Isothermal Stability Research Articles

Thermodynamic and economic analysis of a novel compressed air energy storage system coupled with solar energy and liquid piston energy storage and release

Compressed air energy storage (CAES) is one of the important means to solve the instability of power generation in renewable energy systems. To further improve the output power of the CAES system and the stability of the double-chamber liquid piston expansion module (LPEM) a new CAES coupled with liquid piston energy storage and release (LPSR-CAES) is proposed. The coupled LPEM conducts suction stage B at the end of the expansion stage, ensuring stable exhaust pressure and temperature for the module. By establishing the thermodynamic and economic models of LPSR-CAES, the effect laws of key node parameters on the system performance are investigated. The results show that the heat transfer between liquid droplets and air dominates the heat transfer in LPEM. The proposed LPEM exhibits excellent isothermal performance and stability, with a maximum temperature difference of about 20 K during the cycle, and stable exhaust temperature changes within 10 K. Under the design conditions, the converted electrical efficiency, round-trip efficiency, exergy efficiency and net present value of the system are 68.31 %, 58.86 %, 66.99 % and 12.25 M$ respectively. The higher the solar supplement temperature, the more outstanding the thermal and economic performance of the system. The short-term energy storage system performance of the proposed system is more prominent. Based on the actual light data, the system can achieve 72.09 % and 69.41 % of converted electrical efficiency and exergy efficiency, respectively, at the 219th day. The results of this study provide theoretical support for the engineering application of the proposed system.

A-319 Capillary Blood Collection for Egg-cellent Reproductive Insights

Abstract Background In the United States, an estimated 13% of women between the ages of 15 and 49 years, experience impaired reproductive potential (fecundity). Assessment of fecundity typically requires an in-person physician visit and venous blood collection to evaluate hormone levels and identify potential reproductive health conditions. Exploring less invasive, at-home sampling options could offer couples insights into their personal reproductive abilities, providing peace of mind and aiding in family planning. Methods Capillary blood, obtained using the Tasso®+ capillary blood collection device coupled with a BD Microtainer® serum tube, was utilized for measurements of analytes associated with female fecundity (follicle stimulating hormone, luteinizing hormone, estradiol, progesterone, anti-Müllerian hormone, and prolactin). These are all FDA-approved assays measured on Roche cobas® e801, assay parameters remained unchanged. Professional and self-collected capillary serum samples were acquired in parallel with the standard venous serum samples, to compare clinical equivalency of the capillary sampling option. In addition to isothermal stability studies at room temperature (20-25°C) and refrigerated (2-8°C) conditions, shipping excursion studies based on ISTA 7D recommendations were performed using a novel packaging solution to control sample temperature and thus, specimen integrity. Studies to assess matrix equivalency, linearity, and imprecision of this alternate sample type were also performed to demonstrate analytical performance. Results Method comparison of venous and professional collection of capillary samples demonstrated correlations (R) ≥ 0.9720 with slopes ranging from 0.919 to 0.971 and mean biases within ±8.2% for all analytes (n = 19-79). Self-collected capillary serum samples demonstrated correlations (R) ≥ 0.9827 with slopes that ranged from 0.841 to 0.985 and mean biases within ±10.7% (n = 16-26). Isothermal stability was demonstrated for each analyte up to 7 days at room temperature and refrigerated conditions. Simulated shipping excursion results were found to be acceptable for both winter and summer conditions with mean biases for each analyte within ±10.2% and ±19.2%, respectively. Matrix equivalency, linearity, and imprecision results adhered to current CLIA acceptance limits for each respective measurement. Conclusions The analytical and stability results affirm the feasibility of collecting capillary serum in a patient-centric manner, providing women with relevant information about their reproductive health.

