How the risk of failure in lifetime of tempered glass depends on the size of NiS inclusions and heat soak test duration

The probability of breakage in service lifetime of heat-tempered glass panes contaminated by nickel sulfide inclusions is estimated with a multiscale micromechanically motivated statistical theory, which considers the effects of the heat soak test (HST). Short and long HSTs differently affect the phase transformation of NiS of diverse chemical composition, whose increase in volume can break the glass. The main hypothesis, corroborated by experiments, is that there is a lower limit for the size of NiS stones below which no crack can be initiated from the volumetric expansion. The catastrophic propagation of nucleated fractures in the long term is modeled through a rescaled critical stress intensity factor, which accounts for the subcritical crack propagation and the slow phase transformation of NiS. A parametric analysis evidences how the failure probability is strongly affected by these parameters, depending on the holding time in the HST. Tailored experimental activity is suggested for the proper calibration of the model.     

Effect of nickel sulfide inclusions on the spontaneous failure of toughened glasses

Studies have shown that when smaller NiS inclusions are present the “heat-soak” method of rejecting toughened glasses does not completely guarantee that these glasses cannot fail spontaneously while in use. It is posited that the reason why glasses fail spontaneously is not so much the polymorphism of NiS as high stresses around NiS inclusions and, in consequence, a limitation on the “life” time of glass in accordance with the kinetic theory of long-term strength. __________ Translated from Steklo i Keramika, No. 5, pp. 3–6, May, 2007.     

钢化玻璃自爆机理的新发现——单质硅微粒引裂

通过对6块玻璃自爆残片的电镜观察和成分分析,发现并证明了引起钢化玻璃自爆的主要原因不仅仅是传统认识中的硫化镍(NiS)微粒,很多情况是由单质硅微粒引起的.进一步对单质硅微粒引起自爆的力学机理进行了分析和有限元模拟.结果显示:由于单质硅微粒周边玻璃的切向应力过大从而引起局部拉伸破坏并导致整体破裂,降温过程可以使这种应力增加并加大破裂危险.     

Improved photoluminescence quantum yield of CsPbBr3 quantum dots glass ceramics

We have fabricated CsPbBr₃ perovskite quantum dots (QDs) in a multi-component borate glass by melt-quenching technique. Transmission electron microscopy (TEM) reveals a cubic phase CsPbBr₃ crystal for QDs. As the treatment temperature or the treatment time duration increases, the photoluminescence (PL) peak shifts to long wavelength in the range of 510 to 525 nm, and the full width at half-maximum varies in the range of 24 to 18 nm. The absorption edge shifts to low energy side in the range of 2.54 to 2.41 eV. The different photoluminescence excitation spectra (PLE) reflect the change of microstructure for different samples. The PL peak wavelength and line-shape are independent of excitation wavelength. These results of spectra show typical exciton emission characteristics. As treatment conditions strengthens, photoluminescence quantum yield (PLQY) first increases and then decreases, having the best PLQY 86.9%. Bi-exponential fitting curves show that short lifetime τ₁ continuously decreases. Long lifetime τ₂, weight for long lifetime component, and average lifetime τ_avg first increase and then decrease. The PLQY values are affected by both τ₁ and τ₂, which are relative to the crystal quality in the interior and the surface of QDs, respectively. The high PLQY value corresponds to medium treatment condition, which is attributed to a balanced effect of crystal quality in interior and the surface of QDs.     

建筑玻璃抗风压强度分布与安全可靠性研究

通过模拟风压实验，对玻璃抗风压强度进行了研究，证实了玻璃的强度分布满足正态分布，并以此为基础推导了失效概率与安全因子、变异系数间的关系式，并分析提出了玻璃计失效概率的合理取值。     

Effect of confinement on glass dynamics and free volume in immiscible polystyrene/high‐density polyethylene blends

The effect of confinement on glass dynamics combined with the corresponding free volume changes of amorphous polystyrene (PS) in blends with semi‐crystalline high‐density polyethylene (HDPE) have been investigated using thermal analyses and positron annihilation lifetime spectroscopy (PALS). Two different glass transition temperatures (T_g) were observed in a PS/HDPE blend due to the dissimilarity in the chemical structure, consistent with an immiscible blend. However, T_g of PS in the incompatible PS/HDPE blend showed an upward trend with increasing PS content resulting from the confinement effect, while T_g of the semi‐crystalline HDPE component became lower than that of neat HDPE. Moreover, the elevation of T_g of PS was enhanced with a decrease of free volume radius by comparing annealed and unannealed PS/HDPE blends. Positron results showed that the free volume radius clearly decreased with annealing for all compositions, although the free volume hole size agreed well with linear additivity, indicating that there was only a weak interaction between the two components. Combining PALS with thermal analysis results, the confinement effect on the glass dynamics and free volume of PS phase in PS/HDPE blends could be attributed to the shrinkage of HDPE during crystallization when HDPE acted as the continuous phase. © 2015 Society of Chemical Industry     

