Thermal Shock Resistance Parameters Research Articles

Flexibilizing Mechanisms of Spinel-, Hercynite-, Galaxite-, and Chromite-Containing Basic Refractories for Cement Rotary Kilns

Background: Refractory linings of cement rotary kilns are subjected to severe thermomechanical stresses of cranking, ovality, tyre hooping/migration, and uneven thermal distribution. An insistent demand is to discover the significance of spinel, hercynite, galaxite, and chromite in magnesia refractories, as well as their flexibilizing mechanisms. Objectives: The objectives are to compare the fracture behavior of magnesia–spinel, – hercynite, -galaxite, and -chromite refractories and to unveil the flexibilizing mechanisms of different spinels. Methods: The wedge-splitting test is carried out to produce various fracture parameters. Their flexibilizing mechanisms are unveiled by performing microstructural observations and analyses. Results: Various fracture parameters are obtained, including specific fracture energy, brittleness number, characteristic crack length, and thermal-shock resistance parameter. Generally, magnesia–hercynite bricks and magnesia–galaxite bricks have demonstrated the obvious advantages of fracture resistance, which are more flexible than magnesia–spinel bricks and magnesia–chromite bricks. Conclusion: The flexibility of magnesia–spinel bricks is attributed to microcracks generated from the thermal mismatch between spinel grains and surrounding periclase, which is recognized as the thermal-expansion mismatch mechanism. In magnesia–hercynite and magnesia-galaxite refractories, the active-ion-diffusion mechanism is predominant beyond similar microcracks, to drive the flexibility by the continuous diffusion of Fe2+, Mn2+, and Mg2+ during high-temperature processes. In magnesia–chromite bricks, the pore rims contribute to the flexibility as a silicate-migration mechanism, after silicate envelopes first arise around chromite grains and then vanish into the surrounding magnesia by the suction of capillary force during the burning process.

Study of the influence of ZrB2 content and thermal shock on the elastic modulus of spark plasma sintered ZrB2-B4C composites using a non-destructive ultrasonic technique

Non-destructive ultrasound phase spectroscopy (UPS) was used to study the influence of thermal shock on the longitudinal elastic constant (C11) of ZrB2-B4C composites. C11 of the composites was measured in the as-fabricated condition and after different numbers of thermal shock cycles. The relative change in C11 was used as the thermal shock resistance parameter. Composites with 70 and 50 vol% ZrB2 were subjected to three thermal shock temperature differences (ΔT) of 600 °C, 800 °C, and 1000 °C, respectively. The rate of drop in C11 increased significantly with an increase in ΔT and B4C content. The mechanism of thermal shock damage has been discussed considering the influence of processing-induced thermal residual stresses and the average stress state in both phases during thermal shock. It was shown that the powder particle arrangement plays a major role in the damage mechanism and B4C-B4C particle contacts provide easy paths for crack propagation.

Thermoelectric and thermomechanical properties of invar 36: Comparison with common thermoelectric materials

Most thermoelectric (TE) materials are brittle and exhibit high coefficient of thermal expansion (CTE), both of which are undesirable considering their service conditions. In this context, invar 36 is known to be a ductile material with a very low CTE feature. However, its TE performance is yet to be reported. Accordingly, the present work involves preparation of invar 36 and investigation of its TE performance. The CTE and mechanical properties of invar 36 were also measured to calculate its thermal shock resistance parameter (R’) and to comment on its thermal shock resistance. Further, we calculated R’ of state-of-the-art TE materials using literature data for a detailed comparison. The results show that Seebeck coefficient of invar 36 is −14.4 μV/K at RT and its carrier type is changing from n- to p-type at ∼550 K. This is an unusual behavior, observed in some well-known TE materials like PbTe and CoSb3, and might suggest a mixed conduction in plain invar 36. Also, we report that invar 36 exhibits a PF of ∼2.6 μW/cmK2 at RT, which is comparable to some TE materials. On the other hand, the ZT of invar 36 (∼0.007) was found to be 10–100 times lower than common TE materials at RT. However, considering a possible minority carrier compensation and as-measured thermal conductivity (∼11.9 W/mK), ZT might be improved through careful doping and/or grain size reduction strategies in the future. Besides, unlike most TE materials, invar 36 is ductile with excellent mechanical properties (Elongation: 39%, YS: 436 MPa, UTS: 583 MPa, E: 146 GPa, υ: 0.28, Toughness: 200 MJ/m3). Importantly, invar 36 exhibits 10 times lower CTE (1.7 ×10-6 K-1 between RT – 473 K) and 75–1000 times higher R’ (20125 W/m) than state-of-the-art TE materials, thus, it might attract interest in applications where durability is equally important.

