[A Simple but Effective Device to Avoid Objective Lens Overheating: An Air Blower Device].

The interior of the Earth is a high temperature and high pressure environment. High temperatures cause important changes in the physical and chemical properties of minerals. An increase in temperature leads to significant changes in the molecular and lattice vibrations, elasticity, and seismic velocity of minerals. The high temperature vibrational spectroscopy (infrared and Raman) used to study these changes can provide highly significant understanding of the Earth's interior. During high temperature spectroscopy, the heating device that is used to heat the sample can work at a very high temperature (e.g., 1 500 ℃) because it has a cooling device surrounding it that is used to prevent the temperature of its environments from getting too high. However, radiation from its heating elements is intense and this will shine on and heat the objective lens of the focusing system for the spectroscopic light source, and this would result in damage to the lens. Thus, to avoid damage to the objective lens, an upper limit is placed on the heater temperature. The significance of this work is that it presents a method to exceed the present instrument's temperature limit so that we can perform in situ spectroscopy on samples at higher temperatures. This work extended the temperature limit for the sample to a higher temperature by using an air blower around the objective lens to create a gas flow around it. The gas flow serves to remove heat from the objective lens by forced convection and its turbulent flow also served to increase the rate of heat transport from the lens to the moving gas stream, which together prevented overheating of the objective lens. Our results have shown that although this device is simple, it was highly effective: for a sample temperature of 1 000 ℃, the objective lens temperature was reduced from ～235 to ～68 ℃. Using this device, we performed in situ high temperature Raman spectroscopy of forsterite up to a sample temperature of 1 300 ℃. The results agreed well with previous studies and demonstrated that with our simple air blower device, we can perform in situ high temperature spectroscopy up to 1 300 ℃ without damaging the objective lens and without expensive components like a high temperature composite objective lens or a long focus objective lens.

[Raman Spectroscopic Study on the Determination of SO4(2-) Concentration in Aqueous Solution under High Temperature and Pressure].

In the present work, the Raman spectra of SO4(2-) ions in aqueous solutions were studied. The quantitative analysis shows that there is a significant correlation between the Raman intensity ratio(R) and the SO4(2-) concentration. The SO4(2-) concentration in aqueous solution at ambient temperature and pressure can be determined by the Raman intensity according to the linear fitting equation c (SO4(2-) = 4.779 6R (r2 = 0.999 4). Furthermore, the research proves that the temperature and pressure will af- fect the relationship between the Raman intensity ratio and the concentration of SO4(2-) ions. The quantitative equation for measur- ing the SO4(2-) concentration in aqueous solution at high temperature and high pressure is c(SO4(2-)) = 4.779 6(R + 1.469 x 10(-4)ΔT + 1.340 x 10(-4)ΔP), where R is defined as the ratio of the SO4(2-) ions band intensity to the OH stretching single band intensity, T is the temperature relative to 23 °C, ΔP is the pressure relative to 0.1 MPa, 23 °C ≤ T ≤ 390 °C, the concentration range of the SO4(2-) ions is 0.5-1.5 mol · L(-1), and the uncertainty of the equation is 6.5%. Raman spectroscopy can be used to measure the concentration of the Raman-active species in aqueous solutions.

[Research on Raman spectra of chalcopyrite under 0-1400 MPa and ambient temperature].

The variation characters of the A1 mode Raman spectra of chalcopyrite under 0.1-1400 MPa and ambient temperature were researched using diamond anvil cell. The results show that the shape and intensity of the Raman peak remains constant under experimental conditions, indicating that the chemical bounds of Cu-S and Fe-S remain unchanged. The authors have also noticed that the position of the Raman peak shifts to higher frequency with increasing pressure, which could be described as: nu(290) = 0.031 2p + 290.60 (0.1< or =p<58.8 MPa) and nu(290) = 0.00572p+292.10 (58.8 < or =p<1400 MPa). The rate of the Raman peak shifting with increasing pressure changed abruptly at about 58.8 MPa, the d(nu)/dp is 31.2 and 5.72 cm(-1) x GPa(-1) below and above 58.8 MPa respectively, which perhaps indicate that some structural changes occurred in the chalcopyrite.

Raman spectroscopic quantitative study of NaCl-CaCl2-H2O system at high temperatures and pressures.

