Silicon Phosphate Research Articles

Sol-gel derived silicate-phosphate glass SiO2–P2O5–CaO–TiO2: The effect of titanium isopropoxide on porosity and thermomechanical stability

Despite of several decades lasting extensive research of bioactive and bioresorbable glasses the systematic parametrization and determination of the key factors affecting porosity and thermomechanical characteristics still remains challenging. Here, we present silica-phosphate glasses, with the composition 70SiO2–20P2O5–(10-x)CaO–xTiO2 (mol%; x = 0, 2.5, 5, and 7.5), prepared by sol-gel method and reinforced by titanium dioxide via titanium isopropoxide (TTIP) incorporation which demonstrated tunable variation of porosity from micro-to macro-region and superb mechanical integrity during the calcination process. The presence of 7.5 mol% TiO2 promotes dimensional stability up to 1000 °C as investigated by thermomechanical analysis. The XRD showed the dominant presence of silicon phosphate [Si(P2O7)], titanium phosphate [Ti(P2O7)] and calcium phosphates [β-Ca(P2O6) and γ- Ca2(P2O7)]. The effect of TiO2 doping on the multiscale morphology and porosity was investigated by means of SEM, MIP, μCT, N2 adsorption and USAXS/SAXS. Increasing TiO2 content leads to the formation of open porosity up to 70 vol% and drives the formation of a refined interconnected macroporosity of 2–30 μm. In contrast, mesoporosity with a dominance of 3–6 nm pores decreases in all samples with increasing TiO2 content. USAXS/SAXS revealed an increase in primary particle size with increasing TiO2 content which is in good agreement with the nitrogen physisorption analysis showing that microporosity decreases with increasing TiO2 content.

All-solid integratable device of electric field control of magnetism based on hydrogen ion migration in La1−xSrxMnO3

Field-effect transistors based on semiconductor integration technology have come to a bottleneck, while electric field control of magnetism has great potential for applications in next-generation magnetic memory and calculators based on electron spins. Magnetic properties manipulation from a mechanism of ion migration driven by an electric field has the advantages of low energy consumption, nonvolatility, reproducibility, and durability. Here, we introduce a solid-state integratable hydrogen ion storage electrolyte silicon phosphate as the gate to achieve reversible control of magnetoresistance, magnetism, and magnetic interaction in the La1−xSrxMnO3/SrTiO3 ferromagnetic system. The controllable double-exchange interaction and spin scattering mechanism sketch the theoretical physical picture for these results. This work is expected to open up additional opportunities in the translation of electric control of magnetism into practical applications.

Synthesis of a waterproof geopolymer adhesive applied in DUV LEDs packaging

This paper presents the synthesis of a waterproof geopolymer based on the modification of silicon phosphate (Si3(PO4)4) that adheres to alumina and quartz glass substrate, which can replace traditional organic polymers for packaging deep-ultraviolet light-emitting diodes. The waterproof property of geopolymer strongly depends on the Si3(PO4)4 loading amount due to its hydrolysate H+ substitutes Na+, which is vulnerable to water. FESEM and microhardness results show that aging by 85°C/85% relative humidity for 100 h, the optimal waterproof geopolymer adhesive is successfully synthesized when the mass ratio of metakaolin, water glass, and Si3(PO4)4 is equal to 0.48: 1: 0.08 respectively, and the corresponding adhesion strength of 6.41 MPa to alumina substrate is achieved after the reliability testing. The rheological properties show that the optimal waterproof geopolymer adhesive, with shear thinning behavior and good thixotropy, is suitable for processing while holding the original shape.

Fire behaviour of EPDM/NBR panels with paraffin for thermal energy storage applications. Part 2: Analysis of the combustion residues

