Thermocyclic Treatment Research Articles

Liquid crystalline epoxy nanocomposite material for dental application

Novel liquid crystalline epoxy nanocomposites, which exhibit reduced polymerization shrinkage and effectively bond to tooth structures, can be applied in esthetic dentistry, including core and post systems, direct and indirect restorations, and dental brackets. The purposes of this study were to investigate the properties of liquid crystalline epoxy nanocomposites including biocompatibility, microhardness, and frictional forces of bracket-like blocks with different filler contents for further clinical applications. In this study, we evaluated liquid crystalline epoxy nanocomposite materials that exhibited various filler contents, by assessing their cell activity performance using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and their microhardness with or without thermocycling. We also evaluated the frictional force between bracket-like duplicates and commercially available esthetic bracket systems using Instron 5566. The liquid crystalline epoxy nanocomposite materials showed good biocompatibility. The materials having high filler content demonstrated greater microhardness compared with commercially available bracket materials, before and after the thermocycling treatment. Thus, manufacturing processes are important to reduce frictional force experienced by orthodontic brackets. The microhardness of the bracket-like blocks made by our new material is superior to the commercially available brackets, even after thermocycling. Our results indicate that the evaluated liquid crystalline epoxy nanocomposite materials are of an appropriate quality for application in dental core and post systems and in various restorations. By applying technology to refine manufacturing processes, these new materials could also be used to fabricate esthetic brackets for orthodontic treatment.

Properties of Welded Joints from Alloy Zr – 2.5 % Nb after Electron-Beam Local Thermocycling

Modes of electron-beam local thermocycling treatment of welded joints of ∅ 88 × 4 mm pipes from alloy E125 (Zr – 2.5 % Nb) are tested. The structure of the welds is studied. The characteristics of mechanical properties are determined under tension and static and dynamic bending. The corrosion resistance is determined in long-term tests in an autoclave with water at 285 °C and in fast tests in an autoclave at 360 °C for 336 h in accordance with the International Standard.

Evolution of the Structure and Properties of Cold-Deformed Hardened System-Alloyed Steel 10Kh3G3MF Due to Intense Thermocycling Treatment

Processes of formation of structure and properties in intense thermocycling treatment of steel 10Kh3G3MF preliminarily subjected to quenching and 60% cold plastic deformation by the method of radial forging are studied. The dynamics of variation of the grain structure of austenite, of the temperature of the start of formation of martensite, and of the level of mechanical properties is studied after different modes of heat treatment.

A Study of Phase and Structural Transformations of Hardened Low-Carbon Steel under Conditions of Multiple Intense Heat Effect

The effect of conditions of rapid thermocycling treatment on phase transformations in heating and cooling and on the structure and mechanical properties of steel 12Kh2G2NMFT is studied. The dependence between the structural changes in thermocycling and the position of critical points Ac 1 and M s is determined.

Effect of cryogenic thermocycling treatment on the structure and properties of magnesium alloy AZ91

The effect of cryogenic thermocycling treatment on the microstructure, mechanical and cryogenic properties of alloy Mg – 9% Al – 0.9% Zn (AZ91) is studied. Thermocycling in the cryogenic range causes a change in the content and distribution of particles of segregations, which is responsible for improvement of the mechanical properties and corrosion resistance of the alloy.

Effect of Thermocycling on the Thermal Degradation Kinetics of Goatskin Collagen Matrices

In the present study, the goatskin collagen matrices were tanned by chrome powder and chestnut extract. The samples were then thermocycled in a container at different temperature ranges with a dwell time of 5 h for different cycles. The thermal degradation behaviors of the collagen matrices before and after the thermocycling were investigated. The Coates-Redfern Method was applied to study the thermal degradation kinetics of different samples. The results indicate that the thermocycling exerted more dramatic effect on the native collagen matrices than on tanned samples. The tanning process endows the samples with extra crosslinking structure, and therefore, less sensitivity to thermocycling treatment. It was found that the thermal treatment at moderate temperature (0~50˚̓˹˰̵̵̵̴͈͂̈́˰̵̼̹̼̈́̈́˰̶̵̵̹̼̳̾̾ͅ˰̿̾˰̸̵̈́˰̸̵̱̼̈́͂̽˰̴̵̷̴̱̱̹͂̈́̿̾˰̱̳̹̱̹̈́͆̈́̿̾˰̵̵̷̵̹̾͂̓˰˸ΔE) of the sample. However, for the samples thermocycled at high upper limit temperature (0~150˚̓˹˼˰ΔE was decreased significantly.

