15

CHAPTER 2

HIGH PRESSURE EXPERIMENTAL TECHNIQUES

This chapter is divided into two parts. In the first part the techniques

and instruments used to generate high pressure and study the structural

changes that occur to these materials at high pressure are discussed. The

details about the following experimental setups’ have been explained.

(1) X-ray diffraction facilities utilized to collect diffraction

patterns

(2) Micro Raman setup used for in situ high pressure studies

(3) High pressure resistivity setup using designer diamond anvils

The second part of this chapter focuses on the work that have been

carried out as an attempt to reduce the time consumed in preparation of the

DAC and loading the sample for high pressure experiments. The main aspects

covered are:

(1) Development of a diamond mounting jig

(2) Modified Electric Discharge for micro drilling in DAC

experiments

16

2.1 HIGH PRESSURE EXPERIMENTAL TECHNIQUES

2.1.1 Generation of High Pressure

High pressures can be attained by a variety of methods; it can be

achieved dynamically by shock compression or statically by using different

high pressure techniques, for example, the anvil devices and piston cylinder

apparatus. There are basically two types of anvil devices: multi anvil cells

which consist more than two anvils and Bridgeman opposing anvils in which

two anvils are mounted with their faces opposing each other (e. g the DAC).

Of all the available techniques, the highest static pressure has been achieved

by the DAC (Mao and Bell 1978). The DAC can accommodate very small

sample volumes in the micron range as compared to other anvil cell and

piston cylinder devices, where the sample volumes are in the milliliter range.

2.1.2 The Diamond Anvil Cell

Diamond Anvil Cell has now become the most widely used design

in high pressure research. The hardness of diamonds and their transparency to

visible and X-ray region make them ideal for use as anvils. There are many

different designs of the DAC available. For our studies we have used two

different types of DAC’s, the Mao Bell type cell and the symmetric cell.

The basic principle for both the DAC’s is the same and the Mao Bell type cell

is described here.

17

Load

Load

Sample

Ruby

load

Figure 2.1 Photograph of Mao-Bell type DAC and the basic principle

of operation

(a) (b)

Figure 2.2 (a) Cross sectional view of the symmetric type compact

diamond anvil cell. There are a total of four screws

(b) schematic Figure showing the different parts of the cell.

18

The Mao Bell DAC design (Figure 2.1) used in this study was

developed at IGCAR (Deivasigamani et al 1995). The generation of pressure

in a DAC is based on the principle of massive support. Mechanical load is

applied to the rockers via the bellville spring loaded lever arm mechanism

(Mao and Bell 1978, Sahu and Chandra Shekar 2007, Yousuf 1998). The

sample is placed in a hole [100-250 µm] made in a SS gasket between the flat

parallel faces of two opposed diamond anvils. This hole is referred to as the

sample chamber and is located at the centre of the gasket. The contact point

between the anvils and the gasket is the culet which has the smallest surface

area. For high pressure experiments, a pressure transmitting medium and

pressure calibrant are loaded along with the sample in the sample chamber.

The Figure. 2.1 shows the photographic view of the home built Mao Bell type

DAC. A Maximum of 100 GPa can be attained with this setup. A modified

pair of rockers (a circular disc and a hemisphere) for easy alignment of the

anvils and a new collimator design has been developed by our group (Sahu et

al 2006). The anvil centering and alignment are attained by tilting and

translating the two tungsten carbide rockers.

The symmetric cell shown in Figure 2.2 operates on the same

principle described above except for the fact that the load is transferred to the

rockers via a set of four steel screws.

SS Gaskets which are used to confine the sample are pre intended

using the DAC before drilling the hole. This helps in work hardening the

metal and allows attaining greater pressures with the sample chamber intact.

Within this indented area a micro hole is drilled either with an electric

discharge machine or manually using a tungsten carbide micro -drill. Both the

methods have been employed for the high pressure studies here. The gasket is

then cleaned in the ultrasonicator.

