKenzie even if along with a minimum stress a high level of densification of the layer is needed.     

Deformation behavior of polytetrafluoroethylene films under tensile stress at various temperatures

Deformation behavior of polytetrafluoroethylene (PTFE) films was investigated by thermomechanical analysis (TMA) under various tensile stresses (σ) up to 1.15 MPa in the temperature range from room temperature to 360°C. In the heating process above σ ≈ 0.25 MPa, a contraction of the PTFE film occurs in the melting temperature region. In the cooling process above σ ≈ 0.05 MPa, an elongation occurs in the crystallization temperature region, and above σ ≈ 0.5 MPa, it reaches 20–30% of the original length of the film. The PTFE films in the melt state above σ ≈ 0.5 MPa contract with increasing temperature up to 360°C and elongate with decreasing temperature. For the films that underwent deformation in the TMA, the crystalline orientation and the surface morphology were investigated by wide-angle X-ray diffraction and scanning electron microscopy, respectively. The degree of crystalline orientation in the deformed films increases with increasing σ and approaches a plateau at σ ≈ 0.4 MPa. On the surface of the deformed films, alignment of the bands and deformation of granules, which are formed by heat treatment above the melting point, are observed. © 1994 John Wiley & Sons, Inc.     

Dilational rheological properties of interfacial films containing Branch‐Preformed particle gel and crude oil fractions

Dilational rheology method was used to study the interfacial rheology properties of Branch‐Preformed Particle Gel (PPG) and its interaction with Shengli crude oil fractions at the kerosene/water interface. The results showed that the interfacial dilational modulus increased monotonously with increasing PPG concentration, the high values of the modulus could be due to the formation of multilayer near the interface. Study on the interaction between PPG and crude oil components showed that different crude oil components have different interactions with PPG molecules at the oil/water interface. The acidic components can adsorb onto the interface and form mixed adsorption film by replacing the PPG molecules at the interface because of their smaller molecular size and stronger interfacial activity, which results in a dramatic reduction in dilational modulus, while asphaltenes have little effect on the dilational rheological behavior of PPG solution due to their lager molecular sizes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41337.     

Effects of additives on phase transitions of Poloxamer 407/Poloxamer 188 mixture and release property of monoolein cubic phase containing the poloxamers

The gelling temperature of Poloxamer 407/Poloxamer 188 (16%/10%) mixture solution increased with increasing amount of surfactants. Among surfactants tested, the order of effectiveness in increasing the gelling temperature was sodium dodecyl sulfate (SDS) > tween 20 > cetyltrimethylammonium chloride (CTAC). The gelling temperature increased with the increasing concentration of cyclodextrin (CD). The order of effectiveness in increasing the gelling temperature was gamma CD > beta CD > alpha CD. The gelling temperature increased with increasing concentration of alcohols (ethanol and propylene glycol (PG)). On the contrary, dimethyl sulfoxide (DMSO) decreased the gelling temperature of P407/P188 (16%/10%) mixture solution. On the other hand, the gelling temperature decreased upon addition of NaCl but it increased by addition of MgCl₂. With P407/P188-loaded monoolein cubic phase, the degrees of release in 40 hr were about 52% at 25 °C and 37.5% at 47 °C. The suppressed release at 47 °C is possibly because P407/P188 in the water channel of cubic phase is in gel state at the temperature.     

Far infra-red absorption spectra of undeuterated and deuterated poly(ethylene terephthalate)

An assignment of the absorption spectrum of undeuterated PET (PET-H) is reported, based on a model calculation which uses the moments of inertia of single molecular groups. In order to check this model the spectroscopic measurements were carried out with fully deuterated PET (PET-D). The model developed with PET-H allows a quantitative prediction of the frequency shifts by deuteration. The two absorption bands below 100 cm^?1 are in good agreement with the calculation. A possible assignment of the bands at 139 cm^?1 (PET-H) and 132 cm^?1 (PET-D) to a conformationally-dependent vibration of the ethylene group is discussed.     

