Molten Potassium Nitrate Research Articles

Enhancing bending performance of ultrathin flexible glass through chemical strengthening

AbstractFlexible glass with high bending strength is a remarkable component of flexible electronic displays. However, as a brittle material, its bending properties often do not meet requirements of application. To address this challenge, the application of chemical strengthening stands out as a viable approach to significantly bolster scratch resistance and bending strength in flexible glass. This study focuses on a conventional one‐step chemical strengthening method, employing molten potassium nitrate, to reinforce ultrathin aluminosilicate glass produced through the secondary down‐drawing thermoforming process. Effects of ion‐exchange temperature and time on mechanical properties of strengthened 110 µm flexible glass were investigated, and moreover, properties of strengthened ultrathin flexible glass with various thicknesses were compared. The results indicate that, after chemical strengthening at 380°C for 1 h, the compressive stress (CS) of 110 µm glass reaches 864.60 MPa, and the depth of layer is 15.86 µm, at which time the glass has the best bending performance and scratch resistance, and half of the faceplate spacing during glass breakage can be enhanced from 38.02 ± 2.7 to 8.40 ± 0.62 mm. For ultrathin flexible glass from 40 to 110 µm, after treatment at 380°C for 1 h, the CS of thick glass is higher than that of thin glass, and the enhancement of bending performance is better.

MODELING AND EVALUATING CONCENTRATED SOLAR POWER PLANT PERFORMANCE IN MOROCCO: A PARAMETRIC STUDY

The current paper presents the design and investigation of a 100 MW concentrated solar power (CSP) system composed of a solar tower with a dual-tank direct thermal energy storage system that uses a mixture of molten potassium nitrate and sodium, incorporated with a 111 MWe gross power block composed of a conventional Rankine cycle. The analysis was conducted at Midelt city (Morocco) (32°41'06 latitude and 4°44'42 O longitude). This study aims to evaluate the impact of cooling tower technology on solar tower power plants from a performance and economic standpoint. To achieve this objective, for each cooling tower system, the main parameters were considered: the solar multiple of the system, and the thermal storage hours (TES); their influence on the annual energy generated, the capacity factor, the annual water consumption, and the levelized cost of energy (LCOE) to demonstrate the profitability and the cost-effectiveness of the CSP system on the studied site. The modeling results reveal that in terms of performance and economic perspective, the optimal configuration corresponds to a solar multiple of 3.5 and thermal storage of 16, using the evaporative-cooling system, which resulted in a capacity factor (CF) of 80.47%, and LCOE of 7.68 ¢ per kWh.

Microkinetics of the reaction [formula omitted] in molten sodium nitrate and potassium nitrate salt

Latest development in the concentrating solar power (CSP) tower technology for energy production and storage intends to find a heat transfer and storage material that provides stability at elevated temperatures. The binary nitrate salt mixture Solar Salt (sodium nitrate, 60 wt.% and potassium nitrate, 40 wt.%) is utilized up to its state-of-the-art temperature limit of 560 °C. Knowledge of the ongoing reactions is demanded to assess the potential of Solar Salt for higher temperature applications. The reversible reaction NO3-⇌NO2-+0.5 O2 is fundamental in a sequence of decomposition reactions. It is investigated by thermogravimetric experiments and ion chromatography post-analysis with regard to the chemical equilibrium, and to reaction kinetics. The reaction enthalpy and entropy of 97 +/- 9 kJ mol−1 and 85 +/- 12 J·mol−1 K−1, respectively, coincide with literature values. A detailed reaction mechanism based on literature findings is drafted and discussed. The corresponding kinetic rate law is simplified by means of rate law approximations and by focusing on the reduction reaction path. The kinetic rate constants of this study exceed previous findings, probably due to successful exclusion of mass transport limitations in the <1 mm thin salt samples. The activation energies and pre-exponential factors amount to 212 +/- 11 kJ·mol−1 and 694546727 +/- 6 s−1, and 115 +/- 11 kJ·mol−1 and 25770 +/- 6 s−1 for the reduction and oxidation reaction, respectively.