Raman spectra features of the ternary system NaCl-CaCl2-H2O under high temperatures and high pressures were systematically studied in the present work by using hydrothermal diamond anvil cell (HDAC) and Raman shifts of quartz to determine pressures, and it has been obtained for the quantitative relationship between Raman shifts of the O-H stretching band of water, mass fractions of solutes and pressures was obtained. The mass fractions of salts, where salinity of NaCl equal to that of CaCl2, are 4.0 mass %, 8.0 mass %, and 12.0 mass %, respectively. Experimental results indicate that the standardized Raman frequency shift differences of the O-H stretching vibration (deltav(O0H)) rise with the increasing temperatures when the mass fractions of salts and pressures of the NaCl-CaCl2-H2O system remain constant. deltav(O-H) increases with the increase in mass fractions of salts in the system when the temperatures and pressures are constant. Linear relationship between deltav(O-H) and pressure with similar slopes can be found for the NaCl-CaCl2-H2O system with different salinities. The quantitative relationship between deltav(O-H), temperature (T), pressure (P), and mass fraction of solute (M) is P = -31.892 deltav(O-H) + 10.131T + 222.816M - 3 183.567, where the valid PTM range of the equation is 200 MPa < or = P < or = 1 700 MPa, 273 K < or = T < or = 539 K and M < or = 12 mass %. The equation can be used as a geobarometer in the studies of fluid inclusions of NaCl-CaCl2-H2O system with equal salinities. The method, as a direct geological detecting technique, has a potential application value.

[Research on Raman spectra of oxalic acid during decarboxylation under high temperature and high pressure].

The present research studied the thermal stability of oxalic acid under high temperature and pressure and its in-situ transformation by Raman spectroscopy using a hydrothermal diamond anvil cell. Raman spectra allow the detection of ionic and covalent atomic aggregates through the acquisition of vibrational spectra that are characteristic of their structures and molecular bond types. The result showed that there was no change in characteristic vibrational Raman peaks of oxalic acid in the low-temperature stage. With the increase in temperature and pressure, the characteristic vibrational Raman peaks of oxalic acid became weaker and the peaks disappeared at a certain high temperature, and decarboxylation happened. Oxalic acid decomposes to produce CO2 and H2, according to the reaction: C2 H2O4-2CO2 + H2. It was found that the decarboxylation was highly related with pressure and that the decarboxylation would be hindered at high pressure. Decarboxylation of oxalic acid under high temperature and pressure showed a linear relationship between temperature and pressure. The data fitting generated the formula: P(MPa) = 12. 839T(K)-5 953.7, R2 = 0.99. The molar volume change of decarboxylation of oxalic acid can be described by deltaV(cm(-3) x mol(-1)) = 16.69-0.002P (MPa) + 0.005 2T(K), R = 0.99.

[Raman spectroscopic study on the fluid effects in dissolution and phase transition mechanisms of gypsum].

Raman spectroscopic studies on the process of dissolution and phase transition of gypsum in different fluids were taken. Gypsum took phase transition to be anhydrite in the range from 170 degrees C to 190 degrees C in pure water, and no more change happened with decreasing temperature to room temperature. Gypsum took phase transition to be anhydrite in the range from 170 degrees C to 190 degrees C too in Na2 SO4 solution, but anhydrite can regain to be gypsum when temperature decreases to room temperature. The process of phase transition of gypsum in pure water is not reversible, but it happens in Na2 SO4 solution. The study shows that fluid effects can influence the dissolution and phase transition mechanisms of minerals and cannot be ignored.

[Research on Raman spectra of isooctane at ambient temperature and ambient pressure to 1. 2 GPa].

The experimental study of the Raman spectral character for liquid isooctane (2,2,4-trimethylpentane, ATM) was con ducted by moissanite anvil cell at the pressure of 0-1.2 GPa and the ambient temperature. The results show that the Raman peaks of the C-H stretching vibration shift to higher frenquencies with increasing pressures. The relations between the system pressure and peaks positions is given as following: v2 873 = 0.002 8P+2 873.3; v2 905 = 0.004 8P+2 905.4; v2 935 = 0.002 7P+ 2 935.0; v2 960 = 0.012P+2 960.9. The Raman spectra of isooctane abruptly changed at the pressure about 1.0 GPa and the liquid-solid phase transition was observed by microscope. With the freezing pressure at ambient temperature and the melting temperature available at 1 atm, the authors got the liquid-solid phase diagram of isooctane. According to Clapeyron equation, the authors obtained the differences of volume and entropy for the liquid-solid phase transition of isooctane: deltaV(m) = 4.46 x 10(-6) m3 x mol-1 and deltaS = -30.32 J x K(-1) x mol(-1).