19

In the experiments conducted for this study, a pressure transmitting

medium was used. This is to reduce the stress gradients produced in the

sample chamber.

2.1.3 Pressure Transmitting medium

The majority of high pressure experiments are carried out at

hydrostatic pressure conditions. The reason being that under hydrostatic

conditions, the results are comparable with the theoretical values. The melting

line of fluids increases under pressure and solidification occurs at some

pressure across the sample chamber is generally inhomogeneous and

differential stress and shear stress appears. This leads to a more dramatic

decrease in the quality and accuracy of the data and often the appearance of

anomalies, which might be wrongly assessed as a new physical phenomenon.

A review of the freezing pressures of all the commonly used

pressure transmitting media are given by Koltz et al (2009). Helium shows a

hydrostatic behavior up to 50 GPa and freezes at 11.8 GPa. In our studies we

have used a mixture of methanol, ethanol, water in the ratio (16:3:1) and the

freezing pressure is 14.5 GPa and also remains hydrostatic up to 14.5 GPa.

Argon was also used for Raman studies on Yb2O3. Argon freezes at 1.2 GPa

and it is hydrostatic up to 9 GPa.

2.1.4 Pressure Calibration: Ruby Fluorescence Technique

The common methods for measuring high pressures are: equation of

state (EOS), fixed point method and Ruby fluorescence method. In practice,

pressure measurements are possible only with secondary methods (Sahu and

Chandra Shekar 2007). The ruby fluorescence technique has been used for all

present investigations. Piermarini et al (1975) have reported on the

fluorescence spectra of various materials as a function of pressure. Cr3+

doped

20

Al2O3 (ruby) showed the greatest change in emission wavelength with

increasing pressure and is also linear up to ~ 30 GPa. In the ruby fluorescence

method a small chip of ruby (~5-20 µm) is introduced into the sample

chamber and the fluorescence is excited by an Ar-ion laser and is detected by

an optical spectrometer.

Figure 2.3 Typical Ruby fluorescence spectra

Pressure dependence of the Ruby R1 (694.2 nm) and R2 (692.6 nm)

shifts are used to determine pressure (Figure 2.3). Generally the shift of the

R1 line is taken for pressure calibration. Mao et al (1986) calibrated ruby

against copper as a standard under quasi-hydrostatic conditions in Argon

medium and tungsten in Neon medium up to 110 GPa. This is written as

P (GPa) = 1904/B [{1+( /694.24)}B-1].

where is the ruby R1 wavelength shift in , and B=7.665 and 5 for quasi

hydrostatic and non hydrostatic environments, respectively. The shifts of the

Ruby fluorescence lines have been calibrated against standard substances to

construct a pressure scale. The shifts are linear up to ~ 30 GPa at the rate of

0.365 nm per GPa (Piermarini et al 1975, Barett et al 1973). Broadening of

21

the ruby fluorescence spectra at high pressure is the major problem with this

method. The accuracy of the pressure is ~0.03 GPa, when R1 and R2 lines are

well resolved.

2.1.5 High Pressure X-ray Diffraction Technique

X-ray diffraction (XRD) technique is a non destructive technique to

study the unknown structure of a material. In the high pressure experiments, a

high precision XRD set up is required to investigate the phase transition in

materials. It is well known that a Guinier diffractometer provides high

resolution XRD data with a better signal to noise ratio in the case of samples

at NTP. Hence diamond-anvil with high-pressure X-ray diffractometer was

used in the Guinier geometry for all the experiments (Sahu et al 1995).

