Thermal Decomposition Of Ammonium Perchlorate Research Articles

Design, preparation, and combustion performance of energetic catalysts based on transition metal ions (Cu2+, Co2+, Fe2+) and 3-aminofurazan-4-carboxylic acid.

Development of energetic catalysts with high energy density and strong catalytic activity has become the focus and frontier of research, which is expected to improve the combustion performance and ballistic properties of solid propellants. In this work, three energetic catalysts, M(H2O)4(AFCA)2·H2O (AFCA = 3-aminofurazan-4-carboxylic acid, M = Cu, Co, Fe), are designed and synthesized based on the coordination reaction of transition metal ions and the energetic ligand. The target products are characterized by single crystal X-ray diffraction, Fourier transform infrared spectroscopy, differential thermal analysis, optical microscopy, and scanning electron microscopy. The results reveal that Cu(H2O)4(AFCA)2·H2O crystallizes in the monoclinic space group, Dc = 1.918 g cm-3. Co(H2O)4(AFCA)2·H2O, and Fe(H2O)4(AFCA)2·H2O belong to orthorhombic space groups, their density is 1.886 g cm-3 and 1.856 g cm-3, respectively. In addition, the designed catalysts show higher catalytic activity than some reported catalysts such as Co(en)(H2BTI)2]2·en (H3BTI = 4,5-bis(1H-tetrazol-5-yl)-1H-imida-zole), Co-AzT (H2AzT = 5,5'-azotetrazole-1,1'-diol), and [Pb(BTF)(H2O)2]n (BTF = 4,4'-oxybis [3,3'-(1-hydroxy-tetrazolyl)]furazan) for the thermal decomposition of ammonium perchlorate (AP). The high-temperature decomposition peak temperatures of AP/Cu(H2O)4(AFCA)2·H2O, AP/Co(H2O)4(AFCA)2·H2O, and AP/Fe(H2O)4 (AFCA)2·H2O are decreased by 120.3 °C, 151.8 °C and 89.5 °C compared to the case of pure AP, while the heat release of them are increased by 768.8 J g-1, 780.5 J g-1, 750.9 J g-1, respectively. Moreover, the burning rates of solid propellants composed of AP/Cu(AFCA)2(H2O)4·H2O, AP/Co(AFCA)2(H2O)4·H2O and AP/Fe(AFCA)2(H2O)4·H2O are increased by 2.16 mm s-1, 2.53 mm s-1, and 1.57 mm s-1 compared with the case of pure AP. This research shows considerable application prospects in improving the combustion and energy performance of solid propellants, it is also a reference for the design and preparation of other novel energetic catalysts.

ZIF-8 derived ZnO: a facile catalyst for ammonium perchlorate thermal decomposition

ZIF-8-derived porous ZnO is a facile, low-cost and environmentally benign catalyst with exceptional catalytic efficiency for ammonium perchlorate thermal decomposition at minimal catalyst usage.

A strategy for modulating the catalytic active center of AP thermal decomposition and its application: La-doped MgCo2O4

La diffuses into the main lattice of MgCo2O4 (Lax-MgCo2O4), exposing more Co3+ active centers: (1) La3+, O2−, high Co3+ concentration, high conductivity promote AP decomposition. (2) The highly active Lax-MgCo2O4 becomes potential catalyst for CSPs.

Enhanced Catalytic Effect of Ti2CTx-MXene on Thermal Decomposition Behavior of Ammonium Perchlorate.

Transition metal carbonitrides (MXenes) are promising catalysts due to their special structures. Recently, many studies have shown that MXenes have a catalytic effect on the thermal decomposition of ammonium perchlorate (AP). However, the catalytic effects have not been extensively investigated. Therefore, it is important to illustrate the catalytic mechanisms of pure MXene in AP thermal decomposition. Herein, the catalytic properties of Ti2CTx for ammonium perchlorate (AP) thermal decomposition were investigated by numerous catalytic experiments. The results showed that the high-temperature decomposition (HTD) decreased by 83 °C, and the decomposition heat of AP mixed with Ti2CTx increased by 1897.3 J/g. Moreover, the mass spectrum (MS) data showed that the NH3, H2O, O2, N2O, NO, HCl, and NO2 were formed. In addition, according to the X-ray diffraction (XRD), Raman spectrum, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and X-ray photoelectron spectra (XPS) results, the Ti2CTx nanosheets can adsorb the gaseous products and react with them in-situ, generating anatase-TiO2 and carbon layers. The Ti2CTx, as-resulted anatase-TiO2, and carbon can synergize and further catalyze the thermal decomposition of AP when both electron and proton transfers are accelerated during AP decomposition.