[In situ experimental study of phase transition of calcite by Raman spectroscopy at high temperature and high pressure].

The phase transitions of calcite at high temperature and high pressure were investigated by using hydrothermal diamond anvil cell combined with Raman spectroscopy. The result showed that the Raman peak of 155 cm(-1) disappeared, the peak of 1 087 cm(-1) splited into 1083 and 1 090 cm(-1) peaks and the peak of 282 cm(-1) abruptly reduced to 231 cm(-1) at ambient temperature when the system pressure increased to 1 666 and 2 127 MPa respectively, which proved that calcite transformed to calcite-II and calcite-III. In the heating process at the initial pressure of 2 761 MPa and below 171 degrees C, there was no change in Raman characteristic peaks of calcite-III. As the temperature increased to 171 degrees C, the color of calcite crystal became opaque completely and the symmetric stretching vibration peak of 1 087 cm(-1), in-plane bending vibration peak of 713 cm(-1) and lattice vibration peaks of 155 and 282 cm(-1) began to mutate, showing that the calcite-III transformed to a new phase of calcium carbonate at the moment. When the temperature dropped to room temperature, this new phase remained stable all along. It also indicated that the process of phase transformation from calcite to the new phase of calcium carbonate was irreversible. The equation of phase transition between calcite-III and new phase of calcium carbonate can be determined by P(MPa) = 9.09T x (degrees C) +1 880. The slopes of the Raman peak (v1 087) of symmetrical stretching vibration depending on pressure and temperature are dv/dP = 5.1 (cm(-1) x GPa(-1)) and dv/dT = -0.055 3(cm(-1) x degrees C(-1)), respectively.

Rt-PA thrombolytic therapy in patients with acute posterior circulation stroke: A retrospective study.

At present, recombinant tissue-type plasminogen activator (rt-PA) thrombolytic therapy is widely used in patients with acute ischemic stroke within 4.5 h following stroke onset. However, the efficacy of intravenous alteplase thrombolytic therapy for posterior circulation stroke (PCS) has been rarely described. The present study aimed to predict the outcome of patients with PCS following rt-PA thrombolytic therapy in a more efficient manner. Data were collected from patients who had suffered from posterior circulation ischemic stroke, who had been treated with rt-PA over a period of 4 years (2016-2020), and had been treated at a stroke center. All patients were treated with alteplase at a standard dose of 0.9 mg/kg. According to the onset to needle time (ONT), these patients were divided into the 0-3 and 3-4.5 h groups, and the National Institutes of Health Stroke Scale (NIHSS) score was compared before thrombolysis and at 24 h after thrombolysis. Subsequently, the patients with acute PCS whose ONT was ≤3 h were divided into the NIHSS score >3 points and NIHSS score ≤3 points groups, and the NIHSS score improvement rate was compared 24 h later. A total of 989 patients were included in the study; there were 783 patients with acute anterior circulation stroke (ACS) and 203 patients with acute PCS (of note, 2 patients had negative results from brain magnetic resonance imaging); 63 patients were treated with urokinase (UK) thrombolysis and 140 patients were treated with alteplase intravenous thrombolysis. The 140 patients that received alteplase thrombolytic therapy were divided into two groups, namely the ≤3 h group and 3-4.5 h group, which, on the basis of the ONT, no significant differences were found between the two the groups according to the NIHSS score before thrombolysis (P>0.05). The NHISS scores in the ≤3 h group were significantly lower than those in the 3-4.5 h group following thrombolysis therapy, and the differences between the two groups were statistically significant (P<0.05); the patients with acute PCS treated with rt-PA in the ≤3 h group were divided into the NIHSS score ≤3 points group and the NIHSS score >3 points group. In this ≤3 h group, the average NIHSS score improvement rate following rt-PA thrombolysis was 0.535 (53.5%) in the NIHSS score ≤3 points group and that in the NIHSS score >3 points group was 0.336 (33.6%); the difference between the two groups was statistically significant (P<0.05). The patients treated with intravenous alteplase thrombolysis within 3 h following stroke onset benefited more than those treated with thrombolysis therapy within 3 to 4.5 h after stroke onset. On the whole, the present study demonstrates that the patients with mild stroke (NIHSS score ≤3 points) who were treated at an earlier stage (received alteplase thrombolysis therapy within 3 h after stroke onset) benefited to a greater extent from the therapy.

