Thermal Cycling Process Research Articles

Hot corrosion behavior of magnesia-stabilized ceramic material in a lithium molten salt

The isothermal and cyclic corrosion behaviors of magnesia-stabilized zirconia in a LiCl-Li2O molten salt were investigated at 650 °C in an argon atmosphere. The weights of as-received and corroded specimens were measured and the microstructures, morphologies, and chemical compositions were analyzed by scanning electron microscopy, X-ray energy dispersive spectroscopy, and X-ray diffraction. For processes where Li is formed at the cathode during electrolysis, the corrosion rate was about five times higher than those of isothermal and thermal cycling processes. During isothermal tests, the corrosion product Li2ZrO3 was formed after 216 h. During thermal cycling, Li2ZrO3 was not detected until after the completion of 14 cycles. There was no evidence of cracks, pores, or spallation on the corroded surfaces, except when Li was formed. We demonstrate that magnesia-stabilized zirconia is beneficial for increasing the hot corrosion resistance of structural materials subjected to high temperature molten salts containing Li2O.

Improvement of the Ir/IrO2 pH electrode via hydrothermal treatment

Several Ir/IrO2 pH electrodes were prepared by a cyclic thermal oxidation process via dip-coating in a concentrated solution of NaOH. A hydrothermal hydration treatment at 220 °C for 24 h was used to address the problematic potential drift that is common in Ir/IrO2 pH electrodes. The electrodes that were treated by the hydrothermal method exhibited good stability and high sensitivity compared to those that were hydrated at room temperature. The reasons for this improvement were investigated by Raman spectroscopy, X-ray photoelectron spectroscopy, and field emission scanning electron microscopy. The results suggested that the hydrothermally treated electrode had a more orderly crystal arrangement and a higher content of OH− groups, which drove improvements in the performance of electrode by modification of the Ir/IrO2 structure. The relationship between the electrode structure and performance was investigated and discussed in detail herein.

Rice evapotranspiration at the field and canopy scales under water-saving irrigation

Evapotranspiration (ET) is an important process of land surface water and thermal cycling, with large temporal and spatial variability. To reveal the effect of water-saving irrigation (WSI) on rice ET at different spatial scales and understand the cross spatial scale difference, rice ET under WSI condition at canopy (ETCML) and field scale (ETEC) were measured simultaneously by mini-lysimeter and eddy covariance (EC) in the rice season of 2014. To overcome the shortage of energy balance deficit by EC system, and evaluate the influence of energy balance closure degree on ETEC, ETEC was corrected as $${\text{ET}}_{\text{EC}}^{*}$$ by energy balance closure correction according to the evaporative fraction. Seasonal average daily ETEC, $${\text{ET}}_{\text{EC}}^{*}$$ and ETCML of rice under WSI practice were estimated as 3.12, 4.03 and 4.35 mm day−1, smaller than the values reported in flooded paddy fields. Daily ETEC, $${\text{ET}}_{\text{EC}}^{*}$$ and ETCML varied in a similar trends and reached the maximum in late tillering, then decreased along with the crop growth in late season. The value of ETEC was much lower than ETCML, and was frequently 1–2 h lagged behind ETCML. It indicated that the energy balance deficit resulted in underestimation of crop ET by EC system. The corrected value of $${\text{ET}}_{\text{EC}}^{*}$$ matched ETCML much better than ETEC, with a smaller RMSE (0.086 mm h−1) and higher R 2 (0.843) and IOA (0.961). The time lapse between $${\text{ET}}_{\text{EC}}^{*}$$ and ETCML was mostly shortened to less than 0.5 h. The multiple stepwise regression analysis indicated that net radiation (R n) is the dominant factor for rice ET, and soil moisture (θ) is another significant factor (p < 0.01) in WSI rice fields. The difference between ETCML and $${\text{ET}}_{\text{EC}}^{*}$$ ( $${\text{ET}}_{\text{CML}} - {\text{ET}}_{\text{EC}}^{*}$$ ) were significantly (p < 0.05) correlated with R n, air temperature (T a), and air vapor pressure deficit (D), and its partial correlation coefficients to R n and T a were slightly greater than D. Thus, R n, T a and D are important variables for understanding the spatial scale effect of rice ET in WSI fields, and for its cross scale conversion.