Surface corrosion and fracture resistance of two nickel-titanium-based archwires induced by fluoride, pH, and thermocycling. An in vitro comparative study

The present comparative study aimed to evaluate the surface corrosion and fracture resistance of two commercially available nickel-titanium (NiTi)-based archwires, as induced by a combination of fluoride, pH, and thermocycling. One hundred and ten rectangular section NiTi-based archwires were used, 55 of each of the following: thermally activated Thermaloy® and super-elastic NeoSentalloy® 100 g. Each of these was divided into five equal subgroups. One of these five subgroups did not undergo any treatment and served as the control, while the other four were subjected to 30 days of incubation at 37°C under fluoridated artificial saliva (FS) at 1500 ppm fluoride treatment alone (two subgroups) or combined with a session of thermocycling (FS + Th) treatment at the end of incubation (two subgroups). Within each of the Thermaloy® and NeoSentalloy® groups, the FS and FS + Th treatments were performed under two different pH conditions: 5.5 and 3.5 (each with one subgroup per treatment). Analysis of the surface topography and tensile properties by means of scanning electron microscopy (a single sample per subgroup), atomic force microscopy, and a universal testing machine for ultimate tensile strength were carried out once in each of the control subgroups or immediately after the treatments in the other subgroups for 10 of the archwires. Non-parametric tests were used in the data analysis. Significant effects in terms of surface corrosion, but not fracture resistance, were seen mainly for the Thermaloy® group at the lowest pH, with no effects of Th irrespective of the group or pH condition. Different NiTi-based archwires can have different corrosion resistance, even though the effects of surface corrosion and fracture resistance appear not to be significant in clinical situations, especially considering that thermocycling had no effect on these parameters.

Surface Modification of AISI 4140 Steel Using Electrolytic Plasma Thermocyclic Treatment

Surface modification of AISI 4140 steel has been carried out by using electrolytic plasma thermocyclic treatment (EPTT). Cyclic voltage between 320 and 250 for stipulated period of 1, 2, 3, 4 s and 2, 3, 4, 5 s, respectively, has been performed. At the same time, the effect of average voltage and duration on process has been studied. Microhardness hardness profile measurements have been used before and after thermal treatment to analyze the hardened layer. Scanning electron microscopy (SEM), stereo, optical microscopy, and X-ray diffraction (XRD) have been employed to characterize microstructure and phase composition of the treated layer. The hardening layers are composed of martensite, fine pearlite, oxides with iron, such as FeCr2O4, Fe3O4, and FeO. According to the treatment parameters, max 770 HV hardness and fine martensite, transition zone, and fine pearlite phases have been examined from the surface to the bulk body. When the substrate has been processed at 300–320 V for 42 s, the highest thickness is about 10 mm, and the corresponding microhardness is HV 500–650, which is 4 or 5 times higher than that of the substrate. The depth of hardened layer can be 6–8 mm, depending on the EPTT conditions.

Thermocyclic regulation of the morphology and size distribution of eutectic carbides in high-speed steel

The influence of the temperature and time of softening thermocyclic annealing on the morphology and size distribution of carbides in high-speed steel is investigated. It is established that hot plasticity is facilitated by globular microstructure, when round carbides are uniformly distributed throughout the ferrite matrix. Thermocyclic treatment of high-speed steel creates a structural state with desirable carbide morphology. For maximum effectiveness, thermocyclic treatment is combined with holding at maximum and minimum temperatures. Research permits the development of thermocyclic treatment of hot-rolled high-speed steel bar in industrial chamber furnaces.

Surface Modification of Medium Carbon Steel by Using Electrolytic Plasma Thermocyclic Treatment

In this work, using the electrolytic plasma thermocyclic treatment technique (EPTT), surface modification of medium carbon steel was carried out. The EPTT system was set as industrial scale. Na2CO3 was used as electrolyte in water. Various voltage and ampere values were performed to obtain good surface properties. Moreover, different impulse ratio and cooling rates were performed. Metallographic studies were carried out with an optical microscope, scanning electron microscope (SEM), energy dispersive spectrometer (EDS) to study the hardened and modified surfaces. Also microhardness and Rockwell hardness tests were performed. The reliable microstructure and hardness values were obtained on the surface of steel samples.

Thermocycling treatment of titanium alloys based on polymorphic transformation

The structure and properties of welds of titanium alloys VT6ch and VT22 after thermocycling performed in various modes are studied. The structure of the welds is studied by the methods of metallographic and x-ray diffraction analysis. The mechanical characteristics of the welds are determined by testing them for tensile strength, impact toughness, and crack resistance.