[Research on the experiment of hydrogen isotope fractionation using diamond anvil cell and Raman spectra].

Hydrothermal diamond-anvil cell and Raman spectroscopy were used to measure the hydrogen isotope fractionation factor between gypsum and liquid water. Hydrogen isotopes of deuterium (D) and hydrogen (H) show the largest relative mass difference in all stable isotope systems. The exchange reaction between D and H would easily take place and the extent of exchange would be larger than others under same condition. So we selected the hydrogen isotopes for the investigation. The concept of fractionation factor is the quotient of ratios of heavy and light isotopes in different minerals, and can be expressed as alpha(A-B) = R(A)/R(B). There is a linear relationship between ratio of Raman peak intensities and ratio of corresponding amount of substances. So the fractionation factor between gypsum and heavy water can be expressed as [formula: see text] The experimental study for the isotope fractionation is based on the dissolution and recrystallization of minerals in aqueous solutions. The process can reach the total isotope fractionation equilibrium and get isotope fractionation factors with different temperatures. Compared with other methods, chemical synthesis one has following advantages: (1) short time for the experiment; (2) no problem about the equilibrium for isotope exchanges. It was proved that the new method would be more convenient and reliable for obtaining the isotopic fractionation factor compared with previous ways.

[Raman spectra of aragonite at the pressure of 0.1-2 GPa and ambient temperature].

Raman spectra of aragonite were studied at ambient temperature and pressure of 0.1 - 2 GPa in a moissanite anvil cell using Raman spectrum technique. The relations between the Raman shifts of aragonite and the system pressure are given as follows: v153 (cm(-1)) = 0.003 5p (MPa) +154.0, v206 = 0.006 0p + 206.3, v704 = 0.002 1p + 704.2, v1085 = 0.003 5p + 1 085.3. No phase transition occurred in aragonite within the range of experimental pressure. Similar to other carbonate minerals (magnesite, dolomite), the measured relative pressure-shift of the Raman line of the symmetric stretching vibration of aragonite is greater at 0.1-2 GPa than at ultrahigh pressure, which indicates that the C-O bond compressibility of the CO3 groups is related to the pressure, and it is more compressible at 0.1 - 2 GPa than at higher pressure.

[Raman spectra study of barite at the pressure of 0-1 GPa and ambient temperature].

The variation characters of Raman spectra of S-O symmetric stretching vibration v987 and symmetric bending vibration v452 and V462 of barite at high pressure were studied using moissanite anvil cell. The experimental results show that barite is stable at the pressure of 0-1 GPa and ambient temperature, and the Raman peak positions of barite shift to higher frequency with increasing pressure. The relations between the Raman shifts and system pressure are given as follows: v987 = 0.004 4p+987.42, v452 = 0.002 3p+452.6, v462 = 0.001 8p+ 462.42, and that stretching vibrations are more affected by pressure than bending vibrations. The intensity of 987 cm(-1) Raman peak of barite is six times greater than that of 464 cm(-1) Raman peak of quartz, so barite can be used as a good pressure gauge. Besides, the relation between the system pressure and Raman shift of 987 cm(-1) peak position of barite is given as follows: p(MPa) = 223.16 X (deltav(p))987 -90.35 (987 cm(-1) < v(p) < 992 cm(-1)). The difference in the measured relative pressure-shift of the Raman line of the symmetric stretching vibration among various sulfate minerals shows the compressibility and strength of the S-O bond in the SO4 group.

[Research on Raman spectra of calcite phase transition at high pressure].

The present research studied the process of phase transition from calcite-I to calcite-III under the condition of high hydrostatic pressure using hydrothermal diamond anvil cell and Raman spectrum technique. The hydrothermal diamond anvil cell is the most useful instrument to observe sample in-situation under high temperature and high pressure. The authors can get effective results from this instrument and pursue further research. The method of Raman spectra is the most useful measure tool and it can detect the material according to the spectrum. The result shows that three characteristic Raman peaks of calcite-I move to high-position with adding pressure. Water media in system becomes frozen at the pressure of 1103 MPa, and there is no change in the structure of calcite-I. The abrupt change of characteristic Raman peaks of calcite-I happens when the system pressure reaches 1752 MPa, and changed characteristic Raman peaks explain that calcite-I changes to calcite-III. There are two types of calcite-III, and type A happens in the system because of the effect of hydrostatic pressure. The characteristic Raman peak in different areas of minerals shows that the degree of phase transition becomes larger from inner part to edge part. The research also shows the advantage of hydrothermal diamond anvil cell and Raman spectrum for qualitative analysis of mineral structure using in-situ technique.