Effect of fluorine-containing thermite coated with potassium perchlorate on the thermal decomposition behavior and kinetics of ammonium perchlorate

In the last decade, the decomposition of ammonium perchlorate (AP) has been a major research topic, which is extensively studied by the scientific community. The present work aims to understand the effect of nanothermite on AP thermal decomposition. MgAl-PTFE nanothermite mechanically activated by arrested reactive milling was coated with potassium perchlorate (KP) and characterized. The obtained results revealed that the characteristic XRD signals of phase compositions remain unchanged, indicating that the ball-milling and chemical synthesis processes do not damage the chemical structure of the main components. The SEM micrographs showed that MgAl was uniformly distributed within the PTFE matrix. To assess the decomposition kinetics and understand the catalytic effect of the prepared MgAl-PTFE and MgAl-PTFE@KP on the thermal behavior of AP, DSC analyses were performed. It is demonstrated that the activation energy decreases by about 6%, revealing that the presence of nanothermites promotes the thermal decomposition process of AP.

Preparation of ferrocene‐based Schiff base derivatives for the thermal decomposition of ammonium perchlorate

AbstractAmmonium perchlorate (AP) is a common oxidizer and accounts for over 60 wt% in composite solid propellants (CSPs). Ferrocene (Fc)‐based compounds have become one of the most widely used burning rate catalysts (BRCs) for AP decomposition due to their outstanding catalytic effect. To improve the anti‐migration ability of Fc‐based compounds during long‐time storage, seven Fc‐based Schiff base derivatives were synthesized. Their molecular structures were characterized by UV‐Vis, FT‐IR,1H NMR,19F NMR, ESI‐MS and EA. Meanwhile, their electrochemical behaviors and catalytic effects for AP decomposition were studied by CV and TG techniques. The results showed that these synthesized compounds had good catalytic effect, obviously reducing the thermal decomposition temperature of AP. Moreover, their anti‐migration properties were also investigated by the aging test of simulated propellant. The results showed that they had better anti‐migration ability than commercial BRCs (catocene,Cat). This study demonstrates that Fc‐based Schiff base compounds are possible BRCs for AP‐based propellant.

Dense, Three-Dimensional, Highly Absorbent, Graphene Oxide Aerogel Coating on ZnCo2O4/ZnO Particles Exerts a Synergistic Catalytic Effect for Ammonium Perchlorate Thermal Decomposition.

As a new type of carbon material, graphene oxide aerogel (GA) is widely used in catalysis due to its porous structure, high-efficiency adsorption, and superb conductivity. In this study, GA was prepared into a dense coating layer surrounding ZnCo2O4/ZnO particles to form a composite GA-ZnCo2O4/ZnO by means of a hydrothermal, blast drying, and vacuum-freeze-drying approach applied to catalyze the thermal decomposition of ammonium perchlorate (AP). The physicochemical properties of the obtained GA-ZnCo2O4/ZnO were characterized by different analytical methods. Scanning electron microscopy (SEM) analysis exhibited that GA is coated on the surface of ZnCo2O4/ZnO, forming a dense layer. Brunner Emmet Teller (BET) measurement results show that GA-ZnCo2O4/ZnO has a smooth macropore distribution curve and a larger specific surface area. Moreover, The catalytic effect investigation on AP with GA-ZnCo2O4/ZnO: the high temperature decomposition (HTD) peak temperature of AP in the presence of 5 wt % GA-ZnCo2O4/ZnO was reduced from 441 to 294 °C, and the exotherm of AP was expanded from 205 to 1275 J/g at a heating rate of 15 °C/min. Through the calculation, GA-ZnCo2O4/ZnO makes the activation energy and Gibbs free energy of the AP pyrolysis lower so that the reaction is easier to occur. Thermogravimetric-mass (TG-MS) spectrometry revealed that during thermal decomposition of AP, GA-ZnCo2O4/ZnO leveraged the synergistic catalysis of ZnCo2O4/ZnO and GA that boosted the flow of electrons from ClO4- to O2 and increased the absorption of the gas product to accelerate the AP pyrolysis. These results provided a facile strategy to prepare GA-based composite catalysts with extraordinary application prospects in the domain of solid propellants.