Thermal shock and fatigue lifetime characteristics of ceramic Nd:YAG.

The thermal shock and fatigue lifetime of a ceramic Nd:YAG laser material were analyzed. A new method is proposed to observe the effects induced by the intense temperature difference between the central portion and the surface of the material using a probe beam. The thermal effects of the intensity variations in the probe beam on a 2 at. % ceramic Nd:YAG were measured. The temperature difference and stress were high when the pump power suddenly increased or decreased compared to the thermal equilibrium. The thermal shock was the highest when the pumping started. The thermal shock resistance parameter of the laser material was 0.57 kW/m at a pump power of 14.9 W and zz stress component of 160.8 MPa. With 14.9 W pump power, the fatigue lifetime of the laser material was 238 cycles until it was damaged.

Structure, thermal and spectroscopic properties of Nd:YAlO3 perovskite crystal between 77 to 300 K for the design of cryogenic cooled solid state laser

The solid-state lasers provide an attractive approach to enhance the laser performance benefitting from significant improvements in both thermo-optic and spectroscopic properties of the gain mediums under cryogenic temperature. We have systematically investigated the structure, thermal and spectral properties of Nd:YAlO3 (Nd:YAP) in the temperature range of 77–300 K. We found that the thermal expansion coefficient of a-cut Nd:YAP crystal is about zero around 180 K. The zero-thermal-expansion could lead to negligible thermal effect and suppress optical distortion in high average power lasers, which provides great help for high power and high beam quality laser generation. The increase in thermal conductivity and reduced thermal expansion at cryogenic temperature lead to thermal shock resistance parameter significantly larger than that at room temperature. Furthermore, the detailed thermal and spectral properties of Nd:YAP crystal in the temperature range across 77–300 K were determined. All results of the Nd:YAP crystal, in particular, the emergence of zero-thermal-expansion, provide important information for the design of cryogenic cooled high-power lasers.

Nannochloropsis spp. as Feed Additive for the Pacific White Shrimp: Effect on Midgut Microbiology, Thermal Shock Resistance and Immunology

Simple SummaryWe evaluated Nannochloropsis spp. as a feed additive for the Pacific white shrimp by testing for thermal shock resistance, immunology, and midgut microbiology. Nannochlorpsis spp. are rich in Eicosapentaenoic acid, an n-3 fatty acid. This study demonstrated that the inclusion of these microalgae in the diet increased shrimp resistance to thermal shock and stimulated shrimp immune defense.This work aimed to evaluate Nannochloropsis spp. as feed additive in the diet of Pacific white shrimp for their effect on midgut microbiology, thermal shock resistance and immunological parameters. Initially, the digestibility of the microalgae meal was assessed, and the apparent digestibility coefficient (ADC) was determined. The ADC was, in general, high in lipids (78.88%) and eicosapentaenoic fatty acid (73.86%). Then, Nannochloropsis spp. were included in diets at four levels (0, 0.5, 1 and 2% inclusion). The shrimp were reared in 500 L clear water tanks containing 20 shrimp per tank with an initial weight of 6.05 ± 0.06 g and fed four times a day. Shrimp fed with supplemented diets containing Nannochloropsis spp. (0.5 and 2%) presented higher resistance to thermal shock when compared to the non-supplemented group (control). Shrimp fed with 1 and 2% of algae inclusion had a higher production of reactive oxygen species (ROS) when compared to other treatments. No statistical difference was observed in the immunological parameters and microbiology of the intestinal tract. Thus, the inclusion of Nannochloropsis spp. in shrimp diets at 0.5 and 2% levels increases resistance to thermal shock and ROS production in shrimp.