The new frontier of diagnostics: Molecular assays and their role in infection prevention and control.

Recent advances in technology over the last decade have propelled the microbiology laboratory into a pivotal role in infection prevention and control. The rapid adaptation of molecular technologies to the field of clinical microbiology now greatly influences infectious disease management and significantly impacts infection control practices. This review discusses recent developments in molecular techniques in the diagnosis of infectious diseases. It describes the basic concepts of molecular assays, discusses their advantages and limitations, and characterizes currently available commercial assays with respect to cost, interpretive requirements, and clinical utility.

Shear bond strength of ceramic fused to CAD-CAM milled alloys.

BackgroundThis study evaluated the metal ceramic bond strength of cast Ni-Cr, cast Co-Cr, sintered Co-Cr and milled Co-Cr alloys to ceramic through two application procedures including the ceramic layering technique and ceramic pressed-on technique.Material and MethodsCeramic materials (Ø 8 mm, 1.5 mm thickness) were veneered by either the layering or pressed-on technique to cast Ni-Cr, cast Co-Cr, sintered Co-Cr and hard milled Co-Cr alloy disc (12 × 12 × 0.5 mm) (n=15). All specimens were treated with a thermal cycle process for 500 cycles at the temperature between 5 °C and 55 °C with immerse time of 30 seconds and 5 seconds for specimen transfer. The shear bond strength was determined on a universal testing machine at a crosshead speed of 0.5 mm/min. The de-bonding surfaces were examined under visual inspection and SEM. The metal ceramic interface of specimens for each group was examined in SEM and EDS. The means of bond strength were compared using two-way ANOVA followed by post-hoc Tukey HSD multiple comparison test to determine for statistically significant difference at 95% level of confidence. The Weibull analysis was used for determination survival probability of shear bond strength.ResultsThe bond strength of ceramic to sintered Co-Cr alloys was higher than that to others metal alloys. The metal-ceramic mean bond strength was significantly higher for the ceramic pressed-on technique than that of the ceramic layering technique for all tested alloys (p<0.05). Weibull analysis of the shear bond strength indicated that the sintered Co-Cr alloys veneered with heat pressed ceramic provided the highest characteristic strength of metal ceramic bond.ConclusionsThe sintered Co-Cr alloys significantly contributed the appropriate bond strength for metal ceramic. Ceramic pressed-on was a reliable technique to enhance bond strength for fabrication the metal ceramic restoration. Key words:Bond strength, sintered alloy, milled alloy, Co-Cr alloys, metal ceramic.

Alloying effects of Ga on the Co-V-Si high-temperature shape memory alloys

Co64V15Si21−xGax (x=4, 6, 8, 10) alloys have been prepared to investigate the alloying effects of Ga on various properties of Co-V-Si high-temperature shape memory alloys, including crystal structure, transformation behavior, thermal cycle stability, microstructure evolution, mechanical property and shape memory behavior. Results show that the D022-type martensite single-phase is transformed from the L21-type parent phase in Co64V15Si17Ga4 alloys. With the increase of Ga content, R phase appears along grain boundaries of martensite and martensitic transformation temperatures decrease rapidly. Furthermore, the Co64V15Si17Ga4 alloy exhibits excellent thermal cycle stability and stable microstructure even after heated to high temperatures of ~800°C repeatedly. On the other hand, for the (martensite+R) dual-phase alloys (i.e., Co64V15Si15Ga6, Co64V15Si13Ga8 and Co64V15Si11Ga10), (εCo) phase precipitates during thermal cycle process, with respective thermal cycle stabilities enhanced at different temperatures simultaneously. In addition, although excess Ga addition deteriorates the mechanical property significantly, it is still concluded that the doping of Ga has a positive effect on the development of shape memory effect of Co-V-Si high-temperature shape memory alloys.

