ORIGINAL ARTICLE

Development of in-situ Micro-Raman spectroscopy systemfor autoclave experimental apparatus

Lin Chen1,2• Heping Li1 • Shengbin Li1,2

• Liping Xu3• Sen Lin1

•

Hongbin Zhou1

Received: 2 March 2020 / Revised: 25 March 2020 / Accepted: 30 April 2020 / Published online: 14 May 2020

� Science Press and Institute of Geochemistry, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract We developed a set of in-situ Micro-Raman

spectroscopy system for autoclave experimental apparatus

because of the scientific significance of in-situ Micro-Ra-

man spectroscopy system under the high-pressure

hydrothermal condition. We used this system to measure

the Raman spectrum of water-fluid and quartz crystal at the

temperature ranging from 125 to 420 �C. The signal-to-

noise ratio of the Raman signal is good.

Keywords Micro-raman � Hydrothermal system � In-situ �Autoclave

1 Introduction

In-situ Micro-Raman spectroscopy observation under high-

pressure hydrothermal conditions is an important way to

understand the high-temperature and high-pressure water-

fluid in the Earth’s interior, and to reveal the compositions,

structures, properties and evolution processing of other

materials in the Earth’s interior.

At present, hydrothermal diamond anvil cell (HDAC)

and autoclave are the most commonly used experimental

apparatuses in the high temperature and high-pressure

hydrothermal simulation experiment. Very high tempera-

tures and pressures can be obtained by using HDAC, but

HDAC has some shortcomings, such as the cavity body of

HDAC is too small (only about 10-5 mL), accurate control

and determination of the pressure value are very difficult,

and the operation of HDAC is difficult (Zhang et al. 2009;

Zheng et al. 2004). However, the autoclave does not have

these shortcomings, it has a large volume (larger than

30 mL), and temperatures and pressures can be controlled

and determined accurately. Therefore, the autoclave is

often used as the high pressure hydrothermal experimental

apparatus.

Up to now, most of the reports about the in-situ Micro-

Raman spectroscopy experiments under the high-pressure

hydrothermal condition are about DAC (Qiao et al. 2006;

Yang and Zheng 2009; Zhang et al. 2009, 2015), and also

many reports are about autoclave (Clerk et al. 1997; Gor-

baty et al. 2004; Ma et al. 2009). However, these in-situ

Micro-Raman spectroscopy experimental systems about

the autoclave have two problems: one problem is that the

autoclave in these reports cannot be compatible with dif-

ferent in-situ observation platforms (other in-situ observa-

tion platforms cannot be used when in-situ Micro-Raman

spectroscopy system is operated); and the other problem is

that the objectives in these reports are general microscope

objectives, and cannot be used under the condition of the

high temperature. When a long focal length objective has

to be used, this will reduce the intensity of the Raman

signal.

In this paper, we will solve the problems and develop a

set of in-situ Micro-Raman spectroscopy systems for the

autoclave experimental apparatus without these two prob-

lems. The multi-function autoclave experimental apparatus

we used can be compatible with different in-situ

& Heping Li

liheping@vip.gyig.ac.cn

1 Laboratory of High Temperature and High Pressure Study of

the Earth’s Interior, Institute of Geochemistry, Chinese

Academy of Sciences, 99 Lincheng West Road, Guanshanhu

District, Guiyang, Guizhou Province 550081, People’s

Republic of China

2 University of Chinese Academy of Sciences, Beijing 100049,

China

3 Zhejiang Pharmaceutical College, Ningbo 315100, China

123

Acta Geochim (2020) 39(4):445–450

https://doi.org/10.1007/s11631-020-00419-1

observation platforms, many different in-situ observation

platforms can be operated at the same time, and different

in-situ observation data (Raman spectrum, oxygen fugac-

ity, and so on) can be obtained meanwhile. So we intend to

develop a set of in-situ Micro-Raman spectroscopy system

based on the autoclave experimental apparatus in our

laboratory.

2 Experimental instruments

The schematic diagram of the autoclave experimental

apparatus is shown in Fig. 1. The accuracy of the tem-

perature controller is ± 0.1 �C, however, as the K-type

thermocouple we used does not contact with water-fluid

and samples directly, the uncertainly of temperature mea-

surements is ± 5–10 �C. The full scale (F.S) of the pres-

sure sensor is 100 MPa, and the accuracy is 0.1% F.S, with

the high-precision pressure sensor, pressure value can

directly be obtained with an uncertainty of ± 0.1 MPa.