Effect of impurities on intergranular fracture of cadmium during thermocycling and creep

AbstractThe paper is devoted to an analysis of experimental data obtained as a result of investigation of an influence of the impurity nature on the failure of a model material of a high purity under condition of its thermocyclic treatment and high temperature creep. The fact that impurities promote the process of cavity formation was known long ago. However, since investigations were conducted with commercial materials, which had a variety of impurities, it was impossible to investigate the influence of each chemical element separately on the phenomenon in the presence of other additives. Experimental studies are described that have clarified what sort of impurities are responsible for the phenomenon of cavity formation, in what way they act in combination, over which temperature interval, whether neutralisation of them is possible and how this neutralisation can be achieved.

Influence of heat treatment regimes on the structure and mechanical properties of polyamide composites

We analyze changes in the structural characteristics and mechanical properties of composite materials with a polyamide matrix depending on the type of heat treatment. It is shown that thermocyclic treatment with a decrease of temperature to cryogenic temperatures leads to partial cold recrystallization in nanofilled materials and to an increase in the adhesive strength of glass-filled specimens.

Controlling the thermal regime of combined welding and local thermocyclic treatment of circumferential welded joints

Controlling the thermal regime of combined welding and local thermocyclic treatment of circumferential welded joints

Effectiveness of all-in-one adhesive systems tested by thermocycling following short and long-term water storage

To evaluate and compare the marginal integrity of in vitro Class V restorations made with all-in-one adhesive systems by thermocycling after different periods of water storage, to provide an analysis of static and quasi-dynamic deterioration in water. Standardized Class V cavities (17 groups, 8 specimens each) were prepared in extracted human caries-free anterior teeth. The cavities were filled using 14 all-in-one adhesive systems/composite resin combinations in addition to the multi-bottle adhesive systems Syntac and OptiBond FL (etch-and-rinse technique) and Clearfil SE Bond (self-etching) as controls. The samples were thermocycled after water storage for 21 days, after 1 year and again after 3 years (2000 cycles between 5 and 55 degrees C) and replicas were made before and after each thermocycling treatment (TC) for quantitative marginal analysis in the SEM. In dentin, marginal adaptation showed no significant differences between all groups after the first TC. After one year of water storage and a second TC, the results for Prompt L-Pop (1999), Adper Prompt L-Pop/Tetric Ceram, and One-up Bond F Plus showed a statistically significant decrease of margin quality 1 (MQ1) score compared to the reference groups. When the all-in-one adhesives G-Bond, AQ-Bond, Hybrid Bond, and One-up Bond F Plus were used, the enamel margins of restorations showed lower percentages of "continuous margins" (p < 0.05) after 1 year of water storage and TC. Of the materials tested after 3 years of water storage and TC, only AQ Bond had a significantly lower MQ1 score. While all materials exhibited deterioration in the MQ1 quality score, the rate of deterioration varied, and the results show that different materials have different deterioration rates after initial vs long-term water storage. The deterioration along margins in dentin was not as extensive as predicted from other studies; however, the results from the enamel margins show that one-bottle all-in-one adhesives seem to be significantly affected by water storage. The results of this study suggest that the all-in-one adhesive group members perform very differently from each other: thus, data need to be explored further at the level of each different adhesive product.

Formation of a high-coercive state in sintered Nd-Fe-B-Ga magnets by thermocycling

A comparative investigation of the effect of two types of low-temperature annealing, namely, (1) isothermal treatment and (2) thermocycling treatment (TCT), on the coercive force H c of sintered magnets of an Nd-Fe-B-Ga alloy has been performed. Powders of an Nd 15.5 Fe 77.7 B 6.5 Ga 0.3 alloy were prepared from materials taken in three different conditions: cast alloy (CA), hydrided alloy (HA), and partly dehydrided alloy (PDA). The coercive force of the sintered magnets reaches different maximum values, depending on the time of grinding, which after isothermal annealing at 550°C are 680, 688, and 800 kA/m in the magnets prepared from the CA, HA, and PDA, respectively. It has been revealed that the subsequent application of a TCT con- sisting in the variation of the temperature in a range of 20-550°C additionally increases H c . In fine-grained magnets the increment in H c is 10-15%; in coarse-grained, 100-300%. Thus, after a TCT the extremal depen- dence of H c on the time of grinding of the powder virtually vanishes. To explain the observed effect of a TCT, an assumption is made on the effect of interphase stresses (arising at the boundaries between the grains and the intergrain phase enriched in Nd) on the mobility of atoms and the formation of defect-free grain boundaries, which favor an increase in H c upon annealing.