In the first part of this work, novel elastomeric panels with paraffin for thermal energy storage applications were developed. Ethylene-Propylene Diene Monomer (EPDM) rubber filled with a shape-stabilized paraffin, as phase change material with a melting temperature of 28 °C, was covered with a nitrile-butadiene rubber (NBR) envelope. In order to improve the fire resistance, two selected flame retardants (FRs) were dispersed both in the EPDM core and in the NBR envelope. In this work, the combustion residues from cone calorimeter tests were analysed by various techniques to explain the combustion mechanisms and the interaction of FRs. Nuclear magnetic resonance (NMR) evidenced the complexity of the system, characterized by the formation of char, by the reactivity of organomodified montmorillonite (oMMT) in presence of phosphates and structural rearrangements of the inorganic components. The use of a flame retardant based on ammonium polyphosphate and synergistic agents (based on phosphorus) led to formation of different Al-O-P and Si-O-P compounds. The X-ray diffraction (XRD) analysis highlighted that the formation of silicon phosphate, from the reaction of ammonium polyphosphate and oMMT, was possible only at high phosphorus contents. From the phosphorus content detected through energy dispersive X-ray spectroscopy (EDX) it was possible to indicate that the phosphorus remained in the condensed phase during the combustion.

Thermal stability, pore structure characteristics of char layer and ablation resistance mechanism of new thermal insulation composites based on polyphosphazene polymer

Polyphosphazene (PDPP) composites have emerged as a hot research topic in the field of low-density composite insulation materials because of their good thermal stability and flame retardancy. In this study, the ablative properties and mechanism of PDPP composites reinforced by fiber and functional fillers are studied. The test results show that PDPP composites have good thermal stability and oxidation resistance. The results of the oxyacetylene ablation test show that PDPP composites has strong ablation resistance, and its char layer has high structural strength, as well as high bonding strength with the material matrix. However, the thermal insulation performance of PDPP composites is weak. Based on the physical and chemical analysis of the composite material and the char layer, it is concluded that the excellent ablation resistance is mainly due to the high strength of the char layer, which bnefits from high char yield of polyphosphazene polymer and the formation of silicon phosphate. However, the high thermal conductivity of composite and char layer lead to poor thermal insulation performance.

The effects of aluminum and silicon phosphates on thermal stability and flammability of polystyrene

The effects of aluminum and silicon phosphates on thermal stability and flammability of polystyrene

Acrylic‐based fire‐retardant coatings for steel protection: Employing the concept of in situ ceramization

AbstractTraditional intumescent coatings are widely used as passive fire‐protective coatings for steel structures as they are capable of expanding in the range of 20–50 times the original thickness thereby providing excellent insulation. However, the fragile nature of such residue and susceptibility to thermo‐oxidation given their carbonaceous nature are key problematic issues. The concept of in situ ceramization is explored in this work as a means to form inorganic cohesive char with improved rigidity and thermo‐oxidative stability. Coating samples were prepared by incorporating ammonium polyphosphate, talc, Mg(OH)2, and polydimethylsiloxane as additives into acrylic resin at different weight fractions. Thermal analysis and x‐ray diffraction have confirmed the reactions between the additives to form various crystalline magnesium phosphate phases, and to a small extent, silicon phosphate, thereby ensuring the thermo‐oxidative stability of the residue. This is reiterated by the fire performance tests (by exposing the coatings to a temperature profile in a furnace similar to ISO 834 fire curve). Despite the advantages of rigid char and its thermo‐oxidative stability as a result of formation of inorganic phosphates, the lack of swelling has resulted in relatively poor insulation capabilities of the char, and subsequently, compromised the fire protection times (that are in the range of 45–55 min). However, pyrolysis flow combustion calorimeter results of the coatings are promising and have shown a significant drop of up to 70% in the peak of heat release rate values as compared to neat resin.

From blue to cyan emission: Ce3+ and Tb3+ co-doped silicon phosphate phosphors with high thermal stability.

A series of Ca15(PO4)2(SiO4)6:xCe3+,yTb3+ phosphors have been prepared by a high-temperature solid-state reaction. Under the excitation of near-UV with 371 nm wavelength, Ca15(PO4)2(SiO4)6:xCe3+ phosphors exhibit strong blue emission with a broad peak at 432 nm. Based on the photoluminescence of Ca15(PO4)2(SiO4)6:xCe3+ phosphors, the coordination environment around Ce3+ ions and the concentration quenching mechanism are inferred. With the doping of Tb3+ ions into Ca15(PO4)2(SiO4)6:1.33%Ce3+, the luminescence color from blue to cyan can be well tuned. By measuring the luminescence intensity and lifetime of the as-prepared phosphors, it can be judged that there exists an energy transfer from Ce3+ to Tb3+. To achieve white light, the optimal Ca15(PO4)2(SiO4)6:1.33%Ce3+, 9%Tb3+ phosphors are mixed with commercial SrAlSiN3:Eu2+ powders and finally warm white light emission could be obtained. The results show that Ca15(PO4)2(SiO4)6:xCe3+,yTb3+ phosphors have potential applications in warm white light-emitting diodes.