New frontiers in thermal energy storage: An experimental analysis of thermophysical properties and thermal stability of a novel ternary chloride molten salt

It has been always a daunting task to develop thermal systems with a wide range of thermochemical properties and high stability. It presents a significant challenge, especially when aiming to utilize them for heat storage and transfer applications. In this regard, the thermal characteristics and thermal stability behaviour of molten salt mixture as a heat transfer fluid (HTF) at high temperatures were explored. A novel ternary eutectic salt mixture (base mixture) made of cuprous chloride (CuCl), potassium chloride (KCl) and sodium chloride (NaCl) was investigated as HTF for thermal energy storage (TES) system with a range up to 653 °C in a concentrated solar power (CSP) plant. To extend the temperature span and stability, the effect of an additive was investigated. Different compositions were studied in detail concerning the properties and stability regarding the additive. The molten salt with 7 % CaCl2 additive improved thermal stability and operating temperature from 653 °C to 700 °C. The transport characteristics and thermal stability of the eutectic mixture with and without the additive were measured by high-temperature thermal analyzers. The results indicated that the melting temperature decreased and the average specific heat capacity considerably increased with the addition of CaCl2 additive compared to the ternary chloride base mixture. As the temperature increased, the eutectic salt mixture exhibited a reduction in viscosity and density. The viscosity and density of the salt mixture with and without the additive were almost uniform at 700 °C. The average thermal conductivity of the ternary salt mixture with and without additives was 0.72 W/(m°C) which is much more than that of Solar and Hitec salts. In a 100 h experiment of long-period isothermal stability, the eutectic salt mixture showed less than 4 % weight loss at 700 °C. It was defined as the highest operating temperature at which the eutectic salt mixture remained stable. The stability and recyclability of the salt mixture were confirmed through the short-period stability test. The effect of the CaCl2 additive on thermal stability of base salt mixture was analyzed by X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) techniques. According to the results, this novel eutectic salt mixture had outstanding thermal stability up to 700 °C and could be employed as a viable TES material in CSP plants.

Process and isothermal storage stabilities of a live veterinary vaccine formulated with Plectranthus esculentus tuber starch derivatives as stabilizers

Comparability stability studies of a live Newcastle Disease LaSota vaccine were conducted post freeze-drying and during storage at 5±2, 25±2 and 37±1 °C to demonstrate the equivalence/inequivalence of stability profiles of vaccines stabilized with peptone (reference), trehalose and starch derivatives (acetylated xerogel and carboxymethylated) from Plectranthus esculentus tubers. Variations in moisture content during storage at 5±2 °C; physical collapse/shrinkage, partial microcollapse, and hydrophilicity of lyophilisates were prominent in starch stabilized vaccines without additives. Using the mean embryo infective dose (EID50) test, the derivatives and peptone stabilized vaccines had < 0.5 logEID50 loss in titre during freeze-drying. At the storage temperatures of 5±2, 25±2 and 37±1 °C, using peptone, acetylated xerogel starch, carboxymethylated starch, and trehalose, the average shelf lives of the vaccines were 23–55, 21–26, and 2.6–4.9 months respectively. Acetylated xerogel and carboxymethylated derivatives of Plectranthus esculentus tuber starch with/without additives were able to keep the live ND LaSota vaccine stable during freeze-drying at 1–3 % w/v. The stability of all the vaccines declined as storage temperatures increased. The acetylated xerogel stabilized vaccines were more stable than all of the others at 25±2 and 37±1 °C temperatures.

Isothermal chemical denaturation assay for monitoring protein stability and inhibitor interactions

Thermal shift assay (TSA) with altered temperature has been the most widely used method for monitoring protein stability for drug research. However, there is a pressing need for isothermal techniques as alternatives. This urgent demand arises from the limitations of TSA, which can sometimes provide misleading ranking of protein stability and fail to accurately reflect protein stability under physiological conditions. Although differential scanning fluorimetry has significantly improved throughput in comparison to differential scanning calorimetry and differential static light scattering throughput, all these methods exhibit moderate sensitivity. In contrast, current isothermal chemical denaturation (ICD) techniques may not offer the same throughput capabilities as TSA, but it provides more precise information about protein stability and interactions. Unfortunately, ICD also suffers from limited sensitivity, typically in micromolar range. We have developed a novel method to overcome these challenges, namely throughput and sensitivity. The novel Förster Resonance Energy Transfer (FRET)-Probe as an external probe is highly applicable to isothermal protein stability monitoring but also to conventional TSA. We have investigated ICD for multiple proteins with focus on KRASG12C with covalent inhibitors and three chemical denaturants performed at nanomolar protein concentration. Data showed corresponding inhibitor-induced stabilization of KRASG12C to those reported by nucleotide exchange assay.