Temperature-dependent thermal and spectroscopic properties of Yb:YALO3 perovskite crystal for a cryogenically cooled near IR laser

Temperature dependent thermal and spectroscopic properties of Yb:YAlO3 (Yb:YAP) perovskite crystal at temperatures ranging from 77 to 298 K are presented. Thermal properties including specific heat, thermal expansion coefficient and thermal conductivity were investigated. Thermal shock resistance parameters were evaluated and the thermal shock resistance parameters were significantly increased from 0.68 × 106 W m-1 to 12.32 × 106 W m-1 in Yb:YAP as temperature varies from 298 to 77 K. The spectroscopic parameters, such as absorption, fluorescence, lifetime were also studied. The results of our study indicate that Yb:YAP crystal is a promising laser medium for high-power solid-state laser. The calculated cross-sections together with relevant thermal properties provide important information for the design in a new generation of cryogenically cooled near infrared laser.

Thermo-optic and spectroscopic properties of Yb:GAGG, Nd:GAGG and Nd:GGG laser materials at cryogenic temperature

The solid-state lasers provide an attractive approach to enhance the laser performance benefitting from significant improvements in both thermo-optic and spectroscopic properties of the gain mediums under cryogenic temperature. Here, thermo-optic properties of Yb:Gd3(AlxGa1-x)5O12 (x = 0.1, Yb:GAGG) and Nd:Gd3(AlxGa1-x)5O12 (x = 0.2, Nd:GAGG) laser crystals, including thermal conductivity (κ), thermal expansion coefficient (α) and specific heat at constant pressure (Cp) were measured from 77 to 298 K. In addition, the thermal shock resistance parameters were also calculated. The spectroscopic properties and the fluorescence lifetimes of laser gain mediums Yb:GAGG, Nd:GAGG and Nd:Gd3Ga5O12 (Nd:GGG) were characterized at 77, 150, 298 K.

Computational and Microstructural Stability Analysis of Shock Wave Interaction with NbB2-B4C-Based Nanostructured Ceramics.

Despite extensive research on developing different transition metal boride composites for aero-thermostructural applications, the understanding of the shockwave interaction using high pressure shock testing facilities and computational simulation of such interactions are much less explored. This aspect is even more important for much less explored ceramics, like NbB2-based materials. While addressing this aspect, the present investigation reports the thermostructural stability of spark plasma sintered NbB2-(0-40) mol % B4C composites under the hypersonic aero-thermodynamic conditions using a miniature detonation-driven shock tube facility. All the ceramic discs underwent mild surface oxidation, as a consequence to impulsive load together with the thermomechanical shock. Using the in situ recorded pressure pulse data together with conjugate heat transfer analysis, spatiotemporal evolution of ceramic surface temperature was computationally analyzed for the given test conditions. Importantly, the NbB2-(0 and 20) mol % B4C composite retained structural integrity even after exposure to 10 shock pulses with maximum reflected shock temperature and pressure of 5000 K and 37.5 MPa, respectively. In contrast, NbB2-40 mol % B4C underwent structural failure by shattering to pieces. An attempt has been made to rationalize such results on the basis of thermal shock resistance parameters, estimated using the Kingery and Hasselman model. It is observed that NbB2-(0 and 20) mol % B4C shows higher crack propagation resistance, that is, 20 and 30%, respectively, under thermal shock (R″) than NbB2-40 mol % B4C. Interestingly, all the shock exposed NbB2-B4C ceramics show a measurable increase in hardness, which is attributed to transient melting and solidification of constituent phases due to interaction with shock heated gas, for a short duration of ∼5 ms. Taken together, the present study establishes the potential of NbB2-B4C composites for aero-thermostructural applications.

