Cadmium Sulphide

ABSTRACT

This project examine cadmium sulfide, Based on the results obtained from this study, the following conclusions were made. Since there is a great demand for developing cadmium  sulphide   powder of high photo conductivity and quality, Accordingly, It is an object of the present invention to provide photo conductive cadmium sulphide powder with high photo sensitivity.

CHAPTER ONE

INTRODUCTION

• BACKGROUND

Cadmium sulphide is the inorganic compound with the formula cds.

1. Cadmium sulphide is a yellow solid and it occurs in the nature with two different crystal structures as the rare minerals of greenockite and hawleyite,^{[David R.(1998)]}but is more prevalent as an impurity substituent in the similarly structured zinc ores sphalerite and wurtzite, which are the major economic sources of cadmium.

As a compound that is easily to isolate and purify, it is the principal source of cadmium for all commercial applications. ^{[Egon Wiberg, Arnold Frederick Holleman (2001)]} Its vivid yellow colour led to its adoption as a pigment for the yellow paint (cadmium yellow) in the 18th century.

Cadmium sulphide and cadmium sulfoselenide are intense colorants ranging in colour from bright yellow to deep red. Cadmium sulphide was first synthesized in Germany in 1817 and later marketed as an artist pigment in the mid-19th century.^{[W. Stanley Taft, James W. Mayer, Richard Newman, Peter Kuniholm, DusanStulik (2000)]} Its use was not widespread, however, until about 1917.

• FORMULA: Cds
• MOLAR MASS: 144.46 g/mol
• DENSITY: 4.82 g/cm³

Fig.  a)(Cadmium yellow)                                                         fig.b)

Other Names

Cadmium (II) sulphide

Greenlockite

Hawleyite

Cadmium yellow

1.2 GREENLOCKITE

Greenlockite is a rare cadmium bearing metal sulphide, mineral consisting of cadmium sulphide in crystalline form.^{[C. Fouassier,(1994) ]}

Greenlockite crystallizes in the hexagonal system; it occurs as massive encrustations and as hemimorphic six-sided pyramidal crystals which vary in colour from a honey yellow through shades of red to brown. The Mohs hardness is 3 to 3.5 and the specific gravity is 4.8 to 4.9.

Most of the world supply of cadmium is supplied through the processing of zinc (zn) and lead (pb) ore where cadmium is a common trace element.

 (Greenlockite rock sample)         

Fig. c)

1.2.1   HAWLEYITE

Hawleyite is a rare sulphide mineral in the sphalerite group.

Dimorphous and easily confused with greenlockite. Chemically, it is cadmium sulphide, and occurs as a bright yellow coating on sphalerite or siderite in vugs deposited by meteoric water.

Crystal Class: hex tetrahedral (43m) H-M symbol ;( 43m)

Crystal Habit: powdery massive

Crystal System: cubic

Unit Cell: 5.818a     Z=4

Fig. d)     (rock sample 1)                                               fig.e) (hawleyite rock sample 2)

WURTZITE

Wurtzite is a zinc and iron sulfide mineral with the chemical formula (Zn,Fe)S, a less frequently encountered structural polymorph form of sphalerite.^{[Warr, L.N. (2021).} The iron] content is variable up to eight percent. It is trimorphous with matraite and sphalerite.

It occurs in hydrothermal deposits associated with sphalerite, pyrite, chalcopyrite, barite and marcasite. It also occurs in low-temperature clay-ironstone concretions. ^{[Palache, Charles, Harry Berman & Clifford Frondel (1944)]}

Wurtzite Boron Nitride with plate shape particles is used as a raw material for sintering coarse grit polycrystalline structure powders, which are later used for manufacturing traditional cutting and grinding tools.

The wurtzite group includes cadmoselite (CdSe), greenockite(CdS), mátraite (ZnS), and rambergite (MnS), in addition to wurtzite.^{[Xu, Yong-Nian; Ching, W. Y. (15 August 1993)]}

Its crystal structure is called the wurtzite crystal structure, to which it lends its name. This structure is a member of the hexagonal crystal system and consists of tetrahedrally coordinated zinc and sulfur atoms that are stacked in an ABABABABAB pattern.

The unit cell parameters of wurtzite are (-2H polytype):

• a= b = 3.81 Å = 381 pm
• c= 6.23 Å = 623 pm
• V = 78.41 ų
• Z = 2A

Type of ionic crystal structure in which the anions have a hexagonal close packed arrangement with the cations occupying one type of tetrahedral hole. Each type of ion has a coordination number of 4. Examples of this structure are found in ZnS, ZnO, AlN, SiC, and NH₄F.