Isothermal Dual-Phase Flow Modeling to Assess the Impact of Gas Collection on Geotechnical and Hydraulic Performance of Landfills.

Liquid addition to landfilled municipal solid waste (MSW) is a practice employed to accelerate the biodegradation of the organic fraction of MSW and ensuing gas generation. Pore landfill gas (LFG) and leachate pressure from the added moisture and enhanced gas generation are expected to impact the geotechnical stability of landfill slopes. The impact of moisture addition and gas collection on the stability of landfills was numerically modeled using transient isothermal dual-phase flow and slope stability modeling. The temporal variation in the factor of safety (FS) for slope stability analysis was estimated for the simultaneous flow of LFG and leachate with and without gas collection and leachate recirculation for varying LFG generation rates and waste moisture contents. A significant decline in the FS for landfill slope stability was observed when recirculating leachate without active gas collection. Even without pressurized leachate recirculation, a significant decline in the FS value was observed for landfills with relatively high in situ moisture content without active gas collection. In some modeled scenarios without LFG collection, the FS value was lower than 1. The analysis suggests that the landfill side slope stability analysis should incorporate LFG generation and the resultant pressure for landfills containing high-moisture-content waste and for the landfill with pressurized leachate recirculation. The analysis suggests that an efficient gas collection system plays a critical role in the geotechnical stability of the slope of wet landfills and the performance of leachate recirculation trenches.

Chemical looping conversion of CO2 based on bauxite residue: Thermodynamic behavior and kinetic characteristics

The process of chemical looping conversion of CO2 based on aluminum industry waste bauxite residue (BR) as oxygen carrier (OC) was proposed, and the thermodynamic behavior and kinetic characteristics were explored. The isothermal reaction performance and cycle stability of chemical looping conversion of CO2 by three reduced bauxite residue oxygen carriers H2-RBR1, H2-RBR2, H2-RBR3, pure substances H2-RFe and H2-RFe2O3 were analyzed in a fixed bed reactor. The thermodynamic characteristics of the reaction of CO2 with FeOx in bauxite residue oxygen carriers were clarified, and the thermodynamically feasible region of chemical looping conversion was obtained. When the temperature T < 570 °C, the main process of oxidation is Fe→FeO→Fe3O4→Fe2O3. While the temperature T > 570 °C, the main oxidation process is Fe→FeO→Fe3O4→Fe2O3. Fe3O4 cannot be oxidized to Fe2O3 by CO2 under 1000 °C. The results show that H2-RBR1 shows the highest CO yield, average CO generation rate, and final utilization rate of oxygen vacancy, which are 5.44 mmol g−1, 340.01 μmol⋅g−1⋅min−1and 60%, respectively. The cycling performance of H2-RFe2O3 and H2-RBR1 was compared, and the recyclability of H2-RBR1 is significantly higher than that of H2-RFe2O3. The results showed that the recycling performance of H2-RBR1 was better than that of H2-RFe2O3. The kinetic characteristics of H2-RFe, H2-RFe2O3, H2-RBR1 and H2-RBR2 chemical looping conversion to CO2 were analyzed, and the reaction activation energies were 92.79 kJ mol−1, 96.09 kJ mol−1, 27.27 kJ mol−1 and 74.33 kJ mol−1 respectively.