The pictures of high-temperature furnace, temperature

control unit, and autoclave body are shown in Figs. 2, 3,

and 4 respectively.

The Raman spectra were obtained with Renishaw in Via

Raman Microscope equipped with stabilite 2017 Ar? ion

laser (514.5 nm), and a 2400-groove/mm grating with a

resolution of ± 1 cm-1. The measurement repeatability of

the Raman spectrometer is 0.2 cm-1. The picture of the

Raman spectrometer is shown in Fig. 5.

3 Design and assembly of an optical system

We already have the autoclave experimental apparatus and

Raman spectrometer in our lab, to measure the Raman

spectrum of samples under high-pressure hydrothermal

conditions, we have designed and built an optical system to

connect these two experimental instruments.

For the light to get into the autoclave and get back, we

intended to install an optical window in the stopper of the

autoclave. The sapphire crystal has good optical perfor-

mance, good chemical stability, good thermal stability, and

high mechanical strength (Moriaki 2007). We chose the

sapphire crystal as the material for our optical window (4 in

Fig. 1).

According to the principle of applied optics, since the

strength of Raman signal is proportional to the square of

Fig. 1 Schematic diagram of

the multi-function autoclave

experimental apparatus. 1 High-

temperature furnace; 2 Nut; 3

Stopper; 4 Sapphire window; 5

Autoclave body; 6

Thermocouple; 7 High pressure

capillary; 8 Pressure sensor; 9

High-pressure valve; 10 Usb

cable; 11 Computer; 12

Temperature control unit

Fig. 2 The picture of high-temperature furnace

446 Acta Geochim (2020) 39(4):445–450

123

the numerical aperture of the objective, and the numerical

aperture of the objective is inversely proportional to the

focal length of objective, so the intensity of Raman signal

is inversely proportional to the square of the focal length of

objective (Smith 2007). So to get the strong Raman signal,

we need to choose the lens with a short focal length, which

makes the lens very close to the sample. But the autoclave

is in the high-temperature furnace, general microscope

objectives cannot be used in this condition. According to

the experimental needs, we choose a series of the sapphire

lens with a focal length of 20 mm as our high-temperature

Raman objective.

The picture of the sapphire lens is shown in Fig. 6, the

surface quality of the lens is 40–20 scratch-dig.

The schematic diagram of in-situ Micro-Raman spec-

troscopy system is shown in Fig. 7. Raman fiber optical

detector is coupled with the Raman spectrometer by a set of

optical fibers. The sketch map and picture of Raman fiber

optical detector are shown in Figs. 8, 9 respectively. The

laser passing through an optical fiber and Raman fiber

optical detector converges through objective, stray light

can be filtered by the narrow-band pass filter (3 in Fig. 8).

The reflected laser can be focused on the CCD by the lens.

By observing the image of the laser, we can determine

whether the laser is converged on the surface of solid

samples or in the water-fluid. When it is determined that

the laser is focused on the target position, we can measure

the Raman spectrum by operating the Raman spectrometer.

Rayleigh filter (5 in Fig. 8) can filter out Rayleigh

Fig. 3 The picture of the temperature control unit

Fig. 4 The picture of the

autoclave body

Fig. 5 The picture of Raman

spectrometer

Acta Geochim (2020) 39(4):445–450 447

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scattering light and allow Raman scattering light pass

through. Finally, the Raman signal can be collected by the

Raman spectrometer.

We fixed the optical system (1 in Fig. 7) on a set of

multi-dimensional adjustment platform (shown in Fig. 10).

This set of multi-dimensional adjustment platform consists

of three position stages (x, y, z-direction), an angular dis-

placement stage, and a rotating stage, it can be used to

adjust the positions and angles.