[In-situ research on Raman spectroscopy of 1-pentanol under high pressure].

Raman spectra in 800-3 000 cm(-1) of 1-pentanol were studied under high pressure and at ambient temperature (23 degrees C) using a cubic zirconia anvil cell. The Raman peaks become sharper at higher pressure so that each individual C-H stretching mode is difficult to be distinguished. The Raman frequencies of the C-H stretching modes shift to a higher position with increasing pressures ranging between 0.1 MPa and 1.75 GPa. And the pressure induced frequency shifts are described by P(MPa) = 69.652 65 x (deltanu(p)) (single, T = 23 degrees C) + 105.806 93 where 0 < (deltanu(p)) single (cm(-1) < or = 23 and P(MPa) =77.974 04 x (Anu(p))( 2 960, T = 23 degrees 95.390 5 where 0 < (deltanu(p))2 960 (cm(-1)) < or = 21 and P(MPa) =126.956 39 x (deltanu(p)) (2 863, T = 23 degrees) -110.648 09 where 0 < (deltanu(p)) 2 863(cm(-1)) < or = 13, respectively. The global slope is (thetanu(single)/thetaP)T (14+/- 1) cm(-)1 x GPa(-1), which can be used as a pressure sensor. Both the jumping of the frequencies and the figure under microscope indicate that the frozen pressure of the 1-pentanol at room temperature is 1.75 GPa. The molar volume change of the 1-pentanol is deltaVm = 1.84 x 10(-6) m3 x mol(-1) in the phase transformation from a liquid to a solid at 23 degrees C.

[Study on the accuracy of pressure determined by raman spectra of quartz].

Quartz as a pressure gauge and its accuracy were studied by Raman spectroscopy at 25 degrees C and ambient pressure. The result shows that even at same temperature and pressure, the Si-O vibrational mode for different grains of quartz varies between 463.59 and 464.65 cm(-1), with (+/- 0.1- +/- 0.3) cm(-1) error. The maximum difference of various grains of quartz is up to 1.06 cm(-1), much higher than the measurement error. The authors believe that the variety is resulted from the stress in the internal grains of quartz, which formed during crushing quartz into small grain. Therefore, Raman spectrum for quartz has to be firstly measured as a reference of zero pressure at ambient pressure and temperature in the experimental study by using diamond anvil cell. In addition, wavenumber drift of the spectrometer and the unstable temperature will also cause remarkable error for measuring pressure.

Stability of copper acetate at high P-T and the role of organic acids and CO2 in metallic mineralization.

Many metal deposits were formed by carbonic fluids (rich in CO2) as indicated by fluid inclusions in minerals, but the precise role of CO2 in metal mineralization remains unclear. The main components in fluid inclusions, i.e. H2O and CO2, correspond to the decomposed products of organic acids, which lead us to consider that in the mineralization process the organic acids transport and then discharge metals when they are stable and unstable, respectively. Here we show that the thermal stability of copper acetate solution at 15-350 °C (0.1-830 MPa) provides insight as to the role of organic acids in metal transport. Results show that the copper acetate solution is stable at high P-T conditions under low geothermal gradient of <19 °C/km, with an isochore of P = 1.89 T + 128.58, verifying the possibility of copper transportation as acetate solution. Increasing geothermal gradient leads to thermal dissociation of copper acetate in the way of 4Cu(CH3 COO)2 + 2H2O = 4Cu + 2CO2 + 7CH3COOH. The experimental results and inferences in this contribution agree well with the frequently observed fluid inclusions and wall-rock alterations of carbonate, sericite and quartz in hydrothermal deposits, and provide a new dimension in the understanding of the role of CO2 during mineralization.

A method for isotope exchange kinetics in mineral-water system-an in-situ study on oxygen isotope exchange in Na2CO3-H2O system.