Structural design and energy absorption mechanism of laminated SiC/BN ceramics

The laminated silicon carbide/boron nitride (SiC/BN) ceramics with different structural designs were fabricated by pressureless sintering at 1900?°C for 1?h in argon flow. The alumina (Al₂O₃)-and yttrium(III) oxide (Y₂O₃)-doped SiC ceramic exhibited a significant intergranular fracture behavior, which could be attributed to the yttrium aluminum garnet (YAG) phase located at the grains boundaries. The bending strength and fracture toughness were used to characterize the crack propagation including the delamination cracking, crack kinking, and crack deflection. The energy absorption in the process of crack propagation was characterized by the work of fracture (WOF) and damping capacity. The mode of crack propagation changed with the change in the structure and variation of BN content in the BN layer. The delamination cracks occurred inside the BN layer or at the interface between SiC and BN layers. The sample with a gradient structure exhibited the combination of delamination cracks occurring at the interface and inside the BN layer, which showed the maximum WOF of 2.43?KJ?m^?2, bending strength of 300?MPa, and fracture toughness of 8.5?MPa?m^1/2. The damping capacity varied with the change of the structure and the amplitude. The sample with a gradient structure exhibited the damping capacity of 0.088 and the maximum loss modulus of 9.758?GPa.     

Effects of crystalline quality on the phase stability of cubic boron nitride thin films under medium-energy ion irradiation

To investigate the effect of radiation damage on the stability and the compressive stress of cubic boron nitride (c-BN) thin films, c-BN films with various crystalline qualities prepared by dual beam ion assisted deposition were irradiated at room temperature with 300 keV Ar⁺ ions over a large fluence range up to 2 × 10¹⁶ cm^− 2. Fourier transform infrared spectroscopy (FTIR) data were taken before and after each irradiation step. The results show that the c-BN films with high crystallinity are significantly more resistant against medium-energy bombardment than those of lower crystalline quality. However, even for pure c-BN films without any sp²-bonded BN, there is a mechanism present, which causes the transformation from pure c-BN to h-BN or to an amorphous BN phase. Additional high resolution transmission electron microscopy (HRTEM) results support the conclusion from the FTIR data. For c-BN films with thickness smaller than the projected range of the bombarding Ar ions, complete stress relaxation was found for ion fluences approaching 4 × 10¹⁵ cm^− 2. This relaxation is accompanied, however, by a significant increase of the width of c-BN FTIR TO-line. This observation points to a build-up of disorder and/or a decreasing average grain size due to the bombardment.     

含有机硅纳米凝胶光固化膜的性能研究

以甲基丙烯酸酯改性硅油、二脲烷二甲基丙烯酸酯(UDMA)和甲基丙烯酸异冰片酯(IBMA)为主要原料合成了一种有机硅纳米凝胶(Si15M)。以其为添加剂加入到三乙二醇二甲基丙烯酸酯(TEGDMA)紫外光固化体系中,考查了其对固化膜性能的影响。研究表明,随着纳米凝胶添加量的增多,固化膜硬度、断裂伸长率、凝胶率有不同程度的增加,而其玻璃化转变温度、拉伸强度及吸水性有不同程度的下降。     

Formation of BN from BCNO and the development of ordered BN structure: I. Synthesis of BCNO with various chemistries and degrees of crystallinity and reaction mechanism on BN formation

We synthesized BCNO compounds and investigated how the synthesis conditions impact i) BCNO formation, their chemistry and degree of crystallinity, and ii) BN formation from BCNO and its structural ordering. Heating boric acid (H₃BO₃) and melamine (C₃H₆N₆) mixture yields intermediate amorphous BCNO compound. Increasing the synthesis temperature, and H₃BO₃ to C₃H₆N₆ ratio promote BN formation and its structural ordering. We propose a possible reaction mechanism for BN formation from H₃BO₃ and C₃H₆N₆ mixture and we explain the observations based on thermodynamic and kinetic considerations. An increase in synthesis temperature promotes BN formation since the reactions are endothermic. An increase in H₃BO₃ to C₃H₆N₆ ratio promotes BN formation since theoretical BN formation temperature decreases with the above ratio. Furthermore, it enhances material transfer and mobility of the BN layer by forming B₂O₃ phase. We also propose a processing-structure correlation map that can help determining experimental conditions for single-phase amorphous BCNO synthesis.     

气相中碘分子的吸收工艺研究

采用H_2O_2将湿法磷酸中的碘离子氧化成碘分子,之后采用空气萃取法将碘分子以气相吹出,气相中碘分子经还原剂循环洗涤吸收后便于富集回收。气相中碘分子的吸收最佳工艺条件为:以亚硫酸为还原剂,亚硫酸溶液质量分数为8%,反应温度为35℃,吸收塔内含碘气相停留时间为15 s。最佳工艺条件下,气相中碘分子的吸收率为88.37%。50 t/a碘回收装置中,含碘气相冷凝器换热面积为3 000 m~2,吸收塔规格为ф4 300 mm×15 000 mm,材质为钢衬PO,吸收液喷淋量为175 m~3/h。     

Dielectric properties of cubic bismuth based pyrochlores containing lithium and fluorine

In this work dielectric properties of Bi_1.5Zn_1?xLi_xNb_1.5O_7?xF_x with x = 0.25 were investigated in a 20 Hz–12 GHz frequency and 120–500 K temperature range and compared to that of regular cubic BZN (when x = 0). Measurements showed that both ceramics have dipolar glass type dielectric dispersion with wide relaxation time distributions. Mean relaxation time follows Arrhenius law in the investigated frequency range, although Vogel–Fulcher law was anticipated.     