A Thermal Cycling Route for Processing Nano-grains in AISI 316L Stainless Steel for Improved Tensile Deformation Behaviour

&lt;p&gt;The present work significantly improved the mechanical strength of AISI 316L stainless steel by producing nano-sized grains. Steel was subjected to cold rolling followed by repetitive thermal cycling to produce ultra-fine/ nano-sized grains. The optimum processing parameters including extent of cold deformation, annealing temperature for thermal cycling, soaking period during each thermal cycle, and number of thermal cycles were determined through a systematic step-by-step procedure. After conducting thermal cycling under optimum conditions, a significant amount of grain size reduction was achieved. The effect of nano-sized grains on tensile deformation behavior was analysed. High cold deformation resulted in increased amount of stored strain energy. The stored strain energy accelerated the re-crystallisation kinetics during the thermal cycling process. Every thermal cycle resulted in irregular dispersal of stored energy. This irregular dispersal of stored energy favoured recrystallisation rather than grain growth and led to refinement of grains, in the absence of strain induced martensite. Repetitive thermal cycling promoted grain refinement and resulted in very significant grain size reduction with resultant grain size in the range of 800–1200 nm as compared to initial size of 90–120 μm. The resultant microstructure improved tensile strength by&lt;br /&gt;106.8 per cent, from 590 MPa to 1220 MPa.&lt;/p&gt;

Effect of thermal cycling process parameters on recrystallization kinetics for processing of fine-grained pure copper

ABSTRACTThe present work developed a two-step thermal cycling technique for processing of fine-grained pure copper for improved properties. This included initial annealing of specimens followed by heavy cold rolling and a series of heating and cooling cycles. The study investigated the important microstructural changes occurring in the cold deformed grains in the absence of phase transformations. A major interest of the present research was to closely describe the effect of thermal cycling parameters on the recrystallization and grain growth kinetics for processing of fine-grained structure. The study determined the optimum values of process parameters for the developed thermal cycling route including the extent of cold deformation, annealing temperatures, holding periods, and the number of thermal cycles. The thermal cycling process produced closely distributed fine grains with bi-modal microstructure leading to increased hardness and strength without any significant loss in electrical conductivity.

The chemistry and structural thermal stability of hole-doped single crystalline SnSe

A series of transmission electron microscopy experiments were carried out for studying the structure and chemistry thermal stability of thermoelectric material single crystalline SnSe with Na-doping. With spherical aberration-corrected scanning transmission electron microscopy and high sensitivity energy dispersive X-ray detector, both of the atomic structural and compositional defects of Na-doped SnSe were uncovered. Lamella-shaped defect with depleted-Sn but rich-Na was captured. In situ heating experiments up to 450 °C revealed a thermal-induced elemental segregation process. The elements of Na, Sn and Se were revealed to segregate severely and even porous regions appeared above 350 °C. Isolated Na, Sn and Se islands were formed through the heating processes. These observations revealed a possible performance degradation of hole-doped SnSe through the applications in thermal cycling processes. A comparison experiment carried out on bulk Na-doped SnSe samples showed a much better thermal stability and a stable electronic transport property. However, the current investigation and results suggest more systematic researches need to be considered to completely preclude or delay the nucleation and propagation of these defects and the thermal-induced elemental segregation processes.

Physical and Mechanical Evaluation of Five Suture Materials on Three Knot Configurations: An in Vitro Study.

The aim of this study was to evaluate and compare the mechanical properties of five suture materials on three knot configurations when subjected to different physical conditions. Five 5-0 (silk, polyamide 6/66, polyglycolic acid, glycolide-e-caprolactone copolymer, polytetrafluoroethylene) suture materials were used. Ten samples per group of each material were used. Three knot configurations were compared A.2=1=1 (forward–forward–reverse), B.2=1=1 (forward–reverse–forward), C.1=2=1 (forward–forward–reverse). Mechanical properties (failure load, elongation, knot slippage/breakage) were measured using a universal testing machine. Samples were immersed in three different pH concentrations (4,7,9) at room temperature for 7 and 14 days. For the thermal cycle process, sutures were immersed in two water tanks at different temperatures (5 and 55 °C). Elongation and failure load were directly dependent on the suture material. Polyglycolic acid followed by glycolide-e-caprolactone copolymer showed the most knot failure load, while polytetrafluoroethylene showed the lowest (p < 0.001). Physical conditions had no effect on knot failure load (p = 0.494). Statistically significant differences were observed between knot configurations (p = 0.008). Additionally, individual assessment of suture material showed statistically significant results for combinations of particular knot configurations. Physical conditions, such as pH concentration and thermal cycle process, have no influence on suture mechanical properties. However, knot failure load depends on the suture material and knot configuration used. Consequently, specific suturing protocols might be recommended to obtain higher results of knot security.