Effect of Na contamination on the chemical strengthening of soda-lime silicate float glass by ion-exchange in molten potassium nitrate

Commercial soda-lime silicate float glasses are chemically strengthened at 450 °C for 4 and 24 h in molten potassium nitrate containing small but controlled amount of NaNO3. The ion-exchange efficiency is determined from the measurement of surface compressive stress, potassium penetration and flexural strength. Chemical strengthening remains efficient also for NaNO3 additions up to 0.5 wt% (equivalent to ~1350 ppm Na) and the glass performance being identical to those obtained in pure KNO3, with no significative difference between “tin” and “air” side. For larger Na contamination residual stress and strength are reduced by an amount of about 25%.

Characterization and formation mechanism of pits on diamond {100} face etched by molten potassium nitrite

The morphology of diamond surface etched by molten potassium nitrate was investigated and the formantion mechanism of etched pits was disscussed. The inverted pyramid and square-shaped pits were formed on the {111} face and {100} face of diamond particles, respectively. The size and depth of etching pits on {100} face were apparently smaller than that of {111} face, which suggests {100} face has higher stability due to the role of oxygen functional groups absorb on the structure. At a low etching temperature (600°C), square-shaped pits were firstly formed on {100} face and then gradually changed into octagon shape with the increasing of etching time. The change of shape can be attributed to the configuration of atomic on {100} face of diamond and the change of oxygen partial in molten salt during the etching process. When etch temperature up to 700°C, the edges direction of the preferentially formed square shape pit became an angle of 45°with the edges of later formed square shape pit which indicated that partial oxygen pressure can effect stability of diamond surface and etching direction.

Estimation of Spatially Dependent Heat Flux Transients during Quenching of Inconel Probe in Molten Salt Bath

Abstract Several industrial heat treatment processes, such as martempering and austempering, require a quench bath to be maintained at a temperature ranging between 150°C–600°C. Molten salts, molten alkali, and hot oils are the preferred quenchants for these processes. Molten salts and molten alkali are preferred over hot oil because they possess properties like wide operating temperature range, excellent thermal stability, and tolerance for contaminants. In the present work, the performance of a molten potassium nitrate (KNO3) quench bath was analyzed with an Inconel probe that measured 60 mm in height and 12.5 mm in diameter. The probe was heated to 850°C and subsequently quenched in a bath maintained at 450°C. Cooling curves at different locations of the probe were recorded using the K-type thermocouples inserted into the probe. Spatially dependent transient heat flux at the metal/quenchant interface was estimated using inverse heat conduction technique. The existence of two stages of quenching—boiling stage and convection stage—was confirmed by analyzing the heat flux. The heat transfer coefficient was calculated based on heat flux obtained by the inverse method. The nonuniformity in heat transfer along the length of the probe was quantified by calculating the range of surface temperatures at each instance. The hardness distribution in an AISI 4140 steel was predicted using the temperature distribution in the Inconel probe and obtained using inverse method. Uneven distribution of hardness predicted in the probe was attributed to the nonuniform cooling of the probe during quenching.

Can annealing improve the chemical strengthening of thin borosilicate glass?

In this work, we try to point out the influence of annealing prior to chemical strengthening on the mechanical strength of thin ion exchangeable alkali borosilicate glass. The effect of annealing at 425°C on density, hardness and cracking behaviour were investigated. Then, as-received and annealed samples were subjected to ion exchange in a molten potassium nitrate bath at the same temperature for 4h and the generation of compressive stress in glass was analyzed as well as the bending strength.Annealing makes the glass denser, improves hardness and enhances the compressive stress build-up. However, bending strength of as-received and annealed glass after ion-exchange is substantially the same, this being probably attributed to the limited case depth if compared to surface flaws. Annealing before ion exchange does not appear to be a crucial factor in improving chemical strengthening efficiency in thin borosilicate glass.

SQM will boost potassium nitrate

SQM will increase its potassium nitrate capacity by 50% to 1.5 million metric tons per year by mid-2018. The Chilean firm says it will build a 300,000-metric-ton-per-year plant in Pedro de Valdivia, Chile, that will react potassium and nitrate salts. The balance of the capacity increase will come from expansion of existing facilities. SQM says the new capacity will serve the specialty fertilizer market as well as operators of concentrated solar power plants, which use molten potassium nitrate and sodium nitrate to transfer and store heat.

Characterization of Micrometric and Localised Residual Stresses on Amorphous Materials Using Dispersion of Surface Acoustic Waves

For amorphous materials such as glass, the fragility of the material can be limited using surface reinforcement by chemical tempering. The principle of chemical tempering consists in forming a superficial compression layer on the surface by immersing the glass in a solution of molten potassium nitrate. In this study, dispersion of surface ultrasonic waves caused by the presence of residual surface stresses was studied. The thickness and the level of the stressed cortical zones were estimated using an inverse method.