Fluorocarbon nanosheet@copper oxide microspheres: Simultaneous promotion the decomposition of ammonium perchlorate and ignition performance of aluminum

Carbon fluoride nanosheets modified by CuO/Cu2O microspheres (FCN@CuO/Cu2O) were prepared by a simple method and characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and thermogravimetry coupled with differential scanning calorimetry and mass spectroscopy. The catalytic effect of FCN@CuO/Cu2O on the thermal decomposition of ammonium perchlorate (AP) and the effect on the combustion performance of aluminum (Al) were studied. The combination of CuO/Cu2O microspheres and carbon fluoride nanosheets promoted the decomposition of AP and improved the ignition performance of Al. The decomposition temperature of AP was lower than that of pure AP after adding a small amount of FCN@CuO/Cu2O. The results also showed that FCN@CuO/Cu2O effectively eroded the alumina film on the Al particles. The ignition temperature of Al was reduced after adding FCN@CuO/Cu2O.

Synthesis of CuII and CdII Metal-Organic Frameworks Based on 4,5-Bis(1-hydroxytetrazol-5-yl)-1,2,3-triazole and Their Effects as the Catalyst in Ammonium Perchlorate Thermal Decomposition.

Two new three-dimensional (3D) energetic metal-organic frameworks (EMOFs), namely, [Cu(OBTT)(NC2H8)2]n (1) and [Cd3(OBTT)2(H2O)2]n·4H2O (2), where H3OBTT = 4,5-bis(1-hydroxytetrazol-5-yl)-1,2,3-triazole, were prepared, and their structures were characterized by single-crystal X-ray diffraction analysis, which revealed that the EMOFs feature a rigid 3D framework architecture. The possibility of these two EMOFs as potential catalysts for the thermal decomposition of ammonium perchlorate (AP) was investigated. The results show that they have significant catalytic activity, up to reducing the peak temperature of AP decomposition from 704.0 to 613.6 K and contracting the decomposition temperature range from 451 to 320 K, which is almost one-third less than the decomposition temperature range of pure AP. The Kissinger and Ozawa-Doyle methods were used to calculate the kinetic parameters of the thermal decomposition of pure and mixed AP samples. The experimental results suggest that compound 1 has potential applications in the field of explosives and propellants. All properties suggest that compound 1 can be used as a potential catalyst.

Polymeric Carbon Nitride/Iron Oxide Composites: A Novel Class of Catalysts with Reduced Metal Content for Ammonium Perchlorate Thermal Decomposition.

The ever-growing number of space launches triggering an enormous release of metallic dead weight into the atmosphere has become a global concern. Despite technological advancements, the inclusion of environmental concerns in space research has become the need of the hour. Here, we report the impact of iron oxide (Fe2O3)-doped polymeric carbon nitride (gCN) composites with varying metal contents (namely, GF1, GF2, and GF3 with iron contents of 0.1, 0.25, and 2 mmol, respectively) as a new class of catalysts for ammonium perchlorate (AP) thermolysis. Morphology studies revealed the dendritic morphology of the synthesized Fe2O3, and X-ray photoelectron spectroscopy (XPS) analysis confirmed the effective interaction between Fe2O3 and gCN in the composites. Among all of the synthesized composites, GF2 shows superior catalytic competence toward AP decomposition by amalgamating the double-stage decomposition process into a single stage followed by a considerable decrease in the decomposition temperature. The kinetic parameters calculated for the thermal decomposition of AP with and without catalysts using the KAS method substantiated the above results by significantly reducing the activation energy from 173.2 to 151.7 kJ/mol. Later, thermogravimetric and mass-spectrometric (TG-MS) analysis gives a clear idea about the catalytic efficiency of the synthesized catalyst GF2 toward AP decomposition from the accelerated emission of decomposition products NO, NO2, Cl, HCl, Cl2, and N2O in the presence of GF2. In a nutshell, gCN/Fe2O3 will open up new horizons in the field of synthesis of new catalytic systems with minimal metal content for composite solid propellants.