Influence of processing temperature on mechanical performance of unidirectional polyamide 11–flax fibre composites

This paper reports the mechanical behaviour of novel biocomposites made up from PA11 and flax fibres. We find that, using various flax fibre loadings (i.e. volume fractions), it is possible to obtain bio-based composites with good and reliable tensile properties compared to other biocomposites such as PLA/Flax. Our investigations reveal that the thermal cycle process used for composite moulding has a significant impact on the fibre mechanical properties. Indeed, a 210°C thermal cycle for 8min induces a decrease in fibre stiffness and strength of 32.8 and 12.9%, respectively. A simple micromechanical model, i.e. mixing rule, is applied to estimate composite stiffness and strength based on heat-treated fibre properties. In the case of composite stiffness, our results indicate an underestimation of the Young’s modulus compared to experimental data, especially when the composite stiffness is taken in the first part of the stress–strain curve where the stiffness exhibit unstable values. This implies that the mechanical behaviour of flax fibre bundles compared to fibre bundles constrained within the polymer matrix is not the same, probably due to rotational locking, which prevents the micro fibrillar realignment of the cellulose leading to higher stiffness values.

Direct Y-STR amplification of body fluids deposited on commonly found crime scene substrates

Body fluids detected on commonly found crime scene substrates require extraction, purification and quantitation of DNA prior to amplification and generation of short tandem repeat (STR) DNA profiles. In this research Y-STR profiles were generated via direct amplification of blood and saliva deposited on 12 different substrates. These included cigarette butts, straws, grass, leaves, woodchips and seven different types of fabric. After depositing either 0.1 μL of blood or 0.5 μL of saliva, each substrate containing the dry body fluid stain was punched using a Harris 1.2 mm micro-punch. Each of these punched substrates, a total of 720 samples, containing minute amount of blood or saliva was either amplified directly without any pre-treatment, or was treated with one of the four washing reagents or buffer. In each of these five experimental groups the substrates containing the body fluid remained in the amplification reagent during the thermal cycling process. Each sample was amplified with the three direct Y-STR amplification kits; AmpFℓSTR® Yfiler® Direct, Yfiler® Plus Amplification Kits and the PowerPlex® Y23 System.Complete and concordant Y-STR profiles were successfully obtained from most of these 12 challenging crime scene objects when the stains were analyzed by at least one of the five experimental groups. The reagents and buffer were interchangeable among the three amplification kits, however, pre-treatment with these solutions did not appear to enhance the quality or the number of the full profiles generated with direct amplification. This study demonstrates that blood and saliva deposited on these simulated crime scene objects can be amplified directly.

Effect of surface treatment conditions of zirconia on the shear bond strength of orthodontic metal bracket

The purpose of this study was to examine the effects of various surface treatments of zirconia on the shear bond strength of orthodontic metal brackets after thermal cycling process. Zirconia specimens were fabricated as a cuboids (8 × 8 × 9 mm³) and divided into 8 groups depending on the surface treatments and thermal cycling process after bonding of metal brackets: 1) Polishing (P group), 2) 110 ㎛ A1₂O₃ blasting (B group), 3) 110 ㎛ A1₂O₃ blasting + Silane primer (BS group), 4) 110 ㎛ A1₂O₃ blasting + MDP/Silane primer (BSM group), 5-8) Thermal cycling process (5-55℃, 5000 cycles) after the surface treatments (PT, BT, BST, and BSMT groups). Specimens were measured the changes in surface roughness after surface treatments. Specimens were bonded to metal brackets using resin cement, and shear bond strength was measured by a universal testing machine. After mechanical test, the zirconia and metal bracket surfaces were observed by SEM and optical microscopy. After thermal cycling, surface roughness of the B, BS, BSM groups were significantly higher than P group (p0.05). The averages of shear bond strength in groups were recorded as following order: P B BS BSM. After the thermal cycling process, all groups were significantly decreased in shear bond strength (p0.05). From observations of zirconia and metal bracket surfaces, failure modes of P, PT, B, BT, and BST groups showed adhesive failures, BS group showed a mixed failure (adhesive failure + cohesive failure), meanwhile BSM and BSMT groups showed cohesive failures. All of the results taken together suggest that the 110 ㎛ A1₂O₃ blasting + MDP/Silane primer treatment was suitable for use in clinics due to its high bonding strength even after the thermal cycling treatment.