PREFORMULATION STUDY OF CEFTRIAXONE AND CIPROFLOXACIN FOR LIPID BASED DRUG DELIVERY SYSTEMS

Several tests should be performed to rule out any potential physical or chemical interactions between the active pharmaceutical ingredient and the various excipients that might be utilized in the manufacturing of the drug formula. Fourier Transform infrared spectroscopy is a simple technique for the detection of changes within excipient-drug mixtures. In addition to speeding up the aging process of drugs and their possible interactions with excipients, isothermal stress testing was achieved. In this study, Ceftriaxone sodium (CTX), and Ciprofloxacin hydrochloride (CIPRO) as active ingredients were subjected to several tests to exclude any interaction with the excipients that could be used in the formulation of lipid base biodegradable antibiotic for prevention of post-operative infection. The compatibility was tested by using Fourier Transform infrared spectroscopy (FT-IR) and isothermal stability testing (IST). As a result, the IR spectral interpretation showed that the spectra obtained from the binary mixtures match the original spectra of API. Generally, there was no obvious and influential change of any characteristic peaks which confirms the absence of chemical interaction between the CTX or CIPRO and excipients. In the IST, the API – excipient mixture shows no significant change in physical properties. There was no change in color, gas formation, and liquefaction of the mixture stored under stress conditions. There was no significant change in the amount of API after storage in stressed conditions at statistical significance (p = 0.05). In conclusion, there are no notable interactions between API and the various excipients that could be employed to create biodegradable lipid-based delivery systems that are effective at preventing post-operative infection.

On the stability of shocks in isothermal black hole accretion discs

ABSTRACT Most black holes possess accretion discs. Models of such discs inform observations and constrain the properties of the black holes and their surrounding medium. Here, we study shocks in a thin isothermal black hole accretion flow. Modelling infinitesimal viscosity allows the use of multiple-scales matched asymptotic methods. We thus derive the first explicit calculations of isothermal shock stability. We find that the inner shock is always unstable, and the outer shock is always stable. The growth/decay rates of perturbations depend only on an effective potential and the incoming–outgoing flow difference at the shock location. We give a prescription of accretion regimes in terms of angular momentum and black hole radius. Accounting for viscous angular momentum dissipation implies unstable outer shocks in much of parameter space, even for realistic viscous Reynolds numbers of the order ≈1020.

Decomposition kinetics of expanded austenite with high nitrogen contents

Abstract This paper addresses the decomposition kinetics of synthesized homogeneous expanded austenite formed by gaseous nitriding of stainless steel AISI 304L and AISI 316L with nitrogen contents up to 38 at.% nitrogen. Isochronal annealing experiments were carried out in both inert (N2) and reducing (H2) atmospheres. Differential thermal analysis (DTA) and thermogravimetry were applied for identification of the decomposition reactions and X-ray diffraction analysis was applied for phase analysis. CrN precipitated upon annealing; the activation energies are 187 kJ/mol and 128 kJ/mol for AISI 316L and AISI 304L, respectively. Isothermal stability plots for expanded austenite developed from AISI 304L and AISI 316 were obtained.

Phase diagram, thermodynamic properties and long-term isothermal stability of quaternary molten nitrate salts for thermal energy storage

Thermal energy storage (TES) is a vastly growing technique that allows for the generation of dispatchable electricity in modern concentrating solar power (CSP) plants. In solar tower systems the key to success is the use of a heat transfer fluid (HTF) and storage medium known as Solar Salt. This nitrate salt mixture of NaNO3 and KNO3 is considered thermally stable, non-toxic and environmentally friendly. In line-focusing CSP plants Solar Salt is still not being used as heat transfer fluid due to the inherent risk of freezing and related systematic failure. Accordingly, there is a need to develop nitrate salts with lower melting temperatures but yet acceptably high thermal stability. The information on molten nitrate mixtures with low melting points (⪅100 °C) is limited, especially in terms of isothermal stability tests. This work presents thermo-physical data of the complex quaternary Ca,Li,Na,K//NO3 system. Melting temperatures of more than 100 mixtures were assessed and compositions with melting points below 100 °C were identified. The heat capacity of selected mixtures was in the range of 1.5–1.6 kJ/kg K and generally increased with increasing Li-content. Thermal stability, with Solar Salt as reference salt, indicated that the stability of all mixtures did not exceed 500 °C but that the achievable ΔT was 360 °C, about 90 °C higher than that of Solar Salt. Some compositions are therefore are potential HTF and storage media but the overall Ca-content plays a crucial role in the decomposition of the quaternary mixtures during operation at high temperatures.