Mixed alkali effects in Er3+-doped borate glasses: Influence on physical,mechanical, and photoluminescence properties

Engineering borate glass structure by simple compositional modification is essential to meet the particular demands from both industrial and photonic research communities. In this article, we demonstrate how the mixing of Li₂O with Na₂O, K₂O, or Cs₂O influences the relative abundance of 3- and 4-coordinated borons in the glass network, as exhibited by nuclear magnetic resonance (NMR) and Raman spectra. A systematic study is given of the alkali mixing effect on the glass properties including: glass transition temperature, microhardness, density, refractive index, and particularly the near-infrared photoluminescence properties (eg, bandwidth and lifetime) of Er³⁺ which has been barely studied in mixed alkali borate glasses. It is interesting to note that the glass transition temperature, refractive index and emission lifetime of Er³⁺ manifest mixed alkali effect, in sharp contrast with microhardness, density, and emission bandwidth which vary monotonically upon the alkali mixing. The possible causes for the differences are discussed in the light of the compositional dependence of boron species and nonbridging oxygen upon alkali mixing.     

热力学计算研究浮法玻璃的生产工艺过程

浮法玻璃是最重要的玻璃产品,产量大,生产过程涉及的因素众多.本文简述用化学热力学计算分析的方法来研究复杂实际浮法玻璃体系的相转变机理和生产过程,讨论生产的各个阶段和相关的问题,包括:作为研究工具的化学热力学计算分析平台MTDATA和相应数据库及数据测量的介绍;列为各个阶段的硅酸盐反应,玻璃结构的形成,澄清、均化机理,气泡的产生、转化、平衡的规律,耐火材料侵蚀等以及热力学研究在浮法玻璃研发中的现状和问题.     

Mid‐IR transparent TeO2‐TiO2‐La2O3 glass and its crystallization behavior for photonic applications

In this report, effect of enhanced rare earth (La₂O₃) concentration on substitution of TeO₂ within ternary TeO₂‐TiO₂‐La₂O₃ (TTL) glass system has been studied with respect to its thermal, structural, mechanical, optical, and crystallization properties with an aim to achieve glass and glass‐ceramics having rare‐earth‐rich crystalline phase for nonlinear optical and infrared photonic applications. DSC analysis (10°C/min) demonstrates a progressive increase in glass‐transition temperature (T_g) from 359 to 452°C with the increase in La₂O₃ content. Continuous glass network modification with transformation of [TeO₄] to [TeO₃/TeO₃₊₁] units is evidenced from Raman spectra which is corroborated with XPS studies. While mechanical properties demonstrate enhancement of cross‐linking density in the network. These glasses exhibit optical transmission window extended from 0.4 to 6 μm with calculated zero dispersion wavelength (λ_ZDW) varying from 2.41 to 2.28 μm depending upon La₂O₃ content. Crystallization kinetics of TTL10 (80TeO₂‐10TiO₂‐10La₂O₃ in mol%) glass has been studied via established models. Activation energy (E_a) has been evaluated and dimensionality of crystal growth (m) suggests formation of surface crystals. Glass‐ceramic with crystalline phase of La₂Te₆O₁₅ has been realized in heat‐treated TTL10 glass samples (at 450°C). As predicted from DSC analysis, FESEM study unveils the formation of surface crystallized glass‐ceramics.     

Coating Additives for Improved Mechanical Reliability of Optical Fiber

Fused silica glass is subject to delayed failure, i.e., failure occurring after a certain time under stress conditions far below the level required to have fast, catastrophic rupture. While the behavior at high applied stress may be described, at least empirically, by the subcritical crack growth model, it is well known that fused silica shows a transition, or "knee," to a more severe delayed failure behavior, or "enhanced fatigue," at low applied stress and long time to failure. This makes predictions of the expected lifetime unreliable. The addition of nanosized particles of fumed silica to the polymer coating of fused silica optical fiber is shown to improve long-term mechanical properties of the fiber: it delays the onset of the fatigue transition and reduces the strength degradation due to zero stress aging. Atomic force microscopy analysis shows that the presence of the additive dramatically reduces the rate of development of surface roughness, thus indicating that the effect of the additive is to suppress surface dissolution processes. The additive has little effect on the fatigue behavior before the transition. These results indicate that dissolution is the cause of the transition but has less importance on the pre-transition region.     