Thermal shock of tungsten carbide in plasma-facing conditions

Tungsten carbide (WC) has been found to have higher resistance to plasma-induced thermal shock compared to rolled tungsten. The electron beam device JUDITH 1 was used to simulate likely thermal shock conditions induced by edge localised modes and plasma disruptions. Loading conditions of 100–1000 cycles, heat fluxes of 0.19–1.13 GW/m2 and base temperatures of 400–1000 °C were employed on two candidate WC-based materials: a monolithic WC ceramic, and a WC-FeCr composite. Surprisingly, the monolith outperformed the composite under all conditions. This was unexpected, particularly at 400 °C, based on the calculated thermal shock resistance parameters. The result was explained by preferential melting of the metallic FeCr binder. Compared to available data collected under identical conditions on rolled tungsten plate, monolithic WC had lower surface roughness from thermal shock damage, particularly when tested at 400 °C. This shows promise for its use as a plasma facing material. Strategies for further improving performance are discussed.

Gel casting of mullite for radome applications

AbstractGel‐casting method was used to fabricate mullite ceramics because this method has not been applied to fabricate dense mullite in literature. Gel‐casting parameters such as monomer types (acrylamide and metyhlenebisacrylamide), effect of initiator (ammonium persulfate), and catalyst (tetramethylenediamine) were studied. All samples reached to relative densities of 97% to 98.2% after sintering at 1540°C for 2 hours. Backscattered SEM images revealed anisotropically grown mullite grains, glassy phase located at triple junctions, hexagonally‐shaped and faceted Al2O3 grains, and white‐color grains consisting of ZrO2 and undissolved TiO2. A Weibull modulus of 12.33 (ie, indicating tough ceramics) and characteristic strength of 186 MPa were calculated, below which no failure was expected. A critical quenching temperature was found as about 400°C (ΔT ~ 380°C) by indentation‐quench method. In addition, a thermal shock resistance parameter (eg, R in °C) of 142.4°C was calculated, which was higher than commonly used Al2O3 ceramics. Lower dielectric constant and loss are desired for wide frequency band application and shorter signal transmission delay time in radomes. The dielectric constant was found as nearly 7.5 up to 10 GHz and loss tangent was 0.0031 at 5 MHz. Dielectric and thermomechanical results suggest that mullite is a suitable candidate ceramic for radome applications.

Mechanical, thermal physical properties and thermal shock resistance of in situ (TiB2+SiC)/Ti3SiC2 composite

Dense (TiB2+SiC)/Ti3SiC2 composite with 20 vol% TiB2 and 10 vol% SiC was synthesized by in situ reaction hot pressing. The room and high temperature mechanical and thermal physical properties, as well as thermal shock resistance of the composite were investigated and compared with SiC/Ti3SiC2 composite as prepared by the same process. The synergistic action of TiB2 and SiC produced a significant strengthening and toughening effect and (TiB2+SiC)/Ti3SiC2 composites exhibit superior room- and high-temperature mechanical properties compared with SiC/Ti3SiC2 composite. Especially, (TiB2+SiC)/Ti3SiC2 composite shows higher Young's modulus from 25 °C to high temperature and can retain a high modulus of 313 GPa (about 81% of room temperature value) up to 1200 °C. From 25 °C to 800 °C, (TiB2+SiC)/Ti3SiC2 composite has higher thermal conductivity and slightly lower coefficient of thermal expansion. Both water quenching test results and calculation of thermal shock resistance parameters, R, Rst and RIV indicate an improved thermal shock resistance of (TiB2+SiC)/Ti3SiC2 composite, with an increase of the critical thermal shock temperature difference ΔTc from 325 °C for SiC/Ti3SiC2 to 440 °C for (TiB2+SiC)/Ti3SiC2. Superior properties render (TiB2+SiC)/Ti3SiC2 composite a promising prospect as high temperature structural materials.

Tailoring the thermal shock resistance of titanium carbide by reinforcement with tungsten carbide and carbon nanotubes