Implementation of Compact and Low-Cost PCR Thermal Cycler

This paper describes the design and implementation of a compact and low-cost PCR thermal cycler. Employing the standard computing device such as a personal computer reduced the system cost significantly. The design using the components from IT industry delivers further cost reduction. The total system was implemented with a local-host architecture, where a PC was employed as the host. The local system only executed the thermal cycling process and the management of temperature protocol files was taken by the host with a convenient GUI. Using multiple units of the presented system was also implemented and discussed along with the possible applications on such as finding the optimal PCR temperature condition. The comparison results on the temperature control show that the presented system was compatible to the expensive commercial thermal cyclers. The DNA amplification performance was also compared, which showed no distinct difference with the conventional equipment.

Finite Element Creep-Fatigue Analysis of a Welded Furnace Roll for Identifying Failure Root Cause

Creep-fatigue induced failures are often observed in engineering components operating under high temperature and cyclic loading. Understanding the creep-fatigue damage process and identifying failure root cause are very important for preventing such failures and improving the lifetime of engineering components. Finite element analyses including a heat transfer analysis and a creep-fatigue analysis were conducted to model the cyclic thermal and mechanical process of a furnace roll in a continuous hot-dip coating line. Typically, the roll has a short life, <1 year, which has been a problem for a long time. The failure occurred in the weld joining an end bell to a roll shell and resulted in the complete 360° separation of the end bell from the roll shell. The heat transfer analysis was conducted to predict the temperature history of the roll by modeling heat convection from hot air inside the furnace. The creep-fatigue analysis was performed by inputting the predicted temperature history and applying mechanical loads. The analysis results showed that the failure was resulted from a creep-fatigue mechanism rather than a creep mechanism. The difference of material properties between the filler metal and the base metal is the root cause for the roll failure, which induces higher creep strain and stress in the interface between the weld and the HAZ.

Effect of gas nitriding on the thermal fatigue behavior of martensitic chromium hot-work tool steel

The influence of heat treatment and gas nitriding on the thermal fatigue behavior of martensitic chromium hot-work tool steel was investigated. Thermal fatigue tests were carried out using a special induction heating apparatus, which consisted of induction heating and water spray cooling unit. The process of thermal cycling was simulated using a coupled heat-transfer solid-mechanics finite element model. It was seen that the thermal fatigue resistance was higher in the gas nitrided samples after austenizing at 1020°C than for the gas nitrided samples after austenizing at 1100°C. The thermal fatigue endurance limit was found to be maximum for the samples having a compound layer comprising of the higher phase fraction of γ’ (Fe4 N1−x). It was also found that, lower the ratio of compound layer thickness to the total diffusion depth, the higher is the fatigue life. These results were influenced by two major effects of nitrided (diffusion) layer. First is the high compressive residual stresses imparted on the surface which tend to mitigate the effect of thermal tensile stress and secondly very high surface hardness, due to the diffusion of nitrogen, which increase the threshold for crack initiation at the surface.