Molten salt synthesis of potassium and barium niobates

The interaction of powdered niobium oxide with molten potassium and barium nitrate salts containing KOH was studied. It was shown that KNbO3 can be obtained with the use of binary mixtures of the KOH-KNO3 system. The BaNb2O6 compound can be synthesized in melts of the KNO3-Ba(NO3)2 system. The treatment of Nb2O5 with melts of the system KNO3-Ba(NO3)2-KOH with various KOH percentages allowed us to obtain mixtures of Ba5Nb4O15.33 with Nb12O29 or Ba5Nb4O15.48 with K0.8Ba0.2NbO3.

Catalytic Combustion of Soot on KNO3/ZrO2 Catalysts. Effect of Potassium Nitrate Loading on Activity

Co−KNO3−ZrO2 and Co−ZrO2 were prepared. The concentration effect of potassium nitrate on the activity was studied for the oxidation reaction of soot. Catalysts were characterized using the techniques BET, XRD, DSC, TPR, and SEM and the catalytic activity was measured in a microbalance. An important decrease of the combustion temperature of soot is observed in experiments carried out with zirconium oxide alone and also a significant enhancement of the catalytic combustion rate of soot on KNO3/ZrO2 catalysts. The activity increase can be attributed to the alkaline metal ion and also to the increase of the catalyst/soot contact by the molten potassium nitrate.

Oxidative etching of cleaved synthetic diamond {1 1 1} surfaces

In this study, three commonly used methods for oxidative etching of diamond {1 1 1} faces are compared: gas phase etching using `dry' oxygen, gas phase etching using an oxygen/water vapour mixture and liquid etching in molten potassium nitrate. The synthetic diamond surfaces are prepared by cleavage. The morphology of the surfaces is studied using atomic force microscopy and the kinetics of the reactions is determined by measuring the decrease in thickness of the diamond. The atomic arrangement of the {1 1 1} surfaces etched in oxygen/water is studied using surface X-ray diffraction. Upon dry oxygen etching, the {1 1 1} faces are roughened and become morphologically unstable. This observation conflicts with standard theory, which predicts {1 1 1} to be a stable F-face that should etch via a layer mechanism. A possible explanation for this is chemical roughening. The addition of water vapour to the oxygen has a dramatic effect on the etching mechanism of the {1 1 1} faces. Now etching proceeds via a layer mechanism involving monoatomic steps. Shallow etch pits are formed, of which the slope increases for increasing etching temperature. Surface X-ray diffraction experiments show that the surface is –OH terminated. For potassium nitrate etching, the {1 1 1} face etches also via a layer mechanism and triangular etch pits with rounded corners are formed, having point or flat bottoms. This etching technique appears to be the best method to reveal different types of defects ending on diamond {1 1 1} surfaces.

Oxidative etching of diamond

Three different ways are used to etch diamond {001} and {111} faces by oxidative methods: gas phase etching in dry oxygen, gas phase etching in a mixture of oxygen and water vapour, and liquid etching in molten potassium nitrate. The surface topography of the etched surfaces is compared with the theoretically predicted morphology. It appears that in most cases the experimental results are in contradiction to theory. These discrepancies are explained by the reactions between the diamond surfaces and the adsorbed oxygen, which are able either to stabilise or to destabilise the surfaces. Of these three methods, etching in molten potassium nitrate was found to be the best for revealing dislocations.

Occlusion of KNO 3 and NH 4NO 3 in natural zeolites

The capacity of natural zeolites to occlude ammonium nitrate and potassium nitrate by molten salt treatment has been determined, and the salt-occluded zeolites have been characterized. Molten salt treatment resulted in changes of overall and relative intensities of peaks in X-ray diffractograms of zeolites. The presence of occluded salt in zeolites was confirmed by a i.r. absorption band around 1,390 cm 1 , exothermic response at 280°C in DTA curve, and type-III nitrogen adsorption/desorption isotherms showing type-H3 hysteresis. The occluded nitrate contents of natural zeolites increased in the following order: erionite > clinoptilolite > chabazite > phillipsite with molten potassium nitrate treatment, and phillipsite > erionite ⩾ chabazite > clinoptilolite with molten ammonium nitrate treatment. The present study shows that the capacity of natural zeolites to store nutrients can be increased by salt occlusion and that these occluded zeolites are potential candidates as slow-release fertilizers.