Influence of the thermal stability of ammonium perchlorate in presence of heteroleptic copper (I) complexes bearing ethane-1,2-diimine and biphosphines

The present article contributes to a detailed study of the influence of copper (I) heteroleptic complexes on the thermal stability of ammonium perchlorate (AP). The studied complexes (C1–C4) are based on ethane-1,2-diimine analogues and biphosphines. The complexes C1–C4 were synthesised and characterised by NMR, HRMS, and, in the case of C1 and C3, X-ray diffraction. The effect of C1–C4 on the thermal stability of AP was studied by differential scanning calorimetry technique. These results show that the compound C4 increased the AP maximum exothermic peak from 415 °C to 432 °C and decreased the heat released from 1093 J g−1 to 414 J g−1, exhibiting the higher retardant effect on the thermal decomposition of AP, in contrast to the other evaluated complexes and the reported compounds.

Enhanced anti-migration performance of carbon nanotubes confined ferrocenyl compounds and their synergistic catalytic activity on the thermal decomposition of ammonium perchlorate

To retard high-migration issues of the commercialized ferrocene-based burning rate catalysts (BRCs), six commercial ferrocenyl derivatives (FcR), including catocene, N, N-dimethylaminomethyl ferrocene, n-butylferrocene, tert-butylferrocene, n-octylferrocene and ferrocene, were filled into carbon nanotubes (CNTs) by ultrasonication. The CNTs incorporated ferrocene nanocomposites (FcR@CNTs) were characterized by TEM, SEM, BET, XPS, FTIR, Raman and XRD techniques, which indicated that the ferrocenes are successfully filled into the CNTs. The anti-migration and anti-volatility tests unveiled that the FcR@CNTs exhibit neglectable migration tendency after four weeks of aging at 50 °C and low volatility when tested at 70 °C for 24 h. The combustion catalytic results displayed that the FcR@CNTs nanocomposites play a vital role in promoting the thermal decomposition of ammonium perchlorate (AP), with the best one lowering the peak temperature of high-temperature decomposition stage (HTD) of AP by 114.2 °C and increasing its released heat by 160%. And it was found that the smaller the diameter of a CNT is, the lower the peak temperature of AP and the higher the released heat of AP. In addition, the decomposition mechanism of AP catalyzed by FcR@CNTs(L1) was studied by thermal decomposition kinetics, in-situ solid FTIR and TG-FTIR-MS methods. The results revealed that the nanocomposites can absorb more generated NH3 and HClO4 gases during AP decomposition with formation of superoxide anions (O2−), accelerating the oxidation of N2O to NO, and promoting the AP decomposition at lower temperature. Thus, a possible decomposition mechanism of AP catalyzed by FcR@CNTs is proposed.

Facile preparation of CoFe-based oxide nanosheets derived from CoFe-layered double hydroxide for the thermal catalytic decomposition of ammonium perchlorate

In this work, CoFe-based oxide nanosheets were prepared by a facile method and its catalysis effects on the thermal decomposition of ammonium perchlorate (AP) were studied. CoFe-based oxide nanosheets were obtained from hydrothermal process and high-temperature treatment of CoFe-layered double hydroxide. The samples were characterized by scanning electron microscopy and high-resolution transmission electron microscopy. The thermal catalytic decomposition of AP with CoFe-based oxide nanosheets as catalysts was investigated by differential scanning calorimetry and coupling Fourier transform infrared spectrometer. The results showed that the CoFe-based oxide samples with the width size of 200–300 nm and the thickness size of ∼10 nm show the inherent catalytic ability. With 10 wt% of CoFe-based oxide nanosheets added, the decomposition temperature of AP was reduced by 127.5 °C from 431.0 °C to 303.5 °C. The apparent activation energy was decreased by 61.1 kJ/mol from 177.3 kJ/mol of raw AP to 116.2 kJ/mol of AP with 10 wt% of CoFe-based oxide nanosheets added. The thermal catalysis decomposition mechanism of AP with CoFe-based oxide nanosheet material promoting was proposed. This work offered a novel idea toward preparation and application of functional material layered double hydroxide in the field of energetic materials.

