Abstract: Silicon steel sheets which have a silicate protective coating are further protected by being first coated with an aqueous solution containing (1) phosphate ions, (2) silica grains, (3) iron and/or manganese ions, and (4) negative ions which convert to volatile products at temperatures below 400.degree. C, and then heated to temperatures of between about 400.degree. and 1100.degree. C for periods of between about 1/2 minute to 10 minutes in order to form a further protective phosphate layer.

Abstract: Electrical products formed of silicon steel are provided with a heat resistant electrical insulating coating by suspending particles of an oxide and/or of an hydroxide of earth alkali metal in an aqueous suspension, and adding to the suspension a substance capable of liberating hydroxyl ions which is volatile at a temperature below that at which silicate is formed. Examples of such a substance are ammonia and organic amines. There may also be added to the suspension silicon dioxide particles which are capable of oxidizing silicon to silicon dioxide at temperatures below 1300.degree.C.

Abstract: A steel object, such as sheet and strip for motors, is provided with a heat-resistant, electrically insulating coating in the form of a layer of calcium titanate. An intermediate layer of silicate may be provided between the steel surface of the object and the layer of titanate. The intermediate layer is preferably a silicate of one or more alkaline earth metals or of aluminum, and especially a silicate of magnesium.The coating of calcium titanate may also contain a vanadium compound. Likewise, a layer of phosphate may be provided on the outside of the layer of titanate.

Abstract: An object of silicon steel, such as sheet and strip for motors, generators and transformers, which has an insulating coating of silicate, is provided with a solution of phosphate by applying to the silicate-coated object an aqueous solution containing phosphate ions and complex metal-ammonia ions and heating the coated object to a temperature of at least about 550.degree.C for a time sufficient to anchor the resulting phosphate layer to the silicate coating. The solution has a pH-value of at least 9, and consists essentially of monophosphate ions. The metal ions are cupric ions and/or chromic ions. An insoluble filler may be added to the aqueous solution.