Unique performance of thermal barrier coatings made of yttria-stabilized zirconia at extreme temperatures (>1500°C)

Yttria-stabilized zirconia (YSZ) has been for several decades the state of the art material for thermal barrier coating (TBC) applications in gas turbines. Although the material has unique properties, further efficiency improvement by increasing the temperature is limited due to its maximum temperature capability of about 1200°C. Above this temperature the deposited metastable tetragonal (t´) phase undergoes a detrimental phase transformation as well as enhanced sintering. Both processes promote the failure of the coatings at elevated temperatures and this early failure has been frequently observed in gradient tests. In this paper, we now experimentally shown for the first time that under typical cycling conditions not the time at elevated temperatures leads to the reduced lifetime but the transient cooling rates. If cooling rates were reduced to 10K/s, TBC systems could be operated in a burner rig at a surface temperature well above 1500°C without showing a lifetime reduction. The explanation of these astonishing findings is given by the evaluation of energy release rate peaks during fast transient cooling in combination with the phase evolution during cooling with the used cooling rates.     

Modeling of thermo-viscoelastic material behavior of glass over a wide temperature range in glass compression molding

In glass compression molding, most current modeling approaches of temperature-dependent viscoelastic behavior of glass materials are restricted to thermo-rheologically simple assumption. This research conducts a detailed study and demonstrates that this assumption, however, is not adequate for glass molding simulations over a wide range of molding temperatures. In this paper, we introduce a new method that eliminates the prerequisite of relaxation functions and shift factors for modeling of the thermo-viscoelastic material behavior. More specifically, the temperature effect is directly incorporated into each parameter of the mechanical model. The mechanical model parameters are derived from creep displacements using uniaxial compression experiments. Validations of the proposed method are conducted for three different glass categories, including borosilicate, aluminosilicate, and chalcogenide glasses. Excellent agreement between the creep experiments and simulation results is found in all glasses over long pressing time up to 900 seconds and a large temperature range that corresponds to the glass viscosity of log (η) = 9.5 – 6.8 Pas. The method eventually promises an enhancement of the glass molding simulation.     

Post‐protection effect of heat‐resistant insulations on timber‐frame members exposed to fire

In lightweight walls and floors, the load‐bearing timber members are protected by cladding on the sides to form a divider between two fire compartments or to provide appropriate fire protection to the load‐bearing members. The spaces between the timber members can be void or filled with insulation materials. Although a huge number of different insulation materials exist, the most commonly used material is mineral wool insulation. The existing design model for glass wool‐insulated timber‐frame constructions, given in European standard 1995‐1‐2, assumes collapse of the glass wool after failure of the cladding. However, a new form of glass wool insulation, suitable for use at high maximum service temperatures, is now available in the market. The charring phase after the cladding's failure is known as the post‐protection phase. The behaviour of the new heat‐resistant glass wool in the post‐protection phase is similar to that of stone wool and considerably better than that of traditional glass wool. The protective properties of stone wool have changed over the last decades. Charring is one of the main parameters needed to calculate the resistance of a structure to fire. Based on experimental investigations, this paper describes the analysis of the effect of the insulation with regard to its ability to protect timber members against charring during the post‐protection phase. Copyright © 2011 John Wiley & Sons, Ltd.     

Dynamic study of free volume properties in polyethylene/styrene butadiene rubber blends by positron annihilation lifetime method

Positronium (Ps) formation in low and high‐density polyethylene (LDPE and HDPE) and styrene butadiene rubber (SBR), as well as in their blends (LDPE/SBR: 50/50 and HDPE/SBR: 50/50) has been investigated by positron annihilation lifetime (PAL) measurements as a function of low temperature (100–300 K). The glass transition temperature (T_g) for the initial polymers and their blends are determined by ortho‐positronium (o‐Ps) lifetime, τ₃ versus temperature as well as by differential scanning calorimetry (DSC) measurements. The temperature dependence of nanoscale free volume size shows similar trend for all the investigated samples indicating an abrupt change at T_g, which is found to be higher for SBR sample characterized by its high chain mobility. In addition, The T_g values deduced from PAL measurements are compared with the corresponding data deduced from DSC. The variation of o‐Ps formation probability I₃ versus temperature for polyethylene and their blends were interpreted in the frame work of spur reaction model of Ps formation. On the other hand, the lifetime coefficient below and above T_g is found to be one order of magnitude larger than the linear expansion coefficient. This constitutes evidence that Ps is only probing free volumes. The results obtained from change in free volume–hole distribution with temperature reflect both thermal expansion and increase in free volume–hole size with the rise in temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

玻璃纤维增强碱式硫酸镁水泥的加速老化试验与微观机理

为了研究玻璃纤维增强碱式硫酸镁水泥材料的长期强度,正确评价其耐久性能,采用SIC(Strand In Cement)试验方法,分别测定了玻璃纤维增强碱式硫酸镁水泥GRBMS试样在50℃、80 ℃热水加速老化试验条件下的抗折强度变化.运用XRD和SEM分析其水化产物组成和微观结构形貌,观察了玻璃纤维在碱式硫酸镁水泥基体中的腐蚀特征.结果表明:GRBMS试样试样在老化条件下,抗折强度随着时间的增加有明显的下降,原因是碱式硫酸镁水泥中针杆状的517相分解为片状无胶结性能的Mg(OH)2;80℃老化下试样强度保留率达到50％所用的时间为12d,而氯氧镁水泥试样失效时间只有3d,因此玻璃纤维增强碱式硫酸镁水泥材料老化寿命时间长,更适合应用于实际工程中.     