Whisker growth behaviors in POSS-silanol modified Sn3.0Ag0.5Cu composite solders

Abstract As an ideal modifier, the cage-type polyhedral oligomeric silsesquioxane (POSS)-silanol creates a strong bonding with the solder without agglomeration. It has been shown that the addition of POSS-silanol improves both the mechanical performance and the solder's resistance to electromigration. This study further examined the effect of the addition of POSS-silanol on whisker growth in a Sn3.0Ag0.5Cu (SAC305) solder. The whisker growth was studied for pure SAC305 and SAC305 modified with POSS-silanol under isothermal aging and thermal cycling conditions. The results indicate that the added POSS-silanol not only reinforces the solder joint, but also inhibits whisker formation under both thermal aging and thermal cycling conditions. POSS-silanol can therefore be considered a promising modifier material which enhances the reliability of solders. During the thermal aging process, the added POSS-silanol was found to inhibit the interdiffusion of Sn and Cu atoms at the interface region, thereby preventing the formation of Cu 6 Sn 5 but promoting the conversion of Cu 6 Sn 5 into Cu 3 Sn. During the thermal cycling process, the added POSS-silanol significantly inhibited whisker formation and the deformation of the interface by stiffening the solder matrix and decreasing the driving force for whisker formation.

Effect of the ITER FW Manufacturing Process on the Microstructure and Properties of a CuCrZr Alloy**supported by the International Nuclear Thermonuclear Experimental Reactor (ITER) Specific Program of China (No. 2014GB126000)

The first wall (FW) is one of the core components in ITER. As the heat sink material, the CuCrZr alloy shall be properly jointed with beryllium and stainless steel. At present, the grains of CuCrZr are prone to coarsen seriously in the thermal cycle process of FW manufacturing, which has become a critical issue for ITER parties. To investigate the mirostructure and mechanical properties of the optimized CuCrZr alloy in the first wall fabricating thermal cycle, simulative experiments have been done in this study. The alloy ingot was forged and hot rolled into plates, and then solid solution annealed, cold rolled and aged for strengthening. Several heat treatments were done to the CuCrZr samples, and the changes of microstructure, micro-hardness and tensile strength were investigated. The results indicated that the original elongated grains had changed into equiaxed ones, and the vickers hardness had declined to about 60 after experiencing the process of CuCrZr/316L(N) bi-metallic plate manufacturing, either by hot isostatic pressing at a higher temperature or by explosion welding followed by solution annealing. Joining Be/CuCrZr by hot isostatic pressing acts as an aging process for CuCrZr, so after the simulated heat treatment, the hardness of the alloy increased to about 110 HV and the tensile yield strength at 250°C rose to about 170 MPa. Meanwhile, the average grain size was controlled below 200 μm.

The effect of thermal cycling in superplastic diffusion bonding of 2205 duplex stainless steel

In view of the requirement of large cold rolling deformation and bonding pressure in the conventional superplastic diffusion bonding of 2205 duplex stainless steel, a novel method of introducing thermal cycling into the process was proposed. During the thermal cycling process, due to the change of temperature, surface chemical activity of 2205 duplex stainless steel was improved, activity of atoms and grain boundaries were improved, and the recrystallized grains were refined. The shear bond strength of joint prepared in the mode of thermal cycling using specimens with the cold roll reduction of 60% was 15 MPa higher than that of conventional bonding using specimens with the cold roll reduction of 85%. Compared to the shear bond strength of 430 MPa under the specific pressure of 10 MPa after conventional bonding, shear bond strength of 623 MPa was obtained under the condition of Tmax = 1000 °C, Tmin = 900 °C, cycle number of heating and cooling N = 3, and specific pressure P = 5 MPa.

Dislocation density reduction in multicrystalline silicon via cyclic annealing

Manufacturing processes to reduce dislocation densities in multicrystalline silicon (mc‐Si) solar cells could reduce the cost of photovoltaics by increasing cell efficiency with minimum additional process complexity. The present work investigates how cyclically varying temperature (stress) in mc‐Si blocks can lead to dislocation‐density reduction. Cyclic annealing is found to be more effective at activating immobile dislocations than isothermal annealing. Once immobile dislocations are activated, however, they are hypothesized to impede density reduction of mobile dislocations by accelerating multiplication of overall dislocations. Thus, a combined process of thermal cycling and isothermal annealing is found to provide a maximum dislocation density reduction of ∼70%, with 12 h of static annealing followed by 12 h of cyclic annealing.Dislocation etch‐pit images of as‐grown control and mc‐Si sample after 12 h cyclic annealing followed by 12 h static annealing.