Two amino acid Cu (II)-MOFs via one-pot method: Exhibiting good catalytic effect on the thermal decomposition of ammonium perchlorate and hexogen

Two copper metal–organic frameworks (MOFs) have been synthesized using l-serine Schiff base (2-(2-oxhydryl-phenylmethanimine)-3-oxhydryl-propionic acid ​= ​H2pmpa) and L-tyrosine (L-Tyr). The new MOF {[Cu(pmpa)(H2O)]·H2O}n (1) and another MOF {Cu(L-Tyr)2}n (2) were prepared by a one-pot method, and indicate square-based pyramidal geometry. Both MOFs display outstanding catalytic effects for the thermal decomposition of ammonium perchlorate (AP) and hexogen (RDX).

Simple synthesis of energetic ferrocene‐based coordination derivatives as attractive multifunctional catalysts for the thermal decomposition of ammonium perchlorate

Four novel energetic ferrocene‐based coordination derivatives, namely [M (FcHz)·(NO3)]n (M = Co2+, Cu2+, Zn2+, and Fe3+), were successfully prepared through a solvothermal method using 1,1′‐bis(1‐hydrazinoethylene) ferrocene (FcHz) with excellent electron transfer ability and energy bonds (C=N, N–N) as a ligand to coordinate with transition metals with high catalytic activity to promote the decomposition of ammonium perchlorate (AP). Their chemical structure, crystalline features, and morphology were comprehensively characterized, and their catalytic performance was analyzed. It is found that all [M (FcHz)·(NO3)]n exhibited better catalytic performance for AP decomposition than that of traditional catalyst catocene because of the optimal synergistic effect between FcHz and transition metals. In addition, they had a large specific surface area, strong NH3 absorption capacity, and high thermal property, which also could accelerate AP decomposition. [Co (FcHz)·(NO3)]n was the best one, and AP with [Co (FcHz)·(NO3)]n could decrease the high‐temperature decomposition temperature and apparent activation energy of AP decomposition by 110°C and 75.82 kJ mol−1, respectively, and increase heat release by 1066 J/g. The online thermogravimetric analyzer‐coupled with a Fourier‐transform infrared explored the AP decomposition products at different temperatures catalyzed by [Co (FcHz)·(NO3)]n, and a possible catalytic mechanism was also proposed. The results indicate that [Co (FcHz)·(NO3)]n with high efficiency, high energy, and high anti‐migration has application prospects in AP‐based solid propellants.

Facile fabrication of carbon nanotubes-encapsulated cobalt (nickel) salt nanocomposites and their highly efficient catalysis in the thermal degradation of ammonium perchlorate and hexogen

For reducing particle aggregation and improving catalytic activities of metal salts in composite solid propellants, ten cobalt and nickel compounds were encapsulated into the channels of oxidized carbon nanotubes (CNTs) by ultrasonication, which was proven by TEM, SEM, XRD, Raman, XPS, etc. The catalytic performances of the nanocomposites for ammonium perchlorate (AP) and hexogen (RDX) thermal degradation were evaluated by the DSC technique and the results revealed that the composites exhibit significant effects on the thermal decomposition of AP and RDX. Among them, 5 wt. % Co(NO3)2@CNTs(D1) as the catalyst increased the released heat of AP from 746.53 J/g to 2489.26 J/g, higher in catalytic efficiency than CoO@CNTs(D1) (1791.29 J/g), and advanced the peak temperature of AP at the high-temperature decomposition stage from 406.6°C to 312.4°C; while 1 wt. % Ni(NO3)2@CNTs(D1) as an additive enhanced the pyrolytic heat of RDX approximately three times and was more active than that of NiO@CNTs(D1). Kinetic studies showed that the activation energies of AP and RDX were sharply decreased with Co(NO3)2@CNTs(D1) and Ni(NO3)2@CNTs(D1) as additives. In addition, the thermal decomposition mechanism of RDX was studied by TG-FTIR-MS and it was found that the as-prepared nanocomposites promoted the cleavage of the C-N bonds of RDX and the generation of N2O gas.