Titanium carbide (TiC) is reinforced with 3.5wt% of tungsten carbide (WC) and 2wt% of carbon nanotubes (CNTs) in order to improve its thermal shock resistance and mechanical integrity of oxide layer. Three pellets namely, TiC (T-SD), TiC-3.5wt% WC (TW-SD) and TiC-3.5wt% WC-2wt% CNT (TWC-SD) were thermally shocked at 1700°C in an open atmosphere for 10 numbers of thermal cycles. Raman spectra confirmed the retention of CNTs after thermal cycling, which could be attributed to the thermal shielding offered by the molten TiC to CNTs. HR-TEM image infers the collapse of some of the CNTs into carbon structure after the thermal shocks. The mass loss % of T-SD, TW-SD and TWC-SD pellets were found to be 41.5%, 33.3% and 15.13%, respectively after the 10 numbers of thermal cycles. The rate of mass change in T-SD sintered pellet was found to be ~1.4 × 10−3g/min., which got reduced to ~0.4 × 10−3g/min. on addition of 3.5wt% of WC and 2wt% of CNT. Furthermore, reinforcement of 3.5wt% WC and 2wt% CNTs in TiC matrix showed the dramatic increase of 89% in thermal shock resistance parameter (Rst) compared to T-SD pellet. This significant improvement in thermal shock resistance of TWC-SD pellet is mainly attributed to the following three factors viz. (i) higher fracture toughness (ii) higher density and (iii) homogeneous dispersion of CNTs, which hinders the movement of oxygen atoms along the grain boundaries. Hardness of the thermally shocked TWC-SD pellet was found to be 5.1GPa, which was 1.3GPa i.e. ~74% higher compared to thermally shocked T-SD pellet. This increased hardness of thermally shocked TiC matrix has been shown to suppress the crack formation and restrict oxidation.

Microstructural Characterization, Mechanical, Physical and Thermal Properties of a Diesel Particulate Filter

In the literature, limited studies are available due to the challenges of the detailed microstructural characterization and determination of properties of diesel particulate filters (DPFs). For this reason, the characterization of a commercial DPF was carried out with different techniques with the aim to identify the manufacturing processes, the chemical composition, the microstructure and the mechanical, physical and thermal properties. Scanning electron microscopy (energy-dispersive X-ray spectroscopy, back-scattered electron, secondary electron detectors), X-ray diffraction, universal mechanical testing, Archimedes technique, dilatometer and C-therm thermal conductivity analysis tools were used for the characterization. During DPF regeneration, the tailoring of these properties has crucial effect on the reliability and durability of the filter. The value of the thermal shock resistance parameter group $$\sigma _{\mathrm{f}}/E\alpha $$ was calculated to be 426 K, while thermal conductivity (k) was determined as 1.95 W/mK. When compared to the literature values for dense SiC, the $$\sigma _{\mathrm{f}}/E\alpha $$ value indicated a better thermal shock resistance; however, thermal conductivity was on the limits of an order of magnitude worsening the thermal shock resistance. Therefore, to improve the thermal shock resistance of the filter material, the thermal conductivity value has to be increased to the maximum allowed by the required porosity. The study may lead to tailoring of an optimized SiC DPF material.

Mechanical behavior and thermal shock resistance of MgO-C refractories: Influence of graphite content

The mechanical and thermo-mechanical properties of MgO-C refractories are of major importance in the industrial applications, and highly depend on the optimization of their microstructural design. In the present work, the influence of flaky graphite content on mechanical behavior and thermal shock resistance of such refractories was investigated with the aid of the wedge splitting test, fractal and microscopic fractographic analysis. The results showed that the increase of graphite content in the specimens led to an enhanced non-linear fracture behavior, a reduced nominal notch tensile strength (σNT), and a higher specific fracture energy (Gf), characteristic length (lch) and thermal shock resistance parameter (Rst). The fractal analysis of the crack propagation path of the specimens after the wedge splitting test indicated that increasing graphite content in the refractories can enhance their irregularity of the crack propagation path during fracture. Also, it was suggested from microscopic fractographic analysis that the improvement of thermal shock resistance of MgO-C refractories was positively correlated with the increase of interface crack propagation.

Crystal growth and thermal properties of the laser crystal Yb3+:Gd3(AlxGa1−x)5O12

Bulk single crystals of Yb3+:Gd3(AlxGa1−x)5O12 (Yb:GAGG) with dimensions of Φ26mm×30mm were successfully grown using the Czochralski method. The nominal Yb and Al contents in the raw materials were 5.0 and 10.0at%, respectively. The effective segregation coefficients of Yb3+ and Al3+ ions were measured, and the doping concentrations of Yb3+ and Al3+ ions in the crystal were calculated to be 6.25–6.03at% and 12.0–11.67at% along the crystal growth direction, respectively. The crystalline perfection of the as-grown crystal was evaluated by high-resolution X-ray diffraction (HRXRD). The thermal properties, including thermal expansion, specific heat and thermal conductivity, have been studied in detail. In addition, the thermal-optical coefficient and the thermal shock resistance parameters were also calculated. Our results show that Yb:GAGG crystal has potential application in the field of high power solid state laser.