Decomposition of Some Skarn-Rock Samples in Neutral and Basic Molten Potassium Nitrate for the Extraction and Determination of Iron

Five skarn -rock samples were heated with KNO3 and with a solution of 5% KOH in KNO3 for 2 h at 450°C. The decomposed samples were cooled, dissolved in water and filtered. Iron was extracted from each residue as well as from the original samples by hot conc. HCl , and determined by atomic absorption spectroscopy. These results were compared with the known (X-ray fluorescence) total iron content of the original samples. The amount of iron extracted with HCl from the skarn samples was 3-11% lower, while that extracted after heating with KNO3 alone was 2-4% lower, than the amount present according to the X-ray fluorescence results. However, the amount of iron extracted from the samples treated with a solution of KOH in KNO3 was comparable to that determined by X-ray fluorescence.

Measurement of emittance of metal interface in molten salt

A new technique for measuring the total normal emittance of a metal in a semi-transparent liquid has been proposed and this technique has been applied to measure the emittance of stainless steel (SUS304), nickel, and gold in molten potassium nitrate KNO3. These emittance data are indispensable to analyzing the radiative heat transfer between a metal and a semitransparent liquid, such as a molten salt.

Integrated optical passive ring resonator for optical gyroscopes

A passive ring resonator based on channel waveguides, formed in a K8 glass substrate by diffusion ion exchange in molten potassium nitrate, was made and investigated. The waveguide structure of the resonator included a ring waveguide as well as two Y-type couplers, whose symmetric arms were coupled to the ring waveguide, whereas homogeneous arms were coupled to an external laser and a photodetector. The coupling of the external devices to the channel waveguides was implemented by prisms and butt (end face) contacts. The transfer function of the ring resonator was determined experimentally in order to illustrate its resonant properties and sharpness. Estimates were obtained of the ultimate sensitivity of an optical gyroscope utilizing a ring resonator with the properties described above and ways of improving this sensitivity were analyzed.

Electrochemical behaviour of nickel electrodes in molten potassium nitrate with increased basicity

The electrochemical behaviour of Ni electrodes in a KNO 3 melt in the 350–400°C temperature range has been studied, using the cyclic voltammetry method. The occurence of an anodic double-peak is attributed to some ionic species of nickelite (NiO 2− 2) and nickelate (NiO − 2) type, of a very different electrochemical stability. The decrease of the KNO 3 local basicity, in the presence of Na + and NO − 2 ions, leads to the disappearance of the anodic double peak. The influence of scan rate and temeprature on the anodic branch of the cyclovoltammograms is also discussed.

Stress Buildup and Relaxation During Ion Exchange Strengthening of Glass

A soda‐lime‐silica glass was subjected to an ordinary ion exchange treatment in molten potassium nitrate at temperatures near and substantially below the strain point of the glass. Stress profiles were measured as a function of exchange temperature and time. At all temperatures, the measurements showed rapid relaxation of the surface stress and the development of a pronounced compression maximum in a short period. A simple viscoelastic model with composition‐independent parameters was used to analyze the stress profiles. Neither Maxwell's nor Michelson's relaxation expression could satisfy both characteristics of the residual stress development. Reasons for discrepancies are discussed.

Determination of Ultrasonic Absorption and Velocity and the Derived Thermodynamic Properties of Pure and Binary Molten Salts

The absorption and velocity of ultrasonic waves in molten salts are studied with an improved pulse method, which allows an exact and immediate measurement of the runtime of the impulses and of the amplitude of the recorded signals. The measurements are performed in the pure molten salts sodium nitrate, potassium nitrate, and silver nitrate as well as in the three binary mixtures of these salts in the temperature range between 430 K and 620 K at various compositions. All values are measured at 27.789 MHz, the resonance frequency of the quartz transducers being used. From the ultrasonic velocity, together with the expansion coefficient and the specific heat capacity, the adiabatic compressibility, the adiabactic constant, and the Rao's constant have been calculated. From the ultrasonic absorption and velocity results the volume viscosity, which can be referred to the structural relaxation of the molecules in the fused salts investigated here.