The experiments on the exchange reaction rate of the oxygen isotopes in the mineral-water system with initial conditions of 100 °C and 240 MPa, 100 °C and 924 MPa, 118 °C and 170 MPa are taken. The oxygen isotope 18O exchange reactions between aqueous C16O32- and H218O are mainly traced by measuring the Raman peak intensity of oxygen-containing elements (CO32-) in sodium carbonate solution. The inconsistent trends between the molar fraction and the concentration of C18O216O2- indicate oxygen isotope exchange between sodium carbonate and heavy water accompanied by dissolution and recrystallization between supersaturated sodium carbonate solution and solid sodium carbonate. In the heterogeneous experimental systems the order of oxygen isotope exchange reactions are more than 1 and the dynamics of oxygen isotope exchange conform to JMAK kinetics model with the nucleation and growth processes of sodium carbonate crystal.

Raman scattering spectroscopic study of n-tetradecane under high pressure and ambient temperature.

The Raman spectroscopy of n-tetradecane was investigated in a Moissanite anvil cell at pressure from 0.1 MPa to 1.4 GPa and ambient temperature. The result shows that the liquid-solid phase transition of n-tetradecane takes place at around 302.8 MPa and the corresponding DeltaV(m) obtained is about -9.6 cm(-3)/mol. Above 302.8 MPa, the frequencies of CH(2) and CH(3) symmetric stretching and asymmetric stretching vibration shift to higher wave numbers in a linear manner with increasing pressure, which can be expressed as: nu(s)(CH(3))=0.013P+2882.0; nu(as)(CH(3))=0.014P+2961.6; nu(s)(CH(2))=0.013P+2850.8; nu(as)(CH(2))=0.009P+2923.2. This relationship indicates that n-tetradecane can be a reliable pressure gauge for the experimental study within the pressure range of 0.3-1.4 GPa.

[Raman spectra of carbonate ions as pressure gauge at high pressure and room temperature].

Three aqueous solutions of sodium carbonate (1.5, 2.0 and 2.5 mol x L(-1)) were studied by in-situ Raman spectrum in a moissanite anvil cell in order to measure the Raman shift of symmetric stretching vibration of carbonate ion at around v1 066. The experiment was conducted from 0 to 1.7 GPa under quasihydrostatic conditions at temperature of 22 degrees C. The result showed that the increase in Raman wavenumber shift of in-plane bending vibration of carbonate ion is linearly proportional to the rise of pressure under room temperature. At the three concentrations mentioned above, the correlations between Raman shift ofthe v1 066 peak and the pressure are depicted as three nearly identical curves, with a slope error smaller than 1%. The deviation, being smaller than the systemic error, suggested that the concentration of carbonate ions, within experimental errors, has no detectable influence on the pressure-induced shift of v1 066 peak. Besides, the data fitting generated the formula: p/MPa = 174.13deltavl 066/cm(-1) -59.03 (deltav1 066 = v1 066 -v(0)1 066, where v(0)1 066 denotes the Raman shift of v1 006 peak of carbonate ion under the ambient pressure, which can be used as a pressure gauge in pure Na2CO3 solution.

[Research on Raman spectra of benzoic acid during decarboxylic process].

The present research studied benzoic acid change in water and its Raman spectra in temperature rising period using hydrothermal diamond anvil cell and Raman spectrum technique. The hydrothermal diamond anvil cell is the most useful instrument to observe sample in-situation under high temperature and high pressure. The authors can get effective results from this instrument and pursue further research. The method of Raman spectra is the most useful measure tool and it can detect the material according to the spectrum. The result showed that there was no change in characteristic vibrational Raman peak of benzoic acid in the lower temperature period and there was no reaction between benzoic acid and water. In the process of temperature rising period, the characteristic vibrational Raman peak of benzoic acid became weaker. During the process, benzoic acid began to dissolve in water, but no chemical reaction happened. The reason for weaker Raman peak of benzoic acid is the dissolution. The characteristic vibrational Raman peak of carboxyl disappeared at 150 degrees C, which showed that decarboxylic reaction occurred on benzoic acid. But the main Raman peak of benzoic acid existed which showed that no chemical reaction existed. And then benzoic acid disappeared when temperature ascended to 170 degrees C. When the temperature of system dropped to room temperature, a kind of crystal appeared. The characteristic vibrational Raman peak of this kind of crystal showed that the crystal contained benzene ring, showing that dutrex appeared. At the same time the authors did not find the characteristic vibrational Raman peak of carboxyl, so the crystal was not benzoic acid. The whole research showed that: dutrex can disappear and be regained in the process of dissolution and recrystallization, but carboxyl cannot.