2D metal-organic frameworks endow ammonium perchlorate with enhanced thermal effect

To investigate the effect of different structures of MOF on the catalytic performance of ammonium perchlorate (AP) thermal decomposition. By adding 2-methylimidazole (2-MI) as an inhibitor during the synthesis of MOF-5, a two-dimensional (2D) MOF material was prepared and characterized by SEM, EDS, XRD, FT-IR and other means. The prepared two-dimensional material was added to the AP raw material to investigate its effect on the AP thermal decomposition process. After DSC and TG test, it was found that the addition of this kind of 2D MOF material can completely eliminate the low-temperature decomposition peak of the AP-based composite and advance the high temperature decomposition peak to 296.5 °C, and the apparent heat of decomposition increase to 905.6 J/g, which has a better catalytic effect than the bulk MOF-5. In addition, through the combustion test, it was found that 2D MOF, as a burning rate catalyst, can effectively enhance the burning rate of AP based solid propellant.

Enhanced performance of barium and cobalt doped spinel CuCr2O4 as decomposition catalyst for ammonium perchlorate

The spinel oxide, CuCr2O4 is well known for its catalytic applications. In this study an attempt was made to explore the catalytic effects of CuCr2O4 and Barium and Cobalt doped CuCr2O4 on the thermal decomposition of ammonium perchlorate (AP), a widely used rocket propellant oxidizer. The nano catalysts were prepared by hydrothermal method and characterized by Powder XRD, SEM, TEM and BET. The nano catalyst embedded AP samples were prepared and thermogravimetric analysis was carried out to evaluate the effect of prepared nano catalysts on the AP thermal decomposition process. The prepared nano catalysts were efficient in lowering the decomposition temperature, among which highest efficiency was shown by cobalt doped CuCr2O4. Pure AP showed decomposition at 356 ​°C whereas catalyzed samples showed decomposition below 309 ​°C. Further, an attempt was made to elucidate the possible decomposition mechanism by Coats-Redfern method.

Ferrocene-based hydrazone energetic transition-metal complexes as multifunctional combustion catalysts for the thermal decomposition of ammonium perchlorate

Three novel ferrocene-based hydrazone energetic transition-metal complexes denoted as M/E-FcDz-TMCs (M = Co (II), Fe (III), and Co(II)Fe(III)), were successfully prepared to improve the thermal decomposition of ammonium perchlorate (AP) and anti-migration performance of Fc-based catalysts. 1-hydrazinoethylene-ferrocene (E-FcDz) with unique electronic structure and energy bonds (CN, NN) as ligand reacted with transition metal Co, or Fe mono-metal nodes, and Co-Fe bimetal nodes, respectively. The chemical structure, crystalline texture, and morphology were confirmed, and the catalytic performance was investigated. The thermal decomposition kinetics were estimated by applying Kissinger, FWO, and KAS methods. The results revealed that M/E-FcDz-TMCs had superior catalytic performances for AP decomposition compared to the traditional catalyst catocene due to their high electron transport capacity. Especially, CoFe/E-FcDz-TMCs showed the best catalytic efficiency due to the hybridization between Co (II) 3d and Fe (III) 3d orbitals in the structure led to electron redistribution, driving the optimal synergistic catalytic effect of the bimetal Co-Fe nodes and E-FcDz, and further enhancing catalysis for AP. Moreover, AP/CoFe/E-FcDzTMCs showed the best combustion performance. In addition, the thermal decomposition products of AP were explored by TG/FTIR, and the AP thermal decomposition process could be explained by a possible mechanism following the principle of electron transfer theory.

One-Pot Preparation of HTPB/nNi and Its Catalyst for AP.

The liquid phase reduction method is a common method used for preparing nano-nickel powder (nNi). However, the nNi surface is easily oxidized to form nickel oxide film, which affects its performance. In this work, nNi was prepared using anhydrous ethanol as a solvent and hydrazine hydrate as a reducing agent. Furthermore, HTPB/nNi composites were prepared using hydroxyl-terminated polybutadiene (HTPB) as a coating agent. The structure and morphology of the samples are characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The catalytic behavior of HTPB/nNi on the thermal decomposition of ammonium perchlorate (AP) is studied by differential scanning calorimetry (DSC) and thermogravimetric analyzer (TG). The results show that HTPB/nNi has little effect on the low temperature thermal decomposition of AP, but the peak of high temperature thermal decomposition advances from 456 °C to 332 °C.