Zinc sulphide has two crystalline forms namely. Zinc Blende and Wurtzite. The more stable cubic form is known as zinc blende. The hexagonal form is known as the mineral Wurtzite, although it also can be produced synthetically.

1.3                                   

SPHALERITE

Sphalerite is an important ore of zinc; around 95% of all primary zinc is extracted from sphaleriteore. However, due to its variable trace element content, sphalerite is also an important source of several other metals such as cadmium, gallium, germanium, and indium which replace zinc.^{[Lide, David R. (1998)]} 

Sphalerite is a zinc sulfide mineral with a chemical composition of (Zn,Fe)S. It is found in metamorphic, igneous, and sedimentary rocks in many parts of the world. Sphalerite is the most commonly encountered zinc mineral and the world’s most important ore of zinc.

Sphalerites are found in different deposit types but are primarily found in sedimentary exhalative, Mississippi-Valley type, and volcanogenic massive sulfide deposits. It is most commonly used for zinc, bronze, gemstones, galvanization, cosmetics, and pharmaceuticals.

Physical Properties of Sphalerite

• Adamantine, Resinous.
• Transparent, Translucent.
• Colour: Yellow, light to dark brown, black, red-brown, colourless, light blue. Green.
• Streak: Pale yellow to brown.
• 3½ – 4 on Mohs scale.
• Hardness: VHN₁₀₀=208 – 224 kg/mm² – Vickers.
• Tenacity: brittle
• Cleavage: Perfect. Perfect {011}

Zinc ore                                                                      sphalerite ore                       

ORIGIN OF CADMIUM SULFIDE

Most Cadmium is obtained as a by-product from the smelting of zinc (zn), lead (pb), or copper (cu) ores. Cadmium is release to the environmentfrom natural and anthropogenic source.

Cadmium sulphide was discovered in 1817 by a German physician, Friedrich stromeyer (1776-1835).

The element was first found in the condensation of vapours (mixed with soot and zinc oxides) that rose out of a furnace in which zinc oxide was being roasted.

Cadmium has been widely dispersed into the environment through the air by its mining and smelting as well as by other man-made routes.

• usage of phosphate fertilizers
• presence in sewage sludge, and
• Various industrial uses such as NiCd batteries, plating, pigments and plastics (ATSDR) 1999.

1.3.1                                  HISTORICAL USE IN ART

CdS is used as pigment in plastics, showing good thermal stability, light and weather fastness, chemical resistance and high opacity. As a pigment, CdS is known as cadmium yellow (CI pigment yellow 37).

About 2000 tons are produced annually as of 1982, representing about 25% of the cadmium processed commercially.The general commercial availability of cadmium sulphide from the 1840s led to its adoption by artists, ^{[Hugh MacDonald Smith (2002)]} notably Van Gogh, Monet (in his London series and other works) and Matisse (Bathers by a River 1916–1919). The presence of cadmium in paints has been used to detect forgeries in paintings alleged to have been produced prior to the 19th century. Cadmium sulphide is a direct band gap semiconductor with E_g = 2.42 eV at room temperature. CdS is used in optoelectronics (photosensitive and photovoltaic devices). One simple use is as a photoresistor whose electrical resistance changes with incident light levels. Mixed with zinc sulphide, cadmium sulphide acts as a phosphor with long afterglow.

Cadmium sulfide was used as a pigment in paints as far back as 1819. Synthetic cadmium sulfide pigments are valued for their good thermal stability in many polymers, for example in engineering plastics. By adding selenium it is possible to obtain colors ranging from a greenish yellow to red violet. ^{Hans Lohninger (1994)}

1.4                        STATEMENT OF PROBLEM

• Cadmium sulphide is a yellow-brown poisonous salt (CdS) used especially in electronic parts, in photoelectric cells, and in medicine.
• Cadmium has been widely dispersed into the environment through the air by its mining and smelting as well as by other man-made routes.
• usage of phosphate fertilizers
• presence in sewage sludge, and
• Various industrial uses such as NiCd batteries, plating, pigments and plastics.

1.5                          OBJECTIVES OF STUDY

This project is aimed at:

1. find the origin and occurrence of cadmium sulphide
2. The properties such as chemical, physical, optical, electrical and structural properties of cadmium sulphide.
3. production and technology of cadmium sulphide
4. application, uses and safety of cadmium sulphide

1.6                                  SCOPE OF STUDY

This work will be limited to research with collected samples.

Pages:  54

Category: Project

Format:  Word & PDF               

Chapters: 1-5                                          

Source: Imsuinfo

Material contains Table of Content, Abstract and References.