The schematic and photograph of the Huber-Guinier diffractometer

setup used is shown in Figures 2.4 and 2.5 respectively. It is in the vertical

configuration and in symmetric transmission mode. The incident X-ray beam

is obtained from an 18 kW rotating anode X-ray generator (RAXRG) with a

Mo target. The curved quartz-crystal monochromator is of Johansson- Guinier

type with A = 118 mm and B = 3.55 mm, with its reflecting surface parallel to

the crystallographic (10 1) plane and is mounted on the X-ray tube shield. The

X-ray beam from the monochromator enters the DAC after passing through a

beam reducer attached to the diffractometer. The Mao-Bell-type DAC is

secured on to a multiple stage which has X, Y, Z and tilt movements for

alignment with respect to the incident X-ray beam. The DAC is positioned in

such a manner that the sample inside lies on the Seeman-Bohlin circle of

114.6 mm in diameter. On this circle, either a position sensitive detector

(PSD) or a scintillation detector can be mounted. The PSD, is a linear gas

filled type detector of 50 mm in length (model OED-50, Braun, Germany). A

mixture of 90% argon and 10% methane is used in the continuous flow mode

22

at the rate 0.2 l/h at 0.75 MPa pressure. A platinum wire is used as the anode

in the PSD. The specified positional resolution of the PSD is 100 m.

This corresponds to an angular resolution of 0.05° and d/d =0.005.

For the Seeman-Bohlin circle employed here, the PSD can cover an angle of

10° in a single scan. Since the maximum angular opening in the DAC is 20°,

two positional scans are necessary to record a full HPXRD spectrum. In the

Guinier geometry, the maximum allowable range is -45° to +45°. But in the

present setup, it can cover the range of -30° to +25° due to the mechanical

limitations imposed by the DAC mounting stage. While no slit has been used

for the PSD, a variable linear slit along with a soller slit are used for the

scintillation detector to reduce the noise. It was found convenient to use the

scintillation detector for obtaining XRD patterns of samples at NTP, and the

PSD for HPXRD data. The scintillation detector cannot be used for the latter

purpose due to very weak diffraction intensity from micro samples under high

pressure. Angular scans with this can be carried out with a minimum step of

0.001°. The motor drive control for the detector movement, control of the

detector electronics, data acquisition and analysis, etc. are computerized.

Figure 2.4 Schematic view of Huber-Guinier diffractometer

23

Figure 2.5 Huber-Guinier diffractometer

Figure 2.6 Diffractometer with image plate detector (Mar Research

mar345dtb)

24

An image plate based mar Research mar345dtb diffractometer was

used for recording the high-pressure XRD patterns for studies on Ho2O3

(Figure 2.6). The incident Mo X-ray beam obtained from a Rigaku ULTRAX-

18 (18kW) rotating anode X-ray generator was monochromatised with a

graphite monochromator. The overall resolution of the diffractometer system

is: d/d 0.001. The Mao–Bell-type DAC was fitted to the diffractometer and

the sample to detector distance calibrated using a standard specimen like

LaB6.

2.1.6 High pressure Raman Spectroscopy

Raman spectrometer essentially consists of a light source, a

spectrometer and a detector. The important part of the experimental set up is

the spectrometer for analyzing the scattered light. For Raman investigations, it

is necessary that the spectrometer is able to discriminate the weak in-

elastically scattered light from the Rayleigh scattering which is stronger by

several orders of magnitude. This criterion is usually met by either using a

multiple grating or by using a notch filter to reject the laser line frequency.

The third part is a photo detector to record the light dispersed in the

spectrometer. A CCD detector provides multichannel detection resulting in

one shot detection over a spectral range which is suitable for Raman studies.

Dilor XY spectrometer equipped with an Olympus confocal

microscope (50X) and a CCD detector (Figure 2.7) as well as a SPEX double

monochromator with a cooled photomultiplier tube operated in the photon

counting mode as the detector have been used for the measurements. As the

basic principle is the same, the details of the Dilor system are presented here.

25

The schematic setup for a micro Raman setup using a Dilor XY

Raman spectrometer is shown in Figure 2.7 and the photograph in Figure. 2.8.