Highly active Brønsted acidic silicon phosphate catalyst for direct conversion of glucose to levulinic acid in MIBK–water biphasic system

Due to depletion of fossil fuel reserves and environmental concerns demand the utilization of other renewable feedstocks such as biomass which is available abundantly in different quantities throughout the world. Catalytic transformation of this biomass or biomass-derived products such as glucose to valuable platform biochemicals viz: levulinic acid (LA) is academically as well as industrially important reaction. In the present work, Silicon phosphates (SixPO4) catalysts viz: Si10PO4, Si20PO4, Si30PO4, and Si40PO4 having solely Bronsted acidic properties were prepared by wet impregnation of H3PO4 (10–40 wt%) on fumed silica followed by calcination at 550 °C for 10 h. The prepared catalysts were characterized by various techniques such as XRD; NH3-TPD; FTIR etc. Formation of silicon phosphate structure was found to depend on % of P loading and its interaction with silica. The acidic property of SixPO4 catalyst was characterized by NH3-TPD and Pyridine-IR, confirmed that catalyst has exclusively strong Bronsted acidity. A high LA yield of 81 mol% over Si30PO4 has achieved at an optimized reaction condition of 140 °C; 10 h in MIBK–water (9:1) biphasic system.

Preliminary investigation of the hydration mechanism of MgO-SiO2-K2HPO4 cement

Different from making ordinary magnesium phosphate cements (MPCs) with potassium dihydrogen phosphate (KH2PO4, PDP), magnesium oxide (MgO, M) and borate as retarder, a novel high-strength Magnesium Silicon Potassium Phosphate Cement (MSPPC) created by mixing dipotassium hydrogen phosphate (K2HPO4, DHP (P)), silica fume (SF), MgO and Water (W), without the use of a retarder, is proposed for the first time in this study. The mechanical properties of several MSPPC mixtures prepared with different proportions of P/M (weight ratio of K2HPO4 to MgO), W/C (weight ratio of water to cement paste (C = P + M + SF)) and mass fraction of silica fume were investigated. The hydration reaction mechanism of MgO-SiO2-K2HPO4 system was analyzed with a variety of techniques including pH, X-ray diffraction (XRD), environmental scanning electron microscope-energy dispersive spectrometer (ESEM-EDS) and thermo-gravimetric and differential scanning calorimeter (TG-DSC). The results show that the cement paste with P/M of 1/3, 15 wt% SF and W/C ratio of 0.16, the compressive strength was measured to be 113.16 MPa. The maximum flexural and compressive strength of MgO-SiO2-K2HPO4 system is 16.82 MPa and 101.26 MPa respectively, which is higher than those of MgO-K2HPO4 system. In MgO-K2HPO4 system, the reaction generates a large amount of Mg(OH)2 with poor gelation and expansion, and a small amount of hydration product MgKPO4·6H2O (MKP) with low internal crystallinity, so the structural strength is very low. Inversely, in MgO-SiO2-K2HPO4 system, silica fume plays an important role, and the active silicon components in silica fume are fully involved in the acid-base reaction, improving the mechanical properties and compactness of microstructure of MSPPC. Main hydration product struvite-K has good crystallization, compact accumulation, high density of cross-section structure and good structural integrity of MSPPC. Expected secondary hydration products are magnesium silicate gel (e.g., MgSiO3) and amorphous silicon phosphate phases, contributing to the strength in MSPPC pastes.

Structural, conductive and dielectric properties of silicon phosphate SiP2O7 synthesis from activated clay

The purpose of this study is the manufacture of SiP2O7 powder, using low-cost material, namely, phosphoric acid and activated metakaolin (AMK).The mineralogical characterization by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analysis showed that SiP2O7 has a well-crystalline structure. The conductivity and dielectric behavior have been studied over a frequency range from 40 Hz to 5 × 106 Hz and at temperatures ranging from 20 °C to 300 °C. The results indicate that the SiP2O7 synthesized by activated metakaolin have a high ionic electrical conductivity of 2.96 × 10−6 Scm−1 at room temperature, which increases to 8.8 × 10−3 Scm−1 at 300 °C. Furthermore, the powder exhibited a high dielectric constant (120 × 105) and loss factor (350 × 105) at 300 °C, which both decreased with increasing frequency. The imaginary electric modulus (M") showed that the dielectric relaxation time (τ) varies nearly linearly with temperature.