The effect of thermocycling on microleakage of several commercially available composite Class V restorations in vitro

Statement of the problem Microleakage is a major factor contributing to the occurrence of secondary carious lesions around composite restorations. Purpose of study This in vitro study investigated the effect of thermocycling on microleakage of several composite Class V restorations. Material and methods One hundred twenty molars were randomly distributed into 6 groups of 20 teeth. Class V preparations were made in the buccal and lingual surfaces of each tooth and restored in bulk by use of 6 composites (Arabesk, Silux-Plus, Solitaire 2, Durafill VS, Charisma, and Renew) according to the manufacturers’ recommendations. The teeth were stored in distilled water at room temperature for 24 hours. The teeth in each group were divided randomly into 2 subgroups: (a) thermocycled for 500 cycles between 5° and 55°C with a dwell time of 30 seconds, (b) no thermocycling treatment. All restored teeth were immersed in 1% methylene blue dye for 4 hours and sectioned buccolingually with a diamond wheel. Dye penetration was scored by use of a stereomicroscope at original magnification ×4. The generalized linear models statistical analysis was used (α=.05). Results The preparation margins (enamel/dentin) and thermocycling had a significant effect on microleakage ( P=.0351, P<.0001, respectively); the type of material had no significant effect ( P=.1689). Conclusions Thermocycling significantly increased the microleakage ( P<.0001). The overall microleakage at the enamel margins was significantly less than at the dentinal margins ( P=.0351).

Electric heating using a liquid electrode

This work deals with analysis of the processes occurring in the electrolyte and in the plasma layer formed between the liquid electrode-anode and the solid workpiece surface. The electrolyte-plasma quenching method, in which the formation and stabilization of the plasma layer are supported by periodical increase and decrease of the electric voltage was utilized. Changing of switching on time of an increased electric potential and varying its value, we could control the heating and cooling rates of the workpiece surface within 20–500°C/s. This allowed us to form the quenched layers, with thickness from 1 to 10 mm. The possibility of controlling the rate of this periodical heating and cooling allowed us to realize the thermo-cycling treatment of surfaces. Applications of electrolyte plasma quenching include: inner cylindrical surfaces; workpieces, e.g. rolls, knives, saws in metallurgy, metal mining industry and agriculture.

ココアバターのファットブルーム抑制に対する乳化剤の影響（原標題は英語）

Fat boom stability of cocoa butter to which sucrose fatty acid ester, POS-135, and polyglycerol fatty acid esters, 10G9POS and 10G12POS had been added was studied by scanning electron microscopy (SEM) and X-ray diffraction measurement (XRD) so as to clarify the mechanism for anti-bloom effects of emulsifiers. Fatty acids compositions of the emulsifiers were similar to that of cocoa butter, all involving palmitic, stearic and oleic acids. Cocoa butter was crystallized in form V by seeding β2 form crystals of 1,3-behenoyl-2-oleoyl glycerin and transformation to form VI was examined by tempering for 432 hours through 20°C (12 hours) and 30°C (12 hours) thermocycle. In the case of cocoa butter without emulsifiers, XRD showed cocoa butter to be completely transformed from form V to VI after a 120 hour thermocycle treatment before fat bloom could be visually observed. Bloom was observed after a 292 hour thermocycle. It was observed that POS-135 retarded the transformation to cocoa better and fat bloom formation most enhancedly in comparison with 10G9POS and 10G12POS. This mean that the effect of hydrophilic unit structure of sucrose of POS-135 is important for the inhibition the fat bloom formation.

Enhancement of the Power Intensity of Fibrous Composite Materials by Means of Polygonization of the Matrix

We establish the optimal conditions of thermocyclic treatment of aluminum–steel fibrous composite materials. These conditions represent thermocycling of the material (50–60 times) from 573 and 673 K to 293 K at a rate of 50 K/sec. The application of this treatment ensures the formation of a polygonal dislocation substructure responsible for enhancement of the power intensity of the material and improvement of its heat-resistant properties. We also establish the conditions of its loss of strength. Finally, we determine the possibilities of scientific justification of the technologies of treatment of fibrous composite materials for obtaining higher operating characteristics with the use of less labor-consuming and more economically efficient methods.