Influence of fiber orientation,temperature and relative humidity on the long-term performance of short glass fiber reinforced polyamide 6

As a result of processing of short fiber reinforced thermoplastics, the fiber orientation varies throughout a product giving rise to a pronounced anisotropic mechanical response. Different flow conditions in a product result in spatial variation in both short- and long-term mechanical properties. In this study, a modeling approach is presented to evaluate the lifetime of short fiber reinforced polyamide 6, both in plasticity- and crack growth controlled regions of failure. In the plasticity-controlled region, a viscoplastic model based on separation of the load angle (by means of Hill's equivalent stress formulation) and time dependence of the yield stress is used in the form of an associative flow rule. The influence of temperature and relative humidity on the magnitude of the plastic flow rate is described by using an apparent temperature approach combined with a Ree-Eyring formulation. The depression of the glass transition temperature in the polyamide 6 matrix with increasing amount of absorbed moisture was used to predict the anisotropic deformation kinetics in a humid environment. Similar to the plasticity controlled failure, in slow crack growth controlled failure region the effect of temperature, relative humidity, and load angle on the lifetime under a fatigue load is investigated. The apparent temperature approach could also be successfully applied to predict the slow crack growth failure, while the load angle dependence is shown to scale similar to the plasticity-controlled failure with the Hill's equivalent stress.     

Further evidence against the alleged failure of the classical nucleation theory below the glass transition range

We collected a plethora of new data to test the hypothesis that the failure of the Classical Nucleation Theory (CNT) below the glass transition range is just an experimental artifact. Since reaching the steady-state nucleation regime takes a significant time for treatments below the glass transition temperature, data collected in this temperature range tend not to have reached a steady state. Because of this potential problem, we examined the CNT using new experimental data for three stoichiometric silicate glasses: Li₂Si₂O₅, BaSi₂O₅, and Na₄CaSi₃O₉. We also measured the equilibrium viscosity for the studied glass batches and used it as a proxy for the effective diffusion coefficient. The analysis was conducted by applying a steady-state criterion and evaluating the error propagation throughout all calculations. Using this rigorous procedure, we have not observed the alleged CNT failure. Our comprehensive results support recent studies questioning this possible CNT failure helping solve a longstanding problem in glass science.     

Suppression of phosphor‐glass reactions in YAG:Ce phosphor‐embedded glasses

For high‐power white LED applications, YAG:Ce‐based yellow phosphors were embedded in a low‐T_g Bi₂O₃–B₂O₅–ZnO–Sb₂O₅ glass (BiG) by sintering route. A high‐T_g silicate glass (SiG) was also used for comparison. Dense (porosity<2%) phosphor‐glass composites were obtained after sintered at 800°C (for SiG) and 325°C (for BiG). XRD quantitative analysis indicates that the loss of phosphor content is in the range of 2.5%‐22%, caused by partial dissolution of phosphor particles into the glass matrix during sintering. The element distribution across the interface and within the reaction zone between phosphor and glass was analyzed by TEM/SEM‐EDS. The intrinsic emission characteristic of YAG:Ce is nearly not altered, possibly resulted from the slight modification of the YAG phase during sintering. Thus the final emission intensity of the sintered body is mainly determined by the residual amount of the YAG:Ce phase. Replace the high‐T_g SiG glass by the low‐T_g BiG glass, prenitridize the YAG:Ce phosphor, and change the sintering atmosphere from air to N₂ suppress the loss of phosphor during sintering. Therefore, the resulting loss of emission intensity of the phosphor‐embedded glass material can be reduced to only about 1.8%.     

Physical modeling of the interphase in amorphous thermoplastic/glass bead composites

Mechanical spectrometry was performed on polystyrene/glass bead and poly (styrene-co-methacrylic acid)/glass bead composites to test for the influence of the interphase on molecular mobility. To quantify these motion changes, a physical model was developed to predict the deformation of amorphous materials near T_g. Before applying this model, the dynamic mechanical behavior of the two phases (matrix and inclusions) must be separated to remove the reinforcement effect of the fillers and to keep only the physical crosslinking effect of the amorphous phase by the inclusions. It was shown that (i) the fillers can induce the nation of specific interactions, which act as physical ties, reducing molecular mobility and that (ii) the decrease in molecular motion with increasing filler content is enhanced for fillers coated by a silane coupling agent.