Highly Efficient Piezoelectrets through Ultra-Soft Elastomeric Spacers.

Piezoelectrets are artificial ferroelectrics that are produced from non-polar air-filled porous polymers by symmetry breaking through high-voltage-induced Paschen breakdown in air. A new strategy for three-layer polymer sandwiches is introduced by separating the electrical from the mechanical response. A 3D-printed grid of periodically spaced thermoplastic polyurethane (TPU) spacers and air channels was sandwiched between two thin fluoroethylene propylene (FEP) films. After corona charging, the air-filled sections acted as electroactive elements, while the ultra-soft TPU sections determined the mechanical stiffness. Due to the ultra-soft TPU sections, very high quasi-static (22,000 pC N−1) and dynamic (7500 pC N−1) coefficients were achieved. The isothermal stability of the coefficients showed a strong dependence on poling temperature. Furthermore, the thermally stimulated discharge currents revealed well-known instability of positive charge carriers in FEP, thereby offering the possibility of stabilization by high-temperature poling. The dependences of the dynamic coefficient on seismic mass and acceleration showed high coefficients, even at accelerations approaching that of gravity. An advanced analytical model rationalizes the magnitude of the obtained quasi-static coefficients of the suggested structure indicating a potential for further optimization.

Insight into solidification microstructure control by trace TiCN–TiB2 particles for yielding fine-tuned nanoprecipitates in a hypoeutectic Al–Si–Mg alloy

Solution heat treatment (SHT), immediately followed by water quenching, can significantly improve the strength of precipitation-hardenable metallic materials, but frequently compromises the well-defined dimensional design of the geometrically complex or thin-wall engineering components. Here, to avoid this catastrophic high-temperature scheme, we introduce an alternative conceptual strategy to design a novel hypoeutectic Al–10Si–Mg alloy especially for “as-cast” services, i.e., extraordinarily high Mg addition and trace co-incorporation of innovative in situ TiCN–TiB2 particles coupled with a direct post-solidification isothermal low-temperature stabilization treatment (LTST). The performance was carefully characterized by multi-scale characterization techniques. Solidification kinetics and the resultant microstructural arrangement response to the TiCN–TiB2 particle additions were systematically investigated. Results demonstrated that both α-Al dendrites and eutectic Si structures were substantially refined by the TiCN–TiB2 particles. In the absence of conventional SHT, the precipitation kinetics associated with the customized LTST was also thoroughly studied. Interestingly, an extremely fine dispersion and high number density of perfectly coherent GP zones and pre-β'' nanoprecipitates were found coexisting after LTST. As a result, well-combined strength and ductility were therefore achieved by the synergistic effects of trace TiCN–TiB2 particles and LTST in this Al–10Si-2.0 Mg system.

Linear Stability Analysis of a Magnetic Rotating Disk with Ohmic Dissipation and Ambipolar Diffusion