The excitation radiation was an Ar ion laser operating at 514.5nm with a

power of 300mW (approximately 6mW was incident on the sample). The spot

size of the laser was about 2 µm in diameter. the back scattered signal was

collected using a liquid nitrogen cooled CCD detector (EG8G 1530 C)

integrating over 60 to 180 min depending on the intensity of the spectrum

(Murli. H. Manghnani et al 1999). A prism monochromator was used to

suppress the plasma lines produced by the laser. The commonly used mode

for operation of a micro Raman setup is a microscope equipped with a triple

grating spectrometer working with a multi channel CCD detector. The

scattered light collected by the microscope objective is focused on the

entrance slit of the spectrometer and is reflected by the first parabolic mirror.

The focal point of this mirror is the entrance slit, so that the light is parallel

after passing this parabolic mirror. After the mirror the parallel light hits the

first grating and is diffracted onto the second parabolic mirror.

26

le

Plane

Notch Filter or fore

monochromatorSpectrometer

CCD detectorArgon ion laser

Olympus Confocal

microscope

Diamond anvil

cell with sample

Figure 2.7 The schematic setup for micro Raman setup

27

(a)

(b)

Figure 2.8 (a) The Dilor spectrometer with the Olympus microscope

and (b) The DAC kept under the confocal microscope for

the measurement of high pressure micro Raman spectra

28

The angle of grating is adjusted in such a way that only the spectral

region of interest passes through the central slit. The undesired spectral

components do not enter the second grating stage. The second stage built like

the mirror image of the first stage collects the light passing through the central

slits into one beam again and guides into the third grating stage, the resolving

stage. Here the light is dispersed and projected on to the liquid nitrogen

cooled CCD detector. The signal coming from the CCD detector is read out

by a computer. The two pre monochromating stages work in the subtractive

mode as an optical band pass defining a frequency window.

In a confocal microscope, the object and its image are "confocal."

Confocal is defined as "having the same focus." The microscope is able to

filter out the out-of-focus light from above and below the point of focus in the

object. When an object is imaged through a microscope, normally, the signal

produced is from the full thickness of the specimen and this does not allow

most of it to be in focus to the observer. The confocal microscope eliminates

this out-of-focus information by means of a confocal "pinhole" situated in

front of the image plane which acts as a spatial filter and allows only the in-

focus portion of the light to be imaged. Light from above and below the plane

of focus of the object is eliminated from the final image. This is clearly shown

in Figure 2.7.

The sample for high pressure studies in the DAC is placed under the

microscope through which the laser beam is focused on to the sample as

shown in Figure 2.8. Since the beam size is around 2 µm, and the confocal

setup gives the advantage of selecting that region in the DAC which contains

the sample and also spectra can be taken from various points of the sample.

The diamonds used in the DAC are of the low fluorescence type.

29

2.1.7 High Pressure Electrical Resistivity studies using designer

diamond Anvils

In a traditional diamond anvil cell used for electrical resistance

studies, the electrical microprobes and micro circuits are external to the

diamond crystal and usually cover a much larger probe region than the high

pressure region in the DAC. The process for assembling such external sensors

is vey tedious. In a designer anvil the microprobes are embedded in the

diamond making it much easier to handle.

The development of a technology for diamond encapsulated thin

film metal microcircuits on a diamond anvil substrate was first reported by

(Weir et al 2000). These circuits remain functional under multi mega bar

pressures and overcome many diagnostic difficulties related to small DAC

sample sizes and high shearing stress around the sample.

(a) (b)

Figure 2.9 (a) Designer DAC, having the probes embedded in the

diamond. (b) Center of a designer diamond anvil culet

shows the metal microprobes emerging from beneath the

synthetic diamond layer in order to make electrical contact

with the sample

30

Micro lithographic fabrication of thin film metal circuits directly

onto the diamond anvil has been performed by Grzybowski and Ruoff (1984),

Hemmes et al (1989). The encapsulation of such circuits in a layer of high

quality, synthetic diamond greatly increases their survivability as the shearing

stresses present in the DAC at multi mega bar pressures is around 10GPa.

This method of fabrication was achieved by the recent technological

advances in homo epitaxial diamond deposition with high growth rates.

