Bismuth vanadates

Bismuth vanadate can be produced by chemical precipitation, as weU as by high temperature calciaation methods. In the wet process, the acidic solution of bismuth nitrate, Bi(N02)3, is mixed with the alkaline solution of sodium vanadate, Na VO. The gel formed is filtered off on a filter, pressed, washed, and converted to a crystalline form by calciaation at low temperatures of 200—500°C for 1 h (37,38). 

In the calciaation process, a mixture of corresponding oxides and an optional modifier, eg, molybdic acid, are milled together to achieve a homogenous mixture. The mixture is calciaed at 750—950°C and milled to a desired particle size. Wet milling ia an alkaline medium is recommended to remove any unreacted vanadium salts that ate beheved to degrade the pigmentary properties of bismuth vanadate (39). 

For most appHcations, bismuth vanadate is not thermally or chemically stable enough, and it has to be encapsulated with a dense, amorphous shell of sihca (40,41). It is recommended that bismuth vanadate be granulated to improve its handling and eliminate any dusting problems. 

Bismuth tritelluride, 4 24 physical properties of, 4 20t Bismuth trithiocyanate, 4 25 Bismuth Vanadate Yellow, 19 405-406 pigment for plastics, 7 370t Bismuthyl carbonate hemihydrate, 4 25 Bismuthyl nitrate hemihydrate, 4 25 Bismuthyl nitrite hemihydrate, 4 25 Bis(lV-maleimidomethyl) ether (BME), hemoglobin modifier, 4 113 Bisoprolol fumarate, molecular formula and structure, 5 156t Bis(pentafluorophenyl)borane, 13 638 Bis(pentafluorophenyl)tri-4-tolylbismuth, 4 35... 

An example of a new material without toxicological problems is the brilliant yellow, bismuth vanadate. Cl Pigment Yellow 184, made by the reaction of bismuth nitrate with sodium vanadate, followed by calcining at 300-700 °C. 

Others manganese blue cobalt, manganese violet naples yellow, bismuth vanadate ... 

Recently, BASF placed a new reddish yellow bismuth vanadate pigment on the market (trade name Sicopal Yellow L 1600). 

The production process for bismuth vanadate pigments consists usually of a precipitation reaction followed by a calcination step. This calcination leads to an appreciable increase in particle size as demonstrated in Figure 30. The calcination step is different from producer to producer and can be completely absent depending on the precipitation process and the desired product properties. 

Bismuth vanadate pigments are used in the manufacture of lead-free, weather resistant, brilliant yellow colors for automobile finishes and industrial paints. They are suitable for the pigmentation of solvent-containing paints, water-based paints, powder coatings, and coil-coating systems. It can be mixed with other pigments... 

Figure 31. Flow diagram for the production of bismuth vanadate molybdate pigment a) Reaction vessel b) Filter c) Dryer d) Furnace treatment...

Recently, different producers have developed bismuth vanadate pigments for the use in plastics. These pigments are used in every type of polymer, especially in polyethylene and technical plastics. 

The annual production of bismuth vanadate pigments is now about 500 t. In the near future an increasing market of 1000 to 2000 t/a is expected. 

Bismuth Vanadate, The use of lead chromate pigments has been slowly phased out of many applications. Thus a search for more environmentally acceptable relatively inexpensive yellow pigments having excellent coloristic properties has been ongoing. 

Bismuth vanadate, BiV04, exhibits a ferroelashc-paraelastic phase transition and had been the subject of considerable investigation. This is reported in some detail in the entry on Vanadium. 

It is known that cadmium sulfide (CdS) and ion oxide Te203) are visible light-sensitive materials, in particular, one-step photocata ysis of wate - is possible for CdS.25) Recently, Kudc et at. reported that bismuth vanadate (BiV04) snowed photocatalytic activity for 02 evolution from an aqueous silver nitrate solution under visible light.26 271 BiVCX is a very attractive photocatalyst although it is impossible to decompose water by a one-step process. Thus this material is a candidate for an 02 evolution photocatalyst to construct a two-phoion process 26) In other words, this material is expected to be an 02 evolution photocatalyst to... 

Cadmium pigments Mercury cadmium pigments Lead chromate yellows Lead molybdate oranges Iron blues Chrome greens Bismuth vanadate... 

Bismuth vanadate can be produced by either a wet process or high-temperature calcination. By the first method, an acidic solution of bismuth nitrate, Bi(N03)3. is mixed with an alkaline solution of sodium vanadate, Na3V04. The resultant gel is filtered, washed, and converted to crystalline form by low-temperature calcination at 200-500°C. Multiple-phase pigments can be created by coprecipitation of bismuth vanadate with molybdenum, tungsten, or niobium compounds. 

A limitation in using bismuth vanadate is the care needed in dispersing the pigment. As with other silica-encapsulated pigments, even partial shearing of the encapsulant will noticeably diminish thermal stability and durability. 

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