Effect of silica fume and basalt fiber on the mechanical properties and microstructure of magnesium phosphate cement (MPC) mortar

This paper evaluates the effect of silica fume (SF) and basalt fibers (BF) on the mechanical properties and microstructure of magnesium phosphate cement (MPC) mortar. Several MPC mortar mixtures with different contents of SF and BF were prepared. Experimental results revealed that the compressive strength and flexural strength of MPC mortar was increased by increasing the percentages of SF from 0% to 10%. Incorporation of BF improved the flexural strength and post-peak flexural behaviour of the load-deflection curve of MPC mortars, but its effect on the compressive strength was insignificant. MPC matrix with 10%SF and 0.5%BF demonstrated the highest compressive and flexural strength of 49.42 MPa and 5.31 MPa respectively at the 28 days. XRD and SEM analysis showed that control mixture without SF and BF contained more unreacted magnesia and struvite as compared to MPC mortars containing SF and BF. Moreover, SEM-EDS analysis of MPC mixtures incorporating SF and BF showed that SF and fly ash (FA) reacted within the MPC paste system to produce the secondary hydration products. It was postulated that magnesium silicate, aluminium or silicon phosphate phases were formed during the reaction of SF and FA in the MPC system. These secondary products tend to improve the bonding of solid phase and hence mechanical properties of MPC mortar. Finally, SEM-EDS analysis also confirmed the excellent interaction of BF with the MPC hydration products.

Benign design and the evaluation of pyrolysis kinetics of polyester resin based intumescent system comprising of alkali-activated silica fume

Novel polyester resin based intumesced flame retardant (IFR) coating was fabricated via a facile sol-gel method, which was modified by the Na2SiO3 alkali-activated silica fume. The emphasis was placed on its flame retardancy and pyrolysis kinetics, it focused on benign design and in-depth research on the flame retarding mechanisms of the inorganic-organic hybrid coating. The results demonstrated that the specimen doped alkali-activated silica fume (2 wt%) exhibited the highest flame retardant efficiency through cone calorimeter (CC) test, evidenced by the peak heat release rate (p-HRR) value of 128 kW m−2 (decreased by 42.1% compared with the sample without silica fume). Pyrolysis kinetics calculated using modified Coats-Redfern integral method determined that the D3 diffusion model governed the pyrolysis process, due to the formation of silicon phosphate and sodium silicate, as well as the continuous protecting layer, leading to an increase in the value of Ea during 112–251 °C. It established that the incorporation of appropriate Na2SiO3 activated silica fume in polyester resin based IFR was conducive to benign design of inorganic-organic hybrid coating.

Compatibility and bone bonding efficiency of gamma irradiated Hench's Bioglass-Ceramics

Samples of Hench's bioglass-ceramic derived from thermal heat treatment of parent Hench's bioglass of the normal composition (45SiO2−24.5Na2O-24.5CaO-6P2O5 wt%) were prepared. Combined collective characterization of the effects of both gamma irradiation with varying doses (1→10Mrad) and immersion times in SBF (1→4 weeks) through specific analytical techniques including FTIR, X-Ray diffraction and SEM investigations. The overall extended studies are focused on justifying the bone-bonding efficiency with the interference of both X-Ray diffraction and immersion times. Experimental data indicate the stability of FTIR spectra upon the increase of gamma irradiation but prolonged immersion times cause distinct variations which touch the vibrational bands in consequence to the ion exchange or preferential attack and replacement of modifiers by hydronium ions leading to the surface silica gel layer from the SBF and the final formation of hydroxyapatite as an indicator for bone-bonding ability. The FTIR spectra show some variations as visualized from the IR spectra of the only un-irradiated samples and that for irradiated samples upon prolonged immersion. X-ray diffraction patterns are found to change by gamma irradiation dose and/or immersion time in SBF. Hydroxyapatite and silicon phosphate crystalline phases are identified to be formed upon gamma irradiation alone or with combined immersion and gamma irradiation beside the formation of crystalline sodium calcium silicate phase formed with both the un-irradiated and un-immersed samples.