(Snail et al 1991). The diamond film when deposited homo epitaxially to the

diamond anvil substrate, the bond between the diamond films to the anvil is

extremely strong. For the starting substrate they have used a 1/3 carat (67 mg)

type 1a diamond anvil with a polished culet oriented in the (100) plane. A set

of four thin film metal microprobes is then fabricated onto the anvil

(Figure 2.9). Tungsten was found to be the most suitable choice for

microprobes as it’s a carbide forming metal, it forms a very strong bond to the

diamond anvil substrate. Tungsten is also a refractory material

(T melt = 3683 K). After fabrication of the tungsten microprobes, a layer of

high quality epitaxial diamond was deposited onto the anvil substrate by the

microwave plasma chemical vapor deposition (Catledge et al 1997).

31

(a)

(b)

Figure 2.10 (a)High pressure electrical resistance measurement system

(b)The designer DAC

32

To prepare the diamond anvil for high pressure experiments, the

diamond film is polished to a smooth finish and shallow 7.50 bevels were

added. The thickness of the diamond film after polishing is around 10-20 µm.

For the experiment conducted here-the designer anvils which were

integrated into a specially designed membrane DAC were used. These DAC’s

used a gas membrane for applying load to the diamonds and thus pressurizing

the sample captured between the diamond tips. They have many advantages

over the conventional screw loaded DAC’s and provides a very fine and

precise control of the applied load and can easily achieve pressures of several

mega bars for designer DACs. These cells have a linear relationship between

membrane pressure and sample pressure.

The electrical resistance of the sample was studied using the Vander

Pauw four probe method to eliminate the resistance of the probes and other

contact resistances in the sample chamber assembly (Figure 2.10). A constant

current source meter (Keithley 2400) and nano voltmeter (Keithley 2182)

were used to measure the electrical resistance. The resistance values reported

at each pressure were averaged from 28 independent readings.

2.2 DESIGN AND FABRICATION

2.2.1 EDM machine modified for micro drilling in DAC

experiments

The maximum static pressures attainable nowadays using the

diamond anvil cell (DAC) technique has reached several mega bars. A gasket

for holding the sample in high pressure experiments is prepared by pre-

indenting a SS gasket to 50 to 70 µm and drilling a hole of the desired size

~0.15 mm-0.25 mm for carrying out experiments up to ~50-60 GPa using 500

µm culet diamond anvils. The hole has to be drilled at the centre of the pre

33

indented area. To attain higher pressures smaller culet sizes (100-300 µm)

have to be used which demands smaller hole size (10-100 µm). The common

method for drilling a hole that is larger than ~0.1mm is by mechanical

drilling, which is really tedious as it involves the drilling of the pre indented

gasket placed on a drill (Sahu et al 1993), using a tungsten carbide drill bit.

The centering of the hole is done through a zoom microscope. This process

involves, including other difficulties, breakage of expensive drill bits and

formation of burr while drilling. Other techniques employed for micro drilling

are electric discharge machining, making holes using high power lasers and

ultrasonic methods. A Micro EDM from a JOEMARS EDM TR100 which is

normally used for tap removal, has been developed here..

The set up consists of JOEMARS EDM TR100, X-Y-Z stage for

holding the gasket, tungsten carbide drill bits or wires of required size, a

variac, zoom microscope and the dielectric liquid (Figure 2.11). Plain water is

used as the dielectric medium. The pre indented gasket is placed in the sample

holder, the tungsten carbide drill bit is attached to the head of the EDM,

which serves as one of the electrodes. The gasket holder is connected to the

other electrode. The centering of the hole is done through making a mark at

the centre of the pre indented gasket by viewing through the microscope and

further placing the drill bit exactly above that mark with a gap of about 0.5

mm. The drilling is initiated by applying a voltage of opposite polarity

between the two electrodes (~80 volts) which initiates a spark between the

electrodes. The materials slowly get eroded due to the spark and when the

preset distance is overcome due to the automatic Z movement of the head, a

through hole is drilled.