Mechanical and thermal physical properties, and thermal shock behavior of (ZrB2 + SiC) reinforced Zr3[Al(Si)]4C6 composite prepared by in situ hot-pressing

The mechanical and thermal physical properties, as well as thermal shock behavior of in situ hot-pressed 30vol.% (ZrB2+SiC)/Zr3[Al(Si)]4C6 composite have been investigated and compared with monolithic Zr3[Al(Si)]4C6 ceramic. The composite shows superior hardness (Vickers hardness of 17.5GPa), stiffness (Young’s modulus of 418GPa), strength (room-temperature bending strength of 648MPa, and high-temperature bending strength of 439MPa at 1300°C in air), and toughness (fracture toughness of 7.69MPam1/2) compared with Zr3[Al(Si)]4C6. The composite can retain a high modulus of 362GPa at 1350°C (87% of that at ambient temperature). In addition, the composite exhibits higher specific heat capacity and thermal conductivity but slightly lower coefficient of thermal expansion compared with Zr3[Al(Si)]4C6. The critical thermal shock temperature difference (ΔTc) increases from 225°C for Zr3[Al(Si)]4C6 to 345°C for the composite, and the calculation results of thermal shock resistance parameters also indicate a much improved thermal shock resistance of the composite.

Mechanical Properties of Mullite–Corundum Composites Prepared from Bauxite

Mullite–corundum composites have been prepared by reaction sintering of Indian bauxite having considerable amount of impurities and silica sol. The effect of changing mullite phase proportion on the mechanical properties (i.e., flexural strength, elastic modulus, hot modulus of rupture, thermal shock resistance) of prepared composites has been studied. Flexural strength and elastic modulus increase with increasing free corundum phase content in the composites. Hot modulus of rupture for the sample containing only mullite phase increases with increasing test temperature over entire temperature range. Theoretical thermal shock resistance parameters R and R‴ are well supported by experimental thermal shock data.

Toughening mechanism and thermal shock resistance of ZrO2 (3Y)/Fe28at-%Al composites evaluated by indentation techniques

Toughening mechanism and thermal shock resistance of monoclinic ZrO2 (3Y) and ZrO2 (3Y)/Fe28at-%Al composites were investigated by indentation techniques. ZrO2 (3Y)/Fe28at-%Al composites exhibited more pronounced R curve behaviour than the monolithic ZrO2 (3Y). Quantitative analysis of toughening behaviour indicated that the enhanced toughness was attributed to the synergistic effect between crack bridging toughening and phase transformation toughening. Thermal shock resistance of as prepared composite was evaluated by indentation–quench method. Compared with monoclinic ZrO2 (3Y), ZrO2 (3Y)/Fe28at-%Al composites had higher critical thermal shock temperature difference ΔTU at which cracks grow unstably. The thermal shock resistance parameters R, R′ and R′′′′ were also calculated to evaluate the thermal shock resistance. It was found that the addition of Fe28at-%Al particles could lead to higher KIC, thermal conductivity and lower Yong’s modulus, thus resulting in higher ΔTU values of ZrO2 (3Y)/Fe28at-%Al composites than monoclinc ZrO2 (3Y).

A simple methodology to visualize crack propagation for ceramic materials

Analysis of the crack growth behavior is critical for fracture and thermal shock assessment. The current work presents a simple methodology to visualize cracks in ceramic materials. The procedure is exemplified for refractory materials on the basis of images obtained during mechanical loading using a wedge splitting test. Complementary in situ crack growth observation verify that for one of the materials growth and opening displacement of the main crack is accompanied by pronounced micro-cracking, branching, and bridging processes. Apparent fracture resistance and thermal shock resistance parameters are discussed.