Growth,doping and applications of cubic boron nitride thin films

This article reviews the growth techniques and growth parameters for the formation of cubic boron nitride (c-BN) thin films. It is generally accepted that the impact of energetic ions or neutral atoms is crucial to achieve c-BN film growth. Furthermore, c-BN nucleation is only observed within certain thresholds for the deposition parameters, including the substrate temperature. However, the temperature threshold exists only for the nucleation and not for the growth of c-BN. We will show that three independent characterization methods are necessary for the non-ambiguous identification of the c-BN phase within BN films. The cylindrical thermal spike model developed to describe the formation of diamond-like phases by ion deposition can be used to explain the c-BN nucleation and growth. A short introduction and the basic ideas of this model will be given. Finally, possible tribological applications of c-BN films and the doping of c-BN films will be discussed.     

Effect of heat treatment on phase composition and spectral properties of heterostructures containing titanium and tungsten oxide films

The effect of heat treatment on the optical properties of heterostructures containing titanium and tungsten oxide films is studied. The films were synthesized on a quartz glass substrate in low-temperature lowpressure plasma. It is found that the heat treatment of the samples containing the tungsten oxide films in vacuum at 700°C leads to the formation of hydrogen tungsten bronze with a cubic lattice. The crystallization processes that occur in the heterostructures are affected by both the temperature of the heat treatment and the sequence of the layers on the substrate.     

Combined shock-wave synthesis of noble spinel and laves cubic phase

The paper described the shock-wave synthesis of high-pressure high-temperature mineral MgAl₂O₄ with the parameter a = 8.085(3) Å and the Laves phase MgCu₂ with a = 7.076(2) Å from a mixture of MgO and aluminum powder placed into a copper insert inside a steel conservation ampoule. Spinel MgAl₂O₄ with a smaller lattice parameter a = 8.0798 Å has been formed in an aluminum insert cup. __________ Translated from Steklo i Keramika, No. 6, pp. 21–22, June, 2006.     

AEP-DPA-CuO相变纳米流体吸收CO2稳定性

化学吸收法CO₂捕集技术的核心是吸收剂,吸收剂的稳定性是实现CO₂捕集装置长周期连续运行的关键。本文针对0.6mol/L AEP-0.4mol/L DPA-0.1mol/L ACT相变有机胺吸收体系高温、含氧等条件下降解会带来腐蚀增强、吸收剂损耗的技术难题,进行了降解组分分析,研究了降解的主要影响因素。研究发现,CO₂负载、O₂、温度对降解率均有较大影响,其中影响因素排序为CO₂＞O₂＞温度,Fe³⁺对氧化降解影响大于对热降解的影响。通过GC-MS分析可知,热降解热稳定盐主要有3种,氧化降解热稳定盐主要有6种。为抑制热降解与氧化降解,研究选取酒石酸钾钠等6种抗氧化剂进行考察,得到最佳抗氧化剂为丙酮肟,最佳添加量为800mg/L,其中热降解抑制率为97.9%,氧化降解抑制率达到98.3%,实现了AEP-DPA-ACT相变体系的低降解率,为相变纳米流体的稳定运行提供了保障。     

Improved crack resistance and thermal conductivity of cubic zirconia containing graphene nanoplatelets

Composites of 8 mol.% yttria-stabilized zirconia (8YSZ) with graphene nanoplatelets (GNP) have been pointed as alternative interconnectors in SOFC due to their mixed ionic-electronic conduction. Here we show that GNP addition provides rising crack-resistance behavior, with long crack toughness up to 78% higher than that of 8YSZ, also improving its thermal conductivity (up to 6 times for the in-plane direction). Toughness versus crack length is measured for 7 and 11 vol.% of GNP using single edge V-notched beam technique and ultrashort pulsed laser notching; and thermal behavior is analyzed by the laser flash method. Materials also have highly anisotropic coefficient of thermal expansion. These properties contribute to enhance their performance under the harsh operating conditions of SOFC, as thermal residual stresses could be reduced while significantly improving the system mechanical stability. Moreover, the heat transfer may be enhanced especially along the interface direction which would increase the system efficiency.