34

(a)

(b)

Figure 2.11 (a) The Joemars Electric Discharge Machine (b) Enlarged

view of the drill bit attached to the head of the EDM and the

pre indented gasket being held in the sample holder

35

The commercial machines that have tolerances that are required for

diamond anvil cell applications can cost about 15,000 USD. Therefore

developing one for micro drilling from an already existing drilling machine

seemed to be a better option. The task was challenging because the existing

EDM was intended for tap removal and hence for very coarse applications.

The main challenge was to modify the machine for micro drilling.

(Lorenzana et al 1994)

The drilling in an EDM machine takes place through a spark erosion

process. A spark is produced by applying a voltage between two electrodes,

which breaks down the dielectric strength of the working liquid and a plasma

channel is produced that has high energy in the form of heat and pressure.

(Rehbein et al 2004). This energy is used to remove small portions of the

sample. A series of small craters are produced on the surface of the sample.

These craters follow the geometry of the electrode during every discharge.

The EDM demands a high number of discharges per second without the

formation of arcs. This process is basically contact less and hence one can

avoid the common problem of burr formation. When the two electrodes meet,

the drilling stops automatically with an alarm. Listed below are the major

challenges faced during the development of this modified EDM

1) The molten material was sticking back to the sides of the gasket

and forming huge structures around the gasket hole; 2) Choosing a proper

dielectric liquid; 3) Centering of the hole.

The spark or the discharge is the essential step in the process which

removes the material from both the electrodes. As the discharge ceases, the

plasma collapses and mixes with the molten metal and cools the dielectric and

drives the removed molten particles away from the surface of the sample.

36

Figure 2.12 A hole drilled with the modified EDM with a good surface

finish in a pre indented gasket

Earlier studies indicate that without the usage of a proper dielectric,

the molten metal welds back into the surface again. Assuming that this was

the problem, various dielectric liquids such as demineralized water, various

oils, methanol, ethanol etc at different voltages ranging from 100 to 140 volts

have been tried. The deposition of the molten material was still a problem.

The automatic z motion of the drill head during drilling was arrested

by including a switch in the circuit, the sample was slowly moved upward

manually to initiate the drilling. The idea was to maximize the time interval

between each discharge. With this method there was a consistent

improvement in the surface finish, but still was not always reproducible. This

was also tried with different dielectric liquids.

37

Then finally the voltage was reduced to a minimum ~80V and the

automatic Z movement of the drill head was restored. The dielectric medium

that was used was just plain tap water. For centering the hole, a mark was

made at the centre with ink and the drill bit was lowered to just exactly above

the mark before drilling. This method seemed very successful in producing

fine holes with a good surface finish (Figure 2.12). After restoring the

automatic Z movement of the drill head, the discharge rate was very

controlled and therefore there was enough time for the molten material to drift

away from the site of drilling.

2.2.2 Jig for mounting diamonds in a Mao-Bell type diamond anvil

cell

To generate high pressure in the Mao-Bell type DAC, Belleville

spring-loaded lever-arm mechanism is used. Here, the anvil centering and

alignment are attained by simply translating and tilting the two tungsten

carbide rockers. In order to achieve very high pressure by using Mao-Bell

type DAC, (i) the diamond anvils should be mounted symmetrically about the

rocker holes/slots and (ii) the parallelism between two diamond anvils culets

should be optically parallel (Jephcoat et al 1987).

Mounting diamond anvil on well polished rockers is usually done

with the help of a jig in which the rocker and the anvils are sandwiched

between a base plate and plane glass tipped cylindrical metal piece with a

central hole to view the diamond culet. Fine adjustments of the anvils with

respect to the rocker are made with miniature tweezers under a microscope.

This adjustment has to be carried out until the diamonds are mounted

symmetrically to the rocker hole/slot. Since the piston and cylinder rockers

are different in shape, two different jigs are used to mount the diamonds.