In the experiment, we adjusted the multi-dimensional

adjustment platform to make this set of optical system (1 in

Fig. 7) and the sapphire window (4 in Fig. 1) sealed in the

stopper of the autoclave coaxial firstly. Secondly, we

observed the image of laser, and adjusted the position of

the objective along the optical axis to make the laser focus

on the samples. Then we moved the semi-transparentFig. 6 The picture of sapphire lens

Fig. 7 Schematic diagram of

in-situ Micro-Raman

spectroscopy system. 1 The

sketch map of the optical system

we designed; 2 Objective; 3

Lens tube; 4 Semi-transparent

mirror; 5 Raman fiber optical

detector; 6 Mirror; 7 Lens; 8

CCD; 9,11 Optical fiber; 10

Raman spectrometer; 12 Ar?

ion Laser; 13 Usb cable; 14

Computer

Fig. 8 The sketch map of

Raman fiber optical detector. 1

Laser input optical fiber; 2

Interface coupler and

collimating lens; 3 Narrow-band

pass filter; 4 Mirror; 5 Rayleigh

filter; 6,7 Interface coupler and

collimating lens; 8 Raman

signal collection optical fiber

448 Acta Geochim (2020) 39(4):445–450

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mirror (4 in Fig. 7) away from the optical axis to make sure

the laser is not blocked and operated the Raman spec-

trometer to measure the Raman spectrum.

4 Experiment

In order to test the performance of this set of in-situ Micro-

Raman spectroscopy systems, we did two groups of

experiments and measured the Raman spectrum of water-

fluid and quartz crystal at the different temperatures and

pressures.

In the first experiment, we used pure water as the

sample. The experimental steps are as follows. First, pour

30 mL distilled water into the clean autoclave. Second, seal

the autoclave with the stopper and nut. Third, put the

autoclave in the furnace and adjust the light path. Fourth,

heat the autoclave to the temperatures of 200, 300, and

400 �C. Fifth, keep the target temperature for 2 h and

measure the Raman spectrum.

In the second experiment, we fixed a piece of cylindrical

quartz crystal (10 mm diameter, 3 mm thickness, and 3 arc

min parallelism) in the clean autoclave and poured into 18 mL

distilled water. The following experimental steps were the

same as steps of the first experiment. The autoclave was

heated to 420 �C from room temperature. In this process, we

measured the Raman spectrum of quartz crystal and super-

critical water at different temperatures. Each Raman spectrum

was measured after the target temperature was kept for 2 h.

5 Results and discussions

The acquisition time is 10 s with one accumulation for

each spectrum. The output power of the laser is 80 mW.

Raman spectrum of water-fluid at the temperatures of 200,

300, and 400 �C are shown in Fig. 11. The Raman peak at

about 3550 cm-1 is assigned to the O–H stretching vibra-

tion (Hu et al. 2013; Wang and Sun 2016).

Raman spectrum of quartz crystal in the water-fluid at

different temperatures and saturated vapor pressures are

Fig. 9 The picture of Raman

fiber optical detector

Fig. 10 The picture of multi-dimensional adjustment platform

Fig. 11 Raman spectrum of water-fluid at the temperatures of 200,

300, and 400 �C

Acta Geochim (2020) 39(4):445–450 449

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shown in Fig. 12. The Raman peak at about 465 cm-1 is

assigned to the Si–O symmetrical stretching of the quartz

crystal (John and Arvin 1972; Zheng et al. 2004).

Raman spectrum of quartz crystal and water-fluid in

supercritical water at the temperatures of 400 and 420 �C

are shown in Fig. 13. - 465 cm-1 is the Raman peak of

quartz crystal, and - 3550 cm-1 is the Raman peak of

supercritical water.

6 Conclusions

1. We developed a set of in-situ Micro-Raman spec-

troscopy system for the multi-function autoclave

experimental apparatus. The system can be compatible

with different in-situ observation platforms, and the

high-temperature Raman objective we designed can be

used under the condition of the high temperature.

2. We used the set of in-situ Micro-Raman spectroscopy

system to measure the Raman spectrum of water-fluid

and quartz crystal at the different temperatures and

pressures, and obtained the Raman spectrum of water-

fluid and quartz crystal at the temperature ranging from

125 to 420 �C, and the Raman spectrum have a good

signal-to-noise ratio.

Acknowledgements This study was supported by the National Key

R&D Program of China (Grant No. 2016YFC0600104) and the

Strategic Priority Research Program (B) of the Chinese Academy of

Sciences (XDB 18010401).

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Fig. 12 Raman spectrum of quartz crystal in the water-fluid at

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Fig. 13 Raman spectrum of quartz crystal and water-fluid in

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