Studies of Bone-Bonding Ability and Antibacterial Properties of Ag+, Cu2+ or Zn2+ ions Doping within Hench’s Bioglass and Glass-Ceramic Derivatives

Derived Hench’s bioglasses with specific ionic dopants Ag+, Cu2+, or Zn2+ have been prepared. The bone-boding ability or bioactivity behavior for the prepared glasses and their glass-ceramic derivatives has been investigated after immersion in phosphate solution for two weeks. Collective Fourier transform infrared absorption spectra (FTIR) and scanning electron microscopic (SEM) studies were conducted in order to study the in-vitro bioactivity behavior. X-ray diffraction (XRD) analysis was carried out to identify the crystallized phases upon thermal heat treatment through a two-step regime. The glasses and their glass-ceramic derivatives were tested to study their antibacterial or antifungal efficiency responding to the doped metal ions. FTIR spectra revealed the generation of two split peaks at about 560 and 605 cm−1, after immersion in (0.2 M) sodium phosphate solution (Na3PO4), signifying the formation of a crystalline calcium phosphate phase, leading to hydroxyapatite formation. SEM examinations show characteristic rounded or nodular microcrystals for hydroxyapatite which support the FTIR data. X-ray diffraction analysis indicated crystallization of the main soda-lime silicate phase (1Na2O.2CaO.3SiO2) besides a secondary silicon phosphate phase (SiO2.P2O5) in the studied glass ceramics. The route of crystallization is discussed on the basis of the presence of 6% P2O5; which facilitates the formation of phase separation and voluminous bulk crystallization of the main soda-lime silicate phase. The introduction of dopants is identified to cause no changes in the precipitated phases, with only minor changes in the percent of the crystalline phases. Experimental data indicate that the glass-ceramic samples are effective in bioactivity and antimicrobial efficiency.

Mechanically robust, humidity-resistant, thermally stable high performance antireflective thin films with reinforcing silicon phosphate centers

High performance, function durability, thermal stability and mechanical robustness have long been pursued for advanced antireflective thin films. In the current work, we developed a novel and effective approach to fabricate mechanically robust, humidity-resistant, thermally stable high-performance antireflective thin films with reinforcing silicon phosphate centers from an acid-catalyzed hybrid silica sol. The thin film has a hierarchically nanoporous structure, resulting in favorable antireflective properties. After being coated with the antireflective thin film, the maximum and average transmittances of K9 glass increase from 92.1% and 92.0% (400–800nm) to 99.7% and 98.8% (400–800nm), respectively. In addition, the thin film shows favorable humidity-resistance and heat-resistance, and these extraordinary performances are attributed to its rich heat-resistant and hydrophobic groups. Moreover, mechanical strength measurements indicate the thin film has extraordinary 5H pencil hardness and 5A adhesion to substrate because of the formation of silicon phosphate centers in the thin film, which significantly reinforce the thin film. These high-performance antireflective thin films are promising in solar energy utilization, especially in solar cells.

Thermal and pyrolysis analysis of minerals reinforced intumescent fire retardant coating

Abstract This study presents the results of intumescent fire retardant coatings (IFRCs) developed to investigate the synergistic effects of mineral fillers (clay and wollastonite) based IFRC towards heat shielding, char expansion, morphology, composition, gaseous products and residual weight. The fire test has been performed to study the heat shielding effect of IFRCs on the substrate using UL-1709 standards. The results showed the synergistic effect of clay and wollastonite using 5 wt.% enhanced the fire protection, performance with recorded substrate temperature 113 °C after 1-h fire test. Field Emission Scanning Electron Microscopy (FESEM) and High-Resolution Transmission Electron Microscopy (HRTEM) showed the micrograph of compact char structure that increased char integrity due to the presence of inorganic fillers. X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) results showed the presence of boron phosphate, silicon phosphate oxide, aluminum borate in char that improved the thermal performance of IFRC up to 800 °C. X-Ray Photoelectron Spectroscopy (XPS) confirmed that 5 wt% (IFRC-5) of clay and wollastonite increased the carbon content up to 50.67%, lowering oxygen content to 27.73% in the char that enriched the fire resistance performance of the coating. Pyrolysis-Gas Chromatography-Mass Spectrometry (Pyrolysis GC–MS) confirmed that formulations IFRC-5 released less gaseous product concentration compared to IFRC-C and maximum reduction in gases was recorded from 3.4e +07 to 1.08e +07 . Thermogravimetric analysis (TGA) demonstrated in residual weight was increased to 46.45% for IFRC-5 which resulted in the high thermal stability of the coating.