Abstract We perform a linear analysis of the stability of isothermal, rotating, magnetic, self-gravitating sheets that are weakly ionized. The magnetic field and rotation axis are perpendicular to the sheet. We include a self-consistent treatment of thermal pressure, gravitational, rotational, and magnetic (pressure and tension) forces together with two nonideal magnetohydrodynamic (MHD) effects (ohmic dissipation and ambipolar diffusion) that are treated together for their influence on the properties of gravitational instability for a rotating sheetlike cloud or disk. Our results show that there is always a preferred length scale and associated minimum timescale for gravitational instability. We investigate their dependence on important dimensionless free parameters of the problem: the initial normalized mass-to-flux ratio μ 0, the rotational Toomre parameter Q, the dimensionless ohmic diffusivity η ˜ OD , 0 , and the dimensionless neutral–ion collision time τ ˜ ni , 0 , which is a measure of the ambipolar diffusivity. One consequence of η ˜ OD , 0 is that there is a maximum preferred length scale of instability that occurs in the transcritical (μ 0 ≳ 1) regime, qualitatively similar to the effect of τ ˜ ni , 0 , but with quantitative differences. The addition of rotation leads to a generalized Toomre criterion (that includes a magnetic dependence) and modified length scales and timescales for collapse. When nonideal MHD effects are also included, the Toomre criterion reverts back to the hydrodynamic value. We apply our results to protostellar disk properties in the early embedded phase and find that the preferred scale of instability can significantly exceed the thermal (Jeans) scale and the peak preferred fragmentation mass is likely to be ∼10–90 M Jup.

Gravitational Instability of a Magnetic Rotating Disk with Ohmic Dissipation and Ambipolar Diffusion

Abstract We perform a linear analysis of the stability of isothermal, rotating, magnetic, self-gravitating sheets that are weakly ionized. We include a self-consistent treatment of thermal pressure, gravitational, rotational, and magnetic (pressure and tension) forces together with two nonideal magnetohydrodynamic (MHD) effects: Ohmic dissipation and ambipolar diffusion. Our results show that there is always a preferred lengthscale and associated minimum timescale for gravitational instability. The addition of rotation leads to a generalized Toomre criterion (that includes a magnetic dependence) and modified lengthscales and timescales for collapse. We show that both the nonideal MHD effects qualitatively behave in a similar way but have quantitative differences. We apply our results to protostellar disk properties in the early embedded phase and find that the preferred scale of instability can significantly exceed the thermal (Jeans) scale and the peak preferred fragmentation mass is likely to be ∼10–90M Jup.

Polycarbazole-multiwalled carbon nanotubes based nanocomposite: Synthesis, spectral, biocidal and Acetaldehyde sensing studies

We herein report the functionalization of multi-walled carbon nanotubes (MWCNT) via oxidation method using a concoction of concentrated H2SO4 and HNO3. The electrically conducting polycarbazole-multiwalled carbon nanotubes nanocomposite (PCz/MWCNT) has been prepared by in-situ oxidation polymerization of monomer of carbazole (Cz). Several spectral techniques like FTIR, SEM/EDS, TEM, XRD and TGA were used to characterize PCz/MWCNTs nanocomposite. The spectroscopic data ascertains a strong interaction between PCz and MWCNTs. The nanocomposite exhibits high thermal stability as compared to the pristine PCz. The nanocomposite demonstrated better electrical conductivity and isothermal stability with respect to DC electrical conductivity retention under normal conditions below 100°C. The PCz/MWCNT based sensor was designed for the detection of acetaldehyde. It was observed that the resistivity of the PCz/MWCNT enhances on exposure to acetaldehyde at 25°C, and showed a direct relationship between the response and concentration of acetaldehyde. Moreover, PCz and PCz/MWCNT were also tested for their plausible biocidal activity.

Physicochemical Compatibility Investigation of Mesalazine and Folic Acid Using Chromatographic and Thermoanalytical Techniques.