These jigs come with several associated problems. One of the foremost

problems arises because in these mounting jigs one has to move the diamond

38

for alignment. This cannot be accomplished in a systematic and gradual

fashion because of the frictionless surfaces of the diamond and their minute

sizes. Even a small miscalculated force/jerk can cause the diamond to fly

away. Further, during adjustments, the diamond culets damage the glass

surface and clear view of the diamond culet is hampered. Applying adhesive

around the diamond is another job requiring finesse. The adhesive has to be

applied around the diamond consistently, homogeneously and exposing the

diamond culet sufficiently to allow for sample assembly for high pressure

experiments. This is rendered difficult in the earlier jig as there is very little

daylight around the diamond anvils. In our new design, we have overcome

those difficulties.

In the Mao-Bell type DAC, we use two types of rockers, circular

disc rocker for piston and hemispherical rocker for the cylinder. Figure 2.13

shows the photographic image of a diamond mounting jig on the piston

rocker. The total height of jig is 41 mm. It has a top and bottom plates of 40

mm diameter separated by two narrow supporting rods of length 25 mm. Each

plate has a central hole of diameter 6 mm. Another metallic tube and circular

cap is inserted through the central hole of the top plate for gripping and

viewing the diamond culet. The piston rocker is placed inside the holding ring

welded to the bottom plate. It has 4 numbers of tapped holes 90º apart for

inserting 4 socket set screws which help in positioning the rocker at the centre

of the ring. The top plate and the circular cap of the metallic tube are held

together by 4 screws. Since the cylinder rocker is of hemispherical shape, it

cannot be mounted directly inside the holding ring. For this purpose, the

hemispherical rocker is mounted on another metallic holder which is inserted

inside the holding ring. Photograph of this modified arrangement is shown in

Figure 2.14

39

(A) (B)

Figure 2.13 A) Diamond mounting jig (for piston rockers): (a) bottom

plate, (b) top plate, (c) holding ring, (d) mounting tube;

B) photograph of assembled diamond mounting jig showing

the rocker and the diamond anvil

(A) (B)

Figure.2.14 A) Diamond mounting jig (for cylinder rockers): (a) bottom

plate, (b) top plate, (c) holding ring, (d) mounting tuber,

(e) rocker holder; B) Assembled diamond mounting jig

a

b

c

d

a

b

c

d

e

40

Firstly, well polished rockers are placed inside the holding ring. In

the case of piston rocker (circular disc), it is placed inside the holding ring

directly and is tightened by socket set screws. In the case of cylinder rocker

(hemi- spherical), the rocker is placed in separate holder which is placed

inside the ring. Then the diamond is placed on top of rocker. It is gripped

between rocker and the narrow stainless steel tube with conical cavity. The

conical cavity is designed in such a way as to hold just the culet portion of the

diamond. The culet can be viewed through the central hole of the tube by

using a microscope.

The diamond anvil can be centered with respect to the hole/slot of

the rocker by adjusting the position of the rocker with the help of the 4 socket

set screws of the holding ring. Once the diamond is centered, adhesive can be

applied around the diamond easily.

In conclusion, the unique and salient features of this diamond

mounting jigs which set them apart from others in use are the following: 1).

Instead of moving diamond for accomplishing alignment, the rocker is

aligned with precise movements using socket set screws. This arrangement

circumvents the tricky part of moving diamonds in the traditional jigs. 2). In

this jig, the hemispherical rocker is held rigidly by an annular ring which in

turn is moved on a flat surface by 4 socket set screws. 3). In this jig glue is not

required to fix the rockers. However, instead of glue, 4 socket set screws are

used to hold the rockers. 4). Wide space around the diamonds allow more day

light, and hence applying adhesive on diamond anvils became more

convenient. 5). In this jig, the diamond is gripped between rocker and the

narrow stainless steel tube with conical cavity. This also enables viewing of

the diamond anvil during alignment, and thus avoiding the usage of small

glass plates which frequently get cracked in the traditional jigs.