Influence of modified mesoporous silica SBA‐15 on the flammability of intumescent high‐density polyethylene

This work aims to investigate the fire retardant properties of a novel type of high‐density polyethylene composites. Our intumescent system consists in using classical flame retardants such as ammonium polyphosphate, pentaerythritol in combination with porous mesostructured silica (SBA‐15) fillers. Prior to use, SBA‐15 was chemically modified using different organic and inorganic grafts in order to obtain some specific properties, such as an improved compatibility with the polymer, or different types of surface acidity in order to increase charring reactions. Limiting oxygen index, UL‐94, pyrolysis flow combustion calorimetry and thermogravimetric analysis were used to assess the burning behavior and thermal stability, respectively, of the processed composites. By keeping the total amount of additives always equal to 25 wt%, the better flammability characteristics were in general obtained at low SBA‐15 loadings (<2 wt%). X‐ray diffraction and Fourier transform infrared spectroscopy analyses of the residues showed that the formation of a barrier mainly constituted by crystalline silicon phosphates is probably a key to enhance the fire properties. Further slight improvements brought by the surface modification of SBA‐15 nanofillers are discussed according to type of incorporated particles. Copyright © 2016 John Wiley & Sons, Ltd.

Preparation of SiO<sub>2</sub>-Na<sub>2</sub>O-CaO-P<sub>2</sub>O<sub>5</sub> Glass-Ceramic from Waste Materials and Heat Treatment Effects on its Morphology

Currently, many researchers interested studying waste materials to recycle them or reuse them in new products. From the sustainable perspective development, it is necessary to implement new technologies to help reduce waste and thus minimize the environmental problems associated with disposal. In this study, the preparation of SiO2-Na2O-CaO-P2O5 (SNCP) glass-ceramic is composed of Soda Lime Silicate (SLS), Clam Shell (CS), Na2CO3 and P2O5 in the ratio of 50: 25: 20: 5 respectively. The waste materials that were used for fabricate glass-ceramic are SLS and CS. All the compounds were mixed to fabricate the SNCP glass-ceramic through solid state reaction. The samples were investigated through X-ray diffraction (XRD), field emission microscope (FESEM) and density measurement. The samples were sintered at temperature 550°C, 650°C, 750°C, 850°C until 950°C. The main phase obtained from XRD analysis is Sodium Calcium Silicate, Na2CaSiO4 with cubic crystal system at 550°C. The highest intensity phase of the diffraction peak is (220) and at the angle 33.7°. There was new peak presence at right side of the main phase Na2CaSiO4, which belong to Silicon Phosphate, SiP2O7 at 650°C and 750°C.When heat treatment increased at 850°C - 950°C, the main phase is Combeite, Na4Ca4(Si6O18) at diffraction peak (220) with rhombohedral crystal system which is assigned to high crystallization temperature (Tc). The density of samples increases at 550°C - 750°C and decreases when heat treatment 850°C - 950°C. Sample density decreases at heat treatment 850°C - 950°C due to increases of sample lattice parameter. FESEM analysis showed that the grain size and porosity increased when the heat treatment increased.

A novel solid phosphoric acid from rice hull ash for olefinic alkylation of thiophenic sulfur in gasoline

ABSTRACT A novel solid phosphoric acid (SPA) was prepared from rice hull ash by impregnation with phosphoric acid and followed by calcination. The characterization results reveal that the solid phosphoric acid exhibits high surface area (335 m 2 /g) and acid densities (1.25 mmol/g) compared with commercial SPA catalyst. It was also clearly confirmed that silicon phosphate and silicon pyrophosphate were formed by the reaction of silica with phosphoric acid during the calcination process. The OATS catalytic performance results indicate that the solid phosphoric acid shows very good activity for thiophene alkylation reaction. This research provided a promising way to synthesis high active solid phosphoric acid for OATS desulfurization application.