Inflammatory bowel disease is a common name for Crohn’s disease and ulcerative colitis. These inflammatory states cause damage in the sidewalls of the gastrointestinal tract, resulting in malabsorption of food and vitamins. Folic acid (Vitamin B9) is often associated with inflammatory bowel diseases since reduced overall folate concentration in the human body may lead to the development of colorectal cancer and megaloblastic anaemia. However, its deficiency is easily compensated by taking an additional folic acid pill during regular therapy. At the moment, there are no studies that have examined the compatibility of folic acid with 5-aminosalicylate drugs used in the treatment of inflammatory bowel diseases. In this work, differential scanning calorimetry, forced degradation studies, isothermal stress testing and dissolution stability testing were used to determine the stability of folic acid and one of the most commonly used 5-aminosalicylates, mesalazine, when present in the same solution or blend. To monitor the assay of folic acid, mesalazine and nine of its related impurities, a single HPLC method was developed. Results of compatibility studies showed that no physicochemical interaction between mesalazine and folic acid occurs when combined, opening the path to the development of new formulations, such as a mesalazine/folic acid fixed-dose combination.

Introduction of a Methodology to Enhance the Stabilization Process of PAN Fibers by Modeling and Advanced Characterization.

A methodology for designing the oxidative stabilization process of polyacrylonitrile (PAN) fibers is examined. In its core, this methodology is based on a model that describes the characteristic fiber length variation during thermal processing, through the de-convolution of three main contributors (i.e., entropic and chemical shrinkage and creep elongation). The model demonstrated an additional advantage of offering further insight into the physical and chemical phenomena taking place during the treatment. Validation of PAN-model prediction performance for different processing parameters was achieved as demonstrated by Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). Τensile testing revealed the effect of processing parameters on fiber quality, while model prediction demonstrated that ladder polymer formation is accelerated at temperatures over 200 °C. Additionally, according the DSC and FTIR measurements predictions from the application of the model during stabilization seem to be more precise at high-temperature stabilization stages. It was shown that mechanical properties could be enhanced preferably by including a treatment step below 200 °C, before the initiation of cyclization reactions. Further confirmation was provided via Raman spectroscopy, which demonstrated that graphitic like planes are formed upon stabilization above 200 °C, and thus multistage stabilization is required to optimize synthesis of carbon fibers. Optical Microscopy proved that isothermal stabilization treatment did not severely alter the cross section geometry of PAN fiber monofilaments.

Recent developments in the designing of deposition of thermal barrier coatings – A review

The thermal barrier coatings (TBCs) provide insulation to the components of gas turbine by providing higher amount of thermal energy and also reduce the cooling requirement of the top ceramic surface. The top ceramic coat plays a significant role in surging the efficiency of the TBCs. The 8 wt% Yttria partially stabilized zirconia (YSZ) is the top coat material is widely used because of its ability to withstand aggressive conditions of high temperature and pressure. Air plasma Spraying (APS) technique frequently used in gas turbine industry to deposit 8 wt%YSZ TBCs. There are some important spray parameters which play very important role in the deposition of TBCs such as powder feed rate (g/min), current (A), voltage (V), Power (KW) and standoff/spray distance (mm), and these parameters help to regulate the phase composition, isothermal thermal stability, improved microstructure, corrosion resistance and mechanical properties like residual stresses and bonding strength. Recently new surface modification techniques have been developed such as plasma-enhanced chemical vapour deposition (PECVD), electrostatic spray assisted vapour deposition (ESAVD), and solution precursor plasma spray (SPPS), sol-gel and suspension plasma spraying (SPS). These processes enhance the features of developed coatings which include the formation of vertical cracks by utilizing segmentation process and so on. Furthermore, the effect of varying the deposition process parameters like substrate temperature low plasma gun speed, high passage thickness, contact area between splats have been discussed. This review gives a good understanding about the TBCs and inspires researchers to find new ideas for the improvement in this field.

Phase and Structural Transformation of Polyacrylonitrile Fiber during Two-Stage Thermal Stabilization

The influence of two-stage isothermal treatment on the change in the linear dimensions of the fiber, the average sizes of the coherent scattering regions, the texture and phase composition of the polyacrylonitrile fiber in the process of isothermal thermal stabilization is considered by the methods of dilatometry and X-ray diffraction analysis. It is shown that preliminary short-term heat treatment at a lower temperature affects the process of structural transformations of the polyacrylonitrile fiber material and the formation of a new highly dispersed phase of the thermally stabilized fiber.